Ventilation Inlet question for portable AC


  #1  
Old 05-08-14, 01:26 PM
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Ventilation Inlet question for portable AC

Hi I bought a Tripplite SRCOOL12K to cool a closet in my house which houses my servers and network equipment.

I don't have the exact actual wattage but I estimate it's about 1800 combined without the SRCOOL12K


My question is this, how big should my ventilation hole need to be cut if the specs on the unit say this:
Air Flow Evaporator = 329 CFM / Condenser = 311 CFM
?


Right now I have (3) 4" round soffet vent holes cut into the door but the door still sucks shut. I have a slight gap in the ceiling where my closet had the crawl space access because the duct is mounted up there with the drop ceiling tile spacer and being round it's pushing away from the recessed opening. (I'm going to resolve that at some point making a better platform to mount the duct to the crawl space opening out of plywood and a 6" duct coupler)

My problem is even with the gap under the door and the three 4" soffets when the door sucks shut it ends up drawing the hot air it expels into the crawl space back into the room so for now I have the door propped open with a door stop however I need to know the ideal vent size to cut in the door to eliminate the backpressure (what I'm calling it, not sure what the proper term is)

Do I tally the two CFM's above for the condenser and the evaporator and go with the total? the average?

And after that how do you calculate size of the vent based on CFM, I've been searching the internet but everything I find talks about ducting.

I was assuming if my soffet cuts are ~12.56sq in minus some area for the soffet itself say 8 or 9sq in, Times 3 holes 24 - 27sq in I was hoping would be enough but it obviously isn't. I tried calling Tripplite support but the people on the phone there were no help, they had no information on how to size the vent.

Thanks in advance for any help anyone can provide
 
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Old 05-09-14, 12:55 AM
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I did a Google on that model number and briefly skimmed the specifications. If I am correct that is a spot cooler that has intake and outlet ducts for the condenser that need to be routed outside, or at least to a fairly open space outside the conditioned space. Is that correct? If it ONLY has an exhaust from the condenser then it will be using conditioned air to cool the condenser and exhausting requiring some source of make-up air. Single duct spot coolers are less expensive but also less effective and less efficient than dual duct models.

As for the rest of your post...I am having trouble envisioning just what you are proposing. Can you post some drawings, or better yet, some pictures (marked up if necessary) of your proposed installation?
 
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Old 05-10-14, 09:30 PM
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Furd, thanks for replying.

The unit has two ducts, one for the cooled air, and one for exhausting the evaporate. There are two vented grilles with filters I don't know their specific purposes though. I know when the unit detects frost built up on the condenser it shuts down the cooling mode and just runs the fan until the frost dissipates. It will display "dF" on the status LEDs when this happens.

Their support has said seeing that code too frequently means there is too much humidity in the room but my external temp/humidity sensor says its between 29-45% avg when I check is usually 32% I don't know if that means I should buy a secondary dehumidifier but for now they told me the best thing to do is make sure the airflow isn't causing the unit to work too hard.

I've uploaded pictures, I also included one of Tripplite's images to show the vent grilles on the unit. The picture with the door closed shows how I keep it propped open now with DVD cases, two seem to be enough that the door doesn't try to suck shut on it's own so then from the outside I just put something against the door to keep it from opening further. When it operates this way it seems to keep the room at a normal 70-71 degrees Fahrenheit.

The door vents probably don't show up too well but they are standard home depot 4" round aluminum under-eave soffit vents (but they don't have them on the website) I have the slits bent open as much as possible without breaking them, and even with them off the door still sucks shut on it's own so I know I need more ventilation I'm just trying to figure out exactly how much to do as little damage to the door as possible so I don't have to buy a new one for my landlord when I move out.

If you wonder why I have the unit up on a file cabinet it wasn't working at all when sitting on the floor, it would keep going into dF mode in minutes and the overall temp in the room was generally staying about 80-83 degrees and in my cabinet 90-95.

The cabinet in the open door pic is custom built, and has fans in the bottom skirt as well as in the middle section which move the air from the duct inlet on the back through the cabinet up and out the back.

The picture of the attic crawl space opening isn't great but the best my camera phone took without being too blurry, if you look on the right side you can see the gap I mentioned. I intend to get a piece of wood cut and mount the exhaust duct more properly so that it's sealed better.
 
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Old 05-11-14, 10:49 AM
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I'm not familiar with that unit, but it sounds like it uses air from the closet to cool the coil and blows the waste heat out the exhaust duct. By using closet air it is depressurizing the closet and requires replacement air. For that replacement air to enter any opening it needs a pressure difference and a large enough path. The 3 vents you have installed have a net free area of around 20% each. Back to back will be even less. The total net vent area you have is about the same as a 1.5" open hole.

Just guessing, but I would estimate an 8" x 16" nice wood grill at the bottom. Painted to match you could probably leave it and no one would know the difference.

Bud
 
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Old 05-12-14, 12:54 AM
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I think you are mistaken about a couple of things but it is late. Let me read up on the unit and get back to you tomorrow or the next day.
 
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Old 05-13-14, 02:14 AM
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Give me another day, My brain is pretty much fried at 2 AM.
 
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Old 05-14-14, 12:25 AM
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I was finally able to download the instruction manual and Bud is correct, that is a single duct cooler and it exhausts conditioned room air along with the heat of operation. You need a MUCH larger intake grille in the closet door.

I always recommend dual duct portable coolers because the single duct models, by removing conditioned room air cause a negative pressure inside the room/house and that discharged air MUST be made up, usually with leakage from the great outdoors. This makes the portable cooler, which already suffer from various inefficiencies, even more inefficient.

As to how big a grille you need in the door, you might be able to get away with a 10 by 15 or 10 by 20 inch. For sure those little 4 inch vents are WAY too small.
 
 

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