Air Conditioning Charging Procedures Review Basic Refrigeration Basic

Air Conditioning Charging Procedures Review

Basic Refrigeration

Basic Refrigeration Liquid Line Metering Device Condenser Hi Side Low Side Evaporator Compressor

What is Saturation Temperature? • Saturation temperature is the actual temperature of the evaporator and condenser coils…. • In saturation conditions, both vapor and liquid are present

How do you find Saturation Temperature? • Refrigeration Gauges • The Only purpose of owning a set of gauges is to find the refrigerant saturation temperature….

Saturated Refrigerant Liquid Line Condenser Metering Device Evaporator Discharge Line Compressor Suction Line

First things first… You must verify that you have proper airflow!…and you must have the proper tools to do the job….

Air Flow

Air Flow Measurements • Total Static Pressure • CFM Measurements: -Temperature Rise -Evaporator Pressure Drop -Air – Velocity -Temperature Drop*

Static Pressure Measurement • The key to system airflow diagnostics • A companion to airflow measurement • It takes less than 5 minutes to measure • Similar to blood pressure diagnostics

Total Static Pressure

Air Flow Measurement. Temperature Rise Method to determine CFM

Airflow Measurement (Temperature Rise Method) (Red Book, Pg. 33)

CFM By Temperature Rise BTUH OUTPUT T X 1. 08* = CFM *1. 08 = constant number for std air. It’s a combination of a number of values that are in the complete equation. Std air is 70 F, sea level

CFM By Temperature Rise 55, 200 BTU output 60 X 1. 08 64. 8 = 850 CFM

CFM By Evaporator Pressure Drop

Velocity • Velocity = FPM • CFM= FPM X Area in Square Feet • Free Area

Humid Air Dry Air

Fan Speed Taps • Check Service Facts for proper air speed tap to use • Match tap to size (BTUH) of unit

Blower should always be on high speed? • 2 TON – 800 CFM

The Right Stuff: Basic Tools: 1. Refrigerant Gauges 2. Digital Thermometer (one with Wet Bulb capabilities)

SYSTEM CHARGING • The sub-cooling method is required when charging TXV systems. • The super-heat method is required when charging fixed orifice systems. • Charging charts are included in the Service Facts document that come with the outdoor equipment. • Remember to allow sufficient time for the system to stabilize before adjusting the refrigerant charge.

Beer Can Cold and Sweaty

SYSTEM CHARGING(SC) Using the Charging Chart-TXV • Measure temperature and pressure at liquid line. • Use line length & lift to choose which curve to use. • Plot the intersection of temp. & pressure. • If above the curve, remove refrigerant. • If below, add refrigerant • Wait 20 minutes to stabilize.

Sub-Cooling Calculation • Low Sub-Cooling indicates LOW charge • High Sub-Cooling indicates OVER charge ( or possible liquid line restriction) • Rule of thumb = 10 - 15 degrees of sub-cooling Manufactures’ usually design to 10 degrees

(390 PSIG & 115º F)

SYSTEM CHARGING(SH) Using the Charging Chart-Fixed Orifice • • Measure indoor dry bulb* (R/A) Measure outdoor dry bulb (at unit) Measure suction pressure Measure suction temperature, before suction service valve Use chart to determine SH Above 5 F above, add. If 5 F below, remove. If below 5 F limit line, DO NOT ADD. *If RH >70% or <20%, use ID wet-bulb

Superheat Calculation · Superheat indicates that complete vaporization of liquid refrigerant in the evaporator coil has taken place · Low Superheat means liquid refrigerant is present at or near the outlet of the evaporator - compressor damage is immanent · High Superheat means liquid is boiling off too soon and could mean evaporator is starved

Customer Complaint: • “System does not cool like it before when it was new…” • What do you do? + “Check the Enthalpy of the Evaporator Coil to verify system capacity…”

Use the Formula: Total Heat Removed = CFM X 4. 5 X Change in Enthalpy (Heat Content)

Enthalpy • Same as TOTAL HEAT • The sum of sensible heat and latent heat Where’s the 4. 5 come from? It’s how many BTU’s are in one pound of DRY air (0%Rh)

Total Heat =CFM X 4. 5 X Enthalpy Change 69 WB=33. 25 60 WB=26. 46 Difference = 6. 79 800 X 4. 5 X 6. 79 = 24, 444 BTUH !