Commonsense Building Systems Dynamics

Mark Kelley, a partner at the Hickory Consortium formed under DOE’s “Building America”  program was one of the first mechanical engineers of my ken who started the mantra of “looking at buildings as if they are systems”. As if! Of course they are, as Hafiz pointed out in the 14th century, (paraphrasing), “you will finally understand what every atom and universe understands, when one of us wiggles, we all wiggle.” I used to design jet engines. And yes, today, I am happy to fly with those engines keeping me in the air. Everybody knew that a jet engine was a system, that you could write an equation for the airflow and fuel supply and determine the thrust and then optimize the fuel consumption for a given thrust. But for a building? For the energy related parts a resounding “Yes”; and you could write it so that you could optimize the cost of ownership. Who knew? Better to ask “Who knows?”.

  1. Today we call the practice “Building Energy Performance Analysis”, BEPA (gotta love those acronyms). Usually we use some type of spreadsheet to do the dirty work of equation formation, but when we are done we can “simulate” the building performance before we build it.
  2. Using this tool, we can make trade offs for insulation thickness, window quality, mechanical system type, fuel, and efficiency; as well as exterior shading (trees!), orientation to the sun, window size and configuration, and so forth and arrive at an “optimized” design.
  3. But remember, and this is the commonsense part: The building is not the model, and doesn’t even know about the model- it will perform as it was built. It is up to the construction delivery team to build and verify that the model design intent was executed properly. Henry Gifford has said that the building performance awards so proudly displayed in the lobby should be attached with screws that will allow removal if the building doesn’t perform according to the model predictions. There have been too many examples of buildings not performing as designed, not having equipment as specified, and just plain not even having the equipment installed to corroborate Mr. Gifford’s reservations. For example, we used to think that R-19 insulation in a wooden stud bay gave an R-19 wall. Tests have shown that between the conduction through the wood studs, gaps where the insulation doesn’t touch the studs, and air leakage that we are lucky to get the equivalent of R-11.
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