In article , DanG wrote:
We are running multiple schools on ground source heat pumps. Each
building has a single loop with individual Trane heat pumps
running in each classroom tapped onto that loop. There is NO
auxiliary heat. There are NO heat strips. Our Energy Czar
believes in night set backs and holding temperatures at minimums
until someone gripes. The systems are computerized to central
control and the units can only be changed from the central
location other than a small allowance at the thermostats.

Each building, or even portions of buildings, have different
thermal mass/draft and air leakage issues/poor glazing/etc that
each requires its own start up time. Some take 2 hours, some
almost 4 hours if they have been allowed to get too far out of
design or conditions are extreme. The water loop is circulated
full time through the well field, but the compressors at each heat
pump function by thermostat. The buildings have become so much
easier to control that we continue to install these systems as
money permits. The buildings are so much more stable that we tend
to ignore old fashioned insulation/draft/weatherstrip conditions -
perhaps we will get back to them as energy costs continue to
spiral.

Our HVAC technicians would prefer just letting the systems run
full time and maintain a steady temperature, especially when
equipment is new just to run it through its paces while under
warranty. The Energy Czar tends to win. I will try to remember
to ask tomorrow about the whys.

A 'medium-insulated' school building full of people doesn't need _any_
additional heat source until the outside temperature gets below about
-20F.

Look up how much heat an 'at rest' human body gives off, and multiply by
the 25-30 bodies preset in the average classroom.

Getting the heat _out_ of the building is the issue.

At 'above zero' temperatures, it's _common_ to be venting hot air outside
and pulling in cold outside air for 'make-up'.

Not infrequently, the chillers will be running, in addition.