add Efficiency field to DistrictCooling and DistrictHeating

[MatthewSteen]

Feature request to add a simple efficiency field (e.g. COP) to the District* objects, which would be helpful for cases where the user does not need to explicitly model a central plant but wants to account for its efficiency. This is a common scenario for LEED projects.

[mjwitte]

@MatthewSteen The EnvironmentalImpactFactors object can do one form of this. Is this adequate? At a minimum, this object should be mentioned in the DistrictCooling/Heating docs. Or perhaps better to move these fields to the DistrictCooling/Heating objects. Would you need a choice of what fuel type to convert to?

EnvironmentalImpactFactors,
   \memo Used to help convert district and ideal energy use to a fuel type and provide total carbon equivalent with coefficients
   \memo Also used in Source=>Site conversions.
  N1, \field District Heating Efficiency
      \note District heating efficiency used when converted to natural gas
      \minimum> 0.0
      \default 0.3
  N2, \field District Cooling COP
      \note District cooling COP used when converted to electricity
      \units W/W
      \minimum> 0.0
      \default 3.0
  N3, \field Steam Conversion Efficiency
      \note Steam conversion efficiency used to convert steam usage to natural gas
      \minimum> 0.0
      \default 0.25
  N4, \field Total Carbon Equivalent Emission Factor From N2O
      \units kg/kg
      \default 80.7272
  N5, \field Total Carbon Equivalent Emission Factor From CH4
      \units kg/kg
      \default 6.2727
  N6; \field Total Carbon Equivalent Emission Factor From CO2
      \units kg/kg
      \default 0.2727

[MatthewSteen]

@mjwitte I wasn't familiar with this object, which could work in some situations. However it's nice in general and needed for LEED to have the central plant's fuel separate from the building's, which the District* objects easily do.

[MatthewSteen]

Relevant UnmetHours question. https://unmethours.com/question/84057/getset-default-cop-for-district-cooling-via-openstudio-sdk/

[dnuribe]

I want to add more information regarding this request because @mjwitte did not get what @MatthewSteen meant.

Currently, it is possible to set a COP value for district heating and cooling, but they are used for environmental impact calculations in the PollutionModule.cc (line 6244 to 6255), as shown below.

// Now these fuel types have to be sorted and summed into categories that we have pollution factors for.
// The Off-Site Electricity is the total needed by the facility minus the amount generated on-site.
// The on-site pollutants will end up being other fuel types used by the generators.
// If the difference between the 2 electric quantities is <0.0 then it will be zero for that time step.
// We will also add the District Cooling here with a rough conversion from Energy using the User
// defined COP.
FuelType.Elec = FuelType.ElecFacility - FuelType.ElecProducedFacility + FuelType.PurchCoolFacility / Pollution.PurchCoolCOP;
if (FuelType.Elec <= 0.0) FuelType.Elec = 0.0;

// The Natural Gas fuel type will be summed from the meters with the District Heating using an efficiency.
FuelType.NatGas = FuelType.NatGasFacility + FuelType.PurchHeatWaterFacility / Pollution.PurchHeatWaterEffic +
                  FuelType.PurchHeatSteamFacility / Pollution.PurchHeatSteamConvEffic;

Therefore, when energy consumption is requested, district heating and cooling show the building loads instead of fuel energy consumption. This causes a problem in LEED projects and the report generated by third-party software such as DesignBuilder. The following images show the LEED Report for a simple case where the proposed building uses District Heating and cooling. In this case, it is expected to have less total energy use in the proposed building, but it is not reported correctly because the cooling end use reported the same number as the cooling load. This is clear in the next table, where you can note that district cooling and district heating are reported separate from the other fuels.

Finally, the correct request of this post should be to include the COP in energy calculations and reporting instead of only environmental analyses.

Thanks in advance, and do not hesitate to request more information if necessary.

[mjwitte]

So, what would the ABUPS report look like with these district efficiency inputs active? Would there still be a column for District Cooling or would it be added to Electricity? The boundary volume for ABUPS is what's supplied to the building, so it wouldn't be correct to keep the District Cooling/Heating columns and alter them by the efficiency factor.

[MatthewSteen]

@mjwitte since the control volume for the ABUPS is the building, it would make sense to add the gross district energy use in a dedicated district table. Perhaps the EnergyConsumptionDistrictHeatingCoolingMonthly, the LEED Summary, or a new one.

[mjwitte]

And what would be in ABUPS?

[MatthewSteen]

@mjwitte the net energy use from the district plant to the building?

[rraustad]

And if a user does not request EnvironmentalImpactFactors does the district cooling plant have a COP = 1?

[MatthewSteen]

@rraustad it's my understanding that the EnvironmentalImpactFactors do not effect the reported energy use, but I'm going off of memory from a quick investigation when I originally opened this issue in 2020.

I think emissions and energy should be reported separately and haven't used the former. Could the COPs from the EnvironmentalImpactFactors be moved to the District* objects and used by the EnvironmentalImpactFactors?

The use case for LEED is using the Distric* object(s) without an EnvironmentalImpactFactors object.

[rraustad]

For LEED reporting, where is the COP for district plants reported now? or is it even reported now?

DistrictCooling,
       \memo Centralized source of chilled water, such as a district cooling system.
  A1 , \field Name
       \required-field
       \reference-class-name validPlantEquipmentTypes
       \reference validPlantEquipmentNames
       \reference-class-name validCondenserEquipmentTypes
       \reference validCondenserEquipmentNames
       \reference-class-name validBranchEquipmentTypes
       \reference validBranchEquipmentNames
  A2 , \field Chilled Water Inlet Node Name
       \required-field
       \type node
  A3 , \field Chilled Water Outlet Node Name
       \required-field
       \type node
  N1 , \field Nominal Capacity
       \autosizable
       \units W
       \minimum 0.0
  A4 ; \field Capacity Fraction Schedule Name
       \note Schedule values are multiplied by Nominal Capacity for current capacity
       \type object-list
       \object-list ScheduleNames

[MatthewSteen]

@rraustad that's exactly what this feature request is about, add Efficiency field to DistrictCooling and DistrictHeating. It's not available in EnergyPlus so isn't reportable. This is currently done by a LEED modeler using postprocessing, when it could be a useful field for LEED and other use cases.

[rraustad]

I understand. What I was asking is if there is a place holder for district plant COP somewhere in LEED documents.

[mjwitte]

@mjwitte the net energy use from the district plant to the building?

I'm not sure what that means. Some numbers for the ABUPS and LEED district cooling columns would help. If the building has a district cooling load of 200GJ, then ABUPS must report 200GJ, regardless of the proxy COP. In EnergyPlus, it's a utility, just like Electricity or Gas, and ABUPS reports the building's consumption of that resource. If the building is really served by a district cooling loop, it buys chilled water, how it's made is irrelevant. The source energy reporting applies the proxy COP and turns it into electricity. Same for pollutants. The source energy also applies an electric source efficiency.

I don't know what the LEED rules are for comparing different fuel types, but I'm sure you don't get credit for less energy use with an electric boiler vs gas boiler. It seems that the best solution here is to add some columns to the LEED Summary, Energy Use Summary subtable that would report district sources as equivalent electricity and gas (and labeled as such).

Or just use Chiller:ConstantCOP and a Boiler:HotWater with flat efficiency curves.

I'll give you that the EnvironmentalImpactFactors and FuelFactors and how they interact are confusing. If these aren't in the idf, their default values are used for source energy reporting. For district cooling the source factor for electricity is also applied, which defaults to 3.167. BTW the district heating efficiencies seem awfully low?

EnvironmentalImpactFactors,
   \memo Used to help convert district and ideal energy use to a fuel type and provide total carbon equivalent with coefficients
   \memo Also used in Source=>Site conversions.
  N1, \field District Heating Water Efficiency
      \note District heating efficiency used when converted to natural gas
      \minimum> 0.0
      \default 0.3
  N2, \field District Cooling COP
      \note District cooling COP used when converted to electricity
      \units W/W
      \minimum> 0.0
      \default 3.0
  N3, \field District Heating Steam Conversion Efficiency
      \note Steam conversion efficiency used to convert steam usage to natural gas
      \minimum> 0.0
      \default 0.25

[mjwitte]

@MatthewSteen Yet another question - when using district cooling this way, do you even care that district cooling is reported? One option is to have an efficiency and a fuel type in the district object and just have it consume electricity or whatever directly. That approach would mean all district cooling columns would be zero.

[MatthewSteen]

I'll have to revisit this and the LEED requirements since I haven't done a LEED project with district energy in several years. Here's the documentation for the previous version of LEED. https://www.usgbc.org/sites/default/files/DES%20Guidance.pdf

@mjwitte to answer your question directly above, yes. LEED does/did require district energy to be reported separately so that projects can claim savings for central plant efficiency, which is an option for projects.

The problem with using Boiler:HotWater as a workaround is that it's efficiency doesn't allow values > 1 (e.g. a reversing chiller central plant) and editing the IDD to allow values > 1 doesn't work anymore since the transition to epJSON. Prior to that, I used it as a workaround for modeling a complex central plant with Chiller:ConstantCOP.

[shorowit]

The problem with using Boiler:HotWater as a workaround is that it's efficiency doesn't allow values > 1 (e.g. a reversing chiller central plant) and editing the IDD to allow values > 1 doesn't work anymore since the transition to epJSON. Prior to that, I used it as a workaround for modeling a complex central plant with Chiller:ConstantCOP.

Not to derail the discussion, but I'll point out that we ran into the same issue with the WaterHeater:Foo objects where we wanted to use an efficiency greater than 1 to account for distribution losses per the RESNET 301 standard. Some relevant discussion here. Since E+ doesn't allow it, we have to resort to some pretty ugly EMS that, depending on the situation, can set negative values for actuators... 😱

I keep considering a proposal to relax these E+ object limits and issue a warning if the value is above 1 instead. I'd even do the implementation myself. I know that doesn't solve the larger problem here, but it would at least allow the workaround to function again.

[rraustad]

From this LEED doc for district plants:

2.4.1.2.3 Default Efficiencies
Actual efficiency performance data on the DES serving the project building is preferred, based on
either ongoing operations (existing DES) or design specifications (new DES or DES with added
capacity). If the project team cannot obtain the actual performance data, it is permissible to use
the following default average performance values. These values are conservative, intended to
represent a DES with relatively low efficiency. A well-designed, maintained, and operating DES
will generally offer better performance than the defaults listed here. Default values are as follows:
• DES heating plant – 70% (Higher Heating Value) for the total boiler plant average
efficiency.
• DES cooling plant – COP of 4.4 for the total cooling plant average efficiency (including
cooling towers and primary pumps).
• Thermal distribution losses – the following values may be used to account for seasonal
thermal distribution losses including minor leaks and/or condensate losses (but not
pumping energy, which must be accounted for separately where it applies):
o chilled water district cooling 5%
o hot water district heating 10%
o closed loop steam systems 15%; open loop steam systems 25%
o steam systems that are partially open/closed must prorate between the above
15% and 25% losses in accordance with the fraction of expected or actual
condensate loss 

And this is interesting. The modeler needs to use district plant in baseline and proposed for a stand-alone building.

2.4.1.1 Model for Option 1 (Building stand-alone scenario):
In Option 1, the energy model’s scope accounts for only downstream equipment. This scenario is
modeled in accordance with ASHRAE 90.1 Appendix G requirements with the following
exceptions:
1. The energy source is modeled as purchased energy in both the Proposed and Baseline
buildings for all air handlers, fan-coil units, and other downstream equipment serviced by
district or campus energy systems in order to hold the DES cost-neutral in the model
(Table 2 below).
2. Where necessary, building Baseline HVAC system types from Tables G3.1.A and
G3.1.B are modified to be consistent with the purchased energy source (Table 3 below).
Any system parameters not specifically referenced in Table 3 are modeled as specified
in Appendix G. These changes only apply for building equipment serviced by the DES.

All other portions of the building shall be modeled in accordance with Appendix G
requirements. 

2.4.1.2 Model for Option 2 (Aggregate Building / DES Scenario):
In Option 2, the energy model’s scope accounts for both downstream equipment and upstream
equipment. The DES energy source is no longer modeled as cost-neutral purchased energy;
rather, a virtual DES-equivalent plant for the Proposed case is constructed and compared to
code-compliant on-site equipment for the Baseline case (Table 4). The Proposed case modeling
requirements differ from those in ASHRAE standard 90.1 Appendix G as described below.
However, the Baseline case system type is modeled as instructed in Appendix G.