Re: [GBlist] Setback Thermostats, basic question

["Robert Jordan" <rwjordan@charter.net>]

I read of a Canadian study that concluded that setback thermostats didn't save any money.  The study said that most people who had manual thermostats turned them down at night or when they were away, so that a programmable one didn't save money compared to what they were already doing.

----- Original Message -----

From: Corwyn

To: JNH2@aol.com

Cc: greenbuilding@crest.org

Sent: Thursday, January 03, 2002 9:16 PM

Subject: Re: [GBlist] Setback Thermostats, basic question

On Wednesday, January 2, 2002, at 10:54 PM, JNH2@aol.com wrote:

We have set-back thermostats (in a residence) that allow for 4 different time/temperature settings during the week (day 1 through day 5) and another set of 4 time/temperature settings for the weekend (Day 5 & 6) 

We have found that in a heating situation a setback of between 5 and 8 degrees works pretty well, and is able to compensate (at least to our perception) in the morning and late afternoon when it is programmed to come back up to a comfort level.

In a cooling situation, 5 degrees seems to be the maximum for a reasonable transition in the morning and afternoon, allowing the building to get warmer than that takes much longer to cool down.

With an entire weekend and a full 10 hours each night, you could rather easily set the t-stat to start ramping up somtime around 5:00am - so that for weekends you could tolerate a much cooler/warmer temperature with several hours to get up to comfortable temperature Monday morning. 

The way to determine just where you want to set the thermosats back to is to start with a reasonable guess (8 degrees, 10 degrees, ?) and using a separate thermometer, check to see on similar weather days how long it takes the occupied spaces to get to a comfortable level.  A good guess would be to set-back 10 degrees and expect the system to take roughly 2 1/2 to 3 hours to compensate.

In my old house I had a programmable thermostat that I loved. It performed all its adjustments based on having the house at the temperature desired at the time set. So it ramped up all by itself, it had a simple adjustment to take the lag time of the system into account.

That said, I felt it important to keep reminding myself, that it didn't save ANY energy, it merely compensated for my laziness, It wasn't doing anything that in theory I couldn't do myself. I still recommend them to everybody though. Especially thr seven day variety. I notice that I took advantage of known variations in my schedule on each day.

Also, don't let anyone tell you that the energy to bring it back up to temperature negates the savings of lowering the temperature. The heat loss of the building is proportional to the difference in temperature between inside and outside.

Hope This Helps,

Corwyn


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Corwyn
corwyn@midcoast.com