Avoidable Mistakes that Compromise Cooling Performance in Data Centers and Network Rooms

Avoidable Mistakes that Compromise Cooling Performance in Data Centers and Network Rooms

Problem Several cooling system mistakes are very common and avoidable Mistakes compromise availability and increase cost. Many can be avoided with little or no expense.

Agenda What matters to IT equipment Categories of Flaws Airflow in the rack Layout of racks Distribution of loads Cooling equipment settings Layout of air delivery and return vents Mechanism of these flaws & How to avoid them Quantify financial impact Prevention via Policy

Basic Airflow Requirements IT equipment cares about 2 things: - Appropriately conditioned air at IT equipment air intake - IT equipment airflow is not restricted Problems that prevent 1 and 2 from existing - Improper rack airflow - improper rack layout - improper distribution of loads - improper cooling equipment settings - improper layout of supply / return air systems

Internal Rack Recirculation Failure to Employ Blanking Panels Inset Side Rails Shelved Equipment Low perf or glass doors Poor Cable Management

External Recirculation Improper placement of air delivery and return vents air delivery vents only in cold aisle only as needed to accommodate load density Improper rack layout hot aisle / cold aisle, not front to back! bay racks together Improper CRAC unit placement return airflow parallel to row length - aligned with hot aisle for raised floor environments - aligned with cold aisle for hard floor environments (downflow) - aligned with hot aisle for hard floor environments (upflow) Poorly sealed raised floor cable penetrations

Recirculation Impacts Capital Expense Number of CRAC units needed may increase when recirculation occurs. Why? Heat load is independent of recirculation Recirculation decreases CRAC return air temperature CRAC unit capacity decreases with decreasing return air temperature Therefore, as recirculation increases, customer must buy more CRAC units!

Recirculation Impacts Operational Expense (1) Breakdown of electricity consumption of a typical data center IT Loads 44% Cooling 38% Lighting 3% Power System 15% Cooling equipment power consumption is a large contributor to the electric bill More CRACS = More electrical consumption.

Recirculation Impacts Operational Expense (2) Decreasing return air temperatures causes increased latent cooling (water removed from the air). To maintain humidity in the room, humidifier output increases, therefore electrical consumption increases (major effect) Wet coil further reduces sensible capacity, adding to the need for more CRAC units. (minor effect)

Financial Consequences of Recirculation Summarized

Distribution of Loads IT personnel have tendency to concentrate loads for convenience Concentration of power dissipation leads to hot spot Formation of hot spot puts us back at the top of previous slide. Therefore, evenly distribute loads when possible

Cooling Settings Do not set CRAC temperature lower than necessary (see slide 12) Preventing Recirculation allows higher setpoints 50% RH? old data centers w/ high velocity printers subject to static buildup 35% +-5% results in significant energy savings ASHRAE quotes 40-55% Prevent demand fighting calibrate sensors group communication

Layout of Delivery & Return Vents Delivery Vents Close to IT air intakes Only in Cold Aisle! Empty Rack? No Perf Tile Overhead Systems - Low velocity diffusers pointing directly down (not laterally) Return Air Vents Close to IT air exhaust Align with hot aisle Large suspension ceiling voids work well Evenly distribute

Prevention via policies Policies generate constructive discussions Importance of load placement, floor tile placement, changing CRAC setpoints Use signage. Example; THIS IS A HOT AISLE To maximize the availability of the IT equipment this aisle is intentionally hot. The arrangement of the racks and the use of blanking panels prevent the equipment exhaust air from returning to the equipment air intakes. This decreases equipment operating temperature, increases equipment life, and saves energy.