Air Testing ,Adjusting & Balancing.
A-System Preparation :
1-Obtain updated construction drawings ,specifications,approved shop drawings.
2-Prepare field data forms to record testing and balancing process.
3-Obtain system leakage rate data where duct leak testing specfied.
4-Verify that fresh air intake type units fan are installed, rotating correctly,controlled to supply the required airflow rate .
5-Check for clean filters.
6-Volume control dampers are operable, accessible,and are in an open or normal position.
7-Controls are operable and calibrated.
8-Boxes are installed,operable and accessible.
B-System Testing And Adjusting.
1-Record nameplate data on fan ,motor,and fresh air intake type unit .
2-Test and record the fan rpm to cofirm rated speed.
3-Measure and record motor running amperes and voltages.
4-Set system in the minimum outdoor air mode ,then perform a pitot tube velocity traverse of main ducts and adjust fan speeds for total design supply and return air flow rates .Total design flow must include estimated duct leakage 5% of system total to allow for balancing effects.
5-Minimum outdoor air quantities must be maintained during all system modes.
The following steps 6 through 9 occur after all boxes and related terminals are balanced.
6-Measure and record the static pressure resistance of the duct system and static pressure drop across coils ,filters etc,in the cabinet or out in the duct system.
7-Measure and record the pressures at fan suction and discharge per the pressure rating required ,either static or total.
8-Test the system in the maximum outdoor air mode .If motor overloads or airflow rates are excessive ,adjust fan rpm to suit.
9-Measure and record outdoor ,return ,and supply air temperatures with the system set at minimum outdoor air mode.
C-System Balancing.
After the air system has been prepared according to balance by the procedures set forth in the following subsections.
When system characteristic prevent design flow rates balance the system components to equal percentages of design.
1-Balancing Sub-Main Air Ducts.
1a-Perform a Pitot tube velocity traverse of each sub-main duct to determine flow rate through each.
1b-Adjust the main volume control dampers to provide the required flow through each sub-main air duct.
2-Balancing Branch Air Ducts.
1a-Beginning at the sub-main duct closest to the fan or with the highest percantage of required flow , perform a pitot tube velocity traverse of each branch on that sub-main duct run.
2a-Proceeding from the branch with the highest percantage of required flow ,adjust the branch volume control dampers to provide the required flow through each branch duct.
3a-Proceed to the sub-main duct with the next highest percentage of required flow ,traverse ,and adjust each branch per previous steps 1 and 2.
4a-Continue until all branches are balanced.
3-Balancing Air Terminal Flow Rates.
After obtaining the required airflow rates in sub-main and branch ducts ,then balance each air terminal by the following procedure.
3a-Beginning with the branch nearest the fan or with the highest percantage of required flow ,measure the airflow at each terminal on the branch.
3b-Starting at the air terminal with the highest percantage of design flow and ending with the air terminal having the lowest percantage of design flow ,adjust the runout or terminal volume control damper to provide an airflow rate within 10% design.
3c-If balance without excess pressure has been attained then at least one air terminal on each branch should have the volume control damper full open .Branch dampers may require readjustment.
3d-Repeat steps 1 and 2 for the branch that has the next highest percentage of required airflow.
3e-Continue until all air terminals are balanced to within 10 % of design.
4-Final Adjusting And Balancing.
4a-Measure and record the final airflow rates at each air terminal.If it is necessary to adjust the airflow rate through a terminal by 5 % or less ,in order to achieve the final setting within 10 % of design then it is not necessary to adjust nearby terminals which have been final measured. Otherwise nearby terminals should be remeasured and adjusted accordingly if required.
4b-Secure ,mark.seal and record the final setting position of all volume control dampers installed in submain or branch ducts.
4c-Measure and record the final airflow rate at velocity traverses in main ,sub-main and branch ducts .Do not adjust related volume control dampers.
4d-Measure and record the data required as follows,
4d1-Test and record the fan rpm to cofirm rated speed.
-Measure and record motor running amperes and voltages.
-Measure and record the static pressure resistance of the duct system and static pressure drop across coils ,filters etc,in the cabinet or out in the duct system.
-Measure and record the pressures at fan suction and discharge per the pressure rating required ,either static or total.
-Measure and record outdoor ,return ,and supply air temperatures with the system set at minimum outdoor air mode.
4e-Reset all controls for normal operations.