Home Energy Conservation Exercise

Journal of Geoscience Education, Nov 2003 by Frey, Steven T, Moomaw, William R, Halstead, Judith A, Robinson, Caitlin W, Et al

HOUSE DIMENSIONS AND CHARACTERISTICS

The model house that we use for our exercise is a simple ranch house. We provide students with a sketch of the house (see Figure 1), a cut-away view of the house showing potential sources of convective and conductive heat loss (Figure 2), and a list of characteristics of the un-insulated house (Table 1).

According to the American Society of Heating, Refrigeration, and Air Conditioning (ASHRAE) Fundamentals Handbook (Parsons, 1997), a below-grade basement with a furnace and hot water heater will maintain an average temperature of 50� F. However, the temperature near the ceiling of the basement (the temperature varies from floor to ceiling) will be close to the temperature of the house. For that reason, it is not necessary to calculate heat loss through the floor of the house. The calculation to determine heat loss through the basement is fairly involved and takes into account the amount of insulation on the walls, the number of feet of wall space below grade (7 ft in this case), and a heat loss coefficient for each foot below grade (Parsons, 1997). Hence, we have chosen to simply provide our students with this number. Instructors may wish to have their students do this calculation themselves and provide them with the opportunity to add insulation to the basement walls as another option for improving the efficiency of their model home. Instructions for making this calculation are clearly delineated in the ASHRAE Fundamentals Handbook (Parsons, 1997).

It is also necessary to provide students with information concerning the climate of the region where the house is located. For example, we tell our students that the house is located in Saratoga Springs, NY which has approximately 270 heating days per year and the average temperature differential (between the inside and outside) is 25�F. This temperature differential is used in the convection calculation and in conduction calculations involving the doors, windows, walls, and ceiling (the temperature differential between the basement and outside of the house is 10�F, which is used in the approximation of heat loss through the basement, see above). Information regarding monthly average temperatures and the number of heating degree days per year (a heating degree day corresponds to each degree that a day's mean temperature falls below 65�F), for a particular region of the country, can be obtained from web resources such as http://www.weather.com and http:/lwf.ncdc.noaa.gov/oa/climate/online/ccd/nrmh dd.html. The number of heating days per year can be determined by dividing the number of heating degree days per year by the average temperature differential (relative to 65�F) for days in which the mean temperature fall below 65�F.

LOGISTICS OF THE EXERCISE

Our students complete the exercise during the course of a three-hour laboratory period (most students finish the assignment within two hours). Alternatively, the exercise could be done as an out of class assignment or over the course of several shorter periods. We instruct students to carry out the task in groups of three. To make the assignment more interesting for them, we set up a scenario in which each team of students works for a separate contracting company that specializes in insulating homes for energy and cost conservation. Each company has been asked to provide a family with a bid for improving the insulation and reducing the air infiltration of their house. However, in lieu of a typical bid, the family wants each company to determine how much money they could save per heating month by making $5,000 worth of modifications to their home. Student teams then compete to see which company can win the bid. To complete their bid, student teams must (1) calculate the present heat loss of the clients' home (considering both convection and conduction), (2) decide which modifications to make to the home while staying within the $5,000 budget, (3) calculate heat loss for the modified home, and (4) determine the energy that would be saved by taking the difference between these two values.