CDC 3E151 - HVAC/R JOURNEYMAN VOLUME 2

(201) What affect will dust on fan blades have on heat transfer?

It will reduce heat transfer

(201) Where do you view the rotation and discharge of a centrifugal fan?

On the drive side

(201) Why are vanes used in the vane axial fan?

To straighten out the spiraling motion of the air

(201) What will allow a sheave to be used on different diameter shafts?

Bushings

(201) Where will the classic V-belts ( A through E ) be used?

Medium horsepower applications

(201) If you have four belts and one is bad, how many should you replace?

4

(202) In a single-duct unit, why is the manual damper left in its initial position?

To maintain a constant airflow through the box

(202) Which design(s) do multiple-path systems use?

Separate cold- and warm-air duct distribution systems or separate supply duct to each zone

(202) Why are multi-path, multi-zone systems limited to smaller areas?

Because of the multiple runs of single-zone ducts

(202) If a cooling demand is reduced in a building, what will the supply dampers do?

Begin to close

(202) What is one reason for the use of terminal reheat?

Allow zone or space control for areas of unequal loading

(202) What makes an independent variable air volume (VAV) system truly independent?

They can control the maximum and minimum cfm that can be supplied from the box

(203) How do you prevent carryover into the ductwork while using atomizing sprays?

Using an eliminator or filter

(203) When is the use of a return air system generally essential?

On larger systems

(203) What is the result of a dirty or clogged filter?

Resistance to flow and reduced efficiency

(203) What causes the adjacent blades on an opposed-blade damper to move in opposite directions?

A linkage

(204) What does carbon monoxide combine with no interfere with the oxygen supply?

Hemoglobin

(204) What will affect a person's sensitivity to an odor?

Temperature and humidity

(204) What can make locating an indoor air quality issue difficult?

The different sensitivities of people

(205) How can air be cleaned?

By filtering the air and cleaning the ductwork

(205) What should be considered while planning the ventilation for odor control?

Increases in heat load and the availability of air of adequate quality

(206) When would the greatest pump lift possible occur?

If there were a perfect vacuum at the pump suction

(206) What may cavitation cause?

Pitting and wearing of the impeller

(207) What should be done if a stuffing box leaks too much?

Tighten the stuffing-box gland

(207) A leaking seal is replaced when the fluid leakage rate exceeds

5 drops per minute

(207) What should you check when you are making major repairs on a pump?

The performance of the pump

(208) In a series loop system, how does unit output change from the first to last unit?

It gradually lowers

(208) What is required for one-pipe down feed units to overcome thermal head?

Two special fittings

(208) Why does a direct return system need to be more carefully balanced?

Because there are different flow rates

(209) Where should radiators be located?

Where heat loss is the greatest

(209) What does the square feet of equivalent direct radiation depend on?

Radiator capacity and configuration

(209) What effects are caused by air binding in a piping circuit?

Noise and reduction in flow

(209) What flow arrangement should be used when hot water coils are used with freezing temperatures?

Parallel-flow rather than counter-flow

(209) What should all low points be equipped with in a hydronic system?

Drains

(210) How does an oversized duct affect air flow?

It slows the air down

(210) What effect will too much airflow have on noise?

The levels will increase

(210) What effect will a single-return on a plenum system have on installation cost?

It will make the installation cost cheaper

(210) Why does the plenum reduce in size?

To maintain air velocity

(210) Why are perimeter loop systems placed around the perimeter of a building?

Because that is where the greatest heat loss occurs

(211) What do we treat air as in HVAC/R?

As an individual gas

(211) Besides its molecules increasing speed, what else happens when air is heated?

It expands

(211) You are going to calculate airflow volume, which formula would you use?

cfm= A*V

(211) What is relationship between air velocity and static pressure?

Static pressure is independent of air velocity

(211) Where will you likely find a negative static pressure?

In the suction ductwork

(211) Where is gauge pressure at its maximum in an air system?

At discharge

(211) Where is gauge pressure normally at zero in an air system?

at the ends of duct runs

(212) What is relationship between static pressure and density?

They are directly proportional

(212) To acquire the fan's total pressure, you take the difference between

the total pressure at the fan outlet and total pressure at the fan inlet

(212) How would you obtain fan velocity pressure?

Take the difference between the total and static discharge pressures

(212) Why must all pressure measurements be taken downstream of the fan discharge?

Because the flow is more uniform downstream

(212) How will brake horsepower be affected if revolutions per minute are increased and no other changes made?

It will increase along with energy consumption

(212) What effect does cubic feet per minute (cfm) have on static pressure?

As cfm increases, static pressure increases

(212) What effect does air density have on fan airflow?

No effect

(213) When using a quarter-inch inclined gauge, where are the hose(s) attached on the gauge?

Left side to positive and right side to negative

(213) How is the pitot tube placed in the airstream?

Parallel and facing the airflow

(214) In air balancing, what do schematics allow the technician to plan?

Plan the sequence of balancing and determine where to take pitot traverses

(214) In air balancing, where do schematics provide the best service?

When the system spans several floors

(214) What is the third step in air balancing?

Check the equipment

(214) Which step in air balancing is " balance outlets and branch ducts"?

4

(214) When are diffusers and grilles used in air balancing?

For minor balancing or trim adjustments

(214) What is the first step in proportionate balancing?

Spot-check end outlets closest to fan

(214) What is the next step after a system has been proportionately balanced?

Recheck equipment readings

(214) What is the final general air balancing step?

Finalize the test reports

(215) If balancing valves are used with orifice plates, why is the valve installed with sufficient distance up or down stream?

To avoid flow turbulence of the plate

(216) "List the valves and terminals in the order they occur" falls under which step of preparing water-balance test reports?

Fill out the flow or pressure-drop water-balance report

(216) "List the coil identification and room number in sequence" falls under which step of preparing water-balance test reports?

Fill out the temperature water-balance report

(216) What is one step in balancing water terminals?

Read and record initial flows without making adjustments

(217) Why is it important for you to know there is not a complete set of standards for symbols?

There's room for error and to caution you not to make assumptions with blueprints

(217) Which agency can a HVAC/R technician acquire blueprints?

Engineering flight or the contractor

(217) Once all pipes, fittings and sizes are determined, what should you recheck?

Each part of the system for completeness

(218) If a draftsmen is creating detailed drawings, what type of views should be used?

Sectional and detailed views

(218) How should elevation views be shown when more than one view is used?

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