Finned Tube Radiator

Stencil:  Zone HVAC Stencil: Finned Tube Radiator

Type: Convective Heater

Sub Type: Radiant_Water

Note: Requires a connection to a hot water loop

EnergyPlus IDF Objects

EnergyPlus Object - ZoneHVAC:Baseboard:RadiantConvective:Water

The objective of this model is to calculate the convective and radiant heat transfer from water baseboard heaters to the people and the surfaces within a zone so that surface heat balances can take into account the radiant heat transfer to the surfaces and thus enhance the accuracy of thermal comfort predictions within the space. The radiant heat gains are distributed to the surfaces by fractions defined by user input.

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 Average Water Temperature

This field is the rated average water temperature for the baseboard heater which is published in the manufacturer’s literature in degree Celsius. It typically ranges from 65.56C to 115.36C in the I=B=R rating document while the lowest allowable temperature is 32.22C. The default value is 87.78C. If the user does not enter this field, the default value is assumed.

Field: Rated Water Mass Flow Rate

This field is the rated standard water flow rate in kg/s which is published as part of the manufacturer’s literature. It is used by the manufacturers when determining the rated capacity (see next field). The default value is 0.063kg/s. If it is blank or zero, the default values is assumed.

Field: Rated Capacity

This field is the rated water baseboard capacity in watts at a rated water mass flow rate (see previous field). Almost all publications from manufacturers indicate it as W/m (Btuh per linear foot). The user thus must multiply it by the active length of the unit. The active length is available in the literature. Manufacturers are required to publish the difference between active and total length of the unit (I=B=R rating for boilers baseboard radiation, 2009). This field can be autosized by EnergyPlus. If it is blank or zero, autosizing is assumed.

Field: Maximum Water Flow Rate

This field is the maximum water volumetric flow rate in m³/sec.  It can be autosized by EnergyPlus.

Field: Convergence Tolerance

This field is the control tolerance for the unit heating output. The unit is controlled by matching the unit output to the zone demand. For hot water baseboards, the model must be numerically inverted to obtain a specified output. The convergence tolerance is the error tolerance used to terminate the numerical inversion procedure. Basically this is the fraction:

The default is 0.001.

Field: Fraction Radiant

This field specifies what fraction of the power input to the baseboard heater is actually transferred to the space as radiant heat. The fraction should be between 0 and 1. This is the portion of the total power that is modeled as radiation. The portion that is radiant heat transfer from the baseboard heater is distributed to people and specific surfaces using the remaining fields. Note that the sum of the fractions in the remaining fields (people and surfaces) must equal 1.0 so that all the radiant power is distributed properly. For more information on the specification of this parameter, please see the Engineering Reference for EnergyPlus.

Field: Fraction of Radiant Energy Incident on People

This field specifies the fraction of radiant portion of heat transfer to the zone from the baseboard heater that is incident directly on people within the space. This has an impact on the predicted thermal comfort of the zone occupants. Note that although this energy is “radiant” it is actually modeled in the zone heat balance as convective energy (like an internal gain). The basic assumption here is that most radiant energy falling on people will most likely be re-released to the zone air by convection. This is a simplification of reality, but it maintains the overall energy balance.

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