HVAC Rooftops Units Flashcards
What are the three main sections of an HVAC RTU?
Heating,
Cooling,
Ventilating.
What two parts does the heating section consist of?
Burner area,
Heat exchanger.
How can you tell which type of ignition system an Hvac unit is equipped with?
Look at the main gas valve to see a pilot gas line,if so, it is IP; if none, assume DSI or HSI. Look for high voltage wire to the electrode, if present it is DSI; if not, assume HSI.
What is a typical voltage range of the secondary on an ignition transformer?
5000-30000V.
Able to strike an arc of approx 4-8mm.
What is a flame sensing circuit’s typical current values?
> 4 micro amps.
What is the first thing to start on a call for heat?
The Combustion air blower.
What section is the Evaporator coil mounted in?
Ventilation, so that the building return air may pass through it.
Is an isolating switch required for all RTUs?
Yes, most will have a cooling portion so the disconnect must be within 3 m.
What are three important applications of make up air units?
Restaurants,
Paint booths,
Parkades.
In a direct fired MUA, what is the required minimum ratio of fresh air to products of combustion?
100:1.
What two functions can a two wire thermostat control?
Heating, simple furnace or unit heater.
What functions can a seven wire thermostat control?
Heating and cooling in two stages, as well as a manual fan.
Why would you use a Building Management System?
Because often it’s cost savings offset the high installation costs.
What do inputs accomplish in a BMsystem?
They monitor or sense the changing conditions in a building.
What kind of signal is used to control a damper motor?
0-10V analog signal.
