Determining the Zoned Heating Efficiency of Room

How much does zoned heating help in saving energy? The 1st step is to determine the zoned efficiency of the rooms in your house. Here is how you do it:

Shut off the heat in a large room of the house and place a thermometer in that room. At various times during the week, record the temperature in the room, the thermostat temperature, and outside temperature. Determine the temperature difference between the thermostat and the closed room, and divide it by the temperature difference between the thermostat and the outside temperature. A correlation should emerge to which you can arrive at a efficiency percentage.

A high percentage up to 100% where the zoned room is closer to the outside temperature would mean more energy savings. A low percentage closer to 0% where the zoned room has little temperature difference to the rest of the house would mean little effect in energy savings.

I tried this with a large bedroom, I found the efficiency to be 29%.

Data:
Date Thermostat - outside = Diff 1 Thermostat - room = Diff 2 Diff2/Diff1 = % 2012-01-02 4 p.m. 66.5 - 39 = 27.5 66.5 - 58.6 = 7.9 7.9/27.5 29%
2012-01-02 7 p.m. 64.6 - 37= = 27.4 64.6 - 56.7 = 7.9 7.9/27.4 29%

If your percentage is very low, don't worry too much. Percentages tend to be higher in poorly insulated homes. So if you have a low percentage in might just mean you have good outside ceiling and wall insulation.

So what does this percentage even mean? Determining the actual energy savings is more complicated. The main factor is the reduced surface area of your "envelope", so it will make the greatest effect if the rooms or rooms cut off reduce surface area. If you are not reducing your surface area, it may not make a difference sadly.

For me, Because the room was a peninsula had three sides facing the outside, I reduced the surface area of two walls totaling 240 sq/ft. Assuming no insulation with the brick wall, I came up with 300BTU/Hour per degree of temperature difference of savings. (1/0.8 * 240) A cold day with a 33 degree temperature difference amounts to 10,000 BTUs/hr which equates to about 2 small spaces heaters, (30 cents/hour) or a (1/2 therm/hr) which is 15 cents/hour. These numbers seem high, so I will try investigate the R-Value further of the wall.

Here is an interesting link for calculating heat loss. 5 Step Heat Loss Calculation

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