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
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