Technical data
www.dimplex.de 01.2012 | Project planning manual for heat pumps for heating and domestic hot water preparation | 13
Selection and design of heat pumps 1.3.1
1.2 Heat pumps for new systems
1.2.1 Calculating the heat consumption of the building
The maximum hourly heat consumption
h
is calculated accord-
ing to the respective national standards. It is possible to approxi-
mately estimate the heat consumption using the living space A
(m
2
) that is to be heated:
Table 1.3: Estimated specific heat consumption values
1.2.2 Determining the flow temperatures
When designing the heat distribution system of a heat pump
heating system, it should be borne in mind that the required heat
consumption should be assigned on the basis of the lowest pos-
sible flow temperatures, because every 1 °C reduction in the flow
temperature yields a saving in energy consumption of approx.
2.5 %. Extensive heating surfaces, e.g. underfloor heating, are
ideal. The required flow temperature should generally be 55 °C
max. to enable the use of low-temperature heat pumps. If higher
flow temperatures are necessary, medium or high-temperature
heat pumps must be used (Chapt. 1.1.3 on page 12).
1.2.3 Choice of heat source
The decision as to whether air, brine (ground heat collector,
borehole heat exchanger) or water (well system) should be used
as the heat source should be made based on the following fac-
tors.
a) Investment costs
In addition to the costs for the heat pump and the heating
system (radiators and circulation pump), the investment
costs are heavily influenced by the costs of tapping the heat
source.
b) Operating costs
The expected seasonal performance factors of the heat
pump heating system have a large influence on the operat-
ing costs. These are primarily affected by the heat pump
type, the average heat source temperature and the required
heating flow temperatures.
ATTENTION!
When selecting a heat pump the heat consumption of the building must
be calculated according to the country-specific standard (e.g. EN 12831).
The selection of a heat pump based on previous energy consumption
values or guidelines for the building's heat consumption is not permitted.
The heat pump can be significantly over- or underdimensioned in this
case.
NOTE
The seasonal performance factors which can be expected for air-to-water
heat pumps are lower than for water and geothermal systems. However,
the costs for tapping the heat source system are also lower.
1.3 Additional power requirements
1.3.1 Utility company shut-off times
Most utility companies offer special agreements with a lower
electricity tariff if heat pumps have been installed. According to
the German Federal Tariff Ordinance, the utility company may
offer such an agreement if it is able to switch off and block heat
pumps at times of peak demand in the supply network.
The heat pump is then no longer available for heating the house
during these shut-off times. Therefore, surplus energy must be
produced during the periods in which the heat pump is not avail-
able for use. Hence, the heat pump should be overdimensioned
to allow for this.
Utility company shut-off times normally last up to 4 hours a day,
which must be allowed for with a factor of 1.2.
Dimensioning
The calculated heat consumption values for heating and domes-
tic hot water preparation should be added together. Unless a
second heat generator is additionally used during the shut-off
time, the sum of the heat consumption values must be multiplied
by the dimensioning factor f:
Basis of the calculation:
Table 1.4: Dimensioning factor f for taking shut-off times into consideration
The existing heat storage capacity of solidly built houses, partic-
ularly those with underfloor heating, is normally sufficient to also
bridge longer shut-off times with only a small loss of comfort, so
that it is not necessary to use a second heat generator (e.g.
boiler). However, an increase in output of the heat pump is nec-
essary because of the need for reheating the storage mass.
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= 0.03 kW/m
2
Low-energy house
= 0.05 kW/m
2
According to thermal insulation ordinance 95
and/or the EnEV minimum insulation stand-
ard
= 0.08 kW/m
2
For a house with normal thermal insulation
(houses built from approx. 1980 onwards)
= 0.12 kW/m
2
For older walls without special thermal insula-
tion
T
T
T
T
Blocking time (total) Dimensioning factor
2 h 1.1
4 h 1.2
6 h 1.3
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