ASHRAE 90.1-2019 Appendix G Baseline Model
Table of Contents
Executive Summary: Baseline Model Development Process
This is the step-by-step workflow for building an Appendix G baseline model in Better Building. The phases are roughly in order, though you'll inevitably bounce between them when something doesn't work the first time.
Phase 1: Project Setup and Data Collection
1.1
Identify climate zone from ASHRAE 169 or project location
Section 2.1
1.2
Classify building area type(s) and space functions
Section 2.1
1.3
Calculate gross conditioned floor area and count floors
Section 2.1
1.4
Obtain approved weather file (TMY3/TMY2)
Section 2.2
1.5
Gather proposed design documents (geometry, schedules, loads)
Section 2.1
Phase 2: Building Geometry and Envelope
2.1
Copy proposed geometry exactly (floors, areas, thermal blocks)
Section 3.1
2.2
Calculate baseline WWR from Table G3.1.1-1 or use proposed (max 40%)
Section 3.5.1
2.3
Redistribute fenestration to match baseline WWR per facade
Section 3.5.1
2.4
Remove all shading devices; make windows flush with walls
Section 3.5.3
2.5
Look up envelope U-factors from Tables G3.4-1 to G3.4-8
Section 3.4
2.6
Create baseline constructions: roof (above-deck), walls (steel-frame), floors (steel-joist)
Section 3.3
2.7
Apply fenestration properties (U-factor, SHGC, VT) using SimpleGlazingSystem
Section 3.5.2
2.8
Set roof surface properties (reflectance=0.30, emittance=0.90)
Section 3.7
2.9
Calculate and apply baseline infiltration rate (I75Pa = 5.1 L/s·m² at 75 Pa)
Section 3.8
2.10
Adjust skylight area to 3% or less if proposed exceeds that
Section 3.6
Phase 3: HVAC System Selection and Configuration
3.1
Determine building type category (Residential/Nonresidential/Public Assembly/Heated-only)
Section 4.1
3.2
Select baseline system from Table G3.1.1-3 based on type, floors, area, climate
Section 4.2
3.3
Check for exceptions: mixed use >20,000 ft², labs, computer rooms, unusual loads
Supplemental Doc
3.4
Assign systems to zones (single-zone systems per block; VAV systems per floor)
Section 4.4
3.5
Look up equipment efficiencies from Tables G3.5.1-G3.5.6
Section 4.5
3.6
Configure sizing parameters (1.15× cooling, 1.25× heating)
Section 4.6
3.7
Set up sizing runs with correct schedule assumptions
Section 4.7
3.8
Calculate baseline fan power using Section G3.1.2.9 formulas
Section 4.8
3.9
Add VAV fan part-load curve (cubic polynomial)
Section 4.9
3.10
Configure economizer by climate zone (required in 2B, 3B-C, 4C, 5-8 except 5A/6A limits)
Section 4.10
3.11
Add energy recovery if supply ≥2,400 L/s and OA ≥70% (50% effectiveness)
Section 4.11
3.12
Configure hot water loop: boiler count, 82°C supply, OA reset to 66°C
Section 4.12
3.13
Configure chilled water loop: chiller type/count, 6.7°C supply, OA reset to 12°C
Section 4.13
3.14
Add cooling tower (axial, variable-speed, 3.23 L/s·kW)
Section 4.14
3.15
Set VAV minimum flows (30% or OA requirement, whichever greater)
Section 4.15
3.16
Add supply air temperature reset (+2.3°C at minimum load)
Section 4.16
3.17
Configure heat pump auxiliary heat lockout (<4°C outdoor) if applicable
Section 4.17
3.18
Add preheat coils for Systems 5-8 (setpoint = room heating minus 11°C)
Section 4.18
Phase 4: Lighting Systems
4.1
Look up baseline LPD for each space type from Table G3.7
Section 5.1
4.2
Apply mandatory automatic shutoff (buildings >500 m²)
Section 5.2
4.3
Add occupancy sensors only where mandatory (break rooms, conference, classrooms)
Section 5.2
4.4
Do NOT add daylight responsive controls beyond mandatory spaces
Section 5.2
4.5
Calculate exterior lighting from Table G3.6 allowances
Section 5.3
Phase 5: Service Water Heating
5.1
Select baseline SWH type from Table G3.1.1-2 (gas or electric by building type)
Section 6.1
5.2
Apply minimum efficiency from Section 7.4.2
Section 6.2
5.3
Keep SWH loads identical to proposed design
Section 6.3
5.4
Add condenser heat recovery if criteria of Section 6.5.6.2 are met
Section 6.4
Phase 6: Schedules and Internal Loads
6.1
Copy ALL schedules exactly from proposed (occupancy, lighting, equipment, thermostat)
Section 7.1
6.2
Keep thermostat setpoints and throttling range identical
Section 7.2
6.3
Set HVAC fans to run continuously during occupied, cycle during unoccupied
Section 7.3
6.4
Copy all receptacle and process loads exactly from proposed
Section 7.4
Phase 7: Additional Systems
7.1
Model elevators if in proposed (motor power, cab ventilation, cab lighting)
Section 8.1
7.2
Model refrigeration using AHRI 1200 ratings or Tables G3.10.1/G3.10.2
Section 8.2
7.3
Model transformers only if proposed exceeds Table 8.4.4 efficiency
Section 8.3
7.4
Apply motor efficiencies from Table G3.9.1
Section 8.4
Phase 8: Simulation Execution
8.1
Configure simulation for full 8,760 hours
Section 9.1
8.2
Run sizing simulations first (see detailed procedure below)
Section 4.7
8.3
Run baseline at 0° rotation, record annual energy cost
Section 10.1
8.4
Run baseline at 90° rotation, record annual energy cost
Section 10.1
8.5
Run baseline at 180° rotation, record annual energy cost
Section 10.1
8.6
Run baseline at 270° rotation, record annual energy cost
Section 10.1
8.7
Verify unmet load hours are 300 or less for each run
Section 9.2
8.8
If UMLH exceeds 300, resize equipment incrementally per Section 2.7.2 of PRM Manual
Supplemental Doc
Detailed Sizing Run Procedure (Step 8.2)
Sizing runs determine baseline equipment capacities. Get this wrong and you'll either have unmet load hours (undersized) or an artificially inflated baseline energy cost (oversized beyond the required factors). Neither outcome helps your compliance case.
Design Day Configuration
Create two design days using climate data for your location:
Cooling Design Day
Size cooling coils, chillers, towers
0.4% annual cooling DB/MCWB
Heating Design Day
Size heating coils, boilers
99.6% annual heating DB
Schedule Assumptions (This Is Where People Get Tripped Up)
The schedules used during sizing runs are NOT the same as annual simulation schedules:
Cooling
Use HIGHEST hourly value from annual schedules, applied to entire design day
Use HIGHEST hourly value
Heating
Use LOWEST hourly value from annual schedules, applied to entire design day
Use HIGHEST hourly value
Why highest infiltration for both? Because infiltration is always a load to overcome, whether you're heating or cooling. Cold air leaking in during winter adds heating load. Hot humid air leaking in during summer adds cooling load.
Exception for Residential Dwelling Units: Cooling sizing uses the most-used weekday schedule (not peak values) for infiltration, occupants, lighting, and equipment.
Thermostat Schedule: Use the most typical 24-hour profile from the annual simulation for both sizing runs.
Sensible and Latent Load Considerations
The default sizing approach uses a 20°F (11°C) supply-to-room temperature difference for airflow calculations. This works when sensible loads drive your design.
However, if your proposed building's airflow was sized based on latent loads exceeding sensible loads (humid climates, commercial kitchens, natatoriums, labs with high moisture generation), the baseline must use the same supply-air-to-room humidity ratio difference that drove the proposed design. The baseline doesn't get a free pass on dehumidification requirements.
For cooling coil capacity, Better Building calculates both sensible and latent components. The 15% oversizing factor applies to total capacity (sensible plus latent combined).
Oversizing Factors
Apply these at the zone level to coil loads, NOT to airflow rates:
Cooling capacity
1.15 (15%)
Zone coil loads
Heating capacity
1.25 (25%)
Zone coil loads
Supply airflow
1.00 (no oversizing)
Zone level
Plant equipment
1.00 (no oversizing)
Based on coincident loads
System-level airflow is the sum of zone design airflows (coincident sizing). Plant capacity is based on coincident system loads, not the sum of individual system peaks.
Better Building Sizing Configuration
Orientation for Sizing Runs
Run sizing calculations for each of the four baseline orientations (0°, 90°, 180°, 270°). Use the largest capacity from any orientation as your baseline equipment size. This ensures the baseline can handle loads regardless of rotation.
Verifying Sizing Results
After sizing runs complete, check the Better Building sizing reports. The Zone Sizing Summary shows calculated airflows and coil capacities per zone. The System Sizing Summary confirms system airflows sum correctly from zones. The Plant Sizing Summary lets you check chiller and boiler capacities against coincident loads. And the Component Sizing Summary shows autosized values for all equipment.
If any component shows "Autosized" with a value of 0 or something obviously wrong, you have an input error upstream.
What To Do When Unmet Load Hours Exceed 300
If your baseline shows more than 300 UMLH after applying standard oversizing, check the proposed model first. If proposed also has high UMLH, the problem is usually schedules (HVAC availability not matching occupancy) or zone minimum airflows set incorrectly.
If only baseline has high UMLH for cooling, increase zone airflow by 10% for zones with more than 150 UMLH and by 5% for zones with 50-150 UMLH. Then resize cooling equipment to match increased airflows and resize chillers and towers proportionally.
If only baseline has high UMLH for heating, use the same airflow adjustment procedure, resize heating coils for increased airflows, and resize boilers proportionally. For heat pumps, increase coil capacity rather than auxiliary heat.
Phase 9: Results Processing
9.1
Average the four rotation energy costs to get Baseline Building Performance
Section 10.1
9.2
Calculate PCI = Proposed Performance / Baseline Performance
Section 10.2
9.3
Compare PCI to Building Performance Factor (BPF) from Table 4.2.1.1
Section 10.3
9.4
Document compliance: PCI at or below BPF indicates compliance
Section 10.3
Quick Decision Flowchart
Critical "Same as Proposed" Items
The following must be identical in baseline and proposed models:
Building geometry
Floors, areas, thermal blocks
Weather file
Same TMY file
Schedules
Occupancy, lighting, equipment, thermostat
Internal loads
Receptacles, process, occupancy
Service hot water loads
Usage patterns and quantities
Simulation period
8,760 hours
Critical "Must Be Different" Items
The following must follow baseline rules (not proposed design):
Envelope U-factors
From Tables G3.4-1 to G3.4-8
SHGC and VT
From Tables G3.4-1 to G3.4-8
WWR
From Table G3.1.1-1 or 40% max
Infiltration rate
5.1 L/s·m² at 75 Pa (1.0 cfm/ft²)
HVAC system type
From Table G3.1.1-3
Equipment efficiency
Minimum from Tables G3.5.x
Fan power
Calculated per Section G3.1.2.9
Lighting power density
From Table G3.7
SWH system type
From Table G3.1.1-2
1. Overview
1.1 Purpose of Appendix G
Appendix G (the Performance Rating Method) provides a methodology to demonstrate compliance with minimum energy standards as an alternative to prescriptive compliance. It also lets you quantify energy performance that exceeds standard requirements, which matters for rating programs like LEED.
The basic concept: you build two simulation models of the same building. One represents your actual proposed design. The other represents a hypothetical "baseline" building that meets code minimums using standardized systems. Compare the energy costs, and you get a performance ratio.
1.2 Key Concept: Performance Cost Index (PCI)
A PCI below 1.0 means the proposed design performs better than baseline. The baseline building represents a "minimally code-compliant" building using the same geometry but with standard-compliant systems.
1.3 What This Guide Covers
This guide focuses only on the baseline model requirements. The baseline building is an automated transformation of the proposed building with standardized envelope properties, prescribed HVAC system types, standard lighting power densities, and default service water heating systems.
The proposed model is your actual design. That's on you.
2. Prerequisites and Initial Setup
2.1 Required Information Before Starting
Before creating the baseline model, gather the following:
Climate Zone
ASHRAE 169 or project location
Envelope values, HVAC selection
Building Area Type
Project documents
HVAC system type, WWR, SWH type
Gross Conditioned Floor Area
Architectural drawings
HVAC system selection
Number of Floors
Architectural drawings
HVAC system selection
Building Orientation
Site plan
Rotation analysis
Space Classifications
Program documents
Lighting power densities
2.2 Weather Data Requirements (Section G2.3)
Use the SAME weather file for both proposed and baseline models. This seems obvious, but people occasionally forget.
Use TMY3, TMY2, or equivalent hourly weather data. Select data representative of the actual construction site. The rating authority must approve the weather file for the project location.
2.3 Simulation Program Requirements (Section G2.2)
Better Building meets all Appendix G simulation requirements: 8760 hours per year simulation, hourly schedule variations, thermal mass effects, 10+ thermal zones capability, part-load performance curves, capacity and efficiency correction curves, air economizer modeling, and design load calculations.
Make sure your Better Building version is tested per ASHRAE Standard 140.
3. Building Geometry and Envelope
3.1 Geometry Requirements (Table G3.1, No. 1 & 5)
The baseline building must have the same number of floors as proposed design, same conditioned floor area as proposed design, and same thermal block configuration as proposed design.
You're not redesigning the building. You're swapping out the systems.
3.2 Building Orientation Rotation (Table G3.1, No. 5a)
Run 4 simulations at 0°, 90°, 180°, and 270° rotation. Average the results to get baseline building performance.
This removes any orientation advantage the proposed design might have. A building that happened to land on a favorable site orientation doesn't get credit for luck.
Better Building Implementation:
Exceptions (no rotation required if): Building orientation is dictated by site constraints (documented), or vertical fenestration area varies by less than 5% on each orientation.
3.3 Opaque Envelope Assemblies (Table G3.1, No. 5b)
Use these mandatory construction types for baseline:
Roofs
Insulation Entirely Above Deck
Appendix A2.2
Above-Grade Walls
Steel-Framed
Appendix A3.3
Below-Grade Walls
Concrete Block
Appendix A4
Floors
Steel-Joist
Appendix A5.3
Slab-on-Grade
Unheated F-factors
Appendix A6
The baseline always uses steel-framed walls and steel-joist floors regardless of what the proposed design actually has. This is intentional. It creates a consistent comparison point.
Better Building Implementation (Example Roof):
3.4 Baseline U-Factor and SHGC Values
Step 1: Identify your climate zone. Step 2: Determine building use (Residential/Nonresidential/Semiheated). Step 3: Look up values in Tables G3.4-1 through G3.4-8.
Climate Zone 4A Example (Nonresidential):
Roof (insulation above deck)
0.360
W/m²·K
Above-grade wall (steel-framed)
0.705
W/m²·K
Below-grade wall
C-6.473
W/m²·K
Floor (steel-joist)
0.296
W/m²·K
Slab-on-grade (unheated)
F-1.264
W/m·K
Swinging door
3.975
W/m²·K
Non-swinging door
8.233
W/m²·K
3.5 Fenestration (Windows): Area and Properties
3.5.1 Window-to-Wall Ratio (WWR)
For building types in Table G3.1.1-1:
Grocery store
7%
Healthcare (outpatient)
21%
Hospital
27%
Hotel/motel (75 rooms or fewer)
24%
Hotel/motel (>75 rooms)
34%
Office (465 m² or less)
19%
Office (465-4650 m²)
31%
Office (>4650 m²)
40%
Restaurant (quick service)
34%
Restaurant (full service)
24%
Retail (stand alone)
11%
Retail (strip mall)
20%
School (primary)
22%
School (secondary/university)
22%
Warehouse (non-refrigerated)
6%
For building types NOT in Table G3.1.1-1: Use proposed design WWR or 40%, whichever is smaller. Distribute on each facade in same proportion as proposed.
3.5.2 Fenestration Properties
From Tables G3.4-1 through G3.4-8 based on Climate Zone and WWR.
Example for Climate Zone 4A, Nonresidential, 30-40% WWR: U-factor is Uall = 3.24 W/m²·K, SHGC is SHGCall = 0.39, VT is VTall = 0.43.
Better Building Implementation:
3.5.3 Shading Devices
All vertical fenestration shall be flush with exterior wall. No shading projections shall be modeled. Manual shading devices (blinds) are not modeled.
Yes, this means your beautiful brise-soleil doesn't help the baseline. That's the point.
3.6 Skylights (Table G3.1, No. 5e)
Skylight area equals proposed design area OR 3%, whichever is smaller. If proposed exceeds 3%, reduce baseline proportionally to reach 3%. Properties come from Tables G3.4-1 through G3.4-8.
3.7 Roof Surface Properties (Table G3.1, No. 5f,g)
3.8 Building Envelope Infiltration (Table G3.1, No. 5h)
Baseline air leakage rate: I75Pa = 5.1 L/s·m² at 75 Pa
Conversion formulas (Section G3.1.1.4):
For floor area method:
For above-grade wall area method:
Where S is total building envelope area (m²), AFLR is gross floor area (m²), and AAGW is above-grade wall area (m²).
Better Building Implementation:
4. HVAC System Selection and Configuration
4.1 System Type Selection Process
Step 1: Determine Building Type Category. Options are Residential (dormitory, hotel, motel, multifamily), Nonresidential (all others), Public assembly (worship, theaters, arenas, convention centers, etc.), or Heated-only storage.
Step 2: Count Floors (including basement, excluding parking).
Step 3: Calculate Gross Conditioned Floor Area.
Step 4: Identify Climate Zone. Climate Zones 0-3A use different systems than Zones 3B, 3C, 4-8.
Step 5: Use Table G3.1.1-3 to Select System.
4.2 Baseline HVAC System Types (Table G3.1.1-3)
Residential
System 1 (PTAC)
System 2 (PTHP)
Public assembly <11,000 m²
System 3 (PSZ-AC)
System 4 (PSZ-HP)
Public assembly 11,000 m² or more
System 12 (SZ-CV-HW)
System 13 (SZ-CV-ER)
Heated-only storage
System 9
System 10
Retail, 2 floors or fewer
System 3 (PSZ-AC)
System 4 (PSZ-HP)
Other nonres, 3 floors or fewer AND <2,300 m²
System 3 (PSZ-AC)
System 4 (PSZ-HP)
Other nonres, 4-5 floors AND <2,300 m² OR 5 floors or fewer AND 2,300-14,000 m²
System 5 (Pkg VAV w/ Reheat)
System 6 (Pkg VAV w/ PFP)
Other nonres, >5 floors OR >14,000 m²
System 7 (VAV w/ Reheat)
System 8 (VAV w/ PFP)
4.3 System Descriptions (Table G3.1.1-4)
1. PTAC
Packaged terminal AC
Constant Volume
DX
Hot-water boiler
2. PTHP
Packaged terminal HP
Constant Volume
DX
Electric heat pump
3. PSZ-AC
Packaged rooftop AC
Constant Volume
DX
Fossil fuel furnace
4. PSZ-HP
Packaged rooftop HP
Constant Volume
DX
Electric heat pump
5. Pkg VAV w/ Reheat
Packaged rooftop VAV
VAV
DX
Hot-water boiler
6. Pkg VAV w/ PFP
Packaged VAV w/ fan-powered boxes
VAV
DX
Electric resistance
7. VAV w/ Reheat
VAV with chilled water
VAV
Chilled water
Hot-water boiler
8. VAV w/ PFP
VAV with fan-powered boxes
VAV
Chilled water
Electric resistance
9. Heating only
Warm air furnace, gas
Constant Volume
None
Gas furnace
10. Heating only
Warm air furnace, electric
Constant Volume
None
Electric resistance
11. SZ-VAV
Single-zone VAV
VAV
Chilled water
See note*
12. SZ-CV-HW
Single-zone CV
Constant Volume
Chilled water
Hot-water boiler
13. SZ-CV-ER
Single-zone CV
Constant Volume
Chilled water
Electric resistance
*System 11: Zones 0-3A = Electric resistance; Other zones = Hot-water boiler
4.4 Zone Assignment Rules
For Systems 1, 2, 3, 4, 9, 10, 11, 12, 13: Each thermal block gets a separate system. For Systems 5, 6, 7, 8: Each FLOOR gets a separate system (floors with identical blocks can be grouped).
Special Cases: For significantly different zones (>31.2 W/m² peak load difference OR >40 equivalent FLH/week schedule difference), use System 3 or 4 regardless of base system. Laboratory spaces with >7,100 L/s exhaust use System 5 or 7. Computer rooms with specific criteria use System 11. Hospitals always use System 5 or 7 regardless of climate zone.
4.5 Equipment Efficiencies (Section G3.1.2.1)
Use minimum efficiency levels from Tables G3.5.1 through G3.5.6.
Key efficiency values (excluding fan power):
Air Conditioners (Table G3.5.1):
<19 kW (single-package)
3.0
19-40 kW
3.5
40-70 kW
3.4
70-223 kW
3.5
223 kW or more
3.6
Heat Pumps, Cooling Mode (Table G3.5.2):
<19 kW
3.0
19-40 kW
3.4
40-70 kW
3.2
70 kW or more
3.1
Heat Pumps, Heating Mode (Table G3.5.2):
<19 kW
-
3.4
19-40 kW
8.3°C outdoor
3.4
19-40 kW
-8.3°C outdoor
2.3
40 kW or more
8.3°C outdoor
3.4
40 kW or more
-8.3°C outdoor
2.1
Water Chillers (Table G3.5.3):
Screw/Scroll
<528 kW
4.45
5.20
Screw/Scroll
528-1055 kW
4.90
5.60
Screw/Scroll
1055 kW or more
5.50
6.15
Centrifugal
<528 kW
5.00
5.25
Centrifugal
528-1055 kW
5.55
5.90
Centrifugal
1055 kW or more
6.10
6.40
Boilers (Table G3.5.6):
<88 kW
80% AFUE
-
88-733 kW
75% Et
Max capacity
>733 kW
80% Ec
Hot water
4.6 Equipment Sizing (Section G3.1.2.2)
Cooling equipment: 1.15 × sizing run capacity (15% oversize). Heating equipment: 1.25 × sizing run capacity (25% oversize). Plant capacity: Based on COINCIDENT loads.
Better Building Sizing Parameters:
4.7 Sizing Run Requirements (Section G3.1.2.2.1)
For Cooling Sizing: Use HIGHEST hourly schedule values for internal loads. Apply to entire design day.
For Heating Sizing: Use LOWEST hourly schedule values for internal loads (occupants, lighting, equipment). Use HIGHEST hourly values for infiltration.
4.8 Fan System Power (Section G3.1.2.9)
Baseline fan power calculation:
Systems 1 and 2 (PTAC/PTHP):
Systems 3-8 and 11-13:
Better Building Implementation:
4.9 VAV Fan Part-Load Performance (Section G3.1.3.15)
Use either Method 1 (table) or Method 2 (equation):
Method 2 Equation:
Better Building Curve:
4.10 Air Economizers (Section G3.1.2.6)
Economizer Requirements by System and Climate:
0A, 0B, 1A, 1B, 2A, 3A, 4A
NO economizer
All others
Economizer REQUIRED
High-Limit Shutoff (Table G3.1.2.7):
2B, 3B, 3C, 4B, 4C, 5B, 5C, 6B, 7, 8
24°C
5A, 6A
21°C
Better Building Implementation:
4.11 Exhaust Air Energy Recovery (Section G3.1.2.10)
Required when: Design supply air capacity is 2,400 L/s or more AND minimum outdoor air is 70% or more of supply.
Recovery requirement: 50% enthalpy recovery ratio.
Exceptions (no recovery required): Spaces not cooled and heated below 16°C; toxic, flammable, corrosive exhaust; commercial kitchen hoods (Type 1); heating systems in Zones 0-3; cooling systems in Zones 3C, 4C, 5B, 5C, 6B, 7, 8; largest exhaust less than 75% of outdoor airflow.
4.12 Hot Water System Configuration (Sections G3.1.3.2-G3.1.3.5)
Number of Boilers: 1,400 m² conditioned area or less gets 1 boiler. More than 1,400 m² gets 2 equal-sized boilers.
Hot Water Temperatures: Design supply is 82°C, design return is 54°C.
Hot Water Temperature Reset (Section G3.1.3.4): At outdoor temp of -7°C or below, supply is 82°C. At outdoor temp of 10°C or above, supply is 66°C. Linear interpolation between.
Hot Water Pump Power: 300 W·s/L (or 220 W·s/L for purchased heat).
Better Building Implementation:
4.13 Chilled Water System Configuration (Sections G3.1.3.7-G3.1.3.11)
Number and Type of Chillers (Table G3.1.3.7):
1,055 kW or less
1 water-cooled screw
>1,055 kW to <2,110 kW
2 water-cooled screw (equal)
2,110 kW or more
2+ water-cooled centrifugal (max 2,813 kW each)
Chilled Water Temperatures: Design supply is 6.7°C, design return is 13°C.
Chilled Water Temperature Reset (Section G3.1.3.9): At outdoor temp of 27°C or above, supply is 7°C. At outdoor temp of 16°C or below, supply is 12°C. Linear interpolation between.
Chilled Water Pump Power: Primary (constant) is 140 W·s/L. Secondary (variable) is 210 W·s/L. For 1,055 kW capacity or more, use variable-speed secondary with 25% minimum flow.
Condenser Water Pump Power: 300 W·s/L (constant volume).
4.14 Cooling Tower Configuration (Section G3.1.3.11)
Tower characteristics: Type is axial-fan, open-circuit. Fan control is variable-speed. Efficiency is 3.23 L/s·kW.
Design approach calculation:
Leaving water temperature setpoints (Table G3.1.3.11):
5B, 5C, 6B, 8
18°C
0B, 1B, 2B, 3B, 3C, 4B, 4C, 5A, 6A, 7
21°C
3A, 4A
24°C
0A, 1A, 2A
27°C
4.15 VAV Minimum Flow Set Points
Systems 5 and 7 (VAV with Reheat): (Section G3.1.3.13)
Systems 6 and 8 (VAV with PFP): (Section G3.1.3.14)
PFP fan size is 50% of peak primary airflow. PFP fan power is 0.74 W per L/s. Minimum primary airflow is 30% or OA requirement (whichever larger).
4.16 Supply Air Temperature Reset (Section G3.1.3.12)
For Systems 5-8 and 11: Reset cooling supply air temperature higher by 2.3°C at minimum cooling load.
Better Building Implementation:
4.17 Heat Pump Auxiliary Heat Control (Section G3.1.3.1)
For Systems 2 and 4: Auxiliary heat energized only when outdoor temp is below 4°C. Heat pump continues to operate while auxiliary is energized.
4.18 Preheat Coils (Section G3.1.3.19)
For Systems 5-8: Include preheat coil with fixed setpoint = (Room heating setpoint minus 11°C).
Example: If room heating setpoint is 21°C, preheat setpoint is 10°C.
5. Lighting Systems
5.1 Interior Lighting Power Density (Table G3.1, No. 6)
Baseline LPD determination: Use Table G3.7 (Space-by-Space Method) for baseline interior lighting.
Selected values from Table G3.7:
Office, Enclosed
11.84
30%
Office, Open Plan
11.84
15% (30% for workstation)
Conference Room
13.99
None
Corridor
5.38
25%
Lobby
13.99
25%
Restroom
9.69
45%
Storage Room, 4.6 m² or larger
8.61
45%
Classroom
13.99
None/30%
Retail Sales Area
18.30
15%
Dining, Family
22.60
35%
Guest Room
11.84
45%
5.2 Baseline Lighting Controls
Mandatory baseline controls: Automatic shutoff in buildings over 500 m². Occupancy sensors in employee lunch and break rooms, conference and meeting rooms, and classrooms (except shop, lab, PreK-12).
NOT included in baseline: Daylight responsive controls (beyond those spaces). Additional occupancy sensors.
Better Building Implementation:
5.3 Exterior Lighting (Table G3.6)
Tradable exterior lighting baseline values:
Parking lots and drives
1.6 W/m²
Walkways <3m wide
3.3 W/linear metre
Walkways 3m or wider
2.2 W/m²
Plaza areas
2.2 W/m²
Stairways
10.8 W/m²
Main entries
98 W/linear metre of door
Other doors
66 W/linear metre of door
Canopies
13.5 W/m²
Open sales areas
5.4 W/m²
6. Service Water Heating
6.1 System Type Selection (Table G3.1.1-2)
Baseline SWH system by building type:
Hotel, Motel, Dormitory
Gas storage water heater
Hospital, Gymnasium
Gas storage water heater
School/University
Gas storage water heater
Restaurant (all types)
Gas storage water heater
Office, Retail
Electric resistance storage
Courthouse, Library
Electric resistance storage
Warehouse, Workshop
Electric resistance storage
Healthcare clinic
Electric resistance storage
All others
Gas storage water heater
6.2 Efficiency Requirements
Use minimum efficiency from Section 7.4.2 tables.
6.3 Loads and Usage
Service water heating loads shall be IDENTICAL in proposed and baseline models.
Exceptions: Documented water conservation measures (low-flow fixtures), heat recovery from drain water, or alternative sanitizing (reduced temperature).
6.4 Condenser Heat Recovery (Section G3.1, No. 11d)
Required in baseline when: Large, 24-hour facilities meeting prescriptive criteria of Section 6.5.6.2.
7. Schedules and Internal Loads
7.1 Schedule Requirements (Table G3.1, No. 4)
Schedules shall be IDENTICAL in proposed and baseline models.
This includes occupancy schedules, lighting power schedules, equipment power schedules, thermostat setpoint schedules, and HVAC system operation schedules.
Exceptions allowing different schedules: Nonstandard efficiency measures (automatic controls) approved by rating authority, automatic lighting controls, automatic natural ventilation, demand control ventilation, automatic SWH load reduction.
Never different schedules for: Manual controls, occupancy.
7.2 Thermostat Settings
Temperature control setpoints and schedules must be IDENTICAL in proposed and baseline. Temperature control throttling range must be IDENTICAL.
7.3 HVAC Fan Schedules
Standard operation: Fans ON continuously during occupied hours. Fans cycle ON/OFF to meet loads during unoccupied hours.
Exceptions: Health/safety mandated ventilation keeps fans ON. Systems primarily serving computer rooms keep fans ON. Systems with no heating/cooling installed cycle fans.
7.4 Receptacle and Process Loads (Table G3.1, No. 12)
Receptacle and process loads shall be IDENTICAL in proposed and baseline models.
This includes office equipment, computers, cooking equipment, medical/laboratory equipment, and manufacturing equipment.
Better Building Implementation:
8. Additional Systems
8.1 Elevators (Table G3.1, No. 16)
When proposed includes elevators, baseline must model elevator motor power, cab ventilation fans, and cab lighting.
Baseline cab characteristics: Ventilation fan is 0.69 W/L·s. Lighting is 33.79 W/m². Both operate continuously.
Motor power calculation:
Where (from Tables G3.9.2 and G3.9.3): Buildings with 4 stories or fewer use hydraulic, no counterweight, 58% mechanical efficiency. Buildings with more than 4 stories use traction, counterweight = car + 40% rated load, 64% mechanical efficiency.
8.2 Refrigeration (Table G3.1, No. 17)
If refrigeration is AHRI 1200 rated: Use rated energy. If listed in Tables G3.10.1/G3.10.2: Use table values. If not listed: Model same as proposed.
8.3 Distribution Transformers (Table G3.1, No. 15)
Model in baseline ONLY IF: Proposed design transformers exceed Table 8.4.4 efficiency requirements.
When modeled, use Table 8.4.4 efficiency with same capacity/load ratio as proposed.
8.4 Motors (Table G3.9.1)
Use baseline motor efficiencies from Table G3.9.1:
0.8
82.5
1.1-1.5
84.0
2.2-3.7
87.5
5.6-7.5
89.5
11.1-14.9
91.0
18.7-22.4
92.4
29.8-37.3
93.0
44.8
93.6
56.0
94.1
74.6-93.3
94.5
111.9-149.2
95.0
9. Simulation Settings and Verification
9.1 Simulation Period
9.2 Unmet Load Hours Limit (Section G3.1.2.3)
Unmet load hours must be 300 hours or less (of 8,760) for BOTH proposed and baseline models.
Better Building Verification: Check output variable Zone Thermal Comfort ASHRAE 55 Adaptive Model Temperature or review unmet hours in tabular reports.
9.3 Required Output Variables
9.4 Energy Cost Calculation (Section G2.4.2)
Options: Actual utility rates for purchased energy, or state average prices from DOE EIA.
Do NOT mix rate sources in same project.
10. Performance Cost Index Calculation
10.1 Four-Rotation Baseline Procedure
Run baseline model at 0° rotation and record annual energy cost. Run baseline model at 90° rotation and record annual energy cost. Run baseline model at 180° rotation and record annual energy cost. Run baseline model at 270° rotation and record annual energy cost. Average the four costs to get Baseline Building Performance.
10.2 PCI Calculation
10.3 Compliance Determination
For minimum standard compliance (Section 4.2.1.1):
BPF values vary by climate zone and building type.
For rating programs (e.g., LEED): Lower PCI means better performance. Calculate percent improvement as (1 minus PCI) × 100%.
10.4 Summary Checklist
Before submitting, verify:
Same weather file used for proposed and baseline
Same simulation program used for both
Baseline rotated and averaged (4 orientations)
Unmet load hours 300 or less for both models
Envelope U-factors match climate zone requirements
SHGC values match climate zone and WWR requirements
Correct HVAC system type selected
Equipment efficiencies at minimum levels
15% cooling oversizing, 25% heating oversizing
Fan power calculated per formulas
Economizer included/excluded per climate zone
Schedules identical (except approved automatic controls)
Internal loads identical
Energy costs calculated consistently
Appendix A: Quick Reference Tables
A.1 Climate Zone Envelope Summary
0-1
0.360
0.705
1.986
1.264
6.93
0.25
2
0.360
0.705
0.296
1.264
6.93
0.25
3
0.360
0.705
0.296
1.264
3.24
0.25-0.39
4
0.360
0.705
0.296
1.264
3.24
0.39
5
0.360
0.479
0.296
1.264
3.24
0.39-0.49
6
0.360
0.479
0.214
1.264
3.24
0.39-0.49
7
0.360
0.365
0.214
1.264
3.24
0.49
8
0.273
0.365
0.214
0.935
2.61
0.40
Values are for Nonresidential buildings. Check Tables G3.4-1 through G3.4-8 for specific conditions.
A.2 HVAC System Quick Selection
3 or fewer
<2,300
Nonres
Sys 3
Sys 4
4-5
<2,300
Nonres
Sys 5
Sys 6
5 or fewer
2,300-14,000
Nonres
Sys 5
Sys 6
>5
Any
Nonres
Sys 7
Sys 8
Any
>14,000
Nonres
Sys 7
Sys 8
Any
Any
Residential
Sys 1
Sys 2
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