Pushing the Envelope

(In order to appreciate the events from this past weekend, the reader will want to remember that our straw bale home is currently heated by our backup system, a radiant floor fueled by propane. It's a great incentive to complete our Finnish masonry heater this summer for use in Winter 2010-2011.)

It was inadvertent that we were able to test the passive solar and insulative values of our home last weekend. We really meant to order the propane last week. Really. But it's getting to be good maple weather, which means busy times at home and work.

So we called for propane on Saturday. Sure, they'd be willing to deliver, for an extra $150.00.

Ah. Okay then.

So Saturday began with a feeling of regret that quickly turned into opportunity. As I've mentioned before, the insulation value of the walls of our home is quite high compared to conventional construction. We've created an efficient "envelope" (highly insulated walls, floors, ceilings, windows & doors.) We have a nice amount of passive solar gain through our south-facing windows and a decent amount of thermal mass in the floor. (In layman's terms, thermal mass refers to the ability of a material to absorb heat, to be radiated out over time.) But here's the thing---even though we theoretically knew the insulative value of our home, we had never tested it directly by turning our heat off---until this weekend.

By Saturday morning, we knew we needed to get through two days without using much propane, so we turned the radiant floor system off. (The radiant system works through a thermostat that measures the floor temperature and uses hot water---heated by propane---to keep the floor a constant temperature. The heat from the floor radiates upward and heats everything in its path.) The nice thing is, we can adjust the thermostat to decrease the temperature of the floor, but it also has a switch by which we can simply turn it off.

Looking back, I wish I had treated this weekend more scientifically and taken air and floor temperatures each hour. But anecdotally, here's what happened: we had typical maple weather all weekend, so outdoor temperatures climbed to around 45 degrees F during the day and dipped below freezing at night for both Saturday and Sunday. Each day, the passive solar energy raised Haven's interior temperature to around 69 degrees. Overnight, the air temperature in our home came down to around 64 degrees.

Overall, we were extremely pleased with how we fared at Haven this weekend. There were a lot of variables at play, such as the fairly pleasant March weather with sunshine. (Certainly, if we hadn't had sun, the house wouldn't have been as warm each day.)

So what are the potential implications of our inadvertent experiment? My conclusion is that since I am home during the day, I'll be able to monitor the outside weather and adjust the thermostat on our radiant system accordingly to greatly reduce our demand for propane on sunny days. It makes me think back to a Cape Cod we used to own, to times when we considered ourselves lucky to be able to turn the furnace off toward the end of April. What a great opportunity to be able to reduce our fuel use a month and a half earlier! It also brought me back to our time at Terra Dei, learning to build smaller fires each day as Spring progressed, so as not to waste wood and overheat the house.  It reminded me that life it built on a learning curve.

The owner of the propane company personally made our delivery yesterday. Having helped Fred choose the size and site of the tank for our proposed radiant heating system, he was curious as to how we made out this winter. I described how pleasant the floor was to walk on, then related our "experiment" from turning the system off this past weekend. He smiled ruefully, saying, "Well that's great for you, but not good news for me!" Though I kept quiet, I was dying to say, "Just wait until our masonry heater is in place next year!"

Instead, I chose to smile and wish him a good day.

Thanks for joining me along our journey!
Grace
xxoo