Examples of EnergyPlus HVAC
Simulation 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
2 Zone Air Mixing
2.
Mi ing
3. Dedicated Outdoor Air Systems
2
1. Energy Management System in EnergyPlus
Standard control in EnergyPlus
Models typical operational strategies such as:
Thermostatic control, flow control, daily and
seasonal schedules,
Outdoor temperature reset, economizer control,
Equipment load staging, and daylighting control.
T i ll predefined
Typically
d fi d control
t l sequences with
ith only
l
schedules and set points accessible to the user.
Interactions between components are limited and
are usually hard-coded in the simulation program.
3
Energy Management System in EnergyPlus
Energy management system control
EMS in EnergyPlus is a powerful tool to simulate
complex HVAC system controls
E l t the
Emulates
th types
t
off controls
t l possible
ibl with
ith the
th digital
di it l
energy management systems used in real buildings
EMS enables control interactions between components
Accesses sensor data  initiates control actions
4
Energy Management System in EnergyPlus
EMS
Sensors (to “GET”)
Temperatures
Flow
Status (on/off)
Metered data
Actuators (to “SET”)
Availability on/off
AvailabilitySchedules
Setpoints (temp, humidity)
Flow
Fl
Programs – E+ Runtime Language (Erl)
Keywords (RUN, SET, IF, ELSEIF, ENDIF…)
Operators (+, -, /, …) & Built-in functions (math,
psychrometric,…)
5
Example of EMS in CBP Project
DOE’s Commercial Building Partnerships (CBP) Program
PNNL teamed with one of America’s largest retailers to explore energy design
measures by retrofitting one of their existing stores
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
Building type
Retail
Built
1987
Area
~100,000 ft2
No. of stories
6
Virginia
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
Control signal from main sales floor conditions
OA
VFD
RA
Sales floor (Control Zone)
Storage, offices, and other (Slave Zones)
7
Salon
Main office RTU2
RTU1
Supply Air Flow and Temperature Control
Heating setpoint 70 ºF
Cooling setpoint 75 ºF
Fan speed
control
Temperature
control
8
Modeling with EnergyPlus Standard Controls
Control
Zone
Control
Zone
Slave
Z
Zone
1
Control
Z
Zone
Slave
Zone 2
Control
Zone
9
…
…
Design schematic
Model in E+ with standard
control
Modeling with EnergyPlus Standard Controls
System
level
E+ objects and settings
Problems
AirLoopHVAC:OutdoorAirSystem
p
y
Coil:Cooling:Water
Fan:VariableVolume Max 100% Min 30%
• Slave zones
become control
zones
Coil:Heating:Gas
• Hypothetical central heating coil with zero W capacity
SetpointManager:Warmest
• Strategy: MaximumTemperature
• Supply fan stays
at minimum (30%)
at heating mode
AirTerminal:SingleDuct:VAV:Reheat
• Scheduled Minimum Flow Fraction at 30%
• Gas reheat. Duct furnace’s capacity is proportionally
split to terminal reheat coils based on design flow
Zone level • Reverse damper action
ThermostatSetpoint:DualSetpoint
• Deadband 70F - 75F for Control Zone
• Deadband
D db d 70F - 90F ffor Slave
Sl
Z
Zones
10
• Cannot realize
Heating: 34% at
1st stage, 66% at
2nd stage
• Cannot
synchronize
heating and VAV
damper positions
Simulated Controls with EMS
Control
Zone
Control
Zone
Slave
Zone 1
Slave
Zone 1
Slave
Zone 2
Slave
Zone 2
Design system
11
Simulated controls in
EnergyPlus with EMS
EMS Program Applied
IF Control Zone reheat coil
input, Q
SET
Q > = 50% capacity
2nd stage heating mode
• Slave Zone reheat coil availability = YES
• Slave and Control Zone min damper = 66%
0< Q < 50% Capacity
1st stage heating mode
• Slave Zone reheat coil availability = YES
• Slave and Control Zone min damper = 34%
• Slave Zone reheat coil availability = NO
Q=0
• Slave and Control Zone min damper = 30%
Ventilation or cooling mode • Slave Zone damper opening fraction =
Ventilation or cooling mode
Control Zone damper opening fraction
Sensor / Actuator
12
Hourly Results of Winter and Summer Days
H ti mode
Heating
d
C li mode
Cooling
d
Reheating coil availability and
VAV damper positions are
synchronized
Reheat coils input rate is not
available as actuator. EMS
EMS’
limitation
13
Other Examples of Use of EMS
Turn on a relief fan when economizer is in use
Simulate pressure control
If OA > Min Ventilation  Energize relief fan
Reduce cooling temperature setpoint if space humidity
exceeds threshold
If RH > 60%  Cooling
C li setpoint
t i t 75 72 d
deg. F
14
2. Zone Air Mixing in Energy Plus
ZoneMixing
Simplified treatment of air exchange between zones
User defined air transfer
Transfers energy from one zone to another (sensible and latent heat
transfer)
Input parameters
Source zone
Receiving zone
Airflow rate – flow per zone, flow/person, flow/area, ACH
Schedule
Delta temperature availability
Outdoor air temperature availability
15
Example of Zone Air Mixing in AEDG
Advanced Energy Design Guides
Guidance and recommendations by building
type and climate
Identifies pathways to 30% and 50% energy
savings
g
Collaboration of professional organizations
and DOE
Backed by technical support documents
(TSDs)
http://www.pnl.gov/main/publications/external/
technical_reports/PNNL-19809.pdf
16
Zone Air Mixing – AEDG Quick Service Restaurant
Transfer air from dining room used as MU air for kitchen exhaust
Location
Building type
Restaurant
Built
New Construction
Area
~25,000ft2
No. of stories
17
Various
1 level
Zone Air Mixing – AEDG Quick Service Restaurant
Transfer air from dining room used as MU air for kitchen exhaust
Bathroom
Exhaust
RTU-2
RTU 2
OA2 = 3,120
OA1 = 2,080
RTU-1
RTU 1
BX = 400
SA2
KX = 4,800
RA2
0
Kitchen
18
ZoneMixing,
Kitchen_Exhaust_Fan_Mixing,
Kitchen,
Hours_of_kitchen_operation,
_ _
_ p
Flow/Zone,
1,680,
Dining,
0.0;
RA1
TRA = 1,680
SA1
0
Dining Area
!- Name
!- Zone Name
!- Schedule Name
!- Design Flow Rate Calculation Method
!- Design Flow Rate {ft3/min}
!- Source Zone Name
!- Delta Temperature {deltaF}
Zone Air Mixing – AEDG Quick Service Restaurant
ZoneMixing – Not the perfect solution
Only energy balance is affected – air balance is “left to the user’s discretion”
Kitchen – Need to account for actual kitchen exhaust energy – increased SP
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.
Bathroom
Exhaust
RTU -2
OA2 = 3,120
RTU-1
OA1 = 2,080
OA2 = 3,120
SP2 = SP1 x 4,800
3,120
BX= 400
BX= 400
SA 2 RA2
KX= 4,800
0
RA1
TRA= 1,680
Kitchen
Actual Design
19
RTU-2
Bathroom “Dummy”
Exhaust Exhaust
SP =0
0
Dining Area
TX= 1,680
SA2 RA2
SA1
KX= 3,120
0
Kitchen
OA1 = 2,080
RTU-1
RA1
TRA= 1,680
0
Dining Area
Simulated Design
SA1
3. DOAS in EnergyPlus
DOAS
Two parallel HVAC systems serving a single zone
Decouples OA ventilation load from space loads
Better control of space temperature and humidity
Better control over quantity of OA
Single
S
geO
OA supp
supply
ya
and
de
exhaust
aus e
enhance
a ce e
energy
e gy recovery
eco e y
20
DOAS in EnergyPlus
Like many simulation programs E+ limit is one HVAC system per zone
Only one “air loop” serving a zone
Air loop can be DOAS serving multiple zones with zonal equipment
providing space conditioning (ex. fan coils, heat pumps or radiant panels)
Air loop can be space conditioning system serving multiple zones with
zonal DOAS
EnergyPlus Air Loop
21
Example of DOAS in AEDG Medium Office
Location
Building type
Medium Office
Built
New Construction
Area
~54,000ft2
No. of stories
22
Various
3 story
Example of DOAS in AEDG Medium Office
Fan Coil Units Combined with Multi-zone DOAS
DOAS With Energy Recovery DOAS DOAS control – SA
temperature based on OA
reset schedule
Fan coil control – thermostat
setpoint
OA EA
Conditioned OA
Conditioned OA RA
RA Fan Coil 23
Conditioned OA
Conditioned OA
F C il
Fan Coil
Example of DOAS in AEDG MediumOffice
DOAS Temperature Control
SA Tem
mp Deg. F.
SetpointManager:OutdoorAirReset,
SetpointManager:OutdoorAirReset
DOAS SAT setpoint,
!- Name
Temperature,
!- Control Variable
60,
!- Setpoint at Outdoor Low Temp
!- Outdoor Low Temp
p
50,,
55,
!- Setpoint at Outdoor High Temp
60,
!- Outdoor High Temp
DOAS Supply Outlet Node;
!- Setpoint Node or NodeList Name
DOAS Supply Air Reset
Schedule
61
60
59
58
57
56
55
54
0
20
40
60
80
100
OA Temp, Deg. F.
Fan Coil Control
ThermostatSetpoint:DualSetpoint,
Core_bottom DualSPSched, !- Name
HTGSETP_SCH,
!- Heat Setpoint Temp Sched Name
CLGSETP_SCH;
!- Cool Setpoint TempSched Name
Heating Setpoint
90
80
70
60
50
40
30
20
10
0
1
24
Cooling Setpoint
3
5
7
9 11 13 15 17 19 21 23
y
Weekday
25