The zone saver field trial: Utility controlled demand response with residential zoned cooling


D. Mountain (McMaster University)
T. Strack (Strack and Associates)
W. Zhou (McMaster University)
B. Lomanawski (NRCan)

Publication date: December 2011

The ZoneComfort® (ZC) technology enables occupants of suitably equipped forced-air conditioned homes to direct and schedule the delivery of heating and cooling to multiple zones in the home. Traditionally, to smooth summer peak cooling loads, utilities have controlled whole house cooling loads. To evaluate whether there are opportunities for enhanced load control in houses with zoned HVAC systems, a field study was conducted in Chatham-Kent and Kitchener-Wilmot in the summer of 2010.

The project monitored ten occupied homes equipped with the forced air ZC system.

Recognizing that in the ZC system, all zones would not have to be interrupted simultaneously, a subset of the ZC houses was assigned treatments associated with utility load control of their air conditioning delivered to specific zones of the house. These "Zone-saver" treatments corresponded to interruption schedules which were tailored to the homes’ specific dwelling demographics. Site and equipment specific electricity was collected for these sites. In addition, the project followed control homes similar in structure to the ZC homes over the same time period. For some of these control homes their air conditioning load for their whole house was interrupted periodically for four hour periods. In addition, the study monitored and followed some Peaksaver® homes which were part of the Ontario program of air conditioning load control.

As well, questionnaires were administered to the homes for the purpose of gathering information on dwelling characteristics, demographics and lifestyle and attitudes regarding the ZC system.

While controlling for weather, dwelling characteristics and demographics, with this detailed field data, we are able to develop empirical models to evaluate the benefits of utility control of cooling loads for a residential zoned cooling systems during summer peak-demand periods and to compare with non-zoned systems. A key question to be addressed is whether utility control offers incremental peak saving benefits both to the utility and to ZC homeowners, who are concerned about both comfort and conservation.

Based on this report’s analysis of the field data, there are a number of conclusions:

On average, after controlling for demographics, dwelling characteristics and weather, indeed ZC households do undertake their own (without utility interruption), albeit small peak changes, an average of -0.03 kW air conditioning condenser load during the 1 to 5 pm peak period. The maximum average peak change during the 1 to 5 pm peak period attributable to the household is a change of -0.092 kW. However, Zone-saver style interruptions offer the added benefit of allowing utility interruption schedules to be tailored to different dwelling demographics. The field data indicates that utility interruption provides incremental changes of another -0.35 KW, averaged during daytime interruptions, with a maximum -0.51 kW change. Corresponding to this is 1 to 5 pm hour peak change of -0.35 kW air conditioning condenser load and a -18.6 % change in kWh.

In total, between the household and the utility interruption, the average peak change during daytime interruption is -0.41 kW.

Going from a ZC house without utility interruption to a ZC house with utility interruption, leads to an average change in air conditioning condenser and fan load of - 17.0%, with a maximum change of -23.6%.

Utility control of the cooling load delivered to the upper floor during the day is much more effective in contrast to utility control of cooling load delivered to the main floor during the day. From a policy perspective, if utility control of cooling is combined with a ZC system, it would not be necessary to control the main floor cooling. From another perspective, if utility interruption were to be targeted to particular types of zoned houses, it would be best to offer utility interruption of upper floors of households who are not going to use the upper floor during the day.

Nevertheless, in comparing a non-zoned house with a utility interrupted ZC house, the reduction in air conditioner condenser kWh usage moderates to a -12.3 % change.

An upper floor air conditioning interruption for a full four hours during the day leads to an average peak change of -0.52 kW. This is more than twice the reduction for the curtailment by cycling of air conditioning serving the whole house.

The ZC system was able to produce superior indoor comfort conditions on the upper floor of the house during the critical overnight period.

Only 12.5% of the upper floor disruptions and 4.1% of the main floor disruptions were noticed by ZC houses.

Two thirds of the sample felt the controlling of the cooling delivered to individual zones is preferred to controlling the cooling of the whole house.

Using a building simulation model of a zoned cooling system, we also studied the impact of residential zoned air conditioning systems on the reduction and shifting of peak summer time household electricity demand.

The simulation model provides a valuable tool for examining the impact of particular assumptions while explicitly holding fixed all other parameters of the model.

Compared with the normalized field data, the simulation results showed similar trends.

Both sets of data showed significant peak air conditioning reduction, and in both studies the usage of more electricity in the off-peak nighttime diminished the overall kWh conservation.

For access to the full publication, please contact the CanmetENERGY-Ottawa Business Office.