pex al pex for a heat exchanger??

[fireman31]

Any thoughts on using plain pex or pex aluminum pex for a heat exchanger coil?

I'm finally getting around to some solar and wood boiler projects.

MAN COPPER TUBING AND FITTINGS HAVE GOTTEN EXPENSIVE!!!

Pex is about half the cost of copper and you can get continuous lengths up to 500' so there would be no connections in the length of the coil, only at the ends where it connects to the sides of the vessel.

This particular application would be for a glycol loop for domestic hot water. I'm making the tank out of some plastic barrels... a plastic welder is a wonderful thing!!

I figure that is works in a concrete floor so why not?

 

[ericjeeper]

I have over 1,000 feet of

Non barrier pex hooked up in my 600 gallon storage tank.I have it in 84 feet lengths on six way tube manifolds.. Totaling 500 feet of loop per heat exchanger.. These manifolds are 1 inch to six half inch barbs.
see my photos at www.pbase.com/ericjeeper. Then go to the solar page

 

[fireman31]

Is it pex or pex aluminum pex?

1)The tubing in your pictures looks like plain pex. Is it? plain pex would be even cheaper than pex al pex and I'm all for cheaper!!

2)How does the underground tank work for you?

3)What is the capacity of the tank?

4) what is the total are or the collectors that serve the storage tank?

5)Is it lined with anything besides the styrofoam and plastic? (nice clean,square hole btw!)

6)Did you buy or build your solar panels?

7)Do they have tubes inside or are they the plate collector style?

8)What sort of water temp do you get from the panels on a clear winter day?

9)Do you use antifreeze in the solar loop or is it drainback?

10)How is the pipe wrap system you devised working? Is the ground very wet there?

I'm all for being environmentally friendly but my main interest in alternative heat is because I"M CHEAP!!!!

 

[infomet]

The heat transfer coefficient fot the pexalpex is probably much lower than that of copper. It's likely that you can use half as much copper, or less, and do the job. Once the fluid in the tube gets close to the temperature in the tank, no more transfer takes place and you are just wasting energy in the pump.

The idea of multiple short loops is good, since most of the transfer takes place near the beginning of the loop, if the transfer coefficient is reasonable.

This is the opposite of the pex in floor situation, where you want to use a long loop to minimize the number of connections on the manifolds. Also, in the floor situation you are feeding water only a little warmer than the floor (to avoid hot spots), so you need a relatively long loop to get the heat out of the circulating fluid.

You can play with this, or learn to do heat transfer engineering. Coil up some copper, maybe 20', put it in a tub of coolish water, and pump in some hot. Feel what comes out as you pump at various rates. At very low rates, you'll find cool water coming out. As the rate goes up, hotter. The design task is to get the tube size, pump rate, and coil length to produce the transfer you need.

Small diameter coils take more energy for pumping, but are much shorter, because their surface area is much larger relative to the volume of fluid they carry.

 

[aquan8tor]

The heat transfer coefficient fot the pexalpex is probably much lower than that of copper. It's likely that you can use half as much copper, or less, and do the job. Once the fluid in the tube gets close to the temperature in the tank, no more transfer takes place and you are just wasting energy in the pump.

The idea of multiple short loops is good, since most of the transfer takes place near the beginning of the loop, if the transfer coefficient is reasonable.

This is the opposite of the pex in floor situation, where you want to use a long loop to minimize the number of connections on the manifolds. Also, in the floor situation you are feeding water only a little warmer than the floor (to avoid hot spots), so you need a relatively long loop to get the heat out of the circulating fluid.

You can play with this, or learn to do heat transfer engineering. Coil up some copper, maybe 20', put it in a tub of coolish water, and pump in some hot. Feel what comes out as you pump at various rates. At very low rates, you'll find cool water coming out. As the rate goes up, hotter. The design task is to get the tube size, pump rate, and coil length to produce the transfer you need.

Small diameter coils take more energy for pumping, but are much shorter, because their surface area is much larger relative to the volume of fluid they carry.

This is true about the heat transfer, but the price of copper right now is insane. We just replaced the gutters on the house and ended up going with galvanized steel instead of copper, which is what we wanted originally. Copper has gone up exponentially in the last several years. Wish I'd had money to invest!


So if the transfer is so much less efficient in pex as the temperature differential decreases--gets closer to the same temp, does the system have an adjustable thermostat system that allows you to turn off the pump power before the temperatures are equalized, or what?

 

[infomet]

I'm not sure what system you are asking about. In the floor heating systems, the reservoir tank is typically held at a temp that will be high enough to heat the room but not make part of the slab too warm. There may well be a minimum temp too, so the pump doesn't run when there's not enough differential to be useful.

I wouldn't describe the pex thing as an efficiency matter. Certainly a high transfer coefficient will transfer the heat more quickly (shorter loop), but that's not always good, as discussed for the floor case.

I'm betting that a copper loop will still be cheaper than a pex loop for the same job. But why Pex Al Pex? The Al just makes it easier to put the stuff down and keep it in shape for pouring a floor. Plain pex would be OK as a tank loop. So would black PVC and you can't get much cheaper than that! I've had friends put coils of black PVC on the roof for hot water...works pretty well, especially in summer.

 

[fireman31]

WOW!! I knew there was some science to this!

I knew there was some science to all of this but who knew it would be THIS much.

I'm not trying to over think things but an 80 gallon hot water heater I sold recently had a 120 foot copper coil in it for a a wood boiler or solar array.

Is there some magic ratio of coil length (and tubing diameter) to the capacity of the storage tank?

Any thoughts on proportion of tank size to solar array size?? ie so many gallon tank to so much surface area of collector?

 

[ericjeeper]

1)The tubing in your pictures looks like plain pex. Is it? plain pex would be even cheaper than pex al pex and I'm all for cheaper!!
It is Plain Pex, The oxygen barrier on Pex is not made to be forever submersed in water.
2)How does the underground tank work for you?
The 600 gallon tank was cheap, and very very efficient
3)What is the capacity of the tank?
600 gallons+-

4) what is the total are or the collectors that serve the storage tank? Roughly 400 square feet

5)Is it lined with anything besides the styrofoam and plastic? (nice clean,square hole btw!)
I used one of those pvc type yard pond liners
6)Did you buy or build your solar panels?
Bought em used in Missouri for 150 a piece
7)Do they have tubes inside or are they the plate collector style? They are fin tube style.. Not the latest in technology, but they will make a lot of hot water for the dollars invested.

8)What sort of water temp do you get from the panels on a clear winter day?
I have witnessed 150 degree temps returning
9)Do you use antifreeze in the solar loop or is it drainback?
Due to the configuration of the panels it had to be glycol.

10)How is the pipe wrap system you devised working? Is the ground very wet there? The pipe wrap is pushed into a 5 inch non perforated field tile which I sprayed expanding foam into each end to try to possibly eliminate any infiltration..No my water table is no where near the surface.
Sorry for the delay.. I was away on Holiday

I'm all for being environmentally friendly but my main interest in alternative heat is because I"M CHEAP!!!!

Amen to bucking the OIL GUYS