Need Storage Tank Ideas and Heat Coil Exchanger Input

[intc97]

I would like to have a storage tank of about 1000 gallons for my new heating system. I thought the price of available storage tanks and heat coils exchangers were fairly high. I'm looking for ideas of what others did for hot water storage for their boilers. I would like to place the tank in the basement but could also put it in the outbuilding that I plan to house the boiler in. The outbuilding is not built yet so it would be easier to place a large tank in it as opposed to the basement. Also the coils were very expensive, I'm guessing because the price of copper. Any ideas would be helpfull.
Thanks

 

[free75degrees]

Not sure if you have seen this post, which describes the tank I am working on. Please note that this is still being built, so I cannot attest to the success of this design.
https://www.hearth.com/talk/threads/17627/

I am making my HX from hard 1/2" copper tube that I am bending into coils using an electrical conduit bender (very carefully to avoid kinks). One 10 foot tube makes a coil of about 3 1/2 turns and is about 1 foot in diameter. At the joints of these smaller coils there will be a small segment of straight tube, which I need to leave in order to get a good solder joint. If I use a straight copper joint the cumulative coil will no longer be in line because the straight sections will throw it off. To get around this I am using 45* copper joints to bring the coils back in line. I did one test and it worked great. I will join 6 of the smaller coils to form a tall vertical coil and then plumb 4 of these tall coils in parallel. This will give about 240 total feet for $360.

I think the flat plate HXs are cheaper than my setup so you might want to consider one. I was very much on the fence in deciding between flat plat and coils. I ended up using coils because I like to avoid moving parts whenever possible (coils have 1 less pump) and because the STSS tanks use coils (not sure if that is a valid reason - one should always avoid the "That's the way it has always been done" excuse). Anyway, most people here will probably try to convince you to go with flat plate, and they have more experience than me, so they may be right.

 

[WoodNotOil]

I am also planning to make a heat storage system and wondering about the heat exchangers. Are most of the pre-made copper coils available from places like STSS made of 3/4” copper? Are they using soft copper tubing like a type L or K?

Free75degrees – Is there a reason you are going through the trouble of bending hard copper instead of using soft? Is it less expensive?

The copper heat exchangers seem to be the largest cost in a setup like this. Does anyone have an alternate way of doing it? Could PEX be used?

People have mentioned flat plate HX's as an option. How do they work in this application? Has anyone used them successfully? If so, what make and model? Etc.

Sorry for so many questions. Would love some answers. Thanks!

 

[free75degrees]

Free75degrees – Is there a reason you are going through the trouble of bending hard copper instead of using soft? Is it less expensive?

Yes, I found that hard copper is about half the price of soft copper coils (at least from the sources where I can buy it).

There is a guy on this board that used pex. I think he used about 3x the length as would be used with copper. You can pronanly find his info if you search for pex HX. And there are people using flat HX successfully.

 

[JrCRXHF]

I am going to try a couple Truck radiators to start with. I can get them for about 30 bucks from a newer truck and they have alot of surface area I will see how it works.

 

[jebatty]

I just finished a full heating season using a flat plate hx. I started with one too small for my Tarm, and the only I have now is about right. Sold the first one used on ebay and nearly recovered what I paid for it.

I'm using a 5" x 12" x 30 plate, 1" inlets and outlets. Very satisfied.

 

[chuck172]

What are flat plate heat exchangers? Are they something you can make or something you have to buy. The way copper is going, soon the copper coils and the storage tank will cost more than the boiler!

 

[jebatty]

Do an ebay search "plate heat exchanger" and see if this helps. Do the same thing with Google.

 

[chuck172]

For the Solo 40, the Tarm people recommend 3-180' coils for a 822 gallon tank. At $950.00 a coil that's almost $3000.00 in coils alone, not counting the $2150.00 for the tank.
How can you compare plate heat exchangers in price and efficency to the copper coils?

 

[WoodNotOil]

What are those of you using the flat plate hx using for the domestic hot water? Is there a separate plate for that? Do you heat and draw from the same plate?

I read in another post that to use PEX you have to use roughly 3x as much. That means a 180' copper coil becomes 540' PEX coil. You can get a 1000' roll of PEX-C with an oxygen barrier for $287. That seems less expensive than the hx plates considering it eliminates the need for an additional pump.

 

[sparke]

I installed a Pex Heat exchanger. If I were to do it all over again I would use a plate Hex. The coils took a long time to build. It takes about 8 hours to get the tank from 120* to 180 -190* Approx. 700 gallons. I will say that the Hx works well enough - the boiler can not keep up with it for the first several hours.

 

[WoodNotOil]

sparke - How did you build the coils out of pex? How does 8 hours for a 60* rise compare to using a plate hx? How long are your coils?

 

[sparke]

I have 4 coils of 200' - 1/2" Pex. in parallel. Picture here: https://www.hearth.com/talk/threads/16046/

Not sure how it would compare to a plate Hx. I have never used one. Jbatty has one and like it. Check out his posts...

 

[jebatty]

How can you compare plate heat exchangers in price and efficency to the copper coils?

Efficiency wouldn't be easy as there are so many variables, a few being volume of flow, area of heat exchange, boiler output, heat losses in route, heat losses from different types of storage. I think you would have to have two identical systems to run an actual test. In that case heat temp output and return heat temp would give a comparison of performance.

Price would be easier, but doesn't mean too much without knowing the efficiency. If one is inexpensive with regard to the other but is much less efficient, then it may not actually be inexpensive.

... coils out of pex? How does 8 hours for a 60* rise compare to using a plate hx?

Same answer as above, basically. Plus, is the temp rise being measured the top of tank, bottom of tank, and what is the stratification? And what about heat demand on system during the burn?

I have 1000 gal of storage, Tarm Solo Plus 40, 5" x 12" x 30 plate hx. Last week fired the boiler up for the last time (hopefully) this season. Before that it was over a week since the last firing. I burned one load of pine. Water temp in to hx was 60, water temp out from hx was 140; boiler in to hx was 170, return to boiler was 110 (at these boiler temps the Termovar was diverting some boiler supply directly to return to maintain actual boiler return at 130-140). Top of tank before burn was about 70; top of tank after burn was 120, didn't look to see what bottom of tank was after burn.

 

[sparke]

Nofossil has copper coils and 880 gallons if I remember correctly. He says his tank heats up 10* an hour. Which is a bit better performance then mine. But like Jebatty said, there are a ton of variables.

 

[chuck172]

O.K, all factors being equal, which is more cost effective, HX, or copper coils.
Jim I see your using a 5” x 12” x 30 plate hx. I believe Tarm recommended 3-180' coils @ $3000.00
I'm getting a Tarm solo 40 with a 1000 gal. tank also.

What would the end result be in a comparison - coils vs. HX, cost, efficiency

 

[jebatty]

What would the end result be in a comparison - coils vs. HX, cost, efficiency

I have a gut feeling but due to the many variables, cost is the only objective factor that I can back up. You can get what I have on ebay right now for $210 incl shipping. Search "plate heat exchanger" and you will find a variety available. Add the price of the extra pump (Taco 007 about $50 on ebay), and you have an approximate cost.

You can calculate the surface area of the coils and the surface area of the plate hx you pick, and that will give you an approximate idea on raw efficiency. For the same surface area the plate hx should be more efficient, how much more I don't know, because the water is turbulated between the plates and because the plates are close together, resulting in a very high level of water contact to heat transfer plates. I suspect that scale/corrosion that would reduce heat transfer is reduced in the plate hx, plus you can easily remove a plate hx for cleaning, if needed. Cleaning a coil would not be easy. There are other factors affecting efficiency, as mentioned in my other post.

A plate hx is simple to install, takes up very little space, and is easily used with a variety of tanks that would pose a problem if you had to insert large copper or other coils. Therefore, you have more tank options with a plate hx.

If I had to do it all over again, I would pick the plate hx again -- my gut plus experience tells me they work very well and are very cost effective.

 

[chuck172]

How big a plate heat exchanger would you recommend for a Tarm 40 with 822 gal. tank?

 

[jebatty]

I have a Tarm 40 with 1000 gal storage. I think the 5 x 12 x 30 plate, 1" inlets and outlets, is certainly adequate if not more. It would not hurt to have more plates. All I know for sure is that the approx 3.5 x 8 x 20 plate I had originally was not big enough. With the 5 x 12 x 20 plate, the Tarm will burn full out, no idling, until inlet water from the tank starts to get up to about 140. Then the decreasing delta T starts to play an increasing role and idling begins to increase. The 40 plate is just $13 more than the 30 plate, and I don't see a disadvantage in going with the 40 plate. I just don't have enough data/experience to give solid info here.

 

[MrEd]

Just curious, I like the plate exchanger concept, but not being familiar with how they are built, aren't the susceptible to clogging? How long do they normally last?

 

[WoodNotOil]

Here is a link that shows btu ratings on hx plates (the prices aren't bad either): (broken link removed)

If my tarm 40 has a 140,000 btu output, do I need a plate hx of the same rating or one rated higher? Does it matter if it is 3/4" or 1" that is used so long as the btu/hr rating is high enough?

 

[jebatty]

susceptible to clogging? How long do they normally last?

I believe the recommendation is to use a filter screen to minimize the likelihood of any clogging; I use a 50 micron hot water filter just to make sure; a 100 micron screen probably is sufficient. Most are designed to turbulate the fluid passing through to maintain high surface contact also with resulting scrubbing. Also if cleaning needed, I believe muric acid rinse will do it. No particular knowledge on longevity, but seems to me life should be very good.

Does it matter if it is 3/4” or 1” that is used so long as the btu/hr rating is high enough?

Shouldn't matter, but rating also is based on volume of flow, so pump needs to be factored into rating analysis. I believe I over-sized mine for a safety factor.

 

[chuck172]

Now were getting somewhere in the coil vs. Plate HX discussion. With copper coils going for $1000.00 each, comparable Plate HX's going for 1/3 of that, it seems like a no brainer. I must be missing something here.

 

[MrEd]

With the plate exchangers, you need to buy and run an extra pump. I suspect the pump+plate exchanger is still a lot cheaper than a copper coil for initial purchase, question then (to me anyway), is how much electricity does that extra pump cost over a year, and over the lifetime of usage?

 

[WoodNotOil]

How deep should the pipes be in the tank that for the exchange? When using the same pipes for feeding and drawing it seems to me it would be hard to maintain a good stratification. When feeding it seems like I would want to draw water from the bottom and return to the top. When drawing it seems I would want to pull from the top and return to the bottom. If I have one pump and set of pipes, how can I do both? Maybe I am missing something in the concept. How are people with this setup piping the tank?

I see now how using a plate hx can save both time and money over the copper or pex coils. This forum is a great resource for projects like this.