Solar energy and wasted heat in buildings are capable of supplying enough energy to answer the total demand of energy in dwellings. However, fluctuation in fuel prices and gas emissions are the main driving forces behind efforts. In this experimental study, a direct expansion solar-assisted heat pump system (DX-SAHP) using a bare ternary “retrofitted collectors with black paint” is investigated at the laboratory with a solar simulator and tested for domestic hot water (DHW) and space heating under quasi-static conditions. Unglazed solar collector absorber plates are used as an evaporator, and these are composed of two aluminium plates which are placed externally whilst another plate is mounted internally in the loft space of the house, where operating liquid from the heat pump is directly evaporated. The influence of outside temperature, solar irradiation and/or waste heat on the heating performance of DX-SAHP is investigated. The impact of the parameters such as the inlet temperature and the mass flow rate of the heat transfer fluid is also assessed. Preliminary results elucidate that the refrigeration cycle can be a promising substitute for space heating and hot water when compared to the heat pump systems. This design technique results in higher solar collector/evaporator efficiency and lower system losses due to low evaporating temperature. 相似文献
This Paper presents a new continous operating solar desiccant absorption system in which CaCl2-H2O is used as the absorbent. The flat-plate solar collector is utilized as the desorber where water from the solution is evaporated to ambient air in passing over the collector above the solution film. The plant is equipped with a latent heat accumulation system which is extremely compact in size and very efficient. The coefficient of performance—solar collector efficiency product, indicating the grade of solar energy utilized, is estimated as being the highest of all presently known systems. 相似文献
In this paper, an integrated solar heat pipe wall space heating system, employing double glazed heat pipe evacuated tube solar collector and forced convective heat transfer condenser, is introduced. Thermal performance of the heat pipe solar collector is studied and a numerical model is developed to investigate the thermal efficiency of the system, the inlet and outlet air temperatures and heat pipe temperature. Furthermore, the system performance is evaluated based on exergy efficiency. In order to verify the precision of the developed model, the numerical results are compared with experimental data. Parametric sensitivity for design features and material associated with the heat pipe, collector cover and insulation is evaluated to provide a combination with higher thermal performance. Simulation results show that applying a solar collector with more than 30 heat pipes is not efficient. The rate of increasing in temperature of air becomes negligible after 30 heat pipes and the trend of the thermal efficiency is descending with increasing heat pipes. The results also indicate that at a cold winter day of January, the proposed system with a 20 heat pipe collector shows maximum energy and exergy efficiency of 56.8% and 7.2%, which can afford warm air up to 30°C. At the end, the capability of the proposed system to meet the heating demand of a building is investigated. It is concluded that the best method to reach a higher thermal covered area is to apply parallel collectors. 相似文献
In the present study, a novel solar driven combined power and ejector refrigeration system (CPER) of 50 kW power capacity composed of an ORC (organic Rankine cycle) and an ejector refrigeration system is investigated. Solar driven CPER system is composed of two main cycles: collector cycle and refrigeration cycle. The collector cycle is made of a U-tube ETC and circulation pump and the ejector refrigeration cycle consists of generator, turbine, ejector, heat exchanger, condenser, evaporator, expansion valve, and pump. Thermodynamic performance of the proposed CPER system is evaluated and a thermo-economic analysis is conducted using the SPECO (specific exergy costing) method. A parametric study showed the effects of condenser temperature, evaporator temperature, generator pressure, turbine back pressure and turbine extraction ratio. The genetic algorithm optimization analysis is conducted which shows 25.5% improvement in thermal energy, 21.27% in exergy efficiency, and 7.76% reduction in the total cost of the CPER system. The results reveal that the performance of the CPER system is considerably improved at higher temperatures of generator and evaporator. 相似文献
A direct-expansion solar-assisted heat pump (DX-SAHP) system by using R410A as refrigerant is described, which can supply domestic hot water during the whole year. Based on the distributed parameter and homogeneous flow models of collector/evaporator and condenser, the lumped parameter models of compressor and electronic expansion valve, and the refrigerant charge model, a numerical model is developed to estimate the thermal performance of the system. Given the structure parameters, meteorological parameters, initial and final water temperatures, for a fixed superheat degree, the effects of the refrigerant charge quantity on the performance parameters of the system are analyzed, such as compressor power, heat gain of collector, heating time, collector efficiency and system COP. Furthermore, for a fixed refrigerant charge quantity, the effects of various parameters, including solar radiation, ambient temperature, compressor speed and initial water temperature, have been simulated and analyzed on the thermal performance of the system. 相似文献
With many conventional heat pump systems the energy absorbed by auxiliary equipment (fans, defrosters, pumps) can be higher than the power used by the compressor. For example, with a particular air-air heat pump system the annual energy consumption of the compressor and its crankcase heater is 11 240 kWh, whilst 21 501 kWh of energy are consumed by auxiliary fans, the defrost unit, back-up heating and system heat losses. Some savings can be made by monitoring the interior unit fan to correspond to the running time of the compressor or by increasing the size of the heat pump in order to reduce back-up heating, but the latter solution has proved to be costly.Laboratory experiments since 1976 have been to reduce power consumption of auxiliaries, particularly air-air and air-water systems, by using a solar collector as the heat pump evaporator. The collector is made up of flat plates oriented in such a manner as to receive direct solar radiation, with both faces of the plates absorbing energy from the surrounding air by natural convection. The faces of the plates exposed to solar radiation are preferably painted black, but other colours with a low coefficient of reflection (eg brown, brick red, dark green, etc.) can be used if the evaporator-collector is to be architecturally pleasing. Glazing is not necessary, as is usually the case with solar panels. The collector-evaporator plates, and associated piping, are precharged with refrigerant and ready for connection to the heat pump circuit.A heat pump equipped with this collector-evaporator will provide an annual energy saving of 30% as compared to a standard air—water system. Additional benefits are no defrosting cycles, simplified installation, greater operational reliability, and an increased system COP. A table sets out the performance parameters of this system to show the incidence of back-up solar energy during the months of lesser solar radiation, ie outside the months of June to September, eg the COP during daylight hours (a minimum of about 7 h in December, to a minimum of 14 h in May) averages out at 3.89, and 3.27 during nocturnal hours.The article also describes a water heating system (200 and 300 I) using this collector-evaporator, an air-air heat pump with static (no forced ventilation) heat exchangers, and an air-water system using a static evaporator which will provide a 25% energy saving over its conventional counterpart. 相似文献
The use of heat produced by solar thermal collectors is an interesting option for thermal driven air conditioning processes. A thermal driven cooling technique which fits well to non-tracking solar collectors is the desiccant cooling technique. Recently several projects have been carried out which focus on the connection of desiccant cooling systems with solar thermal energy for regeneration of the sorbents. This communication deals with three main topics: (1) experiences achieved in a realized system which is coupled to a solar collector are discussed, (2) a new concept is presented, in which a solar air collector is integrated into the desiccant cooling cycle as the only heat source and (3) a comparative study is presented which compares system performance for different system configurations and different climatic situations. 相似文献
This article deals with the prediction of parameters in an annular hyperbolic fin with temperature-dependent thermal conductivity. Three parameters such as thermal conductivity, variable conductivity coefficient and the surface heat transfer coefficient have been predicted for satisfying a prescribed temperature distribution on the surface of fin. This is achieved by a hybrid differential evolution-nonlinear programming optimization method. The effect of random measurement errors is also considered. It is observed from the present inverse analysis that many feasible materials exist satisfying the given temperature distribution, thereby providing engineering flexibility in selecting any material from the available choices. For a given material, this is possible by regulating the surface heat transfer coefficient. 相似文献
The primary energy consumption of two kinds of solar assisted absorption systems (solar assisted absorption chiller during summertime and heat pump during wintertime or solar assisted absorption chiller with direct gas combustion for heating during wintertime) is compared with the primary energy consumption of a compression chiller which can work as a heat pump during wintertime. For the absorption systems three technical options were considered: a single effect machine; a double effect machine with the solar energy delivered to the lower temperature desorber and combustion heat of a gas burner delivered to the higher temperature desorber; a double effect machine with both solar energy and combustion heat delivered to the higher temperature desorber. The analysis performed in this article shows that solar assisted absorption chillers, absorption heat pumps and direct solar heating systems even with low and intermediate solar fractions can operate with considerably less primary energy consumption than compression systems. Further, the necessary solar collector area to achieve that goal is compatible with roof area available in buildings. It was also verified that, for the double effect absorption machines, there is no advantage in delivering the solar energy to the higher temperature desorber, thus establishing as preferable the solution in which it is delivered to the lower temperature desorber. 相似文献
In this review, flat plate and concentrate-type solar collectors, integrated collector–storage systems, and solar water heaters combined with photovoltaic–thermal modules, solar-assisted heat pump solar water heaters, and solar water heaters using phase change materials are studied based on their thermal performance, cost, energy, and exergy efficiencies. The maximum water temperature and thermal efficiencies are enlisted to evaluate the thermal performance of the different solar water heaters. It is found that the solar water heaters’ performance is considerably improved by boosting water flow rate and tilt angle, modification of the shape and number of collectors, using wavy diffuse and electrodepositioned reflector coating, application of the corrugated absorber surface and coated absorber, use of turbulent enhancers, using thermal conductive working fluid and nanofluid, the inclusion of the water storage tank, and tank insulation. These items increase the heat transfer area and coefficient, thermal conductivity, the Reynolds and Nusselt numbers, heat transfer rate, and energy and exergy efficiencies. The evacuated tube heaters have a higher temperature compared to the collectors with a plane surface. Their thermal performance increases by using all-glass active circulation and heat pipe integration. The concentrative type of solar water heaters is superior to other solar heaters, particularly in achieving higher water temperatures. Their performance improves by using a rotating mirror concentrator. The integration of the system with energy storage components, phase change materials, or a heat pump provides a satisfactory performance over conventional solar water heaters.
This work emphasizes the exploitation of renewable energy sources for heating a greenhouse, which requires the use of a horizontal heat exchanger, a heat pump associated with a solar collector in numerical and experimental investigations. This study demonstrates the performance of a heat pump system assisted by solar and geothermal energy under the climatic conditions of Tunisia. This system was designed and installed in Thermal Process Laboratory; Research and Technology Centre of Energy CRTEn Borj Cedria. The surface area and of the glass greenhouse used in the experimental model are 14.8 m2 as surface area. We precede several experimental data for realizing a numerical model based on TRNSYS software. For this point of view a numerical model was improved using 100 m2 and 229.5 m3 as surface and volume areas. The water-air heat pump is coupled with a ground heat exchanger (GHE) with 1m of depth. The distance between two consecutive tubes is 0.3 m. The surface area of the solar collector is 8 m2. 相似文献