ALLSHIFT/docs/03-energy-management/bidmc-ucsd-energy-flow-and-balances.md

Energy Flow and Specifications for the Hybrid Hospital

Markdown report of a non-markdown source document.

Source	Shift Matlab Drive/Shift Matlab Drive/Energy_Managment/Beth Israel Deaconess Medical Center/BIDCM-UCSD hybrid hospital energy flow and balances.docx
Format	Microsoft Word (.docx), 162 kB
MD5	27a86f331086ce60c078b412d5205e5b
Owner	Energy Management cluster
Status	Current revision. An earlier copy sits in superseded/ — see Revision history
Report generated	2026-07-25

Note

The source document contains one embedded figure (Fig-1: Energy Flow Diagram) and twelve OOXML equations. The equations are transcribed below in plain notation. The figure is not reproducible in this report — open the original .docx to see it.

The document title spells the hospital "BIDCM"; the correct abbreviation is BIDMC (Beth Israel Deaconess Medical Center). Filename retained as-is for traceability.

Dispatch priority

Priority	Source	Mode	Purpose
Level 1	Solar PV	Sustainability	Normal daylight operations & storage charging
Level 2	Battery / H₂	Resilience	After-hours operations and bridging short gaps
Level 3	MATEP CHP	Reliability	Constant baseload and thermal support
Level 4	Eversource Grid	Redundancy	Last-resort emergency backup for critical areas

MATEP — Medical Area Total Energy Plant, the CHP plant serving the Longwood Medical Area. Eversource — the New England utility serving Boston.

Primary generation (daytime)

• Solar lead. Solar energy is the main source.
• Direct supply. Solar energy flows to the AC electrical bus (distribution point) to power the hospital immediately.
• The "deposit". Any electricity not needed by the hospital is diverted to charge the battery and run the electrolyzer.

Transition to storage (evening)

• Solar fade. Solar production stops.
• The "withdrawal". The battery is the first responder, discharging immediately to keep the bus powered. If the battery runs low, the hydrogen fuel cell activates, converting the stored hydrogen back into electricity.
• Baseload support. The MATEP CHP plant provides a steady stream of natural-gas-generated power to bridge any gaps.

The safety net (emergency)

• Grid activation. The Eversource grid stays on standby until a major failure occurs or on-site storage is depleted.
• Load shedding. To protect the most critical patients, the system pauses power to Tier 2 loads (HVAC, general wards, imaging) to ensure Tier 1 loads (ICU, operating rooms, life safety) stay running indefinitely.

Critical load management

Load tiers

Tier	Priority	Includes	Status in emergency
Tier 1	Critical	ICU, Operating Rooms (OR), Life Safety (fire/alarms), Critical Communications	Always on — guaranteed by battery, fuel cell, and grid
Tier 2	Essential	Clinical HVAC, Imaging (MRI/CT), Medical Wards, Critical Lighting	Shiftable — may be curtailed or cycled to preserve storage
Tier 3	Non-critical	Administrative Offices, Cafeteria, Gift Shop, Non-essential Lighting	Shed first — paused immediately during a grid emergency

Tier 1 — what should not go down. These systems are defined as never interrupted and are the only loads guaranteed during an emergency grid backup scenario: intensive care units (continuous monitoring and life-support), operating rooms (surgical equipment and critical environment controls), and life safety (emergency lighting, fire systems, critical communications).

Tier 2 — shiftable/interruptible. Considered essential but may be paused if on-site storage is depleted or during a grid emergency to prioritise Tier 1: building climate control (HVAC), diagnostic imaging (MRI, CT), and general wards.

Approximate power requirements

Derived from hospital_communication_energy_system.csv at 5-minute intervals:

Tier	Average per interval	Approx. continuous	Note
Tier 1 — Medical Equipment	~3.01 kWh	~36 kW	Baseline for patient monitoring and life-support machines that must never be interrupted
Tier 2 — HVAC & Clinical Support	~4.99 kWh	~60 kW	Largest single draw. Essential for patient comfort, but designed to be shifted when running solely on backup storage
Tier 3 — Lighting & Admin	~2.00 kWh	~24 kW	General lighting and non-clinical support. First area reduced in "Energy Saving Mode"

Warning

These figures come from a synthetic dataset (hospital_communication_energy_system.csv, 10,000 rows covering 2025-01-01 to 2025-02-04) that represents a single patient room snapshot per row, not whole-hospital totals. The ~36/60/24 kW figures are therefore not whole-building loads. For comparison, the NREL ComStock hospital profile puts a comparable 500,000 sq ft hospital at 8,026 MWh/year ≈ 916 kW average. Treat the tier split as a ratio (roughly 26% / 44% / 18% by these numbers), not as absolute magnitudes.

Energy balances

Overall balance

P_solar(t) + P_CHP(t) + P_Grid(t) + P_FuelCell(t) + P_Battery_discharge(t)
      = P_Load(t) + P_Battery_charging(t) + P_Electrolyzer(t)

where P_Load is the sum of all tiers (Tier 1 + 2 + 3) and P_Grid is typically zero unless there is an emergency.

Battery storage — state of charge update

                    P_Battery_charging(t) × η_charging × Δt      P_Battery_discharging(t) × Δt
SoC(t) = SoC(t−1) + ────────────────────────────────────────  −  ─────────────────────────────
                                   E_cap                             E_cap × η_discharging

where η are the round-trip efficiencies and E_cap is the total energy the battery can store when fully charged (kWh). SoC(t) should remain between its min and max values.

Hydrogen loop

Electrolyzer (charging):

                    P_Electrolyzer × Δt
m_H2_produced = ─────────────────────────
                 LHV_H2 × η_electrolyzer

Fuel cell (discharging):

                     P_FuelCell × Δt
m_H2_consumed = ─────────────────────────
                  LHV_H2 × η_fuel_cell

Hydrogen tank balance:

Mass(t) = Mass(t−1) + m_H2_produced − m_H2_consumed

where LHV_H2 is the heat released by combusting a given amount of hydrogen — approximately 33.3 kWh/kg, or 120 MJ/kg.

Load tier dispatch logic

• If P_available ≥ P_Total_Load → all tiers are powered
• If P_available < P_Total_Load → shed Tier 3 (not critical)
• If P_available < (Tier 1 + Tier 2) → shed Tier 2
• P_available must always exceed Tier 1, as it is critical

KPI formulae

Self-Sufficiency Rate (SSR)

      Σ (P_solar + P_CHP + P_FuelCell + P_Battery_discharge)
SSR = ───────────────────────────────────────────────────── × 100
                         Σ P_Load

Grid Dependency Ratio — aiming for 0% in normal operation

       Σ P_Grid
GDR = ────────── × 100
       Σ P_Load

Critical Load Uptime — aiming for 100%, showing critical points have power at all times

       Total hours of full Tier 1 powered
CLU = ──────────────────────────────────── × 100
             Total hours in period

SoC Violation Rate — aiming for 0%, so the battery never goes dangerously low (risking loss of Tier 1 load) or overcharges (risking hardware damage)

       # of intervals where SoC < SoC_min or SoC > SoC_max
SVR = ──────────────────────────────────────────────────── × 100
                        Total intervals

Revision history

Two copies of this document exist in the repository with different content:

Location	Size	MD5	Status
Energy_Managment/Beth Israel Deaconess Medical Center/	161,868 B	27a86f33…	Current — this report
Energy_Managment/ (parent folder)	161,536 B	(differs)	Superseded

The only difference: the current revision adds the SoC Violation Rate KPI and its target. Everything else is byte-identical in content. The parent-folder copy is retired to superseded/.

Notes on scope

The title and content mix two case studies. The dispatch chain described here — MATEP CHP, Eversource grid, Boston — is BIDMC-specific. UCSD's microgrid uses entirely different plant (a 2.8 MW molten-carbonate fuel cell, 30 MW of gas turbines, a 2.5 MW / 5 MWh BYD battery) documented separately in the UCSD Equipment Manual. The "hybrid" in the title refers to combining lessons from both sites, not to a single physical plant.

Note also that this document's three-tier load model does not match the two-way L_crit / L_noncrit split in the Simulator I/O Interface. Mapping Tier 1 → critical and Tiers 2+3 → non-critical is the obvious reconciliation, but it has not been written down anywhere as a decision.

Related

• UCSD Equipment Manual — the other case study's plant
• BIDMC Datasets Manual — the hospital_communication_energy_system.csv schema
• BIDMC ComStock Load Profile — the whole-building load proxy
• Simulator I/O Interface — the simulator contract these balances must satisfy
• Rule-Based Controller — the dispatch logic in policy form