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...
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...
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...
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...
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...
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...
Are there general guidelines for what pressure drop is acceptable in a return duct (for commercial use) and isn't there also a dB related to this?
Bonus: Has anyone found a link to an online ductulator?
Thanks,
Curiously George
I am working with sketchy details of an area I'll never get to visit. Even worse, I can't contact the one who surveyed the area because of budget cuts. Anyway, I have a room with a Liebert which has supply ducts shown coming off it. The supply feeds the immediate room and remote areas.
As...
What can you tell me about the practical meaning behind the numerical results from a blower door test??? For example, I have 1000 ft^2 area I wish to pressurize to a desired value of "x" iwg. The blower door test says I need 500 cfm to achieve "x" iwg. (I assume, a low cfm result means the...
This may be a stupid question, but it bugs me: Are return ducts ALWAYS under negative pressure? I must have been taught some simplistic thinking that air moving towards the fan is negative; hence, it is under negative pressure. And yet, trying to picture a return duct under positive pressure...
In the room I am evaluating for various HVAC needs, I have two Lieberts in a computer room with a raised floor. I need to confirm my thinking that Lieberts typically are used to provide supplemental cooling to the area, but the air itself is supplied/refreshed from some main AHU, correct...
