BUILDING SCIENCE

Zero-Peak Electricity Houses

By Guy Newsham

Twin Houses at the Canadian Center for Housing Technology

Many power utilities in North America experience a peak demand for electricity on hot summer afternoons due, in part, to residential air conditioning loads. Meeting peak demands usually involves expensive forms of generation that are passed on to consumers through time-of-day pricing. However, utilities are also exploring options on the demand side.
NRC Construction conducted a study to investigate how to eliminate or reduce summer peak power use and associated costs using the twin houses at the Canadian Center for Housing Technology (CCHT) in Ottawa. One house was operated in a conventional manner and provided a typical reference case. The test house used a variety of measures designed to reduce or shift load from peak periods.

Reducing Peak Load
There are four general approaches for reducing peak load from the grid: passive design to reduce electricity demand such as overhangs, glazing type and positioning, thermal mass, reflective roofing, and low power lighting and appliances; incentives for occupants to use less power at peak times such as pricing regimes or providing real-time energy use information; automatic controls that respond to climate conditions or utility signals such as direct load control of air conditioning, water heaters or other loads by the utility, or motorized blinds; and, local generation and storage such as photovoltaics and battery storage of off-peak power (either site-generated or grid-supplied).
A combination of such measures was used to reduce peak electrical demand in the Test House. For example, incandescent lights were replaced with compact fluorescent lamps. The schedule for simulated laundry work was shifted out of peak hours. The forced air supply registers to the basement were closed to avoid using mechanically-chilled air to cool an already cool (and unfinished) space. The air conditioning unit was forced into a cycling mode between 15:00 to 19:00 to run for 15 minutes and then shut off for 15 minutes, even if the set point temperature had not been reached. Window shading options were tested. Natural window ventilation was admitted to the upper floor from 20:00 to 08:00 and power generation from a small photovoltaic panel installation (1.2 kW) was used to offset remaining demand during peak times.

Zero-Peak Target
The full-scale house experiments show that a zero-peak target can be achieved in a typical Canadian single-family house. A combination of practical operational modifications (air-conditioner cycling, doing laundry later in the evening) and commercially available technology (exterior shading, modest PV array, energy-efficient lighting) was able to dramatically reduce the peak electrical demand from the grid on the hottest days of the year.
In fact, the zero-peak target was reached on the hottest day of 2012 (July 21) that combined an outside air temperature of 38o C with a humidity of 41 per cent. Indoor temperature and humidity did rise compared to the reference house, but to levels that would likely be tolerable for a few hours. This suggests that zero-peak could be achieved on any sunny summer day in southern Ontario. Further, these conditions are also representative of climates in many other places, which suggests that the measures have wider applicability in areas with hot summers.

Measuring the Data
Although the relative contribution of each measure is difficult to ascertain exactly given the climatic variations from day to day and the fact that most measures were not implemented independently, it is clear that the external blinds contributed more to savings than all of the other measures combined.
The combination of compact fluorescent lamps, delayed laundry schedule, closed basement registers, air conditioning cycling, and horizontal internal blinds reduced air conditioning use on-peak by ~20 per cent; closing the internal blinds increased savings to ~28 per cent. Replacing the internal blinds with closed external blinds raised the on-peak air conditioning savings to ~70 per cent.
All of the measures tested were commercially available technologies or easily implemented changes in homeowner schedules. Some of the measures tested might not be appealing to some householders due to inconvenience or cost; the exterior blinds used were relatively expensive. Nevertheless, more attractive combinations may still reduce peak load substantially.
Based on these results, utilities and governments facing summer peak supply problems might want to consider (greater) incentives for these measures for retrofit, and policies to encourage the incorporation of such measures in new houses. Leading-edge builders of highly energy-efficient houses may opt to implement certain measures as selling features.

Dr. Guy Newsham is a Group Leader with the National Research Council – Construction.