Close Control Air Conditioning Products Cooling Server Rooms

Commissioning and Service Close Control AC Units

Close Control Air ConditioningProducts

Cooling Server Rooms

Y4.19-04-22-01

Topics• Servers & IT Hardware • HVAC & Room Design

• Airflow & Airflow Issues • Systems & Technologies for Cooling

• Energy Saving Techniques• Classic Unit Problems

• Project Examples


Servers & IT Hardware


The market has evolved over a 40 year period :1970’s\80’s: Mainframe Computers in large companies1990’s: Addition of PC’s & rack based Servers

Telecom Fixed & MobileBeginning of Web Hosting

2000’s: Addition of Large Internet Hosting SitesMajor Co-Location Sites

Next Cloud Computing & Who Knows !


Projection of product heat loads in the data center

Load w/m2

Relative contributions to the total thermal output of a typical data center


Survey data regarding the design and actual power density of data centers


Different definitions for data center power density provide different values when applied to the same data center


Rack load densities & Server Room Temperature & HumidityRack Load densities• Typical racks have an IT load of 2-3 kW [ racks not full]• Typical racks if full have an IT load of 3.5-4.0 kW• Typical high density rack has an IT load of 8.0 kW• Latest “ Cloud Computing “ racks have an IT load of 8.0 kW • These values would give a cooling load per m2 of data centre of 500W/m2 to 1500W/m2• There are higher rack load densities but data here is typical average.Server Room Temperature & Humidity• Typical design is 22C & 50%RH • If 26C, 0.5 to 1.0% more power consumed but 5-10% greater cooling efficiency


HVAC & Room Design


Precision Air Conditioning Key Product Design• Application / Misapplication• Internal Design Conditions• Air Distribution• Cooling Load• SHR [Sensible Heat Ratio]• Flexibility• Redundancy• Outside Air• Circulated Air• Vapour Barriers

Airflow & Airflow Issues

Commissioning and Service Close Control AC Units• Once Sufficient Cooling in terms of Close Control units is installed in a room, the critical issue is to ensure that all the air is directed to the load & back from the load as efficiently as possible.• Best idea is to look at Hot Aisle / Cold Aisle layout as benchmark along with main ideals which will be explained.• Utilize proper spacing of the cold aisles. 1200mm wide with two full rows of tiles with can be removed. All perforated tiles are only located in the cold aisle• Utilize proper spacing of the hot aisle. Minimum 900mm width. Do not place perforated tiles in the hot aisle.

• Establish minimum raised-floor height of say 400mm. Recommended 600mm to 700mm if there are serious airflow blockages.

• Establish a minimum clearance of 900mm from the top of the cabinets to a ceiling.

• Place cooling units at the end of the equipment rows & aligned with hot aisles where possible.

• Both Hot & Cold Aisles can be contained / enclosed for better supply or return air to / from Close Control units.

Commissioning and Service Close Control AC UnitsCRAC units should be placed perpendicular to hot aisles so that they discharge cool air beneath

the floor in the same direction.

Airflow pattern for raised floor configuration with hot aisles and cold aisles

• For higher load densities, the aisles can be contained• Contained aisles have a roof & doors at either end

• Both cold aisle & hot aisle containment are available but cold aisle containment is more common


• For higher load densities, the aisles can be contained• Contained aisles have a roof & doors at either end

• Both cold aisle & hot aisle containment are available but cold aisle containment is more common

Cold / Hot Aisle Containment


• Require cabinet door faces to have a minimum of 50 %open perforation, 65 % is better.

• Prevent hot air recirculationby sealing the front of cabinets with blanking plates, including empty areas in the equipment mounting surface & between the mounting rails.

Effect of installation of blanking panel on server air inlet temperature

Seal all penetrations in the subfloor and perimeter walls under raised floor

and above the false ceiling.

Seal all cable cut-outs and other openings in the raised floor.

Spread power cables out on the subfloor, preferably under the hot aisle to minimize airflow restrictions


Systems & Technologies for Cooling

Commissioning and Service Close Control AC UnitsCooling System Types

System types available to cool servers are :Floorstanding room cooling units & in row rack cooling units Floorstanding Room Units• Traditional unit type used & proven technology over 40 years• Units are available in Air Cooled DX, Water Glycol Cooled DX & Chilled Water.• Additionally units can be configured for freecooling with additional water based coil.• Chilled water units can be fed water from chillers + drycoolers or freecooling chillers• Type dependant on project site, services available, Summer and Winter ambients.

Commissioning and Service Close Control AC UnitsAir Cooled DX Compressor Units• 90% of cases on small projects.• Stand alone, can generally operate in most ambients [ -30C to +50C Limit].• Pipe runs can be up to about 80m• Available from 5 kW to 100 kW• Still typically running on R407C but R410A becoming available giving better COP’s• Condenser should never be located below the indoor unit.• Dual cooling with chilled water also an option.Water/Glycol DX Compressor Units• Good for very long pipe runs, 80m+.• Good for ambients below -30C • Available from 5 kW to 100 kW• Drycooler can be below indoor unit ie. basement car park etc.• Good if difficult to locate multiple condensers in a large project.• Easy to locate Drycooler in least noise sensitive area of site. • Easy to install and also water based freecooling option for low ambients.

Commissioning and Service Close Control AC UnitsChilled Water & Freecooling Chillers• Large projects or guaranteed chilled water available.• Freecooling Chillers or Chillers with Drycoolers feeding indoor room units.• Available from 5 kW to 140 kW.• 0-10V cooling output

Rack Cooling Units• Available in chilled water & DX air cooled• Typical footprint of 300mm wide x 48U deep x 2000mm high• Typical cooling capacity of 15 – 30 kW• Biggest advantage is vertical top to bottom cooling of rackLatest Technologies - Energy Savings• EC backward curved plug fans • Electronic expansion valves• VSD compressors• Digital scroll compressors


Energy Saving Techniques

Energy Saving - Close Control Units• Freecooling by water based coils added to DX closed circuit units with drycoolers outside room • Freecooling chillers• Drycoolers in series with standard chillers • Backward curved EC plug fans to move the air• Electronic expansion valves in DX units.• VSD compressors or digital scroll compressors.

Energy Saving - Close Control Units

• Direct freecooling by air

• Indirect freecooling by air

• Freecooling by water / drycooler

• Adiabatic cooling

Freecooling - DX Water Coil, Chillers & DrycoolersDX Water Coil• For DX units, freecooling available depends on local outdoor ambient temperature.• Units can provide any amount of freecooling available & compressor can run to provide the balance.• Need to be careful not to circulate water too cold as this will result in latent cooling Chillers & Drycoolers• Freecooling available depends on the outdoor ambient temperature & the inlet design water temperature on the indoor chilled water unit. • The freecooling side of the chiller or drycooler system provides the freecooling & the chiller compressors can run to provide the balance

EC Direct Drive Plug Fans• Available instead of forward curved belt driven fans & AC plug fans. • The EC plug fan is a backward curved fan using a 0-10V control output. • EMI & RFI Built in.• Soft Start by default.• Overload protection built in.• Reverse polarity protection built in.• Locked rotor motor protection built in.

EBM Papst R3G 500 EC Plug Fan

Unit in Test Lab Punker R63A2 BCR AC Plug Fan

Motor Amps vs Airflow


Additional features in Close Control Units with EC fans• 3 fold additional energy efficiency in that no belts, backward curved & not forward curved & EC motor acts like DC circuit.• Unit is set up with a discrete fan speed based on a fixed 0-10V output to the EC motor based on the design point of operation of the fan. This is the default setting on units shipped.• Unit set up to track the cooling control temperature band with set voltage limits whereby max voltage / fan air volume is at set point plus control band & min voltage / fan air volume at set point. Max air volume is typically design air volume & min air volume is around 60% for chilled water units & 75% for DX units.


• Unit set up to give a reduced fan air volume in dehumidification mode to conserve energy in dehumidification while quickly achieving the dehumidification effect at the cooling coil. This output voltage is again user selectable. • Unit is set up via an underfloor pressure transducer to give a fixed underfloor pressure all the time. Underfloor pressure setpoint is a Pa input through the unit user display.• In rooms where there are units in standby, letting all units run all the time reduces the fan energy of the installation as reduced air through the unit gives a reduced system resistance & fan power. If a unit fails, a pressure transducer runs the remaining units at 100% design airflow.• Unit is setup with an additional temperature sensor in the cold aisle & this sensor has an additional control band which can vary unit air volume & guarantee cold aisle supply air temperature, air volume & pressure.


Running Standby Units

Typical Setup : * 4x units, 3x run + 1x standby* 3x 100% powerEnergy Saving Setup : * 4x units run at 75% airflow & 75% design speed.* Using fan laws where power is speed cubed, new setup is 168%* Saving in fan power 44%

Electronic Expansion Valves

• Available instead of standard mechanical TXV valves.

• Servo controlled electro mechanical device.

• Expands refrigerant flow in variable manner

• Precision modulation of refrigerant flow through unit microprocessor


• Superheat setpoint set through unit display & controlled via pressure & temperature sensors on evaporator outlet.

• Setpoint maintained even as operating conditions or season changes.

• Superheat control more precise & stable than standard TXV.

• Around 400 points on valve travel.• Only 2x valve sizes required for 10-100 kW range.• Compatable with all refrigerants & refrigerant selected

through controller.

• Lower superheat setpoint increases capacity due to the increase in evaporator pressure and better use of the exchange surface of the evaporator.• Compressor reduced run times can save up to 20% of compressor power

VSD Compressors

• Variable Speed using a VSD• Capacity control from 30 – 90 Hz• EMI & RFI Built in.• Soft Start by default.• Overload protection built in.• Optimum efficiency• Less on/off compressor cycles• Longer life expectancy• 20% energy saving over on/off

VSD Compressors

Digital Scroll Compressors

• Digital modulation based on PWM• Constant Speed• Start/stop compression • Scroll sets separated axially over time• Capacity control from 10% - 90% • Optimum system efficiency• Less on/off compressor cycles• Longer life expectancy• 20% energy saving over on/off

Commissioning and Service Close Control AC UnitsDigital Scroll Compressors


Classic Unit Problems


Overcooling in Dehumidification Mode• Unit Reheat designed for coil latent load only & kW is small relative to unit cooling kW. • Unit Requires load in room.• Unit in dehum DX or CW go to maximum cooling in dehumidification.• Unit hits low dehumidification temperature limit & dehumidification stops.• Room never in %RH tolerance.

No load Upflow Applications• Labs, Record Stores, Museum’s etc.• Specifier chooses CRAC DX units with electric reheat• Unit has no load & relies on itself for load• Unit has “on/off” cooling/heating/dehum. Functions• Unit has mismatched cooling & heating• Room TH charts erratic & poor TH control


Shallow Floor Voids• Floor voids of less than 400mm should be avoided.• If possible run piping & cables parallel to airflow.• Ideal void is 600mm • The bigger the room, the larger the circulated air volume & therefore the larger the void

the better.Drain Pipe Material• In units with Humidifiers, drain pipe should be in copper.• In poorly specified & smaller jobs, I have seen drains collapse due to use of 70 °C rated plastic pipe.

Inadequate Service Access• In general, service access should extend the unit length on front & one side by 600mm.• If possible provide unit access on both sides.• Spread units apart & do not clutter together. This is also better for air distribution.


Impossible Noise Specs• Some project specs expect to get NC 30 in the data space.• This is generally impossible as CRAC applications are the only applications where

the noise source is in the room.• All normal CRAC units are 55-65 dBA SPL freefield at 3m.• In a genuine low noise occupied CRAC application, use Chilled Water units uprated by 1 or 2 unit sizes ( next fan size) running at the lower fan size RPM. In Chilled Water units this is cost effective & less expensive than it seems.

Fresh Air• As a rule, no fresh air to the units !• If unavoidable then maximum 5% of unit volume or 8-10l/s per person & not ACR based.

• Winter is the worst problem as the humidifier cannot cope.• In large data rooms, use a separate full function AHU to put air into the data room atCRAC unit set point condition & create a positive pressure of approximately 12.5 Pa.

Commissioning and Service Close Control AC UnitsHumidifier Water Problems• All unit humidifiers require raw water the characteristics of which may betotally different yet the sources may only be a few miles apart.

• 1 or 2 times a year we experience a problem site.• If possible & in particular on large project, raise the issue of having the feed water tested.

2 Port vs 3 Port Control Valves• In 2 port chilled water units, ensure that the valve differential close off pressure is

sufficient to overcome the system hydraulic pressure. Max pressure 4 bar.• The larger the index pipe run, the more the pump must work to guarantee flow

to the last unit which puts the greatest pressure on the first unit.• There should also be a system bypass to ensure that the pumps don’t trip on no load. Duty/Standby Ducted Upflow Units• On ducted duty/standby units on common ductwork, it is important to use backdraft

dampers or motorised dampers so that the air does not short circuit to the standby unit.


Project Examples

Client : Sandia Laboratories, Albuquerque, New Mexico USA. Project : Red Storm Supercomputer Installation : Phase 1 : 3,500 kW Downflow CW Units.

Phase 2 to follow with 5,200 kW of additional units

Installation date : July 2004Additional Note :* 1,000,000 m3/hr of air into floor* Raised Floor 900mm clear* CRAY Computers. ( www.cray.com)* Currently 17th fastest supercomputer in the world ( was fastest in 2004 )

Rank Site Computer

1 DOE/NNSA/LLNLUnited States BlueGene/L - eServer Blue Gene SolutionIBM

2 Oak Ridge National LaboratoryUnited States Jaguar - Cray XT4/XT3Cray Inc.

3 NNSA/Sandia National LaboratoriesUnited StatesRed Storm - Sandia/ Cray Red Storm, Opteron 2.4 GHz dual coreCray Inc.



Client : IBM, Copenhagen, DenmarkProject : Maersk Worldwide Shipping OperationsInstallation : 2,500 kW Downflow CW Units in 6x Basement

Server RoomsInstallation date : July 2002Additional Note :* Indoor units run on 12/18C chilled water.* Drycoolers run in series with YORK chillers providing approx 70%

freecooling year round.* Currently upgrading all units to EC fans

Client : B Sky B, Southampton, UK.Project : Backup broadcasting facility for Sky TV Network Installation : 2,700 kW Downflow CW Units Basement &

Grd floor Data Rooms. 200 kW Downflow CW Units for Robots loading movies for movie channels 300 kW Downflow CW Units for manned broadcast area

Installation date : July 2004Additional Note : Building is only for standby in case of full failure


For more information concerning YORKClose Control Products please contact :

Mr. Ciaran Coughlan - Director , Sales & MarketingEDPAC International - Cork, IrelandPh : + 353 - 21 - 4372850Fax : + 353 - 21 - 4373975E-mail : [email protected] Site : http://www.edpac.com

Close Control Air Conditioning Products Cooling Server Rooms

Documents