heat exchanger help

 
Soupy6914
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Post by Soupy6914 » Thu. Mar. 29, 2018 7:45 pm

Hello folks.

I am in the need of some assistance selecting a heat exchanger. The back story is i just recently installed an EFM 520 which I love but, the hope is to put it to work this summer to heat the pool and spa. i understand that i need a heat exchanger and one of the "best" ones are the triangle tube maxi-flo i was looking into getting the MF 200 ss. the problem is it says for the 200k but output the specs call for an 8 GPM flow. But using a btu calculator I come up with a delta T of 50 degrees that seems like a lot to me, given most people suggest a 20 degree change. what do you guys think? I'm open to any and all suggestions

thanks


 
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lsayre
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Post by lsayre » Thu. Mar. 29, 2018 8:34 pm

The 520 is not going to deliver 200,000 BTUH of output. Not enough boiler there.

 
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lsayre
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Post by lsayre » Thu. Mar. 29, 2018 8:52 pm

30 degrees of Delta-T shouldn't be a problem. For 8 GPM that yields:

8 * 8.33 * 60 * 30 = 120,000 BTUH

That level of output would be within reach for the 520.

 
Soupy6914
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Post by Soupy6914 » Thu. Mar. 29, 2018 8:56 pm

lsayre wrote:
Thu. Mar. 29, 2018 8:34 pm
The 520 is not going to deliver 200,000 BTUH of output. Not enough boiler there.
very true. I'm i correct to assume it can put out 150k BTUH. In which case the temperature drop would still be 37.5. doesn't that still seem like to much.

 
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lsayre
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Post by lsayre » Thu. Mar. 29, 2018 8:57 pm

Soupy6914 wrote:
Thu. Mar. 29, 2018 8:56 pm
very true. I'm i correct to assume it can put out 150k BTUH. In which case the temperature drop would still be 37.5. doesn't that still seem like to much.
Yes, in my opinion, but you can get by with it! Can you get by with 120,000 BTUH?

You might be able to squeeze 175,000 BTUH output from your 520. But allowing for the standard hot water boiler pick up factor of 1.15 gives you 152,000 as readily usable BTUH.
Last edited by lsayre on Thu. Mar. 29, 2018 9:09 pm, edited 1 time in total.

 
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Post by Soupy6914 » Thu. Mar. 29, 2018 9:07 pm

lsayre wrote:
Thu. Mar. 29, 2018 8:57 pm
Yes, in my opinion, but you can get by with it! Can you get by with 120,000 BTUH?
That i am not sure of. right now there is a propane pool heater with an out put rating of 168k BTUH I forget the input something like 212k i was trying to get something close to that 168k.

 
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Post by lsayre » Thu. Mar. 29, 2018 9:10 pm

See the addition I made to my post above. The largest heat exchanger I would consider for the 520 is 150,000 BTUH.


 
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Rob R.
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Post by Rob R. » Thu. Mar. 29, 2018 9:15 pm

If the heat exchanger is oversized, you just throttle the bypass valve. Not a big deal.

That 520 will heat an average size pool easily.

 
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Post by McGiever » Thu. Mar. 29, 2018 11:21 pm

Yes, even if it would have delta of 1 degree at 8 gpm it would heat the pool.

 
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Post by t185 » Fri. Mar. 30, 2018 6:09 am

I have a heat exchanger for my pool that I installed several years ago that I attempted to heat with my EFM 520. If my memory serves me correctly it is a 175K BTU unit.

Pool is around 22-24K gallons. Again going on memory since it's been several years since I used it. Starting at a water temperature of around 50 degrees it would take 24 hours to gain 5 degrees. As the water temperature increase the time would decrease. (Makes sense thermodynamics and all that fancy scientific stuff) In all. It would take around 3-4 days with the stove running 24 hours at full capacity to raise the pool temperature to 70 degrees.
At night the ambient temperature would drop as would the water and the EFM would kick back on...

Besides the EFM running 24 hours for three to four days don't forget you are also running your circulator on the pool. Make sure you check electric meter attachment on the side of your house. That sucker is going to be spinning so fast I was worried it might slow down the rotation of the earth.....

So will your stove heat your pool? Yes. Make sure your coal bin is full because your going to need it.

If your seriously considering heating your pool send me a PM and I'll sell you my heat exchanger.
Last edited by t185 on Fri. Mar. 30, 2018 8:37 pm, edited 3 times in total.

 
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Post by Rob R. » Fri. Mar. 30, 2018 6:35 am

Pool heaters are like snow melt systems. If you have to ask how much fuel it is going to take, you probably shouldn't be doing it.

 
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lsayre
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Post by lsayre » Fri. Mar. 30, 2018 7:07 am

Rob R. wrote:
Fri. Mar. 30, 2018 6:35 am
Pool heaters are like snow melt systems. If you have to ask how much fuel it is going to take, you probably shouldn't be doing it.
Agreed! 24 hours at a full 150,000 BTUH output equals 420 pounds of coal burned in a single day. If it takes 5 days to heat the pool, you are talking more than a ton of coal.

 
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lsayre
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Post by lsayre » Fri. Mar. 30, 2018 7:12 am

Rob R. wrote:
Thu. Mar. 29, 2018 9:15 pm
If the heat exchanger is oversized, you just throttle the bypass valve. Not a big deal.
If he already has a 200K BTUH heat exchanger this makes perfect sense, but if he has to buy the exchanger, why spend more money for a 200K unit and then throttle it down to about 150K, when buying a 150K unit will save $$$'s.

 
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Post by Soupy6914 » Fri. Mar. 30, 2018 9:17 am

I understand understand what you are saying about burning a ton of coal in a week. But it’s still cheaper then propane and once the water is at temp it’s not as bad trying to keep it there. Plus it’s mostly used to heat the spa which is around 1600 gallons.

 
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Post by Soupy6914 » Fri. Mar. 30, 2018 9:18 am

I was looking at a 200BTUh because I found a used one on eBay that size.


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