Sizing AC Unit for Industrial Space - Thoughts and Experiences?
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    Default Sizing AC Unit for Industrial Space - Thoughts and Experiences?

    Hey guys,

    Summer is peeking around the corner already, and our new shop is not air conditioned (yet). I'm a pretty firm believer in AC in the shop. Keeps me and the employees happy and comfortable, work quality is better, and we're not wore out near as much by the end of the day.

    I am looking for any advice on sizing a unit for the shop. Most of the calculators I have found are for residential houses and a house vs. an industrial condo aren't really apples to apples as far as tonnage of refrigerant required.

    We have a 4000 square foot unit (give or take a few feet) with 21 foot ceilings. It is a steel building, insulated OK, not the best, but could be worse. Heat bill (natural gas) is around $180 a month in the coldest months. West Michigan doesn't get too hot compared to like, Arizona, but we get plenty of humidity and 90-100° plus days in late July once the lake heats up and we lose the cooling effect.

    One big room aside from the (small) office and the head. I will probably get a window shaker for the office so I don't have to run too much ductwork.

    Various online calculators have put me in the 10 ton range, not sure if that is enough? Or too much? My last shop had a 3 ton unit, 2000 sq. feet, and it ran constantly so I know it was undersized. But it did manage to at least hold temp and keep the humidity down, so it wasn't that much under. A 5 ton probably would have been enough.

    Sheet metal shop down the street keeps their shop comfy with two 5 ton units, they are at 6000 ft, but lower ceilings.

    Ingram's has a 10 ton Daiken for 6k free shipping and comes with the air handler and all, I'm considering going that route.

    A friend is an HVAC contractor, so I am going to get his input, but I figured I'd run it by the hive mind. What do you guys have in your shop?

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    Quote Originally Posted by Arc-On View Post
    A friend is an HVAC contractor, so I am going to get his input, but I figured I'd run it by the hive mind. What do you guys have in your shop?
    ^^^ This, assuming he's a commercial guy.

    I'm a full-time commercial construction PM (and part-time riflesmith ).

    A lot of considerations go into the calcs. Building exposures, glass area, heat gain from machinery, lighting, people, building insulation...and many others.

    Ceiling height is always an issue. Do you have any BAF's (Big Ass Fans)? As you noted, it's a fine line sometimes. You need the units to operate long enough to dehumidify, but not undersized so as to need to run almost constantly (here in FL, they pretty much do anyway in middle of summer).

    Typically, metal buildings are done with minimal ductwork- using RTU's (roof-top units). Depends on your building design, as to whether these make sense (roof structure needs to support the weight, steel needs to be added, cutting holes in the roof, etc.).

    But, they're usually cheaper in the end because they're self-contained (no separate AHU's), requiring less refrigerant piping and ductwork.

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    Add up the wattage of all the machines that might be running at the same time. This figure has to be added to any residential or office heat loads.
    Bil lD

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    Quote Originally Posted by tobnpr View Post
    ^^^ This, assuming he's a commercial guy.

    I'm a full-time commercial construction PM (and part-time riflesmith ).

    A lot of considerations go into the calcs. Building exposures, glass area, heat gain from machinery, lighting, people, building insulation...and many others.

    Ceiling height is always an issue. Do you have any BAF's (Big Ass Fans)? As you noted, it's a fine line sometimes. You need the units to operate long enough to dehumidify, but not undersized so as to need to run almost constantly (here in FL, they pretty much do anyway in middle of summer).

    Typically, metal buildings are done with minimal ductwork- using RTU's (roof-top units). Depends on your building design, as to whether these make sense (roof structure needs to support the weight, steel needs to be added, cutting holes in the roof, etc.).

    But, they're usually cheaper in the end because they're self-contained (no separate AHU's), requiring less refrigerant piping and ductwork.
    Yeah, he's a commercial guy, so I trust his input. More information and experiences from others is always helpful though.

    I'm not ruling out a rooftop unit. Just comparing options at this point. I would need to add at least a grand to the budget for crane service though, and they are harder to find for a reasonable price in my experience. I don't want to spend more than 6-8k for this if possible, it is a rental after all. I might be able to work out a deal with my landlord to pay for part of it, but I suspect I'm on my own here. I'd have to look at my lease again, but most of the time upgrades like this are considered the landlord's property once installed. I know the landlord well, I can probably work out a deal where we can pro-rate rent or something to help offset the cost but I'm not really planning on it.

    I do have fans, one in each quadrant of the shop, but they are regular commercial ceiling fans. BAF would be neat, but they would probably cost as much as the AC to retrofit, and may interfere with the cranes.

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    Quote Originally Posted by Bill D View Post
    Add up the wattage of all the machines that might be running at the same time. This figure has to be added to any residential or office heat loads.
    Bil lD
    Just one CNC at the moment, HURCO 4020. We do quite a bit of manual work and welding/fab though.

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    Quote Originally Posted by Arc-On View Post
    Hey guys,

    Summer is peeking around the corner already, and our new shop is not air conditioned (yet). I'm a pretty firm believer in AC in the shop. Keeps me and the employees happy and comfortable, work quality is better, and we're not wore out near as much by the end of the day.

    I am looking for any advice on sizing a unit for the shop. Most of the calculators I have found are for residential houses and a house vs. an industrial condo aren't really apples to apples as far as tonnage of refrigerant required.

    We have a 4000 square foot unit (give or take a few feet) with 21 foot ceilings. It is a steel building, insulated OK, not the best, but could be worse. Heat bill (natural gas) is around $180 a month in the coldest months. West Michigan doesn't get too hot compared to like, Arizona, but we get plenty of humidity and 90-100° plus days in late July once the lake heats up and we lose the cooling effect.

    One big room aside from the (small) office and the head. I will probably get a window shaker for the office so I don't have to run too much ductwork.

    Various online calculators have put me in the 10 ton range, not sure if that is enough? Or too much? My last shop had a 3 ton unit, 2000 sq. feet, and it ran constantly so I know it was undersized. But it did manage to at least hold temp and keep the humidity down, so it wasn't that much under. A 5 ton probably would have been enough.

    Sheet metal shop down the street keeps their shop comfy with two 5 ton units, they are at 6000 ft, but lower ceilings.

    Ingram's has a 10 ton Daiken for 6k free shipping and comes with the air handler and all, I'm considering going that route.

    A friend is an HVAC contractor, so I am going to get his input, but I figured I'd run it by the hive mind. What do you guys have in your shop?
    We have that same unit we installed ourself last summer. Our building is 10k square feet. Last summer, It ran all the time and lost some ground in the middle of the day. But the building’s roof had very poor insulation, and the walls. The entire building was just reroofed and reskinned 2 months ago, and noticed right away that the heaters ran 1/2 as much. The installers added much thicker insulation, on top of what was already there. So I think the ac will actually shut off now. The daikin is a good choice. A 10ton will work for you in my opinion


    Sent from my iPhone using Tapatalk

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    I see this as three part. You need to calculate the load for the building itself based on construction, insulation, ceiling height windows etc. Then you need to add the load for the people in the building, they are not sitting around watching TV they are working and generating heat. Third you add the electric load. Every watt of electricity that goes into the building turns into heat in one way or another. An additional thing to consider is how often you need to open any roll up doors.

    Mike

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    If you really want the "right" answer you need to have done what is called a "Manual J Calculation". It's a bit of work to do it right which is why most commercial contractors just want to ballpark the sizing. Plus oversizing the unit means a more expensive unit (and profit) for them and a lower chance that you will call in the middle of the summer on a 100 degree day and complain that it isn't working. Maybe try a local community college and see if they have some students who want to do one for the experience. I can tell you that substantial insulation (going past the minimum fiberglass batts) and air sealing of the structure is the biggest factor in reducing the load.

    Steve

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    Quote Originally Posted by npinson View Post
    We have that same unit we installed ourself last summer. Our building is 10k square feet. Last summer, It ran all the time and lost some ground in the middle of the day. But the building’s roof had very poor insulation, and the walls. The entire building was just reroofed and reskinned 2 months ago, and noticed right away that the heaters ran 1/2 as much. The installers added much thicker insulation, on top of what was already there. So I think the ac will actually shut off now. The daikin is a good choice. A 10ton will work for you in my opinion


    Sent from my iPhone using Tapatalk
    Thank you for your experience. That helps put some perspective on things.

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    Quote Originally Posted by SteveF View Post
    If you really want the "right" answer you need to have done what is called a "Manual J Calculation". It's a bit of work to do it right which is why most commercial contractors just want to ballpark the sizing. Plus oversizing the unit means a more expensive unit (and profit) for them and a lower chance that you will call in the middle of the summer on a 100 degree day and complain that it isn't working. Maybe try a local community college and see if they have some students who want to do one for the experience. I can tell you that substantial insulation (going past the minimum fiberglass batts) and air sealing of the structure is the biggest factor in reducing the load.

    Steve
    All good points.

    My question is how do you actually quantify some of these things? Like, is there a formula or something for people, machines, and such? I realize it will always be basically an educated guess, but some sort of baseline maybe?

    We're at 3 full time bodies in the room, a VMC, welding equipment, saws and other manual machine tools working all day in some capacity. A transformer humming and making some heat. Fridge, and a few other small appliances.

    We don't have many windows, and we only have the door open if we are unloading a steel truck or loading up a customer. Maybe 15 minutes or so at a crack, once or twice a day? Some days it doesn't open at all. Obviously we don't just open up and leave it open to vent all our cool/hot air. Open up, drive forklift out, close. Reverse when truck is loaded/unloaded.

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    I would not want to be in a office with a window unit going and try to use my brain. They are loud, so loud I can not find any numbers. A split system is much quieter and can be ordered as a heatpump/ac unit. be careful about which unit you buy, my Freidrich is rated half as loud as some of the name brand units. I oversized it for my house so I never have run it above medium so it never gets too loud.
    realize the DB sound scale is logrithmic so 5-7DB higher is twice as loud to the human ear. Of course I do not know if my made in china unit is really as quiet as they claim. Who knows how accurate the tests they did for their own units are really that good. Kind of like Sears air compressor horsepower ratings?
    A split system only needs a 3" hole through the wall so it is not a break in point if that matters to you.
    Bil lD
    Bill D.

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    Your personal experience is a big piece of information

    AC guys will oversize, because they won't get call backs

    It costs you money, but makes them money

    Without machines running you probably need very little AC as the building probably has fewer doors and windows than a house

    The big variable is heat input from the machines, and air changes. Welding needs some fresh air
    I am a fan of mini split units and they come commonly up to 3 tons. A pair of them might do your space and be much more efficient than a big 6 ton unit since they are variable rate

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    We put a lot of thought into our building / shop environmental controls PLUS, we had to deal with the latest in city codes and be in compliance with DOAS rules (Dedicated Outside Air System) . . . I don't know if you have these same code requirements or if you would need to upgrade on a new install, but you should be aware of this requirement.

    We couldn't have done this without a competent contractor who ran all the calculations and put a package together that would meet code.

    Within all of our offices - there is a CO sensor that monitors air quality and then introduces fresh air into the building to keep the CO levels below a max acceptable level (and you can adjust it downward for more fresh air).

    The fresh air comes in through a heat exchanger that pulls air out of the building at the same rate - presumably to save energy. We manage 14,000 square feet of office and it is always comfortable upstairs and down. You should at least look into this as I have been surprised how much better I feel mid-afternoon than I did in our old building. I am fairly certain the CO levels got much higher than healthy with 50+ people in our old building.

    The shop is quite a bit different than your situation, and it is not air conditioned - instead we installed 4ea 18ft diameter fans for circulating air, plus 4 large gas heaters, plus 4 roof mounted exhaust fans, plus 4 large 42" x 192" motorized louvered vents. Then we connected them all to drives / PLC and temperature sensors inside and outside the building and manage the shop environment that way . . . we rarely get above 90 degrees in the summer and rarely above 70% humidity as well so our shop situation is different.

    Our ceilings range from 32 to 40 feet tall and it has stayed very comfortable in our shop since we moved in back in August.


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    Your HVAC friend will have computerized load program and know how to use it or his wholesaler will. You might consider type of unit that's used on portable office trailers commonly known as Bard units. Wall hung, no ductwork,no hole in the roof, no crane, and sizes up to 6 tons. I'm thinking 1 each 5tons on opposite walls. The Daiken split system for 6K is just the start of it. Piping, ductwork, and labor will double that and more.

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    Bingo! I have had to keep rooms full of equipment cool. One place where I worked had a large heat load due to that equipment. It was in Iowa where the winter temperature can go below -20F. That area was in the middle of an industrial building, with no windows and few doors which were always kept shut. It gave me and my AC guy fits because the AC needed to run all winter long. In an industrial facility where there is a lot of electricity being used, 100% of that electricity, no matter how it is primarily used, ultimately becomes heat inside the room where it is used. And that is what the AC is fighting. It MUST be added onto the residential style calculators' results.

    You also need to consider things like insulation, open doors, and perhaps other factors. If you want a good estimate, find an HVAC company that is accustomed to industrial work. Or work with computer server installations.

    Here's one more consideration that may or may not apply to your situation. One AC system equals ONE point of failure. I have had facilities where the AC needed to run 24-7-365.25. One system in them was a mistake. There is a good case to be made for doing the calculations and then dividing by two or three. Install multiple systems and then, when one goes down, the other(s) will still work while the bad one is being repaired. This can also provide some flexibility in both the installation costs and the daily usage. You can install perhaps two systems, each with 1/3 of the calculated capacity. Run them and see how it goes. If you need a third one, then add it. As for daily usage, with perhaps three units you can choose to run just one or two of them on cooler days. This can provide better humidity control and perhaps a lower electric bill.

    If you have multiple systems, give some thought to a single duct system for all of them.



    Quote Originally Posted by Bill D View Post
    Add up the wattage of all the machines that might be running at the same time. This figure has to be added to any residential or office heat loads.
    Bil lD

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    Practical machinist = practical answer.

    For a 4,000 sq. ft., 21 ft. ceiling machine shop, a 10-ton package unit would be the bare MINIMUM.

    A 15-ton would be ideal, a 20-ton or (2) 10-tons wouldn't hurt.

    The big ones are two-stage anyway: a 20-ton package unit is actually (2) 10-ton compressors, each running only when necessary.

    Ductwork, air movement, and filtering are critical...of course.

    ToolCat

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    Thank you all for your experiences. I appreciate the perspectives of you guys who have been down this path before. Personal experience is worth way more in my book than some online calculator or a sales pitch.

    I spoke with the landlord this morning, he is willing to work out some sort of deal to help cover the cost. He is also considering upgrading the AC in his unit and the other unit, so we might be able to work a deal with a HVAC company to re-do the whole building at a reduced rate.

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    I'm assuming you have gas or some other heat already (we've been talking about straight A/C, not heat pumps...)?

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    Yes, we just have a natural gas hanging heater. No existing central system.

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    Technology advances in this area have really been amazing over the past few years.
    Variable speed, inverter powered (DC) compressors, etc. with incredible energy efficiency/SEER ratings.

    If the landlord is looking long-term (which he should be, if he plans on long-term ownership), he might consider the higher cost of inverter systems. Longer equipment life for him- and lower electric bills for you.

    Absent the LL footing much of the cost, I know I'd be hesitant to make that kind of investment (likely in the neighborhood of $20K) into a space I was renting unless it was committed, long-term lease. That's a lot of coin to dump into someone else's investment. I 'spose if the rent is dirt cheap might be a different story.

    Maybe air conditioning in shop spaces is "OK" to be optional where you're at.
    I was looking at smaller shop spaces here in FL, and I was amazed at how many were not even air conditioned. In FLORIDA, no less...
    Absolutely insane.


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