HVAC questions for a workshop

Discussion in 'The DIY corner' started by myst173, Jun 2, 2020.

  1. myst173

    myst173 Active Member

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    Hey guys, I could use a little help here. Fair warning it's a long post so unless you're interested in HVAC you might want to skip the thread.

    I'm finally getting to build a workshop, took a couple years of restraining the gun monkey to save up the cash and I'm ready to build. I'm ordering a 40x60x18 ft steel building, r-19 in the ceiling of the shop, r-16 in the walls, with heavy insulated doors. Inside the shop I'm building out an office area of about 400 sq ft, I'll insulate that as well so I can heat/cool the office with a small split unit to different temps than the shop floor.

    I'm planning on a smart thermostat controlling the split unit in the office space, that's easy to figure out sizing, ability to learn when I'm in the office and start adjusting temp to save $ on the heating/cooling bill, etc.

    For the larger shop workspace I'd like to go as energy efficient as I can so I want to install a set of powered louvers for intake, an exhaust fan with louver and either a single large split, or maybe 2 smaller splits for heat/ac. Something along the lines of this is what I have in mind right now for the hvac unit.
    https://www.heatandcool.com/60-000-...d-split-air-conditioner-heat-pump-system.html

    What I want to do is wire everything up to a smart enough controller that it can do the following take the temp inside the building and the temp outside the building and be smart enough to run some basic logic like:

    1) If outside temp is 60, the inside temp is 50 and the desired temp is 55 then open the louvers and run the fan till the inside temp = 55. It's warmer outside then the setpoint I have for inside so bring outside air in
    2) If outside temp is 40, the inside temp is 50 and the desired temp is 55 then run the heat pump. It's colder outside than my setpoint so heat up the air in the shop.
    3) If outside temp is 60, the inside temp is 80 and the desired temp is 70 then open the louvers and run the fan till the inside temp = 70. It's cooler outside than inside so bring in outside air till it cools down to my setpoint.
    4) If outside temp is 90, the inside temp is 80 and the desired temp is 75 then run the ac till it gets to be 75 in the building. It's too hot to cool down by bringing outside air in, so cool the inside air.
    5) Have a manual bypass mode where I can override the automatic settings and turn on the fans, run the ac, run the heater, etc as I want (and if this can be on a timer where I don't leave the AC run down to 60 in the middle of the summer for a week when I forget to change it back it would be even better!).

    With our weather here over 1/2 the year time wise I really wont need the system to do anything but cycle on/off the fan and louvers to keep comfortable temps in the shop so there's a lot of cost savings in not running traditional HVAC 24x7. I know it's not 100% ideal humidity wise but it's way better than what most people do in just running heat/air when they're in the shop and letting it sweat and condense inside the rest of the time. I can always add in a dehumidifier into the mix if I see it's needed.

    Anyone tackled this before, seen a controller that can do that, etc?
    Thanks
     
  2. JimP42

    JimP42 Mostly harmless Benefactor Charter Life Member

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    Bringing hot humid SC (or NC) air into a cool shop fool of iron and steel that can rust when the water condenses on it? There is no dehumidifier that can keep up with blowing outside air in like that.

    A heat pump is pretty efficient at both dehumidifying and at moving heat back and forth, especially if you are trying to move it the way it wants to go (from hot to cold).
    I would not even consider doing what you describe to my tools. It might save a little money, but if you insulate that well, not much. The pain of keeping things clean and trying to fight off the rust would be far more of a cost than a little more HVAC per month. Your tools would be better off in an un-conditioned building than with a system like that.

    Just get a good thermostat you can program and set it to stay at least 50 and no more than 82 or something like that. That will cost very little when you aren't using it. Then just bump it to what you think is comfortable when you go out there. Some you can control over wifi or the internet and so you could bump it up from the house 30 min ahead of time.
     
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  3. Scsmith42

    Scsmith42 Member Benefactor Charter Life Member Supporting Member

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    I cool a 5,300 sq ft shop with a single 2.5 ton air conditioner. It will keep it in the low 70’s all summer long.

    My secret? LOTS of insulation. 36” of loose fill in the attics and 14” in the walls. Plus the slab is insulated.

    One of the best insulation methods is a hybrid. In a 2x6 wall have 1” of closed cell spray foam put against the outer sheathing, and a 3-1/2” batt against the inner wall. That will leave a 1” air gap between the two for a thermal break.

    If you can afford it, increase to a 2x8 wall stud and a 5-1/2” fiberglass batt. Put as much in the attic as you can.
     
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  4. Mirac

    Mirac Epic Replies ---> Charter Member Supporting Member

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    There are controllers that can do that. It's called economizing. Mostly in the commercial settings with BAS ( building automation systems) . Would cost more in equipment than you would save in 10 yrs of extra electricity.
    Do as Scott says and insulate heavily.
     
  5. noway2

    noway2 Senior Member Charter Life Member

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    Agree with all the above. What you’re wanting is called economizer mode. It’s common in big air handlers but those are also typically served by steam (or hot water) and chilled water coils to help control humidity. Humidity is a problem in that if your building is cool and your bring in hot air you will get condensation which means mold and rust. This is why (chilled water) pipes get insulated; it puts the condensation point into the insulation where there is no water and hence no condensation.

    An air intake with an exhaust system might work for part of the year here, but you’ll still need mechanical heating and cooling, for which a heat pump is probably your most efficient option.

    As far as controls go, yes this is typical BAS stuff, but you could also do it yourself with a small PLC or probably even do it with a raspberry pi.
     
  6. GoWolfpack

    GoWolfpack Member Benefactor Charter Life Member

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    Yeah, don't do what you're thinking. In order to keep a handle on humidity and corrosion you need your shop sealed up tight.
     
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  7. BlackGun

    BlackGun Pimpin Ain’t Easy Supporting Member

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    It’s great you are thinking about ways to save money short and long term. A lot of good ideas mentioned in the original post. As mentioned by others that scenario would be a commercial package unit with an economizer and the appropriate controls and sensors. I do not recommend what you linked to and fans.

    Although the front end cost is higher I suggest the best thermal insulation possible with a tight building seal. Spray foam will do both. Bat insulation as well will give a great insulation factor due to the fluff creating air gap thermal qualities. Insulation board in the concrete and perimeter is necessary to achieve effective thermal factors as mentioned by ScSmith42. Don’t skip that process. It’s required by code on homes and businesses with perimeter as well.

    I am assuming you will have garage doors. How much you open and close those big doors and if this is a daily use building may determine whether you need a heat pump or air condition with a gas furnace. Only you can provide that data. If it’s often go gas with AC. Tell me how many days a week, how many hours per day, and what will happen in that building (woodwork, cars, metalwork, etc..) and we will go from there. I assume this is getting inspected. If not rethink that.
     
  8. Scsmith42

    Scsmith42 Member Benefactor Charter Life Member Supporting Member

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    Speaking of garage doors, the insulated ones from Haas are fantastic. Well worth the cost.
     
  9. Schattenreiter

    Schattenreiter Member Supporting Member

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    Think rust and rethink your plan.
     
  10. myst173

    myst173 Active Member

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    Thanks for all the feedback.
    It may not be feasible to do the ambient air thing, I'm not against going with just a conventional system, just want to be as cost efficient as I can. If I can spend an extra $1,000 up front and save $50 a month from now on, then I'll do it as long as I can swing the total spend. I don't want to spend an extra $10,000 up front to save $20 a month as it'll blow my budget and be decades before it breaks even.

    I'm doing a metal frame/panel building. 40x60 with 18ft of height at the eaves. This pic is an example of what the inside will look like before I build an office space in it.
    [​IMG]

    In this kind of building the insulation is placed over the frame and then the roof and siding panels are fastened down to the frame. I can only get away with so much space between the panel and the frame before it increases the chances of leaks. The insulation I'm ordering with the building is r16 for the walls and r19 for the ceiling. I was planning on adding in a reflective radiant sheet on top of that before securing the panels that should add in some more R value, the sheeting I've looked at says it's R12. I'm getting quotes from 4 different building manufacturers who sell in the area and they all are saying that's the standard higher end insulation for this area. I know there's companies building out in the midwest with R values in the high 40s and low 50s but they frame the building differently and have a double layer of insulation which pretty much doubles the cost of the building itself because of the extra framing and all the additional liner panels.

    I'm planning on building around a 400 sqft office space, part of it will be wood framed, planning on insulating it heavily. It looks like my working from home 95+% of the time is going to become a reality so this will be the heaviest used part of the whole building, I'm planning on making it very comfortable. I'll prob end up putting this on it's own small split system with a Nest or similar thermostat for remote control/power savings. Will have stairs leading up to storage above the office to reclaim some storage space.

    The rest of the building it's primary purpose is metalwork/gunsmithing. I might put a 4 post lift in one corner for working on one of my cars from time to time but that's a nice to have later on and I'm ok with it being a pita to get a car on/off to save room for other stuff. One 12x12 rollup to get equipment/car in and out, waiting on a quote on the door now from a vendor who does solid filled rollups that have an R9 rating on the door itself, plus I'll be sticking one of those magnetic roll up dock sealer curtains behind it that adds in another 5-6 in R value. Building will have a 10 ft overhang that should keep the door in the shade most of the day during summer.

    As far as the ac/heat for the main shopfloor I'd like to go ductless if possible, I definitely want to avoid a big roof mounted unit.

    As far as the question about inspection, yeah, it'll have all permits and have to be to code I'm planning on tying an FFL to the location which means business license, inspections, all that crap. Luckily I live out in the country so no crap about being zoned only for housing, no home owners associations, etc to deal with.
     
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  11. Scsmith42

    Scsmith42 Member Benefactor Charter Life Member Supporting Member

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    I'd forego your plan to put reflective radiant sheet on top of the insulation. The metal roofing panels will block the UV, which is what the radiant sheet does. It works fine under a standard shingle roof, but is useless under metal roof.

    In my shop I used a standard split system and suspended an air handler from the roof about 1/3 of the way from one side. I fabricated an oversize filter box on the inlet side of the air handler. Since the main shop is a woodworking shop there is a lot of dust in the air.

    I also have a fan mounted to the wall in one corner that creates a circular air movement within the shop. This helps to keep the temp consistent all the way around.

    Shop air handler 2.jpg
     
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  12. myst173

    myst173 Active Member

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    That sucks, I was hoping I could do something to get some extra R value with that.
    Neat way you have the condensation line with the pump, had any problems with it?
     
  13. Scsmith42

    Scsmith42 Member Benefactor Charter Life Member Supporting Member

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    Thx. No problems in 10 years (other than having to clean the sawdust out of the pump earlier this year). The drain line has a 60' horizontal run with a slight slope, and then it drops straight down 15' to a drain. Because it is pressurized when the pump runs, I could not install a vent in the line. It's kinda funny; every two to three cycles of the pump it will develop a siphon and pull air through the check valve on the pump. It squalls like a banshee when it does so and can freak out anybody standing underneath it!

    It was a fun installation. I did most of the work myself. The components were supposed to be a good, used takeout. ..

    In order to have clean runs of refrigerant lines, I purchased straight copper tubing from Johnstone Supply and elbow fittings. Brazed it all up and then spent 2 frustrating weeks trying to find a leak. Finally narrowed it down to the A coil; replaced it and things have been great ever since.
     
  14. BlackGun

    BlackGun Pimpin Ain’t Easy Supporting Member

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    I suggest you put in a LP gas with AC given the insulation specs. With 18’ ceilings better to stand the unit up on a return box with multiple filter return grills. Add ducting that keeps the velocity high to create a throw long enough to reach at least 20 feet. Heat pumps are not effective for metal building like yours and absolutely useless in a car mechanic’s garage. Make sure you use turning vanes in the ductwork with limited ducting installed. The floor mount will keep the overhead space clear for anything you add.
     
    Last edited: Jun 6, 2020