The electrical energy usage in most industrial and commercial facilities follows a reasonably consistent pattern from week to week, so a one-week monitoring program usually is adequate to determine what can be done to save 10–20 percent on electric bills. It turns out that there are far too many variables in a residential dwelling’s energy usage in any given week to figure out a yearly pattern. A recent assessment of the energy usage and power quality at a 2,800-square-foot, single-family residence made this very clear.


The audit began after the installation of a new 5-ton heating, ventilating and air conditioning (HVAC) system and prior to the installation of rooftop solar panels. The first week of data showed huge variations in energy consumption from day to day as well as throughout the day. It also showed a serious power quality problem (sags) when a load cycled in periodically (see “The Real Answer,” ELECTRICAL CONTRACTOR, September 2015). 


The differences in power consumption ranged from 0.9 kilowatts (kW) to more than 7 kW. To try to understand the extreme variation and figure out how to save on the $600-plus monthly electric bill, daily activities were compared with the variations, focusing on which electric loads were turned on and why.


As shown in Figure 1, on July 27, demand topped out at 7 kilowatt-hours per hour (kWh/h), which is the equivalent of a $38.64 per day rate. As the sun came up, so did the energy, which was traced to a pool sweep and filter at 2.25–2.75 kW for 4 hours. At 6 a.m., demand jumped to 4.25 kW on a typical morning, where the activities included turning on the following:


• Televisions (86W downstairs, 120W upstairs)

• Dining room chandelier lights (40W × 9 = 360W)

• Living room recessed lights (120W × 6 = 720W)

• Kitchen lights (120W × 7 = 840W)

• Coffee pot (1.2 kW)


As it got warmer outside, the HVAC unit cycled on and off more often, adding about 4 kWh/h. As the temperature rose to a high of 86°F, power usage climbed to 7 kW. When all of the residents departed and some of the discretionary loads turned off, the load dropped to 3 kW. 


Two days later, July 29, was one of the hottest days of the summer, with a temperature in the mid-90s into the evening. The HVAC cycled every 22 minutes for most of the day. Again, typical morning usage added 3 kW but increased to 5 kW during the evening with other activities (such as cooking) and people going in and out of the house without closing the interior doors.


Contrast this to August 2, when the house was vacant for most of the day with only the HVAC and pool equipment drawing significant power. Despite afternoon temperatures in the 90s, the demand was below 4 kW for the entire day.


Fast-forward another week with the usual activities followed by one of the highest peaks, nearly 9 kW in the late evening. Along with most of the aforementioned interior lights on, the following added more load:


• Eight 45W lights on the path to pool

• Two candelabra-style lights on post (320W each)

• Eight flood lights (nearly 1 kW) illuminating the outside of the home

• The spa jets of pool pump (720W) circulating the heated water

• People constantly going in and out of the house, leaving lights on and causing the refrigerator to cycle more often


A couple of days later, the house’s residents went on vacation. The thermostat was set up to 79°F instead of the usual 70–72°F. The HVAC didn’t cycle on again even though the temperature outside was in the mid-80s during this period. 


Figure 2 clearly shows the effects of the pool-cleaning equipment running from 6–10 a.m. Most important, demand dropped below 1 kWh/h for most of the day. This establishes the baseline power needed for the refrigerator, standby modes of electronics and other equipment running 24/7. 


How does one decrease the energy consumption in a home with this variability? The audit showed several simple things that can be and have been done at the house:


• As my father used to say: “Turn some stupid lights out,” and not just lights, but TVs, coffee makers and any other equipment left on when not being actively used.

• Close doors and limit unnecessary traffic coming into and out of the house.

• Insulate the home and ensure exterior doors have weather stripping to reduce the heat/cold loss.

• With such a large lighting load that is on for most of the day, swapping out 24 incandescent lamps with LED lamps would reduce 1,440W to 300W.

• Most significantly, you can save 4–8 percent for each degree that you raise the thermostat in the summer. The audit here showed a savings of $250 per month was possible over the summer, if such action were taken.


The heat wasted by the 90 percent inefficient incandescents and other unnecessary loads forced the HVAC system to remove that heat. Each time the lights blinked from the HVAC starting up, the electric bill increased another 25 cents, adding $341 for a summer month. It doesn’t take much to save a lot.