Explanation (idealized graph - above): as the
building performance goes
from terrible/poor (floor surface flux > 30 Btu/hr/sf) to terrific/high (floor
surface flux <10 Btu/hr/sf) the
MRT approaches the conditions of a hypothetical perfect
enclosure. Another way of saying this is the further one moves
away from the hypothetical perfect enclosure the lower the MRT
in winter and higher the MRT in summer and thus the greater the
discomfort. When it comes to calculating fluid temperatures for
heating and cooling systems the
closer one moves toward the hypothetical perfect enclosure (see
operative temperature) the
lower the fluid temperatures in winter and higher the fluid
temperatures in summer and thus the greater the system
Transitional and terrific buildings
enable maximum efficiencies from heating and cooling appliances
like boilers, heat pumps, chillers and solar systems due to the
necessarily lower fluid temperatures in heating and higher fluid
temperatures in cooling.
Message: building enclosures,
HVAC efficiencies and
thermal comfort are not exclusive items unto themselves - they
are in fact one and the same.
Above slide: from our course on building
science for cold climates, effects of insulation on thermal
bridging and the mean radiant temperature. You can
excessively feed a mechanical system fuel and power (calories)
to compensate for a bad building or you can build a good
building and reduce the calorie input.
Insulation, caulking and
good choices in
windows go a long way in solving energy problems
plus these "three amigos" have no moving parts, will never need a
technician and will last longer than the mechanical systems.
See overview of
housing performance categories in North America.