Reading your energy audit report

Posted Wednesday, March 13, 2013 in Sustainable Maine

Reading your energy audit report

The blower-door test during an energy audit tests for leaks in the home.

by Paul Kando

Most older houses were not designed with systemic performance in mind. This is why energy audits are important. Their purpose is to determine a home’s performance as a system, so informed decisions may be made about improving it. The audit report should be reasoned advice by an independent energy professional, backed up by data, not part of a sales pitch for a home-improvement contract. The home owner is entitled to clear, well-reasoned answers to all his or her questions. No one should act based on information that is not clearly understood.

A professional energy auditor involves the residents in the audit itself. They discuss the house and its energy use as they tour the house together. Questions and note-taking are encouraged. Measurements are taken and tests conducted. The blower-door test leaves the house replete with bits of blue painter’s tape marking every air leak, so they can be fixed later. A thermal camera scan shows defects in insulation, moisture damage, air and water leaks and more. The Energy Audit Report provides a list of recommendations with estimates of corresponding energy savings, plus lots of technical information on which the recommendations are based. Numbers can be intimidating, but good auditors encourage requests for explanations. A Midcost Green Collaborative (MGC) energy audit is modeled on the principles of the Passivhaus design process, internationally the most advanced and energy-efficient in the world. The analysis software is continually updated to reflect new research information.

Audit reports come in sections. The first highlights the energy savings attainable by following the report’s recommendations. Section 2 describes the house in terms of energy-related characteristics. The report’s calculations and recommendations are based on this numerical information. For example, surface areas are essential for heat-loss calculations, the precise compass bearing of the home’s south wall is needed in calculating solar-energy gains, and the presence of smokers increases the need for fresh air.

Section 3 details the energy consumption of the home. Dollar amounts reflect the price of fuels used on the day the report was prepared. They are the basis of cost-savings projections in the report. Carbon-dioxide emissions are calculated based on energy use. Under “solar energy” are listed the amounts of solar radiation entering the home. Based on a test conducted during the energy audit, the “solar availability” table lists monthly percentages of solar energy available for collection in front of the southern exterior, accounting for shading and obstructions. Another table compares the audited house to classes of houses in the marketplace on the basis of energy use per heating degree day.

Section 4 is an energy snapshot of the house. This is where amounts of heating energy lost through walls, attic, roof, basement, utilities, windows, and doors — and through air leaks — are tabulated. Line items of this table are color-coded to a schematic representation of the house. The original home and later additions are often shown in different color. Zeros (“0") mean that a line item is not applicable; numbers in red indicate heat gains, rather than losses. 

Section 5 shows how air-leaky the house is, and to what degree the leaks (marked during the audit with painter’s tape) may safely be sealed without creating air-quality or  moisture problems. Air-leak sealing and mechanical ventilation recommendations follow, including projected pay-back information.

Section 6 is a detailed moisture analysis of the house. Moisture moves with warm air that absorbs it. If that air is at or below the dew point, the moisture condenses. This can occur inside the structure, e.g. a not properly sealed wall cavity, where it can cause structural damage. Moisture can also cause mold and mildew problems. This section also provides a brief tutorial on moisture in a house.

Section 7 contains a list of specific recommendations to improve energy efficiency. Anticipated savings are based on seven-year simple payback. Recommendations that may take longer to pay back are listed separately.

Section 8 presents hourly heating and cooling profiles of the house, both under current conditions and after recommended fixes. Instead of how much, this section analyzes when, month by month and hour by hour, energy is used. These charts also show the impact of thermostat setbacks, to aid energy and moisture management.

Finally the reader is invited to address questions to the energy audit team. The purpose of an energy audit,  to provide information based on which intelligent decisions can be made, is defeated if the report is not understood. Attending one of MGC’s free Home Energy Clinics on home weatherization may be of help as well. Upcoming clinics are listed on www.midcoastgreencollaborative.org.

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