CASE35 · Buildings · eQUEST / Appendix G
Comparing LEED energy cost and site energy in a mixed-use building model
A historical ASHRAE 90.1-2004 Appendix G comparison models the proposed mixed-use design against four rotated baseline buildings. District-heat absorption cooling improves cost performance while increasing site energy.
01 · CASE ANALYSIS
Performance-rating objective
Translate architectural, mechanical and electrical drawings into the proposed model. Generate a separate baseline under the historical rating method and compare annual utility cost and peak demand.
Functional use, occupancy and process loads remain comparable so that design effects can be interpreted.
02 · CASE ANALYSIS
Baseline construction and quality checks
The source used Climate Zone 4A, 40% baseline window-to-wall ratio, sizing multipliers of 1.15 for cooling and 1.25 for heating, and rotations of 0°, 90°, 180° and 270°.
Review verification reports, unmet load hours, end uses, peak demand and plant loads. These describe the project method at that time rather than current LEED submission rules.
| Element | Proposed | Baseline |
|---|---|---|
| Envelope | Actual U-factor, SHGC and glazing area | Historical minimum performance; WWR 40% |
| Lighting | Actual space-level LPD | Historical space-by-space LPD |
| Office HVAC | VAV with reheat and four-pipe FCU | System 7: VAV with reheat |
| Hotel HVAC | Four-pipe FCU | System 2: PTHP |
| Cooling | District-heat absorption; COP 0.73 | Electric centrifugal; COP 6.1 |
03 · CASE ANALYSIS
Why energy sources change the result
The proposed design used single-effect district-heat absorption chillers with COP 0.73; the baseline used water-cooled centrifugal electric chillers with COP 6.1.
Reduced electric cooling energy does not establish reduced total site energy when purchased heat increases. Fan, pump and heat-rejection loads also require separate review.
04 · CASE ANALYSIS
Rating result
Proposed annual energy cost was approximately USD 3.574 million versus USD 3.721 million for the average baseline, yielding approximately 4.0% improvement. Process energy cost was approximately 25.27% of baseline cost.
Proposed site energy was approximately 139,539 MBtu/year versus 102,348 MBtu/year, approximately 36.3% higher. The modeled cost benefit and site-energy increase are both retained.
| Indicator | Proposed | Baseline |
|---|---|---|
| Energy cost | USD 3.574 million | USD 3.721 million |
| Site energy | 139,539 MBtu | 102,348 MBtu |
| Interior lighting | 2.78 GWh | 4.64 GWh |
| Electric space cooling | 0.12 GWh | 2.29 GWh |
| Interior fans | 3.07 GWh | 3.27 GWh |
| Pumps | 2.36 GWh | 1.16 GWh |
| Heat rejection | 0.286 GWh | 0.163 GWh |
| Purchased heat for cooling | 56,494 MBtu | Not applicable |
05 · CASE ANALYSIS
Engineering interpretation
Interior lighting fell approximately 40.1%, while pumps and heat rejection increased approximately 103% and 76%. These opposing changes make end-use analysis essential.
A simulated rating is a design comparison, not a measured operating result or confirmation of certification.
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