1. ENERGY EFFICIENCY. Hopefully everyone reading this accepts that global
warming means we are in danger of handing over to our children a planet that
is more precarious than the one we inherited. Reducing the amount of CO2 we
push into the atmosphere has to be a priority, especially for the energy
guzzling nations of Europe and the USA. All strategies for a healthy indoor
environment need to take this into account.
2. BUILD TIGHT, VENTILATE RIGHT ! Let's accept that in order to have a
controllable ventilation strategy, rather than one dependent on wind
velocities, the building fabric must be enclosed. Walls which allow the
transfer of moisture vapour ("breathing walls") can be of benefit, but not
walls which are full of holes.
3. VENTILATION SYSTEMS. The "best" system will be dependent upon the
building, the climate, and the fuels available. For example, mechanical
whole house ventilation with heat recovery may work out as very energy
efficient in cold climates where fuels are limited. In a mild climate where
natural gas is used for heating, however, the electricity used for mechanical
ventilation may outweigh (in CO2 terms) the savings from heat recovery. We
can calculate these things easily enough if we have to. Sometimes opening a
window will be the most effective stategy.
4. VENTILATION REQUIREMENTS. Hopefully for most of us the outside air will be
clean enough to use without fine filtration. Using HEPA filters and the like
carries an energy penalty because of the work needed to push the air through
such fine filters. The best way to adjust ventilation - in terms of internal
CO2 levels, pollutants, etc, still seems open to some debate, although we
have had a lot of sensible advice (Hal et al.). For any system it's
essential that the building's users understand what the system does and how
they can adjust things to their own needs.
We've also had plenty of good advice on how to select safer building
materials, and materials that we bring into our buildings, so that
ventilation rates can safely be kept lower.
5. RELATIVE HUMIDITY. High levels of RH - over 70% - for sustained periods
will encourage mould growth and over about 55%(?) can allow dust mites to
breed. Other factors obviously also influence both of these potential
problems.) Low levels of RH - .less than 30% - can lead to sore throats,
eye irritation & static electricity shocks.
Somewhere in between we can find our prefered environment, and this may be
diferrent for people (and possibly dust mites !) in differering climates.
Matthew Hill , Leeds Environmental Design Associates
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