ASHRAE Journal - July 2011 - 60

solar NZEB projEct
From early January to early April, a heat pump water heater was also connected to the heat pump circuit, which contributed approximately 30 kWh per month, or 10% of this circuit’s energy load. During our final building inspection, the inspector required disconnection of the heat pump water heater while he checked the certification of our system components, so Subpanel A was used to temporarily connect an electric resistance water heater, resulting in the high December energy use of 140 kWh shown in Figure 3. Succeeding months after the electric resistance water heater was disconnected have energy levels in the 30 kWh to 40 kWh per month range, representing various lighting and receptacle uses in the house. Subpanel B shown in Figure 3 includes wall receptacles in the master bedroom and main living area where the two space heaters are located. During December and January, the coldest months of the winter, Subpanel B had energy loads of 900 kWh to 950 kWh, or average space heater loads of 1,200 W, indicating that the rated 3,000 W total space heater power was modulated at 40% capacity if other miscellaneous loads on this subpanel are negligible. By April, the space heaters were operating less than 5% of the time. The heat pump energy recovery system became the dominant heating source along with increased levels of solar radiation. As of the second week in April, the “equinox overhang” on the clerestory windows blocked direct solar radiation. The “minor” circuits shown in Figure 4 are individually quite small, but collectively they represent 110 kWh to 180 kWh per month, equivalent to 150 W to 250 W of continuous power. December and January energy totals for the minor circuits were the highest, with a decreasing trend toward spring. Regarding the overall trend, December shows a substantial load for the double oven and cooktop due to holiday activities and family visitors for nearly two weeks. We held a winter solstice party with 120 people that necessitated significant cooking preparation. Cooking activities subsided through the rest of the winter with only two occupants for the majority of the time. Kitchen receptacles included those used regularly: coffee pot (Ty) and electric teapot (Deb). The refrigerator is energy efficient, although it is a fairly large, French door unit. The trends in its energy use reflect cabinet use with almost a 30% drop in energy from December to April as kitchen activities subsided. The dishwasher shows approximately 5 kWh to 8 kWh per month, which represents five to eight dishwashing loads per month (1 kWh per dish load). The lights in the main room reflect the seasonal change in daylighting. December was again the highest lighting load with snowy days and visitors regularly in the house over a twoweek period. The main room lights consist of 45 LEDs with a power draw of 8 W per bulb for a total of 360 W when all lights are on, but are controllable in 50 W to 75 W groupings. The 40 kWh during December is an average of 55 W of main room lighting, or an average of seven bulbs activated. As the lights contributed to the winter house heating at an efficiency equivalent to that of the electric space heaters, the lights could be considered an alternative heating source. Longer days and
60 ASHRAE Journal

lower occupancy levels since December have significantly reduced lighting loads. For future switching of shower and laundry water to rainwater, we incorporated two small (2 gallon, 1,500 W) electric water heaters for sinks in the “east” end (full bathroom sinks and laundry sink) and “west” end (half bathroom sink, kitchen sink and garage sink) of the house. This ensures potable water at all sinks. These water heaters are poorly insulated (and it’s difficult to add additional insulation). The west end water heater was the dominant load with kitchen sink use. After the first week of April, the sink water heaters were disconnected, and the sink hot water lines were connected to the heat pump water heater. The electric circuit for the heat pump water heater was also shifted from the electric circuit for the heat pump energy recovery system to its own circuit for monitoring. The remaining three weeks of April show that the heat pump water heater required 25 kWh, less than the combined amount of the two small sink heaters for any of the other months. Overall, the heat pump water heater has reduced the water heating energy by a factor of 3 (that is, an average COP of 3.0) since December when all water heating was electric. We plan to add a second heat pump water heater for potable water for sinks at a future date when we are able to convert laundry and shower water to rainwater. Clothes washing requires little energy with today’s modern appliances. Coupled with cold water detergent and low water consumption, clothes washers have little impact on the house energy demand, averaging 2.5 kWh per month as shown in Figure 4. The clothes dryer has a significant energy impact relative to other appliances as discussed in our April 2011 column on appliances. For two occupants, the clothes dryer energy demand is averaging 20 kWh per month. Finally, Figure 4 shows the energy required by the rainwater pump that supplies our toilets. The pump is a typical shallow well pump with diaphragm tank that operates on a pressure switch. Through April we have used nearly 20,000 L (5,300 gallons) of rainwater for toilets and garden watering with an average of 1 kWh per month. Overall, the energy performance of Equinox House is close to our design modeling predictions with no major surprises or unexplained trends. Of course, there is always the possibility that our interpretation of why things are happening and the actual reason are two different things. As we incorporate the full heat pump conditioning system into the house, we expect to realize additional decreases in house energy requirements. Detailed breakdown of the house electric energy use indicates that the patterns in energy loads have some seasonal variations related to both the activities (holidays) and the time-of-year. We are pleased that Equinox House is comfortable with a healthy indoor air environment in addition to being an energy efficient house. Ty Newell is vice president of Newell Instruments and professor emeritus of mechanical engineering at the University of Illinois, and Ben Newell is president of Newell Instruments in Urbana, Ill.
ashrae.org July 2011

ASHRAE Journal - July 2011

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