Heat Exchanger Ideas????

[WStayton]

Hi Guys!

  I'm putting this here becayse it is the best, though by no means a perfect, fit.  If somebody sees a better place to put it, please do!

  Here's my problem:  I have the whole crawl-space pf my small house opened ip with seven access holes about a foot square through the floor into the crawl space to install the electricity/plumbing/etc.  I though that as long as I was in here with everything opened up, I should get everything that is going to be gottten, so that I don't have to come back and open anything up again.  Woring is all done in conduit (EMP, doncha know!  <grin>) and now I am about to tun "Heat" for the water bed.  Since electricity is going to be a valyable comodity, I am trying to minimize the electtric demand, sonce it all has to come from my 3.6 kW of solar panels or the 200 amp diesel generator, or the 4x12 solar panel, or the wood-fired boiler with 1400 galons of water "storage".

  For circulation I am planning on using a 1/12 Hp circulating pump through 1" plastic tubing - the 1" is real overkill for the 1/12 HP pump, but i have it, exxentially for free, so . . .  For a heat exchanger, I was planning on using a pair of 25 ft lengths of 1/2" copper tubing, in parallell, under the water-bed mattress and under the safety liner.

  My back of the envelope calculations leads me to believe that the pump, controlled by a thermostatic switch. should run about 33% of the time max with an ambient of 60 F and a thermostat set at 88F, and circulating water at 195 F about where I like it in the winter.

  Does anybody see a better way to do this BEFORE I get it all buttoned up and tucked away???  <grin>

  Speak or forever hold your piece!  <smile>

Regardz,

Wayne Stayton

[bschwartz]

     "........I was planning on using a pair of 25 ft lengths of 1/2" copper tubing, in parallell, under the water-bed mattress......"


HOLY CRAP.  You have a 25' long WATERBED?!?!?!?   

[billswan]

Well when my wife and I used to use a king size water bed the heater was I am thinking only about a 100 watts. I just checked ebay and looks like 120 on up to 300 watts is what I am seeing.

If you are going to have access to 195 degree water pushed by a 1/12 hp pump I am thinking a single 25 foot length would be enough to about boil you to near death in short order if the thermostat should stick.

Billswan

[LowGear]

Hi Wayne,

I'd stick the pump and the water bed heater on a Kill A Watt before I cut very much copper. 

Let's say someone wants to move the bed in a year or five?

An inch or two of rigid insulation might reduce your heater bill significantly as well.  I'll bet bubble wrap would be impressive as well.

Casey

[Thob]

     "........I was planning on using a pair of 25 ft lengths of 1/2" copper tubing, in parallell, under the water-bed mattress......"


HOLY CRAP.  You have a 25' long WATERBED?!?!?!?   

After crawling through those 1 square foot holes into the crawl space, he NEEDS a 25' long waterbed!      


Seriously though, is that enough surface area to transfer heat from the pipes, thru the waterbed mattress, and into the water?  I don't have any calculations, just imagining it in my head and it appears a little small.  Maybe because I have a small head?

[Ronmar]

Well at best only the top half of the tube will be in contact with the mattress.  .5" DIA X PI means about 1.57" divided by 2 X 50ft = 471 SQ/IN or 3.27 SQ/FT of heat transfer area.  Transfer coefficient of copper from water to water is between 60 and 80 BTU/HR/SQFT/degree F.  Water to air thru copper is 2-3.  Since there are several added layers of plastic, lets go a little lower than the water to water transfer, lets use 40.  So 40 X 3.27 X 107F(195 - 88) = 13.997 BTU/HR, about what my pellet stove puts into my living room:)  SInce the pump costs you power, you want it to run as little as possible.  Two layers of industrial aluminum foil, one under the copper and one on top of the copper might help make more use of the lower half of the copper.  It would also increase the effective contact area between the copper and the liner/water bag.  I would also reccomend insulation.  2" foam board with a router to route a channel for the copper to lay in would probably work nicely.  Line the channel with the heavy foil, set the pipe in and cover with another layer.   

[David Baillie]

you could install 1" energy-shield foamboard (the good stuff not the white foam) groove it out to take the pipes, then lay the thick aluminum foil, then the pipes then more aluminum foil.  Increases your surface area a great deal, cuts down your heat loss through contact with the wood and air underneath. Might as well insulate the sides of the mattress bellow the edge of the frame while your at it...

[David Baillie]

my bad, same as the other guy... time for sleep

[veggie]

Slip one of those flexible solar swimming pool collectors under your mattress and use it as a heat exchanger.
It's a blanket of tubes with a common header at each end.
You can find them all over ebay. I have seen them as cheap as $29.

example:
http://solar-pool-heating-newcastle.street-directory.com.au/index.cgi?PageID=2&PageName=Product

stay warm,
veggie

[veggie]

Oh ! forgot......

lay some heat reflective foil down first, then the exchanger,.....then the water mattress on top.

veggie

[rcavictim]

Slip one of those flexible solar swimming pool collectors under your mattress and use it as a heat exchanger.
It's a blanket of tubes with a common header at each end.
You can find them all over ebay. I have seen them as cheap as $29.

example:
http://solar-pool-heating-newcastle.street-directory.com.au/index.cgi?PageID=2&PageName=Product

stay warm,
veggie

Veggie,

That was a creative idea.  I now have 3 or 4 of these found and drugged home from the dump with some idea of possibly using them to make domestic hot water.  I was thinking of packaging them behind some large double glazed sealed window modules I have also scrounged.  Solar hot water is really low tech and works.

[Carlb]

Slip one of those flexible solar swimming pool collectors under your mattress and use it as a heat exchanger.
It's a blanket of tubes with a common header at each end.
You can find them all over ebay. I have seen them as cheap as $29.

example:
http://solar-pool-heating-newcastle.street-directory.com.au/index.cgi?PageID=2&PageName=Product

stay warm,
veggie

Veggie,

That was a creative idea.  I now have 3 or 4 of these found and drugged home from the dump with some idea of possibly using them to make domestic hot water.  I was thinking of packaging them behind some large double glazed sealed window modules I have also scrounged.  Solar hot water is really low tech and works.

The will never take the temp when enclosed these are made to be unglazed.   

[Ronmar]

I agree it is soft black poly and will cook if you cannot take out enough heat...

[WStayton]

Hi Guys!

    Sorry for the lack of response on my part, but I just got slapped on the hospital becase they discovered a one liter pool of blood filling my paracardiam!  It was touch and got for a couple of days but I am home amd well on my way to recovered . . . now!

   Thanx for the input . . .

David Baillie:

  Actually, I have some (actually, lots!) of 2.5 inch thick polyiso foam and I was thinking that I might use a couple of 2' x 4' sheets of that as a heat sheild for the bottom.  The ONJLY thing wrong with that plan is that if it barfed on a -25 F night, the rest of the house COULD freeze solid before there was any affect to notice at the water bed surface!  <grin>  Maybe i shoud just wire in a bell that rings after the system has been on for an hour?

veggie:

  Idea also ocurred to me - sort of  . . . I have some 0.035 aluminum that I was contemplating using to build a solar panel and due to me skilles as a negotiator (yea, right! <grin>) and a lot of dumb luck, I again wound up with about three times what I actually need to build my 4' x 12' heat exchanger, so I could donate enough of the material to make this exchanger - - - with the polysio foam it would work okay, using the polyiso to stick it all on to . . . I would, however, need to make absolutely sure that I didn't have any sharps sticking up into the water/soon-to-be-air bag!  <grin>

Billswan

  My back of the envelope calculation also indicated that one each 25' length might be enough, but since my calculations were pretty backwoods, and the results of having  80% of the necessary material would be truly sad, I just "fluffed" it and added another hunk of tubing - the cost of  twice as much tubing as is needed is lots less than doing it twice and throwing a bunch of material away.  <smile>

Casey:

  I was sort of planning on roughing the whole thing in and runing it just to see what transpired BEFORE I went the distance - especially since my calcuations are so bush-league  Guess I shoulda said that, huh? <grin>


Guess thats it for now - thanx for all the input folks!

Regardz,

Wayne H. Stayton

[vdubnut62]

Wayne, doggone it, for goodness sakes what did you do to wind up with  blood loose in your pericardium?
Take care, Ron.