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Air to Air Heat exchanger? DIY?

M

mushroombrew

Active member
Veteran
Let me tell you about my ventilation/cooling.

I have a reservoir room/veg room. And a flower room.

Cold outside air is drawn into the "mixing" res room.
That space is also cooled with AC if the incoming air is too warm.

CO2 Burner is in the same room. Then a 12" blower moves cold CO2 rich air into the bottom of the flower room.

10" ceilings in the flower room. So heat rises. Its 82-84 in the canopy
and 95 on the ceiling.

I draw the hot air from the top and exhaust it outside. If I put it in the mixing room my AC demand would increase. About $50-60 per day.

But of course I am losing CO2 all day long. I stay at 800 while burning about $10 per day in propane.

So I had an idea to make a huge heat exchanger. And seal my room.
So I can get CO2 higher. I can do so with AC but the cost is too high.

https://ecorenovator.org/forum/conservation/891-diy-ventilation-heat-exchanger.html

I was thinking about using corrugated metal. 3x3 sheets. Stacked so each sheet is 90 to the last. Cold outside air flows in the opposite direction to the warm grow room air.

I just have no idea how many btu's of cooling I would get? It does stay below freezing for months.

Then I set up a thermostat so if incoming air gets too hot it kills the blower.

I am always looking to cool for "free". Even thought about a 12" pipe going through a pond with heat sink/vanes. Water obviously has 20 times the heat carrying capacity.

Is the flower room RH going to cause freeze up issues in the exchanger? Do you think I need a drain opening of some sort?
 
M

mushroombrew

Active member
Veteran
Yes that is a concern. I was thinking about setting the exchanger square sitting on a corner
like a diamond. So condensate goes to the point. Maybe some small holes there too. A little air will escape but so will the condensate.

Or I will have a big ice cube outside!! lol
 
Drop That Sound

Drop That Sound

Well-known member
How about designing a reverse HRV, so instead of the core recovering heat, it keeps it cold in and pumps the heat back out. I am trying to design such a system. It could even sit outside, and why fight it, might as well make ice cubes too! Outside of course ;)
 
M

mushroombrew

Active member
Veteran
Can you explain a little. The HRV is basically what I would be building on a larger scale.

But we are recovering cold from outside. Its the same thing though right? Blow air in the opposite direction and heat or cool?

I was planning on ground mounting the Heat exchanger outside in the shade. Cold outside air will be blown across it. Ideally I would have a big pond and use the water to cool the air.
That woulds take a shitload of sealant!!

I just have zero Idea how big to make it? Will start with a 3x3 maybe 15 layers so the HRV exchanger is 3x3x3 ish. In a box much like the small commercial HRV ones for a dryer vent.
 
Drop That Sound

Drop That Sound

Well-known member
It's pretty simple how they work. Sitting in the housing you have the main component, the core, which is just a bunch of channeled aluminum plates stacked up in a staggered configuration so that air cross flows through it 2 ways.

Then you have 4 ports.. 2 intakes, and 2 exhausts. As the hot air is being sucked out of the room through one of them, it flows one way through the core and then outside through another port on the other side. The core captures some of the heat but not all. At the same time fresh air is sucked back into the room through the other 2 ports, flowing through the same core and recycling that heat into the new fresh air as it does.

Somewhere on here I drew up a diagram on how it could possibly work sitting outside, for cooling instead of retaining heat, ill look. I was wondering it it would work better to flow directly into the room or through another air to air core.

Also you can really boost the efficiency by using multiple cores, I plan on building a triple core this winter.

One big one could work well if designed properly.. I suppose you could use your corrugated sheets setup like this:
url

but would require more work gluing them.

I recently was talking with a friend about designing a room or structure that uses the entire wall/s as a core, imagine that!

I'm pretty much in the same boat, trying to figure out how to design one or even 2 air handlers that are water and air cooled, basically a hybrid system all in one. Im about ready to go for it.

I got many more idea's so i'll chime back in real soon!
 
M

mushroombrew

Active member
Veteran
Drop That Sound said:
It's pretty simple how they work. Sitting in the housing you have the main component, the core, which is just a bunch of channeled aluminum plates stacked up in a staggered configuration so that air cross flows through it 2 ways.

Then you have 4 ports.. 2 intakes, and 2 exhausts. As the hot air is being sucked out of the room through one of them, it flows one way through the core and then outside through another port on the other side. The core captures some of the heat but not all. At the same time fresh air is sucked back into the room through the other 2 ports, flowing through the same core and recycling that heat into the new fresh air as it does.

Somewhere on here I drew up a diagram on how it could possibly work sitting outside, for cooling instead of retaining heat, ill look. I was wondering it it would work better to flow directly into the room or through another air to air core.

Also you can really boost the efficiency by using multiple cores, I plan on building a triple core this winter.

One big one could work well if designed properly.. I suppose you could use your corrugated sheets setup like this:
View Image
but would require more work gluing them.

I recently was talking with a friend about designing a room or structure that uses the entire wall/s as a core, imagine that!

I'm pretty much in the same boat, trying to figure out how to design one or even 2 air handlers that are water and air cooled, basically a hybrid system all in one. Im about ready to go for it.

I got many more idea's so i'll chime back in real soon!
Click to expand...

Great thanks for your input!

Yeah I get how to build them. Just curious about condensate and
how to remove it before it freezes up like an AC!!

And the daisy chain idea is great. Although will have to decide if parrallel or series is best for multiple cores.

I hope to take temp readings coming in and out of the core(s). At different ambient temps. So I can gauge cooling btu's some what.

I ideally there will be a thermostat that is able to kill blowers and turn AC back on.

We get huge temp fluctuations in the high desert so in fall and spring
it has to switch on and off.

Keep me informed of your progress!
 
M

mushroombrew

Active member
Veteran
I checked out that vid. Not sure if the ERV would work. The wicking material would freeze up I think. It gets cold here! Informative vid none the less!
 
OldPhart

OldPhart

Member
I know this thread is about air 2 air, but if it is below freezing outside why not use water (antifreeze)? I've always wanted to try this, but never had a suitable situation for it. I'm thinking that if you used a couple automotive condenser coils, then pumped water through them, you could move a LOT of heat. I've played around with water cooling using well water, and it worked, but just wasn't cold enough to be efficient. But if you had a source of say 40 degree water, I think that it would work very well.
 
M

mushroombrew

Active member
Veteran
Damn it old phart good thought!!

I was thinking about a radiator but the antifreeze is the ticket. Two radiators. On in a box with the warm air blowing over it; and the other could just run off the 12V fan and shroud and sit out in the cold?

I think I am in the market for two huge used radiators!

OK lets figure this out!
 
OldPhart

OldPhart

Member
mushroombrew said:
Damn it old phart good thought!!

I was thinking about a radiator but the antifreeze is the ticket. Two radiators. On in a box with the warm air blowing over it; and the other could just run off the 12V fan and shroud and sit out in the cold?

I think I am in the market for two huge used radiators!

OK lets figure this out!
Click to expand...

I'm glad you like the idea. By my calculation, you would need about 1 gallon of water per minute, with about a 25 degree swing to achieve 1 ton of cooling. So assuming 30 degrees outside and you can chill the water down to 40 degrees, then warm the water to around 65 degrees indoor, you can hit the 1 ton/gallon of water/minute. I always pictured using condenser coils, but I suppose radiators would work.

It always blows my mind when I see people discussing mini-splits that can work below 0 degrees F. If it is that cold, I would be building some kind of water cooling system.
 
Drop That Sound

Drop That Sound

Well-known member
Ya with the ERV the core is made of fabric like permeable layers. I would think it would have to be cleaned or worse, replaced way to often and possibly trap spores?

I guess you could add a few membranes to a normal HRV's core so you have a mix of both. Or if you do a triple or even quad core, one of them could be on demand ERV to mix into the stream.

The cool thing is even with a DIY HRV unit, is that chaining together and cross flowing through 3 or more decently made cores makes it ridiculously efficient! Probably like 90% instead of 70 or less with a commercial single or dual core that costs 1000's.



Suppose you could simply fill up a 55 gallon drum or a small pool with 50/50 water/glycol (rv antifreeze), to sit outside. Even better add a second stage remote res that is plumbed to it, sitting inside the room as well, for all the coils, pumps ,and controller sensors to sit in, and better control. Pair it to a simple air handler made from car or RV parts. In the summer you could also chill it, if you even needed too..
 
Drop That Sound

Drop That Sound

Well-known member
OldPhart said:
It always blows my mind when I see people discussing mini-splits that can work below 0 degrees F. If it is that cold, I would be building some kind of water cooling system.
Click to expand...

Same with people using gas or electric water heater tanks that are sitting under a +100 roof in the shade ALL day long, lol..
 
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