Ventilate It Right, And Ventilate It Right. Did I Say Ventilate?
Recently, I ordered a copy of the new ASHRAE 62.2-2013 standard and I spent some time sifting through the madness.
In Illinois, this is becoming a pretty regular topic of discussion since all new construction requires mechanical ventilation. Plenty of our clients are still using exhaust only ventilation under the 62.2-2010 standard, but as Joe Lstiburek pointed out in this article, it doesn’t always work as planned. And as an energy modeler, I personally know that designers who use exhaust only ventilation with the new standard are going to be hit hard with some serious energy penalties from the increased rates. While this is not meant to be totally encompassing, here is a quick synopsis:
- Mechanical vent rates have been increased to a total ventilation base model of 7.5cfm( Bedrooms+1) + 0.03cfm(Floor Area) and no longer assume default leakage of 2cfm/100ft^2
- In order to take credit for infiltration, a blower door must be performed, and Effective leakage area, Normalized leakage, and effective annual average infiltration rate must be calculated. The required mechanical ventilation rate is the difference from the total ventilation and the effective annual average infiltration rate [the effective annual average infiltration rate must be NO GREATER than 2/3 of the total ventilation rate]
- 2013 standard assumes no ‘reasonable’ leakage in multifamily buildings
- CO alarms are now required in all dwelling units
- Similar to previous standards, does not address unvented combustion sources, material off-gassing, smoking, etc…
- Thermal comfort not considered in ventilation strategies
- Ventilation rates must be measured and net ventilation must meet the required ventilation
- When atmospheric OR solid fuel burning appliances are within pressure boundary, the net sum of the two largest exhaust fans must not exceed 15cfm/100ft2. If this occurs, capacity must be reduced or outdoor air must be introduced.
- Ducts/air handlers outside the envelope must be sealed to reduce leakage to a rate of 6% of total airflow when tested at 25Pa
- Mechanical systems that supply air though 10 or more feet of ductwork AND through a thermal conditioning component require a minimum MERV 6 filter
- Multifamily dwelling units must meet the total ventilation rates of a single family home, with no credit for infiltration
- Corridors and common areas of multifamily buildings must be ventilated to 0.06cfm (Floor Area)
- Existing building shall be ventilated to the total ventilation as described above and no credit for infiltration may be used unless it is tested. If the credit for infiltration is greater than the total required ventilation, no ventilation is required.
In short, what this says to me is that all buildings need to be tested with a blower door to take advantage of the infiltration credit, and that all ventilation systems should be balanced (meaning supply outdoor air = exhaust air) with heat/enthalpy recovery systems. If you on the ground trying to collect all the dropped HERS points you can, you may just have to make some changes to your ventilation design in order to do so. Luckily, blower doors are required in our state already – but calculating that infiltration credit is something that will cause most designers to pull their hair out.
Need some help ASHRAE 62.2-2013 calculations? Check out this video.
- Explaining Home Performance Using 4-3-2-1 - March 4, 2014
- Ventilate It Right, And Ventilate It Right. Did I Say Ventilate? - January 23, 2013
Posted In: Building Performance
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