Zoning Bypass
How do I deal with excess air volumes?
Intelligent Bypass
On new construction or when inspecting an existing HVAC system that will include an EcoNet Zoning System, the technician should determine if the zones and ducts are correctly sized to handle the volume of air for the system selected. Depending on the system selected, there are minimum and maximum airflow.
Once it has been determined that the HVAC equipment and the duct work are correctly sized, then you may install the EcoNet Zoning system. Otherwise, HVAC equipment and duct-work issues should be addressed prior to installing the zoning system.
Since the zoned heating and cooling requirements will be controlled through air zone dampers, the concern is how to effectively manage the equipment capacity and air volume. This means that as zones are satisfied, the airflow to those zones will be completely or partially shut off. While the EcoNet enabled equipment can stage down, this can create high static in the duct which can be dealt with using a combination of tools that help manage airflow and volume:
To help manage airflow and volume:
It’s best to select variable capacity equipment. All EcoNet enabled air handlers, furnaces, heat pumps and air conditioners are multi-stage. As a reminder the RH2T air handler is constant torque and will not operate with the EcoNet zoning. Fully modulating furnaces and outdoor units provide the most flexibility when it comes to the zoning system.
If necessary, modify the existing duct and/or install new duct that has been sized at a friction rate that will accommodate higher CFM values at OEM specified static pressures and industry standard velocities.
Manage Expectations. Having extremely small zones will create some give and take. For example. An 8” zone will be hard to manage with a 5 ton system. One would either have to wait for other zones to call, install a bypass, overcondition other spaces or expect extreme velocity and static. Often times none of these choices are optimum but it was the false hope that created the problem to begin with.
Overconditioning. The EcoNet zoning system may utilize other zones to open enough to allow the system to run when focused on a smaller zone that otherwise couldn’t demand the equipment on by itself. The user may select how much overconditioning other zones allow. See the overconditioning section of this site for details.
Intelligent Bypass. The System can be configured with a bypass to either return excess air back into the return or into a dump zone that doesn’t have a thermostat. The EcoNet Intelligent Bypass will operate to bypass the difference between the zone or zones that are calling and the minimum airflow and capacity of the equipment.
Because all EcoNet enabled, and zone capable equipment utilize constant CFM (Variable Speed) blower motors, a barometric, or weighted damper cannot be used as the motor and damper would not play well together. Each one would be responding to the other.
The Bypass may be installed only on zone 6 with smart thermostat revision 20 or earlier, and the dip switch settings will tell the system if zone 6 is a bypass or a standard zone. Refer to dip switch settings for instructions on how to set the dip switches.
For revision 26 or later, on a two zone system, zone 3 may be used as a bypass and is set up as such in the thermostat zoning settings screens.
Each system configuration has minimum airflow and while it is not always cut and dry that a bypass is required if a zone doesn’t meet the minimum. Consult the zoning training materials to determine the lowest system airflow capacity.
A note of caution, you probably already know. Modern furnaces require more airflow than older systems did. It is very possible that the airflow for the gas furnace may be higher than that of the cooling system.
As for sizing the bypass, there is a table that gives you an idea based on the most air you would ever need to bypass. Since bypass ducts are generally pretty short and not only are being forced by the supply static, the air is also being pulled by a return so generally we can get by with a slightly smaller damper than one you may use as a supply only.
