Passive RDHx as a Cost Effective Alternative to CRAH Air Cooling

Jeremiah Stikeleather

Applications Engineer

Passive RDHx as a Cost Effective Alternative to CRAH Air Cooling

While CRAH cooling has been a common data center cooling solution, OPEX for RDHx cooling can be better at minimizing today’s energy consumption and operating costs. This will have increasing significance as we look to the future and interest in sustainability grows.

Agenda

• Industry Terminology

• Benefits of the Passive Rear Door Heat Exchanger

• The Study: Comparing 3 Cooling Designso Traditional CRAH Units

o RDHx’s with a Primary Piping Manifold

o RDHx’s with CDU’s and a Secondary Water Loop

• Summary of the 3 Design Alternatives

Industry Terminology

CRAH – Computer Room Air Handler

CRAC – Computer Room Air Conditioning

RDHx – Rear Door Heat Exchanger

IRC – In Row Cooler

CDU – Coolant Distribution Unit

CAPEX – Capital Expenditure

OPEX – Operating Expense

Close Coupled Cooling – Cooling that is adjacent to server racks

Greenfield Building – Construction of a building on greenfield land where there is no work constraints

Front of Enclosure

Rear of Enclosure

Benefits of the Water-Cooled Passive Rear Door Heat Exchanger (RDHx)

• Takes up very little space

• Air-to-Water Heat Exchanger

• Close-coupled cooling solution

• Removes the heat at the source

• Very little energy required

• Significant energy reduction versus a typical CRAH solution

• Heat exchange process occurs at rear of the rack

• Water thermal capacity is 3400 times greater than air

• Significant reduction in maintenance costs

93°F

72°F

91°F

73°F

Benefits of the Water-Cooled Passive Rear Door Heat Exchanger (RDHx)

The Study: 3 Cooling Designs Designs Compared:

• Design 1 – Traditional 30-Ton CRAH Units

• Design 2 – RDHx’s with a primary piping manifold system

• Design 3 – RDHx’s with Coolant Distribution Units

and secondary water loop

Study includes:

• All aspects of deploying solutions in a 1 MW Data Center

• Supply and installation of cooling system

• Electrical connections, valves, piping

• Building monitoring integration system

• Leak detection, smoke/fire detection

• Condensate removal

The Data Center Configuration:• 1 MW of IT power in a raised floor environment

• 5,000 sq. ft. white space

• Planned deployment of 177 IT enclosures

• Infrastructure for a space loading of 200 watts /ft2

• 28 ft2 per IT enclosure (assume 5.7 kW / rack)

The Benchmark Air Cooling System:

• Chilled water Computer Room Air Handlers (CRAHs).

• (12) 30-Ton operating units around perimeter

• CRAH unit air discharge temperature 68°F to 70°F

• Two additional CRAH units installed for redundancy

• Cold air discharged under an 18 inch raised floor

• Hot aisle-cold aisle arrangement

The Benchmark Air Cooling System:

• CRAH running at a reduced load of 80% (4.6 kW)

• Chilled water for the CRAHs (100% water, no glycol)

• Branch connected from a main chilled water loop running external to the white space

• Chiller, water supply, and related energy costs not included in any of the cooling designs

Design 1 – Traditional CRAH Units

Fourteen 30-Ton CRAH units• 12 active, 2 standby

Assume 25% CRAH performance reduction• Large area with unpredictable airflow

• Obstructions (columns, cable runs, etc.) alter airflow

• Wasted air (openings in tiles that do not provide direct access for rack intake)

White space consumption and the required service clearance is factored in

• Footprint required by CRAH system complicates future expansion of IT enclosures

Design 1 Summary – Traditional CRAH Units

Cost includes:

• Supply and installation of CRAH units

• Space fit-out

• Fire protection/suppression systems required for access and CRAH

footprint

De-rating published sensible cooling by 25% considered conservative

due to the

built-in inefficiencies of CRAH based air cooling systems

Power consumption much higher due to fans, humidification, and reheat

functions

Increased rack power density will force a change in cooling infrastructure

– more CRAHs, supplemental cooling, hot aisle/cold aisle containment

Design 1 – Traditional CRAH UnitsCost Summary

Design 2 – RDHx with manifold system• Dedicated chiller

• 177 RDHx

• Chilled water distribution from prefabricated manifold system

• 2 CRAH units for humidification control and room cooling backup

• CAPEX reduced by not using additional pumps or plate-and-frame heat

exchangers

Design 2 – RDHx with manifold system Piping manifold alternatives:

• Manifold and pump tapping into bypass/mixing line• (Manifold return water discharges back into the bypass)

• Manifold and three-way valve tapping into supply and return lines• (Mixing building return water with supply water to achieve higher supply water temperatures for

the RDHx)

• Similar to methods used in the radiant piping industry

Design 2 – RDHx with manifold system

Controls for the proposed system rely on supply air temperature

sensors for the racks and their corresponding RDHx that is

connected to the manifold, and a modulating control valve or circuit

setter at the manifold return

Design 2 Summary – RDHx with manifold

CAPEX comparable to CRAH design (Design 1)

OPEX for RDHx is minimal• (About 3% of the total power consumed by CRAH units)

RDHx units are passive

Small RDHx whitespace footprint • Reduce overall building footprint

• Greenfield project savings

• Construction savings for future expansion

RDHx ROI within first year of operation

Over 3x IT expansion, 5.7 kW to 18 kW / rack(RDHx nominal cooling capacity 18 kW)

Design 2 – RDHx with manifold system Cost Summary

Design 3 – RDHx with CDU and secondary water loop

• 4 Coolant Distribution Units (CDU’s)

• CDU is floor-mounted device – heat exchanger, pumps, controls, distribution manifold

• CDU connects to water from chiller (or cooling tower)

• 2 CRAH units (Humidity control and room cooling backup)

• No condensate (Temperature/humidity sensor regulates secondary loop temperature 2 degrees above dew point)

• The RDHx water loop is isolated from primary water loop

• CDU power consumption 3.7 kW each

Design 3 Summary – RDHx with CDU

• CDU increases CAPEX

• Low OPEX cost CDU pumps use 15% of power for CRAH units

• Break-even point is in Year 3

• Design 2 and 3 are “future proof”5.7 kW racks can grow up to 18 kW

Design 3 – RDHx with CDUCost Summary

Summary

• At 5 kW per rack, CAPEX for RDHx and CRAH cooling

approximately equal• (CAPEX could be further reduced by implementing alternating RDHx’s – CAPEX savings up to 25% compared to

populating each rack with an RDHx)

• OPEX is significantly reduced with RDHx designs

• Reduced energy consumption

• Reduced demand charges

• Reduced maintenance costs

• RDHx allows for future growth without new construction costs

• RDHx performs well with elevated water temperatures

• Minimizing chiller energy usage

• Reducing chiller OPEX

Summary

• OPEX savings increased using waterside economizers•(Free cooling window is increased using elevated water temperatures)

• Hybrid system including some CRAH units with RDHx adds redundancy for greater system availability

• Increasing rack density to 18 kW can minimize infrastructure space

(CAPEX savings 30-40%)

Study Conclusions

• A common misconception that liquid cooling is too expensive to deploy disproved

• CAPEX for liquid cooling and traditional air cooling is approximately the same at 5 kW / rack

• Increasing energy costs encourage data center owners and operators to consider liquid cooling

• Passive liquid cooling enables expansion and flexibility at a lower, incremental, capital expenditure

Future Considerations

• A similar study done by a 3rd party consulting

engineering firm is comparing RDHx’s to IRC’s

• 4 MW Data Center, 5000 sq. ft.

• IRC CAPEX $4.5M, 6 MW cooling capacity

• RDHx CAPEX $2.5M, 7.5 MW cooling capacity

Thank You

Patrick GiangrossoGeneral Manager

Coolcentricpgiangrosso@coolcentric.com

(603) 479-4806