APC Inrow Cooling Group Logics

[mrh7768]

Hi every one

I visited a site with 15 APC InRow cooling systems installed in 3 HACS. My question is the mode of operation and behavioral logic in the group of cooling systems. How does heating of a remote sensor of one inrow cause another system to increase fan speed and change its compressor capacity? How to choose an alternative system to compensate for more demand? How calculate demand? How to identify the problem created in a cooling system?
If there is a document that answers me, please post its link or file

Thank you for the possible response friends

[CiaranR]

Hi @mrh7768,

Thank you for your question. There are a couple of things to cover in your question so I have addressed them separately below:

• My question is the mode of operation and behavioral logic in the group of cooling systems. How does heating of a remote sensor of one InRow cause another system to increase fan speed and change its compressor capacity?

  • The cooling units use a direct expansion coil, a variable speed compressor to modulate refrigerant flow through the coil, and a set of fans to control airflow through the coil. In HACS mode the air flow in the room is controlled by enclosing the hot air aisle. The loads share an enclosed common hot aisle. Each unit in the containment controls their compressor ,EEV & fans independently based on their own supply temperature sensor reading. In a group configuration the supply temperature setpoint is shared among all the units, with each unit managing its own hardware based on its own supply temperature. Thus, there is no need for group control of the supply temperature. The fan speed is controlled by the fan speed preference setting. The fan speed can be selected based on the temperature differential across the cooling unit. As return temperatures deviate from the fan speed preference setting, the fan speed increases to bring the temperature difference back down to the setpoint or decreases fan output to increase the unit temperature differential. By maintaining the desired temperature differential, the system matches the airflow requirements of the load.

• How to choose an alternative system to compensate for more demand?
  • With regards to compensating for an increased demand each unit has a operating range within it is effective. If the IT space has a higher demand than the current units are capable of meeting then additional units can be added to compensate. The issue more generally is when the thermal load is too low for the group of units. In this case there is the option of placing a number of units on Standby mode (dependent on the number of units installed vs the load). Note: Newer units have a “Load Assist” and “Runtime Balancing” functionality to address such a situation.
• How calculate demand?
  • The cooling output is determined by the difference between the supply air temperature setpoint and the actual supply air temperature as well as the airflow (for each of the cooling units in the cooling group if more than one cooling unit is present).
• How to identify the problem created in a cooling system?
  •  The firmware running on the controllers have a predefined list of alarm conditions with varying severity from alarm notices to shutdown commands for safety. This lists are long and specific to the model of unit and firmware revision. To give an example, if the pressure differential across the air filter pressure switch goes outside of a certain band then this will  appear as a change in voltage to the specific controller input. When the controller detects a voltage outside of the optimal range it will generate an alarm to check the air filter for debris or blockages. 

[mrh7768]

Thank you very much for your reply. I am more looking for the logic of the cooling group. Let me put my question like this

1. In a cooling group (for example, 5 systems in a containment), is there a master/slave system that controls the performance status and capacity of the others?

2. In what case, one or more systems from a group increase the capacity for solve group problem? What causes the other coolers in the group to change fan speed or compressor capacity due to the identification of an issue in the group, even though they are in normal condition individually? Is there a problem or what causes it?

3. Is the placement of coolers in a group (physical location) important in group performance? If yes, how?

4. How is the concept of power required (demand) for the whole group determined? The output power of each cooling and the whole group is calculated based on what parameters?

Thanks

[CiaranR]

For grouped InRow (DX) based units ACRDxxx

Response for question 1,2 &4:
• Supply Air Control is handled by each unit independently of the group.
• InRow RD controls the Hot Gas Bypass Valve based on its own Supply Air PID
• Group member’s Fan Level is controlled by Master, based on master’s cooling PID
• All ACRD’s in the Group control to the same Rack Inlet Temperature for InRow Mode, or the average ∆T for HACS/RACS modes.
• All ACRD’s in the Group run at similar fan speeds.
• The ACRD will not support group control functions for Spot cooling mode.
• A Group will allow the user to configure the number of members within the Group. Maximum of 12.
• If the number of members discovered within the group is not equal to the configured number, a warning alarm informing the user of this condition will be issued.
• The Group Controller will ensure that Group configuration data items are consistent throughout all the customer interfaces in the Group
• The Group Controller will ensure the Group Status Data items are consistent throughout all customer interfaces in the Group.
• In the event of a conflict of Group configuration data items between members of the Group, the Group Controller’s data will supersede.
• The cooling demand is determined by the delta T between the supply air temperature (SAT) setpoint and the actual supply air temperature (RAT Rack Inlet) as well as the airflow for each of the cooling units in the cooling group.
• The controller varies fan speed trying to maintain the cooling setpoint. Fan speed min is 30%.
• When the cooling unit is programmed for Spot (Discrete), the fans run at a Fixed speed.

Response for question 3:
Yes, the placement of the units in an aisle is important to the performance. If the heated exhaust air is allowed to return to the air inlet of the equipment, an undesirable overheating condition may occur. Please refer to the links below for published Whitepapers exploring the effects of airflow management on cooling performance.

White Paper 44: Improving Rack Cooling Performance Using Airflow Management™ Blanking Panels

White Paper 50: Cooling Options for Rack Equipment with Side-to-Side Airflow

[mrh7768]

Thanks for the links and full explanation
Regarding question 3, I meant the position of the cooling systems in relation to each other, and I did not mean the condition of the room.
For more explanation: In a room (hot or cold), there are 5 cooling systems. Placement is such that in a row of the cooling system, 1, 2 and 3 are next to each other and at a distance of one rack. System 4 and 5 are located in the opposite row with a distance of 3 racks between each other. If there is a crisis for system 1 and there is a need to increase the power of the group, on what basis does the system manage other cooling systems? How to recognize that system 3 and 5 are located in a place far away from system 1? Is there any control or setting on this placement? Should systems 2 and 4, which are close to system 1, compensate for the crisis of system 1 or the whole group? I mean prioritizing and maintaining balance in the group.
Thankful