With the hot weather this last week comes ripening tomatillos, tomatoes and peppers… And also brings thoughts of energy efficiency. Now that we have been in the house for four months, I thought it would be interesting to put weather data from this spring into our energy model and see how its predictions compare against actual usage.
Just to start with, these numbers are fluffy. To get actual usage, I took July’s usage as a baseline since it was our lowest month and figure that anything above that is a seasonal adjustment. That would include both our heating need, and additional lighting due to early sunsets. To find heating degree days (HDD), I took data from a weather station in our neighborhood and used base 55 because the internal load of the two occupants keeps the house warm when the outside temperature drops as low as 55° F. This doesn’t take into account solar gain, or heat produced by appliances. So with that, here are some very rough numbers:
|Month||HDD||Predicted (kWh)||Actual (kWh)|
As rough as those numbers are, predicted and actual do correlate fairly well and back up my hope for a sub $100 annual heating bill (my model predicts about $95 for this last winter).
We don’t have any sort of air conditioner, so everything we do to deal with the heat is passive… Unfortunately, we haven’t gotten any permanent window covering solutions in place yet so our solar gain is a bit problematic when the temperature outside gets into the 90s like it has been the last several days. We are able to cool the house off pretty quickly at night and in the morning just with opening windows, but the afternoons can get a bit warm inside.
On Friday, in preparation for the Build it Green tour, we’re going to get our blower door test to see what our air changes look like. We’ve been holding off finalizing things for LEED because our yard still needs quite a bit of work, but Earth Advantage would like to complete an energy audit before the tour so that our performance score can be advertised to the visitors.
Some friends of ours are building a residence in the neighborhood that they expect to be certified as a passive house and are also blogging about the process. They’re also on the Build it Green tour so go take a look and say hi.