A/C Size?

[aggie79]

Martin,

Thanks for the input. I'm pretty much settled on an 8k unit. Since you are in the HVAC biz, you may have a knowledgeable answer to this. My first thought was to have a "plenum" made for the heat exhaust that would connect to my existing 5"exhaust line for the portable. The plenum would be about 6" deep and there would b a 5" collar on the side for the existing flex hose to connect to. Would doing this restrict the heat flow too much and cause the unit to run hot?
Thanks,
John

I'm no professional, but a 5" exhaust hose seems to be way too small. You would be transitioning from about 150-200 square inches of area to about 20 square inches of area. For most window A/C units, the condenser cooling fan can't handle much static pressure (back pressure). Reducing the exhaust area for cooling the condenser to less than 20% as on the back side, can't be good for the performance of the unit.

[flboy]

I will use a dehumidifier on ocassions at home when we are in the really humid time of year qiven the AC is doing all it can. They are very nice indeed. The one I have is basically an AC that blows condensor heat back over the evaporator coils so there is no cooling going on in the room, just condensation. With no thermostat the dehumidifier will just run all day pulling moisture from the air. It is really amazing how much moisture is in the air in Fl. Sometimes when you walk out on a hot summer day, the air feels thick and almost looks steamy. Those days are upon us now. :-)

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[jwh92020]

aggie - That is my concern as well. Like I said, I had hoped to be able to do it, but I think it will be way too restrictive. I've talked to 4 HVAC guys here in OK, 2 say go for it, 2 say no way. Since the unit will sit 20" off the floor, I'm going to make a duct that covers the exhaust and vents out through the floor. I'll make 2 boxes to cover the intakes and use the existing ducts to bring in fresh air. I'll add 110v computer fans to each like to increase the draw.

[flboy]

@jwj92020 , sometimes theories and all are good for definite "do not do", but other times when it is more fuzzy, you just have to try your idea and assess whether it is working well enough. You can try it, just be prepared to modify it if it doesn't perform as you need it to. Given the varied opinions, you can see that one size does not fit all. Alot of variables at play here. Best of luck... I am sure you will figure it out. :-) I look forward to seeing your solution.

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[Padilen]

10% chance of rain 90% humidity.At least it's cool.


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[flboy]

Martin,

Thanks for the input. I'm pretty much settled on an 8k unit. Since you are in the HVAC biz, you may have a knowledgeable answer to this. My first thought was to have a "plenum" made for the heat exhaust that would connect to my existing 5"exhaust line for the portable. The plenum would be about 6" deep and there would b a 5" collar on the side for the existing flex hose to connect to. Would doing this restrict the heat flow too much and cause the unit to run hot?
Thanks,
John

I'm no professional, but a 5" exhaust hose seems to be way too small. You would be transitioning from about 150-200 square inches of area to about 20 square inches of area. For most window A/C units, the condenser cooling fan can't handle much static pressure (back pressure). Reducing the exhaust area for cooling the condenser to less than 20% as on the back side, can't be good for the performance of the unit.

I struggled with this too when considering the AC system for my CTC. The area on the rear of the air-conditioner, although the whole backside, is not free flowing for air. As you can see, most of that area is filled with condenser cooling fins that take up most of the space. I assumed about 50% of the space was actually airflow (probably a high estimate at that.. but good liberal approximation). I think if you get somewhere in that ballpark... you probably will have more than enough airflow. I used a propane refrigerator vent on the side and top of the CTC and it seems to be working well. I was going to modify that some to open it up more if needed, but so far, it appears to work rather well. You may not even need the additional fans if it is not too restrictive. The AC fan should create a draw and push out if airflow is not restricted significantly, but that probably won't be obvious until you try it.

[working on it]

Martin,

Thanks for the input. I'm pretty much settled on an 8k unit. Since you are in the HVAC biz, you may have a knowledgeable answer to this. My first thought was to have a "plenum" made for the heat exhaust that would connect to my existing 5"exhaust line for the portable. The plenum would be about 6" deep and there would b a 5" collar on the side for the existing flex hose to connect to. Would doing this restrict the heat flow too much and cause the unit to run hot?
Thanks,
John

I'm no professional, but a 5" exhaust hose seems to be way too small. You would be transitioning from about 150-200 square inches of area to about 20 square inches of area. For most window A/C units, the condenser cooling fan can't handle much static pressure (back pressure). Reducing the exhaust area for cooling the condenser to less than 20% as on the back side, can't be good for the performance of the unit.

I struggled with this too when considering the AC system for my CTC. The area on the rear of the air-conditioner, although the whole backside, is not free flowing for air. As you can see, most of that area is filled with condenser cooling fins that take up most of the space. I assumed about 50% of the space was actually airflow (probably a high estimate at that.. but good liberal approximation). I think if you get somewhere in that ballpark... you probably will have more than enough airflow. I used a propane refrigerator vent on the side and top of the CTC and it seems to be working well. I was going to modify that some to open it up more if needed, but so far, it appears to work rather well. You may not even need the additional fans if it is not too restrictive. The AC fan should create a draw and push out if airflow is not restricted significantly, but that probably won't be obvious until you try it.

• Been there, done that. I used a 5k window unit, mounted in the galley (thru the rear bulkhead) and directed the exhaust towards the curbside inside a fiberglass/foil insulated duct, and outside via an open vent in the sidewall. I made a right angle plenum from a floor vent boot and a steel baking pan, which had an initial exit hole size of 8" diameter. I necked that down to 6", and used insulated ducting hose of that size, then connected that to a 5" dia. opening on my "truck roof vent", mounted on the sidewall, like the three others I used for venting the trailer.
• At first, the A/C would shut-down almost immediately, because the louvered vent was rain-shielded inside, and wouldn't allow enough airflow, so the A/C would get "thermal shutdown" rapidly. I gradually opened up the wall exit size to 6", and made the exterior louvered vent into a hinged cover (non-functional when closed), and the A/C took longer to reach thermal shutdown, but would within 20 minutes. Too much backpressure/heat retention building up in the metal plenum, I figured. So, I installed a high flow, high heat resistant axial duct fan (6" diameter, to fit into the duct), to remove the heat rapidly. That worked, after three re-builds to reach that point, and the system has run perfectly ever since. Once again, air flow is the key.
• vent is non-functional when closed
• view of axial fan inside ducting
• 6" axial fan
• plenum with 8" exit, 6" duct-to-wall after that
• view of completed A/C duct system

[m.colley]

Martin,

Thanks for the input. I'm pretty much settled on an 8k unit. Since you are in the HVAC biz, you may have a knowledgeable answer to this. My first thought was to have a "plenum" made for the heat exhaust that would connect to my existing 5"exhaust line for the portable. The plenum would be about 6" deep and there would b a 5" collar on the side for the existing flex hose to connect to. Would doing this restrict the heat flow too much and cause the unit to run hot?
Thanks,
John

John,
As many have already posted, a 5 inch duct won't cut it, a 8" would be alot closer. The one draw back to mounting a window AC in a cabinet is getting the right/correct amount of condenser intake and exhaust air. Don's (flboy) install achieves it or is mighty damn close. You'd also be better off if you don't fight the nature of heat wanting to rise by trying to force the warm/hot downward. Measure the intake and exhaust areas and try to duplicate the size as closely as possible..


Martin

[McDave]

@jwj92020 , sometimes theories and all are good for definite "do not do", but other times when it is more fuzzy, you just have to try your idea and assess whether it is working well enough. You can try it, just be prepared to modify it if it doesn't perform as you need it to. Given the varied opinions, you can see that one size does not fit all. Alot of variables at play here. Best of luck... I am sure you will figure it out. :-) I look forward to seeing your solution.

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Oh yes indeed, you have to try it. If there is even a chance it might work, you have to try it. We all have to, so do you.

McDave

[jwh92020]

Just picked up a new in box 10K window unit for $150. If this doesn't cool the trailer (along with some shade and venting), I'm going to sell it and build another - in white!

[m.colley]

Just picked up a new in box 10K window unit for $150. If this doesn't cool the trailer (along with some shade and venting), I'm going to sell it and build another - in white!

10K should be plenty.. My 8K cools my CTC down nicely even in the GA sun and humidity. I'm planning to run a few tests this week to post.


Martin

[jwh92020]

I picked up a 6k yesterday. Plugged it in and felt the air coming out (temp was ok, but not much volume) and decided it was too small. Sold it just after I got this one. The guy had an 8k for$120 and this 10k for $150. Figured $30 wouldn't break me, but too small an a/c could, so I went for it.

[Padilen]

While I like my portable's physical size, it does not function well as an AC. It's an 800 BTU single hose with remote. If I turn on AC with the CTC already heated up the AC "cycles" I can get it to stop by adding a fan blowing back at intake. But temp will not lower to temp setting. My CTC is 7X12, half silver and 1/2 black. It's color isn't causing this issue.
I have 2 window AC's an 8000, and a 10,000. Just trying to decide if remodeling for AC is worth it.


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[jwh92020]

Padilen,
When I installed this one, I did it with the idea that at some point I may need to replace it. I talked to the mfg and they told me that portables have smaller condensers and fans than window units, so they put out less air volume. They also said that they are designed to work in "optimal conditions". We all know that CTCs are not exactly optimal settings. That said, for some folks they work great. In my last build (wood framed, wood clad like a tiny house), this same model cooled with no problems. This particular unit was repaired last year and perhaps the repair isn't holding. I don't know. I'm going to put it in and see if it works, and keep the portable around "just in case" at home. I talked to someone who has a 14k window unit in their 7 x 16 and they said it is like a meat locker, plus they have no short cycle issues. Maybe bigger is better.

[Padilen]

I'm first going to do a cheap simple hack. I will get an insulated duct and place it out or by door window. Block off intake to see if it will work like a dual hose. Then I'll decide if it's staying or going.


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