Commercial HVAC Equipment 4th year ILM 110405a Flashcards
What does DDCV stand for?
Dual duct constant velocity system
What does DDVAV stand for?
________________________
Dual duct variable-air-volume system
Which system supplies heating and cooling at the same time through separate ducts to
the zone?
DDCV or dual duct constant velocity
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?*
_______________
Constant volume supply Fan
What is the biggest difference between a “constant volume dual duct system” to a
“variable air volume dual duct system”?*
_______
the difference is that the air is not drawn into building by a constant volume fan as it is in the usual dual-duct system, but it is split into two air streams that flow through two variable volume fans.
What can the mixing boxes do for the DDVAV system?
________________
it serves each thermal zone, these mixing boxes 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?
___________________
make- up air unit.
What happens to the building if the exhaust fan is in operation and there is no air being
replaced?*
poor air flow, undesirable continuous air-pressure difference between the inside and the outside of the home.
What would be an indicator of negative pressure in a building?
________________________________________________________________________
cold air infiltration, increase of energy.
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?*
gas burners are installed directly int he outside make-up air stream, 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?
______________________________
What is the isolation damper used for in a DFMUA?
to prevent cold air from dropping through a unit into a warm building and warm air from escaping through a unit during colder months when it is not in operation.
What helps prevent the burners from operating if the dampers are not fully open?
_____________________
the damper actuator motor.
The air that is flowing past the burner comes from where in a DFMUA?
________________________________________
What is the average range of air that needs to pass the burner for proper burner
combustion?
velocity range 2500 to 3200 fpm.
What is the average discharge supply air temperature for a direct fired MUA?
between 10 celsius and 38 celsius
List the common safety components that could be included in a MUA.
________________________________________________________________________
_________________________
- flame proving sensors
2.high velocity air switches - low velocity air switches
4.high temperature limit
When would a high velocity Air Switch open for a DFMUA?
____________________
when the velocity of air flowing through the unit becomes too high.
When would a low velocity Air Switch open for a DFMUA?
when the velocity of the air is lower than than the set value.
What is the specific velocity range for proper combustion?
___________________________________________
2500-3200 fpm
What is the discharge air temperature range for a DFMUA?
___________________________
10 and 38 celsius.
Main gas shut off, pilot gas manual valve, pilot solenoid valve, main gas pressure
regulator, are a part of what in the DFMUA?
_____________________
valve train
What does an indirect fired make up air have that a direct fired make up air does not?
________________
has a sealed combustion chamber.
What is the substance that a heat pump uses to transfer heat from one place to
another?
______________________
Will the evaporator coil in a heat pump absorb heat or release heat from its
surroundings?*
_____________________
What is the main difference between a standard cooling system and heat pump?
__________________________
List the components of a heat pump.
________________________________________________________________________
________________________________________________________________________
_______________________________________________________________________
Which component of a heat pump reverses the refrigerant flow to change from heating
to cooling mode?*
____________________
Which device lowers the pressure of the refrigerant in a heat pump system?
____________________
What happens to the efficiency of the heat pump when there is frost build up?
________________________________________________________________________
The indoor coil should be installed where when using a forced air gas furnace?
______________________________________________
What does EES stand for?
_________________________________________________
List the possible residential heat pump loop systems.
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
__________________________________________________________________
Where is the heat absorbed from in an open loop system?
____________________________________________________
What are the two types of energy recovery systems?
________________________________________________________________________
________________________
What does an HRV do for a building?
________________________________________________________________________
________________________
When looking at an HRV, do the two air streams, the exhaust air and fresh air, come into
contact with each other?
Can an HRV be used in the summer months?
What happens if there is frost buildup inside the HRV’s heat exchanger?
________________________
An HRV is designed to remove excess what?*
___________
What happens if there is frost buildup inside the HRV’s heat exchanger?
_______________________
An HRV is designed to remove excess what?*
________________________
moisture
At what temperatures do the efficiencies of an HRV become negligible?
_____________________________
Are there filters used in the HRV units?
_________________________________
What are the two different types of duct systems an HRV can be installed?
________________________________________________________________________
________________________________________________________________________
stand alone system
forced air duct system
What are the three different methods that an HRV duct system can be installed?*
________________________________________________________________________
________________________________________________________________________
____________________________________________
What type of HRV duct system would be used for radiant heating?
___________
When the installation of an HRV system is completed, what should be done to the
system at start up?
What kinds of problems could there be if there is a negative pressure in the house?
________________________________________________________________________
____________________________
What kinds of problems could there be if there is a positive pressure in the house?
________________________________________________________________________
______________
can cause moist air to be pushed into the walls and roof of the house where it can condense and lead to deterioration of building materials.
Could the low speed operation of an HRV system meet the ventilation requirements?
______________
yes, for most circumstances
Can an HRV be used for an air cleaner?
no
What is the approximate temperature that the HRV will activate the Defrost cycle?
________________
-5 celcius
What is another way of preventing frost build up in the HRV?
_________________
What does ERV stand for?
________________________________________________________________________
energy recovery ventilator
What is the biggest difference between an HRV to an ERV?
________________________________________________________________________
______________________
the way the heat exchanger works, with ERV the heat exchanger transfers a certain amount of water vapor along with heat energy, while a HRV only transfers heat.
What is the material used for the ERV’s heat wheel to transfer water molecules to the
other air stream?
_________________
type A silica gel
