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In Ireland, residential energy policy has been influenced by thermal inefficiency, high electricity prices and energy poverty. These factors have driven the fabric-first approach, where buildings must undergo extensive thermal retrofitting to qualify for heat pump subsidies. The cost-effectiveness of this approach has not been properly scrutinised to date. This paper addresses this knowledge gap by exploring the cost-effectiveness of the fabric-first approach and other decarbonisation strategies for the residential sector and broader energy system. The study develops scenarios by modifying the Heat Loss Indicator (HLI) threshold, which evaluates the fabric and ventilation heat loss per unit of floor area and is used to determine heat pump subsidy eligibility. The paper also considers scenarios that permit installing sub-optimal performing heat pumps that do not achieve peak performance levels in dwellings with higher HLIs. The analysis uses the TIMES-Ireland Model (TIM), a model of the whole energy system that reflects the interdependence of mitigation pathways across different energy sectors. Our study shows that Ireland's fabric-first approach requires 22 times more thermal retrofits to meet climate targets than alternative pathways. The alternative pathways based on the latest heat pump performance data are more cost-effective, showing that higher heat pump HLI thresholds can reduce the average sectoral marginal CO 2 emission price by 60% compared to the current fabric-first approach. The cost savings indicate that shifting to an HLI threshold of 2.3 W/K/m2 is close to optimal, while cost savings are minimal when moving from an HLI of 2.3 to 3 W/K/m2. Furthermore, electricity prices and household awareness are essential to the cost-optimal transition to residential heat pumps. [ABSTRACT FROM AUTHOR]

With the goal to reach net zero carbon emission, countries around the world are expected to switch from fossil fuel to more eco-friendly alternatives. This suggests that heating, transport, and energy sectors will be more dependent on electricity. Heat pump technology is expected to be the most common and clean technology to be used for heating in buildings due to its Coefficient of Performance. Air-source heat pumps are the most common type due to their ease of installation. This paper investigates how different climates around the world would affect the air-source heat pump electricity consumption and its defrost cycles; and hence the potential overall effect on the grid. A novel heat pump simulation model has been developed to understand the behaviour of the heat pump in cold weather scenarios. An experimental validation has been implemented to ensure the accuracy of the simulation model. Global case studies of cities from around the world including Amsterdam, Copenhagen, Helsinki, Stockholm, Vancouver, Ruse, Moscow, Reykjavik, Harbin and Nottingham are selected to assess the defrost cycles of air source heat pumps. The innovation of this research is in the in-depth investigation of heat pump defrost cycles. Electrifying the heating sector is expected to increase electricity consumption significantly, especially in cold weather. A detailed case study of the UK is presented with heat pumps and the examination of the impact this would have on the electricity grid is presented. Heating demands for buildings in cold weather was also simulated to calculate the required heating demand. The results show that the wide implementation of heat pumps in the UK, for example, would increase the total daily demand of electricity by approximately 144% relative to the present level of grid energy demand. In addition, the average daily energy consumption would increase by roughly 106% over the cold season. The findings are critical, and the novel methodology is applicable to many countries on global level in relation to the future effect of heat pumps on the grid and predicting the power demand needed by the additional heat pumps based on geographical location, u-values of building elements, and heating demand. It is crucial for a household to improve the insulation of their dwelling as this could considerably reduce the power demand by the heat pump and therefore the overall electricity consumption. This paper aims to inform future technology developers and policy makers regarding the expected effect of heat pump technology on the grid and the possible sudden peaks in demand. [ABSTRACT FROM AUTHOR]

[Display omitted] • The LCA methods and findings of 41 papers on air-conditioning systems are examined. • Retrieved studies presented discrepancies in the LCA goals and scope definition. • The global warming potential (GWP) was the most evaluated indicator across papers. • Grid-connected electrical heat pumps generally had a higher life cycle GWP. • Improvements related to AC energy sources and other life cycle aspects are proposed. Air conditioning (AC) has become the fastest-growing energy end-use in buildings worldwide, and its adoption is expected to increase further due to various socioeconomic factors and climate change. Despite this, the decarbonization of space cooling is progressing slowly; hence, the emissions burden at each stage should be examined in detail. Given this context, it is crucial to assess the environmental performance of AC systems by considering a comprehensive approach like the Life Cycle Assessment (LCA). While several studies have already targeted the LCA of AC systems, a clear overview of those studies' methodologies, assumptions, and results is still lacking. Therefore, this systematic review examined the methods and key findings of 41 peer-reviewed articles. Although the results revealed discrepancies among the goals and scope, impact assessment methods, and indicators, most articles predominantly focused on the global warming potential (GWP) impact, and its reported quantification was further analyzed. It was observed that grid-connected vapor-compression heat pumps/chillers (conventional systems) presented higher GWP impacts than other AC systems powered by renewables, which in contrast, exhibited higher impacts in some toxicity and resource depletion-related indicators. However, the share of GWP showed different distributions, as the pre-operation emissions of solar-powered AC systems (either PV or thermal) were higher than those of conventional systems, mainly driven by reduced energy consumption usage. This review concludes with some recommendations for each stage of the life cycle. Since the operation phase generally showed the highest impact, more efforts should be devoted to accelerating the transition to a 100% clean electricity power system at a national scale. In contrast, the need to power AC systems with on-site renewables should be carefully assessed based on the context. [ABSTRACT FROM AUTHOR]

• The algorithms are compared in terms of accuracy, precision, recall, and F1. • A SMOTE was conducted in order to avoid imbalances in the dataset. • Through an artificial neural network a connection weigh approach was conducted. • KNN outperformed the other analysed algorithms by less than 3%, on average. • Ridge Regression revealed to be a promising algorithm for the fault detection. Heat Pumps (HPs) technology had a remarkable diffusion and growth in the Heating, Ventilation, and Air-Conditioning (HVAC) field, with an increase predicted to be greater than 200% until 2030. Therefore, efficient asset management must be achieved by ensuring their maintainability and reliability. For this purpose, several methodologies have been used in the last years for HPs fault diagnosis. These methodologies include, with the advances of computational systems and reduced costs of several components, machine learning and other artificial intelligence techniques. In the present paper, a connection weight approach is used to identify the clout of each component for the fault detection (FD) of HPs. The results show that the method provides a more comprehensive assessment of the importance of each component, yielding a reduction of 50% of the features. A comparative analysis of supervised learning classification algorithms is performed, for fault detection of an air-to-air HP in cooling mode. Such algorithms include Naïve Bayes, Support Vector Machine, Logistic Regression, and K-nearest Neighbors. The faults considered include compressor and reversing valve leakage, improper condenser and evaporator fouling, liquid line restriction, refrigerant undercharge and overcharge, and also the presence of non-condensable gases. Algorithms are compared in terms of accuracy, precision, recall, and F1 Score. The best results were achieved with K-nearest Neighbors, since it presented the highest values for these four metrics, over 99% after a cross validation considering a reduced number of components. Naïve Bayes, Support Vector Machine, and Logistic Regression also achieved over 90% performance metrics. Other models were superficially analysed and Ridge Regression with metrics performance of 100%, on average, revealed to be a promising tool for fault diagnosis in HPs. [ABSTRACT FROM AUTHOR]

Heat pumps allow to decarbonise the heating sector and to provide energy flexibility services. Hence, flexible heat pump control strategies are being developed. When testing these strategies, hardware-in-the-loop experiments using representative test cycles allow to evaluate the real heat pump behaviour. While several works investigated the representative cycle composition for retrieving the yearly energy performance, it is unclear if they can still be used for energy flexibility analysis. This paper investigates the performance of the three mainly used representative day selection procedures available in literature in presence of seven heat pump control strategies. A new approach, in which only consecutive days are used, was also evaluated. Two hydraulic configurations, i.e. with and without an energy storage between heat pump and building, and three climatic zones spread over the European Union were used in order to reach a general conclusion. Simulation results showed that approaches using consecutive days or approaches which select days based on their energy consumption can be used for the energy flexibility analysis. Though, only approaches with consecutive days were able to closely follow the operative room temperature profiles when compared to a full winter simulation due to the avoidance of abrupt temperature variations between the different days. [ABSTRACT FROM AUTHOR]

Trigeneration systems based on renewable energies are useful solutions to provide heat, cooling and electricity in buildings and industries. According to the International Energy Agency, more than 30% of the world population has a profile demand requiring heating and cooling and this percentage is above 70% in many developed countries. This paper experimentally evaluates the energy performance of a trigeneration system based on a solar PVT-assisted heat pump installed in an industrial building. The heat pump is a vapor compression air-to-water type, with a nominal capacity of 16 and 10.5 kW in heating and cooling respectively. The PVT solar field consists of unglazed PVT collectors with a total area of 13.6 m2. Results indicate that this type of system is effective to provide heat, cooling and electricity, using mainly solar energy. The PVT solar thermal fraction is significant to provide domestic hot water, but it is less representative in heating production. On the other hand, solar electrical production gets high representative contributions to feed the heat pump compressor. Different performance indicators were calculated to evaluate the system performance. Besides, a comparison with a reference system, that uses a PV instead of a PVT technology, was also evaluated. [ABSTRACT FROM AUTHOR]

A 5th generation district heating (5GDH) system consists of a low-temperature network used as a heat source for de-centralized heat pumps to serve heating demand. Until now, there is a lack of studies looking into the economic aspect of implementing the 5GDH concept. The performance characteristics, system dynamics, and economic feasibility of the 5GDH system are insufficiently investigated in cold climates. This paper aims to bridge the research gap by performing the techno-economic analysis of a 5GDH system using a case study based in Tallinn, Estonia. A detailed thermo-hydraulic simulation model is constructed in TRNSYS and Fluidit Heat. In addition, the uncertainty and sensitivities on the economic performance are analysed using Monte Carlo method implemented in Python. The study further analyses the effectiveness of using solar power technologies in reducing the cost of heating. For designed boundary conditions, the system can deliver heat at levelised cost of heating (LCOH) of 80 €/MWh. Integration of photovoltaic up to a limited capacity results in 1 % reduction when compared to the base case LCOH. The economic benefit of photovoltaic thermal is lower compared to photovoltaic. This study can provide a benchmark for the application of 5GDH systems in heating dominated regions. [ABSTRACT FROM AUTHOR]

Numerous cost-optimal studies have been undertaken by EU member states to define minimum energy performance requirements for buildings within that member state in accordance with the Energy Performance of Buildings Directive. As few of these studies have examined the effect of heating and ventilation system parameters on life cycle cost (LCC) and energy use in detail, this paper analysed 84 HVAC solution-sets, including parameters for the heating supply system, heating distribution system and ventilation system, for a case study in Norway. The choice of heating supply system was the dominant parameter, with ground source heat pump solutions offering the lowest purchased energy use and LCC. Electric water heating and district heating systems had low capital costs which make these options more attractive to property developers looking for a good return on investment. Using an exhaust ventilation system with an exhaust air heat pump lowered LCC and capital costs for ground source heat pump and district heating systems but does not meet current Norwegian energy regulations. Despite using more energy, a constant setpoint schedule resulted in a lower LCC than a variable setpoint system due to the variation in hourly energy pricing and the dominant role of monthly pricing based on peak load. The choice of yearly heating strategy and heat emitter had a relatively small impact on energy use, capital cost and LCC. With all the parameters combined, there was variation within each heating system of up to 21 kWh/(m2∙year) in energy use, 78 Euro/m2 in capital cost and 236 Euro/m2 in LCC. Therefore, it is important that such system parameters are considered in cost-optimal assessments to give a fair comparison of HVAC systems. [ABSTRACT FROM AUTHOR]

• Five different energy efficiency alternatives for the building were studied. • A ground-source heat pump and solar PV usually provide the highest profitability. • A household battery has become profitable at the 2022 electricity price. • Dimensioning of a solar PV system massively depends on the electricity price level. • At the 2022 electricity price level, the array-to-inverter ratio can be up to 4.9. Buildings and the construction sector make up about a third of the final energy consumption and energy-related carbon dioxide emissions, offering a significant potential for emission reductions. This paper investigates the conversion of a Nordic oil-heated townhouse into a carbon-neutral one. Five different energy efficiency (EE) alternatives including, for example, different heat pump types and their dimensioning are studied. The electricity demand of the EE alternatives is aimed to be covered as cost-effectively as possible with an on-grid system based on solar photovoltaics (PV) and a battery energy storage system (BESS). The cost-optimal dimensioning of the components is based on the 30-year life cycle cost (LCC), and the work is carried out using an hourly level simulation model developed in MATLAB. To maximize the profitability of the BESS, an intelligent control algorithm based on linear programming is implemented based on a day-ahead electricity spot price for the years 2020–2022 and "perfectly" forecasted power demand and generation data. The data used in the simulation consist of measured electricity consumption, simulated heat generation based on annual oil consumption, and simulated solar PV power generation. It was observed that an about 60% partial-power-dimensioned ground source heat pump together with a solar PV system provides almost always the lowest LCC. However, the BESS was shown to be profitable at the current investment costs for the first time at the 2022 electricity prices, enabling a capacity of 210–230 kWh. On average, the cost-optimized on-grid electricity system was found to reduce the 30-year life cycle costs by 6%, 20%, and 85% with the electricity prices of 2020, 2021, and 2022, respectively. When the price of electricity is exceptionally high, it may be justified to implement more extensive energy efficiency improvements, such as additional insulation of the building envelope. Nevertheless, the impact on the life cycle costs is marginal. In addition, the cost-optimized solar PV capacity has increased more than sevenfold between 2020 and 2022. [ABSTRACT FROM AUTHOR]

• EV presents a technical challenge to the grid and an opportunity to introduce sustainable and novel solutions. • A sustainable energy strategy is proposed to exploit the synergy between EV batteries and heat pumps. • Electrification of transport and heat in buildings can reduce typical householder carbon footprint by up to 87%. The demand for electricity has been increasing worldwide and it is predicted that this trend will be particularly reinforced in developing countries by the gradual electrification of the transport sector and heat generation in buildings. The energy supply infrastructure required to meet the additional electricity demand should be carefully managed in light of the climate change carbon emission targets and commitments. A large proportion of the new electricity loads will be met from renewable sources. Therefore, means of power storage become vital to smooth out the intermittent nature of these energy supplies. The introduction of Electric Vehicles (EVs) could provide a viable and dynamic power storage solution through the concept of Vehicle-to-everything (V2X). This involves the storage of renewable energy (RE) in EV batteries during the charging cycle and restitution to the grid (V2G) or homes (V2H) when needed. In this context, this paper presents a methodology involving several strategies to stabilise the grid system and examines the impact of various types of EVs and heat pumps (HPs) for supplying heat in buildings. The results of this research approach show that the synergy of using V2H could reduce the carbon footprint of a typical domestic building in the United Kingdom (UK) by up to 87% and potentially recover up to 21.9 kWh/day of surplus renewable energy. [ABSTRACT FROM AUTHOR]

• A self-adaptive diagnosis method for heat pump systems based on a residual data and data scaling strategy is proposed. • An improved benchmark model of heat pump systems based on the attention mechanism is proposed. • Verification shown that the proposed method can significantly improve the diagnosis generalization under varying severity. The fault diagnosis of heat pump systems is of great significance to reduce system energy consumption and ensure stable operation. Intelligent algorithms based on deep learning have a good diagnostic effect on complex thermal systems such as heat pump systems, but they also face the application problem of poor model generalization, which makes them unable to adapt to complex and actual dynamic scenarios. This paper focuses on the specific problems of the heat pump system's varying severity of fault conditions that cause the actual diagnosis accuracy of the model to decrease. Then, a new self-adaptive diagnosis method was proposed based on a residual data training framework combined with data scaling strategy, which adapts varying severity diagnosis under the condition that the training data derives from a single severity level. This paper analyzes the thermodynamic validity of the residual data training framework and, correspondingly, proposes a benchmark model based on the attention mechanism to greatly improve the quality of the residual data. Analyzing the thermodynamic laws of different fault severity and proposing a local scaling strategy for residual data allows for the residual sample instance of a single severity to be transferred to the residual sample space of multiple severity. Finally, verification of the ASHRAE RP-1043 data set revealed that the fault diagnosis method based on residual data can significantly improve the diagnosis accuracy and generalization. Furthermore, the higher accuracy of the benchmark model results in more obvious performance improvement. At the same time, the local data scaling strategy can significantly improve the upward and downward compatibility of the diagnostic model. It proves that the method proposed in this paper can effectively reduce the sensitivity of the diagnosis model to the severity of the fault, and it must be known that this self-adaptive method can also solve the problems of other actual diagnosis scenarios, such as different systems, varying environments, and varying loads. [ABSTRACT FROM AUTHOR]

• Modelling energy savings of renovations in the Dutch non-profit housing stock. • Assessment of 1.6 million dwellings, 21 building features and 3 empirical models. • Empirical models outperform the theoretical building energy model. • Shortcomings exist when predicting effects of specific energy-saving interventions. In Europe, the energy performance of dwellings is measured using theoretical building energy models based on the Energy Performance of Buildings Directive (EPBD), which estimates the energy consumption of dwellings. However, literature shows large performance gaps between the theoretically predicted energy consumption and the actual energy consumption of dwellings. The goal of this paper is to investigate the extent to which empirical models provide more accurate estimations of actual energy consumption when compared to a theoretical building energy model, in order to estimate average actual energy savings of renovations. We used the Dutch non-profit housing stock to demonstrate the results. We examined three empirical models to predict the actual energy consumption of dwellings: a linear regression model, a non-linear regression model, and a machine learning model (GBM). This paper shows that these three models alleviate the performance gap by giving a good prediction of actual energy consumption on sectoral cross-sections. However, these models still have shortcomings when predicting the effects of specific renovation interventions, for example newly introduced heat pumps. The non-linear and machine learning model (GBM) outperform the theoretical model in terms of estimating energy savings through renovation interventions. [ABSTRACT FROM AUTHOR]

[Display omitted] This paper introduces a non-linear grey-box (GB) model based on stochastic differential equations that describes the heat dynamics of a school building in Denmark, equipped with a water-based heating system. The building is connected to a local district heating network through a heat exchanger. The heat is delivered to the rooms mainly through radiators and partially through a ventilation system. A monitoring system based on IoT sensors provides data on indoor climate in the rooms and on the heat load of the building. Using this data, we estimate unknown states and parameters of a model of the building's heating system using the maximum likelihood method. Important novelties of this paper include models of the water flow in the circuit and the state of the valves in the radiator thermostats. The non-linear model accurately predicts the indoor air temperature, return water temperature and heat load. The ideas behind the model lay a foundation for GB models of buildings that use different kinds of water-based heating systems such as air-to-water/water-to-water heat pumps. Such GB models enable model predictive control to control e.g. the indoor air climate or provide flexibility services. [ABSTRACT FROM AUTHOR]

• Renewable heat performance demonstrated in Air Source Heat Pump field trial. • Useful statistical and machine learning models to predict instantaneous Coefficient of Performance (COP). • Estimate of performance difference between in-situ COP and manufacturer's rated datasheet values. Air Source Heat Pumps (ASHPs) are part of the solution to decarbonise the residential heating sector. The coefficient of performance (COP) is a measure of the instantaneous efficiency of a heat pump. The heat energy produced by an ASHP is deemed renewable if it meets a specified sustained COP over a period of time, e.g., a seasonal performance factor (SPF). Heat pump performance in situ often differs from laboratory test conditions. This paper explores the performance of ASHPs in a field trial of deeply retrofitted Irish houses. Analysis shows that all houses in the trial qualify as producing renewable heat but vary from the manufacturer's laboratory test performance. ASHPs with ratings of 8.5 kW (11.2 kW) underperformed against the manufacturers COP values on average by 16 (24%) at outside temperatures of 7 °C, and 3 (11%) at outside temperatures of 2 °C. The paper evaluates statistical and machine learning models, including a random forest (RF) model, to predict COPs and compare the difference between the manufacturer's laboratory COPs and the trial results. [ABSTRACT FROM AUTHOR]

This paper is the second part of a two-part study on the performance of ground-source heat pumps (GSHPs) in single-family detached houses in Canada. In Part I the cooling performance of two GSHPs was tested, analyzed and evaluated over one cooling season. In this paper, the heating performance of three vertical closed-loop water-to-air GSHP systems installed in three new single-family detached houses in Innisfil (80 km north of Toronto, Canada) is monitored, analyzed and evaluated over one heating season. Results show that GSHP A , GSHP B and GSHP C were able to meet the peak heating load without using the auxiliary heating element. The seasonal coefficient of performance of heat pump of GSHP A , GSHP B and GSHP C is 4.2, 4.0 and 3.4, respectively, whereas the seasonal coefficient of performance of the GSHP system of GSHP A , GSHP B and GSHP C is 3.8, 3.4 and 2.7, respectively. GSHP A has the highest COP mainly because it is equipped with a variable speed compressor while GSHP B and GSHP C are equipped with two-stage compressors. The average temperature of water leaving the ground loop of GSHP A , GSHP B and GSHP C is 3.9 °C, 3.1 °C and 2.7 °C, respectively, where the average temperature of water leaving the ground loop varied by up to 6.3 °C throughout the heating season. The total power consumption and operating cost of GSHP A , GSHP B and GSHP C are less than conventional air-source heat pumps by up to 46%, 40% and 24%, respectively. It is concluded that GSHPs operate at high COPs without operational problems even in very cold climates if designed, sized and installed correctly. [ABSTRACT FROM AUTHOR]

• Households change their heating patterns when they switch to a heat pump. • Typically, a setback temperature 2–5 °C lower than the desired thermostat setting. • We calculate the increase in heat demand with varied parameters. • The increase in heat demand is determined by heat loss and thermal mass. • This would be a useful metric for 'heat pump readiness'. Heating with air source heat pumps is an important step in the transition to Net Zero Carbon for many households. When predicting the resulting energy consumption it is frequently assumed that heating demand is unchanged from before the switch from gas heating. However, heating patterns usually change, with a net increase in heating demand to achieve the same level of thermal comfort. This paper discusses the change in pattern and uses modelling to determine the resulting increase in energy demand. It shows that the increase can be predicted with information about dwelling heat loss and thermal mass as well as weather and the pre and post switch heating pattern. The increase can be 20% or more for homes with high heat loss. It proposes that the metric for heating demand increase would be a useful measure of heat pump readiness, and that the parameters required to assess this should be provided on energy performance certificates. [ABSTRACT FROM AUTHOR]

Gas absorption heat pumps (GAHP) have significant potential to reduce fossil fuel consumption for space heating and hot water production and reduce CO 2 emissions. The paper deals with laboratory and operational verification of GAHPs operating with air as a low-temperature energy source. The laboratory verification was used to specify and analyse the courses of one GAHP cycle in terms of cycle phases, outputs, and operating temperatures at different temperatures of the air supplied to the evaporator and heating water temperatures from GAHP. Comparative operational verification was conducted simultaneously in two identical buildings with the same technology and on two identical GAHPs A. The influence of interventions in GAHP control on the operating parameters and the average time of one cycle was monitored. The decrease in outdoor temperature and the transition from using the GAHP for water heating only to using it for space and water heating significantly affected the performance parameters and the average cycle time. Validation measurements were carried out for one year in twelve boiler rooms with GAHP connected in a cascade with gas-condensing boilers. The results showed that in the seasonal evaluation of GAHP operation for space and water heating, the average operation time of GAHP did not significantly affect the performance parameters. A fixed operation control to a higher required temperature of heating water when applying GAHP for space and water heating significantly negatively affected the performance parameters. Compared to heat production from a gas-condensing boiler (GCB), the monitored GAHP operation had lower emissions by 52 kg of CO 2 per 1 MWh of heat produced. [ABSTRACT FROM AUTHOR]

[Display omitted] • A whole system approach to studying a low-temperature HGSHP system. • 3D coupled TH model with realistic boundaries and dynamic heat pump COP. • Design of a HGSHP system to support a 5th generation DHC network. • Different factors on performance of the HGSHP system and ground thermal behaviour. • Ground moisture transfer, cooling process and buried depth are important. Exploitation of shallow ground and its low-grade heat potential is fundamental to designing 5th generation district heating and cooling (DHC) networks. Horizontal ground-source heat pump (HGSHP) systems are a common way to utilize shallow geothermal energy. Realistic estimation and prediction of performance of a HGSHP system and shallow ground thermal behaviour should consider the whole system including building heating and cooling load, heat pump and ground heat exchanger, and the ground. This should be accompanied by realistic atmospheric and ground conditions. In this paper, a three-dimensional coupled thermal–hydraulic model with realistic boundary conditions adopting a whole system approach is presented. Dynamic heat pump coefficient of performance (COP) that depends on seasonal variation of heating/cooling demand and ground conditions are also considered. Model validations are conducted against experimental and analytical results in literatures. The model is applied for evaluating a HGSHP system to support development of a 5th generation DHC network on a potential site in the UK. Several influencing factors, such as ground moisture transfer, building thermal load mode, buried depth of ground loops, and initial ground temperature profile are studied to assess performance efficiency of the HGSHP system and evolution of ground thermal behaviour in response to heat extraction or rejection into the ground. The results show that 5% of the monthly total heat demand of the site could be met by the designed HGSHP system, consisting of 200 U-shaped ground loops buried at the depth of 3 m and pure water as the heat carrier. Overlooking the ground moisture transfer or hyperbolizing the ground saturation would overestimate the load-carrying capacity of the HGSHP system. The HGSHP system is more efficient with a higher heat pump COP under the heating and cooling mode than under the heating-only mode. Predicted performance of the HGSHP system improves with buried depth of the ground loops. The results also show that a 1 ℃ increase in the undisturbed ground temperature could suffice up to 8% of the monthly total heat demand of the site. [ABSTRACT FROM AUTHOR]

• The common defrosting methods of air source heat pump are summarized and their advantages and disadvantages are analyzed. • A hot liquid subcooling defrosting method with multiple outdoor units connected in parallel is adopted to defrost the air source heat pump. • The influence of outdoor temperature and relative humidity on defrosting of air source heat pump were discussed. • The performance of hot liquid subcooling defrosting and hot gas bypass defrosting were compared, and their advantages were analyzed. Air source heat pumps (ASHPs) are widely used in clean heating because of the high efficiency, energy saving and economic advantages. Efficient defrosting technology for continuous heating is a key issue that must be addressed when operating the large ASHP at low temperatures. To solve the technical problem, this paper designed and built an experimental ASHP system with multi outdoor units connected in parallel, and used the hot liquid from the outlet of the condenser to defrost outdoor units in turn to study the change of heat pump performance with defrosting start time at different outdoor temperatures and outdoor humidity, and compared the system performance of the hot liquid subcooling defrosting (HLSD) with that of the hot gas bypass defrosting (HGBD). The experimental results showed that the HLSD enabled the heat pump to complete rotational defrosting with good defrosting effect in the case of continuous heating. The lower the outdoor ambient temperature and higher the air relative humidity, the worse the heating performance, and the longer the defrosting time. When using the HLSD, the heating capacity and energy efficiency ratio of heat pumps could be increased by 10% to 20% compared with the HGBD. [ABSTRACT FROM AUTHOR]

Ground source heat pumps (GSHP) are one of the most efficient systems that offer a promising reduction in greenhouse gas emissions and energy use in buildings; however, the electrification of buildings' heating and cooling using GSHP is facing two critical challenges: its high initial cost and potential adverse impact on the electrical grid. In this paper, to address these challenges, two novel systems are proposed in which a battery, a water thermal storage tank, and a phase change material (PCM) thermal storage tank are integrated, in different configurations, with a conventional GSHP system. In these systems, the grid electricity during off-peak periods is stored as heat or electricity in the thermal or battery energy storage systems. The stored energy is then used in peak building load conditions to reduce the peak power demand on the grid. New numerical models are developed to quantify the proposed systems' benefits. Furthermore, these newly proposed systems are compared with the conventional systems used in Quebec, Canada, and three previously proposed worldwide systems. Simulations are conducted for different commonly used design practices, including undersized and adequately sized heat pump capacities. The results show that the proposed systems can reduce the peak power demand and total energy requirement of a conventional system by up to 65.4% (9.28 kW) and 67.0% (19,722 kWh), respectively. Furthermore, the proposed systems' borehole length decreases by up to 21.8% (39 m) compared to the conventional GSHP system. [ABSTRACT FROM AUTHOR]

The rise of clean energy such as solar energy provides a new idea to optimize the energy structure, and Photovoltaic thermal (PVT) heat pump system is one of the mainstream development at present. The wrong sensor data will have a great impact on the control and efficiency of the whole PVT heat pump system. In order to deal with this situation, Virtual in-situ calibration (VIC) based on Bayesian inference and Markov chain Monte Carlo (MCMC) is applied to PVT system. This paper presents a generic sensor fault diagnosis and calibration method for building energy systems using a PVT heat pump system as an example. Firstly, the data generated based on the mathematical model of PVT system is used to test the feasibility of VIC in this system. The results show that VIC can well reduce the systematic error and random error of the sensor. However, with the further study, it is found that in the actual system, it is impossible to establish a mathematical model which can reflect the relationship between the sensors with high accuracy. The VIC may fail or even have worse calibration results. Therefore, in order to solve the above problems, this study suggests using sparse autoencoder model instead of mathematical model. The model proved to be more accurate and to reflect the interconnectedness of the sensors, which helped the implementation of the VIC. The calibration method based on sparse autoencoder (SAE) can calibrate not only a single sensor in the PVT heat pump system, but also multiple sensors in a local area. After sparse autoencoder Virtual in-situ calibration (SAE-VIC) calibration, systematic and random errors of all sensors can be effectively reduced, and the accuracy of sensor calibration can reach more than 90 %. [ABSTRACT FROM AUTHOR]

• A novel frosting suppression control strategy for air source heat pump is developed. • Frosting suppression can be effectively achieved by using the control strategy. • Heating duration under the novel control strategy is increased by up to 157.68 % • Daily defrosting duration and energy consumption are reduced by 36.30 % and 32.96 % • The novel control strategy can meet required heating capacity with a high COP value. Effective frosting suppression was crucial to further wider applications of air source heat pumps (ASHPs). However, existing frosting suppression measures may not be fully implementable in practice due to various reasons such as short service life, complex manufacturing process and high costs. A condensing-frosting performance map was obtained in a previous study to enable a comprehensive evaluation of the frosting suppression and heating performances of a variable speed (VS) ASHP unit. Therefore, the maps could also provide a basis for developing a novel control strategy for frosting suppression, while still meeting the requirement of desired output heating capacity. As a result, an experimental study on developing a novel control strategy based on the condensing-frosting performance maps has been carried out using an experimental VS ASHP unit, and the study results are presented in this paper. The experimental results suggested that the experimental VS ASHP unit under the proposed novel control strategy could not only achieve effective frosting suppression, but also output the required heating capacity at high COP values whenever possible. By using the developed novel control strategy, the heating duration in one cycle could be increased by up to 157.68 %, and the daily defrosting frequency, duration and energy consumption reduced by up to 59.09 %, 36.30 % and 32.96 %, respectively. The proposed novel control strategy was straightforward and simple to implement, and could contribute to the further development of frosting suppression for ASHPs. [ABSTRACT FROM AUTHOR]

This paper presents a novel study on the multi-objective energy audit and management of a proposed plus-ZEB covered by a green roof in Tehran's climate. The planning impact of changing a proposed plus-ZEB to an intensive plus-ZEB is also evaluated. The planning is performed for one year based on Tehran's accurate urban climate data. The plus-ZEB consists of renewable and non-renewable resources like CHP, boiler, furnace, photovoltaic, solar water heater, wind turbine, air to the water heat pump, electric heat pump, and chiller boiler units in addition to energy storage to supply diverse electrical, thermal, and cooling demands of the presented building. The planning's functions are included in the total cost and emission of the plus-ZEB. The objective function prioritization is also participated to show the planner's decision on the function. Also, diverse solvers are implemented to evaluate and compare and validate results. The problem is simulated in energy plus to assess the amount of demands, construction materials, and energy audit issues; then, the results transfer to the GAMS software for energy management of the proposed plus-ZEB by utilizing a green roof. The problem in GAMS is modeled as a real mixed-integer programming (RMIP) and solved using the augmented epsilon constraint method (AEC). The final results show the significant effect of the proposed planning on reducing the cost and emission of the plus-ZEB, in which the total cost and pollution are decreased by about 7.4 % and 10.6 %, respectively. [ABSTRACT FROM AUTHOR]

• GB domestic heat pump electricity demand in 2050 is modelled. • Modelling is based on monitored data from heat pumps and gas boilers in homes. • Uptake of heat pumps in all homes more than doubles peak GB electricity demand. • Moderate improvements in HP performance and dwelling fabric reduce peak GB demand. • Flexibility in DHW and space heating provision also reduce peak GB demand. To meet net zero carbon targets by 2050s, countries with cold winters, such as Great Britain (GB), will turn to low carbon domestic heating systems such as electric heat pumps. In this paper, a statistical model is developed using measured performance data from over 550 heat pumps installed in GB homes in 2012. The model is used to predict the additional load on the GB electricity generation and distribution infrastructure for various current and future (2050) climates, dwelling energy efficiencies and heat pump deployment scenarios. For a cold year in the 2020s, a 100% uptake of heat pumps in the existing GB dwelling stock gave a peak electricity demand for the heat pumps of 78 GW and an annual electricity demand of 189 TWh. When added to the other, existing electricity demand, this represents an increase in the GB peak electricity demand in excess of 100% and an annual electricity demand increase of around 60%. Making reasonable assumptions about heat pumps' future efficiency and use, and the future climate and dwelling stock fabric efficiency, and assuming 80% heat pump uptake and no load shifting, the peak heat pump electricity demand for a cold year in the 2050s halved to 37 GW. By shifting demand for water and space heating the 2020s cold year peak demand reduced by 15%. The work provides a more robust estimate of future GB heat pump electricity demands than any previously available. The predicted future ramp rates, peak and annual total electricity demands, are lower than predicted by previous analysts. [ABSTRACT FROM AUTHOR]

• First-time transfer and combination of state-of-the-art approaches of electric hot water heaters to hot water heat pumps (model predictive control, system identification, live state estimation, and demand prediction). • An experimental proof of the model predictive control potential of hot water heat pumps by comparison of the standard hysteresis control to the model predictive control, covered in a realistic setting. • Quantification of the savings and the demand side management potential achievable by a state-of-the-art prediction method in a realistic setting. Hot water heat pumps are well suited for demand side management, as the heat pump market faced a rapid growth in the past years with the trend to decentralized domestic hot water use. Sales were accelerated through wants and needs of energy conservation, energy efficiency, and less restrictive rules regarding Legionella. While in literature the model predictive control potential for heat pumps is commonly shown in simulations, the share of experimental studies is relatively low. To this day, experimental studies considering solely domestic hot water use are not available. In this paper, the realistic achievable model predictive control potential of a hot water heat pump is compared to the standard hysteresis control, to provide an experimental proof. We show for the first time, how state-of-the-art approaches (model predictive control, system identification, live state estimation, and demand prediction) can be transferred from electric hot water heaters to hot water heat pumps, combined, and implemented into a real-world hot water heat pump setup. The optimization approach, embedded in a realistic experimental setting, leads to a decrease in electric energy demand and cost per unit electricity by approximately 12 % and 14 % , respectively. Further, an increase in efficiency by approximately 13 % has been achieved. [ABSTRACT FROM AUTHOR]

• Freeze concentration is applied for solution regeneration in heat pump system. • The test unit is able to regenerate the dilute solution from 13% to 15%. • The specific ice production rate is 8.94 kg/kWh. • COP of total energy efficiency is 5.03. • The heat utilization rate is 62.5% and can be used for heating supply water. Freeze concentration, which is often used in water treatment and the food industry, has a good regeneration effect and is easy for latent heat utilization. Therefore, a solution regenerator unit using freeze concentration with a heat pump system (SRFCHP) is proposed in this paper. In winter, SRFCHP can achieve weak antifreeze solution concentration, and the heat capacity of frozen phase transition is used to raise the supply water temperature. To investigate the performance of the SRFCHP system, a test was built in the enthalpy difference laboratory. Results shown that the SRFCHP system was able to regenerate the dilute solution from 13 % to 15 % in five regeneration cycle cycles. Around 34.5 % of ice production was able to be separated and the average loss mass of solute was about 0.95 kg per test in the regeneration cycle. Moreover, the SRFCHP system has a better performance on energy efficiency. About 62.5 % of total heat capacity had been recovered effectively. The solute recovery rate was 69.1 %. The coefficient of performance of refrigeration efficiency and heat recovery efficiency were 2.01 and 3.01, respectively. The specific ice production rate was 11.03 kg/kWh. These results demonstrate that the proposed system can be used in frosting regions to regenerate the dilution liquid. [ABSTRACT FROM AUTHOR]

• A dimensionless coefficient, COFS , to reflect the level of frosting was proposed. • A method to develop a frosting suppression performance map was introduced. • 50%-100% frosting areas on the maps for experimental ASHP units can be predicted. • The four-point method can reduce map development time by at least 67%. It has been known that for space heating ASHPs, their different configurations and operation may influence their frosting performances. However, there has been no comprehensive coefficient that can be conveniently and comprehensively used to characterize the frosting status, severeness level of frosting, and the potential for frosting suppression during the real-time operation of an ASHP unit. Therefore, in this paper, a novel coefficient of frosting suppression based on the operating characteristic for ASHPs has been proposed, and its development is reported. Firstly, a novel dimensionless coefficient, COFS , to reflect the severeness of frosting for ASHPs was defined. Secondly, an experimental setup with four variable speed experimental ASHP units and test conditions are described. Thirdly, using the experimental results, COFS -based frosting suppression performance maps for the four units were developed. It is shown that because the experimental four units had different frosting suppression abilities, their frosting areas in their frosting maps were 50%, 100%, 94%, and 58%, respectively. In addition, as the test conditions changed, the frosting area on a map area could also change. These have proved that the proposed COFS could effectively reflect the frosting status and the relative level of frosting suppression performances of ASHP in actual operation. [ABSTRACT FROM AUTHOR]

• Air source heat pump fresh air unit with fresh and return air mixing was developed. • The supply air temperature deviation was within ±1 °C. • The heat pump COP was 2.46 when the outside temperature was −20.9 °C. • The heat pump COP was higher than that of the traditional heat recovery device. In order to ensure the indoor air quality of the building, in view of the problem of fresh air heating in severe cold regions, this paper proposes an air source heat pump fresh air unit with fresh air and return air mixing. The mixing process of the fresh air and return air is realized in the mixing box, which increases the inlet air temperature of the condenser, creates a suitable condensation pressure, and ensures the energy-saving and stable operation of the unit. In order to explore the operation effect, heating performance and energy saving of the unit, an experimental bench was built in Harbin for laboratory heating. The experimental results showed that when the return air volume was 1400 m3/h, the fresh air unit could operate continuously and stably under the conditions of ensuring the fresh air volume of 700 m3/h and the supply air temperature of 24.0 °C. When the outdoor temperature was 4.9 °C, the heat pump COP was 4.29. Even when the outdoor temperature dropped to −20.9 °C, the heat pump COP still reached 2.46, while the COP of the fresh air system combining electric preheating, heat recovery and air source heat pump was only 1.44, and the COP of the fresh air system combining electric preheating, heat recovery and electric heat was only 1.21. In addition, the heat pump COP increased with the increase of the return air volume. As the set temperature increased, the heat pump COP increased first and then decreased. [ABSTRACT FROM AUTHOR]

• Novel methodology for calculating cost-optimized refurbishment roadmaps is presented. • Coupling of building model for refurbishment and system model for heating technologies. • Refurbishment roadmap include timing and refurbishment measures for specific buildings. • Applying the optimization achieves cost savings of 6–16 % and CO 2 savings of 6–59 % • Heat pumps play a central role in the context of CO 2 reduction. A novel methodology for calculating optimized refurbishment roadmaps is developed in this paper. The aim of the roadmaps is to determine when and how should which component of the building envelope and heat generation system be refurbished to achieve the lowest net present value. The integrated optimization approach couples a particle swarm optimization algorithm with a dynamic building simulation of the building envelope and the heat supply system. Due to a free selection of implementation times and refurbishment depth, the optimization method achieves the lowest net present value and high CO 2 reduction and is therefore an important contribution to achieve climate neutrality in the building stock. The method is exemplarily applied to a multi-family house built in 1970. In comparison to a standard refurbishment roadmap, cost savings of 6–16 % and CO 2 savings of 6–59 % are possible. The sensitivity of the refurbishment roadmap measures is analyzed on the basis of a parametric analysis. Robust optimization results are obtained with a mean refurbishment level of approx. 50 kWh/m2/a of the building envelope. The preferred heat generation system is a bivalent brine-heat pump system with a share of 70 % of the heat load being covered by the electric heat pump. [ABSTRACT FROM AUTHOR]

Vapor Compression Systems (VCS) are the most common air conditioning technology. VCS cool the air to its dew point temperature (overcooling) to remove water vapor in the air through condensation and then reheats the air back to the comfort temperature for direct use. The VCS process is inefficient due to overcooling and reheating. Liquid Desiccant Dehumidification (LDD) is a potentially energy-efficient air conditioning. LDD removes water vapor in the process air using liquid desiccant's high-water affinity. It hybrids with sensible cooling to control temperature and humidity separately. The LD in the LDD becomes weak after dehumidification. The LDD needs additional heating to regenerate the weak Liquid Desiccant (LD) to a high concentration for dehumidification. Earlier versions of the LDD systems use highly concentrated liquid desiccant (large water removal capability) to dehumidify the air by only dealing with latent load. It leads to highly elevated temperatures above 60 °C of heat sources (combustion or electric resistance-based heating) for regeneration. The energy needed for the elevated temperature heat resource significantly reduces or demolishes the benefit of LDD systems. In the recent two decades, researchers have investigated a new configured LDD system that couples an LDD with a heat pump at both dehumidification and regeneration sides for better efficiency. The heat pump provides cooling (from the evaporator) for both dehumidification and sensible cooling and simultaneous heating from the condenser for regeneration. The highly integrated system (HP-LDD) with improved efficiency enables the LDD to operate at lower concentrations and temperatures in dehumidification and regeneration. This paper depicts the working principle behind HP-LDD and its heating and cooling requirements. It reviews the comparison between the HP-LDD systems and the conventional LDD systems regarding system configurations, component design, energy efficiency, and dehumidification performance characteristics. The main findings from the review include the preferred use of packed bed over membrane-based dehumidifiers, the use of internally cooled dehumidifiers enabled by the HP cooling capacity, the high dispersion of HP operation conditions, and the dependence of dehumidification performance on various dehumidifiers. An outlook for future research on HP-LDD strategies is presented based on the reviewed works and their limitations. [ABSTRACT FROM AUTHOR]

• Over the technologies' typical 20-year lifetime, most UK dwellings have a cost optimum low-carbon heating system using air source heat pumps. • Dwelling properties and spatiotemporal variabilities significantly change the optimum low-carbon technology from blue hydrogen boilers, direct electrical heating, and air source heat pumps, to ground source heat pumps. • Direct electrical heating is economically preferred over heat pumps in lower demand dwellings and with analysis over shorter timescales. • Incentives for low-carbon heating need to target adoption of efficient technologies to reduce the greater increase in network demands. An understanding of heating technologies from the consumers' perspective is critical to ensure low-carbon technologies are adopted for reducing their current associated emissions. Existing studies from the consumers' perspective do not compare and optimise the full range and combinations of potential heating systems. There is also little consideration of how spatiotemporal and dwelling variations combined alter the economic and environmental effectiveness of technologies. The novelty of this paper is the creation and use of a new comprehensive framework to capture the range of heating technologies and their viability for any specific dwelling's traits and climate from customers' perspective which is missing from current studies. The model optimises combinations of prime heaters, energy sources, ancillary solar technologies and sizes, thermal energy storage sizes and tariffs with hourly heating simulation across a year and compares their operation, capital, and lifetime costs alongside emissions to realise the true preferential heating systems for customers, which could be used by various stakeholders. Using the UK as a case study, the results show electrified heating is generally the optimum lifetime cost solution, mainly from air source heat pumps coupled with photovoltaics. However, direct electrical heating becomes more economically viable as dwelling demands reduce from smaller dwellings or warmer climates, as shorter durations of the ownership are considered, or with capital cost constraints from lower income households. Understanding this is of high importance, as without correctly targeted incentives, a larger uptake of direct electrical heating may occur, which will burden the electrical network and generation to a greater extent than more efficient heat pumps. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simulation of residential building energy supply with heat pump or hydrogen systems. • 2050: Hydrogen economically-viable if H 2 -/Elec.-price is less than 34–61 % per kWh. • For conservative price predictions: Electric heat pumps are most economical solution. • Energy carrier switch for single-family houses: H 2 -/Elec.-price below 44 % per kWh. • Energy carrier switch for multi-family houses: H 2 -/Elec.-price below 58 % per kWh. • Fuel cells are emerging as an economically-viable option for multi-family houses. Fossil-fueled heating in the building sector is responsible for 16 % of Germany's total CO 2 emissions. Options for the climate-neutral heating of buildings include renewable electricity or renewable hydrogen. In this paper, we conduct a bottom-up study to investigate the role of hydrogen in the climate-neutral energy supply of ten selected residential buildings in comparison to electricity-based systems. Based on a demand simulation and linear optimization of the supply system, sensitivity analyses identify the threshold values of the hydrogen price for the use of hydrogen technologies (hydrogen boilers or fuel cells) in building energy systems and make the quantities of hydrogen consumed visible. The results specify the first installations of hydrogen-operated fuel cells in multi-family houses if the hydrogen price reaches 0.17 €/kWh H2 in 2050 at an electricity price of 0.31 €/kWh el. Generally, for different building types and electricity supply prices, it indicates that the use of hydrogen becomes economically-viable if the price of hydrogen supply is in the range of 34–61 % of the price of the electricity supply per kWh and below. For the case of green hydrogen obtained using renewable electricity, it is highly questionable whether hydrogen supply will be that much cheaper than direct electricity supply, making its economical use in buildings uncertain. [ABSTRACT FROM AUTHOR]

Integrating thermal energy storage with building energy systems can enable flexible building electric demands at buildings to help mitigate the mismatch between electricity supply and demand. A novel building heating and cooling system that integrates a dual-source heat pump with hybrid thermal storage named dual-purpose underground thermal battery (DPUTB) has been developed for reshaping building electric demands. The proposed DPUTB integrated geothermal heat pump system is an original innovation that enables Grid-interactive Energy Efficient buildings. This paper focuses on the study of the novel DPUTB. The DPUTB works as both a thermal storage tank (an inner tank) and a ground heat exchanger (an outer tank separated from the inner tank by the insulation material). High fidelity and computationally effective models are needed to predict the performance of the novel DPUTB. This study has developed a simplified dynamic model for the DPUTB according to heat transfer and energy conservation principles and validated it by using experimental data obtained from testing a small-scale DPUTB apparatus. A parametric study was conducted to identify a design that can achieve the target thermal storage performance of load shift and energy efficiency. The parametric study results show that the inner tank shell thermal conductivity and the phase change material's melting point are the two most influencing factors on the performance of the DPUTB. One single full-size DPUTB with the identified design could provide 1-ton cooling (3.51 kW) with the supply temperature lower than 11 °C for 4 hours in summer after being fully charged in 8 hours. The inner tank filled with phase change material is for cooling thermal storage as a latent tank in the design. However, its capacity can be as high as 60 MJ as a sensible water tank for heating storage in winter. In the future study, the DPUTB model will be incorporated into the dual-source heat pump system for evaluating the overall system performance of demand side management in the long term. [ABSTRACT FROM AUTHOR]

Heating and cooling of residential buildings is accountable for a significant share of the EU's final energy consumption. In order to determine the current condition of the building stock and to implement appropriate measures and requirements to improve energy efficiency of buildings, a detailed analysis of existing buildings is essential. This paper aims at describing characteristics of the building stock of Salzburg by analysing energy performance certificates. Therefore, the building stock is grouped into archetypes based on the construction period, building condition (not-retrofitted and retrofitted) and building type (single-family house and multi-family house) and then analysed regarding energy need for space heating, energy carrier, heat emission system, share and U-values of building elements and window to wall ratio. The analysis of the data demonstrates that the structure and naming conventions within the EPC-database pose hurdles for a correct investigation of the data. A comprehensible and distinct notation as well as versioning is inevitable for the sake of avoiding a loss of information and enabling international comparability. An analysis of energy carriers of the archetypes reveals, that a significant share of buildings still uses fossil fuels like oil and gas for energy supply, although electricity (heat pumps) and district heating are on the rise for buildings constructed in recent periods as well as for retrofitted buildings, with heat pumps being the most important energy carrier for new single-family houses amounting to a share of 65 % and district heating for new multi-family houses amounting to a share of 46 %. A detailed observation of the thermal performance of buildings and building elements reveals high potential and practicability not only for energy efficient new buildings, but also retrofitted buildings throughout all construction periods and for both, single-family houses and multi-family houses (e.g. median U-values for retrofitted ceilings/roofs range from 0.17 to 0.26 W/(m2K) compared to a median of 0.14 W/(m2K) for not-retrofitted ceilings/roofs from the most recent construction period). The conducted analysis provides detailed statistical information on the Salzburg building stock and hence a robust basis for further studies regarding the thermal performance of the building stock and future scenarios by means of urban building energy modelling approaches. Furthermore, based on this information, policies for energy efficient buildings can be improved and adapted according to current circumstances. [ABSTRACT FROM AUTHOR]

• A heat pump simultaneously driven by a gas engine and an electrical motor proposed. • A prototype was developed and tested to approve the feasibility. • Compressor rotation speed and engine power ratio can both change the heating capacity. • Engine power ratio can be adjusted for better efficiency and economic performance. • The heat pump has higher efficiency and less operating costs than traditional systems. The gas engine-driven heat pump (GEHP) has a higher primary energy ratio (PER) than the electric heat pump (EHP) for heating, but has a lower PER than the EHP for cooling. To exploit the advantages of GEHP and EHP, a heat pump system where the compressor could be driven simultaneously by a gas engine and motor was proposed in the paper. An experimental platform was established to investigate the feasibility and performance of the HPHP system. In addition, numerical models were built for further performance analyses. The results indicate that: (1) Increases in the rotation speed of the compressor and engine power ratio lead to an increase in the total heating capacity. The rotation speed should be adjusted first to meet the required heating load, and then the engine power ratio can be adjusted to achieve better performance; (2) Engine power ratio changes the loads of the engine and motor, thus their efficiencies change, leading to different PERs of the HPHP system. Under different local gas and electricity prices, the engine power ratio can also be adjusted to reach a minimum operating cost; (3) For the case-studied commercial building in Beijing, the annual primary energy consumptions for HPHP, GEHP, and EHP are 94.2, 95.7, and 100.0 kWh/m2, respectively. In addition, HPHP saves operating costs by 17.5 % and 35.1 % compared to GEHP and EHP, respectively, with static payback periods of 2.45 and 1.47 years, even if it is only used for heating in winter. [ABSTRACT FROM AUTHOR]

[Display omitted] The data collection process for thermal energy storage (TES) system is largely still and restricted to data collection only. This leaves a gap to study the transient state physical process of charge and discharge as it proceeds. In addition, these devices are restricted and cannot perform on spot model fitting, prediction and other data curation techniques. This paper demonstrates the application of intelligent data layer with neural networks for evaluating and predicting end to end performance of heat pump integrated stratified thermal energy storage (TES) system. The data modelling – acquisition, curation, and transformation is done in situ (dynamically). The key objectives are: • A method to demonstrate the application of data-layer framework to visualize in real-time energy efficiency of TES. To fit the second law of thermodynamics-based exergy model. This will help engineers to intuitively understand the energy efficiency of their devices using novel data pipeline. • To demonstrate the use-case of hyper-tuned DL framework of LSTM to predict the energy efficiency in the process loop. Predicted results show tuned correlation with the parametrized experimental data, even during the load phase, where substantial amount of math (convection/mixing) is present for the network to learn (train/test). [ABSTRACT FROM AUTHOR]

[Display omitted] • Thermal potential estimation of water source and their energy systems are reviewed. • Practical potential mainly depends on the geographical and temporal potential. • Pumping-well system requires high installation costs but can use high temperature. • Critical parameters for improving performance of entire system were investigated. In recent years, the utilization of a water source heat pump system (WSHP) has been proposed in South Korea as a solution to reduce energy consumption of buildings. To practically utilize the thermal energy of a water source, it is necessary to estimate the thermal potential of water sources and apply suitable energy conversion systems. However, there are extremely limited studies that conduct in-depth analyses to estimate the thermal potential of water sources and the energy conversion systems of water source heat pumps. In this context, this paper focuses on the review of the main issues in thermal potential estimation and energy conversion systems of water source heat pump systems. The estimation of thermal potential was reviewed in terms of theoretical, geographical, environmental, technical, and temporal potentials. The components constituting the system were investigated by dividing into heat pumps, water intake systems, and air handling units. In addition, the critical parameters for improving the performance of the entire system, such as building type, water source, and water intake distance, were investigated. It is expected that this study will be a valuable supplement to enable the thermal energy utilization of water sources to meet the growing energy demands. [ABSTRACT FROM AUTHOR]

• The necessity and rationality of catastrophe theory were addressed. • A new index model was proposed by combining the catastrophe theory with frosting. • The state variable and control variables of the index model were determined. • The predictive capability of the novel index model was validated. • Comparing with original strategy, the increase of COP was 3.9% under new strategy. In winter, the operating performance of air source heat pump (ASHP) units deteriorates due to the accumulation of frost on the outdoor coil surface. In order to reduce the impact of this disaster phenomenon, ensure stable operation and save energy, it is necessary to accurately determine the initiation of defrosting after a period of unit operation. Although some existing defrosting initiation control strategies are effective, too much data volume and accuracy are required. To address these issues, a different perspective on mutation from previous studies is taken. This study combines the cusp catastrophe theory with frost accumulation, and presents a defrosting initiation index model for ASHP. After a brief description of the cusp catastrophe theory, the discriminant index model based on the cusp catastrophe theory (DICC) is proposed, state variable and control variables of the index model are determined. Then, the unit was tested for 10-days. To solve and verify the DICC , 10-days experimental data was used and it was found that DICC can efficiently predict the heating capacity decreases. Consequently, the DICC -based defrosting initiation control strategy was compared with the existing strategies, and the unit's performance improvement compared to the original strategy was evaluated, as the results show, a 3.9% improvement in coefficient of performance (COP) and a 4.9% increase in heating capacity. Therefore, the strategy proposed in this paper is suitable for ASHP units with limited data capacity and low data accuracy, also can ensure the accurate initiation of defrosting and efficient operation. [ABSTRACT FROM AUTHOR]

• Control design for coupled natural ventilation and thermally active building system. • Assessment of operational performance using one-year high-fidelity measured data. • The annual heating and cooling energy consumption is 12.8 kWh/m2. • Issues identified and lessons learned for further improving the design and operation. The thermally active building system (TABS) has emerged as an energy-efficient measure for cooling and heating buildings since it facilitates the use of low-energy technologies, such as free cooling with geothermal sources and heating with low-temperature heat pumps. However, the control of TABS is challenging due to its high thermal inertia. Though a considerable amount of research has been done using simulations or small-scale experiments, few studies have published detailed long-term measured data of TABS operation. In addition, there has been little discussion on the control integration of slow-acting TABS with other fast-acting systems, such as natural ventilation. To fill these gaps, this paper presents a comprehensive assessment of the operational performance of the coupled NV and TABS using one-year high-fidelity measured data of an experimental small office building with an extensive sensor network located in Cambridge, Massachusetts. First, the coupled system and control design are described. Then, the thermal, energy and detailed control performance are assessed by comparing with design intents and simulated predictions. It is found that the coupled system demonstrates its effectiveness to control indoor thermal environment while achieving high energy efficiency. The annual energy consumptions are 11.5 kWh/m2 for heating and 1.3 kWh/m2 for cooling. The heating COP, including heat pump and two water pumps, is 3.5, and the cooling COP is 18.3 by utilizing free cooling from geothermal resources. The issues in operation are identified, including system/equipment faults, implementation of controls, and settings by building operators. Finally, lessons learned from this project are discussed and the strategies for improvement are summarized. [ABSTRACT FROM AUTHOR]

[Display omitted] • In the US, carbon savings are readily achievable by transitioning to heat pump technologies for the vast majority of homes. • The heat pump performance required to achieve carbon and cost neutrality varies by a factor of four across the US. • Energy cost neutrality is much harder to achieve than carbon neutrality. • Achieving carbon and energy costs savings is much easier when replacing older, low efficiency equipment. In order to meet climate goals, it will be necessary to significantly reduce the greenhouse gases emitted by homes. A key factor in the US is to reduce the on-site combustion of fossil fuels for heating end-uses and to replace this with use of electric heat pump technologies connected to a low-carbon grid. The replacement of natural gas furnaces with electric heat pumps is a key home decarbonization strategy. However, the potential for space heating electrification to reduce greenhouse gas emissions depends on the carbon dioxide equivalent (CO 2 e) content of the electricity used by the heat pump. This varies considerably depending on the source of electricity, with large state to state variability. Furthermore, household energy costs are likely to be impacted by the electrification of space heating, because retail energy prices for both natural gas and electricity in each state vary by factors of seven and four, respectively. Contractors, energy programs, government and building code officials, as well as consumers need clear indications of the likely CO 2 e and energy cost impacts of proposed electrification projects, because these will affect decarbonization choices and rationales around scaled heating electrification. Government and utility programs also need to be aware of the likely outcomes of any supported/incentivized measures. In this paper, we investigate these effects by looking at new metrics to analyze the change in CO 2 e emitted and the cost to meet home heating loads when switching from a natural gas furnace to a heat pump for the contiguous 48 states of the mainland US. [ABSTRACT FROM AUTHOR]

• An experiment of SGHP system and the detail description of combi-storage are presented. • Five daily operation modes are identified using the contributions of the energy inputs. • The dynamic thermal behaviors of the combi-storage are investigated and analyzed. Experimental investigations on thermal behavior of a combined solar and ground source heat pump (SGHP) system for a single-family house are presented. The SGHP system was installed at the Lyngby campus of Technical University of Denmark. Detailed experiments were carried out on the system in 2019 under real weather conditions covering domestic hot water (DHW) consumption and space heating (SH) demand. Depending on the contributions of the energy inputs to the combi-storage, five typical daily operation modes are classified. The focus of the investigations is on the dynamic thermal behaviors of the heat storage under different operating conditions. When the combi-storage was primarily heated by solar energy, the inlet stratifier in the storage performed well, ensuring thermal stratification and a good utilization of solar energy. Water temperature in the storage reached up to about 68℃ at the end of the solar heating process. When the combi-storage was primarily heated by the ground heat, the water temperature near the outlet for SH was kept at a temperature range from 26℃ to 31℃ in the heating process to ensure the outlet temperature level of SH, and the water temperature near the outlet for DHW was in the temperature range 47℃∼51℃ in DHW volume. When there was no heat input to the combi-storage, the pre-stored heat can meet the daily heating demand, and the number of days on this mode was up to 9.4% of the total experimental days. The paper gives valuable inputs for researchers and engineers who plan to integrate the combi-storage in a renewable heating system with solar collectors and ground source heat pumps. [ABSTRACT FROM AUTHOR]

• An innovative retrofit Motivation-Objective-Criteria (MOC) approach integrating homeowners' engagement is proposed in this paper. • Retrofit motivations are categorised into three typical types: 1) Self-living, 2) Rental or sale, and 3) Investment. • A novel Multi-motivation Performance Factor (MPF) concept is proposed to assess the holistic post-retrofit building performance with comprehensive retrofit combinations. • Homeowners' retrofit priorities have an apparent influence on selecting optimised retrofit measures. • This decision-making supporting tool accelerate building retrofit user acceptance and market penetration According to the EU Commission projection (2016/547/EU), the current average renovation rate is far below the expected rate of 3% to achieve carbon neutrality in building sectors by 2050. This is due to the fact that, during the building retrofit optimisation process, the decision-making criteria and objectives are generally optimised separately, and homeowners' motivations are often ignored or not carefully defined in most research. Limitations existed with a lack of in-depth and comprehensive understanding of the homeowners' motivations in undertaking building retrofit. To address this, we propose an inclusive Motivation-Objective-Criteria (MOC) approach, aiming to bring forward optimised decision-making for building renovation, accommodating different homeowners' retrofit motivations, objectives and criteria. Retrofit motivations are categorised into three typical types: 1) Self-living, 2) Rental or sale, and 3) Investment, under five objectives: Energy Reduction Rate (ERR), Initial Investment (II), Discounted Payback Period (DPP), Bills Reduction Rate (BRR) and Carbon Reduction Rate (CRR). A novel Multi-motivation Performance Factor (MPF) concept is proposed to assess the holistic post-retrofit building performance with comprehensive retrofit combinations. A UK semi-detached house is applied as the reference building to investigate the impact of homeowners' engagement on the decision-making of various retrofit measures. According to the cost-optimal results neglecting homeowners' motivation, it is evident that the mismatch of optimal retrofit combinations occurs between the minimum Initial Investment (II) and Discounted Payback Periods (DPP), with optimal ERR of 72%-79% and 82%-93%, respectively. Comparing cost-optimal with multi-objective optimisation results, it is concluded that homeowners' retrofit priorities have an apparent influence on selecting optimised retrofit measures. Besides, party wall insulation is fundamental for self-living- and rental or sale-motivated types. The solar-assisted heat pump and air–water heat pump are not necessary under the retrofit motivation of the "investment" type. Moreover, the attic floor and external wall insulation are imperative for rental or sale- and investment-motivated types. The sensitivity analysis results are conducted in this research, indicating that the optimal retrofit measures and baseline energy consumption input are in good agreement, with a 10% discrepancy. Thus, the proposed inclusive Motivation-Objective-Criteria approach can incorporate homeowners' engagement in the building retrofitting design process, serving as a decision-making supporting tool to accelerate building retrofit with maximised user acceptance and market penetration. [ABSTRACT FROM AUTHOR]

• Metal hydrides show potential for year-round energy storage with residential HVAC. • Hydride storage can shift both heating and cooling loads away from on-peak hours. • Using hydride storage results in higher cost savings in winter than in summer. • Hydride storage has a long payback period even for favorable TOU rates. • Long payback periods are due to high initial cost and hydrogen compression costs. Thermal energy storage (TES), such as ice storage, is often used with air conditioning systems to shift cooling loads away from peak hours, reducing operating costs if time-of-use electricity rates are available. Phase change materials (PCMs) have been investigated for energy storage with heating systems; however, a single PCM cannot be used for storage with both cooling and heating since PCMs have fixed phase-change temperatures. Thermochemical energy storage with metal hydrides can be used for this purpose since the reaction used to store energy depends on both temperature and pressure, allowing for variable-temperature storage. In this paper, we propose a novel TES system design using metal hydrides coupled to a heat pump for residential heating and cooling and present a system model. The model is used to analyze system performance and predict cost savings for year-round use in a residential building. This system is shown to be capable of shifting heating and cooling loads, but only achieves cost savings of $13/year at existing utility rates. The payback period of the system exceeds 35 years across a range of rates more favorable to energy storage, primarily due to the high cost of metal hydrides. Potential improvements to the system are discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • EAHE preheating/precooling potential for reducing buildings energy consumption. • Discussion on the chief design and operation aspects that affect EAHE performance. • Survey on advances in hybrid EAHE systems to improve the use of renewables. • EAHE systems coupled with other active and/or passive techniques. • Inventorying of research gaps and emerging trends in the EAHE research domain. This paper provides an up-to-date survey on recent advances in earth-air heat exchanger (EAHE) systems for buildings, and presents systematic information on the main design parameters and operation conditions that affect the overall performance of the technology. This review also aims at providing room for the discussion on how this technology can be used in standalone and/or hybrid schemes, i.e. , EAHE systems coupled with other active/passive techniques, such as air conditioners, air source heat pumps, heat recovery units, mechanical ventilation systems and air handling units, evaporative cooling, air humidity control devices, photovoltaic panels, building integrated photovoltaic systems, solar air heaters and heating ducts, solar chimneys, wind towers, building thermal mass and phase change materials. It was concluded that further research is required to provide reliable design guidelines for different climates, EAHE configurations, typologies of buildings, sorts of construction, types of soils, and finally, to overcome the main drawbacks of the technology that have restrained its worldwide dissemination. Further studies are also required to numerically and/or experimentally assess the thermal performance, the environmental benefits, and the economic viability of innovative hybrid EAHE systems, since a great research gap persists on this matter. [ABSTRACT FROM AUTHOR]

To date, the assessment of the energy flexibility to be delivered by existing buildings and by their legacy HVAC systems is hindered by a lack of commonly agreed-upon methodologies. There are many research works in the field; however, many of them are focused on the design stage or, in case of addressing building operation, they are based on controlled experimental set-ups. The novelty of this paper lies in the fact that it develops and validates an original methodology for the Flexibility Function estimation to evaluate the delivered energy flexibility of several Automated Demand Response services applied on different heat pump systems working under real operations. The active interaction with several electricity markets, ranging from the Spanish day-ahead market to the German and Swiss ancillary services markets, have also been evaluated during the winter and spring seasons. The method results showed that heat pumps could offer a significant potential of flexibility in the analysed countries. Nevertheless, it has also been envisaged that some restrictions concerning reaction times and reliability may affect its readiness for certain ancillary services markets. [ABSTRACT FROM AUTHOR]

Building energy models are a key element in regulatory compliance calculations. These energy performance calculations often do not accurately reflect actual operating conditions. Therefore, evaluation of energy performance comparing actual energy use of a building with the outcome of dynamic simulation models can be misleading, this difference is also known as the energy performance gap. The reduction of the gap is an important task aimed to provide confidence in the use of models for evaluation of energy efficiency. This paper is focused on reducing the technical issues (e.g. poorly adjusted thermal parameters in the envelope, inefficient boiler operator or lack of adjustment in parameters of heat pumps, baseboard radiators or air handling units) which are one of the main causes of the energy performance gap. The application of a multi-step, optimization-based, calibration methodology performed in a white-box simulation environment (EnergyPlus) using three months of ten minute time-step data to adjust HVAC parameter values with a genetic algorithm software (Jeplus) is validated on a real test site. Resulting in a BEM that fits the building's hourly performance benchmark into international standards on three key levels: indoor temperature by Thermal Zone (TZ), heat production and electric consumption from heat pumps, which comprise all the components of a building energy model. A batch of 1500 h of heating operation, obtained from the building management system, has been used to calibrate the model. The results complied with the requirements of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Guideline 14–2002 at hourly interval, with NMBE ⩽±10%,Cv(RMSE) ⩽30% and R2 ⩾75% and with the International Performance Measurement and Verification Protocol (EVO) for Cv(RMSE) ⩽20% and R2 ⩾75% in the three aforementioned levels, which can be considered a step forward in the area of calibrating white box models. In addition, to prove the strength and robustness of the results, the model has been checked in a long testing and independent period of 2.500 h of heating operations with the same level of compliance. The demonstrator is the library of a school located in Denmark. The HVAC system is composed of four air–water heat pumps that deliver heating to the whole compound with the backup support of a gas boiler. The library is heated with baseboard radiators system with the support of an air handling unit used for ventilation purposes. [ABSTRACT FROM AUTHOR]

• Experiments on high-efficiency heat pump with two, three, four simultaneous faults. • Four faults increased refrigerant superheat up to 18 °C. • NC faults tend to increase refrigerant subcooling. • An existing virtual refrigerant charge sensor was tested with simultaneous faults. Faults in air-cooled vapor compression air-conditioning systems are known to reduce performance, including efficiency, capacity, and lifespan. Their effects have been studied, and fault detection and diagnostic (FDD) methods have been developed as tools for field technicians to install or repair systems, or for monitoring to alert operators to the fault's presence. Most of this work has focused on faults that occur singly. It is likely that in some systems, multiple faults occur simultaneously, but it is uncertain what effects this may have on diagnostics. This paper describes a laboratory study of a split system air source heat pump in which combinations of two, three, and four simultaneous faults occur. The study includes all combinations of: improper evaporator airflow; overcharge or undercharge of refrigerant; liquid line restrictions; and non-condensable gas in the refrigerant, each at multiple fault intensities. Fault features – those characteristics that can be determined from measurements, for use in diagnostics – are analyzed, and the key fault features are presented. A robust existing method for determining refrigerant charge, the virtual refrigerant charge sensor (VRC) is tested using the multiple fault data, in order to understand how its performance is impacted by the combined faults. The VRC performs well, typically able to correctly determine whether a system is undercharged or overcharged, but the magnitude estimates are impacted. The results suggest that simple subcooling-based methods of charging a system are likely to provide unsatisfactory results when other faults are present. [ABSTRACT FROM AUTHOR]

• The Solar Decathlon successfully tackles the triple: design, build, operate. • Competition houses demonstrate net energy positive buildings. • All energy supply systems are based on PV and air heat pumps. • Houses with battery storage provide flexibility in building grid interaction. • Online knowledge platform provides building information and monitoring data. • The competition format can be linked to building science. The Solar Decathlon is a competition for universities from all over the world to design, build and operate small experimental solar powered houses. Its first edition took place in the US in 2002. Since 2010 it is in practice in Europe with four competitions and 65 net zero or net energy plus houses build and tested in 10 disciplines (decathlon). This paper provides an overview and analysis on the European edition of the competition. The work was carried out within the framework of Annex 74 "Competition and Living Lab Platform" of the International Energy Agency and an EC funded project named "Solar Decathlon Europe - Analysis of the Results". The analysis was based on the development of a web based knowledge platform, providing a large set of information and monitored data from past competitions. Based on the availability of information and data, the comparative evaluation is centred on the building energy supply systems and their performance. Starting with very large PV systems, the latest competitions rules trigger the teams to apply systems sized comparable to small buildings in net zero energy building practice. As a result not all houses succeed in a positive energy balance. Due to the wider introduction of batteries the self-consumption of the solar yield and the degree of self-sufficiency increases. New developments of the competition rules stimulate the energy flexibility in operation with the power grid. Modifications for the rules and the monitoring procedure for the next edition intend to further link the competition to building science. [ABSTRACT FROM AUTHOR]

Through tests conducted at the Toronto and Region Conservation Authority's (TRCA) Archetype Sustainable Houses, a hybrid residential space heating system with a supervisory controller was monitored and studied to evaluate its performance and effectiveness for the heating season. A high efficiency natural gas furnace (NGF) and an electric air source heat pump (ASHP) were coupled together to meet the space heating demand of the house. This integrated system is called the cloud based Smart Dual Fuel Switching System (SDFSS) that considers time-of-use (TOU) pricing, fuel cost, short-term weather forecast, and equipment efficiencies and capacities. This multi-variable decision-making process defines an optimal schedule for the hybrid system to run more cost effectively. This paper analyses two separate SDFSSs. According to these analyses, the SDFSS systems showed lower operating cost with respect to the furnace or the ASHP system alone with various carbon tax (CT) levels from $0 to $250/tonne of CT with an increment of $10/tonne of CT that were simulated, along with a significant GHG emission reduction relative to the conventional heating systems. Furthermore, with these technologies, Canada's residential sector could potentially meet Canada's Paris Agreement goals. The SDFSS technology is a is flexible, user friendly, ubiquitous technology for the smooth transition from today's natural gas dominated space heating system to the future's low carbon infrastructure powered by a heat pump and renewable energy. [ABSTRACT FROM AUTHOR]

• Models of heating tower heat pump systems are developed and verified. • Performance of heating tower heat pumps are compared with other two common systems. • Technical and economic performance maps of heating tower heat pumps are developed. • Regional suitability of heating tower heat pumps is studied in different climate zones. Heating tower heat pump (HTHP) technology is evolving rapidly owing to its good performance in summer and frost-free operation in winter. However, a lack of comprehensive comparisons between the HTHP and conventional methods, such as the air-source heat pump (ASHP), and the chiller and boiler, significantly limits its applications. To solve this problem, this paper analyzes the technological and economic performance of these three types of systems at 353 locations over China. The principle of energy saving and potential of the HTHP are presented, based on which a comparison of economic performance is conducted by considering the efficiency of energy conversion and cost of the three systems. The results show that the HTHP is superior to the ASHP at most locations in China, with a 10% to 20% higher annual performance factor (APF). For locations in southwest China, this improvement is less than 10% owing to the large regeneration penalty in winter, and minor differences between dry-bulb and wet-bulb temperatures in summer. The APF of the HTHP is 10% to 23% higher than the chiller and boiler system in the hot summer and cold winter zone as well as the cold zone. However, the HTHP exhibits no advantage over this system in the severe cold zone because of the low efficiency of the heat pump in winter, or in the hot summer and warm winter zone owing to the small heating load. The results are used to develop technical and economic performance maps to guide the application of the HTHP in different climatic regions. [ABSTRACT FROM AUTHOR]