Integrating a ERV into existing duct work, or not?
One of our current projects includes a new fully ducted HVAC system. There is one air handler with two zones ducted off of it. The HVAC sub installed the zone dampers so close to the air handler that its not possible to dump the supply side of the ERV into the duct work before the zone dampers so I’m considering splitting the ERV supply in to two and dumping the air into each branch of the system down stream of the zone dampers.
The HVAC sub is concerned that if we do this that when there is a call for heat/AC on one branch only it will back draft from the supply of the other branch, should this be a concern?
I like the idea of using the HVAC duct work for the ERV as it will give better air distribution and tempering of cooler winter air, but maybe my best solution here is to have separate ERV supply duct/register blowing high up in a two story stair well where it seems it would have a good chance of mixing and diluting possible cooler winter air.
Any thoughts on this?
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Replies
Jud,
I'll give your post a bump. I guess it's too late to install dedicated ducts for the ERV?
Hi Steve-
Yes, too late, not enough room and not enough budget to do a separate duct system for the ERV.
So far I will have a separate intake for the ERV, I wont use the return. The supply will either go in the return or into the supply on one of the two zones. If it does go into one of the two zones Ill go for the injection port type set up that I have read about. The house is a mix of new additions that should be pretty tight and a 1747 section that we have tightened up but still has very leaky original windows. We improved the windows dramatically by installing spring bronze weather stripping and they will have a good quality storm window, but that part of the house does not need ventilation.
Have you considered something like the Twinfresh? Room-by-room ventilation might be better than trying to Macgyver the HVAC system.
I have not, but i dont think the owners would approve of the look of them and the two ERVS are already on site, part of the HVAC sub-contract.
You could use a backdraft dampers to prevent an on zone from feeding an off zone.
I question whether your heat/cooling need has much to do with where you need ventilation. In particular, closed door bedrooms need fresh air supply.
Jon-
The house is 4,700 SF and most of the time there will be two people living there. In the future on Holidays and weekends there is the potential for 14 to 18 family members to be staying in the house so with this in mind the ERVs will have there own on/off switch, 20 minutes on, 40 minutes off. I dont see a need for ventilation when there are just two people in the house, but when there are 14-18 it seems like a good option to have. There are (3) AH, each with two zones, out of those 6 zones two are in the 1747 section and that AH will not have an ERV. The other 2 AH/4 zones are much tighter and that's were the ERVS will be located. The compressors are each 2-ton, two stage heat pumps and the air handlers are variable speed with hot water coil backups. Steven Winter Assoc. did the load calcs so I trust the sizing.
Also, the bedrooms and a home gym are what the ERV would supply via the HVAC duct work.
Since you'll be using the HVAC ducting already, I would run the ERV fresh air feeds to the intake of each air handler.
This avoid any issues with zoning but it will also not deliver any fresh air to any zone not using any heating/cooling.
To fix this, you could interlock the air handler with the ERV to run at low speed whenever the ERV controls call for ventilation and set each zone damper to be open enough when off to allow for sufficient air flow. This would mean that each zone would get a bit of heating/cooling even when there is no thermostat call for that zone.
There are no easy solutions to your setup without a fully ducted ERV.