Commercial HVAC Equipment Flashcards
What does DDCV stand for?
Dual Duct Constant Velocity
What does DDVAV stand for?
Dual Duct Variable-Air-Volume
Which system supplies heating and cooling at the same time through separate ducts to the zone?
Dual Duct Constant Velocity (DDCV) system
The duct (DDCV system) that holds and uses the heating coil is known as?
The Hot Deck
The duct (DDCV system) that holds and uses the cooling coil is known as?
The Cold Deck
Which part of the DDCV system varies the hot and cold air streams to a given space?
The dual duct box
What is the biggest difference between a “constant volume dual duct system” to a “variable air volume dual duct system”?
The air is not drawn into the building by a constant volume fan and DDVAV is split into two airstreams that flow through two variable volume fans, where as DDCV has one airstream.
What can the mixing boxes do for the DDVAV system?
They can vary both the proportions of hot and cold air as well as the total flow rate of air to the zone.
What does MUA stand for?
Makeup Air Unit
What happens to the building if the exhaust fan is in operation and there is no air being replaced?
The building experiences a negative pressure
What would be an indicator of negative pressure in a building?
Back drafting of combustion appliances such as gas hot water heater or furnace. … A musty smell or stagnant, stale air. A rush of air or draft when opening an exterior door. Exhaust fans not working properly.
Are there filters used in a make-up air unit?
Yes
What are the two types of MUA systems?
Direct gas fired and indirect gas-fired
Is there a heat exchanger installed in a Direct Fired make up air unit?
No
Where are the products of combustion discharged into from a DFMUA?
Discharged into the makeup airstream and supplied to the building or process.
When referring to a recirculating direct fired MUA, where is the return air damper located compared to the burner?
Right behind the burner
What is the isolation damper used for in a DFMUA?
Prevent cold air from dropping through a unit into a warm building.
What helps prevent the burners from operating if the dampers are not fully open?
The damper actuator motor end switch
The air that is flowing past the burner comes from where in a DFMUA?
Outside
What is the average range of air that needs to pass the burner for proper burner combustion?
2500 to 3200 fpm
What is the average discharge supply air temperature for a direct fired MUA?
Between 50 degrees F (10 degrees C) and 100 degrees F (38 degrees C)
List the common safety components that could be included in a MUA.
Flame proving sensors, high velocity air switches, low velocity air switches, and high temperature limit
When would a high velocity Air Switch open for a DFMUA?
When the air flowing through the unit becomes too high
When would a low velocity Air Switch open for a DFMUA?
When the air is lower than the set value
Main gas shut off, pilot gas manual valve, pilot solenoid valve, main gas pressure regulator, are a part of what in the DFMUA?
The housing
What does an indirect fired make up air have that a direct fired make up air does not?
A heat exchanger
What is the substance that a heat pump uses to transfer heat from one place to another?
Refrigerant
Will the evaporator coil in a heat pump absorb heat or release heat from its surroundings?
Absorbs heat
What is the main difference between a standard cooling system and heat pump?
The heat pump cycle is fully reversible and can provide heat in the winter and cooling and dehumidifying in the summer.
List the components of a heat pump.
Refrigerant, reversing valve, coil, evaporator, compressor, expansion device, plenum, and suction line accumulator
Which component of a heat pump reverses the refrigerant flow to change from heating to cooling mode?
The reversing valve
Which device lowers the pressure of the refrigerant in a heat pump system?
The expansion device
What happens to the efficiency of the heat pump when there is frost build up?
Decreases reducing its ability to transfer heat to the refrigerant.
The indoor coil should be installed where when using a forced air gas furnace?
The warm downstream side of the furnace
What does EES stand for?
Earth Energy Systems
List the possible residential heat pump loop systems
Open loop systems, closed loop systems, domestic hot water heating systems, supplementary heating systems, heat distribution systems
Where is the heat absorbed from in an open loop system?
Ground water from a conventional well
What are the two types of energy recovery systems?
Open system and closed system
What does an HRV do for a building?
It captures the heat from a buildings exhaust air and transfers it to the fresh air entering the building.
When looking at an HRV, do the two air streams, the exhaust air and fresh air, come into contact with each other?
No
Can an HRV be used in the summer months?
Yes but its more important to use in colder climates
What happens if there is frost buildup inside the HRV’s heat exchanger?
Its defrost mechanism comes on
An HRV is designed to remove excess what?
Heat
At what temperatures do the efficiencies of an HRV become negligible?
20 degrees F (-7 degrees C)
Are there filters used in the HRV units?
Yes
What are the two different types of duct systems an HRV can be installed?
A stand alone system and a forced air duct system
What are the three different methods that an HRV duct system can be installed?
Fully ducted systems, simplified systems, and exhaust-ducted systems—fully ducted systems are best
What type of HRV duct system would be used for radiant heating?
Stand alone system
What kinds of problems could there be if there is a negative pressure in the house?
Can cause spillage of carbon monoxide and other combustion by products.
What kinds of problems could there be if there is a positive pressure in the house?
Causes moist air to be pushed into the walls and roof.
Could the low speed operation of an HRV system meet the ventilation requirements?
Yes
Can an HRV be used for an air cleaner?
Yes
What is the approximate temperature that the HRV will activate the Defrost cycle?
23 degrees F (-5 Degrees C)
What is another way of preventing frost build up in the HRV?
By using dampers
What does ERV stand for?
Energy recovery ventilation
What is the biggest difference between an HRV to an ERV?
The rotating enthalpy wheel on the ERV
What is the material used for the ERV’s heat wheel to transfer water molecules to the other air stream?
Type A silica gel
