humidity and ac

[chukk]

Hi,

Howcome everytime i turn on my ac, the level of humidity of the room is increase to 90%?

Thanx!

[Gary]

When it is running does water come out of the condensate drain pipe?

[Brian_UK]

Where are you measuring the humidity?

What are the temperatures, wet and dry bulb, in the room before turning the unit on and when you consider that the RH has increased?

[Magoo]

If in cooling mode, the majority of modern air conditioners have a high SHF [sensible heat factor ] of approximately 85%, as in dry bulb temp reduction, so with a low latent cooling factor of balance at say 15 %, the moisture removel quantity is small.
Therefore the wet bulb temperature does not reduce proportionally to dry bulb reduction, so guess what ... the Relative humidity rises.
Inversly when heating, all the output is sensible heating, so dry bulb temp rises, and wetbuld is un-changed, so relative humidity is low and starts to dry interior of dwelling, sucks up moisture from everything trying to balance out DB and WB. Turn the heating off and interior ambients drops, condensation on all cold surfaces like windows etc., dew point acheived.
A psychometric chart will explain everything.
magoo

[Gary]

A psychrometric chart will explain everything.

Yep... Find your target room temp at the bottom of the psychrometric chart. Draw a vertical line up to the target room RH. Draw a horizontal line left to the 100%RH line. Then draw a vertical line down to find the coil leaving air temp needed to achieve the targets.

If the leaving air temp is higher than this (when the room temp is at target), reduce the blower speed to lower the leaving air temp. Once the blower speed is adjusted, eventually the room will achieve both RH and temp targets.

The downside is that this will lower the system efficiency. It takes energy to remove moisture from air.

[Magoo]

Hi Gary.
We are of similar vintage and probably similar training practices.
Unfortunately these days with all the plug and play systems out of boxes, add that the young techs are not really familiar with real air conditioning systems, add economics as well. In my training days [ along time ago ] airconditioning meant, air filtration and quality, humidity control, and temperature control, ie ., enviroment control.
All lost in space lately, temp control and minimal power consumption is the current criteria.
Ask a young a/c tech about a psychometric chart and a blank look will be common.

magoo

[Gary]

I agree, Magoo. The level of training these days just doesn't seem to be what it used to be.

[udarrell]

I began as a tech in the first half of the 1970's; back then in the SW U.S., oversizing the equipment on undersized duct systems was a major problem. Nobody worried about energy usage.

If you sized those babies right, on proper ductwork, they would flat-out - pull the humidity down big-time even at +400 & 450-CFM per-ton.

They had oversized compressors to the condenser & the evaporator, you could get it close to freezing the condensate & that's why it needed more airflow per ton of cooling.

Now, they have trouble getting the coil below the dew point, ha. Okay, in the desert, but so is a swamp cooler.

I liked the 10 & 12-SEER units; there was no need for the govt to take them off the option table!

There are high humidity situations where they could outperform these units, that too many can't afford to buy. - udarrell