April and May are much like September and October – the house has minimum heat demands through out the day. The primary demand is for bathroom heat and this is accomplished with radiant floor heating. The difference is that in April and May we are not looking forward to a long cold winter. To begin our shift to needing less general heat, we raise the tank back to 300 gallons, which increases our solar domestic hot water capacity and gives us longer storage for bathroom heat.

The next big strategy change is, at some time in March, to discontinue adding heat to the Solar Battery. We won’t need this heat, as a matter of fact, we won’t want it. So we open the ground heat dump loop.

We continue to heat all floors when we reach 130 degrees for the storage tank, but lower the set points a bit to reflect the warmer daily temperatures and thus the reduced need to store heat.

The final strategy change, probably in April, is to shut down the big collector. This is easy because it is a drain back system, so we just drain if for the day and then shutoff the circulator that would charge it when there is heat to be gained. Shutting it off eliminates the concern of it over heating and saves energy!

Because in the Spring we are more concerned with over heating than about storing up heat for the coming heating season, and because the Solar Battery is nearly depleted, we will error more on the side of not saving as much heat as we might want. Thus, we probably will have more wood fires in this season than in the late Fall. Here is one of the opportunities we have to balance our resource book – wood burning. If we have burnt more wood than we planned, we can increase our utilization of the sun pretty easily now, but if we are on plan then we will back off the thermal storage because it is better to sleep in cooler rooms and it is time to set the house up for Summer – totally deplete the Solar Battery and open the house fan exhaust for convective cooling.

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