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Old 01-23-10, 11:44 AM   #31
ynot7201
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Quote:
Originally Posted by Christ View Post
This is exactly like an air to air intercooler, but will not be as efficient as a bar/plate design. Skin xfer of heat is limited to surface area, and the smaller your pipes are, the more surface area there is to xfer heat from one medium to the next. Bar and plate is one of the most efficient because there is a tradeoff between thermal xfer efficiency and pressure drop, and many of the best intercoolers on the market are borderline at 80% efficiency (of this type of design).

Also, keep in mind that the more heat you extract from your exhaust, the more you slow it down, making it more difficult for the intake fan to blow air through the dryer, and more difficult for the moisture to leave. The idea is to snake as much heat as you can right at the exhaust outlet so that there isn't a pressure increase slowing down flow.

Another way you might go about this is to minimize heat loss in all places except where you specifically want the heat to go. Insulate your exhaust and intake. If you want heat exchange from the exhaust to the intake, you don't want heat exchange anywhere else, so if you insulate the tubing, you can mitigate much of the heat loss, making the system more efficient than it would have been before, so your heat exchanger might have less of an impact on exhaust flow velocity.

Keep in mind, also, that you will need to periodically clean the heat exchange surfaces. If you don't, they will stop transferring heat. Lint is a great insulator.
thanks for the info regarind vent heat recovery. about 5-6 years ago I saw a system consising of a metal box with inlet 4" same for exhaust in the box was a fan on rear blowing the hot exhaust air forward to a foam like screen and a drip tray at the bottom this unit worked extremely well..but we are unable to find this sytem...any ideas ..thanks and have a great day.

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Old 01-23-10, 05:53 PM   #32
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Quote:
Originally Posted by ynot7201 View Post
thanks for the info regarind vent heat recovery. about 5-6 years ago I saw a system consising of a metal box with inlet 4" same for exhaust in the box was a fan on rear blowing the hot exhaust air forward to a foam like screen and a drip tray at the bottom this unit worked extremely well..but we are unable to find this sytem...any ideas ..thanks and have a great day.
I'm not sure I have ever seen anything like you describe, sorry.
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Old 01-23-10, 06:02 PM   #33
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thanks for your time anyway.I think we are going to use a solid pipe then suround that withanother enclosure and vent the warmed air into the house. thus avoiding any damp problems ..if you have any other info .we'd love to hear it as heat is a high expense here in quebec,,have a great day.w.weston(tony)
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Old 03-16-10, 09:33 AM   #34
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I spent a long time trying to figure out a way to cheaply retain the heat without the moisture and better yet without sucking the heat out of my house.
Well that didn't happen so I spent a small fortune and got an LG combo washer/dryer WM3988HWA Washer / Dryer Combos Home Appliances ... it solved all my issues except the cheaply part.
this uses a Ventless Condensing drying unit, uses 110 volt, This unit in drying mode warms up the kitchen real nice.
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Old 03-25-10, 09:50 AM   #35
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Lint is likely to collect inside dryer vent duct of any type, and regular cleaning is good practice. Smooth walled duct is better than flex in this regard. The idea to surround the dryer vent with a larger hvac duct to act as a countercurrent heat exchanger is very simple to construct and allows duct cleaning as usual.

Good practice is to provide the dryer location with an outdoor air intake to equalize pressure. This works out, as the heat exchange duct will terminate at the dryer. In a mixed climate, we don't want to temper the incoming air in the cooling seasons. An alternate, parallel air intake without heat exchange can also be fed to the dryer location. Dampers in both intake ducts dictate whether dryer heat-exchange occurs or not. These could also be electronic dampers for automatic operation.
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Old 04-02-10, 07:52 AM   #36
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Hey guys, if you look at a steam heating piping system, and you look at the pressure and temperature guages or instruments, you sill see what is called a steam pigtail siphon, it is just a 360 degree loop of pipe that screws into the tee in the pipe, and the other end goes to the guage or instrument, this protects the gauge from the hot steam, because the steam cannot travel around the loop, instead it condensates and runs back into the steam line. Maybe this could be incorporated into your dryer vent to remove the moisture, create a big vertical loop, and a fitting at the bottom of the loop with a hose to drain the fluid.
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Old 04-05-10, 09:26 AM   #37
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I like the ynot7201's idea, thinking about implementing it.

I'm thinking about putting solid aluminum pipe into a duct, rectangular or flattened 6" round one. May be adding some fins between inner and outer pipes for more efficient heat exchange.
Outer duct will draw air from outside.

I wander if anybody did this.
I'm concerned about a moisture.

In my case I have to run vent pipe 6 feet up. So if heat exchanger is efficient enough and some of the moisture condenses, it will collect in the duct.

Any experience there?
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Old 05-03-12, 07:06 PM   #38
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Isn't the dryer heat already transferring into the basement atmosphere, as the heated stale dryer air travels down the exhaust pipe?
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Old 12-07-12, 12:14 PM   #39
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I'm curious to hear if anyone actually implemented this as I've been considering it for our electric dryer. A condensing dryer sounds nice, but currently not an option on the budget side.

While I understand that other parts of the country want moisture in the winter, here in the PNW we don't, or at least the house I'm in doesn't. I've got condensation issues with the AL framed windows (to be replaced at some point) and am happy to get any and all extra moisture out of the interior envelope as possible.

Because of the ease of assembly I was also toying with this same idea for a simple HVR system for bathroom venting. I have plenty of room in a long crawl-space and a foundation drain (that now works after digging up the yard) there to dump condensation. I know efficiency would be low, but so would project costs.
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Old 12-07-12, 12:37 PM   #40
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One member did do this. Its a bulky system but seems to work.

http://ecorenovator.org/forum/applia...html#post21316

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