AC or windows?

[fabjunkie]

Planning out the new shop since we're moving after finishing my 30x40 that I had built last summer. The new shop will be 36x50x12, maybe 40x50 if I can swing it. Roof is 4/12 pitch so it has a 18' peak. I've been working on the layout in CAD trying to figure out where everything will go and I'm trying to come up with a resolution to a mistake I made on the 30x40, ventilation.

This time around there will be a 18x10 drum door on the 50' side, with a man door next to it. On one end there will be a loft 10' out from the gable end with a 7.5' ceiling underneath. The options I've come up with so far are:

1. Windows. Thinking about six 4020 or 4030 side sliders. Two on the gable end opposite the loft spaced evenly across the wall, bottom of the windows will be 5-6' from the floor. Two more at the same place under the loft, and two more above the loft approximately 2.5-3' from the floor of the loft. I would tint them and build interior bars for security reasons. Cost ~$600

2. AC/Heat unit. From what I can gather I would need a 3.5-4 ton unit. I would do the install myself including duct work, etc. Benefit would be I would have heat in the winter as well. This would eat up real estate inside and probably run ~$5-7k I'm guessing.

3. Windows as described above with a small roll up door strategically placed somewhere else in the shop just for cross ventilation reasons.

I'm east of the Dallas area and we really don't get spring or fall, just summer and not summer with a couple weeks to a couple months of cold in the winter. I have a couple 56" or 60" commercial fans that I took out of the current shop that I will put back up. With windows I thought about maybe putting a couple more in the back wall of the shop for more cross routes for breeze. The back wall will be facing South with the roll up door facing North (opposite of what I would think would be ideal.

As far as heat I currently have a torpedo heater that does fairly well making it comfortable, and have thought about a waste oil system as well. This would of course be instead of the AC/Heat system.

I will be doing primarily auto/metal fab work in here with a plasma table running at times as well, hopefully more often than not. Not all day most days, but I want to make it comfortable on the days that I am in there all day in the hot months which is realistically half the year.

Pic of the current layout I'm leaning towards.

Gable end with the loft and windows laid out. 4030 and 4020 respectively.

And the fans that will be going up in the new shop.

Thoughts, regrets, things you did that you appreciate on those hot days would all be appreciated.

 

[fabjunkie]

So no input so far. Doing some more searching and I found a cfm calculator. Comes out to about 6000cfm exchanging the entire building every 4.5 minutes or so.

My builder was suggesting the powered roof vents today. I found some 1500 cfm units for $131 each. Four of these comes to $570 with tax from the orange or blue box.

Then I found these. http://www.industrialfansdirect.com/General-Use/JD-VES20C.html
Two of these, one for each gable end would be 6280cfm and $570 plus shipping for the fans, hoods, and variable controller.

One of my concerns is too much air movement when I'm welding blowing the gas away which is a proponent of doing AC. Is AC worth the cost if I'm mainly in there in the evenings and weekends?

 

[fabjunkie]

Also by that calculation, I would need a 15 ton AC unit figuring 400 cfm per ton?

 

[Falcon67]

Maybe look at a package unit? Possibly elevated. That would be maybe somewhat cheaper than an inside setup and not take up any floor space. Or a vertical indoor - our house is 1700 sq/ft and the vertical Ruud isn't really that big, if I used one in the shop I might lose as much floor space as an engine hoist, maybe 3x3.

You could also use a horizontal system, suspended from the girders - no loss of floor space and flexibility to run ducting through that space.

>Is AC worth the cost if I'm mainly in there in the evenings and weekends?
It is for me - it's the 2nd week of October and Sunday it'll be 92F here. Average high this time of year is 80 and the next 10 days will be 6-10 degrees above that. And "ya'll in east Texas" lol, with typically higher RH values. Like you, it's pretty much summer and kinda not summer. I do like my windows and on those days when it's moderate with wind (mostly always with the wind LOL) they come in handy. I have my wall AC unit set to fire up at 5PM today so when I get home, it's comfy in the tool room.

 

[My Old Tools]

I'm east of Dallas as well, near Royse City/Union Valley. I did a 30x40x12 3 years ago. I went with an 8/12 pitch to create headroom for a loft. My loft is 20x30 clear span, set 10 feet off the floor. It has standup headroom to within 4 feet of the wall.

Windows or AC? When it's 102 and the wind is moving it is damn hot. I'm going to put in a mini-split. For you the real question is insulation. Mine is plastic faced roll over chicken wire. I can feel radiant heat through it in the roof. I'm going to add foil faced foam board with an air gap up there. I wish I had the ceiling foamed when I built, maybe the walls too, but that makes building shelves and such a bit harder I think. You might consider multiple mini-split units. They are cheap, efficient, easy to install, and take up no floor space.

 

[My Old Tools]

I just looked at your 30x40 build thread. I'm finishing up a 1951 Ford F1 flathead right now. I went with the Costco LED shop lights and really like them so far.

 

[fabjunkie]

Chris - I didn't think of the aspect of setting it to kick on before I walk in. That is nice. And the horizontal unit is a good idea.

Ross - I'm in Caddo now and going to the Royce/Union Valley area. What is your door/window layout? On my 30x40, it wasn't horrible this summer with the fans going and the doors only on one end of the building. That's why I'm thinking of windows across from each other with the ceiling fans and gable fans. The more I think about it I'm leaning this way, at least for now.

Looking at mini splits, I'd probably be in the $3500 range for a couple units required for the space, plus whatever else for install even doing it myself, vs. $1200 for windows and gable fans. That's a good chunk of change to put towards some big $$$ equipment that I will be purchasing at the same time. I do like the idea of the mini splits though.

 

[fabjunkie]

Oh and I love the CFL bulbs. I will be using them again in the new shop.

Are these the ones you used?
http://www.costco.com/4’-LED-Shop-Light-with-Chain-2-pack.product.100223617.html#

 

[Zeke]

I see the advantage of mini splits as one to facilitate a separate condenser and evaporator for ease of installation (no ducts) and quiet. You have a big building with plenty of access for ducts, air handlers hung from the rafters and duct work to distribute if you wish. By having a large BTU condenser unit outside and a air handler inside, you have a split system, just not a mini-split.

The package unit sounds good too if you want to mount it on a platform on a wall somewhere. You should run duct work for the supply and maybe for the return to optimize. AFA air movement affecting welding shielding gas, that will depend on your distribution. IOW, don't put in a return or a supply register that will disturb your welding area. If you weld in the center of the shop, put your supply ducts out from the 4 corners. I can't read your drawings.

I say that realizing that the mezzanine will affect any and all of this. You will have to do some careful planning because of the split level in that end of the shop.

I had an additional thought: put the package unit outside on the wall of the mezzanine and configure your return to operate as high or low with the use of a butterfly to switch up and down for the season, e.g., pull the return air off the lower register during the winter and vice versa.

 

[fabjunkie]

The return is another issue with doing a normal unit. I have zero experience with ac and would probably screw up the ductwork design somewhere. Just another benefit of a couple mini splits.

With mini splits, would they be better situated one on each end or spread out on the back wall say 15' foot or so from each end?

 

[My Old Tools]

I minimized my doors and windows. My overhead door is 12x12 in the west wall, SW corner. My walk door is on the same wall, NW corner. My atrium door faces east into the backyard along with one window. I have two windows high up in the gable ends, west and east to try and let hot air out. They didn't seem to help much this summer. Doors and windows eat a lot of wall space where I want shelves, benches, and machines. Going bigger is a good answer.

 

[Ponchoguy]

No windows and one door on my one garage, I wanted less breach points and potential drafts.

 

[wbrian63]

In my first shop, I put in a fan near the roof line across the shop from the main door. The shop was (if I recall) 20 x 40 with 14' eaves. The fan would move 13,000cfm (again, if I recall), so if I opened the overhead door about 1', I could actually feel a breeze as it was pulled in under the door, across the shop and out the back at the top.

Nice? Not really. I'm in Houston. We've got the same weather as you northern Texans, but more humidity. Shop was in an industrial complex with about an acre of concrete outside the front door. When it's 105 out in the parking lot, guess what temperature the air is that's moving smoothly under the door, across the shop and out the back at the top.

Yep - I've stood in front of hair dryers and felt cooler. Actually made it nearly impossible to use an HVLP spray gun to lay down water based lacquer. Stuff nearly dried before it made it to the part.

I vote for mini-splits. Organize your shop to create work zones - areas where you want/need more cooling, areas where it's OK if it's a bit warmer or cooler. Put the evaporator heads where you need them to be, then add a few fans to stir the air around.

Also - when you think you've added enough insulation to the roof, add some more. White roof, or aluminum color only.

My current shop had ZERO insulation on the roof, and worse it was made up of cobbled-together pieces of varying non-white colors. Even with a 15' eave hight, I could feel the radiative heat off the top of my bald head. I hacked together a system of 2x4 sleepers and sheetrock and blew in some fiberglass insulation. That helped some. Then the landlord finally caved to the demands of other tenants and painted a white elastomeric coating on the roof - that took a good 10f out of the ambient air in my space. Of course, now I've got leaks where there were none before, but there is no free lunch, right?

 

[fabjunkie]

That's a good looking F1 you got there. I think that may have been the first truck I fell in love with as a kid. The dark roof isn't helping you with heat either. Who did your building? Got a pic of your loft area? You've got me pondering going to a higher pitch.

 

[GDPossehl]

A radiant barrier under the rafters will help a lot in a metal building. I'm not sure what your eves look like for ventilation though. Radiant barriers work best with a ridge vent. Thermostatic gable fans should help control temps while you're not in there and A/C for when you are. For the long term, plant a tree on South side and hope you stay long enough to see it shade the shop.

 

[fabjunkie]

In my first shop, I put in a fan near the roof line across the shop from the main door. The shop was (if I recall) 20 x 40 with 14' eaves. The fan would move 13,000cfm (again, if I recall), so if I opened the overhead door about 1', I could actually feel a breeze as it was pulled in under the door, across the shop and out the back at the top.

Nice? Not really. I'm in Houston. We've got the same weather as you northern Texans, but more humidity. Shop was in an industrial complex with about an acre of concrete outside the front door. When it's 105 out in the parking lot, guess what temperature the air is that's moving smoothly under the door, across the shop and out the back at the top.

Yep - I've stood in front of hair dryers and felt cooler. Actually made it nearly impossible to use an HVLP spray gun to lay down water based lacquer. Stuff nearly dried before it made it to the part.

I vote for mini-splits. Organize your shop to create work zones - areas where you want/need more cooling, areas where it's OK if it's a bit warmer or cooler. Put the evaporator heads where you need them to be, then add a few fans to stir the air around.

Also - when you think you've added enough insulation to the roof, add some more. White roof, or aluminum color only.

My current shop had ZERO insulation on the roof, and worse it was made up of cobbled-together pieces of varying non-white colors. Even with a 15' eave hight, I could feel the radiative heat off the top of my bald head. I hacked together a system of 2x4 sleepers and sheetrock and blew in some fiberglass insulation. That helped some. Then the landlord finally caved to the demands of other tenants and painted a white elastomeric coating on the roof - that took a good 10f out of the ambient air in my space. Of course, now I've got leaks where there were none before, but there is no free lunch, right?

I'm from Houston originally, sort of. I try not to go back for many reasons, but the humidity is one of them and I feel your pain. Luckily it's pretty dry up here. On the current shop I matched the walls which is Light Stone. I'm already planning on doing white on this one and sticking with a lighter wall. I don't know if Galvalume would be better than white.

I guess with mini splits, I could do one to start with and add another later as funds allow.

 

[fabjunkie]

A radiant barrier under the rafters will help a lot in a metal building. I'm not sure what your eves look like for ventilation though. Radiant barriers work best with a ridge vent. Thermostatic gable fans should help control temps while you're not in there and A/C for when you are. For the long term, plant a tree on South side and hope you stay long enough to see it shade the shop.

I've got closable ridge vents on the quote from one building supplier. I'm worried about leaks more than anything them, plus for the cost, I'm half way to a mini split unit.

 

[fabjunkie]

For a mini split, can I go with one of the multi zone units? Also can anyone help with the needed btu's? I'm coming up with ~45-50k but not sure if that's right.

 

[My Old Tools]

Tom Hooten down at Point did mine. I got a bunch of recommendations from people at work and he had several recs. He was also the cheapest. I haven't been able to make contact with him lately so don't know if he's still working or not. I love the loft. It provides a ton of storage. I decked it with two layers of 7/16" OSB layed opposite each other. I am going to redo the stairs. Tom was about 6' 6" and I'm 5' 8". I have to hop between steps.

 

[fabjunkie]

I have a feeling he's not doing it anymore as I remember his name from last year and don't think I could ever get a hold of him for a quote. Do you remember how much the loft added to your price? I've been planning on building it out wood, but now that I see how simple yours is, I might change my tune.

 

[My Old Tools]

Not much but I don't know exactly. You can figure the material cost pretty quick. The C channel is on 24" center. Mine is all out of C channel. I would do the center and cross out of I beam if I were doing it again.

 

[fabjunkie]

So now I'm leaning towards a split mini with no windows to help offset the cost. I'm looking at two of the Mr. Cool DIY 24k system. I don't know if this is too much or not enough. Trying to use online calculators, I'm coming up with anywhere from 24k to 56k BTU's needed. So now I don't know if I need one 24k system, two 24k systems, a couple 18k systems, or a single 32k system. I keep reading you can't really over cool with a mini split but I don't want to throw money away either.