Air conditioning in the shop

[RDavidP]

My shop is a detached 9x15 1/2" plywood building insulated with R13 on the walls and R19 in the ceiling. The apex of the ceiling is about 8". I bought a portable A/C for my shop and installed it. The A/C is 750 BTU's and was rated for a 10x20 room. I figured that would be just about the right size. My usage is typically on the weekdays I turn on the A/C in the afternoon once I get home from work. I open up the double doors and turn on the floor fan I have to blow the hot air out. On the weekends, I get up and turn on the A/C and leave it running most of the day as I am in and out of my shop. The problem on the weekdays, is that it is so hot in the afternoon that by the time I turn on the A/C, it just does not cool down much. Anyone with an A/C in the shop leave their's running all the time? What is the hit to your electric bill?

[cabinetman]

Your electric bill will see a difference. If you are running the A/C, and your doors are shut, you have no ventilation per se. If you make dust, your return air filter may clog. In one of my shops I had a 3 ton unit and 16,800 cu. ft. to cool, and in the summer it barely made a dent. These are just a few drawbacks.

.

[Russianwolf]

If you can see the manufactures label, you should be able to do the math and figure it out. You need to see what the max usage level of the unit is and calculate it as a kwh number if its not on the label already, and multiply it by your power cost.

When our AC went out last summer, I bought two 12000 BTU (I'm assuming your unit is actually a 7500) window units and a 12000 BTU portable. Those have been running nonstop since then. Even when the temp is okay, we leave the fans on to move the air. We have not seen a big impact on our bill.

Once the central unit is replaced next week, the portable will become my shop dehumidifier/AC/heater and one of the window units is moving to the garage (wife's orders)

[RDavidP]

(I'm assuming your unit is actually a 7500)

Yes, the A/C is actually 7000BTU, not 750. If it was 750, no wonder it is not really cooling things down. What doesn't help is that my shop gets sun all day long.

Here is the exact unit that I purchased.

http://www.homedepot.com/Appliances-Heating-Cooling-Air-Quality-Air-Conditioners-Portable-Air-Conditioners/h_d1/N-5yc1vZbv64/R-202562960/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053#BVRRWidgetID

[pelligrini]

You didn't say where you are located, but if you're running the AC now I'm assuming you're somewhere down south.

My shop is a 10x12 shed with no insulation. I put a turbine vent on the roof a while back. That helped the heat buildup a lot. I later put an 8" high CFM fan from one of my server cabinets into the vent opening. At full power it will exhaust the hot air in a matter of no time. Then I'll turn on my window AC unit that is installed through the back wall and cut the fan off. I think the AC unit is 24000btu though. It was the biggest one available that would run on 120v. The thing will pull 14.9 amps when on and cooling. It was left over from when I was in a 1920's house with no central air.

Your AC unit probably won't cost too much to keep it running all the time. It looks like it might use ~.9 KWH, so .9*24hrs*30days*.10(or your elec. rate)= ~$65 a month if it were on constantly and cooling. I'm guessing probably 1/2 or less depending on the degree delta you need to cool and how well the thermostat on it works.

[charliex]

A thought or 2, as I'm thinking that 7k should be large enough. In that small of an area your unit may be freezing up, due to high humidity. OR My son had that problem with a portable unit. He had to raise it up toward the ceiling as it was cold enough on the floor to keep shutting the unit off. Cold pools on the floor where the thermostat is while your standing up top in the heat. Good luck.

[dbhost]

A little background on my shop may be in order as I don't recognize your user name so I am not sure if you know much about my shop...

I am in a 2 car attached garage, no wall insulation except the common wall, R30 in the ceiling, and R10 with radiant barrier in the rollup doors. My A/C is ducted in the 1' wall section between the rollup doors, and at present the exhaust duct is "insulated" with an old 20 degree sleeping bag that the dog chewed up... (I am insulating it to keep from adding the heat back to the shop as it goes out the duct).

My shop is 18' wide, 20' long, with a sloping floor that gives me a celing that is 9' at the beginning and 8' 6" at the end.

My unit will cool my shop down from 90 deg F on a 105 deg F day down to 75 in about an hour IF I open the shop door, turn the air filter on HIGH to get the hot air blown out, then shut it up, turn the A/C on and keep the air filter blowing on low. This is a real blessing since the workbench is on the opposite end of the shop... Using the air filter as a fan as well does a LOT more than just help keep the air clean, it moves a LOT of air and helps keep me comfortable. If you don't have one, use a box fan, but move that air around as well. Mixing the cooled air with the hot air will help with heat exchange, and allow the overall temp to come down perceptibly quicker.

I can cool down even faster if I leave the man door to the house open, and use a box fan to blow cold air from the house in...

Your space is less than half of mine that needs to be cooled, and your unit is a bit over half of mine. Plus you have more insulation in the walls... Honestly, I can't say enough about insulating and radiant barrier ABOVE, not to mention ventilation. If you don't have a ridge vent, or a turbine of some sort on that shed, you REALLY need one. Add some more insulation and a radiant barrier if you can. (That 8' at the apex ceiling is a bit of a concern, but not unworkable...) Check out the guys at www.atticfoil.com and see if they have any suggestions for you.

It is FAR better to not need to expend the extra energy in the first place to heat it up, or cool it off... And I am not saying that from some political agenda, just me being a cheapskate...

[capncarl]

I have a 12000 btu window type heat pump ac installed through the wall in my wood shop. The wood shop is aprox 250 sf and the adjoining garage area is 500 sf. The ac idles 24/7 and maintains the wood shop around 70 and the garage around 80 with just a couple of breeze box fans keeping the air stired up. This 12000 btu unit is under-rated and should be a 14000 or 16000 btu unit. The shop is well insulated like yours and when the ac is first turned on it slowly cools down to the desired temp overnight and maintains it fairly well in our south Georgia high 90's and low 100's. I fabricated a filter holder for a large pleated filtter on the ac unit to capture all dust before it gets into the units filter, and also keep my shop air filter and dust collector running when any dust producing equipment is operating. It looks like my utility bill increases by about $25 per month for the 6 months of summer, and about the same during our 4 month winters. I think that we pretty much skip spring and fall now. When this ac dies I will repace it that day, operating without it is not an option. All windows are vinyl insulated pane type with reflective film added and the garage door is a vinyl insulated residental unit with reflective film as well. The most heat/cool loss is noted around the garage door. Keeping the doors shut and letting the ac get the inside of the shop cool allows the ac to idle on low at what seems to be it's sweet spot. Running it on high and cycle on and off more gets it cooler faster but doesn't seem to accomplish any more. The ac seems to help the humidity control as I have not noticed any rust on the cast iron tools while it is running.
Stay cool
capncarl

[RDavidP]

I thought I had put my location in my profile earlier, but I just updated it. I am in Maryland and we are currently having July in June. I do have the duct going out the wall, and R13 insulation covers the last bit of duct pipe at the wall, and blocks air flow coming through the wall cut out. I was wondering about actually wrapping the duct pipe itself too because there is alot of heat coming from that. I don't have a dog torn sleeping bag, but I do have a sleeping bag and three dachshunds.

If the hygrometer I have is to be believed, the humidity in my shop runs between 70 to 80% through out the year. If I could control the temperature without affecting the humidty and ever got tired of woodworking, I would build several spanish cedar shelves, get rid of the tools and have one nice walk in cigar humidor. Running the A/C actually drops the humidity down to between 60 and 70%, which helps make it feel better. I also have the A/C on a wooden box that I built for it after realizing the power cord would not reach the closest plug in, so the A/C is not sitting on the floor.

Here is a current picture of the inside of my shop from one end to the other. I have the A/C on one end, and have the fan at the other end. Right now the fan is on the workbench because I had the doors open blowing the heat out. My A/C also have a fan only function, and I can use that to blow heat out. I have now shut the doors and turned the A/C to cool. It has been almost 30 minutes now, and I will check it again in a little while. Of course I am going to have a ceiling vent fan put in, but it is a matter of (time x extra money)/current money flow.

And excuse the mess on the table saw, I am currently in the process of making a muzzleloader stock while restocking a friend's shotgun.

[big tim]

If I were you I would also make a serious effort to locate the AC unit such that your exhaust duct can be shortened significantly. That long uninsulated
duct is actually helping to heat your shop.
Just my 2 cents worth!

Tim

[dbhost]

Okay, from my experience with my portable AC, it's a LOT like dust collection. Keep that hose as straight and short as possible... My AC simply put would shut off if I extended the hose all the way and bent it at a 90 deg angle. Too much restriction, and the compressor would get hot and the safety would shut it off...

Is your unit a single or dual hose model?