Air Conditioning - Central A/C w/ dehumidifier

I'm thinking about replacing my 20-year old 4T Lennox setup. I live in SE Texas, 10 miles from the coast, so high humidity is as much a problem as heat.

We leave our thermostat at 78*. Our house is well insulated and has a radiant barrier. Many nights during the summer when the temperature will get down to the low 70's, our A/C may only come on once or twice, so the temp stays relatively close to 78* but the humidity in the house is high. That got me thinking about getting a new A/C system with a dehumidifier.

I talked to my A/C guy about it. He gave me a bid on two Lennox sytems and on Amana system. All are two stage variable speed systems. He said with these types of systems, a whole house dehumidifier is not necessary because the system will run at a very load speed at night to remove the humidity without dropping the temp below 78*. Sounds reasonable, but later when I looked at the Lennox Signature series brochure he gave me, it said it was "optimized for use with the Humiditrol whole house dehumidification system."

So...who is correct? The Lennox brochure or my A/C guy? Under what conditions would you want to add a dehumidifier to a two stage variable speed system? Can one of these A/C systems perform similar to a whole house dehumidifier and remove humidity without noticeably lowering the temp? When the A/C system is only trying to remove humidity, is it as cost effective as a dehumidification system?

Thanks,
Ira

Hog wash! You tech is correct that a 2 stage heat pump will remove more RH. But he is wrong when it comes to not needing one. In no load times how is the RH going to be removed from your home? Only way is with a dehumidifier.

The "Humiditrol" will function in conjunction (in parallel) with the thermostat to keep the compressor and indoor blower running at a low speed, thereby acting as a dehumidifier.
In other words, instead of transferring sensible heat (dry bulb) it will transfer latent heat (wet bulb). I daresay it will do it more efficiently the a dehumidifier, and more conveniently, too. Dehumidifiers need frequent cleaning, which hardly ever gets done, so they end up ineffectual, but still using the electrickery!
Tom Beer 4U2

The "Humiditrol" will function in conjunction (in parallel) with the thermostat to keep the compressor and indoor blower running at a low speed, thereby acting as a dehumidifier.
In other words, instead of transferring sensible heat (dry bulb) it will transfer latent heat (wet bulb). I daresay it will do it more efficiently the a dehumidifier, and more conveniently, too. Dehumidifiers need frequent cleaning, which hardly ever gets done, so they end up ineffectual, but still using the electrickery!
Tom Beer 4U2

So Lennox's Humiditrol is not a whole house dehumidifier? I thought it was just their brand name for one. It looks like one, and it fits in the same place in the HVAC system as others I've seen.

Do whole house dehumidifiers require cleaning more than twice a year? That's how often I have my HVAC system serviced.

To clear up a previous comment...I'm not getting a heat pump. I'm looking at a "conventional" central A/C unit.

Oops! My bad. I thought humiditrol referred to a humidistat type control. I googled and found this>
Humidity Control | Home humidity controls | Humiditrol Whole-Home Dehumidification System | Lennox Residential (http://www.lennox.com/products/overview.asp?model=HD)
It appears their 'Humiditrol' is a reheat coil. That is, if the relative humidity after the cooling coil is too high, it heats the air, thus reducing the R.H. This may be done electrically or by using some of the discharge gas on it's way to the condensor coil.
I'm not sure, according to that literature, whether there is water piped to it to add moisture in cold weather. Or whether it would pertain to your area...
It seems like a marginal extra, unless someone has sinus or respiratory problems.
TomBeer 4U2

I have a carrier single speed compressor but two speed blower. I have a humidistat attached. No matter what temperature it is, as long as the humidity inside is higher than the % I set it at (65), when the A/C kicks on it runs at slow speed to wring out the air. When it reaches 65% it shifts to high speed to concentrate on max cooling. I was listening yesterday when it was 97 outside yesterday, the compressor ran 10 min and high speed blower. At 5 this morning outside was 70, RH was 85%, when the unit kicked on it would run at slow speed. It's a good setup for the Gulf Coast. I bet you could have a qualified dealer install one for around $200. Get a quality job done though, it's not a job for a part-timer who "had a brother who installed one once".

If you or saying you keep the RH in your home at 65% that is way to high. Id try for 50%.

Thx for the input.

I used to put it at 50% but if I put it at anything less then 65% it runs at slow speed way too much. Here it is 97 degrees, I shouldn't be running at slow, wasting energy and wear and tear. At 65% it might start slow but shifts to high shortly which tells me it's working pretty good.

I did alot of research on the web and constantly found this message....

Tips & Warnings
Beware of having the humidstat below 60 percent humidity level. This will cause the home to be extremely cold.

I'm not sure why.

Besides, alot of places recommend setting it between 65 and 70%. Do you have a source that recommends 50%?

Mold will grow with anything above 55% RH. Lower RH will also make warmer temps feel cooler. So you could get by with a higher temp in your home.