Air Conditioning 101. STN Presentation AC101

Transcription

1 Air Conditioning 101

2 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.

3 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 = 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 Data Cooling System Rating 43,031 Btu/hr (12.6 kw) Cooling System IMACA Rating 81,964 Btu/hr (24 kw)

4 Low Pressure Switch Thermostatic Expansion Valve (Block Type) 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 Suction Access Valve Evaporator Coil Discharge Access Valve High Pressure Switch Filter Dryer Sight Glass Condenser Coil Road Compressor Small Bus (Split System) - Air Conditioning Refrigerant Cycle

5 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

6 Major Components of an Air Conditioning System: 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

7 Major Components of an Air Conditioning System: 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

8 Simple, Single AC Circuit

9 Basic Refrigeration System 4 Component Flow Diagram

10 Thermal Expansion Valve HT HP SCL HT HP S.M. Condenser HT HP SHV Legend HT HP SHV HT HP S.M. HT HP SCL Discharge Service Valve Compressor The High Side

11 Thermal Expansion Valve Equalization Line Flash Gas LT LP S.M. Evaporator TXV Bulb LT LP SHV Legend LT LP S.M. LT LP SHV Compressor The Low Side Suction Service Valve

12 High Side Conditioned Space Ambient Air Return Air Supply Air Low Side

13 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

14 Sample Single Circuit System Rear Mounted - Free Blow Evaporator Skirt Mounted Condenser Supplied Compressor

15 Tie-In Single System Rear Mounted - Free Blow Evaporator Skirt Mounted Condenser Tied in With OEM Dash Unit

16 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

17 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

18 Types of AC Systems Air Delivery in School Buses: Corner Ducted Free Blow Corner Ducted Rooftop System Corner Ducted Evaporator on Both Sides

19 Types of AC Systems Air Delivery in School Buses: Corner Ducted Free Blow Free Blow Evaporator In Wall Design Free Blow Evaporator Side Mounted

20 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

21 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)

22 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 shall pull 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).

23 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

24 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

25 Basic AC Maintenance: 1. Return Air Filter on Evaporator, Continued Dirty Return Air Filters

26 Basic AC Maintenance: 1. Return Air Filter on Evaporator, Continued Dirty Evaporator Coils

27 Basic AC Maintenance: 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)

28 Basic AC Maintenance: 2. Condenser Coil, Continued Tube and Fin Condenser Fin Comb

29 Basic AC Maintenance: 2. Condenser Coil, Continued Tube and Fin Condenser Do Not Clean with a Pressure Washer The Fins can be Damaged Use a Standard Garden Hose and Nozzle

30 Basic AC Maintenance: 2. Condenser Coil, Continued Micro Channel Condenser Newer Technology All Aluminum Construction This Design can be Cleaned with a Pressure Washer Close up View of Construction

31 Basic AC Maintenance: 3. Compressor Belts Keep it Aligned Keep it Tight Check for Belt Cracks Check for Belt Wear Check for Idler Wear

32 Basic AC Maintenance: 4. Hoses Look for Rubbing Oil Leaks/Refrigerant Check for Hose Cracks

33 Basic AC Maintenance: 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

34 Basic AC Maintenance: 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

35 Basic AC Maintenance: 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

36 Resources: 1. Pull Down Tests: Florida DOT APTA White Book and Houston Pull Down Standards 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

37 Questions?