3
ASSUME 4-TON EQUIPMENT WITH 10" ROUND SMALLEST ZONE
1600 CFM
(EQUIPMENT)
– 400 CFM
(SMALLEST ZONE – NORMAL CFM )
= 1200 CFM NEEDED
SO, FROM THE ROUND DAMPER MAX CFM,
A 14" ROUND DAMPER SHOULD BE USED FOR BYASS.
EXAMPLE
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”
BELOW CHART ASSUMES 400 CFM PER TON *USE
NEXT SIZE UP ROUND BYPASS DAMPER FOR ANY
SYSTEM WITH A SINGLE ZONE LESS THAN 200 CFM.
A PROPERLY SIZED BYPASS DAMPER AUTOMATICALLY MAINTAINS CONSTANT PRESSURE INSIDE THE
SUPPLY AIR DUCT WHEN ZONES OPEN AND CLOSE. WHEN THE CORRECT SIZE BYPASS DAMPER IS
INSTALLED AND ADJUSTED ACCURATELY, IT WILL BE FULLY CLOSED WHEN ALL ZONES ARE CALLING
(NO AIR BYPASSING) AND WILL OPEN PROPORTIONATELY AS ZONE DAMPERS CLOSE.
RECTANGULAR CFM
*
SURFACE AREA IN SQ. FT.
=
(“HEIGHT” X “WIDTH”) / 144
NORMAL CFM =
(SURFACE AREA IN SQ. FT.*) X 600 FPM
MAX CFM =
(SURFACE AREA IN SQ. FT.*) X 900 FPM
6” 100 200
7” 150 250
8” 200 300
9” 300 450
10” 400 600
12” 600 900
14” 900 1400
16” 1400 2000
DAMPER NORMAL MAX
SIZE CFM CFM
ROUND CFM CHART
BYPASS - PRESSURE RELIEF
BYPASS SIZING
SELECT A DAMPER SIZE WITH A MAX CFM GREATER THAN THE CFM-NEEDED TO BYPASS. USE
THE FORMULA BELOW TO CALCULATE CFM NEEDED TO BYPASS AND THE ROUND DAMPER CFM
CHART TO CHECK MAX CFM.
TYPICALLY 400
CFM PER TON
USE A BYPASS DAMPER THAT
HAS LARGER “MAX CFM”
800 2
1200 3
1600 4
2000 5
EQUIPMENT AIRFLOW
CAPACITY IN CFM (HIGH SPEED)
CFM OF
SMALLEST ZONE
CFM-NEEDED
TO BYPASS
USE “NORMAL CFM”
BYPASS
DUCT
RETURN AIR
F
ILTER
SUPPLY
AIR
EVAP.
COIL
(COOLING)
BLOWER
(FAN)
FURNACE
(HEATING)
FRESH
AIR
AIR NOISE
SHOULD BE ALWAYS BE MINIMIZED AND IN A ZONING SYSTEM WITH OPENING &
CLOSING DAMPERS IT CAN BE MORE CHALLENGING. INSTALL THE DAMPER AS
CLOSE AS POSSIBLE TO THE SUPPLY PLENUM TO PREVENT AIR NOISE
TRANSMISSION INTO THE CONDITIONED SPACE. TO MINIMIZE NOISE AND
MAINTAIN ADEQUATE THROW, SUPPLY AIR DUCT SYSTEM SHOULD BE DESIGNED
TO PROVIDE 600 TO 700 FPM VELOCITY AIRFLOW. THIS CAN BE ACHIEVED BY
PROVIDING LARGE ENOUGH DUCTS/DAMPERS TO SUPPLY THE VOLUME (CFM)
OF AIR NEEDED FOR THE ZONE. USE THE “NORMAL CFM” CHART TO CHECK
ROUND DUCT SIZE(S) THAT WILL ACHIEVE THIS VELOCITY.
►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.
SMARTZONE DUCT SYSTEM
A ZONING SYSTEM CAN TYPICALLY USE THE SAME DUCT SIZING AS A TRADITIONAL SINGLE-THERMOSTAT SYSTEM IF THE PRESSURE RELIEF
IS INSTALLED CORRECTLY AND THE SYSTEM IS 4 OR LESS ZONES. TO MINIMIZE BYPASS AIR FLOW, INCREASE THE DUCT CAPACITY BY ONE
SIZE FOR EACH ZONE LESS THAN 25% OF THE TOTAL SYSTEM AIR FLOW CAPACITY AS SYSTEMS GET LARGER THAN 4 ZONES, IT MAY
BECOME NECESSARY TO INCREASE THE DUCT & DAMPER SIZES OF THE SMALLER ZONES (OR ALL THE ZONES) IN ORDER TO MINIMIZE THE
AMOUNT OF PRESSURE RELIEF NEEDED WHEN ONLY THE SMALLEST ZONE IS OPEN.
NOTE: CONNECT DAMPERS DIRECTLY TO THE PLENUM WHEN POSSIBLE AND BRANCH OFF SMALLER DUCTS GOING TO DIFFERENT AREAS
WITHIN THE ZONES. USING THIS TRUNK/BRANCH DUCT DESIGN WILL MINIMIZE COST AND REDUCE AIR NOISE.
DESIGN & PRE-INSTALL
RETURN AIR
PROBLEMS WITH ZONING CAN
OCCUR WHEN THE RETURN AIR
REGISTERS OR DUCT ARE
UNDERSIZED. INSUFFICIENT CFM
WILL PREVENT SATISFYING VELOCITY
REQUIREMENTS WHEN ALL DAMPERS
ARE OPEN. 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
To Next Page
Loading...
