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Efficient electric heat pumps that replace fossil-fueled heating systems could significantly reduce greenhouse gas emissions. However, electric heat pumps can sharply increase electricity demand, causing high utility bills and stressing the power grid. Residential neighborhoods could see particularly high electricity demand during cold weather, when heat demand rises and heat pump efficiencies fall. This paper presents the development and field demonstration of a predictive control system for an air-to-air heat pump with backup electric resistance heat. The control system adjusts indoor temperature set-points based on weather forecasts, occupancy conditions, and data-driven models of the building and heating equipment. Field tests from January to March of 2023 in an occupied, all-electric, 208 m 2 detached single-family house in Indiana, USA, included outdoor temperatures as low as − 15 ° C. On average over these tests, the control system reduced daily heating energy use by 19% (95% confidence interval: 13%–24%), energy used for backup heat by 38%, and the frequency of using the highest stage (19 kW) of backup heat by 83%. Concurrent surveys of residents showed that the control system maintained satisfactory thermal comfort. The control system could reduce the house's total annual heating costs by about $300 (95% confidence interval: 23%–34%). These real-world results could strengthen the case for deploying predictive home heating control, bringing the technology one step closer to reducing emissions, utility bills, and power grid impacts at scale. • First field deployment of predictive control for an air-to-air heat pump in a cold climate. • Review of all known field studies of supervisory control for residential HVAC. • Reduced heating energy use by 13%–24% and use of highest-stage backup heat by 83%. • Occupants reported similar thermal comfort to benchmark control system. • Discussion of deployment labor, costs, challenges, and scalability. [ABSTRACT FROM AUTHOR]

This study assesses alternative energy technologies (i.e., PV and battery systems, electric heat pumps, hybrid gas heating with solar thermal energy) in terms of profitability and CO 2 emissions, for the case of two simulated typical households living in detached houses in Germany. Under the status-quo regulatory framework, the energy transition in the heating sector is fostered through grants for replacing old heating systems, whereas PV generation is fostered by feed-in tariffs and indirect subsidies for self-consumption. This study considers an alternative regulatory scenario with a more market-oriented approach, finding that a CO 2 -oriented reform of energy surcharges and taxes, as well as a reform of network charges, can support a more cost-efficient energy transition in the residential sector. The paper concludes with a discussion of the consistency, cost efficiency and effectiveness of past and current policies underpinning the energy transition in the residential sector. • Assessment of home energy systems across 2 households and 2 regulatory scenarios. • Consideration of PV, batteries, heat pumps and hybrid gas-solar heating systems. • Comparison of subsidies and flat energy tariffs vs. cost-reflective, dynamic tariffs. • Market-oriented approach incentivizes far more cost-efficient CO 2 emission reduction. • The German residential energy sector needs a consistent regulatory framework. [ABSTRACT FROM AUTHOR]

Demand-side flexibility is an important tool for enhancing the interaction of renewable energy resources and reducing the need for grid upgrades. To employ this flexibility as a market product, it is necessary to aggregate and coordinate by coordinating responsive loads. In this regard, designing effective load coordination mechanisms that consider the preferences of aggregators, end-users, and network operators is critical for the successful implementation of demand response (DR) programs. This paper proposes an incentive-based method for coordinating a group of controllable devices that is practical, does not require complex, high-order models of the entire system, respects end-users privacy and quality of service (QoS), and can readily incorporate network conditions to ensure grid reliability. The proposed method includes algorithms at both the end-user level for controllable device operation and the aggregator level for managing the grid access requests. These algorithms are fast and with low computational burden which makes them suitable for the designed framework, reduces the implementation cost and increases the chance of scalability. The method is illustrated with a realistic test system consisting of a set of controllable heat pumps used in pool heating systems and uncontrollable loads placed in a distribution feeder and supplied by a distribution substation transformer. Simulation results highlight the effectiveness of the proposed method in satisfying the controllable device, end-users, and grid constraints. Comparing the results with similar existing methods shows that the method is 11% more cost-effective than traditional ON/OFF methods while reducing the number of rejected grid access requests from the devices, significantly. • Proposing a bottom-up methodology for coordinating grid access requests of devices. • Introducing a computationally lightweight incentive-based device controller algorithm. • Designing the method in such a way as to guarantee the quality of service for end-user. • Simulation-based implementation of the method on a set of swimming pool heat systems. • Decrease in electricity costs by 11% compared to conventional methods. [ABSTRACT FROM AUTHOR]

Air-to-water heat pumps are one of the most common and energy efficient heating systems for buildings, particularly floor-heating plants. One way to further improve their effectiveness is to control the heat pump exploiting the dependence of its coefficient of performance (COP) on the external temperature and temperature of the return water from the load. In particular, it is possible to exploit the heat pump when its efficiency is higher, so optimizing its performance in a predictive manner, anticipating the impact of external conditions. For the case of an air-to-water heat pump, the optimization problem is nonlinear due to the load dependence of the heat pump COP and variable supply water flow rate. This may pose implementation problems. If we address a standard control hardware, simplified optimal control formulations are more effective. In this paper, we specifically address this issue, and a reduced-order, linear, but adaptive time-varying predictive model of the heat pump COP is designed. Our solution takes into account the variation of the heat pump efficiency based on the external temperature and the load profile, which are changing within the control horizon. The proposed COP model is then used within a linear time-varying model predictive controller formulation which provides a prediction of the heat pump dynamical behavior based on the load dependence of the heat pump COP, while tackling the nonlinearities of the system imposed by the variable water flow rate in the hot water tank and also by the load dependence of the heat pump COP. The proposed approach has been implemented and in detail tested on a reference model based on a real case study from the Denmark Technical University, Risø Campus, SYSLAB. An intensive simulation analysis and complements the testing, showing the accuracy and the potential of the method, also in the perspective of practical implementation. • Optimization of heat pump behavior considering variable COP. • On-line estimation of simplified COP models with EKF. • Experimental validation of the model used. • Feasibility of realtime optimization proved. [ABSTRACT FROM AUTHOR]

Distributed solar heating systems have high energy-saving potential as clean and energy-efficient production units in residential building applications. Solar energy resources are weak in hot summer and cold winter zone in China, which makes it difficult to completely rely on solar energy to heat residential buildings. A critical challenge is the lack of a theoretical basis for how to choose the solar-assisted heating system form. In this paper, seven solar-assisted heating systems are modeled and their performances are evaluated in six cities by using TRNSYS software. In terms of performance indicators, the solar fraction, the season performance factor, and the heat efficiency are used to thoroughly discuss the viability of using solar heating technologies in this zone. Based on the results, the average indoor air temperature was maintained between 16 °C and 20 °C, and the lowest solar fraction obtained was 10.1%. The carbon emission reduction in each city ranged from 60 kg to 400 kg, yielding good environmental benefits. According to the comprehensive comparison of the six evaluation indexes considered, the parallel or dual-source solar-assisted air source heat pump system can be used in a zone with medium solar energy resources. It is more suitable to use a dual-source solar-assisted air-source heat pump system in a zone with poor solar energy resources. The findings of this work can guide and promote the widespread application of distributed solar heating in household residential buildings in the hot summer and cold winter zone in China. [Display omitted] • The application status of solar heating technology is investigated in HSCW zone. • TRNSYS simulation verifies the feasibility of 7 different solar-assisted systems. • Comprehensively evaluate the thermal performance of 7 systems in 6 cities. • Multi-dimensional investigations of which system is suitable in HSCW zone. [ABSTRACT FROM AUTHOR]

International Energy Agency predicts that the global number of installed heat pumps (HP) will increase from 180 million in 2020 to approximately 600 million by 2030, covering 20% of buildings heating needs. Electric power consumption is one of the main key performance indicators for the heat pump systems from techno-economic perspective. However a common issue prevalent in many existing heat pumps is the lack of electric power measurement. The modern installations might be equipped with electric power measurement sensors but this comes at a higher system cost for the manufacturers and end-users. The primary objective of this work is to propose a virtual measurement for estimating power consumption, thereby eliminating the need for field measurement of power for heat pumps. To achieve the objective, a data-driven approach is proposed. Firstly, the in-situ data is preprocessed through data merging, cleaning, and normalization. Then, input features are pre-selected using Spearman correlation coefficients, and further refined by addressing multicollinearity problem. Following this, Extreme Gradient Boosting (XGBoost) models and polynomial models are developed by considering different features as inputs. All models are finally validated against the in-situ data from multi-units of ground source heat pump (GSHP) and air source heat pump (ASHP) installations. The results showed that the electric power consumption of GSHP can be estimated with high accuracy (99% for R 2 , 10 W for MAE, and 1% for MAPE) through generic data-driven models using only four easy-to-measure input features. Taking three input features as inputs for ASHP generic model, the accuracy can be reached to 83% for R 2 , 125 W for MAE, and 9% for MAPE. The method presented in this paper can be applied to estimate power consumption of millions of heat pumps and consequently add a significant value as well as provide different types of services, such as cost-saving benefits for manufacturers and end-users, flexibility services for aggregators and electricity grids. • Collect and analyze in-situ data from multiple residential GSHP and ASHP units. • Propose a two-step feature selection method to indicate the most essential inputs. • Evaluate the most predominant features by data-driven models with different inputs. • Develop high accuracy generic data-driven models with limited inputs features. [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]

• The first review of electrical heat pumps assisted by natural gas is performed. • Many different layouts and control strategies were found. • In most of the analyzed case studies, a rule-based control strategy is assumed. • Researchers presented very heterogeneous key performance indicators. • Exhaustive environmental analyses are very rarely presented. In this paper, a comprehensive review is performed on hybrid systems using electrical Heat Pumps for Heating, Ventilation & Air Conditioning systems and Domestic Hot Water production using case studies from 2016 to 2022. This work particularly focuses on studies that investigated systems with electrical Heat Pumps assisted by a gas boiler. Some studies that considered the exploitation of renewable energy sources, but not as a whole substitute for fossil sources, have also been included. In particular, the analysis investigated the layouts of the systems by considering the type and the size of the components, the control methods applied (by distinguishing rule-based control methods and predictive control methods), and the main performance indices used to calculate energy, exergy, environmental and economic performance. Most of the analysed studies demonstrated that the hybrid systems could be very advantageous if the switch or the integration of the two generators is well managed. Nevertheless, the energy and economic performances are very different for each system studied. They are highly influenced by the control strategies implemented and by the objective functions adopted. Furthermore, climate can influence performance while affecting the Coefficient Of Performance of the heat pump and the availability of energy sources. Regarding economic issues, the systems' performances vary according to specific Country tariff structures. The review reported a promising research activity also pursued by manufacturers of components and equipment. Nevertheless, the paper highlights new possible research and development directions. [ABSTRACT FROM AUTHOR]

Abstract The paper presents the annual results of monitoring a hybrid heat source consisting of a condensing gas boiler, ground and air heat pump, and solar collectors. A boiler with a nominal heat output of 186 kW works with an 81.1 kW ground-source heat pump, a 27.4 kW air-to-water heat pump and six solar collectors. The hybrid heat source is located in the fire brigade building to provide heat for space heating and ventilation and to supply domestic hot water. The annual monitoring results of the hybrid heat source were analysed in detail. The entire heat plant was equipped with measuring instruments enabling determination of heat output of individual devices, average boiler efficiency in the heating and summer season, the heating seasonal performance factor for ground and air heat pump, gas consumption by the boiler and electricity consumption by individual devices. The heat energy produced by individual devices was determined for a given period. Selected results of the economic analysis are also discussed. The annual costs of purchasing gas and electricity consumed by heat pumps were compared. Boiler efficiency as a function of parameters characteristic for a hybrid heat source was presented. The use of ground and air-source heat pumps and solar collectors reduced the consumption of natural gas during the year by 21,621 m3. As a consequence of the reduced natural gas consumption, the carbon dioxide emissions decreased during the year by 13.32 Mg. Highlights • A system of a gas boiler, solar collectors, ground and air heat pumps was studied. • One year operation of a hybrid heat source system was experimentally assessed. • The efficiency of a boiler was 0.96 in the heating season and only 0.6 in summer. • The share of the ground heat pump in annual heat production was 43% and boiler 51%. • Significant reduction in the gas consumption and CO 2 emission was achieved. [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]

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 very low heating load of deep renovated buildings following standards such as EnerPHit, and the limited space in renovation create the need for compact heating systems. An innovative heating and ventilation system - consisting of an exhaust air to supply air heat pump combined with a heat recovery ventilation unit, both integrated into a prefabricated timber frame façade - was developed and installed in a flat during the renovation of a multi-family house in Ludwigsburg, Germany. The system and the flat were monitored for the complete heating season 2016/2017. This paper presents: (a) an analysis of the monitoring data, (b) the development and validation of the models of the system and the flat, and (c) the results of the dynamic simulations that were performed for further system optimisation. Inside the flat, good thermal comfort and indoor air quality conditions were achieved. The monitored SPF of the system was 2.8. Simulation results showed that with the optimised system and control, there can be an electricity savings of 25%. The developed system has the potential to be cost-effective due to prefabrication and low heating capacity. It represents a compact solution with moderate energy performance, appropriate for minimally disruptive renovations. [ABSTRACT FROM AUTHOR]

• World's first grid-scale PHES demonstrator system has been described. • Performance of a novel heat pump/engine has been tested and losses are quantified. • Round-trip efficiency of the system has been identified numerically. • Round-trip efficiency is within a range of 70–80 % for single storage cycle. • Periodic operation can yield a steady global round-trip efficiency of about 73 %. Among the known energy storage technologies aiming to increase the efficiency and stability of power grids, Pumped Heat Energy Storage (PHES) is considered by many as a promising candidate because of its flexibility, potential for scale-up and low cost per energy storage unit. Whilst there are numerous demonstration systems under development, as it stands the only PHES demonstration system to be realised at scale is located in Hampshire, UK. This paper aims to present the results and analysis obtained from its commissioning and testing as part of an on-going study. The system was designed to offer a nominal power size of 150 kW e and energy storage capacity of 600 kWh e for an 8-hour storage cycle. This work presents evidence of the system Round-trip efficiency (RTE), which is considered as a fundamental performance metric for large-scale energy storage technologies. Recorded Pressure-Volume (P-V) measurements from recent heat pump/engine testing at part-load offers useful insight in terms of overall performance. Models are also developed to simulate the system to finally predict the performance at full-load conditions. The system and principle of operation are described first, followed by mathematical modelling outlining heat transfer mechanism and associated key losses involved in thermodynamic processes within components, and finally results are presented and compared at different operating conditions using different working gases. The results show good agreement with earlier studies, which indicate that expected electricity-to-electricity RTE is quite comparable to other mature technologies such as Pumped Hydropower Storage and Compressed Air Energy Storage. The cyclic operation of the system is also discussed. One-off storage cycle results in lower RTEs compared to a load-levelling cyclic operation where the efficiency is significantly improved due to stable packed-bed behaviour and better utilisation after an initial transient state. [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]

[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]

Heating electrification powered by distributed renewable energy generation is considered among potential solutions towards mitigation of greenhouse gas emissions. Roadmaps propose a wide deployment of heat pumps and photovoltaics in the residential sector. Since current distribution grids are not designed to accommodate these loads, potential benefits of such policies might be compromised. However, in large-scale analyses, often grid constraints are neglected. On the other hand, grid impact of heat pumps and photovoltaics has been investigated without considering the influence of building characteristics. This paper aims to assess and quantify in a probabilistic way the impact of these technologies on the low-voltage distribution grid, as a function of building and district properties. The Monte Carlo approach is used to simulate an assortment of Belgian residential feeders, with varying size, cable type, heat pump and PV penetration rates, and buildings of different geometry and insulation quality. Modelica-based models simulate the dynamic behavior of both buildings and heating systems, as well as three-phase unbalanced loading of the network. Additionally, stochastic occupant behavior is taken into account. Analysis of neighborhood load profiles puts into perspective the importance of demand diversity in terms of building characteristics and load simultaneity, highlighting the crucial role of back-up electrical loads. It is shown that air-source heat pumps have a greater impact on the studied feeders than PV, in terms of loading and voltage magnitude. Furthermore, rural feeders are more prone to overloading and under-voltage problems than urban ones. For large rural feeders, cable overloading can be expected already from 30% heat pump penetration, depending on the cable, while voltage problems start usually at slightly higher percentages. Additionally, building characteristics show high correlations with the examined grid performance indicators, revealing promising potential for statistical modeling of the studied indicators. Further work will be directed to the assessment of meta-modeling techniques for this purpose. The presented models and methodology can easily incorporate other technologies or scenarios and could be used in support of policy making or network design. [ABSTRACT FROM AUTHOR]

Space heating and cooling appliances consume a significant amount of energy in buildings. In recent decades, ground source heat pump (GSHP) systems have become popular for space heating applications in many countries. However, countries like India need both space heating and cooling and hence its performance needs to be evaluated in both heating and cooling functions for economical operation. The experimental results obtained for both modes of operation are discussed in detail in this paper. Details of the experimental setup used, measurements, performance of ground heat exchanger (GHX) used and calculation of COP, effectiveness and extraction/injection are explained. Using the experimental data the coefficient of performance (COP) of heat pump and GSHP are obtained. The average COP of the GSHP system obtained during space cooling was found to be 21% less than the value obtained for heating mode operation and also heat extraction by the GHX fluid is observed to be high at the starting of the operation. In heat injection mode, as the operational time increases, the surrounding soil temperature also increased thus creating more resistance for heat flow. The average effectiveness of GHX was found to be 0.29 and 0.33 in heating and cooling mode operations respectively. [ABSTRACT FROM AUTHOR]

This paper aims to investigate a solar driven direct-expansion heat pump system employing the novel PV/micro-channels-evaporator modules, in terms of its solar thermal, electrical and overall efficiency, as well as coefficient of performance (COP), at the real-time operational condition. This work was undertaken through a dedicated system design, construction, field-testing and performance analysis. It was found that the novel PV/micro-channel-evaporator modules could achieve an average thermal, electrical and overall efficiency of 56.6%, 15.4% and 69.7% respectively at the specified operational condition, while average COP of the system reached 4.7. The innovative feature of the system lied in the structure of the evaporator that was made of the parallel-laid micro-channels. Such a structure created the reduced interior cross-sectional area and thus increased vapor flow velocity within the channels, while the high vapor velocity generated a higher shear stress exerted upon the liquid-vapor interface, leading to the reduced liquid film thickness, increased refrigerant evaporation rate, and increased electrical and heat outputs. The research has provided the fundamental data and experience for developing a highly efficient and practically feasible solar heat pump system applicable to the cold climatic conditions, thus contributing to significant fossil fuel saving and carbon reduction in the global extent. [ABSTRACT FROM AUTHOR]

Ground-coupled heat pumps are widely applied in cold regions, but soil thermal imbalances in some projects greatly deteriorate the systems’ practical performances and heavily inhibit the systems’ reasonable applications. This paper presents a comprehensive overview of the main problems caused by soil thermal imbalance and the existing solutions targeting on them. The caused problems mainly present in the following aspects: soil temperature decrease, heating performance deterioration, heating reliability decline, and even system failure. Three kinds of existing solutions can be classified. Ground heat exchanger-modified solutions including increasing borehole space, increasing borehole length, modifying borehole layout, and improving thermal properties, can retard the thermal imbalance to some extent, suitable to projects with slight imbalance. System-modified solutions integrating auxiliary energy sources like fossil fuel, solar energy, ambient air and waste heat with ground-coupled heat pumps or using ground-coupled absorption heat pumps, can eliminate serious thermal imbalance essentially by increasing soil thermal injection and decreasing the extraction. Thus, they are dominant in the applications and attract more attention along with the utilization of renewable energies. Apart from the modifications of system design, operation-modified solutions, like seasonal and intermittent operations, are also helpful to maintain better soil thermal balance. Based on the overview, the current application situations and economic performance of different solutions are discussed. Finally, some suggestions for the applications of ground source heat pumps in cold regions are proposed to make the overview helpful for the system research and applications. [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]

Abstract: The article described the dilatancy technology of district heating system with high-temperature heat pump (HTHP). For the exploitation of low-temperature return network sources, a high-temperature heat pump with a heat exchanger was planned. As the core technology of the dilatancy district heating system, HTHP units and heat exchanging systems had been described detailedly through theoretical and experimental analysis. The model was proved to be in good agreement with the experiment data. It could be used for engineering design. In this paper the district heating system in Datong was taken as a case study. The main characteristics of the dilatancy district heating system had been presented in the form of diagrams. The principal advantage of dilatancy technology in the district heating system lies in increasing the temperature difference, reducing the diameters and the initial investment of primary side network. This paper shows clearly the analysis of the dilatancy technology for characterising and improving the performance of district heating systems. [Copyright &y& Elsevier]

Storage tanks are widely used in heat pump driven heating systems. In this application, storage tanks can: reduce the number of times the heat pump compressor starts; adapt the capacity of heat generation to heat demand; which can offer the possibility to use low rate electricity. This last point will assume increasing importance as smart grids become more prevalent. Floss and Dietrich (Optimierte integration von Pufferspeichern in hydraulische Systeme, in: Proceedings of the International Congress e-nova 2008, Pinkafeld, Austria, 2008, pp. 129–136, ISBN 978-3-9500919-8-4) points out that due to different effects such as mixing or heat conduction inside the tank, the supply temperature at the consumer is lower than the outlet temperature of the heat pump. The average (mass flow weighted) of this temperature drop was named drop of mean temperature (DoMT). It varies between 0.2 °C and 10 °C, depending on the hydraulic integration inside the storage tank, and can reduce the efficiency of the system up to 30%. This paper discusses options to reduce the DoMT, thereby raising the efficiency of the heat pump system through an optimized integration of storage tanks, and a variation of the mass flow rate in the hydraulic system. These results are based on theoretical and practical investigations undertaken at the Institute of Building Energy Systems, University of Applied Sciences, Biberach, Germany. [ABSTRACT FROM AUTHOR]

The coefficient of performance (COP) of air-source heat pumps (ASHP) decreases toward low outdoor temperatures. This paper presents an auto-cascade heat pump system (ACHPS) with the objective to improve the heating performance of ASHP in cold climate. The auto-cascade process is achieved based on the separation of binary zeotropic refrigerant mixture consisting of pure refrigerants with different boiling points. Fluid selection for the ACHPS is carried out to validate the feasibility for potential application. Based on the performance analysis on COP, 15 qualified binary mixtures are obtained. R143a/R600 (0.8/0.2) tops the potential working fluid with a COP of 2.15. The effects of system parameters, such as circulation composition, heat transfer fluid (HTF) temperature glide and temperatures of heat source and sink on COP and exergy efficiency of ACHPS are thereafter investigated. The simulation results show that there exist a maximum COP of 2.15 and a maximum of exergy efficiency of 37.2% at the R143a mass fraction of 0.8 when the ambient temperature and heating temperature are −10 °C and 50 °C, respectively. Finally, by comparison with the single-stage heat pump operating with commercially available refrigerants, the proposed ACHPS shows an advantage of compressor isentropic efficiency. The compression isentropic efficiency of ACHPS could be increased by 25.5% compared to the single stage cycle working with R407c when the ambient temperature is −10 °C. [ABSTRACT FROM AUTHOR]

• Paper presents a novel approach for optimising the mix of heat supply technologies. • Heat supply choices are affected by local and national interactions with power. • Heat sector flexibility can support decarbonisation of electricity supply. • Emission limits and grid constraints shape the optimal heat plant portfolio. • Increasing heat storage capacity can help with local network constraints. Decarbonisation of the heating and cooling sector is critical for achieving long-term energy and climate change objectives. Closer integration between heating/cooling and electricity systems can provide additional flexibility required to support the integration of variable renewables and other low-carbon energy sources. This paper proposes a framework for identifying cost-efficient solutions for supplying district heating systems within both operation and investment timescales, while considering local and national-level interactions between heat and electricity infrastructures. The proposed optimisation model minimises the levelised cost of a portfolio of heating technologies, and in particular Combined Heat and Power (CHP) and polygeneration systems, centralised heat pumps (HPs), centralised boilers and thermal energy storage (TES). A number of illustrative case studies are presented, quantifying the impact of renewable penetration, electricity price volatility, local grid constraints and local emission targets on optimal planning and operation of heat production assets. The sensitivity analysis demonstrates that the cost-optimal TES capacity could increase by 41–134% in order to manage a constraint in the local electricity grid, while in systems with higher RES penetration reflected in higher electricity price volatility it may be optimal to increase the TES capacity by 50–66% compared to constant prices, allowing centralised electric HP technologies to divert excess electricity produced by intermittent renewable generators to the heating sector. This confirms the importance of reflecting the whole-system value of heating technologies in the underlying cost-benefit analysis of heat networks. [ABSTRACT FROM AUTHOR]

• Data-driven and comprehensive thermodynamic technology models are developed. • Multi-fidelity approaches are used to compare heat-generation solutions. • Centralised CHP systems appear to be the most profitable option at present. • Heat pumps can achieve a significant degree of heat decarbonisation (55–62%). • Thermodynamic models reduce uncertainty by 75% compared to black-box approaches. This paper presents a multi-scale framework for the design and comparison of centralised and distributed heat generation solutions. An extensive analysis of commercially available products on the UK market is conducted to gather information on the performance and cost of a range of gas-fired combined heat and power (CHP) systems, air-source heat pumps (ASHPs) and ground-source heat pumps (GSHPs). Data-driven models with associated uncertainty bounds are derived from the collected data, which capture cost and performance variations with scale (i.e. , size and rating) and operating conditions. In addition, a comprehensive thermoeconomic (thermodynamic and component-costing) heat pump model, validated against manufacturer data, is developed to capture design-related performance and cost variations, thus reducing technology-related model uncertainties. The novelty of this paper lies in the use of multi-fidelity approaches for the comparison of the economic and environmental potential of important heat-generation solutions: (i) centralised gas-fired CHP systems associated with district heating network; (ii) gas-fired CHP systems or GSHPs providing heat to differentiated energy communities; and (iii) small-scale micro-CHP systems, ASHPs or GSHPs, installed at the household level. The pathways are evaluated for the case of the Isle of Dogs district in London, UK. A centralised CHP system appears as the most profitable option, achieving annual savings of £13 M compared to the use of decentralised boilers and a levelised cost of heat equal to 31 £/MWh th. However, if the carbon intensity of the electrical grid continues to reduce at current rates, CHP systems will only provide minimal carbon savings compared to boilers (<6%), with heat pumps achieving significant heat decarbonisation (55–62%). Differentiating between high- and low-performance and cost heat pump designs shows that the former, although 25% more expensive, have significantly lower annualised costs (£4.9 M vs. £7.7 M) and 12% higher CO 2 -equivalent savings. The uncertainty propagation reveals that data-driven and detailed thermoeconomic models can reduce the uncertainty in the total annualised energy cost and emissions by more than 75% compared to simplified black-box approaches, while the economic comparison of centralised CHP systems and domestic heat pumps for various electricity and gas price scenarios provides guidance to support energy policy. [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]

• Examine preference heterogeneity for renewable home heating systems. • Combined psychological construct statements and a discrete choice experiment. • Identify four types of viewpoints towards heat pumps using latent class analysis. • Estimate willingness to pay for non-monetary attributes of new home heating systems. This paper aims to understand heterogeneity in preferences for renewable home heating systems such as heat pump systems, using a combination of psychological construct statements and a discrete choice experiment. We employ a latent class analysis for a nationally representative sample of Irish households to identify and characterize distinct respondent classes based on their responses to statements on attitude, subjective norms, perceived behavioral control, and intention to install a heat pump that are constructed based on the theory of planned behavior. This allows us to identify four types of people with different viewpoints towards heat pumps. Furthermore, we conducted a discrete choice experiment with a subsample of randomly selected respondents to estimate preferences for different attributes of a new home heating system and the corresponding marginal willingness to pay. Our estimated results show that, in addition to upfront cost and bill savings, non-monetary attributes such as installation hassle, environmental sustainability, and an increase in home comfort of use are important determinants of the uptake of new home heating systems, including heat pumps. The findings of this study should provide useful information to policymakers and companies on end-user profiles, heterogeneity in preferences, and willingness to pay estimates for new home heating alternatives. [ABSTRACT FROM AUTHOR]

• Techno-economic analysis of low-carbon heat supply options for UK supermarkets. • RIHC, an ASHP, and a thermal storage tank with advanced control is recommended. • Best investments provide a 16-to-18-year payback without a carbon price. • The UK renewable heat incentive subsidy (for ASHP) generates 89% of the 'savings' • When a £100/tCO2e tax is considered, paybacks are reduced to a 9–11 years. Eliminating the use of natural gas for non-domestic heat supply is an imperative component of net-zero targets. Techno-economic analyses of competing options for low-carbon heat supply are essential for decision makers developing decarbonisation strategies. This paper investigates the impact various heat supply configurations can have in UK supermarkets by using heat recovery principles from refrigeration systems under different climatic conditions. The methodology builds upon a steady-state model that has been validated in previous studies. All refrigeration integrated heating and cooling (RIHC) systems employ CO 2 booster refrigeration to recover heat and provide space heating alongside various technologies such as thermal storage, air-source heat pumps (ASHPs) and direct electric heaters. Seven cases evaluating various technology combinations are analysed and compared against a conventional scenario in which the building is heated with a natural gas boiler. The specific combinations of technologies analysed here contrasts trade-offs and is a first in the literature. The capital costs of these projects are considered, giving insights into their business case. Results indicate that electric heaters are not cost-competitive in supermarkets. Meanwhile, RIHC and ASHP configurations are the most attractive option, and if a thermal storage tank system with advanced controls is included, the benefits increase even further. Best solutions have a 6.3% ROI, a payback time of 16 years while reducing energy demand by 62% and CO 2 emissions by 54%. Such investments will be difficult to justify unless policy steers decision makers through incentives or the business case changes by implementing internal carbon pricing. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the electricity, heating and cooling demands of a Southern Ontario residence are assessed and compared. Five specific systems are analyzed: ground and air source heat pumps, stand-alone PV, PV/fuel cell hybrid and a wind turbine/fuel cell hybrid system. Actual monitored data from a residence using a ground source heat pump is taken as a reference and compared with the others. Average weather conditions, electricity prices and average electricity loads in Toronto, Ontario, are used as reference data. Thermodynamic, economic and environmental comparisons are performed. It is found that heat pump systems offer significant advantages over the other systems. [Copyright &y& Elsevier]

Abstract: This paper presents the numerical simulation of a solar assisted ground coupled heat pump (SAGCHP) system which can provide both space heating and domestic hot water (DHW). The optimization process is completed on the TRNSYS based platform by simulating the influence of solar collector area on the total borehole length and system performance. Simulations are also carried out under different meteorological conditions to explore the applicability of the proposed SAGCHP system in northern China. The simulating results show that the optimized system under the specified load conditions has a collector area of 40m2 and a borehole length of 264m. The annual total heat extraction plus 75% of the hot water requirement can be provided by solar energy in the optimized design. Furthermore, the energy balance of the optimized design is confirmed with a minor difference of 0.75%, and the system is proved more efficient and economical for its application in Beijing area. [Copyright &y& Elsevier]

Abstract: When an air source heat pump (ASHP) operates in heating mode, frost can be accumulated on the surface of its finned outdoor coil. Frosting deteriorates the operation and energy efficiency of the ASHP and periodic defrosting becomes necessary. Currently the most widely used standard defrosting method for ASHPs is reverse cycle defrost. On the other hand, electronic expansion valves (EEVs) are commonly used in heat pump/refrigeration systems, including ASHP units, as throttle regulators of refrigerant flow. This paper reports on an experimental investigation of the performance of a reverse cycle defrost operation for a 6.5kW experimental heating capacity residential ASHP whose outdoor coil had four-parallel refrigerant circuits, and with an EEV as the refrigerant flow throttle regulator. The detailed descriptions of the experimental ASHP unit and the experimental procedures of ASHP are firstly presented. This is followed by reporting the comparative experiments of two control strategies for the EEV to investigate their effects on defrosting performance: the EEV being fully open and the EEV being regulated by a degree of refrigerant superheat (DS) controller. Experimental results revealed that when the EEV was regulated by the DS controller during defrosting, a higher defrosting efficiency and less heat wastage would be resulted in. [Copyright &y& Elsevier]

Abstract: The experimental part of the study of the reverse cycle defrosting performance on a four-circuit outdoor coil unit in an experimental 6.5kW heating capacity residential ASHP has been reported in Part I of a two-part series. The experimental results indicated that downwards flowing of the melted frost along a multi-circuit outdoor coil surface would have negative effects on defrosting performance. In order to quantitatively analyze the effects, this paper, the second part of the two-part series, reports on a modeling analysis where a semi-empirical model of the airside defrosting in the four-circuit outdoor coil unit was developed. The model was validated by comparing the predicted defrosting duration and temperature variation of collected melted frost with the corresponding experimental data presented in Part I of the two-part series. Using the validated model, the frost-melting rate and the temperature of melted frost on the surface of each circuit were predicted. The effects of the downwards flowing melted frost along the entire outdoor coil surface on defrosting performance were quantitatively analyzed. [Copyright &y& Elsevier]

Abstract: When an air source heat pump (ASHP) unit operates in heating mode, frost can be accumulated on the surface of its finned outdoor coil which normally has multiple parallel circuits on its refrigerant side for minimized refrigerant pressure loss and enhanced heat transfer efficiency. On its airside, however, there is usually no segmentation corresponding to the number of refrigerant circuit. Frosting deteriorates the operation and energy efficiency of the ASHP unit and periodic defrosting becomes necessary. Currently the most widely used standard defrosting method for ASHPs is reverse cycle defrost. This paper, the first part of a two-part series, reports on the experimental part of a study of the reverse cycle defrosting performance on a multi-circuit outdoor coil unit in an experimental 6.5kW heating capacity residential ASHP unit. Firstly the experimental ASHP unit is described and experimental procedures detailed. Secondly, the experimental results are reported. This is followed by the discussion on the effects of downwards flowing of the melted frost along a multi-circuit outdoor coil surface on defrosting performance. Finally, the evaluation of the defrosting efficiency for the experimental ASHP unit is provided. In the second part of the series, a modeling analysis on the effects of downwards flowing of the melted frost along the multi-circuit outdoor coil surface on defrosting performance of the experimental ASHP unit will be presented. [Copyright &y& Elsevier]

Abstract: The use of groundwater for cooling and heating purposes is of interest from both the economical and the ecological perspective. The groundwater heat pump (GWHP) system utilizes groundwater as alternative renewable and clean energy source for space heating and/or cooling, withdraws water from a production well, passes it through a heat exchanger and discharges the water into an injection well. By utilizing the relatively stable temperature of groundwater, GWHP system can achieve a higher coefficient of performance. Due to the utilization of groundwater stored in the aquifer, the assessment of the hydraulic capacity of the aquifer based on numerical groundwater models is always needed for the optimum design and the efficient performance of GWHP. In this paper, numerical methods of underground heat-water transfer, energy balance method and thermal storage method were presented to calculate the capacity of unit area of shallow groundwater aquifer. The model results indicate that the numerical method, which is based on performance efficiency of GWHP, represents the behaviour of groundwater pumping/recharging processes, and serves better than energy balance method and thermal storage method, in addition it has been proven itself that this method has the advantages of energy saving and environmental protection. The calculated capacity is positively related to aquifer thickness. It is found that it is easy for ground water recharge in alluvial and pluvial fan located at the piedmont, while the calculated capacity is relatively smaller compared with that of south-east plain where it is not easy for groundwater recharge. [Copyright &y& Elsevier]

Abstract: This paper introduces a solar-assisted ground-coupled heat pump (SAGCHP) system with heat storage for space heating and domestic hot water (DHW) supply. The simulation results of the system''s detailed operating performance are presented. The optimization of the system design is carried out by the TRNSYS and a numerical simulation is performed for continuous operation of 20 years under the meteorological conditions of Beijing. Different control strategies are considered and the operational characteristics of each working mode are studied. The simulating results show that the long term yearly average space heating efficiency is improved by 26.3% compared to a traditional ground coupled heat pump (GCHP) system because the solar thermal collecting system is used to elevate the thermal energy in the soil and to provide direct space heating with heat storage. At the same time, the underground heat load imbalance problem for a heating load dominated GCHP is solved by soil recharging during non-heating periods, while extra solar energy is utilized to supply DHW. The flexibility and high efficiency of the SAGCHP system could offer an alternative for space heating and DHW supply by heat pump technology and solar energy in cold winters of northern China. [Copyright &y& Elsevier]

This paper describes the applicability of artificial neural networks (ANNs) to estimate of performance of a vertical ground coupled heat pump (VGCHP) system used for cooling and heating purposes experimentally. The system involved three heat exchangers in the different depths at 30 (VB1), 60 (VB2) and 90 (VB3)m. The experimental results were obtained in cooling and heating seasons of 2006–2007. ANNs have been used in varied applications and they have been shown to be particularly useful in system modeling and system identification. In this study, the back-propagation learning algorithm with three different variants, namely Levenberg–Marguardt (LM), Pola–Ribiere conjugate gradient (CGP), and scaled conjugate gradient (SCG), and tangent sigmoid transfer function were used in the network so that the best approach could be found. The most suitable algorithm and neuron number in the hidden layer were found as LM with 8 neurons for both cooling and heating modes. [Copyright &y& Elsevier]

Abstract: Exergy is naturally related to the concept of quality of energy. Therefore, exergy analysis has been widely applied in parallel with energy analysis in order to find the most rational use of energy. Within the built environment a wide margin for exergy saving may be found. Actually, buildings require mostly low quality energy for thermal uses at low temperatures and nowadays their energy demand is mainly satisfied with high quality sources. Exergy analysis of renewable energy-based climatisation systems may be considered an emerging field, where different and often contrasting approaches are followed. Then, in this paper a comprehensive and critical view on the most recent studies on this topic is presented. Special attention is paid to the methodological aspects specifically related to climatisation systems and renewables, and to the comparison of the results. Main renewable energy-based heating and cooling systems are considered in detail. Finally, conclusions regarding the state of the art and possible trends on this field are derived, with the aim to highlight future research issues and promote further developments of this method. Furthermore, conclusions regarding the usability of the exergy method as a tool to promote a more efficient use of available energy sources are also derived. [Copyright &y& Elsevier]

Abstract: A hybrid ground-coupled heat pump (HGCHP) with domestic hot water (DHW) supply system has been proposed in this paper for space cooling/heating and DHW supply for residential buildings in hot-climate areas. A simulation model for this hybrid system is established within the HVACSIM+ environment. A sample system, applied for a small residential apartment located in Hong Kong, is hourly simulated in a typical meteorological year. The conventional GCHP system and an electric heater for DHW supply are also modeled and simulated on an hourly basis within the HVACSIM+ for comparison purpose. The results obtained from this case study show that the HGCHP system can effectively alleviate the imbalanced loads of the ground heat exchanger (GHE) and can offer almost 95% DHW demand. The energy saving for DHW heating is about 70% compared with an electric heater. This proposed scheme, i.e. the HGCHP with DHW supply, is suitable to residential buildings in hot-climate areas, such as in Hong Kong. [Copyright &y& Elsevier]

To increase the heating capacity of air-source heat-pump in cold regions, an improved heat pump cycle with scroll compressor economizer was developed. The measured results of the prototype demonstrate that it can provide a high temperature and high-capacity water supply even under a low ambient temperature of −10∼−15 °C. The performances of the improved heat-pump cycle are comprehensively analyzed with aid of the proposed thermodynamic model in this paper. The design parameters and the components of the cycle are optimized and the predicted results. The predicted results discussed indicate that the improved heat pump has high efficiency under all weather conditions and that this improvement is conducive to enlarging the running region of the heat pump and providing an alternative heating service for cold regions. [Copyright &y& Elsevier]

[Display omitted] • Waste heat seasonally stored in the subsurface provides a source of renewable energy. • Borehole thermal energy storage (BTES) can reduce space heating GHG emissions. • BTES integrated with heat pumps has a potential to deliver building heat economically. On average, fossil fuel space heating constitutes 56% of a building's total energy usage in Upstate New York due to the cold winter climate. Similar levels of fossil fuel heating pertain in at least 15 states in the U.S. northern tier. To meet aggressive carbon reduction goals in this tier, decarbonizing the heat supply in the residential and commercial sector must be pursued. Using Borehole Thermal Energy Storage (BTES) to seasonally store excess thermal energy in the subsurface for later heating use is an innovative way to increase heating efficiency and lower carbon emissions. This paper investigates the technical and economic feasibility of heating Snee Hall on Cornell campus with unused summer steam from Cornell's Combined Heat and Power Plant stored in an optimized BTES array. Snee Hall is a 6855 m2 building with an annual total heating load of 3040 GJ. A standard 2-D transient subsurface conductive heat transfer model is coupled to a high temperature heat pump (delivering > 60 °C) that can supply Snee Hall's existing radiators with 70 °C water. For local geological parameters, 94% of Snee Hall's winter space heating demand can be supplied by a 37-borehole array (90 m depth, 3 m spacing) and a 250-kW high temperature heat pump capacity with average coefficient of performance of 3.85. The calculated storage efficiency is 68.7% and the system has a 30-year net present value of about $526,400, an internal rate of return of 13%, and a payback period of 10 to 11 years. The system offsets about 6900 MMBTU (7280 GJ) of natural gas combustion and saves 250 MT CO 2 emissions annually. The results of the single building analysis can be applied to other buildings on campus or in similar geologic settings in the U.S northern tier. [ABSTRACT FROM AUTHOR]

This paper analyses optimal electricity investments (PV and battery storage) to decarbonise heat supply in residential buildings under different heat pump and energy retrofitting scenarios in a detailed representation of the Swiss power and heating system. The sensitivity of PV and storage deployment, including lithium-ion (LiB) and vanadium redox flow batteries (VRFB), with respect to distribution network capacity is also investigated. We propose an open-source dispatch sector coupling model (GRIMSEL-AH) to minimise energy system costs (social planner perspective) for heating and electricity supply in Switzerland with hourly and daily time resolution for electricity and heating respectively. Moreover, our representation of the Swiss energy system includes various types of consumers and urban settings which are represented with monitored electricity demand data for each sector and simulated heat demand data at the building level for the residential sector. We find that under a "business as usual" heat pump deployment and retrofitting rate, the optimal electricity investments correspond to 27.8 GW p of PV combined with 16.9 GW (33.8 GWh) for LiB and 1.9 GW (7.6 GWh) for VRFB. For this case, 57% (13.3 TW th /year) of the residential heat demand is covered by heat pumps with a total installed capacity of 19.7 GW th by 2050 (capacity exogenously set with its operation optimised). With increasing heat pump deployment, retrofitting rates are found to have a large impact on the investment in storage and a 100% heat pump scenario for the residential sector appears to be feasible. Our results show that heat pumps do not only decarbonise heat but also provide extra flexibility to the power system, since they increase local PV self-consumption, resulting in higher PV deployment. The model and the methodology presented in this study can be applied to other countries. • Open-source sector coupling modelling framework with flexible heat pump operation. • Impact of heat pump and energy retrofitting scenarios on electricity investments. • Retrofitting rates have a significant impact on the storage investment. • Heat pumps provide extra flexibility by increasing local PV self-consumption. • Trade-offs between storage and distribution grid upgrade are discussed. [ABSTRACT FROM AUTHOR]

• Solar assisted heat pump coupled to a seasonal storage allows heating production. • Seasonal storage of thermal energy is technical and economically feasible. • Seasonal storage is able to be implemented in middle latitude. • PVT panels performance increase with the inclusion of a seasonal storage tank. • Key sizing factors are solar field area, volume of storage and capacity of heat pump. A water-water solar-assisted heat pump (SAHP) is projected on an under construction academic building at the University of Zaragoza (Spain). It integrates a heat pump heating system with photovoltaic/thermal collectors and seasonal storage. Because of its innovative design, considerably higher performances than a conventional type air-source heat pump are expected. This paper shows the simulation of the system performed in TRNSYS, a graphically based software used to simulate the behavior of transient systems. In addition, starting from the current design of the energy system, different sensibility analysis are simulated in order to study alternative configurations of the heating system. The solar coverage of the current installation design is about 60% and the expected savings yield to a payback period of 15,4 years. Three alternative configurations are proposed in this work, reaching up to around 98% of solar coverage. The study results show the technical and economic feasibility of the heating installation based on a solar assisted heat pump with implementation of seasonal storage in an educational building located in a middle latitude. [ABSTRACT FROM AUTHOR]

• Demand-Side-Management with air-to-water heat pump in a Nearly-Zero-Energy-Building. • Model Predictive Control with Artificial Neural Network for heat demand prediction. • Variation of storage capacity and heat pump power shows cost savings up to 24.3% • Market based concepts need further incentives to exploit the flexibility potential of heat pumps. The rollout of the supply dependent generators wind turbines and photovoltaics leads to a flexibility demand that can be adressed from the consumer side, via Demand-Side-Management, as well. In single family houses, the heat pump, in combination with thermal energy storage, can shift their energy comsumption according to price signals in order to reduce consumer costs. This paper analyses the impact of different heat storage sizes and heat pump powers on cost savings and shifting potential, focussing on the Luxembourgish context, when variable electricity prices based on the electricity market are applied. A model predictive controller determines the cost-optimal operating cycles of the heat pump. The building's heat demand is predicted with the help of a neural network. The results of the parametric study show significant differences in energy efficiency and cost savings. Furthermore limitations of taking advantage of variable electicity prices due to the price structure are disclosed. The cost savings however do not give a sufficient incentive for the consumer to invest in optimizing the heating system for Demand-Side-Management purposes. By consequence, the potential and the efficiency of Demand-Side-Management are limited and further incentives are necessary. [ABSTRACT FROM AUTHOR]

• The replacing of a coal-fired boiler by a GWHP system is investigated. • The operation of each system has been monitored over one-year period. • The boiler has lower investments and covers lower thermal load than the GWHP. • GWHP shows higher economic performance considering Average Energy Price. • GWHP system may be cost effective over traditional boilers for applications. Currently in China, the replacement of coal-fired boilers by clean and renewable energy sources is considered as an essential measure to alleviate air pollution. This paper investigates the thermo-economic performance of replacing a coal-fired boiler by a Groundwater Heat Pump (GWHP) system for a greenhouse, where the GWHP system was constructed to reduce emission and also to provide cooling. The operation of this system has been monitored over a one–year period. The results show that the thermal efficiency factor of the boiler varies in the range of 0.53–0.68 and the Coefficient of Performance (COP) of the GWHP system averages at 4.1 for cooling and at 3.3 for heating. Although the boiler has both lower capital costs and lower operating costs, the analysis of Average Energy Price (AEP) shows that the GWHP system has a higher economic performance, since it has a lower AEP of 0.040 USD /kWh in heating and 0.023 USD/kWh in cooling over an expecting lifetime of 20 years, in comparison to the boiler at 0.052 USD/kWh over a lifetime of 10 years. This indicates that GWHP system may be considered as an alternative over traditional boilers in terms of thermo-economic performance for applications in other places of the world with similar climate condition. [ABSTRACT FROM AUTHOR]

• A novel bed-based air source heat pump (B-ASHP) system was proposed. • A prototype experimental B-ASHP system was established and tested. • The B-ASHP system can be operated at both nighttime and daytime modes. • Better thermal comfort and bed surface temperature distribution can be achieved. • A number of issues requiring further considerations were identified. Air source heat pumps (ASHPs) have been increasingly used for space heating due to their high energy efficiency and installation flexibility. On the other hand, in many rural areas in northern Chinese provinces, Kangs, a kind of traditional heating systems based on burning biofuels, are still being used for space heating in winter. Based on the pros and cons of both ASHPs and Kang-based heating systems, a novel bed-based ASHP (B-ASHP) system has been proposed to combine the advantages from both an ASHP and a Kang heating system. In this paper, a prototype experimental B-ASHP system was designed and established, and its dynamic and steady-state operating performances tested in four test cases. The test results from the four test cases demonstrated that the prototype experimental B-ASHP system can achieve quicker increases in indoor air temperatures and bed-surface temperatures than Kang-based heating systems. The use of experimental B-ASHP system can lead to a more uniformed vertical indoor air temperature gradient, thus a better occupants' thermal comfort, than the use of a conventional convection-based ASHP system. Furthermore, compared to using a Kang-based heating system, a more uniformed bed surface temperature may be obtained when using a B-ASHP system. Nonetheless, although currently the prototype experimental B-ASHP system can be satisfactorily operated, a number of issues related to the designs of a B-ASHP system such as choices of refrigerant, refrigerant tube layout optimizations, and the use of variable speed compressors for capacity control, should be carefully considered to further improve its operational safety and energy efficiency. [ABSTRACT FROM AUTHOR]

• Net-zero emissions are modelled for electricity, heating and cooling in Europe. • System cost decreases thanks to heat savings, but not for climate change scenarios. • Lower heat demand disfavours heat pumps as surplus electricity is used by resistors. • Cheaper heat pumps impact resistive heaters substantially, but not the opposite. To limit the global temperature increase to 1.5 °C, fossil-free energy systems will be required eventually. To understand how such systems can be designed, the current state-of-the-art is to apply techno-economical optimisation modelling with high spatial and temporal resolution. This approach relies on a number of climatic, technical and economic predictions that reach multiple decades into the future. In this paper, we investigate how the design of a fossil-free energy system for Europe is affected by changes in these assumptions. In particular, the synergy among renewable generators, power-to-heat converters, storage units, synthetic gas and transmission manage to deliver an affordable net-zero emissions system. We find that levelised cost of energy decreases due to heat savings, but not for global temperature increases. In both cases, heat pumps become less favourable as surplus electricity is more abundant for heating. Demand-side management through buildings' thermal inertia could shape the heating demand, yet has modest impact on the system configuration. Cost reductions of heat pumps impact resistive heaters substantially, but not the opposite. Cheaper power-to-gas could lower the need for thermal energy storage. [ABSTRACT FROM AUTHOR]

Decarbonisation of the building sector is driving the increased use of heat pumps. As increased electrification of the heating sector leads to stress on the electricity grid, the need for district level coordination of these heat pumps emerges. This paper proposes a novel hierarchical coordination methodology, in which a price coordinator reduces the total instantaneous power demand of a building network below a power supply limit using a price signal. Each building has a model predictive controller (MPC) which maximises thermal comfort and minimises electricity costs. An additional term in the MPC objective function penalises the heat pump power demand quadratically, which when multiplied by a pseudo electricity price allows the price coordinator to reduce the peak power demand of the building network. A 2 building network is studied to analyse the price coordinator algorithm's behaviour and demonstrate how this approach yields a trade off between comfort, energy consumption and peak demand reduction. A 100 building network case study is then presented as a proof of concept, with the price coordinator approach yielding results similar to that of a centralised controller (less than 0.7% increase in energy consumption per building per year) and a roughly fourfold decrease in computation time. [ABSTRACT FROM AUTHOR]