Next, we searched for air leaks. We sealed all the ducts, replaced broken window panes, and weather-stripped the outside doors. Because all the electrical outlets and switches had to be extended 2.5 inches to accommodate the thicker walls, we even sealed out any drafts around the boxes with insulation pads specially made for this purpose.
Lighting Strategies. The building’s only natural light came from a bank of inoperable, steel-framed, single-pane windows on the south and west walls. A fresh coat of light-colored paint covered dark, ugly interior walls and helped to brighten the office space some, but the building needed serious help in the lighting department. We swapped out the existing 10-kilowatt lighting system—40 industrial light fixtures drawing 250 watts each—with industrial-sized tubular skylights, reducing the need for supplemental lighting during the day. Eight tubular skylights provide 90% of the lighting for the shop/warehouse space and office during business hours.
Next, we added two tube-fluorescent fixtures for task lighting in the production area. For our most creative lighting project, we fit 1-foot-square glass blocks—filled with water for thermal mass—into the frames of a permanently locked, south-facing garage door that had been covered with drywall by the previous owner. For an interesting and colorful effect, we added yellow and orange dye to the water in some of the glass blocks.
All of these upgrades dropped our lighting load from 80 KWH to approximately 2 KWH per day, reducing our lighting costs by $240 per month. The skylights cost about $1,000 each, installed ($450 materials; $550 labor). At present electricity rates, it’ll take us less than three years to recoup our costs.
Solar Water Heating. Within a year of moving into the building, we installed a solar water heating system and removed the backup electric water heater. Solar energy now provides 100% of the building’s hot water, which serves two lavatories and two showers in the bathrooms. The system features a 56-square-foot thermal collector typically suited for a family of four. We located the solar storage tank in the showroom area so visitors can observe the water temperatures from the solar collectors—typically 140ºF in the summer and 80ºF in the winter. Even on the cloudiest days, visitors are pleasantly surprised to see the results of the system’s PV-powered pump (a 12-volt DC Hartell pump directly powered by a 36 W module) in the glass flow meter.
Space Conditioning. The mass of the slab-on-grade concrete floors in the building help moderate interior temperature swings. In the summer, the cool soil below the concrete floor tempers summer temperatures, while an awning shades the south-facing side of the building and prevents the summer sun from charging the concrete floor mass. As a result, our air conditioning unit is never used. On sunny wintertime days, the concrete absorbs solar energy, providing some offset for the electric air-source heat-pump system that serves the office space.
To improve the efficiency and operation of the heat-pump system, which was installed in the 1950s, I hired an HVAC contractor to inspect and service the equipment. He inspected the ducts, sealed air leaks, and replaced the dirty, blackened filter that looked as if it was original to the system. For added conservation, I installed a programmable setback thermostat.
Heating 2,000 square feet of segregated space efficiently takes some creativity and staff buy-in. Employees dress warmly in the winter, when the thermostat remains at 65°F during work hours. As needed, a 1,000 W radiant electric heater supplements the main heating system in the colder back offices. Overnight, the programmable thermostat allows interior temperatures to drop as much as 20°F. But because the functional mass of the concrete floor tempers heat loss through the night, the space reheats quickly—about an hour after the thermostat turns on the heating system in the morning.
The 8,000-square-foot warehouse is mainly used to store vehicles and renewable energy equipment inventory, so heating and cooling it is less of a priority. In the winter, which tends to be mild and mostly overcast, another 1,000 W electric radiant heater keeps temperatures tolerable in a production area. In the summer, two solar attic fans help by drawing hot air out.
After almost two years of tightening our energy belts and making efficiency upgrades, we were ready to calculate what it would take to reach net zero-energy usage. Our utility, Pacific Power, made it easy by providing a bar graph with the average daily KWH consumption for each month of the year. Upon poring over a year’s worth of utility bills, we determined that our PV system would need to average at least 23 AC KWH per day to offset our usage.