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.
 • Whenusinga“ByPass”backtotheReturnit
is suggested to use a Restrictive Hand Damper.
Model # ND-HD or RD-HD in the Return.
 • 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EBD
(Electronic By-pass Damper) on all zoning
installations. EWC Controls highly recom-
mends the use of the EBD on all 3 zones or
more applications, as well as systems that will
exceed 2000 CFM.
As stated previously, there are several ways to accom-
plish these rules. EWC Controls recommends two types
of methods for two different types of applications. The
first application 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 (baromet-
ric) and the EBD (electronic).
HVAC
UNIT
SUPPLY AIR
RETURN AIR
BYPASS DAMPER
Figure 1
Figure 2
HVAC
UNIT
SUPPLY AIR
RETURN AIR
BYPASS DAMPER
HAND DAMPER
HAND DAMPER