Energy Conservatory Articles
APT System used to Automate Home Inspections in "Minneapolis Sound Insulation Program"
(from TEC Update - Fall 1998)
Approximately 80 houses per month around the Minneapolis/St. Paul International Airport are currently receiving improvements to reduce the level of noise inside the home from jet aircraft flying overhead. The sound abatement program, managed by the Center for Energy and Environment (CEE) for the Metropolitan Airport Commission, installs acoustical windows and doors, air conditioning systems (to allow windows to be closed during the summer), as well as traditional weatherization improvements such as wall and attic insulation and airsealing to reduce the interior sound levels by at least 5 decibels. The improvements, installed at no cost to the homeowner, average around $25,000 per household.
As part of the program, detailed 3 to 5 hour inspections are performed on each house before improvements are installed to identify existing health and safety problems such as inadequately drafting combustion appliances, very tight building envelopes, appliances producing carbon monoxide, and excessive combustion zones depressurization from exhaust fans. If health and safety problems are identified during the initial inspection, homeowners are provided with a work plan and required to correct the problems, at their own cost, before sound abatement improvements are undertaken. Problems found after improvements have been installed are corrected by the program. The detailed inspections also include a "series leakage" quality control procedure which measures pressures in unconditioned attics and garages during a blower door airtightness test to help determine if airsealing work needs to be done in those spaces.
Using the APT System to Solve the Program's Complex Data Collection Needs
The detailed inspections being used in the noise abatement program incorporate some of the most comprehensive and complex test procedures ever utilized in a residential improvement program. In addition to the obvious problems of collecting and documenting such a large amount of data for each house, it is important that the tests be conducted in a consistent and repeatable manner, and that the inspectors be able to look at and interpret the data on a real-time basis. Dave Bohac, who manages the program for CEE, decided that automating many of the test procedures would be the best solution for meeting these wide ranging program needs.
The heart of the automation process is The Energy Conservatory's Automated Performance Testing (APT) System. Using custom software written by Dave Bohac, the APT system is used along with a laptop computer to automate a vent performance and worst-case combustion zone depressurization test, appliance CO production test, and the blower door and "series leakage" pressure tests.
Vent Performance Tests
During the automated vent performance test, appliance draft and combustion room pressures are continuously monitored under a variety of house conditions using the APT's precision pressure channels. Spillage is also detected and recorded using 3 APT temperature sensors mounted just below the appliance draft hood. The main purpose of the test is to insure that the appliance can vent properly under both normal and worst-case pressure conditions. By examining the real-time draft, spillage and combustion zone pressure data under the various house conditions, technicians can quickly assess venting performance and determine if a venting problem is due to a venting system deficiency, or a house depressurization problem. In addition, all data collected by the APT system is stored, and later copied into a master data base to allow for program wide comparisons and reporting.
CO Production Test:
CO production under normal operating conditions is measured using a hand-held digital monoxer for all combustion appliances in the house. For water heaters, furnaces and boilers, CO levels are also monitored under chimney downdraft conditions using a unique test procedure developed by CEE and TEC. To create the downdraft condition, the APT system is used to control a blower door fan which depressurizes the house to the point where a steady 2 Pa positive pressure is maintained in the vent connector. The noise abatement program measures CO levels under downdraft conditions because recent field observations have shown that some appliances can produce large amounts of CO under downdraft conditions, while producing little or no CO under normal operating conditions. During the downdraft test, the APT system is also monitoring ambient CO levels using a CO sensor sold be TEC to help protect the inspector against excessive CO exposure.
Blower Door and Series Leakage Tests
The detailed inspections also include a blower door airtightness test to help determine if mechanical ventilation is needed in the houses. Using the APT's fan speed control feature and built-in pressure channels, the blower door test procedure has been completely automated. During the blower door test, the APT system is also used to simultaneously measure the pressure in unconditioned zones such as attics and garages to allow for a quick assessment of airsealing priorities. Automation of the blower door and series leakage tests speeds up the entire procedure, helps insure that the tests are done consistently, and allows for much more repeatable measurements in all weather conditions.
Inspection Results
Results from approximately 1,900 pre-improvement inspections showed that 86% of the houses failed one or more portions of the health and safety test procedure. The largest reason for failure has been venting system deficiencies including undersized chimney liners and vent pipes, excessive horizontal vent pipe length, water heaters not vented into liners, and holes and gaps in the vent pipes themselves due to poor maintenance or improper installation.
Excessive CO production accounts for the next highest failure rates. Test results have shown that about 5% of water heaters and 11% of furnaces have excessive CO levels under natural draft conditions. When the appliances are tested under down draft conditions, failures due to excessive CO increases by 50%.
The measured airtightness level in about 25% of the predominately 1920 - 1960 era houses has also been found to be tighter than program standards, even before improvements have been installed. Once improvements are installed, the houses become significantly tighter with 75% failing the airtightness standard. Mechanical ventilation systems are automatically installed in all houses that test tighter than the program standard.
Jim Fitzgerald, senior building analyst for the project, says that the automated test procedure gives CEE much more confidence in their testing system. "Using the APT system has allowed us to institutionalize detailed quality control measurements in a high production program that would otherwise be impossible. We now have a great deal of confidence that all our houses work properly once we've finished the improvements." For more information on the Minneapolis Sound Insulation Program, email Dave Bohac at dbohac@mncee.org.
