This is the ninth live-blog of my spring 2026 DERs class.
The last post talked about solar energy. This post discusses why we might care about buildings in general and their thermal equipment in particular. The next post will introduce thermal modeling techniques for buildings.
When people in the energy world say “buildings,” we generally mean all structures other than industrial facilities. We subdivide the buildings sector into residential (detached single-family houses, small apartment buildings, condos, row houses, etc.) and commercial (offices, shops, bars, restaurants, hotels, schools, hospitals, etc.).
For whatever reason, we categorize big apartment buildings — a skyscraper with hundreds of apartments, for example — as commercial, even though they’re full of residences. Similarly, we lump factories into the industry sector, even though they’re buildings used for commercial purposes. Energy nerds are weird.
Why might a DERs student care about buildings? Well, buildings host most of the DERs we cover: The heating and cooling equipment that keeps buildings comfortable, the solar photovoltaics on their roofs, the electric vehicles in their garages and parking lots, the water heaters and tanks in their basements and mechanical rooms, and so on.
Americans also spend some 90% of our time indoors. The indoor environments we inhabit — how they look, feel, and sound; the quality of the indoor air we breathe — strongly influence our health and happiness.
Buildings use three-quarters of United States electricity (industrial structures — technically not buildings to energy nerds! — use the other one-quarter) and emit one-third of United States climate pollution.
Americans spend some $400 billion per year on utility bills for residential (~$250 billion) and commercial (~$150 billion) buildings. For context, only eight companies in the world take in more than $400 billion per year in gross revenue.
Within the United States buildings sector, thermal equipment — furnaces, boilers, air conditioners, refrigerators, compressors, pumps, fans, etc. — uses two-thirds of the energy and half the electricity. I show this in the chart below, which I assembled from various Energy Information Administration datasets.
In addition to using ~35% of United States electricity, emitting ~22% of United States climate pollution, and costing Americans ~$250 billion per year in utility bills, thermal equipment in buildings almost always has some degree of flexibility in the timing of its energy use. This flexibility is a vast, and largely untapped, resource. We’ll talk about how to use that resource to improve the efficiency, reliability, and affordability of electricity systems. The next post starts that conversation with an overview of modeling buildings’ thermal dynamics.