Kris, HVAC related question

Cool! Sounds like you have a pretty interesting job, and one that would most certainly keep you learning and studying all the time.   I am blessed to have fallen into the job I have.... I started here about 10 yrs ago, as a lighting technician, when I was going to school to get my A&P license. It was originally just something to do to pay for school, but I started running permits, and doing basic engineering drawings because there was a need, and have gained experience from there... funny how you never know what things will really fit you until you walk in those shoes for a while. Surely I have a lot to learn, on the job and off....
    One of the reasons I have enjoyed this site is that ski boats fascinate me, and I know so little about them. I'm excited to learn more about these machines, and how they work.... and to hopefully avoid some ownership/maintenance pitfalls along the way. I look forward to getting to know you and the others more as I continue learn and grow in knowledge understanding and someday skill regarding these boats.


Kris

Hey Pete,
   - you didn't loose me, I was being toungue-in-cheek about the ductulator.... we do use them all the time here.    We call a lot of the home guys "trunkers", meaning they pack their station wagon and go, no engineering, no over head, crappy product.   Of course, that's not true of everybody, just a bunch of them

Not familiar with the term "blow pipe", I guessed that the spiral rounds with gate dampers shown were for your dust collection, so looks like I was correct.     You're correct that I wouldn't use basic flex for negative pressure systems,   I was saying that since you spent the money to have a shop make you some quality looking spiral pipe, you probably wouldn't want flex hanging around for your transfer from the utility room . I've read quite a few of your responses here on the site, and wouldn't pin you as someone who would go the cheaper route with something if it wasn't the best solution for long term.

    Hydronic heat is going to be fabulous for your application, if your looking at cooling, a geothermal loop might be your best option, depending on your lake temps, you could do a water heat exchanger....      

My work involves tenant improvements in commercial buildings - design, permits, drawings, and design review etc for buildings we oversee. Our part of the country uses a lot of DX cooling, hydronic loops, and gas heat as our utility rates are so low.

What's your background?   line of work?   I tried to read up on your profile, but just found your diary link instead.... How do you access profiles?

Kris

Glad to hear it :) yeah.... ductulator?   who needs one of those!   didn't figure you'd go for the flex, after checking out the garage thread, your pickup ducts are looking really nice.... seems like you have some connections to do it well.   We do use the flex in our work, but limit it to 7.5', and hang it straight and tight. it's often used in ACT ceilings where me may need to move a couple of tile spaces over the course of the build... its amazing how often an architect will change his design right up till the end :)

Pete,
    good question!   Here are my thoughts.   Typical filter design is in the neighborhood of 300 ft/min, although with your velocity calc, you are not taking into account that there will be a free area restriction with any grille....(sometimes up to 50%). The velocity of air traveling through your filter is going to be more determined by grille size/free area than the filter itself, because of it's proximity to the grille. Say your grille is 75% free, it would push your original design to a nominal 298 fpm thru the filter... the 24/24 would be about 466 fpm.   Your original design would have been more effective, as the filter decreases in efficiency with velocity, but I think that the smaller opening will work also. I would venture a guess that up to about 500 fpm would not be a big deal.   Of course the Delta P across the filter may be final deciding factor on the whether to keep the filter or not, as too great a pressure drop across the transfer opening will force the air to find another route of escape, esentially eliminating the filter anyway.   

I can see three solutions to your dilemma.... first, you could install two filter grilles to get you in the velocity range that you were originally anticipating, or you can go with the 24x24 frame size and purchase an electro-static filter to fit the frame. (The electro-statics are often less pressure drop than a media filter because of their construction.)      Third option I see is to go with the contractor's filter size, and just remove the filter if there is a problem later.   I would guess that you'll see quite a bit of collection on the filter, just because of the sheer volume of air movement stirring up dust in the room, so option 3 would be my least favorite :)

Brady's suggestion above regarding the double elbows is a method that we use also, just make sure if you use this method, that you sound line the elbows :)   some extra flex that has bends in it works also, but the pressure drop is greater.... not many home owners I know have access to a sheetmetal bending shop though, so the flex may be more practical.

btw, i'd love to know the method you're using to find the stress on those bottom trailer bolts...   and the conversion from ft/lbs to psi as that is the measurement that the bolts are rated in

Kris

Pete,
What you are talking about is what we call a transfer, I would'nt worry about filtering it as the cyclone is already discharging though a HEPA filter. I would be concerned about how much noise is carried through the transfer into the shop. We generally use internally insulated elbows, often in pairs, to reduce sound transmission.

Kris,
Thanks for the explanation. Interesting! Yes, there are several "mechanical" areas and it was presumptuous on my part mistaking that.

Now that I know your engineering area, I've got a question! I don't know if you caught that I'm currently having my shop built. It's over in the "show me your garage" thread. Anyway, there's a woodworking dust collection system going in. The actual dust collector is located in a separate utility room and it's rated at about 1400 CFM max. recommended. Being located in the other room, there's a return air duct going in back to the shop area. Even though the collector has it's own HEPA filtration (besides the cyclone) I had thought it would be a good idea to put a filter grill on one side of this return air duct just as a little extra precaution. Now the problem!! To keep the FPM across the filter to a min. I had spec'd out a 30x30 duct. This calculates out to a nominal 224 FPM across the filter. The contractor is having a difficult time getting that 30x30 to fit in the soffit over my workbench cabinets and wants to drop the duct size down to a 24x24 but this bumps the FPM across the filter up to a nominal 350. At this point with that high of a FPM across the filter, I'm wondering if it will actually do any good. Should I just forget about the filter grill?