Author Topic: Proposed poor man’s heat exchanger design  (Read 6882 times)

Horsepoor

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Proposed poor man’s heat exchanger design
« on: July 28, 2009, 07:04:16 AM »
What do forum members think of the feasibility for building the following device:

Heat exchanger criteria: Must be cheap, easy to connect and uninstall, use commonly available components, and be reasonably reliable.

I’ve been thinking about the transmission cooler in the radiator connected to my 20/2 and soon I will also have a 6/1. Both utilize a GEO Metro radiator (16 X 20 inch) with cooling fans attached. This transmission cooler is pretty much a “Shell and Tube” single pass heat exchanger sitting on my generator set. Now since I have several Grundfos Brute three speed heating recirculation pumps ($75). I use one to circulate coolant through the engine and radiator. I have spares. The with a nominal setting with a three foot head is about 4 gallon per minute through the radiator.

http://cgi.ebay.com/GRUNDFOS-UPS15-58FC-BRUTE-3-SPEED-PUMP-59896341-2-PACK_W0QQitemZ120325997773QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item1c03fd04cd&_trksid=p4634.c0.m14.l1262
   
If I were to use one of my spare Grundfos pumps to circulate water through the transmission cooler in a separate closed circuit system, this could be connected easily to a hot water heater. I am thinking about using two Homeless Depot ¾ inch contractor grade 75 foot water hoses, one to the bottom fitting of the hot water heater, the second to hot water fitting next to the washing machine close to the hot water heater. I could then use the pump to circulate water through the transmission cooler in the radiator and “slowly” heat water in the hot water heater connected to the house.

Now thinking about the mass flow through the transmission cooler. I think a gallon per minute through a ¼ tube near the radiator is reasonable for a mass flow rate some where around 500 lbs /hr H2O. I use a 185 F thermostat with bottom radiator temperatures hovering around 170 F. So I basically have a single pass shell and tube heat exchanger with a large heat sink on the radiator side, low flow rate through the tube, and lots of heat losses along the lines. But, since the listeroid is running 24/7 for weeks during prolonged power loss during hurricane operations, I really don’t care if it takes all day or night to heat up 80 gallons of water in my hot water heaters.

So what do you think of the concept?

Looks like for about $15 in fittings, since I have everything else, I’ll find out how tough these contractor grade water hoses are and if the concept actually works. I want something simple, easy, and reasonably reliable. I can always heat water by pulling power from the generator, but if push came to shove, it might be nice to capture some of the waste heat.

Bruce
GTC 20/2 down rated to 850 rpm - ST 15
Metro 6/1 800 rpm on cart - ST 7.5

ronmar

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Re: Proposed poor man’s heat exchanger design
« Reply #1 on: July 28, 2009, 03:29:46 PM »
Probably not worth your time or parts Bruce. That trans cooler may be good to preheat some fuel, but I don't think it will work to heat much water.  The biggest problem with that 1/4" trans cooler in the Radiator is it's lack of surface area.  A 1/4" pipe 24" long has around 22 SQ/IN of surface area.  I doubt the ones in the metro radiators are that large.  Even if it has fins on it, it is still not going to be all that large.  As a comparison, my flat plate heatex has 600 SQ/IN of surface area and is good for about 20,000 BTU/HR at the temps and flows we are talking about. You just are not going to harvest many BTU from that small heatex.  The next problem is that it is at the bottom of the radiator.  That is where the coolest water is just before it returns from the radiator to the engine.  I would hazard a guess that the radiator is typically less than 100F at the bottom.  If you are talking about your domestic water tank, it is probably already warmer than the radiator is at that point. 

Heat transfer is mainly about surface area, temperature difference and flow(and a few other things). If you are serious about harvesting heat, you need to do it at the heat input to the radiator.  Brazed flat plate heat exchangers are common, relatively inexpensive and very small. Something similar to My 5X12, 10 plate can probably be had for less than $100 on Ebay.  One on the radiator input would give your domestic hot water tank first crack at that 195F water comming off the engine.  If the tank didn't need the heat, the hot coolant would continue on to the radiator to be cooled that way, like it is now...     
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Horsepoor

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Re: Proposed poor man’s heat exchanger design
« Reply #2 on: July 30, 2009, 05:13:44 AM »
Yep, I see these flat plate heat exchangers as stated on eBay for about $60, including free shippimg. Thats is the way I will go, thank you.
GTC 20/2 down rated to 850 rpm - ST 15
Metro 6/1 800 rpm on cart - ST 7.5

ronmar

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Re: Proposed poor man’s heat exchanger design
« Reply #3 on: July 30, 2009, 03:22:09 PM »
Bruce
   If you are wanting it for domestic hot water, you might also look into a thermostat from a mercury mariner outboard.  It is a 120F thermostat.  I use one on the output of my heat exchanger.  This throttles the secondary water thru the heatexchanger and gives me an output at 120F with the volume varying with engine load.  That combined with the circulating pump wired into the temp control switch on the water tank, or add a 120F snap switch on the tank outlet to shut off the pump when the tank is full of 120F water, and you have a complete domestic hot water heating system.  As far as hoses, they make hot water rated hoses.  I have seen them at Home Depot.  They are usually made of heavier red rubber hose(looks like heater hose).

Good luck   
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Horsepoor

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Re: Proposed poor man’s heat exchanger design
« Reply #4 on: July 31, 2009, 07:58:03 AM »
I never though about an outboard motor thermostat, that is an excellent idea, thank you.
GTC 20/2 down rated to 850 rpm - ST 15
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ronmar

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Re: Proposed poor man’s heat exchanger design
« Reply #5 on: July 31, 2009, 03:08:27 PM »
The Mariner thermostat is the smallest I have ever seen.  To give you an idea of it's size, it plugs almost perfectly into a piece of 3/4" PVC pipe.  That is how I installed it in my test rig.  I plugged it into a piece of 3/4" pvc, slid a section of 1" rubber hose over that, and another length of 3/4" went in against the top of the thermostat flange.  this of course is not good enough for a system with domestic water pressure applied, so I cobbled together a rig out of pipe fittings to do the same thing and handle the pressure.
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Horsepoor

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Re: Proposed poor man’s heat exchanger design
« Reply #6 on: August 09, 2009, 09:52:42 AM »
I am convinced that a simple eBay plate head exchanger is the way to go, very cost effective, reliable. I am almost embarrased that I even proposed using the oil cooler in the radiator. I guess this is what happens when the mind woonders at 4 AM.

Now, any suggestions on an inexpensive way to run hot water lines under ground 150 feet from domestic hot water heater to radiator? I was thinking about styro foam sheets and cutting 4 foot sections about 3 inches wide and pressing a 1/2 CPVC water line into it with glue and tape. I want to stick with cheap and easy (I.e. Home Depot type stuff). I live in Florida so no freeze issues, perhaps I could just cut a trench out bound to the engine shed with a return line also under ground. A sprinkler system trencher will cut through the root system easily down about six inches.

I am not sure if the CPVC is a good idea but I figured it gets installed in houses for domestic water systems. I'll need the pipe to take about 160 F max teemperature at the closest point to the heat exchanger under 40 psi pressure with a flow rate of a gallon or two per minute. Your thoughts please.
GTC 20/2 down rated to 850 rpm - ST 15
Metro 6/1 800 rpm on cart - ST 7.5

billswan

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Re: Proposed poor man’s heat exchanger design
« Reply #7 on: August 09, 2009, 01:51:17 PM »
I am convinced that a simple eBay plate head exchanger is the way to go, very cost effective, reliable. I am almost embarrased that I even proposed using the oil cooler in the radiator. I guess this is what happens when the mind woonders at 4 AM.

Now, any suggestions on an inexpensive way to run hot water lines under ground 150 feet from domestic hot water heater to radiator? I was thinking about styro foam sheets and cutting 4 foot sections about 3 inches wide and pressing a 1/2 CPVC water line into it with glue and tape. I want to stick with cheap and easy (I.e. Home Depot type stuff). I live in Florida so no freeze issues, perhaps I could just cut a trench out bound to the engine shed with a return line also under ground. A sprinkler system trencher will cut through the root system easily down about six inches.

I am not sure if the CPVC is a good idea but I figured it gets installed in houses for domestic water systems. I'll need the pipe to take about 160 F max teemperature at the closest point to the heat exchanger under 40 psi pressure with a flow rate of a gallon or two per minute. Your thoughts please.

Bruce

Go to ebay and search for PEX. If I were going to do this I would use pex. not sure what you could use for insulation. If you search long enough through ebay you will see some pre insulated double pex lines inside drainage tile but boy is it EXPENSIVE. I thought about posting some ebay listings but because they expire anyone reading this a year from now won't be able to link to them......

My guess is 1/2 inch pex would work but to be safe 5/8 might be better.

Billswan
16/1 Metro  in the harness choking on WMO ash!!

10/1 OMEGA failed that nasty WMO ash ate it

By the way what is your cylinder index?

DRDEATH

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Re: Proposed poor man’s heat exchanger design
« Reply #8 on: August 09, 2009, 04:56:28 PM »
Ok Bruce I may be a newby at this forum but I do know a little about plumbing. First of all your idea is good. The one thing you have to remember is that the distance you are running this water through the ground is going to loose probably 50 % of your heat. Now right off your heat exchanger you might need special pipe because of the temp. After you are in the groung 10 or 15 feet there will be a drastic drop just because the ground temp will be less than 100 degrees. Regular PVC schedule 40 pipe I believe is good for temperatures greater than 120 or 140 *. As for insulating the pipe if you are able to make a fairly desent trench then go to a hardware store or Home Depot and get some vermiculite. It has fairly good insulating factors since it was used for years in block walls. Pour about 2 to 4 inches in bottom. Them lay you pipe then pour in about the same. You could then use a black plastic to cover top to keep it in place and you could even put the plastic in first and wrap it. This will be so much easier and insulate so much better. Just an idea if I were going to do it. Good Luck
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Tijean

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Re: Proposed poor man’s heat exchanger design
« Reply #9 on: August 09, 2009, 06:41:59 PM »
Any of the schemes that depend on keeping ground water out of loose or porous insulation would only work in very dry situations. If you have to contend with frost movement, ground water, or all the ground boogers like moles, chipmunks etc., they are easily defeated and once full of water, almost zero insulation value. I agree with Jens; it is a lot of work and fair expense to go to, if the result is not guaranteed.
Frank

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ronmar

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Re: Proposed poor man’s heat exchanger design
« Reply #10 on: August 09, 2009, 06:53:25 PM »
You will only loose a lot of the heat to the ground if you don't insulate it.  Even a small ammount of insulation will allow you to retain most all the heat.  Attached is a cross section drawing of what Jens was talking about.  It is made from 2" thick foam insualtion board.  A 4' X 8' sheet of the stuff is about $10-$15 at home depot and will insulate 32' of a dual pipe run with 1" OD pipe/tube/hose...  The foam itself is not permeable, but the places where it is joined is.  They make poly safe spray adhesives that will not melt the foam.  It can also be joined by using the spray expansion foam.  Using this to join the 8' sections together at the ends would be the way I would do it as the foam will expand down into the pipe channels further sealing them.

I would(will) wrap it in visqueen open on the bottom, and bed it in sand, buit even if moisture gets inside with the pipe, I believe it will still retain most all of it's insulation ability as the foam will still not absorb moisture...  

   
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Horsepoor

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Re: Proposed poor man’s heat exchanger design
« Reply #11 on: August 13, 2009, 10:20:19 AM »
Thank you all for your comments. I am going to stop by Homeless Depot and start pricing out some of these options. What I'll end up with is a pretty good idea of cost per foot of outbound and inbound pipe. Since I live is South Florida, frost is not an issue, but I did not fully consider the effects of pooling gound water seeping into to the system, like after a hurricane and when I need everything to work properly. I can see a deeper trench in my future, one with some time of sand or something to encourage water getting that deep to drain faster to the suurounding area or lower. Thank you all for your very interesting comments, now I need to look up what PEX pipe is and also visqueen.
GTC 20/2 down rated to 850 rpm - ST 15
Metro 6/1 800 rpm on cart - ST 7.5

BruceM

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Re: Proposed poor man’s heat exchanger design
« Reply #12 on: August 13, 2009, 02:53:21 PM »
I did a 50' domestic and in floor heat hot water run by using blue board (closed cell, extruded polystyrene and sprayed urethane foam (Handifoam- check out ebay).  I put foam board underneath and on the sides to make a "form" for the spray foam. Urethane foam can't be used in the ground if it is always wet. 

The spray foam is easy to use and great stuff, though spendy.  It insures that water can't leak into the hot pipes.

I've also used Tiger Foam, it's the same stuff.