Air Exchanger for Woodshop

[John]

I was thinking of putting an air exchanger in the woodshop to allow me to paint in the colder months. I'm wondering if anyone has any experience or recommendations that they'd like to share.

John

[LdB]

I have one in my house. I would not have another house without one. That said, these are heat recovery units. They were very expensive and I assume they still are. It will take many hours of operation for the unit to earn it's keep. That will happen in a house, but in a workshop probably not. You will have to put in a good air filter in front of the exchanger or it will clog up. Factor that cost in as well. You would probably be better off with a simple exhaust fan.

LdB

[Puckdropper]

LdB wrote in news:l6adnWMOXtfrXunTnZ2dnUVZ [e-mail]:

I've got a Jet air filter (not an air exchanger). One thing I've noticed is the filter tends to get dirty really quickly. If you have anything that does air filtering, make sure you get washable filters or you'll spend a fortune on disposable.

I haven't tried it yet, but there's an adjustable charcoal filter available that should absorb odors. It might be good for finishing work in the shop.

Puckdropper

[Eric]

I was thinking of putting an air exchanger in the woodshop to allow me to paint in the colder months. I'm wondering if anyone has any experience or recommendations that they'd like to share.

John

================

HRV units would be plugged up severely in a few minutes of woodshop usage. The cores would be too expensive to replace on a regular basis.

Wood dust may need to be vented but painting vapors without overspray may work. Good prefiltering to ensure this would be a necessity.

I understand HRV units are commonly used in new home construction in Canada. Not so common in the USA where our energy consciousness is not as predominate.

[LdB]

Modern construction practices make the air to air heat exchangers necessary. HVAC (heating, ventilation, and air conditioning).

More so for health reasons rather than heat recovery. A properly built house is almost airtight. That's great for heating or air conditioning bills but not for the occupants. Radon along with a multitude of chemicals out gassing from the building contents will build up to high levels very rapidly. They just have no way to escape the house. Even carbon dioxide from breathing will build up if there are enough people in the house at any time.

I built my house and can honestly say that the amount of air infiltration through the walls and windows is so close to zero that it is insignificant. If it wasn't for the doors opening occasionally it would be like living inside a balloon.

By the way there is a big difference in heating costs between new and old construction. My old 900 sq ft 1950's style bungalow cost about

30% more a year to to heat than does the new 1800 sq ft house. That considering the new house has over three time the window area than the old house had is quite impressive.

My air exchanger runs whenever the house is closed up. Winter heating and on the summer days when the A/C is running.

If you live in a well sealed house anywhere you should be doing some sort of air exchanging all the time. A few open windows is usually good enough but few of us live in an ideal climate where we at not either heating or cooling our homes for days on end.

LdB

[John]

Yeah, I'm looking to be able to paint in the winter in those -30C days... Opening a window isn't an option. I also want to prevent the paint fumes from getting outside of the woodshop by using negative pressure (most air exchangers allow you to put the return air vent in a different room that the exhaust). I could do this via a simple exhaust fan, and absorb the extra heating costs. This house is 25 years old, and not completely air tight, so it would likely work.

John

[Eric]

Yeah, I'm looking to be able to paint in the winter in those -30C days... Opening a window isn't an option. I also want to prevent the paint fumes from getting outside of the woodshop by using negative pressure (most air exchangers allow you to put the return air vent in a different room that the exhaust). I could do this via a simple exhaust fan, and absorb the extra heating costs. This house is 25 years old, and not completely air tight, so it would likely work.

John

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Heat exchangers typically perform by large exchange surface areas and small spacing between. Any overspray in the fumes of paint or other coating type substances will coat these surfaces with same and block up the heat exchange membranes very quickly.

You will require some special commercial HRV / ERV unit to perform this function. A residential unit will be clogged in a few spray painting operations and quite possibly be an expensive write off. Brush painting should work OK and should not plug up the air system.

A warm room with some good "heat inertia" and an exhaust fan, and fresh air intake, for short durations of spray painting may work best. After the initial fumes are removed an HRV unit may work fine for keeping gasses to lower levels and conserving heat energy during the paint hardening phase.

[whit3rd]

By the time paint moves a few yards, it's semisolid (dust), and a standard disposable house-ventilation filter will likely collect it fine. If it's liquid, it'll certainly stick to a filter. So, a stack of filters, and a little excess power to the ventilation fan, should do the trick. When the filters get clogged (you can use a colored-water-in-glass manometer to detect this) just change 'em out. Such porous filters won't catch all the fine wood dust, though.

[Eric]

By the time paint moves a few yards, it's semisolid (dust), and a standard disposable house-ventilation filter will likely collect it fine. If it's liquid, it'll certainly stick to a filter. So, a stack of filters, and a little excess power to the ventilation fan, should do the trick. When the filters get clogged (you can use a colored-water-in-glass manometer to detect this) just change 'em out. Such porous filters won't catch all the fine wood dust, though.

===

All that may help for occasional jobs but it doesn't in the paint shop exhaust fan systems. Most of them have to scrape the vents and fans blades out every year or two. I have never seen a heat exchanger used in an industrial or commercial setting. I don't think it can be made to work without huge maintenance. Perhaps somebody has experience in a paint shop can comment??

If you use a paint that is dry enough to not stick to anything that fast you will not need an exhaust then either. It should just fall to the floor. (sarc)

[whit3rd]

What 'fast' are we talking about? I'd do spraying in still air, and afterward (minutes) turn on the airflow. Someplace-away-from-wind is the prime requirement for a good spray environment, IMO.

[kaylward]

Hi John, I was considering just such a unit for my Laser Engraver, as it produces some pretty nasty exhaust gases when working on certain materials. It was going to double for exchange of air in my wood-shop as well. After talking to a few engineer friends, and shopping around for the needed blowers, filters, Frame materials and fabrication, sheet materials and fabrication, insulation and hardware I arrived at the conclusion that it was best to do one of two things . . .

1) Bite the financial bullet, and pay the cost of a well designed commercial unit. Expect it to cost about $5,000 to $10,000 depending on the size of your shop, and add on the additional expense of pre-filter devices and media. Don't expect it to deliver any type of super efficiency either. The best units available don't exceed 75 - 80 percent efficiency. There will still be substantial thermal loss when you factor in the relatively small quantity of air to be exchanged in your type of application. This makes sense when you are working with the potential losses in a commercial environment, working constantly for a large space over 8 hours a day, but the overall cost benefit would take years to recover in a small shop, especially for infrequent use. The unit would likely rust out and need costly replacement long before you reach the break even mark. 2) Design and build my own unit which ended up consuming a considerable amount of space to reach the efficiency threshold that would make it cost effective. I considered this to be above 85% efficient. It takes a long exposure time to the opposing air flow (read long passage) and slow movement ( huge cross sectional area by creating a tall narrow cross section) to accomplish. This type of design results in quite good efficiency, at a cost that was very close to or exceeds that of a commercial unit, but requires a large amount of space consumption. And don't forget that you need to bleed off the condensate, and also keep the entire air path clear and clean of mold, mildew and funguses too. Quite a job when you consider how large the chambers will be on an effective unit. Both of these options led me to one final result . . . It turns out that it is actually cheaper and easier to just exhaust the gases to the outside, placing properly sized vents on an upper floor, (preventing instant chilling of the work area), and simply absorb the expense of the additional utilities utilized by blowing the contents of the houses warm air out the blower. If you resign yourself to this type application, you just learn to shut the heat off for a short time while you do your work, and plan it carefully so you don't have to chill the house for too long. It really isn't any worse than having young kids running in and out of the house on a busy day. But it does work best if you plan your work for times when the rest of the family is out doing other things. You will get to do your work, they will get the benefit of breathing in a freshly ventilated house, and nobody is going to be too uncomfortable for too long. Plus we don't have to worry about legionaire disease, and other such negative health effects from accidental neglect of maintenance. The list of dangerous pathogens that thrive in these units (all of them) is extensive! We prefer to just put up with some cold air in the house on occasion, and so far it is working for us. If you decide you want to build your own exchanger, I may be able to share what I learned in greater detail, and you can make your own decision. The design my buddies and I came up with exceeds the efficiency of commercially available units, but it isn't going to be 100% efficient, or even close. Nor is it going to be inexpensive to build either. You can expect to commit some serious time to building it and maintenance is hard and time consuming. Either way, an efficient unit is going to be a large item in your shop/house. The air has to be filtered in both the exhaust AND the intake. And even then the unit will need to be kept very clean in order to maintain efficiency and health standards. That is the main advantage of the commercial unit... most of the research has been done ahead of time by professionals. They don't want to get sued by not telling you about the pitfalls ahead of time. As for the little household units . . . Don't waste your time! They will neither serve the function you require, nor provide the level of efficiency required for the volume of air you will need to move. Bottom line . . . Go big, expensive and effective and safe, or just plan on saving some serious time, money and aggravation by making due with a few chilly Saturday mornings when the family is out and busy elsewhere. I hope this bit of insight helps you. This is not a simple installation when you add in the substantial requirements of woodworking/paint/finishing/smoke etc.. Do a LOT of homework, and ask lots of questions of QUALIFIED professionals before you jump in to this project . . . it may just save you and your families lives.