Introduction to Building Performance
Homes in the United States produce 21% of the country’s emissions, which accounts for more CO2 emissions than from autos and light trucks combined. Usually, homeowners don’t realize that there is significant room for improving their home’s energy efficiency and overall comfort, which would lower their carbon footprint. Original construction and design flaws cause homeowners to spend more money than they need to in order to keep a comfortable home. The purpose of the BPI home energy audit is to identify areas within your home that can be improved or upgraded to increase the energy efficiency and total comfort of your home. We use both diagnostic equipment and building science to determine areas that can be improved and to identify the best solutions.
Once a full diagnostic test is completed, we can take a systematic and data-driven approach to address different aspects of your home that contribute to energy loss or an uncomfortable living environment. Test results will be presented, and technical terms and concepts will be explained. Just a few of the areas addressed include:
Building Envelope Leakage
One common complaint within a home is the presence of “drafts”. We complete a blower door test to pressurize the house, which provides us with information about the presence and intensity of drafts and air leakage. A healthy home should have 0.35 ACH, which is the same as replacing 1/3 of the house’s air every hour. A higher ACH means the house is draftier than recommended, which wastes energy and brings in dirt, dust, and outdoor contaminants. A lower ACH means that the house is sealed tightly, and mechanical ventilation is recommended to ensure healthy air.
Windows are a focal point in a home, enhancing a room’s décor with natural light and providing a view of the world. However, old windows may be leaking energy from your home! Windows without low-e film allow UV rays to enter the home, discoloring furniture and carpet, and heating up the home. This creates more work for your heating and air system! Windows with metal frames pull heat into the home; this heat can break the seal between the dual panes, causing condensation or hard water spots to form. Wood frames are very high maintenance, needing to be painted or stained every winter season.
Vinyl, dual pane windows with a clear low-e film can help reduce these effects. The vinyl frames have little to no maintenance, and the low-e film helps reduce the UV rays entering the home, saving on heating and cooling costs.
Almost all homes have insulation of some sort, but are usually under-insulated, or insulated with such low-quality insulation that it is actually useless. Insulation has to be installed over 100% of a surface to be effective, as gaps and voids reduce the effectiveness of the insulation exponentially. Upgrading insulation R-values will usually have a dramatic effect on energy savings throughout the year, as it will allow the home to stay cooler during the summer and warmer during the winter.
Within most homes in California, heating and cooling accounts for 30% of the total energy bill. These systems are usually outdated, oversized, and inefficient. Having the system maintained and tuned up every year or installing a high-efficiency and correctly sized system can make a large difference in heating and cooling costs.
Distribution System & Duct Leakage
Having leaking ductwork not only lowers the efficiency of the HVAC system, it can also negatively impact your indoor air quality and overall home comfort.
- Efficiency: According to the US Department of Energy, “You can lose up to 60% of your heated air before it reaches the register if your ducts aren’t insulted and they travel through unheated spaces, such as the attic or crawlspace.” In the homes we test, we have found that most duct systems leak an average of 30-40%. That is the equivalent of throwing away $0.40 for each dollar you spend on heating and cooling!
- Air Quality: Ductwork is usually located in the attic or crawlspace, which can cause harmful indoor air quality. During the winter months, the crawlspace usually gets damp, which combined with the dark environment, encourages mold growth. Every time the heater comes on, the leaking ducts can pull this damp, moldy air into the home!
- Comfort: A very common concern of homeowners is that some rooms are too hot or too cold, and others don’t receive enough air flow. Older duct systems don’t have dampers, which help balance air flows by room and direct heat where you want it. Fixing leaks and installing dampers can alleviate most of these concerns.
SMUD Home Performance Program (HPP)
With SMUD’s Home Performance Program, you can discover where your home is leaking energy and how to qualify for up to $5,000 in SMUD rebates. It starts with a home energy assessment, also known as a home energy audit; SMUD focuses on electricity saving. You’ll receive a detailed report of where your home is losing energy and where opportunities for improvement are. That report will also include an energy savings plan with an estimated rebate amount and a quote to complete the work. For more details, click here.
Glossary of Terms
ACH Air Changes per Hour: The air-tightness of a home is measured in ACH; the number of times the home’s air is replaced by outside air in an hour. Air outside a building is constantly infiltrating through cracks in a building’s shell and exchanging with inside air. ACH is the measure of the rate at which this occurs.
Air Infiltration: Air infiltration is the unintentional or accidental introduction of outside air into a home, typically through cracks in the building envelope and when doors are open. Infiltration is sometimes called air leakage.
Air Sealing: Air sealing is the process of sealing penetrations in a building shell, which included the walls, floor, and ceiling where outside air enters the home.
Baseline: This is the energy used other than that used for cooling and heating your home. It typically includes energy used for water heating, refrigeration, lighting and electronics. The baseline tends to be fairly consistent year-round.
Blower Door: A blower door is a device used to pressurize the home in order to locate areas of air infiltration and energy loss.
BTU; British Thermal Unit: The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.
Building Envelope: The structural elements that separate the interior and the exterior environments of a home. This includes wall, roof, floor and foundation.
Phantom Load: A phantom load is the electric power used by electronic devices which where are switched off or are in standby mode.
R-Value: R-Value is the measure of insulation efficiency used in the building industry. The bigger the number, the better the insulation effectiveness.