# ASHRAE 90.1 Appendix G 2019 Baseline HVAC Systems

This page defines the baseline HVAC systems required by ASHRAE 90.1 Performance Rating Method (PRM) Appendix G. The system selection is based on building type, number of floors, floor area, and climate zone.

## System Selection Table

### ASHRAE 90.1 Baseline HVAC Systems (Systems 1-13)

| System No. | System Name      | Type                           | Fan Control     | Cooling Type     | Heating Type                 | Application                                     |
| ---------- | ---------------- | ------------------------------ | --------------- | ---------------- | ---------------------------- | ----------------------------------------------- |
| 1          | PTAC             | Packaged Terminal AC           | Constant Volume | Direct Expansion | Hot Water Boiler             | Residential; Small buildings                    |
| 2          | PTHP             | Packaged Terminal Heat Pump    | Constant Volume | Direct Expansion | Electric Heat Pump           | Residential with electric heating               |
| 3          | PSZ-AC           | Packaged Single Zone AC        | Constant Volume | Direct Expansion | Gas Furnace                  | Small non-residential; ≤3 floors; <2,300 m²     |
| 4          | PSZ-HP           | Packaged Single Zone Heat Pump | Constant Volume | Heat Pump        | Electric Heat Pump           | All climates with electric heating              |
| 5          | PVAV with Reheat | Packaged VAV Reheat            | VAV             | Direct Expansion | Hot Water Reheat             | Mid-size buildings; 4-5 floors; 2,300-14,000 m² |
| 6          | PVAV with PFP    | Packaged VAV with PFP Boxes    | VAV             | Direct Expansion | Electric Resistance          | Mid-size buildings; electric heating            |
| 7          | VAV Reheat       | VAV with Reheat                | VAV             | Chilled Water    | Hot Water Reheat             | Large buildings; >5 floors; >14,000 m²          |
| 8          | VAV PFP Boxes    | VAV with PFP Boxes             | VAV             | Chilled Water    | Electric Resistance          | Large buildings; electric heating               |
| 9          | Gas Furnace      | Warm Air Furnace (Gas)         | Constant Volume | None             | Gas Furnace                  | Heating and Ventilation Only                    |
| 10         | Electric Furnace | Warm Air Furnace (Electric)    | Constant Volume | None             | Electric Resistance          | Heating and Ventilation Only (Electric)         |
| 11         | SZ-VAV           | Single Zone VAV                | VAV             | Chilled Water    | Variable (Climate Dependent) | Medium buildings; single thermal zone           |
| 12         | SZ-CV-HW         | Single Zone Constant Volume    | Constant Volume | Chilled Water    | Hot Water Boiler             | Medium buildings; constant volume system        |
| 13         | SZ-CV-ER         | Single Zone Constant Volume    | Constant Volume | Chilled Water    | Electric Resistance          | Medium buildings; electric heating              |

## Detailed System Descriptions

### System 1: PTAC (Packaged Terminal Air Conditioner)

**Component Configuration:**

* Supply Fan: Single-speed constant volume fan
* Cooling: Direct expansion (DX) cooling coil
* Heating: Hot water heating coil connected to building hot water loop
* Controls: Thermostat with heating/cooling setpoint

**EnergyPlus Objects:**

* `Fan:OnOff` or `Fan:ConstantVolume` (supply fan)
* `Coil:Cooling:DX:SingleSpeed` (cooling coil)
* `Coil:Heating:Water` (heating coil)
* `ZoneHVAC:PackagedTerminalAirConditioner`

**Application:**

* Residential buildings (apartments, hotels, dormitories)
* Small commercial buildings
* One unit per thermal zone

**Climate Zone Application:**

* All climate zones with fossil fuel heating (CZ 3B-8)
* Electric heating alternative (PTHP) for CZ 0-3A

### System 2: PTHP (Packaged Terminal Heat Pump)

**Component Configuration:**

* Supply Fan: Single-speed constant volume fan
* Cooling/Heating: Air-source heat pump with DX coil
* Supplemental Heating: Electric resistance coil for heating

**EnergyPlus Objects:**

* `Fan:OnOff` or `Fan:ConstantVolume` (supply fan)
* `Coil:Cooling:DX:SingleSpeed` (cooling coil)
* `Coil:Heating:DX:SingleSpeed` (heat pump heating)
* `Coil:Heating:Electric` (supplemental heating)
* `ZoneHVAC:PackagedTerminalHeatPump`

**Application:**

* Residential buildings in mild to warm climates
* Electric heating alternative to PTAC
* One unit per thermal zone

**Climate Zone Application:**

* CZ 0-3A (mild climates)

### System 3: PSZ-AC (Packaged Rooftop Air Conditioner)

**Component Configuration:**

* Supply Fan: Single-speed constant volume fan
* Cooling: Direct expansion cooling coil
* Heating: Gas-fired furnace
* Controls: Thermostat; economizer for cooling

**EnergyPlus Objects:**

* `Fan:ConstantVolume` (supply fan)
* `Coil:Cooling:DX:SingleSpeed` (cooling coil)
* `Coil:Heating:Gas` or `Coil:Heating:Fuel` (furnace)
* `AirLoopHVAC` with outdoor air damper

**Application:**

* Small non-residential buildings
* 3 floors or fewer
* Floor area < 2,300 m² (24,800 ft²)
* Can serve multiple zones from single rooftop unit

**Climate Zone Application:**

* CZ 3B-8 (fossil fuel heating)

### System 4: PSZ-HP (Packaged Rooftop Heat Pump)

**Component Configuration:**

* Supply Fan: Single-speed constant volume fan
* Cooling/Heating: Air-source heat pump with DX coil
* Supplemental Heating: Electric resistance coil

**EnergyPlus Objects:**

* `Fan:ConstantVolume` (supply fan)
* `Coil:Cooling:DX:SingleSpeed` (cooling coil)
* `Coil:Heating:DX:SingleSpeed` (heat pump heating)
* `Coil:Heating:Electric` (supplemental heating)
* `AirLoopHVAC` with outdoor air damper

**Application:**

* Small non-residential buildings with electric heating
* Alternative to PSZ-AC in areas without gas availability

**Climate Zone Application:**

* CZ 0-3A (mild climates with electric heating)

### System 5: PVAV with Reheat (Packaged VAV with Reheat)

**Component Configuration:**

* Supply Fan: Variable volume fan with VFD control
* Cooling: Direct expansion cooling coil
* Zone Heating: Hot water reheat coils in each zone
* Controls: VAV terminal units with heating/cooling logic

**EnergyPlus Objects:**

* `Fan:VariableVolume` (supply fan with VFD)
* `Coil:Cooling:DX:SingleSpeed` (cooling coil)
* `AirTerminal:SingleDuct:VAV:Reheat` (VAV terminal with reheat)
* `Coil:Heating:Water` (zone reheat coils)
* `PlantLoop` (hot water loop)

**Application:**

* Mid-size non-residential buildings
* 4-5 floors or 5 floors with 2,300-14,000 m² floor area
* Multiple thermal zones served by single air loop
* VAV terminals reduce air volume at part load

**Climate Zone Application:**

* CZ 3B-8 (fossil fuel heating via hot water loop)

**Key Features:**

* Demand-controlled ventilation capability
* Energy recovery potential
* VFD saves energy at part load

### System 6: PVAV with PFP Boxes (Parallel Fan Power Boxes)

**Component Configuration:**

* Supply Fan: Variable volume fan with VFD control
* Cooling: Direct expansion cooling coil
* Zone Heating: Parallel fan-powered boxes with electric resistance or hot water heating
* Controls: VAV terminal units with parallel fan operation

**EnergyPlus Objects:**

* `Fan:VariableVolume` (supply fan)
* `Coil:Cooling:DX:SingleSpeed` (cooling coil)
* `AirTerminal:SingleDuct:ParallelPIU:Reheat` (parallel fan power box)
* `Coil:Heating:Electric` or `Coil:Heating:Water` (terminal heating)

**Application:**

* Mid-size buildings with electric heating preference
* Improves comfort in perimeter zones
* Parallel fan boxes maintain circulation

**Climate Zone Application:**

* CZ 0-3A (electric heating)

### System 7: VAV with Reheat (Central Chilled Water System)

**Component Configuration:**

* Supply Fan: Variable volume fan with VFD control
* Cooling: Central chiller with chilled water loop
* Zone Heating: Hot water reheat coils in VAV terminals
* Central Heating: Gas or oil-fired boiler
* Condenser Heat Rejection: Cooling tower

**EnergyPlus Objects:**

* `Fan:VariableVolume` (supply fan)
* `Coil:Cooling:Water` (cooling coil on air loop)
* `AirTerminal:SingleDuct:VAV:Reheat` (VAV terminal with reheat)
* `Chiller:Electric:EIR` (centrifugal or screw chiller)
* `Boiler:HotWater` (heating boiler)
* `CoolingTower:SingleSpeed` or `CoolingTower:TwoSpeed`
* `PlantLoop` (chilled water and condenser water loops)

**Application:**

* Large buildings
* > 5 floors or >14,000 m² floor area
* Most efficient for large multi-zone buildings
* Serves multiple air handling units

**Climate Zone Application:**

* CZ 3B-8 (fossil fuel heating)

**Key Features:**

* Centralized cooling for multiple zones
* Demand-controlled ventilation
* Energy recovery with heat wheel capability
* VFD reduces fan energy at part load

### System 8: VAV with PFP Boxes (Central Chilled Water)

**Component Configuration:**

* Supply Fan: Variable volume fan with VFD control
* Cooling: Central chiller with chilled water loop
* Zone Heating: Parallel fan-powered boxes with electric resistance heating
* Central Heating: Not used (zone heating only)
* Condenser Heat Rejection: Cooling tower

**EnergyPlus Objects:**

* `Fan:VariableVolume` (supply fan)
* `Coil:Cooling:Water` (cooling coil)
* `AirTerminal:SingleDuct:ParallelPIU:Reheat` (parallel fan power box)
* `Coil:Heating:Electric` (electric resistance in terminals)
* `Chiller:Electric:EIR` (central chiller)
* `CoolingTower:SingleSpeed`
* `PlantLoop` (chilled water and condenser water)

**Application:**

* Large buildings with electric heating
* Provides zone-level heating control
* No central boiler required

**Climate Zone Application:**

* CZ 0-3A (electric heating)

### System 9: Gas Furnace (Heating and Ventilation Only)

**Component Configuration:**

* Supply Fan: Single-speed constant volume fan
* Heating: Gas-fired furnace (no cooling)
* No mechanical cooling system
* Controls: Thermostat for heating setpoint

**EnergyPlus Objects:**

* `Fan:ConstantVolume` (supply fan)
* `Coil:Heating:Gas` or `Coil:Heating:Fuel` (furnace)
* `AirLoopHVAC` (ventilation and heating only)

**Application:**

* Buildings with heating only requirements
* Unheated or naturally ventilated spaces
* No summer cooling needed (storage facilities, warehouses)

**Climate Zone Application:**

* CZ 3B-8 (fossil fuel heating)

### System 10: Electric Furnace (Heating and Ventilation Only)

**Component Configuration:**

* Supply Fan: Single-speed constant volume fan
* Heating: Electric resistance heater
* No mechanical cooling system

**EnergyPlus Objects:**

* `Fan:ConstantVolume` (supply fan)
* `Coil:Heating:Electric` (electric resistance heating)
* `AirLoopHVAC` (ventilation and heating only)

**Application:**

* Heated storage spaces
* Ventilation-only with heating backup
* Electric heating alternative to System 9

**Climate Zone Application:**

* CZ 0-3A (electric heating)

### System 11: SZ-VAV (Single Zone VAV System)

**Component Configuration:**

* Supply Fan: Variable volume fan with VFD control
* Cooling: Chilled water cooling coil (central plant)
* Heating: Climate zone dependent
  * CZ 0-2B: Electric resistance heating
  * CZ 3A and warmer: Hot water reheat or electric resistance
* Controls: Zone thermostat with VAV modulation

**EnergyPlus Objects:**

* `Fan:VariableVolume` (supply fan)
* `Coil:Cooling:Water` (cooling coil)
* `Coil:Heating:Water` or `Coil:Heating:Electric` (heating)
* `AirLoopHVAC:UnitarySystem` or `AirLoopHVAC`

**Application:**

* Medium-size buildings with single thermal zone control
* Flexible heating fuel based on climate

**Climate Zone Application:**

* CZ 0-2B: Electric heating
* CZ 3A+: Hot water or electric heating

### System 12: SZ-CV-HW (Single Zone Constant Volume with Hot Water)

**Component Configuration:**

* Supply Fan: Single-speed constant volume fan
* Cooling: Chilled water cooling coil
* Heating: Hot water heating coil
* Controls: Thermostat with continuous operation

**EnergyPlus Objects:**

* `Fan:ConstantVolume` (supply fan)
* `Coil:Cooling:Water` (cooling coil)
* `Coil:Heating:Water` (heating coil)
* `AirLoopHVAC:UnitarySystem`

**Application:**

* Medium-size buildings
* Simpler control without VAV
* Constant air volume regardless of load

**Climate Zone Application:**

* All climates with fossil fuel heating availability

### System 13: SZ-CV-ER (Single Zone Constant Volume with Electric Resistance)

**Component Configuration:**

* Supply Fan: Single-speed constant volume fan
* Cooling: Chilled water cooling coil
* Heating: Electric resistance heating coil
* Controls: Thermostat with continuous operation

**EnergyPlus Objects:**

* `Fan:ConstantVolume` (supply fan)
* `Coil:Cooling:Water` (cooling coil)
* `Coil:Heating:Electric` (electric resistance)
* `AirLoopHVAC:UnitarySystem`

**Application:**

* Medium-size buildings with electric heating
* No fossil fuel boiler required
* Simple constant volume control strategy

**Climate Zone Application:**

* CZ 0-3A (electric heating climates)

## System Selection Decision Tree

```
START: Building Type, Number of Floors, Floor Area, Climate Zone

RESIDENTIAL BUILDINGS
├─ CZ 3B-8 (Fossil Fuel) → System 1 (PTAC)
└─ CZ 0-3A (Electric) → System 2 (PTHP)

PUBLIC ASSEMBLY < 11,000 m²
├─ CZ 3B-8 → System 3 (PSZ-AC)
└─ CZ 0-3A → System 4 (PSZ-HP)

PUBLIC ASSEMBLY ≥ 11,000 m²
├─ CZ 3B-8 → System 12 (SZ-CV-HW)
└─ CZ 0-3A → System 13 (SZ-CV-ER)

HEATED-ONLY STORAGE
├─ CZ 3B-8 → System 9 (Gas Furnace)
└─ CZ 0-3A → System 10 (Electric Furnace)

NON-RESIDENTIAL SMALL (≤3 floors, <2,300 m²)
├─ CZ 3B-8 → System 3 (PSZ-AC)
└─ CZ 0-3A → System 4 (PSZ-HP)

NON-RESIDENTIAL MEDIUM (4-5 floors, <2,300 m² OR 5 floors, 2,300-14,000 m²)
├─ CZ 3B-8 → System 5 (PVAV Reheat)
└─ CZ 0-3A → System 6 (PVAV PFP Boxes)

NON-RESIDENTIAL LARGE (>5 floors OR >14,000 m²)
├─ CZ 3B-8 → System 7 (VAV Reheat)
└─ CZ 0-3A → System 8 (VAV PFP Boxes)
```

## Component Specifications by System

### Cooling System Efficiencies

| System Type   | Component     | Baseline Efficiency  | EnergyPlus Input         |
| ------------- | ------------- | -------------------- | ------------------------ |
| DX Cooling    | Packaged Unit | Variable by capacity | EIR from AHRI ratings    |
| Chiller       | Centrifugal   | 0.5-0.6 kW/ton       | Chiller:Electric:EIR     |
| Chiller       | Screw         | 0.55-0.65 kW/ton     | Chiller:Electric:EIR     |
| Cooling Tower | Single Speed  | Approach = 6.7°C     | CoolingTower:SingleSpeed |

### Heating System Efficiencies

| System Type         | Baseline Efficiency | EnergyPlus Input            |
| ------------------- | ------------------- | --------------------------- |
| Gas Furnace         | 0.80 (80%)          | Coil:Heating:Gas            |
| Gas Boiler          | 0.85 (85%)          | Boiler:HotWater             |
| Electric Resistance | 1.0 (100%)          | Coil:Heating:Electric       |
| Heat Pump (Heating) | 3.0 COP             | Coil:Heating:DX:SingleSpeed |

### Fan Specifications

| System Type     | Fan Control              | Power Per Flow | EnergyPlus Input   |
| --------------- | ------------------------ | -------------- | ------------------ |
| Constant Volume | On/Off or Always On      | 400-600 Pa     | Fan:ConstantVolume |
| Variable Volume | VFD with 0.5-1.0 minimum | 400-600 Pa     | Fan:VariableVolume |

## EnergyPlus Simulation Inputs

### Air Loop Configuration

```
AirLoopHVAC
├─ Outdoor Air Intake
├─ Supply Fan
├─ Cooling Coil
├─ Heating Coil
├─ Supply Air Nodes
└─ Thermal Zones
```

### Plant Loop Configuration

```
PlantLoop (Chilled Water)
├─ Pump
├─ Chiller
├─ Supply Nodes to Air Loops
└─ Return Nodes

PlantLoop (Condenser Water)
├─ Pump
├─ Cooling Tower
└─ Chiller Condenser Connection

PlantLoop (Hot Water)
├─ Pump
├─ Boiler
├─ Supply Nodes to Air Loops and Zones
└─ Return Nodes
```

## Climate Zone Definitions

| Climate Zone | Description    | Heating       | Cooling      | Baseline Fuel |
| ------------ | -------------- | ------------- | ------------ | ------------- |
| 0A           | Very Hot/Humid | Minimal       | Significant  | Electricity   |
| 0B           | Very Hot/Dry   | Minimal       | Significant  | Electricity   |
| 1A           | Hot/Humid      | Low           | Significant  | Electricity   |
| 1B           | Hot/Dry        | Low           | Significant  | Electricity   |
| 2A           | Hot/Humid      | Moderate      | Significant  | Electricity   |
| 2B           | Hot/Dry        | Moderate      | Significant  | Electricity   |
| 3A           | Warm/Humid     | Moderate      | Moderate     | Gas           |
| 3B           | Warm/Dry       | Moderate      | Moderate     | Gas           |
| 3C           | Warm/Marine    | Moderate      | Low          | Gas           |
| 4            | Mixed/All      | Moderate-High | Moderate     | Gas           |
| 5            | Cool           | High          | Moderate     | Gas           |
| 6            | Cool           | High          | Low-Moderate | Gas           |
| 7            | Very Cool      | Very High     | Low          | Gas           |
| 8            | Subarctic      | Very High     | Low          | Gas           |

## Key Controls and Setpoints

### Thermostat Setpoints (PRM Baseline)

* **Heating Setpoint:** 21°C (70°F)
* **Cooling Setpoint:** 24°C (75°F)
* **Deadband:** Minimum 1.7°C (3°F)

### VAV Terminal Minimum Flow

* **Default Minimum:** 50% of design air flow
* **Can be reduced to:** 30% with justification
* **Based on:** Ventilation requirements per ASHRAE 62.1

### Supply Air Temperature (SAT) Reset

* **Warmest Zone:** Increase SAT based on warmest zone heating load
* **Outside Air:** SAT reset based on outdoor temperature
* **Typical Range:** 13-21°C (55-70°F)

### Economizer Operation

* **Dry Bulb Cutoff:** 21°C outdoor (varies by climate)
* **Enthalpy Cutoff:** When outdoor air enthalpy exceeds return air
* **Integrated Mode:** Damper modulation for cooling assistance