Ponderings with Richard Bleil
Some days, I just cannot seem to get warm. Well, in the summer there are days I simply can’t cool down, so I guess the door swings both ways. As I’m sure most people do, I try to strike a balance between comfort and economy. Some days, this is the perfect temperature, but days like today it just doesn’t cut it. It’s an old house; so maybe it’s because of drafty rooms or cold spots caused by the tormented souls of haunting spirits. Seriously, how cool would that be?
But the reality is that the thermostat does not reflect the actual temperature of the house. First of all, each room has a unique characteristic that may or may not be detected by the thermostat. But beyond that, the thermostat has a natural variation as part of its function. See, when you set the temperature, say, for example, 65, that becomes (hopefully) the median temperature. Not the mean, per se, but the median.
For those who don’t remember, the “median” temperature is the middle of the temperature range. The furnace doesn’t run continuously to keep the house at 65, but rather it turns on and off. This means that it will turn on when the house cools to some given set number of degrees below the set point, and it will turn on when the temperature is a set number of degrees above. For arguments sake, let’s say that the thermostat turns the furnace on or off within two degrees of the set point. So, if we’re set at 65, it will turn the furnace on when the temperature drops to 63. Once on, the furnace will heat the house until the temperature (in our example) hits 67, two degrees above the set point. The house, then, should (hopefully) be somewhere in the range of 63 to 67 degrees, not just 65.
The mean temperature should be close to the median but may not be exactly the same. For those who may not remember, the “mean” (sometimes called the “average” but this is not exactly correct) of a group of numbers is what you get when you add all of the numbers up and divide by the total numbers in the set. For example, the mean of 21, 19, 19 is (21+19+19=59/3=)19.667. The mean temperature of the house, then, is dependent on things like the responsive nature of the furnace, and the efficacy of the insulation of the house. When I say efficiency, I mean, for example, how quickly does the furnace heat up, and to what temperature. My furnace, for example, has a delay on the blower so it won’t begin blowing until the air in the furnace is hot enough (or cold enough in the summer). Other furnaces (like my car) don’t do this, so it will initially blow cold air (or hot air in the summer) immediately. This will affect the minimum temperature before I start getting heat. Insulation will affect how quickly the house will cool once the furnace turns off.
Another factor that you might not think about is the furniture and items in the house. When I moved into this old house, the heat had been off for a considerable time. I used a kerosene space heater to warm the living room until the gas and utilities were turned on. The house heated up (using a malfunctioning system that simultaneously ran the heat and air conditioner when it turned on) to the set point and turned off, but it was still bitterly cold in the house. This is because everything else in the house, the floors, the walls, the stairs, everything was still very cold.
Chemists speak of “heat capacity” (which some idiot authors of chemistry books call “specific heat capacity”, but this phrase is completely meaningless). This refers to the amount of heat required to raise the temperature of the substance at hand. Wood has a significantly higher heat capacity than air. This means that it takes a lot more heat to warm up the wood in the house, and the air does not have a significant amount of heat to do so. The thermostat measures the temperature of the air, so it shuts off long before the temperature of the wood, plaster, doors, glass and other materials of the house warm up. The air then loses the heat it gained from the furnace as it touches and transfers the heat to the solids in the house. The temperature of the solids in the house will increase as this occurs, but will not reach the temperature of the air for quite some time, perhaps even days after the furnace begins working. This, too, affects how cold the house is, and feels.
It’s a lot to consider. I don’t really have a point to this post. I just find these kinds of exercises in logic interesting.