Direct And Indirect Evaporative Cooling - Tranecds.custhelp
Direct and indirect evaporative coolingUsing the evaporative process to precool the supply air streamcan reduce the energy consumption of mechanical coolingequipment. Two methods of evaporative cooling exist: direct andindirect. The effectiveness of each method depends on theextent to which the dry-bulb temperature of the supply airexceeds the wet-bulb temperature of the supply air.Figure 4–14 Examples of evaporative cooling arrangementsInset Adirect evaporative coolingInset Bindirect evaporative coolingInset Cstaged evaporative coolingDirect evaporative cooling (Figure 4–14, Inset A) introduces waterdirectly into the supply air stream, usually with a spray or wettedmedia. The water evaporates as it absorbs heat from the passingair, which lowers the dry-bulb temperature of the air. However, italso increases the moisture content of the air, which raises thedew point.By contrast, indirect evaporative cooling (Inset B) uses anadditional waterside coil to cool the supply air. Positionedupstream of the conventional cooling coil, the indirect coil ispiped to a cooling tower where the evaporative process occurs.This method of precooling does not increase the moisturecontent (dew point) of the supply air because evaporation occursat the tower. It is, however, not as effective as the directevaporative cooling process.4–40System Design OptionsDirect and indirect evaporative coolingTRACE 700 User’s Manual CDS-PRM001-EN
A third option blends both direct and indirect evaporativeprocesses. Staged evaporative cooling systems (Inset C) arearranged so that the indirect coil activates first, precooling thesupply air without increasing the moisture content. The supply airthen passes through the direct evaporative coil, where it iscooled further with only a slight increase in humidity. Aconventional cooling coil, if used, provides the additional coolingneeded to satisfy any remaining load.Application considerations Although evaporative cooling can effectively reduce the amountof mechanical cooling an application requires, it seldomeliminates the need for a conventional cooling coil altogether. Using evaporative coils in conjunction with a conventional coolingcoil typically adds from 0.2 in. wg to 0.4 in. wg to the staticpressure of the air-distribution system. Direct evaporative cooling systems require additional care toensure proper cleanliness and operation.Sample scenariosScenario 1: Heat-pipe or fixed-plate heat exchanger (HX)with supply-side on return outside air deck and evaporativeprecool of exhaust side. In this configuration, the supply side ofan air-to-air heat exchanger (heat pipe, flat plate or wheel) islocated upstream of the main cooling coil. The exhaust side ofthe HX transfers heat to a scavenger outside air streampretreated by a separate evaporative HX. The example below isshown as a completely recirculated system typical of datacenters but a mixed air ventilation deck could be added to provideairside economizer operation for part of the year.Figure 4–15 Fixed-plate heat exchanger with evaporative precooling of exhaust-side airflowheat pipe (or fixed plate HX)with evaporator precooldata centerscavengeroutside airwettedmediaoutside airfanenergy recoverydevicesupplypumpCDS-PRM001-EN TRACE 700 User’s ManualSystem Design OptionsDirect and indirect evaporative cooling4–41
In TRACE, this configurationcan be created via the CreateSystems - Options dialogusing the standaloneEvaporative Cooling.1 Click Options next toIndirect Efficiency tochange the defaults asfollows:2 Heat Exchanger Type: Airto-air heat exchanger.3 Indirect Efficiency: Overallwet-mode effectiveness atrated supply airflow.4 Dry Effectiveness: Refers tothe overall dry-modeeffectiveness at rated supplyairflow.5 Switchover Oadb: Thewater circulation pump willnot operate below this Oadbwhich causes the HX tooperate in dry mode. Abovethis Oadb, the HX canoperate in wet mode.6 Makeup Water Drift andBlowdown Ratio: Used tomodel additional waterconsumed by the coolerfrom drift and blowdown.7 Circulation Pump: Powerper design scavenger OAairflow. Operates at itsdesign value whenever theHX is in wet mode.4–42 Be sure to include the supply-side static pressure drop across the HX byincluding it with the primary fan's static pressure via the Create Systems Fan Overrides screen. In a similar manner, be sure to include the exhaustside (scavenger OA) static pressure drop by defining it in the auxiliary fan'sstatic pressure field via the Create Systems - Fan Overrides screen (see p4-43). The controls are designed to minimize scavenger fan energy consumptionrather than minimize water consumption. The scavenger airflow is firstmodulated between the max and min scavenger airflow settings to achievethe primary air leaving dry bulb setpoint. If the HX is operating in wet mode,the circulation pump (and associated water flow) operates at its maximum.Once the scavenger fan has slowed down to its minimum speed to preventovercooling, the circulation pump modulates, if necessary, to maintaindesired HX leaving setpoint. The circulation pump shuts off when the HXruns in dry mode or when Oawb primary air leaving dry bulb setpoint orwhen Oadb Switchover Db.System Design OptionsDirect and indirect evaporative coolingTRACE 700 User’s Manual CDS-PRM001-EN
Next the scavenger outdoor air fan should be specified on theCreate Systems - Fan Overrides screen.acts as an outdoorair scavenger fanTo save fan energy, the scavenger airflow is modulated between the Minimumand Maximum OA% of Supply values to maintain target supply air dry bulb. Ifboth Minimum and Maximum OA % of Supply are set to the same value, then thescavenger fan is constant volume and the ERD is modulated by reducing orshutting down the evaporative cooler first.Scenario 2: Polymer tube HX with supply-side on ROA deckwith exhaust side using scavenger outside air. In thisconfiguration, the supply side of a Polymer tube HX is locatedupstream of the main cooling coil. The exhaust side of the HXtransfers heat to a scavenger outside air stream. With thisdesign, outdoor scavenger air is drawn across the exterior ofelliptical tubes, which are wetted by a recirculation water pump.The example below is shown as a completely recirculatedsystem typical of data centers but a mixed air ventilation deckcould be added to provide airside economizer operation for partof the year.Figure 4–16 Wetted plate/tube heat exchanger with scavenger outside air on exhaust deckwetted plate/tube heat exchangerpumpdata centerscavengeroutside airsupplyoutside airfanpolymer tubeheat exchangerCDS-PRM001-EN TRACE 700 User’s ManualSystem Design OptionsDirect and indirect evaporative cooling4–43
In TRACE, this configurationcan be created via the CreateSystems - Options dialog.1 Click Options next toIndirect Efficiency tochange the defaults asfollows:2 Heat Exchanger Type:Wetted plate/tube heatexchanger.3 Indirect Efficiency: Overallwet-mode effectiveness atrated supply airflow.4 Dry Effectiveness: Refersto the overall dry-modeeffectiveness at ratedsupply airflow.5 Switchover Oadb: Thewater circulation pump willnot operate below thisOadb which causes the HXto operate in dry mode.Above this Oadb, the HXcan operate in wet mode.6 Makeup Water Drift andBlowdown Ratio: Used tomodel additional waterconsumed by the coolerfrom drift and blowdown.7 Circulation Pump: Powerper design scavenger OAairflow. Operates at itsdesign value whenever theHX is in wet mode.8 As in the previous scenario,the scavenger OA fanshould be designated inCreate Systems-FanOverrides (see p. 4-43)4–44 Be sure to include the supply-side static pressure drop across the HX byincluding it with the primary fan's static pressure via the Create Systems Fan Overrides screen. In a similar manner, be sure to include the exhaust-side(scavenger OA) static pressure drop by defining it in the auxiliary fan's staticpressure field via the Create Systems - Fan Overrides screen (see p 4-43). The controls are designed to minimize scavenger fan energy consumptionrather than minimize water consumption. The scavenger airflow is firstmodulated between the max and min scavenger airflow settings to achievethe primary air leaving dry bulb setpoint. If the HX is operating in wet mode,the circulation pump (and associated water flow) operates at its maximum.Once the scavenger fan has slowed down to its minimum speed to preventovercooling, the circulation pump modulates, if necessary, to maintain desiredHX leaving setpoint. The circulation pump shuts off when the HX runs in drymode or when Oawb primary air leaving dry bulb setpoint or whenOadb Switchover Db.System Design OptionsDirect and indirect evaporative coolingTRACE 700 User’s Manual CDS-PRM001-EN
Scenario 3: Indirect evaporative cooling via water-to-air HX withcooling tower. In this configuration, a water-to-air HX is locatedupstream of the main cooling coil on the supply deck. The water-to-airHX is similar to a regular finned tube water cooling coil except that the"chilled" water comes from a cooling tower rather than a chiller. Theexample below is shown with a mixed air ventilation deck to provideairside economizer operation for part of the year.Figure 4–17 Indirect evaporative cooling via water-to-air heat exchanger on the ROA deckexhaustdampersystemexhaustindirect evaporatorwater-to-airheat exchangerventilationoutside airdata centersupplyoutdoor airdamperpumpcoolingtowerGo to Create Systems - Optionsdialog.1 Click Options next to IndirectEfficiency to change the defaults asfollows:2 Heat Exchanger Type: Water-to-airheat exchanger with tower.3 Indirect Efficiency: Refers to theeffectiveness above SwitchoverOadb.4 Dry Effectiveness: Refers to theeffectiveness below Switchover Oadb5 Switchover Oadb: Used todetermine the value of the HXeffectiveness. Above this value, theindirect effectiveness is set to equalthe Indirect Efficiency field; belowthis value, the indirect effectivenessis set to equal the Dry Effectivenessfield.CDS-PRM001-EN TRACE 700 User’s Manual When the HeatExchanger Type is"Water-to-air heatexchanger withTower", the makeupwater is calculatedaccording to thecooling tower chosenas the Heat Rejection Type on the Create Plants Cooling Equipment screen. The Secondary Airflowinputs are disabled because the cooling tower is modeledseparately in the Equipment section.System Design OptionsDirect and indirect evaporative cooling4–45
The cooling tower and associated pump attached to the water-toair HX need not be specified for design or system simulation butare needed for the equipment simulation. On the Create Plants Cooling Equipment screen, create a separate cooling plant (610).6 Category set to Watercooled Chiller.7 Equipment Type set toIndirect EvaporativeCooling.8 Choose Heat RejectionType that matches yourcooling tower or fluid cooler.9 Leave cooling capacityblank and set coolingenergy rate to zero.10Choose a CondenserWater Pump and set itsFull Load Consumptionrate.Second, on the Assign System Coils screen, attach the IndirectEvaporative Cooling Coil to the above cooling plant.4–46System Design OptionsDirect and indirect evaporative coolingTRACE 700 User’s Manual CDS-PRM001-EN
Scenario 4: Staged direct (wetted media) and indirectevaporative (water-to-air HX) in ROA deck. In thisconfiguration, a direct evaporative heat exchanger is placedupstream of an indirect evaporative heat exchanger locatedupstream of the main cooling coil on the ROA deck. The examplebelow is shown with a mixed air ventilation deck to provideairside economizer operation for part of the year.Figure 4–18 Staged direct (wetted media) and indirect evaporative (water-to-air HX) in ROA decksystemexhaustexhaustdamperdirect evaporatorindirect evaporatorwater-to-airheat exchangerventilationoutside airdata centerwettedmediasupplyoutdoor airdamperpumppumpwettedmediaThis configuration is modeled in Evaporative Cooling Options.CDS-PRM001-EN TRACE 700 User’s ManualSystem Design OptionsDirect and indirect evaporative cooling4–47
Scenario 5: Indirect evaporative (water-to-air) heat exchangerin ventilation deck (DualCool system). This configuration is notused for data centers but was added to implement the DualCooladd-on to DX rooftops. In this configuration, a water-to-air heatexchanger integrated with a separate evaporative media coil isplaced in the ventilation deck. A submersible pump moves coolwater from the reservoir beneath the evaporative media to, andthrough, the vent air pre-cooling coil, and then back to adistribution tube above the evaporative media. Water flowing bygravity downward through the wetted media cools the airentering the large condenser coil through which refrigerant isdischarging heat to the outdoor air.Figure 4–19 Indirect evaporative (water-to-air) HX in ventilation deck (DualCool e airindirect coolingcoilpumpscavengeroutside airair-cooled DXoutdoor airdampersupplywettedmediaair-cooled condenserThe Stage 1 Air-to-Air Energy Recovery/Transfer Type is astandard library member called DualCool (OA Evap Precooling)and would be defined on the Create System - Options screenvia the Stage 1 Energy Recovery. Because the evaporative mediais precooling the condenser air,this must be accounted for inthe Cooling Equipment librarymember attached to this systemby specifying the EvaporativePrecooling Flag Yes and EvapPrecool Effectiveness 65% asillustrated.4–48System Design OptionsDirect and indirect evaporative coolingTRACE 700 User’s Manual CDS-PRM001-EN
Schedule lockoutsSchedule lockouts can be used to limit direct and/or indirectevaporative coil or Energy Recovery operation within a specificOadb range.In Schedule Library, createa Utilization Schedule fora specific rangeIn Create Systems-Options screen select the custom schedule for therespective coil.Suggested defaults:Evaporative HX TypeWater-to- Water-toair HX w/ air HX w/ Air-to-airHXEvapTowerWetted plate/tube HXSprayWettedmediaMax OA% of Supply, %n/an/an/a125125125Min OA% of Supply, %n/an/an/a25252585Optional Scavenger AirflowHX EffectivenessDefault Effectiveness, %9595807080Dry Effectiveness, %007007075Switchover Oadb, 0.050.050.05Makeup WaterDrift Loss Fraction, %Blowdown RatioCirculation Pump Power, W/cfmCDS-PRM001-EN TRACE 700 User’s ManualSystem Design OptionsDirect and indirect evaporative cooling4–49
Scenario 3: Indirect evaporative cooling via water-to-air HX with cooling tower. In this configuration, a water-to-air HX is located upstream of the main cooling coil on the supply deck. The water-to-air HX is similar to a regular finned tube water cooling coil except that the "chilled" water comes from a cooling tower rather than a chiller. The
air-coolers using HMX's patented Indirect Direct Evaporative Cooling technology (also known as two-stage evaporative air cooling). This cooling solution consumes considerably less power than air-conditioners and provides better comfort than ducted evaporative coolers, bringing evaporative air cooling technology a step closer to air-conditioning.
Developers have moved to green cooling technique to save energy in unique way. Besides air cooling, evaporative water cooling, oil immersion cooling has gained rapid acceptance in data center cooling area. [1]. Evaporative cooling has been taking place over air-cooling system because of the cooling
Fig. 3: Indirect Evaporative Cooling 3) Combined Evaporative Cooling This type of evaporative coolers combines both direct and indirect evaporative cooling. This is accomplished by passing air inside a heat exchanger that is cooled by evaporation on the outside.In the second stage the pre cooled air is passes
Two-stage indirect/direct evaporative coolers as shown in Figure 4 can cool air to lower temperatures than are attainable with direct ("one-stage") evaporative coolers, and add less moisture to the indoor air. In these coolers, a first-stage indirect evaporative cooler lowers both the dry bulb
air-coolers using HMX's patented Indirect Direct Evaporative Cooling technology (also known as two-stage evaporative air cooling). This cooling solution consumes considerably less power than air-conditioners and provides better comfort than ducted evaporative coolers, bringing evaporative air cooling technology a step closer to air-conditioning.
The sub wet-bulb evaporative chiller (SWEC) uses an evaporative cooling process to chill water for use in building cooling systems. The SWEC utilizes a two-stage evaporative cooling system to chill water below the web-bulb temperature of the outdoor air. The theoretical limit for the supply water temperature is the dew point of the outdoor air.
Refrigerated air conditioning range including VRF (heat pump and heat recovery) Industrial and commercial evaporative air conditioners. Indirect evaporative air conditioners Heating, cooling and ventilation. Indirect evaporative air conditioners. Seeley International is Australia’s largest a
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