NATIONAL INFORMATION TECHNOLOGY CENTER

Air Flow Management Inside the Server Room

Sudeep K.C.(Electrical Engineer)

2/23/2015

This proposal intends to create alternating "hot aisle/cold aisle" rows. Such a layout, if organized by ducts and forced ventilation, greatly reduces energy losses and also prolongs the life of the servers.

Background GIDC has used an open-area approach to cool racks of servers and storage systems. With this approach, three number of Computer Room Air Conditioners (CRAC) are placed on the periphery of the data center room. IT equipment (ITE) racks are arranged in a uni-direction layout. Cool air is forced through a raised floor plenum and up through vented floor tiles throughout the room. During this the hot air from the racks and cold air from the CRAC mixes. Hence instead of cool air from CRAC, the mixed warm air as well as hot air from back of the front rack is drawn through the ITE racks, and hot air is vented out the rear of the racks and upward toward the ceiling.

Air circulation works on the basic strategy of providing cool air at the floor level and collecting warm air near the ceiling as shown in figure above. So the typical remedy has been to set the cooling system to run colder to compensate this requiring much more energy to cool the equipments.

The figure above describes our server orientation. Due to several parallel rows of racks placed with the same orientation, a significant efficiency problem has arisen. The hot exhaust air from the first row of racks gets sucked into the "cool" air intakes of the second row of racks. With each progressive row, the air temperature increases as hot air is passed from one row of servers to the next. Due to this, the temperature of the room has to be set below 20oC.

Rationale Mixing the cooled air and exhausted air increases refrigeration costs. Research has shown, however, that the practice of keeping data centers at or below 70 °F (21 °C) may be wasting money and energy.i To overcome this problem, the rows of server racks should be oriented so that the fronts of the servers face each other. In addition, the backs of the server racks should also face each other.

This orientation creates alternating "hot aisle/cold aisle" rows. Such a layout, if properly organized, greatly reduces energy losses and also prolongs the life of the servers.

Alternatively, ductwork as shown in above figure can add efficiency if hot air from the servers can directly be carried to the CRAC inlet making less chance of mixing of the hot and cold airs.

Considerations • Hot aisle/cold aisle row layout makes sense for our data centers or future expansion of data center.

However, retrofitting an existing data center with a new layout has cost associated that should be taken into consideration.

• All equipment in a server rack must be shut down prior to moving it, and cables must be labeled and unplugged.

• The power pathway need to be realign so all devices can be plugged into an outlet in their new location.

• The new server rack orientation will substantially change the airflow in a room, so it will be necessary to work with facilities to evaluate the data center's new HVAC needs. Many computer room air conditioning (CRAC) units use return air temperature to indicate room temperature. (Return air refers to warm air entering the CRAC for cooling.) This will not work in a hot aisle/cold aisle configuration because the return air has been concentrated in hot aisles and its temperature is therefore substantially higher.

• There may be creation of new hot spots in the data center due to concentration of hot air.

Budget for the proposed project Costs to consider include:

o Adjustments to the CRAC (3 nos)

o Installation of new ductwork (3 nos)

o New cabling for repositioned racks(40 nos)

o Intelligent control ERV/HRV ventilation fan (15 nos)

o Thermography Thermal Imager to determine hot spots (1 nos)

o Electrical costs to reconfigure power distribution to the racks (40 nos)

o Associated manpower, overtime, and vendor costs (1 lot)

Sn Item No Unit Price Total Price 1 Adjustments to the CRAC 3 2000 6000 2 Installation of new ductwork 3 25000 75000 3 New cabling work for repositioned

racks 40 1000 40000

4 Intelligent control ERV/HRV ventilation fan

12 10000 120000

5 Thermography Thermal Imager to determine hot spots

1 140000 140000

6 Electrical costs to reconfigure power distribution to the top of racks

12 6000 72000

7 Associated manpower, overtime, and vendor costs

1 100000 100000

Total 553000 VAT (13%) 71890 Grand Total 624890

Expected Benefit 1. Hot aisle/cold aisle arrangements lower cooling costs by better managing airflow. 2. PG&E's experience with hot aisle/cold aisle retrofits indicated that the payback was greater than

two years.ii

Attachments 1. Thermal camera and image

2. Expected Layout After Work

i Cosmano, Joe (2009), Choosing a Data Center, Disaster Recovery Journal, retrieved 2012-07-21 ii Conversation with Mark Bramfitt, former Principal Program Manager, High Technology Energy Efficiency Team, PG&E, July 14, 2010