Evo Heat Pump Manual Version 5
Page 16 of 84
4.5.1 Type of DHW Tank
The larger size the coil within the tank, the better the heat transfer area and hence the better the DHW
performance will be.(Refer to table 3.2). Please ensure that the tank is suitable for the water supply other-
wise the warranty may become void.
4.5.2 DHW Tank Size
The tank will need to be carefully sized to meet the DHW demand (including showers, baths, taps, etc),
based on the number of occupants and should have an acceptable recovery rate. Due to the lower DHW
temperature achieved by the heat pump, a tank 30% larger than normal is recommended. This is due to
the higher demand on the tank, as less cold water is used at the point of use to mix the lower temperature
DHW to an acceptable temperature.
4.5.3 Immersion Heater
Although not required by Building Regulations, it is generally advised that to provide legionella protection
the tank is raised to about 65
o
C at least once a week. To provide this we would recommend that a 3 kW
electric immersion heater is fitted to the bottom of the tank, and the EVO controller programmed to
provide immersion control. If DHW is required higher than 60
o
C then it is advisable that the immersion
heater is programmed to operate for a period following the heat pump operation period to raise the
temperature. This avoids the immersion heater taking all of the load.
4.5.4 Three Port Diverting Valve
If the DHW option is ordered, a 3 port diverting valve
(‘
W
’
plan) is provided by Kensa and is used to divert
the flow when the timeclock calls for DHW production from space heating to the DHW tank. The valve
’
s
electrical connections are connected to the heat pump
’
s internal wiring. Please note connection
‘
A
’
is
DHW and
’
B
’
is space heating.
4.5 Domestic Hot Water (DHW) —Schematic
The DHW option needs to be specified at time of ordering.
Warning
-
when a heat pump is used for heating domestic hot water, it may not get the water hot enough
to kill the dangerous
Legionella that can breed in hot water cylinders. Alternative arrangements should
therefore be made to ensure the cylinder is pasteurised regularly.
Under normal conditions the heat pump will provide heat for the space heating distribution system at its
design temperature (typically 35
o
C for underfloor and 45
-
50
o
C for radiators).
When the DHW time clock calls for production of DHW, the three
-
port valve diverts the flow from the
heating distribution circuit into the indirect coil. The temperature of the water from the heat pump is
raised to approximately 63
o
C. The controller indicates when DHW production is operational.
When the DHW production time period ends, the three port valve switches back to the underfloor
distribution and the temperature drops back to its space heating design temperature. The heat pump then
reverts to space heating mode or switches off if no zones are calling for heat. The heat pump will not
re
-
enter into DHW mode until 2 hours has passed. This time period can be adjusted via the controller if
required.
The maximum DHW temperature that the heat pump can achieve at the cylinder will be approximately
60
o
C. If 65
o
C is required all year round, it is recommended that an immersion heater is linked to Evo and
the Evo is programmed to operate the immersion heater for a period immediately following the DHW
production. This means that the majority of the heating load for the DHW is produced at a lower cost
using the heat pump, as opposed to using only the direct immersion heater.
The EVO can be programmed to raise the temperature to 65
o
C once a week to provide pasteurisation.
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