Industrialised, Integrated, Intelligent sustainable Construction - I3con

SUSTAINABLE CONSTRUCTION HANDBOOK 2
Night ventilation is only beneficial if the PCM plates have absorbed so much thermal energy during
the day that they have (nearly) heated up past the phase change and are unable to cool during the next
day. In the simulation model this means that if the indoor temperature exceeds 22°C, the PCM has
most likely accumulated enough heat to warrant night ventilation. In addition, the model requires the
outdoor temperature be at least two degrees lower than the indoor temperature to prevent unnecessary
energy consumption by the fans that force the airflow; a smaller difference has negligible influence on
the efficiency of night cooling.
Night heating
In the Netherlands, the average temperature throughout the year is approximately 10°C, while a
comfortable indoor temperature is generally required to be at least 20°C. This suggests that, especially
in winter, additional heating of the PCM is necessary to enable it to stay in phase change stage and
utilise its latent heat storage to condition the incoming ventilation air.
The heating of the PCM plates can be done through:
a. Electric heating foil or strips that heat up when an electric current is applied to them, or
b. through a Peltier element (Thermal electric heating).
Both are used to regenerate the PCM. The heating foil however is applied directly to the PCM plates
and heats the PCM directly through conduction, while the Peltier element is connected to the fresh air
supply, heating the air which in turn heats the PCM plates through convective heat transfer.
Because of the buffering capabilities of PCM, it is possible to heat the PCM during the night, using
cheaper night electricity and reducing peak energy demands during the day, especially in the morning.
The PCM will be heated during the night when the indoor temperature drops below 20°C. This
temperature indicates that the PCM is no longer able to heat the air to such temperatures that a
comfortable indoor climate is created, and therefore requires night heating.
Of course, this is in a simulated environment, where the phase change and thermal behaviour of the
PCM is uniform and constant. Testing in a controlled environment using commercially available PCM
plates is necessary to validate the outcome of the simulations.
Energy consumption
Two processes consume energy in the CAS: the fans that drive the ventilation, and (potential) heating.
The power consumption by the two fans would be (two fans drawing 15W for 12 hours a day, six
days a week) approximately 112 kWh per year. If two efficient photovoltaic panels would be attached
to the façade with a total of 1.26 m 2 of active surface, the yield in the Netherlands could be
approximately 123 kWh per year [3], assuming an 80° angle placement and southern orientation of
the panels. This means the total energy consumption of the fans could be offset using photovoltaic
panels on the façade, leaving only energy required for additional heating.
Windows and shading
The façade is fitted with manually openable windows that enable additional natural ventilation on top
of the mechanically supplied fresh air from the PCM unit.
Although the operation of the windows is user dependent, the influence of the additional ventilation is
studied in the simulation model. Windows are assumed to be opened when the indoor temperature
exceeds 24°C and closed when the outdoor temperature drops below 23°C. This only applies when the
indoor temperature is at least the same as, or higher than, the outdoor temperature. The influence of
open windows is simulated as a (conservatively estimated) increase in the ventilation rate of 0.5 per
hour.
The U-value of the façade is supposed to be equal to the best insulating glass used in the design,
taking the large amount of glass of the façade into account. This U-value is supposed to be 1.0
116