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Is the efficiency of an AC decreased by dry air?

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[OP]
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Jun 27, 2015
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East York, ON

Is the efficiency of an AC decreased by dry air?

Let's say I have a dehumidifier running in the house
Would that (dry air) impact the efficiency of the AC unit? In what sense (will it improve it or it is the opposite?
15 replies
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Dec 30, 2008
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I think it would be more efficient.
The AC unit would have less water vapor to cool, which would take less energy to cool.
AC unit also dehumidify, as you can see all the water dripping from a windows mounted unit.
[OP]
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Jun 27, 2015
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East York, ON
cats_on_burners wrote: I think it would be more efficient.
The AC unit would have less water vapor to cool, which would take less energy to cool.
AC unit also dehumidify, as you can see all the water dripping from a windows mounted unit.
So if you have both an AC and the DH you should run them both to speed up the cooling?
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Dec 19, 2009
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CuriousC wrote: So if you have both an AC and the DH you should run them both to speed up the cooling?
Because your dehumidifier does not exhaust the heated air generated in the dehumidification process to outside you are actually increasing the temperature of the room running the dehumidifier.
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Apr 20, 2011
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pootza wrote: Because your dehumidifier does not exhaust the heated air generated in the dehumidification process to outside you are actually increasing the temperature of the room running the dehumidifier.
Yes, running both is counterproductive.
The dehumidifier is doing the job the AC will do in time, but is adding heat to the room, so the AC has to work the same (or longer) regardless.
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Feb 4, 2015
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aqnd wrote: Yes, running both is counterproductive.
The dehumidifier is doing the job the AC will do in time, but is adding heat to the room, so the AC has to work the same (or longer) regardless.
Plus added hydro cost
[OP]
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Jun 27, 2015
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Well the AC has to run much longer to dehumidify the basement (that is already 4-degrees colder than the main floor) than the AC
To bring the RH down 4-5% I need to run the DH a lot
I need just 1.5-2h of DH running to get to the same result
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Feb 8, 2014
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CuriousC wrote: Well the AC has to run much longer to dehumidify the basement (that is already 4-degrees colder than the main floor) than the AC
To bring the RH down 4-5% I need to run the DH a lot
I need just 1.5-2h of DH running to get to the same result
The dehumidifier dumps the heat it uses plus the heat of vapourization into your house then the AC has to acquire both then move them out. The AC dumps the heat if its own use and the heat of vapourization directly outside, one less step.
If you want a warmer basement and a larger energy bill use the dehumidifier with the AC

You could achieve the same bill by using only the AC and using a small space heater in the basement.
In fact in Rand McNally they wear hats on their feet and hamburders eat people
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Dec 19, 2009
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CuriousC wrote: Well the AC has to run much longer to dehumidify the basement (that is already 4-degrees colder than the main floor) than the AC
To bring the RH down 4-5% I need to run the DH a lot
I need just 1.5-2h of DH running to get to the same result
Might try and leave the fan setting on your thermostat to on instead of auto overnight and the temperature and humidity of the basement and main floor should balance out. That is unless you played around with the dampers and covered up return air grilles.
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May 23, 2009
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I recall you bought new Trane units last year. Ask your contractor if they can return to enable the comfort-r mode. With comfort-r, it keeps the blower fan at 80% for the 7.5mins at startup. This concentrates on enhanced dehumidifying before cooling.

Additionally they can break the BK jumper and attach a humidistat. This will set the blower at 80% till the humidity level is achieved.

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[OP]
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Jun 27, 2015
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bubuski wrote: I recall you bought new Trane units last year. Ask your contractor if they can return to enable the comfort-r mode. With comfort-r, it keeps the blower fan at 80% for the 7.5mins at startup. This concentrates on enhanced dehumidifying before cooling.

Additionally they can break the BK jumper and attach a humidistat. This will set the blower at 80% till the humidity level is achieved.

Image
I have a Trane XR15-018 for AC.
Not sure if this is a two steps AC or what you said above needs a two steps AC
Maybe that is just a setting on the controller of the blower which I guess it is still controlled by the furnace
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May 23, 2009
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It works with single stage or 2-stage cooling as you can seee below. The enhanced fan speed setting is adjusted on your furnace board(XV95). The contractor should know when you mention comfort r.

Image
[OP]
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Jun 27, 2015
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East York, ON
thanks, I will have a look at this when I have some time.
This looks like something that the owner can do himself. It might affect the warranty though ..I might chose to run the idea through the vendor first.
although it does not sound fair that all the adjustments have to be done by the vendor in order not to lose the 10Y warranty (parts and labor) that I have.
I have not been told anything in this respect but I will play safe and ask them
[OP]
Deal Addict
Jun 27, 2015
1825 posts
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East York, ON
At a second thought I don't think that running the AC is going to hurt...the basement is much colder than the rest of the house but at the same time more humid.
Removing humidity from there while the AC is not running it is going to be OK.
Deal Expert
Feb 29, 2008
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CuriousC wrote: thanks, I will have a look at this when I have some time.
This looks like something that the owner can do himself. It might affect the warranty though ..I might chose to run the idea through the vendor first.
although it does not sound fair that all the adjustments have to be done by the vendor in order not to lose the 10Y warranty (parts and labor) that I have.
I have not been told anything in this respect but I will play safe and ask them
This is the proper solution. I have a Lennox heat pump, and in dehumidification mode it runs the fan at lower speed. This increases contact time with the air and improves extraction of humidity. A proper thermostat will allow you to control target humidity and degree of overcooling that is acceptable.

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