# Mitsubishi Electric CAHV-P500YA-HPB Service Handbook Page 35

Hot water heat pump.

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[ II Restrictions ]
5. Minimum and maximum water flow rates
A low flow rate will not only compromise the performance of the unit but also increase the water temperature difference be-
tween the periods when the unit is in operation and when the unit is stopped. A high flow rate will cause the pipes to corrode.
Adjust the circulating flow rate so that the difference between the inlet and outlet temperatures will be between 3 ºC and 5 ºC.
Refer to the table below for the standard, minimum, and maximum flow rates.
Standard, Minimum, and Maximum flow rates
CAHV-P500YA-HPB
The flow rate will be considered appropriate if the difference between the inlet and outlet water temperatures is between 3 ºC
and 5 ºC.
If the temperature difference is less than 3 ºC
Decrease the flow rate.
If the temperature difference is more than 5 ºC
Increase the flow rate. Check the pipes for air pockets, and make sure that the pump has enough capacity to sustain appro-
priate water pressure in a given water circuit.
6. Maintaining the appropriate amount of water in the water circuit.
(1) Amount of water in the water circuit
Shortage of water in the circulating water circuit may shorten the operation time of the unit or cause large fluctuations of water
temperature. It also causes the unit not to operate properly during the defrost cycle. The table below shows the minimum al-
lowable amount of water in the water circuit. If the piping length is too short to secure this amount, install a cushion tank to
ensure that the circuit has enough water in it.
Model
CAHV-P500YA-HPB
(2) Calculating the amount of water in the circuit
The amount of water in the circuit can be obtained using the following formula.
Amount of water in the water circuit = Amount of water in the water piping + Amount of water in the heat source unit + and
Amount of water in the load-side unit
The table below shows the amount of water in the water piping per 1 m
Amount of water in the piping
Internal volume per meter (ℓ/m)
The table below shows the amount of water in the heat-source unit.
Amount of water in the heat-source unit
Amount of water in the heat-source unit (ℓ)
7. Sizes and the material types of the inlet and outlet pipes on the unit
The table below shows the sizes of the inlet and outlet pipes.
Inlet and outlet pipe sizes
CAHV-P500YA-HPB
HWE10060
Standard flow rate (50Hz)
Heating
7.74
Minimum allowable amount of water (ℓ)
360
3/4B (20A)
1B (25A)
0.37
CAHV-P500YA-HPB
Inlet pipe
R1-1/2 female thread pipe <SUS304>
Minimum allowable flow
rate
7.5
Pipe size
1 1/4B (32A) 1 1/2B A(40A)
0.60
0.99
14
R1-1/2 female thread pipe <SUS304>
- 28 -
3
Unit: m
/h
Maximum allowable flow
rate
15.0
2B (50A)
1.36
2.20
Outlet pipe
1 1/2B (65A)
3.62
GB

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