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Scheduling VRF system

asked 2015-07-24 15:04:00 -0500

rkbest gravatar image

updated 2015-11-08 11:03:20 -0500

I am trying to model and compare results with actual measurement from a commercial building with 4 VRF heat pump and 7 Thermal Zone. What is the best way of using the schedules:- Requirements:- The 4 outdoor units are set to VRF and operate only between morning 5:30 to evening 8 pm. My understanding

  1. seven schedules on OS each for each zone with set temperature 74 and other times 100+(so that the system does not operate) or
  2. 4 schedules for each systems and common for common zones.

I am using VRF systems and VRF terminal units. My system can only provide heating or cooling at a time not simultaneously. Are my selections ok? Also for creating new schedule I did could not select the type of schedule for such operation. What other schedules will be required for the full model i.e.

  1. people
  2. equipment
  3. outdoor units
  4. Terminal units
  5. any other.
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answered 2015-07-24 17:25:04 -0500

updated 2015-07-24 22:12:22 -0500

With regards to the EnergyPlus side of the model, scheduling the VRF terminal units should be performed using the coil availability schedules. Using the thermostat temperature schedule to dictate operation (i.e., 74F otherwise 100F) will lead to the heating coil turning on when the system is expected to be off. Use of People and Equipment should be associated with their own independent schedules. See the VariableRefrigerantFlow_5Zone.idf example file for more information.

ZoneHVAC:TerminalUnit:VariableRefrigerantFlow,
  TU1,                     !- Zone Terminal Unit Name
  VRFAvailSched,           !- Terminal Unit Availability Schedule

Example Availability Schedule:

Schedule:Compact,
  VRFAvailSched,           !- Name
  Fraction,                !- Schedule Type Limits Name
  Through: 3/31,           !- Field 1
  For: AllDays,            !- Field 2
  Until: 24:00,1.0,        !- Field 3
  Through: 9/30,           !- Field 5
  For: WeekDays,           !- Field 6
  Until: 7:00,0.0,         !- Field 7
  Until: 17:00,1.0,        !- Field 9
  Until: 24:00,0.0,        !- Field 11
  For: SummerDesignDay WinterDesignDay, !- Field 13
  Until: 24:00,1.0,        !- Field 14
  For: AllOtherDays,       !- Field 16
  Until: 24:00,1.0,        !- Field 17
  Through: 12/31,          !- Field 19
  For: AllDays,            !- Field 20
  Until: 24:00,1.0;        !- Field 21

ZoneControl:Thermostat,
  SPACE1-1 Control,        !- Name
  SPACE1-1,                !- Zone or ZoneList Name
  Zone Control Type Sched, !- Control Type Schedule Name
  ThermostatSetpoint:DualSetpoint,  !- Control 1 Object Type
  DualSetPoint;            !- Control 1 Name

ThermostatSetpoint:DualSetpoint,
  DualSetPoint,            !- Name
  Htg-SetP-Sch,            !- Heating Setpoint Temperature Schedule Name
  Clg-SetP-Sch;            !- Cooling Setpoint Temperature Schedule Name
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@rraustad the Example VRF_5Zone.idf has 8 schedule objects and the type of schedule is Fraction. However, on inspection I see most of them including the one you mentioned above have either 0 or 1 value. 2. The VRFAvailSched above has value of 1.0 all the time, what is the significance of the Until:24:00, Until:7:00 etc. And why this one is Through: 3/31 instead of 12/31? I am trying to understand the selection criteria for the Schedule Type in OpenStudio/Energyplus. As my model from Openstudio only have 'Always On Discrete'. Oepnstudio tutorial don't talk about these VRF system configuratio

rkbest gravatar image rkbest  ( 2015-07-27 13:31:53 -0500 )edit

The VRFAvailSched determines if a VRF component will be on or off, thus a 0 or 1. You can also manipulate operation using the thermostat schedules. The schedule type can be any that will accept a 0 or 1, fraction, discrete, temperature, etc. You will typically select a schedule type that corresponds to the entries. In the VRFAvailSched above, there are 3 "Through:" entries, each of which should have a "For:" (daytypes) and "Until:" (times) field. You could also compress this schedule to have just Through: 12/31, For: Alldays, Until: 24:00,1; if you wanted the system "available" all the time.

rraustad gravatar image rraustad  ( 2015-07-27 14:51:34 -0500 )edit

So what I have understood is the for my VRF system+ Terminal units that run from morning 5:00 to evening 6:30 only cooling mode. I should have one schedule- VRFAvailSched, People, Equipment and a cooling set point schedule. Will these 4 schedules be complete to take care of all the HVAC control and operation.

rkbest gravatar image rkbest  ( 2015-07-31 14:40:40 -0500 )edit

EnergyPlus is quite flexible which is why there are so many schedules available to modify operation. To answer your question, yes...for now. Run the simulation and review the results. Don't just look at annual energy consumption, look closely at hourly equipment performance, zone occupancy, lighting, and equipment, etc. There are plenty of report variables to choose from in the rdd file. Critique everything. If things are not as you expect you can modify inputs or schedules to get the operation you desire.

rraustad gravatar image rraustad  ( 2015-08-06 11:51:54 -0500 )edit

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Asked: 2015-07-24 15:04:00 -0500

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Last updated: Jul 24 '15