When Data Center Airflow Containment Is Modularized
Definition and implementation of modular containment in existing data centers.
|TRADITIONAL VS. MODULAR|
|PREREQUISITES TO CONTAINMENT|
|GOALS OF MODULAR CONTAINMENT|
|MODULAR CONTAINTMENT BENEFITS|
|WHY NON-SEALED WORKS|
Traditionally, the separation of hot and cold air required the implementation of fixed, highly customized hot aisle and cold aisle containment systems. This approach requires detailed engineering plans, is costly to implement, is disruptive to data center operations, and does not accommodate rack configuration changes well. The concept of modular containment offers a new approach.
Unlike hard and soft containment designs, modular containment presents complete flexibility to adapt to current aisle configuration without the need for engineered services or construction within the computer room. A true do-it-yourself containment concept, modular containment offers containment solutions designed to be implemented with ease, grow to accommodate needs, and adapt alongside changes in the data center.
Before moving to aisle level AFM it is essential to implement the best practices of raised floor open area management and rack AFM. For the raised floor, this means sealing all cable openings with grommets, sealing unnecessary openings under electrical equipment such as PDUs, and managing the number and placement of perforated tiles. Rack AFM best practices include installing blanking panels in every open U space, sealing between cabinet rails and the sides of cabinets, and under cabinets. Implementing raised floor and rack level AFM best practices will assure the greatest benefits of row or aisle level AFM such as containment.
Modular containment can achieve several specific AFM goals desired by data centers across the industry:
• Reducing energy costs by allowing higher supply / return temperature setpoints on the cooling units. This increases the efficiency of cooling units by enabling a larger temperature differential across the heat extraction coils inside the units. In addition, this will effectively increase the utilization of the air conditioning units and the total capacity of the cooling system within the computer room as a whole.
• Eliminating hot spots. The desire of managers everywhere, this increases the reliability of the IT equipment by providing a lower IT inlet temperature and less thermal stress on the components. It also enables increased utilization of the racks. Eliminating hot spots also reduces energy consumption by allowing IT equipment fans to run at a slower speed.
• Increasing economizer hours for those sites that are taking advantage of economizers. Reducing humidification/dehumidification costs. Increased cooling unit temperature setpoints reduces moisture condensation on the coils (latent cooling). This reduces, or eliminates, the cost of latent cooling and humidification.
• Increasing rack densities. Improved AFM results in increased cooling capacity to the rack, and therefore higher potential rack densities. Modular containment better manages the airflow to the racks, reduces hot and cold air mixing, and diminishes bypass and recirculation air. This allows rack densities to increase without exceeding ASHRAE TC9.9 guidelines for rack inlet temperatures.
Modular containment addresses five primary airflow areas in the computer room:
• Containing cold air in cold aisles
• Preventing airflow over the top of racks
• Containing and directing hot air to the cooling units
• Filling the gaps between racks in the equipment rows
• Preventing conditioned or exhaust air from flowing around the ends of equipment rows
And there are four corresponding major AFM benefits of implementing modular containment:
• It enables the reduction of supply airflow volume, which reduces operating costs and bypass airflow volume. For data centers with fixed drive cooling units it could mean reducing the number of cooling units operating at any one time. For data centers with variable-frequency drive cooling units, it would allow the blower speed to be reduced, significantly reducing energy usage and costs.
• Prevention of hot air recirculation from back to front over the top of the racks. This would reduce the rack inlet temperatures at the top of the rack and may enable increasing the setpoints on the cooling units.
• Prevention of hot air recirculation wrapping around the end of rows. This would reduce the rack inlet temperatures along the height of the rack and may also enable increasing the setpoints on the cooling units.
• Prevention of bypass and recirculation air in gaps between the racks in a row. Bypass air simply goes back to the cooling unit without doing any work in cooling the IT equipment. This is inefficient and a waste of energy. The recirculation air coming around the side of the racks mixes with the cold supply air and increases rack inlet temperatures. Reducing or eliminating the mixing will also aid in possibly increasing the setpoints of the cooling units.
A modular containment system ultimately meets airflow management goals with high efficiency. It prevents air recirculation over the tops of racks, through gaps between racks in a row, and from wrapping around the ends of rows. This solution also allows for the reduction of supply airflow volume, lowering operating costs and bypass airflow volume. Containment in any computer room is best attained when there is a structured hot aisle / cold aisle layout. Specifically, when each equipment row has an equal length so the ends of the aisles can be effectively sealed with a pair of aisle end doors. While this is the ideal configuration, significant benefits can be realized from installation in other configurations such as a single row aisle, standalone equipment, legacy layout, rows of different lengths, etc. The benefit to installing containment with a modular approach means that no matter the layout the system design is flexible enough to accommodate variances within the room while still raising AFM to the next level.
A modular containment approach improves AFM by utilizing components of rack top panels, aisle end doors, and rack gap panels.
• Rack top panels. Rack top panels are fitted to be either angular or vertical, depending on overall containment design and location installed. Typically installed on the top front edge of the IT rack, angular rack top panels extend from the front edge of the racks into the aisle, partially closing the open area of the cold aisle. In addition, these rack top panels significantly reduce the recirculation of hot exhaust air from the rack equipment across the top of the rack and into the intakes on the front of the rack.
• The vertical rack top panel is typically installed on the top rear edge of the IT rack. These rack top panels further restrict hot/cold air mixing by directing the hot exhaust air up toward the ceiling and then into the return airstream to the cooling units. The vertical rack top panels typically work best in the hot aisle, where they help to create a chimney effect, directing hot air towards the ceiling plenum while also limiting hot air recirculation over the top of the rack. Some data centers find the vertical rack top panels also perform well when used in the cold aisle.
• Aisle end doors. In addition to rack top panels, doors at the end of the aisles are another component of modular containment that further isolates hot/cold air mixing in the computer room. In most computer rooms, hot exhaust airflow around the end of rows is significant and causes overheating and hot spots in the end row racks. The usual compensation for this is to increase the CRAC/CRAH airflow and/or reducing the setpoint temperatures of the CRAC/CRAH units. Though this implementation often works, it is using a brute force approach. Increasing fan speeds or decreasing temperature setpoints has a significant impact on electrical usage and energy costs. To incur these inefficiencies for the sake of a few racks is a waste of resources and compromises utilization.
• Rack gap panels. A rack gap panel is essential for sealing the space between the racks when they are not adjacent to one another. In many computer rooms, cabinets are not contiguous in the rows. The gaps are often due to obstructions, such as support columns, variable width cabinets, cabinets removed and not replaced, or many other reasons. The openings in the rows allow significant bypass and or recirculation of the exhaust air. Prevention of this improves overall data center efficiency and reduces hot spots at the rack level.
Modular containment is designed as a non-sealed architecture for hot and cold aisle containment. A non-sealed architecture may initially seem like a contradiction for a containment system, but this design provides considerable benefit. Since there is variation in the volume of air required by IT equipment, even sites with highly refined airflow management will still deliver a slight excess volume of conditioned air to the cold aisle. This is primarily done to accommodate variations in IT equipment airflow volume demands.
A slight excess airflow volume is also the result of having redundant cooling capacity running in the room, so that when a cooling unit fails there is still a sufficient volume of conditioned air available. If there is no opening for the excess volume to escape within a containment system excessive pressure can develop in the cold aisle. When this occurs, more air is forced through the IT equipment than required by the equipment. ASHRAE explicitly recommends against this condition of over pressurized cold aisles. The open-sealing architecture of modular containment solves this problem by containing cold air to the level needed while allowing any excess volume to escape when required.
Upsite Technologies conducted computational fluid dynamic (CFD) analysis in the design of modular containment. Also, a third-party provided independent analysis to confirm how modular containment can achieve many of the core benefits of traditional containment, such as reduced inlet temperatures, energy savings, and increased rack densities. The major benefit of modular containment is its ability to attain a similar level of efficiency with a simple, flexible, and cost-effective design.
• Baseline. This first CFD model (Figure 3) shows significant recirculation air around the ends of the aisles and elevated IT equipment inlet temperatures as a baseline thermal map of the facility. Also, we see cold air in the aisle is mixing with the hot air very close to the front of cabinets.
• Rack top panels. After installing rack top panels, the CFD model now shows (Figure 4) the air being contained in the cold aisle. There is still significant recirculation air around the ends of the aisles however, and elevated inlet temperatures
• Rack top panels and aisle end door. The CFD model with the addition of aisle end doors shows (Figure 5) significant improvement in recirculation air around the ends of the aisles, and contained air throughout the length of the cold aisle. For the cabinets at the ends of the aisle the maximum inlet temperature reduction was 10.2°F and the average inlet temperature reduction was 6.2°F.
Figure 6 shows results from field-testing of modular containment.
Data center specs
• Raised floor computer room
• 25% open area perforated tiles in a 4-ft wide cold aisle
• Down flow peripheral CRAH units
Installed components of modular containment
• Angular rack top panels in cold aisle
• Aisle end doors
• The field test results show across-the-board rack inlet temperature reductions with the end aisle cabinets showing a most significant decrease from installation of the aisle end doors.
Prevention of hot and cold air mixing is a key to all efficient computer room cooling strategies. The modular approach to containment enables these efficiencies, creates an environment where substantial cost reductions can be achieved, and allows for increased rack, row, and infrastructure utilization. Modular containment allows optimization to the configuration and operations of the data center cooling infrastructure. This includes changes to the cooling systems such as raising chilled water setpoints, increasing both water and airside economizer hours, reducing fan speeds, cycling CRAC/CRAH units, etc.
The modular containment implementation also means significantly reduced installation complexity and costs, the ability to install in an existing computer room without interruption to operations, and the flexibility to change the modular containment configuration as the needs of the computer room infrastructure change. Other means of sealing both hot and cold aisles include hard wall containment, soft curtain containment, and other products on the market. Though these products work well they typically require a complex process of quoting, design, customization, and professional installation and are often unnecessary for the densities present in the room.
Modular containment provides a means to achieve similar containment results without the cost and complexity of full containment systems.