3.2 Basis of Design (BOD) & Current Facility Requirements (CFR)

3.2 Basis of Design (BOD) & Current Facility Requirements (CFR)

Quick Summary: While the Owner's Project Requirements (OPR) defines what performance criteria the facility must satisfy, the Basis of Design (BOD) documents how the architectural and engineering design team plans to satisfy those requirements. In existing facilities undergoing retro-commissioning (EBCx), where the original OPR is almost always obsolete or non-existent, the Current Facility Requirements (CFR) serves as the operational baseline under ASHRAE Guideline 0.2-2015. Mastering the distinctions, review methodologies, and boundaries among these foundational documents is essential for the ASHRAE BCxP professional.

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1. Basis of Design (BOD): Definition, Ownership, and Purpose

Under ASHRAE Standard 202-2024 and ASHRAE Guideline 0-2019, the Basis of Design (BOD) is defined as:

"A document that records the concepts, calculations, decisions, and product selections used to meet the Owner's Project Requirements and to satisfy applicable regulatory requirements, standards, and guidelines. The document includes both narrative descriptions and lists of individual items that support the design process."

Authorship and Legal Liability

The BOD is authored exclusively by the licensed design professionals—the Architect of Record and the professional mechanical, electrical, plumbing, and structural Engineers of Record (EOR).

• The BOD embodies the design team's intellectual work product and professional judgment.
• The Engineer of Record retains exclusive legal liability for the design, equipment sizing, system capacities, and code compliance under their professional engineering (PE) seal.
• The CxP does NOT author, seal, or modify the BOD. Usurping the BOD drafting process strips the design team of their legal responsibility and exposes the commissioning firm to catastrophic professional engineering design liabilities.

Why the BOD is Not Merely 'Drawings and Specifications'

Contract drawings show what to build (geometry, pipe sizes, duct paths), and project specifications describe the quality of materials (pipe wall thickness, fan motor efficiency). However, neither document explains why a particular engineering path was selected.

The BOD provides the missing technical narrative:

• Why was a variable-primary chilled water plant selected over a primary-secondary system?
• What outdoor ambient wet-bulb design temperature was assumed when sizing the cooling towers?
• What tenant plug load diversity factor (watts per square foot) was incorporated into transformer sizing?
• How does the economizer control sequence transition between mechanical cooling and free cooling?

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2. Primary Technical Components of a Rigorous BOD

A compliant BOD document must be submitted by the design team at each major design milestone (Schematic Design, Design Development, and 95% Construction Documents). Per ASHRAE Guideline 0, an exhaustive BOD must contain four core technical pillars:

1. Ambient Design Conditions & Load Calculations

• Outdoor Design Criteria: Specific geographic climate data cited from the ASHRAE Handbook—Fundamentals (e.g., 99.6% annual heating dry-bulb temperature, 0.4% annual cooling dry-bulb and mean coincident wet-bulb temperatures, and extreme dehumidification dew-point criteria).
• Indoor Environmental Parameters: Winter heating setpoints (e.g., 70°F dry-bulb), summer cooling setpoints (e.g., 75°F dry-bulb, 50% max RH), ventilation airflow rates per occupant, and room pressurization relationships (positive, neutral, negative).
• Internal Heat Gain Assumptions: Occupant sensible and latent heat loads, lighting power density ($W/sq ft$), computer/plug load densities ($W/sq ft$), process equipment loads, and safety/diversity factors utilized in load calculation software (e.g., TRACE 3D Plus, Carrier HAP, EnergyPlus).

2. System Narrative Descriptions & Equipment Selection Rationale

• Mechanical Systems: Narrative describing the central plant architecture (e.g., magnetic-bearing centrifugal chillers, condensing hydronic boilers), air distribution systems (e.g., Dedicated Outdoor Air Systems [DOAS] paired with active chilled beams), and hydronic distribution schemes.
• Electrical Systems: Service voltage, transformer kVA ratings, emergency generator sizing calculations (starting kVA and steady-state kW), Automatic Transfer Switch (ATS) transition schemes (open vs. closed transition), and uninterruptible power supply (UPS) runtimes.
• Plumbing Systems: Domestic hot water heating technology (e.g., air-to-water heat pump water heaters), storage volume, circulation loop velocity, and backflow prevention architecture.
• Building Automation & Controls: Architecture of the Direct Digital Controls (DDC) network, supervisory BACnet IP communication protocols, field bus baud rates, server virtualization, and high-level sequences of operation.

3. Redundancy and Reliability Strategies

• Detailed descriptions of system redundancy levels ($N+1$, $2N$, or run-and-standby configurations) for critical pumps, chillers, boilers, computer room air handlers (CRAH), and emergency power distribution.

4. Regulatory Codes, Standards, and Energy Guidelines Cited

• Explicit identification of governing building code editions: International Building Code (IBC), International Mechanical Code (IMC), International Energy Conservation Code (IECC), ASHRAE Standard 90.1, ASHRAE Standard 62.1, ASHRAE Standard 55, NFPA 70 (National Electrical Code), NFPA 72 (National Fire Alarm Code), and local municipal amendments.

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3. The CxP's BOD Review Protocol & Professional Boundaries

Under ASHRAE Standard 202, the Commissioning Provider must conduct formal peer reviews of the BOD during the design phase. The objective is to verify that the design team's proposed technical approach fully satisfies every parameter articulated in the OPR.

The Golden Boundary: Review vs. Redesign

A foundational tenet of the ASHRAE BCxP Code of Ethics and professional practice is respecting the design engineer's legal boundaries:

┌─────────────────────────────────────────────────────────────┐
│                     COMMISSIONING PROVIDER                  │
│  - Audits BOD for completeness and clarity                  │
│  - Verifies BOD alignment against OPR criteria              │
│  - Identifies unstated design assumptions                   │
│  - Checks for testability, maintainability, and sensors     │
│  - RECOMMENDS solutions via formal technical inquiries      │
└──────────────────────────────┬──────────────────────────────┘
                               │ CANNOT DIRECT OR REDESIGN
                               ▼
┌─────────────────────────────────────────────────────────────┐
│                  ENGINEER OF RECORD (EOR)                   │
│  - Selects systems, equipment capacities, and schematics   │
│  - Performs engineering calculations                        │
│  - Holds legal responsibility under Professional Seal (PE)  │
│  - DIRECTS changes to design drawings and specifications    │
└─────────────────────────────────────────────────────────────┘

Step-by-Step BOD Review Methodology

1. Cross-Referencing the OPR-to-BOD Traceability Matrix: The CxP creates a tracking log matching every requirement in the OPR to its corresponding technical solution in the BOD. If the OPR mandates "Maintain indoor relative humidity below 55% during extreme summer storms," the CxP verifies whether the BOD includes dedicated dehumidification sequences, sub-cooling/reheat coils, or active desiccant systems.
2. Evaluating Equipment Sizing & Load Assumptions: The CxP examines whether the design assumptions reflect reality. For example, if an engineer sizes a laboratory HVAC system assuming an internal plug load of $8.0 W/sq ft$, but modern low-power laboratory equipment draws only $2.5 W/sq ft$, the air handlers will be severely oversized, causing severe low-load hunting, poor dehumidification, and coil freezing.
3. Auditing Maintainability and Accessibility: The CxP checks whether the BOD accounts for operational clearances: Are filter pull spaces documented? Can chiller tubes be pulled without demolishing an exterior wall? Are isolation valves provided on both sides of control valves?
4. Verifying Commissionability & Sensory Instrumentation: The CxP verifies that the BOD includes the necessary sensory instrumentation required for functional testing and continuous monitoring: airflow measuring stations (AFMS) on outside air intakes, pressure test plugs (P/T ports) across heat exchangers, flow meters on hydronic headers, and temperature wells on coil supply and return lines.

How to Write Constructive Review Comments

Review comments must never take the tone of personal criticism or prescriptive design mandates. The CxP should use the Observation - Reference - Recommendation format:

• Defective Comment: "The chiller plant design is terrible. You forgot N+1 redundancy and your pumps are piped incorrectly. Redesign this with variable-primary pumping immediately."
• Professional BCxP Comment: "Observation: The mechanical BOD (Section 3.2, Page 14) describes a single 400-ton chiller without backup. Reference: The OPR (Section 4.1, 'Mission Critical Reliability') requires N+1 chiller redundancy to safeguard surgical suites. Recommendation: Please coordinate with the Owner to clarify if standby cooling capacity is required, or update the BOD to detail how surgical operations will be maintained during chiller maintenance."

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4. Current Facility Requirements (CFR) in Existing Buildings

While the OPR governs new construction, existing facilities operate in a radically different context. Over 10, 20, or 30 years of occupancy, buildings undergo constant evolution:

• Private perimeter offices are demolished to create dense open-plan cubicles.
• Storage closets are converted into high-density IT server rooms.
• Occupancy counts double while operating hours expand from 8 hours/day to 24/7.
• Original mechanical equipment suffers bearing wear, coil fouling, and damper leakage.
• The original design drawings and OPR are often lost, outdated, or completely irrelevant.

ASHRAE Guideline 0.2-2015: The CFR Benchmark

In response to these operational realities, ASHRAE Guideline 0.2-2015 (Commissioning Process for Existing Systems and Assemblies) establishes the Current Facility Requirements (CFR).

Current Facility Requirements (CFR) Defined: The written document detailing the current functional requirements of an existing facility and the expectations of how it is currently utilized and operated. It replaces the OPR as the baseline benchmark for Existing Building Commissioning (EBCx / Retro-commissioning).

Developing the CFR: Investigation and Discovery Protocols

Developing a CFR is an investigative engineering process conducted during the Planning and Investigation phases of EBCx:

1. Executive and Financial Alignment: The CxP interviews building ownership to identify corporate capital objectives: Are they preparing the building for sale (seeking quick 1-year paybacks)? Or do they plan a 30-year hold (seeking deep carbon reduction and equipment electrification)?
2. Facility Staff Interviews: The CxP conducts in-depth interviews with front-line operating engineers: What pneumatic controls are bypassed? Which chillers surge during part-load? Why are outside air dampers wired shut with zip-ties?
3. Occupant Surveys and Complaint Log Audits: The CxP reviews computerized maintenance management system (CMMS) work orders over the preceding 24 months to identify chronic hot/cold calls, IAQ complaints, or acoustic issues.
4. Walk-Through Visual Audits: The CxP performs comprehensive field audits to document current space usage vs. original architectural plans, measuring actual occupant density and lighting power.
5. Utility Bill Benchmarking: The CxP analyzes 24 to 36 months of interval utility data (electric, gas, steam, water) to calculate weather-normalized EUI, peak electrical demand (kW), and load factor, benchmarking performance against ENERGY STAR Portfolio Manager.

Reconciling Operational Realities in the CFR

The resulting CFR does not pretend the building is brand new. Instead, it documents practical operational baselines:

• If an air handling unit has 15% coil fin deterioration that cannot be repaired without total replacement, the CFR documents the derated airflow capacity.
• If a corporate tenant requires a space temperature of 68°F for intensive software engineering teams, the CFR documents 68°F as the active setpoint (rather than the 1995 design setpoint of 74°F) and calculates the resulting thermal impact on central cooling coils.

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5. The Foundational Comparative Triad: OPR vs. BOD vs. CFR

The following comparative table synthesizes the distinct characteristics, governing standards, and technical roles of the OPR, BOD, and CFR: