Dear Forum Members,
We are currently working on a multi-phase data center project pursuing LEED v4 BD+C: New Construction certification as a single combined project across all phases. The overall development consists of four data center blocks, each with independent HVAC systems, and design for the first block has recently commenced.
The facility is functionally divided into:
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Critical areas: data halls and electromechanical rooms (e.g., IT rooms, battery rooms, PDU rooms).
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Non-critical areas: office spaces.
Project highlights:
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Data halls are served by air-cooled chillers.
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Electromechanical rooms are housed in modular steel containers, which are fully conditioned.
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Some of these containers are served by Precision Air Handling Units (PAHUs) connected to the air-cooled chiller system.
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Others are equipped with standalone DX systems.
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Office areas are conditioned using VRF systems.
We are seeking guidance on the following questions related to the baseline HVAC system assignment and use of the exceptional calculation method, as per ASHRAE 90.1-2010 Appendix G:
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Baseline HVAC System Type Determination:
Since the project will be certified as a single LEED project, should the baseline system be selected based on the total combined conditioned floor area of all four blocks, or should it be determined individually per block, considering each has its own HVAC system? -
Treatment of Modular Container Rooms:
The electromechanical spaces inside modular steel containers are served by a mix of systems — some with PAHUs connected to the central air-cooled chillers, and others with dedicated DX units. Should these spaces be considered in determining the baseline system type, or do they qualify for modeling under the exceptional calculation method, given their modular nature and system diversity? -
Applicability of Exceptional Calculation Method:
In a data center project, office spaces are typically regarded as non-predominant areas. However, the containerized electromechanical rooms, although critical in function, may also be non-predominant in area. Should the exceptional calculation method be applied to the office areas, the electromechanical rooms, or both? -
COP Comparison – Baseline vs. Proposed Systems:
Based on the current modeling approach, the baseline has been identified as System 6 – Packaged VAV with reheat, which requires a minimum full-load COP of 2.84 for air-cooled systems, per ASHRAE 90.1-2010 Table 6.8.1A. The proposed air-cooled chillers have a minimum full-load COP of 2.80, which offers limited improvement over the baseline. Given this narrow margin, what modeling strategies can be adopted to demonstrate meaningful energy savings — for example, can part-load performance (IPLV/NPLV), redundancy, or load profiling be considered?
We would greatly appreciate insights from the community or project teams who have handled similar configurations in data center projects, especially under LEED v4.
