decreased humidity control with higher seer

[heetseeker]

I was wondering why the higher seer units are supposed to be less able to dehumidify. My old unit, carrier 4 ton 1982 kept the house comfortable at 78 degrees 50% RH and my new 12 seer a/s 4 ton feels warmer at 78 degress 54% RH. I am hoping turning on comfort R will help. Why do the higher seer unit dehumidify less?

[ruud-man]

Higher SEER - lower compression ratio- lower head, higher suction- higher suction and larger evap- less latent heat capacity.

Certainly there are other factors but this is the one that greatly reduces hunidity control.

Thats my story and I'm stickin' to it.

[docholiday]

I dont know, I think some of that is silly nonsense. While some is legitimate.

In this case we have a wet bulb of 65.01 last year and 66.19 this year. Depending on your location the summer was significantly different than last year and yet we only have a 1 degree WB difference and that is uncomfortable. My suggestion would be set it to 77 and be done with it. If you get the wet bulb to 65.01, then you would have to ask yourself, how much is in your head?

No two systems are alike, the airflow is different from your previous system, the capcity is different (4 ton is not always 48,000 btuhs). The latent and sensible capacity differences between models. There are too many variables. Was the house rearanged to where now you spend your time in a different part of the room? Were there any duct changes to address room issues? Is the hygrometer calibrated the same as it was previously?

[heetseeker]

The a/c was installed the end of august and nothing has changed other than the equipment. I don't understand the talk about wet bulbs. Is the coil not as cold making it more difficult to dehumidify?

[docholiday]

wet bulb temperatures are basicly the combination of heat and humidity. The coil is probably not as cold as your previous set up but it is larger in all likelyhood. The larger coil should make up for the difference in temperature. Engaging comfort R may resolve your issue.

[teddy bear]

The indoor %RH is a function of the hours of cooling per day, the amount of moisture removed per hour, and the outdoor dew point. Comparing the %RH Aug/Sept which has fewer hours of cooling plus this year the midwest has had high outdoor dew points. Slowing the air flow more will increase the latent removal of any coil regardless the size. For times with little or no cooling, use a good dehumdifier to control %RH. TB

[big al2]

It is like the difference between an old 6-cylinder chevy truck and a race car. The race car runs better, but requires more things to be tuned properly.

We will see more people complaining about 12 SEER system. They should be complaining about the cheap install job they saved soo much money on.
Most of those complaints could be solved that Aeroseal stuff. Seal the ducts and leave more of the outside air outside.

Also you can't overcharge TXV systems and get the same results we got from cap tube systems.

[beenthere]

Your new 12 seer unit may have a slight higher indoor coil temp, and if it does it won't remove as much moisture.

Also, the new VS blower may be moving more air, and that means its also cooling the house a little quicker, which means its removing less moisture.

Activating comfort r should help.

[udarrell]

The lower the sensible ratio the better; i.e., a .75 sensible is better for latent control than a .82 sensible ratio.
An extremely important factor is NOT to oversize the system, a little undersized is better because you need more run-time to remove moisture. (Always use a TXV refrigerant control!)

Have a blower door test done to indicate the amount of air infiltration and seal your home as tight as possible. That will stop most of the moisture infiltration.

Slow the blower to around 350-cfm per ton (12,000-BTUH) of cooling.

The cooling coil's capacity to remove moisture increases with an increase in humidity; that helps!

http://www.udarrell.com/air-conditio...tent-heat.html

The ultra high SEER units operate with a higher evaporator pressure and temperature, and therefore have to use a lot of other more expensive aids to reduce the humidity.
- Darrell - udarrell

[jrbenny]

Here's an idea...install equipment with a SHR that matches the load.

[amickracing]

My vote is it's not set up right. Most come from the factory set kinda high (air flow), to be safe. Plus most newer units come with a comfort system that should suck way more moisture out than the older models.

[docholiday]

I like JRBenny's answer best. Thats why they print spec sheets. That way, the right system for the job can be selected.

[heetseeker]

jrbenny
What is SHR? Is it sensible heat rating? Shouldn't I consider both sensible and latent heat loads?