The Functions And Matching of Air Source Heat Pump Buffer Tank
A heat pump is an energy-saving device that uses high-level energy to flow heat from a low-level heat source to a high-level heat source. As the low-level heat source of the heat pump, air is inexhaustible. It is available everywhere and can be obtained free of charge. Moreover, the installation and use of air source heat pumps are relatively convenient. Buffer tank is very important to keep air source heat pump working efficiency, Eurostars engineer shares some knowledge about buffer tank of heat pump.
1.Functions of buffer tank for air source heat pump
(1)If the buffer tank is not used, it will cause the heat pump to start and stop frequently. Due to the limited amount of circulating water in the loop, it will cause the air source heat pump to reach the design temperature in a short time, and the heat pump will stop working, and then in a short time, the water temperature will reach the start condition, and the heat pump will start again, such frequent starting will greatly reduce the service life of the heat pump and waste electrical energy. Not only is the buffer tank required, but the capacity of the tank should be larger.
(2)Efficient defrosting and short defrosting time
When used in severe winter, especially between -3°C and 5°C, air source heat pump is easily frosting.The defrosting has impact on indoor temperature. Because the heat pump unit needs to consume heat in the pipeline during reverse cooling, if the water volume of the water system is small, the defrosting time will increase, and the water temperature in the pipeline will be lower, and the defrosting effect will not be good. If a buffer water tank is installed, during the defrosting process, because there is a certain temperature in the water tank, the defrosting can be completed in a short time, and the heat consumption is also small, which avoids the indoor temperature fluctuates caused by the heat pump defrosting. Fluctuation changes have a great effect on the stabilizing the terminal system, such as fan coils, AHUs.
(3)It can ensure the smooth flow of water in the heat pump system, complete automatic exhaust, and prevent heat pump failures.
We know that when the water tank is located in the return water system, the circulating water enters from the upper part of the water tank and discharges from the lower part, so that the gas in the water will accumulate in the upper space of the water tank, and the pressure in the closed system will automatically force the gas to be discharged from the upper exhaust valve, in this case, as there is no gas at the water outlet at the bottom of the buffer water tank, and at the suction port of the water tank, buffer tank can not only protect the impeller of the water pump, but also make the system free of gas and ensure the normal operation of the heat pump. If there is no buffer water tank, heat pump will sometimes malfunction and high-pressure alarm due to the presence of gas.
(4)It can make the heat pump system drainage more thoroughly and prevent blockage
There are a lot of impurities in the water system. These impurities will slowly accumulate to the bottom of the buffer tank through circulation. When passing through the Y-type filter, the water quality of the water pump will be better, thereby reducing the cleaning of the Y-type filter.
2.Buffer tank size selection
Buffer tank capacity = water volume required for heat pump system stability-actual water volume of the heat pump system.
First calculate the amount of water required for system stability, set it as M1, then M1=QT/(C△T), where Q is the heat pump heating capacity in KW; T is the defrosting time in seconds, and C is the specific heat capacity of water, take 4.187, △T is the maximum allowable drop of water supply temperature, take 3℃.
The actual water volume of the system = the water capacity per meter of the floor heating pipe × the total length of the heat pump system pipe. If the terminal is a radiator, the water capacity of the radiator should also be included.
Take Eurostars heat pump as an example, 150 square meters, equipped with 7HP low-temperature heat pump, heating capacity 20KW, the water required by the system is 20×4×60÷(4.187×3)=382(L).
The actual water capacity of the system: Taking the pipes commonly used in the north of China, the water capacity of pipes is about 0.314L per meter. According to a square meter of about 5 meters, the actual water capacity of the system is about 235L. Therefore, the volume of the buffer water tank required is: 382L-235L=147 (L), and 150L can be used for actual installation.
If you are first time to deal with residential heating and you don’t know how to calculate, you can use 100L and 150L unified configuration, that is, regardless of the size of the heat pump system, the buffer tank is combined with 100L or 150L. These two models are always available, which are sufficient for most projects.