Solar Solutions Continued from page 22
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 pre- heating any of these units and shutting them down during good, sunny weather.
Intermittent Heat is sometimes generated out of sync with the need
for heat and not controlled by the need for heat. Some typ- ical 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 sys- tems). 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.
heat, using mostly concrete floors. The homeowner chose to install a large wood-fired
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. The homeowner could make one large wood fire on a
cold day and run the heating system (using standard auto- matic home heating solar controls) on the heat stored in the water tank. When that was depleted, the condensing boiler would kick in. When the solar collectors were even- tually installed both wood and propane usage was reduced significantly, and more heat was stored in the mass floors by the control system. The two-pipe, primary-loop con- nections allowed each heating device to be easily installed and controlled in a modular way over time.
Example: “Waste” heat from a generator An off-grid home built around 2007 near Cerrillos, N.M.
gets most of its electricity, which is stored in batteries, from photovoltaic panels. During extreme weather, an Onan generator fires up (on propane) to recharge the bat- teries when the solar cannot supply all the electrical needs in the home. This house was built from the ground up with solar heated warm mass floors, solar hot water and condensing boilers. When we realized (in 2009) that most of the propane heat from the generator was heating the great outdoors in winter, we decided to capture it. The top rubber hose on the automotive-style radiator was diverted to a stacked- plate heat exchanger. This allowed the automotive “water pump” in the engine to pump hot antifreeze from the engine through the heat exchanger before returning to the engine. The heat exchanger was treated like a solar collector, with controls that pumped heat away from the engine into the prima- ry loop whenever the engine was hot enough. In this way, the “waste heat” from the propane burned by the generator is allowed to contribute to heating the floors, the DHW and even the swimming pool. The primary loop in this home was connected in a simi- lar configuration to the labels shown in Figure 31-2. These articles are targeted toward residential and
Figure 31-2
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 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
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small commercial buildings smaller than ten thou- sand square feet. The focus is on pressurized gly- col/hydronic systems, since these systems can be applied in a wide variety of building geometries and orientations with few limitations. Brand names, organizations, suppliers and manufacturers are mentioned in these articles only to provide
examples for illustration and discussion and do not consti- tute any recommendation or endorsement. n
Bristol Stickney has been designing, manufacturing, repair-
ing and installing solar hydronic heating systems for more than 30 years. He holds a Bachelor of Science in Mechanical Engineering and is a licensed mechanical contractor in New Mexico. He is the CTO for SolarLogic LLC in Santa Fe, N.M. Visit
www.solarlogicllc.com for more information.
The views and opinions expressed in this column are those of the author and do not reflect those of Plumbing Engineer nor its publisher, TMB Publishing.
February 2011
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