[BlueBSH]

I have a Trane xc95m fully modulating furnace with a XL950 Comfortlink II communicating thermostat..

One of the settings is 1st stage heat cycle rate which has a value between 2 and 6.. it's currently set to 5

I know that's the number of times in an hour it cycles to stage 1, but for a fully modulating is this the correct setting? Just feels odd having a full modulating furnace cycle that may times?

I also have cycle rates for 1st and 2nd stage compressor cooling (I have a xl20i unit outside 2 stage 55% and 100% cooling) rates are 2 - 6 also, both set at 3 right now. Does this seem like a good setting?

I'm mainly interested in the heating cycle rate though, just want to know more info on how that works with fully modulating and what is optimal

 

[user_12345a]

excessive for all furnaces, i would go for 2 if the furnace is correctly sized. 3 on a 2-stage or single stage.

5 cph is hard on the furnace.

 

[BlueBSH]

Do CPH even apply to modulating furnaces? I was under the impression they decided based on temp / runtime to raise temp based on the past, etc and calculated what to modulate at... we the more advanced ones, I guess some just have an algorithm that ramps up until it reaches a set point then jumps around?... never got a straight answer on how they figure out what to modulate at since everyone has their own system on how to do it ha...

 

[user_12345a]

If it's a rebatched honeywell is uses the cph setting, rate of change and other things to determine how to cycle on low.

When heat loss exceeds output on the minimum, it should be modulating up and down. cph may still govern how aggressively it adjusts itself.

A lot of modulating furnaces are actually 3-stage. All modulating furnaces do it in steps and aren't fully variable to my knowledge.

 

[BlueBSH]

What about the AC unit with it's 1st and 2nd stage cycle count, what would be an optimal setting for those?

 

[user_12345a]

3 sounds fine, i think that's the default on most.

 

[beenthere]

Set first stage heat CPH to 3.

Set first stage A/C CPH to 2, And second stage CPH to 4.

 

[sktn77a]

I'm not too familiar with the engineering design of the Trane system but I would imagine there's a balance between CPH in low fire and up-modulating to maintain set point. I wouldn't mess with it unless you know how this all comes together.

 

[beenthere]

I'm not too familiar with the engineering design of the Trane system but I would imagine there's a balance between CPH in low fire and up-modulating to maintain set point. I wouldn't mess with it unless you know how this all comes together.

Worse comes to worse, he can always set it back to what it was.

 

[veesubotee]

"A lot of modulating furnaces are actually 3-stage. All modulating furnaces do it in steps and aren't fully variable to my knowledge."

The Rheem (Ruud) modulating furnace fully modulates up and down, based on the thermostat calculating the difference (firing rate) between room temperature and set point.

On a cold start (setback), it will start up hot and continue to ramp down as RT approaches set point, eventually settling in at a rate to maintain temp.

Cycling only occurs if the unit is grossly oversized.

V

 

[beenthere]

York mod is 100 steps of modulation.

 

[supers05]

York mod is 100 steps of modulation.

Comes out to 0.65% increments. Sounds like a decently smooth curve to me...

Cheers!

 

[BlueBSH]

not 100% sure what ours does but it is suppose to modulate from 40% to 100% in 1% increments... I've seen it all over the place when looking at the status of the furnace valve (on the furnace lcd screen it tells you the modulation)

 

[Bob Sanders]

Set first stage heat CPH to 3.

Set first stage A/C CPH to 2, And second stage CPH to 4.

This BT, I just plain don't understand. I have seen this before and don't get why one would want to set a cph value for 2nd stage higher than the 1st

Can you explain what happens with the system when you set it this way? Does this force stage 2 to come into play more often?

 

[beenthere]

Makes it go back down to first/lower stages to provide longer run times. Which increases comfort. By helping to minimize cool draft feelings.