Energy Recovery Ventilator & Energy Recovery Ventilator Controller

Stencil:  Zone HVAC Stencil: Grp-VAV Terminal

Type: Unitary Zone Equipment

Sub Type: Energy Recovery Ventilator

EnergyPlus IDF Objects

EnergyPlus Object - ZoneHVAC:EnergyRecoveryVentilator

EnergyPlus Object - ZoneHVAC:EnergyRecoveryVentilatorController

Energy Recovery Ventilator

EnergyPlus Object - ZoneHVAC:EnergyRecoveryVentilator

The ZoneHVAC:EnergyRecoveryVentilator - stand alone energy recovery ventilator (ERV) is a single-zone HVAC component used for exhaust air heat recovery. This compound object consists of 3 required components: a generic air-to-air heat exchanger (see object Heat Exchanger:Air to Air:Generic), a supply air fan, and an exhaust air fan (see object Fan:OnOff).

An optional controller (see object ZoneHVAC:EnergyRecoveryVentilator:Controller) may be used to simulate economizer (free cooling) operation, modify air flow rates based on high indoor humidity, or simulate a “push-button” type economizer controller.

This compound object models the basic operation of supply and exhaust air fans and an air-to-air heat exchanger. The stand alone ERV operates whenever the unit is scheduled to be available (Availability schedule). The stand alone ERV object can be used in conjunction with an economizer feature whereby heat exchange is suspended whenever free cooling is available (i.e., air flow is fully bypassed around a fixed-plate heat exchanger or the rotation of a rotary heat exchanger is stopped). The economizer feature may also be activated based on a time-of-day schedule. Heat exchange is also suspended when air flow rates through the heat exchanger are modified in response to a zone humidistat. When an economizer is used in conjunction with high humidity control, high humidity control has the priority.

Component Properties - Energy Recovery Ventilator

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.

Field: Name

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

Field: Availability Schedule Name

The name of the schedule (ref: Schedule) that denotes whether the unit can operate during a given hour. A schedule value greater than 0 (usually 1 is used) indicates that the unit can operate during the hour. A value less than or equal to 0 (usually 0 is used) denotes that the unit will not operate.

Field: Heat Exchanger Name

Field: Supply Air Flow Rate

The supply air flow rate through the ERV unit in cubic meters per second at standard temperature and pressure (dry air at 20^o C dry bulb). The program uses local barometric pressure to account for altitude using the equation for "standard atmospheric" pressure on p 6.1 of the ASHRAE 1997 HOF (SI edition) to initialize the air systems being simulated.

p=101325*(1-2.25577E-05*Z)**5.2559

where p=pressure in Pa and Z=altitude in m

Note that this flow rate must be within the valid air flow range for the heat exchanger (ref: HeatExchanger:AirToAir:SensibleAndLatent in the Engineering Document). In addition, this flow rate must be less than or equal to the supply fan air flow rate (Fan:OnOff). If the supply air flow rate is less than the exhaust air flow rate, the zone infiltration (ref: ZoneInfiltration) should be specified accordingly (the infiltration induced by imbalanced air flows is not accounted for automatically). The ERV supply air flow rate may also be autosized using the ventilation rate per floor area and/or ventilation rate per occupant fields below. When autosizing, the heat exchanger and fan air flow rates should also be autosized.

Field: Exhaust Air Flow Rate

The exhaust air flow rate through the ERV unit in cubic meters per second at standard temperature and pressure (dry air at 20^o C dry bulb). The program uses local barometric pressure to account for altitude using the equation for "standard atmospheric" pressure on p 6.1 of the ASHRAE 1997 HOF (SI edition) to initialize the air systems being simulated.

p=101325*(1-2.25577E-05*Z)**5.2559

where p=pressure in Pa and Z=altitude in m

Note that this flow rate must be within the valid air flow range for the heat exchanger (ref: HeatExchanger:AirToAir:SensibleAndLatent in the Engineering Document). In addition, this flow rate must be less than or equal to the exhaust fan air flow rate (Fan:OnOff). If the exhaust air flow rate is greater than the supply air flow rate, the zone infiltration (ref: ZoneInfiltration) should be specified accordingly (the infiltration induced by imbalanced air flows is not accounted for automatically). The ERV exhaust air flow rate may also be autosized using the ventilation rate per floor area and/or ventilation rate per occupant fields below. When autosizing, the heat exchanger and fan air flow rates should also be autosized.

Field: Supply Air Fan Name

The name of the supply air fan used in this object. Fan type must be Fan:OnOff.

Field: Exhaust Air Fan Name

The name of the exhaust air fan used in this object. Fan type must be Fan:OnOff.

Field: Controller Name

This optional field specifies the name of the controller used by this compound component if economizer (free cooling) mode or high humidity control operation is desired. Controller type must be ZoneHVAC:EnergyRecoveryVentilator:Controller.

Field: Ventilation Rate per Unit Floor Area

This optional numeric field defines the ventilation rate per unit floor area in cubic meters per second per square meter. This field is only used when the supply and exhaust air flow rates are autosized.

Field: Ventilation Rate per Occupant

This optional numeric field defines the ventilation rate per occupant in cubic meters per second per occupant. This field is only used when the supply and exhaust air flow rates are autosized.

Energy Recovery Ventilator Controller

EnergyPlus Object - ZoneHVAC:EnergyRecoveryVentilatorController

This controller object is used exclusively by the stand alone energy recovery ventilator (ZoneHVAC:EnergyRecoveryVentilator, see Figure 127). The purpose of this controller is to simulate economizer operation for the stand alone ERV and provide free cooling whenever possible or modify the outdoor air flow rate during high indoor humidity conditions. During economizer operation, if all of the limits are satisfied, the controller activates economizer mode (fully bypassing the fixed-plate air-to-air heat exchanger or stopping the rotation of a rotary heat exchanger). If any of the selected limits are exceeded, economizer operation is terminated. A time-of-day schedule may also be used to simulate a “push-button” type economizer controller.

In addition, the outdoor air flow rate may be modified and heat exchange suspended in response to high indoor relative humidities. When the indoor relative humidity exceeds the zone humidistat’s relative humidity set point, high humidity control is activated. When activated, if high humidity control is based on the outdoor air humidity ratio and the outdoor humidity ratio is greater than the indoor humidity ratio, high humidity control is terminated.

Component Properties - Energy Recovery Ventilator Controller

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.

Field: Name

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

Field: Temperature High Limit

The input for this field is the outdoor air temperature high limit for economizer operation. If the outdoor air temperature is above this limit, economizer (free cooling) operation is terminated. No input (blank) in this field means that there is no outdoor air temperature high limit control.

Field: Temperature Low Limit

The input for this field is the outdoor air temperature low limit (°C) for economizer operation. If the outdoor air temperature is below this limit, economizer (free cooling) operation is terminated. No input (blank) in this field means that there is no outdoor air temperature low limit control.

Field: Enthalpy High Limit

The input for this field is the outdoor air enthalpy limit (in J/kg) for economizer operation. If the outdoor air enthalpy is above this value, economizer (free cooling) operation is terminated. No input (blank) in this field means that there is no outdoor air economizer limit control.

Field: Dewpoint Temperature Limit

Input for this field is the outdoor air dewpoint limit (°C) for economizer operation. If the outdoor air dewpoint temperature is above this value, the outdoor airflow rate will be set to the minimum. No input (blank) in this field means that there is no outdoor air dewpoint limit control. This limit applies to the conditions at the Actuated Node regardless of whether or not there are any other components on the outdoor air path upstream of the mixer.

Field: Electronic Enthalpy Limit Curve Name

Input for this field is the name of a quadratic or cubic curve which provides the maximum outdoor air humidity ratio (function of outdoor air dry-bulb temperature) for economizer operation. If the outdoor air humidity ratio is greater than the curve’s maximum humidity ratio (evaluated at the outdoor air dry-bulb temperature), the outdoor air flow rate will be set to the minimum. This limit applies to the conditions at the Actuated Node regardless of whether or not there are any other components on the outdoor air path upstream of the mixer. No input (blank) in this field means that there is no electronic enthalpy limit control.

Field: Exhaust Air Temperature Limit

This input establishes whether or not there is a limit control on the exhaust air temperature. The choices are ExhaustAirTemperatureLimit or NoExhaustAirTemperatureLimit. If ExhaustAirTemperatureLimit is chosen, the controller deactivates economizer mode whenever the outdoor air temperature is greater than the exhaust air temperature. If NoExhaustAirTemperatureLimit is chosen, no limit check on the exhaust air temperature is performed.

Field: Exhaust Air Enthalpy Limit

This input establishes whether or not there is a limit control on the exhaust air enthalpy. The choices are ExhaustAirEnthalpyLimit or NoExhaustAirEnthalpyLimit. If ExhaustAirEnthalpyLimit is chosen, the controller deactivates economizer mode whenever the outdoor air enthalpy is greater than the exhaust air enthalpy. If NoExhaustAirEnthalpyLimit is chosen, no limit check on the exhaust air enthalpy is performed.

Field: Time of Day Economizer Flow Control Schedule Name

This alpha field is the name of a schedule which controls the change in air flow rate based on time-of-day. Schedule values equal to 0 disable this feature. Schedule values greater than 0 activate the economizer. Note that heat exchange between the air streams is suspended when the economizer is active. This schedule can be used with or without the high humidity control option. When an economizer is used in conjunction with the high humidity control option, high humidity control has priority.

Field: High Humidity Control Flag

This optional choice field establishes whether or not the supply and exhaust air flow rates are modified in response to high indoor relative humidity. Valid choices are Yes and No. If Yes is selected, the supply and exhaust air flow rates may be modified when the indoor relative humidity is above the humidistat set point. If No is selected, this option is disabled and the following three fields are not used. Note that heat exchange between the air streams is suspended during times when high humidity control is active. The default value is No.

Field: Humidistat Control Zone Name

This optional input defines the zone name where the humidistat is located. This is the same zone name used in the Zone Control:Humidistat object. This field is required when the High Humidity Control Flag is specified as Yes.

Field: High Humidity Outdoor Air Flow Ratio

This optional input is the ratio of the modified supply (outdoor) air flow rate to the supply air flow rate specified in the Energy Recovery Ventilator:Stand Alone ERV object. When the high humidity control algorithm determines that the supply air flow rate will be changed (i.e. increased or decreased), the operating supply air flow rate is equal to the supply air flow rate specified in the Energy Recovery Ventilator:Stand Alone ERV object multiplied by this ratio. The minimum value for this field is 0. This field is used to modify both the supply and exhaust air flow rates when high humidity control is active. The supply and exhaust air fan volumetric flow rates must be able to account for the increase in air flow when this input is greater than 1. The default value is 1.

Field: Control High Indoor Humidity based on Outdoor Humidity Ratio

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