An answer to a question posed by a colleague a few months ago on whether plumbers should be included in the STEM circle sprang alive this morning, when being schooled on the finer workings of a zoned hydronic heating system at home during a repair.
Spoiler alert – this story is coming to you from a physicist STEM-ite who is steeped in a regard for the interdisciplinarity and inclusiveness necessary in solving complex problems.
A natural gas-fired boiler is the secondary heart to a parallel electric boiler zoned hydronic heating system that warms our home in western Minnesota. Hydronic systems cycle hot water via pumps to radiators located throughout the house, heating by radiation coupled with natural convection air currents, versus forced air systems that BLOW the warm air into the rooms. We’ve always advocated for the hydronic systems which do not seem to dry the air as much, and are quieter, any knockings being romanticized by apartments from earlier years while in graduate school. Actually, its the sounded knockings that had been lingering for a couple years that complemented the need for the schoolings.
Hydronic systems are closed systems, in this case the pump circulating water estimated as 25 gallons, with a reservoir tank located above the system which allows separators in the boiler workings to loft any air that accumulates in the system, whether from summer condensations in a dormant system, or from an injection of turbulent water that might be coupled to an inlet that allows the user to top off the water level.
Water levels (volume), temperature, and system pressure are coupled in a closed hydronic system, a relationship we teach our students for ideal gases in introductory science courses. It should be well known that when materials are heated they expand, whether water, steel/iron, or copper, water being the most expansive of the three for the applicable temperature and pressure ranges. What might not be evident is that under certain conditions the expansion of the water could generate an almost irresistible force and exert an enormous pressure if expansion is prevented, a dangerous situation indeed.
Water expansion is parameterized experimentally by a coefficient of cubic expansion, represented by the greek letter Beta, β, below I have tabulated using data from the Enginnering Toolbox:
Heating 25 gallons (94.6 liters) or 0.0946 m3 of water from 20oC to 80oC in a closed hydronic system will result in an expansion dV=V0β(T1-T0) = 0.0946*0.000424(80-20)=0.00241 m3, that is the warming will expand the volume by 0.638 gallons (inviting you to flex your math muscles to verify the conversions, noting 1 gallon = 3.785 Liters, 1 mL = 1000 cm3, 1 m = 100 cm, 1 m3 = 1,000,000 cm3).
The dual fuel system was noted earlier because gas burns hotter than electric elements in heating water where extremes of volume and pressure seemed to be correlated over the past few years; think investigation or detective story. What I had been seeing was as the water warmed to near maximum, the pressure would increase wildly. Evidently the standard is 5 psi, I was seeing 15. When explaining that to my plumber friend (Gary at G&T Plumbing and Heating, Fargo) he quickly declared that my expansion tank was waterlogged, translating that there was no room for expansion (air is compressible, water not nearly as much) providing motivation to review the situational interdisciplinarity, artfully.
Okay, a plumber could forgo the calculations, the graphs and use look up tables, but somehow, whether in a transfer of knowledge from a master craftsman to journeyman to apprentice, an ill informed plumber not having the experience and intelligence to design, build, and maintain common-place hydronic systems would likely not be plumbing for long.
I contend that plumbers, electricians, and the lot of tradesman are a significant component of a STEM workforce, specifically when addressing new situations, adapting experiences to solve problems while delivering services. Moreover for large building projects the multiple trade disciplines need to stage and coordinate their efforts respecting other disciplines, something we suggest should happen when building solutions, and betting some of you never questioning the implicit STEM nature of the trades.