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Variable Condenser Flow Request | ||
================================= | ||
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**Jeremy Lerond, Pacific Northwest National Laboratory** | ||
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## Justification for New Feature ## | ||
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Issue [#7111](https://github.com/NREL/EnergyPlus/issues/7111) | ||
- "User file with Chiller:Electric:EIR always requests full condenser flow rate" | ||
- "This is a problem not only when using cooling towers, but also when using seawater cooling by PlantComponent:TemperatureSource. Unlike cooling towers, it is not possible to make a compromise of variable tower fans instead of variable condenser water." | ||
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## E-mail and Conference Call Conclusions ## | ||
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Notes from the 5/15/2024 technicalities call: | ||
- TRANE trace scales the condenser flow request based on the chiller PLR | ||
- The new chiller input is different than the existing chiller flow mode input (evaporator side) | ||
- Implement the new inputs and logic for both the `Chiller:Electric:EIR` and `Chiller:Electric:ReformulatedEIR` | ||
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## Overview ## | ||
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Chilled water plant designs can include variable flow condenser requests from chillers. Currently, the `Chiller:Electric:EIR` and `Chiller:Electric:ReformulatedEIR` objects request the maximum condenser flow rate every time a chiller is active. This new feature will implement new control strategies to allow users to model variable flow condenser requests from chillers. | ||
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## Approach ## | ||
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Three new control approaches will be implemented: | ||
1. When used in conjunction with a cooling tower, users will be able to use the approach from the _Fundamentals of Design and Control of Central Chilled-Water Plants_ which correlates the condenser water flow ratio to the chilled water plant's PLR as follows: `CWFR = C . PLR + D`, where `CWFR` is the condenser water flow ration (actual/design), `C` and `D` are user specified coefficients (for proposed values see _Optimizing Design & Control Of Chilled Water Plants, Part 5_, S. Taylor, ASHRAE Journal June 2012) and `PLR` is the chilled water plant loop part load ratio (actual/design). The condenser loop flow would be calculated as `m_dot_CW = CWFR * m_dot_CW_design`. Because the request comes from the chillers, the chiller request will be determined as follows: `m_dot_CW_chiller = m_dot_CW * Q_chiller / Q_CHW`. Where `Q_chiller` is the chiller load and `Q_CHW` is the chilled water loop load. So if a chilled water plant loop has two chillers, then `Q_CHW = Q_chiller_1 + Q_chiller_2`. | ||
2. When no cooling tower are used, users will be able to specify that the condenser water flow request will be determined as follows: `m_dot_CW_chiuller = Q_condenser / (C_p .dT)` where dT is the delta T across the condenser. | ||
3. A simplified approach to 1. will also be implemented which will set the request condenser flow rate for each chiller to be `m_dot_CW_chiller = PLR_chiller * m_dot_max_condenser_chiller`. | ||
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## Testing/Validation/Data Sources ## | ||
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Unit tests will be added to confirm the correct implementation of these control strategies. | ||
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## Input Output Reference Documentation ## | ||
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A description of the new field will be added to the input output reference manual. | ||
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## Input Description ## | ||
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``` | ||
Chiller:Electric:EIR, | ||
\min-fields 23 | ||
\memo This chiller model is the empirical model from the DOE-2 building Energy | ||
\memo simulation program. Chiller performance at off-reference conditions is modeled | ||
\memo using three polynomial equations. Three curves objects are required. | ||
[...] | ||
A16, \field End-Use Subcategory | ||
\note Any text may be used here to categorize the end-uses in the ABUPS End Uses by Subcategory table. | ||
\type alpha | ||
\retaincase | ||
\default General | ||
A17, \field Condenser Flow Control | ||
\note Select the chiller condenser flow request mode. With "ConstantFlow" a chiller will always request | ||
\note its maximum condenser flow rate. With "ModulatedChillerPLR" the condenser flow request corresponds | ||
\note to the chiller part load ratio multiplied by the chiller maximum condenser flow rate. With | ||
\note "ModulatedLoopPLR" the chiller will request a flow rate that is function of the chilled water | ||
\note loop's part load ratio, see the "Condenser Loop Flow Rate Fraction Function of Loop Part Load Ratio | ||
\note Curve Name" input. With "ModulatedDeltaTemperature" the chiller will request the flow rate required | ||
\note to meet a condenser loop delta temperature, see the "Temperature Difference Across Condenser" and | ||
\note "Temperature Difference Across Condenser Schedule Name" input. | ||
\note Use "ConstantFlow" when modeling a constant flow condenser plant loop, choose one of the other inputs | ||
\note when modeling a variable flow condenser plant loop. | ||
\key ConstantFlow | ||
\key ModulatedChillerPLR | ||
\key ModulatedLoopPLR | ||
\key ModulatedDeltaTemperature | ||
\default ConstantFlow | ||
A18, \field Condenser Loop Flow Rate Fraction Function of Loop Part Load Ratio Curve Name | ||
\note Condenser loop flow rate fraction as a function of the chiller water loop part load ratio. A linear | ||
\note curve is expected. | ||
\note CWFR = C * PLR + D | ||
\note Where: | ||
\note CWFR is the condenser water flow fraction (actual/design) | ||
\note C and D are coefficients, see "Optimizing Design & Control Of Chilled Water Plants, Part 5", | ||
\note S. Taylor, ASHRAE Journal June 2012 PLR is the chilled water plant loop part load ratio | ||
\note (actual/design). This input is only used when the "ModulatedLoopPLR" condenser flow control | ||
\note option is used. | ||
\type object-list | ||
\object-list UnivariateFunctions | ||
A20, \field Temperature Difference Across Condenser Schedule Name | ||
\note A schedule that defines the temperature difference across the condenser. This input is used to | ||
\note calculate the condenser flow. This input is only used when "Condenser Flow Control" is set to | ||
\note "ModulatedDeltaTemperature". | ||
\type object-list | ||
\object-list ScheduleNames | ||
N19; \field Condenser Minimum Flow Fraction | ||
\note This input corresponds to the minimum flow fraction to be simulated. The minimum condenser flow | ||
\note corresponds to this fraction multiplied by the maximum condenser flow rate. This input is only used | ||
\note when the "Condenser Flow Control" input is set to "ModulatedChillerPLR", "ModulatedLoopPLR" or | ||
\note "ModulatedDeltaTemperature". | ||
\type real | ||
\minimum 0.0 | ||
\maximum 1.0 | ||
\default 0.2 | ||
``` | ||
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Similar input will be implemented for the `Chiller:Electric:ReformulatedEIR` object. | ||
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## Outputs Description ## | ||
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No new output will be added. | ||
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## Engineering Reference ## | ||
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A new section will be added to the Chiller section of the Engineering Reference to provide details on the control approach as shown in the Approach section of this document. | ||
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A note will be added indicating that chiller performance will be only impacted when simulating a `Chiller:Electric:ReformulatedEIR` since this chiller object has its part load performance impacted by the leaving chiller condenser temperature. | ||
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## Example File and Transition Changes ## | ||
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No transition will be necessary. | ||
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New example files will be provided to showcase the new feature. | ||
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## References ## | ||
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- "Optimizing Design & Control Of Chilled Water Plants, Part 2", S. Taylor, ASHRAE Journal Sept 2011 | ||
- "Optimizing Design & Control Of Chilled Water Plants, Part 5", S. Taylor, ASHRAE Journal June 2012 | ||
- "Optimizing Chilled Water Plan Control", M. Hydeman, ASHRAE Journal June 2007 | ||
- "Carrier® ChillerVu™ Variable Flow Condenser Pump Application Guide", https://www.shareddocs.com/hvac/docs/1000/Public/0A/11-808-577-01.pdf | ||
- "Achieving Variable Condenser Water Flow with VFDs" https://www.esmagazine.com/articles/99689-achieving-variable-condenser-water-flow-with-vfds |
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f9a444f
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extendedHI (Unknown) - Win64-Windows-10-VisualStudio-16: OK (2855 of 2855 tests passed, 0 test warnings)
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extendedHI (Unknown) - x86_64-MacOS-10.18-clang-15.0.0: OK (3639 of 3647 tests passed, 0 test warnings)
Messages:\n
Failures:\n
regression Test Summary
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extendedHI (Unknown) - x86_64-Linux-Ubuntu-22.04-gcc-11.4: OK (3678 of 3688 tests passed, 0 test warnings)
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Failures:\n
regression Test Summary
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extendedHI (Unknown) - x86_64-Linux-Ubuntu-22.04-gcc-11.4-UnitTestsCoverage-Debug: OK (2051 of 2063 tests passed, 0 test warnings)
Failures:\n
API Test Summary
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extendedHI (Unknown) - x86_64-Linux-Ubuntu-22.04-gcc-11.4-IntegrationCoverage-Debug: OK (723 of 795 tests passed, 0 test warnings)
Failures:\n
integration Test Summary