Heat Pump Pipe Sizing
Heat pump pipes need to be larger than boiler pipes because the flow rate is higher for a given output. This will lead to a greater pressure loss through the pipework and fittings. Table 1 for copper pipework and glycol
Table 1 shows the typical capacities of heat pumps and recommended pipe sizes. If the maximum pipe run is exceeded either find a shorter route or increase to the next pipe size. If using plastic pipe of any description consider the larger size since plastic pipe and the fittings have a greater friction factor. The table above assumes an air source heat pump with a 30% mixture of propylene glycol for frost protection down to -13 degC. A ground source system will be just water so the flow rate is slightly less and lower pressure loss therefore possibly smaller pipes (see table 2).
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Table 2 Copper pipework and inhibited water
Calculate the total pressure loss through the system then check it against the available free pressure from the heat pump circulation pump. The free pressure must be greater than the system pressure loss. Example 1:
Example 2:
(1 Bar = 100K Pa = 10m (water used))
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