|
'Passive' Cooling
(Above results are based on measurements
made during the European 'Joule' NatVent Programme. The final report is
published by BRE, UK)
See
also: Sustainable Cooling in Mild Climates
The Problem
Buildings in moderate to mild climates can overheat in Summer. This may
be due to a combination of:
 Poor Glazing
Systems;
Inadequate
Solar Shading;
Excessive
indoor heat gains (e.g. from electrical equipment and lighting)
The Solution
The conventional response is to cool the building by refrigerative air
conditioning. An alternative is to 'passively' cool the building by:
Minimising solar gain (through glazing control, solar shading and coated
windows);
Minimising indoor heat gains (by using energy efficient
appliances, and taking advantage of daylighting);
Cooling the thermal mass of the building at night ('night'
cooling);
For success, all three approaches must usually be
introduced together.
‘Night’ cooling by ventilation is used to lower the temperature of
the thermal mass of the building at night when the outdoor air temperature
is substantially below that of the mid-day air temperature. When correctly
designed and controlled, this enables the daytime peak (dry bulb)
temperature to be reduced (typically by up to 3K) even during extended
periods of hot weather. Latent cooling (dehumidification) does not take
place, therefore the technique is not suitable for high humidity climates
(e.g. above 60% relative humidity).
To accomplish night cooling effectively, ventilation air must be in
direct contact with the thermal mass of the building (i.e. there should be
no insulated coverings, false ceilings or suspended floors etc.).
Comparison between the performance of a well coupled building and a poorly
coupled building is illustrated in the figure above. Good coupling keeps
the indoor mid-day temperature below the outdoor temperature, poor
coupling keeps it above.
Further Information:
Further information is available from:
 NatVent Case
Studies (contact Martin Liddament
for details);
ECBCS Low Energy
Cooling Study Case Study Buildings (Contact Martin
Liddament for details)
|
