GREEN SYSTEMS
| SOLAR SOLUTIONS | CONTINUED FROM PAGE 60
changes seasonally. So, for example, a ground- source heat-pump or an electric boiler might be placed just before a propane boiler in Figure 31-2 so that these fuels can be used exclusively or combined to achieve the best backup fuel costs from month to month. Solar heat, when placed upstream in the loop, is used for fuel offset by preheating any of these units and shutting them down during good, sunny weather.
Intermittent Heat is sometimes generated out of sync
62
with the need for heat and not controlled by the need for heat. Some typical examples would be Solar, a wood stove with heat coil, fireplace with heat coil, wood fired hydronic boiler, other multi fuel hydronic boilers (coal, pellet fuel, small biogas digester) and waste heat from other mechanical equipment such as generators or large refrigeration compressor systems). These sources can be used, stored and controlled in much the same way as solar heat is treated and can be a nice complement to the solar heat. When installed upstream of the solar heat storage system (as seen in Figure 31-2), non-solar intermittent heat can be stored in the solar storage as well.
Example: Wood-fired hydronic backup.
In 2006, a homebuilder near Santa Fe found that the
building site provided an ample supply of firewood that was essentially free. The only other backup fuel in that location
Figure 31-2
was propane. The construction of the home was planned in two stages; solar collectors were to be added in the second stage. This meant that the house would be occupied for several years before the solar collectors were installed. The house was well insulated with radiant floor heat, using mostly concrete floors. The homeowner chose to install a large wood-fired
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hydronic boiler (outdoors) that came with a built in 600- gallon tank. This was used as both a heat storage tank and as an intermittent alternative heat source. A primary loop was installed in the mechanical room with the wood-fired hydronic heat connected with two pipes upstream of a condensing propane boiler. The piping connections were done in the same order as labeled in Figure 31- 2.
L G ® The homeowner
could make one large wood fire on a cold day and run the heating system (using standard automatic home heating solar controls) on the heat stored in the
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