BSUG EnergyPlus HVAC Features

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Examples of EnergyPlus HVACSimulation Features

Michael Rosenberg, Jian Zhang, Yunzhi Huang

Building Energy Simulation Forum

• November 16, 2011



EnergyPlus – Example HVAC Simulation Features

1. Built in Energy Management System

. x

3. Dedicated Outdoor Air Systems

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1. Energy Management System in EnergyPlus

Standard control in EnergyPlus

Thermostatic control, flow control, daily andseasonal schedules,

Outdoor temperature reset, economizer control,

Equipment load staging, and daylighting control.yp ca y pre e ne con ro sequences w on y

schedules and set points accessible to the user.

Interactions between components are limited and

are usually hard-coded in the simulation program.

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Energy Management System in EnergyPlus

Ener mana ement s stem control

EMS in EnergyPlus is a powerful tool to simulatecomplex HVAC system controls

mu a es e ypes o con ro s poss e w e g aenergy management systems used in real buildings

EMS enables control interactions between components

Accesses sensor data initiates control actions

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Energy Management System in EnergyPlus

EMS

Sensors (to “GET”)

TemperaturesFlow

Metered data

Actuators (to “SET”)-

Schedules

Setpoints (temp, humidity)

owPrograms – E+ Runtime Language (Erl)

Keywords (RUN, SET, IF, ELSEIF, ENDIF…)

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Operators (+, -, /, …) & Built-in functions (math,

psychrometric,…)



Example of EMS in CBP Project

DOE’s Commercial Building Partnerships (CBP) ProgramPNNL teamed with one of America’s largest retailers to explore energy design

Retrofit project goal: cutting site energy use by 30%Pre/post-renovation metering data available to calibrate simulation

Detailed simulation is required: EnergyPlus 4.0

Location Virginia

Building type Retail

Built 1987

6

Area ~100,000 ft2

No. of stories 1 level



Building HVAC System and Thermal Zoning

Built‐up air handling unit (AHU)

Chilled water cooling

Central system duct furnace

Operates like a single zone VAV system with inputs from main sales floor (Control Zone).

Other areas and zones (Slave Zones) are also served by zone heaters

OAVFD

Control signal from main sales floor conditions

RA

Main office

RTU1

Salon

RTU2Sales floor (Control Zone)

Storage, offices, and other (Slave Zones)

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Supply Air Flow and Temperature Control

Heating setpoint 70 ºF

Cooling setpoint 75 ºF

Fan speed

Temperature

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Modeling with EnergyPlus Standard Controls

Zone

Slave

Zone

Control

Zone 1

SlaveZone 2

Zone

ControlZone

Design schematic Model in E+ with standard

control

… …

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Modeling with EnergyPlus Standard Controls

E+ objects and settings Problems

AirLoo HVAC:OutdoorAirS stem • Slave zones

System

level

become control

zones

• Supply fan stays

Coil:Cooling:Water

Fan:VariableVolume Max 100% Min 30%

Coil:Heating:Gas

at minimum (30%)

at heating mode

• Cannot realize

• Hypothetical central heating coil with zero W capacity

SetpointManager:Warmest

• Strategy: MaximumTemperature

Heating: 34% at

1st stage, 66% at

2nd stage

• Scheduled Minimum Flow Fraction at 30%

• Gas reheat. Duct furnace’s capacity is proportionally

split to terminal reheat coils based on design flow•

• Cannotsynchronize

heating and VAV

damper positions

ThermostatSetpoint:DualSetpoint

• Deadband 70F - 75F for Control Zone• ea an - or ave ones

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Simulated Controls with EMS

ControlZone

ControlZone

Slave

Zone 1

Slave

Zone 1

Design system Simulated controls in

Zone 2

Zone 2

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EMS Program Applied

IF Control Zone reheat coil

input, Q SET

Q > = 50% capacity2nd stage heating mode

• Slave Zone reheat coil availability = YES• Slave and Control Zone min damper = 66%

0< Q < 50% Capacity1st stage heating mode

• Slave Zone reheat coil availability = YES

• Slave and Control Zone min damper = 34%

Q = 0

• Slave Zone reheat coil availability = NO

• Slave and Control Zone min damper = 30% Control Zone damper opening fraction

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Hourly Results of Winter and Summer Daysea ng mo e oo ng mo e

Reheating coil availability andVAV damper positions are

Reheat coils input rate is not’.

limitation

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Other Examples of Use of EMS

Turn on a relief fan when economizer is in use

Simulate pressure controlIf OA > Min Ventilation Energize relief fan

Reduce cooling temperature setpoint if space humidity

exceeds thresholdoo ng se po n eg.

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2. Zone Air Mixing in Energy Plus

ZoneMixing

User defined air transfer Transfers energy from one zone to another (sensible and latent heat

Input parametersSource zone

Receiving zone

Airflow rate – flow per zone, flow/person, flow/area, ACH

Schedule

Delta temperature availability

Outdoor air temperature availability

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Example of Zone Air Mixing in AEDG

Advanced Energy Design Guides

type and climateIdentifies pathways to 30% and 50% energysavin s

Collaboration of professional organizationsand DOE

Backed by technical support documents(TSDs)

http://www.pnl.gov/main/publications/external/technical_reports/PNNL-19809.pdf

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Zone Air Mixing – AEDG Quick Service Restaurant

Transfer air from dining room used as MU air for kitchen exhaust

Location Various

Building type Restaurant

Built New Construction

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Area ~25,000ft2

No. of stories 1 level




Transfer air from dining room used as MU air for kitchen exhaust

OA2 = 3,120 OA1 = 2,080

Bathroom

Exhaust

-

BX = 400

-

0 0KX = 4,800

TRA = 1,680

RA1SA2 RA2 SA1

Kitchen Dining Area

ZoneMixing,Kitchen_Exhaust_Fan_Mixing, !- Name

Kitchen, !- Zone Name

Hours_of_kitchen_operation, !- Schedule Name

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Flow/Zone, !- Design Flow Rate Calculation Method

1,680, !- Design Flow Rate {ft3/min}

Dining, !- Source Zone Name0.0; !- Delta Temperature {deltaF}




ZoneMixing – Not the perfect solutionOnly energy balance is affected – air balance is “left to the user’s discretion”

– –

Dining - Not an issue since equivalent air flow to transfer is relieved through RTU-1.Unless ERV is also included in dining zone, then “dummy” exhaust added.

RTU-1

BathroomExhaust

RTU-2 RTU-1

BathroomExhaust

RTU-2

“Dummy”Exhaust

SP =0SP2 = SP1 x 4,800

3,120

OA2 = 3,120 OA1 = 2,080OA2 = 3,120 OA1 = 2,080

0 0KX= 4,800

BX= 400

TRA= 1,680

RA1SA 2 RA2 SA1

0 0KX=3,120

BX= 400

TRA= 1,680

RA1SA2 RA2 SA1TX= 1,680

Kitchen Dining Area Kitchen Dining Area

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3. DOAS in EnergyPlus

DOASTwo parallel HVAC systems serving a single zone

Better control of space temperature and humidityBetter control over quantity of OA

Sin le OA su l and exhaust enhance ener recover

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DOAS in EnergyPlus

Like many simulation programs E+ limit is one HVAC system per zone

Only one “air loop” serving a zone

providing space conditioning (ex. fan coils, heat pumps or radiant panels)

Air loop can be space conditioning system serving multiple zones withzonal DOAS

EnergyPlus Air Loop

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Example of DOAS in AEDG Medium Office

Location Various

Building type Medium Office

Built New Construction

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Area ~54,000ft2

No. of stories 3 story



Example of DOAS in AEDG Medium Office

Fan Coil Units Combined with Multi-zone DOAS

DOAS DOAS With Energy Recovery –

OA OA temperature based on OAreset schedule

Fan coil control – thermostat

EA

RA RA

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Fan Coil an o



Example of DOAS in AEDG MediumOffice

DOAS Temperature Control DOAS Supply Air Reset,

DOAS SAT setpoint, !- Name

Temperature, !- Control Variable60, !- Setpoint at Outdoor Low Temp

50, !- Outdoor Low Tem58

59

60

61

p D e g .

F .

55, !- Setpoint at Outdoor High Temp

60, !- Outdoor High Temp

DOAS Supply Outlet Node; !- Setpoint Node or NodeList Name54

55

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0 20 40 60 80 100

S A

T e

OA Temp, Deg. F.

Fan Coil ControlThermostatSetpoint:DualSetpoint,

Core_bottom DualSPSched, !- Name 708090

Heating Setpoint Cooling Setpoint

HTGSETP_SCH, !- Heat Setpoint Temp Sched NameCLGSETP_SCH; !- Cool Setpoint TempSched Name

01020304050

1 3 5 7 9 11 13 15 17 19 21 23Weekda

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BSUG EnergyPlus HVAC Features