Test Balance International Final Flashcards
What are the steps of the General Balancing Procedure?
- Prepare reports. 2. Check building and systems are complete and functional. 3. Check equipment. 4. Balance outlets and duct runs. 5. Recheck equipment. 6. Finalize Reports
How do Magnehelic Gauges work and what do they measure?
Dry-type Manometer with internal bellows for sensing pressure. Pressure drops, inlet and discharge pressures, and velocity.
How do Hook Gauges work and what do they measure?
U-tube liquid level principle for reading very low pressures and velocities. Differential between indoor and outdoor pressures, low duct velocities with pitot tube, calibrate other insturments. High pressure on left side, low pressure on right side
What is an Anemometer used for?
Measuring velocity in FPM at outlets. Timed readings
What is on the Chiller Test Report?
Compressor data, manufacturer, model, size, type, capacity, refrigerant, pounds, serial number, design water pressures of evap and cond
How do Differential Pressure Gauges work and what do they measure?
Two connections and reads in inches WC, feet of water, or mercury. Bourdon, Bellows, or Diaphragm elements
What are the two major categories of pumps?
Positive Displacement and Centrifugal
Where do you set the OA Dampers for balancing on single fan systems?
Minimum, recirculation to maximum
What are Balancing Valves, how are they calibrated, and how are they used?
Balance flow in a system, calibrated to measure flow-pressure relationship for each incremental setting of the valve. Totating plug, globe valve types and more. Used for presetting system balance, adjustable flowmeters, and shutoffs
What is Ak Factor?
Unobstructed air flow area of outlet
What is a Stuffing Box?
Second protective provision against leakage inside of the pump casing and ambient atmosphere. Seals between the shaft or shaft sleave and stationary support achieved by rings of asbestos or metal packing
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 different types of low pressure systems?
Single zone, low pressure reheat, multizone, Low Pressure Exhausts (return air and toilet exhaust)
What are the different types of high pressure systems?
High pressure reheat, dual duct, induction
What is a VAV system?
System that auto varies air flow proportionately to current space needs at constant volume
What are the types of Centrifugal Fan Wheels?
Backward inclined, air foil wheel, forward curve wheel, radial blade wheel
How do you Bump a fan?
Turn fan on and off quickly to ensure proper rotation
How do you Traverse a fan?
Straight run of duct in main supply duct away from fittings, dampers, coils, etc
What could be done is there is a large difference between the fan and outlet CFM?
15% or more, check duct leakage, accuracy of pitot traverse or method of reading CFM, Instrument calibration, incorrect Ak Factors, for open ducts or missing end caps, math, and design errors. Could throttle main duct damper is partially closed
How do you balance a multi-zone system?
Max cooling 100% OA, pitot all main ducts at unit discharge, and compart to total CFM of zones against fan CFM. Manual zone dampers for correct amount of air in each zone and proportionately balance
How much difference is there between RA and SA?
RA can handle 70-80% of SA
What are the components of a Toilet Exhaust Fan?
Belt driven centrifugal fan (mushroom housing), Backdraft damper, main ducts and plenum, grilles
How are VAV systems efficient?
20-30% more energy efficient
What is the procedure for balancing a Constant Volume System?
Pressure control balanced. System is filled with air and pressurized. Volume of air then metered out at terminal boxes and pressure controlled with constant volume regulators and controllers, which are set.
What are the two types of Auto Volume Mixing Boxes?
Self actuated spring-loaded volume regulator (closes as system pressure rises), and Constant volume mixing box (uses static pressure flow controller to maintain constant volume)
How do you balance Cold Decks and Hot Decks in a Dual Duct System?
Stats set to max cooling (100% air flow through cool coil), identical to General Procedure. Balance cold deck, then check hot deck, which may not need to be rebalanced
What are Induction Systems?
Generally used for perimeter conditioning under windows. Small volumes of 100% OA which inducts with RA. Smaller fans and ductwork
What is the procedure for balancing Induction Systems?
Usually 1/3 OA, 2/3 RA. Follow General Procedure, 1. take static at nozzles with magnehelic, compare readings to manu. CFM ratings. 2. Start with nearest unit to fan, may take two or three passes. 3. Pitot mains and risers
What is the theory behind VAV?
Delivers air at constant temp (usu. 55) with varying volumes
What are some details on the pressure of the return side of a VAV?
Usually low pressure low velocity ductwork. Separate return air fan needed on larger systems
Where is the Static Sensor located on a VAV system?
Downstream in main duct to monitor changing supply duct pressure, then alters fan accordingly to whatever total volume the terminals are set to
Where are cooling only VAV systems located?
Interiors of multi-story buildings requiring cooling year round
How do you balance a VAV system?
Same as General Procedure.
How do you measure OA% and what is the formula?
% of Outside Air: OA% = Tra - Tma / Tra - Toa & Outside Air Balance: Tma = (OA% x Toa) + (RA% x Tra)
How do Centrifugal Fans work and what are they?
Most widely used, scroll housing with air entering round inlet on one or both sides, turning 90 degrees, and discharging through rectagular opening
How do Vane Axial Fans operate?
Wheels in housed in tubes like centrifugal inline fan wheel, but wheel is a turbine type. Air flow is in a straight line. More blades than propeller and are either flat or curved
How do Prepeller fans operate?
Best with very little or no static. Can’t tolerate load and much ductwork
What is the best way to measure grilles and registers?
Evenly spaced readings across the surface of the outlet with Velometer
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 system did VAVs replace?
Constant volume high pressure system
What is a Venturi Flow Meter and how does it work?
Narrow neck of venturi causes pressure drop, manu has calibrated curve to match readings against in inches WC versus GPM flow
How does a Tachometer work?
Direct contact or photo type. Timed readings and touches shaft or reads marked point on and counts revolutions
