2.  On average, home heating uses more energy than any other system in a home  About 45% of total energy use  More than half of homes use natural gas.

3.  In the winter homes lose heat to the outside through conduction, convection, radiation, and infiltration  These losses can be reduced by good home design, but there is always some loss of heat  To keep the inside of a home warm the lost heat needs to be replaced  Capturing solar energy can reduce the energy used by a home heating system

4.  Passive solar heating can reduce energy use in many areas of the country where there are sunny days during cold winter months  Solar heating takes advantage of available sunshine to heat a home  Passive means the heating occurs without active mechanical systems or daily intervention of the people living in the home  Solar can also produce hot water and electricity

5.  Passive solar homes typically include ◦ Ample window area with southern exposure ◦ High efficiency windows that better retain inside heat ◦ Construction techniques and materials that reduce heat loss and store warmth ◦ Features that reduce solar heat input during summer months

6.  Simplified Model  The heating system is off  At any time, heat is being lost in proportion to the temperature difference between the inside and the outside  The inside temperature drop from this heat loss is modeled assuming and average heat capacity for everything inside the house (furniture, air, fixtures, etc.)

7.  The resistance to heat loss of a building material is often called the R-value  Different materials have different R-values ◦ Glass is low ◦ Wood is moderate ◦ Insulation is high  Heat loss is reduced by using materials with a high R-value and by using more than one layer  Heat loss is increased when there is more surface area exposed to the outside

9.  Heat capacity is a measure of an object capacity to store heat  Heat capacity is calculated as the amount of energy needed to raise the temperature by one degree  Specific heat capacity is similar to heat capacity, except that it is the property of a material and not an object

10.  When heat is lost, the temperature of the inside of the house will decrease (we are assuming the heating system is off in our model)  The change in temperature for a given amount of heat lost depends on the heat capacity of all the items and building materials inside the home.  The greater the heat capacity, the smaller the temperature change since more heat is stored at a given temperature  The more time that passes, the more heat is lost and the greater the temperature change  These factors can be combined in an approximate formula for indoor temperature change:

11.  Inside is 22 °C, outside is 0 °C  R-value is 5 m²·°C/W  Surface Area: 650 m²  Heat capacity inside house: 5,000,000 joule/ °C  Calculation of temperature drop over 30 minutes (1800 seconds): ◦ Heat loss = (22 – 0)* 650/5 = 2,860 joule/second ◦ Temp. change = 2,860*1800/5,000,000 = 1.0 °C ◦ Final temperature = 22°C – 1.0° C = 21°C