Cooling a 22ft high 1250sq ft warehouse store

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  #1  
Old 06-11-12, 04:13 PM
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Cooling a 22ft high 1250sq ft warehouse store

I have recently leased a warehouse style unit with garage door, it used to be a auto shop but is now a flex unit for retail. The store is an IT services & electronic repair shop. The ceiling is very high. The building is concrete floors and walls.

I purchase a 7000 BTU portable AC unit since i did not have much cash and have been using it for about a mth. With it on it seems to do nothing, i left it on overnight as well and the temp remained the same. I realized that it was actually cooler with it off and having the garage door open.

I just purchased a 2nd 14000 btu unit to help, these units are both portable and connected to the windows. The earlier unit i turned on to dehumidifier as i realized that humidity is also an issue and the new unit is set at 70f to cool.

I have an exhaust fan in the ceiling that the previous auto shop had. I figured this would be better since the windows are in the front and the back room is the hottest i could connect the portable ac units to the exhaust fan.

I was wondering the best way to cool this warehouse. I am pretty clueless for this type of thing.
 
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Old 06-11-12, 04:22 PM
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Ever hear the term fart in a windstorm? That's what your 7,000 BTU unit is. Even with the addition of another 14,000 BTU unit you are still woefully small. The exhaust fan will get rid of the hot air at the ceiling level but it will also pull in an equal amount of outside air and if that is hot and humid you have gained little to nothing.

I assume that your portable unit (Are they both portables?) is a single hose model. If yes, then this unit is no different than the exhaust fan in that it requires an equal amount of outside air to come into the building as is pumped out through that single exhaust duct. Further, if that duct is not insulated it WILL radiate a fair amount of heat right back into the space effectively cutting that 7,000 BTU rating significantly.

You really need to do a heat load calculation on the building and incorporate any internal heat gains including people in the calculation BEFORE trying to cool the place.
 
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Old 06-11-12, 06:48 PM
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Yes that makes perfect sense to me. Both units are single hose portable units. Right now i realised that the AC function is useless on the small unit. So i will keep that on dehumidifier.

How would i go about doing a heat load calculation? If the calculation is done and it is determined that 4 tons is needed would having 2 tons help at all or do i need to have 4 tons or nothing?

Since the office is in the front where the windows are would 2 2 ton units work, or would it take too long to cool the back room?
 
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Old 06-11-12, 07:10 PM
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i found this on craigslist for a grand Portable Air Conditioners, AC, Spot Cooler, Outdoor & Computer Cooling

the retail price is over $4k which is very expensive considering i could get 2 14000 btu units at about $600 each so $1200 for 28000 btu which is 4000 btu more which doesnt make sense to me but perhaps it does something that makes it worth much more

its 220v but all my repair equipment is 220v so its not a big deal to find the outlet for it
 
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Old 06-11-12, 07:25 PM
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Do a Google for heat load calculation (or heat gain calculation) and you will get several hits. Most will be for paid programs but a few will be for simple calcs using the volume of the building and a few fudge factors for insulation, windows and such. The free ones are not all that good but they will get you in the ballpark.

The calculation will be a worst case scenario, or what is called "design conditions". This means that the inside temperature will be maintained at a certain outside temperature by applying the BTU removal requirements. At conditions less than "design" it will take a lesser amount of BTU removal to maintain the desired indoor temperature. This means that yes, under less than design outdoors temperature you can get by with a smaller unit. Whether or not that would be a two ton or a twenty ton I cannot say without having all the info that is required by the heat gain calc.

The bottom line is that you need to remove ALL the excess heat from the building on a continuing basis. If your cooling capacity is (for example) 20,000 BTUs per hour and the heat load at the moment is 24,000 BTUs per hour the temperature inside will rise. If the same size of equipment is operating but the heat load drops to 15,000 BTUs per hour the temperature inside will fall. It's that simple. How much difference there is between the equipment size and the heat load determines how fast the temperature will change, within limits based upon several different factors.

If the building contents "heat up" before the cooling equipment is started then all that heat must be removed before any actual cooling takes place. This is called "latent heat". If you ran the A/C 24/7 and the outside temperatures cool significantly at night you might be able to get a "head start" on the cooling; actually cooling the building below what you want to maintain during the day. The temperature would still rise during the day (due to insufficient cooling capacity) but starting our cooler would perhaps mean not reaching as high a temperature by the end of the day.

Whether or not units discharging cooler air in the from of the building will eventually cool the entire area is also something that I cannot predict. The better the air distribution from the cooling unit(s) the better the overall effect.
 

Last edited by Gunguy45; 06-20-12 at 11:40 AM. Reason: added some 000's to a figure
  #6  
Old 06-20-12, 10:59 AM
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i found a movincool officepro24 for sale on craigslist for a grand it has 24000 btu and is 220v MovinCool Office Pro24 24,000 BTU Portable Air Conditioner With Digital Control Panel

apparently the retail price is around 5 grand WOW, i can buy 2 14000 btu units for $400 each so that would be 28000 btu for $200 less than that single unit

also the $400 units are dual hose which i found on amazon and are much better so i have no idea why the unit cost 5 grand new

we put a plastic tarp over the back room to help keep it cooler and reduce the ceiling height to about 8 ft now which should help at least keep that room cool

the front office is about 200sq ft with a height of 8 ft or so and has 2 windows in the room, i was thinking if i get a 25000 btu window unit and leave the office door open combined with either the 28000 2 units or the single 24000 btu unit that would meet the 4 tons
 
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Old 06-20-12, 03:13 PM
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14 tons would be a left field guess.
 
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Old 06-20-12, 03:27 PM
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14 tons airman? Lord...that would cool 4 or 5 houses out here in 100 degree weather.
 
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Old 06-20-12, 04:09 PM
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xboxhaxorz,

Stop it. Showing us ads for a/c units is not going to solve your problem. Do the math. You are spending more money on guessing than what it would cost to buy the appropriately size unit. It will be worth your money to spend it on the right sized central unit than those portable units. They will be more efficient and last far longer.
 
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Old 06-20-12, 04:42 PM
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its not an ad, its a unit i am just going by the fact that its a large unit

the landlord for the space said central ac would cost around $6000 so that is way more than spending $2 grand or so on portable units

i was not aware however that central ac was more efficient than portable
 
  #11  
Old 06-20-12, 04:59 PM
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Just wondering...Pro's can answer...what about a mini-split or 2?

xbox...a central or mini-split would be much better than the portable units. Next up would be a couple of window units.
 
  #12  
Old 06-20-12, 05:46 PM
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yea i tried doing a lot of research with mini split, evaporative coolers, window, and portable

the mini splits were much more but with a lot less btu, i will keep researching, but as it gets hotter i might just die trying
 
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Old 06-20-12, 06:35 PM
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How about a mobile home self contained unit? Might be able to get a couple of used ones.
 
  #14  
Old 06-20-12, 08:50 PM
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Gunnguy yea it sounds large. But I'm picturing a steal roof with no insulation on it our walls. 22 ft ceiling!! As said he needs a heat load. I did say left field. Lol
 
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