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111 Cards in this Set
- Front
- Back
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The danger of freezing in steam coils is minimal when the tube length is _____ or less. |
1.1m (42 inches) |
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Steam coils with long length freezing problems occur at what temperature. |
-2c - -1c (28f - 30f) |
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What temperature does the TC start opening at. |
3.5c (38f) and fully open at 1.5c (32f) |
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What is the max temperature should the air be that is entering the preheat coil. |
18c (32f) |
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What is the temperature should the return air be . |
24C |
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Why is the inlet to the fan 17c. |
The fan will warm it up by 1c. |
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How much of the steam coil capacity should be used when the air temperature is -1c. |
40% |
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It is important to keep the tube lengths are _____ as possible. |
Short |
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I is common practice to select a control valve for a pressure drop corresponding to_____ of its inlet steam pressure. |
50% |
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The steam pressure entering he coil should not be less than _____Kpa |
34 Kpa (5psig) |
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What is the minimum constant flow velocity of water be inside the tubes. |
0.9m/s (3ft/sec) |
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Air velocity through the col should not exceed. |
3.55m/s (700ft/min) |
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_____ air venting in the coil is essential. |
Positive |
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The two greatest fears in hot water coil installations handling subfreezing air are. |
The failure of the circulating pump The failure of the heating source |
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The use of Ethylene glycol solution will result in. |
Lower heat transfer rate Increased friction losses in coil piping Larger pump and higher power costs |
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Why is Ethylene glycol not recommended |
Because is is slightly toxic |
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Why do we use Propylene glycol. |
It is not toxic But it has different heat transfer rates at higher pressures |
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What is the recommended velocity of glycol a turbulent and reasonable transfer efficiency. |
1.2 - 1.8m/s (4 - 6ft/s) |
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Dry air builds and _____ on people when walking on a wool or nylon carpet. |
Static electric charge |
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Static electric charge may cause a painful shock when discharging when touching |
Any metallic object or another person |
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Humidity depends on the _____ and _____ of the air. |
Pressure and temperature |
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The higher the temperature of the air the more _____it can hold. |
Moisture Lower temperatures will hold less moisture |
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What is the term used to tell the capability of holding moisture in the air. |
Relative humidity |
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How do you calculate relative humidity. |
(Actual humidity / max allowable humidity) x100 |
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For comfort humidity should be kept around. |
30-60% |
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Pan humidifiers with plates offer a very low humidification rate? True / False |
True |
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Wetted element humidifiers can be dived into 2 general groups, They are ? |
Power type and Bypass type |
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Describe how a Power type works. |
Small fan draws air from the furnace plenum or the room and forces it through a wetted pad and returns the humidified air into the room |
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Describe how a Bypass type works. |
This type is equipped with a rotating wetted pad. It uses the difference between supply and air return pressure to draw dry air through the pad |
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How does an Atomizing humidifier work? |
Water is broken into small particles using a: Rotating disk Spinning cone Spray nozzle |
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Most water contains _____ in solution. |
mineral salts |
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How do you clean a plate unit. |
soaking them in a slightly acid solution and then washing them with soapy water The pan or tray should be cleaned of all salts/build up The solenoid valve should be checked for leaks. |
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What is the main disadvantage of Atomizing humidifiers. |
They spray the salts into the duct and they build up as a white dust on the surface of the ducts and the rooms Regular cleaning is required to remove the dust |
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Why cant we soften the water using an ion exchange in Atomizing humidifiers. |
This will make it worse by replacing the Magnesium and calcium salts with sodium salts |
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What are the 4 main type of air cleaning devices. |
Disposable filter Fine filter Charcoal filter Electric air filter |
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List the 4 type of of Humidifiers in order from best to worst |
Steam Humidifier Hot water Humidifier Cold water atomizing Pan type |
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The ASHREA says we need minimum __-__ % fresh makeup air |
5-7% |
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Use this for reference |
Hi. |
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Motorized dampers are controlled by ? |
Air operated motors 3-5 psi signal |
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What should the temperature of output air be. |
18c |
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Why should air be 17C before entering the fan. |
The fan adds 1c |
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Return air should be around ___C. |
24C |
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Mixing air supplied fro outdoor and return air should be ___C before being heated/cooled. |
12.5C |
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4 types of cooling coils are. |
All air All water Air water Direct refrigerant |
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The bigger the building the ___ control zones there should be. |
More |
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AHU stands for ? |
Air handling unit |
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DX coils are used for buildings with less than ___ tonnes of cooling capacity. |
100 |
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Chilled water coils are used in bigger buildings with more than ___ tonnes of cooling capacity. |
100 |
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All water systems are better in bigger buildings because they ________. |
Take up less space for piping. |
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Direct re-fridge systems eliminate most of the _____, and are good for use in ____. |
Piping and duct work. Small rooms like apartments and hotel/motels |
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A general system cycle is . |
Condenser > Compressor > Liquid receiver device > Evaporator |
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Mixing dampers are usually automatically controlled to keep the mixing air temperature at? |
12.5C |
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Know these 4 pictures. |
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Note the amount of outdoor air for 12.5c mixed air temperature is reduced to approx ___% during the coldest winter days but insincere to ___% as the temperature rises to 12.5c |
15% 100% |
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The process of using dampers to mix air and not mechanically is called. |
Free cooling. No need to heat/cool the air when it reaches 12.5c from the air outside. |
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Unitary AC systems are installed where and cool how many areas? |
This unit is usually fully assembled and is installed adjacent to the zone to be cooled. It conditions that one area only. |
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Unitary AC systems are installed with ____ duct work. |
Little to no |
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Window air conditioners utilize ____ |
Direct expansion refrigeration system to provide cooling and dehumidification in a local area. |
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Window air conditions require ___ and can be powered by a ___. |
No piping Standard wall outlet. |
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The Condenser compartment in a Window AC system in exposed to ___ and houses ___,___ and a ___. |
Outdoor air Compressor Air cooled condensing coil Condenser fan |
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Condensate is thrown against the condensing coils from the pan by a ___ |
Slinger ring |
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Capacities of window units typically range from ___ to ___ tonnes of refrigeration |
0.3 - 1.8 tonnes ( 1/3 - 2 tons) |
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Packaged air conditions are normally available in a ___ to ___ tonne range. |
2.7 - 13.6 tonnes ( 3 - 15 ton) |
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Unit ventilators are developed to provide ___ room temperature control in buildings. |
Individual |
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Unit ventilators are mounted where ? |
Building exterior walls |
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Unit ventilators are subject to ___ problems in the ___ because no humidification is provided |
Freezing Winter (colder climate) |
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Rooftop units supply ___ to ___ tonnes of cooling |
2.7 - 68 tonnes ( 3 - 75 tons) |
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Roof top units may consist of. |
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These roof top units are usually mounter where. |
On the roof adjacent to the area to be served |
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The mixing section of roof top units is usually capable of ___ on 100% outdoor air. |
Free cooling |
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Roof top units are ___ to maintain due to there exposed location. |
More difficult |
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Central AC systems are commonly used in ___ buildings. |
Larger |
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Categories of AC systems are |
Unitary systems Central systems Combined systems |
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Air handling units may include |
Fans Filters Humidifiers Heating/cooling source Dampers |
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Central AC systems are ___ to maintain because ___. |
Easier All major components are located in the mechanical room. |
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In Central systems ___ and ___ generated by large components can be more easily and effectively controlled. |
Noise Vibrations (Vibrations maaaaan) |
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The main drawbacks of Central systems are: |
Large room for mechanical and distribution room The cost of duct work If one main component breaks the whole system may need to be shut down |
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Single zone Constant air volume systems are not effective for ___. |
Multi zone layouts |
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The main advantage of single zone systems are ___. |
Conditions may be maintained by adjusting the thermostat in the room |
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Mechanical room must be provided for single zone units because ___. |
To assess and clean/repair the unit |
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In multi zone units the dampers are linked together but are ___. |
90degress out of phase |
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Cold check normally supplies air at. |
12.5C |
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Where in Vancouver do we have a dual duct system. |
Vancouver International Airport |
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Why does YVR use a Dual duct 100% fresh air system.
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So they can always have fresh air in the airport to get arid of any Viruses/illnesses in the air. |
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Multi zone systems are normally used in ___ because there application is limited. |
Schools |
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Dual duct system designs result in significant variations in ___. |
Duct static pressure |
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___ are used in dual duct systems to try to adjust for pressure variances. |
Pressure regulators |
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Combined systems require less ___ than central systems. |
Space for a mechanical room and duct work |
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Combined systems are ___ (smaller/larger) than central systems because ___. |
Smaller They are supplemented by smaller units in each zone. |
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Combined systems are ___ (more/less) energy efficient than central systems because they are more ___. |
More Flexible |
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Constant air volume system with perimeter heating combines ___. |
A central air system with perimeter heating elements such as wall fin radiators along exterior walls in each zone. |
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Perimeter heating is installed below ___ to offset heat loss and prevent cold drafts. |
Windows |
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Constant air volume system with perimeter heating ___(are/are not) suited for bigger buildings because ___. |
Are not Space requirements for low velocity duct work |
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Fan-coil units with make up air systems are installed in ___. |
Each room to provide heating and cooling |
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Fan-coil units are located ___ and are good for use in ___ because they can use 100% outside air.
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On exterior walls of false ceilings above the entrance to the room Hotels |
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A four pipe arrangement is not commonly used barbecue it is ___. |
Very expensive |
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Water temperature in a Hydronic heat pump system is maintained to be with in ___ - ___. |
15-32C (59-90f) |
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Hydronic heat pump system is ___ in certain seasons. |
Thermally self balanced |
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Hydronic heat pump system provides ___. |
Multi zone control capacity and reduced mechanical room space requirements |
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D B D |
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D D C B B |
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What is this a picture of ? |
Spray Humidifier |
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E 3.3% C D |
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B |
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Remember this |
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A Capital cost C |
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A ___ can be used to get extra heat out of the exit air to warm up water. |
Economizer |
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Hi. |
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Advantages of heat pipe recovery units are ? |
No pipes / pumps No constantly moving parts No cross-contamination No external power is required Can be treated to resist corrosion Adaptable to available space Recovery rate of 60-70% |
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Disadvantages of heat pipe recovery units are ? |
Difficult to retrofit Recovery is limited when there is possibility of frost forming More expensive |
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C |
