Robert, as you said, bodies and lights make a huge load on a
building. Our Energy Czar (EC) lets the buildings get cold enough
that they typically require a morning warm up before the occupant
load takes over. We have one 2 pipe school that requires a full
conversion to either heat or cool that can be quite troublesome on
those moderate days. We turn all chillers off and dump the
cooling towers as we head into the freezing months. The buildings
can usually be tempered by outside air. The geothermal schools
eliminate this problem and allow partial usage of buildings for
special events and summer school type needs.

I did ask about the setback issues. We had one series of heat
pumps whose open/close valves did not have stops installed. These
machines have a sensor that says if the water is too cold it
prevents the unit from running rather than make ice - this issue
was rectified by installing stops that never allow the valves to
completely close which keeps the water circulating back to the
loop. We now install all systems to run the well field pumps
continuously as we have one that turns off the circulating pumps
if there is no demand anywhere on the system which can allow some
of the loop to reach that same "don't run" temperature. Believe
it or not, the pumps have shut down several times because the
building is that stable. As Robert says, lights and people can
keep a large building quite warm or too warm when the rest of us
need heat. We do continue to have a problem with people wanting
cooling on warm afternoons turning the thermostat down to the
bottom at 55°: the computer limits the units so the 55 never
happens, but the units also don't come up on morning warm-up,
though the rooms seem to recover quickly if the rest of the
building is satisfied. He swears emphatically that no matter what
system is used, intense run time in the mornings uses less energy
than the start/stop cycle of leaving the system at temperature
around the clock. They have put in-line monitors with recording
capability on units set up each way on highly similar usage, run
them for a week, then reversed the study for another week on the
same units. Setback with a substantial run time to recover uses
less energy than maintaining the temperature during non critical
times. The setback needs to be able to protect critical needs as
in not freezing water lines or baking cookies in the attic.


______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)




"Robert Bonomi" wrote in message
...
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.