Performance of a multi-functional direct-expansion solar assisted heat pump system

This paper reports on the long-term performance of a direct-expansion solar assisted heat pump (DX-SAHP) system for domestic use, which can offer space heating in winter, air conditioning in summer and hot water during the whole year. The system employs a bare flat-plate collector array with a surface area of 10.5 m², a variable speed compressor, a storage tank with a total volume of 1 m³ and radiant floor heating unit. The performance under different operation modes is presented and analyzed in detail. For space-heating-only mode, the daily-averaged heat pump COP varied from 2.6 to 3.3, while the system COP ranged from 2.1 to 2.7. For water-heating-only mode, the DX-SAHP system could supply 200 l or 1000 l hot water daily, with the final temperature of about 50 °C, under various weather conditions in Shanghai, China. For space-cooling-only mode, the compressor operates only at night to take advantage of a utility’s off-peak electrical rates by chilling water in the thermal storage tank for the daytime air-conditioning. It shows that, the multi-functional DX-SAHP system could guarantee a long-term operation under very different weather conditions and relatively low running cost for a whole year.     

Transient analysis of heat pump assisted distillation systems. 1 The heat pump

A simple algorithm to simulate the transient behaviour of a vapour compression heat pump is described. Individual models are developed for various components of the heat pump such as compressor, evaporator, condenser and expansion valve. The components are simulated separately and are combined to form the total system. The compressor is a hermetically sealed, reciprocating piston type with adiabatic compression, the evaporator and condenser are coiled copper tubes, and the expansion valve is assumed to be adiabatic. The transport and thermodynamic properties of the refrigerant used are obtained from empirical equations. The total system is viewed in a simplified manner in order to apply the results of this transient analysis to the behaviour of a chemical process operation, namely, distillation.     

Experimental results of a solar assisted heat pump rice drying system

In the last rice harvest season, experimental results have been obtained on the efficiency and drying quality of a solar assisted heat pump drying prototype system. The system has been operated as a solar and heat pump system and drying curves for the different options have been obtained. The advantage of the low temperature and better control in the drier shows that the heat pump assisted solar drying system is an excellent alternative to traditional drying systems.     

Heat pump assisted continuous drying part 1: Simulation model

The addition of a heat pump to a conventional hot air drying system can enhance the efficiency of drying. To investigate the performance of heat pump assisted continuous drying system a detailed simulation model has been developed. The system modelled consists of a vapour compression heat pump coupled to a continuous cross-flow dryer. The model takes account of detailed heat and mass transfer phenomena taking place in each component of the system and can be used to investigate many different system configurations.     

Evaluation of a rice drying system using a solar assisted heat pump

The use of a combined solar-heat pump rice drying system is being developed as an alternative to conventional mechanical dryers. The experimental equipment developed is a modified 7 kW R-22 air conditioning unit and is combined with a solar colector for a more precise control of temperature and humidity.     

A solar assisted heat pump drying system for grain in-store drying

For grain in-store drying, a solar assisted drying process has been developed, which consists of a set including a solar-assisted heat pump, a ventilation system, a grain stirrer, etc. In this way, low power consumption, short cycle time and water content uniformity can be achieved in comparison with the conventional method. A solar-assisted heat pump drying system has been designed and manufactured for a practical granary, and the energy consumption performance of the unit is analyzed. The analysis result shows that the solar fraction of the unit is higher than 20%, the coefficient of performance about system (COP_S) is 5.19, and the specific moisture extraction rate (SMER) can reach 3.05 kg/kWh.     

Heat pump assisted distillation. II: Matching an external heat pump to a fractional distillation system

The problems in matching an external mechanical vapour compression heat pump to a distillation process in heat pump assisted distillation are discussed. There are four main design parameters to consider when selecting a working fluid for the heat pump, of which only two are independent. Various arrangements for imperfectly matched systems are presented, including the use of a two stage heat pump. A number of other factors which affect the choice of a heat pump assisted distillation system, including economic factors, are also considered.     

First and second law analysis of a solar assisted heat pump based heating system

We propose a model for the heating system of an ecological building whose main energy source is solar radiation. The most important component of the heating system is a vapour compression heat pump. Both the first law and the second law were used to analyse the heat pump operation. The state parameters and the process quantities were evaluated by using, as input, the building thermal load. The second law analysis emphasised that most of the exergy losses occur during compression and condensation. Preliminary results show that the photovoltaic array can provide all the energy required to drive the heat pump compressor, if an appropriate electrical energy storage system is provided.     

Experimental study of photovoltaic solar assisted heat pump system

A novel photovoltaic solar assisted heat pump (PV-SAHP) system has been proposed in this study. Performance tests with a range of condenser supply water temperature were conducted on an experimental rig. The dynamic performance of this PV-SAHP system in a 4-day period with very similar weather conditions was analyzed and the influencing factors were identified. The results indicate that this PV-SAHP system has a superior coefficient of performance (COP) than the conventional heat pump system and at the same time, the photovoltaic efficiency is also higher. The COP of the heat pump was able to reach 10.4 and the average value was about 5.4. The average photovoltaic efficiency was around 13.4%. The highest overall coefficient of performance (COP_p/t), bringing into consideration both the photovoltaic and thermal efficiency, was about 16.1.     

Performance of a solar air composite heat source heat pump system

For the shortcoming of air source heat pump in heating condition, a composite heat exchanger was designed which integrates fin tube and tube heat exchanger, and it can achieve synchronous and composite heat exchange in one heat exchanger between working fluids, gaseous and liquid heat source. With the above composite heat exchanger as the core component, the Solar Air Composite Heat Source Heat Pump System (SACHP) was developed which has three working modes, including single solar heat source mode, single air heat source mode and solar air dual heat sources mode. A SACHP experiment table was established and conducted a comprehensive experimental study of three working modes of this system in the standard enthalpy difference laboratory. The results show that when the ambient temperature was −15 °C, compared to the single air heat source mode, the dual heat source mode increased 62% in heat capacity and 59% in COP; when the temperature difference of combined heat transfer was 5 °C, compared to the single air heat source mode, the dual heat source mode increased 51% in heat capacity and 49% in COP. Experimental results demonstrate that the application of the solar air composite heat pump technology can accelerate the application process of the solar heat pump in air conditioners for buildings.     

Performance analysis of a novel dual-nozzle ejector enhanced cycle for solar assisted air-source heat pump systems

In this study, a novel dual-nozzle ejector enhanced vapor-compression cycle (DEVC) for solar assisted air-source heat pump systems is proposed. In DEVC, the use of the dual-nozzle ejector for recovering the expansion losses is a very promising approach to improve the cycle performance. A mathematical model of the DEVC is developed to predict its performance under specified operating conditions. The simulation results indicate that for the range of given operating conditions, the coefficient of performance (COP) and the volumetric heating capacity of the novel cycle using refrigerant R410A are theoretically improved by 4.60–34.03% and 7.81–51.95% over conventional ejector enhanced vapor-compression cycle (CEVC), respectively. The results imply that the solar-air source heat pump systems could take advantage of the best features of the DEVC. The potential use of DEVC therefore deserves further experimental validation. It is expected that this new cycle will be beneficial to developing dual-source coupled heat pump applications.     

Transient analysis of heat pump assisted distillation systems. 2 Column and system dynamics

A model to simulate the transient behaviour of a heat pump assisted distillation column is presented. The packed bed distillation column is treated as a distributed parameter system with time and space as independent parameters. The column modelling using appropriate basic equations, their application to binary systems, the solution scheme to the model equations and the distillation column simulation algorithm are described. The heat pump simulation algorithm is then coupled with this algorithm and the column transient behaviour with and without heat pump assist is obtained. The results are compared with earlier steady state data in the literature.     

Second law limits in convective heat pump driers

The loss mechanisms in convective drying systems are examined from a second law viewpoint. The avoidable and unavoidable loss processes in heat pump driers are identified and compared with those in conventional heat and vent driers. In the quasi-static limit the only unavoidable loss in a heat pump system is due to the irreversible diffusion of water vapour into the unsaturated atmosphere of the drier. Thermal losses, due to heat transfer within the drier and venting to the atmosphere are avoidable in principle by the use of a heat pump. In practice the efficiency of a heat pump drier depends on how effectively these processes are managed, whereas in conventionally-heated driers the major loss is due to the heating process. Manipulation of the residual thermodynamic loss can have only a restricted effect on the efficiency in such driers. The influence of drier design on the unavoidable losses in heat pump driers is shown to be important. In the most advantageous case, a multi-pass system with a high recirculation ratio, the unavoidable loss is related only to the relative humidity. Temperature is an important parameter in other systems, especially single-pass driers. The significance of the unavoidable thermodynamic loss is that it is closely related to the actual thermodynamic loss in an effective heat pump drier design because it sets the scale of the actual losses. Thus, the limiting loss is a relevant consideration when selecting the operating conditions for heat pump driers.     

Analysis of rankine cycle heat pump driers

We present a simulation analysis of closed Rankine cycle convective heat pump driers in which the product air recirculation ratin within the chamber is high. The configurations include driers with both external and internal refrigerant evaporators. The effects of modifications to basic designs are examined and real plant details are added in successive stages. Throughout the study the efficiency of each system is related to the second law loss mechanisms discussed by Carrington and Baines (1988). A detailed audit of exergy losses is presented for two driers in particular situations using data based on operational timber driers. The simulation results illustrate the need for the drier control strategy to take advantage of the performance characteristics of the heat pump drier. In addition, it is important to carefully match fans and heat exchangers to the drier requirements because the fan power will often be comparable with the compressor input.     

Energy analysis of hazelnut drying system‐assisted heat pump

In this experimental study, a proportional integral derivative (PID) controlled heat pump dryer was designed and manufactured. Heat pump dryer was tested drying of hazelnut and energy analyses were made. Drying air temperatures were changed as 50,45 and 40°C in the drying system. Drying air velocities were changed as 0.25 m s^?1 for 50°C, 0.32 m s^?1 for 45°C and 0.38 m s^?1 for 40°C. Heating coefficient of performance of whole system (COP_ws) of the heat pump dryer was calculated as 1.70 for 50°C, 1.58 for 45°C and 1.40 for 40°C drying air temperatures. Energy utilization ratio changed between 24 and 65% for 50°C, 17 and 63% for 45°C and 14 and 43% for 40°C drying air temperatures in the heat pump dryer. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermodynamic analysis of a hybrid geothermal heat pump system

A thermodynamic analysis of a hybrid geothermal heat pump system is carried out. Mass, energy, and exergy balances are applied to the system, which has a cooling tower as a heat rejection unit, and system performance is evaluated in terms of coefficient of performance and exergy efficiency. The heating coefficient of performance for the overall system is found to be 5.34, while the corresponding exergy efficiency is 63.4%. The effect of ambient temperature on the exergy destruction and exergy efficiency is investigated for the system components. The results indicate that the performance of hybrid geothermal heat pump systems is superior to air-source heat pumps.     

The potential for heat pumps in drying and dehumidification systems II: An experimental assessment of the heat pump characteristics of a heat pump dehumidification system using R114

An experimental heat pump dehumidifier is described. Actual coefficients of performance (COP)_A are plotted against the gross temperature lift (T_CO - T_EV) for various bypass ratios and air velocities. Interpolated values of (COP)_A for a specified temperature lift were obtained by fitting each set for various dry bulb temperatures of air leaving the humidifier using a linear equation. These values of (COP)_A are plotted against the linear velocity of the air stream approaching the evaporator at different dry bulb temperatures. The curves show a maximum of (COP)_A at approach velocities in the region of 1·6 ms^?1.     

热泵干燥系统运行特性的有效能研究

热泵干燥能源消耗少，环境污染小，干燥品质高，适用范围广，是一种性能优良的种子干燥机械。从热力学第一、第二定律两方面分析了热泵干燥系统的节能优势所在，得出采用辅助冷凝器是闭式热泵干燥系统的理想方式；而且热泵干燥系统存在一个最佳的蒸发温度，可使系统除湿率和效率最大。     

Heat pump assisted distillation. III: Experimental studies using an external heat pump

An experimental study has been carried out on a continuously operated pilot fractional distillation column equipped with an external heat pump. The distillation column was a 15 cm diameter glass unit containing eleven single bubble cap plates. A methanol-water mixture was fed to the column and the heat pump working fluid was R114. The actual coefficient of performance (COP)_A of the heat pump increased with an increase in the mass flow rate of the working fluid. A maximum (COP)_A value of 4–3 was obtained with a gross temperature lift of 41–3°C. The performance of two reciprocating compressors was compared. The experiments have shown that continuous heat pump assisted distillation using an external working fluid can greatly reduce the energy used in a distillation process. No control problems were encountered in the experiments.