ACHRNEWS

Thermal Imaging Points the Way to HVAC Profits

January 29, 2007

In energy audits of homes and other buildings, technicians are using blower doors in conjunction with thermal imagers. The blowers create positive or negative pressures within interior envelopes, making leaks much more apparent in thermal images.

For nearly 30 years, the U.S. Department of Energy (DOE) has helped low-income families save energy by weatherizing their homes. Called Weatherization Assistance, the program is funded by DOE and administered by individual states. In July of 2005, the DOE announced awards to 19 states for home weatherization totaling $92.5 million. The program’s total budget for 2005 was $288 million.

Today’s Weatherization Assistance Program includes a comprehensive series of energy-saving measures based on audits of residential units. They take a whole-house approach that includes a wide variety of energy-efficiency measures and are leading the way in founding a growing industry that makes energy-efficient homes available to everyone. Among the tools they use in conducting residential energy audits are handheld thermal imagers.

WHAT TO CHECK

Blower doors consist of a frame and shroud that fit inside doorframes. Mounted in each blower door is a variable-speed fan that allows it to induce pressure on the inside of a dwelling. Certain instruments are used along with a blower door. Using pressure gauges, a technician can measure the flow of air through the fan, as well as the pressure differential between the living space and the outdoors.

With a blower door in operation, a technician armed with a thermal imager and pressure gauge (to verify the pressure differential in various parts of a dwelling) can find areas that contribute to the loss of conditioned air by convection - heat in winter and cooling in summer. Even before turning on your infrared (IR) camera, you will probably already have a general idea of the relative leakiness of a dwelling. The greater the airflow required to reach a certain pressure differential, the leakier a living unit is.

Thermal imaging is useful for monitoring rotating equipment; many impending failures are accompanied by overheating. Here, a handheld thermal imager captures two-dimensional images that represent the equipment’s surface temperatures.

The most effective thermal imaging work in an energy audit will occur indoors when a living space is being heated or cooled; that is, during winter or summer, not in the spring or fall when there is little discernable difference between inside and outside temperatures.

Conventional wisdom would have you concentrate your imaging on windows and doors. However, windows and doors, typically located mid-height in a home, contribute very little to total air leakage in most dwellings and therefore account for a relatively small percentage of the total heating-cooling losses due to convection. In fact, the most serious leaks in most housing units occur at the top and bottom of the conditioned building envelope: in attics and basements.

Large gaps are often found around plumbing pipes, recessed light fixtures, chimneys, eave soffits, chase ways, and basement rim joists (where the foundation meets the wood framing). Look carefully at the tops and bottoms of plumbing runs and plumbing vents, especially in attics and basements.

Also, scan the places where utilities, such as electricity and TV cables, enter the conditioned air space. Look for uncharacteristically cold floors in winter, especially floors above garages and crawl spaces. Even if these floors are insulated, the insulation contractor could have left air space between the insulation and the floor, allowing the floor to cool by convection. Of course, look for duct leaks.

Heating and cooling losses occur by conduction as well as by convection. Conduction losses can happen, for example, at floor slabs that extend outdoors and have no thermal barrier between the indoor portion and outdoor portion. Conduction can also happen in conjunction with convection when insulation is missing from an outdoor wall.

SAVINGS

Given rising electricity prices, followup actions based on the findings of an energy audit are almost certain to save at least 15 percent of the energy a household uses. Figures available on the DOE Energy Efficiency and Renewable Energy (EERE) Website illustrate what savings are available from even modest energy-conserving investments.

DOE’s Weatherization Assistance Program has weatherized more than five million homes since 1976. The department did 92,500 in 2005 at an average cost of $2,672 per home.

On average, weatherization reduces overall heating bills by 31 percent and overall annual energy costs by $275 (in 2003 U.S. dollars). Based on heating savings alone, the average payback on a weatherization project takes less than 10 years. Similar results can be expected for any housing unit that experiences an audit and has appropriate followup measures performed on it.

FOLLOW-UP ACTIONS

The remedy for energy-wasting leaks is to seal them:

• Seal plumbing runs and vents at tops and bottoms.

• Seal utility access holes and recessed lighting fixtures as required. (Warning: If not done properly, sealing recessed lighting cans ICAT [insulation-contact-air-tight] will create a fire hazard. Seek expert help.)

• At a minimum, if you cannot fill suspected air gaps between walls, floors, and insulation, seal the ends of the gaps. Also, create thermal barriers where there are conduction losses.

Sealing materials for specific applications vary from aluminum flashing and fiberglass insulation to reflective foil insulation. They also include standard or high-temperature caulks and expanding spray foam. Whatever the materials required, a 30 percent decrease in energy use can save a homeowner $450 or more per year in energy costs.

Publication date: 01/29/2007