The facility will then either have one or several transformers in place to take in the energy, while also ensuring the power coming in is of the right voltage and the right type of current typically. Some data centers supplement their energy from the grid or completely remove it by on-site electrical generation equipment -either in the form of combustion-based generators or with alternative energy sources such as solar photovoltaic panels and wind-powered turbines. The power then gets transferred to the main distribution boards which house fuses, circuit breakers, and ground leakage protection units, take the low-voltage electricity and distribute it to a number of UPS systems. UPS are responsible for supplying power to a number of racks while helping clean up the electricity pulsing through by ensuring that issues like surges don’t impact equipment. UPS systems also serve as an initial backup, in case of a power outage or similar issue. In a nutshell, a UPS battery turns on after the system senses a loss of power. Their purpose is to maintain the infrastructure until consistent power returns, or if needed, until longer-term emergency power backup systems kick in. A typical UPS can provide power to servers and breakers for up to five minutes; that way, there’s enough time to get a backup generator going immediately following an outage or similar issue with the wider electric grid. In order to ensure continuous uptime and minimize outages as much as possible,nft hydroponic system most data centers have a backup power source on site or nearby. Often backup power supply comes from a fuel generator powered by gasoline or diesel.
In a data center, not only servers and other critical pieces of IT equipment require a lot of electricity to operate, but also all of the ancillary equipment. Lights, cooling systems, monitors, humidifiers, etc. also need electricity. The amount of electricity that goes towards servers versus non-IT equipment is called Power Usage Efficiency score which measures usage effectiveness. A score of 1 means that all the energy in a data center goes towards servers, while a score of 2 means that ancillary equipment uses just as much electricity as servers and other IT components . The Uptime Institute survey shows that the average PUE of a data center stands at 1.58. The average PUE for a Google data center is 1.12, but its facility in Oklahoma had a score of just 1.08 during the last three months of 2018. Today, the average power consumption for a rack is around 7kW depending upon the data center. However, almost two-thirds of data centers in the US experience higher peak demands, with a power density of around 15kW to 16kW per rack. Some data centers may hit 20kW or more per rack at times. The Uptime Institute’s latest survey found that around one in five have a density of 30kWor higher, indicating the growing presence of high-density computing. Half said their current rack density was between 10kW and 29kW. One of the most critical challenges associated with increasing power density within data centers is cooling. Alternative cooling technologies and methodologies such as liquid cooling, use of solar and wind for power cooling systems are being developed against that need. One of the largest operational expenses of data centers is the cost of energy. Cooling power consumption accounts for up to 40% of data center energy use. The original American Society of Heating, Refrigerating and Air-Conditioning Engineers air temperature envelope was 20-25℃ in 2004 based on reliability and uptime as the primary concern. Nowadays, changes to data center environmental conditions are being driven by the need to save energy and reduce operational expenses.
From 2016, ASHRAE recommended range of temperature and humidity is 18˚C to 28˚C dry bulb temperature, 9˚C to 15˚C dew point and 60% relative humidity. The Uptime Institute, however, recommends an upper limit of 25˚C. There are different common ways of to remove excess heat in data centers as shown in Figure 5.A Computer Room Air Handling is similar to a chilled water air handling system. In this system, the cooling is accomplished by blowing air over the cooling coil filled with the chilled water. The chilled water is typically supplied to the CRAHs by an electric powered chiller. The chiller then removes the heat from the warmer chilled water and transfers it to another stream of circulating water called condenser water which flows through a cooling tower. These CRAHs can have Variable Frequency Drives that modulate fan speed to maintain a set static pressure either under floor or in the overhead ducts. Heat removed from the returning chilled water can be rejected to a condenser water loop for transport to the outside atmosphere or to an air-cooled condenser, or to a glycol cooled chiller. A CRAC unit works like an air conditioner which has an in-built direct expansion refrigeration cycle. The compressors which are required to power the refrigeration cycle is also located within the CRAC unit. Thus, the cooling is accomplished by blowing the air over the cooling coil filled with refrigerant. Heat from the IT environment is pumped to the outdoor environment using this circulating flow of refrigerant. New CRAC units are developed that can vary the airflow with the help of multistage compressors. However, most of the existing ones have on/off control only. Modern data centers try to use adiabatic direct air cooling whenever the weather conditions allow. The common types of cooling are as follows: Free Cooling: Free cooling is an approach for cooling the air temperature in the target environment by using ambient cool air or water from the local environment instead of mechanical refrigeration. In this method, pumps, fans, and other air/water-handling equipment are needed. Cooling systems that use this approach are also called air-side economizers. The primary method is evaporative cooling, where ambient air is passed through a wet filter that cools it. The air then enters the cooling system at a lower temperature, which allows for more efficient operation. Evaporative assist is most beneficial in dry climates.
Alternatively, in water side economizer a source of cold water from local rivers, lakes or oceans is circulated into a data center and used instead of refrigerating a closed water loop with a chiller. Evaporative assist is an adiabatic cooling system which does not have heat exchange to the environment. Adiabatic cooling incorporates both evaporative and air cooling into a single system. An indirect ambient air cooling system uses outdoor air to indirectly cool data center air when the temperature outside is lower than the temperature set point of the IT inlet air, resulting in significant energy savings. Fans blow cold outside air through an air-to-air heat exchanger which in turn cools the hot data center air on the other side of the heat exchanger, thereby completely isolating the data center air from the outside air. Heat exchangers can be of the plate or rotating type. Heat removal method normally uses evaporative assist whereby the outside of the air-to-air heat exchanger is sprayed with water which further lowers the temperature of the outside air and thus the hot data center air. Indirect adiabatic data center cooling: The indirect adiabatic cooling consists of two different airflows named primary and secondary airflow as shown Figure 6. Primary airflow is the airflow that is used to cool the IT load. The secondary airflow is the outside or the ambient air which is used to discharge the IT load of the primary airflow. The primary airflow and secondary airflow are completely separated from each other because mixing them will create pollution and inconsistencies. During warm days water is sprayed on the heat exchanger to increase the cooling capacity of the secondary airflow according to the physical laws of psychrometrics. The water also provides a better conductivity between the two airflows by optimizing the energy transfer. Most units require a basic water softening system to produce the required water. A water storage tank is required to store a certain amount of water in case of water outage from the main water connection. There are basically two operating modes, Summer/wet: If conditions are not met for the secondary airflow, the air is humidified by adding a specific amount of water to the secondary air flow to increase its cooling capacity. In addition to these adiabatic cooling systems, direct expansion cooling systems ,hydroponic nft system powered by electricity, may be required in specific locations to reach the cooling demand of the data center. Winter/dry: Primary airflow transfers its heat towards the cooler secondary airflow without the requirement of water.
The indirect adiabatic cooler is known for its high energy efficiency reaching a cooling PUE of 1.05 at a single moment. There are three basic approaches for distributing air in a data center: flooded, targeted, and contained. In a flooded supply and return air distribution system, the only constraints to the supply and return air flow are the walls, ceiling, and floor of the room. This leads to heavy mixing of the hot and cold air flows. In a targeted supply and return air distribution system, a mechanism directs the supply and return airflow within 3m of the IT equipment intake and exhaust. In a contained supply and return air distribution system, the IT equipment supply and return air flow is completely enclosed to eliminate air mixing between the supply and the return air streams. Hot aisle/cold aisle arrangements lower cooling costs by better managing airflow, thereby accommodating lower fan speeds and increasing the use of air-side or water-side economizers. When used in combination with containment, Department of Energy estimates reduction in fan energy use of 20% to 25%. Another data center cooling technique is open bath immersion cooling which implies fully submerging IT equipment in a dielectric liquid. These baths allow the coolant fluid to be moved through the hardware components or servers submerged in it. Single phase immersion requires circulation of the dielectric liquids by pumps or by natural convection flow. These liquids always remain in the liquid state while operating. The dielectric coolant is either pumped through an external heat exchanger where it is cooled with any facility coolant, or the facility coolant is pumped through an immersed heat exchanger, which facilitates heat transfer within the dielectric liquid. In two-phase immersion systems, heat is removed through the phase change that the coolant undergoes at its operating temperature. The server heat literally boils the dielectric fluid that has an appropriate boiling point temperature. This two-phase immersion system takes advantage of the dielectric fluid latent heat of vaporization. This occurs when the two-phase coolant comes in contact with the heated electronics in the bath that are above the coolants boiling point. Once the two-phase coolant enters its gas phase it must be cooled or condensed, typically through the use of water-cooled coils placed in the top of the tank. Once condensed the two-phase coolant drips back into the primary cooling tank. The two-phase coolant in the tank generally remains at its “saturation temperature”. Energy transferred from the servers into the two-phase coolant will cause a portion of it to boil off into a gas. The gas rises above the liquid level where it contacts a condenser which is cooler than the saturation temperature. This causes the gaseous state coolant to condense back into a liquid form and fall back into the bath. In order to safely submerge an electronic device in a liquid, the liquid must be non-conductive to avoid short-circuit electronic signals or change in the signal characteristics of sensitive, high-speed electronic devices, such as Central Processing Unit s and memory modules. The liquid must also be completely noncorrosive and avoid any sort of damage to electronic packaging, contacts, or printed wet or dry circuit layouts. The liquid must be nonflammable, nontoxic, and easy to clean up if there is a spill. Immersion cooling mainly work in baths of mineral oil, and companies that have developed liquids such as Novec, which meet the criteria for electronic immersion cooling.Fuel cell devices are capable of converting fuel directly into electricity without the need of turbines or any major moving parts. The following section discusses how fuel cells work and some of the motivating principles behind their operation. Hydrogen is the most basic fuel used in the fuel cell electrochemical reactions, but fuel cell systems can operate on a wide variety of fuels. All fuel cells also require an oxidant, which is usually oxygen taken from air.