venting a dehumidifier

[oldjarhead100]

I have a space I can install a window unit ,I just cant get to it right now , I need to get this grow done first I think raising the head pressure is my best option right now or go back to watering every 3 days with no runoff and flushing every couple of weeks IDK

[hycheese]

Think of a water slinger as a baby seal playing in a kids pool, just slapping the water around until it splashes out... take a wire cutter of sorts and cut it off - you'll know what it is when you see it because it dips down into the bottom condensate pan. pay attention to centrifugal forces and keep the fan in balance or your bearings will suffer.

When the vent is only a few feet it is probably not a problem as the high discharge heat keeps it in the vapor stage but at 25 feet it will re-condense and grow molds and such.

If you drill a hole low enough so that the water level never hits the slinger then you are good to go without further modifications.

[Toripony]

So, if I understand this right, the best way for this to work in my case would be to mount the AC into the wall of my grow room so it would use the garage air to cool the condenser, exhausting that out the window instead of the conditioned air in the grow room? In that case, by what you said in your next post below, this might actually be a better solution than the single-vent portable AC? Wow, this is all great information, Hycheese, thanks so much for the education! Now the only part that scares me is that last sentence about cutting out parts and drilling; sounds like something I could screw up, lol.

[hycheese]

Now to throw a wrench into your gears, I bought this hot water AC unit about 10 years ago. It is designed to sit on top of your water heater with a long copper tube that feeds into the tank, it heats your water while it cools your room. I never got around to installing it and ultimately bought an instantaneous tank free water heater.

Anyways the other day I ripped it apart to see if I could redneck a cheap dehumidifier out of it, nope bought a $100 unit instead. When looking at the picture you can see the outside condenser coil has been replaced with about 20 feet of copper tubing that should be placed in a cool water source. This unit can make 135F water all while cooling your house.

[hycheese]

oldjarhead100 after our previous conversation I have verified my suspicions, here is a blurb I found on single vent portables;

"Unlike a window air conditioner, all the mechanical parts of a portable air conditioner are sitting in the room you’re trying to cool. It’s also a reason for the less-than-capable cooling: The portable unit uses conditioned air from the room to cool the condenser and exhausts the hot air out an exhaust hose. That creates negative pressure, causing unconditioned warm air from surrounding rooms or outdoors to be drawn into the room you’re trying keep cool."


Being an oldster I was only familiar with dual vent portables (I owned 2 of them up to a few years ago) didn't know single vents existed until just recently. Now that I read up on them I can see why they don't come in the smaller 5kbtu model like a window unit, it's because they are inefficient and scavenge conditioned room air for condenser cooling to reduce the manufacturing costs and ease of installation.

Single vent portables seem to meet the needs for simplified residential cooling with practicality overtaking efficiency, in a small dynamic grow room where a portable is exhausting 30% or more of your newly conditioned air can be a challenge, especially while trying to maintain a balanced pressure and not draw in crap air from elsewhere.

[hycheese]

if I try ducting a window A/C to make it "portable", per your suggestion above, I would have to run that duct 25 feet to nearest window. Would that act as damping also, similar to blocking part of the exhaust? Or is that 25 ft. TOO much "damping"?

25 feet of the corrugated duct can cause quite a bit of restriction, best to go with as large a diameter that is feasible the bigger the better. If the outside coil is 12" x 12" that equals 144 square inches, a 12" round duct is 113 square inches so that is already a restriction, an 8" duct would only be 50 square inches. It would be best to test bench it first with a cardboard box taped on the back (don't block side louvers) then roll a tube the size that you think will work and point it out the window. You can always use a cheap inline axial fan to downsize the duct but a free cardboard mockup would be the best approach before spending money.

Remember a window AC is divided into two separate compartments, the front end sits in the conditioned room while the back end is located outside a window, the backend also has side louvers that take outside air and blows it through the condenser exhausting through the back to cool it. however, if the whole unit is inside then it will use the air from whatever room the backend is located in essentially acting as a room vent. That is how a single vent portable AC works.

And now the caveat, most newer window units have a water slinger attached to the motor shaft that takes the condensed humidity and chucks it through the condenser to help cool it but also negates the need for a condensate drain. If you have a model like that you need to cut the slinger off and drill a drain hole or you will fill your vent pipe with water.

[Toripony]

hycheese, if I try ducting a window A/C to make it "portable", per your suggestion above, I would have to run that duct 25 feet to nearest window. Would that act as damping also, similar to blocking part of the exhaust? Or is that 25 ft. TOO much "damping"?

[oldjarhead100]

ok thanks will try it

[hycheese]

No, you partially block the exhaust, it will simulate a higher outside temperature and reduce the capacity hopefully increasing the inside evaporator temp while dehumidifying more. only for the AC unit

[oldjarhead100]

you block the intake correct

[oldjarhead100]

I'll give that a shot

[Toripony]

Omg, I shouldn't have read that right before bed... now my hillbilly engineering mind is racing! I like playing w/foam board... built my grow room with it... and duct tape, lol.

[hycheese]

Another thought, for those who work in HVAC probably know that when trying to charge an AC in low outside temperatures you either had to reduce the air flow by blocking the condenser fan with cardboard or install a low ambient kit on the fan motor.

The theory is to increase the head pressure which will also increase the suction pressure thereby raising the evaporator temperature, blocking off the right amount so as not to trip the compressor out on high head but enough to keep the evaporator below the dew point should allow for some cooling but even more dehumidification. On bigger central AC's we did this by oversizing the A-coils by a ton or so over the condenser tonnage.

On a portable unit, I could see reducing the duct size or installing a variable restriction could achieve the same effect, on a window AC just block off part of the back where the warm air blows out.

[hycheese]

Don't forget you can cobble a $50 window unit into a makeshift portable by using a bit of foam board, duct tape, and a dryer vent hose.

[hycheese]

There is nothing wrong with the portables except they tend to only come in the larger BTU sizes which will do very little dehumidification in a small room. When all else fails you must resort to the KISS principle and remove all variables until a cause and effect can be realized. Shut off all ventilation close all vents, set AC to 75F and DH to 50% and see what happens over a complete care cycle of a day or two.