Basics

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Basics
Airflow...
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Air Flow Basics
Basics

• -Air is invisible
• -Everyone assumes adequate airflow
• -Frequently airflow is 30-50 low
• -Cooling 400 CFM per ton
• -Heating 100 to 500 CFM /10,000 BTU
• -Duct leakage or high static pressure
• -Air properties must be measured

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Basics
Air Flow Basics

• Low airflow can cause temperature stratification
• More fan power is not always the answer
• Select equipment based on available airflow
  400 CFM
• Inadequate air flow can waste 10 in energy
• 400 CFM per ton wet coil needed
• Select equipment with reserve CFM
• Freeze-up occurs at 200 CFM per ton

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The Equipment Or The System?
Basics

• -If the problem is with the equipment, the
  solution is up to you.
• -If the problem is with the air distribution
  system, the primary responsibility for the
  solution lies elsewhere, and/or possibly you.

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Correct Air Flow

• You cannot get the performance from an air
  conditioner without it
• You cannot accurately charge orifice or capillary
  tube systems without it.
• So, how do we determine it?

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Correct Air Flow

• Total Static Pressure
• Temperature Rise
• Evaporator Pressure Drop

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System Static PressureMeasurement
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System Static Pressure
(See Handout)
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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 External Static Pressure
• .65 (Supply side reading)
• -.45 (Return side reading)
• 1.10 Total External Static Pressure

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System Static Pressure
(See Handout)
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• CFM
• By
• Temperature
• Rise Method

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Airflow Measurement(Temperature Rise Method)
(Red Book, Pg. 33)
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CFM By Temperature Rise
BTUH OUTPUT ?T X 1.08
CFM
1.08 constant number for std air. Its a
combination of a number of values that are in the
complete equation. Std air is 70F, sea level
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CFM By Temperature Rise

• 425 CFM Per Ton (Wisc.-Dry Coil)
• Humidifier bypass closed
• Switch Heating and Cooling Speed Tap!!!
• Relocate Heating Speed tap to proper speed!

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Blower should always be on high speed?

• 2 TON 800 CFM

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CFM By Evaporator Pressure Drop
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