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design/FY2024/NFP-labHeatExchangerHR.md

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+Enhancement for Variable-Speed Heat Recovery Ventilation in Laboratories
+================
+
+**Yujie Xu, Tianzhen Hong**
+
+**Lawrence Berkeley National Laboratory***
+
+ - Original Date: Oct 24, 2023
+
+## Justification for Feature Update
+
+For lab buildings, the heating-cooling air flow rate could vary substantially
+depending on the occupancy, the type of experiment, and the operation protocol.
+Correctly capturing its HVAC energy consumption and heat recovery performance
+requires accurate information on heat exchangers' sensible and latent
+effectiveness at various flow conditions. However, in EnergyPlus, the heat
+exchanger object, HeatExchanger:AirToAir:SensibleAndLatent, describes the
+sensible and latent effectiveness at only two reference points (100% and 75%
+airflow) for either heating or cooling. This feature will add four new optional
+fields at the end of the HeatExchanger:AirToAir:SensibleAndLatent object. These
+new fields will specify four performance curves to more flexibly express the
+relationship between sensible and latent effectiveness at different relative
+airflow (the percentage of the actual airflow relative to the nominal supply
+airflow). Being able to characterize the efficiency at low-flow-rate conditions
+can allow more accurate modeling of the heat recovery system and justify the
+adoption of high-potential energy-saving strategies like using variable speed
+fans in the exhaust air heat recovery systems in laboratories.
+
+A team led by Jon McHugh, who is doing EnergyPlus modeling to support California
+Title 24 development, requested the feature. This feature supports ANSI/ASSP
+Z9.5-2022 Laboratory Ventilation standard, which requires variable-airflow
+exhaust system operations.
+
+## Overview ##
+
+### Existing approach ###
+
+Currently, the HeatExchanger:AirToAir:SensibleAndLatent in EnergyPlus only has
+two reference points to describe the relationship between relative airflow and
+heat exchange effectiveness in transferring sensible and latent heat (the fields
+between the two arrows in the following example).
+
+Example:
+
+    HeatExchanger:AirToAir:SensibleAndLatent,
+        OA Heat Recovery 1,            !- Heat exchanger name
+        FanAndCoilAvailSched,          !- Availability schedule name
+        0.05,                          !- Nominal supply air flow rate {m3/s}
+        .76,                           !- Sensible effectiveness at 100% airflow heating condition     <--
+        .68,                           !- Latent effectiveness at 100% airflow heating condition
+        .81,                           !- Sensible effectiveness at 75% airflow heating condition
+        .73,                           !- Latent effectiveness at 75% airflow heating condition
+        .76,                           !- Sensible effectiveness at 100% airflow cooling condition
+        .68,                           !- Latent effectiveness at 100% airflow cooling condition
+        .81,                           !- Sensible effectiveness at 75% airflow cooling condition
+        .73,                           !- Latent effectiveness at 75% airflow cooling condition        <--
+        ERV Outdoor air Inlet Node,    !- Supply air inlet node name
+        Heat Recovery Outlet Node,     !- Supply air outlet node name
+        Zone 1 Exhaust Node,           !- Exhaust air inlet node name
+        Heat Recovery Secondary Outlet Node,  !- Exhaust air outlet node name
+        50.0,                          !- Nominal electric power {W}
+        Yes,                           !- Supply air outlet temperature control
+        Rotary,                        !- Heat exchanger type
+        MinimumExhaustTemperature,   !- Frost control type
+        1.7;                           !- Threshold temperature
+
+### The gap in the modeling capability ###
+
+In current EnergyPlus, a linear relationship is specified for the heat exchanger
+effectiveness at different relative airflow, using the performance at 75% and
+100% of the supply air flow rate. The linear performance curve is valid for
+relative airflow from 50% to 130%. However, some heat exchangers could have
+non-linear performance curves as shown in Figure 1.
+
+![Figure 1](9-Comparison-of-effect-of-airflow-rate-on-heat-exchanger-effectiveness-for-cooling-and.png)
+
+Figure 1. An example of a heat exchanger with non-linear performance curves at different airflow conditions [1]
+
+Furthermore, when the relative airflow is below 50% or above 130%, the program
+will throw a warning, "Average air volume flow rate is <50% or >130% of the
+nominal HX supply air volume flow rate.", indicating that there could be an
+issue of linearly extrapolating the curve. This also suggests the need for more
+points to better capture the heat exchanger performance at very low or very high
+airflow conditions.
+
+## Approach
+
+This feature proposes to add 4 optional fields holding 4 performance curves at
+the end of the HeatExchanger:AirToAir:SensibleAndLatent. These fields will
+specify the sensible and latent effectiveness of heating or cooling as a
+function of relative airflow. When any of the curves is specified, the
+effectiveness will be calculated using this curve instead of the effectiveness
+specified in N2 through N9 will not be used. The warning message of "Average air
+volume flow rate is <50% or >130% of the nominal HX supply air volume flow
+rate." will also be silenced if four new curve fields all have inputs and the
+specified curves all cover the range of relative airflow below 50% and above
+130%.
+
+    HeatExchanger:AirToAir:SensibleAndLatent,
+          \memo This object models an air-to-air heat exchanger using effectiveness relationships.
+          \memo The heat exchanger can transfer sensible energy, latent energy, or both between the
+          \memo supply (primary) and exhaust (secondary) air streams.
+          \min-fields 19
+      A1,  \field Name
+          \required-field
+          \type alpha
+          \reference HXAirToAirNames
+          \reference HXAirToAirSensibleAndLatentNames
+          \reference AFNHeatExchangerNames
+          \reference-class-name validBranchEquipmentTypes
+          \reference validBranchEquipmentNames
+          \reference-class-name validOASysEquipmentTypes
+          \reference validOASysEquipmentNames
+      A2, \field Availability Schedule Name
+          \note Availability schedule name for this system. Schedule value > 0 means the system is available.
+          \note If this field is blank, the system is always available.
+          \type object-list
+          \object-list ScheduleNames
+      N1, \field Nominal Supply Air Flow Rate
+          \required-field
+          \type real
+          \autosizable
+          \minimum> 0.0
+          \units m3/s
+      N2, \field Sensible Effectiveness at 100% Heating Air Flow
+          \type real
+          \units dimensionless
+          \minimum 0.0
+          \maximum 1.0
+          \default 0.0
+      N3, \field Latent Effectiveness at 100% Heating Air Flow
+          \type real
+          \units dimensionless
+          \minimum 0.0
+          \maximum 1.0
+          \default 0.0
+      N4, \field Sensible Effectiveness at 75% Heating Air Flow
+          \type real
+          \units dimensionless
+          \minimum 0.0
+          \maximum 1.0
+          \default 0.0
+      N5, \field Latent Effectiveness at 75% Heating Air Flow
+          \type real
+          \units dimensionless
+          \minimum 0.0
+          \maximum 1.0
+          \default 0.0
+      N6, \field Sensible Effectiveness at 100% Cooling Air Flow
+          \type real
+          \units dimensionless
+          \minimum 0.0
+          \maximum 1.0
+          \default 0.0
+      N7, \field Latent Effectiveness at 100% Cooling Air Flow
+          \type real
+          \units dimensionless
+          \minimum 0.0
+          \maximum 1.0
+          \default 0.0
+      N8, \field Sensible Effectiveness at 75% Cooling Air Flow
+          \type real
+          \units dimensionless
+          \minimum 0.0
+          \maximum 1.0
+          \default 0.0
+      N9, \field Latent Effectiveness at 75% Cooling Air Flow
+          \type real
+          \units dimensionless
+          \minimum 0.0
+          \maximum 1.0
+          \default 0.0
+      A7, \field Supply Air Inlet Node Name
+          \required-field
+          \type node
+      A4, \field Supply Air Outlet Node Name
+          \required-field
+          \type node
+      A5, \field Exhaust Air Inlet Node Name
+          \required-field
+          \type node
+      A6, \field Exhaust Air Outlet Node Name
+          \required-field
+          \type node
+      N10,\field Nominal Electric Power
+          \type real
+          \units W
+          \ip-units W
+          \minimum 0.0
+          \default 0.0
+      A7, \field Supply Air Outlet Temperature Control
+          \type choice
+          \key No
+          \key Yes
+          \default No
+      A8, \field Heat Exchanger Type
+          \type choice
+          \key Plate
+          \key Rotary
+          \default Plate
+      A9, \field Frost Control Type
+          \type choice
+          \key None
+          \key ExhaustAirRecirculation
+          \key ExhaustOnly
+          \key MinimumExhaustTemperature
+          \default None
+      N11,\field Threshold Temperature
+          \type real
+          \units C
+          \default 1.7
+          \note Supply (outdoor) air inlet temp threshold for exhaust air recirculation and
+          \note exhaust only frost control types. Exhaust air outlet threshold Temperature for
+          \note minimum exhaust temperature frost control type.
+      N12,\field Initial Defrost Time Fraction
+          \type real
+          \units dimensionless
+          \minimum 0.0
+          \maximum 1.0
+          \default 0.083
+          \note Fraction of the time when frost control will be invoked at the threshold temperature.
+          \note This field only used for exhaust air recirc and exhaust-only frost control types.
+      N13,\field Rate of Defrost Time Fraction Increase
+          \type real
+          \units 1/K
+          \minimum 0.0
+          \default 0.012
+          \note Rate of increase in defrost time fraction as actual temp falls below threshold temperature.
+          \note This field only used for exhaust air recirc and exhaust-only frost control types.
+      A10,\field Economizer Lockout
+          \type choice
+          \key Yes
+          \key No
+          \default Yes
+          \note Yes means that the heat exchanger will be locked out (off)
+          \note when the economizer is operating or high humidity control is active
+      A11, \field Sensible Effectiveness of Heating Air Flow Curve Name
+          \note optional
+          \note if this field has value, then field N2 and N4 will be ignored
+          \type object-list
+          \object-list UnivariateFunctions
+      A12, \field Latent Effectiveness of Heating Air Flow Curve Name
+          \note optional
+          \note if this field has value, then field N3 and N5 will be ignored
+          \type object-list
+          \object-list UnivariateFunctions
+      A13, \field Sensible Effectiveness of Cooling Air Flow Curve Name
+          \note optional
+          \note if this field has value, then field N6 and N8 will be ignored
+          \type object-list
+          \object-list UnivariateFunctions
+      A14; \field Latent Effectiveness of Cooling Air Flow Curve Name
+          \note optional
+          \note if this field has value, then field N7 and N9 will be ignored
+          \type object-list
+          \object-list UnivariateFunctions
+
+
+## IDD Object changes
+
+A field (N4) will be added to the ZoneHVAC:EvaporativeCoolerUnit
+
+    ZoneHVAC:EvaporativeCoolerUnit,
+        \memo Zone evaporative cooler. Forced-convection cooling-only unit with supply fan,
+        \memo 100% outdoor air supply. Optional relief exhaust node
+        \min-fields 15
+    A1 , \field Name
+        \required-field
+        \reference ZoneEquipmentNames
+    A2 , \field Availability Schedule Name
+        \note Availability schedule name for this system. Schedule value > 0 means the system is available.
+        \note If this field is blank, the system is always available.
+        \type object-list
+        \object-list ScheduleNames
+    A3,  \field Availability Manager List Name
+        \note Enter the name of an AvailabilityManagerAssignmentList object.
+        \type object-list
+        \object-list SystemAvailabilityManagerLists
+    A4 , \field Outdoor Air Inlet Node Name
+        \required-field
+        \type node
+        \note this is an outdoor air node
+    A5 , \field Cooler Outlet Node Name
+        \required-field
+        \type node
+        \note this is a zone inlet node
+    A6 , \field Zone Relief Air Node Name
+        \type node
+        \note this is a zone exhaust node, optional if flow is being balanced elsewhere
+    A7 , \field Supply Air Fan Object Type
+        \required-field
+        \type choice
+        \key Fan:SystemModel
+        \key Fan:ComponentModel
+        \key Fan:ConstantVolume
+        \key Fan:OnOff
+        \key Fan:VariableVolume
+    A8 , \field Supply Air Fan Name
+        \required-field
+        \type object-list
+        \object-list Fans
+    N1 , \field Design Supply Air Flow Rate
+        \required-field
+        \units m3/s
+        \minimum> 0
+        \autosizable
+    A9 , \field Fan Placement
+        \required-field
+        \type choice
+        \key BlowThrough
+        \key DrawThrough
+    A10, \field Cooler Unit Control Method
+        \required-field
+        \type choice
+        \key ZoneTemperatureDeadbandOnOffCycling
+        \key ZoneCoolingLoadOnOffCycling
+        \key ZoneCoolingLoadVariableSpeedFan
+    N2 , \field Throttling Range Temperature Difference
+        \note used for ZoneTemperatureDeadbandOnOffCycling hystersis range for thermostatic control
+        \type real
+        \units deltaC
+        \default 1.0
+        \minimum> 0.0
+    N3 , \field Cooling Load Control Threshold Heat Transfer Rate
+        \type real
+        \units W
+        \default 100.0
+        \note Sign convention is that positive values indicate a cooling load
+        \minimum> 0.0
+    A11, \field First Evaporative Cooler Object Type
+        \required-field
+        \type choice
+        \key EvaporativeCooler:Direct:CelDekPad
+        \key EvaporativeCooler:Direct:ResearchSpecial
+        \key EvaporativeCooler:Indirect:CelDekPad
+        \key EvaporativeCooler:Indirect:WetCoil
+        \key EvaporativeCooler:Indirect:ResearchSpecial
+    A12, \field First Evaporative Cooler Object Name
+        \required-field
+        \type object-list
+        \object-list EvapCoolerNames
+    A13, \field Second Evaporative Cooler Object Type                           <- added new fields starts here
+        \note optional, used for direct/indirect configurations
+        \note second cooler must be immediately downstream of first cooler, if present
+        \type choice
+        \key EvaporativeCooler:Direct:CelDekPad
+        \key EvaporativeCooler:Direct:ResearchSpecial
+        \key EvaporativeCooler:Indirect:CelDekPad
+        \key EvaporativeCooler:Indirect:WetCoil
+        \key EvaporativeCooler:Indirect:ResearchSpecial
+    A14, \field Second Evaporative Cooler Name
+        \note optional, used for direct/indirect configurations
+        \type object-list
+        \object-list EvapCoolerNames
+    A15, \field Design Specification ZoneHVAC Sizing Object Name
+        \note Enter the name of a DesignSpecificationZoneHVACSizing object.
+        \type object-list
+        \object-list DesignSpecificationZoneHVACSizingName
+    N4; \field Shut Off Relative Humidity
+        \note Zone relative humidity above which the evap cooler is shut off.
+        \type real
+        \minimum 0.00
+        \maximum 100.00
+        \units percent                                                          <- added new fields ends here
+
+## Testing/Validation/Data Source(s)
+
+The feature will be tested and demonstrated with a test file derived from 5Zone_Unitary_HXAssistedCoil.idf.
+
+## Acknowledgments
+
+LBNL had a few meetings with Jon McHugh and his team who made the original request of the new feature.
+
+## Proposed additions to Meters:
+
+N/A
+
+## Proposed Report Variables:
+
+N/A
+
+## References
+
+[1]	W. J. Turner, "Investigation and Development of Hybrid Ventilation Wall Convector," The University of Reading, 2009. [Online]. Available: https://www.researchgate.net/publication/263209666_Investigation_and_Development_of_Hybrid_Ventilation_Wall_Convector/figures?lo=1