Monday, January 24, 2011

Winter chills bring (slightly) higher bills

Sarah mentioned yesterday that we have had to run our heater, and we aren't getting nearly as much free hot water from the solar water heater. This has driven up our energy usage a bit. As you can see in the following chart from Portland General Electric, before winter we were averaging around 14 kWh per day.  Virtually all of that energy was for non-heating and -cooling needs (TiVo, computers, stove, lights, etc).

Note that the months in this chart are for the period ending that month.  So the January numbers are for mid-December to mid-January.  Our energy usage clearly spiked as the temperature dropped, but on the whole it's not a huge increase.  During this time last year at the old house, we used 31 kWh per day plus $154.56 in natural gas for the furnace (which was unusually high).  During a one-year period we spent $1,620.76 on energy (electricity + gas) at the old house.  We are on track to save about $950 per year in our Passive House.  And all of this while being more comfortable than we ever were in the old house.  No more cold drafts, no more chilly corners, no more icy floors.

Every home is different, so don't expect these numbers to reflect every Passive House project.  But we are thrilled with the results we have seen.

Sunday, January 23, 2011

Passive House in winter

So we took a very long break from the blog, as we have had a very busy last few months. However, I know many people have been wondering how our house is performing during winter, so this is the first of two posts addressing that. I plan to talk about some of the day-to-day living in the house, and Stuart will follow with actual energy data.

Based on how much internal heat we generated during the summer, we anticipated that we would rarely have to use the heater during the winter (if at all). It turned out that we have needed our heater, although much less than we would have in a non-Passive House.

The picture above was taken Nov. 23 -- the day we received our first snow of the season, and also the first time we had to turn on the heater. The fact that we made it almost until Thanksgiving without using our heater once is amazing to me. On this day, we got a light dusting of snow and temperatures around freezing. The cold temperatures continued to stick around off and on throughout most of December. Also, as is typical in the Pacific Northwest winter, it was cloudy almost every day.

Our biggest lesson from this experience was that we did not realize just how much we had relied on solar gain during the summer and fall. During December, we opened our curtains all day to let in sunlight, but there wasn't much sunlight out there, so our house did not warm up much during the day (neither did our solar hot water heater, meaning the electric heating element kicked in). With the continually cold temperatures, it meant that our house would lose a few degrees inside overnight, and wouldn't warm back up during the day. As a result, whenever we would get home from work after 5 p.m., we would need to turn on the heater to warm the place back up a bit.

The very positive news, however, was that we would only turn on the heat between one and four hours a day -- sometimes a bit longer on a weekend when we were at home -- and that was sufficient. This even held true as the temperatures outside stayed in the 30s and 40s. The inside temperature was around the mid-60s -- slightly colder than the levels we had kept during the fall -- but still quite comfortable. In our old home, we had to run the heater constantly and were never warm.

Another interesting test came for us over New Year's. We left town for the holiday and were gone three and a half days. We left the heater off while we were gone. I'm told that temperatures in Salem while we were away were still quite cold, enough for a very light snow (although it didn't stick). When we got back after the holiday, the temperature inside the house was about 55. So after several days with no people inside and no heat on, and freezing temperatures outside, the internal temperature had dropped about 10 degrees. I think that's not bad at all!

As I said, Stuart will follow up with some actual numbers about our energy use. It went up a bit during December and January because of using the heat, but is still very low compared to what we used in our old home. Overall, we're quite excited about how our house has performed during winter.