Programmable Thermostats Fact or Fiction - Contractor Talk - Professional Construction and Remodeling Forum

woodmagman · 11-24-2007, 09:58 PM

Tell me I am wrong, in order to bring mass to a constant temperature, energy is used. To keep that mass as a constant temperature, bursts of energy are required. If I add insulation to the perimeter of this mass do I not use less energy to maintain that mass. So then if I let that mass give up all its stored energy, and then if I reheat the mass to a constant temperature again would I not be using more energy then if I had just maintained it all along…

**Teetorbilt** · 11-24-2007, 10:02 PM

Time would be the definitive factor.

**Leo G** · 11-24-2007, 10:16 PM

When you heat up a room you are trying to heat the air in the room. But because the air is touching 6 walls you are also heating the walls too. The thermal mass of the air is low and the thermal mass of the walls are higher. The higher the thermal mass the more energy you need to make to change the temperature. When you insulate the walls you are isolating it from the air. It will still heat the walls but to a lesser degree because of the properties of the insulation. If you set your thermostat to 70* and leave it there you will come into an equilibrium when, after a time all of the surroundings will be at or close to 70*. When you lower the thermostat to 60* the walls will give off heat because the mass of the objects in the room have stored it. After they have given off the heat and come back into equilibrium at 60* and you change the thermostat back to 70* you now have to reheat everything in the room, not just the air. It would be more efficient to keep things at the same temperature all the time but then you have to put the cost of fuel into the equation. After this is put into the equation it is more equitable to lower the temperature. It works on a logarithmic scale, the higher the temperature the more energy it takes to maintain it. So it is more economical to keep your room at a constant temperature 60* cost less to maintain than 70*. But to go up and down in temperature will waste money when fuel prices are not taken into consideration. But since you need to take the cost of fuel into consideration it is best to set you thermostat back when the room is not in use.

woodmagman · 11-24-2007, 10:35 PM

Quote:

Originally Posted by Leo G

When you heat up a room you are trying to heat the air in the room. But because the air is touching 6 walls you are also heating the walls too. The thermal mass of the air is low and the thermal mass of the walls are higher. The higher the thermal mass the more energy you need to make to change the temperature. When you insulate the walls you are isolating it from the air. It will still heat the walls but to a lesser degree because of the properties of the insulation. If you set your thermostat to 70* and leave it there you will come into an equilibrium when, after a time all of the surroundings will be at or close to 70*. When you lower the thermostat to 60* the walls will give off heat because the mass of the objects in the room have stored it. After they have given off the heat and come back into equilibrium at 60* and you change the thermostat back to 70* you now have to reheat everything in the room, not just the air. It would be more efficient to keep things at the same temperature all the time but then you have to put the cost of fuel into the equation. After this is put into the equation it is more equitable to lower the temperature. It works on a logarithmic scale, the higher the temperature the more energy it takes to maintain it. So it is more economical to keep your room at a constant temperature 60* cost less to maintain than 70*. But to go up and down in temperature will waste money when fuel prices are not taken into consideration. But since you need to take the cost of fuel into consideration it is best to set you thermostat back when the room is not in use.

As neither of us have hard evidence to back up our hypothesis, I feel when mass gives up energy for no good reason it is wasted. The maintaining of a constant providing not to an extreme seems so much more economical to me.
My thought goes to walking, jogging and running.
I can walk all day
I can jog for a couple of minutes
And if you asked me to run you had better be pointing a loaded gun at me and be prepared to use it because I can walk faster then you can run with a gun wrapped around your neck. Sorry I got side tracked.
I can not run very far..
Now I would consider walking to be maintaining a constant temperature
Running to be bringing mass up to a constant so that walking can continue this would be when combined considered jogging.

And as Teetor said time needs to enter the equation.

**Teetorbilt** · 11-24-2007, 10:52 PM

Here we mostly cool and remove humidity. Humidity being a major factor. It can takes days to suck the humidity out of furniture, carpets, etc. According to my 30 yrs. of monitoring my KwHrs it's best to keep everything constant EXCEPT in the winter. In the winter it's usually dry and heat is expensive. My rule of thumb is 3 days, if I'm gone this long or more lower the thermostat. If you have pets or fish you may want to keep the temp pretty constant. I stay from 78 -76* year round.

randomkiller · 11-25-2007, 10:17 AM

If you want to know about heating, it works saving energy if you use a small setback, like 70 occupied and 65 unoccupied, because if you need to bring the space back to 70 from say 55 it will take much more energy to do so. The last company I worked for had software from Lennox and Carrier that proves these points. Not sure if you could find the info on the web or not. As Teetor mentioned it is different for humid areas in the cooling mode, because of the moisture held in the space. So a smaller setback is advised unless you install a humidistat in parallel with the thermostat for a baseline humidity level.