EnergyPlus

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  1. One DX coil object to rule them all

    Problem: There are several coil object types that represent DX heating or cooling with different input fields, capabilities, and source code.

    Rationale: Providing a single, generalized DX coil for both heating and cooling with all capabilities will enforce consistency.

    Solution: Create a single DX cooling coil that covers:

    - Coil:Cooling:DX:VariableRefrigerantFlow
    - Coil:Cooling:DX:VariableRefrigerantFlow:FluidTemperatureControl
    - Coil:Cooling:DX:SingleSpeed
    - Coil:Cooling:DX:TwoSpeed
    - Coil:Cooling:DX:TwoStageWithHumidityControlMode
    - Coil:Cooling:DX:MultiSpeed
    - Coil:Cooling:DX:VariableSpeed
    - CoilPerformance:DX:Cooling
    - Coil:Cooling:WaterToAirHeatPump:ParameterEstimation
    - Coil:Cooling:WaterToAirHeatPump:EquationFit
    - Coil:Cooling:WaterToAirHeatPump:VariableSpeedEquationFit

    and the equivalent coils for a single DX heating coil.

    5 votes
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  2. New single-duct constant volume air terminal without reheat

    The existing AirTerminal:SingleDuct:Uncontrolled is different from all other terminal units. It only has a single node (not an inlet and outlet) and it sits directly on the zone equipment list instead or being referenced by a ZoneHVAC:AirDistributionUnit object. This causes fits for interfaces, and it prevents this terminal unit from using the simple duct-leakage features in ZoneHVAC:AirDistributionUnit.

    Propose adding a new terminal unit type AirTerminal:SingleDuct:ConstantVolume:NoReheat that has an inlet and outlet node and sits under an air distribution unit. Then deprecate the old AirTerminal:SingleDuct:Uncontrolled object.

    Reference issue #4988
    https://github.com/NREL/EnergyPlus/issues/4988

    2 votes
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  3. Improve the AirLoop:UnitarySystem object to support VAV fan control

    Currently, the AirLoop:UnitarySystem object does not support representation of variable-speed RTUs, even with the inclusion of EMS control logic. From emailing with the E+ team, my understanding is that this is an effect of the unitary system "not having an EMS actuator for flow rate, since the DX coils need to be modeled at full flow, and the unitary system needs to know the average flow rate over the time step (a function of PLR) so that it can model the DX coil with the correct flow." The only viable workaround for this is to pull the Fan:VariableVolume object outside…

    1 vote
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  4. Allow User to Set Primary Airflow Rate Through AirTerminal:SingleDuct:Mixer Object

    The AirTerminal:SingleDuct:Mixer object functions well with respect to its goal to enable the connection of central air systems to the inlet side of Zone:HVAC equipment. One feature that would be helpful, however, would be the ability to set the primary air flow rate through the terminal. Currently, E+ just sets this value equal to the central air flow rate / # branches, which makes it impossible to apportion OA appropriately between non-identical zones. Based on examination of eio files, I do not believe that E+ even attempts to size the terminal unit, so it is also not currently possible to…

    1 vote
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  5. Improve Ideal Air System to Allow Modeling of Plenum Return

    Currently in EnergyPlus, ideal air system does not have input to specify a return plenum. So it always assumes ducted return.

    Practically, with a return plenum, the zone peak cooling and heating loads should be smaller than that of a ducted return case.

    The suggestion is to add an input in ideal air system object to specify a space as return plenum so that zone return air can be used to cool or heat the return plenum and affect the zone load.

    2 votes
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  6. Use practically available system mass flow rate and capacity to perform simulations with autosize

    Problem: The mass flow rate and system capacity obtained from autozing may not be practically available in real systems, since system manufactures provide discrete values of mass flow rates and capacity for the same type of equipment.

    Rationale: E+ determines system size based on peak loads in design day and system multipliers, when autosize is required. However, the system size may be different from practically available system size provided by manufacturers, since manufactures only provide discrete system sizes. Simulation results may have large differences using autosized system and practically realistic systems. It is needed to provide a choice either to…

    3 votes
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  7. Water cooled condenser for DX coils

    DX cooling coils currently have options for air-cooled and evaporatively cooled condenser. This would add water cooled as an option. Some users use the water-to-air heat pump coil (Coil:Cooling:WaterToAirHeatPump:EquationFit) to model this, but this cannot be used in every type of system, and is not as convenient to use.

    8 votes
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  8. Run-Around Heat Recovery System

    Problem: EnergyPlus cannot model run-around heat recovery systems.

    Rationale: A run-around system can reduce peak heating and cooling loads as well as total heating and cooling loads. EnergyPlus already has models for all the underlying pieces and it makes sense to finish out what is needed so that the air loop and plant can handle such configurations.

    Solution: Add whatever is needed to allow setting up a plant model with just two or more coils and a pump. Allow coils in air loop to run wild without a Controller:WaterCoil. Allow coils for run-around to be located virtually anywhere in the…

    12 votes
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  9. Turn Off DX Cooling Coil in Low Ambient Temperature

    In EnergyPlus, for DX heating coils, the input field "Minimum Outdoor Dry-Bulb Temperature for Compressor Operation" is used to turn compressor off under low ambient temperature.

    This field does not exist in DX cooling coil. Usually we would not expect a cooling coil to operate under low ambient temperature. However, this could still happen in certain applications. Can this field be added to the DX cooling coil inputs?

    5 votes
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  10. Auto-sizing based-on latent loads

    EnergyPlus can't size equipment based on latent load. That is, it can't save the results of a sizing run done at the dehumidification design condition and apply these results in conjunction with the sensible requirements when sizing coils and setting flow rates and supply temperatures. ASHRAE Standard 62 requires that dehumidification capable systems maintain 65% relative humidity in the zones at the dehumidification design condition with design cooling internal loads and zero solar load.

    We propose adding a latent design day (to the current heating and cooling), saving the latent sizing results, and making them available to the air flow…

    4 votes
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  11. Increase number of Speeds in "UnitarySystemPerformance:Multispeed" object

    Following is the proposed improvements to "UnitarySystemPerformance:Multispeed" object:

    1. Increase the maximum number of speeds for heating and cooling to 8, add supply air flow ratio inputs for cooling and heating speeds from 5 to 8.
    2. Add an input for “No Load Supply Air Flow Ratio”, this would override the inputs in object “AirLoopHVAC:UnitarySystem” (Figure 1). If there is no input in this object, use the flow rate specified in the “AirLoop HVAC:UnitarySystem” object.

    Justification

    Many commercial large capacity RTUs (30-200 tons) offer from 2 to 8 stages of compression. For the constant volume version of these products the…

    4 votes
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  12. Cycling On/Off Fan Operation for Built-up Air Loop

    Problem: AirLoopHVAC systems only support continuous fan operations, however some built-up air handlers cycle the fan on and off.

    Rationale: The air loop model is supposed to be flexible and customizable yet it does not allow on/off fan.

    Solution: Upgrade air loop system model to allow cycling fan operation.

    Context: User often try to use on/off fans in built-up air handlers

    Suggestion from legacy enhancement list (HVAC_2007_49, HVAC_AirLoop_2011_10)

    4 votes
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  13. Add Head Pressure Control Performance Model to DX Cooling Coils

    For DX Cooling coil performance, add an option to model the DX coil performance under head pressure control mode, head pressure control mode is triggered when condenser inlet air dry-bulb temperature is below a predefined temperature.

    Head pressure control is a common factory option or accessory for many rooftop, split DX AHU, and vertical packaged unit products. Many manufacturers offering this feature to allow equipment operation at low ambient dry-bulbs.

    If we curve fit head pressure control mode andnormal operation mode data with a single set of EnergyPlus correlation, the accuracy will be poor in the head pressure control mode.…

    2 votes
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  14. Autosizing based on nighttime precooling

    Add autosizing capabilities to EnergyPlus for building nighttime precooling using ventilation.

    1 vote
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  15. Central Air Humidity Control Based on Return Air

    Problem: Humidity controls for central air systems are cumbersome and don’t always reflect actual system configurations.
    Rationale: Multizone air handlers might locate a single humidistat in the return air duct rather than separate humidistats in every individual zone. EnergyPlus could implement similar controls and avoid a lot of separate zone humidistat input and the need to calculate predicted-moisture-load-to-setpoints in the zone balance and save computation.
    Solution: Create some kind of setpoint manager (or maybe a controller) that senses return air moist air conditions and adjusts supply air dewpoint temperature to meet high and low targets.

    Context: The concept is similar…

    3 votes
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  16. AirTerminal:SingleDuct:ParallelPIU:Reheat

    ASHRAE 90.1 states:
    G3.1.3.14 Fan Power (Systems 6 and 8). Fans in parallel VAV fan-powered boxes shall be sized for 50% of the peak design flow rate
    In order to respect that statement quickly I would like to impose that the field "Maximum secondary air flow rate" is a proportion of the autosized "Maximum primary air flow rate". The user could choose if he prefers to fix the "Maximum secondary air flow rate" directly or as proportion of the "Maximum primary air flow rate".

    2 votes
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  17. Allow multiple air loops to one thermal zone

    There are many situations in which this can happen and quite often the equipments (AHUs, rooftops, etc) have not the same characteristics and cannot conveniently reduce to one single "equivalent" air loop.

    10 votes
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  18. cooled beam with VAV

    I would like to model cooled beam connectd with VAV system. It seems that the object AirTerminal:SingleDuct:ConstantVolume:CooledBeam can be connected only with a constant velocity system (CAV).

    16 votes
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  19. Modeling DOAS to AHU

    This feature develops the modeling and simulation approach for a dedicated outdoor air system (DOAS) connected to multiple air handling units (AHUs). Many buildings have a separate DOAS system that feeds outdoor air directly to individual AHUs on each building floor. Currently EnergyPlus can only model a DOAS delivering outdoor air directly to zones or to the inlet or outlet of some zone equipment acting as terminal units. This feature will allow a single DOAS to supply air to the outdoor air inlet of multiple air systems.

    26 votes
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  20. Allow Heat Recovery from the Return Air Stream to the Supply Air Stream

    Problem: EnergyPlus does not allow energy to be recovered from the return air stream to be used in the supply air stream. I attempted to do this with the HeatExchanger:AirToAir:SensibleAndLatent object by specifying the object in the main AirLoop branch at the return air stream location for the exhaust flow and at the supply air stream location after the cooling coil to add the recovered heat to the supply air stream. EnergyPlus errors saying that the same component cannot contain different sets of nodes in a branch.

    Rationale: One dehumidification strategy is to recover heat from the return air stream…

    10 votes
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