Section 5: Domestic Hot WaterPage 18
5.1 Temperature Control
If a DHW demand is made, the heat pump will continue to provide
space heating for a minimum period of 15 minutes (parameter 3122
- refer to Table 5-1). If space heating is already being demanded and
has been on for this minimum period, then the heat pump will change
over to prioritise DHW.
In either case, once DHW is being provided, the flow temperature
will target 60°C, irrespective of the space heating target temperature.
Also note that there is no weather compensation control when in DHW
mode.
The time limit for DHW can be set using parameter 3121. The default
setting is 60 minutes but you may want to increase or decrease this
time period. After this time period has been reached, the heat pump
will default back to the original demand that was in place prior to the
DHW demand or to a stand by state if the change is demand state
occurred during the DHW demand.
If the unit times out on parameter 3121, remember the motorised valve
of the DHW circuit will remain open as it is controlled by the cylinder
thermostat and not the heat pump and will not heat up to the correct
temperature when using the space heating flow temperature. It is
also possible that the cylinder could be robbed of heat to the space
heating circuit if the stored water is hotter than the flow temperature to
the space heating circuit.
If the motorised valve for space heating is open during DHW demand,
the 60°C flow temperature will also enter the space heating circuit,
increasing the recovery time of the cylinder.
To minimise this high temperature period and higher than normal
running costs, ensure that space heating and DHW demand times to
not occur simultaneously.
5 Domestic Hot Water
Table 5-1: DHW and space heating parameters
Level
Parameter
Function description
Display and input value
Remarks
Group Code Default Min. Max. Unit
I 31 11 DHW comfort set temperature 50.0 40.0 60.0 0.5°C
I 31 21 Maximum time for DHW request 60 0 900 1 min
I 31 22 Minimum time for space heating 15 0 900 1 min
For details of how to access the parameter settings, refer to Section 9.3.
5.2 Heat Pump Cylinders
As the water temperature from the heat pump is lower than from a
traditional system using a boiler, a much larger coil is required inside
the cylinder to transfer the heat efficiently.
Grant UK has developed a 200 litre high-efficiency cylinder (Band A)
for use with a combination heat pump. Other Band B and C cylinders
are available but consideration should be given to system efficiency.
In order to ensure that a minimum of at least 8K temperature
difference is maintained between cylinder flow and return, the correct
Grant UK heat pump cylinder must be selected to match the heat
pump output.
Failure to use the correct cylinder can result in a reduced heat transfer
in the cylinder and a lower temperature differential.
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