When choosing a water pump in a solar hot water system, follow the following principles:
①In the solar hot water system, a pump with a lower power should be selected under the requirements of head and flow;
②In the forced circulation system, hot water should be used when the water temperature is ≥50℃
③The pump and the heat transfer working fluid should have good compatibility;
④When selecting the pump, pay attention to the pipe diameter and power supply selection (220V or 380V).
The flow and head of the water pump should be determined according to the flow pressure required by the water supply system. Check the pump performance table (working curve) from the flow and head to determine its model. According to the role of the water pump in the system, it can be divided into heat collection circulating pump, inter-tank circulating pump, make-up pump, feed water pump (or booster pump), and pipeline circulating pump. Therefore, the water pump must have water replenishment, circulation, and pressurization.
Circulation pump selection: heat collection circulation pump needs to use hot water pump. (>100℃)
Determination of the parameters of the heat collection circulating pump:
Flow determination
Due to the uncertainty of the amount of solar radiation, the heat collection circulation flow rate of the header hot water system cannot be accurately calculated. Generally, the flow rate of the collector per square meter is 36~72L/h. (The national standard requires the flow rate of the collector per square meter to be 0.01L/s~0.02L/s). We generally set a value of 50L/h in our design, and 70L/h can be used in areas with good solar radiation such as Tibet.
Determination of head
Hb≡H1+H2+H3-H0
In the formula: Hb——pump head m
H1——The height difference between the introduction pipe and the most unfavorable point m
H2——Calculate the total head loss of the pipeline, m
H3——The outflow head of the most unfavorable point distribution point m
HO—the minimum pressure provided by the water supply system, m.
After determining the flow rate of the solar collector system, the resistance loss along the path and the local resistance loss of the branch can be calculated for the specific pipeline, that is, the pipeline pressure drop. In the combined header system, if the number of units in series is 6 single-layer collectors, the pipe diameter is configured according to the standard, and the water pump selection is appropriate, the pipe flow resistance of the hot water system can be selected as 0.03 meters water column/meter pipe.
Generally, there are three situations:
⑴The heat collector and the water tank are placed on the same plane, and the water pump is selected as the highest point of the heat collector plus head loss;
(2) The water tank is higher than the collector, and the head provided by the pump can overcome the flow resistance of the pipeline. It does not need too much head to avoid the collector from being too pressured and leaking. The maximum pressure on the collector should not exceed 10 Meter water column, that is, the sum of the height difference between the water tank and the collector and the head of the water pump shall not be greater than 10 meters;
(3) The heat collector is higher than the water tank, and the pump lift takes the static height of the highest point of the water tank and the heat collector plus the head loss.
Selection of pipeline circulating pump
Timed circulation is a circulation method in which the cold water in the pipe network is withdrawn and supplemented with hot water before the hot water is supplied every day
Qb≥(2~4)V
Hb≥hp+hx+hj
Qb——Circulating water pump flow (L/h)
∨——Water volume of circulating pipe network (L)
Hb——Circulating water pump head (mmH2O)
Hp-head loss of circulating flow through water distribution pipeline (mmH2O)
Hx-head loss of circulating flow through the return line (mmH2O)
H——head loss of heating equipment
The circulating pump is installed on the bypass of the water supply pipeline, and the head takes the total loss along the supply and return pipeline.
