Re: [GBlist] Setback Thermostats, basic question

["malcolm.scott" <malcolm.scott@ntlworld.com>]

----- Original Message -----
From: "Bettina & Steve" <bpearl@rcn.com>
To: <GreenBuilding@crest.org>
Sent: Wednesday, January 02, 2002 11:16 PM
Subject: [GBlist] Setback Thermostats, basic question


Hey-- anybody familiar with thermal/heating system engineering stuff?

I'm trying to get clear about how to set a basic setback thermostat for max
energy efficiency during unoccupied times in the heating season.

We have short periods (36hrs. over holidays and 10 hrs.every night) when the
3,200sq.ft. building is unoccupied.  Normal setting during the occupied
parts of a day is 68F.  Natural gas, forced air (roughly 20,000 BTUs/heating
season, 2,000cu.ft).  Medium+  interior thermal mass (a guess, how and time
to measure?).  Insulated ceilings (R22),  walls (R8, ho boy), 700ft.sq
stormed windows.  Perhaps one+ air turnover/hr.  Normal overnight outside
air temp is about 28F (Philadelphia, PA).

I guess I'm looking for a layman's cover-all answer or direction to do more
research/data building).   (You can tell by the info given, no?).  This
isn't a fancy system that measures outside temps, anticipates, etc.

Do we turn the system down to 40, 50, 60F during unoccupied times?  We've
been using 55 or 60F without any guidance or monitoring...Does a setting
recommendation change when a variable changes, say thermal mass or method of
heating?  Same principles apply during the cooling season, where we use many
more BTUs?

Every minute you have the system off you are saving energy.  The lower you
allow the temperature to fall(or rise) the more energy you are saving.  If
for some reason you can't just use the clock to turn the system off
altogether then use the lowest set back temperature available(or fit an
additional clock which will). The only thing you need to experiment with or
calculate is how long before starting time the system should be turned on
and how long before leaving time the thing can be turned off.
For the water heater, why not just use a clock to heat enough water for the
times when it will be used. The principle is simple. It can only use energy
when it is turned on, and the longer it is off the more will be saved.
Malcolm



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