Mini split for a dusty workshop?
MKCF
| Posted in General Questions on
I’ve been heating my workshop with a propane space heater because I happened to have several of these on hand, and also several large propane tanks.
I am thinking of using a heat pump in my workshop, but my shop is very dusty. I make concrete furniture and dangerous silica dust is always blowing around in there. Sometimes I have to grind concrete, and I do have a huge fan to clear the air, but while I am grinding it can get very dusty indeed. I have heard that if the filter on minisplit indoor units gets clogged it is very bad and you should never let that happen.
Any suggestions?
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Replies
I would suggest using a ducted type unit with a large MERV 13+ filter on it. This will get you a lot more surface area to work with. Depending on the unit and it’s CFM, something like a 20”x30” 2” or 4” pleated filter or an Aprilaire type unit.
You can instal a differential pressure gage to tell you when you need to change the filter as well.
I don’t know all the requirements, but there are certainly OSHA requirements if you have anyone working for you. You seem somewhat aware that there are requirements.
For work like this, I like to have clean and dirty zones of the shop. This way much of your tools and storage does’t get covered in dust. If you put your filtered return in the dirty room and most of your supply in the clean side, you can create a negatively pressurized dirty spacey I better contain dust. There is a lot more to this, but something to think about.
How do you deal with the dust?
It seems to me there are 2 possibilities. One is to keep the air in the shop and filter out the dust. The other strategy is to the open the doors and windows and blow the dust out of the shop. The colder it is where you are the better filtering looks.
If you are going to filter look for a cyclone type that spins the air the mass of the dust makes it hit the wall and fall out of the air. Something like this will get 90% of the silica.
https://www.oneida-air.com/dust-collectors/5hp-dust-gorilla-pro-smart-boost-dust-collector
If you are going to vent look for a radiant heating tubes that heat the objects in the shop and not so much the air so you blow out the dusty air and keep some heat.
https://www.gordosales.com/product/sir35-15/?gclid=Cj0KCQiAl5zwBRCTARIsAIrukdNO2l7aH8lhAm5gT0pASIE5zXkZZ6NhzZOLPWXIvGkacndmMeCBhwoaAtAjEALw_wcB
Walta
I had one installer say he didn't recommend Mini-splits in workshops due to the dust. This was even after seeing a cyclone dust collector in the room. I'm also wondering how big an issue this really is.
In your case, if you aren't collecting dust, I can imagine it certainly is a problem.
I was surprised to hear, though, that even with collection there might be a problem. It could be the installer didn't have a good sense for how well the cyclone works, or thought there was enough ambient dust from general operations to cause problems?
In my case, things have never seemed that dusty, but there are the occasional operations that kick up something the collector isn't mated to, so I'm not sure what to make of it.
wear a mask. If your grinding, i would use something like Hilti offers. A hepa "shopvac" that attaches directly to a shroud installed on a grinder. Near 100 % collection. $1000-$1800
Maybe you need to create a plastic sheeting tent area- to contain the worst dust while working. There are also room air scrubbers, that collect stray particles made by a few brands that are designed to run 24/7 for this type of dust.
blowing the dust around with compressed air just seems like a waste of time.
MKCF,
You really, really need to focus on the dust you are creating first and foremost. The rates of major disability from lung issues is a serious issue in the stone and synthetic counter top industry. Just google that topic for further info. The filter on your mini is the last concern.
Depending on the sizes and manageability of what you make, is there any way you can create the equivalent of a sandblasting box? I realize it makes things awkward to handle tools precisely while reaching through a wall, but a "dust room" where you wear a mask and grind in the open will still leave you exposed to very dangerous particles each time you stop and unmask. The air will be filled with the smallest and most dangerous particles. Plus the dust is all over you to be carried and dispensed into the clean shop area.
If you can enclose the grinding process to a small volume, then filtering out the danger will be cheaper and faster. Changing filter media frequently will be necessary due to the high percentage of very small particles. I am not sure that cyclonic extraction will work as well with super fine dust as it does with wood processing output. Oneida would definitely be a good resource to find out though. Or figure out a way to wet grind only.
I have four HEPA rated vacs and while I trust the hood on my angle grinder for very specific tasks, I wear a mask as well and wet wipe everything in the enclosed area I create. Please don't cripple your lungs, it won't take long if you aren't careful.
I certainly hope he is wearing a mask! Industry standard seems to be wet grinding. Many shops have banned all dry grinding. The good shops also run continuous PM monitoring. There are some reasonably priced PM monitors available now. You can also get a used one off eBay.
Coincidently, I have a few Flex brand wet grinders I am selling. Let me know if you are interested.
Does anyone run a mini-split in a shop?
Even with best efforts to collect dust, is it a problem with mini-splits given that dust levels may be, at times, higher than the average living room?
Tyler,
I asked a friend about his experience with them:
"Finished all the interior cabinets, etc after installing mini-split in son's ADU. Needed to clean filter screens everyday. About a month of interior work before finished (26 ft bookcase, wood floors, window casements, etc. At end of it all blew the indoor unit out with compressed air - there was a LOT of dust in the heat exchanger. A shop mini-split would probably need to be blown out with compressed air at least every month and daily screen cleaning."
Doesn't sound like mini splits are good for workshops.
Too bad!
So then, how should we heat our shops?
My best guess is to use a radiant slab, and a Marathon water heater (powered by solar panels, of course), or an air-t0-water heat pump like the Sanden? The problem here being that many of us have pre-existing slabs. Also, shops need high ceilings- the advantages are too numerous to list. So maybe a radiant wall?
The common way I've seen (if you have the height) is radiant tube heaters (gas, propane or oil). They are great if you don't want to keep the shop up to temperature all the time, you feel the heat as soon as they turn on.
The ducted option with large filter is a reasonable option for a shop you want to heat continuously. The duct can you usually be dead simple, like return filter and a single supply grill.
“Doesn't sound like mini splits are good for workshops.”
I need to disagree slightly with your statement. I would agree if you said “Doesn't sound like mini splits are good my workshop”
The way most of us read your description of your shop left us concerned for your life and safety. Your hobby sounds much messier than the normal wood shop.
I agree with Matt F that wet cutting and grinding is the best practice.
All the electric heating options will have very similar operating costs. Electric baseboard heaters will cost the same to operate as a slab and water heater at a much lower installed cost. If the usages is intermittent a water heater would likely take 12 hours to bring the shop from 50 to 70 a big heater with a fan could do it in a minutes.
Walt
Good dust collection is critical. Both for health and for HVAC.
In my experience heat is best done with in-floor hydronic. IR is great from a quick to heat standpoint but it's really difficult to avoid hot, like really hot, spots. IR can also cause problems for wood expansion/contraction that can make some things difficult. I'd guess that's not an issue for concrete? A heat pump cooling system or electric heat can help to heat an area faster if that's an issue for you with hydronic.
Cooling, as far as I know, requires air movement and so dust becomes a problem. Overwhelmingly the best thing is to remove the dust before it gets near the HVAC filter. Multiple mini-split cassettes have an advantage of keeping dust localized vs a central system that spreads dust all over. Either way you'll need to clean the filters frequently. A differential pressure switch is beneficial to let you know when they need to be cleaned.
Various ways of passively reducing heat can be helpful. Great insulation and air sealing is obvious. Awnings over windows, shade trees, painting the structure white and other things can help. Solar panels on the roof might help as well. A big exhaust fan (5k-10k CFM) + open windows is a good option if temps are below about 90°f and humidity isn't too high. This latter can also be used to reduce the initial heat load before turning on the AC.
My new shop is in-floor hydronic for heat. I'll likely keep it about 45-50°f when not occupied. I've a 240v/80a portable heater that I can plug in when necessary to quickly heat things up but it's expensive to run so won't use it often. For cooling I'm initially planning to rely on a 7500 CFM variable speed exhaust fan and open windows. I'm pre plumbing/wiring for 4 mini-split heads in case I need them but hope to be able to forego that expense.
I'm going w/ an Oneida 5HP gorilla DC (https://www.oneida-air.com/dust-collectors/5hp-dust-gorilla-pro-smart-boost-dust-collector) that will be located in a closet. When weather is good I'll exhaust it outside and open windows on the south side of the shop for MUA. Otherwise it will send return air from the closet to the shop via ducts on the south side. Most woodworking is either in the middle or along the north side so my hope is that air flow will generally be from south to north and help contain dust.
This another good option to consider for dust collection. Clear vue is usually a better value than Oneida. Great for woodworking.
https://www.clearvuecyclones.com/cyclone-bundles/67-cvmax-1p-cyclone-bundle-with-filters.html
For stone and concrete though, the goal should be to make no dust from cutting and grinding in the first place by performing wet operations.
No dust collection system catches everything, and you'll find push brooms in even the best shops to sweep the stuff off the floor as it does accumulate.
Concrete dust is a different beast than wood dust (trust me, I'm familiar with both). In my experience, it settles much faster out of the air, although there may be fines which do not. They are too fine for me to notice but they are exactly the kind of thing that clog air filters (and cause silicosis in human lungs). I wear an excellent respirator when I grind, and as I mentioned, I also draw air through my shop using a 3' shop fan and an open garage door. Based on my observation of the dust I'd say I get one air change per minute. Unfortunately my process is not simple enough to simply use wet grinding equipment... if you see my work you'll understand why: http://www.foggfauxbois.com
Because of the weight of the dust particles, many of them still end up on various surfaces, tools, etc. I think the partition idea is a good one and I may rethink the layout of my shop. I'm always rethinking things but unfortunately I have very limited time to play around with it- I will get there eventually.
I'm not sure why one would put the intake side of an air handler in the dusty side of a partition? I would think the reverse would be better (filter on the clean side, supply in the dusty side).
My Modine works extremely well as a shop heater- it's unaffected by the dust as it seems to be more or less self-cleaning (I blow it out once a year with compressed air). However Propane is a fossil fuel. I can depreciate the purchase of some fancy solar panels since I am a small business, so it is a good time to think about greener systems.