1. Technician’s Guide and Workbook for Zoning Section 6: Zone Balancing Basics

2. Manual D Duct Sizes
Room
Cooling CFM
% Total CFM
Heating CFM
Kitchen
200
15.8
100
8.2 GR
150
11.9
Dining
140
11.0 90
7.4
Bed 2
128
10.0
130
10.7
Bed 3
120
9.5 MB
220
18.0 CR
330
26.0
450
36.9
Total
1,268
1,220
100.1
As with the single zone air balancing covered in lesson 3, Zone balancing is not based on the duct size CFM.

3. Balancing
1st step for any zone system is to measure the airflow through the system with all of the supply and return dampers open. Note: if a bypass duct is installed the damper should be in the closed position for this measurement.

4. Airflow Measurement Methods
Medium Speed Fan Tap
Supply =
(+) 0.20
+ (-) 0.40
Return =
0.60 ESP
____

5. OEM Fan Performance Chart (1/2 HP)
× Watts = HP
× 195 = 0.26 HP
× 240 = 0.32 HP

6. Heating and Cooling Changeover
Automatic Manual Automatic Latent Load Humidity Control (Low Speed) Single-Speed; Multi-Speed; Variable-Speed Single-BTUH; Multi-BTUH; Variable-BTUH

7. Zone Balancing Total CFM Step 2
Pick the highest CFM total to be used for the balancing process CFM calculations.
Cooling or heating total value?
Calculate out the CFM values for each room based on the actual room load (for heating and cooling).
Check for Diversity:
Diversity is where the total of the zone CFM values is larger than the equipment’s total CFM capability

8. Step 3: Set Fan Speed to High
Set the System so the cooling will stay on. Make sure the system is operating in a steady state. Know what correction factors are needed for the measurement tools and how to use the tools (see Manual B for balancing tool details). If a bypass duct is used the bypass damper must be set before balancing any of the zones.

9. Bypass Damper Adjustment
Once the minimum and maximum airflows for heating and for cooling are known, the bypass duct can be easily balanced. The steps below are designed to prepare the equipment for testing:
Make sure the system is operating in as-new as possible condition; coils & blower clean, new air filter.
Make sure all of the system supply registers and return grilles are wide open.
Make sure the damper(s) in the bypass duct are closed.
Make sure any makeup or outside air duct that is attached to the system is sealed or closed off so no outside air can enter the return ducting (leave closed until balancing is completed).

10. Step 4
4. Measure the ESP in cooling mode (unless heating has the greater CFM)
Note: ESP is measured based on the pressure drop across the OEM’s “box.” It determines the airflow using the OEM charts. Thus, it may or may not include the filter and/or a coil. Be sure to read the table notes and follow the OEM instructions.

11. ESP
Dampers
Closed

12. Step 6 Measure SP
Dampers
Closed

13. Steps 5 & 6
Move the thermostat to the maximum heating position, and repeat steps 3 & 4 above.
Note: be sure to write down the ESP and SP values for each step.
The system is then placed in the operational mode that requires the most CFM (heating or cooling), and all of the zone thermostats are again set to keep the system operating during the balancing. Operate the system for 10 minutes to allow for stable operation.

14. Steps 7, 8, & 9
Shut down all of the zones except for the one with the lowest designed airflow. Note: Manual Zr provides guidance on how much bypass airflow is allowable.  Zr warns those doing balancing that the smallest zone CFM should be sized utilizing the Manual Zr Bypass Airway Sizing Worksheet to ensure the supply and return air temperatures remain in the OEM’s operating range.
Fully open the bypass damper(s).
Re-measure the SP on the supply trunk.

15. Step 10
Adjust the manual/hand damper on the bypass duct until the SP on the main trunk is back to the original value it had in the step 6 test. Double Check options to verify that the bypass CFM is less than or equal to the Manual Zr worksheet value: Measure the total CFM value to the smallest zone using an air measuring device (that value subtracted from the ESP OEM table value will equal the bypass CFM) or traverse the bypass duct. Note: when zones have a minimum airflow setting allowing some air to bypass, their CFM values must also be measured used in the total CFM calculation.

16. Step 11
Lock down the manual/hand damper and make sure the SP is still equal to the original value. For the example it would be 0.20 iwc. If the value is different, readjust the manual/hand damper until it is the same, and then lock down the damper again. A good practice is to then mark the position and the SP value on the duct, dated and initialed.

17. Step 12
The basic bypass damper balance is now complete. Before leaving, the zone thermostats/controls should be turned back to their normal operational setting, outside air dampers should be opened back up, and the ESP should be checked in both heating and cooling modes with only the smallest zone open to make sure the balanced airflow CFM falls within the OEM’s minimum/maximum airflow requirements for the system

18. Minimum Set Point Set Minimum and maximum in largest zone
Open largest Zone and set minimum and maximum for second largest zone.
Open 2nd largest Zone and set minimum and maximum for 3rd largest zone.
Open 3rd largest Zone and set minimum and maximum for 4th largest zone (etc.),
Go back and double check minimum settings for all zone combinations.

19. Balancing Challenges

20. Thermostat Placement Strategy
Near a return inlet ok, near a supply outlet, not ok.
Locations where the thermostat will be in direct sunlight, not ok.
Interior walls preferable to exterior walls.
Height now needs to be 42’-48” to be Americans With Disabilities Act (ADA) compliant
Avoid placing thermostats near an exterior door.
Away from heat sources such as TVs, ovens, computers etc.

21. Sound Check All Zones
The final step is to set each zone up so it is operating by itself, and check to ensure the sound level through the diffuser(s) is not too loud. If the system is too loud when operating in the occupied area of any zone, the diffuser design and/or size for that zone should be changed.

22. Draft Check (done with sound check)
When the velocity of airflow across the inhabited area of a room is too high, occupants will complain it is too cold, or drafty. Using a veined or hot wire anemometer, the velocity of the airflow in the occupied areas can be measured . When airflow is above 50 FPM in heating mode or 75 FPM in cooling mode, the likelihood of getting complaints is greatly increased. One method of avoiding those complaints is to adjust the diffuser throw direction and/or angle. Other fixes include, changing the diffuser design and/or size.

23. Field Notes
The homeowner’s complaint is simple, the zone system never has worked right, it ices up in cooling and short cycles on heating. The Technician immediately knew what the problem was…there was no balancing damper on the bypass duct. After installing a balancing damper on the bypass trunk, and measuring the airflows to all of the zones the technician properly balanced the system.