Lecture 10: Zone and Modeling Controls, Simple HVAC for Load Calculations

Material prepared by GARD Analytics, Inc. and University of Illinoisat Urbana-Champaign under contract to the National Renewable Energy

Laboratory. All material Copyright 2002-2003 U.S.D.O.E. - All rights reserved

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Importance of this Lecture to the Simulation of Buildings

Almost all buildings are “controlled thermal environments”

To calculate how much energy is required to maintain the appropriate thermal environment, an energy simulation program needs the control strategy

Resulting heating and cooling loads can be a good basis for comparing different envelope designs before addressing HVAC issues

Simulation programs always have “details”—this lecture discusses some of the simulation parameters that might be of importance to some runs

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Purpose of this Lecture

Gain an understanding of how to: Obtain heating and cooling loads for

zones without defining an entire HVAC system

Calculate approximate air flow rates for zones

Control some of the modeling details of a thermal simulation using EnergyPlus

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Keywords Covered in this Lecture

Zone Control:ThermostaticSingle Heating Setpoint, Single Cooling

Setpoint, Dual Setpoint With DeadbandSchedule (review)Purchased Air (and some affiliated input)Simulation Control Parameters: TimeStep

in Hour, Inside/Outside Convection Algorithm, Sky Radiance Distribution, Solution Algorithm, Shadowing Calculation, Convection Coefficients

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Thermostatic Control

Controls zone to a specified temperature

Control options include:0 – Uncontrolled

1 – Single heating setpoint

2 – Single cooling setpoint

3 – Single heating/cooling setpoint

4 – Dual setpoint with deadband

No heating or cooling, zone “floats”

Heats to setpoint, no coolingCools to setpoint, no heating

“Perfect” control

Heating below lower setpoint,Cooling above higher setpoint,Zone “floats” in deadband between setpoints

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Zone Thermostat

Basic Format of EnergyPlus Input:ZONE CONTROL:THERMOSTATIC,

Zone Name,

Control Type SCHEDULE Name,

Control Type #1,

!-Single Heating Setpoint Control type sched = 1

!-Single Cooling SetPoint Control type sched = 2

!-Single Heating Cooling Setpoint Control type sched = 3

!-Dual Setpoint with Deadband Control type sched = 4

Control Type Name #1,

…(Repeat for each thermostatic control type in zone)… ;

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Zone Thermostat - Example

ZONE CONTROL:THERMOSTATIC,

SPACE1-1 Control, !- Thermostat Name

SPACE1-1, !- Zone Name

Zone Control Type Sched, !- Control Type SCHEDULE Name

Single Cooling Setpoint, !- Control Type

Cooling Setpoint with Setback, !- Control Type Name

Single Heating Setpoint, !- Control Type

Heating Setpoint with Setback; !- Control Type Name

Schedules of setpoint temperatures (example on slide 9); allows setpoint temperature to vary (i.e., setback)

Schedule of control type parameter (0-4);determines which control type is valid at a particular time

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Zone ThermostatControl Type Schedule

DAYSCHEDULE, Summer Control Type Day Sch, Control Type, 2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2; ! 2=single cool SP

DAYSCHEDULE, Winter Control Type Day Sch, Control Type, 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1; ! 1=single heat SP

WEEKSCHEDULE, Summer Control Type Week Sch, Summer Control Type Day Sch, . . . ;

WEEKSCHEDULE, Winter Control Type Week Sch, Winter Control Type Day Sch, . . . ;

SCHEDULE, Zone Control Type Sched, Control Type, Winter Control Type Week Sch, 1,1, 3,31, Summer Control Type Week Sch, 4,1, 9,30, Winter Control Type Week Sch, 10,1, 12,31;

Values can change hourly if necessary (0-4) to model situations such as heating/cooling during the day and heating only at night for freeze protection

J F M A M J J A S O N D

Control Type Schedule

heating cooling heating

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Zone ThermostatHeating Setpoint Object

SINGLE HEATING SETPOINT, Heating Setpoint with Setback, !- Setpoint control object nameHeating Setpoints; !- Setpoint schedule

DAYSCHEDULE, Heating Setpoint Day Sch, Temperature, 15.,15.,15.,15.,15.,15.,15.,20.,20.,20.,20.,20.,20.,20.,20.,20.,20., 15.,15.,15.,15.,15.,15.,15.;

WEEKSCHEDULE, Heating Setpoint Week Sch, !- Name Heating Setpoint Day Sch, !- Sunday DAYSCHEDULE Name Heating Setpoint Day Sch, !- Monday DAYSCHEDULE Name Heating Setpoint Day Sch, !- Tuesday DAYSCHEDULE Name Heating Setpoint Day Sch, !- Wednesday DAYSCHEDULE Name Heating Setpoint Day Sch, !- Thursday DAYSCHEDULE Name Heating Setpoint Day Sch, !- Friday DAYSCHEDULE Name Heating Setpoint Day Sch, !- Saturday DAYSCHEDULE Name Heating Setpoint Day Sch, !- Holiday DAYSCHEDULE Name Heating Setpoint Day Sch, !- SummerDesignDay DAYSCHEDULE Name Heating Setpoint Day Sch, !- WinterDesignDay DAYSCHEDULE Name Heating Setpoint Day Sch, !- CustomDay1 DAYSCHEDULE Name Heating Setpoint Day Sch; !- CustomDay2 DAYSCHEDULE Name

SCHEDULE, Heating Setpoints, Temperature, Heating Setpoint Week Sch, 1,1, 12,31;

midnight 6am noon 6pm

1520

heating

no conditioning

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Set Point Objects - Examples

SINGLE HEATING SETPOINT,

HeatingSetpoint, !- Name

Htg-SetP-Sch; !- Setpoint Temp SCHEDULE Name

SINGLE COOLING SETPOINT,

CoolingSetpoint, !- Name

Clg-SetP-Sch; !- Setpoint Temp SCHEDULE Name

DUAL SETPOINT WITH DEADBAND,

DualSetPoint, !- Name

Htg-SetP-Sch, !- Heating Setpoint Temp SCHEDULE Name

Clg-SetP-Sch; !- Cooling Setpoint Temp SCHEDULE Name

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Purchased Air

Used to compute zone heating/cooling loads without modeling an HVAC system

Unlimited capacity at specified temperature and humidity

Controls only Zone dry bulb temperatureResulting humidity level calculatedControlled by Zone thermostat (dry bulb

setpoint)Calculates required flow rate at specified

supply air temperature

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Purchased Air – Example

PURCHASED AIR, Zone1Air, !- Purchased Air Name NODE_1, !- Zone Supply Air Node Name 50, !- Heating Supply Air Temp {C} 15, !- Cooling Supply Air Temp {C} 0.02, !- Heating Supply Air Humidity Ratio {kg-H20/kg-air} 0.02; !- Cooling Supply Air Humidity Ratio {kg-H20/kg-air}CONTROLLED ZONE EQUIP CONFIGURATION, RESISTIVE ZONE, Zone1Equipment, Zone1Inlets, , NODE_4,NODE_5;ZONE EQUIPMENT LIST, Zone1Equipment, PURCHASED AIR, Zone1Air, 1, 1;NODE LIST, Zone1Inlets, NODE_1;

These keywords will be discussed in more detail in a future lecture; all are required to get purchased air to work

Note that the colors in the above example denote the interconnections of these different statements

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Complete Purchased Air Example (Everything you need to condition a zone)

SCHEDULETYPE,ControlType,0:4,DISCRETE;DAYSCHEDULE,Zone Control Day, ControlType,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4;WEEKSCHEDULE, Zone Control Week, Zone Control Day,Zone Control Day,Zone Control Day,Zone Control Day,Zone Control Day,Zone Control Day, Zone Control Day,Zone Control Day,Zone Control Day,Zone Control Day,Zone Control Day,Zone Control Day;SCHEDULE, Zone Control Type Schedule, ControlType, Zone Control Week,1,1,12,31;DAYSCHEDULE,Heat Temp 5,Temperature, 20.0, 20.0, 20.0, 20.0, 20.0, 20.0, 20.0, 20.0, 20.0, 20.0, 20.0,

20.0, 20.0, 20.0, 20.0, 20.0, 20.0, 20.0, 20.0, 20.0, 20.0, 20.0, 20.0, 20.0;DAYSCHEDULE,Cool Temp 5,Temperature, 25.6, 25.6, 25.6, 25.6, 25.6, 25.6, 25.6, 25.6, 25.6, 25.6, 25.6,

25.6, 25.6, 25.6, 25.6, 25.6, 25.6, 25.6, 25.6, 25.6, 25.6, 25.6, 25.6, 25.6;WEEKSCHEDULE,HEAT-DEAD BAND, Heat Temp 5, Heat Temp 5, Heat Temp 5, Heat Temp 5, Heat Temp 5, Heat Temp 5,

Heat Temp 5, Heat Temp 5, Heat Temp 5, Heat Temp 5, Heat Temp 5, Heat Temp 5;WEEKSCHEDULE,COOL-DEAD BAND, Cool Temp 5, Cool Temp 5, Cool Temp 5, Cool Temp 5, Cool Temp 5, Cool Temp 5,

Cool Temp 5, Cool Temp 5, Cool Temp 5, Cool Temp 5, Cool Temp 5, Cool Temp 5;SCHEDULE,ZONE 1 Heating Setpoints,Temperature,HEAT-DEAD BAND, 1, 1,12,31;SCHEDULE,ZONE 1 Cooling Setpoints,Temperature,COOL-DEAD BAND, 1, 1,12,31;

ZONE CONTROL:THERMOSTATIC, ZONE 1 CONTROLS, ZONE 1,Zone Control Type Schedule,DUAL SETPOINT WITH DEADBAND, ZONE 1 SETPOINTS;

DUAL SETPOINT WITH DEADBAND, ZONE 1 SETPOINTS,ZONE 1 Heating Setpoints,ZONE 1 Cooling Setpoints;PURCHASED AIR, ZONE 1 PURCHASED AIR, ZONE 1 INLETS, !- Zone Supply Air Node 50, !- Heating Supply Air Temperature {C} 13, !- Cooling Supply Air Temperature {C} 0.015, !- Heating Supply Air Humidity Ratio {kg-H2O/kg-Air} 0.010; !- Cooling Supply Air Humidity Ratio {kg-H2O/kg-Air}CONTROLLED ZONE EQUIP CONFIGURATION, ZONE 1, ZONE 1 EQUIPMENT, ZONE 1 INLETS,, ZONE 1 NODE, ZONE 1 OUTLET;ZONE EQUIPMENT LIST, ZONE 1 EQUIPMENT, PURCHASED AIR, ZONE 1 PURCHASED AIR, 1, 1;NODE LIST, ZONE 1 INLETS,ZONE 1 INLET;

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TimeStep in Hour

EnergyPlus is a “sub-hourly” simulation program—capable of simulating the building at time steps of less than one hour

Example:TIMESTEP IN HOUR, 4; !- Number of time steps in an hour--validity 1 to 6--4 suggested

Sets time step for zone portion of simulation to 15 minutes;HVAC may run at time steps of less than 15 minutes to insure the stability of the system response (adaptive time step discussed in future lecture)

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Solution Algorithm

User has ability to control the details of the simulation algorithm Options include standard heat

transfer only, heat and mass transfer, and detailed (layer-by-layer) heat and mass transferSOLUTION ALGORITHM,

\memo Determines which Heat Balance Algorithm will be used \unique-object A1 ; \field Solution Algorithm \required-field \type choice \key CTF—Conduction Transfer Functions (heat transfer only) \key MTF—Moisture Transfer Functions (detailed heat+mass) \key EMPD—Effective Moisture Penetration Depth (heat+mass) \default CTF

Note that requesting heat and mass transfer simulations can significantly increase execution time

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Inside Convection Algorithm

User may selection the inside convection correlation from following options: Simple—constant natural convection Detailed—variable natural convection CeilingDiffuser—ACH-based correlation TrombeWall—closed rectangular cavity

from ASHRAE

from research

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Inside Convection Algorithm (cont’d)

ASHRAE Simple Correlation for Interior Convection Cool floor or warm ceiling: hconv = 0.948 W/m2-K Tilted surface, reduced: hconv = 2.281 W/m2-K

where reduced means a surface tilted in such a way as to mimic the poorer conditions for natural convection as in the cool floor/warm ceiling situation

Vertical surface: hconv = 3.076 W/m2-K Warm floor or cool ceiling: hconv = 4.040 W/m2-K Tilted surface, enhanced: hconv = 3.870 W/m2-K

where enhanced means a surface tilted in such a way as to mimic the better conditions for natural convection as in the warm floor/cool ceiling situation

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Inside Convection Algorithm (cont’d)

ASHRAE Detailed Correlation for Interior Convection

Reduced convection:

Vertical surface:

Enhanced convection:

surf

3airsurf

conv cos382.1

TT81.1h

3airsurfconv TT31.1h

surf

3airsurf

conv cos283.7

TT482.9h

where surf is the tilt of the surface(surf=0 for roof, =90 for vertical wall, =180 for floor)

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Inside Convection Algorithm (cont’d)

Ceiling Diffuser Correlation

Floor:

Wall:

Ceiling:

98.0conv ACH082.0873.3h

where ACH is the air changes per hour of the HVAC system

604.0conv ACH012.1208.1h

503.0conv ACH099.4234.2h

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Outside Convection Algorithm

User may selection the outside convection correlation from following options: Simple—constant natural convection

where D, E, and F vary with surface roughness

Detailed—variable natural convection

where A incorporates surface and wind direction factors while B takes roughness into account and hnatural is identical to the natural convection correlation for the detailed inside convection algorithm

2windroughwindroughroughconv VFVEDh

windroughsurfnaturalconv VBAhh

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ConvectionCoefficients

Allows user to set interior and/or exterior convection coefficients Could be used for comparison to other

programs or to determine influence of convection coefficients on simulation

ConvectionCoefficients, A1, \field SurfaceName A2, \field Convection Type #1 (either “Interior” or “Exterior”) A3, \field Convection Value Type #1 (either “Value” or “Schedule”) N1, \field Convection value #1 (W/m2-K, only used if A3 is Value) A4, \field Convection Schedule #1 (only used if A3 is Schedule) A5, \field Convection Type #2 (either “Interior” or “Exterior”) A6, \field Convection Value Type #2 (either “Value” or “Schedule”) N2, \field Convection value #2 (W/m2-K, only used if A3 is Value) A7; \field Convection Schedule #2 (only used if A3 is Schedule)

Two per surface to allow specification of both interior and exterior

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Shadowing Calculation

EnergyPlus does shadowing calculation for periods of time and assumes that the shadow casting over this time period is the same each day

User can control how often this is done through Shadowing Calculation input Can force EnergyPlus to do this every day Shorter shadowing periods result in longer

run times for EnergyPlus

SHADOWING CALCULATIONS, N1 ; \field Shadowing period length in days (0 will use E+ default)

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Airflow Model

This parameter is only needed if the user is trying to do detailed airflow studies using the EnergyPlus link to COMIS

This statement tells EnergyPlus to do the COMIS simulation but much more input data is required (see next lecture)

Airflow Model, COMIS; !- Airflow model type (COMIS or Simple, default is Simple)

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Summary

Zone Thermostat input allows control of the air temperature within individual zones—control setpoint can change on an hourly basis

Purchased Air can be used as a simple HVAC system when doing initial studies or trying to determine the size of the air handling system

User has the option to control various details of the simulation such as time step, convection algorithms, shading calculations, and air flow modeling