Zone Dehumidifier

Stencil:  Zone HVAC Stencil: Zone Dehumidifier

Type: Unitary Zone Equipment

Sub Type: Dehumidifier DX

EnergyPlus IDF Objects

EnergyPlus Object - ZoneHVAC:Dehumidifier:DX

This object can be used for modeling conventional mechanical dehumidifiers. These systems use a direct expansion (DX) cooling coil to cool and dehumidify an airstream. Heat from the DX system’s condenser section is rejected into the cool/dehumidified airstream, resulting in warm dry air being supplied from the unit. In EnergyPlus, this object is modeled as a type of zone equipment.

The model has inputs for water removal, energy factor and air flow rate at rated conditions (26.7°C, 60% RH). Curve objects must be specified to describe performance at off-rated conditions. A part-load cycling curve input must also be specified to account for inefficiencies due to cycling. Other inputs including minimum and maximum operating temperatures for dehumidifier operation, off-cycle parasitic load, and an input to direct the removed water to a storage tank.

The model assumes that this equipment dehumidifies and heats the air. If used in tandem with another system that cools and dehumidifies the zone air, then the zone dehumidifier should be specified as the lowest cooling priority in the ZoneHVAC:EquipmentList object for best control of zone temperature and humidity levels (e.g., if there are 3 pieces of equipment in ZoneHVAC:EquipmentList, then the zone dehumidifier should have Cooling Priority = 3). With this zone equipment prioritization, the other cooling and dehumidification system would operate first to meet the temperature setpoint (and possibly meet the high humidity setpoint as well). If additional dehumidification is needed, then the zone dehumidifier would operate. The sensible heat generated by the dehumidifier is carried over to the zone air heat balance for the next HVAC time step.

Component Properties

The table shows the properties that are displayed when the component is selected while in diagram mode.  The second column shows the selection options available that are dictated by EnergyPlus or it shows the source for the library entries that are displayed in the drop down list.

Name

Simergy automatically defines a unique name for each component.  This can be changed by the user if desired.

Field: Availability Schedule Name

Schedule that this component will operate or is available to operate.

Field: Rated Water Removal

This numeric input is the full load water removal rate, in liters per day, at rated conditions (air entering the dehumidifier at 26.7°C [80°F] dry-bulb and 60% relative humidity, and air flow rate as defined by field “Rated Air Flow Rate” below). This is a required input field and the entered value must be greater than zero.

Field: Rated Energy Factor

This numeric input is the energy factor (liters of water removed per kWh of electricity consumed) at rated conditions (air entering the dehumidifier at 26.7°C [80°F] dry-bulb and 60% relative humidity, and air flow rate as defined by field “Rated Air Flow Rate” below). This is a required input field and the entered value must be greater than zero.

Field: Rated Air Flow Rate

This numeric input is the volumetric air flow rate through the dehumidifier, in m³ per second, at rated conditions (air entering the dehumidifier at 26.7°C [80°F] dry-bulb and 60% relative humidity). This is a required input field and the entered value must be greater than zero.

Field: Water Removal Curve Name

This alpha field defines the name of a biquadratic performance curve (ref: Performance Curves) that parameterizes the variation of water removal as a function of the dry-bulb temperature (°C) and relative humidity (%) of the air entering the dehumidifier. The output of this curve is multiplied by the Rated Water Removal to give the water removal of the dehumidifier at specific operating conditions (i.e., at temperatures and relative humidity levels different from the rating point conditions). The curve should be normalized to have the value of 1.0 at the rating point (air entering the dehumidifier at 26.7°C [80°F] dry-bulb and 60% relative humidity, and air flow rate as defined by field “Rated Air Flow Rate” above).

Field: Energy Factor Curve Name

This alpha field defines the name of a biquadratic performance curve (ref: Performance Curves) that parameterizes the variation of the energy factor as a function of the dry-bulb temperature (°C) and relative humidity (%) of the air entering the dehumidifier. The output of this curve is multiplied by the Rated Energy Factor to give the energy factor of the dehumidifier at specific operating conditions (i.e., at temperatures and relative humidity levels different from the rating point conditions). The curve should be normalized to have the value of 1.0 at the rating point (air entering the dehumidifier at 26.7°C [80°F] dry-bulb and 60% relative humidity, and air flow rate as defined by field “Rated Air Flow Rate” above).

Field: Part Load Fraction Correlation Curve Name

This alpha field defines the name of a quadratic or cubic performance curve (ref: Performance Curves) that parameterizes the variation of electrical power input to the dehumidifier as a function of the part load ratio (PLR, defined as the water removal load to be met (kg/s) divided by the dehumidifier’s water removal rate (kg/s) at the current operating conditions). The part load fraction (PLF) correlation accounts for efficiency losses due to compressor cycling.

The part load fraction correlation should be normalized to a value of 1.0 when the part load ratio equals 1.0 (i.e., no efficiency losses when the dehumidifier runs continuously for the simulation timestep). For PLR values between 0 and 1 (0 <= PLR < 1), the following rules apply:

0.7 <= PLF <= 1.0   and   PLF >= PLR

If PLF < 0.7 a warning message is issued, the program resets the PLF value to 0.7, and the simulation proceeds. The runtime fraction of the dehumidifier is defined as PLR/PLF. If PLF < PLR, then a warning message is issued and the runtime fraction of the dehumidifier is set to 1.0.

Mechanical dehumidifier typically have long runtimes with minimal compressor cycling. So, a typical part load fraction correlation might be:

      PLF = 0.95 + 0.05(PLR)

If the user wishes to model no efficiency degradation due to compressor cycling, the part load fraction correlation should be defined as follows:

      PLF = 1.0 + 0.0(PLR)

Field: Minimum Dry-Bulb Temperature for Dehumidifier Operation

This numeric field defines the minimum inlet air dry-bulb temperature for dehumidifier operation. The dehumidifier will not operate if the inlet air temperature is below this value. This input value must be less than the Maximum Dry-Bulb Temperature for Dehumidifier Operation, and the default value is 10°C.

Field: Maximum Dry-Bulb Temperature for Dehumidifier Operation

This numeric field defines the maximum inlet air dry-bulb temperature for dehumidifier operation. The dehumidifier will not operate if the inlet air temperature is above this value. This input value must be greater than the Minimum Dry-Bulb Temperature for Dehumidifier Operation, and the default value is 35°C.

Field: Off-Cycle Parasitic Electric Load

This numeric field contains the off-cycle parasitic electric power in Watts. This is the parasitic electric power consumed by controls or other electrical devices associated with the dehumidifier. This parasitic electric load is consumed whenever the dehumidifier is available to operate, but is not operating. The model assumed that this parasitic power contributes to heating the zone air (i.e., affects the zone air heat balance). The minimum value for this field is 0.0, and the default value is also 0.0 if this field is left blank.

Field: Condensate Collection Water Storage Tank Name

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