Application of Air Source Heat Pump Chiller

I. Overview

According to the "Language Standard for Heating Ventilation Air-Conditioning Technology" (GB50155-92), a heat pump is defined as a refrigerator that enables the function of the evaporator and the condenser to be switched. We can also call the heat pump a unit that works on the principle of inverse Carnot cycle, both for cooling and heating. There are many types of heat pump, heat pump can be divided into: air - air heat pump, air - water heat pump, water - water heat pump, water - air heat pump, soil - Air heat pump and soil - water heat pump. Air-water heat pump units, that is, air-source heat pump water chiller units are more widely used in engineering.

The research, production and application of heat pump units began to take the road of sound development in developed countries such as the United States in the 1970s. In 1980, China designed and produced the first air-to-water heat pump unit with R12 as working fluid and compressor power of 55KW in Shanghai and put it into practical application. Until the end of the eighties of the 20th century, air-source heat pump hot and cold water unit research, production, application in our country had a rapid development. At the beginning, the application of heat pump project mainly to set the condition of the boiler or the land price is too expensive or no space for the construction of freezer room, available for selection only a few imported brands of units, the unit is relatively simple, mostly for the overall piston compression Air-cooled heat pump. In recent years, the use of heat pump project, both in the area or in the building function and size have a great breakthrough, heat pump unit brand, type of choice greatly expanded the space, there are many imported brands, there are many Domestic brands, there are piston compression heat pump units, there are screw-type units, there are integral units, there are modular heat pump units, single unit cooling capacity from 3RT-400RT, everything, and the unit's cooling, heating performance, quality , Reliability, etc. have significantly improved.

Second, heat pump characteristics

Air source heat pump hot and cold water unit has the following characteristics:

1, air-conditioning system, a combination of hot and cold, and placed in the roof of the building, do not need to set up a special refrigeration room, boiler room, but also eliminates the chimney and cooling water pipe occupied by the building space.

For the construction of bustling city lots of land, or unconditional boiler room construction, air-source heat pump hot and cold water unit is undoubtedly a more appropriate choice.

2, no cooling water system, no cooling water system power consumption, no cooling water loss.

Air-conditioning systems such as water-cooled chillers, tap water loss not only evaporation loss, drift loss, as well as blowdown losses, loss of winter antifreeze drainage, system washoff when the summer is enabled, chemical cleaning dilution loss, etc., all of these losses And the equivalent of about 2-5% of the cooling water circulation water, according to the different nature of the chiller, the equivalent unit of cooling capacity loss 2-4t / 100RT · h. This is a considerable amount for some of our severely missing cities. In addition, a considerable part of the project under partial load cooling water circulation remained unchanged. Or according to the number of host operating units, only for the appropriate number of adjustments. Our previous economy paid much less attention to this point.

3, because there is no boiler, no corresponding fuel supply system, no flue gas, no cooling water, system safety, sanitation and conciseness.

For the professional heating, the boiler room is most likely to be a security risk, In addition, the formation of cooling water contamination of Legionella infections have been reported in many cases, from a health and safety point of view, air-source heat pump has obvious advantages.

4, system equipment and less concentrated, operation, maintenance and management simple and convenient. Some small systems can be used to control the opening and closing of indoor fan coil heat pump unit switch.

5, stand-alone capacity from 3RT to 400RT, complete specifications, strong adaptability of the project, which will help the system to refine the division, can be layered, sub-block, sub-user units set up independent systems.

6, COP COP value lower than water-cooled units in summer, more power consumption, saving energy consumption in winter operation. For a typical building in Nanjing, a hot and cold winter city, the annual energy consumption of a heat pump system is lower than that of a water-cooled unit plus a boiler. However, at current energy prices, the annual operating cost of the heat pump system is higher than that of a water- Program.

7, higher cost. As a cold and heat source of air-conditioning system investment in equipment, air-source heat pump water heater unit cost is higher than the water-cooled unit plus the program of the boiler system cost more than 20-30% of the cost, such as only cold and heat source equipment, heat pump The price is about 1.5-1.7 times of water-cooled machine + boiler.

8, air-source heat pump chiller units exposed to the outdoors all year round, operating conditions worse than water-cooled chillers, their life is also shorter than the water-cooled chillers.

9, heat pump unit noise, the environment and adjacent rooms have a certain impact.

Heat pump usually placed directly on the podium or roof, noise isolation effect, directly affect the neighboring rooms and the surrounding use of some rooms. Reasonable location and isolation noise isolation measures in place, the impact of heat pump noise can be basically eliminated.

10, air-source heat pump performance with the obvious changes in outdoor climate. When the outdoor air temperature is higher than 40-45 ℃ or lower than -10 ~ -15 ℃, the heat pump unit can not work normally.

Third, heat pump output and climate

Under the rated conditions, the COP of the air-source heat pump is about 3.0 in the summer and about 3.0 in the winter (air 7 ℃ and 45 ℃) if the temperature is 35 ℃ and the water is 7 ℃. 3.0 or so, air-source heat pump cooling and heating performance has a direct relationship with the outdoor climate, air-source heat pump chiller units with cooling capacity decreases with outdoor temperature increases, unit power consumption with the outdoor temperature increases increase. When outdoor air temperature is increased to 40 ℃, the cooling capacity will generally drop about 5-7%. Air-source chiller normal cooling maximum temperature is generally 40-45 ℃, individual brands with condenser fan speed control system, the maximum allowable outdoor temperature of up to about 50 ℃. It should be pointed out that with the cooling tower is not the same, the relative humidity in cooling conditions on the air source heat pump did not adversely affect the contrary, the relative humidity, the cooling is beneficial. Nanjing summer relatively high humidity, so in fact the difference between the cooling effect of air-cooled and water-cooled, smaller than people think.

Air-source heat pump water heating unit more complex heating characteristics, when the coil surface temperature is below the air dew point temperature, the air will be dew condensation, coil surface heat transfer occurs at this time, help to improve the heat pump unit Heating capacity, but when the coil surface temperature is below the freezing temperature of air (below 0 ℃), if the relative humidity in the air at the same time reach a certain level, the coil surface will frost, if not timely defrosting, frost Will be more knot the thicker, affecting the actual flow of air, and hindered the heat exchange on the coil, the heavier will freeze, the compressor appears low voltage protection downtime. Corresponding to the different oncoming wind speed and climatic conditions, there are three states of humid air on the air coil of the outdoor side of the heat pump unit, namely, the frosting zone, the condensation zone and the dry cold zone (without frosting nor condensation). Frosting transition curve, which is close to the wet-bulb temperature line on the psychrometric chart. When the frontal wind speed is 2.5M / S, the ambient temperature is 0 ℃, and the relative humidity is 73%, the frosting begins on the coil. If the head speed is increased to 4M / S and the ambient temperature is 0 ℃, the relative humidity 82%, the coil began to frost, improve wind speed can reduce the accumulation of frost. When the surface wind speed is 2M / S, the outdoor air dry-bulb temperature is the most serious when the dry air temperature is 0-5 ℃ and the relative humidity is more than 85%. When tw <-5 ℃, the frosting rate slows down, because the air In the moisture content has been significantly reduced.

Heat pump unit frosting appears on the coil, will affect the unit's normal and effective heating, it must be defrosted. At present, most of the units use reverse circulation to defrost. At this time, not only the compressor stops heating operation, but also the cooling operation, so the system heat supply is obviously affected. Frosting serious, an average of half an hour of cream, a defrost time of about 5 minutes, due to defrost reduced heat about 17%. In addition, the outdoor temperature decreases, the output of heat pump significantly reduced. 0 ℃ conditions, the actual rate of heat pump units under rated conditions of about 70%. -6 ℃ case, the output is only about 62% under rated conditions, -10 ℃ under the conditions of heat supply is only about 55% under rated conditions. Cold weather, rain and heat have a significant impact on the heat pump output, while affecting the normal operation of heavy, some users to extend the defrost time, pouring warm water and other methods to remove frost. Ambient temperature is below -10 ℃ - -15 ℃, the heat pump unit generally can not be normal operation.

Nanjing area is hot in summer, cold in winter and high in humidity. The temperature in winter of 1993 was lower than -5 ° C for a total of 69 hours during the daytime. During the daytime, the temperature dropped below -5 ° C during the daytime from 8: 00-18: 00 for 7 hours. In summer of 1994, the temperature was higher than 37 ° C for a total of 10 hours. In 1993 and 1994, the winter heat pump was in the frosting work area respectively for 1613 hours and 1527 hours (heat exchanger windward wind speed 2.0m / s) And 8: 00-18: 00 during the daytime, 711 hours and 653 hours for the winter heat pump in frosting operation in 1993 and 1994 respectively (average wind speed of 2.0m / s on the windward side of the heat exchanger). On the average, Air source heat pump unit frost time in 1500 hours, if only in daytime operation, the year frost accumulation time in a total of about 680 hours.If to improve the coil head to the 3M / S, air source heat pump unit frost time 1300 Hours or so, if only run during the day, the total frost-free time throughout the year in about 600 hours.

Fourth, heat pump applications

Nanjing is a city with hot summers, cold winters and high humidity in winter. Although many people are skeptical about the reliability and rationality of winter heat pump heating in Nanjing, due to some of the above advantages of air source heat pump, air source heat pump The development of hot and cold water units in Nanjing is also quite fast. In the early nineties of the twentieth century, Nanjing began to use air-source heat pump chillers. The number of air source heat pumps put into service in 1995-1998 increased significantly. According to the information we currently have, there are currently about 250 projects in Nanjing that use air-source heat pump chillers as the hot and cold source of air conditioning systems. Among them, a design institute in recent years the selection of heat pump for the cold source of about 35 as many projects, accounting for the hospital air-conditioning project number of 30%. An engineer one person has nearly 10 projects using air-source heat pump hot and cold water units as a hot and cold air conditioning. In our understanding of the air source heat pump hot and cold water units as a cold source of shopping malls, office buildings, office buildings, hotels, factories, comprehensive buildings.

It should be pointed out that the import referred to here is wholly owned or imported by foreign investors. In addition, the higher proportion of domestic shares (the number of construction projects) is related to the better sales performance of a Taiwanese-funded enterprise in Nanjing during a period. Recently, Engineering heat pump unit imported products market share has risen. Although after years of digestion, engineering heat pump unit market is not like the home air conditioners, domestic enterprises did not gain a dominant position, which is worth our thinking.

From the survey results, the air source heat pump water heaters in recent years, the rapid development of Nanjing, and most of the engineering heat pump air conditioning system can still basically meet the required cooling and heating requirements. Below on the situation of several typical projects for some introduction.

The Yangtze River Trade Building was designed in 1991 and completed in 1994 with a modern office building. The building has a building area of ​​about 35,000 m2 and a total building height of 95 meters. There are 23 floors above ground level. Peripheral structure for the whole glass curtain wall. Six American Awakened AWHC-200 heat pump units were selected in the building. The installed capacity is 3672KW (1044RT), the area cold index is 105W / m2, and the heat pump rated heat capacity is 107W / m2. The heat pump unit is placed on the roof of the main building. The system is equipped with 8 pumps, each with a circulating water volume of 200m3 / h and a lift of 32mH2O. The heat pump and the pump are respectively connected in parallel and then in series. The heat pumps in and out of the water pipe are directly connected with the sub-catchment and the pump is placed indoors.

Heat pump units using spring shock absorber damping, pump also uses vibration damping base damping. The end of the air conditioning system is designed to change the volume of water, the host machine is the fixed number of water control. According to the site survey and measurement, the staff of the building had a higher degree of satisfaction with the air conditioner. In the summer, when the suction temperature was 40 ℃ (local short-circuit inhalation excluded), the system effluent was 7.58 ℃, the backwater temperature was 12 ℃ and the water temperature difference was 4.42 ℃ (heat pump running 5, 3 pumps running, there are a few floors are not in use), the indoor basically meet the design requirements of 26 ℃. In the winter of 1999, there was a heavy snowfall in the world. The temperature of water supplied by the system was fluctuated in the range of 39-40 ℃. The indoor temperature of a room in the south was maintained at 23 ℃. Winter bad weather, artificial defrost time interval of 30 minutes, defrost time lasted 5 minutes. Individual weather occurs in the morning can not boot normally, the administrator first set the conditions of the cooling and defrosting, and then enter the heating conditions. As the heat pump unit placed in the main building open roof, good ventilation. However, due to higher daughter wall, some heat pump appeared short-circuit airflow phenomenon. Short-circuit airflow phenomenon in winter is more obvious, this phenomenon can be easily observed through the fog flow path when defrosting. The noise of standard heat pump unit (200RT) in York Company is about 82dB (A), but due to the suitable position of heat pump, civil engineering treatment and vibration reduction measures are all appropriate (high daughter wall, heat pump and evacuation stairs are separated by pump room, And the stairs are separated by a certain horizontal distance), these comprehensive measures make the heat pump unit no significant impact on the building noise, heat pump in the hall floor where the measured noise of about 45dB (A), in close The heat pump at the lower office, the noise is about 45dB (A), the ceiling noise is about 50dB (A) or so. It can be seen that the comprehensive measures of vibration and sound insulation of the project have received obvious effects.

A foreign trade company office building construction area of ​​about 27000 m2, a total of 21 layers, a total height of 90 meters, the building envelope structure for the semi-glass curtain wall structure, building in 1996 January began to put into use. Building selected American York company AWHC-200 heat pump unit 4, the total rated cooling capacity of 2448KW, rated for 2500KW, equivalent to the unit area of ​​cold targets 91W / m2, heating area index 93W / m2 (corresponding to the heat pump rated worker Condition, temperature 7 ℃, water 45 ℃).
The heat pump is placed on the top of the tower, the top of the roof is a triangular horizontal opening of the top of the Venetian blind. The system is equipped with 5 sets of IS125-100-400 pumps 5 sets, the rated flow of the pump is 100m3 / h, rated head 50mH2O, motor power 30KW, the pump 4 with a backup, the pump unit first parallel and then connected in parallel with the heat pump series . The air conditioning system uses a variable volume air conditioning system. The building is still part of the floor has not yet put into use, has opened the room temperature and humidity to meet the basic design and comfort requirements. However, due to overemphasis on the appearance of beautiful, will set the pump roof layer covered with triangular horizontal blinds, heat pump poor ventilation, due to a large number of short-circuit airflow, hot weather can not be normal operation, the heat pump where the floor to heat pump exhaust fan Air outlet for the sector, the air conditioner is divided into two parts up and down. Oblique roof part of the louver as exhaust, under the roof part of the blinds for inhalation. Although the situation has improved, but the louvers are horizontal, so the discharge of short-circuit the phenomenon of suction more obvious, high-pressure heat pump shutdown occurred from time to time. Pump configuration is too large. Resulting in high operating costs of the system. The field test in summer shows that the actual suction temperature of a heat pump unit reaches about 45 ℃ due to short-circuit of airflow when the outdoor ambient temperature is 33 ℃. When the host suction temperature reaches 45 ℃, the compressor starts to have a protective shutdown. In addition, the host measured the average temperature of water entering and leaving the average about 3 ℃, indicating that the pump configuration is too large. In order to ensure efficient operation, the management company in the heat pump heat exchanger side of the additional sprinkler mist spray in the summer to receive some results. Winter, severe frost on the heat pump, the implementation of the mandatory defrosting method. In addition, due to the characteristics of civil engineering and other reasons, the noise of the heat pump water pump room can still hear the noise of the equipment room (45 ~ 50dBA) in the elevator hall which is 5 floors away from the engine room. Can be seen, though, the same brand of the same type of heat pump, due to different civil engineering separation and vibration isolation equipment, there will be a significant difference in the degree of impact.

Hotel tomorrow, the construction area of ​​about 7800M2, of which about 20% of the hotel public rooms about 80% of the rooms. Hotel selected a total of three 110RT heat pump, the actual use of only two. Good effect in winter, one night, outdoor temperature 0-2 ℃, cloudy weather, heat pump water temperature maintained at 39-41 ℃, room temperature up to 25 ℃. When it is snowing, the heat pump can still operate normally. Has been used until now, the second frosting more serious, automatic defrosting difficult, managers with top-living boiler hot water shower, everything is normal. Heat pump placed on the roof of the hotel, three pumps placed in the outdoor platform next to the heat pump, and the heat pump one by one, that is, each pump and heat pump in series and then in parallel. Adjacent to the heat pump floor for the hotel's internal office space, the indoor noise is about 45-50dB (A), winter individual rain and cold days, due to the rubber vibration isolation mat is frozen, the vibration damping effect, close to the floor noise Has increased. However, the rooms were not significantly affected due to the fact that the heat pump was not attached to the rooms. The actual operation shows that the system has 2 heat pumps enough to meet the air conditioning requirements, very few bad weather in winter only need to open 3 heat pumps.

Fifth, the application of the problem

Among the projects under investigation, although most of the project heat pumps still meet the basic requirements of refrigeration and heating, they can meet the requirements of reasonable design, investment and operation economy, obvious effect of vibration damping and noise insulation, excellent cooling effect, etc. . Many projects also exist such a kind of problem. Can be summarized as:

1, heat pump quality and service issues

The design of the problem (a. Program is not appropriate; b. Improper host selection; c host location improper; d. Pumps and other equipment improperly matched; e. Water system is not properly organized)

3, the installation of quality problems

4, the subjective nature of the owners decision

5, poor operation and maintenance management

Sixth, the conclusion:

1, air source heat pump water heater unit in Nanjing can be used as one of the hot and cold air conditioning system for various projects;

2, under normal circumstances, according to the summer load selected heat pump to meet the requirements of the load in the freezing season, without additional auxiliary heater, but the selected heat pump should have good heating performance, heat pump group should be not less than 4-6 independent The refrigeration circuit. In addition, building envelope structure should have good insulation properties;

3, the annual energy consumption of heat pump system is lower than the air-conditioning system with water-cooled units plus boilers, but according to the current equipment and energy prices, heat pump system investment and annual operating costs higher than the water-cooled unit plus the boiler program. Whether the selection of heat pump water chiller as a hot and cold air conditioning system should be based on the specific characteristics of each project for technical and economic comprehensive comparison, combined with the specific requirements of the owners may be. Rooms, wards, used for larger projects;

4, the project using heat pump should take full account of its cooling and heating characteristics, should pay full attention to the noise and vibration effects and the corresponding measures should ensure good ventilation conditions, the system should be designed to optimize the selection of equipment, and strive to make The most energy-efficient investment and system throughout the year;

5, there are still many problems in many projects, urgent need to be added to solve, in order to improve the effectiveness and reduce energy consumption, considerable benefits.

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