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51 Cards in this Set
- Front
- Back
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How do you determine rotation of a Axial fan
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By looking at the discharge side of the fan. (In your face)
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When is a Axial fan very inefficient?
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When working against static pressure.
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What is the efficiency of the Axial fan?
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40% or less
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Where is the forward curved fan used? (Most common)
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Low pressure CAV systems up to 2" static
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What causes the forward curve fan to overload?
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Adding static pressure to the system. Ex: taking off the blower door.
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Smaller Package units use what kind of fan?
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Forward curved fan.
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What fan is used for high static?
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Backward incline
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Backward incline fans overload with high static? T/F
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False. They do not overload. They can handle it.
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T/F backward incline is more efficient then forward curved.
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True they are.
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Describe a Airfoil fan.
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It's a refinement of the backward incline BUT has a thicker blade the looks like a airplane wing.
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Which fan is more efficient? Backward incline or Airfoil?
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Airfoil. It has similar characteristics but is more efficient.
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In terms of efficiency describe the Airfoil fan
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It is the most efficient fan used in our industry.
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VAV fans use this kind of fan
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airfoil
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What is wide open CFM
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Total flow with all diffusers and grills open
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What is blocked tight static pressure?
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static pressure with all diffusers closed.
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Duct system pressure. Describe what it means.
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Space considerations in building may require forcing larger volumes of air through smaller ducts. The associated increase in velocity will result in a increase of static pressure
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What is low pressure on a duct. What fan do we use
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2" w.c 2000ft/min or less. Forward curve
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What is medium pressure in a duct?
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2-6" w.c 2000ft/min or above
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What is high pressure in a duct
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6-10" w.c
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Which way should the condenser face on a RTU? Why?
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Into the prevailing winds. Because it will ensure the air is not recirculated in the condenser.
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What should you use when craning a RTU?
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Spreader bars. So you don't crush the unit.
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The most important thing when craning a RTU is?
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Ensure the load is secure with no crossed cables.
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On start up what do you need to check?
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Rotation of the fans.
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Should you change the rotation of a compressor after it has been running.
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NO. Bearings wear a certain way with each rotation. Changing it will damage them.
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When do you insulate a liquid line?
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When it runs through ambient air warmer then the condenser
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A chilled water coil should have the water supply inlet where?
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On the bottom of the air leaving side.
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What is the maximum voltage imbalance?
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2%
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How do you calculate voltage imbalance?
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Calculate average voltage.
Calculate max deviation Calculate %deviation from average. |
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Voltage must remain ______ of name plate spec
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10%
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Sleepers for a condensing unit must be made of what?
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Non-combustible materials.
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RTU MUST BE how far from the edge of the roof?
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10ft as per b-52 code
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B-149 gas code states a unit can be ________ from the edge
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6 ft
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If a RTU is to close to the edge. What must be installed?
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Guardrail.
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With a stacked evaporator unit. Which evaporator should come on first and go off second. Why?
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The bottom should. Because you don't want condensate to flow over the bottom evaporator and be reintroduced into the building.
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ASHRAE states that the body can handle a maximum thermal shock of?
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20 *F
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What is the optimum cooling set point. Why?
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75*F because it offers the best cooling ability and efficiency.
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Face velocity of a cooling cool should be?
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400-600 ft/min
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How many CFM for a/c
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400
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How many CFM for a heat pump
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450
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Outdoor air dampers in Canada should what?
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Spring return closed.
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Opposed blade dampers have what flow conditions.
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Linear
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Why are parallel blade dampers not good?
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They do not have a good low end operating range.
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What is the max temperature difference across the test points in a reversing valve?
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5*F
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What position should a reversing valve be installed?
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Horizontally. With the discharge line facing up.
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What pressure differential is required for a reversing valve to operate?
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75-100psi
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What should be done if a reversing valve is stuck?
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Switch between heating and cooling.
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How do you charge a fixed orfice?
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System charge to 10* superheat
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How do you charge a TXV system?
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System charge to 10* subcooling.
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What could happen to a RTU without a crankcase heater?
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Loss of oil damage to bearings and valves. Leading to compressor failure.
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How would you tell if your compressor valves were bad?
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Low discharge, high suction and low amp draw
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Most likely cause of water in the duct work with a steam humidifier?
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A cracked steam distributor.
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