Energy & Carbon Modeling
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Build and Calibrate the Initial Energy Model
The initial energy model was developed using the graphical interface DesignBuilder® with EnergyPlus as the calculation and simulation engine. Building attributes such as floor dimensions, lighting, plug loads, HVAC layouts, and detailed schedules were included in the model to reflect the general parameters of the existing building conditions.
Figure 7 – Energy Model Renderings
Through an iterative process, the energy model inputs were modified to align the calculated energy model outputs with actual building utility data (sample compound years as discussed previously).
The following resources were used in calibrating the energy model:
- Electric, steam and natural gas consumption.
- Electric and steam onsite generation.
- Information on HVAC operation and set points from the Facilities team.
- Actual Meteorological Year (AMY) weather data for a compound calendar year, sourced from White Box Technologies.
- WMO# 725053
- ASHRAE Climate Zone: 4A
- Onsite lighting and electrical survey of sample offices.
- Domestic hot water was calibrated using shoulder season heating loads.
- Window fenestration U-value and SHGC were estimated using construction descriptions matched with the software’s library data.
- Adjusted facade infiltration to improve accuracy of heating demand during the Winter.
Figure 8 – Energy Model Calibration
It should also be noted that the building’s cogeneration plant was undergoing maintenance in May through July. These outages were deemed atypical; consequently, the calibrated energy model ignores this anomaly and was programed to match natural gas consumption during a typical year when the cogeneration plant is fully operational.
Create the Baseline Energy Model
To create a “baseline” model to serve as a starting point for further E/CRM modeling, the calibrated model was altered as follows:
- Weather data was changed to a Typical Meteorological Year (TMY3) file sourced from the modeling software library data.
- Recently completed projects, including the installation of a new chiller plant, were added to the model.
Generate Detailed End-Use Breakdowns - The baseline energy model outputs were utilized to determine the annual distribution of energy across building end uses. This analysis allowed the team to determine where there were opportunities for improvement.
Figure 9 – Annual End Use Breakdown
Figure 10 – Monthly Energy Breakdown by End Use
Analyze Individual ECMs
During the study, the project team identified nine (9) decarbonization strategies the building could undertake over the next 10-15 years. The energy modeler analyzed the ECMs through the baseline energy model to extract the associated energy, carbon and cost savings. As examples, below is a list of a few ECMs that the project team studied, with details on the energy modeling methodology used.
|ECM||Description||Summary of Energy Modeling Methodology|
|DOAS Conversion |
This measure includes the replacement of all office CV recirculating air handling units and perimeter induction units with 100% central outdoor air units with energy recovery wheels. All induction units and constant volume terminal units would be replaced with DOAS terminal units, similar to overhead fan-powered boxes, that locally mix outdoor air and return air to meet space set point temperature while also providing code-minimum ventilation airflow. Interior- and exterior-zoned DOAS boxes would be provided a cooling coil fed from the secondary chilled water loop for space sensible cooling loads; only exterior boxes would be provided a heating coil for overhead perimeter heating.
- 20% mixed-air AHUs serving interior office spaces and 67% OA AHUs serving perimeter induction units were altered to 100% OA AHUs with energy recovery wheels with the following effectiveness:
- Sensible: ƞ = 0.69 @ 75% airflow; ƞ = 0.67 @ 100% airflow
- Latent: ƞ = 0.60 @ 75% airflow; ƞ = 0.55 @ 100% airflow
- 100% OA units were sized based on the non-coincident ventilation requirement for all the spaces served.
- Fan static pressures were modified per the following static pressures:
- Existing interior AHUs serving CV boxes: 4.5” W.C. supply, 2.5” W.C. return.
- Existing exterior AHUs serving induction Units: 9.5” W.C. supply, 2.5” W.C. return.
- New 100% OA AHUs: 6 in. w.c. supply, 3 in. w.c. exhaust.
- New DOAS Boxes: 1.5 in. w.c.
- DOAS boxes were connected to the secondary chilled and hot water loops to provide overhead sensible cooling and perimeter heating.
- AHU operation schedules, EPDs, LPDs, and non-office spaces were held constant.
|High Performance Glazing |
The existing facade at PENN 1 consists of 6 mm single-pane vision glass and spandrel glass with 1” insulation. This measure incorporates replacing the single-pane vision glass with high-performance triple-pane insulated glazing unit (IGU). This measure assumed no improvement to the infiltration rate of the existing facade and no modifications to the existing window-to-wall ratio.
- The facade window openings were modified as follows:
- Existing Single-Pane: U = 1.022 SHGC = 0.6
- Outermost pane: Tinted 6mm glass
- New Triple-Pane IGU: U = 0.21 SHGC = 0.31
- Outermost pane: Clear 6mm glass
- Internal gas: 13 mm air gap
- Middle pane: Low-e coated 6mm glass
- Internal gas: 13 mm air gap
Figure 11 & 12 – Individual Energy and Carbon Reduction Measure Results
Group, Sequence, and Package ECMs
The project team initially explored two (2) packages of combined reduction measures to assess the impact of eliminating fossil fuels and electrifying the building’s heating end uses. Individual measures studied earlier in the project were selected and combined with additional infrastructure enhancements to develop two electrification packages summarized as follows:
- Beneficial Electrification: Incorporates a suite of Tenant, airside, and envelope upgrades along with the installation of air source heat pumps working in conjunction with the cogen plant to keep the building heated; eliminates all district steam resources.
- Full Electrification: Incorporates the same set of upgrades but utilizes more air-source heat pumps in place of the cogen plant.
The packages are comprised of the following measures:
The Full Electrification package created the best scenario for PENN 1 to become carbon neutral by 2040, with the assumption that the grid is decarbonized per the CLCPA requirements; however, the Beneficial Electrification package offered a more favorable financial outlook that could be more feasibly attained in the near term.
Figure 13 & 14 – Emissions Reductions & LL97 Impact with Electrification Packages
Establish the Final List of ECMs – The project team presented the electrification package results to a various stakeholders within Vornado, and while everyone agreed that that the initial set of ECMs would produce deep carbon emissions reductions, there were certain strategies that were deemed impractical after preliminary capital cost estimates were obtained.
Figure 15 – Phase 1 vs Phase 2 ECMs
At this point, the project team shifted its approach to the project. The team re-evaluated individual ECMs and electrification packages and adjusted measures to align with the following guiding principles:
- How can we re-use existing infrastructure?
- How can we electrify heating end uses affordably?
- How can we compress space requirements for electrification equipment?
- How can we take advantage of load shifting and smoothing for grid flexibility?
In addition, the team dialed in on the most impactful phasing of strategies to reduce capital costs, space requirements and infrastructure demand impacts through a Reduce, Recycle, Electrify framework.
Figure 16 – Resource Efficient Electrification Approach
The team generated a thermal dispatch model to optimize how the building’s loads are satisfied. The figure below shows how the various Phase II ECMs are deployed to meet the building’s heating demand on a winter day. Instead of eliminating steam and the cogeneration plan immediately, the team settled on a more measured approach which uses some district steam and cogen waste heat in the short term to avoid stranded assets, and then shifts to a substantially electrified building in the 2030 -2035-time frame.
Figure 17 – Thermal Dispatch Model
Generate a Decarbonization Roadmap
Once the finalized phase II ECMs were packaged, the energy model was run for each ECM package to obtain energy and carbon and cost impacts. The project team compared the results of this analysis and calculated the energy and carbon savings from the baseline model.
Figure 18 – Finalized ECMs & Packages
Figure 19 – Deep Decarbonization Pathway
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