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Big Dad

Big Dad

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It has been extremely hot / dry locally here .. We do get into the 100's in the summer for a few days often but, this year we seem to be stuck in upper 90's to 100 day after day

Talking to a person last night , he said he only sets his t-stat to 8 degrees below expected high of the day .. i said so, like 88 ?

Claims he was told to never expect it to cool beyond that ? I guess this is news to me ?

I was always said to expect at least 20-25 degrees from outside temps ?
 
Not sure where he is from, but expect 15 degree difference at 95 degrees outside air.
At 85 expect even better, I sleep better when cold, I set mine on 66 at night, and its been 85 at night, its 66 in my house by 11 thirty pm..
 
It bangs on the 100 door here sometimes, last two years were hot. The "rule of thumb" around here is 15-20F difference between OD and ID temp. This year has been a bit cooler, yesterday was knocking on low 90s. I have stat at about 78
 
If an AC system is sized properly, there's no reason it shouldn't easily maintain mid-70's inside when over 100 outside. My understanding the that the air coming out of the register should be 15-20* colder than the air going into the return. So, if your inside air temp is 80*, the air coming out of the HVAC register should be at least 65*.
 
mopowers said:
If an AC system is sized properly, there's no reason it shouldn't easily maintain mid-70's inside when over 100 outside. My understanding the that the air coming out of the register should be 15-20* colder than the air going into the return. So, if your inside air temp is 80*, the air coming out of the HVAC register should be at least 65*.
Click to expand...
"Things may be different"

First I realize that with modern variable speed compressors, now you can change system capacity

But around here we have cold weather!! An example of that is say, a small business with lots of "sun" exposure, and a high indoor heat load. Lights, maybe copy equipment etc, and or lots of people. BUT on cooler days when the ID load wants AC it might be a sunny 40-45F day OUTSIDE. "Back then" a "high" sized system will just tend to ice up under those conditions.

You want to be careful over-sizing, you can create a clammy interior
 
67Dart273 said:
"Things may be different"

First I realize that with modern variable speed compressors, now you can change system capacity

But around here we have cold weather!! An example of that is say, a small business with lots of "sun" exposure, and a high indoor heat load. Lights, maybe copy equipment etc, and or lots of people. BUT on cooler days when the ID load wants AC it might be a sunny 40-45F day OUTSIDE. "Back then" a "high" sized system will just tend to ice up under those conditions.

You want to be careful over-sizing, you can create a clammy interior
Click to expand...

I was responding to the OP who mentioned 90-100 outside temps.
 
mopowers said:
I was responding to the OP who mentioned 90-100 outside temps.
Click to expand...
Well it still applies. We get 100 up here too, but if you size the unit (fixed capacity) on the high side, you may end up with this very problem. This is especially an issue with "lower cost" units using an orifice/ piston instead of a TXV
 
67Dart273 said:
Well it still applies. We get 100 up here too, but if you size the unit (fixed capacity) on the high side, you may end up with this very problem. This is especially an issue with "lower cost" units using an orifice/ piston instead of a TXV
Click to expand...

I'm not sure what you're arguing. All I said was "If an AC system is sized properly, there's no reason it shouldn't easily maintain mid-70's inside when over 100 outside."
 
Today is "only" 87 here but it's been upper 90's all week.

Ours is usually set to 76 or 77.

Used to have a programmable one that set it to 80-82 during the time we're not here.

Those 4-6 degrees can knock quite a bit off the electric bill, and not cause excessive load when going back down to 76/77.
 
mopowers said:
I'm not sure what you're arguing. All I said was "If an AC system is sized properly, there's no reason it shouldn't easily maintain mid-70's inside when over 100 outside."
Click to expand...
And I'm saying it "ain't that easy." As I mentioned, "lower end" systems with piston/ orifices can sometimes "not" be sized properly--even if they are "sized properly" because of wide variation in operating conditions. It's one thing to size systems in a climate like tucson and quite another "up here" and I have been there done that. That is why, EG, back in the day, some systems required add-on head controls. It's why under those conditions (and it not always can be done or is done) talk the customer into "more money" for a TXV instead of an orifice. Or maybe even two smaller systems that can be staged. As I ALSO mentioned--some modern systems with capacity control HELP TO alleviate this problem.
 
Our old relic of ac gets a "checkup" every year, and maintenance if need be($30 month plan). Its approx 30-40 years old. Tech checked amperage and it pulls 20 amps at startup lol. Typical apparently is 10-12??
 
From a local HVAC person said that undersize is as bad as oversize .. guess there is a formula but, I do know.. the one in my shop works great I can make it as cool as I want or in winter as warm as I want .. quiet too
 
We just installed a Carrier dual Stage Heat Pump/AC System . Our 12 year old American Standard would run 24/7 to keep the house at 80 when it got above 100 .The Carrier keeps it at 78 and runs less than 3/4 of the time . The old one was undersized at 2 /1/2 Ton 8 Seer where the new one is 3 ton 18 Seer.
 
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