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D
OMESTIC HOT WATER PRODUCTION
Amicus can produce domestic hot water either as a standalone system or by Pre-heating a gas fired water
heater. It is important that any indirect cylinders used have been designed to work with Air source heat
pumps, standard indirect cylinders will give poor performance and possible nuisance high pressure alarms
with the Amicus unit. Only the solutions shown in this section should be used, further guidance can be
obtained by contacting Lochinvar Ltd
SIZING INDIRECT CYLINDER COILS
Standard Indirect cylinders must not be used with Air Source Heat Pumps due to the sizing of the internal
coil which are sized using typical gas boiler figures. We can calculate the kW output of an indirect coil using
the formulae below:
2
1m
coil kW rating =Specific heat capacity water x flow/return temperature differential x flow rate (l/sec) or:
Kw = 4.18 x flow/return DT x flow rate (typical .33l/sec for gas boiler systems)
4.18 x 20 x .33 =27.58kw
2
A typical 500 litre indirect cylinder requires 29kw to heat the contents in 1 hour, with a 1m
coil within it, the
heat up time would be:
29 x 60/27.58 =64.4 minutes
With a heat pump it is not possible to achieve the supply temperature or work at the large ΔT's associated
with fossil fuel boilers hence the output of a standard indirect coil would be substantially less than that
calculated above. Special, enhanced surface area coils for use with smaller heat pumps (<20kW) and plate
heat exchanger/buffer tank combinations for larger units should be used.
Both options are available from Lochinvar Limited.
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