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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 HereSeismic 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.

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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 HereSeismic 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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