Air Conditioning

Charging Procedures

Review

Basic Refrigeration

Basic Refrigeration

Liquid LineLiquid Line Metering Device

Evaporator

Compressor

Condenser

Hi SideLow Side

What is Saturation Temperature?

• Saturation temperature is the Saturation temperature is the actualactual temperature of the temperature of the evaporator and condenser coils….evaporator and condenser coils….

• In saturation conditions, In saturation conditions, bothboth vapor and liquid are presentvapor and liquid are present

How do you find Saturation Temperature?

•Refrigeration GaugesRefrigeration Gauges•The The OnlyOnly purpose of owning purpose of owning

a set of gauges is to find the a set of gauges is to find the refrigerant saturation refrigerant saturation temperature….temperature….

Saturated Refrigerant

Liquid Line

Suction Line

Evaporator

Condenser

Discharge Line

Compressor

MeteringDevice

First things first…

You must verify that you You must verify that you have proper airflow!…have proper airflow!…and you must have the and you must have the proper tools to do the proper tools to do the

job….job….

Air Flow

Air Flow Measurements

• Total Static PressureTotal Static Pressure

• CFM Measurements:CFM Measurements:

-Temperature Rise-Temperature Rise

-Evaporator Pressure Drop-Evaporator Pressure Drop

-Air – Velocity-Air – Velocity

-Temperature Drop*-Temperature Drop*

Static Pressure Measurement

• The key to system airflow The key to system airflow diagnosticsdiagnostics

• A companion to airflow A companion to airflow measurementmeasurement

• It takes less than 5 minutes to It takes less than 5 minutes to measuremeasure

• Similar to blood pressure Similar to blood pressure diagnosticsdiagnostics

Total Static Pressure

Air Flow Measurement-

Temperature Rise Methodto determine CFM

Airflow Measurement(Temperature Rise Method)

(Red Book, Pg. 33)

CFM By Temperature Rise

BTUH OUTPUTBTUH OUTPUT

T X 1.08*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 70F, sea level

CFM By Temperature Rise

55,200 BTU output55,200 BTU output

60 X 1.0860 X 1.08= 850 CFM

64.8

CFM By Evaporator Pressure Drop

Velocity

• Velocity = FPMVelocity = FPM

• CFM= FPM X Area in Square CFM= FPM X Area in Square FeetFeet

• Free AreaFree Area

Humid Air

Dry Air

Fan Speed Taps

• Check Service Facts for proper air Check Service Facts for proper air speed tap to usespeed tap to use

• Match tap to size (BTUH) of unitMatch tap to size (BTUH) of unit

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

The Right Stuff:

Basic Tools:Basic Tools:

1.1. Refrigerant GaugesRefrigerant Gauges

2.2. Digital Thermometer (one with Digital Thermometer (one with Wet Bulb capabilities)Wet Bulb capabilities)

SYSTEM CHARGING

• The sub-cooling method is required when The sub-cooling method is required when charging TXV systems.charging TXV systems.

• The super-heat method is required when The super-heat method is required when charging fixed orifice systems.charging fixed orifice systems.

• Charging charts are included in the Service Charging charts are included in the Service Facts document that come with the outdoor Facts document that come with the outdoor equipment.equipment.

• Remember to allow sufficient time for the Remember to allow sufficient time for the system to stabilize before adjusting the system to stabilize before adjusting the refrigerant charge.refrigerant charge.

Beer Can Cold and Sweaty

SYSTEM CHARGING(SC) Using the Charging Chart-TXV

• Measure temperature and pressure at Measure temperature and pressure at liquid line.liquid line.

• Use line length & lift to choose which Use line length & lift to choose which curve to use.curve to use.

• Plot the intersection of temp. & pressure.Plot the intersection of temp. & pressure.• If above the curve, remove refrigerant.If above the curve, remove refrigerant.• If below, add refrigerantIf below, add refrigerant• Wait 20 minutes to stabilize.Wait 20 minutes to stabilize.

Sub-Cooling Calculation

• Low Low Sub-CoolingSub-Cooling indicates LOW indicates LOW chargecharge

• High High Sub-CoolingSub-Cooling indicates OVER indicates OVER charge ( or possible liquid line charge ( or possible liquid line restriction)restriction)

• Rule of thumb = 10 - 15 degrees of Rule of thumb = 10 - 15 degrees of sub-cooling Manufactures’ usually sub-cooling Manufactures’ usually design to 10 degreesdesign to 10 degrees

(390 PSIG & 115º F)

SYSTEM CHARGING(SH) Using the Charging Chart-Fixed Orifice

• Measure indoor dry bulb* (R/A)Measure indoor dry bulb* (R/A)• Measure outdoor dry bulb (at unit)Measure outdoor dry bulb (at unit)• Measure suction pressureMeasure suction pressure• Measure suction temperature, before Measure suction temperature, before

suction service valvesuction service valve• Use chart to determine SHUse chart to determine SH• Above 5 F above, add. If 5 F below, Above 5 F above, add. If 5 F below,

remove.remove.• If below 5 F limit line, DO NOT ADD.If below 5 F limit line, DO NOT ADD.• *If RH >70% or <20%, use ID wet-bulb *If RH >70% or <20%, use ID wet-bulb

Superheat Calculation

SuperheatSuperheat indicates that complete indicates that complete vaporization of liquid refrigerant in the vaporization of liquid refrigerant in the evaporator coil has taken placeevaporator coil has taken place

Low Low SuperheatSuperheat means liquid means liquid refrigerant is present at or near the refrigerant is present at or near the outlet of the evaporator - compressor outlet of the evaporator - compressor damage is immanentdamage is immanent

High High SuperheatSuperheat means liquid is boiling means liquid is boiling off too soon and could mean evaporator off too soon and could mean evaporator is starvedis starved

Customer Complaint:

• ““System does not cool like it System does not cool like it before when it was new…”before when it was new…”

• What do you do?What do you do?

+ “Check the Enthalpy of the Evaporator Coil to verify system capacity…”

Use the Formula:

Total Heat Removed =Total Heat Removed =

CFM CFM XX 4.5 4.5 X X Change inChange in Enthalpy Enthalpy (Heat Content)(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 !