58/Plumbing Engineer February 2020

I

m a solar engineer - not a mechanical one. That's one reason that I found out the hard way that designing domestic hot water (DHW) production and distribution systems for multifamily buildings is a lot harder than design- ing a single-family residential system. Here are two main reasons: 1. Renters expect hot water on-demand - no interruption 2. Renters expect a good shower experience - no excuses How do I know? Last year, I designed from scratch and guided the installation of a hybrid solar/heat pump DHW production system married to a hybridized 3/8" cross-linked polyethylene pipe (PEX) home run distribution system at Solara. Solara is an upscale all-electric netzero multifamily 24-apartment four-building (soon to total 11 buildings) com- plex near Schenectady, NY. While this was an arduous experience, these systems have been working well. I reaped many realizations and got the chance to work closely with the inimitable Gary Klein (Mr. Tiny Twig) - what's not to like? Well, we had issues. Read on. We decided that our Solara experiences have been unique enough to justify a series of articles in Plumbing Engineer about the design, specification and operational factors that are critical to a successful and cost effective netzero cold climate multifamily hot water system. This article sets the stage for articles to follow. Background Before Solara, I had been a solar thermal guy for a decade or so - designing and installing dozens of custom com- mercial and single-family residential solar hot water (SHW) systems, wrote a textbook, taught courses - I kinda did it all. When I got a chance to design and install the SHW sys- tems at the new Netzero Village complex (26, six-apartment duplexes) near Schenectady, NY, I was delighted. While working alongside the plumbing crew one day, I suggested that instead of the default " to 1/2" PEX DWH trunk/ branch/twig distribution systems, they consider home runs from the utility room and the use of 3/8" PEX tubing - just like Gary had been preaching about for years. (Twigs are the last mile" of tubing to fixtures in a distribution system.) The GC's interest was piqued and asked for some pressure loss and delivery time calculations. I obliged him and my home run and 3/8" PEX design was adopted - just like that. The shower twig remained " PEX to be on the safe side. We all knew that 3/8" tubing and the reducers at the valve and manifold for each apartment could add pressure loss and we knew that a good shower was king. None of us wanted any surprises there. I went back to finishing my solar systems. The home run/3/8" tubing design was a big success and that's how I started an unlikely mini-career in hot water plumbing design. The Solara Development Arises and Our Shower Surprise! Months passed and my solar client itched to build a more plush development. He finally procured funding and some land for another second netzero development. This one had 24 apartments per building, instead of six, and was just down the road from netZero Village. Would you design the hot water distribution and produc- tion system for us," he asked. Sure," I said. I was thinking, "How hard can it be to design a multifam- ily hot water system? Just scale up that netZero Village sys- tem and add a small trunk and recirculation line." What ensued was not a simple exercise at all! Rather, there were days of number-crunching. There were weeks of pres- sure drop and delivery time calculations, bench testing, and multiple design iterations and refinements. Turns out what seemed simple was not. The plumber voiced concerns about how different the

Netzero multifamily hot water production and distribution

The leading edge of plumbing optimization.

By Pete Skinner P.E., Gary Klein

DHW supply for 24 apts

FLOOR 1 Non Pressurized SOLAR HEAT VAULT (1200 g)

Back up electric DHW tank pair (218 gallons) CWS 40-50 psig

3/4" CSST CWS preheat coils 6 @ 100' long.

d

Two arrays of 7 flat 4x10 foot Sunearth panels @ 42 deg. tilt

Solara Solar Hot Water Mass Storage Drainback

SHW-DHW Design

24 Apartments Rotterdam, NY Dave Bruns - Developer 12-2019 P. Skinner P.E.

(simplified - some details not shown) Line set to follow chase east of elevator

Electric element & A-W P solar backup heat.

Grundfos stacked pumps.

Solar Line Set

1 1/4" M copper 1" wall FG insul or equiv.

Solar roof piping

1" M copper w/UV protected 1" wall Differential Controller with second pump timer relay Enhanced sensor set to prevent accidental cold night operation.

Solara hybrid SHW/DHW/HP system schematic