# 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 | **Status** | **Current revision.** An earlier copy sits in [`superseded/`](../../superseded/) — see [Revision history](#revision-history) |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](bidmc-parquet-load-data-manual.md) 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/`](../../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](ucsd-equipment-manual.md). 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](../02-specifications/simulator-io-interface.md). 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](ucsd-equipment-manual.md) — the other case study's plant
- [BIDMC Datasets Manual](bidmc-datasets-manual.md) — the `hospital_communication_energy_system.csv` schema
- [BIDMC ComStock Load Profile](bidmc-parquet-load-data-manual.md) — the whole-building load proxy
- [Simulator I/O Interface](../02-specifications/simulator-io-interface.md) — the simulator contract these balances must satisfy
- [Rule-Based Controller](../02-specifications/rule-based-controller.md) — the dispatch logic in policy form