Passive heat exchanger ?

K

Kevin the grey

Joined
Aug 26, 2005
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Did anyone ever build one for their home ? I have to have fresh air even in the winter or I,m just not comfortable . I have my bed right next to the window just for this .

When it gets to twenty below it must affect my heating bill and it also makes it a bit too nippy at times . I want to build a vertical passive unit for my window .
I just can,t quite picture the mechanics of it . I realise the cold air coming in must be warmed by the heated air going out . I am thinking a vertical rectangular box with the warm air going in from the top of the box and exiting the bottom as it cools . The cold exterior air must come in the bottom through a second conduit and pass through the warm air . This thereby cools the heated air and warms the cold air .

Anybody know the most efficient way to build one out of easily found parts ?
 
Maybe you could build something out of pvc pipe. There's a wide range of readily available elbows and other fittings. You could perforate sections selectively to enhance airflow as well, though I don't know if that'd really help matters.
 
Josh as I understand the idea the conduit walls must be as thin as possible . I am thinking of aluminum flex conduit for clothes dryers . I was thinking of roughly one inch diameter to make the unit a feasible size .

You did mention a telling point in this . The fact that P:V:C: has elbow fittings .Getting aluminum flex conduit into a tight bend might be tough .
 
How are you going to work out the top-down heat circulation? Or is this to be just a ducted, vertical opening?

Chris
 
namaarie said:
How are you going to work out the top-down heat circulation? Or is this to be just a ducted, vertical opening?

Chris
Click to expand...

As passive suggests at least in a figurative sense there are no active or moving parts apart from the air
itself . I believe it works on the principal that hot air rises and cool air sinks . This is all relative to ambient temperature .

The hot air nearer the top of the room will sink as it cools . Given ingress to the system via a conduit near the top the hot air will enter into the system and sink as it gradually cools . For it to move it must have an exit which would have to be at the low end . I think it is simply vice versa for the cold air excepting the cool air must be warmed by the exiting hot soon to be warm air . This is where my design becomes a little sketchy . I was hoping for input for someone more familiar with heat exchangers .

There seems to be something that reeks of the perpetual motion machine about it . Of course there is a constant input of energy by the heating system of the dwelling and the difference of potential between indoor and outdoor temperatures .
 
you could stack up a bunch of aluminum plates and build plenum chambers on 4 sides such that every other gap was filled with a filler strip, and thus every other gap open to the air, opposing plenums would have the same gaps, alternating plenums would have the filler strip in theother gap to prevent mixing. you'll also have to allow for drainage & condensation....the more plates you stack up the more efficient it will be & the thinner the filler strips will need to be.

(plenum chambers are just the bits that transition the duct to the sides of the plates)

sketch:

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installed in house: (these show fans, you'd have to be clever in the ducting to allow for convection to do the driving force (or just make up a set of fans, out of - fans?)

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or

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probably be cheaper in the long run to buy a commercially made one: do a google on 'air-to-air' heat exchangers & there are loads.
 
Kronck me shipmate , ye are making a diving board out of a simple plank . It was a good trick even if it only worked the once . L:O:L

The design of my dwelling and the fact it has electric baseboard heaters with no ductwork involved precludes the use of your design . I,ll check out the sites to try and firnm up my grasp of the theory behind the practice . The plenums plates are a good idea which seem not only to channel air but also add thermal mass .
 
Just my 2 cents. I worked on/ built one of these exchangers you are thinking about years ago. As well as solar things. Not to get your hopes up as it did indeed work ... well kinda worked... however there are many hidden elements at work . #1 To start with the air barrier between the cold and warm air needs to be paper thin and able to conduct the heat to the cold easily.. and thats not easy to do. I used a thin plastic mylar barrier , this seemed to be the most efficent i could find. #2 After you get warm moist air giving up its heat to the cold air coming in... you instantly have a frost /condensation issue of the worst kind imaginable... the commercial built ones have heaters in the air paths to keep the air ways defrosted. #3 You will invaribly lose much heat from your room as its not possible to exchange air temps in the small space you are attempting to confine your exchanger in. Bending air ways isnt practical and causes lots of air turbulance. You would need a longer air path way maybe 10 ft to be effective. #4 You would need fans blowing air in and out as well. Fans and mylar? A little noisy. Like i said... it kinda worked... it was a learning experence, if you get the thing to work well i'd like feedback! Good luck and dont let this keep you from attempting a project! Its all about learning!!:thumbup:
 
updated top view sketch, you could put the thingy in the window, the hot duct exhausting thru duct from near the ceiling and the warm
inside inlet ducted to the floor to allow the cooler air to sink, collapsable dryer ducting would be cheap.. the plenums for the plates could be plywood and the spacers between the plates could be cork gasket strips, alum. plate can be fairly thin stuff as long as you use enough layers....even with quite a few layers it could be fairly short height wise. i'm sure you could come up with a window mounted design .....how effective it would be would then depend on the no. & size of the plates (total surface area). as it freezes up there i'd make sure the gap was enough to keep it from getting blocked by hoar frost condensing on the fridgid plates out of the nice warm moist air being exhausted. i'm showing rhomboidal plates rather than square to make it wider to fit the window while keeping the inside-outside depth narrow for ease of keeping it in the window. the 'points' at the corners would butt the wood box it all sits in & along with the cork seals would keep the air paths seperated.
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anyways, bound to be better than just leaving the window part open & gives you something to do in the workshop. if needed you could probably get an inexpensive quiet computer case fan to mount in the duct & feed it with a cheap radio shack power supply. mebbe even mount the fans to the holes in the wood box where the ducting attaches, they would really be case fans then.
 
Michaelp I appreciate the voice of experience . Someone else mentioned condensation/frost and I didn,t really pick up on it . My home has a somewhat higher humidity level than some in winter due to the few plants , aquarium with venturi bubbler and a small wall fountain .

I figured flexible aluminum conduit would be thin enough and conduct well enough to suffice . I thought its serpentine nature would allow fairly tight Radi(plural of radius?) as well .

I figured small entrances and exits would somewhat slow down flow which would allow a longer time for the heat to exchange . If I can get the Equivalent of a few square inches of open window it would suit my needs .

I do not think fans are necessary to give a positive exchange . After all when you open the window in winter there is a free exchange between hot and cold and therefore outside air comes in and heated air moves out .

The condensation issue does seem to be a major concern .
 
Kronckew I,m demoting ye . Ye now be cabin boy second class . We do not be going fer such talk as hoar frost around here . Keep yer sexooal dysfunctions and maladys private . L:O:L

I,ll be looking over your design and if it is feasible and not too unsightly I may be allowing you back up on deck . Fer now I wants me supper served in me cabin . Coulds ye be wearing that pink dress ? I know , I know you swore it was a shower curtain when we caught ye behind the bilge pump .
 
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