April 13, 2021

Design and Application of Air Source Heat Pump Unit and Case Analysis

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 unit:?
The piston compressor is a positive displacement compressor with complex structure, low rotational speed, large vibration, large noise and small unit capacity. The multi-head combination can be assembled into a heat pump with a capacity of 1 million kcal / h. The COP = 3.0 ~ 3.5. ?
3. Screw compressor heat pump unit:?
Screw compressors are also positive displacement compressors with simple structure, stable operation, small vibration, low noise and long service life. COP = 3.5 ~ 4.5. Suitable 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. Selection principle:?
Compared with the capacity of single chilled water chillers, the heat pump unit has large power consumption, high cost, severe decay of heat with outdoor temperature drop in winter and severe frosting. Therefore, when a project has a steam source When the air-conditioning hot and cold sources should be used as far as possible "single cold water unit heat exchanger" program. Wuxi is forming a city steam heating network, we should give priority to the above programs. â‘¡ 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 cooling load in the southern region is greater than the heat load, the Air Conditioner designer should calculate the summer cooling load in the project and the winter heat load, select the heat pump unit type according to the unit cooling capacity ≥ Air Conditioning cooling load, and then see if the following inequality holds: In the winter outdoor air-conditioning calculation temperature (such as: Wuxi area -5 ℃) heating capacity ≥ engineering winter heat load. ① If 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 malicious slander of a brand or piston, screw-type heat pump units, we designers can not be a problem, we must carefully and carefully understand the performance of various models to make the right selection judgments. ? â‘  Compressor problems: One of the reasons is the wrong type of evaporator. For example, piston or screw heat pump unit (F-22 refrigerant) Compressor; the second reason is the lubrication system has impurities caused by 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; The third reason is the overheating protection, Over-voltage protection, short-circuit protection caused by failure;
â‘¡ liquid hit the problem: In fact, liquid-based piston and screw compressors are negative, both compression efficiency should be reduced;
Compressor efficiency control issues: Piston and screw-type heat pump 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 sliding Valve adjustment. At partial load, both shaft power is reduced, the COP value of operation is almost [1];
â‘£ lubricant problem: Piston and screw compressor in the summer and winter are required to heat the oil, the refrigerant in the volatile oil to ensure the normal lubrication of the compressor;
⑤ maintenance problems: about 268 piston compressor parts, wearing parts and more, 1000 hours to be in the repair, maintenance of large; and screw compressor parts about 26, less wearing parts, trouble-free operation time long. In normal operation, just a few years later as long as the replacement of lubricants, filters, bearings, etc .;
â‘¥ Noise: The main noise source of the screw-type heat pump unit is the fan. The general noise of the unit is about 80dB (A). Therefore, the unit should use the fan products with low noise, low speed and small vibration (static and dynamic balance test) 100 companies 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 test of noise and the difference between sounding room and normal environment.
⑦We also need to pay attention to the manufacturer's sample heat pump unit in winter heating is the value of the ambient temperature of 8 ℃, not the temperature calculated in winter air conditioning. ?
Third, heat pump design case analysis:
Following the I encountered in the design in recent years or to see the case of heat pump unit after the discussion with their 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), 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 earlier, was adjusted together to bring the balance to a suitable 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 the form of parallel, the system is running normally, but five parallel heat pump unit, the pump appears larger water flow, The heat pump unit outlet temperature above 10 ℃. ?
Case III: C project for the eighteen high-rise buildings, an area of ​​nearly 20000M? 2, the roof of three 698KW piston heat pump units, the plan view shown in Figure II. In the figure, the roof is surrounded by a 2.8M high-rise reinforced concrete wall, while the dotted line is a square-shaped steel-framed glass curtain wall. The bottom edge of the outer wall of the curtain wall is 1.80M higher than the roof, while the top of the inner ring is hollow but smaller in 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
It can be seen from Table 1 that the Z unit is in normal operation, the Y unit is slightly lacking and the X unit is in poor operation 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: ① unit 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, the D project (twenty-first floor) preliminary design two sets of 698KW piston heat pump unit 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 less Breathable place. After learning about the C project, the designer changed the heat pump unit to a spacious podium roof. ?
Fourth, the conclusion:
1, HVAC designers should conduct a comprehensive comparison of the economic performance of the design project to determine whether the Heat Pump System, steam or rooms, ward building priority to adopt a single cold host heating exchange system after the program is optimized;
2, HVAC designers must accurately calculate the thermal load of the project to ensure that the heat pump unit to meet the needs of summer and winter load;
3, Screw-type heat pump unit COP value or maintenance costs, vibration frequency, noise and other performance are better than piston heat pump units;
4, small and medium-sized projects using a small heat pump unit with a pump or pump system can be matched, but more than the best pump does not exceed three [?]?
5, we should pay attention to the heat pump operating environment, to meet the heat pump operating environment under the premise to allow architects aesthetic requirements of the building.

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