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Author Topic: Sizing plate heat exchanger  (Read 1154 times)

gardnert

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Sizing plate heat exchanger
« on: August 20, 2012, 06:29:55 PM »

I just put in a heatmor 200 and also have a 90,000 btu lp boiler inside. Now i need to plumb in a water to water plate heat exchanger but i dont know what size or how many plates. Heating 2400 sq ft slab.  Thanks for any help!
« Last Edit: August 20, 2012, 06:41:12 PM by gardnert »
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ThatGUY

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Re: Sizing plate heat exchanger
« Reply #1 on: August 21, 2012, 08:51:39 AM »

I woudl call you local Plumbing Supplier; but make sure you know the approximate heat loss of your slab, the expected head loss and flow; cause they will ask that information to properly size a heat exchanger.
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willieG

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Re: Sizing plate heat exchanger
« Reply #2 on: August 21, 2012, 05:32:14 PM »

not being a hvac or heating guy i would make a guess if it were my house to match the heat exchanger to meet the same output as yoru LP furnace (if it could always keep up with demand in the past)  if you are using radiant heat if your exchanger is oversized the floor will only take asmuch heat that is needed. i think you just have to make sure you do not starve the system for btu's? i would thinks haveing extra available qould be OK
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RSI

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Re: Sizing plate heat exchanger
« Reply #3 on: August 21, 2012, 07:49:40 PM »

A 40 plate (5x12) would probably do it ok but i like to oversize a couple just to be safe. Going too big wont hurt anything but if you go too small you will have to replace it with a bigger one.
also going oversize will get you a little hotter water on the secondary side.
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gardnert

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Re: Sizing plate heat exchanger
« Reply #4 on: August 21, 2012, 08:19:45 PM »

The plumber i bought the stove from told me a 10 plate is what i should use and it just seemed undersized
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RSI

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Re: Sizing plate heat exchanger
« Reply #5 on: August 21, 2012, 08:48:58 PM »

This plate is needed to isolate the outdoor boiler from the indoor? Unless you are running the indoor one 50+ degrees colder than the outdoor I don't see how a 10 would work. (Unless it is a 10" x 20" plate heat exchanger.

I don't like to use 10s at all because they have way too much head pressure loss.

If you want to try a 10, I have a used one on the shelf you can put to see how it works but I really don't think it will do what you want.

Here is a chart of plate heat exchangers. The last number is the pressure drop. Multiply that by 2.3 the get feet of head.

Model Btu/hr Flowrate GPM Hot Inlet ℉ Hot Outlet ℉ Psi
LB10 40,000 6.20 180 160 5.175
LB20 80,000 7.44 180 160 3.5
LB30 110,000 8.93 180 160 1.7
LB40 156,000 10.71 180 160 1.02
LB50 220,000 12.86 180 160 0.7
LB60 300,000 15.43 180 160 0.56
LB70 400,000 18.51 180 160 0.42
LB80 538,000 22.22 180 160 0.36
LB90 710,000 26.66 180 160 0.3
LB100 930,000 31.99 180 160 0.24
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gardnert

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Re: Sizing plate heat exchanger
« Reply #6 on: August 21, 2012, 09:05:22 PM »

Yes that is what the plate exchanger is for. I am very green with this so i dont really know how to use that chart to figure out what i need. And are these models that youu carry? Thanks
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RSI

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Re: Sizing plate heat exchanger
« Reply #7 on: August 21, 2012, 10:04:50 PM »

the number after lb is the number of plates. The list is from 10 to 100.
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gardnert

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Re: Sizing plate heat exchanger
« Reply #8 on: August 22, 2012, 06:25:42 PM »

So am i matching the btus of the lp boiler to the plate exchanger? And would it hurt to be a little oversized?
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RSI

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Re: Sizing plate heat exchanger
« Reply #9 on: August 22, 2012, 09:08:55 PM »

You matching the BTU's but also need to look at the flow restriction. If you lose 2 or 3 gallons per minute of flow because of going with a smaller HX then the available heat in the water may not be enough.

Going bigger on a heat exchanger won't hurt anything. There is just a point where you get very little return on the cost.  Going by the numbers a 30 will probably work but it is only $90 more to go up to a 50 plate. (~$300)
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It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so. - Mark Twain