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[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]

Occupant behaviour on air conditioning directly influences building energy consumption. Current building energy simulation typically assumes that occupants operate air conditioners ideally ignoring the stochastic characteristic of occupant behaviour, which leads to a large deviation of predicted energy performance from real consumption. This paper proposed a methodology framework for modelling occupants’ stochastic behaviour on air conditioning. This method combined measured data, statistical analysis and logistic regression to derive stochastic behaviour models that give the probability of when and above which temperature occupants may turn on air conditioning, at what temperature they may set and when they may turn off air conditioning. The behaviour models developed in this paper were further incorporated in widely used building simulation engine—EnergyPlus. The accuracy of the developed simulation model was validated against field measurement. Using this model, the cooling energy performance was simulated and compared with results from building energy standard based settings. The result shows that simulation using settings according to building energy standard over-predicts cooling load and total cooling energy requirements by 113% and 5.6 times respectively, which are very large discrepancies and may lead to a misunderstanding of energy savings potential of energy efficiency measures. The methodology developed in this paper has generality and can be extended and applied in other buildings for constructing behaviour models of air conditioning. The limitations of the current research as well as future research works were also discussed. [ABSTRACT FROM AUTHOR]

Hospitals present a widely recognized margin for energy conservation due to their elevated final energy use intensity. Specifically, operating rooms are among the functional areas with greatest energy demand in hospitals, given the stringent indoor conditions for patients and surgical staff. However, energy efficiency in surgical facilities has traditionally been overlooked by the scientific literature in favor of guaranteeing adequate air quality conditions. This paper assesses the potential energy savings that could be achieved in a surgical suite in a Spanish hospital by lowering the current ventilation rates to the lowest energy-demanding values recommended by the proper Spanish standard and other international codes. Likewise, the paper assesses the actual hygrothermal and ventilation conditions in the suite based on the results of a continuous monitoring campaign performed for a period of 12 days. Simulations undertaken with a dynamic energy model specifically developed and calibrated for this work revealed that the average energy intensity of the suite is 1021 kWh/m 2 /year (1685 kWh/m 2 /year for operating rooms), with 80% of the total annual thermal demand corresponding to periods of inactivity. In addition, energy savings between 40% and 80% are possible while complying with both national and international standards. [ABSTRACT FROM AUTHOR]

In this paper, the problem of dispatching the operation of a distribution feeder comprising a set of heterogeneous resources is investigated. The main objective is to track a power trajectory, called the dispatch plan , which is computed the day before the beginning of operation. In this paper, we propose a method to optimally compute the dispatch plan so as to optimize the operation of the feeder while making sure to allocate enough local reserves to absorb deviations of the realizations. Indeed, during real-time operation, due to the stochasticity of part of the resources in the feeder portfolio, tracking errors need to be absorbed in order to track the committed dispatch plan. This is achieved by modulating the power consumption of a utility-scale battery energy storage system and of the heating, ventilation and air conditioning system of a commercial controllable building. To this end, a hierarchical controller is designed to coordinate these two controllable entities while requiring a minimal communication infrastructure. Due to the inherent different response times of these systems, the power injection of the electrical battery is controlled at a sub-minute time-scale so as to absorb high-frequency tracking errors and, therefore, deliver the dispatch service. At a slower time-scale, the controllable building is controlled to maintain the state of charge for the electrical battery at a scheduled level by means of a model predictive controller. The model predictive controller is designed in order to account for both comfort and operational constraints of the controllable building, as well as power limits for the electrical storage. The effectiveness of the proposed control framework is demonstrated by means of both an extensive simulation analysis, as well as a set of 12 full day experimental results on the 20 kV distribution feeder in the campus of the Swiss institute of technology in Lausanne, that is comprised of: 1) A set of uncontrollable resources represented by five office buildings (350 kWp) and a roof-top photovoltaic installation (90 kWp), 2) a set of controllable resources, namely, a grid-connected electrical storage (720 kVA–500 kWh), and a fully-occupied multi-zone office building (45 kWp). [ABSTRACT FROM AUTHOR]

This paper examines the provision of demand-side ancillary services using building thermodynamics and heating ventilation and air-conditioning (HVAC) systems. In particular, we consider the secondary frequency control service where the load has to declare a power capacity and a nominal power at the beginning of the regulation period and then in real-time track the received regulation signal around its declared nominal power. A hierarchical control scheme is proposed in this paper. The local building controllers at the lowest level track the temperature setpoints received from the thermal flexibility controller which maximizes the flexibility of building’s thermal consumption. At the highest level, the electrical flexibility controller controls the HVAC system while maximizing the flexibility provided to the grid. The two flexibility control layers are based on robust optimization methods. A control oriented model of a typical HVAC system is developed, and simulations are carried out to demonstrate the efficacy of the proposed approach. Results show that extra flexibility may be attained by exploiting the coefficient of performance (COP) of the chiller. Furthermore, occupant comfort increases as a consequence of providing ancillary services. [ABSTRACT FROM AUTHOR]

This paper describes a method for residential water use modeling predicated on metered energy data. Actual measured hot water volumes for major indoor consumption are used to verify and adjust the outputs in gallons of hot water consumption based on climate variables, water heater technical features, and set-point and intake temperatures. Three independent datasets for residential energy (RECS 2009), water heater efficiency (Air-conditioning, Heating and Refrigeration Institute-AHRI), and end-use domestic water (Residential End Uses of Water, Version 2-REU II) are applied to identify specific demographic, built environment and geographic factors that relate patterns of energy demand to water consumption. The proposed model acts within the broader Integrated Urban Metabolism Analysis Tool (IUMAT), a system-based analytical framework for evaluating the environmental performance of the built environment. The method described in this paper offers an alternative approach to residential water consumption modeling by implementing volume of hot water consumption as a proxy for indoor water use. It provides utilities with the potential to parse and prioritize energy and water conservation measures. [ABSTRACT FROM AUTHOR]

Cooling of buildings is an essential target for engineers and builders in the hot arid climate of Egypt. Performance of inclined solar chimney with passive cooling tower (SCPC) was studied. The system was integrated into a single room built in Assiut University (El-Gorib site) in Assiut, Egypt. Testing of indoor environment for the room with passive cooling was done during August and September 2015. A passive cooling technique was integrated inside a short wind tower made from expanded paper (wet pad) 0.1 m thick. A water tube was installed on the top of the expanded paper with small nozzles. Water is recirculated through the system using water pump. A reduction of room indoor temperature was observed with the integrated system (SCPC). There is a significant reduction of indoor temperature between 6 and 7 K due to passive cooling with surface temperature 19.4 °C for the cooling pad. The relative humidity did not exceed 57% most of the time. The maximum air speed inside the solar chimney was 3.5 m/s under the effect of a high solar radiation of 890 W/m 2 . The findings show that SCPC system achieves comfortable thermal conditions with a significant improvement in building energy conservation. The result of development this new cooling system helps to develop building code for low energy houses in Egypt and propose a new system to be integrated in the housing project of people with low income. [ABSTRACT FROM AUTHOR]

Demand response (DR) of air-conditioning systems is important to shift or reduce the peak electricity demand of commercial buildings by shift or reduce the cooling load. Popular DR strategies of air-conditioning systems include zonal temperature reset and direct control of the main equipment. Many DR studies have been conducted on the thermal inertia of buildings for temperature resetting, but there are few studies on the thermal inertia of air-conditioning systems, which is relatively small but not negligible. In this paper, the thermal inertia of air-conditioning systems is defined as the character that causes the variation of the supply cooling capacity to zones lagging behind the variation of the cooling capacity from plants after DR strategies are implemented. This paper develops an inertia model of chilled-water systems with three sub-models, including chiller model, chilled-water pipe model and cooling coil model. The model describes the dynamic process from the cooling plant to terminal units when DR strategies on chillers are implemented. A new parameter Q ( t ) named the “refrigerant cooling capacity” is introduced in this study to simplify the thermal inertia model. The Q ( t ) patterns during the dynamic processes of two series of common chiller-side control strategies (On/Off control and resetting the chilled-water temperature) are obtained and validated using experiments and field tests. In the end, the entire transient model of air-conditioning systems is validated using experiments. [ABSTRACT FROM AUTHOR]

• FDD tools are increasingly adopted in commercial buildings. • Using FDD tools to correct hunting faults can mitigate issues cost-effectively. • We developed and implemented automated control hunting correction in FDD tools. • The algorithm was tested in nine VAV boxes and successfully eliminated hunting faults. • We discussed challenges and future research areas for scaling the technology up. Control hunting due to improper proportional–integral–derivative (PID) parameters in the building automation system (BAS) is one of the most common faults identified in commercial buildings. It can cause suboptimal performance and early failure of heating, ventilation, and air conditioning (HVAC) equipment. Commercial fault detection and diagnostics (FDD) software represents one of the fastest growing market segments in smart building technologies in the United States. Implementation of PID retuning procedures as an auto-correction algorithm and integration into FDD software has the potential to mitigate control hunting across a heterogeneous portfolio of buildings with different BAS in a scalable way. This paper presents the development, implementation, and field testing of an automated control hunting fault correction algorithm based on lambda tuning open-loop rules. The algorithm was developed in a commercial FDD software and successfully tested among nine variable air volume boxes in an office building in the United States. The paper shows the feasibility of using FDD tools to automatically correct control hunting faults, discusses scalability considerations, and proposes a path forward for the HVAC industry and academia to further improve this technology. [ABSTRACT FROM AUTHOR]

A sleeping person is naturally immobile in a relatively small space. Hence, task\ambient air conditioning (TAC) can be best applied to a sleeping environment because of its proven performances in energy saving. However, when using previously developed the TAC systems for sleeping environment applications, cold draft was a serious issue and could hardly be avoided due to a high air velocity and a low air temperature inside an occupied zone. Therefore, in the experimental study reported in this paper, a radiation-based TAC (R-TAC) system has been developed, and its performances experimentally evaluated. In this paper, firstly, an experimental setup for a prototype R-TAC system, and experimental conditions and methods are reported. This is followed by presenting experimental results on the thermal comfort and ventilation performance. Finally, the issues of condensation risk when using the proposed R-TAC system are discussed. The study results presented in this paper have shown that the use of the R-TAC system could not only result in better thermal comfort and ventilation performances, but also effectively resolve the cold draft problem. In addition, the potential problem of potential condensation on a surface may be resolved by raising the panel surface temperature, or using a lower fresh air supply humidity. [ABSTRACT FROM AUTHOR]

The carried scientific research regarding evaluation the hygrothermal effects of integration the vegetation into the building envelope was influenced with the differences in necessity to use air-conditioning in the houses, which are not surrounded with vegetation in horizontal structure and which have such vegetation during the summer time. The experimental testing is based on the precise measurements of the relative humidity and temperature, which were carried close to the building plaster in the place without influence of vegetation and between the wall and vegetation. Vegetation on the house, which was used for experimental purposes, is made up of the vine species with a thickness of 40 cm in the place where measurement was carried. Although the investigation takes longer, the paper aims to one month to show the summer time. The mathematical modelling of the obtained data was realized using the numerical as well as the statistical methods The paper aims especially on modelling the differences in relative humidity and temperature of the air and between the wall and vegetation. The dependence of temperature differences was expressed as a piecewise function using the method of Least squares of multiple regression as statistical method. Also the proportional energy to that which might be saved daily instead of its use for air-conditioning in the house was determined. The measurements as well as the used methods: showed sufficient accuracy. [ABSTRACT FROM AUTHOR]

This paper investigates a novel terminal unit that integrates a radiant cooling floor (RCF) with an underfloor air distribution system (UFAD). The unit consists of rectangular modules that are installed above the standard structural floor of the building, creating a raised floor. The upper face of these modules incorporates a grid for easy installation of the pipes of the RCF, while the space between the raised floor and the structural slab is used as the air supply plenum of the UFAD system. The proposed system presents some advantages over the standard air systems: (1) it allows increasing production and zone set point temperatures, which improve the efficiency of the chiller plant, (2) improved comfort, and (3) improved air quality due to reduced mixing within the occupied zone. The proposed system can also solve or mitigate some of the drawbacks of cooling floors: (1) prevent water condensation over the surface of the floor, (2) increase the cooling capacity of the floor, and (3) reduce the response time to changes in the space thermal loads. The interactions between the RCF and the UFAD are not evident. In this paper, the thermal behavior of the combined unit is investigated by means of a numerical model implemented in COMSOL Multiphysics. The accuracy of this model is checked against three experiments undertaken in laboratory using a scale model of the system. In the first experiment, the air above the floor is kept quiescent and the cooling capacity is measured. The maximum relative error between the predicted and measured capacities is 19.5%. The numerical model is then used to study how the air movement within the plenum modifies the transient thermal response of the unit. The second and third experiments are designed to quantify the temperature change of the air circulating within the plenum (thermal decay or TD). In nominal operating conditions, TD is about 2.7 °C. In short, the new terminal unit is like a radiant cooling floor and a UFAD system working separately, but integrated in the same terminal unit. [ABSTRACT FROM AUTHOR]

This paper describes an experimental set-up used to validate predictions from a numerical model for ventilated wall cavity with spray evaporative cooling systems. The validation analysis results have indicated that the numerical model, developed and described in a companion paper, can accurately predict the outlet air temperatures and relative humidity levels achieved by a ventilated wall cavity with a spray evaporative cooling system utilized to air condition buildings in hot and dry climates. Air velocity predictions of the ventilated cavity have been also verified against results obtained from a detailed CFD analysis. Moreover, the experimental testing results indicate that the ventilated wall cavity with an evaporative cooling with 5 μm spray droplets can significantly reduce outdoor air temperatures. Specifically, the system was able to reduce air temperature from 45 °C to 25.5 °C. Moreover, the results of a parametric analysis obtained using the validated numerical solution suggest that there is a significant reduction potential in heat transfer through cavity walls while providing acceptable supply air temperature capable of maintaining indoor thermal comfort. In addition, the parametric analysis has evaluated the effect of climatic conditions (temperature and humidity) on the required distances for spray droplets to fully evaporate. The presented results could help in designing effective and energy efficient ventilated wall cavity with spray evaporative cooling systems to condition buildings in hot and dry climates. [ABSTRACT FROM AUTHOR]

This paper aims to provide the current state of the art of solar sorption systems. Through comprehensive literature review of solar sorption systems, it was concluded that these technologies have several limitations and drawbacks. The low performance and the high cost are the main disadvantages of these technologies. However, solar cooling is considered attractive because solar radiation is in phase with the demand for cooling. Due to its attractiveness, the research is still going and focusing on solving the technical, economical, environmental problems, to achieve high performance and low cost of solar sorption systems. Improvements through investigating geometrical, system configurations, physical parameters, and operational modes on the performance of solar thermal sorption cooling systems are presented. A survey of the new configurations, novel additions, new techniques, new methodologies are also presented in this paper. Several cases studies in different climatic conditions are summarized. Economic feasibility for absorption and adsorption systems is discussed. It can be concluded that cost and energy effective solar sorption systems can be developed if suitable combinations of system components with operating conditions are selected. Finally, there is still the need for more research on solar sorption systems to make them both cost and energy competitive with the conventional cooling technologies. [ABSTRACT FROM AUTHOR]

This paper describes a step-by-step procedure for using measured end-use energy data from a campus building to calibrate a simulation model developed in EnergyPlus. This process included identification of key input parameters for reducing uncertainties in the model. Building thermal zones were modeled to match the actual heating ventilation and air conditioning (HVAC) zoning for each individual variable air-volume (VAV) zone. We evaluated most key building and HVAC system components, including space loads (actual occupancy number, lighting and plug loads), HVAC air-side components (VAV terminals, supply and return fans) and water-side components (chillers, pumps, and cooling towers). Comparison of the pre- and post-calibration model shows that the calibration process greatly improves the model's accuracy for each end use. We propose an automated model calibration procedure that links the model to a real-time data monitoring system, allowing the model to be updated any time. The approach enables the automated data feed from simple measuring and actuation profile (sMAP) into the EnergyPlus model to create realistic schedules of space loads (occupancy, lighting and plug), performance curves of fans, chillers and cooling towers. We also field-tested demand response (DR) control strategies to evaluate the model's performance in predicting dynamic response effects. Finally, this paper describes application of the calibrated model to analyze control systems and DR strategies with the goal of reducing peak demand. [ABSTRACT FROM AUTHOR]

The variable differential pressure (DP) set-point control strategy has become the main energy-saving measure for central air conditioning water system variable volume adjustment. In optimal operation control, it is critical to use the right reference object to implement global, accurate, and online control. In mainland China, the most unfavorable loop is typically used as the reference object for variable DP set-point control in the majority of cases of variable volume air conditioning system adjustment. However, its concept and feasibility require further clarification. First, this paper analyzes the difference in the characteristics of a most unfavorable loop under air conditioning design work conditions versus under operational conditions. Under design operational conditions, the referenced most unfavorable hydraulic loop only reflects the distribution of the pipe network's hydraulic characteristics, whereas under system operational conditions, the variable volume adjustment strategy should be chosen according to each user's load requirement, i.e., a most unfavorable thermodynamic loop. Then, this paper provides definitions of the most unfavorable thermodynamic loop and online identification method and proposes a variable DP set-point optimal reset strategy based on the maximum valve position loop's optimal reset valve position domain and best valve position domain. Finally, the variable DP set-point control of a primary pump variable volume air conditioning water system in an industrial factory is used as an example to conduct a test studying 6 variable DP or constant DP control strategies, including the method proposed in this paper. The test results show that the most unfavorable loop-based variable DP control strategy saves 47–58% water pump power consumption (up to 985 kWh electric power consumption per day) when compared with the conventional variable DP control strategy, whereas the most unfavorable thermodynamic loop-based variable DP control strategy is more advantageous in ensuring the overall cooling energy supply for each user. [ABSTRACT FROM AUTHOR]

This paper summarises the results of a study to identify and quantify the potential impact of measures and policies to reduce the energy consumption of air conditioning in European countries over a 10-year period. The market penetration of air conditioning in Europe has increased steadily over several decades. On a “business as usual” basis, its energy consumption would increase by over 50% by 2020. Measures to restrict this increase are therefore important, but the savings potential straddles several overlapping areas which are subject to different constraints including those imposed by the replacement rates of systems and products, and the refurbishment rates of existing buildings. This work reported in this paper is based on the use of information from a variety of sources in a highly disaggregated model to assess the “realisable” savings over a 10-year period, taking into account relevant constraints. The paper summarises results at a European level, focussing on those cases that generate the greatest realisable savings. Savings are possible in three areas: improved equipment and system efficiency, reduced cooling loads, and more effective operation. The cases that offer the largest savings provide the basis for recommendations for policy measures, often using existing policy instruments. In addition, areas where further work is needed are identified. More detailed results and information about the study and additional recommendations can be found at http://www.bre.co.uk/searchresults.jsp?category=5&q=energy+management [1] . [ABSTRACT FROM AUTHOR]

Previous work by the same authors has shown that in mixed-humid climates, tight, super-insulated residential structures can experience high humidity events in summer months. Standard, commercially available vapor compression-based air conditioners struggle to control humidity in such structures with low cooling loads. Therefore a desiccant-assisted heat pump system for tight, super-insulated residential structures is proposed. This paper first reviews solid desiccant cooling cycles. Then a hybrid desiccant cooling cycle is explained and a prototype machine based on the cycle is described. The machine, known as HAWC (hybrid air/water conditioner), accomplishes cooling, dehumidification, ventilation, and domestic hot water heating. This paper models the HAWC within the framework of dynamic building energy modeling software and concludes that a refined version of the HAWC prototype is capable of completely eliminating high humidity events in the summer time while still saving energy as compared to a traditional HVAC system. [ABSTRACT FROM AUTHOR]

Energy consumption and air quality index (AQI) prediction is important for efficient heating, ventilation, and air conditioning (HVAC) system operation and management. A data-mining approach is presented in this paper for modeling and short-term prediction of the complicated non-linear system. The multilayer perceptron (MLP) ensemble performs best among the data mining algorithms discussed in this paper. A clustering-based method from preprocessing input data to construct the prediction models is proposed to decreases the prediction errors and the computational cost. The effectiveness of the proposed method is validated through a practical case study with both modeling and short-term prediction. The analytical results showed that the method was capable of reducing the prediction errors for modeling and short-term prediction by 11.05% and 12.21%, respectively, comparing with the models built without clustering method. [ABSTRACT FROM AUTHOR]

To facilitate the integration of buildings to the power grid, battery-equivalent models have been proposed to characterize and quantify aggregate flexibility from building loads. An analytical method has been proposed to construct such a flexibility model for thermostatically controlled loads. Since this analytical method is derived from a simplified representation of building thermal dynamics, it is necessary to evaluate the resulting flexibility model in a more realistic context. This paper focuses on the validation of this analytical method for estimating aggregate flexibility from residential air conditioning (ACs) systems. A high-fidelity model is first developed to mimic thermal behaviors of a residential AC system through a co-simulation between Modelica and EnergyPlus. A population of virtual residential AC systems is then generated by randomizing parameters of the high-fidelity model. Finally, an aggregate flexibility model is constructed for the residential AC population using the analytical method and validated using results from simulation of the high-fidelity model. It is found that the flexibility estimated using the analytical method is with reasonable accuracy, but can be improved by explicitly incorporating heat gains into the method. [ABSTRACT FROM AUTHOR]

In this paper the results of a wide investigation on a geothermal-integrated air HVAC system are reported: in the first part, the energy performances of an Earth to Air Heat eXchanger (EAHX) operating in Pomezia (a locality of the area of Rome, Italy) are carried out through a comprehensive numerical two-dimensional model based on the finite element method and the system is forced under real time-changing weather conditions over 1 year. The model is able to reproduce the time- and space- dependent thermo-fluid-dynamic behavior of the EAHX system, the humid air flux and the surrounding soil, as well as to account for the mass of condensed water in the tubes. In the second part of the investigation, the EAHX is coupled to an air handling unit of a company building for office use and tested while operating both in cooling and heating mode. The hourly results, in terms of power savings and energy consumption were reported for representative days of all the months belonging to the cooling or the heating working seasons, monthly and seasonal assessment. The convenience in terms of seasonal energy savings is +40.8% in cooling mode and +44.1% in heating mode. Then, the economic impact in terms of payback time and net present value was investigated through a cost analysis to examine the return of the economic investment under two possible soil morphologies and different prices of electrical energy in Italy. The simple payback with the real price of energy in Italy (0.50 €/kWh) is 3.3 years for the tufa-soil and 5.8 years for soft rock-soil; the economic return in terms of net present value is around 500 k€ for both the morphologies (560 k€ for the tufa; 446 k€ for the soft rock), per effect of the energy saving and, consequently, for a reduced expense of electrical energy. Therefore, in all the considered cases the installation of EAHX systems in support of traditional systems would generate both energy and economic advantages. [ABSTRACT FROM AUTHOR]

• The effect of the inaccurate load label on prediction models is analyzed. • The method of extracting load from cooling capacity is proposed. • Practical cases are used for validation. • The accuracy of ultra-short-term load prediction models is improved. Data-driven modeling achieves excellent performance in building load prediction by mining the actual load characteristic from operation data. When predicting room air-conditioning load, however, the measured data of cooling capacity cannot be used as the load label in the modeling as customary. The reason lies in the unstable automatic control of the air-conditioner, which makes the cooling capacity oscillate at the actual load. The mismatch of cooling capacity and actual load will affect prediction modeling. This paper first sets up a simulation experiment to quantitatively analyze this effect. The results indicate that the more the cooling capacity deviates from the load, the greater the error of the prediction model. To solve this problem, a load extraction method based on the Fourier decomposition is proposed, which involves transforming the actual cooling capacity data into the frequency domain and extracting the low-frequency components as load data, which is further used for modeling. The experiments show that the accuracy between extracted data and real load exceeds 90%. Additionally, the load extraction method improves the prediction accuracy by up to 17.55% compared to the model using cooling capacity data directly. Finally, a practical case demonstrates the effectiveness of the proposed load extraction method. [ABSTRACT FROM AUTHOR]

In the era of post-Coronavirus Disease 2019, the dedicated outdoor air system (DOAS), which provides 100% outdoor air for the building, is widely acknowledged as it can ensure acceptable indoor air quality by delivering fresh outdoor air to occupied space. The DOAS with a proper design and operation can provide sufficient ventilation and dehumidification while achieving energy efficiency. Nonetheless, there is limited guidance in determining the optimal control sequence of the DOAS for the designers and operators to implement in practice. Accordingly, in practice, a number of issues have been acknowledged in the design and control phases of DOAS, including insufficient ventilation and dehumidification, and increasing supply air dry-bulb temperature in fear of over-cooling, which might cause significant discomfort and energy waste. There have been efforts to develop high-performing DOAS controls for better energy efficiency. However, such controls are often complex, or difficult to interpret, for building designers and operators to consider in practice. In this regard, this paper explores a simulation-based framework for generating a supply air temperature control sequence of the DOAS not only to ensure improved energy-saving potential but also to guarantee the implement-ability of the control logic. The U.S. Department of Energy prototype primary school with dynamic occupancy profiles was modeled with a whole building simulation program, EnergyPlus. The model consists of a DOAS with an exhaust air energy recovery system for ventilation and fan-coil units for space cooling and heating. Then, a Genetic Algorithm was adopted to find the true optimal supply air temperature control sequence in terms of minimizing the energy cost of the heating, ventilation, and air conditioning system operation. Lastly, Decision Tree was adopted to extract rules out of the optimums to derive an implementable sequence of operation for the DOAS supply air temperature. A total of 12 week-simulation including four weeks of heating, cooling, and shoulder seasons, separately, under the weather condition of New York City was conducted for the case study. This case study identified that the optimization-informed rule extraction-based control, when compared to conventional outdoor air temperature-based reset control, could save about 13% of energy cost and 25% of energy consumption throughout the heating, cooling, and shoulder seasons. It is notable that the energy-saving was mainly achieved by reducing the heating energy consumption. Importantly, it nearly corresponds to the true optimal control result, which reduces approximately 14% of energy cost and 27% of energy consumption. From the results, it can be highlighted that the optimization-informed rule extraction can be as energy effective as the optimal control, while significantly reducing the complexity of the control. [ABSTRACT FROM AUTHOR]

• A gray-box energy model for residential ACs is developed, calibrated, and validated. • State variables (evaporation and condensation temperatures) are keys in the model. • Heat transfer at condenser and evaporator correlate state variables to model inputs. • Seven performance properties functions are identified for model calibration. • The cooling capacity and electrical power input can be accurately predicted. Energy models for vapor compression refrigeration in residential air conditioners have been developed through white-box, gray-box, and black-box methods in decades. However, existing white-box and gray-box models require complicated equations with detailed geometries while black-box models require substantial experimental data. This paper aims to develop and validate a simple gray-box steady-state energy model without the need for detailed geometries, which can accurately predict the cooling capacity and electrical power input based on outdoor and indoor air conditions, and supply airflow rates. First three state variables, including the evaporation and condensation temperatures, and refrigerant mass flowrate, are applied to develop the energy model and are solved by three physical equations, including the energy conservations at the evaporator and condenser, and the refrigerant volume-mass flow correlation of the compressor. Secondly, seven performance property functions related to three state variables and three physical equations are identified and calibrated by simple temperature and power measurements. Finally, field experiments are conducted on a residential air conditioner to calibrate these performance property functions and validate the developed model. The validated results reveal the model can accurately predict the cooling capacity and electrical power input, with the normalized root mean square errors of 2.3% and 0.87% respectively. [ABSTRACT FROM AUTHOR]

• Propose a novel machine learning-based model predictive control (MLB-MPC) framework with predictive inputs of cooling load and outdoor wet-bulb temperature. • Obtain the optimal match of prediction models and optimization algorithms for improving the performance of the MLB-MPC. • Investigate the impact of disturbances on the performance of global optimization. • Achieve an energy-saving ratio of 7.1% for the air-conditioning system when compared with the measured operation data. The dynamic optimization of key setpoints (e.g., supply water temperatures of chillers and cooling towers, or indoor temperature and humidity) can track the efficient performance point of the air-conditioning system (ACS), thus obtaining a great energy-saving effect. The model predictive control is an effective way to precisely adjust these setpoints. However, most of the existing studies focused on simple linear strategies, e.g., experience-based, rule-based, or component-based, which results in unsatisfactory energy efficiency. Aiming at this, the paper proposed a novel machine learning-based model predictive control (MLB-MPC) framework with predictive inputs of disturbances. The framework first employed the grid search and cross-validation to optimize the total energy consumption prediction models (TECPMs), which were built by data-driven models (e.g., multiple linear regression, artificial neural network, support vector regression (SVR), and random forest). And then the optimization performances of each TECPM to the controlled variables were obtained by using different optimization algorithms (e.g., genetic algorithm, particle swarm optimization (PSO), and simulated annealing). Finally, the optimal match of TECPMs and optimization algorithms was achieved by trade-off among prediction accuracies, optimization accuracies, and optimization time. The case studies demonstrated that the optimal match for the MLB-MPC is SVR and PSO as they had the highest prediction accuracy (mean absolute percentage error of 2.5%) and shortest optimization time (41 ms/per) and optimization accuracies with little difference. After adopting the optimal match, the MLB-MPC with predictive disturbing inputs achieved a great energy-saving ratio of 7.1% for the ACS, which was only less than the MLB-MPC with ideal disturbing inputs by 0.4%. This indicated that exact predictions of disturbances (e.g., cooling load and outdoor wet-bulb temperature) are important for the MLB-MPC. The proposed MLB-MPC framework would provide a method for improving the energy efficiency of ACSs. [ABSTRACT FROM AUTHOR]

• An improved system is proposed based on multi-fans with frequency conversion. • The improved system meets pressure control requirement in non-working modes. • The energy saving and cleanliness can be achieved by switching operation modes. Pressure control for cleanrooms in the pharmaceutical industry is a necessary means to avoid the cross-contamination. The pressure control of traditional air conditioning can only handle the working stage. In the non-working stage, the system cannot reduce the air change rate per hour (ACH) in order to alleviate the problem of high energy consumption. This paper proposes an improved air conditioning system, which focuses on the ability to control pressure gradient of the system in working and non-working mode. By theoretical derivation of the combined fan frequency conversion, when the impedance and volume of the infiltration air satisfy S i G Z , i = S j G Z , j = S k G Z , k = c o n s t a n t , the pressure gradient in multi-zone cleanrooms can remain stable. A mathematical model of the system has been established, which includes five modules: air pipe network, fan characteristic curve, fan operating point solution, variable volume damper characteristic curve and multi-zone network pressure gradient solution. The correctness of the model is verified by field measurements. Taking a clean workshop as case study, the room pressure can be stabilized in the range of ± 3 Pa by switching the working and non-working mode, which can save 39.8% of the energy consumption in non-working mode, while ensuring cleanliness. This paper demonstrates the process of the air pipe network's influence on cleanrooms pressure and proves the effectiveness of improved purification air conditioning system in pressure gradient control and energy saving potential. [ABSTRACT FROM AUTHOR]

Abstract: Accurate understanding of the thermal behaviour of building components is essential for predicting heating or cooling needs and facilitates the implementation of more successful energy saving strategies and retrofits. This paper focuses on a specific measure commonly introduced through the residential energy efficiency retrofit programmes in Ireland–insulation. Traditionally, assessments of the performance of building envelopes have been based on assumed thermal resistances of the materials involved, laboratory tests and computer modelling. The aim of the present work is to investigate the in situ thermal behaviour of a case study building and its components under transient and quasi-steady environmental conditions, comparing data before and after the fixing of cavity wall and ceiling insulation. The paper concludes by proposing that predicted values of heat loss using standardised assumed material properties of the existing structure do not reflect the actual values achieved in situ for this test case. These values greatly overestimated the impact of the retrofitted insulation on heat loss through the ceiling and wall. [Copyright &y& Elsevier]

Abstract: Liquid desiccant cooling system (LDCS) is an alternative air-conditioning system with promising energy-saving potential. To further explore the potential of LDCS, it is important to reveal the mass transfer mechanism of dehumidification process. The classical mass transfer model does well in theoretical analysis, but failed to explain the dehumidification reverse phenomenon in experiments. Therefore, this paper proposes a mass transfer model based on the kinetic theory for improvement. Through theoretical and experimental research, it proves the new model clearly describes the dehumidification mechanism and did better in predicting the dehumidification reverse phenomenon. This paper also gives a method through which we can get some important parameters of the new model from the mass transfer coefficient of the classical model. [Copyright &y& Elsevier]

Abstract: This paper summarizes a study undertaken to reveal potential challenges and opportunities for integrating optimization tools in net zero energy buildings (NZEB) design. The paper reviews current trends in simulation-based building performance optimization (BPO) and outlines major criteria for optimization tools selection and evaluation. This is based on analyzing user''s needs for tools capabilities and requirement specifications. The review is carried out by means of a literature review of 165 publications and interviews with 28 optimization experts. The findings are based on an inter-group comparison between experts. The aim is to assess the gaps and needs for integrating BPO tools in NZEB design. The findings indicate a breakthrough in using evolutionary algorithms in solving highly constrained envelope, HVAC and renewable optimization problems. Simple genetic algorithm solved many design and operation problems and allowed measuring the improvement in the optimality of a solution against a base case. Evolutionary algorithms are also easily adapted to enable them to solve a particular optimization problem more effectively. However, existing limitations including model uncertainty, computation time, difficulty of use and steep learning curve. Some future directions anticipated or needed for improvement of current tools are presented. [Copyright &y& Elsevier]

Abstract: Reducing the energy consumption of air-conditioning systems is becoming increasingly important. This paper focuses on the air-conditioning system in Terminal 3 in Xi’an Xianyang International Airport, the first airport terminal to adopt radiant cooling in China. In the large spaces of this airport terminal, a temperature and humidity independent control (THIC) system has been adopted instead of a conventional nozzle air supply method, which significantly reduces the energy consumption of the air supply. The radiant floor is the main mechanism for indoor temperature control, while a liquid desiccant outdoor air processor combined with displacement ventilation is responsible for humidity control. Ice storage is adopted to reduce operating costs, and the supplied chilled water temperature can be as low as 3°C. This paper examines the performance of the THIC system in detail. The indoor environment is determined through measurements to be comfortable, and the on-site performances of key components in both the airport terminal and the cooling plant are investigated. The outdoor air processor supplies air of appropriate temperature and humidity ratio; two kinds of radiant floors are used for temperature control, both with measured cooling capacities of about 30–40W/m2; and the energy efficiency ratio (EER) of the cooling plant is 2.62. [Copyright &y& Elsevier]

Abstract: This paper models the past and future sales, replacement rates and installed stock levels of air conditioning products in Europe. Established market diffusion models have been reformulated to allow their calibration against product sales data, and then used to estimate future and past sales levels, time-dependent product replacement rates and installed stock levels in each EU-27 country for each of the major energy-using air conditioning products. The results show that, for most air conditioning products, continuing growth of sales and stock is to be expected, albeit at lower rates than in previous years. Expressed in terms of kW cooling power, split-system room air conditioners and chillers continue to account for the majority of sales and stock, with variable refrigerant flow (VRF) systems taking an increasing share of first-time installations. The results provide fundamental information on which to base policy assessments (which are not part of this paper). [Copyright &y& Elsevier]

Abstract: Despite the large economic and ecologic costs, museum storage spaces are often equipped with extensive air conditioning, to provide the desired stable interior climate. The new “passive conditioning” paradigm aims at resolving these costs: a high-hygrothermal-inertia building with a high-hygrothermal-resistance envelope is to satisfactorily stabilise that interior climate, with no need for mechanical air conditioning hence. This paper first studies the reliability of full passive conditioning for museum storage spaces. It is shown to be an illusion, since it usually results in excessive interior humidities. Auxiliary dehumidification is thus required to provide good conservation conditions, and it is secondly investigated how the dehumidification load can be diminished. The study reveals the crucial impact of air tightness, while thermal insulation only has a minor influence. To further reduce the economic and ecologic cost of conditioning, the paper finally assesses “concentrated dehumidification”: dehumidification during a part of the day only, while leaving the humidity free-running during the rest of the day. It is established that the hygric inertia of the interior air, building walls and stored objects keeps the fluctuations of the interior relative humidities to a minimum when considering adequately air tight museum storage spaces. [Copyright &y& Elsevier]

Abstract: Most air handling units (AHUs) in commercial buildings have an air economizer cycle for free cooling under certain outside air conditions. During the economizer cycle, the outside air and return air dampers are modulated to seek supply air temperature at its setpoint. The supply air temperature is typically set at 55F (13°C) to control humidity in the space. However, dehumidification is not necessary when the outside air is dry. Meanwhile, the space may have less cooling load due to envelope heat loss and/or occupant schedule changes. These facts provide an opportunity to use higher supply air temperature to reduce or eliminate mechanical cooling and terminal box reheat. On the contrary, a higher supply air temperature requires increased air flow as well as fan power. Therefore, an optimization question is formed, through which an optimal supply air temperature is identified to minimize total energy consumption. In this paper a steady-state energy consumption model is established for AHU systems under the economizer, and then an analytical optimization method is used to seek an optimal supply air temperature setpoint to minimize the energy cost. This paper presents AHU system energy modeling, supply air temperature optimization, simulated energy savings, and control sequence development. [Copyright &y& Elsevier]

Abstract: This paper applies the Analytical Hierarchy Process (AHP) in calculating the weights and uses Cause–Effect Grey Relational Analysis (CEGRA) to rank system performance based on multiple criteria evaluation. AHP is compared with CEGRA in ranking the alternatives, thus achieving improved environmentally friendly system performance. This paper uses the TFT-LCD chiller in Taiwan to measure the model''s reliability and validity through comparison with the traditional strengths and weaknesses assessment. Businesses should cooperate with collaborative vendors and apply the service science management concept to improve performance and reduce energy waste. [Copyright &y& Elsevier]

Abstract: This paper presents an investigation of how Model Predictive Control (MPC) and weather predictions can increase the energy efficiency in Integrated Room Automation (IRA) while respecting occupant comfort. IRA deals with the simultaneous control of heating, ventilation and air conditioning (HVAC) as well as blind positioning and electric lighting of a building zone such that the room temperature as well as CO2 and luminance levels stay within given comfort ranges. MPC is an advanced control technique which, when applied to buildings, employs a model of the building dynamics and solves an optimization problem to determine the optimal control inputs. In this paper it is reported on the development and analysis of a Stochastic Model Predictive Control (SMPC) strategy for building climate control that takes into account the uncertainty due to the use of weather predictions. As first step the potential of MPC was assessed by means of a large-scale factorial simulation study that considered different types of buildings and HVAC systems at four representative European sites. Then for selected representative cases the control performance of SMPC, the impact of the accuracy of weather predictions, as well as the tunability of SMPC were investigated. The findings suggest that SMPC outperforms current control practice. [Copyright &y& Elsevier]

Abstract: This paper sets the viewpoint of air-conditioning system from heat sources and humidity sources, especially focusing on the temperature distribution of heat sources and how it influences the efficiency of air-conditioning system. For humidity sources, they are different from heat sources for their physical essence, which provides the possibility of separate treatment of heat and humidity. This paper establishes the ideal air-conditioning system of cooling and dehumidifying, based on the ideal treatment of heat sources, and humidity sources. Then the difference between ideal system and actual system are explored by a case study showing the decrease of efficiency step by step. The gap between ideal system and actual system can be concluded into three main imperfections: the method of treatment of heat sources, transmission temperature difference and heat exchange temperature difference, and the energy consumption of transportation. In the last, according to the actual influencing factors, some improving directions are proposed to improve the current system correspondingly. [Copyright &y& Elsevier]

Conceptually, many energy poverty studies to date have been narrowly focused on inadequate indoor heating, paying little attention to other domestic energy services. Yet there are indications that a growing number of households in Europe are struggling to achieve adequate levels of indoor cooling, with adverse consequences for their health, well-being and productivity. This situation is exacerbated by changing global weather patterns, with many countries facing increases in the frequency and intensity of extreme heatwaves. There is limited understanding of the ways in which households respond to extreme heat, and consequently how this might create greater demand for indoor space cooling and air conditioning, and the consequences for increased stress on power grids and conflicts with carbon reduction goals. Using custom-built survey data collected from 2337 households in Gdańsk (Poland), Prague (Czech Republic), Budapest (Hungary) and Skopje (North Macedonia), along with in-depth qualitative fieldwork with 55 households in the same cities, this paper presents novel evidence on the issue of summertime energy poverty and space cooling difficulties. We identify the driving forces of household vulnerability to excessive indoor heat, in terms of risk of exposure, adaptive capacity, and sensitivity, and explore the implications for addressing energy poverty. [ABSTRACT FROM AUTHOR]

• Investigation of novel hollow porous ceramic cuboids-heat pipes as heat and mass exchanger for evaporative cooling systems. • Formulation of mathematical model for heat and mass transfer. • Testing a proof-of-concept laboratory model. The work presented in this paper investigates design, computer modelling and testing of a sub-wet bulb temperature evaporative cooling system for space air conditioning in buildings. The target application of evaporative cooling technology is particularly for geographical regions with hot and dry climate. A laboratory prototype made of integrated finned heat pipes and a water filled hollow porous ceramic cuboids was been built and tested. The design exploits the high thermal conductivity of heat pipes as effective heat transfer device and the good wettability characteristic of porous ceramic material. Key thermal performance metrics of the prototype were modelled and validated experimentally under controlled laboratory conditions of temperature (30, 35 and 40 °C) and relative humidity (35–55%). Under typical dry climates conditions (ambient air dry bulb temperature of 35°C and relative humidity of 35%), the measured supply air dry bulb temperature was 22.3 °C, which is lower that the ambient air wet bulb temperature, and maximum cooling capacity of approximately 196 W per unit surface area (m2) of wet porous ceramic cuboid. Furthermore, it was shown that the measured prototype cooler wet bulb effectiveness was 1.05 while the dew point effectiveness was 0.73. [ABSTRACT FROM AUTHOR]

The American Society for Heating, Refrigeration, and Air Conditioning Engineers (ASHARE) prescribes fixed ventilation rates for the operation of heating, ventilation, and air conditioning (HVAC) systems, which is sub-optimal in terms of controlling indoor air pollutants and energy consumption. This paper relies on a physics-based model of a residential house to predict the concentrations of indoor pollutants such as ozone, formaldehyde (HCHO), and particulate matter (PM) as function of time, outdoor conditions, and indoor emissions. The model captures real-world scenarios such as pollutants entering the house from ambient air through an air handling unit (AHU) and pollutants emitted in the house. A dynamic optimization problem is then formulated and solved to calculate the optimal ventilation rate at each time instant, that minimizes the total energy consumption, while maintaining the indoor pollutant concentrations below or as close as possible to their respective acceptable thresholds. For the considered example day, operation under optimized conditions reduces the peak pollutant concentration by 31%, time of exposure to undesirable concentrations by 48%, and energy consumption of the AHU by 17.7%. [ABSTRACT FROM AUTHOR]

Highlights • A 12 month mixed-method longitudinal study of energy demand in Kuwaiti villas. • Building energy models grounded with physical and social empirical data. • Space cooling accounts for 50% to 75% of total energy use in the case study villas. • Air conditioning thermostat settings are a key driver of energy use. • Insulation and double glazing contribute to more uniform internal temperatures. Abstract This paper investigates the physical and social determinants of energy use in four case study villas in Kuwait. The investigation consisted of a 12 month mixed-method longitudinal monitoring and surveying study followed by building energy modelling. Monitoring and surveying provided empirical data about household energy use, internal temperatures, building and system characteristics and occupant energy-use behaviours. This data was used to ground models to better predict energy use. Models grounded with empirical data show that space cooling accounts for 50% to 75% of total energy use in villas. Results suggest that drivers of cooling energy are varied, with 30% of cooling energy in some villas attributable to heat gains from appliances. Furthermore, while the study found no distinct reduction in measured and modelled annual energy use intensities of villas with improved levels of efficiency (insulation and double glazing), such measures did contribute to more uniform internal temperatures. The study also identified key occupant energy-consuming behaviours including a tendency not to adjust air conditioning (AC) thermostat settings during periods of summer travel and lack of regular AC maintenance. The approach and findings of the study can inform future studies in Kuwait seeking to understand energy use in a nationally representative sample. [ABSTRACT FROM AUTHOR]

Highlights • A nominal output capacity based performance index for ASHPs, ɛ NL , was proposed. • ɛ NL was influenced by ambient air conditions and defrosting initiating time. • A four-layer GRNN model for predicting ɛ NL was developed. • ɛ NL at varying operating conditions was predicted using the GRNN model. Abstract Air source heat pump (ASHP) units have been widely used for space heating in recent years. While a space heating ASHP unit is normally rated at its nominal operating condition, however, during its actual space heating operation, it rarely works at the nominal condition. The actual output heating capacity can remarkably deviate from that at the nominal condition, due to the influences of ambient air temperature and frosting-defrosting operation. Therefore, to enable a comprehensive and convenient evaluation of the operating performance of ASHP units with frosting-defrosting operation and to provide designers with appropriate design guidelines to size a space heating ASHP unit, a new performance index has been proposed. The new performance index, ɛ NL , or the loss coefficient in the nominal output heating energy, was actually based on the nominal output heating capacity of ASHP units, which was readily available and stayed unchanged irrespective when and where ASHP units were operated. In this paper, the definition of ɛ NL was firstly given, following a detailed explanation of the frosting-defrosting operation of an ASHP unit. Secondly, a GRNN model for predicting the ɛ NL of a field ASHP unit was established following a correlation analysis using a total of 473 groups of field measured data from the field ASHP unit. Finally, a modeling study using the developed GRNN model was carried out, and the study results suggested that when an ASHP unit was operated at a fixed ambient condition, defrosting initiating time would affect the ɛ NL , and there may exist an optimal defrosting initiating time at which ɛ NL was at its minimum. The model results also demonstrated that an increase in ambient air relative humidity or a decrease in ambient air temperature would result in an increase in ɛ NL , when an ASHP unit was operated with a fixed defrosting initiating time. [ABSTRACT FROM AUTHOR]

Highlights • The energy performance of all variable-speed packaged units needs to be evaluated. • Field test and simulation are combined in the performance evaluation. • The evaluated unit has > 30% higher cooling efficiency than most units in the field. • All variable-speed units can save 22%−29% electricity than the code requirement. Abstract Packaged air-conditioning units are widely used in commercial buildings. Most packaged units in the field are equipped with constant-speed supply fans and constant-speed compressors. Many efforts have been made to increase the operational efficiency of packaged air conditioners by retrofitting existing units with improved controls or developing innovative products with advanced designs. This paper evaluates the energy performance of a packaged unit with all variable-speed components, including the supply fan, the compressor, and the condenser fan. Both a field test and energy simulation are used to quantify the potential of energy savings from the variable-speed unit (VSU) against reference units. In the field test, the reference is a six-year-old existing unit. It was determined through monitoring for one year that the VSU had a 31% higher cooling efficiency than the reference unit. In the simulation, a retail building model was used to compare the performance between the VSU and two reference units—one representing existing units in the field and the other representing units meeting the latest energy code requirements by ASHRAE Standard 90.1. Simulation results showed that depending on the climate, the VSU can save electricity consumption (including both cooling and fan) by 45%–54% relative to the first reference and by 22%–29% relative to the second reference. These findings are valuable for building designers and contractors in selecting packaged rooftop units for both new constructions and retrofits. [ABSTRACT FROM AUTHOR]

Abstract Taking advantage of the thermal inertia of a building to shift the cooling load during a demand response (DR) period is an important strategy for commercial buildings. However, researchers have consistently ignored the effects of the thermal inertia of air-conditioning systems on the DR potential of buildings. This study focused on the coupling effect of a building and an air-conditioning system. This paper describes the construction of a coupled thermal inertia model of a building and an air-conditioning system, which was validated experimentally; analyzes the accuracy of the thermal inertia of a building solely, as well as the accuracy of both the building and air-conditioning system together by comparing the model and experiment results; and quantifies the DR contributions of the thermal inertia of both the building and the air-conditioning system. A considerable demand reduction effect of the thermal inertia of the air-conditioning system was found, and the results of coupling the thermal inertia of both the building and air-conditioning system showed greater accuracy. [ABSTRACT FROM AUTHOR]

Abstract: GeoCool plant was the result of a EU project whose main purpose was to adapt ground coupled heat pump technology to cooling dominated areas. The execution of this experimental plant was completed at the end of year 2004, starting on February 2005 the regular operation of the air conditioning system. Since then, GeoCool facility has been monitored by a network of sensors characterizing its most relevant parameters. Several aspects of the performance and behaviour of the system during its first operational year were presented on a previous paper. This paper presents the energy performance measurements of GeoCool ground coupled heat pump system acquired during five years of operation as well as the evolution of the return water temperature from the ground as a representative of the ground temperature. The analysis of the experimental results shows that the system energy performance is maintained through the years with no appreciable impact on ground thermal response. [Copyright &y& Elsevier]

Abstract: This paper presents a review of studies on natural convection heat transfer in the triangular enclosure namely, in attic-shaped space. Much research activity has been devoted to this topic over the last three decades with a view to providing thermal comfort to the occupants in attic-shaped buildings and to minimising the energy costs associated with heating and air-conditioning. Two basic thermal boundary conditions of attic are considered to represent hot and cold climates or day and night time. This paper also reports on a significant number of studies which have been performed recently on other topics related to the attic space, for example, attics subject to localized heating and attics filled with porous media. [Copyright &y& Elsevier]

Abstract: The use of hygroscopic materials for moisture buffering is a passive way to moderate the variation of indoor humidity. Through absorption and desorption, surface materials in the indoor environment, such as curtains, carpets and wall paper, are able to dampen the moisture variations. The moisture buffering capacity of these materials may be used to improve the relative humidity of the indoor environment at reduced energy costs. The objectives of this paper are threefold. The first objective is to derive a theoretical model for the transient moisture transfer between a curtain system and the indoor air for the case where the curtain is placed in front of a wall. The second objective is to conduct experiments inside environmental chambers to validate the theoretical model and to test the ability of curtains to moderate indoor humidity. It is shown that the experimental results for the curtain moisture uptake and the relative humidity inside the chamber compared well with the model simulation results. The third and final objective is to test and evaluate the model under “real environment conditions” for a case study of a hygroscopic cotton curtain, placed in a “typical” office space in the city of Beirut with an area of 25m2 that uses direct expansion (DX) air conditioning system. It is found that hygroscopic curtains maintain humidity of less than 65% during part load operation compared to the upper limit of 70% relative humidity when no curtain is used. On the other hand, it is found that the energy use, as determined by the daily electrical power consumption of the DX system, is almost the same for the two cases, (with and without a curtain), where approximately 20kWh of energy input is required 13kWh of sensible energy and 7kWh of latent energy. [Copyright &y& Elsevier]

Abstract: Heat is transferred through building envelopes by conduction, radiation, and convection. Of these, convective heat transfer is often the weakest ‘link’ in the overall heat transfer model. While conduction and radiation heat transfer are supported by well-established analytical and numerical models, the treatment of convection is much less rigorous. Convection modeling involves solution of fluid dynamics problems in which the complexity of an enclosed space''s geometry and the diversity of indoor airflow patterns require many fit-for-purpose convection correlations. These must take into account specifics of the space and of the heating ventilation and air-conditioning (HVAC) system. This paper provides an overview of the current knowledge on the modeling of convective heat transfer in load calculation and building energy simulation programs. The paper also discusses various issues related to the robustness of convection coefficient correlations, and reports on new experiments conducted to test the sensitivity of existing convection correlations. The discussed issues relate to: (1) the non-uniformity of the indoor temperature field; (2) the selection of a proper characteristic dimension; (3) the effect of adiabatic and non-adiabatic obstructions in the zone; and (4) the impact of airflow disturbance. [Copyright &y& Elsevier]

Abstract: The performance of different HVAC systems varies when coupled with different buildings. This paper examines the relationship between building heating and cooling load and subsequent energy consumption with different HVAC systems. Two common HVAC systems in use throughout the UK office building stock, variable air volume (VAV) system and fan coil (FC) with dedicated outside air system, have been coupled with a typical narrow plan office building with and without daylight control and for both cellular and open plan. The results presented in this paper clearly indicate that it is not possible to form a reliable judgment about building energy performance based only on building heating and cooling loads. For the two investigated systems, variable air volume system and fan coil with dedicated outside air system, the difference between system demand and building demand varied from over −40% to almost +30% for cooling and between −20% and +15% for heating. If a heat recovery unit is used, the difference in heating performance is even greater, rising to −70%. [Copyright &y& Elsevier]

Abstract: In this paper, a solar heating system, which combines the technologies of evacuated tube solar air collector and rotary desiccant humidification together, has been configured, tested and modeled. The system mainly includes 15m2 solar air collectors and a desiccant air-conditioning unit. Two operation modes are designed, namely, direct solar heating mode and solar heating with desiccant humidification mode. Performance model of the system has been created in TRNSYS. The objective of this paper is to check the applicability of solar heating and evaluate the feasibility and potential of desiccant humidification for improving indoor thermal comfort. Experimental results show that the solar heating system can convert about 50% of the received solar radiation for space heating on a sunny day in winter and increases indoor temperature by about 10°C. Compared with direct solar heating mode, solar heating with desiccant humidification can increase the fraction of the time within comfort region from about 10% to 20% for standalone solar heating and from about 30% to 60% for solar heating with auxiliary heater according to seasonal analysis. It is confirmed that solar heating with desiccant humidification is promising and worthwhile being applied to improving indoor thermal comfort in heating season. [Copyright &y& Elsevier]

Abstract: In arid climates, evaporative cooling technologies are generally valued for their reduced energy consumption in comparison to compressor-based air conditioning systems. However, two concerns that are often raised with respect to evaporative cooling equipment are their on-site water use and the impact of poor water quality on their performance. While compressor-based systems do not use water on-site, they do consume water through their use of electricity, which consumes water through evaporation at hydroelectric power plants and cooling at thermal power plants. This paper defines a water-use efficiency metric and a methodology for assessing the water use of various cooling technologies. The water-use efficiencies of several example cooling technologies are compared, including direct evaporative, indirect evaporative in two different configurations, compressor-based systems, compressor-based systems with evaporative pre-cooling of condenser inlet air, and hybrid systems that consist of an indirect evaporative module combined with a compressor-based module. Designing cooling systems for arid climates is entwined in the close relationship between water and energy and the scarcity of both resources. The analyses presented in this paper suggest that evaporative systems that significantly reduce peak electricity demand and annual energy consumption need not consume any more water than conventional systems. [ABSTRACT FROM AUTHOR]