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49 Cards in this Set
- Front
- Back
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Axial fan is how efficient? |
The most efficient |
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Single zone VAV system? |
Modulates supply air temperature |
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Changeover bypass system Regular VAV (Note: “bypass” in the name) |
Has zones that can open independently. The bypass damper will push excess static air pressure into the ceiling space or into the return air plenum. |
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Motors over 5 hp need what type of control system according to Ashae |
5 hp motors need 2 speed or variable speed |
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Changeover VAV systems True VAV |
Controls static pressure with static pressure sensor in duct. Controls fan speed. |
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Cool air controlled by VAV is modulating between what temperatures? |
12-18C 55F supply primary air |
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What does first stage heating call for? |
The dampers to close to minimum position. This is because most VAV are cooling only. |
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What is the high pressure side or the low pressure side of a VAV system. |
High pressure is upstream of the VAV box. Low pressure is downstream of the VAV box |
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Pressure dependent vs pressure independent VAV box? |
Pressure independent flow box has a total pressure-static pressure sensor that can adjust the cfm delivered to the space between the min and max cfm design parameters. Pressure dependent will not have a sensor and will not be able to adjust the CFM as required. |
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How far down the duct is the main static pressure sensor down the duct on a variable air volume system?
Wht is the common static pressure setpoint? |
2/3 down the main duct on a hvac system
Setpoint is 1 inWC (or 2 inWC if the duct sensor is near the main fan unit to account for downstream losses). |
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What piece of equipment indicates the system is a constant air volume system (and not being a variable air volume)? |
The bypass duct will open on high static pressure and dump it into the ceiling space. |
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Do VAV systems supply a temp constant? |
Yes, true VAV do. 55F |
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Do VAV systems supply a temp constant? |
Yes Constant air volume will adjust the supply temperature |
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TQ: Feed a water coil from the bottom of a coil and the air feeding side? |
For a VAV box the inlet water is fed from the bottom and supply side so the water flows towards the return side of the coil and the top. |
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What is unique about a series fan powered VAV box? |
It has an additional fan in the VAV box that is in series with primary Main benefit is it allows you to downsize the main VAV fan, lower pressure, box is negative pressure. Con: VAV box fan runs continuously. The primary supply will have a damper that adjust |
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What are the 4 types of boxes? |
Shut off boxes? Just a damper Shutoff boxes with reheat? Damper and coil Parallel fan powered box? Series fan powered box? Has a fan and pulls air from space |
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What is the difference between Parallel and series VAV box? |
Fan is in series with primary air and fan is in parallel (aka fan is controlling the amount of mixing air pulled into the box from the room. |
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The perimeter |
Outside wall to 8-15ft
These units will need reheat coils |
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What is dual duct (hot deck/cold deck)? |
It has an independent hot ducting system and it has an independent cold deck. The VAV box system will have a mixing box that can pick the ratio of supplied hot and cold air |
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What is dual duct (hot deck/cold deck)? Remember this as dual duct. ;) |
It has an independent hot ducting system and it has an independent cold deck. The VAV box system will have a mixing box that can pick the ratio of supplied hot and cold air |
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What is the difference between multizone system vs multizone unit |
System will mix at terminal box Unit will mix at the unit |
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Is the hot deck cold deck constant volume? |
Yes
Dampers fail to open on heat coil. |
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What happens on a freeze stat trip for an AHU? |
(1) OA damper closed (2) fan off (3) Hot water valve full open |
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What are the control pressures for a VAV system with pneumatic control? |
Back (Definition) |
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Critical zone reset? |
A critical zone will be a zone will be furthest away. The VAV will lower the static pressure and increase the damper to 100% to allow for the minimum airflow allowed to the critical zone. Supplying the necessary air changes for that zone. This will allow the supply fan to lower its RPM and increase the system efficiency. |
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What does DOAS? |
Dedicated outdoor air system 100% outdoor air |
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What is the minimum flow setting for a VAV? |
It is set to maintain a minimum indoor air quality.
Maximum is set to maintain maximum cooling. |
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Where are the building pressure sensors installed? Low pressure and high pressure? |
Low pressure is outside High pressure is inside Building pressure maintains 0.05 PSI (a 10 mph wind can have a 0.05 PSI influence on the sensor if it is improperly installed |
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The return fan is controlled by building pressure and the economizer relief air dampers will control building pressure? True or false? |
True. |
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What are some common signs of building pressure issues? |
• Return or relief fans operate near 100-percent speed most of the time. • Building differential static pressure fluctuates widely and/or rapidly. • Return- or relief-fan speed fluctuates widely and/or rapidly. • Exterior doors are hard to open or do not close securely. |
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What are the two most common ways of controlling building pressure? |
(1) measure air coming in and leaving building. Control with relief fan and outside air damper. (2) measure interior (high pressure) and exterior (low pressure) of building. Control with relief damper. (The return air fan should pressurize the return plenum and allow the relief damper to operate effectively.) |
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Neutral deck uses 100% outside air in a …….. ? |
Three deck multizone |
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How do you winterize a heating coil? |
Drain it and flush it with glycol |
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What are the three advantages of VAV? |
(1) comfort (2)dehumidification (3) fan capacity control reduces energy usage |
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What is an acceptible amount 400-500 pm in ambient air what is an unacceptable amount? |
1000 ppm or over |
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For the test know what all the systems look like with a picture because that will be on the test. Also know what an induction coil is… know the exact wording of the system definitions of the different systems. |
;) |
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Complex HVAC |
More than one mode of heating or cooling? |
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What is a terminal reheat system? What is a dual duct system? What is a multi zone system? |
? |
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A multi zone UNIT mixes hot and cold at the UNIT? T/F? |
True |
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constant air volume system cools the air in the air handling unit down to the lowest temperature? |
Terminal reheat system |
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There are a lot of complex HVAC system questions on the TQ |
…. Apparently. |
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What position do shutoff VAVs go to during heating? |
Back (Definition) |
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What is a pro and a con for a series VAV? |
Back (Definition) |
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How much savings for a VAV over a CAV? |
Back (Definition) |
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What are the main differences between Parallel and series fans? |
Back (Definition) |
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Perimeter of the building is 8-15ft needs what? |
Reheat coils |
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What is the difference between multi zone system vs multizone unit? |
Multizone system mixes at the VAV Multizone unit mixes at the unit |
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Constant air volume: What type of system supplies the minimum heating temperature and uses a reheat coil at the terminal unit? |
Terminal reheat system
(Mixed air controls the temperature at the unit.) |
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Constant air volume: what is a mixed air system? |
Final supplied temperature is controlled at air handling unit Uses an averaging sensor |
