HEALTH AND SANITATION 33
Understanding the reasoning behind Hunter ’ s Curve
By
Christoph Lohr
Misunderstanding Roy — Part 1
After four gruelling years at the Virginia Military Institute , upon graduation as an engineer I decided to follow my own prudent path : I would find the best paying job in an area with the lowest cost of living that afforded me training opportunities . I knew myself well enough that I didn ’ t want to be stuck behind a desk ; I desired interpersonal contact . I always aspired to be not the world ’ s best engineer , but an incredible leader of engineers . As a result , I ended up working for an engineer consulting firm based out of the Midwest that had an in-depth multiyear new engineer training program .
At this particular firm , which hired predominantly mechanical and electrical engineers , the incoming mechanical engineers were developed as generalists who designed both HVAC and plumbing systems for a variety of buildings , including universities , healthcare and laboratories . My first buildings , mostly for higher-education institutions , allowed me to begin honing my craft as I learned how to size ducts , select air-handling units , and design plumbing systems .
It was the latter of these items that at first gave me much consternation . While my engineering classmates were travelling the world working on nuclear reactors , going to prestigious graduate schools , or importantly serving our country as military officers , I was stuck indoors , while practically arctic conditions seemed to last outdoors for months , designing plumbing systems ... for toilets . For a young man who went to college with dreams of flying or designing airplanes , this new reality struck me in the face . Additionally , I had some difficulty making friends in this area . As someone who loved soccer , was an immigrant and read a lot , I seemed to have little in common with people who preferred American football , had little exposure to the world outside of the United States , and preferred to party . In fairness , I probably made life difficult for myself too , as I hadn ’ t fully developed some social awareness and made many “ mistakes ” along the way that further ostracised me . In short , I made a bad decision for myself , compounded the mistake , and was now dealing with the consequences : disliking my work , feeling lonely , and being left uninspired .
I do feel I let my emotions get the better of me at this time and did not put in as much effort as I know I am capable of . However , despite struggling to motivate myself in the challenging conditions , especially as I was engineering “ piping for toilets ,” I came across the concept that no one could truly explain to me : the fixture unit . For HVAC piping systems , I added gallons per minute . For ductwork systems , I added cubic feet per minute . But for plumbing systems ( water or waste ), I added fixture units and used “ Hunter ’ s Curve ” to convert the fixture units to gallons per minute . But the flows were not additive , nor 100 % aligned with the fixture units . What on earth was this fixture unit ?
I asked several of the engineers with whom I was working at the time to explain the concept to me — no one could . Answers I received ranged from “ It was just what was used to size plumbing piping systems ,” to “ That ’ s the way it was done .” “ Besides , you still have to do the ductwork design , which is where the real engineering is .” But my curiosity remained — what exactly was this fixture unit ? It wasn ’ t until years later that I got my answer .
Several years and several thousand miles later , I was working on a hospital bed tower addition project and had used code , as I had the preceding half decade , to size my plumbing system . For this specific hospital , the incoming water was very hard , and in order to keep the plumbing system and equipment efficiencies high , we were going to utilise a water softener system . As I had countless times before , I gave the water softener manufacturer my calculated flow rate . However , unlike previous times the water softener manufacturer told me my number was not only wrong but grossly oversized and asked what I calculated for the existing hospital and the new hospital . I gave them the numbers . The water softener manufacturer told me both numbers were too high .
This was a first , and even though I explained that I had used the code-mandated sizing criteria , the water softener manufacturer wouldn ’ t budge . In fact , to prove they were right , they put an ultrasonic flowmeter on the incoming water service to the building and measured the peak flow rate over two weeks . Sure enough , they found that their number was correct , and my estimation was too high . This
David Viola , IAPMO CEO
In the spirit of the sharing of unique experiences that shape the plumbing industries in our respective nations , the following article looks at the importance of product certification , particularly in the plumbing industry . Written by IAPMO Product Review Engineer Jocelyn Quinonez , it is the next in a regular series of similar articles that will run in this magazine .
February 2023 Volume 28 I Number 12 www . plumbingafrica . co . za