Technical data

10 | Project planning manual for heat pumps for heating and domestic hot water preparation | 01.2012 www.dimplex.de
1 Selection and design of heat pumps
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 heat
output of the existing boiler cannot serve as a gauge for the ac-
tual 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 re-
spective national standards (e.g. EN 12831). However, an ap-
proximate estimate can be made on the basis of the existing en-
ergy consumption of the living space to be heated and the
specific heat consumption.
The approximate heat consumption can be determined as fol-
lows:
Calculation for oil:
Calculation for gas:
Simplified calculation:
with:
 QN = heat consumption building
 Ba = annual consumption gas (in kWh) or oil (in l)
 eta = degree of efficiency gas or oil heating
 Bvh = number of full usage hours per year
 Hu = heating value heating oil (in kWh/l)
The number of full usage hours per year depends on the building
type and climate region. The following table shows the number of
full usage hours per year for different building types in accord-
ance with VDI 2067.
Table 1.1: Number of full usage hours per year for different building types
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 thermal 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
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 val-
ues or guidelines for the building's heat consumption is not permitted.
The heat pump can be significantly over- or underdimensioned in this
case.
1.1.2 Determining the required flow temperature
In most oil and gas boiler systems, the thermostat is set to a tem-
perature ranging from 70 °C to 75 °C. As a rule, this high temper-
ature is only required for preparing domestic hot water. Down-
stream regulator systems within the heating system, such as
mixing and thermostat valves, prevent the building from over-
heating. If a heat pump is retrofitted, it is imperative to calculate
the actual flow and return temperatures required, so that the cor-
rect renovation measures can be determined.
There are two ways of doing this.
a) Heat consumption calculation and heat consumption
per room are known.
The output according to the respective flow and return tem-
peratures is listed in the heat output tables for the radiators
(see Table 1.2 on page 11). The room for which the highest
temperature is required determines the maximum flow tem-
perature in the heating system.
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Building type
Full usage hours
(h/a)
Detached house 2,100
Apartment building 2,000
Office building 1,700
Hospital 2,400
School (single-shift operation) 1,100
School (multiple-shift operation) 1,300