The heat pump technology is one kind of new energy conservation refrigeration heating technology, since long mainly applies in building’s heating air conditioning domain. Because the heat pump system heat falls in the energy conservation consumes and the environmental protection aspect good performance, the hygienic hot water supply system also more and more use heat pump equipment takes heat source . And take the outside air as the heat source heat pump, the structure is simple, does not need the special-purpose engine room, installs the easy to operate, has the unreplaceable superiority in the hygienic hot water supply side, besides the quite large-scale heat pump hot water system, had many brand small home use heat pump water heaters also to put in the market now. But an air source heat pump s major object is heating ability and the heating coefficient of performance reduces along with the outdoor temperature reduces, therefore its use receives the ambient temperature the limit, generally is suitable for lowest temperature – 10? above area .
The heat pump technology and the solar energy union supply life hot water, domestic and foreign has conducted many this aspect research, mainly has two ways, one kind takes the solar energy system’s auxiliary heater directly by the air source heat pump , another kind is takes using the solar energy hot water for the low temperature heat source or the solar energy collector heat pump’s evaporator’s solar energy heat pump system. The former take solar energy direct heating primarily by heat pump as auxiliary, the solution solar energy heats continuous question, but was still unable to get rid of the ambient temperature to the heat pump system thermal properties influence; The latter takes the heat pump heat source completely by the solar energy, raised the solar energy use efficiency greatly, but time solar energy resources insufficiency still needed to increase other auxiliary heat sources, and heat pump heating ability the solar energy collection quantity of heat’s limit, the scale is quite been generally small.
In the large-scale solar energy central hot water system, the heat pump is one kind of quite ideal auxiliary heater without doubt, to improve the heat pump under the low temperature environment the system hot movement performance, expands its use region, unifies in the domestic and foreign solar energy heat pump research the advanced experience, we developed one kind to suit the solar energy – heat pump central hot water system which worked in the low temperature environment. This system uses one kind of new use low temperature solar energy auxiliary heat pump unit and the solar energy collection hot system union, the solar energy and the heat pump is the auxiliary heat source mutually, use solar energy maximum limit, solution overcast weather and when winter ambient temperature low solar energy resources insufficiency the hot water supply guarantee rate, achieves the whole year, all-weather supply hot water.
1 solar energy – heat pump central hot water system composition
1.1 solar energy – heat pump central hot water system composes basically
The solar energy – heat pump central hot water system’s key component for the solar energy collector and the solar energy auxiliary heating heat pump unit, other supporting facilities and the conventional central hot water system is the same, including solar energy circulating pump, hot water heating link pump, heat interchanger, hot water tank and controller and so on. As shown in Figure 1.
1.2 solar energy auxiliary heating heat pump unit
1.2.1 solar energy auxiliary heating heat pump unit principle of work
In order to cause the heat pump in the low temperature environment highly effective, stable, the reliable movement, the domestic and foreign numerous Scientific research Unit and the Production enterprise have carried on the research and development and the improvement, induces mainly has three ways. First, depends upon the outside auxiliary heat source to enhance the heat pump low temperature system thermal properties, for instance enhances the heat pump system hot water leakage temperature through the electric heating, to use the burner auxiliary heating chamber external heat exchanger, to lay around the compressor changes the regeneration material increases under the low temperature condition system hot movement output and so on; Second, enhances heat pump’s low temperature system thermal properties through the improvement refrigerant circulatory system, for instance uses the two-stage compression the air source heat pump, among supposes restores vital energy return route’s heat pump and so on; Third, uses the frequency conversion system, under the low temperature operating mode lets the compressor high speed work increase the working substance circulation, simultaneously prevents to the compressor working chamber spray its overheated, thus enables the heat pump unit the normal operation.
The solar energy auxiliary heating heat pump unit is produces based on the above first way, as shown in Figure 2. Increased an auxiliary heat interchanger on unit’s evaporator. Heat pump when low temperature environment system hot movement, is higher than the ambient temperature the solar energy hot water to flow through this auxiliary heat interchanger, with will enter evaporator’s outside air to carry on the interchange of heat to enhance its temperature, thus causes the refrigerant to evaporate the heat absorption in the relatively high environment, enhanced the vaporization temperature, improved compressor’s working condition.
2nd, solar energy auxiliary heating heat pump unit schematic drawing
1.2.2 solar energy auxiliary heating heat pump unit performance characteristic 
Compares with the ordinary air source heat pump , the solar energy auxiliary heating heat pump unit moves under the low temperature operating mode has the following several obvious characteristics:
(1) COP remarkable enhancement
Under the same ambient temperature, the solar energy auxiliary heating enables the refrigerant system’s vaporization temperature to enhance, unit’s system thermal properties coefficient ordinary air source heat pump unit had the distinct enhancement, the heat pump system thermal properties coefficient along with vaporization temperature change situation as shown in Figure 2.
(2) prevents the evaporator rime, reduces the defrosting time
As a result of the auxiliary heat source’s heating function, enhanced entered evaporator’s air temperature, caused its rime the possibility to reduce, like this might prevent the evaporator surface rime, caused it maintains the high heat transfer efficiency, simultaneously, the unit the frost number of times and the time also greatly reduced, might save the massive electrical energies, and guaranteed the heat pump unit continuously uninterrupted movement.
(3) improves the air conditioning compressor working conditions, the extension unit service life
When the ambient temperature is low, the air conditioning compressor’s compression ratio elevates suddenly, compressor’s discharge temperature will surpass the compressor permission frequently the operating region, will thus cause the compressor frequently to open stops, will be unable the normal work, continuously for a long time hence, will damage compressor’s overall performance, will reduce air-conditioning plant’s service life. Takes the auxiliary heat source through the solar energy to enhance the system vaporization temperature, indirect improvement compressor’s working conditions, not only solved the compressor under the outside low temperature environment not to be able the normal work question, and might make the entire heat pump unit the service life to lengthen effectively.
1.2.3 solar energy auxiliary heat interchanger’s design
The auxiliary heat interchanger located at vapor-recompression evaporator’s flank, as a heat pump unit’s part and the heat pump unit synchronization design production, uses with the evaporator similar outlook size and the material quality finned tube heat interchanger. The auxiliary heat interchanger’s heat transfer area, the air through the temperature rise and with vapor-recompression evaporator’s spacing should auxiliary thermal which, the solar energy water temperature, the ambient temperature and heat pump unit parameters and so on vaporization temperature, platoon amount of wind may provide according to the solar energy collector carry on the design calculation.
1.3 solar energy collectors
At present the solar energy collector which usually uses in the solar energy hot water project mainly has the plate solar energy collector, the entire glass vacuum tube collector, the U tubular vacuum tube collector, the heat pipe type vacuum tube collector and direct-current type vacuum tube collector five kind of . Regarding the annual use’s quite large-scale solar energy central hot water system, the request solar energy collector should have certain bearing pressure ability, compared with the Gaoji thermal efficiency, compared with the small pipeline resistance, anti-frozen ability, easy to maintain. In these kind of solar energy collector, entire glass vacuum tube collector, although the hot collection thermal efficiency is high, the market share is big, but because of it cannot the bearing pressure movement, easy crack as a result of freezing, is not suitable uses in the big area solar energy hot water system, the major part serves as the home use solar-powered water heater’s collection hot part. Other four kinds are the metal absorber solar energy collectors, may the bearing pressure movement, be suitable in applies in the large-scale solar energy hot water project.