Technical data

10
4.3 Radiators. Space heating only
The following section includes typical schematics of how a heat pump can be connected. Only the load
side is shown i.e. the heating distribution system. It is important to note that the schematics are only
general arrangements and hence do not illustrate all required valves or fittings. They are only a guide and
should not be used as full installation plans.
When operated with radiators to avoid short circulating problems, one bypass radiator should be left
‘open’, i.e. any TRV is removed. This radiator can be positioned in areas such as halls or bathrooms.
Vent-Axia would always recommend fitting an expansion vessel on the heating distribution circuit.
4.4 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 50
o
C.
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 maximum DHW temperature that the heat pump can achieve will be approximately 50-55
o
C. In
summer, it could be higher, due to the warmer ground conditions. If 65
o
C is required all year round, it is
recommended that an immersion heater is linked to a second channel on the DHW timeclock and this is
Fig 4 Heat Pump with
Radiators Schematic
Vent-Axia Supply
Expansion vessel
Radiator with TRV
Bypass Radiator
Heat Pump
Radiator with TRV
Return
Flow