Heat Recovery Ventilator DIY Disaster

TLR It was a pain the the ass and didn't help much
 
 
So I was looking for a way to save on heating bills and I found a thingy called a heat recovery ventilator. It takes your warm exhaust air and uses it to heat your fresh intake air. It has a metal core inside with a cross flow design that keeps the air separate, but transfers heat. The Internets said it could be like %70+ efficient, OK GREAT! But the whole unit cost multihundreds of dollars, and just the core was a few hundred. Not so great. I figured "hell, I could build one!" and that's what I set off to do.
 
It works like this.

I looked up plans and people were building the core out of coroplast. Coroplast is an extruded plastic sheet with holes in the center layer, pretty much a plastic radiator. It's what political signs are made out of, so it's made for hot air. I go and price out some coroplast and it's about $25 a 4x8' sheet, not too bad. How many do I need? 4 sheets!! EEK so I downsize my design some, skimp some, and get away with a pile of scraps the shop had that cost $25 but was probably about 1.5 sheets.
 
I'm getting all my ducks in a row, got templates setup and start cutting it. UGH, not fun! So awkward, and because they're scraps they've been precut not straight and squished in places so also not square. The other problem is that you can't glue this stuff with anything you would have lying around. The only stuff that works is $100 a tube! F that, I break out the hot glue gun and start frantically gluing and pressing it together hoping I don't run out of glue sticks or it cools too fast and makes it crooked. I must have used 50 glue sticks on this project!
 
It's ugly but it's getting there.
 

 
OK DONE!
 

 
 
So now I need a way to feed it air, one trip to home depot later and I've got some vent ducts that will work perfectly. They're 6" inlet, 12X6" outlet and cost $12 each. I figured since the core is half in one direction and half in the other I would need at least double the area of the 6" ducting. Ducting is 3.14 x 3" sq x 2 = 56.5" sq, vents are 12 x 6 = 72" sq, double and extra! Oh, did I mention that the coroplast is 1/8" think so I need 48 layers of the damn stuff? And since it's crooked and annoying to cut, everything came out kinda off and I had to trim it to fit? I used only hot glue to attach everything, so it's a total goober mess, but it's sealed and pumps air and heat!
 
It's so ugly it's beautiful.
 

 
Ok, so it isn't really pumping heat with just an oscillating fan hitting it every 10 seconds. Time for some computer fans!! 4x 120mm sounds like not enough, so lets get that.
 
Now we're cooking with gas.

 
Lets do some testing! I put some gaffer tape on the inlet and outlet to take some temp readings with the IR thermometer. 74 in 71 out. IT WORKS!! I can feel the warm air coming out the other side. But not much. I have the lights on at night, so lets see what the high/low temps are for the room overnight in the last 24 hours. 76 / 63 Eww, it got cold! That must have been in the morning after the lights went off and the day hadn't warmed up yet. We rarely use the heater in the house, we just put on another layer of clothes.
 
I was hoping for 80 / 70, what a disappointment. It really only helped a little, and with nothing heating the exhaust air it's basically doing nothing. Even with the light on it's only pulling a few degrees off the exhaust. So mine is not efficient, or well built, or worth the time or money I spent. Story of my fucking life!

 

Take drugs, fly to the sun!