This low temperature electric radiant system is a component of zone equipment that is intended to model any “radiant system” where electric resistance heating is used to supply energy (heat) to a building surface (wall, ceiling, or floor).
In cases where no other systems are serving the zone in which this system resides it uses the heating equipment priority to determine which system will run first. If the radiant system is serving a zone with forced air equipment, the radiant system will follow the priority order established by the zone thermostat but will still base its response on the controls defined for the radiant system.
Control is accomplished by varying the electrical power supplied to the unit based on a setpoint and a deadband. This model covers either a radiant panel system or wires embedded in entire walls, floors, or ceilings. It is not intended to simulate high temperature electric or gas radiant heaters. Those devices are handled by the High temperature radiant heaters.
This field is a unique pre-defined user name for this radiant surface.
This option, along with the throttling range and heating setpoint, defines how the low temperature electric radiant system is to be controlled. The temperature defined in the setpoint schedule (whether defined here on this dialog or by using Simple HVAC activity settings) can refer to one of 5 different temperatures: the zone mean air temperature, the zone mean radiant temperature, the zone operative temperature, the outdoor dry-bulb temperature, or the outdoor wet-bulb temperature. Select from the following options:
1-Mean air temperature
2-Mean radiant temperature
3-Operative temperature - average of Mean air temperature and Mean radiant temperature
4-Mean air temperature setpoint
5-Mean radiant temperature setpoint
6-Operative temperature setpoint
See the throttling range and control temperature schedule fields below for more information.
Select the schedule that denotes whether the electric low temperature radiant system can operate during a given time period. A schedule value less than or equal to 0 (usually 0 is used) denotes that the unit must be off for that time period. A value greater than 0 (usually 1 is used) denotes that the unit is available to operate during that time period.
Select the method to be used to determine the maximum power output of the unit. Allowed settings are:
1-Heating design capacity - the maximum or nominal heating capacity is specified, or when autosize is entered the program calculates the maximum capacity.
2-Capacity per floor area - the program calculates the design heating capacity from user specified heating capacity per floor area and floor area of the zone served by the low temperature radiant electric unit.
3-Fraction of autosized heating capacity - the program calculates the design heating capacity from user specified fraction and the auto-sized design heating capacity.
This autosizable field is available when the Heating design capacity method is set to 1-Heating design capacity. It defines the maximum electric power converted into heat in the low temperature radiant electric unit (in W or Btu/h).
The controls for the radiant system vary the amount of power supplied to the surface between zero input and the maximum power specified in this field as the lower and upper bounds, respectively.
This field is available when the Heating design capacity method is set to 2-Capacity per floor area. It defines the heating capacity per unit floor area (in W/m2 or W/ft2) of the low temperature radiant electric system. The program calculates the heating capacity from the floor area of the zone served by the low temperature radiant electric unit and the heating capacity per unit floor area value specified here.
This field is available when the Heating design capacity method is set to 3-Fraction of autosized heating capacity. It defines the heating capacity of the radiant surface as a fraction of the zone autosized heating capacity. The program calculates the heating capacity from the design autosized heating capacity and this fraction. Design day sizing must be specified. The default value is 1.0.
When Detailed HVAC activity data is set to 2-Detailed HVAC data you can select a schedule to define the heating setpoint for the radiant system (in °C or °F). Used in conjunction with the heating throttling range, it defines whether or not the system is running and the power input to the radiant surface. Power input to the system is varied linearly around the setpoint temperature based on the throttling range and the maximum electrical power parameters (see above).
This schedule allows different heating setpoint temperatures to be defined for different periods through the year. In addition, it may be different that the thermostatic control schedule defined for overall operation of components serving the zone in which the radiant system is located. The thermostatic control determines whether or not there is a heating or cooling load in the space and thus whether the systems should be operating. This field simply controls the flow rate to the radiant system.
When Detailed HVAC activity data is set to 1-Simple HVAC data the heating setpoint is defined by the Heating setpoint temperature, Heating setback temperature and Heating operation schedule and this setting is not available, but otherwise it works as for when using 2-Detailed HVAC data.
This field specifies the temperature range (in delta °C or °F) over which the radiant system varies heat input, from zero up to the maximum defined by the maximum electrical power field described above. The throttling range parameter is used in conjunction with the zone heating control setpoint temperature to define the response of the system to various zone conditions. The zone heating setpoint specifies the temperature where the power input to the system is at half of the Maximum power input. For example, if the setpoint is currently 15°C and the heating throttling range is 2°C, then the electrical power supplied to the radiant system will be zero when the controlling temperature (MAT, MRT, Operative Temperature, ODB, or OWB; see control type field above) is at or above 16°C and the maximum power input when the controlling temperature is at or below 14°C. This represents a throttling range of 2°C around the setpoint of 15°C. For zone temperatures between 14°C and 16°C, the power input to the radiant system is varied linearly. The minimum throttling range is 0.5°C.