Copper Coil HX Performance?

[jebatty]

If anyone with a coppers coil (STSS or homemade, etc.) hx into a tank has performance data, it would be interesting to see it. In particular, measured at the tank: input from boiler temp , output return to boiler temp, gpm flow rate, size of coil (diameter of copper pipe and # feet of copper pipe to compute surface area).

If this already appears somewhere, please post the link. Thanks.

 

[Nofossil]

If anyone with a coppers coil (STSS or homemade, etc.) hx into a tank has performance data, it would be interesting to see it. In particular, measured at the tank: input from boiler temp , output return to boiler temp, gpm flow rate, size of coil (diameter of copper pipe and # feet of copper pipe to compute surface area).

If this already appears somewhere, please post the link. Thanks.

I don't quite have it exactly. What I do have is boiler inlet and outlet temps for periods where the tank was the only heat load. That should be pretty close to the tank inlet and outlet temps. No flow rate, but it's a Grundfos 15-58 running mostly on high speed with a bored-out zone valve as the only major restriction. It's an 880 gallon tank that's 48" high. I have three sensors at 6", 24", and 42" so they cover the top 25%, the bottom 25%, and the middle 50%.

My HX is 50' of 3/4" copper with a rectangular array of 5 50" parallel 1/2" pipes 6" apart with 3/4" headers - one array like this on the top and one on the bottom.

If you have the patience, follow the 'voyeur' link in my signature and find a few fires. Easiest way is to select a period of several days, find a fire, then zoom in on it. You can download the dataset for any graph in spreadsheet format.

I don't have time right now, but I'd be glad to walk you through the analysis - PM me if you'd like.

 

[free75degrees]

I have homemade cu coils - 4 in parallel, 1/2" x 10' hard cu sticks bent into coils with conduit bender and then joined with 45 degree couplings. Each coil has 8 sections plus a vertical return, so they are each about 85 feet for a total of about 340 feet. i don't have gpm or tank output temp readings, but i do have some other numbers that tell a little about the performance.

The lowest I allow my tank top temp to get before I start a new fire is 130*. When gasification kicks in and the top is at 130* and the bottom at 115* the top rises by about 1 degree every two minutes. Typically after about 2 hours of full gasification (subtracting the time when the tarm is heating the zones instead of the tank), the top is at 170* and the bottom is at 130*. At this point the top temp is rising by about a degree every 4 minutes. The max temp I get at the top is about 180 and when it gets to that point the top stops rising in temp and the bottom starts catching up. The tank input temps during the tank charging range between 170* and 195*.

My coils are not perfect because the blower fan goes off periodically when the boiler temp gets too high becuase the hx/tank are not able to remove enough heat. However, i am pretty happy overall. One thing i plan to do in the future to try to avoid the idling when the boiler gets too hot is to sense when the boiler is getting close to the temp where the fan will go off, and then dump some heat into my house zones. I think this would work because my logging shows that the zones are pretty effective at lowering the boiler temp. I would only do this once i get my zone thermostats replaced with temp sensors so that i can put a limit on how much heat i would dump into the house (for example if I set the zones at 70* the system might allow them to get up as high as 75* for heat dump purposes, but wouldn't allow them to go beyond 75).

 

[mole]

Jebatty,
I just got my storage system up and running 6 weeks ago and I'm loving it. Want to share it with all...I have two 3/4"x120ft coils in my tank plus a bottom coil that's a combination of 3/4" and 1" scavenged from my old loop. The bottom coil is 5 rectangular laps around the square tank and is about 100' in length. The supply header is 1-1/4" black pipe. The tank heats in three stages, depending on the loop temperature. See attached diagram.

P1 - Taco 007-Seton pump - always on.
P2 - Taco 007- controlled by Aq 2 and comes on when the loop reaches 175.
P3 - Taco 007 IFC- controlled by Aq 3 and comes on when the loop reaches 178.
P4 - Taco 00R IFC - controlled by thermostat -supplies the forced air Hx.
Aq4 - controls fan blower motor for forced hot air
Tv - 160F Danfoss thermic valve. It's on the suppply, opposite of most designs.

When the tank is cool (155 or less), only P1 runs. With 170-175 deg supply, the tank return comes back very cool, usually equal to my bottom tank temperature. The top of the tank will warm dramatically at this point with little warming on the bottom.
As the tank reaches 160F, P2 starts running intermittently. By 165F, P2 is on most of the time. When P3 kicks on, the bottom warms quickly. As the tank approaches 175, there's only 1-2 degrees betweem the bottom and the top tank temperatures. I'm probably pushing 18gpm in the third stage with all three pumps on?

One of the goals of my design was to be able to run the Seton with minimal cycling so it would burn clean. The system exceeded my expectations. I heat the tank to 175 without any cycling. The Seton is set to cycle at 183 deg loop temp.

When the fire is out and heat is drawn, P4 gets most of its supply from the boiler loop, which cools quickly, closing the Danfoss. This isolates the boiler loop from storage. Then the water reverse flows from the two tank coils (not the bottom coil ) through P2 (an idea copied shamelessly from WoodNotOil) to heat the house.

Hope this helps
Mole

 

[Bad Wolf]

Jim I don't have temps I'll have to get them tonight when I go home, but I use two 150 coils copied from STSS. I used 3/4 refrigeration tubing which is slightly smaller than 3/4 type L. (3/4 OD vs 3/4 ID). STSS recomended two 120' coils so I went with 150'. That and they came in 50' coils. I biult my own coil winder based on someone elses design (the name escapes me right now) I try to keep the tank (1200 gallons round 48" deep) at 170. Bottom is usally 12 to 15 degrees cooler. I'm running a Tarm excel 2000 rated at 100,000btu/hr. I plumbed it according to Tarms diagram "E", using bull head "T"s. If I've got a rip roaring fire going and I'm at the high end around 167 or better it will start to idle about 20%. Boiler high temp shut of is 183. So I guess its sized about right.