Exam 2 Flashcards by Frank Quintana

The Big Four

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

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

Outside

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

Inside

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Name the different parts of the condensing unit:

Compressor
Condenser Fan
Condenser Coil

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Common size for commercial offices:

25-30 tons

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Roof Curb

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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RTUs must have a what installed? Describe it.

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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What does Texas have to say about Economizers?

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

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

They will not reject heat very well

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What is Francis Hall’s floor area?

40,000 sq. ft.

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CSI Section 23 00 00

Heating, Ventilating, and Air Conditioning (HVAC)

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Cooling coils/heat exchangers are known as

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

55 degrees F

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

45 degrees F

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Air cooled chiller systems can vary in capacity from _______ tons

10-125 tons

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CSI Section 23 64 00

Packaged Water Chillers

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The primary component of a typical chilled water loop cooling system

The Chiller

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Compressor Types

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

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Heat Rejection

Air-cooled condenser

Cooling tower

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Zachry Engineering complex cooling load:

About 1,000 tons

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

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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Parts of a Centrifugal Chiller

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

Normal design operation for water-cooled centrifugal chiller

Chilled water supply = 45°F.

Chilled water return = 55°F.

Cooling tower supply = 80°F.

Cooling tower return = 90+°F.

Is the condenser barrel on a chiller typically insulated?

Condensation on the surfaces is not an issue.

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

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

Chilled water cooling loop component

Chilled water pump Building cooling load Chiller - Evaporator - Expansion Valve - Condenser - Compressor Cooling tower pump Cooling tower

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

Partial "free cooling"

What is the primary limit on cooling tower thermal performance?

Wet bulb temperature

Where would you find parallel fan powered VAV box?

Perimeter zones in office buildings.

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

Must be sized larger for a given capacity.

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

10 to 15° F "approach"

What does a 10 to 15° F "approach" mean?

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.

Two most common cooling tower configurations used in various HVAC applications

Counter flow and cross-flow

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

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

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

CSI Section 23 82 19 - Fan Coil Units

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

CSI Section 23 36 16 - Variable Air Volume Units

Differences/similarities between AHU and FCU?

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.

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

``` Parallel = open Perpendicular = close ```

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

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

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

Where there is a need for both heating and cooling simultaneously

What type of system dominates the commercial HVAC market?

Variable Air Volume (VAV)

Configurations of VAV Boxes

``` 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 ```

How does a VAV system control flow?

By maintaining a constant duct pressure

What is a common control pressure?

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

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

Variable speed drive (VSD)

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

50%

What is the primary function of a roof curb?

Provide a secure mounting location for the RTU

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

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.)

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

Heat from the refrigerant

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

Physical size of the condenser

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?

Evaporator

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

It is not insulated

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

Cooling towers are used to proved chilled water

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

Centrifugal compressor, water cooled