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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TL;DR Summary
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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Engineering news on Phys.org
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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.”
 

1. Why is evaporator airflow important for an air conditioner's performance?

Evaporator airflow is important because it allows for the transfer of heat from inside the building to the outside. Without proper airflow, the evaporator coil cannot effectively absorb heat from the indoor air and release it outside, resulting in poor cooling performance.

2. How does decreasing evaporator airflow affect the air conditioner's efficiency?

Decreasing evaporator airflow can significantly reduce the air conditioner's efficiency. This is because the reduced airflow causes the evaporator coil to become colder, which can lead to frost buildup and decreased heat transfer. As a result, the air conditioner has to work harder and use more energy to achieve the desired cooling temperature.

3. Can decreasing evaporator airflow cause damage to the air conditioner?

Yes, decreasing evaporator airflow can cause damage to the air conditioner. As mentioned earlier, reduced airflow can lead to frost buildup on the evaporator coil, which can eventually lead to damage to the coil or other components of the air conditioner. Additionally, the strain on the system from working harder to cool the space can also cause wear and tear over time.

4. How can I tell if the evaporator airflow is too low?

There are a few signs that can indicate low evaporator airflow. These include reduced cooling performance, longer cooling cycles, and higher energy bills. You may also notice a decrease in the amount of air coming out of the vents and a buildup of frost or ice on the evaporator coil.

5. What can I do to increase evaporator airflow and improve my air conditioner's performance?

To increase evaporator airflow and improve your air conditioner's performance, you can start by regularly changing the air filters. Clogged or dirty filters can restrict airflow and should be replaced every 1-3 months. You can also check the condenser unit outside and make sure it is clear of any debris or obstructions. If the issue persists, it is best to consult a professional HVAC technician to ensure proper airflow and functioning of your air conditioner.

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