Brochure

7
Duct Sizing with Ultra-Zone
When tapping back into the return duct, the tap is rec-
ommended 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 Return.
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 con-
dition 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 damp-
er CFM capacities, see the chart below.
The dump-zone method, which should only be used
when it is not possible to install a connection between
the supply 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 pres-
sure build-up and dump it into a non-critical area of the
home. Non-critical can be interpreted many ways, what
EWC Controls has seen most commonly used are base-
ments, 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
environment. 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 indi-
vidual 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 single 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 install-
ing EWC Controls zoning systems. These are just a few
suggestions, other methods and techniques can be used if
they are more successful for your applications.
Bypass Dampers and their CFM Capacity
Rectangular Round
12”x8” PRD 750 CFM 8” PRD-RD 350 CFM
12”x10” PRD 950 CFM 10” PRD-RD 650 CFM
12”x12” PRD 1,200 CFM 12” PRD-RD 1,000 CFM
20”x8” PRD 1,000 CFM 14” PRD-RD 1,300 CFM
20”x10” PRD 1,400 CFM 16” PRD-RD 2,000 CFM
20”x12” PRD 2,000 CFM *CFM amounts calculated a .3” w.c.
(See Page 15)