Water to air heat exchanger

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Joelharris58
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Post by Joelharris58 » Mon. Dec. 10, 2018 6:41 pm

So does any one have any info on what size heat exchanger is a good to stick around looking to possibly build a contraption of sorts and run some duct work off of it in the future looking at around 50k needed but is still a little over kill at the same time are they rated lower than what they produce that I need to overshoot or just stick with what I need I’m planning to build my own sort of possibly just hot air furnace and tear out what I do t need but that is kind of what I’m thinking but with a plenum to add duct work off of later

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McGiever
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Post by McGiever » Sat. Dec. 15, 2018 12:56 pm

A lot of variables there, water temp in, pump speed or flow, air speed or flow and coil rating by mfg'r.

 
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Post by Rob R. » Sun. Dec. 16, 2018 6:24 am

If you need 50,000 btu's per hour, pick a unit with that rating and install according to the manufacturer recommendation.

A lot of guys just install a water to air HX in an existing furnace, but if you are starting with nothing it might make sense to buy a packaged air handler.

 
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Post by McGiever » Sun. Dec. 16, 2018 10:23 am

As for your 'overkill' question, in that case you can just run either or both the fan or pump a bit slower speed till a time of more output is needed.


 
Joelharris58
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Post by Joelharris58 » Sun. Dec. 16, 2018 5:29 pm

Awesome guys thank you for your knowledge I grabbed a 15x15 for a decent price and have two hot air furnaces at my disposal to build my own air handler of sorts and that will be the Xmas present heat and lots of it up here in the mountain I live on lol now just gotta wait on the fedex guy to bring it

 
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Post by lsayre » Sun. Dec. 16, 2018 8:09 pm

Just curious. Is a 15 x 15 rated at about ballpark 65,000 BTUH? That should work well, provided that you do not have to restrict your plenum much (if at all) in order to channel all of its blower CFM through it.

 
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Post by Joelharris58 » Sun. Dec. 16, 2018 11:12 pm

15x15 is rated for close to 83 k at 180 at 11 gpm and 1250 cfm I believe the blower I have is around 1200 but I have to clean it up to get the numbers and find out for sure I’m sure it will be some trial and error but I’m going to install duct work around the first floor this summer hopefully

 
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Post by franpipeman » Mon. Dec. 17, 2018 8:10 am

the bigger the supply AND RETURN the less noise you get A properly sized duct system is silent


 
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Post by McGiever » Sat. Dec. 22, 2018 12:59 am

Joelharris58 wrote:
Sun. Dec. 16, 2018 11:12 pm
15x15 is rated for close to 83 k at 180 at 11 gpm and 1250 cfm I believe the blower I have is around 1200 but I have to clean it up to get the numbers and find out for sure I’m sure it will be some trial and error but I’m going to install duct work around the first floor this summer hopefully
While you are looking over the curve on that chart, what happens if fan with losses can only do 900 CFM?
What happens if if your pump can only do 8GPM?
What happens if both happen together?

What size pipe were you thinking of running to get your 11 GPM thru?

Hint: Velocity = 4 feet per second for copper, 8 feet per second for PEX.

 
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Post by lsayre » Sat. Dec. 22, 2018 3:38 am

1" PEX (0.863" ID) will be at 6 FPS when also at 11 GPM.

Fortunately, the OP only needs to achieve 50K BTUH from his 83K BTUH exchanger, as moving water at 11 GPM is not something that most affordable circulators can do, when considering the friction head (whether measured in Ft. or PSI of drop) of the loop at 11 GPM. That, plus a 1200 CFM blower will be diminished in output to some measurable (and perhaps substantial) degree when forced to squeeze its air through the fins of the exchanger.

If he can achieve 180 degrees at the inlet, 8 GPM flow, and 1,000 CFM from the blower through the exchanger I think he will be right close to 50k BTUH, and in the end it was probably quite wise to choose an 83K BTUH exchanger for a 50k BTUH requirement, as it appears to me that the typical real world output of these exchangers is likely to be appreciably below the manufacturers strained (while at the same time legitimate) claims.

 
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Post by coalkirk » Sat. Dec. 22, 2018 7:30 am

When you plumb it take the supply water into the last pass side. In other words the last row of coils that the air passes over. I can't explain why but you will get much more heat out of it that way. I had mine hooked up the other way for years and it would take about 5 degrees off of the water temp. Hooked up the other way it takes about 20 degrees off of the water.

 
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Post by franpipeman » Sat. Dec. 22, 2018 8:05 am

On the coil supply connections the hottest water , in order to get the most heat exchange from it , needs to hit the air ready partially heated by the coil . After that waters btu content is spent on the partially heated air and water temp is reduced it can still give out more btu by hitting the cooler air of the new return to maximize the heat exchange capacity of the coil and the supply water sent through it .

 
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Post by Joelharris58 » Tue. Jan. 01, 2019 10:41 pm

So far so good I’ve noticed a big difference so far. I put two holes in the kitchen floor for right this second till I can get some duct work run but ran a seperate thermostat and taco zone relay so it doesn’t kick on the furnace just kicks on the blower and all of the rest of the house kicks the furnace to run the slant fin baseboard. I just keep my hi lo limit at 180/150 10 diff and the house is staying toasty now hopefully that cuts back on my coal usage going through close to a ton a month which I think is high for what I’m doing with it but not sure which is about 3000 sqft glass block old coal mining company home that isn’t that greatly insulated

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