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High humidity and air conditioning


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#1 toomanytoys84 ONLINE  

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Posted June 16, 2016 - 08:39 PM

Currently outside according to my weather station is 94%. It's not that hot but it seems as if my air conditioner is running constantly.

Does outdoor humidity affect the efficiency of your ac system? As in it doesn't blow as cool? Or am I crazy and it doesn't affect anything? I've googled this but I only find about indoor humidity
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#2 larrybl ONLINE  

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Posted June 16, 2016 - 09:58 PM

Yes the humidly makes a difference here. the equipment definitely works harder to remove the humidity.


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#3 Bruce Dorsi OFFLINE  

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Posted June 16, 2016 - 09:58 PM

I don't know the reason, but my a/c runs a lot more when the humidity increases (even though the outside air temp may be dropping).

 

I have not heard an explanation of why that happens.  ....What confuses me is that the a/c is controlled by a thermostat, not a humidistat. 


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#4 Cvans ONLINE  

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Posted June 16, 2016 - 10:24 PM

  It's been my experience that contractors tend to under size their heating and cooling systems. Price being a big factor in this more than weather extremes. I ran into this years ago when we were looking for our furnace and central air. They took all the information concerning the house and fed it into a computer program and presto this is what you need. I told them they were wrong which didn't go over real well. I worked with industrial refrigeration systems at the time. I told them to up size it by 25% and to figure the highest efficiency condensing unit available. Now when it is hot and humid outside the condensing fan is still running on low and the house is dry. The biggest mistake a home owner can make is to scrimp on the condenser coil. The second is not keeping it clean.

 Too many times it's money that dictates the choice that's made when considering a new heating or cooling system.   


Edited by Cvans, June 16, 2016 - 10:25 PM.

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#5 ol' stonebreaker ONLINE  

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Posted June 16, 2016 - 10:34 PM

  When humidity is high the outside air holds more heat making it harder for the condenser to get rid of the heat it has extracted from the house. As Cvans said w/ a larger condenser it can get rid of that heat easier.

                                     mike


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#6 boyscout862 ONLINE  

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Posted June 16, 2016 - 11:50 PM

When it is more humid outside, the humidity gets in more because the family leaves the doors open more. When working with heating and cooling problems one thing to consider is lag time. The house gets heated up during the day and it takes a while to cool it off.

 

I open up my house a 2200hrs to ventilate it and cool it off. The inside high was 77* today. Tomorrow morning it will cool down to 68* by 0800 when I close it up. The temp in the house will slowly rise during the day until the sun goes down. I then wait for the outside temp to drop lower than the inside temp, and I open up. An attic fan keeps the attic cooler during the day and draws the air in at night.

 

If the doesn't cool to 70* or less by 0900hrs, I close up and run my single 10,000btu A/C until noon and shut it off. Four years ago, I moved my A/C from the south side to the north side of the house. It works alot better now. The sun used to hit it and make it hotter. Now its in shade and gets better breezes. BTW use a bucket to catch the dripping water to use in the garden. Good Luck, Rick


Edited by boyscout862, June 17, 2016 - 06:53 AM.

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#7 MiCarl ONLINE  

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Posted June 17, 2016 - 06:31 AM

Air doesn't have much thermal mass, you can change its temperature easily.  Water on the other hand has a lot of thermal mass and you need to remove a lot of heat energy to cool it.

 

An interesting side effect of this:  When we installed the AC in my shop it was very humid and the AC worked great.  A couple weeks later the humidity dropped and my evaporator started icing up.  Turns out we were a bit low on refrigerant so the evaporator was over chilling.  When the humidity was high all that water was giving up enough heat to prevent the freezing.


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#8 Sawdust OFFLINE  

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Posted June 17, 2016 - 07:22 AM

When it is more humid outside, the humidity gets in more because the family leaves the doors open more. When working with heating and cooling problems one thing to consider is lag time. The house gets heated up during the day and it takes a while to cool it off.

I open up my house a 2200hrs to ventilate it and cool it off. The inside high was 77* today. Tomorrow morning it will cool down to 68* by 0800 when I close it up. The temp in the house will slowly rise during the day until the sun goes down. I then wait for the outside temp to drop lower than the inside temp, and I open up. An attic fan keeps the attic cooler during the day and draws the air in at night.

If the doesn't cool to 70* or less by 0900hrs, I close up and run my single 10,000btu A/C until noon and shut it off. Four years ago, I moved my A/C from the south side to the north side of the house. It works alot better now. The sun used to hit it and make it hotter. Now its in shade and gets better breezes. BTW use a bucket to catch the dripping water to use in the garden. Good Luck, Rick


Your right on keeping the water for the garden. It's like miracle water.

#9 Arti ONLINE  

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Posted June 17, 2016 - 07:57 AM

If you check Latent Heat and Sensible Heat with a search engine there are a lot of good articles of what is taking place.

What is happening is that you need to remove the moisture in the air before the AC can drop the temperature, Dew Point is another good term to search


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#10 ol' stonebreaker ONLINE  

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Posted June 17, 2016 - 09:38 AM

If you check Latent Heat and Sensible Heat with a search engine there are a lot of good articles of what is taking place.

What is happening is that you need to remove the moisture in the air before the AC can drop the temperature, Dew Point is another good term to search

  And that translates into more heat to be removed out at the condenser.

                                          Mike



#11 toppop52 OFFLINE  

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Posted June 17, 2016 - 09:52 AM

My uncle was in the HVAC business in the 60's, he always said that ac is a water pump, not an air pump. :D


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#12 Auburn David OFFLINE  

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Posted June 17, 2016 - 10:03 AM

I use a dehumidifier along with my 5 ton package unit..Humidity gets crazy down this way..today for instance the high temp is going the be in the mid 90s..but  heat index... from 104 to 109 degrees

* impacts... these hot and humid conditions will elevate the risk
of heat stress and heat related illnesses such as heat
exhaustion or heat stroke.

 

I will have to empty my dehumidifier 2-3 times today(it holds 2.5 gal)



#13 Auburn David OFFLINE  

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Posted June 17, 2016 - 10:07 AM

I might add without the dehumidifier my AC runs continually..but with the dehumidifier its cycles on and off as it should even on the hottest days.I am thinking of plumbing the dehumidifier into a catch drum to use for plants and such.



#14 chieffan ONLINE  

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Posted June 17, 2016 - 11:28 AM

To many make the mistake to run their AC way to cold.  Ours stay on 78° all the time.  We don't open up the house to let all the humid air in just to hear the AC run a lot to complain about it.  AC just kicked on and ran for about 10 min at 11;20 AM and the outside temp is at 85°.  If you think you saving by open up the house your only fooling yourself.  This is not a new home either.  1972 double wide on a new basement.  New windows,  1/2" insulation under new siding about 12 years ago.  80% of the home is in the shade of trees about 80% of the time.  this makes a big difference.  Furnace and AC is the original one in the home.  Bet I don't hear the AC for over an hours or more.  Have a nice 15mph SE breeze blowing.  A shade tree and a lawn chair in the breeze make it a nice summer day in  SW Iowa.


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#15 Gtractor ONLINE  

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Posted June 17, 2016 - 11:50 AM

I agree with Roger on opening the house in the evening only lets the humidity in. 

 

We have a Patton [brand] whole house air circulator in an upstairs window.  I can only run it on low or medium because its blowing through a standard window screen.   The screen won't take that fan on high.  Very old story and a half farm house that is in no way shape or form energy efficient.  I used to open the house at night and turn that fan on.  We live on top of a pretty good hill and its almost always cooler than down by the hwy.   Makes for a very nice breeze but I found when I did that my electric bill was more every month than if I just ran the air-co 24/7. 

Unless that fan burns more electricity than a window AC units compressor, it proves the humidity is a very significant factor.






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