Honeywell IAQ Thermostat Dehumidity Question

[thegov3]

The previous action of the stat must be a call for cooling, before the stat will use the A/C for dehumidification.
If it was powered down(as it should have been to wire it) it will need to do a regular A/C call, before it will do dehumid calls.
If your indoor temp is already at the droop set point, it won't cool to dehumid either.
If you set the humidity to 50%, the humidity has to be 5% above set point befor it will do a dehumid call. I set them to 45%, so they call if the RH gets above 50%.

Set your temp to call for cooling, after that cycle, it will cool to dehumidify.

beenthere, if the temp set point has been reached, but the indoor humidity level is 5% greater than the humidity set point, doesn't the low speed dehumidification come on and work until it is three degrees below the temp set point or the humidity set point has been reached? Please confirm or explain.

[beenthere]

Yes, as long as the previous call was a cooling call.

Set your dehumidity set point to 45%, leave it in cool mode. And see how it works today.

[thegov3]

Yes, as long as the previous call was a cooling call.

Set your dehumidity set point to 45%, leave it in cool mode. And see how it works today.

For the past 48 hours, I have run the t-stat on "cool" and "on". The desired humidity level is set at 40%. The system has called for cool countless times to help maintain the desired 72* temp (which it has maintained), but the humidity has stayed steady at 48%. Outside humidity has been around 79%Based on the mis-wiring, I am assuming that the low speed fan is not dehumidifying. However, it is moving air constantly.

[a0128958]

For the past 48 hours, I have run the t-stat on "cool" and "on". The desired humidity level is set at 40%. The system has called for cool countless times to help maintain the desired 72* temp (which it has maintained), but the humidity has stayed steady at 48%. Outside humidity has been around 79%Based on the mis-wiring, I am assuming that the low speed fan is not dehumidifying. However, it is moving air constantly.

A lot of the humidity (latent heat) you're removing when the compressor is running you're putting right back in to your house when the compressor is off / blower motor is still running:




This is because you have all of this water sitting in your evaporator coil at the time your compressor turns off:




You need to run your blower motor (fan) on 'Auto,' not 'On,' to achieve maximum dehumidification.

As an experiment, I just ran my system with the blower motor 'On' with no compressor running for a couple of hours. The chart below shows the sudden inside humidity increase - it's come back down now that I set the fan back to 'Auto - you can see the RH spike up to 50% in the cyan colored line:




Hope this helps.

Best regards,

Bill

[beenthere]

Yes, make sure the fan is set to auto, not on. And check that its not set to on, in any or the set back programs, or recovery times.

Something is wrong, it should be over cooling to dehumidify with dehumidity set point at 40% and reading 48%.

You are going to the duhumidity screen and not the humidity screen correct.

[andserco]

Make sure there is no ventilation cycles are enabled also..

[thegov3]

Well, the installer's tech came out today to check on my concerns that the system was not dehumidifying properly and I was missing a "dehumidifying" screen on my IAQ t-stat (you know, the one they said did not exisit and professor "beenthere" said did).

Guess what? The Honeywell IAQ t-stat and module, furnace and HP had indeed been wired and set-up incorrectly during install. Worse yet, the t-stat had never been set up for controlling a two stage HP. It was set up for one stage only.

I now have a screen on my IAQ to set and control dehumidification.
I have low speed dehumidification ability after my cooling temp set point has been reached.
I have two stage cooling.

Afterwards, I went from 50% humidity to 40% humidity (my set point) in only 3 hours...despite the temp setpoint having been met and the outside humidity level being 74%.

Ahhhh..I am comfortable!

I hope the mis-wiring did not affect the compressor or any other system component. Would it?

a0128958: if I leave the t-stat on "on" to fully utilize the "Pureair" air cleaner 24x7, am I giving up dehumidify efficiency or am I hurting my system?

[mayguy]

I hope the mis-wiring did not affect the compressor or any other system component. Would it?

a0128958: if I leave the t-stat on "on" to fully utilize the "Pureair" air cleaner 24x7, am I giving up dehumidify efficiency or am I hurting my system?

No, I don't there is any damaged done if it was not set up to run like it should.


You can try to run the fan ON and see how the humidity behaves.. In my house, it spikes back up... My parents house is large enough that they don't get the spike like I do.

[beenthere]

If it was just wired to run in second stage no harm. 2 stage units have safeties that would help to protect the compressor from running in second stage with teh ID blower only at 50% speed for too long.

With the fan set to on, it could ring your humidity up. And cause it to go into dehumidify again quicker then needed.
Try setting it to circ. That will allow teh blower to shut off after a cycle, and if the A/C doesn't have to run for a while, the blower will time back on.

[a0128958]

... a0128958: if I leave the t-stat on "on" to fully utilize the "Pureair" air cleaner 24x7, am I giving up dehumidify efficiency or am I hurting my system?

See above for good answers from the professionals and the professors.

Best regards,

Bill

[thegov3]

Thanks to all that offered advice. It worked. My system is running great now and I love the 40% humidity level. The house is cooool.

[mayguy]

Glad to help out. You leave the fan in AUTO or switched back to ON?

[EmilG]

Thanks all, this discussion has been very helpful.