HVAC Rooftop Units Flashcards
Makeup air units are required in commercial kitchens and operate in conjunction with an
EXHAUST FAN
When the makeup air unit has no heat exchanger, it is called a
Direct Fired Makeup air unit
All HVAC units have a ___________ section.
Ventilation
The mechanical components in the heating section are:
Burners
Pilot Assembly
Gas Manifold
Gas line connection
The pilot flame burner and its components are referred to as a
Pilot assembly
What does the heat exchanger do
Transfers heat from the combusted flue gasses to the zone supply air that is circulated through the HVAC RTU
Rollback switches sense:
Higher than normal temperature and close the gas valve.
(NC Temp switches)
An ignition transformer is a high voltage transformer with a primary voltage of 120v and a secondary voltage of
5000V-30,000V
4mm-8mm arc
The flame sensing circuit current value is approximately
1.5 milli Amps to 4.0 milli Amps
The pilot flame burner and its components are referred to as
a pilot assembly
An air prove switch is a pressure switch that closes on
Airflow
The cooling section components are
Compressor
Condenser fan motor
Safety switches
Compressor heater
compressor lockout controller
The compressor is the heart of the cooling system. Its function is to
take low pressure vapour and compress it, increasing both the pressure and the temperature.
The low pressure switch resets when pressure rises to approximately
55 psi
The high pressure switch opens when pressure rises to approximately:
410psi
Low Temp switch opens at approximately
4C
The compressor lockout controller locks out the compressor so that it wont restart if the :
LP, HP, or low temp switch shut down the cooling system.
The key elements for the heating section are the
gas valve
burners
heat exchangers
ignition system
The disconnecting means for RTU must be
within sight of an equipment and within 3m
Why is the sequence of operation shorter when the DSI system for ignition is used?
It is not necessary to ignite a pilot flame before the main gas burner
The free cooling function provides
Comfort cooling without running the mechanical HVAC system.
The free cooling function requires :
a free cooling control system
a mixed air control system
an actuator
dampers
