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

ABSTRACT

We have developed a home energy conservation exercise that illustrates the ways in which heat energy is lost from a home and ultimately, how it can be conserved. Students are asked to calculate the heat loss from a model home before and after applying energy conserving modifications. The difference in these calculations represents the amount of heat energy that could be conserved by making the modifications. To calculate total heat loss for each version of the home, students must account for convection, (heat transfer via air movement), and conduction, (heat transfer through solid materials). Students are provided with a list of building material costs and a budget of $5,000 and are asked to retrofit the un-insulated home in such a way as to conserve the maximum amount of energy and heating cost per heating month. Introductory geology courses commonly include material on resources, energy, and the environment. Current news topics include discussion of the energy resources in the Artic National Wildlife Refuge and the shortage of natural gas. This exercise takes a practical approach to energy conservation and applies it directly to conservation of a geological resource. When used in conjunction with classroom discussions concerning the detrimental effects of the use of fossil fuels and their limited supply, it is an effective way of demonstrating the concept of conservation as a source of energy and a means to preserve the environment. It is also a practical way to incorporate quantitative reasoning into the classroom.

Keywords: Environmental education exercise, home energy conservation, home heat loss calculations

INTRODUCTION

For a number of years, we have used a laboratory exercise, in its various stages of development, to illustrate the ways in which heat energy is lost from a home and, ultimately, how it can be conserved. We have used the home energy conservation exercise in an interdisciplinary course that is entitled Field Studies in Environmental Science. We use the exercise in conjunction with classroom discussions concerning the environmental problems associated with the use of fossil fuels (Hinrichs, 2002, p. 239-313), their diminishing supply (Minniear, 2000), and conservation as a cost effective, alternative source of energy. This exercise is easily worked into a resource, energy, or conservation unit in an introductory geoscience or environmental geology course. Lectures congruent with this exercise include the origin of petroleum, its geology, production, reserves, chemistry, environmental concerns, use, and conservation. This laboratory goes beyond a simple exercise in gas mileage to challenge students to consider several factors that affect energy efficiency and provides an activity that may be useful in the students future. Those of us who have built and/or upgraded homes using energy efficient technologies realize how important energy efficiency is for conservation of a geologic resource.

The premise of the exercise is very simple. We ask the students to calculate the amount of heat that is lost from a model house before and after energy conserving modifications have been made. By taking the difference between these calculated values, students are able to determine the amount of energy that can be conserved by insulating and sealing the home. The exercise is not only effective in demonstrating how to reduce energy consumption in a home, but also serves to acquaint students with the concept of heat transfer and the insulating characteristics of various building materials. Most importantly, the exercise clearly demonstrates the cost and environmental benefits of home energy conservation.

The utility of cooperative learning (Rogers, 2001) and the integration of quantitative reasoning into undergraduate science courses (Carlson, 2000, Guertin, 2000, Keller, 2000, MacDonald, 2000) have received a great deal of attention recently. This exercise encourages teams of students to examine a problem on a quantitative level in order to achieve an outcome that has practical significance. As such, it is an excellent tool for teaching quantitative skills.

HOME HEAT LOSS CALCULATIONS

Heat energy is transferred by the processes of (1) convection, the motion of a fluid or gas (air in this case); (2) conduction, molecular collisions of a not object with a colder one; and (3) radiation, electromagnetic waves (Hinrichs, 2002, p. 125-149). Since radiation accounts for only a minor portion of the total heat loss experienced by a home, the present exercise focuses on convective and conductive heat loss.

Convective heat loss (q^sub v^) equals the amount of heat carried out of the house through air exchange with the outdoors. This is dependent on the volume or the house, the number of air exchanges per hour (i.e., the number of times that the entire volume of air in the house is exchanged in one hour), the heat capacity of air, and the temperature inside and outside of the house (T^sub inside^ and T^sub outside^).

Conductive heat loss (q^sub d^) depends on the inherent resistance to heat flow (R-value) of each material per unit area, the total area of the material (wall, floor, window, ceiling), and the difference in temperature between the inside and outside of the house. The resistance to heat flow is additive just like electrical resistance, but the conductance of heat, like electrical conductance, is proportional to the reciprocal of the total resistance.