## 12.3 Basis of Design (BOD)

§120.8(c)

A written explanation of how the design of the building systems meets the OPR shall be completed at the design phase of the building project, and updated as necessary during the design and construction phases. The Basis of Design (BOD) document shall cover the following systems and components:

1. (HVAC) systems and controls.

2. Indoor lighting system and controls.

3. Water heating systems and controls.

4. Any building envelope component considered in the OPR.

### 12.3.1 Intent

The BOD describes the building systems to be commissioned and outlines design assumptions not indicated in the design documents. The design team develops the BOD to describe how the building systems design meets the OPR, and why the systems were selected. The BOD is most effective when developed early in the project design and updated when necessary, throughout the design process.

### 12.3.2 Compliance Method

Compliance requires the completion of the BOD document, which should include the following:

A. HVAC Systems and Controls

1. Provide narrative description of system – system type, location, control type, efficiency features, outdoor air ventilation strategy, indoor air quality features, environmental benefits, and other special features.

2. Describe reasons for system selection – why chosen system is better than alternatives, considering issues such as comfort, performance, efficiency, reliability, flexibility, simplicity, cost, owner preference, site constraints, climate, maintenance, and acoustics

3. Provide design criteria including the following:

a. Load calculation method/software

b. Summer outdoor design conditions, °F drybulb and °F wetbulb

c. Winter outdoor design conditions, °F drybulb and °F wetbulb

d. Indoor design conditions, °F drybulb cooling, %RH cooling; °F drybulb heating, %RH heating

e. Applicable codes, guidelines, regulations and other references used

f. Load calculation assumptions

4. Sequence of Operations – operating schedules, setpoints, (may refer to plans or specifications).

5. Describe how the system meets the OPR

B. Indoor Lighting System and Controls

1. Provide narrative description of system – type of fixtures, lamps, ballasts, and controls

2. Describe reason for system selection – why chosen system better than alternatives, considering issues such as visual comfort, performance, efficiency, reliability, cost, flexibility, owner preference, color rendering, integration with daylighting, ease of control

3. Provide design criteria for each type of space including the following:

a. Applicable codes, guidelines, regulations and other references used.

b. Illumination design targets (footcandles) and lighting calculation assumptions

4. Provide lighting power design targets for each type of space.

a. Lighting power allowance and lighting power design target (watts/ft²).

5. Describe how system meets the OPR.

C. Water Heating Systems and Controls

1. Provide narrative description of system – system type, control type, location, efficiency features, environmental benefits, and other special features.

2. Describe reason for system selection – why chosen system is better than alternatives, considering issues such as performance, efficiency, reliability, space constraints, cost, utility company incentives, owner preference, and ease of maintenance.

3. Water heating load calculations.

4. Describe how system meets the OPR.

D. Building Envelope Components

1. Provide narrative description of system – type, energy savings, and payback period.

2. Describe reason for system selection – why chosen system is better than alternatives, considering issues such as performance, efficiency, reliability, flexibility, simplicity, expandability, cost, payback period, utility company incentives, and owner preference.

3. Describe how system meets the OPR

### 12.3.3 Enforcement

At their discretion, the building official confirms demonstrated compliance at Plan Review by either:

1. Receipt of a copy of the BOD document (optional).

2. Receipt of a completed NRCC-CXR-01-E indicating the BOD was reviewed at the Design Review Kickoff attesting that the BOD has been completed and meets the requirements of the OPR.