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COSC 326 > EXAM 2 > Flashcards

EXAM 2 Flashcards

1
Q

The Big Four

A

Split DX
Roof Top Unit
Air Handling Unit (AUH) / Fan Coil Unit (FCU)
Chiller / Boiler

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2
Q

Where is the condensing unit located in a Split DX System?

A

Outside

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3
Q

Where are the evaporator coil, expansion device, and fan located in a Split DX System?

A

Inside

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4
Q

Name the different parts of the condensing unit:

A

Compressor
Condenser Fan
Condenser Coil

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5
Q

Common size for commercial offices:

A

25-30 tons

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6
Q

Roof Curb

A

a device that allows the mounting of the RTU on top of the roof and provides the penetrations for duct, pipe, conduit, etc.

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7
Q

RTUs must have a what installed? Describe it.

A

Economizer.
Mechanical devices intended to reduce energy consumption, or perform useful functions such as preheating a fluid. It allows up to 100% use of outside air for cooling

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8
Q

What does Texas have to say about Economizers?

A

The energy code for most municipalities has an exception that allows the installation of RTUs without the economizer

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9
Q

What will happen if the condenser coils on an RTU are damaged?

A

They will not reject heat very well

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10
Q

What is Francis Hall’s floor area?

A

40,000 sq. ft.

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11
Q

CSI Section 23 00 00

A

Heating, Ventilating, and Air Conditioning (HVAC)

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12
Q

Cooling coils/heat

A

HX

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13
Q

The chilled water typically exits the HX at about what temperature?

A

55 degrees F

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14
Q

In a chilled water system, the water is cooled to what temperature?

A

45 degrees F

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15
Q

Air cooled chiller systems can vary in capacity from _______ tons

A

10-125 tons

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16
Q

CSI Section 23 64 00

A

Packaged Water Chillers

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17
Q

The primary component of a typical chilled water loop cooling system

A

The Chiller

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18
Q

Compressor Types

A

Centrifugal for large systems (>200 ton)
Screw (150 – 600 tons)
Scroll (5 – 25 tons)

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19
Q

Heat Rejection

A

Air-cooled condenser

Cooling tower

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20
Q

Zachry Engineering complex cooling load:

A

About 1,000 tons

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21
Q

What type of HVAC system is recommended for Zachry Engineering complex?

A

4 water-cooled Chillers each of them distributing the cooling load. That way if one fails, the client would still have some cooling capacity.

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22
Q

Parts of a Centrifugal Chiller

A 
Condenser water connections 
Condenser 
Compressor 
Motor
Electrical Service 
Lubrication Pump
Controls 
Evaporator 
Chilled water connections
23
Q

Normal design operation for water-cooled centrifugal chiller

A

Chilled water supply = 45°F.

Chilled water return = 55°F.

Cooling tower supply = 80°F.

Cooling tower return = 90+°F.

24
Q

Is the condenser barrel on a chiller typically insulated?

A

NO

Condensation on the surfaces is not an issue.

25
Q

What is the primary difference between an air-cooled chiller and a centrifugal chiller?

A

Physical limitation on size. They top out at about 150-200 tons of capacity.

26
Q

Chilled water cooling loop component

A

Chilled water pump
Building cooling load

Chiller

  • Evaporator
  • Expansion Valve
  • Condenser
  • Compressor

Cooling tower pump
Cooling tower

27
Q

Any chilled water loop system MUST implement at least _______________ operation when outside ambient conditions allow such operation at the cooling towers

A

Partial “free cooling”

28
Q

What is the primary limit on cooling tower thermal performance?

A

Wet bulb temperature

29
Q

Where would you find parallel fan powered VAV box?

A

Perimeter zones in office buildings.

30
Q

For very high wet bulb temperatures, the cooling tower must be sized larger or smaller?

A

Must be sized larger for a given capacity.

31
Q

For most HVAC applications, the design engineer would specify a tower with what approach?

A

10 to 15° F “approach”

32
Q

What does a 10 to 15° F “approach” mean?

A

a design point that will ensure that the cooling tower can provide cooling water back to the chiller at a temperature that is 10 – 15°F warmer than the coincident wet bulb temperature.

33
Q

Two most common cooling tower configurations used in various HVAC applications

A

Counter flow and cross-flow

34
Q

What CSI Section contains information about Air Handling Units (AHU)?

A

CSI Section 23 73 00 - Indoor Central-Station Air-Handling Units

35
Q

What CSI Section contains information about Fan Coil Units (FCU)?

A

CSI Section 23 82 19 - Fan Coil Units

36
Q

What CSI Section contains information about Variable Air Volume Terminal Units (VAV Boxes)?

A

CSI Section 23 36 16 - Variable Air Volume Units

37
Q

Differences/similarities between AHU and FCU?

A

Differences:
Size
FCU typically has an integrated fan/motor assembly whereas an AHU has a motor separately mounted from the fan.

Similarities:
Both have fans, heat exchangers (coils) and connect via duct-work to diffusers and grilles.

38
Q

How do you know if a valve is open or closed?

A 
Parallel = open 
Perpendicular = close
39
Q

In what type of climate would you recommend a 2-pipe chilled water unit?

A

Predominantly cooling (interior zones of multi-story high rise)

40
Q

In what type of climate would you recommend a 4-pipe chilled water unit?

A

Where there is a need for both heating and cooling simultaneously

41
Q

What type of system dominates the commercial HVAC market?

A

Variable Air Volume (VAV)

42
Q

Configurations of VAV Boxes

A 
Single duct VAV Box
Single duct VAV Box with reheat (hot water or electric)
Series fan-powered VAV Box
Series fan-powered VAV Box with reheat 
Parallel fan-powered VAV Box
43
Q

How does a VAV system control flow?

A

By maintaining a constant duct pressure

44
Q

What is a common control pressure?

A

Around 2.0 inches of water gage (w.g.)

45
Q

The variable frequency drive (VFD) is also known as the:

A

Variable speed drive (VSD)

46
Q

The energy use with a VAV System is about _____% less than a Constant Volume (CV) based system

A

50%

47
Q

What is the primary function of a roof curb?

A

Provide a secure mounting location for the RTU

48
Q

Chilled water loop systems using chillers can reject heat at their condensers through:

A

Air or water as needed for the application.

(Either air or water depending on application because if it is a small capacity unit, we wouldn’t go to the expense of using a cooling tower. Scale (size) become important for “break point” of air vs. water.)

49
Q

What “heat” is being rejected from a chiller condenser?

A

Heat from the refrigerant

50
Q

What is the main constraint limiting the size (capacity) of air-cooled condensing for a chiller?

A

Physical size of the condenser

51
Q

When talking to an HVAC contractor about a chiller and they mention that “insulation on the barrel needs to be protected” which barrel are they talking about?

A

Evaporator

52
Q

Why is it so easy to identify the condenser barrel on a centrifugal chiller?

A

It is not insulated

53
Q

“Free cooling” as described in the latest ASHRAE energy standard is referring to what?

A

Cooling towers are used to proved chilled water

54
Q

If using a water cooled chiller on your 300,000 sq. ft. commercial tower, you would expect what kind of chiller on this project?

A

Centrifugal compressor, water cooled

COSC 326 (2 decks)

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