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Methodology -
Hourly records are kept of outside, inside, and floor temperatures. These values are averaged over the 24 hours from midnight to midnight for daily averages.
The outside temperature is from a Taylor ??? (the manufacture is ashamed to put a model number on the unit) indoor outdoor temperature guage that is mounted on the north wall of the house. The sensor is insulated from the house, in addition to being on the outside of an R-30 wall, so there should be negligible heat conducted from the house. The sensor is further shielded from the early and late summer sun by three layers of sheet metal, so there is negligible biasing from the sunshine.
The indoor temperature is from a Taylor ??? temperature guage mounted in the living room and the external probe is suspended at about 5 feet above the floor.
The floor temperature is from a sensor immediatly under the four-inch concrete slab floor. The sensor is a thermistor which had been calibrated and installed before the floor was poured. The sensor is located in approximately the center of the house, some 24 feet from the east or west walls, and some 12 feet from the south or north walls.
The running time for the heating system, a 40,000 btu fireplace, is logged on an hourly basis. The fireplace is derated for the current elevation to effectively some 56 percent of rating, i.e., approximately 22,400 btu per hour. In practice, a low flame setting, of some 3/8 of rating is used nearly all the time, which yields some 8400 btu per hour.
From the average outside temperature and the fireplace running time, a btu/DD/ft**2 value is calculated. The btu/DD/ft**2 value, where btu is the British Thermal Unit of heat, DD is the degree day obtained by subtracting the average outside temperature from 65, and f**2 is the floor area of the house, is a common architectural measure of heating efficiency. It amounts to a figure of merit that can be used to compare houses of varying floor areas and in various climates.
An empirical estimate is made of whether the day was sunny, hazy, or cloudy. Sunny amounts to the sun shining and producing sharp distinct shadows. Hazy amounts to cloudy bright but indistinct shadows. Cloudy amounts to severe cloud cover where there are no shadows on the ground.
An empirical estimate is made of whether the day was windy, breezy, or no wind. Windy amounts to ongoing, sustained winds which would be described by the Beaufort scale of 6 or more, which is large branches are moving, overhead wires are whistling, an umbrella use is problematical. Breezy amounts to light, but sustained winds of Beaufort scale of 3 to 6, in which leaves, twigs move, the wind would extend a flag. No wind is no ongoing or sustained air motion. which would be a Beaufort scale of 0 to about 2.
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