DOE Data Center Air-Management (AM) Tool: Engineering Reference, Version 3
Lawrence Berkeley National Laboratory / ANCIS Incorporated · Lawrence Berkeley National Laboratory, ANCIS Incorporated
This 2023 document from LBNL and ANCIS describes the inputs and heat-balance calculations behind the DOE air-management tool. It relates equipment heat, air volume and temperature rise, and explains how bypass and recirculation affect cooling.
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Overview
The aim of air management is to keep cold and hot airstreams from mixing: cold supply air from the AHU should enter the IT equipment unmixed and hot exhaust should return to the AHU unmixed. From user input the tool gives air-management recommendations and the potential for lowering supply airflow and raising supply temperature; it estimates energy, cost and carbon savings for supply fans and chillers, plus on-site water use and simple payback.
The core of the calculation is the sensible heat equation: sensible heat transfer equals volumetric airflow times air density, specific heat and temperature change, and the tool treats density and specific heat as approximately constant. The tool uses four input sheets (AHU, equipment, RCI, main input) and two result sheets. The AHU sheet accepts up to 40 operating units and computes the Return Temperature Index (RTI).
RTI is delta-T(AHU)/delta-T(equipment), which equals total equipment airflow divided by total AHU airflow. 100% means balanced flow, above 100% net recirculation and below 100% net bypass. The Rack Cooling Index (RCI) measures how well intakes comply with the ASHRAE A1 recommended (18-27 degC) and allowable (15-32 degC) ranges; RCI-HI of 100% means no over-temperatures. The tool assumes stable conditions and mostly raised-floor halls with hot and cold aisles, and does not replace a detailed investment-grade audit.
Key points
- Sensible heat transfer = volumetric flow x density x specific heat x temperature change; the tool takes density and specific heat as approximately constant.
- RTI = delta-T(AHU)/delta-T(equipment) x 100 = equipment airflow / AHU airflow x 100; 100% balanced, above net recirculation, below net bypass.
- RCI-HI of 100% means no over-temperatures; RCI-LO of 100% means no under-temperatures.
- ASHRAE A1 recommended 18-27 degC (65-80 degF), allowable 15-32 degC (59-90 degF).
- The AHU sheet accepts up to 40 operating units.
- The tool has four input and two result sheets and is stated to be validated against CFD.
- Stable operating conditions are assumed; the tool does not replace an investment-grade audit.
Using it in design
- Calculate required sensible airflow from heat load with a stated temperature rise, air density and specific heat.
- Keep the airflow balance separate from proof that the room distributes air adequately.
- Use RTI to diagnose bypass and recirculation: consider cutting supply airflow below 100%, and removing recirculation above it.
- Track RCI after energy-saving measures to confirm the thermal environment has not degraded.
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Who should read it
Thermal designers optimising cooling airflow and supply temperature who need to measure bypass and recirculation.
Publication details
- Authors
- Lawrence Berkeley National Laboratory; ANCIS Incorporated
- Publisher
- Lawrence Berkeley National Laboratory / ANCIS Incorporated
- Year
- 2023
- Document number
- AM Tool Engineering Reference v3
- Document language
- English
- Source type
- Government / public
- Access
- Free to read
- Licence
- Copyright retained; citation only — the publisher’s terms apply to the original document
Citation
Lawrence Berkeley National Laboratory; ANCIS Incorporated (2023). DOE Data Center Air-Management (AM) Tool: Engineering Reference, Version 3. Lawrence Berkeley National Laboratory / ANCIS Incorporated. AM Tool Engineering Reference v3. https://datacenters.lbl.gov/sites/default/files/2023-03/DOE%20AM%20Tool--Eng%20Reference%20v3%20%283-15-2023%29.pdf
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