Custom Designed HRV

This system was installed a few years ago as a prototype.
We sell a great little air to air heat exchanger for welding shops called "Keep The Heat".
Their only real drawback is that they only make one size of unit that exhausts about 1500 CFM.
If a customer needs more air flow they just add more units to achieve the desired total.

We ran into a few jobs where the customer simply didn't have enough room to install the required number of systems.

We sat down and we designed a large system that we were pretty sure would work and we sat on it for a while. One day a local welding shop owner came into the shop to talk to me and he was one of these people. He needed 6 systems but the design of his building would not allow for it. I told him about our idea and he simply said "Let's try it!"
Now seeing as this was about a $90,000.00 gamble on a theory. We were really excited....and nervous as hell.

The system took about 6 weeks to fabricate and install and actually exceeded our expectations in every way.

The system moves 9200 CFM, is as close to silent as you can get and the ventilation effect was absolutely fantastic. With an outdoor ambient temperature of -10F and a ceiling temperature of 60 degrees F, we were supply fresh air back to the building anywhere from 52 to 56 degrees. (No additional heat source other than heat exchange from the exhaust)

To say the customer was happy is an extreme understatement.

2 years later he built a brand new building 3 times the size. He called me up and said "lets get 3 systems into the new building please".

We have now installed 5 ½ systems and all are working great. (Towards the end of that project this customer sold his 3rd unit to another welding shop that needed something fast. so we have 2 systems fully installed in his building and a 3rd half done.)

The air handlers in these pictures were built by my brother and I in our shop. We have since designed a new air handler with the first customer that they build for us.

We use 6" Sch 20 PVC for our supply air drops. Believe it or not we actually get a bit of heat "reclaim" from the ceiling using that. We get about a 2 deg rise in air temp from the outlet of the actual exchanger to our air outlets.

We boxed in the main building beams and used them as fresh air supplies.

We did a duct within a duct design for a cleaner look, single wall penetration and possibly a little bit more heat exchange. We used turning vanes everywhere we changed air direction.

There's definitely something to the static electricity because the pipe will attract dust. I don't think it's a huge buildup by any means. Our small package system is 100% plastic so I can see it being more of an issue on those. Our big system is all grounded to the ductwork, steel chassis of the air handler etc so my thought would be that it would dissipate any static buildup.

The only codes that we found that hamper our use of the PVC is if we were to put auxiliary heat banks in. We designed in the beginning around installing auxiliary heat banks if they ended up being needed as we only had theoretical efficiencies in mind. If we fired up and found our efficiency to be lower than expected, we wanted to be able to do a bit of a heat boost after the exchanger so we didn't cool the building off too much.
The codes really only refer to flammable ductwork and required us to have a minimum 6 foot separation between the heater and the ductwork as well as redundant high limit safeties. (Easy stuff).

The noise issue really isn't an issue at all you just have to keep your velocities in check. We shoot for 1500 fpm or less whenever possible and the system is actually very quiet.
The first system we installed, (top pictures with the spiral duct), was virtually silent. If the shop was dead silent all you could hear was the small whine caused by the variable speed drives on the motors.

The other system we had a bit of turbulence noise that we tracked down to our main duct within a duct. We now know to size that far differently than we did. When we first started that system our exhaust airflow (outer duct), was way lower than we had expected. What we found and a few people are gonna say "not possible" (I did till I saw it), we had 3" static on 2 sides of the duct and almost zero on the other 2. The sides that we had zero flow on also had no air flow. We made a minor change (giant pain in the arse at that point) and our airflow got way better. In the future we will be oversized that outer duct.

Thanks to John L.