Here's a new concept: "Thermal Noon." I think it might be a valuable way to help people understand building performance.
It's similar to the phenomenon, which I think ordinary people understand, that the Summer Solstice is not the hottest day of the year.
For any building, the balance between gains & losses are strongest at Solar Noon, all else being equal. If the building were perfectly responsive, it should be hottest at Solar Noon each day. But because of insulation and thermal mass lag time (plus internal gains and static shading), a typical building is hottest at 4:00 or 5:00. In a lossy house it's earlier, and in a Passivhaus it might occur when cooking dinner. That time could be called Thermal Noon. And it changes day by day. In heating season, you'd like thermal noon to occur as late as possible, to offset lower outdoor temperatures.
By modeling gains & losses we can compute this time for a given building on a given day. Architectural engineers effectively do this when determining peak loads. It can be pulled out of simulation data, or in a finished building it can be measured empirically.
The other critical value, besides the time, is the high temperature. And higher isn't necessarily better. We're getting much more attuned to the problem of overheating. In a workspace, you probably can't tolerate it reaching 80°F in the afternoon. The ventilation will kick in and defeat the energy savings you want. In a house you probably can tolerate 80°F but maybe not much more.
Do you think Thermal Noon, and the difference between Solar Noon and Thermal Noon, are valuable things to know for a building? Please comment!