Example 11.19 For a building located in Minnesota with an annual heating degree-days of 8382 and a heating
load (heat loss) of 62,000 Btu /h and a design temperature difference of 82°F (68°F indoor and
14°F outdoor), estimate the annual energy consumption. If the building is heated with a fur-
nace with an efficiency of 94%, how much gas is burned to keep the home at 68°F?
We will solve this problem using Equations (11.29) and (11.31).Assuming the gas used in Minnesota has a heating value of 1,000 Btu /ft
3
, then the amount of
gas burned in the furnace can be estimated from:Summary
Now that you have reached this point in the text
- You should have a good understanding of what temperature means, how it is measured, and
how heat transfer occurs. - You should know the difference among temperature scales and understand how they are
related. - You should understand what absolute zero temperature means.
- You should know what we mean by the termheat, know its common units, and be familiar
with different modes of heat transfer. - You should know what theR-value orR-factor for insulation means.
- You should be able to perform some simple heat transfer calculations.
- You should be familiar with some thermophysical properties of materials such as thermal
conductivity, specific heat, and thermal expansion. - You should understand what the heating value of a fuel means.
T 1 °R 2
9
5
T 1 K 2 T 1 K 2
5
9
T 1 °R 2
T 1 K 2 T 1 °C 2 273.15 T 1 R 2 T 1 °F 2 459.67
T 1 °F 2
9
5
T 1 °C 2 3 T 1 °C 24 32
5
9
3 T 1 °F 2 324
161,700 ft
3
/yearVolume of gas burnedc
1152 10
6
Btu/year 20.94
dc
1
1000 Btu/ft
3 dQyearly18,146a
Btu
DD
b1 8382 DD/year 2 152 10
6
Btu/yearQDD
62,000a
Btu
h
b 24 hrs
82 1 °F 2
18,146 Btu/DD
Summary 337
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