Brochure
6
Ultra-Zone Duct Design
When laying out a duct system for a job that will include
an EWC Controls zoning system, many people think
that there needs to be drastic changes to accommodate
the zoning feature, this is not so. The ducts still need to
deliver an adequate amount of CFM to the zoned area as
they would if it were not zoned. The square footage of the
home or building is not changing. What will change is the
amount of square footage that will need to be heated or
cooled at the same time. With zoning allowing for setback
thermostats and different temperature settings throughout
the home or building during the day and night, demand
on the heating and cooling equipment should be a lot less
due to zoning off areas that will not need to be heated or
cooled during certain times of the day.
Since the heating and cooling requirements are now going
to be controlled through zones, the concern is the excess
pressure, or build up of pressure, from closed zones. What
this means is that when some zones are in setback mode,
the airflow to those zones will be shut off. The airflow
will cause a pressure build up in the duct system which
will be dealt with by using a form of “Bypass” to alleviate
that pressure build-up. There are several ways of dealing
with this excess pressure and what works for one contrac-
tor may not work for another, but EWC has some long
standing rules that should be followed. These rules are
important to follow to insure proper airflow throughout
the system and to insure proper operation of the EWC
Controls zoning system. EWC Controls follows the prin-
ciples outlined in the ACCA Manual Zr zoning guide.
• When using a “By Pass” back to the Return
it is suggested to use a Volume Control Hand
Damper. Model # ND-HD or RD-HD in the
ByPass Return Run.
• 100% of the rated CFM must always move
through the Air Handler when zoning with Heat
Pumps and High cooling demand areas (i.e.
Florida).
• Always assume the worst case scenario, which
is the smallest zone will be the only one to call
at any given time.
• EWC Controls recommends the use of the
SBD (Smart Balancing By-pass Damper) on all
zoning installations. EWC Controls highly
recommends the use of the SBD on all 3 zones
or more applications, as well as systems that
will exceed 2000 CFM.
As stated previously, there are several ways to accomplish
these rules. EWC Controls recommends two types of
methods for two different types of applications. The first
application (not recommended for high cooling demand
areas) is on 2 and some 3 zone jobs when there is no room
to install a bypass damper. On these jobs it is possible to
oversize the supply ducts to handle the increased pressure
of closed zones. For example, oversize each zone supply
duct to handle 65%-70% of the CFM. This way when the
other zones close, the one calling can handle the pressure
safely. The supply ducts should never be oversized more
than 20% of their intended capacity. (This method will
reduce the velocity of the system so it is important to
know your customer’s expectations of the system.)
The BEST method for relieving excess pressure in a
zoning system is the Bypass damper. This method will
take the excess pressure from the supply duct and return
it back to the return duct. This is done by tapping into the
supply air and running a duct back to the return air and
mounting a bypass damper in that run (see below). EWC
Controls by-pass dampers are PRD & PRD-RD (baro-
metric) and the EBD (electronic), and the SBD (Smart
Balancing By-Pass Damper).
HVAC
UNIT
SUPPLY AIR
RETURN AIR
BYPASS DAMPER
Figure 1
Figure 2
HVAC
UNIT
SUPPLY AIR
RETURN AIR
BYPASS DAMPER
HAND DAMPER
HAND DAMPER