Layout
A precise calculation of the building’s heating load
according to EN 12831 is required for the design
and dimensioning of a heating system. However,
approximate requirements can be determined
based on the year of construction and the type of
approximate specific heating load for a few types
of building. The required heating system output
can be calculated by multiplying the area to be
heated with the given values.
For a precise calculation, various factors must be
considered. The transmission heat requirement,
the infiltration heat loss and an allowance for water
heating and blocking times comprise the total
heating capacity which the heating system must
provide.
The total area of the floor surfaces, exterior wall
windows, doors and roofing is required in order to
determine the transmission heat requirement. In
addition, information about the materials used in
the building is required, as well as about the dif-
ferent thermal transmission coefficients (known as
the K value). Also required are the room tempera-
ture and the standard outside temperature, that is,
the lowest outside temperature on average that will
occur during the year. The equation for deter-
mining the thermal transmission requirement is
Q=A x U x (t
R
-t
A
) and must be calculated for all
enclosed room floor areas.
The infiltration heat requirement takes into consid-
eration how often the heated room air is
exchanged for cold external air. The room volume
(V), the air exchange frequency (n) and the spe-
cific heat capacity (c) of the air is also required in
addition to the room temperature and average low
temperature. The equation is: Q=V x n x c (t
R
-t
A
)
An approximate addition for the preparation of
domestic water per person amounts in acc. with
VDI 2067: 0.2 kW.
Design example
n
By way of a design example, a residential
home with a living area of 150 m
2
and a
heating requirement of approx. 35 W/m
2
was
selected. A total of five persons live in the
house. The heat load amount to 5.3 kW.
Adding a drinking water allowance of 0.2 kW
results in a required heating capacity of 6.3
kW. Depending on the power company, an
additional charge must then be made in order
to factor in any service time-out periods that
may apply. The rating and determination of the
heat pump’s balance-point temperature derives
graphically from the heat pump’s inlet tempera-
ture specific heat-output diagram (in this
example 35 °C for underfloor heating). Next,
the heat load for the standard outdoor temper-
ature (the lowest temperature of the year
locally) and the heat threshold are marked on
the graph. The outside-temperature-dependent
heating requirement, (Fig. 9) simplified here as
a straight-line relationship between heat-load
and the start of the heating season, is recorded
in the graph of heat-load curves. The intersec-
tion of the two straight lines with the rated heat-
load curve is plotted on the X axis, where the
balance-point temperature is read (in this
example approx. -3 °C). The minimum perform-
ance of the 2nd heat source is the difference
between heat load and the heat pump’s max-
imum heating capacity on these days (in this
example, the required power required to cover
peak load requirements is approx. 3 kW).
Building type
Specific heating capacity
in W/m
2
Passive energy house
10
Low-energy house built in 2002
40
According to energy conservation order regarding heat insulation 1995
60
Modern building constructed around 1984
80
Partially-renovated old building constructed pre-1977
100
Non-renovated old building constructed pre-1977
200
REMKO series WSP
22