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Modern Building systems > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

What are the primary functions of hvac systems

A

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

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2
Q

Hvac used in commercial can have what features

A

Constant or variable volume supply systems
Multiple zones of occupancy
Provide ventilation, circulation, filtration, heating, cooling, humidification

Pneumatic electric or computerized controls

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3
Q

What are the 2 classifications of fans

A

Centrifugal and axial

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4
Q

What are three important principles of fan speed changes?

A

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)

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5
Q

What are 2 basic types of dampers

A

Opposed blade dampers

Parallel blade dampers

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6
Q

If you see NC or NO next to each damper, what does this mean

A

Their fail safe position

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7
Q

What happens when power is cut off to a damper

A

They return to their fail safe position by a built in spring return

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8
Q

Hot water is commonly produced by what 2 things

A

Gas fired or electric boiler systems

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9
Q

What are other hot water heating systems

A

Steam coils, natural gas furnace, electric dust heaters, solar heat

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10
Q

What are circulating pumps used for

A

Move hot and chilled water

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11
Q

Where are circulating pumps usually located

A

Typically in the boiler/ chiller mechanical rooms

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12
Q

What are valves used for

A

To regulate the flow of water through the heating and cooling coils

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13
Q

What are the 2 classifications of control valves

A

Two ways and three ways

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14
Q

What are the 2 mechanical methods for chilling water

A

Chilling and cooling tower ,

Refrigeration

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15
Q

What is free cooling

A

Cooling with just the use of cold air outside

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16
Q

What percentage of outside air for ventilation does the building code require

A

10 and 25%

17
Q

Explain what an economizer is

A

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

18
Q

What are the constant temperatures that the economizer uses

A

Between 24° (winter) and 27°(summer)

19
Q

What does a freeze stat do

A

Protects the water from freezing ,

They are usually a manual reset device

20
Q

Can class 1 circuits be installed with power supply conductors? If so, when

A

Conductors must be rated for the highest voltage and temperature, and connect to the same equipment

21
Q

What is the fail safe positions for outside, exhaust and return air dampers

A

Outside : Nc
Exhaust : NC
Return air : NO

22
Q

What is the typical set point for a mixed air controller

A

13°

23
Q

List 3 advantages of electric heat spacing

A

Cleanliness
Efficiency
Self contained

24
Q

What is the usual watts per length rating of standard baseboard heaters

A

250w/ft

25
Q

What type of heater is normally installed at ceiling height

A

Unit heaters

26
Q

Residential furnaces are available in single and 3 phase ratings of

A

5 kw to 40 kw

27
Q

What are three types of thermostats commonly used in residential space heating applications

A

Line voltage
Low voltage
Electronic

28
Q

Typical efficiency of gas fired furnaces are what

A

70% and 80%

29
Q

The smallest baseboard heater available is what

A

500w and they increase by 250w increments

30
Q

What are commonly used cables for heating cable sets

A

Polyvinyl chloride-sheathed or mineral insulated

31
Q

What is an anticipator resistor used for

A

It is used for pre heating, to eliminate the overshoot of the setpoint when heating a room

32
Q

What is a heat exchanger used for

A

Pilot flame ignites the burner and warms the heat exchanger. When the set point temperature is reached the blower motor turns on

Modern Building systems (2 decks)

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