subject: Use Air-cooled Heat Pump Should Pay Attention To The Problem - Heat Pumps, Heating - Hvac Industry [print this page] HC HVAC & R Network Chiller with one machine, Energy And so on, so the unit in Central air conditioning The application of more and more units this article from the throttling device, water side Heat exchanger Air-side heat exchanger, built-in pump, unit frame panels corrosion and crew to discuss the arrangement and so on in the selection and use of units to be aware of the problem.
1, Unit of throttling device The current air-cooled Heat Pump Throttling device commonly used units are: a single heat Expansion Valve One that is winter and use the same thermal expansion valve; flow with one pair of thermal expansion valve is one of the expansion valve flow (summer) and anti-flow (winter) can be adjusted to achieve savings and Refrigerants Flow; thermal expansion valve with two separate one that is winter, the use of a thermal expansion valve; Electronic Expansion valve.
Through the heat pump heat calculations indicate a larger difference between winter and summer working conditions, refrigerant flow is less in winter than in summer, 20-40%; pressure difference in winter than in summer is 10 --- 30%; evaporation and condensation temperature to the temperature tI are more different. Conventional thermal expansion valve there: in the low to lower superheat increases, to instability, decreased cooling efficiency; small range of refrigerant flow control; allow load change is small, not suitable for Energy Regulation Unit. Therefore, winter and summer heat pump with a thermal expansion valve is not rational. Double-flow thermal expansion valve unit pipeline system can simplify and reduce the flow resistance, but because of restrictions on the construction of valves, when the reverse flow, the result in the valve assembly of static superheat increases, while the refrigerant flow valve down, according to manufacturers present some down more than 20%. For heat pump with liquid receiver systems, piping to be difficult, difficult to ensure that the winter into the evaporator to the liquid-based preparations. Summing up the situation, to adapt to the different summer conditions in winter, using two thermal expansion valve of the system is more reasonable.
Electronic expansion with the cooling capacity can be accurately adjust the size of the refrigerant flow; resorted to evaporator superheat the steam to keep a small (2 ); it is not cold (hot) water and outdoor air temperature; in winter defrost cycle, the electronic expansion valve can defrost time required to achieve opening; use of electronic expansion valve can more effectively adapt to load changes, to improve the performance of units under part load factor. At present, family unit electronic expansion valve, such as Shanghai Carrier's 30AQA/30GH/30GT type air source heat pump and air-cooled chiller with EXV electronic expansion valve, it describes the operating efficiency under low load than that of the thermal expansion valve 28% higher unit cold (hot) water temperature can be controlled within O. 1 accuracy. On the electronic expansion valve control, the proposed export control in the evaporator temperature and pressure sensors on the set (available corresponding to), its pressure and temperature signals transmitted to the controller, through the operation of guaranteeing exports evaporator superheat 1 0.5 , the control of electronic expansion valve to open a large, open a small, non-realization of the refrigerant flow rate adjustable. It is understood that foreign well-known companies around 350kw units use an electronic expansion valve sensor + controller +2 support priced at about l million, the investment is expected to increase 1 to 2 years can be recovered.
2, the water-side heat exchanger Present small air cooled heat pump machine (group 60kw) Water side heat exchanger with brazed plate heat exchanger and the casing are most welcome; medium and large (> 116kw) with dry and horizontal shell and tube shell tube heat exchanger are most welcome. Plate heat exchanger, high efficiency, small size, light weight, compact structure, but must pay attention to the issue of the use of cubicle space is small, easy to scale; high requirements on water quality; if water will cause obstruction evaporator temperature decreases, cubicles the cracking ice; as thin wooden partition, is also prone to mechanical damage: General water side resistance of large, higher prices; in areas of poor water quality issues using the plate heat exchanger more.
Dry shell and tube heat exchanger is the flow of refrigerant in the pipe, the water flow in the pipe outside. Refrigerant flows usually have several processes, due to the gradual evaporation of liquid refrigerant, the more mess up, the more the control of its processes. In order to increase the water side heat transfer, heat transfer tubes in the tube and located outside a number of baffles, the water flow multiple ACROSS pipe cluster. The advantages are: oil can with the refrigerant gas into the compressor, integrated oil problem generally does not exist; less refrigerant system CHARGE; to the 0 ~ C near the water will not freeze; winter frost run time, water temperature fluctuation. Main problem is: refrigerant flow in the cover over the corner, such as the processing fluid into the next well will be flow of liquid unevenly distributed, affecting heat transfer; do condensation in winter, the refrigerant condensing in the tube , the heat transfer coefficient outside the pipe than the refrigerant condensing in the small: water side of the existing problems of leakage, because outside baffles and the shell, generally l ~ 3mm gap, and the heat transfer tube between the gap of about 2mm, which will cause water leakage, proved the water leak will cause the water side heat transfer coefficient by 20 to 30% of the total heat transfer coefficient by 5 ~ 15%.
Horizontal shell and tube heat exchanger is the tube running water, the refrigerant in the evaporation or condensation pipe outside clusters. The advantage is that heat transfer coefficient, compact structure, small size, convenience of operation. The disadvantage is that: the full summer heat exchanger evaporator, shell injection refrigerant flow more simplified about 55 ~ 60%; winter as a condenser, the charging is only about 5%, so heat pump system needs to be set higher liquid receiver, and the system more complicated pipeline: O lower than when the cooling system, easy to freeze water pipes, damaged Tube; summer for the evaporator, the refrigerant liquid column by a high degree of influence , the bottom tube to the high side, reducing heat transfer temperature difference: do evaporator, the simplified bottom product oil, oil return must have a reliable measure; winter defrosting operation, the heating water temperature fluctuated.
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