REMKO WKF 120 Duo - Manual (Page 23)

Heat pump operating mode
Heat pumps can work in various operating modes.
Monovalent
The heat pump is the only heat generator for the
building all year round. This mode is particularly
suitable for heating plants with low inlet tempera-
tures and is primarily used in combination with
brine/water and water/water heat pumps.
Monoenergetic
The heat pump has an electrical heater to handle
peak loads. The heat pump covers the majority of
the required heating capacity. Occasionally, when
it is extremely cold outside, an auxiliary heater
switches on as required in order to support the
heat pump.
Bivalent alternative
The heat pump provides the entire heating energy
down to a predetermined outside temperature. If
the outside temperature drops below this value, a
second heat generator switches on, while the heat
pump switches off. There is a distinction to be
made here between alternative operation with oil-
or gas heat and regenerative operations with
solar energy or wood-fired heating. This mode is
possible for all heat distribution systems.
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
building. Table Ä on page 24 shows the approx-
imate specific heating loads for a number of
building types. 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 comprise the total heating capacity which
the heating system must provide.
To determine the transmission heat requirement,
the surface areas of flooring, external walls, win-
dows, doors and roof are necessary. Likewise nec-
essary is information on the building materials
used, the different heat transfer coefficients (the
so-called U value). Also required are the room tem-
perature and the standard outside temperature,
that is, the lowest outside-temperature on average
that will occur during the year. The equation for
determining the transmission heat requirement is
Q=A x U x (t
R
-t
A
) and must be calculated individu-
ally for all room-enclosing surfaces.
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 standard out-
side temperature. The equation is: Q=V x n x c (t
R
-
t
A
) In accordance with VDI 2067, an appropriate
allowance for water heating per person is: 0,2 kW.
Example layout
For an example layout, a block of flats was
selected with 170 m² of living area and a heat
requirement of 100 W/m². A total of five persons
live in the house. The heat load amount is 17 kW.
Adding a drinking water allowance of 0.2 kW
results in a required heating capacity of 18 kW.
Depending on the power company, an additional
charge must then be made, to factor in disable
periods. The dimensioning and determination of
the bivalence point of the heat pump occurs graph-
ically in the inlet-temperature-specific heating
capacity diagram of the heat pump (in the example
55°C for a radiator heating system). Next, the heat
load for the standard outside temperature (the
lowest temperature of the year locally) and the
heat threshold are marked on the graph. In the
heating capacity diagram (Fig. 23) with the heating
capacity curve the outside-temperature-dependent
heat requirement is entered in simplified form as a
straight connecting line between the heat load and
start of heating. The point where the straight line
intersects with the nominal heating capacity curve
is measured on the x-axis and the temperature for
the bivalence point is read off there (in the
example this is approx. -4°C). The minimum
capacity of the second heat generator is the differ-
ence between heat load and the heat pump's max-
imum heating capacity on these days (in the
example the capacity required to cover the peak
load is approx. 6 kW).
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