Positive pressure ventilation systems

This is a response to Janine Wardius' query about positive pressure
as a way of preventing infiltration of air from a vestibule.  In the
design of most environmental control systems in museums, a slight
positive pressure is usually called for.  This is to prevent
infiltration of uncontrolled air through cracks and when doors are
opened and closed as visitors enter. Whether the proposed system
will do what is called for--that is, act as a kind of air curtain to
prevent the infiltration of unconditioned (and polluted) air through
a large opening, is difficult to say.  What will happen is the
expenditure of (I assume) scarce resources to condition the make-up
air that will be required to create the pressurization.  This
make-up air will have to be humidified in winter, dehumidified in
summer, heated and cooled, and filtered all of the time.  Most
successful HVAC systems in museums are designed to use as little
make-up air as possible, since the extra conditioning is so costly,
especially when added to the already expensive fuel costs of such
systems.  Clearly, keeping doors closed (perhaps glass ones would
make it more acceptable) is a cheaper more foolproof strategy.

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                  Conservation DistList Instance 12:12
                   Distributed: Friday, July 24, 1998
                       Message Id: cdl-12-12-003
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