Basic: Rule of Thumb for Newton's Cooling for ACs

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Discussion Overview

The discussion revolves around applying Newton's cooling law to air conditioning systems, specifically seeking a rule of thumb to estimate how long it takes for the temperature to rise from a set AC temperature to an unacceptable level after the AC is turned off. The conversation touches on practical considerations, insulation, and ambient conditions.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about a rule of thumb for estimating temperature rise after turning off an AC set to 60 degrees.
  • Another participant humorously suggests that if one's thumb feels warm, the temperature is likely above 60 degrees, emphasizing the lack of a straightforward answer without knowing insulation and ambient conditions.
  • A participant proposes a formula involving the area exposed to ambient temperature, temperature difference, thickness of insulation, and heat capacity, noting that larger, well-insulated systems cool or warm slowly compared to smaller, poorly insulated ones.
  • Further details about the apartment's insulation and environmental conditions are shared, indicating an average insulation scenario and a description of the apartment's exposure to sunlight and humidity.
  • Participants discuss the potential influence of neighbors' heating habits on the apartment's temperature, suggesting that older residents may keep their spaces warmer, which could affect the AC's efficiency.
  • Areas of Agreement / Disagreement

    Participants do not reach a consensus on a specific rule of thumb or formula for estimating temperature rise, and multiple views regarding the influence of insulation and ambient conditions remain present.

    Contextual Notes

    The discussion highlights limitations in estimating temperature changes without specific data on insulation thickness and ambient temperature, as well as the variability introduced by neighboring units.

WWGD
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Hi, just curious:
Is there a nice rule-of-thumb to apply Newton's cooling to ACs? Specifically, if I know the AC temperature is , say 60 deg. , how long will it take, after I turn off the AC, before thetemperature rises to an unacceptable level of 85 degrees?
Thanks.
 
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WWGD said:
rule-of-thumb
If your thumb feels warm, it's probably no longer 60 F. Practically, without knowing anything about thickness of insulation, or ambient temperature, you can say nothing.
 
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Bystander said:
If your thumb feels warm, it's probably no longer 60 F. Practically, without knowing anything about thickness of insulation, or ambient temperature, you can say nothing.
Thanks, is there a formula/rule of thumb in function of those two variables?
 
(Area exposed to ambient temperature times temperature difference between ambient and system) divided by (thickness of insulation times heat capacity of system) in appropriate units.

Large, well insulated systems cool/warm slowly, and small, poorly insulated systems cool/warm quickly.

Are we talking about bait buckets or meat lockers?
 
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Bystander said:
(Area exposed to ambient temperature times temperature difference between ambient and system) divided by (thickness of insulation times heat capacity of system) in appropriate units.

Large, well insulated systems cool/warm slowly, and small, poorly insulated systems cool/warm quickly.

Are we talking about bait buckets or meat lockers?

Thanks, sort-of in-between . My AC goes down to around 61, I have your average apartment, 2nd floor. I think insulation is average. I will look it up, thanks.
 
Sunny side? Neighbors overhead?
 
Bystander said:
Sunny side? Neighbors overhead?
Ah, sorry and thanks again. I have a small window facing sort-of inner garden, around 15' x 15' facing the north side, and it faces another building, i.e., there is a small garden separating my apartment from a 5-story building. No other windows I have 5 stories above me, one below, and and I don't get much direct sunlight. Strangely-enough, the place remained warm in Winter with little, if any heating, but the reverse is not so in Summer, the place is very humid and hot.
 
WWGD said:
remained warm in Winter with little, if any heating,
Neighbors below, behind, and to either side are elderly?
 
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Bystander said:
Neighbors below, behind, and to either side are elderly?
Ah, sorry again. Neighbors to the right, to the left, top and bottom, but not behind. I don't think are elderly, pretty sure not, but not 100% but how does that make a difference?
 
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There is a tendency for older folks to run their living spaces slightly warmer. Just thought your AC might be having to fight someone's rheumatism.
 
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  • #11
I see. Thanks for your patience and sorry for my slowness. I will be out for a run for around an hour just in case.
 

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