Z E M C H 2 0 1 2 I n t e r n a t i o n a l C o n f e r e n c e
162
0
= − ln(( − )/( − )
where:
is the final temperature of equilibrium between the building and the environment,
and it was supposed to be equal to the average external temperature of the
considered period,
is the instantaneous temperature at the time ,
is the initial temperature of the building, when the heating system of the building
was switched off.
For the monitored data, the result of this equation was equal to 100 hours and for the
model the time constant resulted of nearly 70 hours.
This second value is more similar to that one calculated during the design stage using
the following formula:
0
=
where:
is the total thermal capacity of the building,
is the total thermal losses coefficient.
Indeed, in this way the result was equal to 58 hours with the same values of thermal
capacity and thermal losses coefficient also used for the model.
There is an evident similarity between these two results, which are both calculated
without taking into account the presence of internal thermal masses, such as partitions
and furniture. This confirms the hypothesis made comparing the real behavior of the
home with its simulation (Graph3 and Graph4).
Once validated the model with all the considerations above, it is possible to affirm that
the calculated net heating and cooling needs of the building, which are respectively 20
kWh/m
2
year and 12 kWh/m
2
year, can be reasonable and they could be even lower than
expected thanks to the higher thermal mass contribution.
It is important to underline that this building is not provided of a mechanical ventilation
plant with heat recovery. Therefore, the calculated energy demand is very low and the
possibility to implement such kind of system would give greater energy results, but at the
same time it would affect the concept of bioclimatic architecture of the building.
Anyway, with this current configuration, all thermal loads can be totally covered by the
renewable energy produced onsite by solar collectors and PV panels.
Considering the energy efficiency of the geothermal heat pump in both heating and
cooling mode, 14 MWh are still left and they can be used for domestic electric energy
needs and the left over can be sold to the grid.
Another analysis was made to check the effective contribute of the sunspace to reduce
net heating energy consumption. For this reason, average day net heating power for the
living space with and
without sunspace
ware compared (Graph5) and the green house
contribute could be truly appreciated, reducing the net heating need of the building of 4
kWh/m
2
year.
One last performed analysis was related to the possibility to further simplify the energy
model, unifying the living space zone with the laundry and the office, in order to have a
model composed of only
two thermal zones: the house and the sunspace
.
In this model standard ventilation rates and standard internal gains were used and the
calculated net heating and cooling needs were respectively equal to 19 and 10
kWh/m
2
year.
Since the small dimension of the office and the laundry, this model could be used to
assess the building energy needs and for heating and cooling plant sizing, but because
