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34
ZEB
annual report 2014
The reduced heat loss through the building
skin, the reduction of air leakages and the
use of a mechanical ventilation with heat
recovery (MVHR) in low-energy and passive
house buildings have substantially reduced
or even eliminated problems with too low
temperatures, as experienced in old leaky
buildings throughout history. This improvement
is highly appreciated by the occupants.
However, user surveys as well as simulations
and measurements in residential low-energy
and passive house buildings have revealed
that there is a high degree of oversupply of
unnecessary and even unwanted heat. There
has simply become too much of a good thing.
In old buildings it is common that only some
rooms are heated, they are often only heated
when in use, and the room temperatures
are generally kept at a moderate level. In
contrast, in new residential buildings the
whole building is usually continuously heated
to higher temperatures. Those changed
thermal conditions in dwellings are more or
less consciously chosen and controlled by the
occupants.
However, current building concepts and
commonly used heating and ventilation
systems limit the possibility to have different
temperatures in different parts of the dwelling.
A reduced heat loss through the building skin
will lead to an increased degree of evening
out of the temperature within the dwelling. In
addition, commonly used one-zone MVHR-
systems supply the same temperature to all
rooms and consequently also contribute to a
balancing of the temperature.
Simulations for a bedroom in a row house
with only one exterior wall show that with a
typical factory set point of 20°C for the supply
air from the MVHR, the lowest achievable
room temperature is around 19°C during the
coldest period in winter (Figure 2). Even if
the set point for the supply air temperature
is reduced to 10°C, the lowest achievable
room temperature is nearly 18°C. Besides,
a reduction in the supply air temperature of a
one-zone MVHR will cool down other rooms in
the dwelling and substantially reduce the heat
recovery efficiency.
Other influential factors, such as solar
insolation, commonly higher temperatures in
adjacent bathrooms or an open bedroom door
TOO HOT IN THE BEDROOM?
|
FOR HETT PÅ SOVEROMMET?
If you can’t sleep, don’t count sheep.
Check the supply air temperature!
Magnar Berge (NTNU/HiB)