Minimizing Structural Energy Loss

Andrew Layman

Lisa Phillips

Our Question

• What is the primary source of energy loss in a house and what are some solutions to minimize this loss?

How Heat is Lost

• Energy in your home is lost through your walls, windows, ceiling, doors, etc....... but not all energy loss is equal. The percent of energy lost through these mediums are as follows:

Infiltration / Air Leakage: 35%

Windows and Doors: 18%-20%

Floors and Below Grade Space 15%-18%

Ceilings: 10%

Walls: 12%-14%

Where is Most of the Energy Lost?

• Based on these percentages, although investing in more efficient insulation and better windows can help, the most energy is lost through air leakage/infiltration. The most important thing you can do to reduce this energy loss is to make your home more “air tight”

Air Exchange Rates• The average air

change rate per hour in a typical home is 10-18 changes/ hour. In other words the air in your house is replaced by new air (that then needs to be heated or cooled) 10- 18 times an hour.

Equation for Heat Change

• The amount of heat required to raise the temperature of air is given by the equation:

Q= cp x m x dT

where

Q = amount of heat (KJ)

cp= specific heat (KJ/Kg)

m= mass (Kg)

dT= template difference between hot and cold side (K)

CalculationWe figured that the volume of an average house is 7,750ft so the mass of air in the house would be-----261 kg of air

Calculation-

1.004KJ/Kg x 261Kg x (293K – 280K) =

3406 KJ to heat the air in a house

If the air in a house is exchanged 10 -18 times an hour that means that we use up to

61318 KJ an hour to heat or cool a house.

Things You Can do to Lower the Air Exchange Rate

• Increasing seals around your doors, windows, plumbing vents, wall electrical outlets, switches, recessed lights exposed to the attic, attic stairs, and vertical plumbing stacks open in the basement can lower the air exchange rate in you house by reducing air leakage.

• The blower door test can help pinpoint the biggest source of air leaks in your house

What Does a Lower Air Exchange Rate Mean?

• If we can reduce the amount of air changes in an hour by reducing air leakage than we can reduce the amount of energy used and decrease energy loss.

How Much Energy Can I Save?

• If you can lower your air exchange rate by half of the average rate (from around 14/hour to 7/hour) then using the calculation form before we can calculate the amount of energy you could save.

Possible Difference in Energy Loss

Knowing that it takes 3406 KJ to heat the air in a house and that non efficient houses can use up to 61318 KJ an hour to heat or cool the air then lowering the air exchange rate to 7/hour would use 23842 KJ.

This would save 37476KJ and hour

Lowest Healthy Air Exchange Rate

• One thing to take in to consideration when talking about eliminating air leakage is that a certain amount of air change is needed to keep a healthy breathing space.

Health Hazards Associated with Low Air Exchange Rates

• Stagnant air can accumulate allergens, promote mold growth, and gas build up. Because of this you do not want your air change rate to go below 3 per hour

Highly Efficient Homes

• It is possible to have an air exchange rate of lower then 3/ hour and still have a healthy breathing space. Some highly efficient homes are equipped with special air filtration systems that allow an air exchange rate of .35/hour!

Conclusion

• Most energy is lost through air leakage• There are ways you can diagnose and help

minimize air leakage in your home to save energy and money

• If the air exchange rate in your home is lower than 3/hour make sure you home has a filtration system to reduce health risks associated with stagnate air.