Lecture 10: Zone and Modeling Controls, Simple HVAC for Load Calculations Material prepared by GARD Analytics, Inc. and University of Illinois at Urbana-Champaign under contract to the National Renewable Energy Laboratory. All material Copyright U.S.D.O.E. - All rights reserved

2 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

3 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

4 Keywords Covered in this Lecture  Zone Control:Thermostatic  Single Heating Setpoint, Single Cooling Setpoint, Dual Setpoint With Deadband  Schedule (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

5 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 cooling Cools to setpoint, no heating “Perfect” control Heating below lower setpoint, Cooling above higher setpoint, Zone “floats” in deadband between setpoints

6 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)… ;

7 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

8 Zone Thermostat Control 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 heatingcoolingheating

9 Zone Thermostat Heating Setpoint Object SINGLE HEATING SETPOINT, Heating Setpoint with Setback, !- Setpoint control object name Heating 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 heating no conditioning

10 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

11 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 temperature  Resulting humidity level calculated  Controlled by Zone thermostat (dry bulb setpoint)  Calculates required flow rate at specified supply air temperature

12 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

13 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;

14 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)

15 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 transfer SOLUTION 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

16 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

17 Inside Convection Algorithm (cont’d)  ASHRAE Simple Correlation for Interior Convection Cool floor or warm ceiling: h conv = W/m 2 -K Tilted surface, reduced: h conv = W/m 2 -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: h conv = W/m 2 -K Warm floor or cool ceiling: h conv = W/m 2 -K Tilted surface, enhanced: h conv = W/m 2 -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

18 Inside Convection Algorithm (cont’d)  ASHRAE Detailed Correlation for Interior Convection Reduced convection: Vertical surface: Enhanced convection: where  surf is the tilt of the surface (  surf =0 for roof, =90 for vertical wall, =180 for floor)

19 Inside Convection Algorithm (cont’d)  Ceiling Diffuser Correlation Floor: Wall: Ceiling: where ACH is the air changes per hour of the HVAC system

20 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

21 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

22 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)

23 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)

24 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