Brochure

7
Duct Sizing with Ultra-Zone
When tapping back into the return duct, the tap is recom-
mended to be at least 6 ft. away from the equipment. The
farther the better. This is done to ensure that the hot or cold
air coming off the plenum has time to mix with the return
air before going across the coil again. Temperature sensors
are mandatory when using the bypass method. The sensors
will prevent any damage to the equipment from overheating
or coil freeze-up. EWC Controls includes the SAS (Supply
Air Sensor) with every Ultra-Zone control panel. The use
of a Hand Damper is recommended to be installed in the
ByPass Return Run.
If the bypass is used, it would be sized to handle the excess
pressure build up under the worst case scenario rule. The
reason we use the worst case scenario is that this is the
worst possible condition of airflow. This condition will
cause the most excess pressure build up that is possible. The
calculation is done by taking the total CFM capacity of the
smallest zone, let’s say 600 CFM, and subtract that from the
total CFM of the system, let’s say 2000 CFM.
Total system CFM 2000
Less smallest zone’s CFM -600
Bypass amount CFM 1400
The bypass duct would be sized to handle the 1400 CFM
which would be the excess pressure when only that one
zone calls. The excess air can also be routed through the by-
pass damper and “dumped” into an area that has access to
an open return. This method will not provide the efficiency
of the By-Pass Method. For by-pass damper CFM capaci-
ties, see the chart below.
The dump-zone method, which should only be used when
it is not possible to install a connection between the sup-
ply and return, will provide some of the same benefits as
the by-pass method. This method will still use a bypass
damper, but it will not go through the return duct. The dump
zone will take the excess pressure build-up and dump it into
a non-critical area of the home. Non-critical can be inter-
preted many ways, what EWC Controls has seen most com-
monly used are basements, entrance foyers, work shops or
mechanical rooms. These areas are considered non-critical
because they are non-living areas where temperature control
is not as important. This method should be used responsibly
by the installer. Determining what is a non-critical area is
not to be taken lightly, this should be a thought-out process
keeping the homeowners needs and expectations in mind.
Using some method of bypass is the most effective way to
zone a home or building. Bypassing will accommodate the
homeowners or occupants demand for a controlled environ-
ment. Some zoning systems call for bypassing the air into
a zoned area, this will NOT allow for maximum comfort.
This method allows the bypassed air to over shoot the
thermostats temperature set point. What this type of system
does is leave the zone dampers partially open when they
should be fully closed, allowing for the bypass air to flow
into an already satisfied zone. This will negate the effect of
zoning and drastically reduce the comfort level, and savings
potential of the home. Zoning is the control of the airflow
from the HVAC equipment that allows for Individual Room
Temperature Control. With proper installation there is
no reason why an individual room cannot maintain a one
degree differential from set point.
Duct design will be uniquely different from one zoning job
to another and because of that, unfortunately there is no sin-
gle way of laying out a zoning system. What EWC Controls
has tried to do is to give you the critical information that is
needed before a zoning system can be installed. We have
also tried to show a few common techniques that are being
used by others who are installing EWC Controls zoning sys-
tems. These are just a few suggestions, other methods and
techniques can be used if they are more successful for your
applications. EWC Controls always recommends following
ACCA Manual Zr specifications
(See Page 15)
As a barometer use 1400 Fpm to achieve smaller by-pass runs at higher velocities.
Bypass Damper CFM Capacity
Rectangular By-Pass CFM Round By-Pass CFM
12"x8" 1000 8" 400
12"x10" 1200 10" 750
12"x12" 1400 12" 1200
20"x8" 1600 14" 1800
20"x10" 2000 16" 2400
20"x12" 3000
@ 1400 fpm @ 1400 fpm
or .3" w.c. or .3" w.c.