17
Flow Rates
To achieve good system efficiencies higher flow rates are recommended on the
radiator/ under-floor circuit.
Hot water cylinder heat-up times
Hot water heat up times vary depending on the size of the tank. Typically it will
take about one hour to recover a 150 litre storage tank from cold. This heat up
time is dependent on the size of the hotwater cylinder and the size of the heat
pump connected to it. When heating up the hot water cylinder, try to do so dur-
ing off peak hours. By selecting an appropriate electricity supply offering off peak
economy tariffs. It is recommended to have either one or two hot water heat up
cycles per day, though this is dependent on usage patterns.
These figures are not exact as the starting temperature of the tank as well as the
ambient temperature can vary. They should be treated as guidelines. It should also
be remembered that during winter the mains water entering the house will be
colder and require slightly longer to heat up to the required temperature.
These figures are based on the 8.5kW unit. The heat up times are based on cold
water from the mains heated to 55°C.
Control Strategy
An inverter driven air source heat pump delivers heat in a different manner to a
traditional fossil fuelled heating system. A gas or oil fired system will produce
water at higher flow temperatures and have a large excess capacity in order to
heat the property up relatively quickly. An air source heat pump works most
efficiently when it is producing lower flow temperatures (for space heating be-
tween 35
o
C and 50
o
C depending on the type of emitter i.e. radiators or under-
floor heating).
Due to the low flow temperatures it is necessary and more efficient for the heat
pump to be running constantly when heating is required, this not only maintains a
more consistent indoor temperature but also means that the heat pump will use
considerably less electrical input due to the lower flow temperatures. It is possi-
ble to run the Ecodan like a traditional boiler using a timed control strategy, this
will however result in fluctuating internal temperatures and a higher overall
power consumption meaning increased running costs.
Ecodan required system flow rates
Minimum
Maximum
Flow Rate (l/m)
Flow Rate (l/m)
PUHZ-W50VHA-BS
6.5
14.3
PUHZ-W85VHA-BS
10
25.8
PUHZ-W140VHA-BS
20
40
Ecodan® Model
Tank Size
(litres)
Heat up times
(minutes)
150
52
180
62
210
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