Flat plate heat exchangers

The size overall (5"X12") will make a difference in usefullness, bigger is faster at transfering heat. the same is true of the number of plates they will increase the amount of surface area that allows faster heat transfer. the more plates the more passages between them so less flow restriction, the other thing to look at is the size of your inlet diameter, once again bigger is faster.
I have a 5"X12" 20 plate HX with 1" fittings, it is equal to 5 square feet of surface area, this is enough for my house, but I only had a 50,000 btu furnace. the water temp in my oil furnace will be about 5-7* lower than my OPB during the heat cycle, afterward it takes a few min. for the last few degrees to transfer until my oil furnace is back at 180*. this will be true for any HX it is least effecient at transferring the last few degrees, but a larger HX would be faster, I just don't need any more so I didn't buy any more.
I got my HX off of Ebay, much cheaper than from my CB dealer. (He also only went down to 40 plate)

the Ebay seller I bought from had a chart right there in thier listing (freeheat4U is the seller) according to thier rough chart up to 100K btu a 20 plate was ok. so far they are correct. there are websites that you could find references to in the forum that will give you a much more a precise idea of what you need. good luck.

That is the same guy I bought my 40 plate heat exchanger from. It was $250 which was quite a bit cheaper than what the CB dealer wanted.

A larger hx will make the biggest difference when the temperature of the "load" fluid approaches the "supply" fluid.

A good time for oversizing a hx is when you want to "squeeze" the most heat out of storage.

It doesn't make sense to oversize much when running radiant heat off a boiler without storage since the boiler fluid would be at around 180 and the radiant at 120. The added expense of the hx would likely not improve efficiency enough to make it worthwhile.

DC

The flat plate selection software is helpful in sizing to meet your needs.

http://www.flatplate.com/resources_SOFT.htm

Rickard said:

Does anyone have any experience putting an FPHE on a primary loop?

I have a Taco 007 running the 1 1/4" primary loop with Taco twin tees and I am guessing that slowing down the flow by putting a large (40 or maybe 70 plate) FPHE with 1" fittings in the loop would not impede the ability for the primary loop to transfer heat too much. I am guessing that it is the secondaries that need to move the higher volume of water to get the heat transfer.

Does this sound right?

Thanks

Dean

Click to expand...

Hey Dean ,

I'll try this one. I am going to say that the primary loop needs the higher flow and/or higher temps. You'll never get 100% heat transfer through the heat exchanger, and you need to be sure the secondaries don't overwhelm the primary loop. Add up the heat load for each secondary loop. You should be able to meet this load with the primary loop and then some. Though I don't have experience with hydronics on this I got a similiar question wrong on a test for industrial waste heat recovery boilers once.

Anybody else?

Mike