Lecture 8: Schedules and Internal Heat Gains

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

Every building is different in many ways: Location/exterior environment Construction/building envelope Space usage/interior environment HVAC system

Thermal simulation requires information about the functions taking place inside the building and how these might add or subtract heat from the zones

Thermal simulation requires information on air leakage to and from the building to determine its effect on the building heating and cooling needs

Nothing is constant inside a building—people come and go, lights and equipment gets turned on and off, etc.—and the thermal simulation needs details on what is happening through the day and year within a building

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Purpose of this Lecture

Gain an understanding of how to internal heat gains impact and space and how to specify them People, Lights, Equipment, etc. Infiltration Schedules

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Keywords Covered in this Lecture

ScheduleType DaySchedule WeekSchedule Schedule People and AngleFactorList Lights Equipment—Electric, Gas, Hot Water, Steam,

Baseboard (scheduled), Other Exterior Equipment Infiltration

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Schedules

In general, schedules are a way of specifying how much or many of a particular quantity is present or at what level something should be set, including: Occupancy density Occupancy activity Lighting Thermostatic controls Shading element density

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Schedules (cont’d)

For internal gains, schedules allow us to come a little closer to the real variation of building quantities than single values

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how we account for internal gainsaverage

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Schedules in EnergyPlus

EnergyPlus uses a hierarchy of schedule pieces to create unique schedules

DaySchedule: 24 hour period of schedule values

WeekSchedule: Consists of various DaySchedule definitions for an entire week

Schedule: Consists of various WeekSchedule definitions for an entire year

ScheduleType: Optional feature that allows for some validation and limitation of schedules (avoid mistakes)

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ScheduleType

ScheduleType, Any Number; !- ScheduleType NameScheduleType, Fraction, !- ScheduleType Name 0.0:1.0, !- range CONTINUOUS; !- Numeric TypeScheduleType, Temperature, !- ScheduleType Name -60:200, !- range CONTINUOUS; !- Numeric TypeScheduleType, Control Type, !- ScheduleType Name 0:4, !- range DISCRETE; !- Numeric Type

Used to validate schedule values (optional)

Notes: Maximum and minimum of range (inclusive) separated by colonDiscrete refers to distinct integer valuesContinuous to any value in the range

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DaySchedule

DAYSCHEDULE, OC-1, !- Name Fraction, !- ScheduleType 0.0, !- Hour 1 0.0, !- Hour 2 0.0, !- Hour 3 0.0, !- Hour 4 0.0, !- Hour 5 . . . 1.0, !- Hour 17 1.0, !- Hour 18 0.0, !- Hour 19 0.0, !- Hour 20 0.0, !- Hour 21 0.0, !- Hour 22 0.0, !- Hour 23 0.0; !- Hour 24

The day description is simply a name and the 24 hourly values associated with that name

Other forms DaySchedule:Interval DaySchedule:List Can handle subhourly schedule changes

Hour 1 is Midnight to 1am

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WeekSchedule

WEEKSCHEDULE, ActWeekSchd, !- Name ActDaySchd2, !- Sunday DAYSCHEDULE Name ActDaySchd1, !- Monday DAYSCHEDULE Name ActDaySchd1, !- Tuesday DAYSCHEDULE Name ActDaySchd1, !- Wednesday DAYSCHEDULE Name ActDaySchd1, !- Thursday DAYSCHEDULE Name ActDaySchd1, !- Friday DAYSCHEDULE Name ActDaySchd2, !- Saturday DAYSCHEDULE Name ActDaySchd3, !- Holiday DAYSCHEDULE Name ActDaySchd4, !- SummerDesignDay DAYSCHEDULE Name ActDaySchd4, !- WinterDesignDay DAYSCHEDULE Name ActDaySchd3, !- CustomDay1 DAYSCHEDULE Name ActDaySchd3; !- CustomDay2 DAYSCHEDULE Name

The week description has an identifier and 12 names corresponding to previously defined DaySchedules

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Schedule

SCHEDULE, OCCUPY-1, !- Name Fraction, !- ScheduleType OC-WEEK, !- Name of WEEKSCHEDULE 1 1, !- Start Month 1 1, !- Start Day 1 12, !- End Month 1 31; !- End Day 1

Annual schedule contains an identifier and the names and from-thru dates of the week schedules associated with the annual schedule

Up to 52 week schedules can be specified, allowing unique specification of every day of the year Other forms

WeekSchedule:Compact Schedule:Compact

Repeat as needed

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Complete Schedule Specification

Example of an EnergyPlus Schedule:ScheduleType, Any Number;

DaySchedule, Weekday, Any Number, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.10, 0.50, 1.00, 1.00, 1.00, 1.00, 0.50, 1.00, 1.00, 1.00, 0.50, 0.10, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00;DaySchedule, Weekend, Any Number, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00, 0.00;WeekSchedule, Office Occupancy Schedule, Weekend, Weekday, Weekday, Weekday, Weekday, Weekday, Weekend, Weekend, Weekend, Weekend, Weekend, Weekend;Schedule, Office Occupancy Schedule, 1, 1, 12, 31;

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Types of Internal Gains

PeopleLightsEquipmentInfiltrationSee “Input Output Reference” –

Space Gains

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Heat Additions from Internal Gains

Sensible vs. Latent Sensible—energy addition associated with

(dry-bulb) temperature change in zone Latent—energy addition associate with

moisture/humidity change in zoneSensible Heat Gains

Convection Thermal (Long Wavelength) Radiation Visible (Short Wavelength) Radiation

(generally lights only)

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People

Peak ValueScheduleRadiant fraction (remainder of sensible

gain is convection)Activity level schedule (W/person)

Total heat gain—broken up into sensible and latent fractions within the program automatically

Thermal comfort reports Fanger Pierce Two-Node Kansas State University Two-Node

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People: Example

PEOPLE, EAST ZONE, !- Zone Name 3.000000, !- Number of People BLDG Sch 1, !- Number of People SCHEDULE Name (real--fraction) 0.3000000, !- Fraction Radiant Activity Sch, !- Activity level SCHEDULE Name (units W/person) EAST ZONE, !- PEOPLE Group Name ZoneAveraged, !- MRT Calculation Type , !- Surface Name/Angle Factor List Name Work Eff Sch, !- Work Efficiency SCHEDULE Name (0.0-1.0,real) Clothing Sch, !- Clothing Insulation SCHEDULE Name (real) Air Velo Sch, !- Air Velocity SCHEDULE Name (units m/s, real) Fanger; !- Thermal Comfort Report Type (Fanger, Pierce, KSU)

Options are ZoneAveraged, SurfaceWeighted, or AngleFactor; determines the position that MRT is calculated at (center of zone, near a surface, or at a particular point through user supplied angle factors)

Apply only to thermal comfort models, not the heat balance

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People: Other Notes

Estimating the Number of People Based on type of space/activity See ASHRAE Standard 62 for estimates Example: 7 people/100m2 for an office setting

Estimating the Activity Level Based on activity within the zone See ASHRAE Handbook of Fundamentals, Thermal

Comfort Chapter or Nonresidential Cooling and Heating Load Calculation Procedures Chapter for estimates

Example: 115W/person for seated, light office work Estimating the Percent Radiant

Common values range from 30-40% (0.3-0.4)

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AngleFactorList

Allows user to specify angle factors for various surfaces to define influence on Mean Radiant Temperature (MRT) for thermal comfort evaluation

AngleFactorList, West Wing Angle Factors, !- Angle Factor List Name West Wing, !- Zone Name Zone001:Surf001, !- Surface Name 1 0.20, !- Angle Factor 1 Zone001:Surf002, !- Surface Name 2 0.20, !- Angle Factor 2 Zone001:Surf003, !- Surface Name 3 0.20, !- Angle Factor 3 Zone001:Ceiling001, !- Surface Name 4 0.15, !- Angle Factor 4 Zone001:Floor001, !- Surface Name 5 0.25; !- Angle Factor 5

SurfacesofNumber

1iiiTAFMRT

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Lights

Peak Value (all sensible)ScheduleRadiant, visible, replaceable,

return air fractions (remainder is convection)

Meter end use categoryLIGHTS, EAST ZONE, !- Zone Name BLDG Sch 3, !- SCHEDULE Name 1464.375, !- Design Level {W} 0.0000000E+00, !- Return Air Fraction 0.2000000, !- Fraction Radiant 0.2000000, !- Fraction Visible 0.0000000E+00, !- Fraction Replaceable GeneralLights; !- LightsEndUseKey

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Lights: Other Notes

Estimating the Input for Lighting Level Count the number and wattage of

bulbs in zone Estimate using information from:

Typically ranges from 1.0 – 2.0 W/ft2, example: 1.3 W/ft2 for office setting

ASHRAE Standard 90.1 ASHRAE Handbook of Fundamentals,

Nonresidential Cooling and Heating Load Calculation Procedures Chapter

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Electric Equipment

Peak ValueScheduleLatent fraction is fraction of totalRadiant and lost fractions of

sensible only (remainder of sensible is convection) ELECTRIC EQUIPMENT,

NORTH ZONE, !- Zone Name BLDG Sch 2, !- SCHEDULE Name 2928.751, !- Design Level {W} 0.0, !- Fraction Latent 0.3, !- Fraction Radiant 0.0; !- Fraction Lost

Basically, energy that does not affect the zone heat balance (vented to exterior environment)

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Electric Equipment: Other Notes

Estimating the Input for Design Level See ASHRAE Handbook of Fundamentals,

Nonresidential Cooling and Heating Load Calculation Procedures Chapter for approximate levels for individual components

Note: Nameplate ratings are generally not good estimates of power consumption of electrical equipment (example—nameplates might add up to 35 W/m2 but actual consumption might only be 8W/m2 in an office setting)

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Other Types of Equipment

Other equipment types in EnergyPlus that have same input format as Electric Equipment (just a different keyword) Gas Equipment Hot Water Equipment Steam Equipment Other Equipment

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“Scheduled” Baseboard Heaters

Moderately controllable baseboard heaters that do not interact with the rest of the HVAC system

Keyword is “Baseboard Heat”Baseboard Heat is first priority and will

react based on outside dry-bulb temperature and input definition

Baseboard that interacts with the HVAC system and controlled based on zone temperature under the following keywords: BASEBOARD HEATER:Water:Convective BASEBOARD HEATER:Electric:Convective

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Baseboard Heat Example

Example of Baseboard Heat usage:

Response:

BASEBOARD HEAT, North Zone , !- Zone Name Baseboard Availability Schedule , !- SCHEDULE Name 15000, !- Capacity at low temperature in W (> 0) 32, !- Low Temperature in degrees C 0, !- Capacity at high temperature in W (>= 0) 65, !- High Temperature in degrees C 0.3; !- Fraction Radiant (remainder of heat is convective)

Outside Dry-Bulb

Temperature

Baseboard Output (W)

0

5000

10000

15000

30 40 50 60 70

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Exterior Equipment

Convenient way to account for elements on exterior of building that add to overall energy consumption of site but do not affect heat balance of any zones ExteriorLights ExteriorFuelEquipment

ExteriorWaterEquipmentExteriorLights, !- only used for reporting, does not affect loads Outside Lighting, !- Descriptive Name ExtLightingSched, !- SCHEDULE Name 200.0; !- Design Level (Watts)

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Infiltration

What is it? Definition: uncontrolled or unintended

flow of outdoor air into a building due to… Cracks and other unintentional openings Normal use of exterior doors Through building materials

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Infiltration (cont’d)

What it’s not: Exfiltration: uncontrolled flow of indoor air

out of the building, caused by “pressurizing” the building through a mechanical system (no effect on zone heat balance but effect on HVAC system)

Ventilation: purposeful opening of windows or doors to promote air exchange with the outside environment (see future lecture)

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Infiltration: Causes

Cause: pressure differential Flow of mass from higher pressure to

lower pressure areaDriving forces:

Wind Buoyancy or “stack” effect HVAC system Note: all of these can vary based on

location within a building

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Accounting for Infiltration Heat Gain/Loss

Difficult to estimateMore sophisticated estimates

generally take a form similar to: Q=c(p)n

Estimation based on either ACH or “crack” method See ASHRAE Handbook of Fundamentals,

Ventilation and Infiltration Chapter for more details

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ACH: Air Changes per Hour

Definition: fraction of room air volume exchanged with outside air in a given hour

An ACH of 1.0 means that the entire air volume of a space is replaced with outside air each hour Heat gain/loss can be significant Effect moderated by energy storage

within the building

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Infiltration in EnergyPlus

INFILTRATION, !- Infiltration is specified as a design level which is modified !- by a schedule fraction, temperature difference and wind speed: !- Infiltration = Idesign * Fschedule * !- (A + B*|Tzone-Todb| + C*WindSpd + D * WindSpd**2) West Wing, !- Zone Name CONSTANT, !- SCHEDULE Name (Fschedule in Equation) 0.12, !- Design Volume Flow Rate in m3/s (Idesign in Equation) 1.0, !- Constant Term Coefficient (“A” in Equation) 0.0, !- Temperature Term Coefficient (“B” in Equation) 0.0, !- Velocity Term Coefficient (“C” in Equation) 0.0; !- Velocity Squared Term Coefficient (“D” in Equation)

Example from an IDF file:

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Summary

Schedules are a vital part of EnergyPlus input and play a role in the definition of many different components

Schedules are a hierarchy of: Day schedules Week schedules Schedules

Scheduled heat gains/losses such as People, Lights, Equipment, Infiltration, etc. can have a significant impact on conditions within a zone and must be taken into account