Duct Sizing Program
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From: Speed on 10 Feb 2006 18:25 I've recently graduated with a BS in Mechanical Engineering. As it turns out, my first job out of school is designing HVAC systems. All of the designers run around with these cardboard "ductilators" that are used for sizing duct based on volume flow rate and either velocity or pressure loss. I apparently have a disability that prevents me from using this apparatus properly, so I've decided to write a program on my calculator (hp49g+) that will do this for me. I've generated the equations using my ductilator (hopefully the right way) One of the equations is exponential, and the other is actually quadratic. So i'm thinking "This is pretty easy, I wonder if anyone has done it already?" And that is my question! Does anyone know of a program for the hp49g/g+ that will size duct work for air conditioning and heating? I'll be writing one if no one responds, but I don't want to do work that someone else has already done. Thanks, --CS
From: Stefano Priore on 10 Feb 2006 19:56 Speed wrote: > I've recently graduated with a BS in Mechanical Engineering. As it > turns out, my first job out of school is designing HVAC systems. > > All of the designers run around with these cardboard "ductilators" that > are used for sizing duct based on volume flow rate and either velocity > or pressure loss. I apparently have a disability that prevents me from > using this apparatus properly, so I've decided to write a program on my > calculator (hp49g+) that will do this for me. > > I've generated the equations using my ductilator (hopefully the right > way) One of the equations is exponential, and the other is actually > quadratic. So i'm thinking "This is pretty easy, I wonder if anyone > has done it already?" > > And that is my question! Does anyone know of a program for the > hp49g/g+ that will size duct work for air conditioning and heating? > I'll be writing one if no one responds, but I don't want to do work > that someone else has already done. > > Thanks, > > --CS Well, if it's just two equations you wouldn't even need a program, the multiple equation solver just fits your case. On www.hpcalc.org there is a nifty program called "MSOLVR Program maker" that automatizes the use of MSOLVR creating a stand-alone program given the equations, the units and so on. BTW I assume that the quadratic equation you mention is deltap/(0.5*rho*V^2)=4*Fanning(x/D,Re)*(x/D)+K to relate geometry of the pipe with pressure loss while the exp one is m*sqrt(R*Ttot)/(A*ptot)=sqrt(gamma)*M*[1+M^2*(gamma-1)/2]^[-(gamma+1)/2*(gamma-1)] to compute m/rho (=Q, volumetric mass flow) MSOLVR shouldn't have problems in solving these, but SOLVESYS is my solver of choice for these kind of problems. -- Stefano Priore | Debian Sarge 3.1r0 --------------------------------+-------------------------------- "Video meliora proboque, | Linux Registered User #210152 autem deteriora sequor..." | Linux Registered Machine #97752
From: Speed on 13 Feb 2006 18:35 > deltap/(0.5*rho*V^2)=4*Fanning(x/D,Re)*(x/D)+K to relate geometry of the > pipe with pressure loss > > while the exp one is > > m*sqrt(R*Ttot)/(A*ptot)=sqrt(gamma)*M*[1+M^2*(gamma-1)/2]^[-(gamma+1)/2*(gamma-1)] > > to compute m/rho (=Q, volumetric mass flow) Actually, I hadn't really even gotten into that level of detail! Thanks for the information, now I have a little better understanding of why things worked out the way they did. What I did was use the ductilator (cheap piece of cardboard) to generate a list of volume flow rates and their corresponding duct sizes. Then I plotted them into excel, and found the trend line that worked the best (for this one I used a log/log plot for instance which gave me a straight line). The research that I did regarding this subject made it look like I needed top solve four non-linear equations. This sounds like a very slow way of getting an answer that only needs to be accurate to the nearest inch. Since I only wanted a not-so-accurate number quickly, I decided to throw physics to the wind, and just get the calculator to generate numbers. Then I can work on getting the calculator to round the numbers to the nearest preferred size (which MES won't do). Thank you very much for your input! --CS
From: bpwalsh on 15 Feb 2006 15:42 Some time ago I wrote a comprehensive set of routines (in a directory) for calculating HVAC duct friction loss, etc. using the DARCY function. The stuff works on both 48GX and 49g+, the latter being much more satisfactory in terms of speed although the 48 version is usable. Round and rectangular sizes are accommodated, as well as different absolute roughness, density, and dynamic viscosity. A companion set of routines accommodate round and flat oval sizes. The programs were presented at last fall's HP handheld users' conference here in Chicago and were published on the CD distributed. Email me for a copy of the paper. bpwalsh(at)speakeasy(dot)net I would very much appreciate any improvements you make. Brian Walsh
From: Speed on 15 Feb 2006 20:10
Thanks, I've already e-mailed you. I'm anxious to see what you've got! Have you thought of submitting it to hpcalc.org? --CS |