Mentor Graphics Selects Munters Oasis to Cool High-Efficiency Data Center

Mentor Graphics Corporation (MGC), a leader in EDA (Electronic Design Automation) technology, made a decision to consolidate several small data centers into a single, larger data center to improve efficiency and meet growing demand.

With their many data centers in operation around the world, MGC facilities engineers had experience with a variety of energy efficient design strategies.  The engineers knew they needed to focus on three key aspects of the design to maximize efficiency and minimize cost in relation to the heat rejection aspect of the design:  fan energy, hot-aisle containment, and minimization of refrigeration cooling.

MGC’s Critical Infrastructure Technician, John Wozniak, stated, “Today the needs of servers are very different from the needs of people. While the temperature requirement of the “intake” of servers is currently similar to the “intake” of humans, the exhaust temperatures from servers is radically different (much hotter). The approach we took was to implement a design tailored around servers, but also comfortable for humans.”

Mentor Graphics selected chimney cabinets with integral electronically commutated (EC) variable speed exhaust fans to house their servers. These cabinets, along with return air ductwork, provide excellent containment of the hot server exhaust all the way back to the roof top air-handlers. This allowed Mentor Graphics to raise the design room temperature to 72-74 degrees F, resulting in better operating efficiency of the cooling equipment and downsizing of supplemental mechanical cooling.  

After evaluating numerous cooling system methods, layouts and manufacturers, the decision was made to use rooftop mounted air-handling units manufactured by Munters.

Munters OASIS air-handlers selected for the project operate using the principle of Indirect Air-Side Economization (IASE), where outdoor air is used to reject heat from a recirculating data center airstream by way of an air-to-air heat exchanger. With this approach there are two completely separate airstreams. The first airstream is the recirculating air from the data hall. This air enters the air-handlers warm, after server heat pickup, and must be cooled before delivery back to the room. The second airstream is outdoor air, referred to as scavenger air. This air is drawn over the opposite side of the air-to-air heat exchanger by separate variable speed scavenger fans, for the purpose of extracting heat from the warmer recirculating data hall air. Since the cooling units simply extract heat from a recirculating airstream, they do not impact room humidity levels and risk of ambient pollutants impacting the servers is greatly mitigated compared to direct air-side economizer designs.

Munters polymer tube heat exchanger was selected for the job because of its high efficiency, resistance to corrosion, and the inherent scale resistance of the flexible polymer tubes. The OASIS data center units typically operate in a dry mode when ambient conditions are about 40°F and lower, and in a wet “Indirect Evaporative Cooling” (IEC) mode in the warmer ambient conditions. During IEC mode, water from an all welded stainless steel sump located beneath the heat exchanger is circulated through piping up to the top of the heat exchanger, where the water then falls down by gravity over the exterior of the polymer tubes. Outdoor scavenger air is drawn up over the exterior of the tubes, leading to evaporation of the water and enhanced heat removal from the warmer data center air that flows through the inside of the tubes. Only during the higher wet bulb ambient conditions, where the wet bulb temperature exceeds  68°F to 70°F, is mechanical “trim” cooling required to meet the target air delivery temperature of 72° to 74°F. Trim cooling coils typically provide a mere few degrees of cooling as needed to get to set-point. For the mechanical trim cooling MG selected an air-cooled chiller, with chilled water coils installed in the Munters air-handlers, located downstream of the polymer HX.

Munters air-handling units were customized to provide optimal efficiency of fans and heat rejection components. The intent is for the flow of the supply fans in the air-handlers to precisely match the flow of air exhausted from the chimney cabinets. The result is optimal efficiency in the cost to circulate the cooling air, which for economizer cooled data centers is the single greatest power consumer.

Since the units were installed, operating efficiencies have exceeded Mentor Graphics expectations.  John Wozniak, MG’s Critical Infrastructure Technician, summed it up well by saying “The result of using this quality equipment and the detailed design process has allowed us to be efficient on day one, and from this point on we are saving money, energy, and everything is working correctly.”