# Presentation: 233781

## Building Systems Simulation

- Fred Buhl

## General Philosophy of the EnergyPlus Interface

## Trade-off Between Simulation Flexibility and Simplicity

- HVAC Simulation Based on Configurable Input Template Systems
- Code Allows Connection Flexibility
- Input Defines Specific System Configurations - Connections are in the Input
- Completely Modular Systems and Real-Time Controls Handled by Links to SPARK and TRNSYS

## HVAC Simulation High Level Structure

## Defining HVAC Systems as Components on a Fluid Loop

- Loops Define the Movement of Mass and Energy Within an HVAC System
- Air Loop
- Plant Loop
- Condenser Loop
*Electric Loop*
- Systems Defined by the Components on the HVAC Loops

## Air Loop Simulation

- Connects water side with zone equipment
- Simulates central air distribution, mixing, and conditioning
- Equipment: supply & return fans, central heating and cooling coils, heat recovery, mixed air box
- Control: supply air temperature, outside air economizer

## Zone Equipment Simulation

## Simplified Plant Node and Equipment Diagram

## Typical System

- <date/time>

## Demo Building

## Describing a System

- System Configuration
- directed graph: arcs and nodes
- Component Instantiation
- create each component with unique data
- Attach Components to System Graph
- associate components with nodes
- Specify System Control

## Eplus Components

- Simple
- input; initialize; calculate; report
- Compound
- assembled from multiple components
- simulated sequentially with overall control
- Complex
- component may be a system

## Eplus System Control

- High Level: Set Point Managers
- algorithms establish fluid loop set points
- similar to an EMS
- Control Inividual Components
- sense state at one point in system
- control flow at another point to match setpoint
- Plant: component sequencing & load management

## Zone Equipment

- Exhaust Fan
- Fan Coil Unit
- Window Air Conditioner
- Unit Ventilator
- Unit Heater
- Hot Water Baseboard

## Terminal Units

- Dual Duct Constant Volume
- Dual Duct Variable Volume
- Single Duct Constant Volume Reheat
- Single Duct Variable Volume Reheat

## Air System Components

- Hot Water Coil
- Chilled Water Coil
- Electric Heating Coil
- Gas Heating Coil
- DX Coil Unit
- Supply & Retrun Fan
- Outside Air Mixer & Economizer

## Plant Equipment

- Boiler
- Water Heater
- Chiller (performance curve based)
- Pump
- Cooling Tower
- Air Cooled Condenser

## Special Input Objects

- Schedules
- Curves
- Branches and Connectors
- Nodes
- Plant Operation Schemes
- Etc.

## Summary

- Loops are backbone of HVAC simulation
- all equipment attached to fluid loops
- zone connected to fluid loops via zone equipment
- Loop structure permits assembly of any system through input--not hardwired code
- Manager software structure allows future use of general solvers

## General Philosophy of Input/Output/Weather

- Simple, free-format text files
- SI units only
- Comma-separated
- Object-based
- Somewhat self-documenting
- Two parts—dictionary and data or simulation results
- Not user-friendly » Interfaces needed
- Can become large
- Designed for Flexibility for Developers

## Input Data Dictionary Example

- ZONE EXHAUST FAN,
-   A1 , \field Exhaust Fan Name
-   A2 , \field Availability Schedule
-        \type object-list
-        \object-list ScheduleNames
-   N1 , \field Fan Total Efficiency
-        \type real
-        \minimum 0.0
-        \maximum 1.0
-   N2 , \field Delta Pressure
-        \units Pa
-   N3 , \field Max Flow Rate
-        \units m3/sec
-   A3 , \field Fan_Inlet_Node
-   A4 ; \field Fan_Outlet_Node

## Input Example

-  ZONE EXHAUST FAN, Zone 2 Exhaust Fan,
-         FanAndCoilAvailSched,
-         0.6,   ! efficiency
-         125., ! pressure rise
-         0.1,   ! flow rate
-         Zone 2 Exhaust Node, ! inlet node
-         Zone 2 Exhaust Fan Outlet Node; ! outlet node

## Input Summary

- IDF Objects can be in Any Order
- IDF Objects are retrieved by each module to keep data local
- There are No Hard-wired Input Limits in EnergyPlus; Limits depend on Disk and Memory of User’s Computer

## User Output Reporting Flexibility

- User can Select Any Variables Available for Output
- User can Specify Output at Time Step, Hourly, Daily, Monthly, or Environment Intervals
- User can Schedule Each Output Variable
- User can Supply a Meter, i.e. Specify All Chiller Plants for Total Energy Consumption