User:Hamed-Asadollahi/sandbox

Air management for data centers is all the design and configuration that go into minimizing or eliminating mixing between the cooling air and the hot air from the equipment. It included rejected from hot air equipment. Effective air management is minimizing the bypass of cooling air around rack intakes and the recirculation of heat exhaust back into rack intakes. When model designed correct, an air management system can make less operation cost and at the same time, decrease costs of equipment. totally help to increase the data center’s power density (Watts/ square foot) and reduce the risk of heat-related interruptions or failures happened. The key design issues include the configuration of equipment’s air intake and heat exhaust ports. Second, the location of supply and returns, the large-scale airflow patterns in the room, and the temperature set points of the airflow. Airflow Management is kind of the management can increase data center energy efficiency by freeing up stranded airflow and cooling capacity and make it available in future. Data center operators can get the benefit though during visualization models created by using computational fluid dynamics Computational fluid dynamics (CFD). Therefore, we need to understand the airflow management within data centers is complicated because under-floor air distribution and unguided pathways often result in unintended turbulences and vortices.

Overhead and supply are two common way used in air delivery schemes underflow. Overhead supply is the cold air from the computer room air conditioning (CRAC)[] units are pumped into overhead plenums and supplied through perforated roof tiles into the cold aisle. The average heat load per cabinet rises, simply arranging cabinets in a traditional open hot aisle/cold aisle configuration is not an effective approach.

History
in the past, Airflow didn't need to perform very efficiently. Since the first computer rooms, airflow has been an important component of data center design. Nowadays, high-performance servers doing many times the work of their predecessors in a much smaller space, data center airflow needs to keep effectively efficient. The electrical energy supplied to servers get converted to heat and needs to be removed to maintain a safe operating temperature for the electronic components. Now, Data center operators are better at cooling management than ten years ago, many facilities want to find the way to prevent them from either using their full capacity or wasting energy. The ultimate goal in airflow management focus to control of cooling in temperature set points for IT air intake -+while minimizing the volume of air you’re delivering to the data hall. Airflow retrofits can support data center energy efficiency by freeing up stranded airflow and cooling capacity and make it available for future needs. Effective implementation requires information technologies (IT) staff, in-house facilities technicians, and engineering consultants working collaboratively.

Overview
Identifying airflow deficiencies Data center operators are needed. it can get the benefit from airflow visualization models created by using computational fluid dynamics ((CFD)). You must understand airflow within data centers is complicated because under-floor air distribution and unguided pathways often result in unintended turbulences and vortices. These turbulences and vortices would limited cooling capacity and wasted energy. The feedback of the thermal map gives to the data center operator to initially optimize floor tile outlet-size and location and to subsequently identify operational problems. Wireless sensors are a lower cost alternative to hard-wired sensors and can be relocated easily when a data center is modified. Air leaks, obstructions, perforated tile locations, cable penetrations, and missing blanking plates are the objects that can cause poor air distribution that can be remedied with low-cost solutions. In certain situations, customized solutions with more extensive construction costs can still have acceptable payback periods because they can free-up existing cooling capacity. Achieving this goal without having to rebuild the entire data center is one of the challenges, though this sometimes can be the best economic solution. The passive components such as sealing leaks under the floor, repairing ductwork, replacing floor tiles, and adding blanking-plates are usually beneficial and cost-effective solutions. Generalized Approach to Airflow Improvement Each of these measures will contribute to increase the cooling capacity of your existing data center systems and may help avoid the complexity of installing new, additional cooling capacity. Identify common airflow problems, Hotspots, Leaks, Mixing, Recirculation, Short-circuiting, Obstructions, Disordered pathways, Turbulence, Reverse flows using the power usage effectiveness (PUE) metric can calculate Infrastructure energy consumption (cooling equipment, uninterrupted power supplies, lighting, etc.). They can improve data center PUE increase with larger data centers that have the ability to develop better airflow management and employ more efficient cooling equipment or advanced cooling technologies such as liquid cooling.

Generalized Approach to Airflow Improvement
Each of these measures helps to increase the cooling capacity of your existing data center systems and may help avoid the complexity of installing new, additional cooling capacity. Identify common airflow problems Hot spots, Leaks, Mixing, Recirculation, Short-circuiting, Obstructions, Disordered pathways, Turbulence and Reverse flows.

Implement Cable Management
Under-floor and over-head obstructions often interfere with the distribution of cooling air. Such interferences can significantly reduce the air handlers’ airflow as well as negatively affect the air distribution. Cable congestion in raised-floor plenums can sharply reduce the total airflow as well as degrade the airflow distribution through the perforated floor tiles. Both effects promote the development of hot spots. A minimum effective (clear) height of 24 inches should be provided for raised floor installations. Greater underfloor clearance can help achieve a more uniform pressure distribution in some cases. A data center should have a cable management strategy to minimize airflow obstructions caused by cables and wiring. This strategy should target the entire cooling air flow path, including the rack-level IT equipment air intake and discharge areas as well as under-floor areas. Persistent cable management is a key component of maintaining effective air management. Instituting a cable mining program (i.e. a program to remove abandoned or inoperable cables) as part of an ongoing cable management plan will help optimize the air delivery performance of data center cooling systems.

Aisle Separation and Containment[]
A basic hot aisle/cold aisle configuration is created when the equipment racks and the cooling system’s air supply and return are designed to prevent mixing of the hot rack exhaust air and the cool supply air drawn into the racks. As the name implies, the data center equipment is laid out in rows of racks with alternating cold (rack air intake side) and hot (rack air heat exhaust side) aisles between them. Strict hot aisle/cold aisle configurations can significantly increase the air-side cooling capacity of a data center’s cooling system. All equipment is installed into the racks to achieve a front-to-back airflow pattern that draws conditioned air in from cold aisles, located in front of the equipment, and rejects heat out through the hot aisles behind the racks. Equipment with non-standard exhaust directions must be addressed in some way (shrouds, ducts, etc.) to achieve a front-to-back airflow. The rows of racks are placed back-to-back, and holes through the rack (vacant equipment slots) are blocked off on the intake side to create barriers that reduce recirculation, Additionally, cable openings in raised floors and ceilings should be sealed as tightly as possible. With proper isolation, the temperature of the hot aisle no longer impacts the temperature of the racksor the reliable operation of the data center; the hot aisle becomes a heat exhaust. The air-side cooling system is configured to supply cold air exclusively to the cold aisles and pull return air only from the hot aisles. The hot rack exhaust air is not mixed with cooling supply air and, therefore, can be directly returned to the air handler through various collection schemes, returning air at a higher temperature, often 85°F or higher. Depending on the type and loading of a server, the air temperature rises across a server can range from 10°F to more than 40°F. Thus, rack return air temperatures can exceed 100°F when densely populated with highly loaded servers. Higher return temperatures extend economizer hours significantly and allow for a control algorithm that reduces supply air volume, saving fan power. If the hot aisle temperature is high enough, this air can be used as a heat source in many applications. In addition to energy savings, higher equipment power densities are also better supported by this configuration. The significant increase in economizer hours afforded by a hot aisle/cold aisle configuration can improve equipment reliability in mild climates by providing emergency compressor-free data center operation when outdoor air temperatures are below the data center equipment’s top operating temperature (typically 90°F to 95°F). Using flexible plastic barriers, such as plastic supermarket refrigeration covers (i.e. “strip curtains”), or other solid partitions to seal the space between the tops of the rack and air return location can greatly improve hot aisle/cold aisle isolation while allowing flexibility in accessing, operating, and maintaining the computer equipment below. One recommended design configuration supplies cool air via an under-floor plenum to the racks; the air then passes through the equipment in the rack and enters a separated, semi-sealed area for return to an overhead plenum. This approach uses a baffle panel or barrier above the top of the rack and at the ends of the hot aisles to mitigate “short-circuiting” (the mixing of hot and cold air). These changes should reduce fan energy requirements by 20% to 25%, and could result in a 20% energy savings on the chiller side provided these components are equipped with variable speed drives (VSDs). Fan energy savings are realized by reducing fan speeds to supply only as much air as a given space requires. There are a number of different design strategies that reduce fan speeds. Among them is a fan speed control loop controlling the cold aisles’ temperature at the most critical locations—the top of racks for under-floor supply systems, the bottom of racks for overhead systems, end of aisles, etc. Note that much Direct Expansion (DX) Computer Room Air Conditioners (CRACs) use the return air temperature to indicate the space temperature, an approach that does not work in a hot aisle/cold aisle configuration where the return air is at a very different temperature than the cold aisle air being supplied to the equipment. Control of the fan speed based on the IT equipment needs is critical to achieving savings.

Optimize Supply and Return Air Configuration
Hot aisle/cold aisle configurations can be served by overhead or under-floor air distribution systems. When an overhead system is used, supply outlets that ‘dump’ the air directly down should be used in place of traditional office diffusers that throw air to the sides, which results in undesirable mixing and recirculation with the hot aisles. The diffusers should be located directly in front of racks, above the cold aisle. In some cases return grilles or simply open ducts have been used. The temperature monitoring to control the air handlers should be located in areas in front of the computer equipment, not on a wall behind the equipment. Use of overhead variable air volume (VAV) allows equipment to be sized for excess capacity and yet provide optimized operation at part-load conditions with turn down of variable speed fans. Where a rooftop unit is being used, it should be located centrally over the served area—the required reduction in ductwork will lower cost and slightly improve efficiency. Also, keep in mind that overhead delivery tends to reduce temperature stratification in cold aisles as compared to under-floor air delivery. Under-floor air supply systems have a few unique concerns. The under-floor plenum often serves both as a duct and a wiring chase. Coordination throughout the design and into construction and operation throughout the life of the center is necessary since paths for airflow can be blocked by electrical or data trays and conduit. The location of supply tiles needs to be carefully considered to prevent short-circuiting of supply air and checked periodically if users are likely to reconfigure them. Removing or adding tiles to fix hot spots can cause problems throughout the system. Another important concern to be aware of is high air velocity in the under-floor plenum. This can create localized negative pressure and induce room air back into the under-floor plenum. Equipment closer to down flow CRAC units or Computer Room Air Handlers (CRAH) can receive too little cooling air due to this effect. Deeper plenums and careful layout of CRAC/CRAH units allow for a more uniform under-floor air static pressure. For more description on CRAH unites as they relate to data center energy efficiency, refer to the Air Handler subsection of "Cooling Systems" below.

Raising Temperature Set Points
Raising Temperature Set Points Higher supply air temperature and a higher difference between the return air and supply air temperatures increases the maximum load density possible in the space and can help reduce the size of the air-side cooling equipment required, particularly when lower-cost mass produced package air handling units are used. The lower required supply airflow due to raising the air-side temperature difference provides the opportunity for energy savings. Cooling Systems When beginning the design process and equipment selections for cooling systems in data centers, it is important to always consider initial and future loads, in particular, part- and low-load conditions, as the need for digital data is ever-expanding. Direct Expansion (DX) Systems Depending on the data center’s climate zone and air management, a DX unit with air-side economizer can be a very energy-efficient cooling option for a small data center. A higher return air temperature also makes better use of the capacity of standard package units, which are designed to condition office loads. This means that a portion of their cooling capacity is configured to serve humidity (latent) loads. Data centers typically have very few occupants and small outside air requirements, and, therefore, have negligible latent loads. While the best course of action is to select a unit designed for sensible-cooling loads only or to increase the airflow, an increased return air temperature can convert some of a standard package unit’s latent capacity into usable sensible capacity very economically. This may reduce the size and/or the number of units required. A warmer supply air temperature setpoint on chilled water air handlers allows for higher chilled water supply temperatures which consequently improves the chilled water plant operating efficiency. Operation at warmer chilled water temperatures also increases the potential hours that a water-side economizer can be used.

Cooling Systems
When beginning the design process and equipment selections for cooling systems in data centers, it is important to always consider initial and future loads, in particular, part- and low-load conditions, as the need for digital data is ever-expanding. Direct Expansion (DX) Systems Packaged DX air conditioners likely compose the most common type of cooling equipment for smaller data centers. These units are generally available as off-the-shelf equipment from manufacturers (commonly described as CRAC units). There are, however, several options available to improve the energy efficiency of cooling systems employing DX units. Packaged rooftop units are inexpensive and widely available for commercial use. Several manufacturers offer units with multiple and/or variable speed compressors to improve part-load efficiency. These units reject the heat from the refrigerant to the outside air via an air-cooled condenser. An enhancement to the air-cooled condenser is a device which sprays water over the condenser coils. The evaporative cooling provided by the water spray improves the heat rejection efficiency of the DX unit. Additionally, these units are commonly offered with air-side economizers. Depending on the data center’s climate zone and air management, a DX unit with air-side economizer can be a very energy-efficient cooling option for a small data center. Indoor CRAC units are available with a few different heat rejection options. Air-cooled CRAC units include a remote air-cooled condenser. As with the rooftop units, adding an evaporative spray device can improve the air-cooled CRAC unit efficiency. For climate zones with a wide range of ambient dry bulb temperatures, apply parallel VSD control of the condenser fans to lower condenser fan energy compared to the standard staging control of these fans. CRAC units packaged with water-cooled condensers are often paired with outdoor dry coolers. The heat rejection effectiveness of outdoor dry coolers depends on the ambient dry bulb temperature. A condenser water pump distributes the condenser water from the CRAC units to the dry coolers. Compared to the air-cooled condenser option, this water-cooled system requires an additional pump and an additional heat exchanger between the refrigerant loop and the ambient air. As a result, this type of water-cooled system is generally less efficient than the air-cooled option. A more efficient method for water-cooled CRAC unit heat rejection employs a cooling tower. To maintain a closed condenser water loop to the outside air, a closed loop cooling tower can be selected. A more expensive but more energy-efficient option would be to select an oversized open-loop tower and a separate heat exchanger where the latter can be selected for a very low (less than 3°F) approach. In dry climates, a system composed of water-cooled CRAC units and cooling towers can be designed to be more energy efficient than air-cooled CRAC unit systems. A type of water-side economizer can be integrated with water-cooled CRAC units. A pre-cooling water coil can be added to the CRAC unit upstream of the evaporator coil. When ambient conditions allow the condenser water to be cooled (by either dry cooler or cooling tower) to the point that it can provide a direct cooling benefit to the air entering the CRAC unit, condenser water is diverted to the pre-cooling coil. This will reduce, or at times eliminate, the need for compressor-based cooling from the CRAC unit. Some manufacturers offer this pre-cooling coil as a standard option for their water-cooled CRAC units.

Air Handlers
Better performance has been observed in data center air systems that utilize specifically-designed central air handler systems. A centralized system offers many advantages over the traditional multiple distributed unit system that evolved as an easy, drop-in computer room cooling appliance (commonly referred to as a CRAH unit). Centralized systems use larger motors and fans that tend to be more efficient. They are also well suited for variable volume operation through the use of VSDs and maximize efficiency at part-loads. An ideal data center would use 100% of its electricity to operate data center equipment—energy used to operate the fans, compressors and power systems that support the data center is strictly overhead cost. The data center supported by a centralized air system uses almost two-thirds of the input power to operate revenue-generating data center equipment, compared to the multiple small unit systems that use just over one-third of its power to operate the actual data center equipment. The trend seen here has been consistently supported by benchmarking data. The two most significant energy saving methods are water cooled equipment and efficient centralized air handler systems. Most data center loads do not vary appreciably over the course of the day, and the cooling system is typically significantly oversized. A centralized air handling system can improve efficiency by taking advantage of surplus and redundant capacity to actually improve efficiency. The maintenance benefits of a central system are well known, and the reduced footprint and maintenance traffic in the data center are additional benefits. Implementation of an airside economizer system is simplified with a central air handler system. An airside economizer system is simplified with a central air handler system. Optimized air management, such as that provided by hot aisle/cold aisle configurations, is also easily implemented with a ducted central system. Modular units are notorious for battling each other to maintain data center humidity set points. That is, one unit can be observed to be dehumidifying while an adjacent unit is humidifying. Instead of modular units independently controlled, a centralized control system using shared sensors and set points to ensure proper communication among the data center air handlers. Even with modular units humidity control over make-up air should be all that is required.

Low-Pressure Drop Air Delivery
Low-Pressure Drop Air Delivery A low-pressure drop design (‘oversized’ ductwork or a generous under the floor) is essential to optimizing energy efficiency by reducing fan energy and facilitates long-term buildout flexibility. Ducts should be as short as possible in length and sized significantly larger than typical office systems since a 24-hour operation of the data center increases the value of energy use over time relative to the first cost. Since loads often only change when new servers or racks are added or removed, periodic manual air flow balancing can be more cost-effective than implementing an automated air flow balancing control scheme. High-Efficiency Chilled Water Systems Efficient Equipment Use efficient water-cooled chillers in a central chilled water plant

Efficient Equipment
A high-efficiency VFD-equipped chiller with an appropriate condenser water reset is typically the most efficient cooling option for large facilities. Chiller part-load efficiency should be considered since data centers often operate at less than peak capacity. Chiller part-load efficiencies can be optimized with variable frequency is driven compressors, high evaporator temperatures, and low entering condenser water temperatures. Oversized cooling towers with VFD-equipped fans will lower water-cooled chiller plant energy. For a given cooling load, larger towers have a smaller approach to ambient wet bulb temperature, thus allowing for operation at lower cold condenser water temperatures and improving chiller operating efficiency. The larger fans associated with the oversized towers can be operated at lower speeds to lower cooling tower fan energy compared to a smaller tower. Condenser water and chilled water pumps should be selected for the highest pumping efficiency at typical operating conditions, rather than at full load condition. Optimize Plant Design and Operation Data centers offer a number of opportunities in central plant optimization, both in design and operation. A medium-temperature, as opposed to low-temperature, chilled water loop design using a water supply temperature of 55°F or higher improves chiller efficiency and eliminates uncontrolled phantom dehumidification loads. Higher temperature chilled water also allows more water-side economizer hours, in which the cooling towers can serve some or the entire load directly, reducing or eliminating the load on the chillers. The condenser water loop should also be optimized; a 5°F to 7°F approach cooling tower plant with a condenser water temperature reset pairs nicely with a variable speed chiller to offer large energy savings.

Efficient Pumping
A well thought out efficient pumping design is an essential component to a high-efficiency chilled water system. Pumping efficiency can vary widely depending on the configuration of the system, and whether the system is for an existing facility or new construction. General guidelines for optimizing pumping efficiency of any configuration.
 * Reduce the average chilled water flow rate corresponding to the typical load.
 * Implement primary-only variable flow chilled water pumping.
 * Specify an untrimmed impeller, do not install pump balancing valves and instead use a  VFD to limit pump flow rate.
 * Design for a low water supply pressure set point.
 * Specify a water pumping differential pressure setpoint reset control sequence.
 * Design a low-pressure drop pipe layout for pumps.
 * Specify 2-way chilled water valves instead of 3-way valves.
 * Install VFDs on all pumps and run redundant pumps at lower speeds.

Free Cooling
The cooling load for a data center is independent of the outdoor air temperature. Most nights and during mild winter conditions, the lowest cost option to cool data centers is an air-side economizer; however, a proper engineering evaluation of the local climate conditions must be completed to evaluate whether this is the case for a specific data center. Due to the humidity and contamination concerns associated with data centers, careful control, and design work may be required to ensure that cooling savings are not lost because of excessive humidification and filtration requirements, respectively. Outside air economizing is implemented in many data center facilities and results in energy-efficient operation. Control strategies to deal with temperature and humidity fluctuations must be considered along with contamination a typical ultrasonic humidifier only requires 30 Watts to atomize the same pound of water. These passive allow the use of a medium temperature chilled water supply (55°F to 60°F rather than 44°F) and by reducing the approach that uses the heat present in the air or recovered from the computer heat load for humidification by chillers. A thermal storage tank can also be an economical alternative to additional mechanical cooling capacity; for example water storage provides the additional benefit of backup make-up water for cooling towers. chilled water loops with significant surplus air handler capacity in normal operation. For data centers with active humidity control, a dewpoint Controls cooling coils installed directly onto the rack to capture and remove waste heat. The under-floor area is often cooling tower to produce chilled water to cool the data center during mild outdoor conditions.

Direct Liquid Cooling
Direct liquid cooling refers to a number of different cooling approaches that all share the same characteristic economizer can remove heat from the hot chilled water but not enough to reach set point, the chillers operate at evaluated. Generally, concern over contamination should be limited to unusually harsh environments such as facilitate the pairing of liquid cooling with a water-side economizer, further increasing potential energy savings. flow is a much more efficient method of transporting heat. Energy efficiencies will be realized when such systems fluid cooled via a heat exchanger. Free cooling can be provided via a waterside economizer, which uses the evaporative cooling capacity of a further saves energy by reducing the load on the cooling system.

Humidification
low-energy humidification techniques can replace traditional electric resistance humidifiers with an adiabatic approach that uses the heat present in the air or recovered from the computer heat load for humidification. Ultrasonic humidifiers, evaporative wetted media, and microdroplet spray are some examples of adiabatic humidifiers An electric resistance humidifier requires about 430 Watts to boil one pound of 60°F water, while a typical ultrasonic humidifier only requires 30 Watts to atomize the same pound of water. This passive humidification approaches also cool the air, in contrast to an electric resistance humidifier heating the air, which further saves energy by reducing the load on the cooling system. It can result in peak electrical demand involve filtration or other measures. Other contamination concerns such as salt or corrosive matter should be it reaches the chillers. During those hours when the water-side economizer can remove enough heat to reach Liquid cooling can serve higher heat densities and be much more efficient than traditional air cooling as water Low-energy humidification techniques can replace traditional electric resistance humidifiers with an adiabatic More option are now available for dynamically allocating IT resources as computing or storage demands vary. of transferring waste heat to a fluid at or very near the point the heat is generated, rather than transferring it or being pursued, ranging from water cooling of component heat sinks to bathing components with dielectric outside air and locking out the economizer when the air is either too dry or too moist. Mitigation steps may prevent high outside air dehumidification and humidification loads by tracking the moisture content of the pulp and paper mills or large chemical spills.

Controls
Within the framework of ensuring continuous availability, a control system should be programmed to maximize the energy efficiency of the cooling systems under variable ambient conditions as well as variable IT loads.

Thermal Storage
Thermal storage is a method of storing thermal energy in a reservoir for later use and is particularly useful these loops from each other. Locating the heat exchanger upstream from the chillers, rather than in parallel to room air and then conditioning the room air. One current approach to implementing liquid cooling utilizes towers can directly charge a chilled water storage tank; using a small fraction of the energy otherwise required typically installed to transfer heat from the chilled water loop to the cooling tower water loop while isolating Ultrasonic humidifiers, evaporative wetted media and microdroplet spray are some examples of adiabatic used to run the coolant lines that connect to the rack coil via flexible hoses. Many other approaches are available usually best suited for climates that have wet bulb temperatures lower than 55°F for 3,000 or more hours per Water-Side Economizer where there is significantly less solar heat gain compared to the south side.