Test Balance Final Flashcards
What is a Parallel Fan Powered VAV?
Parallel: 2 separate parallel chambers, primary cool air flow, ceiling return air flow. With or w/o reheat. A fan in the return air chamber powering the return air flow
What are the two types of Fan Powered VAVs and how do they work?
Series: have fans in primary air stream and operate continuously. Blend col primary air and warm plenum air maintaining constant flow while adjusting temps. Interlocked with central fan, higher operating costs
What does the acronym for AMCA mean and what do they do?
Air Movement and Control Association
What is AMCA Standard 210 state?
Defines procedures and conditions of fan testing so ratings published by manufactures can be compared
What does Diversity Factor mean?
Sum of total ind. Max loads / Max Demand Load for System. If the size of the cooling, heating, and air distribution equipment is selected based on a lower actual max occupied simultaneous load, rather then a higher design, there is a diversity factor.
What is a General Information Report and what is on it?
Describes the type of systems with key information. Lists job location, type of systems, manufacturer, instruments of measure used, building and system completion check
After balancing, with what formula do you use to determine how much to increase RPM for the correct amount of CFM?
RPM and CFM are directly proportional. RPMnew = RPMold x CFMnew / CFMold
What heating or cooling condition should most systems be put in before balancing?
Max flow through cooling coil by setting t-stat to 55 degrees. In winter, may have to leave t-stat at current setting
What is the range for a High Pressure system?
2000 fpm and up, 6 in. WC and up
What is the CFM formula?
CFM = Duct Size / 144 x fpm or CFM = A x V
What is a Velometer and what does it measure?
Instantaneous direct reading for velocity in fpm and pressures in in. WC. Great for SA at ceiling diffusers. Also reads exhaust velocities at grilles, hoods and duct openings, currents in open spaces, etc.
What does misalignment cause in fans with Inlet Cones?
Sharp loss of air volume and cycling within the fan
What is a Rotating Vane Anemometer and what does it measure?
Reads velocities in fpm at grilles, louvers, exhaust hood openings, duct openings, etc. Operates as a windmill with timed counts
What are the pressure ranges for a Medium Pressure System?
2000 fpm and up, 2-6 in. WC
What is a VAV system and how does it work?
Auto varies air flow to spaces proportionately to current space needs at a constant temp. Usually, constant 55 degrees, programmed min and max damper settings. For heating, cool air reduced then air is heated with hot coil, RA used, or induction units used. Static pressure sensor maintains proper flow
What is Fan Break Horse Power?
Horsepower absorbed by the fan, not just the motor. A fan will deliver deliver a constant volume of air at a constant RPM in a constant system regardless of density of air, but static and hp change with density
What does an Oriface Plate do?
Creates a temporary pressure drop across the plate in in. WC and correlated against flow in gpm. Placed straight length of pipe and read with a Dial Type differential pressure gauge.
How does a Photo Tachometer work and what does it measure?
Light beam directed a shaft or pulley and reads 120-19,999 rpm. The rotating item must be marked for it to count
What is Standard Air?
air at 70 degrees F and 50% RH at 14.7 psi atmosheric pressure
What is on an Outlet Balance Report?
Info from blueprints, shop drawings, schematics and grille schedule from manufacturer. Gives models, size, AK, velocity, cfm, and final measurements
What is the temperature rating for a VAV system?
55 degrees
What are the calibration parameters for Anemometers?
About once a year, sent to a factory, or checked against another unit
What is a Shunt Motor Control?
Connected in parallel to allow for variable speed control of the motor in response to heat loads in the space. Can also alter dampers to aid
What is the most efficient way to balance?
Proportional Balancing
How do you balance a single zone system?
- Pitot Total Air at fan, in mains, and branch ducts, use outlets if other not possible. 2. Add air flow in all branches and compare with fan CFM. 3. Compare each branch with design for the branch, adjust dampers as needed. 4. Reread branch flows with pitot. 5. Read outlets from near fan to furthest, reduce excessive flow at each outlest. 6. Make another pass if inbalance exists still. 7. Add all outlet CFM and compaire to fan CFM. Take amp and static pressure
How is a Rotating Anemometer positioned to measure a grille?
Most accurate is to divide grille into equal sections and take multiple readings and average them. Also could sweep in an S curve across the grille one or more times (takes less time)
What are the basic belt tensioning rules?
Alignment: belt 100% straight from sheave to sheave. Tension: 1/2” - 1” deflection on top side in center for one or two belt sheaves 2 - 4’ apart. Check manufacturer for higher horsepower (1/64” per inch from center of sheave to sheave)
How do you calculate the OA % actually entering the building?
% of Outside Air: OA% = Tra - Tma / Tra - Toa
What is an Air System Recap Report and what is on it?
Tie everything together and keep track of balancing progress. System, location, status, CFM, RPM, S.P. inches, AMPS
What is meant by Traversing?
Taking several air velocity readings in a duct over a cross sectional area of air flow and averaged out
How do you change a VAV to a Constant Volume System?
All terminals are set maximum or minimum flow settings
What is meant by Capture Velocity of an exhaust system?
Velocity required to pick up contaminants from their source area. It must overcome spillage, air, and heat currents, and contaminants’ weight and velocity
How do you change CFM?
Run calculation: RPMnew = RPMold (CFMnew / CFMold) & DIA Fan Sheave = DIA Motor Sheave (RPM motor / RPM fan)
What is the most accurate way of measuring a flow on a Hydronic system?
Reading the actual flow (oriface plate flow meter, venturi flow meter, pitot flow meter, etc.)
How do you connect and use a Manometer and Pitot Tube together?
Velocity Pressure: traverse with both tubes hooked up to pitot tube in the discharge duct. Total Pressure: hook up bottom connection to left side (+) Static Pressure: parallel pitot connection to right side (-) manometer
How do you use a Flow Hood?
Place over outlet. Good if Ak Factor not known for diffusers and grilles. Set range and traverse it
What are the classifications of Residential Systems?
Constant Volume Variable Temperature Low Velocity. 200-1200fpm, 1/2” to 1 1/2”
Name all of the benefits of balancing.
Reduced energy, lower operating costs, safer systems, reduction or elimination of service callbacks, preventions of premature wear, healthier air, customer satisfaction, improved reputation, and profitability
When balancing a High Pressure System, what components need to be set for what?
Auto Dampers to 100% OA, no recirculation of RA, close all doors and windows, max AC, all outlets open
What is the formula for Max Leakage, from ASHRAE?
Max sys leakage (in CFM) / Feet of ductwork - 1% max allowed
What are the components of a Grille?
Vanes only, no dampers
What are the components of a Register?
Vanes and a control damper
How do Tubular Inline Fans operate and what is their sequence?
Centrifugal fan wheel in tubular housing with inlet cone and vanes. Air discharged parallel to flow, unlike most fans.
How do VAVs measure static pressure?
2/3 downstream the main duct is where the Static Pressure Sensor monitors. Directs fan volume controller to adjust proportionately
How do you determine duct leakage?
- Test one section of duct at a time 50 - 150’ long (length can’t exceed instruments ability). 2. Determine Max Allowable CFM leakage and determine allowed leakage for each section. 3. Seal both ends of segment and all tees. 4. Connect Testing Rig. 5. Start Blower and gradually open damper at inlet until Test Pressure is reached. Allow to run at test pressure for one minute. Air entering system is = to air leakage out. Pressure drop across oridace plate measure leakage with U Manometer
How do you hook up a Manometer with a Pitot Tube?
Left side of manometer is Positive, right side is Negative. Total Pressure on the bottom of pitot to (+) and Static Pressure on side port (-)
What is the formula to set OA based on MA Temp?
Outside Air Balance: Tma = (OA% x Toa) + (RA% x Tra)
