New to the Forum, questions about hydronic heating systems
I'm new here and have a lot of questions about hydronic heating systems. Due to some recent retirements I have been pulled outside my comfort zone at work (Vertical Transportation) and put in charge of many heating system renovation projects. Almost all of them involve either a steam or hot water boiler that is being replaced or upgraded. I have some support from a couple Engineers in the office but the good ones are always real busy and it takes them days to get back to me with an answer to even a simple question. Admittedly I'm starting from near zero knowledge and background beyond the oil-fired steam boiler that heats my home, and a class in Psychrometrics I took in community college 15 years ago.....:confused:
I have one project I'm trying to design that was about 2/3 finished when my predecessor retired. We're replacing a large steam boiler with two hot water boilers (Weil McLain 680's) sized at 66% of load running in a lead/lag configuration. The building is an "L" shaped garage with unit heaters out in the bays (replacing with like-in-kind Btu ratings) and some fin tube in miscellaneous office spaces around the boiler room, which is located at the bend in the L.
I've tried calling around to local distributors with questions about a boiler and just get "usually you just tell us which one you want and we get it for you". I called one of the major manufacturers directly and waited half an hour to talk to somebody who frankly didn't seem too interested in helping either.
Here's my question: In trying to size a loop pump for one leg of the "L" I was told to make sure the pump could overcome the pipe friction loss to the furthest unit heater and also the unit itself. I was provided with a B&G System Syzer wheel to run out all the values I'd need and luckily I already had all the pipe sizes laid out, the boilers and the unit heaters selected and I had all the cut sheets and stats right in front of me. The trouble is I thought I was doing something wrong because my figures for total dynamic head were coming out in the 6 to 7 foot range @ 55 GPM, but B&G didn't seem to have a lot of pumps that small, at least not any that looked like the ones in our standard CAD details. In talking with my mentor, he started throwing numbers out like 10 to 12 feet and by the time he was done talking he was up to 20 as a rule of thumb. So I picked out one that fit that curve. If he says so I guess that's okay but I'm a little leery of fudging a critical dimension by a factor of three....
So what gives? I sure as hell don't want my first system to crap out as soon as they turn it on, but this just doesn't feel right and I don't have the experience to back up my gut feeling. I freely admit that I don't understand the exact function of every component in the system or the theory behind it, yet. Any thoughts?