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Message
Do dehumidifiers assist in A/C efficiency?
Posted on 5/27/15 at 2:57 pm
Posted on 5/27/15 at 2:57 pm
It would make sense that they do.
6
Posted on 5/27/15 at 3:01 pm to Tigertown in ATL
I don't know, man.
Posted on 5/27/15 at 3:01 pm to Tigertown in ATL
To a degree but if the dehumidifier is another electrical appliance then you aren't saving any money. Considering most electronic dehumidifiers are basically an ac unit packaged in one plastic box with a condensate sump you aren't doing much other than creating another source of heat that the main AC has to compete with.
Posted on 5/27/15 at 3:03 pm to Clames
quote:
To a degree but if the dehumidifier is another electrical appliance then you aren't saving any money.
very good point
Posted on 5/27/15 at 3:03 pm to Tigertown in ATL
quote:
It would make sense that they do.
i've heard no.
if you are running your ac, you are dehumidifying your air.
if your ac is off, you running a dehumidifier you are going to be blowing hot air back into your home, thus increasing your ac usage to keep up with keeping temps down.
Posted on 5/27/15 at 3:52 pm to Tigertown in ATL
less humidity results in an increase in the available sensible cooling (coil temp) capacity of an AC system since it is having to do less latent cooling (water removal). So yes, it can cool more using the same energy to an extent.
Using equipment to lower the humidity level will not result in less energy usage overall. It will increase the overall energy needed to maintain temperature.
Using equipment to lower the humidity level will not result in less energy usage overall. It will increase the overall energy needed to maintain temperature.
Posted on 5/27/15 at 3:58 pm to Tigertown in ATL
There are two ways to dehumidify the air. one is the use of a humidifier, the other is by cooling the air to its dew point temperature (typically around 55 degrees)
Typical A/C residential units achieve this by the 55 degree discharge air temperature. But humidification is only done when the condenser is running. so when the unit is not running no humidity is taken out out the air. If you are using a humidifier to work while the unit is running you can achieve a "comfort index" benefit. 72 with 60% humidity will not feel as good a 74 with 40% humidity.
however, you do not want to go below 40% humidity (static issues)or above 60% (mold issues)
Typical A/C residential units achieve this by the 55 degree discharge air temperature. But humidification is only done when the condenser is running. so when the unit is not running no humidity is taken out out the air. If you are using a humidifier to work while the unit is running you can achieve a "comfort index" benefit. 72 with 60% humidity will not feel as good a 74 with 40% humidity.
however, you do not want to go below 40% humidity (static issues)or above 60% (mold issues)
Posted on 5/27/15 at 4:15 pm to Tigertown in ATL
In certain situations, decoupling the temperature control and dehumidification functions (assuming they both reject heat outside of the conditioned space) of an HVAC system makes sense from a human factors standpoint and can provide better system performance than a standard HVAC system that couples the two functions.
However, a portable dehumidifier in a conditioned space will never make the main HVAC system work less unless the dehumidifier can get the comfort of the space right on its own. In exchange for reducing the absolute humidity of the air, the dehumidifier is going to put that energy right back into that space by raising the temperature when it rejects the heat it pulled out of the water to condense it. If the air is too hot for comfort even after it's dried, then the main AC has to work to lower the room temperature that the dehumidifier just increased. Further, the inefficiencies of the mechanical system mean that the machine itself is going to dump some heat into the space above and beyond the amount it removed from the air in the first place to condense the water out.
EDIT: So, pretty much exactly what tigeraddict said about how higher temp at lower humidity can feel more comfortable than lower temp at higher humidity. If the circumstances are right, then it may be cost-effective to dehumidify and control temperature separately, but it's rare that it makes sense not to just use the standard dehumidification technique of just making the air uncomfortably cold to get the moisture right, then reheating it or mixing it with outside or return air to get the temperature right.
However, a portable dehumidifier in a conditioned space will never make the main HVAC system work less unless the dehumidifier can get the comfort of the space right on its own. In exchange for reducing the absolute humidity of the air, the dehumidifier is going to put that energy right back into that space by raising the temperature when it rejects the heat it pulled out of the water to condense it. If the air is too hot for comfort even after it's dried, then the main AC has to work to lower the room temperature that the dehumidifier just increased. Further, the inefficiencies of the mechanical system mean that the machine itself is going to dump some heat into the space above and beyond the amount it removed from the air in the first place to condense the water out.
EDIT: So, pretty much exactly what tigeraddict said about how higher temp at lower humidity can feel more comfortable than lower temp at higher humidity. If the circumstances are right, then it may be cost-effective to dehumidify and control temperature separately, but it's rare that it makes sense not to just use the standard dehumidification technique of just making the air uncomfortably cold to get the moisture right, then reheating it or mixing it with outside or return air to get the temperature right.
This post was edited on 5/27/15 at 4:40 pm
Posted on 5/27/15 at 4:17 pm to tigeraddict
Do you live in south LA? When is dew point typically about 55? Not that often...
Relatively speaking, warm air can suspend more grains of moisture than cold air, but there's a limit. On very humid days, the dew point can often be over 70 degrees. Think of all the summer mornings when the overnight temperatures didn't drop below 70, but there is condensation on cars, decks, etc.
IIRC, HVAC systems are designed to provide about 50% relative humidity.
Relatively speaking, warm air can suspend more grains of moisture than cold air, but there's a limit. On very humid days, the dew point can often be over 70 degrees. Think of all the summer mornings when the overnight temperatures didn't drop below 70, but there is condensation on cars, decks, etc.
IIRC, HVAC systems are designed to provide about 50% relative humidity.
Posted on 5/27/15 at 4:32 pm to White Roach
quote:
Do you live in south LA? When is dew point typically about 55? Not that often...
Water starts to drop out of suspension at the dew point, with is normally way above 55 degrees. But to "wring out" a noticeable quantity you need to go well below the dew point. Typical HVAC discharge are goals are 55 degrees to achieve this
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