# Group – Humidifiers and Dehumidifiers[LINK]

The electric steam humidifier is a component that represents an electrically heated, self contained steam humidifier. The component uses electrical energy to convert ordinary tap water to steam which it then injects into the supply air stream by means of a blower fan. The actual unit might be an electrode-type humidifier or a resistance-type humidifier.

The humidifier model includes local control of the humidifier unit to meet a humidity ratio setpoint on its air outlet node. A set point manager is needed to put a setpoint on the exit node but no other local controllers are needed. The humidifier will add moisture to meet the humidity ratio setpoint.

A unique user assigned name for a particular humidifier unit. Any reference to this unit by another object will use this name.

The name of the schedule (ref: Schedule) that denotes whether the unit can run during a given time period. A schedule value of 0 indicates that the unit is off for that time period. A schedule value greater than 0 indicates that the unit can operate during the time period. If this field is blank, the schedule has values of 1 for all time periods.

The nominal full output water addition rate of the unit in m/sec of water at 5.05 C. This field is autosizable.

The nominal full output power consumption of the unit in watts, exclusive of the blower fan power consumption and any standby power. This field can be autosized. When it is autosized, its calculated from the rated capacity in kg/s and the enthalpy rise in J/kg of the feed water from the a reference temperature of liquid water at 20 °C to a saturated steam at 100 °C.

The nominal full output power consumption of the blower fan in watts.

The standby power consumption in watts. This amount of power will be consumed whenever the unit is available (as defined by the availability schedule).

#### Field: Air Inlet Node Name[LINK]

The name of the HVAC system node from which the unit draws inlet air.

#### Field: Air Outlet Node Name[LINK]

The name of the HVAC system node to which the unit sends its outlet air.

#### Field: Water Storage Tank Name[LINK]

This field is optional. If left blank or omitted, then the humidifier obtains its water directly from the mains water. If the name of a Water Storage Tank is specified, then the humidifier will try to obtain its water from that tank. If the tank can t provide all the water then the rest will be drawn from the mains and the humidifier will still operate.

An IDF example:

Humidifier:Steam:Electric,
Humidifier 1,                   !- Name
FanAndCoilAvailSched,   !- Availability Schedule Name
0.00000379,                       !- Rated Capacity {m3/s}
10200.,                               !- Rated Power {W}
27.,                                     !- Rated Fan Power {W}
2.,                                       !- Standby Power {W}
Cooling Coil Air Outlet Node, !- Air Inlet Node Name
Air Loop Outlet Node;   !- Air Outlet Node Name

• HVAC,Average,Humidifier Water Volume Flow Rate [m3/s]

• HVAC,Sum,Humidifier Water Volume[m3]

• HVAC,Average,Humidifier Electricity Rate [W]

• HVAC,Sum,Humidifier Electricity Energy [J]

• Zone,Meter,Humidifier:Water [m3]

• Zone,Meter,Humidifier:Electricity [J]

• HVAC,Average,Humidifier Storage Tank Water Volume Flow Rate [m3/s]

• HVAC,Sum,Humidifier Storage Tank Water Volume [m3]

• HVAC,Average,Humidifier Starved Storage Tank Water Volume Flow Rate [m3/s]

• HVAC,Sum,Humidifier Starved Storage Tank Water Volume [m3]

• Zone,Meter,Humidifier:MainsWater [m3]

• HVAC,Sum,Humidifier Mains Water Volume [m3]

#### Humidifier Water Volume Flow Rate [m3/s][LINK]

This field reports the water consumption rate of the steam humidifier in cubic meters of water per second.

This ouput is the cubic meters of water consumed by the steam humidifier over the timestep being reported.

This output is the electricity consumption rate in Watts of the steam humidifier.

This is the electricity consumption in Joules of the steam humidifier over the timestep being reported.

This meter output contains the sum of the water consumed (in cubic neters of water during the report timestep) by all the steam humidifiers at the HVAC level in the simulation.

This meter output contains the sum of the electricity consumed (in Joules during the report timestep) by all the steam humidifiers at the HVAC level in the simulation.

#### Humidifier Storage Tank Water Volume [m3][LINK]

These outputs contain the rate and volume of water obtained from water storage tank. These are only present if the humidifier is connected to a Water Storage Tank for its water supply.

#### Humidifier Starved Storage Tank Water Volume [m3][LINK]

These outputs contain the rate and volume of water that could not be obtained from the water storage tank. The component will still operate as if it did get all the water with the balance obtained directly from the mains

#### Humidifier Mains Water Volume [m3][LINK]

This output contains the volume of water obtained from the mains.

The gas fired steam humidifier is a component that represents a gas fired self-contained steam humidifier. The component uses gas fired energy to convert ordinary tap water to steam which it then blows or injects into the supply air stream. Blower fan may not be required depending on how the dry steam is delivered into the supply air stream. The humidifier model includes local control of the humidifier unit to meet a humidity ratio setpoint on its air outlet node of the unit. A humidity set point manager is needed to put a setpoint on the outlet node but no other local controllers are needed. The humidifier either blows or injects dry steam to meet the humidity ratio setpoint requirement. If the Rated Gas Use Rate input field is not autosized, the thermal efficiency input specified will be ignored and ovverriden by a thermal efficiency value determined from user specified Rated Gas Use Rate, rated capacity (m3/s) and design conditions for sizing calculation.

A unique user assigned name for a particular humidifier unit. Any reference to this unit by another object will use this name.

The name of the schedule (ref: Schedule) that denotes whether the unit can run during a given time period. A schedule value of 0 indicates that the unit is off for that time period. A schedule value greater than 0 indicates that the unit can operate during the time period. If this field is blank, the schedule has values of 1 for all time periods.

The nominal full capacity water addition rate in m3/s of water at 5.05 C.

#### Field: Rated Gas Use Rate {W}[LINK]

The nominal gas use rate in Watts. This input field can be autosized. When this input field is autosized, it is calculated from the rated capacity in kg/s, the enthalpy rise in J/kg of the feed water from a reference temperature of liquid water at 20 °C to a saturated steam at 100 °C and user specified thermal efficiency. If this input field is hardsized and the Inlet Water Temperature Option input field is selected as FixedInletWaterTemperature, then the thermal efficiency input field will not be used in the calculation or else if the Inlet Water Temperature Option input selected is VariableInletWaterTemperature, then the user specified thermal efficiency value will be overridden using internally calculated efficiency from the capacity, rated gas use rate and design condition.

The thermal efficiency of the gas fired humidifier. The thermal efficiency is based on the higher heating value of the fuel. The default value is 0.8. If Rated Gas Use Rate in the field above is not autosized and the Inlet Water Temperature Option input field selected is FixedInletWaterTemperature, then the thermal efficiency specified will be ignored in the calculation, or else if the Inlet Water Temperature Option input field is specified as VariableInletWaterTemperature, then the user specified thermal efficiency value will be overridden using internally calculated matching the capacity, rated gas use rate specified and design condition defined for sizing calculation.

#### Field: Thermal Efficiency Modifier Curve Name[LINK]

This is thermal efficiency modifier curve name of unit. This curve is normalized, i.e., the curve output value at rated condition is 1.0. If this input field is blank, then constant efficiency value specified in the input field above will be used. Allowed thermal efficiency modifier curve types are linear, quadratic, or cubic. These curves are solely a function of part load ratio.

The nominal full capacity electric power input to the blower fan in Watts. If no blower fan is required to inject the dry steam to the supply air stream, then this input field is set to zero.

The auxiliary electric power input in watts. This amount of power will be consumed whenever the unit is available (as defined by the availability schedule). This electric power is used for control purpose only.

#### Field: Air Inlet Node Name[LINK]

The name of the HVAC system node from which the unit draws inlet air.

#### Field: Air Outlet Node Name[LINK]

The name of the HVAC system node to which the unit sends its outlet air.

#### Field: Water Storage Tank Name[LINK]

This field is optional. If left blank or omitted, then the humidifier obtains its water directly from the mains water. If the name of a Water Storage Tank is specified, then the humidifier will try to obtain its water from that tank. If the tank can t provide all the water then the rest will be drawn from the mains and the humidifier will still operate.

#### Field: Inlet Water Temperature Option[LINK]

This field is a key/choice field that tells which humidifier water inlet temperature to use: fixed inlet temperature or variable water inlet temperature that depends on the source. Currently allowed water sources are main water or water storage tank in water use objects. The key/choice are: FixedInletWaterTemperature, with this choice, the gas fired humidifier will use a fixed 20C water inlet temperature. VariableInletWaterTemperature, with this choice, the gas fired humidifier will use water inlet temperature that depends on the source temperature. If a water use storage tank name is specified, then the gas humidifier water inlet temperature will be the storage water temperature, or else it uses water main temperature. The default main water temperature is 10 °C. If left blank or omitted, then the humidifier assumes fixed inlet water temperature of 20 °C.

An IDF example:

Humidifier:Steam:Gas,
Main Gas Humidifier,!- Name
ALWAYS_ON,          !- Availability Schedule Name
4.00E-5,            !- Rated Capacity {m3/s}
104000,             !- Rated Gas Use Rate {W}
1.0,                !- Thermal Efficiency {-}
,                   !- Thermal Efficiency Modifier Curve Name
0,                  !- Rated Fan Power {W}
0,                  !- Auxiliary Electric Power {W}
Mixed Air Node 1,   !- Air Inlet Node Name
Main Humidifier Outlet Node,  !- Air Outlet Node Name
;                   !- Water Storage Tank Name

Steam Gas Humidifier Outputs

• HVAC,Average,Humidifier Water Volume Flow Rate [m3/s]

• HVAC,Sum,Humidifier Water Volume[m3]

• HVAC,Average,Humidifier Gas Use Rate[W]

• HVAC,Sum,Humidifier Gas Use Energy [J]

• HVAC,Average,Humidifier Auxiliary Electricity Rate [W]

• HVAC,Sum,Humidifier Auxiliary Electricity Energy [J]

• HVAC,Meter,Humidifier:Water [m3]

• HVAC,Meter,Humidifier:Gas [J]

• HVAC,Meter,Humidifier:Electricity [J]

• HVAC,Average,Humidifier Storage Tank Water Volume Flow Rate [m3/s]

• HVAC,Sum,Humidifier Storage Tank Water Volume [m3]

• HVAC,Average,Humidifier Starved Storage Tank Water Volume Flow Rate [m3/s]

• HVAC,Sum,Humidifier Starved Storage Tank Water Volume [m3]

• Zone,Meter,Humidifier:MainsWater [m3]

• HVAC,Sum,Humidifier Mains Water Volume [m3]

#### Humidifier Water Volume Flow Rate [m3/s][LINK]

This field reports the water consumption rate of the steam humidifier in cubic meters of water per second.

This output is the cubic meters of water consumed by the steam humidifier over the timestep being reported.

#### Humidifier Gas Use Rate [W][LINK]

This output is the gas use rate of the gas fired steam humidifier in Watts.

#### Humidifier Gas Use Energy [J][LINK]

This output is the gas consumption of the gas fired steam humidifier in Joules.

#### Humidifier Auxiliary Electricity Rate [W][LINK]

This output is the auxiliary electricity consumption rate in Watts of the gas fired steam humidifier. This is the auxiliary electric power input to the blower fan and control unit.

#### Humidifier Auxiliary Electricity Energy [J][LINK]

This is the auxiliary electricity consumption in Joules of the gas fired steam humidifier over the timestep being reported. This is the auxiliary electric energy consumed by the blower fan and control unit. This auxiliary electric energy is reported meter output Humidifier:Electricity.

This meter output contains the sum of the water consumed (in cubic meters of water during the report timestep) by all the steam humidifiers at the HVAC level in the simulation.

This meter output contains the sum of the gas consumed (in Joules during the report timestep) by all the steam humidifiers at the HVAC level in the simulation.

#### Humidifier Storage Tank Water Volume [m3][LINK]

These outputs contain the rate and volume of water obtained from water storage tank. These are only present if the humidifier is connected to a Water Storage Tank for its water supply.

#### Humidifier Starved Storage Tank Water Volume [m3][LINK]

These outputs contain the rate and volume of water that could not be obtained from the water storage tank. The component will still operate as if it did get all the water with the balance obtained directly from the mains

#### Humidifier Mains Water Volume [m3][LINK]

This output contains the volume of water obtained from the mains.

This object models a solid desiccant dehumidifier (excluding associated fans). The process air stream is the air which is dehumidified. The regen air stream is the air which is heated to regenerate the desiccant. This object determines the process air outlet conditions, the load on the regeneration heating coil, the electric power consumption for the wheel rotor motor, and the regeneration air fan mass flow rate. All other heat exchangers are modeled as separate objects connected to the inlet and outlet nodes of the dehumidifier. The solid desiccant dehumidifier is typically used in an AirLoopHVAC:OutdoorAirSystem object, but can also be specified in any AirLoopHVAC. The regeneration heating coil can be Gas, Electric, Steam , or Hot Water coil. When hot water coil is selected as regeneration heating coil user-defined curves designed for lower temperature operation must be specified in the input field Performance Model Type along with the Nominal Regeneration Temperature input field. The default performance model type is valid for higher nominal regeneration temperature (e.g. 121C).

This alpha field contains the identifying name for the desiccant dehumidifier.

The name of the schedule (ref: Schedule) that denotes whether the desiccant unit can run during a given time period. A schedule value of 0 indicates that the unit is off for that time period. A schedule value greater than 0 indicates that the unit can operate during the time period. If this field is blank, the schedule has values of 1 for all time periods.

#### Field: Process Air Inlet Node Name[LINK]

The name of the node entering the process side of the desiccant wheel.

#### Field: Process Air Outlet Node Name[LINK]

The name of the node leaving the process side of the desiccant wheel.

#### Field: Regeneration Air inlet Node Name[LINK]

The name of the node entering the regeneration side of the desiccant wheel after the regeneration coil.

#### Field: Regeneration Fan Inlet Node Name[LINK]

Node name for air entering the regeneration fan, mass flow is set by this desiccant dehumidifier model.

Type of setpoint control. Options are

• LeavingMaximumHumidityRatioSetpoint

• SystemNodeMaximumHumidityRatioSetpoint

LeavingMaximumHumidityRatioSetpoint means that the unit is controlled to deliver air at the Leaving Maximum Humidity Ratio Setpoint, using bypass dampers to prevent overdrying.

SystemNodeMaximumHumidityRatioSetpoint means that the unit is controlled to deliver air at the maximum humidity ratio setpoint (System Node Humidity Ratio Max) on the Process Air outlet node, using bypass dampers to prevent overdrying. This setpoint must be established using a set point manager which sets the MaximumHumidityRatio control variable:

This will also require the use of a ZoneControl:Humidistat object. If the dehumidifer is located in the outdoor air stream, it may also be necessary to use SetpointManager:OutdoorAirPretreat.

#### Field: Leaving Maximum Humidity Ratio Setpoint[LINK]

Fixed setpoint for maximum process air leaving humidity ratio. Applicable only when Control Type = LeavingMaximumHumidityRatioSetpoint.

#### Field: Nominal Process Air Flow Rate[LINK]

Process air flow rate in m/s at nominal conditions. This field is autosizable.

#### Field: Nominal Process Air Velocity[LINK]

Process air velocity in m/s at nominal flow. The default value is 3m/s.

Power input to wheel rotor motor in W. If this field is unknown, electricity consumption of the unit can be obtained from nominal power per unit air flow rate below.

#### Field: Regeneration Coil Object Type[LINK]

Type of heating coil object for regeneration air. The hot water and steam heating coils require specifying plant loop, branches, and connector objects to support the heating coils, and are placed on the demand side of the plantloop. The hot water flow modulation through the regeneration air heating coil does not require additional controller or Controller:WaterCoil object. The parent object (Dehumidifier:Desiccant:NoFans) itself provides the “controller” function of modulating water flow. The valid choices are:

Name of heating coil object for regeneration air.

#### Field: Regeneration Fan Object Type[LINK]

Type of fan object for regeneration air. For UserCurves performance (see below) Fan:SystemModel, Fan:VariableVolume and Fan:ConstantVolume are valid. For Default performance (see below) only Fan:SystemModel or Fan:VariableVolume are valid.

Name of fan object for regeneration air.

Specifies whether the Default performance model or UserCurves curves should be used to model the performance. The default model is a generic solid desiccant wheel using performance curves of the form:

curve = C1 + C2*edb + C3*edb**2 + C4*ew + C5*ew**2 + C6*vel + C7*vel**2 + C8*edb*ew + C9*edb**2*ew**2 + C10*edb*vel + C11*edb**2*vel**2 + C12*ew*vel + C13*ew**2*vel**2 + C14*ALOG(edb) + C15*ALOG(ew) + C16*ALOG(vel)

edb = process entering drybulb temperature [C]
ew = process entering humidity ratio [kgWater/kgDryAir]
vel = process air velocity [m/s]

The Default curves are valid for the following range of process inlet conditions: dry-bulb temperatures of 1.67C (35F) to 48.9C (120F) and humidity ratios of 0.002857 kgWater/kgDryAir (20 gr/lb) to 0.02857 kgWater/kgDryAir (200 gr/lb). If the process inlet conditions are outside this range, the dehumidifier will not operate.

If UserCurves are specified, then performance is calculated as follows:

Leaving Dry-bulb = (Leaving Dry-Bulb Function of Entering Dry-Bulb and Humidity Ratio Curve) * (Leaving Dry-Bulb Function of Air Velocity Curve)

Leaving Humidity Ratio = (Leaving Humidity Ratio Function of Entering Dry-Bulb and Humidity Ratio Curve) * (Leaving Humidity Ratio Function of Air Velocity Curve)

Regeneration Energy = (Regeneration Energy Function of Entering Dry-Bulb and Humidity Ratio Curve) * (Regeneration Energy Function of Air Velocity Curve)

Regeneration Velocity = (Regeneration Velocity Function of Entering Dry-Bulb and Humidity Ratio Curve) * (Regeneration Velocity Function of Air Velocity Curve)

The UserCurves are limited to the following range of process inlet conditions (essentially not limited): dry-bulb temperatures of 73.3C (-100F) to 65.6C (150F) and humidity ratios of 0.0 kgWater/kgDryAir (0 gr/lb) to 0.21273 kgWater/kgDryAir (1490 gr/lb). If the process inlet conditions are outside this range, the dehumidifier will not operate.

When the Default performance model is selected, the remaining fields are ignored.

#### Field: Leaving Dry-Bulb Function of Entering Dry-Bulb and Humidity Ratio Curve Name[LINK]

This field is applicable only when UserCurves performance model type is specified.

Leaving dry-bulb of process air as a function of entering dry-bulb and entering humidity ratio, biquadratic curve.

curve = C1 + C2*edb + C3*edb**2 + C4*ew + C5*ew**2 + C6*edb*ew

edb = process entering drybulb temperature [C]

ew = process entering humidity ratio [kgWater/kgDryAir]

#### Field: Leaving Dry-Bulb Function of Air Velocity Curve Name[LINK]

This field is applicable only when UserCurves performance model type is specified.

Leaving dry-bulb of process air as a function of air velocity, quadratic curve.

curve = C1 + C2*v + C3*v**2

v = process air velocity [m/s]

#### Field: Leaving Humidity Ratio Function of Entering Dry-Bulb and Humidity Ratio Curve Name[LINK]

This field is applicable only when UserCurves performance model type is specified.

Leaving humidity ratio of process air as a function of entering dry-bulb and entering humidity ratio, biquadratic curve

curve = C1 + C2*edb + C3*edb**2 + C4*ew + C5*ew**2 + C6*edb*ew

edb = process entering drybulb temperature [C]

ew = process entering humidity ratio [kgWater/kgDryAir]

#### Field: Leaving Humidity Ratio Function of Air Velocity Curve Name[LINK]

This field is applicable only when UserCurves performance model type is specified.

Leaving humidity ratio of process air as a function of process air velocity, quadratic curve.

curve = C1 + C2*v + C3*v**2

v = process air velocity [m/s]

#### Field: Regeneration Energy Function of Entering Dry-Bulb and Humidity Ratio Curve Name[LINK]

This field is applicable only when UserCurves performance model type is specified.

Regeneration energy [J/kg of water removed] as a function of entering dry-bulb and entering humidity ratio, biquadratic curve

curve = C1 + C2*edb + C3*edb**2 + C4*ew + C5*ew**2 + C6*edb*ew

edb = process entering drybulb temperature [C]

ew = process entering humidity ratio [kgWater/kgDryAir]

#### Field: Regeneration Energy Function of Air Velocity Curve Name[LINK]

This field is applicable only when UserCurves performance model type is specified.

Regeneration energy [J/kg of water removed] as a function of process air velocity, quadratic curve.

curve = C1 + C2*v + C3*v**2

v = process air velocity [m/s]

#### Field: Regeneration Velocity Function of Entering Dry-Bulb and Humidity Ratio Curve Name[LINK]

This field is applicable only when UserCurves performance model type is specified.

Regeneration velocity [m/s] as a function of entering dry-bulb and entering humidity ratio, biquadratic curve

curve = C1 + C2*edb + C3*edb**2 + C4*ew + C5*ew**2 + C6*edb*ew

edb = process entering drybulb temperature [C]

ew = process entering humidity ratio [kgWater/kgDryAir]

#### Field: Regeneration Velocity Function of Air Velocity Curve Name[LINK]

This field is applicable only when UserCurves performance model type is specified.

Regeneration velocity [m/s] as a function of process air velocity, quadratic curve.

curve = C1 + C2*v + C3*v**2

v = process air velocity [m/s]

This field is applicable only when UserCurves performance model type is specified.

Nominal regeneration temperature upon which the regeneration energy modifier curve is based. This input is ignored when Performance Model Type = Default, which assume a regeneration temperature of 121C.

#### Field: Nominal Power Per Unit Air Flow Rate[LINK]

This field is nominal power consumption per unit air flow rate. It is used to calculate electricity consumption of the unit when no rotor power is entered.

An example of this statement in an IDF is:

Dehumidifier:Desiccant:NoFans,
Desiccant 1,                         !- Name
FanAndCoilAvailSched,       !- Availability Schedule Name
Outside Air Inlet Node,   !- Process Air Inlet Node Name
Desiccant Process Outlet Node,   !- Process Air Outlet Node Name
Regen Coil Out Node,         !- Regeneration Air Inlet Node Name
Outside Air Inlet Node 2,!- Regeneration Fan Inlet Node Name
SystemNodeMaximumHumidityRatioSetpoint,   !- Control Type
0.007,                                     !- Leaving Maximum Humidity Ratio Setpoint {kgWater/kgDryAir}
1,                                             !- Nominal Process Air Flow Rate {m3/s}
2.5,                                         !- Nominal Process Air Velocity {m/s}
10,                                           !- Rotor Power {W}
Coil:Heating:Fuel,               !- Regeneration Coil Object Type
Desiccant Regen Coil,       !- Regeneration Coil Name
Fan:SystemModel,           !- Regeneration Fan Object Type
Desiccant Regen Fan,         !- Regeneration Fan Name
UserCurves,                           !- Performance Model Type
Desiccant DryBulb fTW Curve, !- Leaving Dry-Bulb Function of Entering Dry-Bulb and Humidity Ratio
!                                                 Curve Name
Desiccant DryBulb fV Curve,   !- Leaving Dry-Bulb Function of Air Velocity Curve Name
Desiccant HumRat fTW Curve,   !- Leaving Humidity Ratio Function of Entering Dry-Bulb and Humidity Ratio Curve Name
Desiccant HumRat fV Curve,     !- Leaving Humidity Ratio Function of Air Velocity Curve Name
Desiccant RegenEnergy fTW Curve, !- Regeneration Energy Function of Entering Dry-Bulb and Humidity Ratio Curve Name
Desiccant RegenEnergy fV Curve,   !- Regeneration Energy Function of Air Velocity Curve Name
Desiccant RegenVel fTW Curve,       !- Regeneration Velocity Function of Entering Dry-Bulb and Humidity Ratio Curve Name
Desiccant RegenVel fV Curve,         !- Regeneration Velocity Function of Air Velocity Curve Name
121,                                         !- Nominal Regeneration Temperature {C}
;                                  !- Nominal Power Per Unit Air Flow Rate {W/m3/s}

• HVAC,Sum,Dehumidifier Removed Water Mass [kg]

• HVAC,Average,Dehumidifier Removed Water Mass Flow Rate [kg/s]

• HVAC,Average,Dehumidifier Part Load Ratio []

• HVAC,Average,Dehumidifier Electricity Rate [W]

• HVAC,Sum,Dehumidifier Electricity Energy [J]

• HVAC,Average,Dehumidifier Regeneration Specific Energy [J/kgWater]

• HVAC,Average,Dehumidifier Regeneration Rate [W]

• HVAC,Sum,Dehumidifier Regeneration Energy [J]

• HVAC,Average,Dehumidifier Regeneration Air Speed [m/s]

• HVAC,Average,Dehumidifier Regeneration Air Mass Flow Rate [kg/s]

• HVAC,Average,Dehumidifier Process Air Mass Flow Rate [kg/s]

#### Dehumidifier Removed Water Mass [kg][LINK]

Mass of water removed from process air stream.

#### Dehumidifier Removed Water Mass Flow Rate [kg/s][LINK]

Rate of water removal from process air stream.

Dehumidifier water removal rate divided by full-load water removal rate.

Dehumidifier rotor electric power.

Dehumidifier rotor electric energy.

#### Dehumidifier Regeneration Specific Energy [J/kgWater][LINK]

Regeneration heating coil energy divided by water removed.

Regeneration heating coil output rate.

Regeneration heating coil output energy.

Regeneration air velocity.

#### Dehumidifier Regeneration Air Mass Flow Rate [kg/s][LINK]

Regeneration air mass flow rate.

#### Dehumidifier Process Air Mass Flow Rate [kg/s][LINK]

Process air mass flow rate.

The Dehumidifier:Desiccant:System object models the dehumidification of an air stream, normally called the process air stream. A second heated air stream, called the regeneration air stream, is used to remove the collected moisture from the desiccant heat exchanger and this moisture-laden air is then usually exhausted from the building. This Dehumidifier:Desiccant:System object is similar to the Dehumidifier:Desiccant:NoFans object but has some additional modeling capabilities.

The Dehumidifier:Desiccant:System object in EnergyPlus is a compound object that can be placed anywhere in an air loop (AirLoopHVAC). Common locations for this object are in an AirLoopHVAC:OutdoorAirSystem or in the main air loop (AirLoopHVAC) downstream of a cooling coil (postcooling desiccant dehumidifier). This compound object coordinates the operation of several children objects: a desiccant heat exchanger, a regeneration air fan, and an optional regeneration air heater. Gas, Electric, Steam, or Hot Water heating coils can be used for regenerator air heaters. If this dehumidifier is placed in the main air loop immediately downstream of a direct expansion (DX) cooling coil, then the dehumidifier’s operation can be coordinated with the operation of the companion DX coil and it is also possible to specify that the DX system’s condenser waste heat can be used to help regenerate the desiccant heat exchanger. For the case of condenser waste heat regeneration, an optional exhaust fan can also be modeled by this desiccant dehumidifier compound object to help maintain a set point temperature for air entering the regeneration side of the desiccant heat exchanger.

It is important to note that the optional exhaust air fan is modeled internal to the Dehumidifier:Desiccant:System and a separate fan object should not be added to the input data file (idf) for this fan. On the other hand, a separate fan object is required in the input data file for the regeneration air fan.

A schematic of the compound object Dehumidifier:Desiccant:Systemis shown in Figure 1 with the draw through regeneration air fan placement. Figure 2 shows the Dehumidifier:Desiccant:System object configured with the blow through regeneration air fan placement.

NOTE: As with any air loop compound object, the Dehumidifier:Desiccant:System object itself is specified on the AirLoopHVAC Branch or in the AirLoopHVAC:OutdoorAirSystem:EquipmentList for an AirLoopHVAC:OutdoorAirSystem. The children objects (e.g., desiccant heat exchanger, regeneration air fan, and optional regeneration air heater) must be specified separately in the input data file and their inlet/outlet connections must be as shown in Figure 1 or Figure 2.

Currently the only heat exchanger choice for this object is HeatExchanger:Desiccant: BalancedFlow. So to model a Dehumidifier:Desiccant:System located in an air loop, the input data file should include the following objects:

If the user wants to model the Dehumidifier:Desiccant:System in an AirLoopHVAC:OutdoorAirSystem, then the process air path of the dehumidifier should be located in the outdoor air stream and the regeneration air path may be placed in the relief air stream or modeled by the desiccant dehumidifier itself where the first node for the regeneration inlet air stream must be an outdoor air node. If the user wants to model the Dehumidifier:Desiccant:System in an air loop (AirLoopHVAC) Branch, then the process air path of the dehumidifier should be located in the air loop Branch object. For this case, the regeneration air stream is modeled by the desiccant dehumidifier object itself (i.e., not part of an air loop Branch statement) and the first node for the regeneration inlet air stream must be an outdoor air node (ref. Figure 1 or Figure 2).

A description of each input field for this object is provided below:

A unique, user-assigned name for a particular Dehumidifier:Desiccant:System. Any reference to this dehumidifier by another object will use this name.

The name of the schedule (ref: Schedule) that denotes whether the dehumidifier can operate during a given time period. A schedule value greater than 0 (usually 1 is used) indicates that the dehumidifier can operate. A value less than or equal to 0 (usually 0 is used) denotes that the dehumidifier will not operate (i.e., no heat exchange will take place and the regeneration air fan does not operate). If the field is blank, the schedule has a value of 1 for all time periods. For the case where companion cooling coil regeneration air heating has been specified, the desiccant dehumidifier’s exhaust fan serves as the condenser air fan for the cooling coil system so this availability schedule will not disable exhaust fan operation.

#### Field: Desiccant Heat Exchanger Object Type[LINK]

This alpha field contains the type of desiccant heat exchanger used with this dehumidifier. Currently, the only valid choice is HeatExchanger:Desiccant:BalancedFlow.

#### Field: Desiccant Heat Exchanger Name[LINK]

This alpha field contains the name of the desiccant heat exchanger used with this dehumidifier.

This alpha field specifies the name of the air loop node used to control desiccant heat exchanger operation. A set point manager must be used to place a maximum humidity ratio set point on this node (e.g., SetpointManager:SingleZone:Humidity:Maximum or SetpointManager:OutdoorAirPretreat).

#### Field: Regeneration Air Fan Object Type[LINK]

This alpha field contains the type of regeneration air fan used. Available fan types are Fan:SystemModel, Fan:OnOff and Fan:ConstantVolume.

#### Field: Regeneration Air Fan Name[LINK]

This alpha field contains the name of the regeneration air fan used with this dehumidifier.

#### Field: Regeneration Air Fan Placement[LINK]

This alpha field specifies the fan configuration used in the desiccant dehumidifier. Valid choices are BlowThrough and DrawThrough , with a default of DrawThrough if this field is left blank.

#### Field: Regeneration Air Heater Object Type[LINK]

This alpha field contains the type of heating coil used to heat the regeneration air stream. This field may be left blank when no regeneration air heater is required. The hot water and steam heating coils require specifying plant loop, branches, and connector objects to support the heating coils, and are placed on the demand side of the plantloop. The hot water flow modulation through the regeneration air heating coil does not require additional controller or Controller:WaterCoil object. The parent object (Dehumidifier:Desiccant:System) itself provides the “controller” function of modulating water flow. For autosizing regeneration air heating coil the Design Coil Inlet Air Condition used is the outdoor air condition if the desiccant system is on the primary air loop, or else if the desiccant system is on outdoor air system then it is the return air condition. The Design Coil Outlet Air Temperature is the Regeneration Inlet Air Setpoint Temperature specified in the input field below. Valid heating coil choices are:

#### Field: Regeneration Air Heater Name[LINK]

This alpha field contains the name of the heating coil used to heat the regeneration air stream. This field may be left blank when no regeneration air heater is required.

#### Field: Regeneration Inlet Air Setpoint Temperature[LINK]

This optional numeric field specifies the regeneration air inlet temperature setpoint in Celsius. The regeneration air heater and/or the companion coil regeneration air heating will be controlled to this temperature to the extent possible. This field may be left blank when no regeneration air heater is required or when control of the exhaust fan used with the companion coil regeneration air heating option is not required. If regeneration air heating coils is autosized, then the value of this input field is used as the Regeneration Air Heater Design Outlet Air Temperature for the coil sizing calculation. The default value is 46.0 degrees.

#### Field: Companion Cooling Coil Object Type[LINK]

This optional alpha field contains the type of companion cooling coil used with this desiccant dehumidifier. The only valid choices are Coil:Cooling:DX:SingleSpeed, Coil:Cooling:DX:VariableSpeed, and Coil:Cooling:DX:TwoStageWithHumidityControlMode.

#### Field: Companion Cooling Coil Name[LINK]

This optional alpha field contains the name of the companion cooling coil used with this desiccant dehumidifier. This field may be left blank when no companion cooling coil is being modeled.

#### Field: Companion Cooling Coil Upstream of Dehumidifier Process Inlet[LINK]

This choice field specifies if the companion cooling coil is located immediately upstream of the dehumidifiers process inlet. Valid choices are Yes and No. If Yes is selected, then the outlet air node for the companion cooling coil must be the same as the dehumidifier’s process air inlet node (i.e., the process air inlet node name for the desiccant heat exchanger specified for this desiccant dehumidifier). For this case, the companion cooling coil and the desiccant dehumidifier are assumed to operate in tandem ; that is, if the simulation determines that the companion cooling coil is unable to meet the humidity set point specified on the sensor node based on its own operation, then the desiccant dehumidifier operates at the same time and for the same duration as the cooling coil to provide improved dehumidification. If No is selected, then the dehumidifier will control to the humidity set point specified on the sensor node to the extent possible. The default value is No if this field is left blank.

#### Field: Companion Coil Regeneration Air Heating[LINK]

This choice field determines if the companion cooling coil’s condenser waste heat is used to heat the regeneration inlet air. Valid choices are Yes and No. The default value is No if this field is left blank.

#### Field: Exhaust Fan Maximum Flow Rate[LINK]

This optional numeric field contains the maximum fan volumetric flow rate for the exhaust fan in cubic meters per second. As noted previously, this exhaust fan is modeled internally by the Dehumidifier:Desiccant:System object and a separate fan object should NOT be specified in the input data file for this fan. This field is used only when a companion cooling coil is specified and the Companion Coil Regeneration Air Heating field is set to Yes . This field must be used in conjunction with the Exhaust Fan Maximum Power and the Exhaust Fan Power Curve Name input fields. The model assumes that the exhaust fan will operate as needed to maintain the Regeneration Inlet Air Setpoint Temperature , up to the maximum flow rate specified in this input field. If the desiccant dehumidifier is OFF for a simulation timestep but its companion cooling coil is operating and is specified to provide regeneration air heating, then the exhaust fan operates at this maximum air flow rate (i.e., this fan serves as the condenser fan for the companion cooling coil system when regeneration air heating is specified, so the inputs to the companion cooling coil object should not include the condenser fan energy since the condenser fan energy is modeled by the Dehumidifier:Desiccant:System object).

#### Field: Exhaust Fan Maximum Power[LINK]

This optional numeric field contains the maximum power for the exhaust fan in Watts (i.e., at the Exhaust Fan Maximum Flow Rate). This field is used only when a companion cooling coil is used and the Companion Coil Regeneration Air Heating field is set to Yes . This field must be used in conjunction with the Exhaust Fan Maximum Flow Rate and the Exhaust Fan Power Curve Name input fields.

#### Field: Exhaust Fan Power Curve Name[LINK]

This optional alpha field contains the name of the exhaust fan power modifier curve. This field is used only when a companion cooling coil is used and the Companion Coil Regeneration Air Heating field is set to Yes . This field must be used in conjunction with the Exhaust Fan Maximum Flow Rate and the Exhaust Fan Maximum Power input fields. If this field is blank, the exhaust fan operates (when required) at the maximum power specified in the field above. The curve object type for this Exhaust Fan Power Curve Name must be Curve:Cubic or Curve:Quadratic. The curve object (Curve:Cubic or Curve:Quadratic) defines the change in exhaust fan power as a function of the ratio of the actual exhaust air flow rate divided by the maximum flow rate.

Following is an example input for this object:

Dehumidifier:Desiccant:System,
Desiccant 1,                         !- Name
FanAvailSched,                     !- Availability Schedule Name
HeatExchanger:Desiccant:BalancedFlow,   !- Desiccant Heat Exchanger Object Type
Desiccant Heat Exchanger 1,   !- Desiccant Heat Exchanger Name
HX Process Outlet Node,   !- Sensor Node Name
Fan:SystemModel,           !- Regeneration Air Fan Object Type
Desiccant Regen Fan,         !- Regeneration Air Fan Name
DrawThrough,                         !- Regeneration Air Fan Placement
Coil:Heating:Fuel,               !- Regeneration Air Heater Object Type
Desiccant Regen Coil,       !- Regeneration Air Heater Name
46.111111,                             !- Regeneration Inlet Air Setpoint Temperature {C}
Coil:Cooling:DX:SingleSpeed,   !- Companion Cooling Coil Object Type
Desiccant DXSystem Cooling Coil,   !- Companion Cooling Coil Name
Yes,                           !- Companion Cooling Coil Upstream of Dehumidifier Process Inlet
Yes,                                         !- Companion Coil Regeneration Air Heating
1.05,                                       !- Exhaust Fan Maximum Flow Rate {m3/s}
50,                                           !- Exhaust Fan Maximum Power {W}
EXHAUSTFANPLF;                     !- Exhaust Fan Power Curve Name

• HVAC,Sum,Dehumidifier Removed Water Mass [kg]

• HVAC,Average,Dehumidifier Removed Water Mass Flow Rate [kg/s]

• HVAC,Average,Dehumidifier Part Load Ratio []

• HVAC,Average,Dehumidifier Exhaust Fan Electricity Rate [W]

• HVAC,Sum,Dehumidifier Exhaust Fan Electricity Energy [J]

#### Dehumidifier Removed Water Mass [kg][LINK]

This output is the mass of water removed from the process air stream in kilograms for the timestep being reported.

#### Dehumidifier Removed Water Mass Flow Rate [kg/s][LINK]

This output is the average rate of water removal from the process air stream in kilograms per second for the timestep being reported.