(3) Household air source heat pump storage tank
In order to avoid frequent startup of the compressor and increase the thermal stability of the system, we should check whether the water capacity of the system can meet the thermal stability requirements of the system. That is, when the energy stored in the system (water) is not sufficient to maintain the water temperature fluctuation requirement during a short shutdown (such as defrosting) (no more than 5 °C in summer and no more than 3 °C in winter), an energy storage tank should be provided. However, for the traditional wet backfill floor heating, the ground has a large heat storage capacity, which is enough to resist the fluctuation of the water temperature, and there is no storage tank.
1. System water capacity calculation
The water volume M1 of the system is the sum of the pipe water volume and the equipment water volume, ie
M1=Mg+Ms
In the formula, Mg is the pipe water volume, kg;
MS - is the sum of the water volume of the equipment, kg;
Pipeline water volume is calculated as follows
Mg=∑qi×li
Where qi is the volume of water per meter of pipe diameter, kg/m;
Li——the length of a pipe with a diameter, m;
2. System thermal stability requirements
The requirements for the thermal stability of the household centralized air conditioning system are: the comfort of the indoor environment, the life of the mainframe, the cost of the system and the possibility of project implementation.
1) During summer operation, the host stops for 10 minutes, and the water supply temperature is allowed to rise no more than 5 °C;
2) When the main engine defrost time is 3 min during winter operation, the water supply temperature is allowed to decrease by no more than 3 °C.
3. Minimum water volume required by the system
According to the heat balance and thermal stability requirements, the minimum water capacity of the winter and summer systems can be calculated separately as follows:
M2=(Q×t.)/(c×Δt)
Where: Q - cooling or heat supply for the end equipment, kW
t. ——Time required for thermal stability (summer t.=10×60s, winter t.=3×60s)
C——the constant pressure specific heat capacity of water, kj/(kg.K)
△t——the required value of water temperature fluctuation (summer Δt=5°C, winter △=3°C)
Among the calculation results of the system water volume in winter and summer, the larger value is the required value of the water volume of the air conditioning system. If M1 < M2, the water pipe diameter should be enlarged and the water capacity should be recalculated until the requirements are met or an energy storage tank is added.
(4) Storage tanks common sense
The storage tank can be divided into open and closed tanks according to whether it is under pressure. Both tanks can be used. Household air source heat pump heating units use 50~200L closed water tanks. The number of closed water tank openings is related to the system form, and generally includes heat pump side inlet and outlet water, end side inlet and outlet water, drain hole, exhaust hole, water supply constant pressure hole, and temperature control probe. It is best to supplement the soft water that has been softened and deaerated. The connection between the two types of water tanks is shown in the following figure (the way in which the first type of water tank is used in the household type)
