When accounting for sensible heat in outside air, Carrier shows the following formula: OASH = 1.08*cfm*(Toa - Trm). Where OASH = outside air sensible heat, Toa = outdoor air temp, and Trm = room (conditioned space) temp.
But, why isn't it: OASH = 1.08*cfm*(Toa-Tsa)? Where Tsa = supply air...
An EE (whose speciality is communications, not power) asked me if I knew why all residential generators have a rating of about 14 hrs. He thought this meant it should not be operated for more than 14 hrs non-stop. My brother-in-law (civil eng.) says operation is limited by the fuel tank...
The front door is ALL glass? ...Must be some thick-butt kicking glass! (You've never been robbed?) Maybe you should just swap-out the door for a more conventional exterior, security door! - CuriouslyGeorge
Circa 2001, I worked for a mid-sized engineering firm in Baltimore that did some big HVAC jobs. The rule of thumb was to avoid odd dimensions. Do you think it was an old stigma that failed to die? Was it once a problem getting odd sized rectangular duct?
As I understand it, rectangular duct is commonly stocked and/or fabricated in even dimensions. Therefore, when sizing ducts, select only even dimensions for wxd. Is this correct? Do you avoid odd dim's, even if you have to go up to the next equivalent duct diameter to find even dim's on your...
Thanks, CME...your info is a great help. To all, sorry for ranting, but people quicky forget where they came from when they were cutting their teeth. In my case, it's more like cutting my throat! - C.George
You all must work in the real world where you have access to all these references. I have squat, but I am expected to perform. My neck is on the line, and I've spent the past 18 months out of work. How you would feel in my shoes? I hope you guys sleep well at night because I sure don't. You...
Is anyone familiar with G-90 ducting? It is a (special?) material used for outdoor ducts designed to withstand the elements. Also,I believe it has extra-thick walls for strength and/or to better guard against leakage.
I need pricing information (materials, labor, O&P) to install rectangular...
Hmm...wasn't thinking about the long-term costs. Also, in this case, I should mention this is rectangular, galvanized ducting...if that factors into your thinking.
Am I correct if I conclude that sizing a duct based on rec'd maximum velocities (V) will lead me to accepting greater total dP; hence, needing a more robust fan in my AHU. As opposed to minimizing total dP even if my ducts become slightly larger than the velocity sizing method would pick?
And...
I require 525 cfm OA to mix with 2350 cfm RA before entering the AHU. I assume I need a plenum to make this possible where the OA is coming in perpendicular to the RA. Should the OA and RA ducts meet in the same plane, or is it best to let one enter the plenum first and then the other lower...
CountOlaf, you said "I third 62hog. Those pd's are my usual starting points, then I realize that duct is going to be way too big, and I start increasing allowable pd and adding motor hp to compensate!"
...Doesn't that lead into noise control issues?
CuriouslyGeorge
I forget...what is the rec'd minimum tolerance to leave when cutting a branch duct into a main? Assume cutting a rectangular duct into a rectangular duct. Hmm, what about a small circular duct cut into a duct of larger diameter?
I believe you must maintain a 2" minimum tolerance correct? If...
Besides not looking pretty, is there any code issues (or other concerns) which come to mind when running a duct along the outside of a building? From the ground to a 2nd floor? I know this is atypical, and code varies state to state, but I'm doing atypical HVAC applications...
Does this set...
Thanks everyone for their replies. Quark has the right idea for a preliminary design which is where I am. While I was taught good HVAC practice via a Carrier course, in reality, on the job short-cuts are taken to rough out some numbers (for an existing system with poor documentation on the...
Everyone states (in a nasal tone) "An A/C unit is sized to drop the temp by 20 degrees". But, is that RA - SA = 20? Because in all the examples in HVAC books, Tmix - Tapparatus is greater than a delta of 20 degrees.(Persoanlly, I thought it was a delta of 20 dgrs across the evaporative...
I was taught to think of losses in terms of equivalent lengths. But, the ASHRAE Fundamentals handbook prefers to use C (coefficient) values for losses in fittings. Their method is so involved for applications where ballpark figures can do.
Is there an easy conversion between C values and...
