2 -2.5 10"
3 -3.5 12"
4 -4.5 14"
5 14 -16"
UNIT SIZE ROUND DAMPER
(TONS) SIZE (INCHES)*
BYPASS DAMPER “RULE OF THUMB”
RETURN AIR
FILTER
SUPPLY
AIR
EVAP.
COIL
(COOLING)
BLOWER
(FAN)
FURNACE
(HEATING)
FRESH
AIR
AIR NOISE
TO MINIMIZE AIR NOISE INSTALL THE DAMPERS AS CLOSE AS POSSIBLE TO THE
SUPPLY PLENUM. A GOOD RULE FOR ACCEPTABLE AIR NOISE AND STILL
MAINTAINING ADEQUATE THROW, IS THAT THE SUPPLY DUCT SHOULD BE
DESIGNED TO PROVIDE 600 TO 700 FPM VELOCITY AIRFLOW. USE THE “NORMAL
CFM” CHART TO CHECK ROUND DUCT SIZE(S) THAT WILL ACHIEVE THIS VELOCITY
RANGE.
►FOR ZONES WITH MULTIPLE DAMPERS, THE TOTAL ZONE CFM IS THE SUM OF
ALL THE DAMPERS “NORMAL CFM”
►FOR RECTANGULAR DUCT SYSTEMS USE THE RECTANGULAR CFM EQUATION
PROVIDED FOR “NORMAL CFM”
ZONE BALANCING
TO MAINTAIN OPTIMAL EQUIPMENT PERFORMANCE IN A TYPICAL ZONING APPLICATION, IT IS PREFERABLE TO DESIGN ALL ZONES TO BE
CLOSE TO EQUAL IN SIZE.(IN TERMS OF CFM). THIS DOES NOT MEAN THAT EVERY ZONE MUST HAVE EXACTLY THE SAME CFM REQUIREMENTS
BUT THE SYSTEM WILL WORK MOST EFFICIENTLY IF THEY ARE APPROXIMATELY THE SAME SIZE. FOLLOWING THIS GUIDELINE WILL MINIMIZE
THE AMOUNT OF PRESSURE RELIEF (BYPASS) NECESSARY. FOR MOST RESIDENTIAL ZONING INSTALLATIONS USING SINGLE SPEED
EQUIPMENT, AVOID CREATING MORE THAN THREE ZONES WITH NO ZONE SMALLER THAN 20% OF THE TOTAL EQUIPMENT CFM CAPACITY.
RETURN AIR
UNDERSIZED RETURN AIR DUCTS/
REGISTERS CAN RESULT IN PROBLEMS
DUE TO INSUFFICIENT AIRFLOW (CFM
& VELOCITY) SUCH AS INCREASED RUN
TIME, EVEN EQUIPMENT FAILURE. TO
ENSURE THE RETURN AIR IS LARGE
ENOUGH, VERIFY THAT ITS SURFACE
AREA IS SUFFICIENT TO PASS FULL
SPEED BLOWER CFM. ENSURE ALL
ZONES HAVE UNRESTRICTED AIRFLOW
PATH “BACK” TO A RETURN AIR GRILL
EQUIVALENT TO THE ZONE CFM.
ROUND AND RECTANGULAR DAMPERS
SPRING DAMPERS USE A MOTOR TO POWER THE DAMPER BLADE IN ONE
DIRECTION AND A SPRING TO MOVE THE BLADE IN THE OPPOSITE DIRECTION.
WHEN POWER IS APPLIED TO THE DAMPER, THE MOTOR MOVES THE BLADE.
WHEN POWER IS REMOVED, THE SPRING MOVES THE BLADE IN THE OPPOSITE
DIRECTION.
WARNING: SPRING DAMPERS CONSUME MORE ELECTRICITY THAN POWER-OPEN/
POWER-CLOSE DAMPERS. (10 TO 12 VA WHEN POWERED)
POWER DAMPERS POWER OPEN /POWER CLOSE DAMPERS USE THREE WIRES
TO POWER THE DAMPER OPEN OR POWER IT CLOSED. THE ZONE PANEL IS
RESPONSIBLE FOR SUPPLYING A 24VAC SIGNAL TO EITHER THE PO (POWER
OPEN) OR PC (POWER CLOSED) TERMINAL OF THESE DAMPERS. PRIMARY
ADVANTAGES OF POWER OPEN/POWER CLOSE DAMPERS INCLUDE LOWER
POWER CONSUMPTION, QUIET
OPERATION AND GREATER RELIABILITY. (2.5 TO 3VA)
4
