Comfort-R.....Dehumidifying Tstat.....Is Constant-On Fan Mode Incompatible???

[key1cc]

No, it does not.

I kind of knew that....but I was hoping that since the non-programable version can do it....

Key1

[wormy]

I'm not too familiar with that stat (TCONT803)
But... even though it has a humidity sensor built in...
it uses a concept I'm not too fond of to dehumidify....

Dehumidification Droop Control
The dehumidification control attempts to control to the
user's humidity setpoint by turning on the air conditioner.
In extremely high humidity conditions, the comfort control
keeps the air conditioner running for up to 3°
F below the
temperature setpoint. It does this while trying to achieve
the desired humidity setpoint and balancing that with the
temperature setpoint

IT would be really nice if there was an output from
the stat that would 'turn on' when the humidity is above
setpoint so the furnace would know its time to dehumidify
and can run its blower at a slower speed.

ITs a shame Trane does not have a programable stat that
utilizes both the humidity sensor and BK terminal to
get the most out of the variable speed blower.

I must admit, Carrier does a fabulous job in that department
with the Infinity system.
(The company I work for sells both Trane and Carrier)


For what it's worth, the Infinity is able to give you custom fan speeds
during 'Fan On' operation.
Don't know the percentages off the top of my head.
All I remember at the moment is Low, Med, High settings

I haven't messed with an infinity in a while, so I wouldn't be
able to answer too much about that.... but I'm sure someone on
here can.

I did a little checking, the Honeywell IAQ does have a dehumidify
signal that can be sent to the furnace.
Basically, you set the humidity on the stat.
If the humidity is too high in the summer,
it will send the signal back to the furnace.
The furnace will only allow the blower to run at most 80%
so it can remove the max amount of humidity from the air
during the run cycle.

The furnace will still utilize the Comfort-R strategy...
it just won't let it go over 80% when the time comes.
So you'd have....
1 minute @ about %50 airflow
THen the rest of the cycle at 80% airflow
as long as there is a high humidity in the house.
Once it gets the humidity under control, it will allow the
furnace to go up to 100% airflow.


IF you also have a humidifier installed for winter moisture,
the IAQ can bring it on as well if the humidity in the house drops too
low.
The IAQ is equiped with two seperate terminals.
One is 'energized' when the humidity is too high(used in summer) the other is energized when
the humidity is too low (used in winter)

Side by side comparison:

Tcont402
Not programmable (has a setback feature.. hit dollar sign and temps setback to amount you want.. default is 5 degree heat/5 degree cool. I don't use it
at home for that.... I hit it when my wife or I am fixing to jump in the shower... easy way to 'pause' the operation of the unit till we get out
of the shower)

IAQ and TCONT803
Both are programmable
and pretty much look the same as you can see (wonder who makes the 800 series stats for trane LOL)


Tcont402
Fan On: customizable fan speed
Any other stat: Fan on 50% airflow (or is it 60%) A jumper can be added in the furnace to provide 100% airflow
Comfort-R can be used with any stat (its just built into the tcont402)
even if the fan is set to ON

TCONT402 (without humidistat) vrs IAQ with built in humidistat
The TCONT 402 has: Cooling Efficiency Booster - (Single Stage Compressor
Only) - BK Enabled
The indoor air flow is reduced to 80% at outdoor
temperatures below 87°F in cooling mode. The outdoor
temperature sensor must be installed and enabled
This is Trane's way of trying to get away with not having a humidistat....
THey figure the cooling is not going run as much at temps below 87, so
the humidity will be higher at temps below that. Once you get above 87, the
unit will run longer and in turn remove more humidity.
If you actually have a humidistat control (like whats built into the IAQ)
then the fan will run at 80% anytime it needs to based on "real world"
conditions instead of a "calculated risk" method.

TCONT803
Has built in 'dehumidification' feature
that runs the cooling up to 3 degree's colder than setpoint
so the compressor gets extra runtime.
Sounds a bit uncomfortable to me.
Too much temp swing.
This feature can be turned off at that stat and
An ADDITIONAL humidistat CAN be added to the FURNACE to
limit the fan speed to 80%, BUT.....
If installed where it supposed to (right beside the thermostat) it makes things
really stand out.
It can be installed in the furnace, you'd have to set it and forget it...
which most people do anyway.
You can set it to 50% humidity, and leave it be.
The furnace will then only allow the blower to go up to 80% just like if it had
the IAQ stat since its using the same terminal.
Grant it, if you have a humidifier, you'd have to add another humidistat to control it... but that one would be best to have by the indoor stat since it
needs to be adjusted based on outdoor temp to keep the windows from sweating in the winter. The IAQ don't need the additional humidistat for heat, its built in.
A compromise would be to install the humidistat(s) behind a filter grill.


TCONT402
the humidistat can be connected to terminals in the stat
to allow for the same 80% limit
When the thermostat reaches setpoint,
it continues to run the compressor for 2 minutes longer
then shuts the compressor and blower off (no 3 minutes of running
the blower at 50%).
This is less noticeable than the TCONT803 method of running
the compressor till its 3 degrees cooler in the house


There is one important thing to remember about all this.
If you are expecting to have high humidity conditions.
ie You live in Florida
Then I'd recommend a two stage/speed compressor.
This will do way more than the blower alone can.

Under normal conditions....
If the system is sized correctly and installed correctly,
then the humidity in the house is typically within reason even
with a standard blower.
The variable speed blower with Comfort-R is going to make
'good enough' into something better
The TCONT402 is a really nice stat and does a wonderful
job at controlling the temp as well as some nifty features for
a variable speed unit. It does an absolute fantastic job with
dual fuel heat pumps and with two stage heating units like the furnace
you are interested in. It can also work with two stage cooling as well.
With an additional humidistat, it makes
the system even more better (But we reach a point where
its hard to tell if its even worth it)
If you're looking for the best control of humidity and want a programmable,
then I'd suggest the IAQ. Although I haven't messed with the IAQ,
I have installed a couple of the 803's and since the IAQ is a better
stat than that, coupled with the high support of technicians that visit
this site... I don't hesitate to recommend it myself.
If you're in a high risk area for high humidity, then you'd benefit more
from a two stage compressor.
If you have an indoor pool, then you'd be better off having
a dehumidifier from Desert Air

[SmackDabAOK]

Some REALLY great info here. So kind of you guys, no doubt about it.

So appreciate the Tstat comparisons, Wow.

This will not only be helpful to me, as I figure this stuff out, but to many others who'll study these posts.

Thank you beenthere for explaining the uniqueness of Tstat fan control to the Tcont402.

Is that the only Trane Tstat with this feature? Sorry if that's too broad a question to ask.

Would Tcont402 features work well with my present AmStd Allegiance 11 … Single Stage 2.5 ton ... Model # 2A7A1030A 1000AA, & my Evap Coil 2004 AmStd ... TXA-030C4HPCO?

Also, I wonder if it would work with a new SingleStage Trane or AmStd A/C & Coil later when purchased down the road? I guess it depends on the model I use (not all models?)?
Not sure I want to keep putting money into new Tstats every time I turn around, hopefully what I get now will satisfy needs later too.


wormy,
You said the following ...
If you do get this stat and BK is enabled,
then be sure not to turn on Comfort-R at the furnace.
The stat will control fan timing and speed control.

Does this indeed mean that Comfort-R is not compatible with any use of Constant-On Fan mode?

And instead that I'm having to choose either Comfort-R, or Constant-On Fan mode (one over the other)?

But, what would happen if I had Comfort-R on at furnace, but then turned constant fan on at Tstat? (If anyone cares to explain, Ha.)


If that's the case about Comfort-R / Constant-On, maybe I should just use the 40% Constant-On Fan-speed wiring setup at furnace (referred to in this thread & Comfort-R Pocket Guide) instead of using Tcont402 for lower fan speed. And then have a different Tstat.

Problem is, I mostly only want to use Constant-On during heating months, but then use Comfort-R for cooling months.
Sounds like wiring change would be necessary per season to do this. Of which I would likely just choose one permanently though.
I'm trying to grasp this & understand it. I'm a little
naive with this.

Also, I thought I read in a thread once that Dehumidify mode of Tstat can work in concert with, or in addition to, Comfort-R.
Is this True?

Thanks to all.

[Airmechanical]

if you're looking for the best control of humidity and want a programmable t-stat then I'd suggest the IAQ.
that is absolutely correct sir, also the IAQ can be set as a non-programmable if desired

.

[beenthere]

Thank you beenthere for explaining the uniqueness of Tstat fan control to the Tcont402.

Is that the only Trane Tstat with this feature? Sorry if that's too broad a question to ask. As far as I know, yes.

Would Tcont402 features work well with my present AmStd Allegiance 11 … Single Stage 2.5 ton ... Model # 2A7A1030A 1000AA, & my Evap Coil 2004 AmStd ... TXA-030C4HPCO?

Not sure.

Also, I wonder if it would work with a new SingleStage Trane or AmStd A/C & Coil later when purchased down the road? I guess it depends on the model I use (not all models?)?
Not sure I want to keep putting money into new Tstats every time I turn around, hopefully what I get now will satisfy needs later too.

Whats wrong with a new stat every couple years.

[teddy bear]

Why not sset-up the fan to the lowest amount of air flow possible short of freeze-up. This would max the amount of dehumidification. Seldom do have any over-dehumidification. Having times of 45%%RH gets the home dried out for all those evenings and rainy days of low cooling loads which even two-speed can not remove much moisture. I have yet to see anyone demonstrate <50%RH dehumidification with fresh air ventilation and occupants during wet cool weather. A whole house dehumidifier maintains <50%RH with no sweat. Regards TB

[beenthere]

Because the lowest fan setting that won't freeze the coil.
May be too low for the days when its near design conditions outside.

A thermostat that can slow the blower when the indoor humidity gets high, will give the highest system efficiency when humidity is below set point and the blower can run at its higher speed. And still provide good moisture removal on days were humidity is high, and the blower needs to be ran at a lower speed.

[wormy]

Comfort-R is basically a setting in the furnace to allow the blower to run for
1 minute @ 50%
7.5 minutes @ 80%
Then ramp up to 100% till the end of the cycle (If humidistat OR IAQ's dehumidify terminal is connected to furnace, then if humidity is above setpoint then keep blower at 80%, if humidity is below setpoint, go ahead and ramp up to 100%)
At end of cycle, it drops down to 50% for 3 minutes


The TCONT402 with the BK terminal connected has the following options built into the thermostat.
Variable speed turn-on profiles:

1 minute @ 50%, 7.5 minutes @ 80%, then 100% (If humidistat connected to THERMOSTAT and sensing high humidity, then it will keep it at 80%. If humidistat senses low humidity, it will go ahead and advance to 100%

1 minute @ 50%, 4 minutes @ 80%, then 100% (unless humistat is connected to stat)

7.5 minutes @ 80%, then 100% (unless humidistat is connected to stat)

4 minutes @ 80%, then 100% (unless humidistat is connected to stat)

1 minutes @ 50%, then 100% (unless humidistat is connected)

30 seconds with no blower on, then 100% (unless humidistat is connected)
(Note: there is a setting separate from these in the stat for units without variable speed that can
do the same delay of the fan for so many seconds to allow the cooling coil to 'pre-chill')

FAN TURN-OFF PROFILES:

NO Delay

1.5 minutes @ 100%

45 seconds @ 100%

30 seconds @ 50%

1.5 minutes @ 50%

3 minutes @ 50%

30 seconds @ 35%

IF humidistat is connected to thermostat AND humidity is above setpoint
Compressor and Blower will run for additional 3 minutes then both will
shut off at the same time.


If Comfort-R is turned on in the furnace,
the thermostat no longer has control.
The furnace board will take over and use its Profile


I'm not sure how the system does the profiles if the fan is in the on position. If there is a humidistat connected (or IAQ dehumid connected)
then it will still limit the blower to 80%

I might have missed it somewhere... but why are you wanting to run
the fan in continuous mode?

[teddy bear]

Because the lowest fan setting that won't freeze the coil.
May be too low for the days when its near design conditions outside.

A thermostat that can slow the blower when the indoor humidity gets high, will give the highest system efficiency when humidity is below set point and the blower can run at its higher speed. And still provide good moisture removal on days were humidity is high, and the blower needs to be ran at a lower speed.

How many days a year is that? My data logging indicates no days in WI last year. Regards TB

[beenthere]

You DATA logging is for one house.

At one time you use to say your system was over sized. Shortly after it was installed

And the most recent post say its sized right (The ones since you started posting the charts, or a liitle before you started posting your charts).

You seem to prefer 74 or 75° as an indoor temp in the summer.
Many people prefer 72°F at RH% levels of 50% or less.

You can't use just your home and personal preferences to say that the nation would work the same.

So, while your homes A/C had no problems keeping up at your prefered conditions, at what ever its current size is.
You don't know how the rest of the homes in your county did, let alone the rest of the country.

Just look at the number of post this board gets, of people saying there house gets X degrees above set point, when its what ever temp outside.

[motoguy128]

My unit is particular is oversized for heating so capacity in cooling mode is not an issue.

I was wondering what the impact of the reduced airflow (350CMF/ton instead of 400) would be on efficiency on a heat pump in heating mode.

ON my XL16i, if I'm reading the tables right, I see about a 5% improvement in latent capacity at the lower airflow with a 2% drop in total capacity.

In heating it's a 1-2% drop in capacity, but it doesn't look like there's any significant change in efficiency as the power consumption drops about the same.

So it might be a useful if humidity becomes a problem. 350CMF/ton is only a 12.5% reduction so is icing really a concern?

Obviously the best scenerio is for Trane to offer a non communicating thermostat with a the features of the 402 and XL900 to help out those that mistaken purchased a XL16i... instead of a XL15i

[beenthere]

35 a ton, is seldom a problem in average humidity climates areas.

In Las Vegas, it would probably be a problem.

[key1cc]

I run my Trane XL15i fulltime at 320CFM/ton without issue (so far ).
I've only used it 1 full season as it was installed spring 2008.
Key1