The future of bypass ducts in zoned California heating and cooling systems appears very bleak.

The California Energy Commission (CEC) recently proposed a code change that would prohibit the use of bypass ducts in zoned heating and cooling systems, and eliminate existing Title 24 zonal performance compliance credits. The proposed legislation would also establish a minimum system output of 350 cfm/ton and a maximum watt draw of 0.58 W/cfm.

The code change could largely affect manufacturers who specialize in the production of bypass ducts and zoning systems, distributors who sell the units, and contractors who install them. The CEC is scheduled to discuss the matter during its 2012 rulemaking hearing, and adopt the legislation in May. Pending any setbacks, the new regulations are expected to become effective Jan. 1, 2014.

CEC Code Change

The CEC insists the change is being made to ensure efficient functioning of air conditioners, furnaces, and heat pumps that employ ducted zoned systems.

CEC representatives sponsored a “2013 Building Energy Efficiency Standards Staff Workshop on Residential Zoned Air Conditioners” case study in July 2011 that examined HVAC efficiency at 80 Sacramento-area homes built in 2007 or later.

The study, facilitated by Bruce Wilcox, John Proctor, and Rick Chitwood, examined 16 multiple or zoned split systems. Upon their investigation, Wilcox, Proctor, and Chitwood suggested the examined cooling systems featured low-capacity efficiency, very high cooling duct pressures, and high cooling fan wattage. They also believe that the added comfort provided by zoned systems is accompanied by an increased energy cost.

“Providing the most agreeable temperature to all zones is comfortable, but it carries with it the distinct possibility of increased energy consumption,” said the case study authors. “Since the most common home is single zoned and has only one thermostat placed near the center of the house, temperatures in the rooms distant from that thermostat will vary, sometimes significantly. If zoning is added, the more distant rooms can be conditioned to a more comfortable temperature, requiring the use of more energy.”

The case study also states that mixing in bypass air lowers the return air temperature entering the cooling coil, which significantly lowers EER and airflow — even when all zones are calling.

Through comparisons, the study claims that typical homes using dampered multizone air conditioning systems boasted a 17 percent degraded SEER and EER, and 4.4 percent degraded furnace AFUE.

“The energy commission investigation demonstrated that using bypass ducts not only doesn’t save energy, it actually consumes more energy than systems with no bypass ducts,” said Adam Gottlieb, CEC acting assistant executive director of media and public communications. “With that knowledge, the commission proposes to disallow bypass ducts in order to save energy.”

The CEC believes the ban on bypass ducts and increased efficiency standards could save residents an average of 318 kWh per year (when compared to existing zoned systems using bypass ducts), and upward to $3,363 annually.

Criticism of CEC’s Proposed Changes

Because of the potential impact of the proposed changes, AHRI members have been very vocal in their disagreement with the CEC’s proposal, stating that in addition to providing occupant comfort, a properly designed and installed zoning system utilizing bypass ducts is energy efficient and provides cost savings for consumers.

“We have issues with the way they conducted the study, and how they concluded that zoning provides comfort, but does not save energy,” said Aniruddh Roy, AHRI regulatory engineer. “We pointed out scenarios with the use of zone damper systems and setback thermostats to show that zoning, when used appropriately, can save energy.”

AHRI representatives shared their displeasure through stakeholder meetings, workshop events, written letters, and face-to-face meetings with CEC representatives. In addition, AHRI submitted a 160-page document to the CEC that includes multiple letters, a slide-by-slide response to the CEC’s case study, a Canadian study showing that zoning saves energy, and more.

“Just as you have a light switch for every room, zoning provides a thermostat for each zone,” said Francis Dietz, AHRI vice president, public affairs. “Having one light switch for the whole house would not save any energy, just as having only one thermostat, thereby wasting heating and cooling in areas not being used at a particular time, will waste energy.”

A field investigation, sponsored by Carrier Corp. and presented by AHRI, demonstrated an average of 28 percent energy savings through the 1993-1994 cooling and heating seasons in a fully instrumented and unoccupied 2,225-square-foot home in Upper Marlboro, Md. The test home utilized thermostat setup/setback strategies in five zones and was monitored using 150 unique data points.

Principal Carrier Corp. field investigation authors Thomas M. Kenney and C. Edward Barbour reported that zoning can cause higher operating costs if thermostat temperature setup/setback is not used; however, the level of comfort is dramatically increased over the central thermostat.

Zoned system manufacturers, such as Zonefirst’s Dick Foster, believe the CEC is missing the point. “The California Energy Commission is supposed to come up with ways to save energy, right?” said Foster, Zonefirst president. “I provided three or four independent studies showing overall energy savings. The CEC has ignored these based on their study of seven poorly designed zoned systems. Their consultants would rather kill the incentive and bypass than learn the proper way to bypass and fix poorly designed systems.”

Foster believes the CEC is ignoring the fact that zoned systems offer more benefits than drawbacks.

“Zoning is the answer to the nation’s energy crisis,” he said. “Even if every home has the most efficient furnace and air conditioner, homeowners will still be heating or cooling unused rooms, and that wastes energy. Zoning combined with variable speed HVAC is the way to go, but the CEC is even outlawing this, establishing a minimum of 350 cfm/ton. Any variable speed unit goes well below this and the CEC has stated that variable speed equipment is not sold in California. These people are out of touch.”

Zoning Without Bypass Ducts

The CEC is insistent that the prohibition of bypass ducts does not imply that zoning air conditioning systems are not allowed or welcomed. “It should be noted that the commission will still allow air condition zoning as long as it does not involve bypass ducts. Examples of acceptable zoning strategies include multiple air conditioning systems and variable capacity systems,” said CEC’s Gottlieb. “These alternatives are currently being used in the state and are far more energy efficient than bypass duct systems.”

In a letter to the CEC, AHRI representatives contested the adequacy of such alternatives.

The letter stated: “AHRI’s zone control equipment manufacturers believe that certain alternatives proposed in the CEC’s study make no sense whatsoever, as utilities are looking to decrease their load requirements. These manufacturers feel that the proposed alternatives would only increase generation capacity requirements for utilities.

“Damper stop relief can certainly be a supplement to a bypass, but not a cure-all. The damper stop adjustment may be at a point where too much air enters a zone, and will only result in over-shooting thermostat set-points in those zones, causing homeowner discomfort.”

Sidebar: How Does Zoning Work?

Zoning provides the ability to only condition rooms that need or request heating or cooling. Each zone uses a thermostat to control the heating, cooling, and fan operation for its individual zone. Motorized dampers are installed at the air outlet for each room, or zone, and open and close based on the demands of the zone thermostats.

Zone thermostats and dampers are wired into a central control panel. As each thermostat calls, be it for heating or cooling, the panel takes the first call from any zone. If it is heating it will keep open the damper to the calling zone, close the dampers to satisfied zones not calling for heating, activate the furnace or heat pump, and begin supplying air only to that zone. If during this call other zones call for heating, those zone dampers would open and heated air would be supplied to those zones as well. Once all heating calls are satisfied, the panel will shut off the furnace or heat pump.

In some instances, a separate bypass damper is installed to relieve any excess air from zones that are open and may be too small to handle the full capacity of the blower. This air is typically bypassed into the return air duct or into a common area such as a hallway. When air is bypassed into the return air duct, capacity controls for both the heating and cooling are also used to prevent overheating or overcooling in the unit.

Information courtesy of Zonefirst. For more information, visit

Sidebar: What Is Title 24?

Title 24 is an energy efficiency standard for residential and nonresidential buildings providing specific regulations in the state of California. In 1978, the Energy Efficiency Standards for Residential and Nonresidential Buildings were established in response to a legislative mandate to reduce California’s energy consumption. The standards are updated periodically (typically every three years) to allow consideration and possible incorporation of new energy efficiency technologies and methods.

The Title 24 Energy Code sets an energy budget for new buildings, additions, and alterations. The budget is measured in units of energy (kBtu per square foot), not financially. Each structure must be designed with appropriate energy efficiency features necessary to come in “under budget.” Energy budgets vary across all 16 of California’s climate zones.

Through the standards, construction firms are required to design building or residence additions and alterations with appropriate energy efficiency features and submit documentation with permit applications.

Energy compliance must be demonstrated through Title 24’s prescriptive list of minimum requirements, or by running a computer simulation showing that building performance exceeds that of an identical building with the prescriptive measures.

If CEC’s proposed code change is implemented, compliance credits previously granted for zoned air conditioning units will no longer be eligible when computing a structure’s energy budget.

The CEC states California’s building efficiency standards (along with those for energy efficient appliances) have saved more than $56 billion in electricity and natural gas costs since the program’s inception. The CEC estimates the standards will save an additional $23 billion by 2013.

Publication date: 03/05/2012