[et_pb_section fb_built=”1″ module_class=”page-service” _builder_version=”4.4.8″ use_background_color_gradient=”on” background_color_gradient_start=”#17A6E3″ background_color_gradient_end=”#433A8D” background_color_gradient_direction=”102deg” z_index=”9″ custom_padding=”200px||||false|false” locked=”off”][et_pb_row column_structure=”1_2,1_2″ _builder_version=”4.4.8″ width=”90%” max_width=”2560px” custom_margin=”-200px||||false|false” custom_padding=”200px||||false|false”][et_pb_column type=”1_2″ _builder_version=”4.4.8″][et_pb_text _builder_version=”4.4.8″ text_text_color=”#ffffff” header_font=”Soleil Bold|700|||||||” header_text_color=”#ffffff” header_font_size=”35px” header_line_height=”39px” z_index=”90″ background_layout=”dark” width=”100%” custom_margin=”0px||0px||false|false” custom_padding=”0px||20px||false|false” custom_padding_tablet=”” custom_padding_phone=”” custom_padding_last_edited=”on|desktop”][\/et_pb_text][et_pb_text _builder_version=”4.4.8″ text_text_color=”#ffffff” header_font=”Soleil Bold|700|||||||” header_text_color=”#ffffff” header_font_size=”35px” header_line_height=”39px” z_index=”90″ background_layout=”dark” width=”100%”]<\/p>\n
[\/et_pb_text][\/et_pb_column][et_pb_column type=”1_2″ _builder_version=”4.4.8″][\/et_pb_column][\/et_pb_row][\/et_pb_section][et_pb_section fb_built=”1″ admin_label=”section” module_class=”page-service” _builder_version=”4.4.8″ z_index=”140″ custom_margin=”0px||||false|false” custom_padding=”0px||0px||false|false”][et_pb_row column_structure=”1_2,1_2″ _builder_version=”4.4.8″ transform_translate=”0px|13px” z_index=”9″ width=”90%” max_width=”2560px” custom_margin=”0px||0px||false|false” custom_padding=”0px||0px||false|false” custom_css_main_element=”margin-top:-125px;”][et_pb_column type=”1_2″ _builder_version=”4.4.8″ background_enable_color=”off”][et_pb_cta button_url=”\/contact-us\/” _builder_version=”4.4.8″ header_level=”h3″ header_font=”Soleil Bold|700|||||||” header_text_color=”#0C435E” header_font_size=”30px” header_line_height=”30px” body_font=”Soleil Regular||||||||” body_line_height=”20px” use_background_color=”off” custom_button=”on” button_text_size=”16px” button_text_color=”#0C435E” button_border_color=”#17A6E3″ button_border_radius=”2px” button_font=”Soleil Bold|700||on|||||” button_use_icon=”off” button_custom_padding=”5px|50px|5px|50px|true|true” text_orientation=”left” background_layout=”light” custom_margin=”0px||||false|false” custom_padding=”40px||0px||false|false” custom_css_promo_button=”margin-top:24px” custom_css_promo_title=”margin-bottom:0px”]<\/p>\n
What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> Cabs always have doors (as opposed to \u201cracks\u201d, which can be open). At one time the doors were usually glass but now, with the adoption of front-to-back cooling of servers, the doors should always be perforated.<\/p>\n What is it?<\/strong> Further Explanation<\/strong> It applies to any project lasting longer than 30 days or involving more than 500 person days. This means all but the very smallest server room projects.<\/p>\n All projects to which CDM applies have to be notified to the Health And Safety Executive before any work commences on site.<\/p>\n What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> The name \u201cdry cooler\u201d originates from the days when cooling towers were in common usage. A cooling tower has water sprayed into the atmosphere whereas a dry cooler does not.<\/p>\n What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> EN1047 limits the temperature rise across the relevant structure (wall, ceiling, floor etc) to 50\u00b0C for the stated time (as opposed to 180\u00b0C) which will give time for a fire outside the data centre to be extinguished.<\/p>\n What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> \n [\/et_pb_cta][\/et_pb_column][et_pb_column type=”1_2″ _builder_version=”4.4.8″][et_pb_cta button_url=”\/contact-us\/” _builder_version=”4.4.8″ header_font=”Soleil Bold|700|||||||” header_text_color=”#0C435E” header_font_size=”30px” header_line_height=”44px” body_font=”Soleil Regular||||||||” body_line_height=”20px” use_background_color=”off” custom_button=”on” button_text_size=”16px” button_text_color=”#0C435E” button_border_color=”#17A6E3″ button_border_radius=”2px” button_font=”Soleil Bold|700||on|||||” button_use_icon=”off” button_custom_padding=”5px|50px|5px|50px|true|true” text_orientation=”left” background_layout=”light” custom_margin=”0px|0px||0px|false|true” custom_padding=”40px|0px|0px|0px|false|true” custom_css_promo_button=”margin-top:24px” custom_css_promo_title=”margin-bottom:0px”]<\/p>\n What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> They are also faster to build and avoid the need for any \u201cwet trades\u201d.<\/p>\n The insulation can be mineral wool or foam.<\/p>\n Some, but not all, meet the requirements of EN1047-2<\/p>\n What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> Power factors can be lagging (inductive load) which was normal for IT equipment unit a few years ago or leading (capacitive) which is becoming more common particularly for blade servers. A purely resistive load (e.g. an electric fire) has a power factor of 1.0 (i.e. it draws the same in kW as in kVA).<\/p>\n What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> What is it?<\/strong> Further Explanation<\/strong> [\/et_pb_cta][\/et_pb_column][\/et_pb_row][\/et_pb_section]<\/p>\n","protected":false},"excerpt":{"rendered":" Glossary Adiabatic Cooling What is it? Lowering the dry bulb air temperature without changing the total amount of heat in the system Further Explanation For water in liquid form to evaporate to become a vapour heat is required. This can be done by adding heat as in a kettle, or by allowing the water to […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"_et_pb_use_builder":"on","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"class_list":["post-5716","page","type-page","status-publish","hentry"],"acf":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/www.future-tech.co.uk\/wp-json\/wp\/v2\/pages\/5716","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.future-tech.co.uk\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.future-tech.co.uk\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.future-tech.co.uk\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.future-tech.co.uk\/wp-json\/wp\/v2\/comments?post=5716"}],"version-history":[{"count":0,"href":"https:\/\/www.future-tech.co.uk\/wp-json\/wp\/v2\/pages\/5716\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.future-tech.co.uk\/wp-json\/wp\/v2\/media?parent=5716"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\nLowering the dry bulb air temperature without changing the total amount of heat in the system<\/p>\n
\nFor water in liquid form to evaporate to become a vapour heat is required. This can be done by adding heat as in a kettle, or by allowing the water to absorb heat from air passing over it. In the latter case Evaporative Cooling takes place with, the total heat in the system being unchanged but more as latent heat and less as sensible heat.<\/p>\nAir-Side Free Cooling<\/h2>\n
\nCooling by bringing outside air into the data centre<\/p>\n
\nSee \u2018Fresh Air Free Cooling\u2019<\/p>\nASD<\/h2>\n
\nAspirating Smoke Detection<\/p>\n
\nThe generic term for systems such as VESDA, HSSD and HART. These systems provide a very early warning of a potential fire by sampling air through an aspirating system and detecting particles using a laser based system at the incipient (i.e. pre-combustion) stage.<\/p>\nAutonomy (battery)<\/h2>\n
\nThe duration, usually expressed in minutes, that a UPS can support its load<\/p>\n
\nThe time for which a UPS can support the load is a function of the power drawn and the battery capacity. Typically in a data centre this will be something like 10 to 15 minutes. It is possible to have longer autonomy times but the cost and bulk of batteries involved becomes prohibitive and generally it is better to install a standby generator.<\/p>\nBig Data<\/h2>\n
\nBig data is a blanket term for any collection of data sets that are extremely large and complex.<\/p>\n
\nBig Data is used to describe datasets whose volume and complexity is beyond the ability of typical database software tools to capture, store, manage, and analyse.<\/p>\nCab; Cabinet<\/h2>\n
\nAn enclosure for housing computer equipment also often called a rack<\/p>\n
\nCabs are usually either 600mm wide for servers or 800mm wide for comms (to allow for the amount of cabling) and 1,000mm deep. Heights are expressed as \u2018U\u2019 (1 \u2018U\u2019 being 1.75 inches). Typical cab heights are 42U (overall height around 2,000mm) up to 48U (overall height around 2,300mm).<\/p>\nCDM<\/h2>\n
\nConstruction ( Design & Management) Regulations 2007<\/p>\n
\nLegislation that, put simply, states that every construction project must be designed and managed so as to be safe to build and safe to run. So the design has to take into account both the construction and the on-going maintenance of the completed facility.<\/p>\nCRAC Unit<\/h2>\n
\nComputer Room Air Conditioning Unit<\/p>\n
\nAn air conditioning unit specifically designed for use in an IT environment . Features which differentiate these from ordinary office air conditioning (comfort cooling) units include: high sensible heat ratio thus making them far more energy efficient; ability to control relative humidity; higher standard of filtration; greater cooling capacities available; designed to run 24 hours x 365 days a year.<\/p>\nDCiE<\/h2>\n
\nData Centre Infrastructure Efficiency \u2013 see also PUE<\/p>\n
\nThis is one of the key metrics used to express the energy efficiency of a data centre. It is the energy supplied to the IT equipment divided by the total energy supplied to the data centre and is the reciprocal of PUE<\/p>\nDiesel Rotary UPS (DRUPS)<\/h2>\n
\nA combined UPS and diesel generator<\/p>\n
\nA DRUPS comprises an electric motor, a fly-wheel and a diesel generator. Under normal operation the mains power drives the fly-wheel and generator supplying the data centre. In the event of a mains power failure the kinetic energy in the fly-wheel keeps the system running while the diesel engine starts and then this takes over. Advantages of the system are that the data centre supply is always isolated from any disturbances on the mains and there is no change-over required from mains to batteries and back is in a static UPS. Also more efficient than traditional static UPS\u2019s although this is changing with the introduction systems such as Eaton\u2019s EMS.<\/p>\nDry Bulb<\/h2>\n
\nThe temperature of the air measured by a thermometer with a dry bulb (as opposed to a \u201cwet bulb\u201d \u2013 see below)<\/p>\n
\nWhether it is a weather report or the specification for a data centre, unless it specifically states otherwise, a reference to air temperature will mean dry bulb temperature. It is the dry bulb temperature which determines the rate of heat transfer from the hot servers to the air passing through them.<\/p>\nDry Cooler<\/h2>\n
\nA device comprising a coil and fan(s) by which heat is rejected to the outside air<\/p>\n
\nIn simple terms a dry cooler is a big car radiator placed outside with fans blowing across it. Water (or more often a mixture of water and glycol) from the data centre air conditioning system is pumped through the dry cooler and thus any time the outside air is cooler than the data centre hot aisle air it is possible to get \u201cfree\u201d cooling.<\/p>\nDX<\/h2>\n
\nDirect Expansion (air conditioning unit)<\/p>\n
\nType of air conditioning unit where the evaporator coil (i.e. the coil in which the refrigerant gas expands) is positioned directly in the air flow (as opposed to in a chilled water circuit). The heat rejection side of a DX system is also usually directly from the condenser coil to the outside air although increasingly it is to a condenser water circuit \u2013 see Water Cooled DX.<\/p>\nEEV<\/h2>\n
\nElectronic Expansion valve<\/p>\n
\nThe cooling in a compressor driven air conditioning unit relies on the cooling effect which occurs when a gas is allowed to expand. The rate of expansion has to be controlled and this is achieved with an expansion valve. Traditionally these have been mechanical devices known as TEVs (Thermostatic Expansion valves). EEVs, being electronically controlled, are better at maintaining the optimum pressure and temperature with a marked improvement in efficiency.<\/p>\nEN1047-2<\/h2>\n
\nBritish Standard for fire protection of data storage and IT equipment<\/p>\n
\nThe normal fire ratings of buildings are designed primarily to protect life and as such are concerned with limiting the spread of fire and preventing the early collapse of structures which could then impede escape. The temperatures allowed would very quickly destroy storage media cause damage to IT equipment.<\/p>\nEvaporative Cooling (also see Adiabatic Cooling)<\/h2>\n
\nCooling air by passing it over a wet surface<\/p>\n
\nPassing air over a wet surface causes the dry bulb temperature of the air to fall and so can be used to assist with data centre cooling. It is achieved by passing air through a fibrous matt which is continually wetted with water. It can only be used on full fresh air systems otherwise the RH of the air will quickly rise to the point where no more evaporation takes place. It is only effective when the RH of the incoming air is low, and it causes the RH to rise which means air at high RH is delivered to the servers which can be problematic.<\/p>\nFree Cooling<\/h2>\n
\nCooling without the operation of a compressor<\/p>\n
\nMany older air conditioning systems have to run the compressors even when the outdoor temperature is well below the temperature of the data centre. \u2018Free cooling\u2019 systems operate without the need to run the compressors, bringing considerable savings in energy use \u2013 see \u2018Fresh Air Free Cooling\u2019 and \u2018Indirect Free Cooling\u2019.<\/p>\nFresh Air Free Cooling<\/h2>\n
\nCooling by bringing cool outside air into the data centre<\/p>\n
\nCooling using outside air which is filtered, and, if required, tempered by mixing with return air and humidified using an evaporative humidifier.<\/p>\nHART<\/h2>\n
\nProprietary ASD system<\/p>\n
\nSee ASD<\/p>\nHSSD<\/h2>\n
\nHigh Sensitivity Smoke Detection<\/p>\n
\nSee ASD<\/p>\nHybrid UPS<\/h2>\n
\nA UPS comprising more than one means of energy storage e.g. fly-wheel +batteries<\/p>\n
\nA number of companies now produce hybrid UPS\u2019s which combine batteries with fly-wheels, super capacitors or compressed air.<\/p>\nIndirect Free Cooling<\/h2>\n
\nFree Cooling using a water circuit \u2013 also called \u2018Water-side free cooling\u2019<\/p>\n
\nSystem using a dry cooler or cooling tower to provide compressor-free cooling via a chilled water coil.<\/p>\nIntelligent PDU<\/h2>\n
\nPDU which allows remote switching and\/or monitoring<\/p>\n
\nThe term \u2018Intelligent PDU\u2019 is usually only applied to \u2018Rack PDU\u2019s\u2019.
\nRemote switching and monitoring can be per PDU or per individual outlet.
\n<\/span><\/p>\nkVA<\/h2>\n
\nKilovolt amp (i.e. Volts\/1000 x amps)<\/p>\n
\nKilovolts x amps which if the Power factor (see below) is 1 will be the same as kW.<\/p>\nkW<\/h2>\n
\nKilowatt<\/p>\n
\nKilowatts are the actual power used. Whatever is delivered in kW to the room comes out in heat so has to be removed by the air conditioning system.<\/p>\nLatent Heat<\/h2>\n
\nChange in thermal energy due to a change of state (e.g. water to steam)<\/p>\n
\nIn the context of air conditioning, Latent Heat is heat removed in order to reduce the humidity of air.<\/p>\nModular Room<\/h2>\n
\nA room constructed from pre-formed insulated steel panels<\/p>\n
\nModular rooms generally give a higher for rating better protection against water ingress than other forms of construction.<\/p>\nMPDU<\/h2>\n
\nMain Power Distribution Unit<\/p>\n
\nA panel comprising an incoming isolator and outgoing circuit breakers supplying all of the equipment in the data centre such as the air conditioning, lighting and ancillary equipment as well as the IT load ( via the UPS system) \u2013 see also PDU<\/p>\nPDU<\/h2>\n
\nPower Distribution Unit<\/p>\n
\nA panel comprising an incoming isolator and outgoing circuit breakers supplying the IT load and fed from a UPS (see also \u2018MPDU\u2019 and \u2018Rack PDU\u2019).<\/p>\nPF<\/h2>\n
\nPower Factor<\/p>\n
\nPower factor expresses the difference between kW and kVA expressed as a ratio i.e. if the data centre is drawing 100kVA with an 80kW load the power factor is 0.8.<\/p>\nPUE<\/h2>\n
\nPower Utilisation Effectiveness \u2013 see also DCiE<\/p>\n
\nThis is one of the key metrics used to express the energy efficiency of a data centre. It is the total energy supplied to the data centre divided by the energy supplied to the IT equipment and is the reciprocal of DCiE<\/p>\nRack PDU<\/h2>\n
\nThe power distribution strip within a rack<\/p>\n
\nStrip of socket outlets mounted within the rack \u2013 minimum two per rack fed from separate circuits on the PDU(s). Sockets are usually 10amp IEC but can be others particularly for high power computers and blade servers. See also \u2018Intelligent PDU\u2019<\/p>\nRack; Server rack; Comms rack<\/h2>\n
\nAn enclosure for housing computer equipment also often called a rack \u2013 also see \u201ccab\u201d<\/p>\n
\nThe term \u201crack\u201d is used interchangeably with \u201ccab\u201d or \u201ccabinet\u201d but the term originates in the telecommunications industry and strictly speaking refers to an open frame.<\/p>\nRelative Humidity (RH)<\/h2>\n
\nThe amount of moisture in air expressed as a percentage of the total moisture it could hold (at its present temperature of pressure)<\/p>\n
\nAs air temperature rises its capacity to hold water vapour increases, hence the Relative Humidity falls even though the amount of moisture remains the same.<\/p>\nRotary UPS<\/h2>\n
\nA UPS which uses a rotating mass to store energy<\/p>\n
\nSee \u2018DRUPS\u2019 and \u2018Hybrid UPS\u2019<\/p>\nSensible Heat<\/h2>\n
\nA change in thermal energy without a change of state<\/p>\n
\nIn the context of air conditioning, Sensible Heat is the heat removed in order to reduce the temperature of air without adding to or reducing the amount moisture held.<\/p>\nSHR<\/h2>\n
\nSensible Heat Ratio<\/p>\n
\nThe sensible cooling duty as a proportion of the total cooling duty. Ideally in a computer room the SHR should be 1.0. A typical \u2018comfort cooling\u2019 air conditioner will have an SHR of about 0.7 i.e. only 70% of its power consumption is going into cooling the room the other 30% is condensing water vapour out of the air, resulting in low R.H.<\/p>\nStatic UPS<\/h2>\n
\nA UPS which uses batteries to store energy and therefore has no moving parts (as opposed to a Rotary UPS)<\/p>\n
\nA piece of equipment comprising a rectifier, batteries and inverter which maintains its power output in the event of a failure in the incoming supply. The time for which it can maintain the supply is determined by the capacity of the batteries and is referred to as the \u2018autonomy\u2019.<\/p>\nTIA<\/h2>\n
\nTelecommunications Industry Association<\/p>\n
\nUS based trade association for the telecoms industry.<\/p>\nTIA 942<\/h2>\n
\nTelecommunications Infrastructure Standard for Data Centres<\/p>\n
\nThe most commonly used standard for specifying data centre infrastructure. Categorises by \u2018Tiers\u2019 from 1 to 4 with Tier 1 being the lowest and Tier 4 the highest.<\/p>\nTier<\/h2>\n
\nSpecification of data centre infrastructure from TIA 942 or The Uptime Institute<\/p>\n
\nThe TIA \u201cTiers\u201d run from Tier 1 to Tier 4 and define all the parameters of a data centre from its location in relation to transport and urban centres to the number of power supplies. Tier 1 is the lowest and almost any computer room will meet this, up to Tier 4 which requires 2N mechanical and electrical systems and dual incoming mains supplies.<\/p>\nTier Certification<\/h2>\n
\nSpecification of data centre infrastructure<\/p>\n
\nThere are two organisations, both based in the USA, offering standards for data centre infrastructure. These are the TIA and The Uptime Institute. Both rate data centres on their ability to cope with events such as power outages and component failures using a grading system from Tier 1 (lowest level) to Tier 4 (highest level). The TIA standard also covers a wide range of other criteria including such things as location in relation to transport and urban centres.<\/p>\nTotal Cooling Capacity<\/h2>\n
\nSensible cooling + latent cooling<\/p>\n
\nAir conditioning units are usually rated by their total cooling capacity whereas is a data centre it is only the sensible cooling that matters (see SHR). With comfort cooling units the difference is significant with a unit rated at say 10kW (total cooling) only providing 7kW of useful cooling in data centre.<\/p>\nUPS<\/h2>\n
\nUninterruptible Power Supply<\/p>\n
\nA piece of equipment in the event of a failure in the incoming supply.<\/p>\nVESDA<\/h2>\n
\nVery Early Smoke Detection Apparatus<\/p>\n
\nSee ASD<\/p>\nVIEW<\/h2>\n
\nVery Early Intelligent Warning (smoke and fire detection)<\/p>\n
\nAn alternative to ASD \u2013 uses a large number of laser detectors distributed around the room as opposed to drawing the air to a central sampling unit.<\/p>\nWater Cooled DX<\/h2>\n
\nDX air conditioning system where heat rejection is by a water cooled condenser<\/p>\n
\nThe main advantage of these systems and the reason for their increasing popularity is that they allow \u2018free cooling\u2019 during low ambient conditions by having a chilled water coil as well as the DX coil.<\/p>\nWater side free cooling<\/h2>\n
\nFree Cooling using a water circuit<\/p>\n
\nSee \u2018Indirect Free Cooling\u2019<\/p>\nWet Bulb<\/h2>\n
\nThe temperature of the air measured by a thermometer with a bulb which is wetted by a wick<\/p>\n
\nWhen air passes over a wet surface it causes some of the moisture to evaporate. This change of state from liquid (water) to gas (water vapour) requires energy which comes from the air. This results in a fall in temperature which is how adiabatic (evaporative) cooling works. The rate of evaporation is dependent on the relative humidity (RH) and so the difference between the wet bulb and the dry bulb temperatures, known as the wet bulb depression, can be used to measure RH.<\/p>\n