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How to calculate total space heating/air conditioning in EP?

asked 2021-05-05 14:09:55 -0600

ChrisW gravatar image

updated 2021-05-06 15:39:54 -0600

Hi everyone. I am using EnergyPlus to calculate actual space conditioning load for the entire building (facility). The IDF file I am using is one of the prototypes from here (https://www.energycodes.gov/developme...). I know we can add new outputs in "Output:Meter" for IDF file in IDF Editor, but the available meter options do not include total space heating energy or total AC energy.

For example, based on mtd file, the energy use for cooling should include supply fans, pumps, and cooling coil, but the option "Cooling:Electricity" only considers cooling coil. Other options such as "Fans:Electricity" includes fans for both heating and cooling, which is impossible to separate heating fans from cooling fans.

Is there any option we can use to output total energy use separately for space heating and air conditioning? Thank you.

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answered 2021-05-05 19:56:50 -0600

Typically, cooling/heating energy implies the amount of fuel (electricity or gas) consumed to provide the thermal energy only. Equipment such as fans and pumps are generally not included in "cooling energy", because it's difficult to determine whether a fan/pump is being used for heating or cooling at any given time. For example, in a VAV reheat system, the air handler could be providing air to multiple zones with a single fan, some of which are calling for heating (reheating at the terminal unit), while others are calling for cooling (no reheat) or neutral supply air to satisfy ventilation requirements. Similarly, a pump that circulates condenser water to water-sourced heat pumps could be serving some units that are heating and others that are cooling.

If your systems are setup such that you can separate heating and cooling fans/pumps, you could label them as such in their end-use subcategory field, and they will be delineated in the End Uses By Subcategory output table.

I'm not sure what you mean by:

based on mtd file, the energy use for cooling should include supply fans, pumps, and cooling coil.

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For "based on mtd file, the energy use for cooling should include supply fans, pumps, and cooling coil" - I was thinking that we should consider energy use of supply fans, pumps, and cooling coil as the total energy used for cooling. But I understand this according to your explanation. Thank you!

ChrisW gravatar image ChrisW  ( 2021-05-06 01:19:28 -0600 )edit
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answered 2021-05-06 09:42:48 -0600

updated 2021-05-06 09:44:08 -0600

We looked into adding a feature to EnergyPlus that would disaggregate fans/pumps into heating and cooling, but like @ericmartinpe says, it's not so simple. But if you have a simple HVAC system where there is only ever heating or cooling when the fan is running, you can use a small EMS program like so:

EnergyManagementSystem:Sensor,
  gshp_clg_coil_s,                        !- Name
  gshp clg coil,                          !- Output:Variable or Output:Meter Index Key Name
  Cooling Coil Electricity Energy;        !- Output:Variable or Output:Meter Name

EnergyManagementSystem:Program,
  gshp_pump_disaggregate_program,         !- Name
  Set gshp_pump_clg = 0,                  !- Program Line 1
  Set gshp_pump_htg = 0,                  !- Program Line 2
  If gshp_clg_coil_s > 0,                 !- Program Line 3
    Set gshp_pump_clg = gshp_pump_s,      !- Program Line 4
  Else,                                   !- Program Line 5
    Set gshp_pump_htg = gshp_pump_s,      !- Program Line 6
  EndIf;                                  !- Program Line 7

EnergyManagementSystem:OutputVariable,
  gshp pump clg disaggregate,             !- Name
  gshp_pump_clg,                          !- EMS Variable Name
  Summed,                                 !- Type of Data in Variable
  SystemTimestep,                         !- Update Frequency
  gshp_pump_disaggregate_program,         !- EMS Program or Subroutine Name
  J;                                      !- Units

EnergyManagementSystem:OutputVariable,
  gshp pump htg disaggregate,             !- Name
  gshp_pump_htg,                          !- EMS Variable Name
  Summed,                                 !- Type of Data in Variable
  SystemTimestep,                         !- Update Frequency
  gshp_pump_disaggregate_program,         !- EMS Program or Subroutine Name
  J;                                      !- Units

Output:Variable,
  *,                                      !- Key Value
  gshp pump clg disaggregate,             !- Variable Name
  runperiod;                              !- Reporting Frequency

Output:Variable,
  *,                                      !- Key Value
  gshp pump htg disaggregate,             !- Variable Name
  runperiod;                              !- Reporting Frequency

This will create two annual outputs -- in this example, one for GSHP pump energy associated with heating and one for pump energy associated with cooling.

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Thank you @shorowit. I never used EMS program before. Can this be done using IDFEditor?

ChrisW gravatar image ChrisW  ( 2021-05-06 20:49:14 -0600 )edit

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Asked: 2021-05-05 14:09:55 -0600

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Last updated: May 06