FROM THE FLOOR FOUR
The ASHRAE Winter Conference had plenty of examples of innovative engineering for technical editor Tim Dwyer to get his teeth into. Here are his highlights
Indoor air quality in airtight homes
Andy Persily from the US National Institute of Standards and Technology (NIST) considered indoor air quality (IAQ) in a zero energy home by discussing the construction and testing of the purpose built ‘net zero energy residential test facility (NZERTF)’ at NIST. This impressive four-bedroom timber- framed house was built under the close supervision of scientists from NIST. Persily showed that to ensure good airtightness, regular briefings were required of the complete contracting team so that they understood the importance of preserving the integrity of a complete air barrier by maintaining high standards of workmanship in areas such as sealing around ‘interfaces’ (windows and at junctions of surfaces). The resulting 260 m2
house (with 150 m2
basement) achieved an airtightness of 0.5 air changes per hour (at 50 Pa pressursation). The
46 CIBSE Journal March 2014
building was mechanically ventilated using a heat recovery ventilation system. ASHRAE Standard 62.2 requires 39 1.s-1
. of fresh air for
a home of this size but, due to the control limitations of the HRV unit, the system actually supplied 47 1.s-1
The project team noticed that the filter became blocked very quickly following construction and questioned how likely it would be for a normal householder to have discovered the partially obstructed filter. The filter also suffered from regular clogging with a white powder – the cause was finally traced to the dust produced by the ultrasonic humidifiers that were being used to simulate the moisture production of the home’s imaginary family. A deionisation unit in the water supply significantly reduced this problem. The first results collected over the summer of 2013 showed a clear trend for increased
chemicals in the indoor air as the outdoor temperatures rose. Careful design and selection of materials and fixing methods (minimising the use of glues and preferring mechanical fixings) have contributed to formaldehyde levels below 10 micro g.m-3
.
The team continue to monitor comfort levels and 12 VOCs including toluene, ethylene glycol and formaldehyde. By carefully monitoring IAQ, and having detailed knowledge of the construction methods, they are attempting to establish the key sources of contaminants so future designs can be improved. The goal is to produce specifications that may practically be used by architects to reduce the deleterious impact of building materials and techniques on IAQ. The project website
www.nist.gov/el/nzertf/ contains extensive details of the project, including full plans of the house.
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