Solar Solutions Continued from page 22
provided both by the piping configuration and by the con- trol logic. Solar direct heat for the floors has a priority over heat storage in the water tank. Heat storage is provided by the mass floors and controlled by the SLIC controller, using virtual two-stage room thermostats under central software control. Heat storage is also optimized in the DHW water tank and recirculator by software control. The SLIC con- troller is programmed to save heating fuel in every way pos- sible such as stranded heat recovery and intelligent priority control, based on temperatures and critical loads.
Electrical saving strategies The opportunities for electrical savings in a heating sys-
tem, although sometimes small, are always worth consider- ing. Here are some of the steps taken on this job. The boiler circulator is disabled when solar-only temperature is avail- able. Multi-speed circulators are used and set to the lowest
with cool fluid from the garage floor (or other floor zones) when needed. The floors in the warmest rooms in summer can be cooled by night circulation through the solar panels.
Report from the owner The heating fuel consumption for this house has been
Figure 32-2
speed that is effective for each job. The minimum number of transformers is installed to eliminate the “phantom load” that transformers consume. “Latching” zone valves are used that require no power when fully open or closed. There is no primary pump; all circulation through the
flow center is provided by the secondary pumps that supply flow from the heat sources to the heat loads. Solar circula- tion for collectors using closed glycol loops can be achieved with very small pumps and/or solar electric PV pumps.
Overheat control and cooling schemes The SLIC controller is programmed to prevent solar
overheating and to maintain safe high limits and comfort temperatures in a variety of ways. The DHW tank is used as a heat accumulator by day and can be cooled through the solar panels by night, if needed. The solar glycol high limit temperature can be controlled
Page 24/Plumbing Engineer
carefully recorded by the owner, before and after the solar heating retrofit and dating back 10 years. The results show unmitigated success in consistently reducing the heating fuel consumption after the solar retrofit. (See Figure 32-2 for a graph of the owner’s record of fuel consumption ver- sus heating degree days. Note that between 2004 and 2006, some fuel savings was achieved using ther- mostat setbacks with the old boiler but, because some of the rooms became uncomfortably cold, the thermostats were raised to around 65 F between 2006 and 2009.) The owner’s analysis of this data includes some interesting high- lights. Propane use has been reduced from about two — three heating degree days per gallon of propane before the retrofit to about five — seven heating DD/gallon after the retrofit. For domestic hot water, propane use is down to 0.6 gallons a day, versus the historic rate of 1.5 gallons/day. The house has typically netted 80 to 110 kWh/day (273 – 375 kBtu/day) of solar heat this winter. Annual propane consumption has dropped by about two-thirds, which amounts to about 1,300 gal-
lons per year saved. This is worth more than $3,000 per year at current local prices and will be worth more as the price of propane goes up. As an added bonus, the owner has noted that the energy
savings documented here was achieved in spite of an increased room temperature setting of 68 F (up from 65 F). So, along with significant fuel savings, the occupants are enjoying increased comfort levels. These articles are targeted toward residential and small
commercial buildings smaller than 10,000 feet. The focus is on pressurized glycol/hydronic systems since these systems can be applied in a wide variety of building geometries and orientations with few limitations. Brand names, organiza- tions, suppliers and manufacturers are mentioned only to provide examples for illustration and discussion and do not constitute any recommendation or endorsement. n
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.
March 2011
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