Installation manual

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1 Selection and Design of Heat Pumps
1.1 Design of Existing Heating Systems - Heat Pumps for the Renovation
Market
1.1.1 Heat consumption of the building to be heated
In the case of existing heating systems, the heat consumption of
the building to be heated must be recalculated because the
existing boiler cannot serve as a gauge for the actual heat
consumption. Boilers are - as a rule - overdimensioned and
therefore produce a heat pump output which is too large. The
actual heat consumption is calculated according to the
respective national standards (e.g. EN 12831). However, an
approximate estimate can be made on the basis of the existing
energy consumption of the living space to be heated and the
specific heat demand.
The specific heat consumption for detached and semi-detached
homes built between 1980 and 1994 is around 80 W/m
2
. For
homes built before 1980 in which no additional heat-insulation
measures have been carried out, it is between 100 W/m
2
and
120 W/m
2
. In existing systems, the actual state of the system
must be taken into consideration.
NOTE
In exceptional cases in which the actual consumption deviates widely
from the norm, approximate estimates can also deviate greatly from exact
calculations carried out according to the accepted standards.
1.1.2 Determining the required flow temperature
In most oil and gas boiler systems the thermostat is set to a
temperature ranging from 70 °C to 75 °C. As a rule, this high
temperature is only required for preparing domestic hot water.
Downstream regulator systems within the heating system such
as mixing and thermostat valves prevent the building from
overheating. If a heat pump is retrofitted, it is imperative to
calculate the actual flow and return temperatures required so that
the correct renovation measures can be determined.
There are two ways of doing this.
a) The heat consumption calculation and the heat
consumption of each room are known.
The output according to the respective flow and return
temperatures is listed in the heat output tables for the
radiators (see Table 1.1 on p. 10). The room for which the
highest temperature is required determines the maximum
flow temperature in the heating system.
Fig. 1.1: Heat output of radiator elements (at a room temperature of t
i
=20 °C, according to DIN 4703)
b) Experimental determination during the heating period
(see Fig. 1.2 on p. 11)
The flow and return temperatures are continually reduced
during the heating period with the thermostat valves fully
open until a room temperature of approx. 20-22 °C is
reached. Once the desired room temperature has been
reached, the actual flow and return temperatures plus the
external temperature are noted and entered in the diagram
shown below. The actual required temperature level (low,
medium, or high temperature) can be read from the entered
value using this diagram.
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Cast iron radiators
Height mm 980 580 430 280
Depth mm 70 160 220 110 160 220 160 220 250
Heat output per element in W,
at mean water temperature T
m
50 °C 45 83 106 37 51 66 38 50 37
60 °C 67 120 153 54 74 97 55 71 55
70 °C 90 162 206 74 99 129 75 96 74
80 °C 111 204 260 92 126 162 93 122 92
Steel radiators
Height mm 1000 600 450 300
Depth mm 110 160 220 110 160 220 160 220 250
Heat output per element in W, at mean
water temperature T
m
50 °C 50 64 84 30 41 52 30 41 32
60 °C 71 95 120 42 58 75 44 58 45
70 °C 96 127 162 56 77 102 59 77 61
80 °C 122 157 204 73 99 128 74 99 77