Arkansas HVACR NewsMagazine September 2023

HVACR NewsMagazine September 2023

Tech News

Does Your Kitchen

Exhaust Suck? https://hvacrschool.com/does-your-kitchen-exhaust-suck/ Article by Adam Mufich Have you ever been tasked with installing the exhaust duct for a kitchen hood? I have, and when doing so, I wondered how to size the duct run correctly. Since I had a basic understanding of how airflow works, I knew that there had to be a limit on the resistance the fan can handle; more fittings added to the duct and longer runs equated to reduced airflow. Residential duct design is performed by using a process called Manual D . I considered trying to calculate a friction rate for an exhaust fan by using the given equivalent lengths in ACCA’s Manual D. How ever, I reconsidered since I knew that supply ELs in Manual D are based on an arbitrary 900 FPM. I decided to use my “phone -a- friend” option, and this time, I called my friend and mentor, Tony Amadilo. Tony is an engineer and owner of P.E. Load Calcs . My first question to Tony was, “Should I use the velocity correction for the equivalent lengths since it will be running at velocities much faster than 900 feet per minu te?” He said, “It's time I show you how to do your first commercial pressure drop calculation.” Man, I felt like Luke Skywalker getting ready to learn some Jedi mind tricks from Master Yoda himself. After learning this process, my mind was blown, and I figure there has to be someone else out there with the same struggle. The steps are pretty simple, really. All you will need is a good Ductulator, a copy of ACCA’s Manual Q , and the blower curve for the fan you want to install.

STEP 1: First, we must look at the fan's spec sheet and reference the maximum design CFM and the corresponding static pressure. In this case, we are using model CP55IQ, which is rated for 600 CFM @0.1” W.C.