Technical data
www.dimplex.de 01.2012 | Project planning manual for heat pumps for heating and domestic hot water preparation | 63
Domestic hot water preparation with heat pumps 6.1.2
Safety valve
A tested and non-closing safety valve should be installed where
the cylinder is connected to the system. No constrictions, e.g. dirt
traps, should be installed between the cylinder and the safety
valve.
Water should be able to flow (drip) out of the safety valve when
the cylinder is being heated up to compensate for the expansion
of the water and to prevent a severe build-up in pressure. The
safety valve overflow pipe must flow freely into a sewage system
without any constrictions. The safety valve should be mounted in
an easily accessible and observable location so that it can be
vented during operation of the system. A sign should be fixed on
the valve itself or in its vicinity with the following inscription: "Wa-
ter may be discharged from the air outlet pipe during heating! Do
not close!."
Use only spring-loaded diaphragm safety valves that have been
tested.
The air outlet pipe should have at least the same cross section as
the safety valve outlet. If it is necessary for the air outlet circuit to
have more than two bends or if it is more than 2 m in length, an
air outlet pipe in the next largest nominal size should be selected.
It is not permissible for the air outlet circuit to have more than
three bends or to be more than 4 m in length. The cross section
of the outlet pipe located downstream from the collecting hopper
must be at least twice the size of the cross section of the valve in-
let. The safety valve must be adjusted so that the permissible op-
erating overpressure of 10 bar is not exceeded.
Check valve, test valve
A check valve (return inhibitor) must be installed to prevent the
heated water from flowing back into the cold water pipe. Its func-
tion can be tested by closing the first isolating valve in the direc-
tion of flow and opening the test valve. Only the water contained
in the short piece of pipe should be discharged.
Isolating valves
As illustrated in Fig. 6.2 on page 63, isolating valves are to be
installed on the cylinder in both the cold and domestic hot water
pipes as well as in the heating water flow and return.
Fig. 6.2: Water pipe connections
Pressure drops
The pressure drops of the internal heat exchanger should be
taken into consideration when dimensioning the charge pump for
the domestic hot water cylinder.
Temperature settings for domestic hot water
preparation with the heat pump for heating
purposes
Low-temperature heat pumps have a max. flow temperature of
55 °C. This temperature must not be exceeded during the prep-
aration of domestic hot water in order to prevent the heat pump
from being switched off by the high pressure switch. The temper-
ature setting of the controller should, therefore, be below the
maximum attainable cylinder temperature.
The maximum attainable cylinder temperature is dependent on
the output of the installed heat pump and the amount of heating
water flowing through the heat exchanger. The maximum attain-
able domestic hot water temperature for heat pumps for heating
purposes is calculated according to Chapt. 6.1.3 on page 64. It
should also be taken into consideration that the thermal energy
stored in the heat exchanger will cause a further reheating of ap-
prox. 3 K. The set temperature can be 2 to 3 K lower than the de-
sired domestic hot water temperature when preparing domestic
hot water with the heat pump.
Legend
1) Isolating valve
2) Pressure reducing valve
3) Test valve
4) Return inhibitor
5) Pressure gauge connecting stubs
6) Drain valve
7) Safety valve
8) Circulation pump
9) Outlet
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