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Amherst College has adopted best practices for insulation, windows, doors, lighting, plumbing fixtures, and materials in order to reduce the amount of energy and natural resources it takes to provide a good environment for students, faculty and support staff to work in.
Among those practices is paying attention to the details of the exterior envelope and air barrier – the best insulation is useless if outside air can flow through it unimpeded. The paths for air infiltration can be hard to see and plug even with careful attention to the insulating details around doors, windows, roof eaves, as well as anything that penetrates the roof. For these areas that are particularly difficult to insulate, the College uses blown-in insulation. Blown-in insulation is particularly useful in improving the insulation in older buildings, where demolition to gain access to these difficult spots is impossible for structural or historical reasons. But even the most careful application of blown-in insulation can have hidden flaws, especially in the most difficult spots.
One of the tools we use to locate gaps in the envelope and insulation is the blower door. A blower door is a very basic tool, essentially a fan put in place of an outside door. The fan creates a slight vacuum that mimics, in a well controlled way, the chimney effect that all buildings experience in cold weather and when the wind blows. Measuring the air flow and pressure allows us to measure the tightness of a building. The blower door test is a widely used test of the quality of a building’s envelope and the effectiveness of its insulation. The results of the blower door test can be compared to international standards to gauge the construction.
The volume of air flow at a specified pressure, typically 50 Pascals, is a standard used in international codes and is generally expressed as total air changes per hour. Some of the toughest codes are enforced in Sweden and these have become a touchstone for advocates of energy conservation. Other agencies that publish recommended air flows are the US EPA and Energy Star.
As an added refinement to the measurements, using the blower door in cooler weather allows an infra-red video camera to pinpoint leaks of cold air. Skillful use and interpretation of the infra-red images can efficiently direct remediation efforts and lead to cost-effective repairs. Some of the most powerful tools used in this remediation are the caulking gun and pieces of insulation. In warm weather, smoke is used to make these leaks visible.
Recently, the oldest building operated by Amherst College was extensively renovated. The Scott House was built in 1793 and was updated to meet modern requirements. The house was originally heated with a central fireplace (that has been preserved in the renovation). In the days of heating with a central hearth, air leaks helped the fire burn and kept the smoke moving up the chimney.
Today, with a modern furnace, the high cost of energy, and modern expectations, drafts are no longer acceptable: it is important that the building envelope and insulation work well, so blown-in insulation was used extensively in this historically sensitive renovation. When the project was nearly complete, a blower door test was made and we found that the Scott House met (and bettered) even the strict Swedish requirement of fewer than three air changes per hour (the EPA allows ten air changes to qualify as an efficient building). A little detective work with smoke showed that most of the air was leaking through electrical outlets after traveling down the walls from the attic. Now the carpenters have tightened up the corner where the walls meet the attic floor and roof.
It has been estimated that repairing a one cubic foot per minute (CFM) leak discovered during a blower door test will save $50 a year in energy. It is hoped that the carpenters working a few hours in the attic of the Scott House will be able to reduce the air leakage by a few hundred CFM and so realize substantial savings.
Given the success of making this simple test on a building renovated using new materials and techniques, the blower door will be taken to other buildings on campus. A recent test of an older house revealed many leaks that were traced to easily repaired sources: some windows didn’t sit properly in their tracks, window air conditioning units were left uncovered and were not tightly installed in their windows, the hatch to the attic and cellar door didn’t close tightly, there were some cracked window panes and the draft damper on the dryer vent was stuck open. It doesn’t take long to fix all these things and realize real savings. Other buildings and their occupants will benefit from pinpointing and repairing these sometimes invisible problems. Defects in a building’s envelope that can’t be repaired without major disruption to the use of the building can be noted and opportunities for renovation can be planned.