Air-cooled heat pump hot and cold water unit is the nineties in China began to apply a new air-conditioning host, such units can both cold and heat, save the boiler room and cooling water system, installation flexibility. Unit operation using microcomputer control, high reliability. Therefore, many air-conditioning projects in the Yangtze River Basin to be widely used. However, due to the different climatic conditions in various places, there is also a lack of experience in engineering design. So in use also found a lot of problems. The author of this article based on my own experience in recent years to talk about a few experiences, for the majority of peers reference.
During the design of a project, if the local climate and environment allow, at the same time after technical and economic analysis to determine the project air-conditioning heat source using air-cooled heat pump units, then designers should proceed to the relevant domestic and foreign manufacturers of products for analysis and comparison , For the user to choose a more economical and reasonable heat pump products. The main content of the selection is firstly the overall performance analysis of the unit, which includes the heat pump unit cooling capacity, heating capacity, COP value, noise, dimensions, operating weight and other parameters. Secondly, the paper analyzes the internal configuration of this type of heat pump. It includes the compressor type, the structure and layout of the condenser, the configuration of the thermal expansion valve, the type of evaporator, the mode of energy regulation, the way of defrosting, the safety protection and automatic control projects. After doing the above analysis and comparison, we can choose an ideal unit. The next task is to arrange the equipment. During this process, we must consider the reasonable spacing between the equipment, the configuration of the auxiliary heat source, and the overall operation noise of multiple heat pumps The impact on the surrounding environment. The following are some of the above issues are described.
Performance Analysis of Air-cooled Heat Pump
Air-cooled heat pump heat and cooling: These two parameters are the most critical parameters that determine the normal use of air-cooled heat pump, which refers to the air-cooled heat pump inlet temperature, inlet and outlet temperatures in the design conditions when it has the cooling capacity Or heating capacity. It is available from the manufacturer's product samples found. However, the current design is also found in such a situation, that is, some manufacturers have provided the sample parameters have not been tested but copied from other manufacturers of the relevant samples. This gives designers the correct selection has brought some difficulties. Therefore, I suggest that under the conditions of the designer can be based on the manufacturer's air-cooled heat pump configuration of the compressor model from the compressor manufacturer to get the compressor performance changes in the performance curve, according to the heat pump design conditions Check the compressor in the heat pump design conditions cooling capacity and heating capacity, to determine the sample provided by the authenticity of the parameters.
COP value of air-cooled heat pump: This value is to determine the performance of air-cooled heat pump is an important parameter, the value of the level of a direct impact on the use of air-cooled heat pump power consumption, therefore, should try to choose a high COP value of the unit. At present, China's national standard is a COP of 2.57, most of the imported or joint-venture brands have a COP of about 3. Some imported brands have a capacity of 3.8.
Noise: Noise is also a measure of an air-cooled heat pump unit, an important parameter, which is directly related to the heat pump operation on the surrounding environment. Relevant domestic experts have been based on engineering measurement of various types of imported heat pump noise is divided into third gear, the first gear at 85dB or more, the second gear at 75 ~ 85dB, the third gear at 75dB or less. We should carry on engineering design selection should give priority to the noise below 80dB units.
Dimensions: Most of the air-cooled heat pump units are arranged in the outdoor roof, it is in the layout of the equipment on the device and the surrounding wall spacing, the spacing between devices have clear requirements, so we have to consider when selecting equipment Whether the size of the device meets the size requirements of the device layout. In the same premise of the same performance should give priority to the use of smaller units to reduce the equipment area.
Operating weight: As most of the air-cooled heat pump units are arranged on the roof, the load-bearing capacity of the roof must be taken into account when selecting the type of the roof. If necessary, professional consultation should be made with the structure to enhance the load bearing capacity of the roof. However, in the selection of equipment we should give priority to the operation of light weight units.
System Analysis of Air-cooled Heat Pump
The so-called air-cooled heat pump system analysis, that is, in the air-cooled heat pump selection process in addition to comparing their respective cooling capacity, heating capacity, COP value, noise, operating weight, dimensions and other parameters, but also their respective compressors Type and arrangement of the condenser, configuration of the thermal expansion valve, evaporator type, defrosting mode, energy regulation mode and the automatic control and safety protection of the heat pump system, etc. are compared to compare their advantages and disadvantages in the system configuration. Compressor type:
Currently used for air-cooled heat pump compressor type mainly piston, scroll, screw three types. According to the heat pump is characterized by long running time, large compression ratio, etc., I believe that scroll and screw compressors will become the mainstream of heat pump compressors. The reason is:
1, Scroll and screw compressors have less transmission parts than piston compressors, so that the friction loss of the compressor is correspondingly reduced, and the efficiency of the whole machine is correspondingly increased.
2, due to the heat pump unit compression is relatively large, so for the piston compressor volume loss in the same clearance volume decreased, resulting in a decline in the efficiency of the machine. The scroll and screw compressors do not have this problem.
3, the compressor for air-cooled heat pump its working environment than other air compressors working under normal conditions to be harsh, each running time is longer, a larger range of changes in conditions, the reliability of the compressor Sexual requirements are higher. Scroll and screw compressors with fewer parts, compact structure, it is especially suitable for heat pump units.
4, the current use of air-cooled heat pump units are generally used hot gas defrosting method to exclude the accumulation of frost on the air side heat exchanger in winter heating conditions. At the beginning and at the end of the defrost the system is run in reverse and the liquid refrigerant accumulating in the original condensing one of the coils is flooded to the compressor due to a sudden drop in pressure therein to the suction pressure causing the compressor's wet stroke, This is not a big problem for scroll and screw compressors, which can easily cause damage to the air valve and connecting rod for piston compressors.
5 In addition to the heat pump compressor itself, the vortex and semi-closed screw-type piston than the noise is lower.
Condenser type and arrangement
The type of fin used in the condenser currently has two kinds of windows and corrugated sheets, heat transfer windows high efficiency, so the first two years of production of heat pump units are often used. However, due to poor urban air quality in our country, such fins are very easy to foul and harder to clean up. As time goes by, the heat exchange effect greatly decreases. Therefore, the current heat pump condenser multi-use corrugated sheet with internal thread brass, which has a higher heat transfer efficiency, easy to fouling, wind resistance and other small features.
Condenser fin pitch is also very particular, as the condenser to use the ribbed ratio, the number of large heat transfer system is good, so I hope the smaller chip better. However, when used as an evaporator, the fins frost, the use of the heat transfer effect will be greatly reduced, so I hope the larger chip distance; general film to 3mm is appropriate.
The layout of the condenser with its heat transfer effect and dimensions have a direct relationship. Condenser coil heat pump is usually arranged in a straight coil, V-coil, W-coil three types. However, there is no other components in the larger space between the V-type coils besides the axial fan, so the space utilization rate is low. Although the straight-type coil arranged between the compressor, four-way valve, evaporator and other system-related components, but due to the coil height is higher, the wind speed is uneven, the condenser heat transfer efficiency is low, and the air flow is not organized Ideal, air resistance larger. The W-type layout to overcome the above shortcomings, not only can improve the air flow to improve the efficiency of heat transfer and reduce air resistance, and because of the same space conditions, the condensing coil heat transfer area increases, space utilization is higher, thus reducing the unit Dimensions.
Thermal expansion valve configuration
Now the heat pump refrigeration system has a single expansion valve and dual expansion valve in two ways, the so-called dual expansion valve is the heating conditions and cooling conditions using an expansion valve. If the system uses an expansion valve, according to the standard cooling conditions selection, the heat pump system in the heating conditions when the system heat with the decline in ambient temperature will also decline. At this time expansion valve heating capacity will decline, but the extent of its decline is less than the system heating capacity decline. This heating conditions with the decline in ambient temperature, the configuration of the system expansion valve is too large. Excessive expansion valve will cause the evaporator too much liquid supply, evaporation pressure increases, and outdoor air heat reduction, resulting in reduced heat pump heat.
Many current heat pump manufacturers use double expansion valve type, refrigeration expansion valve according to the standard refrigeration conditions to choose. If the thermal expansion valve according to the standard heating conditions to choose, then when operating under low temperature conditions the expansion valve will appear too large, so according to my own experience suggest that the thermal expansion valve according to the ambient temperature -7 ℃, hot water inlet temperature 40 ℃, the outlet temperature of 45 ℃ to select, according to such conditions after the selected expansion valve can be no less than -15 ℃ ambient temperature in normal operation.
Evaporator type
At present, the evaporator commonly used in air-cooled heat pump units are mainly plate heat exchangers and dry shell and tube heat exchangers. Plate heat exchanger used in small air-cooled heat pump, it has high heat transfer efficiency, the evaporator is not easy oil production characteristics; especially the new plate with a built-in distribution device to solve the uniformity of refrigerant distribution between the plates A key issue is to increase the evaporation temperature by 15 to 2 ° C at the same effluent temperature to improve the refrigeration efficiency.
Dry shell and tube evaporator used in large and medium-sized air-cooled heat pump, the heat pipe has been widely used efficient tubes, so the heat transfer efficiency has greatly improved. But generally not as plate heat exchanger. And its back to the oil is relatively difficult, often accumulated in the bottom of the heat exchanger. If the return pipe and the suction pipe are connected at the bottom, the superheat degree of the refrigerant is unstable due to the liquid refrigerant brought in, which affects the operation of the expansion valve and the cooling capacity of the system.
Axial fan configuration
Axial fan configuration must first meet the condenser (air side heat exchanger) heat transfer requirements, according to the experience of air-cooled heat pump units equipped with axial fan air flow and standard cooling capacity (ambient temperature 35 ℃, the water temperature 7 ℃) Ratio of about 0.071 ~ 0.095 / kJ, in addition to ensure the wind speed of the windward side of the condenser, because it relates to the frost speed of the air-side heat exchanger in winter operation, the windward speed of the windward side is more difficult in winter operation frost. However, excessive air flow fan fan power consumption should also increase, but also increase the noise, so the wind speed under normal winds take 3 ~ 5m / s. In addition, the fan configuration should also consider the noise, the current general selection of large diameter, low speed, and the blade angle smaller axial fan to reduce fan noise.
Energy regulation method
Currently in the air-cooled heat pump units commonly used in energy regulation compressor number control, compressor clearance operation, cylinder unloading regulation (piston), frequency control (scroll), stepless adjustment of the valve (screw). From the energy regulation we can see that the number of units control, compressor clearance operation, cylinder unloading adjustment are all level regulation, and variable frequency speed regulation and stepless adjustment of the valve are infinitely adjustable. Stepless adjustment with energy saving, noise and vibration is small, good starting performance also reduces the interference to the power supply system. From this point can also be seen vortex and screw compressors of the heat.
Defrost method
The units produced by the various defrost methods are basically the same, most of the steam defrost method; the difference is the defrost control technology. Common pressure control method, temperature control method, temperature and time control method, of which the most common method of temperature and time control. Defrost parameters in this control technology settings are the most critical. Defrost parameters include defrost temperature, defrost time, defrost interval. The defrost temperature is sensed by the temperature sensing element located behind the expansion valve. The temperature is set to -5 ° C. The defrost interval is controlled by a timer, typically 4 min. Defrosting time is also controlled by the timer, generally not more than 10min. Heat pump temperature dropped to -5 ℃, and from the last defrost interval enough 40min, the unit will enter the defrost mode. If the defrost time exceeds 1010 min and the temperature of the liquid in the coil has not risen to + 5 ° C, the unit will stop defrost and resume heating.
In the above three parameters defrost interval is directly affected by the environment, but most manufacturers defrost interval is still using a fixed value, this approach led to low temperature and humidity in the area of ​​severe frost, because there is no Set the time and can not be defrosted, resulting in frost layer is too thick or even frozen, low pressure unit shutdown and the phenomenon. This issue should be noted in the unit debugging. Therefore, I suggest on the one hand the heat pump defrosting parameters should be based on local conditions, can not be generalized. On the other hand is the previously mentioned in the low temperature and humidity areas should not be used heat pump units.
Security and control
At present, the domestic air-cooled heat pump unit to protect and control the use of computer control, which in turn includes programmable control and microcomputer control, the two control principle is roughly the same.
A wind heat pump safety protection system to include at least the following aspects
1) Insufficient suction pressure protection 2) Exhaust pressure overload protection 3) Hydraulic pressure protection 4) Cold water temperature protection 5) Water side heat exchanger water protection 6) Compressor start-up time interval protection 7) Inside the compressor Tibetan motor overheat protection 8) Motor overload protection 9) Low power supply voltage protection 10) Three-phase power phase loss protection 11) Oil temperature control?
Air-cooled heat pump control to be included at least
1) Defrost control 2) Sequence control of multiple compressors 3) Energy regulation 4) Fault stop and display 5) Remote control interface (for remotely setting operation parameters and controlling start and stop of the unit, displaying the operation parameters and fault contents of the unit in Control terminal)
Air-cooled heat pump engineering design
Air-cooled heat pump layout:
Air-cooled heat pump water heaters in use in varying degrees, there is such a phenomenon that the lack of cooling capacity in the summer, lack of heat in winter phenomenon. The reasons for this phenomenon are many, here in addition to the factors of the equipment itself also has engineering problems. Mainly due to the unreasonable arrangement of the equipment, the air current is short-circuited, and the high-temperature exhaust of the unit is re-inhaled in summer, causing the temperature of the inlet air to rise and the condensing pressure to rise, resulting in a decrease of the cooling capacity of the unit. In the winter, Unit inhalation caused by inhalation of air humidity is too high, exacerbating the heating unit frosting speed, so that the defrost time is extended, reducing the heating time, so that the unit to reduce heat.
Therefore, air-cooled heat pump should be arranged outdoors as far as possible, the wind should be smooth, exhaust should not be blocked. Avoid air flow short circuit. If obstructions, should meet certain requirements. Many production units and other design manual provided on the spacing between the units and the distance between the unit and the wall have clear requirements, are as follows: The distance between units should be maintained at 2 meters above the main unit and the main building (or a higher height The daughter of the wall) should be kept at a distance of 3 meters or more. In addition, in order to avoid the exhaust short circuit in the upper part of the unit should not be set shelter like shelter. If the unit must be arranged indoors, take measures to increase the static pressure of the fan and then connect the air duct to discharge the exhaust air outdoors. Venting wind speed (7 m / s), so that it has a certain range, and the air inlet velocity is small (2 m / s), the air inlet vertical height should be as large as possible to avoid air flow Short circuit.
Auxiliary heat source configuration
Air-cooled heat pump heating in winter with the decline in the outdoor temperature decreases, the outdoor temperature decreases by 1 ℃, the heat reduction of about 2%; with the decline of outdoor temperature, indoor heat needs to be increased, it should consider setting Auxiliary heat source, auxiliary heat source can be electric boilers, oil-fired boilers, gas boilers, steam - water heat exchangers and so on. According to the engineering experience of 1RT air-cooled heat pump unit is configured 0.6kW auxiliary heat source is more secure, this configuration can fully guarantee the entire building in winter air conditioning. Of course, at present, many projects do not always have auxiliary heat sources for investment consideration. This is also one of the reasons why many heat pump buildings are not effective in winter air conditioners.
Affect the air-cooled heat pump winter heat is mainly due to the relative humidity of winter outdoor air, especially in outdoor air relative humidity greater than 75% of the area, the wind-cooled heat pump frost faster; defrosting to stop heating, the unit The total heat loss, power consumption increases. Therefore, I suggest that winter outdoor air relative humidity is higher than 75% of the average area should not use such units. If for any other reason you must use the heat pump unit, you should consider configuring the auxiliary heat source.
Engineering noise control:
Air-cooled heat pump air conditioning engineering noise control is the first choice in the equipment selection phase will give priority to lower noise brands, the current single-air-cooled heat pump noise is generally between 65 ~ 85dB, for each additional unit, the overall noise will be Increase 3dB, when the number of heat pump in a project is more, the noise is more difficult to control. Therefore, the selection of heat pump works in the number of units should not be too much, in other words heat pump is not suitable for large-scale air-conditioning projects, in general, a project should not exceed the number of heat pump 5 units.
In addition, in the layout of the unit should be considered in addition to smooth exhaust air to avoid exhaust back to the wind, the base of the unit and the inlet and outlet pipes must be installed damping device, isolation efficiency to meet the design requirements. In the cooling, heating station air conditioning water main pipe to be installed with a damping hanger or bracket, to prevent the unit and pump vibration through the pipe to other places.
In addition, the unit should, where possible, be arranged on the main building roof as much as possible to reduce the impact of noise on the main building itself and the surrounding environment.
Indoor Sports Park,Indoor Sports Complex,Indoor Sports Center,Indoor Adventure Park
HANGZHOU JOY TECHNOLOGY CO., LTD. , https://www.joyplaypark.com