Subcooling of the refrigerant at the exit of the condenser in a vapor compression refrigeration system could be an effective method to improve the coefficient of performance (COP). This method allows the refrigerant entering the evaporator with a lower mass fraction of vapor and absorbs more heat in the evaporator. The effort in this paper investigates a solar based integrated system of an electricity-driven vapor-compression chiller (VC) and an absorption heat pump (ABS) to provide both heating and cooling to space. Thermodynamic and heat transfer models of the integrated system were developed to estimate the system performance. The modeling results showed the integrated system can achieve 40% of the reduction on electricity consumption and 66% of the improvement in cooling COP. Furthermore, the hot water supply temperature can reach 50.25°C. The models have also been used to conduct parametric sensitivity analysis. The key parameters which affect the performance of the system were the heat source temperature, the hot water return temperature, and the outdoor air flow rate. Hot water flow rate only has significant influence on the hot water supply temperature. Increasing the temperature and flow rate of the heat source can have benefits on both heating and cooling performance. However, increasing the outdoor air flow rate can only benefit on energy saving and cooling performance.

All the previous theoretical models of the dynamic thermal behavior of the periodic–flow Air Pre-Heater (APH) have ignored the effects of the baskets walls. Therefore, the purpose of this work is to develop experimental and a numerical model simulating transient energy transport in a periodic-flow regenerative APH to involve the important thermal effect of the basket walls surrounding the heating element matrices. Three main different types of matrices that are intended to be used in periodic-flow APH have been investigated and comparison was made between them. These materials are corrugated plates matrices (CPMs), wire mesh matrices (WMMs) and stone media matrices (SMMs). Total of (13) different configurations of matrices have been tested. The investigations covered a range of geometrical parameters of corrugated plate angle, wire diameter of mesh, pitch and screen to screen position and size of stones. The investigation has been carried out for hydraulic – diameter base Reynolds number, Re, in the range of 680<Re < 10100. The basket wall was determined to have a significant influence on the thermal behavior of the packing matrices especially in the near–wall region, and had been seen to introduce different thermal response for each type of the tested materials. New (13) correlation equations for the overall J-factor have been developed for each matrix type to provide the best matching between the gathered experimental data with the numerical model.

Approximately half of the water heaters sold in the U.S. and Canada for residential and small commercial applications are natural gas fired storage water heaters, with a maximum theoretical thermal efficiency of 96%. A packaged water heater heated by a 2.9 kW absorption heat pump was designed and demonstrated in this study to achieve performance exceeding these limitations. The modeling and validation of the absorption cycle and of the natural gas-fired combustion system are discussed here. Heat transfer characteristics of the absorption components at expected operating conditions were used to model cycle performance. A single-effect system based on these models was fabricated and yielded a cyclic COP of 1.63, within 3% of predictions. A corresponding GAX cycle-based system yielded performance 20% lower than predicted values, indicating the need for larger heat and mass exchangers to achieve the expected system level performance. The gas-fired burner configuration required for this heat pump is governed by the water heater envelope, desorber geometry and process requirements, coupled with emissions requirements. Parametric CFD analyses were conducted to estimate the impact of chamber design on burner performance, and revealed a beneficial recirculation pattern within the combustion chamber that was strongly influenced by chamber height. Emission reductions depended on chamber diameter, and prototype burners with smaller outer diameter fabricated based on these designs met emission targets.

Portable energy storage will be a key challenge if electric vehicles become a large part of our future transportation system. A big limiting factor is vehicle range. Range can be further limited if heating and air conditioning systems are powered by the electric vehicle’s batteries. The use of electricity for HVAC can be minimized if a thermal battery can be substituted as the energy source to provide sufficient cabin heating and cooling. The aim of this project was to model, design, and fabricate a thermal storage battery for electric vehicles. Since cost and weight are the main considerations for a vehicular application — every attempt was made to minimize them in this design. Thus, the final thermal battery consists of a phase change material Erythritol (a sugar alcohol commonly used as artificial sweetener) as the storage medium sealed in an insulated, stainless steel cooking pot. Heat exchange to the thermal battery is accomplished via water (or low viscosity engine oil) which is pushed through a copper coil winding. A CFD model was used to determine the geometry (winding radius and number of coils) and flow conditions necessary to create adequate heat transfer. Testing of the fabricated design indicates that the prototype thermal battery module losses less than 5% per day and can provide enough heat to meet the demand of cruising passenger vehicle for up to 1 hour of full heating on a cold day. Other metrics, such as $/kJ and kJ/kg, are competitive with Lithium ion batteries for our prototype.

This paper describes the design and construction of a solar thermal adsorption refrigerator in Patna, Bihar, India. After a brief description of the local situation and planning prerequisites the reasons for choosing an ethanol based adsorption system are explained. The following sections are focused on the description of the design and the theory behind the system. Lastly, practical aspects that arose during the construction of the first prototype are mentioned.

Thermal energy storage (TES) is a vital component of concentrated solar power (CSP). TES makes up for intermittent solar radiation, bad weather, and peak power demand. Currently, a sensible heat storage system using two tanks containing molten salt is considered the most practical and economical TES. Yet further system development is needed in order to improve its performance and economics. In this study of molten salt storage tanks, spherical tanks were investigated as an alternative to cylindrical tanks. Structural and thermal aspects of cylindrical tanks with varying H/D ratios (0.25–5) and spherical tanks of the same volume were compared. Comparison showed that utilization of spherical instead of cylindrical tanks resulted in significant savings in shell building material (28–47%). Heat transfer from the spherical tank’s shell is at least 35% less than cylindrical tanks. Reduction in building material, foundation, and insulation cost can lead to significant cost savings.

Condensing boiler for flue gas waste heat recovery is widely used in industries. In order to gain a portion of the sensible heat and latent heat of the vapor in the flue gas, the flue gas is cooled by return water of district heating through a condensation heat exchanger which is located at the end of flue. At low ambient air temperature, some boilers utilize the air pre-heater, which makes air be heated before entering the boiler, and also recovers part of the waste heat of flue gas. However, there are some disadvantages for these technologies. For the former one, the low temperature of the return water is required while the utilization of flue gas heat for the latter one is very limited. A new flue gas condensing heat recovery system is developed, in which direct contact heat exchanger and absorption heat pump are integrated with the gas boiler to recover condensing heat, even the temperature of the return water is so low that the latent heat of vapor in the flue gas could not be recovered directly by the general condensing technologies. Direct contact condensation occurs when vapor in the flue gas contacts and condenses on cold liquid directly. Due to the absence of a solid boundary between the phases, transport processes at the phase interface are much more efficient and quite different from condensation phenomena on a solid surface. Additionally, the surface heat exchanger tends to be more bulky and expensive. In this study, an experimental platform of the new system is built, and a variety of experimental conditions are carried out. Through the analysis of the experimental data and operational state, the total thermal efficiency of the platform will be increased 3.9%, and the system is reliable enough to be popularized.

Parabolic trough technology is currently one of the most extended solar thermal systems for the production of electricity. This paper describes a thermo-economic study of an integrated, combined-cycle parabolic trough power plant. The parabolic trough plant is considered an economizer or a superheater of the HRSG (heat recovery steam generator). The main objective is to obtain the optimum design of the different sections of the boiler and the size of the parabolic field. The configurations analyzed are two pressure levels with and without a reheater. A Euro Trough (ET) concentrator was used in this study, the working fluid being water with direct steam generation. There will be no problem with the evaporation in the absorber, since the solar plant will be the economizer of the HRSG and an approach point greater than 3°C is considered. The methodology applied for the optimization is Genetic Algorithms. This methodology was employed in previous works developed by the authors and yielded good results. So that method is applied to the configurations analyzed but including the parabolic trough plant. As a result, a thermoeconomic optimum design of a parabolic trough plant used as the section of the HRSG is obtained. The results show that the solar field increases the power and efficiency of the combined-cycle plant during the operation and makes it less susceptible to load variations.

The current heating system in Yinchuan city, the capital of the Ningxia Autonomous Region in northwest China, is investigated and analyzed. Lacking an integrated planning, the heating systems have developed with low energy efficiency, high environment emission and economic cost. The choice of heating energy structure vary between coal and gas, the heating modes including gas-fired CHP, coal-fired CHP, gas-fired boiler and coal-fired boiler are facing challenges. In this paper, several innovative planning scenarios are proposed to achieve high energy efficiency, low environment emission and reasonable economic cost. In the heating schemes, three innovative technologies are designed. The first technology is waste heat recovery based on the Co-generation-based absorption heat-exchange (Co-ah) cycle. The waste heat can be both from circulating water or flue gas in CHP heating system and the industrial waste heat recovery. The second technology is the heating network with large temperature difference. The third technology is the gas distributed peak-shaving, gas-driven absorption heat-exchange in the substation.

In order to use real-time energy measurements to identify system operation faults and inefficiencies, a cooling coil energy baseline is studied in an air-handling unit (AHU) through an integration of physical models and a data driven approach in this paper. A physical model for an AHU cooling coil energy consumption is first built to understand equipment mechanism and to determine the variables impacting cooling coil energy performance, and then the physical model is simplified into a lumped model by reducing the number of independent variables needed. Regression coefficients in the lumped model are determined statistically through searching optimal fit using the least square method with short periods of measured data. Experimental results on an operational AHU (8 ton) are presented to validate the effectiveness of this approach with statistical analysis. As a result of this experiment, the proposed cooling energy baselines at the cooling coil have ±20% errors at 99.7% confidence. Six-day data for obtaining baseline is preferred since it shows similar results as 12-day.

This paper presents an artificial neural network (ANN) for forecasting the short-term electrical load of a university campus using real historical data from Colorado State University. A spatio-temporal ANN model with multiple weather variables as well as time identifiers, such as day of week and time of day, are used as inputs to the network presented. The choice of the number of hidden neurons in the network is made using statistical information and taking into account the point of diminishing returns. The performance of this ANN is quantified using three error metrics: the mean average percent error (MAPE); the error in the ability to predict the occurrence of the daily peak hour; and the difference in electrical energy consumption between the predicted and the actual values in a 24-hour period. These error measures provide a good indication of the constraints and applicability of these predictions. In the presence of some enabling technologies such as energy storage, rescheduling of non-critical loads, and availability of time of use (ToU) pricing, the possible DSM options that could stem from an accurate prediction of energy consumption of a campus include the identification of anomalous events as well the management of usage.

Simulation results from a hybrid ground source heat pump model are presented for a residential home that integrates a compact cooling tower into an existing ground source heat pump model. The tower is introduced to assess its impact on the operational and economic performance over that of a GSHP alone. Metrics include initial and lifetime operational costs, ground heating effects, heat pump efficiency, and ability to control the temperature of the conditioned space. A single story, 195 m 2 house located in Austin, Texas is used as a cooling-dominated test case. Simulations spanning 10-years of operation show that adding the cooling tower is cost effective, but more importantly, it extends the lifetime of the borehole system and maintains the heat pump efficiencies at high levels.

This paper describes a thermodynamic model that simulates the discharge cycle of a single-tank thermal energy storage (TES) system using supercritical fluid in a concentrating solar power plant. Current state-of-the-art TES design utilizes a two-tank system with molten nitrate salts; one major problem is the high cost of the fluid. The alternate design explored here involves the use of less expensive fluids at supercritical temperatures and pressures. By cycling the storage fluid between a relatively low temperature two-phase state and a high temperature supercritical state, a large excursion in internal energy can be accessed which includes both sensible heat and latent heat of vaporization. Supercritical storage allows for the consideration of fluids that are significantly cheaper than molten salts; however, a supercritical TES system requires high pressures and temperatures that necessitate a relatively high cost containment vessel that represents a large fraction of the system capital cost. To mitigate this cost, the proposed design utilizes a single-tank TES system, effectively halving the required wall material. A single-tank approach also significantly reduces the complexity of the system in comparison to the two-tank systems, which require expensive pumps and external heat exchangers. However, a single-tank approach also results in a loss of turbine power output as the storage fluid temperature declines over time during the discharge cycle. The thermodynamic model is used to evaluate system performance; in particular it predicts the reduction in energy output of the single-tank system relative to a conventional two-tank storage system. Tank wall material volume is also presented and it is shown that there is an optimum average fluid density that generates a given turbine energy output while minimizing the required tank wall material and associated capital cost. Overall, this study illustrates opportunities to further improve current solar thermal technologies. The single-tank supercritical fluid system shows great promise for decreasing the cost of thermal energy storage, and ensuring that renewable energy can become a significant part of the national and global energy portfolio.

A novel approach to storing thermal energy with supercritical fluids is being investigated, which if successful, promises to transform the way thermal energy is captured and utilized. The use of supercritical fluids allows cost-affordable high-density storage with a combination of latent heat and sensible heat in the two-phase as well as the supercritical state. This technology will enhance penetration of several thermal power generation applications and high temperature water for commercial use if the overall cost of the technology can be demonstrated to be lower than the current state-of-the-art molten salt using sodium nitrate and potassium nitrate eutectic mixtures. An additional attraction is that the volumetric storage density of a supercritical fluid can be higher than a two-tank molten salt system due to the high compressibilities in the supercritical state. This paper looks at different elements for determining the feasibility of this storage concept — thermodynamics of supercritical state with a specific example, naphthalene, fluid and system cost and a representative storage design. A modular storage vessel design based on a shell and heat exchanger concept allows the cost to be minimized as there is no need for a separate pump for transferring fluid from one tank to another as in the molten salt system. Since the heat exchangers are internal to the tank, other advantages such as lower parasitic heat loss, easy fabrication can be achieved. Results from the study indicate that the fluid cost can be reduced by a factor of ten or even twenty depending on the fluid and thermodynamic optimization of loading factor. Results for naphthalene operating between 290 °C and 475 °C, indicate that the fluid cost is approximately $3/kWh compared with $25-$50/kWh for molten salt. When the storage container costs are factored in, the overall system cost is still very attractive. Studies for a 12-hr storage indicate that for operating at temperatures between 290–450 °C, the cost for a molten salt system can vary between $66/kWh to $184/kWh depending on molten salt cost of $2/kg or a more recent quote of $8/kg. In contrast, the cost for a 12-hr supercritical storage system can be as low as $40/kWh. By using less expensive materials than SS 316L, it is possible to reduce the costs even further.

The United States (U.S.) Department of Energy (DOE)’s Pacific Northwest National Laboratory (PNNL) is spearheading a program with industry to deploy and independently monitor five kilowatt-electric (kWe) combined heat and power (CHP) fuel cell systems (FCSs) in light commercial buildings. This publication discusses results from PNNL’s research efforts to independently evaluate manufacturer-stated engineering, economic, and environmental performance of these CHP FCSs at installation sites. The analysis was done by developing parameters for economic comparison of CHP installations. Key thermodynamic terms are first defined, followed by an economic analysis using both a standard accounting approach and a management accounting approach. Key economic and environmental performance parameters are evaluated, including (1) the average per unit cost of the CHP FCSs per unit of power, (2) the average per unit cost of the CHP FCSs per unit of energy, (3) the change in greenhouse gas (GHG) and air pollution emissions with a switch from conventional power plants and furnaces to CHP FCSs; (4) the change in GHG mitigation costs from the switch; and (5) the change in human health costs related to air pollution. CHP FCS heat utilization is expected to be less than 100% at several installation sites. Specifically at six of the installation sites, during periods of minimum building heat demand (i.e. summer season), the average in-use CHP FCS heat recovery efficiency based on the higher heating value of natural gas is expected to be only 24.4%. From the power perspective, the average per unit cost of electrical power is estimated to span a range from $15–19,000/kilowatt-electric (kWe) (depending on site-specific changes in installation, fuel, and other costs), while the average per unit cost of electrical and heat recovery power varies between $7,000 and $9,000/kW. From the energy perspective, the average per unit cost of electrical energy ranges from $0.38 to $0.46/kilowatt-hour-electric (kWhe), while the average per unit cost per unit of electrical and heat recovery energy varies from $0.18 to $0.23/kWh. These values are calculated from engineering and economic performance data provided by the manufacturer (not independently measured data). The GHG emissions were estimated to decrease by one-third by shifting from a conventional energy system to a CHP FCS system. The GHG mitigation costs were also proportional to the changes in the GHG gas emissions. Human health costs were estimated to decrease significantly with a switch from a conventional system to a CHP FCS system. A unique contribution of this paper, reported for the first time here, is the derivation of the per unit cost of power and energy for a CHP device from both standard and management accounting perspectives. These expressions are shown in Eq. (21) and Eq. (31) for power, and in Eq. (24) and Eq. (34) for energy. This derivation shows that the average per unit cost of power is equal to the average per unit cost of electric power applying a management accounting approach to this latter calculation. This term is also equal to the average per unit cost of heat recovery power applying a management accounting approach. A similar set of relations hold for the average per unit cost of energy. These derivations underscore the value of using Eq. (21) for economic analyses to represent the average per unit cost of electrical power, heat recovery power, or both, and using and Eq. (24) for energy.

In recent years with the sustainable development of economy, the energy consumption of air conditioning system has accounted for over 40% of the total of buildings in China. Energy conservation has become an important issue. Various energy wastes exist in the operation process of central AC systems. So the central air conditioning system of energy saving has great potential. Central air conditioning load changes with time-varying characteristics, the load and operating conditions are influenced by various factors such as season, weather, traffic and environmental conditions changing and so on. They are always changing, and always fluctuating. Even in the day, morning and evening have temperature changes. According to statistics it is only a short time for the occurrence of most buildings’ maximum load time, and air conditioning systems are running at part load conditions in most time. If air conditioning system operating control way cannot change load according to the dynamic adjustment, which necessarily causes enormous energy waste. In this paper, with the help of a typical building located in Baoding, China, the simulation of a central air-conditioning system was carried out. First, the simulation models of main equipments of a central air conditioning system are established. Second, according to the actual loads, simulation of the different energy control modes and the operation schemes were carried through. Third, the simulation curves were obtained. Finally, based on the comparison of simulation curves, the optimal energy saving control mode and the operation scheme of the central air conditioning system were analyzed, the energy saving potentials existing in the actual operating process were proposed. All these above will be very important for the AC system operation optimization of building energy-efficient and air conditioning system operation and management.

The performance of dry-cooled ORC systems varies significantly with environmental conditions, diurnally and seasonally. This study analyzes the impact of environmental conditions on overall performance and operational control of dry-cooled ORC systems with fixed and variable geometry expanders. Performance analysis results are extended to time-series environmental data to determine the expected performance of a system over long durations. Analysis results indicate that, if other factors are held constant, variable speed condenser fans produce minimal performance improvement, while variable-geometry expanders have a significant impact.

Many food processing plants in New York State generate large volume waste streams with a wide variety of physical and chemical properties. With greater environmental regulation and increasing fees for municipal sewer and solid waste disposal, additional innovative ‘disposal’ methods for these wastes need to be developed. One attractive alternative is to use the food processing waste as feedstock for a waste-to-energy conversion process comprising two distinct systems, namely waste-to-fuel and fuel-to-energy. The fuel can either be sold to generate revenue, or converted on-site to electrical or thermal energy to offset the plant power requirements. In this study, the technical viability and economic benefit of applying waste-to-energy solutions to a diverse selection of companies producing milk, cheese, beer, and tofu were assessed. Depending upon the volumes and composition of the available waste streams (including analysis of sugar content, biological oxygen demand, etc.) there may be a compelling business case to utilize the food waste as feedstock for ethanol, biodiesel or methane-rich biogas production.

This research numerically studies the performance of absorption solar cooling systems operated under climates of the major cities in Taiwan. Both single-effect and double effect absorption solar cooling systems are studied. The single-effect system uses flat-plate solar collectors and the double-effect system uses linear concentration collectors. The results show a promising solar fraction (the fraction of cooling load provided by solar energy) for most of Taiwan areas. In addition, the double-effect systems provide better solar fraction than the single-effect systems. This study provides design reference and system optimization for the development of absorption solar cooling systems in Taiwan.

Tracer gas and blower door testing are two widely used methods to determine the rate of air infiltration through a building envelope. Blower door testing is performed at elevated pressure differentials across the building envelope whereas tracer gas testing is conducted at near zero differential pressures, better reflecting the air leakage rate at near normal building operating conditions. The primary objective of this study was to determine whether extrapolation of blower door test data to normal building operating conditions provides a good estimate of annual average air infiltration at those conditions. Two methods were used to extrapolate the data and were then compared to the baseline tracer gas tests. A secondary objective was to determine the ventilation rate of a residential facility using tracer gas tests. Tracer gas testing seems to be more reliable in determining the air leakage rate at normal operating pressures, but is sensitive to the tracer gas and ambient weather conditions. Regardless, for the subject facility, the ACH50/20 rule and Sherman’s ACH50/N correlation, extrapolated from the blower door tests, are within 6%–33% and 4%–38% of the tracer gas results, respectively. However, these errors are dependent on the assumptions used. Nevertheless, it appears that simple blower door testing can provide a reasonable measure of a building’s annual average air infiltration rate regardless of ambient conditions, whereas the more expensive and complex tracer gas tests may better reflect seasonal variations in air infiltration rates.