A/C ideas needed

[namsag]

I am planning a rigid frame steel building, 60x40x10'. It will have an inside wall dividing it into two 40x30 rooms. Both rooms will be finished inside, one will be a workshop area and the other will be a place for my other hobbies and general man cave/hang out area. I am looking for heating and A/C solutions. Here in north MS we can see temps in the teens in winter and 100 in the summer. I am not that worried about heat. The building will be well-insulated and I will mainly rely on woodstoves with the heating unit for backup, and I like it cold. My concern is cooling it off in the summer. I'm thinking of a separate unit for each room as I may not often need to cool them both at the same time , but not sure whether it might be better to have one big unit that can handle the whole load if I want to. I don't know a thing about HVAC, so explain it like I'm a dummy. Am I looking at a central unit or could I use some other type of unit for a building this size? This building is a long-held dream and I'm trying to plan it out and get it right! Any ideas/advice appreciated. Thanks, namsag.

 

[tomroblee]

For proper equipment sizing, always have a good heat load calculation done. Off the top of my head, you are probably going to need a total cooling capacity somewhere in the neighborhood of 3 to 4 tons (36,000 Btu to48,000 Btu)

I believe that it will be difficult to find a single unit this large in much other than central air conditioning or heat pumps. If you use two units (one for each room), you shouldn't have much difficulty finding window air conditioners up to 24,000 Btu. PTAC (Packaged Terminal Air Conditioners---like used in motel rooms) seem to top out at about 15,000 Btu. A variety of mini-split air conditioner or heat pump sytems would be large enough to one room.

The chief advantage of central systems is that conditioned air can be more evenly delivered by the use of a duct system. A single window air conditioner can provide enough cooling for a 30' x 40' room, but all the conditioned air will come from a single point. The use of ceiling fans could help distribute the air, but they also produce a draft that may not be desirable. (I enjoy a fan blowing in a man-cave, but not a woodworking shop with lots of saw dust.)

A single large central unit will be cheaper than two smaller units. To some degree, a large central unit could be zone controlled to keep each room at a different temperature.

One of the largest drawbacks for using a single central unit is that the air will be recirculated through both rooms. This normally isn't an issue in a house, but you may doing things in your shop that you don't want spread to your man-cave (gasoline fumes, paint fumes, welding fumes, saw dust, various chemical smells, etc).

A window type unit would probably be the cheapest in terms of equipment cost---but also the least efficient in terms of energy usage.

 

[namsag]

Well I guess everybody looks but has nothing to say. Thank you Tom, your post is very helpful. I am trying to educate myself about HVAC, right now I don't know enough to even discuss this intelligently with a contractor.

 

[pseudorealityx]

I would suggest 2 systems to keep the air from recirculating, and like you said... no need to cool both spaces if you're only using one. From there, give us a budget that you're looking to spend. If you want to do it for under $500, you're looking at window units. If you've got some money to spend, and want a dropped ceiling in your man cave, then start looking at a small split system with ductwork. Minisplits of various designs are also popular.

When it's 100 outside, what do you want each interior space temperature to be?

Is noise a concern? On both sides?

What's going on in the shop? Woodworking? Welding? Painting?

 

[tylernt]

PTAC (Packaged Terminal Air Conditioners---like used in motel rooms) seem to top out at about 15,000 Btu.

Amana AH183E35AXAA is 16kBTU heat and 17kBTU cool. Also, GE AZ85H18DAC is 16kBTU heat and 18kBTU cool. Those exceptions aside though, you're right, most are in the ~14kBTU range. Also the PTACs usually aren't as efficient (SEER/COP) as mini-splits or ducted systems. But, PTACs are also cheaper up front.

Usage also helps determine which is better. Leave it on 24/7 and a PTAC can maintain a large space. But if you let your building cool off in the winter or heat up in the summer and then you come in and want to work, the PTAC will struggle to condition the space in a reasonable time, whereas a mini-split or ducted system will have more "muscle" to move the temperature to where you want it.

 

[namsag]

Thanks guys. Workshop side will be mainly woodworking and maybe some mechanical projects. Noise not an issue. When it's really hot outside I want to be able to make the building cool enough to be comfortable to work/hang out in. As for budget , well, I'll say I'm willing to spend what it will take to get it done right, I plan to be here the rest of my life. I have been looking and reading about mini-splits. Just wondering, with the single ductless unit, does it create a cold spot right in the immediate area of the unit, and hotter zones 'way across the room from it? I don't think I have ever seen a mini-split in operation. Will have to get out and find one to check out.

 

[Jinks]

Thanks guys. Workshop side will be mainly woodworking and maybe some mechanical projects. Noise not an issue. When it's really hot outside I want to be able to make the building cool enough to be comfortable to work/hang out in. As for budget , well, I'll say I'm willing to spend what it will take to get it done right, I plan to be here the rest of my life. I have been looking and reading about mini-splits. Just wondering, with the single ductless unit, does it create a cold spot right in the immediate area of the unit, and hotter zones 'way across the room from it? I don't think I have ever seen a mini-split in operation. Will have to get out and find one to check out.

My mini-split has only been in for a couple of days so I'm by no means any kind of authority, but I am impressed. My shop is considerably smaller than what you're building, but it's two areas open to each other. A slightly over sized single car garage, & an area that used to be a large guest room. I had a 12000 BTU Mitsubishi installed. I also have a ceiling fan in each room. The vanes on the mini-split can be set to oscillate, but even stationary it doesn't seem to create a cold spot. The 12000 BTU unit is more than enough to cool here in Florida. Both the indoor & outdoor units are scary quiet, & once the room is cooled off they seem to just idle along to maintain the temp. I would imagine it's simply a matter of sizing to find a mini-split with two heads that will maintain each room of your new shop at whatever temp. you're lookin' for.

 

[Motofixxer]

My 25x32 is using a simple 10k window unit built into the wall. It has no problems maintaining a comfortable temperature. My shop stays closed up basically all the time and rarely even needs the A/C on.

 

[tomroblee]

If you aren't on a very tight budget I would think that you would be happiest with a separate unit for each room. In your climate I would want to use heat pumps rather than plane air conditioners. It's a lot easier than fooling with wood stoves when the temperature is above freezing.

I've never seen a min split installed in a 30' x 40' room, so I can't say how even the temperature would be. It's more energy efficient to keep any ductwork in the conditioned space (rather than in a hot attic), so a mini split might make a neater and easier install in the man cave room. I don't think that having exposed ductwork at ceiling level would be much of an issue in a workshop.

I would think that a ducted system would have some advantage in a woodworking shop just because it would allow you to install larger and better air filters. Air filters can take a lot of attention in a dusty environment.

Others have mentioned that the size of the system required will depend on whether you run it all the time or just when you are using a particular room. This is especially important for air conditioning in a humid area of the country. When you first turn on an air conditioner in a hot humid environment most of the energy will be used to cool and condense the water vapor out of the air.

You might also want to consider the orientation of your building. You don't really want to locate the ourside units of a split system in the bright sun at the hottest part of the day, nor do you want an extreme distance between the inside and outside units. This may or may not have an impact on your choice.

 

[namsag]

Thank you very much for your input and for the points you raise. I actually was thinking the other day about exposed ductwork, and I wouldn't even mind it on the man cave side if it can be at least a little tastefully done.