Duct manifold for a stand-alone ERV
Adam Emter - Zone 7a
| Posted in Mechanicals on
I’m trying to figure out the best way to install my ERV ductwork. I don’t have a forced air system, so each supply or exhaust will have it’s own duct. I have seen the typical trunk/branch method, but a manifold system seems easier. Does anyone have experience with building a manifold system for mechanical ventilation? I will have three exhaust ports and four fresh air ports. I’ve looked at the Zehnder systems and they look pretty slick, but I cannot afford the price. I am leaning toward Thermaflex ducts, which are high quality flexible ducts usually used in commercial applications. Thank you!
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Replies
Adam,
If you err on the side of oversized ducts rather than undersized ducts, and you pay attention to sealing air leaks, I think that you'll be fine, no matter which route you take. Here's a link to an article with a few hints on ventilation ductwork: Installing a Heat-Recovery Ventilator.
Adam, we have a plenum/manifold that collects exhaust air from our four bathrooms. I have attached some quick pictures to show it and the HRV.
We have dampers on the input side to that exhaust plenum, they more fully open via control from a simple Intermatic mechanical timer switch in each bathroom. An end switch on the master relay box also puts the HRV into high speed at that time. (That master relay box can be seen at the right of the plenum picture.)
We have one fresh air discharge into the upper portion of our great room. I don't think it would be worthwhile to bother with fresh air discharge into each bedroom, then you would have to worry about cool drafts hitting occupants. Since the HRV constantly pulls air out of each bathroom there is enough circulation anyhow.
BTW, another Green Building Advisor user asked about the benefits of having a small duct high velocity (SDHV) cooling system. Occurred to me while writing this that one of those benefits was leaving enough room in the floor trusses and inter-floor chases to have this kind of ducted HRV system.
Andrew - thanks for sharing the detail and pictures. What size are the ducts between the plenum and bathrooms?
Yes, thank you for the photos, Andrew. Trevor, comparing those ducts to other items in the picture, I'm guessing 4". The ComfoTubes that you've referenced in other threads is 3", I believe. If those 3" ducts work on Zehnder systems, I don't know why it wouldn't work on any other system. I'm planning to use 3" or 4" high-quality flex ducts in my system. All of my homeruns will be less than 25'.
Adam & Andrew, the round ductwork inside our mechanical room as seen in the pictures is 6" diameter. 6" was run as long as possible with transitions to oval as the ducts turned up into walls and into the outlet boxes in the bathrooms. I opened up one and snapped a pix, believe that is 6" oval at that point.
Thanks for the post and comments. I'm finishing up 6" round and 6" oval runs and planning to use a manifold system on both supply and return. It's nice to see an example, and using a Honeywell unit too!
I'm planning to add dampers for balancing on each leg, because they're cheap and I'm a typical engineer.
Did you build your manifold from duct board? I would appreciate any recommendations on that material/method. I also need to look up how large and dimensions to ensure good mixing. The Honeywell ERV is nominally 150 CFM. I have about six legs on each side.
Thanks in advance on this older thread!
User-7558150, did you build your manifolds? I am also an engineer, have Honeywell 150 CFM unit and ran 6" round to oval everywhere. I plan to add dampers and attach to manifolds. Now that I'm done with the hydronic heating system, I can focus on fresh air. Thank you in advance!
I think you and user-7558150 should get a beer. You certainly have a lot in common!