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BlueBSH 07-12-2012 07:38 AM

Trane XL20i cycle time and dehumidify
 
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In our one house we had a trane XL20i installed as part of a communicating system with a xc95m and a TCONT900 thermostat.. the entire system is communicating via 3 wire to the furnace and 2 wire to the AC unit (Voltage + Data)

I have been watching the unit runtime lately and it seems to run a lot in stage 1 even when the house would require stage 2 to bring down the temp.

Have a look at the graph attached. this is the wattage pull from the house over time for about four and a half hours. the highs are 2nd stage (100% 3 ton cooling) the lows are 1st stage (1.5 ton cooling) this was captured at night when there was no sun, and it was only 67 degrees outside, the thermostat was set to 71 the house ambient temp was at 71. Why does it need to cycle to 2nd stage so much when "maintaining" the temp? I thought 1st stage was supose to be capable of doing that?

then around midnight you have the long run of 2nd stage, which made no sense because there was virtually no heat gain during that time.

I am just a little confused by why there is so much cycling, I was under the impression 1st stage would be used unless it really needed 2nd stage. Just yesterday alone our AC unit / furnace used 44 KWh for one day and it wasn't even that hot out! compared to our old system that used a third that and that old system was only 9 SEER, this one is 17.9 SEER with its current configuation.

We don't have the thermostat set to 71 all day, it gradually drops over the day. But that's what bugs me, when we are not home it is set to cool if it goes over 75 degrees (8am to 5pm) and drop it to 72 degrees from 5pm to 11pm and 71 degrees overnight till 5am (cant sleep in a hot bedroom, but thats another issue! :laughing:)

but that's where the oddness comes in, during the day the AC unit will run... at 2nd stage! when the house is only 70 degrees! the thermostat says 70 on its ambient temp readout, and the setpoint says 75... why would this system decide it has to run then?!

The other issue that might be the reason, but I'm not sure, is this thermostat also is supose to control humidity, is it trying to dehumidity when the temp is below the setpoint? the dehumidity setpoint is 60% right now, what is considered normal to set it at? that was just the default number the thermostat had.

BlueBSH 07-12-2012 12:43 PM

well just did it again, the AC came on at stage 2, it's 70 degrees in the house, the set temp is a max 75... humidity is 50% max humitity for dehumidifying is 60%.... anyone know of any "installer" setup codes to look at that might cause this? we have continuious airflow on at 50%... Stage 1 compressor cycle per hour is 3 stage 2 compressor cycle per hour is 3

beenthere 07-12-2012 06:39 PM

Do you have it set to cool to dehumidify.

BlueBSH 07-12-2012 08:41 PM

Quote:

Originally Posted by beenthere (Post 964313)
Do you have it set to cool to dehumidify.

not sure what you mean, The thermostat is set to "Cool" mode, I don't know how the dehumidification works on this system, you can press the "more" button on the screen and it takes you to humidify and then dehumidify options relative humidity percentage.. somehow the thermostat figures out the dehumidification I think by using the 1st stage of the AC unit? the AC unit has an outdoor temp sensor that communicates back, somehow it figures all that out.. that's all I know...

just don't understand why its cycleing high low high low so much and running when it's not needed (temp is higher then the set point, and current humidity level is below the max humidity setting)

the system should of had the house to 73 degrees by 4pm today, when I came home at 5pm it was still 75 in the house and the setpoint was still 73... and it ran constant from 3pm trying to cool the house... but the whole time instead of staying in second stage and getting there fast it kept going low, high, low, high, off, low, high, low, high, off in about 15 minute increments...

I just dont understand how its working, its taking forever to cool the house and I thought they only went 2nd stage when needed, and only back to 1st to "maintain" the temp not cycle back and forth and never go anywhere temp wise

the installer did a Manual J and Manual D for the house, sized the houe at 2.5 Ton, but the XL20i ony comes in full ton increments, so we have a 3 ton.. they resized some ducts, and did CFM checks on the rooms... so the duct, sizing, and CFM per room "should" be right.... but it just seems like the unit isn't cooling the house down

BlueBSH 07-12-2012 09:50 PM

I just went through the installer setup and changed the setup number 0380 from 1 to 0

the options for it where

0 - Off
1 - Integrated Temperature and humidity control (RH Setpoint)
2 - Trane Droop (RH Setpoint)

I think I turned the dehumidifier completely off now since I can no longer change the dehumidifier setpoint on the user screen..

not really sure dehumdifier was doing anything to start with besides running the AC at stage one until its a few degrees below the set temp *scratches head* haven't had humidity inside the house above 60% all summer, so haven't seen it really do that or show any reason to believe it tried to dehumidity

beenthere 07-13-2012 04:00 AM

What was the humidity set point set at. Also check what the CPH is set to. Set first stage to 3, and second stage to 2.

BlueBSH 07-13-2012 06:16 AM

Quote:

Originally Posted by beenthere (Post 964608)
What was the humidity set point set at. Also check what the CPH is set to. Set first stage to 3, and second stage to 2.

humidity was set to a max 60% before dehumidify

CPH was 3 and 3, changed it to 2 and 2 last night to see how it ran, I'll try 3 and 2 this weekend

yesterday when it was supose to be 73 degrees it took over 3 hours and the temp never dropped... but when it was to go to 71 degrees it took 30 minutes and the temp dropped... at night 2nd stage kicked off and stayed on until it dropped... during the day it cycles between 1st and 2nd... I just don't get why it acts different depending on time of day

beenthere 07-13-2012 03:01 PM

What CFM is the blower running at in low and in high stage.

BlueBSH 07-13-2012 03:10 PM

Quote:

Originally Posted by beenthere (Post 964961)
What CFM is the blower running at in low and in high stage.

it was at 400 CFM per ton (its a digital controller, I can set the CFM per ton on screen at the furnace)

highest it can go is 450 CFM per ton, and lowest is 290.. I can set it to these CFM/ton settings

290, 310, 330, 350, 370, 400, 430, 450

Since it is a 1.5 Ton stage 1 and 3 ton stage 2, I'd assume it was running at 600 CFM and 1,200 CFM

beenthere 07-13-2012 03:23 PM

Quote:

Originally Posted by BlueBSH (Post 964965)
it was at 400 CFM per ton (its a digital controller, I can set the CFM per ton on screen at the furnace)

highest it can go is 450 CFM per ton, and lowest is 290.. I can set it to these CFM/ton settings

290, 310, 330, 350, 370, 400, 430, 450

Since it is a 1.5 Ton stage 1 and 3 ton stage 2, I'd assume it was running at 600 CFM and 1,200 CFM


You know what happens when you "assume".

BlueBSH 07-13-2012 03:30 PM

Quote:

Originally Posted by beenthere (Post 964975)
You know what happens when you "assume".

yeah, I don't have a air speed meter though to verify it... right now the screen says it's "requesting" 1255 CFM for stage 2 and it's sucking pretty hard

put the system into "Test" mode and tell it to run at stage one it is "requesting" 688 CFM

beenthere 07-13-2012 03:35 PM

I'd slow it to either 375 or 350 CFM per ton.

Your refrigerant charge may also not be right.

BlueBSH 07-17-2012 07:22 AM

well they tested the refrig levels using the trane "quick charge" feature and it told them the levels are optimum for the current conditions... guess the thing can do automatic charging and removal of r-410a without user intervention (user gauges)... they also checked with gauges just to make sure...

but the thing runs non-stop! I know the 1st stage is for maintence cooling, but should it really run all the time?! using 40KW a day just for AC is getting ridicilous, when the old AC unit only ran when needed

after 2nd stage gets the house to temp, the 1st stage just runs forever! until I move the thermostat up a degree to stop it

beenthere 07-17-2012 01:35 PM

Try setting the first stage CPH to 4, and leave the second stage CPH at 2.

BlueBSH 07-17-2012 01:54 PM

Quote:

Originally Posted by beenthere (Post 968010)
Try setting the first stage CPH to 4, and leave the second stage CPH at 2.

I'll change it to that tonight and see what happens..


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