Shop Ventilation System - Basic Design

[brianpgriset]

I have a 30x60x14 shop near Houston TX (hot, humid). Insulated "flash and batt" with 3" closed cell roof, 2" walls. R13 for the batts on both. This is a wood frame (16" OC 2x6) steel exterior building. 3X panel doors, insulated R18, and one entry door. The building is very tight, no windows.

I plan to cool with a 36kBTU mini split with a single head, in the middle of one of the 60' long walls. I also want to install a separate ventilation system to do three things - filter the interior air with a MERV11 filter, help distribute the cool air, and setup a fresh air intake for air exchange.

I thought about doing multiple mini split heads but I like this idea better because the ventilation system can do all the "other" things I want other than cooling.

I want some pointers on making the ventilation system. My first thought is simply buying a used furnace blower (many locally available), build an intake plenum with wood or sheet metal to house the blower and have a spot for filter(s), place that in the middle of the ceiling, then have two ducts running to each end of the shop to exhaust.

For fresh air makeup I'l get one of the eletronic controlled fresh air valves and have it tie into the plenum and run it to a gable end with a louvre.

Is this reasonable? Has anyone done anything like this? Overkill?

 

[PWilks]

I’d personally just roll with ceiling fans, especially with 14 foot ceilings.

Not entirely sure how you would then deal with the filtration you desire, but the good ol’ furnace filter on the back of box fans works better than most anticipate.

As for fresh air intake, with a building that tight, most of your losses are going to be due to conditioning the outside air. You should have adequate fresh air “intake” just from natural convection driving the flow when the overhead doors open throughout the day.

 

[Yankeefarmer]

You should take a look at the Mr Cool Universal heat pump system, instead of two different systems. The inside air handler is a good base unit for return air filtration and supplying ductwork for good distribution. Remember that you can also run such a system in fan only mode for those days when cooling or heating is not required.

 

[brianpgriset]

Bringing this back up. Per Yankee Farmers' recommendation I picked up a 3T Mr Cool split. About halfway on the install.

My question is on ducting. I would prefer to go right to an 18" flex duct just off the discharge of the handler and run that to the center of the building. Then, with a small box plenum, branch to four 10" flex lines, each terminating to a register at each corner of the shop. The AHU is wall mounted.

Would like some opinions. I know many dont like flex but if sufficiently large it should keep pdrop sufficiently low right? AHU is rated at 1200cfm.

The 18" trunk would be 15' long with a single 90 degree bend before entering the small box plenum. Each 10" run would be about 15-20' also with a single 90 to turn into a ceiling mounted register.

I like the idea because it is fairly inexpensive and i can install it myself with easyto source materials. But Im not sure the static pressure will be low enough.

 

[Sumboodie]

I have an 800 cfm vent fan (like from growing weed) that I need to install for the garage.

It'll work like a bathroom fart fan. Have a dampered intake that'll draw outside air when there's a negative pressure.

Sure it'll mean heating a but more, but still cheaper than having the doors open to clear the smoke or fumes.