Copper Coil Heat Exchanger Sizing

[avc8130]

I am planning out my Tarm Excel 2200 install and am working through my exact storage needs/desires.

Today's goal: design the copper coil heat exchangers.

I have a good friend in the plumbing industry who can setup me up with copper coils at his cost, so I figured I would take a stab at building my own exhangers.

The Tarm is 140k btu rated on wood.

What length/diameter copper coils will I need for space heating?

How about DHW?

I am planning on a ~800 gallon storage tank.

ac

 

[Bad Wolf]

I copied the STSS design and put in two 3/4" x 150' coils for a Tarm excell 2000, on a 1200 gallon tank. Plus one 150' for DHW and one 150' for solar. Its worked fine so far.

 

[avc8130]

I copied the STSS design and put in two 3/4" x 150' coils for a Tarm excell 2000, on a 1200 gallon tank. Plus one 150' for DHW and one 150' for solar. Its worked fine so far.

I thought STSS claims 1/2" on their site?

I guess for 150', that would be the same as a 75' radiator run out and back. All of my heating is done with 3/4" lines, so that probably makes the most sense for the heat exhanger too.

ac

 

[Bad Wolf]

Interesting, on one part of their site they say 1/2 but elsewhere they say 3/4 and thats what I remember. I did a total of 300' of 3/4 for the heat exchanger coils. It must be doing its job because the return water is the same temp as the water at the bottom of the tank so its obviously shedding all of its heat on the way through.
With 1200 gallons I get it up to 180 and get 500,000 BTU's of storage.

 

[avc8130]

Interesting, on one part of their site they say 1/2 but elsewhere they say 3/4 and thats what I remember. I did a total of 300' of 3/4 for the heat exchanger coils. It must be doing its job because the return water is the same temp as the water at the bottom of the tank so its obviously shedding all of its heat on the way through.
With 1200 gallons I get it up to 180 and get 500,000 BTU's of storage.

That sounds great...and sounds like you have a very similar setup to what I am working towards.

How did you construct your tank?

ac

 

[Thomas Anderson]

I would think that you could get away with shorter coils if you went with 1/2" than with 3/4", because you'd get more surface area for the given volume. It would also tend to flow more quickly.

 

[Bad Wolf]

Surface area is what you want for heat transfer, plus you need a certain amount of dwell time. There is a trade off but 3/4 seems to be a good compromise.

avc8130- I built a swimming pool in the basement. Literaly. I bought 54" high by 24' dia pool sides, cut it down to make a 8' dia pool. bolted it together and lined it with HDPE. Now I know some folks say that wont stand up but I've seen a lot of folks here that have used it, including STSS.

Let me know if you want pics.

 

[Thomas Anderson]

My tank uses a layer of HDPE sandwiched between two 1"-thick styrofoam boards (joints sealed with high-temp caulk), then on the inside of that I have a sheet of cement board, and I tiled that with porcelain tile (from the sale rack at Home Depot, 45 cents/sqft), grouted and sealed. It looks like a big jacuzzi. My hope is that the HDPE will be a never-needed backup.

 

[avc8130]

Surface area is what you want for heat transfer, plus you need a certain amount of dwell time. There is a trade off but 3/4 seems to be a good compromise.

avc8130- I built a swimming pool in the basement. Literaly. I bought 54" high by 24' dia pool sides, cut it down to make a 8' dia pool. bolted it together and lined it with HDPE. Now I know some folks say that wont stand up but I've seen a lot of folks here that have used it, including STSS.

Let me know if you want pics.

Heck yeah, I would LOVE pics!

ac

 

[Bad Wolf]

Here is my tank and coil set up.