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AC_Hacker 07-08-10 10:26 AM

KiwiMark, Welcome to Ecorenovator
 
Quote:

Originally Posted by KiwiMark (Post 7305)
Sorry to waffle on... maybe pictures to follow.

Thanks for the description of your HRV project.

Yes, your pictures would be most welcome.

If you click the "edit" button, and (sometimes) you need to click the "go advanced" button, it will take you to a page that will easily enable you to upload photos. If you go to the "manage attachments" button, you can browse to your photo(s) and then click the "upload" button to get your pix onto the server. Once this is done right-click on the hyper-linked image reference and do "copy link address". This will allow you to then use the picture attachment button, using the file reference already on the server. It's easier to do than to explain, but your images will be in-line, look really cool, and be available for the duration of the EcoRenovator blog.

Best Regards,

-AC_Hacker

AC_Hacker 07-08-10 11:09 AM

Fans, Condensation and Too-Short Fan Life...
 
2 Attachment(s)
Dave,


On page 20 of your "Homemade heat Recovery Ventilator" PDF, you mourned the passing of your favorite fan:

Quote:

After more than six years of faithful service, the intake fan motor wore out.
I read of someone working on a very different project having the very same problem. In this case, he was trying to data-log the temperature of the outdoor air at his residence, and he took the 'maximum technology' approach and affixed a small diameter, dual-ball-bearing computer fan to blow through a 3"diameter ABS tube, within which was a digital thermal monitoring device. The fan, itself was reputed to have a life of 5 years continuous use, but it bit the bullet after half a season. His analysis of the situation was that the fan was designed for a computer environment, where it was working in warm dry clean air. But in his application it was exposed to a moisture-condensing environment with quickly wrought it's ravages on the little fan. His fix was to use a centrifugal fan, the design of which kept its motor outside the condensing-moisture air-stream. Problem solved.

In your paper, you refer to the option "dual centrifugal fans" as are found in range hoods. These fans, if designed properly, move the motor and it's bearings outside the hot, humid bacon fat laden air-stream, or in our case outside the condensing moisture air-stream.


I think the dual centrifugal fan would remedy the problem of too-short fan life.

What do you think?

-AC_Hacker

* * *

jrandom_EE 07-12-10 10:16 PM

Wow, I just wanted to compliment you guys on an awesome thread! I've been looking at how to design an air-air heat exchanger, with particular focus on recovering the latent heat of vaporization as well as the sensible. It has been very elucidating to read the thread, and interesting to see that other people have thought of using a computer case fan as well! (I would think that if you put the fans on the dry side of both streams, it would work better?) Series is also possible, computer case fans are cheap so worth looking at perhaps. Some googling for "static pressure" computer fans yields that Yate Loon fans might be a good option. Apparently they make centrifugal computer fans as well.

I've been wondering how hard it would really be to design an energy wheel type ERV. These types are noted for not lasting more than a year or so. But maybe that's not a problem.

Although I'm an engineer I'm a novice at this. However, I can't help but think that if you can get an electric motor to turn at the appropriate rate and build a wheel, and build the wheel housing for easy disassembly, you'd just use crystalline kitty litter for the heat and water transfer medium. Crystalline kitty litter is just silica gel. With $20 worth of materials, you could choose to either turf the kitty litter every year, or perhaps just hose it down? Or filter the ends? It's cheaper than buying good filters.

For filters, I'd design it to incorporate some of the IQ air filters. The IQ air is the premium air purifier on the market, using a prefilter (mainly pollen), a VOC filter and a hyper HEPA filter (in that order), it filters pretty much all the crap out of the air in one pass, making it ideal for HRV or ERV requirements. I have had one for several years, it is worth every cent. The pre-filters run about $60, which would last maybe a year or so, but meaning the inside would be pretty clean.

Thoughts?

(Note, I wanted to insert a couple of links or images, but need to get my post count higher! I guess I'll try and post some more. Or something.)

jrandom_EE 07-12-10 10:40 PM

Just having a look around at ebay, it looks like the options for fans are either:
  • Axial flow CPU/PC case fans, maybe in series? Advantage: cheap
  • Centrifugal flow PC case fans (no experience with them)
  • Centrifugal flow blower, as used by pot growers^H^H^H^H^H^H^H^H^H^H^Hhome hydroponics enthusiasts. Disadvantage: Cost $150 or more, use more power/higher CFM than probably necessary, probably noisy.

I'd just put this out there too - can anyone think of an appropriate motor for the wheel?

AC_Hacker 07-13-10 09:44 PM

Quote:

Originally Posted by jrandom_EE (Post 7350)
Just having a look around at ebay, it looks like the options for fans are either:
  • Axial flow CPU/PC case fans, maybe in series? Advantage: cheap
  • Centrifugal flow PC case fans (no experience with them)
  • Centrifugal flow blower, as used by pot growers^H^H^H^H^H^H^H^H^H^H^Hhome hydroponics enthusiasts. Disadvantage: Cost $150 or more, use more power/higher CFM than probably necessary, probably noisy.

I'd just put this out there too - can anyone think of an appropriate motor for the wheel?

jrandom_EE,

I really like your thinking about the enthalpy wheel ERV. There are also enthalpy type HRVs that use a permeable membranes to put condensed water back into the air.

Also, I think the right fan will be important. My interest is in case fans because if the very low cost, fairly high quality and also, for me the low CFM. I know that in Europe in general and Germany in particular, using variable speed fans is very important in order to get an acceptable level of performance at a minimum level of energy consumption.

European energy seems to be about 2x the cost compared to the states, and the sophistication of technology is also about 2x.

So, about a year ago, I bought a small mini-split heat pump that had 'inverter technology'. That is the trade name for rectifying the line AC into DC and then turning the DC back into AC, only with a variable frequency. This is used to control the speed of the compressor and also the speed of the fans, both inside and outside. Very quiet and efficient.

So on the outside unit, they use an axial fan, where the noise will not be so much a problem and on the inside unit they use a variable speed fan that is like a squirrel-cage fan, only the squirrel-cage is stretched out. It works really well.

Something like this would be perfect.

I have seen fans like this used in laser printers, but I don't know if they would be easy to control.

With all the developments in 'inverter technology' heat pumps, I just bet that there is an IC that would greatly simplify fan speed control.

Parallel to this line of thinking, I have found out that there are computer case fans with:
  • two wires (volts and ground)
  • three wires (volts, ground, sense)
  • four wires (volts, ground, sense and PWM for controlling speed)

I just bet there is an Arduino out there looking for a fan speed control project.

What do you think?

-AC_Hacker

NiHaoMike 07-13-10 10:27 PM

If the fan motor has a resolver, it is just a matter of decoding the signals into the signals that drive the motor. Speed control is by PWMing the outputs on and off. For closed loop operation, the controller monitors the resolver signals.

The 12cm ECM fan assembly I have recently stopped working, and the inverter board broke into pieces while I tried to take it apart so I don't know exactly what's wrong. It had a PIC12F508, 4001 NOR array, two MOSFETs, and a lot of surface mount components. I just soldered some wires to the stator coils and resolver IC, then built a simple drive circuit consisting of two MOSFETs and a few passive components. It actually ran better than with the overcomplicated inverter board.

AC_Hacker 07-13-10 11:19 PM

Quote:

Originally Posted by NiHaoMike (Post 7366)
...built a simple drive circuit consisting of two MOSFETs and a few passive components...

Sounds great.

Got a schematic?

-AC_Hacker

AC_Hacker 07-13-10 11:33 PM

BTW...

This is very off topic, but here's an interesting How-To:

How to Convert a Computer ATX Power Supply to a Lab Power Supply.

-AC_Hacker

NiHaoMike 07-14-10 12:00 AM

Quote:

Originally Posted by AC_Hacker (Post 7367)
Sounds great.

Got a schematic?

-AC_Hacker

I just connected the resolver output signals (internally buffered) to the gates of the MOSFETs. The MOSFETs simply drive the two stator coils (2 phase unipolar motor) with two 1uF capacitors as snubbers. The method of control is very basic and does not allow for variable speed, nor does it offer features like inrush current limiting or overload protection. I'm going to design a better control circuit later on.

jrandom_EE 07-14-10 06:03 AM

Quote:

Originally Posted by AC_Hacker (Post 7364)
jrandom_EE,

I really like your thinking about the enthalpy wheel ERV. There are also enthalpy type HRVs that use a permeable membranes to put condensed water back into the air.

Thanks. I know about those too, but have no idea how I'd design one. But as for the enthalpy wheel ones, they look to be not too hard - just search for the right motor. I'd love to know what their main failure modes are.

Quote:

Also, I think the right fan will be important. My interest is in case fans because if the very low cost, fairly high quality and also, for me the low CFM. I know that in Europe in general and Germany in particular, using variable speed fans is very important in order to get an acceptable level of performance at a minimum level of energy consumption.
Most probably. PWM is not a bad idea. If you can't get PWM and high static pressure, you could have several of them in parallel with a one-way valve after each, so you'd have several different settings. Or vary the voltage. When I get 5 posts up I'll start posting some links I've found.

I suspect that dust problems can be solved with filtration and humidity problems could be solved by sticking the fans on the "dry end", whichever that is.

Quote:

With all the developments in 'inverter technology' heat pumps, I just bet that there is an IC that would greatly simplify fan speed control.

Parallel to this line of thinking, I have found out that there are computer case fans with:
  • two wires (volts and ground)
  • three wires (volts, ground, sense)
  • four wires (volts, ground, sense and PWM for controlling speed)

What do you think?
Not sure. Given how cheap CPU fans are I was thinking simply have several of them and use on/off on each of them, as said above. Also, sizing the fan to the application rather than having to step it to the right level. But being able to adjust it would be a plus. I guess I'll cross that bridge when I come to it.

I think first getting an idea of the appropriate static pressure needed would be a good first step. Make a manometer tube, use an oversized fan, and block it until it gives the right flow rate. A simple hack method of measuring would be using a cylindrical outlet and wafting smoke from an incense stick down it, and calculating the CFM from the rate of movement of the smoke. Then use that to look up the right fan.

Xringer 07-14-10 06:58 AM

OT, but interesting..
 
Quote:

Originally Posted by AC_Hacker (Post 7369)
BTW...

This is very off topic, but here's an interesting How-To:

How to Convert a Computer ATX Power Supply to a Lab Power Supply.

-AC_Hacker

Those things are pretty well made.. At least this design looks nice..
200W ATX PC POWER SUPPLY

Wow! 300vdc! The 120-240 switching is simple anyways.. :)

AC_Hacker 07-14-10 02:16 PM

Help!
 
3 Attachment(s)
Quote:

Originally Posted by jrandom_EE (Post 7373)
I think first getting an idea of the appropriate static pressure needed would be a good first step. Make a manometer tube, use an over-sized fan, and block it until it gives the right flow rate. A simple hack method of measuring would be using a cylindrical outlet and wafting smoke from an incense stick down it, and calculating the CFM from the rate of movement of the smoke. Then use that to look up the right fan.

I have a dandy blower to do tests with but I can't make it work.

It's a capacitive-start AC motor.

Here's a photo of the wires & connector:


Here's a photo of the connector with the DC resistance I measured across the various terminal combinations:


...and here's a photo of the only identification on the fan:


The fan came from a range hood blower. This fan was one of two., the other motor has a broken internal support. As I read the label, it says Elica, which seems to be a maker of range hoods made in Italy.

I searched for "Elica schematic", "Elica wiring", "Elica diagram", but wasn't able to find any helpful info.

Any ideas?

-AC_Hacker
? ? ?

AC_Hacker 07-14-10 03:49 PM

Brushless DC Motor Control using ATmega32M1
 
1 Attachment(s)

Quite by accident, I came across this app note:

Brushless DC Motor Control using ATmega32M1

Looks like the ATmega32M1 is similar to the processor used by the Arduino community plus a Power Stage Controller.

-AC_Hacker

jrandom_EE 07-17-10 07:48 PM

Sorry AC Hacker, I'm not familiar with US wiring, so I wouldn't want to speculate on how to wire it up correctly. I'm also not really a power EE, and haven't done anything in that area since university anyway. I'd be just googling the same as you.

Xringer 07-17-10 08:26 PM

There is some stuff around on the web.. Is there a switch in that fan unit?
One that opens, when the fan motor starts running?

I had one of those flying balls centrifugal gizmos on an old oil burner motor once.
It broke one night at 3AM.. I drilled two small holes in some spring thing that held
one of the weights and tied them together with a paper clip..
It worked for years, until the system was replaced..

Connecting the CSIR Motor for a Change of Rotation

http://i110.photobucket.com/albums/n...ack/baldor.jpg

http://img.photobucket.com/albums/v4...nut/SBLMTR.jpg

igor.chudov.com/manuals/ElectricMotors.pdf

AC_Hacker 07-18-10 09:12 AM

Quote:

Originally Posted by jrandom_EE (Post 7446)
...I'm not familiar with US wiring...

jrandom,

This is actually a euro-fan. Made in Italy I suspect and sold all over Europe and apparently also sold in the US.

So your knowledge might be relevant.

-AC_Hacker

AC_Hacker 07-18-10 09:14 AM

Quote:

Originally Posted by Xringer (Post 7447)
... and tied them together with a paper clip...

Xringer,

Thanks for the links.

I'll check them out.

-AC_Hacker

laderload 09-02-10 12:58 PM

Hi,

i am new to this great group and i would like to thank you all for your contributions and thoughtful work. also i did not find the usual off topic sliding on private or ego issues :)

thank you Dave Meinert for sharing your work and showing us that this is feasable and working.

i am going to start building these weeks and would like to ask if any of the "plastic " versions have been finished and are working?

is there anyone who tried the metal version in comparison?

also, did someone experiment with the old AC/dehumidifiers (the surface is great, but just not even for both streams, due to the water-air mechanism )?

thank you very much for your help

laderload

Piwoslaw 09-02-10 01:57 PM

Quote:

Originally Posted by laderload (Post 7914)
Hi,

i am new to this great group and i would like to thank you all for your contributions and thoughtful work.

Welcome to EcoRenovator. Please drop a few lines about yourself and your planned and finished projects in the Introductions section.

Quote:

Originally Posted by laderload (Post 7914)
also i did not find the usual off topic sliding on private or ego issues :)

Welcome to EcoRenovator;)

AC_Hacker 09-02-10 03:35 PM

Quote:

Originally Posted by laderload (Post 7914)
i am going to start building these weeks and would like to ask if any of the "plastic " versions have been finished and are working?

My plastic version is on hold due to other projects.

-AC_Hacker

Daox 11-02-10 02:07 PM

Any updates?

AC_Hacker 11-02-10 03:16 PM

Quote:

Originally Posted by Daox (Post 9044)
Any updates?

Yes, I'm about 1.5 weeks away from having my bathroom remodel done, and sanitation functionality restored.

-AC_Hacker

Daox 11-02-10 03:40 PM

woohoo :)

Drake 02-14-11 06:18 PM

Don't know if anyones coroplast stacking is yet completed but might not cutting some 1" wide spacers to be used to separate cross layer giving you just one layer of separation over most of the area. Strips could be stapled(construction hand staple gun) in place until "core" can be placed in a custom mechanical compression form(from your pics of cross flow box line up corners with air flow dividers and and have "bottom" and "top" of box "press" core together when assembled. As not sure how well or how long(possible rusting) staples would last.

Always been interested in the theory HRV/ERV but living in a climate with several months of sub zero heating days effectively resolving "frost up" still isn't evident to me.
Heat pump xfer seems intriguing but won't it need a fairly large amount of in/out going air? I am exploring maitaining indoor air quality in my SI passive addition by minimizing VOC's, lifestyle, low temp solar fresh air preheaters(daytime) and still researching where I might recover some heat at night or just use small amount of direct ventln. Of coarse greatly reduced cost of DIY HRV system would make it more advantageous.

Piwoslaw 02-16-11 07:56 AM

1 Attachment(s)
Here is a picture of the DIY countercurrent HX (see post #3) in place:


On the right is the bypass, even more to the right is the box that houses filters and fans.

AC_Hacker 02-16-11 10:30 AM

Quote:

Originally Posted by Piwoslaw (Post 11948)
Here is a picture of the DIY countercurrent HX

Piwoslaw,

Is this a unit you built?

Please share more details.

-AC_Hacker

Piwoslaw 02-16-11 12:17 PM

Quote:

Originally Posted by AC_Hacker (Post 11955)
Piwoslaw,

Is this a unit you built?

Please share more details.

No, unfortunately:( This is from a thread on a Polish builders' forum. You can try to decipher its Google translation. The thread is VERY informative, but there is also a lot of it, most of it noise. I sifted through it and posted most of the good stuff earlier in this thread.

Ko_deZ 07-31-11 03:20 PM

Just poking my head in here too. This cross heat recovery unit has a major drawback. It sends moist air out, and dry air in. With a rotating wheel you will condense the moisture from the outgoing air, and evaporate it to the ingoing air, so you keep a decent humidity level indoors. Also, this helps against the unit freezing up. If only the outgoing air is dehumidified, there will be a build up of water, which might freeze if the outdoor temperature is cold enough. We regularly have -20 here, so even the wheel based models have some issues. My unit is made by ener(.no), and they have two large aluminium fins and a 3 way air walve that directs incoming and outgoing air back and forth between them. To my mind this should work better when it is really cold, as the hot and cold side will alternate. Also, the unit should be somthing like 93% efficient when running in low mode.

-Ko_deZ-

Drake 07-31-11 07:39 PM

I have only found large commercial "wheel" ERV's in the US. Anyone know of a "residential" sizes one? Ko deZ what is the brand name? 93% of what? How can two passing air flows do more than reach equilibrium? The same with relative humidity of the air flows. Without a HP extracting it.

Piwoslaw 08-01-11 01:08 AM

1 Attachment(s)
Quote:

Originally Posted by Drake (Post 14943)
How can two passing air flows do more than reach equilibrium? The same with relative humidity of the air flows. Without a HP extracting it.

If the angle between the two airflows is perpendicular or less (ie they are going in the same direction) then you are correct. But in a countercurrent HX it is possible extract much more heat: Imagine air (or any other gas or liquid) in the cold intake - when it enters the HX it starts to collect heat from the 'hot' side (which at this point is barely 'warm', since it is already leaving the HX having given up most of its heat). As the 'cold' air makes its way through the HX the 'hot' side is getting warmer, so it still has heat to give up. The 'cold' air exits the HX where the 'hot' air enters, ie where the 'hot' side's temperature is highest.


Ko_deZ 08-01-11 01:25 PM

Quote:

Originally Posted by Drake (Post 14943)
I have only found large commercial "wheel" ERV's in the US. Anyone know of a "residential" sizes one? Ko deZ what is the brand name? 93% of what? How can two passing air flows do more than reach equilibrium? The same with relative humidity of the air flows. Without a HP extracting it.

In the US, I have no idea. In Norway, Villavent are quite popular.
93% heat recovery. 0C outside, 20C inside gives me incoming air at approx 18.5C.
piwoslav got it right. Countercurrent flow. Check out heat exchanger in wikipedia, loads of good info there.

Daox 08-01-11 01:38 PM

Quote:

Originally Posted by Ko_deZ (Post 14939)
Just poking my head in here too. This cross heat recovery unit has a major drawback. It sends moist air out, and dry air in. With a rotating wheel you will condense the moisture from the outgoing air, and evaporate it to the ingoing air, so you keep a decent humidity level indoors. Also, this helps against the unit freezing up. If only the outgoing air is dehumidified, there will be a build up of water, which might freeze if the outdoor temperature is cold enough. We regularly have -20 here, so even the wheel based models have some issues. My unit is made by ener(.no), and they have two large aluminium fins and a 3 way air walve that directs incoming and outgoing air back and forth between them. To my mind this should work better when it is really cold, as the hot and cold side will alternate. Also, the unit should be somthing like 93% efficient when running in low mode.

-Ko_deZ-

Do you have any diagrams of how a unit like this works? Its pretty easy to see how the others work, but I'm not understanding a rotating wheel heat exchanger. I'd certainly LOVE to have a 93% efficient unit though!

Ko_deZ 08-01-11 02:58 PM

Indeed I do: Thermal wheel - Wikipedia, the free encyclopedia

There are brushes between the two sides that helps avoid that much air is resirculated. Poor maintenance of these often results in bad odors returning back into the house.

It is very important that you position the input and outputs at the right places, and that you make extensive use of noise traps on all incoming places (bedrooms, living room). Usually it is enough with two noise traps in series at the heat recovery unit shared by all outgoing places (all bathrooms, washing room (because of damp air) and kitchen. Have a separate output for the cooking place with a non return valve on it in addition). Make sure that there is a little lower pressure inside the house than outside (pull fan and exit valves more open than for incoming). This to make sure that you don't push hot and moist air out trough the leaks in the walls where it will condense and give you rot and fungus problems. If outside is hot and humid most of the time, and indoors is cooler than outdoors, do the opposite.

DoctorDoctor 09-22-11 08:08 AM

I actually have been thinking about this very problem, a diy, inexpensive air to air heat exchanger. I would like to do this for my crawl space. I am not a big believer in radon risks. I thought about doing a traditional heat exchanger with lots and lots of sheets of aluminum. One could do this in a rectangular duct.

But I thought that this would be simpler and very cheap: Take a three inch round aluminum vent pipe and put it in a four inch round vent pipe. Wrap it in insulation and make it pretty long, say 20-25 feet. The cold, outside air goes in the center pipe. The warm, moist inside air exits through the large vent pipe outside of the center (the "annulus" part). There would be condensation developing on the inside pipe, dripping down, so it would have to be inclined down somewhat with a collection pan.

One couldn't move the air too quickly, but it is my contention that with a sufficiently long pipe (again about 20 feet) the temperature of the air in the center pipe would be coming out warmed to almost the temperature of the inside air temperature.

Other variations: two three inch pipes in a six inch outer pipe. This would match the areas inside the smaller pipes with the outside remnant area. Or seven three inch pipes in a honeycomb pattern inside a nine inch outer pipe.

One would want the inner pipe to stick out somewhat so that one isn't sucking in what one is blowing out.

Daox 09-22-11 08:17 AM

I think your solution would work, but how do you keep the smaller tube centered in the larger tube?

I also think the DIY rectangular setup would be superior just because you can have so much more surface area per amount of area the exchanger takes up.

Piwoslaw 09-22-11 08:48 AM

Quote:

Originally Posted by DoctorDoctor (Post 16010)
Other variations: two three inch pipes in a six inch outer pipe. This would match the areas inside the smaller pipes with the outside remnant area. Or seven three inch pipes in a honeycomb pattern inside a nine inch outer pipe.

  • I'd go with the honeycomb pattern, since it would have much more surface area than just one concentric tube. It may not be as efficient as the layered version, but may be easier/cheaper to build.
  • Make sure that the tubes are spaced from the outer tube and from each other. There won't be good (if any) airflow/heat exchange in the vicinity of where they touch.
  • Have the inbound cold air in the outer layer. That way the warmer, outbound air doesn't lose heat through the outer wall - more of it can be absorbed by the inbound stream.
  • Of course, both air streams should be flowing in opposite directions. But that is obvious.
Quote:

Originally Posted by Daox (Post 16014)
I think your solution would work, but how do you keep the smaller tube centered in the larger tube?

Add fins/spacers. They would also slightly increase the HX area.

Xringer 09-22-11 08:49 AM

I've heard of this kind of rig before. It used iron pipe buried with stone under it
and had drain holes drilled in the bottom of the entire run of pipe.
But, the system was a basement dehumidifier.

DoctorDoctor 09-22-11 06:32 PM

Really simple heat exchanger
 
Yes, I was thinking of using fins to hold the center pipe. My point is to use K.I.S.S. (keep it simple stupid). Sure one can design and make a air to air heat exchanger with near perfect numbers - outside air is heated to almost that of inside air and vice versa, so that no heat energy is lost. Surface area is indeed the critical factor for heat exchange. The ideas like the "thermal wheel" look great but no one is going to build them. If you want better heat exchange, just make the exchanger longer. Not sure that the honeycomb is actually better than just adding another section of aluminum vent pipe to make it longer.

One would probably want an air flow so that the entire volume of air in the crawlspace (or basement) is pumped out at least once a day. If one increases airflow too much, one doesn't get as good heat exchange. Also, the humidified air in the outside part of the larger pipe will start freezing on the inner pipe (if the ambient temp is less than freezing).

One issue is that one doesn't want the fresh outside air that you have just pumped in to be pumped out. So the out-take can't be too close to the intake. I was think that a 90 degree corner on the outer tube with a hole cut out so the inner tube goes through it. One would seal all around this hole. I wish I could draw a picture.

DoctorDoctor 09-22-11 06:38 PM

Piwoslaw writes, "Have the inbound cold air in the outer layer. That way the warmer, outbound air doesn't lose heat through the outer wall - more of it can be absorbed by the inbound stream."

My reason to have the inbound cold but warming air on the inside and the warm and moist but cooling outbound air on the outside is that there would be condensation on the surface of the inner pipe. This would drip down and if the whole thing was slightly declined, one could collect it and get rid of it.

ThomSjay 09-24-11 11:57 PM

I just had an idea!:eek::D
Have the outer pipe on a slight decline as it exhausts the air. This would allow any condensation to drop off. Now, here is my brain wave, haha....the intake would be a single length of down spout pipe to give a slight pre-heat to the air before entering the inner pipe of the heat exchanger.
The only down side to this is in the summer when one wants to have air conditioning.


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