Relative humidity question

So it's been two days since I had my complete HVAC system (except the ductwork) replaced with a high-efficiency Lennox system (two stage, variable speed, etc.). The thermostat is the Lennox ComfortSense 7000. The thermostat is set to "Basic" for dehumidification mode, which I read to mean that the A/C will continue to try to dehumidify the air until it matches the RH setpoint (50%).

I have an Oregon Scientific WMR100 "weather station" that I use to track indoor temp/RH. I have a wireless temp/RH sensor that is within five feet of the thermostat (at the same height from the floor). With my old system, we kept the temp at 76*. Humidity during the summer was almost always between 45% and 50%. I live in SE Texas 15 miles from the Gulf, so humidity is always high.

With the new system, the ComfortSense has been showing the RH as 54% for the last 24 hours. We have the temp set at 79*, and it seems colder than before. When we set the new system at 76*, both my wife and I thought it was a lot colder than before. The thermostat temperature display and the OS weather station temps are within a degree of each other. However, the really odd thing is that the thermostat shows the RH to be 54% (why not 50%?) while the OS weather station shows it to be 40%. I bought a Radio Shack temp/RH display, and it matches the OS readings within a point.

So...what am I missing here? Why does the thermostat display 54% RH while the other three show 40%? I don't believe the thermostat RH reading because even at 79* in the home, it still seems a little colder than the old system at 76*. I'm thinking that may be the result of the RH really being 5% to 10% less than it was with the old system. Why does the system stop trying to dehumidify at 54% in basic mode instead of 50%? The system seems to be cycling normally. Hard to tell because it is really quite.

I will call my dealer/installer on Monday to discuss, but I wanted to see if I could get some comments/opinions before then.

Thanks,
Ira

 

Well, that comfort level is actually great news, & the humidity is probably lower.

The T-stat humidity gage is only for the indoor humidity, so see how it syncs with the Radio Shack gage indoors.

Perhaps the t-stat can be adjusted to sync with the other humidity stat.

The outdoor humidity varies due to many factors, so weather casts not a reliable test of accuracy.

 

The OS temp/RH sensors and the Radio Shack device are all inside the house. The OS wireless sensor and Radio Shack device are within five feet of the thermostat. I actually had the OS wireless sensor sitting on the thermostat for a while to see if that made the readings a little closer, but it didn't. All the temperature readings are reasonably close.

The outdoor RH is currently 68% and on its way up.

 

Ira -- did you ever get a reponse from your HVAC guy. Your scenario sounded a like mine. I installed a new Lennox indoor and outdoor (XC14) units last week. I don't have the model number of the inside unit handy. I have the same thermostat (Lennox ComfortSense 7000) that you have. I also set my Dehumidification to Basic. I've set my Humidity at 45%, yet the dehumidification seems to stop at around 54%. I do not have the Humiditrol unit that Lennox sells. Any idea why the dehumidication stops at around 54%?

Thanks

 

Theres an installer setting that allows you to "adjust" the RH displayed on the t-stat. For some reason, mine was originally set to +10% or something like that. So the display was showing 55% RH when it was really 45% RH. The installer didn't know if it was set like that at the factory, or if someone set it to that value during installation startup. He set it to zero, and now the t-stat displays within a percent or two of what the OS sensors display.

I kept the t-stat at 78* or 79* all summer and it stayed comfortable the whole time.

The one thing I don't like about the t-stat is the loud relays. I can hear it clicking from almost everywhere in the home. I thought it would be less obvious as I got use to it, but I think the opposite happened. I may end up changing it out for one of the Honeywell t-stats that has its relays mounted in the attic instead of the t-stat itself. It's also more adaptable to home automation than the Comfortsense 7000 (which doesn't have any communications features).

 

Thanks for the reply. My offset was set to 0, so that's not causing my issue. However I noticed that my dehumidification mode is currently set to PRECISION, not BASIC. According to the manual, with BASIC, you have to have a demand for cooling before dehumidification kicks in. With PRECISION, you do not have to have a demand for cooling, however the maximum over cool is 2*. I'm thinking that because the temperature in the house is cooler than where I have the t-stat is set by 2* or more, my dehumidification is shutting off.

However, I am confused has to how you can get your humidity down so low if you are setting your temperature at 76* or 79* in BASIC mode. Did you notice that the dehumidification only kicked on if your house temperature was above your t-stat temperature which would make the "cooling demand exists" requirement true? According to the manual, this condition must be true in BASIC mode.

 

My RH will get over the RH setting for part of the year because I use basic instead of precision mode. It maybe gets up to 55%, but that's okay with me. I think I tried running it on precision for a while, but it was was more comfortable to live with the higher percentage than the lower temperature. It's only for a few weeks in the Spring and a few weeks in the Fall.