Why does decreasing evaporator airflow impact an air conditioner's performance?

In summary, a lower evaporator airflow causes lower low pressure side saturation temperatures and higher delta T on an air-conditioner. This is because less air is moving over the evaporator, and this causes the evaporator to be able to cool the (small) amount of air that goes through the evaporator more quickly and effectively. But I cannot figure out why a lower evaporator airflow would cause the low pressure side saturation temperature to be lower.
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Why does lower evaporator airflow cause lower low pressure side Saturation temperature on an air-conditioner?
The other day I read on a website that a lower evaporator airflow causes lower low pressure side saturation temperatures and higher delta T on an air-conditioner. Now I think I know why a lower evaporator airflow would cause a high delta T. If there is less air moving over the evaporator, the evaporator would be able to cool the (small) amount of air that goes through the evaporator more quickly and effectively. But I cannot figure out why a lower evaporator airflow would cause the low pressure side saturation temperature to be lower.

Why does low evaporator airflow cause the low pressure side saturation temperature to be lower on an air-conditioner?
 
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Copied from:
https://hvacrschool.com/impacts-of-decreasing-evaporator-air-flow/

“What Happens When Airflow is Decreased?

In this theoretical system, when the airflow is decreased and all else stays the same, the following things will occur:

  • Mass airflow will decrease, meaning fewer molecules are moving across the coil.
  • Air velocity will decrease, meaning the air is moving over the fins and tubing more slowly.
  • The bypass factor decreases; more air molecules will be touching the metal as a ratio.
  • Air temperature decreases (to a point) due to the air moving more slowly across the coil with less bypass factor.
  • Coil temperature decreases because less overall heat is being picked from the air.
  • Coil drops further below the dewpoint, causing more moisture to be removed from the air, increasing dehumidification.
  • Suction pressure decreases because less heat energy being picked up means less pressure, and as the superheat falls, the TXV also further throttles the flow of refrigerant through the coil.
  • The compression ratio increases as the suction pressure drops, meaning the compressor moves less refrigerant as the refrigerant density entering the compressor falls.
  • Coil TD increases as indicated by the colder coil in relation to the return air.”
 

FAQ: Why does decreasing evaporator airflow impact an air conditioner's performance?

Why does decreasing evaporator airflow reduce an air conditioner's cooling efficiency?

Decreasing evaporator airflow reduces an air conditioner's cooling efficiency because it limits the amount of warm air passing over the evaporator coil. This results in less heat being absorbed and transferred out of the air, leading to reduced cooling capacity.

How does decreased airflow affect the evaporator coil temperature?

Decreased airflow over the evaporator coil causes the coil to become colder than normal. This can lead to the coil freezing, which further impedes airflow and reduces the system's ability to cool the air effectively.

What impact does reduced evaporator airflow have on energy consumption?

Reduced evaporator airflow can increase energy consumption because the air conditioner has to work harder and run longer to achieve the desired indoor temperature. This inefficiency leads to higher energy use and increased utility bills.

Can decreasing evaporator airflow cause damage to the air conditioner?

Yes, decreasing evaporator airflow can cause damage to the air conditioner. Prolonged operation with inadequate airflow can lead to ice buildup on the evaporator coil, which can damage the coil and other components. It can also cause the compressor to overheat and fail.

How can I improve evaporator airflow in my air conditioner?

To improve evaporator airflow, ensure that air filters are clean and replaced regularly, keep vents and registers open and unobstructed, and check for any blockages in the ductwork. Additionally, regular maintenance by a professional can help identify and resolve airflow issues.

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