Technical data
64 | Project planning manual for heat pumps for heating and domestic hot water preparation | 01.2012 www.dimplex.de
6.1.3 Domestic hot water preparation with heat pumps
6.1.3 Attainable domestic hot water cylinder temperatures
The maximum domestic hot water temperature which can be at-
tained using a heat pump is dependent on:
The heat output of the heat pump
The heat exchanger surface area installed in the cylinder
and
The discharge rate (volume flow) of the circulating pump.
The domestic hot water cylinder must be selected on the basis of
the max. heat output of the heat pump (summer operation) and
the desired cylinder temperature (e.g. 45 °C).
The pressure drops of the cylinder should be taken into consider-
ation when designing the domestic hot water circulating pump.
The heat supplied by the heat pump cannot be transferred if the
maximum domestic hot water temperature (HP maximum) to be
attained using a heat pump is set too high on the controller (also
see the chapter Control and Regulation).
When the maximum permissible pressure in the refrigerating cir-
cuit is reached, the heat pump manager's high pressure safety
program switches off the heat pump automatically, blocking do-
mestic hot water heating for 2 hours.
If the domestic hot water cylinder is equipped with a sensor, the
set domestic hot water temperature (HP maximum new = current
actual temperature in the domestic hot water cylinder – 1 K) is
corrected automatically.
If higher domestic hot water temperatures are required, the water
can be reheated electrically according to need (flange heater in
the domestic hot water cylinder).
NOTE
The domestic hot water temperature (HP maximum) should be set approx.
10 K below the maximum flow temperature of the heat pump.
In mono energy heat pump systems the domestic hot water preparation
takes place exclusively via the flange heating as soon as the heat pump
cannot cover the heat consumption of the building on its own.
Example:
Heat pump with a maximum heat output of 14 kW with a maxi-
mum flow temperature of 55°C
Domestic hot water cylinder - 400 l tank
Volume flow of the domestic hot water circulating pump: 2,0 m
3
/h
This yields a
domestic hot water temperature of: ~47 °C
Fig. 6.3: Design of a domestic hot water cylinder using WWSP 800 as an ex-
ample
6.1.4 Design support for combination and domestic hot water cylinders
The table shows the allocation of domestic hot water circulating
pumps and cylinders to the individual heat pumps with which a
domestic hot water temperature of approx. 45 °C is reached in
operation with 1 compressor (maximum temperatures of the heat
sources: Air: 25 °C, Brine 10 °C, water: 10 °C, maximum pipe
length between heat pump and cylinder: 10 m). The maximum
domestic hot water temperature which can be attained with heat-
pump-only operation is dependent on:
The heat output of the heat pump
The heat exchanger surface area in the cylinder
The volume flow in relation to the pressure drop and the ca-
pacity of the circulating pump.
NOTE
Higher temperatures can be reached by implementing larger heat ex-
changer areas in the cylinder, by increasing the volume flow or by tar-
geted reheating using a heating element (see also Chapt. 6.1.3 on page
64).
NOTE
The design takes place based on the integration set-ups recommended in
this manual and standard boundary conditions.
NOTE
In accordance with Article 3, Para. 3 of the European Pressure Equipment
Directive, buffer and domestic hot water cylinders may not carry a CE la-
bel. The directive stipulates that "pressure equipment and/or assem-
blies... must be designed and manufactured in accordance with the good
engineering practice valid in a member state to guarantee that they can
be used safely."
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