Sudden drop in discharge temps for Bryant (Climatemaster)
Last Post 18 Apr 2015 09:57 PM by arkie6. 16 Replies.
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fstanekUser is Offline
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09 Apr 2015 12:19 PM
Location: Cincinnati, OH
Model: Bryant GT-PB 50YFV036JD2C311 - 4313V13092 furnace (aka Climatemaster Tranquility 22 TZ)
Loop: Vertical, Closed 3-ton

I noticed a sudden drop in the max discharge temperatures (LAT) in my system for stage 1 compressor. The system was installed a year ago. The entire winter the discharge temps were mostly in the 94°-100° range for stage 1 compressor. However, on March 12th, between 3PM and 4PM, the discharge temps dropped to a VERY consistent 89°-90°. The system doesn't seem to be capable of getting anywhere into the mid-90s° again, and it happened on that specific day at that specific hour.

I had a tech come in and look at the system. They measured the water temp and it was somewhere in the low 40s°. But he didn't really know what could have caused the drop in temps and he simply stated that 89° is pretty good. However, before March 12th, the discharge temps were never this low. After March 12th, they're extremely consistent at 89°.

I have been keeping logs of my system. I created a viewer that can be easy to read over the web. It can be accessed here.

To see the issue, change the "Mode" to "Compressor Heat", and the "Span" to "Daily". You can pretty easily see what I'm talking about if you go back a few days and look at the max discharge temps before and after March 12th.

I'm really looking for some help in figuring out what could cause a very sudden 5-8 degree drop in the discharge temps.

Thanks!
ChrisJUser is Offline
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09 Apr 2015 01:54 PM
Interesting, my first thought was perhaps insulation around the sensor was moved slightly. Or when access doors were put back on some room air is leaking in near sensor.

To bad a temp reading at a room vent wasn't taken at some point as a benchmark. That could confirm if temps have really changed or not.

Chris
fstanekUser is Offline
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09 Apr 2015 02:03 PM
I can confirm that the temps I have recorded are valid.

In November, a technician came in with his own thermometer and we verified that my system was reading the same numbers he was (mid 90s°).

A couple weeks ago, the technician again brought his own thermometer, and we again verified that the system can no longer get above 90°.

The validity of the temperature readings really isn't an issue here. They're valid :)
ChrisJUser is Offline
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09 Apr 2015 02:50 PM
Ok sorry I thought the temps were from a thermostat read-out or other monitoring.

Chris
BergyUser is Offline
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09 Apr 2015 04:52 PM
Are you SURE aux heat wasn't running? Delta T in first stage should be about 18*~24*. (generally speaking) Your spec manual should show what the Delta-T specs are. Also, you said a Service Tech was there... What was the MEASURED Heat of Extraction? How did that compare to the specs?

arkie6User is Offline
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09 Apr 2015 05:24 PM
What heating setpoint do you maintain?

What is the measured return air temperature?

Do you have backup electric resistance heat? If so, is it powered from a separate circuit breaker (it should be)? Assuming the first two questions are yes, have you checked your breaker panel to verify that the backup resistance heater circuit breaker is closed / not tripped?
fstanekUser is Offline
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10 Apr 2015 10:28 AM
I just noticed that I can use HTML tags, so this should be much easier to read now :)

AUX Heat:
We do have backup (AUX) heating. Its electric, and the breakers are not tripped. There were times in this winter where the AUX heat did run, but I can also find plenty of data where AUX heat was not running. Also, I have specific tests where I forced stage 1 compressor to run in the past, and I observed discharge temps going all the way up to 98°. Right now, when I perform the exact same tests, the discharge temps will not go over 90°. The logs I have do not mix data between stage 1 and AUX heat - those are separate readings. When I say stage 1 compressor, AUX heat is not running. When my AUX heat runs, the discharge readings top out over 130°.

ΔT readings
The log on my site also has the ΔT readings. Prior to March 12, the ΔT usually topped out around 22°-27° . After March 12, the ΔT bottoms out at 17° and is never over 20°.

Heating setpoint & return temps
For the whole winter, my house was set to 72°. I have two sensors in the house: the thermostat downstairs and a wireless sensor upstairs. The thermostat uses the average temp from these two sensors. The measured return temperatures are typically between 71° and 73°. I also have the manual and I pointed out to my technician that my system was running very close to spec prior to March 12, and after March 12 it is now consistently lower than the spec, but he dismissed it stating that systems never perform up to spec (even though my system did perform up to spec until March 12).

My measurement method
I just want to clarify how I'm measuring all of this. I have the Honeywell Prestige IAQ thermostat. I have purchased the two additional sensors that plug into the interface module (I believe it was this sensor, although I'm not 100% sure on the model number). One sensor is plugged into the return duct, and the other sensor is attached past the first corner turn from the discharge (the install manual stated not to install it within line of sight of the backup heating coils - hence it was installed after the first 90° turn). We have checked the sensors and verified that the temperatures they're reading are within 1° of other thermometers, so the readings should be fairly accurate.

Thanks!

PS: I'll go through my previous posts and fix the formatting.
BergyUser is Offline
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10 Apr 2015 05:50 PM
Again... What was the MEASURED Heat of Extraction? How did that compare to the specs?
fstanekUser is Offline
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11 Apr 2015 11:19 AM
Sorry, I had no idea what heat of extraction was. I just looked it up. Looks like I'll need to get a special thermometer and a pressure gauge before I can get that info. I'll order those and hopefully have those numbers later in the week.
DickRussellUser is Offline
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11 Apr 2015 05:50 PM
That CM unit has a two-stage compressor, according to mfg literature. If the LATs are like on my CM Tranquility 27 (TT026), for which the stage 1 LAT is around 89-90 F and stage 2 at around 99 F, then I have to wonder if what happened to drop your LAT suddenly is just a drop from stage 2 to stage 1 only, occurring due to something in the tstat or whatever else controls staging, such as a zone board between the tstat and HP unit or a rise in outside air temperature if there is a sensor on that feeding into the controls. The other thing to consider is that blower speed will affect LAT, higher flow absorbing the heat at a lower rise in temperature. If blower speed is tied to staging, then perhaps that has changed. Something to explore.

One more thought: the mfg literature typically provides tables of performance vs water flow, water temperature, and air flow. Also, the flashing lights on the control board will tell you the air flow. You may need a technical manual for that; I got one for mine so I can tell what's going on.  You can use those tables to reconcile measurements and see if what you are seeing is as expected. That 89 F LAT is what is expected for my unit, and I suspect it would be for yours, as your tech guy said. Why it may have been much higher in just first stage (if it was in first stage) and suddenly dropped is something else, and the only thing that comes to mind is an increase in air flow.
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12 Apr 2015 12:26 AM
This is a measurement your service tech should have done, FIRST! This simple test tells a service tech if the unit is operating as it should. If the numbers are within spec don't worry...
mtrentwUser is Offline
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13 Apr 2015 07:33 AM
Where is the air handler? Before you get all wrapped up in the machinery, maybe a quick look at the ductwork (especially if this is an attic unit) to verify something didn't come loose, allowing more unconditioned air into the return stream.
fstanekUser is Offline
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13 Apr 2015 09:36 AM
I have my spring checkup coming up at the beginning of May, so I'll just wait until then and have them verify that the heat of extraction is within spec.

Also, I have noticed that the discharge temps have been getting better.
  • Until March 12th,Average is 95°-96°.
  • March 13th to March 30: Average 89°
  • March 31 to April 3: Average is 91°
  • April 4 to April 12: Average is 92°
The trend seems to be going in the right direction. I had actually expected my discharge temps to go down slightly over the winter. But I did not expect a 6°-7° degree drop in one day. But now that it appears to be getting back to what I was experiencing before March 12th, I feel a lot better about the system. I'm still not sure what caused the large drop, and I'll probably never know, but if the system gets back to where it was before, I guess it doesn't really matter.

Thanks!
joe.amiUser is Offline
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14 Apr 2015 07:42 AM
Without inlet temps your discharge temps mean little.
I suspect your over scrutinizing 1/2 a picture.
Joe Hardin
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fstanekUser is Offline
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14 Apr 2015 10:07 AM
Posted By joe.ami on 14 Apr 2015 07:42 AM
Without inlet temps your discharge temps mean little.
I suspect your over scrutinizing 1/2 a picture.


The return temps are pretty constant around 71°-73°. Its the discharge that changed, the return temps have always been the same.
Bill NeukranzUser is Offline
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14 Apr 2015 03:13 PM
Posted By fstanek on 09 Apr 2015 12:19 PM

I noticed a sudden drop in the max discharge temperatures (LAT) in my system ...


I'd be cautious making any conclusions based on a point measurement involving air temperatures.  It's very difficult to accurately measure, and likewise performance measures that are based on air temperatures.

Here's an example: http://www.welserver.com/perl/plot/...rTemps.png .  Here's the EAT, LAT and DeltaT air flow temps for my two GSHP units, along with indoor RH (it has an affect on these air temps).  Now's not so good of time to look at this for maximum learning (I live in Dallas and right now I don't need hardly any heating or cooling) but the point to illustrate here is that it's not unusual for me to see pretty good variation amongst the temperatures at any given moment in time.  In fact this is why it's a 4 week rolling chart - what's more important is the trend, not the actual measurement.

And here's one more example: http://www.welserver.com/perl/plot/...UperHr.png .  Here's the Heat of Extraction (when running in Heat mode) or Heat of Rejection (when running Cool mode) for each of my two GSHP units.  These lines pretty much stay lined up with the 1st stage specification capacities - two-thirds of 36,000 BTU/hr (3 ton) and two-thirds of 60,000 BTU/hr.  Again the point here is that you have to look at trends, not any one particular point.

Best regards,

Bill
Energy reduction & monitoring</br>
American Energy Efficiencies, Inc - Dallas, TX <A
href="http://www.americaneei.com">
(www.americaneei.com)</A></br>
Example monitoring system: <A href="http://www.welserver.com/WEL0043"> www.welserver.com/WEL0043</A>
arkie6User is Offline
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18 Apr 2015 09:57 PM
What about the desuperheater (DSH) / hot water generator (HWG)? Do you have one installed? If so, is it turned on and plumbed to a hot water tank or buffer tank? Has the system operation been consistent over the entire time? Has your hot water use been consistent over the entire time?  The reason I'm asking is that the DSH robs the hottest refrigerant from your air coil to heat your domestic water. If it was not working, then I could see hotter refrigerant available to the air coil and higher discharge air temps. Then when it is working, I could see it slightly reducing the refrigerant temperature available to the air coil and corresponding lower discharge air temps.
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