Need help with duct design for shop

[alkknight]

I just built a 40x60 metal building that basically has 3- 20x40 bays. It has 12ft side walls and was insulated with 4" (standard is 3") insulation. I have made rooms in a the first bay (16x40) which consist of a 10x 40 workshop that opens into the other two bays with a cased opening (would fit a 6'0" door later). There are three more rooms (2- 6x10 and 1- 6x 16). That area is decked and finishes around 8ft to the decking. I have a 5 ton split heat pump with 20kw strips and I have suspended the AHU from the ceiling at about the center of the 40 ft wall and 3 feet from that wall. I would lile to run come out of the unit and split it into two branches. One would feed the 40 x 44 open area (hung from purlins at 10 feet off front of building) and the other to turn down and run along the 40ft wall on the decking to with takeoffs to supply the other rooms from the ceiling. My problem is that I have no idea what size ducts woul be required to acheive this. I would like to use spiral pipe for at least the open area if not for the entire system. I can make a schetch of this and post it if none of this makes sense. Please help me figure this out. Thanks!

 

[alkknight]

Oh, I plan on dropping a 24x30 return down through the ceiling into the short hallway between the 6x16 room and the two 6x10 rooms. It is open into the 10x40 shop area and where the door to the side of the building is. There is another walkthrough door in the front of the 10x40 room (centered in the 10') and three insulated 10x10 roll up doors, two in the second bay (front and back) and one on the front of the third bay. Planning on the spiral pipe running above the track to the roll up doors (the doors actually stop around that area when completely raised.

 

[rburke65]

No help here but welcome to Garage Journal from Ohio! You might want to update a location in your profile. Good luck to you.

 

[alkknight]

Thanks! I updated it. Also, I went and measured and think that I may need to run the duct down the center so that it doesn't block my lights. I only have 11 inches of space between the I beams and the door tracks if I get far enough from the canopy lights to not cause problems. See revised layout.

 

[zmaxmotorsports]

Can you post a more detailed floor plan of the entire area you want to heat/cool?

 

[pseudorealityx]

1. You likely want "round" ductwork, not spiral. Spiral is expensive in comparison, and for a shop, not a huge improvement.

2. Since you've got 5 ton unit, you're looking at ~2000 cfm.

2a. Decent guide for supply duct work:

6" for any tap less than ~100 cfm
8" for any tap less than ~225 cfm
10" for any tap less than ~400 cfm
12" for any tap less than ~650 cfm
14" for any tap less than ~1000 cfm
16" for any tap less than ~1400 cfm
18" for any tap less than ~1950 cfm

You can get away with 18" for the main supply even at 2000 cfm.

For returns, basically provide 1 size larger than called for and you'll never have a problem.

If you've got some odd condition at the very end of a run that has all sorts of twists and turns and elbows, consider up-sizing 1 size.

 

[alkknight]

So, I hope this helps... I am not an architect. Also, would like some suggestions on register size. For the open area on right, I would like to use the grills you cut in to the duct and for the covered area on the left, ceiling boots. I plan on sheetrocking the area on the left. I am leaving the area on the right unfinished for now. I would prefer to use spiral pipe, but may decide on round if price is too high.

 

[alkknight]

Here's some pics of my shop. Please excuse the mess... never enough room or enough hours in the day.

 

[raceman17]

What's the difference between "round" and sprial duct? Is "round" duct the cheap snap lock kind that comes in 5' sections? If so that method would seem like a PITA to work with to me. More splices and pretty thin materials to work with. I did my 40 x 80 with sprial and I had about $1200 in materials including all the fittings and expensive registers.

When I did my shop I used the sprial duct and used a drywall lift to raise the sections up in place. I could easily raise 20' of duct up at a time by myself. Hell I did my whole shop by myself in about a day and a half. I hung the duct with 1/16" coated steel wire cable and cable crimps. It went up quick and you really can't see how the duct is hanging in the air unless you look real close.

 

[pseudorealityx]

Well, you may want to ask your contractor if you have someone else put it in, or ask your local metal shop the cost difference. This is a small enough application that spiral might make more sense, but it is pricier per ft.

 

[alkknight]

It's not much more and I will probably go with spiral. I still need some help with sizing the ducts for the spaces covered/ registers needed. Thanks pseudo for the general guidelines... but I don't know what I would need for the different areas. There are 2 rooms- 6x10x7.5' tall (one of those has a water heater and an air compressor in it), 1 room- 6x16x7.5' tall, 1 room - 10x40x7.5' tall. Then there's the open shop that is 44'x40'x12' (sidewall height- about a 1/12 pitch roof). Also there is the area above the first rooms (16x40 storage area). How many registers and what size for the shop area? What about the smaller rooms?