1 Introduction
Air-cooled heat pump chiller as a cold and heat source of central air conditioning has its equipment utilization rate, a machine winter and summer, eliminating the need for water-cooled chiller cooling water systems and heating boilers, water saving, energy saving and Environmental protection has positive significance, as well as easy installation, can be placed on the roof, does not occupy the construction area and other characteristics, in recent years in the Yangtze River and the Yangtze River South area has been widely used. In this paper, the overall layout of air-cooled heat pump chiller units and the main components of the configuration made a more comprehensive analysis for the design and selection of such units provide a reference.
2 air-cooled heat pump hot and cold water unit side of the heat exchanger type and overall layout
Cooling capacity of about 3-15RT air-cooled heat pump water chiller is generally referred to as villa-style small units, large and medium-sized units of the cooling capacity of about 20-400RT.
Small villa type unit side of the wind heat exchanger type and out of the way:
(1) oblique side of the wind, the compressor and so on in the lower part;
(2) flat side of the wind, the compressor in the lower part;
(3) flat side of the wind, the compressor at one side;
(4) Top wind, finned tube upright in the end, the compressor on the inside. For the flat side of the wind using two fans up and down, and each fan corresponds to an independent refrigeration system, it should be noted that the two systems in the case of defrosting defrost, unfavorable to the lower fin heat exchanger, when the upper part of the defrost, Defrosting water falls on the lower fins, causing severe freezing of the lower fins.
Integral unit air side heat exchanger type and unit layout are the following:
(1) Upper upright fin air side heat exchanger. Lower compressor and water side heat exchanger and other components;
(2) air side heat exchanger upright in the end, the compressor and water side heat exchanger in the interior,
(3) air-side heat exchanger upright in the end, water-side heat exchanger in the interior, the compressor in one or two;
(4) upper W-type air side converter, the lower part of the compressor and water side heat exchanger;
(5) V-shaped air side heat exchanger, the compressor is arranged on the outside of the fin. Therefore, consider the maintenance of the unit, the compressor on one or two as well.
For modular units, most of the air side heat exchangers are V-shaped. The heat exchanger in the middle of the heat is far less than the two sides, the central module of insufficient air intake, wind speed small.
Large air-side fin heat exchanger fan matching is very important, to achieve the desired heat transfer effect, should give full consideration to uneven heat exchanger surface into the wind. Adequate intake air volume for the summer high temperature operation and winter solution fin surface frost are beneficial, if necessary, consider the use of variable speed fan to meet the requirements of different conditions. Many of the lower part of the air-side heat exchanger designed to be a common section of the cold (overheating), so the machine is stable and more favorable.
Air-side heat exchanger types are flat, corrugated sheet and window fins. From the overall efficiency of use; medium and large fin heat exchanger to use the corrugated film as well. Fin spacing should not be less than 2mm. In order to strengthen the heat transfer inside the finned tube, the use of internally-threaded tube instead of light pipe can greatly improve the heat transfer coefficient. Finned tube surface treatment, such as coated with hydrophilic film to reduce the air side of the wind resistance and corrosion resistance, coated with anti-oxidation layer to prevent air (especially the use of the sea) on the aluminum fin corrosion and black fin treatment can enhance the Surface heat transfer coefficient.
The optimization of the indoor heat exchanger of a small-air heat pump with the maximum COP as its objective function is optimized under cooling conditions. The number of heat exchangers is 6, and the cooling and heating are optimized simultaneously. The heat exchanger The number of loops is four.
3 water side heat exchanger
Small villa type and modular air-cooled heat pump hot and cold water unit of the water side heat exchanger type: casing, Plate and vertical coil.
Heat pump water chillers in the water ---- water heat exchanger to corrugated-shaped female pipe is more appropriate.
Various water-side heat exchangers have their own characteristics, for the casing and vertical coil heat exchanger, pay attention to the design and manufacture to solve its major problems, the use of plate heat exchangers should also enable users to understand its characteristics , Pay attention to water quality problems. Water side heat exchanger has effective antifreeze protection.
4 throttling device
Small air-cooled heat pump hot water unit with a force expansion valve, controlled by the four one-way valve cooling, heating toward, but also useful to do when the capillary heat control throttling, medium and large units due to refrigeration, heating refrigerant in different conditions Large changes in circulation, the need for two or more thermal expansion valve to meet the requirements of the working conditions, liquid pipe resistance in large occasions, such as liquid head resistance, should pay attention to appropriately increase the corresponding expansion valve empty volume, so as to avoid Insufficient fluid supply.
Air-cooled heat pump manufacturers should pay attention to the application of electronic expansion valve research. As far as the electronic expansion valve itself is concerned, it can control the suction pressure and superheat of each circuit, control the circulation of the refrigerant, adapt to the change of load more effectively than the thermal expansion valve, and improve the partial load performance of the unit. In the defrost cycle, the electronic expansion valve can also be defrost required to achieve the opening in time to improve the unit defrosting performance.
5 compressor type
Small villas and modular units use fully enclosed reciprocating compressors or fully enclosed scroll compressors. Monolithic units generally use semi-hermetic reciprocating compressors or semi-hermetic screw compressors. At present, the use of more fully enclosed compressors are reciprocating compressors. In the villa-type units and modular units using fully enclosed scroll compressor, scroll compressor in all aspects of superior performance than the reciprocating compressor, scroll compressor parts, energy efficiency is high, not sensitive to wet compression , In the high compression ratio can be spray cooling, compared with the reciprocating compressor because of its small leakage, no clearance volume, low flow loss, heat pump operation in the high pressure ratio can still have a higher positive volumetric efficiency, this machine Type is more suitable for heat pump operation, will become the reciprocating compressor within the range of alternative models. For integral units, semi-hermetic screw compressors also outperform reciprocating compressors. Its summer cooling season energy efficiency than the reciprocating compressor 6-8% higher, winter running heating coefficient than the reciprocating compressor increased by 12-13%. For relatively cold, poor working conditions in the region to use screw compressors is appropriate.
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