Air source heat pump unit (hereinafter referred to as "heat pump unit") since its invention in the 1940s so far, its technology has been improved, has been widely used in office buildings, hotels, entertainment, factories, residential and other industries of different sizes , The market share has been higher, the reason is because they have the following advantages: heat pump unit in summer cooling, heating in winter, no need to set up a separate boiler room; host installed in the roof, you can save the frozen building investment and cooling System investment; COP value is high, a high degree of automation. First, the type of heat pump units and their characteristics: 1. Scroll compressor heat pump unit: Scroll compressor for the volume compressor, with smooth operation, small vibration, low noise, common air - air heat pump unit, suitable for medium and small projects.  2. Piston compressor heat pump units:  piston compressor is a positive displacement compressor, complex structure, low speed, vibration, noise, single capacity is small, multi-head combination can be assembled into one million kcal / h heat pump COP = 3.0 ~ 3.5; 3. Screw compressor heat pump unit:  Screw compressor is also a positive displacement compressor, simple structure, stable operation, small vibration, low noise, long life, COP = 3.5 ~ 4.5, For medium and small projects, multi-head heat pump units can be used for larger projects. Single-screw balance for one-way operation, wear small, no axial thrust, the exhaust efficiency slightly lower than the twin-screw. Second, heat pump unit design: 1. The selection principle:  heat pump has advantages and disadvantages, compared with the same capacity of single chiller, the power consumption, high cost, winter with the outdoor temperature declining heat attenuation serious, serious frosting, etc., so ①when a When the project has a steam source, the air-conditioning hot and cold source should try to adopt the scheme of "a single chiller unit heat exchanger". Wuxi is forming a city steam heating network, we should give priority to the above programs. ② I think hospitals, hotels and other projects that require high heating temperature in winter are not suitable for heat pump units, office buildings, restaurants and other projects are more appropriate because they are generally used during the day, heat pump unit heat attenuation is small, even if the heating effect is poor , Indoor staff may wear more clothes, affect smaller. 2. Selection method:  Although the general project in the southern area of ​​the cold load is greater than the thermal load, but the air conditioning designers should calculate the project summer cooling load and winter heat load, cooling capacity of units ≥ air conditioning cooling load to select the heat pump unit model, and then look at the following inequality Whether or not to set up: heat pump unit in the winter outdoor air-conditioning temperature (such as: Wuxi area -5 ℃) heating capacity ≥ engineering winter heat load. ①If the inequality is true, the selection of heat pump unit is appropriate. ②If the inequality does not hold, then auxiliary heating devices or heat pump units should be installed on the air conditioning pipes. The above general inequality in Jiangnan area is established.  3. Piston and screw-type heat pump performance comparison:  Many manufacturers sales staff out of business interests, often one-sided or even malicious wounded a brand or piston, screw-type heat pump units, our designers can not be a leaf barrier, to be meticulous Understand the performance of various types of aircraft to make the right selection judgments. ①burning compressor problems: one of the reasons is the wrong type of evaporator, for example, piston or screw-type heat pump unit (using F-22 refrigerant) selection of flooded evaporator due to difficult to return to oil compression compression Machine; the second reason is that the lubrication system is contaminated with dirty oil or compressor suction filter plugging due to impurities and was sucked into the compressor suction impurities, etc., easy to damage the motor insulation; reason three is overheat protection, too Pressure protection, short circuit protection caused by failure;  ② liquid hammer problem: In fact, liquid-piston and screw-type compressors are negative, both compression efficiency should be reduced; ③ compressor efficiency control problems: piston And screw-type heat pump unit cooling (heat) by its capacity regulation solenoid valve to adjust the partial load of the piston compressor can reduce the number of operating cylinders to adjust the screw-type compressor is adjusted by the slide valve. In part load, both the shaft power is reduced, the operating COP value is almost [1];  ④ oil problem: piston and screw compressors in the summer and winter are required to heat the oil, the refrigerant in the volatile oil Out, to ensure the normal lubrication of the compressor; ⑤ maintenance problems: piston compressor parts about 268, wearing parts and more, 1000 hours required repair, maintenance of large; and screw compressor parts about 26, easy Less damage, trouble-free operation for a long time. Under normal operation, as long as the replacement of oil, filters, bearings, etc. a few years later; ⑥ noise problems: Screw-type heat pump unit is the main source of noise fan, unit noise is generally about 80dB (A), so the unit should use low noise, Low speed, low vibration (static and dynamic balance test) fan products, such as the selection of Germany Xerox 100 axial fans, 100RT screw heat pump noise can be controlled at about 74dB (A). The piston heat pump noise is generally above 80dB (A). We should pay attention to the standard noise measurement and measurement room and the difference between the ordinary environment;  ⑦ we also pay attention to the manufacturer's sample heat pump heat in winter is at 8 ℃ ambient temperature value, not calculated in winter air temperature The value of.  Third, the heat pump design case analysis: The following I put in the design in the past few years to meet or see the heat pump case after the case study, and colleagues to discuss.  Case I: A project is a long history and has the local characteristics of foreign business hotel, located in the roof of the six central air-conditioning heat pump unit model YCA90H (cooling capacity: 81KW), the pump model SB-X80-65-155K ( 90T / H; 31M; 11KW). Figure 1 for the roof heat pump piping layout plan. After the system is running, it is found that some heat pump units can not be started. I first check the frozen water pump and found that the pump current is half the rated current, the pump plant acknowledged the quality of a problem, after changing the impeller its basic parameters close to the design value. The system is running again, the individual heat pump unit can not start the problem still exists, indicating that the root cause of the problem is not before and after the pump maintenance chilled water flow problems. At this time, some designers began to suspect that a pump dragged six heat pump unit program not, frozen pipe is not the same program, the application of pumps, heat pumps one by one corresponding program. I always think that the above two options are feasible. After I found that individual heat pump units or even the outlet pipe on the water flow adjustment screw adjusted to the lower limit, still can not start, to use the screwdriver hard pressure balance board unit can be opened. After repeatedly studying the structure of the water flow switch in the field, it was finally found that at the other end of the water flow switch balance plate there was a very small screw which, contrary to the force of the adjusting screw mentioned above, was adjusted together to bring the balance plate into position , The flow switch to work properly. After troubleshooting, the system is operating normally until now.  Case Ⅱ: B project heat pump unit type A project with five, it uses a heat pump unit in parallel with a pump and then in parallel, the system is running normally, but five parallel heat pump units, the pump appears larger water flow , The heat pump unit outlet temperature above 10 ℃.  Case III: C project for the 18-story high-rise buildings, an area of ​​nearly 20000M  2, the roof of three sets of 698KW piston-type heat pump unit, the roof around the high 2.8M reinforced concrete wall, the dotted line part of the square trapezoidal steel frame glass Curtain wall, curtain wall outer edge of the roof than the high 1.80M, hollow top of the inner ring, but a smaller area. I found these cases that: heat pump unit bored in the glass cover, will inevitably affect the unit summer cooling effect of the condenser and the winter evaporator cooling effect, after a period of time will heat pump unit high pressure protection (summer) and evaporation Low voltage protection (winter) and downtime. Therefore, I suggest to cancel the trapezoidal glass curtain wall, but the owners fear of affecting the effect of the facade and do not agree to cancel, in this case can only lift the outer edge of the outer wall of the curtain to the roof 2.8M, the curtain wall to enlarge the appropriate top Openwork area. This summer, the project three heat pump unit running its chilled water outlet temperature measured data in Table 1.  Table 1 heat pump one day in summer Frozen water outlet temperature Outdoor dry-bulb temperature ℃ X unit (℃) Y unit (℃) Z unit (℃) 37 ~ 38 14 ~ 15 8 ~ 9 6.8 ~ 7 30 15.1 14.1 11.1 from the table As can be seen, the Z unit is operating normally, the Y unit is slightly lacking and the X unit is in poor operating condition. In the hot days, when the three units are turned on at the same time, there is an automatic shutdown of the X unit, so the owners generally use the X unit as a short time, and most of the time the startup plan is: Y + Z; X + Z; Y or Z, when the crew are running normally. The reason why the above situation occurs, I think: ①unit in the daughters wall plus glass cover, "Tongtengfeng" smaller, the atmosphere can not immediately disperse the hot and cold environment around the dilution unit; ② Although the inlet into the wind Phenomenon, but did not completely form the ideal top hot side into the fresh air flow form: Y, Z unit is above the trapezoidal top glass cover hollow (from the unit top height difference of about 7.50M), hot gas can be out of the glass cover, The X unit close to the West glass wall, just above the inclined glass cover, the unit discharges the heat toward the inclined glass, can not be directly discharged to the hood, on the contrary the heat rebounded downward, spreading around; ③ Each heat pump unit condenser row The air volume reaches 19 × 104M3 / H. When Y and Z units are running, there is no backflow. However, when all three units are on and the condenser ventilation is large, there are reflux on both sides of unit X, causing condensing of units X and Y Poor heat dissipation, evaporation temperature, unit cooling capacity decreased. Solution: Connect the air duct to the outlet of condenser X of unit X to direct the airflow outside the glass cover. Case IV: Coincidentally, D Engineering (twenty-first floor) preliminary design two 698KW Piston heat pump units located in the main building roof, tall ship-shaped glass curtain wall heat pump unit package is tangible, the top of the beautifully shaped curtain wall only a few Breathable place. After learning about the C project, the designer changed the heat pump unit to a spacious podium roof.  IV Conclusion: 1, HVAC designers
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