The Landlord's Chiller: Modeling Shared and District Energy Systems
A 200,000 ft² mixed-use building contains 150,000 ft² of office tenant space and 50,000 ft² of retail. The office tenant is pursuing LEED ID+C. Heating comes from a district steam system; cooling comes from a central chiller plant owned by the landlord, and the tenant's lease includes HVAC in the rent. The tenant pays electricity only for lighting and plug loads. The project's energy model shows 6% cost savings against an ASHRAE 90.1 baseline, below the 15% the team targeted. To improve the result, the modeler proposes to exclude the central chiller plant and district steam from the proposed model because the tenant does not control them, and to model only lighting and plug loads. The landlord will not share plant efficiency data but will provide monthly building-level utility bills. The project is two months from construction review.
1. Is excluding the landlord-controlled central plant from the energy model acceptable? Explain the principle.
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No. The governing principle is that the energy model must represent the energy the project actually consumes, not just the energy the tenant controls or pays for directly.
- HVAC included in rent is still HVAC consumed by the project. Removing it from the proposed model while leaving it in the baseline is not an optimization-it is a comparison of two different buildings.
- The proposed result would show large savings because the largest load has disappeared, not because anything improved. That is precisely the pattern a reviewer is trained to catch.
- Control is a different question from consumption. The tenant's lack of control is relevant to lease negotiation and to how systems are documented, not to whether their energy counts.
If the team submits a lighting-and-plug-only model, expect a prerequisite challenge and a likely denial, which costs more schedule than the two months remaining.
2. What are the compliant options for modeling shared and district systems with the data available?
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There are several defensible routes; choose one and document it clearly.
- Whole-building model with allocation: model the full building, then allocate energy to the tenant by floor area, sub-metering, or an engineering method agreed in the narrative. Building-level bills support this approach even without plant efficiency data.
- Tenant-level model using rating-system guidance for leased space: include the tenant's HVAC energy, estimated from bills, run-hours, or temporary sub-metering, with the same method applied to the baseline.
- District energy: model the actual district system characteristics in the proposed case, and use the same district characteristics in the baseline. The intent is that district energy is neither artificially rewarded nor penalized-the comparison should isolate the project's measures, not the fuel source.
- Fill the data gap deliberately: install temporary sub-metering on the chiller and air handlers for a cooling season, or obtain a landlord letter with plant capacity, efficiency, and schedules. An engineering estimate with stated assumptions beats an unexplained omission.
Whatever route is chosen, the baseline and proposed models must treat shared systems consistently.
3. What prerequisite and credit risks does this create, and how should the team manage them before submittal?
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The risks are concentrated in prerequisites, which are pass/fail and therefore more dangerous than a lost point.
- Minimum energy performance: if savings are demonstrated only by omission, the prerequisite is at risk. Rebuild the model before submittal rather than responding to a review comment.
- Fundamental commissioning: systems serving the project must be commissioned within the project's scope. Where the landlord owns the plant, obtain the landlord's commissioning documentation or a letter defining responsibility.
- Measurement and verification: tenant-level metering or an agreed allocation method is needed to verify performance; a lease with HVAC in rent often has no tenant metering at all.
Management plan for the next two months:
- Request an interpretation early and in writing if the shared-system approach is ambiguous.
- Obtain the building-level bills and a landlord letter on plant operation and schedules.
- Install temporary sub-metering now-even a short measurement period strengthens the narrative.
- Write a model narrative that names every assumption and explains how shared energy was allocated.
- Consider a lease amendment giving the tenant access to plant data; it is often the cheapest fix and outlasts the certification.