APC Inrow Compressor cycling

[fgasimzade_apc]

Hello everyone,

We have 3 APC ACRD101 modules installed in one of our datacenters

They were newly installed but I have some questions, hope someone can clarify

1. Our datacenter developers installed a hot aisle, but ARCDs are not configured with HACS option, Inrow option is selected. Is it normal or I should select HACS mode on them? 3 ARCDs are installed between 4 racks and configured as standalone units

2. Compressor is cycling way to often as I can see. If the outside temperature is around 20C or less, when compressor turns off, the air is supplied from the outside and humidity level is rising up to 80% sometimes (outside humidity is high since we are located near the sea). If the outside temperature is 30C and more, when the compressor turns off, I get alarms of "Supply air high temperature violation" since the outside air is being supplied to the server room. Alarm resets when compressor turns on and starts supplying cool air. Compressor cycling happens every 15-20 min sometimes, I assume it is bad for its health. Is there anything I can do to make the compressor cycle less often?

3. If I set up Supply Air Temp to 19 or 20, the web interface shows that the Supply Air Temp is 16.5 or 17C, seems like it does not maintain the level I set up. Is it normal?

Thank you in advance

[GilbertoG]

Hi!

Hope this information help you.

1. Our datacenter developers installed a hot aisle, but ARCDs are not configured with HACS option, Inrow option is selected. Is it normal or I should select HACS mode on them? 3 ARCDs are installed between 4 racks and configured as standalone units

             The best option is to use HACS mode but all the units need to be connected using the A-link cable, take a look the installation manual following this path:

https://download.schneider-electric.com/files?p_File_Name=JBOR-76AG8H_R5_EN.pdf&p_Doc_Ref=SPD_JBOR-7...

If you can share me the serial numbers of all the units I can verify if there is a documentation related during the installation (only if Schneider Electric did the installation)

2. Compressor is cycling way to often as I can see. If the outside temperature is around 20C or less, when compressor turns off, the air is supplied from the outside and humidity level is rising up to 80% sometimes (outside humidity is high since we are located near the sea). If the outside temperature is 30C and more, when the compressor turns off, I get alarms of "Supply air high temperature violation" since the outside air is being supplied to the server room. Alarm resets when compressor turns on and starts supplying cool air. Compressor cycling happens every 15-20 min sometimes, I assume it is bad for its health. Is there anything I can do to make the compressor cycle less often?

             You are right that is not normal, this issue can be addressed doing some changes in the setpoint values, but first you will need to change your operation mode to HACS.

The cooling unit is equipped with compressor cycling control that tries to minimize the number of times the
compressor cycles on and off. The compressor will cycle off when the supply air temperature drops below 15°C
(59° F) whether or not the minimum compressor on time of 3 minutes has elapsed. Once off, the compressor
will not normally cycle on until the supply temperature reaches its setpoint and the minimum off time of 2
minutes has elapsed. My recommendation its to have the cooling setpoint 3 degrees above the supply setpoint and monitor.

3. If I set up Supply Air Temp to 19 or 20, the web interface shows that the Supply Air Temp is 16.5 or 17C, seems like it does not maintain the level I set up. Is it normal?

The air supply setpoint on 20 C is fine, can you help me to identify the Deadband? normally you find this option following this path:

Path: Main > Set Group Setpoint

• Cool: 18.0 – 32.2 °C (64.4 – 90°F)
• Deadband: 0 – 10.1°F
• Supply Air: 13.8 – 21.0 °C (57 – 69.8°F) Spot (Proportional) only
15 – 21.0 °C (59 – 69.8°F) HACS, RACS or InRow
NOTE: The Supply Air setpoint must never be set higher than the Cool setpoint (normally 1 degree, max 4)

Thanks.

[fgasimzade_apc]

Hello Gilberto,

Regarding my second question about compressor cycling - I finally managed to find a workaround - I set other two units to Cool Setpoint - 19C and Supply Air Setpoint - 18C, and the one which was cycling to 20C/20C respectively. Now it keeps the compressor of with these readings:

Rack Inlet Temperature:	18.8 °C
Supply Air Temperature:	21.3 °C
Return Air Temperature:	21.3 °C

[GilbertoG]

Hi!!

I think you are changing threshold, those parameter should be higher, try something like this:

Path: Main > Set Unit Thresholds
When the monitored input exceeds the unit threshold, an alarm occurs. Set high temperature thresholds for the
following sensors:

Threshold:

Rack Inlet Temperature:	28 °C
Supply Air Temperature:	28 °C
Return Air Temperature:	40 °C

The cooling setpoint always need to be higher, it should be 2 or 3 degrees above the supply setpoint try something like this:

Path: Main > Set Group Setpoint

Cooling setpoint:	21 °C
Supply Air Temperature:	19 °C

[fgasimzade_apc]

Hi Gilberto,

No, it is not thresholds, these are current readings, please see attached

[GilbertoG]

Hi.

Ok that is normal, the unit is not running, Can you show me the same view from the picture attached? complete view..

Thanks

[fgasimzade_apc]

Hello,

Please find attached. I set it to these values and it stopped cycling the compressor. Can you please tell me what Cool Deadband is?

You also said "The best option is to use HACS mode but all the units need to be connected using the A-link cable" - Is it mandatory to interconnect all units for HACS?

Thank you

[GilbertoG]

HI!!

Please find attached. I set it to these values and it stopped cycling the compressor. Can you please tell me what Cool Deadband is?

The cooling setpoint shouldn´t be equal to the supply setpoint, please help me change them in this way:

Cooling sp - 21

deadband - 1

Supply sp - 18

This will help you keep the temp in control.

You also said "The best option is to use HACS mode but all the units need to be connected using the A-link cable" - Is it mandatory to interconnect all units for HACS?

Yes and it will be more efficient, please take a look the manual to properly connect and configure all the units, on this web page click on the manual 

Check page 32

https://download.schneider-electric.com/files?p_File_Name=JBOR-76AG8H_R5_EN.pdf&p_Doc_Ref=SPD_JBOR-7...

Check page 28

https://download.schneider-electric.com/files?p_File_Name=MLAN-772JZ8_R4_EN.pdf&p_Doc_Ref=SPD_MLAN-7...

Thank you

[fgasimzade_apc]

Hello Gilberto,

I am sorry for a late reply

I set it the values you suggested

One more thing I noticed - when compressor turns off, Supply Air Temp gradually rises from around 17C to 25-26C and I start getting these alarms:

Warning - InRow RD 10KW: Supply air high temperature violation exists

Informational - InRow RD 10KW: Relay output abnormal state exists.

When compressor turns on, and it lowers down Supply Air temp to 17 again and alarms are gone. Why is the Supply Air Temp rises when compressor turns off?

And the second question is that why does it supplies 17C even if I set it to 19C?

Thank you