We’ve been dealing with the ASHRAE ventilation standard for a while. 62-89 goes way back. We used that one for a long time, and it worked well enough. After we taught our students how to use 62-89, they could understand it and implement it. Then came 62.2. We first wrote about 62.2-2010 in this blog back in 2011. Then in 2012 we vented about the complexity of the calculations. Unfortunately 62.2-2013 isn’t much better.
We recently updated our training module for the ASHRAE Ventilation standard from 62.2-2010 to 2013. A lot of folks stumble on the infiltration credit. We’re simply saying that it’s too complicated of a calculation to do by hand and to just use a tool like RedCalc from Residential Energy Dynamics. The folks at RED have done a great job with that calculator, but I question why the calculation needs to be so complicated that a such a tool is needed. I also think that many people get so caught up in calculating the infiltration credit that they fail to learn about the other parts of the standard. I know some of our students do that.
So in our lesson I’m trying to at least mention each section of the standard and describe its intent. But some of the sections are so unclear that its very difficult to understand or interpret what the requirement is, let alone teach it to our students.
Here’s some examples and the questions I’m asking.
- Section 6.4 – Combustion Appliances: Combustion Ventilation Air (CVA) must be installed according to NFPA 54, 31, 211, etc. I only have NFPA 54, but section 22.214.171.124 of that says that makeup air shall be provided if fans interfere with equipment operation. I’m assuming that the other standards referenced by 62.2 also specify CVA.
- Question: If the equipment is installed according to NFPA, like 62.2 says it must be, then the fan interference is already mitigated. So why does ASHRAE need to insert this stuff about two fans exceeding 15 cfm / 100 ft2? Also, if the fans exceed that limit, then 62.2 says to reduce the exhaust flow or provide outdoor airflow. Does reducing the exhaust flow compromise the whole-building ventilation that I just calculated? What if the “biggest fan” is the 100 cfm fan in the kitchen? Do I now reduce that and then deal with the resulting local deficit?
- 6.5 Airtightness: Simply saying that caulking or gasketing joints and such doesn’t mean the zone is air-sealed.
- Question: How do you know the zone is sealed without testing for a pressure differential? Maybe that’s assumed by saying that all joints must be sealed. If we at least try, when we have succeeded?
- 6.5.2 Ducts: “Leakage should be no more than 6% of total fan flow.”
- Question: We discussing a lot of fans in this standard. Does this refer to air-handler fan flow? And is it 6% of measured fan flow or rated air flow? I would specify to reduce confusion.
- 6.6 Ventilation Opening Area: I’m assuming that “Ventilation Opening Area” means windows, etc as described in 6.8.1. If so, then I think what it’s getting at is this: If the room’s windows aren’t at least 4% of the floor area (min 5 ft2) then a portion of the whole-building ventilation has to be supplied to that room, and the area of that ventilation opening must make the up for that 4%.
- Question: If that’s true, then a 10×10 room would need at least 4 ft2. If that room was in the middle of the house, and had no windows, would the whole-building ventilation opening need to be 4 ft2? That doesn’t seem right.
- Section A2 Whole Building Mechanical Ventilation Rate: This section says that the local exhaust deficit must added to the Qtot rate before the infiltration credit is applied.
- Question: Why does that matter? The deficit increases the Qtot rate, and the credit reduces it. The net result is the same either way. The only reason I can think of is a scenario where the infiltration credit makes the Qtot rate ≤ 0cfm. But even then you can add the deficit to the negative Qtot number. So why add the language about one before the other?
Here at Saturn we’ve always said that standards should be written to be understood by the intended audience, rather than by the engineers and scientists that write them. Confusion for the audience distracts from mission. Over time parts of a standard may become outdated, irrelevant, or actually contradictory to other parts of the standard. We’re picking on ASHRAE here, but the problem persists with a lot of standards that we have to deal with in our industry.
We’re interested to hear what you think. Has the ASHRAE ventilation standard, or some other standard, made it difficult, or even impossible for you to complete your job successfully? What do you do in your work if you can’t comprehend a standard that you’re supposed to follow? Do you just follow the parts you understand and ignore the parts that are too complicated?