DIY HVAC For Control Room

I'm thinking of doing a cheapo DIY HVAC for my control room (see picture). Basically, I'm going to use a wall A/C unit with its front portion enclosed in a box to enable connection of flex duct from the A/C to the control room. This will take care of blowing cold fresh air into the room. Then a centrifugal blower connected with flex duct to the room's exhaust vent will suck the stale air out (see arrows indicating direction of air flow). These will all be placed on the attic space above a room that is adjacent to the control room. First of all please let me know if you think this plan is workable or not. One problem I see is how to remotely control the A/C. An ordinary remote control would clearly not work because in this setup it would not have an unobstructed path to the A/C unit. Can you suggest a workaround or maybe some units that have separate, wire-connected controls? Your help is greatly appreciated. Thanks in advance! Mitch

radio shack and other such places sell IR repeaters that will relay the IR signal from a remote to another room or area that's not directly in line of sight. I can answer that part for you, but don't know about if your idea is a good one or not.

Mitch, you first need to follow the forum guidelines http://www.johnlsayers.com/phpBB2/viewtopic.php?t=3231 including the part about updating your profile to include a location; Also, have you seen this thread? http://www.johnlsayers.com/phpBB2/viewtopic.php?t=644 I'm anything BUT a HVAC guru, Rod Gervais is the man for that (whenever he shows up)... Steve

Sam: That Radio Shack repeater is a nice idea! Solves one problem. I'll definitely give it a try. Thanks! Steve: I've seen the thread you mentioned. However, my design is different, that's why I started a new thread. I think it is cheaper and simpler. I hope it will work. Thanks! Mitch

Mitch, I'm not an expert but I've been thinking/planning about ventilation a bit (see my comments here http://www.johnlsayers.com/phpBB2/viewt ... 0147#30147 ), so here are some comments for what they are worth: 1) is your attic finished/insulated etc? if your attic is anything like mine (unfiinished), this is dirty, dusty nasty air up there, which may have fiberglass or even asbestos, etc. you don't want to breathe that air. when i even go IN my attic i wear a mask. so hopefully your attic is an actual room of some kind. anyway your AC unit will not like it either. but even if it IS a room, is this going to be a real source of fresh air? don't you need to get air from OUTDOORS in?? more importantly, if your AC unit is in an enclosed room, after you suck all the air out of that space, you will have a vacuum and there will be no more air coming into your system. it won't work and maybe will damage the AC unit too. 2) where i come from attic air gets HOT, like maybe 130 degrees? or more? not the ideal starting temperature for a cooling system. 3) flex duct for the exhaust. i worry that if you try to SUCK air through flex duct it may collapse ... obviously this flex duct will have to be pretty rigid, otherwise if it collapses (and may do so over time, when you can't see it) your system will fail or not work very well. so maybe don't use flex duct on the outtake leg. or make sure it is rigid enough. otherwise, this plan looks reasonable. :) but i haven't done this myself, so again take that for what it's worth. :wink: also i don't think it is ideal from a sound isolation point of view, but you didn't ask about that dan :)

I agree with all of Dan's comments. There's no way that would meet code (and I'm by no means a code expert), for good reason. There's also no way a window air conditioner could cool 130+ degree Fahrenheit air to a comfortable level inside the room. You'd be darned lucky to get a 40 degree reduction.

I don't necessarily agree that this can't be done; need to know more about your construction first. For example, if construction is such that insulation is rigid foam board ABOVE the attic space, then the attic won't be that hot and the window unit may be able to keep up. Also, anyone who subscribes to Recording Mag, check out the September issue; there are a couple articles (kind of vague though) on using just such an approach. I did notice though that Chet McCracken (Doobies, along with Keith, RIP :cry: ) had used a mini-split in his space, no mention whatever of fresh air :? Steve Oh, the REALLY cheap way on this would be to use one of the more basic units with REAL switches, (Friedrich comes to mind) then just leave it turned to MAX and connect the power through a dedicated 20 amp breaker, and just turn it on/off with the breaker...

Guys, thanks for pointing out those factors! My attic has wooden slats on the side walls for ventilation but it's only for a small portion... probably not big enough for a good, strong inflow of fresh air. Also, the insulation is below the attic, not above it, so it would be pretty hot especially in the summer. And the attic is dusty from years of neglect as nobody ever cleans it. I guess the option then is to cut a hole like a window on the side wall of the attic and hang the A/C there so it gets fresh air from outdoors. The only thing is, this location is like 17 ft. away from the power outlet and the power cord won't reach. Is it safe to use a heavy duty extension cord with 12-gauge wires? Thanks, Mitch

I'm not a fan of the plan at all, but at the very least, do not use an extension cord on the unit. Typically the operating manual advises against this. There is risk of electrical fire. You'd be better extending a circuit to place another outlet in that area, but be sure not to overload the circuit. Even better, run a new circuit.

Alright, I'll give this project a try. It's the only way to find out for sure if it will work. :wink: Now for the details: 1. How much BTU rating for the A/C? Is 5400 BTU enough for my small room area/volume of 124 sq.ft./1027 cu.ft.? 2. Recommended diameter of the flex ducting? 3. Recommended type and CFM rating of exhaust fan - Is centrifugal the best type for this application? Is the exhuast fan even necessary at all? (I'm beginning to wonder because Steve's design in the other HVAC thread does not use an exhaust fan.) BTW, I got the idea of this design from my PC case, seeing that it has a front intake fan and a rear exhaust fan. :lol: Thanks, Mitch

mtl777 wrote:

1. How much BTU rating for the A/C? Is 5400 BTU enough for my small room area/volume of 124 sq.ft./1027 cu.ft.?

If the window air conditioner were located in the actual room, you could use the sizing chart on the California Energy Commission's Web site. However...

Recommended diameter of the flex ducting?

When you use ducts, static pressure will reduce the flow. Also, window air conditioners were not designed for ducting to be added to them. (If you or anyone find one that does, post a link because I'd be extremely interested!) Determining how to fasten the duct to the unit will be a challenge in and of itself, let alone the loss of pressure you'll encounter. I can't advise you on the size of the ducting here, mostly because (as I've already gone on record to say, sorry to be a buzz kill) I don't think it's a good way to go at all.

Recommended type and CFM rating of exhaust fan - Is centrifugal the best type for this application? Is the exhuast fan even necessary at all? (I'm beginning to wonder because Steve's design in the other HVAC thread does not use an exhaust fan.)

See my post about California Building Code requirements for habitable space without a window. You'll need to determine for yourself exactly what model codes your municipality uses.

mtl, if i were you i'd multiply the height and width of your AC unit's output grille and use a duct that gives you AT LEAST that same square inch cross section. to figure square inch cross section of a round duct, simply multiply 1/2 the diameter times 1/2 the diameter times 3.14 (pi). so for a 8" duct that would be roughly a bit more than 48 square inches (4x4x3). so an 8" round duct would be a good match for a grille that is 6 inches by 8 inches (also 48 square inches ... 6x8=48 ) you could try to do it without the exhaust fan. if it doesnt work, then add the exhaust fan later :) :) however it might be a good idea just to do the exhaust fan from the get-go, because there may be a risk of overheating the AC unit's fan (and ruining it :( ) if your design results in too much backpressure (static pressure). it will certainly make it work better. certain fan designs do work better than others. your best bet is to buy a fan that tells you how much CFM is lost at a given static pressure. then you will know what you are getting. remember, i haven't done this before, i'm not an expert etc. :wink: dan

Dan: I haven't bought the A/C yet, but the one I have in my bedroom has a 16"W x 2"H = 32 sq.in. area where I can feel most of the air flow. I guess that's what you call the "output grille", correct me if I'm wrong. Based on that, an 8" round duct should satisfy and even exceed the minimum cross sectional area requirement. Is larger better? What if I use 10" or even 12" duct? What is the point of diminishing returns of increasing the duct size? Thanks, Mitch

i don't know. but i imagine that if you go TOO big then you won't get enough airflow speed, which might mean that the air warms up by the time it reaches its destination. my thought was to make it just a little oversized. so 8 inch would be in that range i'm guessing. imagine the duct as a small room, and the room you want to cool is the one next to that room. the bigger the first room, the less cool your second room is going to be, right? at some point the sheer voume of the air in the oversized duct probably absorbs all the coolness your ac puts out. but as i said, i'm no expert. i'm just making comments until someone who knows what he's talking about comes along ... :)

From what I've read, the recommended room ventilation in the U.S. is 15 CFM per person and in Canada it is 20 CFM per person. Most of the time I am the only one inside the control room, so I would like to design the ventilation for only one person. Between the U.S. and Canada standards, I think I'll choose the Canada one (20 CFM) just to be on the safe side. Do you think 20 CFM is fine for one person in a small 1027 cu. ft. room? Assuming that I aim for 20 CFM air flow inside the room, does it mean then that the window A/C supplying the cold air must be able to deliver that amount of air flow also, 20 CFM, after all the static pressure along its duct path have been considered? And does it also mean that the exhaust fan for the return must be spec'd for 20 CFM at whatever the static pressure is in its duct path? Thus, exhaust CFM must equal intake CFM to maintain the desired air flow? Now what if I want slightly positive pressure in the room. Can I spec the intake for 22 CFM and the exhaust for 18 CFM to maintain the desired 20 CFM (since the average of 22 and 18 is 20 CFM)? I'm asking these questions to verify if my understanding of what I've read is right. Please do not hesitate to correct me of any misconception I may have. Thanks! :) Mitch

No one seems to want to answer my questions. Are they too difficult or am I just not making any sense? :wink: Anyway, please let me bump this thread to the top with another possibly stupid question :oops: that betrays my ignorance: Let's suppose that a window A/C is installed in the normal way (hung on a window) in a room that is sealed, i.e., all doors and windows are closed. What happens to the air that goes into the window A/C's side vents from outside the house? Does that air get sucked into the room as fresh air supply? If not, then how will the room get its supply of fresh air? I would really appreciate a reply as the answer will impact my HVAC design. Thanks in advance! :) Mitch

mtl777 wrote:

Let's suppose that a window A/C is installed in the normal way (hung on a window) in a room that is sealed, i.e., all doors and windows are closed. What happens to the air that goes into the window A/C's side vents from outside the house? Does that air get sucked into the room as fresh air supply? If not, then how will the room get its supply of fresh air?

Those vents allow the unit itself to breathe when the unit is set to recycle air. (There's usually a lever to switch between fresh air and recycled air, just like most cars today.) Habitable rooms are designed to get their fresh air from the window of the exterior wall. If it gets stuffy, we open windows. I too was confused about HVAC for a long time. Once I allowed my mind to separate the air conditioning requirements from the ventilation requirements, and allowed myself to think of them as separate challenges that can be solved by separate solutions, workable ideas started flowing. Think of "ventilation" as "a machanical window replacement" as far as air is concerned. As far as the amount of air flow you'll need, figure out what your building code requires for mechanical ventilation in habitable rooms in terms of minimum ACH (air changs per hour). In my case, the answer was "2." Then figure the total cubic feet of the space and how many CFM (cubic feet per minute) you need to move in order to exchange all of the air in the room within that time frame (e.g., 30 minutes in my case). Be sure to take into account static pressure for ducting and turns, as they will reduce the flow significantly. I was just as stuck as you were a couple of months ago, but I now have a workable (albeit expensive) plan that my city has officially approved. Follow me! 8) --Keith :mrgreen:

Keith: Thanks for replying!

Those vents allow the unit itself to breathe when the unit is set to recycle air. (There's usually a lever to switch between fresh air and recycled air, just like most cars today.)

Does it mean that when the unit is switched to fresh air, the room is able to get fresh air supply from outside through the side vents? If so, does the cooling still work or does the unit go into fan only mode? Thanks again! :) Mitch

When the gate is switched to fresh air, the unit does continue to work in air conditioning mode, although it may not be very efficient if the outside temperature is higher than the inside temperature or if the outside temperature is significantly more humid. The reason the recirculate/fresh gate is even there is for efficiency. If it's cooler outside than inside, and you want to cool the room, then you'd want to draw in fresh air because it's more efficient to cool the already somewhat cooler outside air. However, when it's cooler inside than it is outside, then recirculating and conditioning the inside air makes more sense. The same principle applies to air conditioners in cars, even though I'd bet most people don't fumble with the gate very often.

In my first project studio... a two room setup in a basement. Control room, live room basic. There was a third un-used storage room with a window. I put in a 5200btu window air conditioner. Then I used flexible metal dryer vent pipe which I shaped square on the air conditioner end to fit right onto the vent fins. I removed the fin housings (they snap in), used ducting tape and taped the square ended vent pipe to the fin housing, and put the fin housing back into the ac unit. Ran one pipe to my control room (through the wall) and one to the live room and viola! It works great and is a quiet cool flow of air. The control room was about 10ft by 14ft and the live room 15ft by 20ft. 8ft ceilings with insulation. I would imagine (because it has been done) that you could build a duct out of rigid fiberglass that would fit the front of the AC unit and pump that in from a window in another room or from a remote box as you have in your illustration and get decent flow. I worked in a radio station in the early 80's that did just that and it worked great. Sometimes you have to throw out the paper, and pick up the hammer to find out if it is REALLY going to work. Just my 2 cents. BTW, if you would like pix of the AC, I will post.

Keith: Thanks for your great info! Now I finally understand how a window A/C works. Andy: Finally, a real life successful example of a very similar design! Thank you for restoring my confidence in this design. I'd like to know some details: Did you use only one 5200 BTU window A/C to cool both the control room and the live room? That unit must have had a strong CFM. What brand/model was that? What was the diameter and length of the supply pipe that you used? And did you need to put an in-line duct fan in the pipe to boost the air flow? What did you do for the exhaust/return? Did you also use a pipe with an exhaust fan? Thanks again! :) Mitch

mtl777 wrote:

Andy: Finally, a real life successful example of a very similar design! Thank you for restoring my confidence in this design. I'd like to know some details: Did you use only one 5200 BTU window A/C to cool both the control room and the live room? That unit must have had a strong CFM. What brand/model was that? What was the diameter and length of the supply pipe that you used? And did you need to put an in-line duct fan in the pipe to boost the air flow? What did you do for the exhaust/return? Did you also use a pipe with an exhaust fan? Thanks again! :) Mitch

Mitch, I am sure that it is not a perfect solution but it did keep the temp at around 73 deg F on 90+ days in the summer. Thats with 3 big PC's chuggin away as well. Model/Brand: GE Window AC. Not the cheapest but seemed to be pumping the coolest out of all the models we demonstrated. I am at work but can post the model # for you when I get home. Piping: Standard dryer vent hose. 4" diameter. I stretched it out quite a bit. (its accordian like) This is an aluminium/foil style hose. I chose it over the plastic as I thought the metal would retain it's coolness and help promote the movement of air. And, I had a bunch of it in the garage! LOL. Distance from the AC to the control room is about 9ft and about 12ft to the live room. I did put a non powered 4" muffin fan on the end of the control room vent...mainly just to swirl the air around instead of just blowing out in one direction. Exhaust/Return? hehe No. The basement is far from air tight. I ran the AC unit on VENT as well, just to bring in fresh air. In the VENT mode, most AC units return themselves. You would only need an Exhaust/Return if you were mounting outside an airtight room. I would bet you could use rigid foam and make a 3 chambered setup that would butt right up to a window AC unit. Set it to VENT mode and use the AC's return to suck air back out. 2 small chambers for the cool air coming in.. one big one for the air going out. Just a thought.

GE MODEL:Model#: ASM05LB http://products.geappliances.com CAPACITY Cooling E.E.R. (BTUH / Watt) 10.8 Dehumidification (pts./hr.) 1.5 FEATURES Cooling BTUH 5400 Energy Star®-Qualified Yes Unit Type Cool Only Airflow (cfm) Roomside (hi/low) 140 Chassis Fixed Filter Type Rigid Frame/Slide-Out Plug Type Parallel/Right Angle Thermostat Type Electronic Fan Speed Selections - Cooling 3 Fan Speed Selections - Fan Only 3 APPEARANCE Installation EZ Mount ECONOMICAL / QUIET Energy Saver Yes APPEARANCE Color Appearance Cameo White WEIGHTS & DIMENSIONS Overall Depth 12 7/16 in Overall Height 12 7/32 in Overall Width 16 11/16 in Approximate Shipping Weight 46 lb Depth to Louvers (in.) 4-1/4 Min./Max. Window Opening Width (in.) 22/36 Minimum Window Opening Height (in.) 12-7/8 Net Weight (lbs.) 41 lb POWER / RATINGS Cooling - Rated Cooling Amps AHAM 4.5 Cooling - Watts 500 Voltage 115 WARRANTY One Year Warranty Entire Unit; Parts & Labor; In-Home Full Five Year Sealed System Refrigeration System; In-Home Here is a simple diagram: Http://WiseMinds.no-ip.com/SimpleHVAC.jpg Keep in mind that if you look on that page at GE you will see that they make 13800 BTU units that pump out a whopping 350 CFM roomside for 419.00. The layout is better as well with a single large cool air output. Have fun!

Andy: Thanks a lot! I really appreciate your help. You have given me good info and great ideas to incorporate in my design. I will further refine my design taking into consideration your suggestions. Rock on! :) Mitch

mtl777 wrote I guess the option then is to cut a hole like a window on the side wall of the attic and hang the A/C there so it gets fresh air from outdoors. The only thing is, this location is like 17 ft. away from the power outlet and the power cord won't reach. Is it safe to use a heavy duty extension cord with 12-gauge wires? Thanks, mtl777 This seems to be the best solution but consider running a new power receptacle. I believe all window units need to eliminate the condensate that the evaporating coils collect. Also why not just pop threw a control room wall to the outside? And then build a sound trap.