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|-+  Heat exchangers/thermal storage
| |-+  Coolant & Exhaust exchangers (Moderator: Ronmar)
| | |-+  Looking for some help..
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Fordguy64
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« on: January 30, 2018, 07:54:58 AM »

I’m in the process of putting together my trigen. I’ll have a few different heat exchangers and I need some help with that..

I’ve got a Kubota z482 it’s a 2cylinder liquid cooled diesel at apporox 13hp. I want to recover the coolant and exhaust heat for heating house and domestic water.. I know most of you have “build threads” on here but most are scrambaled and missing pictures..

I basically want to know your motor, load, and what size and or kind of heat exchangers you are using..

Any info would be appreciated

Rob
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mobile_bob
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« Reply #1 on: January 30, 2018, 11:04:25 PM »

the system i built about 11 years ago now is based on a S-195 changfa (12hp nominal)

the coolant recovery was setup to be harvested by the coolant loop in a water tank exchanger, i can't remember the brandname, but basically it is meant as a potable water heater, that is driven by a boiler.
the idea being the coolant that circulates in the loop is via a double wall construction, so that if there was a leak, antifreeze would leak out on the floor and not into the potable water that is being heated.  the efficiency is reportedly quite high.

i ran the system where all the heat would be harvested for domestic hot water, up until the temperature reached about 125F, then the radiator system on the trigen would dump the rest to keep the domestic hot water from getting to hot.

the engine coolant then was controlled to run between 205 and 214F, fan controlled heat dump on the radiator, using a 195F tstat, which would remain open during normal operation.  the fan on the radiator would regulate the heat and dump what is not harvested.

the heat exchanger was one of my own design, and no i have not published the design, but some day may very well do so.

the design was intended for batch fire use, intermittent operation, in that the system would run for an hour or so, then shutdown and not restart until there was sufficient and efficient demand to be serviced.  this would allow for the exchanger to cool down to room temp which allows for condensation to form so that it would flash to steam and as such be used to self clean at the next startup. this self cleaning keeps the efficiency quite high.

the design came out pretty much like i had hoped, in that the inlet temp is 640F at full rated load, (70f ambient) with the exhaust from the exchanger coming out at 240F.  240F being above the steam point of water, assures that there is no condensation formed while in full load operation and things stay cleaner that way, less corrosion, and less nasty black drips and soot around the outlet.

i have seen others use different exchangers, and if used on some engine's at part load, are somewhat of a problem having to clean them out from time to time, manually. which of course is a dirty proposition, and if not done with some regularity efficiency drops pretty fast.

having said all that

there are lots of folks using plate exchangers for the hot water, and i think they would be great for heating water for space heating, just not sure i would want to risk it for potable water heating?  there might be double wall designs that are safe? i don't know.

as for exhaust, it all comes down to how you are going to operate the unit?  if part load or low load, i would expect more carbon issues?  and as such more frequent cleaning?  once i got my design worked out, i gave up exploring other options.

fwiw, i can make 60 gallons of 140F water (starting from 70F in an uninsulated tank) in 55 minutes running at full load of approx 8kw electrical, and have just a touch of gray color in the exhaust.  in my opinion that is pretty useful and iirc pretty darned efficient.  i know i am losing some heat out the uninsulated tank over the 55 minutes, so i think had i used an insulated tank it would be even better in recovery.


bob g
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glort
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« Reply #2 on: January 31, 2018, 02:11:58 AM »


For the coolant side, a FPHE is about as efficient a liquid to liquid HE as you can get.

Something like this,
http://www.ebay.com.au/itm/Stainless-steel-30-PLATE-HEAT-EXCHANGER-Home-Brew/291728002154?hash=item43ec580c6a:g:PxMAAOSwJQdXAOfb
would be way overkill for the output of that little engine.  I'd get a 20 plate if you could. Be cheaper and still over kill.

For the exhaust, I reckon you could get away with something like a car heater core IF you put something like water injection in the exhaust pipe. You could have a simple $5 ebay  timer board squirt water into the exhaust every so often which as Bob Says would basically steam clean the core.

Whatever you do, for gods sake don't frig around with copper coils. Don't know why the hell everyone thinks of copper coils when they think heat exchanger but it's a near useless and ridiculously inefficient HE and complete waste of time.
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Fordguy64
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« Reply #3 on: January 31, 2018, 04:28:19 AM »

thanks for some input. i had planned on using FPHE for the coolant side of things. just wasnt sure on a size and number of plates. i was leaning towards a 3"x7.5" with 30 plates. i can get one for 60usd shipped. as for the exhaust side i figured i would end up making something. the water misting idea is an interesting idea for keeping it clean.
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mobile_bob
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« Reply #4 on: February 01, 2018, 07:25:21 PM »

i think the fphe you are thinking of using, would be more than adequate to harvest the heat of your engine's coolant system

probably get by with fewer plates even.

bob g
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glort
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« Reply #5 on: February 01, 2018, 08:16:48 PM »

i think the fphe you are thinking of using, would be more than adequate to harvest the heat of your engine's coolant system

probably get by with fewer plates even.

bob g

I agree.
Can be a bit hard to find but i looked up the actual rated capacity's of these things years ago when I was in the veg oil fuel game. People were bolting 2 30 plates into their cooling system to heat the fuel oil up.
It was ridiculous overkill.  They could have done the same job with a 5 plate let alone 2x 30's.  But, as wtih most things, you can't put the heard mentality off with irrelevant things like fact, proof or science.   Roll Eyes

These things have incredibly efficient heat transfer and for this job a 20 would be more than you needed anyway.

Mate of mine works with public Pool heating.  To heat an Olympic size pool he uses FPhe's about the size of 4 loafs of bread, 2side by side and 2 end to end.  He can transfer several hundred KW with something that small. To use a tube HE the thing is the size of 2  205L drums end to end.

20 Plates would be all you need and if you could make a saving over a 30, so much better.  On'y going to have so much heat to start out with and a bigger HE is Not going to get more heat out of it once you get all the available efficency there is.
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