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Best Practices in HVAC Design/Retrofit

Little Server Room – BIG $AVINGS

Justin Lewis, P.E., LEED AP, DCEPSr Energy Project ManagerC:530.400.6042 | O:530.754.4870 | jlewis@ucdavis.edu

What’s the problem here?

Hot Exhaust Here Seismic Brace Here

Not Enough room for a ventilation tile

New computers placed with inlets facing exhaust.Plate leaned against rack to direct cold air into computer inlets

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What’s a Data Center?

Enterprise Data Center – Focus on cost and uptimeBackground on the Speaker:

I helped save 11 enterprise class data centers and colocations around the country a total of 19.5 million kWh while working for SynapSense as a Sr. Field Engineer.

Today I’ll share those techniques.

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This is a “Server Room”Grad Student built “Super Computing Center” – Focus on “Get it working.”

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Servers put out a ton of heatand need cooling or they break

My experience has been server racks are more typically in the 6-12 kW rangeThat is still 1.7 to 3.4 tons of cooling per rack.

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They also compute

How to Optimize the Data Center’s HVAC

• Optimize the heat equation• Reduce fan speed• Increase delta T

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Old Conditions• Setpoints: 65°F, 50%RH

±5%• Coils have low Delta T• Hot and cold spots• Unbalanced ventilation

Optimization Opportunities

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New Conditions

• Setpoints: 80.6°F, RH 10%-80% • Coils have high Delta T• Hot aisles Hot, Cold aisles Cold• Balanced ventilation

• 2011 ASHRAE recommends inlet conditions to servers be:• between 64.4 and 80.6 °F, and dew point between 41.9 and 59 °F

• Typical Server Specs (Dell PowerVault MD3000)• between 50 and 95 °F, and RH between 20% and 80%

Q = 1.08 * (Air Flow) * (Temp)[BTU/hr] [CFM] [oF]

Divide by 12000 to get [Tons]Divide by 3412 to get [kW]

1 kW = 1.08 * (150) * (20°)For Example:

Heat Equation for Air

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Goal: Raise return temps to at least 80.6 °F

Q = 1.08 * (Air Flow) * (Temp)For every 10% reduction in fan

speed

An increases temp rise by 10%

Fan Affinity Law: Power% = (Speed%)^3 (…really more like 2.5)Flow%=Speed%

Slow Fans Down Reduce Air Mixing

Heat remains constant

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equal$Decrea$e power of 25%

Implement Hot/Cold Aisle

• Orient Equipment to have common intake and exhaust directions to reduce hot air mixing with cold air. 10

Return Plenum

Reduce By-Pass Air

• Don’t over blow cold aisles• Block penetrations outside of cold

aisles • (Power/Data penetrations)

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Manage Recirculation

• Use Blanking panels• Manage air to keep top servers below

~80.6 °F 12

< 80.6°F

Servers aren’t that sensitiveYMMV (your may vary)

7 months of no mechanical cooling, no air filtering, no humidity control-date: 2008 13

Servers aren’t that sensitiveYMMV

-date: 2008

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What UCD did in their Server Room

• Area: 125,810 sqft• Load: 31.3 tons cooling≈ 110 kw plug load

• Approximately 37 populated racks. 46 capacity

• improved ventilation (delta t of 12 to 20°f)

• by removing the over provisioned tiles• by balancing the air to top server

intake temperature to below 80 °f• plugging holes• installing controls in the returns• installing pressure controls in the floor • control fan speed to maintain hottest

return temp

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Why a pressure sensor?3kW = 1.08 * (476) * (20°)

[CFM]

[oF]

1x perf = 3kw1x Grate =

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Results Graphs

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Old “Economizer” Mode

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New Economizer Mode

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Delta T Rose

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Fan Power Reduced 78%

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Challenges: Communication Culture Change

• In a culture of only answering maintenance calls, it’s hard to sell a higher touch continual optimization process. Set it and forget it is the norm.• Communication Silos: IT services has not had

to check with HVAC in the past.

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What’s the problem here?

Hot Exhaust Here Seismic Brace Here

Not Enough room for a ventilation tile

Better Solution:Better hot/cold aisle planning. Disconnect seismic brace, move rack, or just move some cardboard boxes on the adjacent rack.

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New computers placed with inlets facing exhaust.Plate leaned against rack to direct cold air into computer inlets

What we did… in summary• Improved air flow by blocking leaks and orienting servers

Hot/Cold Aisle• Balanced air to servers so tops of servers were below 80 °F• Placed return grills and temperature sensors in hot aisles • Control supply temp to a constant temperature (57 °F)• Control supply fan speed to maintain hottest return temp is

<82 °F• Control return fan to maintain room pressure only

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Looking Ahead• Virtualization – Eliminate 80% of your plug load.• Fanless cooling – Oil bath, Chilled plate.• Outsourced Computing – Cloud providers may offer

computing power and storage cheaper than the cost to maintain onsite servers.

Until then… I suggest you implement these easy improvements

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Questions?

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