Air Conditioning 101 - School Transportation Newsstnonline.com/images/expo/presentations/ppt_air conditioning101.pdf · Air Conditioning 101 ... •Electromagnetic Clutch controls

Air Conditioning 101

STN Presentation AC101

•What is Refrigeration?

–Refrigeration is Cooling by the Removal of Heat

•Heat is Measured In BTU’s

–A BTU is a British Thermal Unit

–It is the Amount of Heat to Raise One Pound of Water, One

Degree Fahrenheit.



AC System Basics

- BTU’s Listed by Rating Methodology

- IMACA (International Mobile Air Conditioning Association)

- ARI (American Refrigeration Institute) – Refrigerated Transport and Transit Buses

- KW (Kilowatts – European / Metric Measure)

- ASHRAE – (American Society of Heating, Refrigeration and Air Conditioning Engineers)

Used in Residential and Commercial Building Applications

- 1 ARI BTU = 2 IMACA BTU’s (approximately)

-1 KW = 3.415 ARI BTU’s or 6.83 IMACA BTU’s

- Know which standard is being referenced and why

- IMACA used mostly in small bus / school bus split systems

Performance DataCooling System capacity @ARI Rating 43,031 Btu/hr (12.6 kW)

Cooling System capacity @ IMACA Rating 81,964 Btu/hr (24 kW)

AC 101

Each Component has a Rated

Capacity. The system cannot

produce cooling greater than the

least rated component in the system.

Major Components of Split Systems:

1. Compressor

2. Condenser

3. Expansion Valve (TXV) Not

Adjustable

4. Evaporator


Small Bus (Split System) - Air Conditioning Refrigerant Cycle

Road Compressor

DischargeAccess Valve

Filter Dryer

Evaporator Coil

Condenser Coil

ThermostaticExpansion Valve(Block Type)

SightGlass

Low PressureSwitch

High PressureSwitch

SuctionAccess Valve

Major Components of an Air Conditioning System:

–Compressor•Belt Driven by the Bus Engine•Compresses Low Pressure, Low temp Vapor into High

Pressure High Temp Vapor•Electromagnetic Clutch controls On/Off

–Condenser•Mounted On the Roof or Skirt of Bus•Refrigerant Enters as High Temp/High Pressure Vapor•Condenser Rejects the Vapor’s Heat•Refrigerant Vapor Condenses into High Pressure Liquid



–Expansion Valve•Meters Flow of Refrigerant into Evaporator

•High Pressure Liquid turns into Low Pressure, Low

Temperature Sat Mixture in Evaporator

–Evaporator•Evaporator Absorbs Heat from the Passenger Compartment

•The Refrigerant Turns from a Saturated Mixture to a Low Pressure, Low

Temperature vapor in the Evaporator

•Vapor Returns to the Compressor Through the Suction Line



–Refrigerant•A Fluid that Picks up Heat by Evaporating at a Low Temperature

and Pressure.

•It Rejects Heat by Condensing at Higher Pressure and

Temperature

•134a is the Refrigerant Used Today In Split Systems



Simple, Single AC Circuit

BasicRefrigeration

System

4 Component Flow DiagramSTN Presentation AC101

Condenser

Compressor

DischargeServiceValve

Thermal Expansion Valve

HT HP SHV

HT HP S.M.

HT HP SCL

Legend

HT HP SHV

HT HP S.M.

HT HP SCL

The High Side


Thermal Expansion Valve

Evaporator

TXV Bulb

Equalization Line

SuctionService Valve

Compressor

Flash Gas

Legend

LT LP S.M.

LT LP SHV

The Low Side

LT LP S.M.

LT LP SHV


High Side

AmbientAir

Low Side

ReturnAir

Supply Air

Conditioned Space


Types of AC Systems found in School Buses:

–Single Circuit

–Type A Buses or a Cooler Environment–One Automotive Type Compressor

–Original Equipment Compressor OR

–Add on Compressor

–One or More Evaporators

–One Condenser


Sample Single Circuit System

Rear Mounted - Free Blow Evaporator

Skirt Mounted Condenser

Supplied Compressor

Tie-In Single System

Rear Mounted - Free Blow Evaporator

Skirt Mounted Condenser

Tied in With OEM Dash Unit

Types of AC Systems found in School Buses:

–Dual Circuit or Loop–Type C & D Buses or Warmer Environment

–Two Automotive Type Compressors OR–Two Add On Compressors OR

–OEM Compressor and One or Two Add On Compressors

–One Transit Type Compressor

–Two or More Evaporators

–One High Capacity Condenser OR

–Two Smaller Capacity Condenser

–Split Systems are Modular–Components can be Mixed and Matched

–You have to know what you are receiving in the system


Types of AC Systems found in School Buses:–Dual Circuit or Loop

–Type C & D Buses or Warmer Environment–Two Automotive Type Compressors OR

–One Transit Type Compressor


Two Automotive Compressors

One Transit Compressor

Types of AC Systems Air Delivery in School Buses:–Corner Ducted

–Free Blow


Corner DuctedRooftop System

Corner DuctedEvaporator on Both Sides

Types of AC Systems Air Delivery in School Buses:–Corner Ducted

–Free Blow


Free Blow EvaporatorIn Wall Design

Free Blow Evaporator Side Mounted

What Size AC System is Right?:

–It All Depends–Location

–Environmental Conditions–Heat–Humidity–Non AC Season Conditions

–Your Use–Special Needs–Route–Trips

–Do Your Homework–Talk to Your Peers–Talk to Your Bus Dealer(s)–Be an Informed Buyer


What Size AC System is Right?:–Performance Specification–Actual Performance of the Installed Air Conditioning System in a

Controlled Environment–No Industry Standards for School Bus Air Conditioning Systems–Pull Down Test

–Start at a Designated Temperature in the Test Chamber–Thermocouples in the Bus Measure the Temperature at Specific Locations–The Bus is Heat Soaked until the Starting Temperature is Stabilized–The Bus is Started, Engine Speed is usually High Idle–Data is Captured for the Time Specified in the Test (usually 30 minutes)–The System passes the Test if all Thermocouples reach the required Temperature in the Time Required.

–Houston Pull Down–Las Vegas Pull Down–American Public Transportation Association White Book (Transit Bus

Specifications)


Las Vegas Specifications: (Partial)

No simulated solar load shall be used.Turn on the air conditioner and note that all doors are closed as they would be under normal operation.The engine speed for this test is the manufacturers recommended high idle speed.Hold the 110 degrees Fahrenheit +/- 1 degree Fahrenheit temperature ambient while recording data for a minimum of 45 minutes. No humidity need be added but it must be monitored and recorded.

The requirement for passing this test is that the system shallpull the interior (four thermocouples previously noted) from 110 degrees Fahrenheit down to 70 degrees Fahrenheit +/- 3 degrees Fahrenheit within 30 minutes from the start of the A/C system. That is all four thermocouples must be below 73 degrees Fahrenheit in 30 minutes (not an average).


What Size AC System is Right?:–Performance Specification, Continued

–A Requirement in most Transit Bus Specifications

–Increasing use in the School Bus Market

–Removes Doubt the System will Perform in that Bus

–Evidence for the District before the Bus is Delivered

–There May be a Cost for this Test


Basic AC Maintenance:

1. Return Air Filter on Evaporator

–Keep It Clean!

–Any Restriction Decreases the System Capacity

–Wash out Dirty Evaporator with Cleaner–Many Products on the Market

–Fin Comb to Remove Heavy Buildup / Straighten

Fins



1. Return Air Filter on Evaporator, Continued

Dirty Return Air Filters



1. Return Air Filter on Evaporator, Continued

Dirty Evaporator CoilsSTN Presentation AC101


2. Condenser Coil

–Keep It Clean

–Mud, Leaves, Paper Can Restrict Airflow!

–Keep the Screen Clear

–Keep the Fins in Good Condition

–Two Types of Coil Construction

–Tube and Fin

–Micro Channel (Automotive Style)



2. Condenser Coil, Continued

–Tube and Fin Condenser

Fin Comb




–Tube and Fin Condenser

–Do Not Clean with a Pressure Washer

–The Fins can be Damaged

–Use a Standard Garden Hose and Nozzle




–Micro Channel Condenser

–Newer Technology

–All Aluminum Construction

–This Design can be Cleaned with a Pressure

Washer

Close up View of Construction


Basic AC Maintenance:3. Compressor Belts

–Keep it Aligned

–Keep it Tight

–Check for Belt Cracks

–Check for Belt Wear

–Check for Idler Wear


Basic AC Maintenance:4. Hoses

–Look for Rubbing

–Oil Leaks/Refrigerant

–Check for Hose Cracks



5. AC Switches

–Turn Them Off when the Bus not Running

–Easier to Start the Bus with the AC Compressor

Clutch(es) Disengaged

–Turn the AC on when the Engine is Warmed Up

–Simple Switches to Sophisticated Electronic

Control

–Know How to Use the Controls



6. Water Inside the Bus

–Evaporator Condenses Water from the Air

–Evaporator Catch Pan Drain can Plug

–Water Spills/Drips out when Turning a Corner

–Let the Maintenance Staff Know



7. Use Quality Refrigerant!

–Cheap Import Brands are Available

–Get References on Import Brands

–Check the References!

–Some are Contaminated, Not Pure 134a

–They Won’t Cool and will Contaminate Your

Systems


Resources:1. Pull Down Tests:

• Florida DOT

• http://www.tripsflorida.org/pdfs/AC%20Pull%20Down%20Version%208.pdf

• APTA White Book and Houston Pull Down Standards

• http://apta.com/resources/reportsandpublications/Pages/BusParatransit.aspx

• The Houston Pull Down is the Hotter Climate portion of the specification.

• Choose the “Standard Bus Procurement Guidelines” on the Web page

• APTA has Committees working on Para Transit and Coach Bus Standards


http://www.tripsflorida.org/pdfs/AC Pull Down Version 8.pdf

http://apta.com/resources/reportsandpublications/Pages/BusParatransit.aspx

Questions?


Documents

Air Conditioning 101 - School Transportation Newsstnonline.com/images/expo/presentations/ppt_air conditioning101.pdf · Air Conditioning 101 ... •Electromagnetic Clutch controls