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Author Topic: Flat Plate Exchanger Install For DHW and Heat  (Read 2730 times)

rsv101

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Flat Plate Exchanger Install For DHW and Heat
« on: July 20, 2018, 10:38:10 AM »

Hello group, I am in the process of installing a new wood boiler and want to make sure I hook up the system correct. my current system is a viessmann with and indirect storage tank. I would like to hook a 20 plate flat plate in the incoming cold Domestic water line to heat the tank and then install a 100 plate flat plate with wraparound pump for heating gas fired boiler. family size is 5, house is 4000 sq ft (2000 sq ft in floor radiant basement, 2000 sq ft main level with baseboard) 500 sq ft attached garage with radiant in floor. Does this flat plate hook ups sound correct? I have attached schematic of my gas fired boiler system. thank you for the insight
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E Yoder

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #1 on: July 24, 2018, 04:12:44 AM »

What size flat plate or you using? 4x12, 5x12? 
I'm not quite following all of what you're looking to do, do you have a drawing or sketch of all the piping layout?
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RSI

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #2 on: July 24, 2018, 07:52:21 AM »

If the DHW is already heated by the boiler, why do you need to add a plate for that?
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wreckit87

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #3 on: July 24, 2018, 03:43:11 PM »

I would pipe the OWB in a constant circulation loop like usual, with the 100 plate being the point of return. Then pipe the Viessmann through the other side of the 100 plate. Your existing DHW circ would still get the call from the indirect and pull heated water off the 100 plate to heat the DHW, just as it does now. The other 3 heating zones could be pulled from a manifold, just after the DHW tee in the primary loop. DHW first tee with circ, baseboard second tee with circ, then both radiant zones through a third tee with a circ pulling through a mixing valve and into a pair of zone valves- which is likely already the case if everything is currently piped. Hard to say without seeing your current setup how easy it'd be, but sounds relatively simple. Aquastat on the incoming OWB line to keep the Veissmann from firing unless OWB water is below X temperature. No need for the 20 plate for DHW
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rsv101

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #4 on: July 25, 2018, 01:42:40 PM »

I have attached a drawing of my current setup in the house. currently I have a 50 plate 5x12 and my 53 gallon tank runs out of hot water and takes a while to replenish, I thought if I added a second heat exchanger to cold water coming into tank it would pre-heat water. I always hear how people never run out of hot water. I am in the process of installing a new wood boiler and 1 1/4 inch thermopex. could it be the old wood boiler was just not getting enough hot water to house?
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wreckit87

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #5 on: July 25, 2018, 04:12:07 PM »

The lines in/out of the 50 plate- are those S/R from outdoor boiler? Your DHW circ seems to be pulling from a cross? It says tee but has 4 branches, 2 of which going opposite directions which cannot flow. What's the pump above the 50 plate in the pic? Wrap pump?? You've got a whole lot of unnecessary stuff happening on the high temp side. I'll draw you a rough, simplified sketch of how it ought to be piped in order to work. It's open to modifications of course, but gets the rough idea across. There is no reason anyone should ever run out of hot water with an indirect- they'll put out as much DHW as the boiler can produce BTU, so if you have a 200 Vitodens for example, you should have 200,000 BTU worth of hot water recovery. 5x more than a standard 50 gallon gas unit.
« Last Edit: July 25, 2018, 04:24:00 PM by wreckit87 »
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rsv101

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #6 on: July 25, 2018, 05:21:48 PM »

yes the lines in and out of the 50 plate are from wood boiler. I made a mistake in the drawing as far as the tee with 4 branches. the pump above the plate exchanger wrap pump is a wraparound pump the keeps boiler hot 24/7, it appear not to be needed in your drawing which is simplified and would be easier to work with. so just to clarify I do not need a wraparound pump? in your drawing what is XT  in the supply line right out of boiler?
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wreckit87

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #7 on: July 25, 2018, 05:38:10 PM »

What model is your Veissmann? Most only hold a couple gallons of water and if that is the case with yours, there is really no reason to keep it hot at all times as it'll only take 15 seconds to heat it up on a call for heat. That can be modified with a primary loop (wrap pump, as you call it) if you wanted to keep it hot 24/7 and run the DHW and BB as secondary loops. Even if that tee that appears to have 4 branches is in fact a tee, it's still not wise to feed the bullhead of a tee (the branch) and try to make water go both ways. XT stands for expansion tank, which I assume you already have? Along with air separator and relief valve. It's tough to say without physically standing there but I believe my drawing is a considerably more simplified version of what you need
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E Yoder

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #8 on: July 25, 2018, 08:21:56 PM »

I might be missing something but it appears like the hotter supply water is being sent to the flat plate to be heated then mixing the heated water back with the cool return. Result being a lower temp mixed water being fed to the zones.
 I would normally send the cool return water to the flat plate and dump hot back into the supply... Maybe I'm missing something tho.
Something weird is going on there I think?
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rsv101

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #9 on: July 26, 2018, 09:50:41 AM »

Thank you for the info, I am going to re-plumb in like wreckit87 suggests. another question that I am coming to is my viessmann boiler has two supplies and two returns, one side is high temp/dhw the other is low temp in floor radiant two zones. do I need a separate heat exchanger for that side? if so what size would you recommend?
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shepherd boy

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #10 on: July 26, 2018, 11:28:20 AM »

Yeh, wreckit's got it right from what I can tell. I was afraid to comment on your drawing as I just didn't see how it was working and thought I was the dummy.
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E Yoder

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #11 on: July 26, 2018, 02:53:15 PM »

When I commented on the backward flow messing up the temps I was referring to the first drawing, wreckit's drawing is correct in heating the cool return water.
« Last Edit: July 26, 2018, 02:55:17 PM by E Yoder »
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rsv101

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #12 on: July 26, 2018, 02:59:47 PM »

another question that I have is my viessmann boiler has two supplies and two returns, one side is high temp/dhw the other is low temp in floor radiant two zones. do I need a separate heat exchanger for that side? if so what size would you recommend?
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E Yoder

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #13 on: July 26, 2018, 04:51:11 PM »

As long as you heat the boiler the mixing valve should turn the temp down to the radiant zones, correct?
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wreckit87

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Re: Flat Plate Exchanger Install For DHW and Heat
« Reply #14 on: July 26, 2018, 07:30:27 PM »

Those separate S/R ports come from the same heat exchanger within the boiler, so will be seeing the same temp water supplied by the plate. As Eldon said, the mixing valve will take care of the radiant zones, piped as-is assuming it was performing well previously. Everything ought to be fine over there, but it wouldn't hurt to send the return from the radiant over to the incoming line to the new plate to prevent mixing within the Veissman, as this would drop your BB and DHW temps slightly. Not necessary if it was performing fine before, but not a terrible idea
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