skipnchar wrote: If I read correctly, you're using Coroplast to separate the CO laden exhaust air from the air blowing into the RV? Have you tested the CO content? Sounds like an ingenious device as long as it's very well sealed and remains so.
The design presumes a propane system, which exhausts mainly CO2 (carbon DIoxide) and water.
Levels of "CO" (carbon MONoxide) in the exhaust from a properly operating propane system are vanishingly small, and once exhausted outside probably non existent.
I think it's also safe to presume that a user of this very clever system would take care not to locate a gasoline/diesel fired generator anywhere near the opening, as that combustion does produce very lethal levels of CO.
" Not every mind that wanders is lost. " With apologies toJ.R.R. Tolkien
With the simple design, I'm a little surprised at the 75% efficiency, but trust your numbers. At the 0.2A/hr draw, it is probably recovered by the reduced furnace run time while also providing better humidity control.
Glad to also see you add ducting to help pull the air from desired locations. If you ran the duct up to the front side of the cab-over, you would also help pull the warm air into that area, and thus raise the benefit.
To raise the efficiency, you could decrease the space between the layers and add more layers to maintain the over all thickness. Or increase the size of the box. Efficiency will increase as the contact area increases and air speed decreases, but the % gain decrease as they increase, so you have to find the balance between the two.
It would be interesting to do a comparison of two similar nights. Measure battery useage and humidity with the unit on one night and the humidity off another.
After you complete that test, please, please add more photos and details.
Do have two questions: Which computer fan are you using (2.5", 3", etc) and can you provide more detail on the coroplast?
Thanks for the great write-up!
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So, how well does the seal around the window and the unit hold up to horizontal rain? I note that you have it located in the pass through window on your rig, but for someone without a pass through, it would be located on an outside wall that isn't quite as sheltered, which asks the question of how water tight the setup is.
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sleepy wrote: Well thought out, good design, nice build.... you get an "A+" on this project. This is among the "best" of the best projects.
I'd like to do it to replace the screamer exhaust fan over the stove. Kill two birds with one stone.
Congratulations... this one should be in the TC University.
BTW... please add the "boring " stuff... we all seem to like it on the TC forum.
Sleepy
I like Sleepy's Idea to use the Exhaust Hood Area and opening to do this vital operation. In the hood area, a slightly larger unit could be incorporated, and with the variable fan speed, you would be able to crank it up during cooking, then slow it down for the evening/night... Great Idea!!! Since I don'r have a hood yet, I could even fabricate the hood from aluminum, and then use the fans and the space for the heat exchanger!! Again THANKS!!!!
Garry in very cold Kodiak... (-9F this AM...)
Garry K
Wife + 4 kids
Retired Military Family.... Alway's on the move....
2002 F350 CCSB 5.4 6spd 4x4 in AK
1966 Avion C-10 Truck Camper
love it
I have been thinking of something to do that job in the roof vent----I always had a problem with the condensation coming back inside-------never even thought of a window!!!!!!!!
Nigel & Pamala------------Spain
I do think that I'd try to mount the system inside the camper. I have a deep area behind the stove top... probibly 10 inches deep, 20 inches high, and wide as the stove top.
I'd dump the stove vent screamer and use muffin fans similar to the OP... probibly jut one.
Put on you thinking caps...
An exhaust fan close to the stove might grease up
the muffin fan incoming might push the cooler fresh air in too hard...
I'd only use one fan to exhaust air. The incoming air may warm up more that way, if the RV is "tight". If it is not, then pushing air in and out may be slightly better.
FK-The incoming air will be at the dewpoint (wetbulb) of the outside air. As it is warmed by the exchanger, the relative humidity goes down. This assumes no mixing of air streams in the Hx.
Steve-I think of Apollo 13 when I get discouraged, if they could do it there, I can certainly do it here. This one is designed to be portable. I considered the lower hatch but mine is blocked by the wheel well and I would need to duct the inlet and outlet apart to prevent recirculation. All you need is to separate a small inlet and outlet somewhere.
Sleepy-Thank you for the ultimate compliment. I will try to bore you later...
gbopp-ditto above
Silver-Can (have) you measure the thermal efficiency of your house units? I understand they run between 70% to 90%.
ticki2-thank you
Chief2-answered by VintageRacer. thank you.
skipnchar-see reply by FK. The coroplast is the framework of the plate to provide the air passage, nothing more. The Hx simply exchanges inside air with outside air. If the level of CO (or CO2 or H2O) outside is less than inside, then the level inside will decrease with exchange of air. At low speed, I estimate about one air change in an hour to hour and a half for my small TC. Sealing the two air flows apart is not trivial and some cross leakage will occur.
msiminoff-thank you, more to follow.
FK-I chose to put it under the cabover in the slide-through window. It is shielded from rain and no generator is there (especially when the TC is on the truck!).
kohldad-your analysis is spot on. If I do a next one, it will be in a larger box.
Added ductwork is added pressure drop, lower air flow and part of the engineering balance. I may not conduct tests before more info. The real test is, "Are you are more comfortable when using it?"
The computer fans for this prototype are 80 mm. Coroplast (corrugated plastic) is used for signs. It costs me next to nothing to acquire coroplast sheets on the first Wednesday after the first Tuesday in November in even numbered years. Mark your calendar.
In this design, one lawn sign makes 5-6 frames. The Hx shown uses 24 plates.
JoeChiOhki-The window seal is a garden kneeling pad cut to fit. Not permanent and would probably leak if sprayed with the hose. I could add a rain shield to the window if needed.
The size of my slide through window constrained my design. For others, put the inlet and outlet through the wall, use flex hose to duct, increase the fan size, change the plate size and put it wherever it will fit, like in the back of a cabinet.
FYI I went to the sports show this weekend and the new TC's I saw no longer have slide through windows as standard.
garryk6-my design is flat plate. You can also use a concentric duct design (one metal duct inside another with counterflow). Think a single shell and tube heat exchanger with air.
sundowners-keep up the good thoughts (and share them!).
Sleepy2-The optimum efficiency occurs when the counter air flows are equal. That requires two fans. Taking the Hx out of the window releases some design constraints. For example, your outlet could also go into the refrigerator coil area.
pianotuna-see above. Note that my fans are both on the outside, and one blows into the Hx and one sucks from the Hx. I learned this causes plate deformation and makes the air flows unequal unless the sucking fan (outlet) is higher speed than the blowing fan (inlet). I am able to compensate by controlling each fan. If both fans blow into the Hx, this problem goes away.
Speaking of a tight TC, take this basic design with two fans and separate controls on each fan. Put a high efficiency filter on the inlet. In theory, when traveling, powering only the inlet fan will slightly pressurize a tight TC and keep road dust from infiltrating.
Whew. You guys are thinking faster than I can respond.
A good primer on air to air Hx systems can be found at xetexinc.com.
RickW wrote: It costs me next to nothing to acquire coroplast sheets on the first Wednesday after the first Tuesday in November in even numbered years. Mark your calendar.
As Red Green would say...Why wait???
He'd probably also provide us with numbers that prove that the "Hotter" the Contest, the better!
But seriously...
Per the effect on humidity:
RickW wrote: FK-The incoming air will be at the dewpoint (wetbulb) of the outside air. As it is warmed by the exchanger, the relative humidity goes down. This assumes no mixing of air streams in the Hx.
I confess to being confused by the use of the word "relative"...
In your opening post, you noted a reduction in the interior humidity you'd first raised by boiling water.
In Plain Language Designed For Educationally Challenged Francesca:
Does this system actually result in the expulsion from the interior of some of the water vapor in the air????
Or is it just...like ...you know...."relative"???????
Good grief- I'm making myself even MORE confused.....
Perhaps it would help if I explain that I use a catalytic heater and as you probably know, every gallon of propane consumed produces almost a gallon of water coming off as vapor. Much of it condenses in the trailer and I'm sure interested in any improvement that might direct it elsewhere...
Everybody keeps telling me to "use a dehumidifier", but I drycamp without 110 power almost exclusively, often in pretty cold temperatures. More heat results in more water!
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