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53 Cards in this Set
- Front
- Back
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The flow control device establishes a pressure differential between what 2 things? |
The condenser and the evaporator |
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Lowering of pressure causes refrigerants to vaporize in where? |
The evaporator |
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What type of metering valves are used in conjunction with the flooded evaporator? |
Float type |
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What type of metering valves are not suitable for AC systems and why? |
Constant pressure valves, they do not respond to changes in temperature |
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Which valve opens and closes In response to the downstream superheat temperatures of the evaporator? |
The thermostatic valve |
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The orifice or capillary tube will allow refrigerant in the system to do what when the compressor is off? |
Equalize pressure |
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T/F: a perimeter loop falls under the 1 pipe system? |
True |
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T/F: 2 pipe systems can be used for both heating and cooling regardless of the season. |
False |
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T/F: a 3 pipe system HTU must be sized for both heating and cooling load. |
False |
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T/F: a 2 pipe system with a 3 way mixing valve assembly requires a secondary pump. |
True |
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T/F: a 4 pipe system has 1 3 way valve with branch connections to the HWS, HWR, CHWS, & CHWR? |
False |
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What are the 3 main factors that determine the cooling effect of air surrounding the human body? |
Air motion Temperature Humidity |
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In order for a temperature difference to occur, what type of heat change must take place? |
Sensible heat change |
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When air is exhausted from a building, what type of pressure do you not want to have? |
Negative pressure |
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T/F: Air conditioning for industrial processes can dictate the quality of the product produced in several cases. |
True |
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What is the number of grains of water vapor contained in 1 lb? |
7000 grains |
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T/F: The high side of a refrigeration system does not include the intake valve on a compressor? |
True |
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A flooded evaporator would have this for a metering device. |
High side float |
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What is an example of an indirect refrigeration system? |
A pipe coil in a curling tank |
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Where a condenser is used, what is the best type of heat removal? |
Evaporative |
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The type of metering valve that Is manually operated and will require continuous supervision is what? |
A needle valve |
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The thermostatic metering valve operates by sensing what? |
Superheat |
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The type of valve that senses temp change with a thermistor is what? |
A thermal electric valve |
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A one pipe system is ideally suited for what type of installations? |
Perimeter baseboard installations |
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What will a 3 pipe system not contain? |
A split AC system |
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A chilled water coil will be piped in which manner to a steam coil? |
Piped opposite of a steam coil |
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Bacteria and disease can be controlled by using what? |
Filtration |
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A priority of air conditioning in pulp mills is to do what? |
Reduce the amount of humidity |
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What 3 things are mechanical refrigeration systems classified by? |
1. Type of flow control device 2. Condition of refrigerant in the evaporator 3. Whether the evaporator comes into direct or indirect contact with the medium being cooled |
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When the evaporator coil comes into direct contact with the medium to be cooled, what type of system is being used? |
Direct contact system |
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What happens with air flow in a direct contact system? |
Air circulates through ducts and passes through an evaporator coil within the duct |
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What type of system uses a secondary refrigerant to cool the primary refrigerant in the evaporator? |
Indirect contact system |
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What type of system always has a chiller to exchange heat between 2 refrigerants? |
Indirect contact system |
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Where does the secondary refrigerant flow through? And what makes it flow? |
Secondary refrigerant flows through or around the space to be cooled. Moved by a pump |
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Name 5 types of mechanical refrigeration systems based on the type of flow control Device. |
1. Low side float system 2. High side float system 3. Capillary tube system 4. Automatic expansion valve system 5. Thermostatic expansion valve system |
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What is another name for flow control or metering devices? |
Expansion valves |
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What type of evaporator coil is a float valve classified as? |
Flooded type |
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Where is a float valve located? |
In the Flash chamber |
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High side float valves differ from low side float valves in what way? |
The location of the float |
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Where are the floats located on a high side versus low side system? |
High side = high pressure side in the receiver Lowside = low pressure side in the upper portion of the evaporator |
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Constant pressure valves respond to changes in what ? |
Pressure not temperature |
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Why are constant pressure valves better than manual valves? |
They are completely automatic |
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A thermostatic valve regulates movement of liquid refrigerant by what 2 factors? |
1. Refrigeration load 2. Degree of super heat leaving evaporater coil |
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What systems are thermostatic valves most frequently used in? |
AC and refrigeration |
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What can be used in place of thermostatic valves? |
Capillary tubes |
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What factors are critical to operation of capillary tubes? |
Proper bore, length of tube, and number of turns |
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What is the only metering device compatible with modern electronic sensing/monitoring devices? |
Thermal electric expansion valves |
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AC systems involve the simultaneous control of what 3 main factors? |
Is temperature, humidity, and air motion |
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What type of heat is transferred by humidity and air motion? |
Latent heat |
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As dry bulb temperature rises, what happens to the amount of sensible heat lost by human bodies? |
It is Reduced |
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What is psychrometrics ? |
The studies of the properties of air |
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What are the 7 properties of air controlled by AC systems? |
1. wet bulb temperature 2. Dry bulb temperature 3. Dew point temperature 4 Relative humidity 5. Grains of moisture per pound of dry air 6. specific volume (of dry air) 7. Enthalpy (amount of BTUs/lbs if dry air) |
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What are the most commonly used heating mediums? |
Steam and hot water |
