cheap air to air heat exchanger

[terranaught]

https://cheap-easy-living.weebly.com/

 I thought of this 25 years ago, even sold plans in pm.
I live in the pacific north wet and condensation is a problem, this helps keep the air dry for a few watts.
might also help smokers.


while burning some cardboard I noticed how fast the smoke shot out between the corrugations.
I knew cardboard isn't the best conductor of heat but it is cheap so just use more.
I have built a few, I put a 1200w hair dryer in one side and the computer fan in the other and most of the heat was exchanged ( burning hot on the computer fan side and room temp on the dryer side).

 

[DannyB1954]

Coroplast is basically a plastic cardboard. I have seen that used. Use spacers that are 90 degrees to the corrugations.  You then install the assembly like a diamond with a corner facing down. You then put this in a box that is open on both ends with a divider going across the middle to the corners of the coroplast that are on the sides.    Now when you blow air into both  sides it will come out on the opposite end.  Here is a commercial unit.

Youtube has many DIY heat exchangers. Some use aluminum cans to make a tube that fits inside another tube.
Somewhere I seen plans for one made out of aluminum foil with thin plywood spacer frames. Here is my sketchup version of that assembly.

 

[MrNoodly]

Where do you envision something like this being installed?

 

[DannyB1954]

Something like this you could hang where the wall meets the ceiling or above the rear doors.
For the box type, you could mount it to a wall, under a bed, and run hoses.
For a van it would not have to be very large as you are only talking about maybe 500 cubic feet of air to replace about once an hour.
I thought about building one but for me it was not worth the effort. If you live in an area that is prone to mold it becomes more important.

 

[skyl4rk]

I was designing a heat exchanger for winter camping in my 4x8 cargo trailer. It was insulated and small enough that body heat would raise the inside temp by 20 or 30 degrees. But as soon as you opened a vent it would cool off.

I was going to vent out cool air near the floor which was still warmer than the outside air, and us the heat exchanger to raise the temp of the outside air being drawn in. I never built it but was concerned about moisture and condensation.

 

[MrNoodly]

Here's the way I understand things (and I might be wrong). A heat exchanger works on the idea you have two gases or liquids of different temperatures and you want to either lower the temperature of one of them (like with your vehicle radiator -- air to cool liquid) or raise the temperature of one of them (like your vehicle heater core -- liquid to warm air). And you don't want the two to mix. Am I right so far? Since we're talking about cardboard, I assume liquid isn't part of this (except the moisture you hope to remove from the air). So it's air-to-air with the intention of heating cool air or cooling warm air. Am I still right? And I'm assuming you want to change the temperature of the air in your vehicle, because there's no way you're going to change the outside temperature.

So why run outside air through an exchanger instead of just blowing or sucking it directly into the vehicle? If you're going to raise the temperature of incoming air, what with? The air that's already in the vehicle? What's to keep the cool outside air from cooling the warmer inside air? Or if you're trying to cool the interior, what's to keep the warm inside air from warming the cooler outside air? Because temperature is being exchanged between the two, and not necessarily in the direction you want unless you have some other mechanism in the circuit applying heat or cold. At least that's the way I understand it.

Oh, and neither cardboard nor plastic are good at transferring temperature. They're more like insulators.

 

[MrNoodly]

If you're dealing with PNW-level moisture, then you need a dehumidifier, not just an exchanger. (Otherwise you'd just be exchanging humid air with humid air of a different temperature.) A dehumidifier requires a way to refrigerate a surface which moist air can condense on, and a way for that condensation to drain.

 

[DannyB1954]

If you're going to raise the temperature of incoming air, what with?

Oh, and neither cardboard nor plastic are good at transferring temperature. They're more like insulators.

The objective is to raise the temperature of the incoming air with the heat from the air that you are venting out. Say the temp inside is 70 and the temp outside is 30. If you were to just vent out the air, cold air would be sucked into the vehicle. By running the air out and air in next to each other with a barrier in between, the heat from the warm air going out will transfer some of it's heat to the air coming in.

It is not a perfect transfer, but now instead of the air coming in at 30 degrees it might be 50 degrees.
Plastic is not bad at heat transfer. At least some car radiators today are made of it. Plastic is an electrical insulator but it doesn't stop heat. fill a plastic glass with boiling water and pick it up. A beverage in a plastic bottle does not stay cold long. I would not use cardboard as it is porous and might absorb moisture and cause mold. This system may not be perfect for every situation but it does work well in a lot of homes. Particularly if the person is sensitive to chemicals that are released from a lot of the new building materials.

 

[MrNoodly]

...Say the temp inside is 70 and the temp outside is 30....

...It is not a perfect transfer, but now instead of the air coming in at 30 degrees it might be 50 degrees.

As you add 50° air to your 70° air, the 70° air slowly becomes cooler, say 68°. Then the 68°air can only warm the incoming air to, say, 48°, which drops the internal temperature slightly more, which means it can warm the incoming air slightly less, and so on -- unless you have another heat source.

 

[lenny flank]

Alas, the laws of thermodynamics always win.

And I agree with MrNoodly--if you wanna remove humidity, you need a dehumidifier. And that takes a lot of energy to do.

 

[DannyB1954]

As you add 50° air to your 70° air, the 70° air slowly becomes cooler, say 68°. Then the 68°air can only warm the incoming air to, say, 48°, which drops the internal temperature slightly more, which means it can warm the incoming air slightly less, and so on -- unless you have another heat source.

Nobody said that it was a perpetual motion machine. You will still need a heater but now instead of having to heat 30 degree air to 70 you are heating 50 degree air to 70. You can use a smaller heater or run it at a lower setting.
People have been using these for years in houses. This is not a new contraption but nobody has applied them to vehicle dwelling because most people don't live in vehicles. If you burn anything in a vehicle you should have ventilation. This is just a way to save some of the heat that you are paying for. So far for me it hasn't been worth the effort to build one.

 

[terranaught]

cold air does not hold as much water as hot air so there is significant moisture reduction.
it is very efficient I would guess 95% or better but I have no way to verify,
the temps are very close to the same within a degree or 2.
I have not had any condensation problems with cardboard.

people loose a litter of water/day through sweat and breathing,
in a van this ends up on your windows.
this unit uses reverse flow which accounts for the great efficiency the one pictured in the earlier post used right angle flow which is easier but not very efficient.

 

[DannyB1954]

cold air does not hold as much water as hot air so there is significant moisture reduction.

I have not had any condensation problems with cardboard.

My concern about cardboard is the cardboard absorbing water and mold growing where you could not see it, pumping spores into the air. Some people are real sensitive to it.

 

[terranaught]

That could be a concern, but mold will grow in your vehicle with excess moisture too.
most trailers here rot from the inside out due to moisture condensing inside the walls.

 

[DannyB1954]

I guess we will have to agree to disagree. For me cardboard has two separate things going against it. It isn't the best at heat transfer and it absorbs moisture. I have used cardboard as a cheap insulator. I would glue layers together then paint it with latex paint. Once the paint dried it was reasonably water resistant. Plain cardboard absorbs water. So why not use something that doesn't? Something that transfers heat better, and is waterproof.

 

[John61CT]

Coroplast or polycarbonate sheeting?

 

[Redbearded]

Maybe what you want for moisture removal and heat transfer is called an enthalpy wheel.
http://www.dac-hvac.com/energy-recovery-wheels-what-is-an-enthalpy-wheel/

 

[Land-Pilot]

The objective is to raise the temperature of the incoming air with the heat from the air that you are venting out. Say the temp inside is 70 and the temp outside is 30. If you were to just vent out the air, cold air would be sucked into the vehicle. By running the air out and air in next to each other with a barrier in between, the heat from the warm air going out will transfer some of it's heat to the air coming in.

It is not a perfect transfer, but now instead of the air coming in at 30 degrees it might be 50 degrees.
Plastic is not bad at heat transfer. At least some car radiators today are made of it. Plastic is an electrical insulator but it doesn't stop heat. fill a plastic glass with boiling water and pick it up. A beverage in a plastic bottle does not stay cold long. I would not use cardboard as it is porous and might absorb moisture and cause mold. This system may not be perfect for every situation but it does work well in a lot of homes. Particularly if the person is sensitive to chemicals that are released from a lot of the new building materials.

Vehicle radiators are not entirely made of plastic. The side tanks might be but that big peace between them is of metal and for a really good reason, it conducts hot and cold way more efficiently than plastic. Any hot liquid in a thin walled container will make it feel hot unless it's vacuum walled. So stick that in your thermal-dynamic pipe and smoke it.

 

[DannyB1954]

Vehicle radiators are not entirely made of plastic. The side tanks might be but that big peace between them is of metal and for a really good reason, it conducts hot and cold way more efficiently than plastic. Any hot liquid in a thin walled container will make it feel hot unless it's vacuum walled. So stick that in your thermal-dynamic pipe and smoke it.

OK make yours out of cardboard as the OP suggests. I believe I mentioned I would make one out of aluminum foil with spacers, But feel free to find some kind of fault with this post as well. No need to add positive info to the OP, when you can get more pleasure out of criticizing what someone else has posted. Do tell us how to make one.

 

[Land-Pilot]

OK make yours out of cardboard as the OP suggests.  I believe I mentioned I would make one out of aluminum foil with spacers, But feel free to find some kind of fault with this post as well. No need to add positive info to the OP, when you can get more pleasure out of criticizing what someone else has posted.   Do tell us how to make one.

Hey man I'm sorry, I should have put a smiley face at the end of my comment. I think you had an interesting idea that has some flaws but you'll notice I was not criticizing this method to cool or heat a space. My rebuttal was purely directed to your statement assuming vehicle radiators where made of plastic, and your plastic cup analogy, thus being a good medium for thermal transference. No offence meant sir.