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.
  • #1
sevensages
59
10
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?
 
Last edited:
Engineering news on Phys.org
  • #2
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.”
 

Similar threads

Replies
11
Views
2K
Replies
53
Views
9K
  • Mechanical Engineering
Replies
10
Views
2K
  • Mechanical Engineering
Replies
18
Views
5K
  • Mechanical Engineering
2
Replies
36
Views
7K
Replies
12
Views
2K
  • Mechanical Engineering
Replies
15
Views
956
Replies
8
Views
3K
  • Mechanical Engineering
Replies
3
Views
2K
  • Mechanical Engineering
Replies
8
Views
2K
Back
Top