Solar assisted heat pump on air collectors: A simulation tool

The heating system of the bioclimatic building of the Greek National Centre for Renewable Energy Sources (CRES) comprises two heating plants: the first one includes an air source heat pump, Solar Air Collectors (SACs) and a heat distribution system (comprising a fan coil unit network); the second one is, mainly, a geothermal heat pump unit to cover the ground floor thermal needs. The SAC configuration as well as the fraction of the building heating load covered by the heating plant are assessed in two operation modes; the direct (hot air from the collectors is supplied directly to the heated space) and the indirect mode (warm air from the SAC or its mixture with ambient air is not supplied directly to the heated space but indirectly into the evaporator of the air source heat pump). The technique of the indirect mode of heating aims at maximizing the efficiency of the SAC, saving electrical power consumed by the compressor of the heat pump, and therefore, at optimizing the coefficient of performance (COP) of the heat pump due to the increased intake of ambient thermal energy by means of the SAC. Results are given for three research objectives: assessment of the heat pump efficiency whether in direct or indirect heating mode; Assessment of the overall heating plant efficiency on a daily or hourly basis; Assessment of the credibility of the suggested simulation model TSAGAIR by comparing its results with the TRNSYS ones.     

Experimental investigation of thermal performance of a solar assisted heat pump system with an energy storage

An experimental solar assisted heat pump space heating system with a daily energy storage tank is designed and constructed, and its thermal performance is investigated. The heating system basically consists of flat plate solar collectors, a heat pump, a cylindrical storage tank, measuring units, and a heating room located in Gaziantep, Turkey (37.1°N). All measurements are automatically collected as a function of time by means of a measurement chain feeding to a data logger in combination with a PC. Hourly and daily variations of solar radiation, collector performance, coefficient of performance of the heat pump (COP_HP), and that of the overall system (COP_S) are calculated to evaluate the system performance. The effects of climatic conditions and certain operating parameters on the system performance parameters are investigated. COP_HP is about 2.5 for a lower storage temperature at the end of a cloudy day and it is about 3.5 for a higher storage temperature at the end of a sunny day, and it fluctuates between these values in other times. Also, COP_S turns out to be about 15–20% lower than COP_HP. Copyright © 2004 John Wiley & Sons, Ltd.     

Heat pump assisted distillation. V: A feasibility study on absorption heat pump assisted distillation systems

The problems in matching a heat driven absorption heat pump to a distillation process in heat pump assisted distillation are discussed. The performance of an absorption system is a function of the temperatures in the evaporator, the condenser, the absorber and the generator and the ratio of the mass flow rate in the secondary circuit to the mass flow rate in the primary circuit. In absorption systems design choices are limited by the Gibbs phase rule. Plots are given of the coefficient of performance against the temperatures of the top and bottom products and also against the energy saved.     

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.     

Optimization of systems with the combination of ground-source heat pump and solar collectors in dwellings

The use of ground-source heat pumps for heating and domestic hot water in dwellings is common in Sweden. The combination with solar collectors has been introduced to reduce the electricity demand in the system.     

Performance of evaporator-collector and air collector in solar assisted heat pump dryer

A solar assisted heat pump dryer has been designed, fabricated and tested. This paper presents the performance of the evaporator-collector and the air collector when operated under the same meteorological conditions. ASHRAE standard procedure for collector testing has been followed. The evaporator-collector of the heat pump is acting directly as the solar collector, and the temperature of the refrigerant at the inlet to the evaporator-collector always remained below the ambient temperature. Because of the rejection of sensible and latent heats of air at the dehumidifier, the temperature at the inlet to the air collector is lower than that of the ambient air. Hence, the thermal efficiency of the air collector also increases due to a reduction of losses from the collector. The efficiencies of the evaporator-collector and the air collector were found to vary between 0.8–0.86 and 0.7–0.75, respectively, when operated under the meteorological conditions of Singapore.     

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.     

Energy and economic analysis of an integrated solar absorption cooling and heating system in different building types and climates

The use of solar energy in buildings is an important contribution for the reduction of fossil fuel consumption and harmful emissions to the environment. Solar thermal cooling systems are still in their infancy regarding practical applications, although the technology is sufficiently developed for a number of years. In many cases, their application has been conditioned by the lack of integration between cooling and heating systems. This study aims to evaluate the potential of integrated solar absorption cooling and heating systems for building applications. The TRNSYS software tool was used as a basis for assessment. Different building types were considered: residential, office and hotel. The TRNSYS models are able to run for a whole year (365 days), according to control rules (self-deciding whether to operate in heating or cooling modes), and with the possibility of combining cooling, heating and DHW applications. Three different locations and climates were considered: Berlin (Germany), Lisbon (Portugal), and Rome (Italy). Both energy and economic results are presented for all cases. The different local costs for energy (gas, electricity and water) were taken into account. Savings in CO₂ emissions were also assessed. An optimization of solar collector size and other system parameters was also analysed.     

太阳能辅助供暖的地源热泵经济性分析

在冬季土壤温度较低，而且以热负荷为主的北方地区，若完全采用地源热泵来供暖，则地热换热器和机组的初投资均比较高，连续运行的效率也较低，因此，可利用太阳能集热器作为辅助能源。白天完全依靠地源热泵供暖，夜间利用太阳能集热器蓄存的热量，使地热换热器与太阳能集热器串联运行，通过分析比较，该方案比完全用地源热泵供暖更经济。     

Improvement of an existing solar powered absorption cooling system by means of dynamic simulation and experimental diagnosis

This paper focuses on the validation of a dynamic simulation model used to describe the performance of an existing solar cooling installation located in Zaragoza (Spain). The dynamic model has been developed under the simulation environment TRNSYS. The aim of this simulation model is to dispose of a tool in order to use it to evaluate different energy improvement actions in a real solar cooling installation. This solar cooling installation has been monitored and analyzed since 2007. The COP of this experimental solar cooling system presents a great influence from its heat rejection sink, a dry cooling tower. Once the model was validated with the experimental data obtained from the real installation, it was used to predict the chiller performance with a new geothermal sink, which started to operate in 2009. The present work describes the design and validation model process, as well as the comparison between the model results and the monitoring ones with the geothermal heat rejection system.     

Numerical simulation of the performance of a solar-earth source heat pump system

Solar-earth source heat pump (SESHP) is a new type of energy saving air conditioner. In this paper, numerical simulation of the performance of a solar-earth source heat pump system (SESHPS) operated at alternate or combined mode is carried out respectively. The results indicate that a resuming-rate of 30–60% of the earth temperature near buried coil can be preferable when SESHPS is operated alternately at a period of 24 h, and the proportion of the operation time of solar-assisted heat pump (SAHP ) should be confined to 42–58%. When SESHPS is operated at combined modes 2, the energy-saving rate with and without heat storage water tank is 14.5% and 10.4%, respectively, compared with ground source heat pump (GSHP). As for the overall effect, the combined operation mode with water tank in which the heated water flows through the solar collector first and then through the buried coil is preferable. The results are significant for the engineering design, operation and management of SESHPS.     

Wood chip drying with an absorption heat pump

This paper presents the thermal and economic analysis of a mobile wood chip drying process. The dryer was subjected to different operating conditions, which were studied in order to determine the optimal characteristics of the dryer in terms of energy consumption. In addition, the impact of the exterior climatic conditions on the dryer's performance was also evaluated. The performance of the dryer coupled with an absorption heat pump was modeled in steady-state conditions under different operating parameters. Finally the system's energy performance was compared to the performance of two other systems (a wood burning furnace and a waste-heat recovery system). The results demonstrate that single-stage absorption heat pumps are only interesting when the set point temperature of the drying air is below 60 °C. Otherwise, a two-stage absorption heat pump must be used. In terms of energy and financially, this type of drying is very costly. Of the three processes that were studied, heat recovery systems proved to be the most energy efficient and economic solution.     

Experimental comparison of a solar-assisted heat pump vs. a conventional thermosyphon solar system

A solar-assisted heat pump system (SAHPS) for hot-water production has been developed and compared for its experimental performance, under similar ambient conditions with a conventional thermosyphon solar system (CTSS) with a single direct tank. Both systems were monitored from 1993 to 1997 during summer and winter time periods. The performance of CTSS was seriously affected by weather conditions, whereas SAHPS could always operate with no significant variation and with a COP above 3·0. A comparison between the two systems proved the performance of the SAHPS to be better than that of CTSS under all climatic conditions. © 1998 John Wiley & Sons, Ltd.     

Long-term performance of solar-assisted heat pump water heater

A long-term reliability test of an integral-type solar-assisted heat pump water heater (ISAHP) was carried out. The prototype has been running continuously for more than 13,000 h with total running time >20,000 h during the past 5 yr. The measured energy consumption is 0.019 kWh/l of hot water at 57 ^oC that is much less than the backup electric energy consumption of the conventional solar water heater.     

Investigation of thermal performance of a ground coupled heat pump system with a cylindrical energy storage tank

An analytical and computational model for a solar assisted heat pump heating system with an underground seasonal cylindrical storage tank is developed. The heating system consists of flat plate solar collectors, an underground cylindrical storage tank, a heat pump and a house to be heated during winter season. Analytical solution of transient field problem outside the storage tank is obtained by the application of complex finite Fourier transform and finite integral transform techniques. Three expressions for the heat pump, space heat requirement during the winter season and available solar energy are coupled with the solution of the transient temperature field problem. The analytical solution presented can be utilized to determine the annual variation of water temperature in the cylindrical store, transient earth temperature field surrounding the store and annual periodic performance of the heating system. A computer simulation program is developed to evaluate the annual periodic water and earth temperatures and system performance parameters based on the analytical solution. Copyright © 2003 John Wiley & Sons, Ltd.     

Experimental and theoretical study on a solar assisted CO2 heat pump for space heating

In this paper, a solar combi-system which consists of solar collector and a CO₂ heat pump is investigated experimentally and theoretically. Two experiments are primarily conducted to show the performance of this solar combi-system under different operation conditions. A system model is developed and validated in TRNSYS to analyze the influence of main components parameters. Subsequently, a multi-parameter optimization is carried out in GENOPT to obtain a final optimal result. The simulated results show that the optimized system can save 14.2% electricity and improve the solar fraction by 8%. The solar fraction of the optimized system can reach 71.1%. Finally, the optimized system performance is studied with the weather and load characteristics in Shanghai. Compared with the CO₂ HP heating system alone, the solar assisted system can save 1790.8 kWh electricity on the basis of year round operation.     

Exergy analysis of a solar assisted absorption cooling system on an hourly basis in villa applications

A solar assisted absorption refrigeration system (SAARS) was designed for acclimatizing of villas in Mardin which is located in Turkey and the performance of the system under different temperatures was analyzed by using MATLAB. Hourly cooling load calculation of the villas was done between 15th of May and 15th of September by considering the season for the cooling. Cooling capacity of the system (SAARS) was calculated as 106 kW. During the cooling period, the temperature of the environment shows the alteration between 40.3 °C and 13.2 °C. In the study, hourly exergy loss values are calculated with the software developed in matlab program and for the entire components of SAARS. The effect of the temperature alterations of the dead state on the exergy results is determined by taking dead state temperature as 25 °C and with more realistic approach, by taking it as the environment temperature. It was observed that the most of the exergy losses in the system have taken place in the solar collectors and then in the generator. Exergy loss in the collector changes between 10% and 70% while exergy loss in the generator changes between 5% and 8%. The effects of environmental temperature and solar insolation were stated for optimization.     

A new version of a solar water heating system coupled with a solar water pump

This research target was to improve the thermal efficiency of a solar water heating system (SWHS) coupled with a built-in solar water pump. The designed system consists of 1.58-m² flat plate solar collectors, an overhead tank placed at the top level, the larger water storage tank without a heat exchanger at the lower level, and a one-way valve for water circulation control. The discharge heads of 1 and 2 m were tested. The pump could operate at the collector temperature of about 70–90 °C and vapor gage pressure of 10–18 kPa. It was found that water circulation within the SWHS ranged between 15 and 65 l/d depending upon solar intensity and discharge head. Moreover, the max water temperature in the storage tank is around 59 °C. The max daily pump efficiency is about 0.0017%. The SWHS could have max daily thermal efficiency of about 21%. It is concluded that the thermal efficiency was successfully improved, except for the pump one. The new SWHS with 1 m discharge head or lower is suitable for residential use. It adds less weight to a building roof and saves electrical energy for a circulation pump. It has lower cost compared to a domestic SWHS.     

分液热泵空调系统的制热性能研究

随着热泵空调的普及,热泵空调的能耗占比不断增大,其节能问题成为了关注焦点。换热器对系统性能有着重要的影响,如何通过改进换热器来提升系统性能则成为了研究的热点。其中分液冷凝器作为一种新型的换热设备,能对系统制冷性能产生积极影响。但热泵空调系统在制热工况下,分液冷凝器变成气液分离式蒸发器,其系统制热性能尚未可知。通过实验研究,调整毛细管长度和制冷剂充注量,发现在国家标准工况下分液热泵空调系统的最大制热量比原系统高4.50%,C OP比原系统高7.93%,所对应的毛细管长度为700 mm,制冷剂充注量为700 g。且制冷剂过充注的情况下,分液热泵空调系统的制热性能比较稳定。