EGEE 102
Energy Conservation and Environmental Protection

Calculating Annual Heat Loss Examples

PrintPrint

Example 1

Please watch the following 3:29 presentation on Example Problem #1. For the 150-day heating season in Roanoke, VA, the average temperature was 47° F. How much heat is lost through a 176 ft2 wall (R=16) during the entire season?

Click here for a transcript of Annual or Seasonal Heat Loss Problem #1 video.

Lesson 7a, Screen 32: Calculating Annual or Seasonal Heat Loss

Example 7 (formerly Example 3-11)

For the 150-day heating season in Roanoke, VA, the average temperature was 47°F.

How much heat is lost through a 176 ft2 wall (R=16) during the entire season?

Ok. In this problem, 3-11, we are trying to calculate the heat loss for a 150 day season in Roanoke, VA. It is a 150 day heating season. The outside temperature is given as 47°F. Inside, is obviously 65°F. Ok?

Outside: 47°F
Inside: 65°F

Degree Days can be calculated like this. Heating Degree Days are equal to the number of days, which is 150 in a season here times the temperature difference. 65 minus 47°F.

HDD = 150 days × ( 65  47°F )

Now we can calculate that. That is equal to 150 days times 18. So that turns out to be 2700 °F days.

HDD = 150 days × 18 = 2700 °F days 

Now, what else do we need? We need the area. Area is given. Area is equal to 176 ft2 and we are also given the R-value. R-value is 16.

Area = 176 f t 2   R = 16 

Therefore, we can calculate the heat loss, heat loss through a season. Heat loss through the season is equal to Area times HDD times 24 over R.

Heat loss thru season =  Area × HDD ×24 hours in a day  R = 176 f t 2  ×  2700°F days × 24 hours  16 f t 2  °F h/Days  = 712,800 Btus 

Now, what can we cancel? ft2/ ft2, °F/°F, hour/hour and days/days are canceled. So when we do this calculation here, we get the answer of 712,800 Btus in this 150 day heating season.

Example 2

Please watch the following 3:42 presentation on Example Problem #2. In Fargo, ND, the heating season lasts about 220 days and the average outside temperature is around 27° F. How much heat is lost through an 8 ft by 6 ft window (R=1) during the heating season?

Click here for a transcript of Annual or Seasonal Heat Loss Problem #2 video.

Lesson 7a, Screen 33: Calculating annual or Seasonal Heat Loss

Example 8 (formerly example 3-12)

In Fargo, ND, the heating season lasts about 220 days and the average outside temperature is around 27°F. How much heat is lost through an 8 ft by 6 ft window (R=1) during the heating season?

This problem is very similar to the last one, 3-11. Now this 3-12 involves again heat loss through a season. We need to calculate the HDD’s. The heating days are 220 days. Now the temperature difference is, inside, 65°F as usual and outside, the temperature, the average temperature happens to be 27°F for all 220 days. Therefore, Heating Degree Days (HDD) can be calculated like this: 220 days times (65°F minus 27°F). And this is equal to 220 days times 38°F which is equal to 8,360°F days.

220 days  Inside = 65°F, outside = 27°F  HDD = 220 ×( 65°F  29°F ) =220 days× 38°F = 8360 °F days 

Now, do we know the area? Area is given actually. The dimensions of the window are 8ft by 6ft. Therefore the area is 8ft times 6ft, which is 48ft2

Area = 8ft × 6ft  =48 f t 2

We know the temperature difference, we know the HDD, and we can calculate the heat loss provided we have the R value. R-value is also given. 1 ft2 °F h over BTU.

R =  1 f t 2  °F h BTU  

Now it is easy to calculate heat loss. Heat loss for the season is equal to area (and I am trying to repeat this), area times HDD times 24 over R. So in this case it is, area is 48 ft2 and we have 8360 degree days times 24 hours divided by a day over R value of 1 ft2 °F h/BTU.

Heat loss in a season = Area × HDD × 24 hrs/day R =  48 f t 2  × 8360 °F days×24 hrs/day 1 f t 2 °F h/BTU

So ft2/ft2, °F/°F will be canceled, hours and hours are canceled, days and days are canceled here.

48 f t 2 × 8360 °F days × 24h/days 1f t 2  °F h/BTU  = 9,630,720 BTUs  

So, when you do this math, it comes out to be 9,630,720 BTUs. This is in one full season.