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Posted by udarrell on June 7, 2007, 6:34 pm
hvacrmedic wrote:
>
>
>>compquest wrote:
>>
>>
>>>I was wondering if someone would have an idea as to what might be
>>>going on with my apartment's AC! :) First if the temp was 84 and I
>>>set the AC for 78, it would not stop until the thermostat registered
>>>around 72. Maintenance corrected the reversing valve. Now, it will
>>>cut off at the temp it should, but once it reaches the temp it needs,
>>>it cuts on and off about every ten minutes to maintain the temp. I
>>>called them to see if they could look at it again and they said this
>>>was normal. I do notice some gaps near the doors when they are closed,
>>>and I do live on the top floor of the building, but nothing that
>>>should make it lose cool air that fast. Any ideas would be greatly
>>>appreciated. Thanks.
>>>
>>>
>>It sounds as though the AC is a bit oversized, or the thermostat cooling
>>anticipator is keeping the temp differential too narrow.
>>
>>
>While that is possible, it isn't likely in this case. (What's the Latent load?-
udarrell)
>The indoor/outdoor differential is only 6 deg. The load isn't that great;
>10 min doesn't seem out of the ordinary. (In fact it's very ordinary.- udarrell)
>
>
While what you say IS TRUE, I will always set my ACs up so they do not
short cycle even under lighter load conditions.
The outdoor temp was 84-F , we don't know what the humidity level is,
what was the Heat Index; I assure you that NO AC I own will ever run for
only 10 minutes when it is 84-F outdoors. In high humidity climates
with a proper sized system the runtime needs to be long and continuous,
and it probably would be as sensible temp drops would be slower.
>>You would get much higher SEER if the room TH had a differential setting
>>that might vary the room temp by several degrees but result in longer
>>Off & On Cycle. - udarrell
>>
>>
>>It takes close to 5 minutes to reach optimal cooling operation, so half
>>the cycling is lowering (seer) efficient conditioner operation. -
udarrellhttp://www.udarrell.com/air-conditioner-capacity-seer.html
>>
>>
>
>That isn't true for all systems, e.g. hard shut-off TXV. Regardless,
>you shouldn't pick a number out of thin air. The stabilization times
>of systems isn't a unviersal constant of nature.
>
>
TRUE, I am aware that you know AC inside & out & you are correct;
however, it takes time to reach optimal operating cooling conditions for
any system.
That is too short a cycle for me, and in my opinion every system should
come with an adjustable differential room TH, the idea that you have to
keep the temp to an extremely narrow differential is costly and will
also tend to shorten the life of some of the system 's components.
http://www.udarrell.com/air-conditioning-total-heat-enthalpy-latent-heat.html
- udarrell
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