Technical data
www.dimplex.de 01.2012 | Project planning manual for heat pumps for heating and domestic hot water preparation | 15
Selection and design of heat pumps 1.3.4.2
1.3.4 Determining the heat pump output
1.3.4.1 Air-to-water heat pump (mono energy operation)
Air-to-water heat pumps are primarily operated in mono energy
systems. The heat pump should fully meet the heat consumption
down to an outside temperature (bivalence point) of approx.
-5 °C. In the event of very low temperatures and high heat con-
sumption, a second, electrically operated heat generator will be
activated.
In the case of mono energy systems, dimensioning of the heat
pump output has a particularly strong influence on the level of the
investment and the annual heating costs. The higher the heat
pump output, the greater the investment costs of the heat pump
and the lower the annual running costs for heating.
Experience has shown that a heat pump should be selected
which intersects the heating characteristic curve for a limit tem-
perature (bivalence point) of approx. -5 °C.
According to the DIN 4701 T10 standard, this yields a 2% ratio
for the second heat generator (e.g. heating element) when oper-
ated as a bivalent-parallel system.
Fig. 1.2 on page 15 shows the annual characteristic curve of the
outside temperature in Essen, Germany. According to this, there
are less than 10 days in the year with an outside temperature
under -5 °C.
Fig. 1.2: Annual characteristic curve: Number of days on which the outside
temperature is below the specified value
Example for Table 1.7 on page 15:
A bivalence point of -5 °C yields a heat pump proportion of ap-
prox. 98% for a bivalent-parallel (mono energy) mode of opera-
tion.
Table 1.7: Coverage ratio of the heat pump of a mono energy system or a system operated as a bivalent system according to bivalence point and mode of operation
(source: Table 5.3-4 DIN 4701 T10)
1.3.4.2 Design example for an air-to-water heat pump
The heat pump is dimensioned on the basis of the heat con-
sumption of the building in relation to the outside temperature
(simplified as a straight line) in the heat output diagram and the
heat output curve of the heat pump. The building's heat con-
sumption in relation to the outside temperature is entered on the
basis of the selected room temperature (corresponding to the
outside temperature point 1) on the horizontal axis (x-axis) for
the calculated heat output (point 2) for the standard outside tem-
perature according to national standards.
Fig. 1.3: Heat output curves for two air-to-water heat pumps with different
heat outputs for flow temperatures of 35 °C and a building heat con-
sumption in relationship to the outside temperature
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Bivalence point [°C] -10-9-8-7-6-5-4-3-2-1 0 1 2 3 4 5
Coverage ratio [-] for
biv.-paral. operation
1.00 0.99 0.99 0.99 0.99 0.98 0.97 0.96 0.95 0.93 0.90 0.87 0.83 0.77 0.70 0.61
Coverage ratio [-] for
biv.- altern. operation
0.96 0.96 0.95 0.94 0.93 0.91 0.87 0.83 0.78 0.71 0.64 0.55 0.46 0.37 0.28 0.19
Building data:
Mono energy mode of operation
(Heat pump with electric heating element)
Heating system with a maximum
flow temperature of 35 °C
Shut-off time 2 hours
(factor f from Tab. 1.3 on p. 13)
Heat consumption heating 9.0 kW
Heat consumption domestic hot water
preparation
1.0 kW
Calculation:
required heat output of the heat pump
= (heat consumption heating + heat consumption domestic hot
water preparation) x factor f
= (9.0 kW + 1.0 kW) x 1.1 = 11.0 kW
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