Exam 2 Flashcards
(32 cards)
What are the primary functions of hvac systems
Heat the building during the cooler seasons
Provide ventilation to maintain a healthy flow of fresh air all the time
Cool the building during warmer seasons
Hvac used in commercial can have what features
Constant or variable volume supply systems
Multiple zones of occupancy
Provide ventilation, circulation, filtration, heating, cooling, humidification
Pneumatic electric or computerized controls
What are the 2 classifications of fans
Centrifugal and axial
What are three important principles of fan speed changes?
Airflow varies directly with fan speed
Static pressure varies with the square of the fan speed. Doubling the fan speed = 4 times the static pressure
Power is cubed with the fan speed. Doubling the fan speed will result in double the airflow, but requires 8 times the HP (power)
What are 2 basic types of dampers
Opposed blade dampers
Parallel blade dampers
If you see NC or NO next to each damper, what does this mean
Their fail safe position
What happens when power is cut off to a damper
They return to their fail safe position by a built in spring return
Hot water is commonly produced by what 2 things
Gas fired or electric boiler systems
What are other hot water heating systems
Steam coils, natural gas furnace, electric dust heaters, solar heat
What are circulating pumps used for
Move hot and chilled water
Where are circulating pumps usually located
Typically in the boiler/ chiller mechanical rooms
What are valves used for
To regulate the flow of water through the heating and cooling coils
What are the 2 classifications of control valves
Two ways and three ways
What are the 2 mechanical methods for chilling water
Chilling and cooling tower ,
Refrigeration
What is free cooling
Cooling with just the use of cold air outside
What percentage of outside air for ventilation does the building code require
10 and 25%
Explain what an economizer is
It is the outside air thermostat.
Whenever the outside air temperature is greater than the return air temperature the OAT closed the dampers to their minimum positions.
Reduces the costs of cooling the hot outside air
What are the constant temperatures that the economizer uses
Between 24° (winter) and 27°(summer)
What does a freeze stat do
Protects the water from freezing ,
They are usually a manual reset device
Can class 1 circuits be installed with power supply conductors? If so, when
Conductors must be rated for the highest voltage and temperature, and connect to the same equipment
What is the fail safe positions for outside, exhaust and return air dampers
Outside : Nc
Exhaust : NC
Return air : NO
What is the typical set point for a mixed air controller
13°
List 3 advantages of electric heat spacing
Cleanliness
Efficiency
Self contained
What is the usual watts per length rating of standard baseboard heaters
250w/ft
