DIY Heat Exchanger for Automated Water Change System

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I researched the thermal conductivity of common materials and I can see why copper is usually used. I can also see why pvc is not used.

Copper is 2,110 times more thermally conductive than pvc
2,000 times more than acrylic
399 times more than Pyrex glass
25 times more than stainless steel
1.6 times more aluminum

If money is not a problem, silver is more conductive than copper.

Personally, I would go with the copper pipe. Most people still have copper in their houses and that's the water their fish are living in. Also, you are talking about a relatively short piece of pipe.
 
FishFlake;5081139; said:
I researched the thermal conductivity of common materials and I can see why copper is usually used. I can also see why pvc is not used.

Copper is 2,110 times more thermally conductive than pvc
2,000 times more than acrylic
399 times more than Pyrex glass
25 times more than stainless steel
1.6 times more aluminum

If money is not a problem, silver is more conductive than copper.

Personally, I would go with the copper pipe. Most people still have copper in their houses and that's the water their fish are living in. Also, you are talking about a relatively short piece of pipe.
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Well, I think you have convinced me to have the copper tubing in direct contact with the water. I still have a full 50' roll of the 1/4" copper tubing, so I think I will make a coil out of it and nest it inside a 3" piece of PVC. I will have the incoming fresh water go through the copper coil and have the outflow from the first heat exchanger flow through the PVC. My first unit is running at at least 25% efficiency, so if I can capture 50% of the remaining heat I will be doing pretty well.
 
No doubt the copper is an excellent thermal conductor, I would still look into the PEX a little closer.

I don´t have any prices at hand but it is quite cheap the last I remember looking. It is designed for in floor heating etc so it should be at the least a ¨fair¨ thermal conductor. By far better than PVC? There also will be no heavy metal deposits to worry about that I am aware of. And, it is quite flexible.
 
fg4608;5082924; said:
No doubt the copper is an excellent thermal conductor, I would still look into the PEX a little closer.

I don´t have any prices at hand but it is quite cheap the last I remember looking. It is designed for in floor heating etc so it should be at the least a ¨fair¨ thermal conductor. By far better than PVC? There also will be no heavy metal deposits to worry about that I am aware of. And, it is quite flexible.
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This is a fair point... efficiency is a big deal with in floor heating and pex is used there all of the time...

That said I have all copper lines running into my house and my fish tank is as far away from the incoming line as it can be....

Inverts are the most sensitive to copper and I've not had an issue with my baby crays...

I do like your heat exchanger idea... I too am concerned about heat loss in my tanks, but it doesn't seem that others are as concerned :)
 
fg4608;5082924; said:
No doubt the copper is an excellent thermal conductor, I would still look into the PEX a little closer.

I don´t have any prices at hand but it is quite cheap the last I remember looking. It is designed for in floor heating etc so it should be at the least a ¨fair¨ thermal conductor. By far better than PVC? There also will be no heavy metal deposits to worry about that I am aware of. And, it is quite flexible.
Click to expand...

I have thought about PEX quite a bit. It is excellent stuff - I plumbed my house with it when we built it seven or eight years ago. It is nonreactive, tough, and easy to work with.
A few drawbacks:
It is relatively expensive. Copper is more, but I have several rolls of copper that have been gathering dust in my parents' shop for over fifteen years.
It is flexible, but has incredible memory. So while you can coil it around something, it won't hold that coiled shape the way copper does.

suds1421;5082951; said:
This is a fair point... efficiency is a big deal with in floor heating and pex is used there all of the time...

That said I have all copper lines running into my house and my fish tank is as far away from the incoming line as it can be....

Inverts are the most sensitive to copper and I've not had an issue with my baby crays...

I do like your heat exchanger idea... I too am concerned about heat loss in my tanks, but it doesn't seem that others are as concerned :)
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I haven't seen the numbers, but I suspect PEX has fairly low heat conductivity. The reason why this doesn't affect the efficiency of hydronic heating systems is that the heated water recirculates - any heat that isn't transferred into the floor is just returned to the boiler, not lost.

The fact that people are keeping invertebrates in homes with all copper plumbing helps to relieve my anxiety about copper. I have a feeling that water continuously flowing through a relatively small amount of copper isn't going to add any significant amount of metal to my tank.

I am also a little surprised that more people haven't looked into something like this - heat loss through water changes is wasteful and expensive...

Thanks for the discussion, it is really helping me to finalize the design of my next unit!
 
my two penny worth. Pvc is not the way to go it is an insulator by make up. If your worried about disloved metals in your system you could use activated carbon to remove. Heat exchangers work on two methods either create as large an area as possible to exchange or move as much as the liquid as possible, but both require good conduction materials. With your system you have stated that you need to peform 100 gal water changes so if you were to run this as 24 hr method that will give your flow rate of about 4.2 gal an hour. what you need to achive is a greater contact time i.e incresase the overall time by increasing your length of heat exchanger. The conducter cop (co efficence of perormance) needs to be ally or copper, stainless stell would also be good as it corodes very little. A Refrigeration/ air con/ evap coil would work like a dream because you could pass the heated waste water though the copper coil( more prone metal to corrosion0 with clean supply water arround the ally fins, incase this in a container and insulate. This has the advantage of a pre made high surface area, maximum contact time set up which you buy from a scrap yard for cheap hope this long winded reply helps.
 
FishFlake;5083211; said:
Don't forget to patent it and sell it to the rest of us.
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:grinno:

Undertheradar;5086361; said:
my two penny worth. Pvc is not the way to go it is an insulator by make up. If your worried about disloved metals in your system you could use activated carbon to remove. Heat exchangers work on two methods either create as large an area as possible to exchange or move as much as the liquid as possible, but both require good conduction materials. With your system you have stated that you need to peform 100 gal water changes so if you were to run this as 24 hr method that will give your flow rate of about 4.2 gal an hour. what you need to achive is a greater contact time i.e incresase the overall time by increasing your length of heat exchanger. The conducter cop (co efficence of perormance) needs to be ally or copper, stainless stell would also be good as it corodes very little. A Refrigeration/ air con/ evap coil would work like a dream because you could pass the heated waste water though the copper coil( more prone metal to corrosion0 with clean supply water arround the ally fins, incase this in a container and insulate. This has the advantage of a pre made high surface area, maximum contact time set up which you buy from a scrap yard for cheap hope this long winded reply helps.
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Yeah, it might be worth looking for a commercially built unit at the scrap yard. I looked into them new, but they are a lot more than I want to spend.
 
you would need to soak in an acid bath or connect to pump and use something like a engine flush but to be honest if the water is allways flowing to waste then you shouldn't get contaminates entering sys. you can also get a a couple and braze the copper together if you wanted a compact desighn. I weigh these coils in at equivelant of 2 $ a kg to scrap yard
 
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