The high temperature radiant system is a component of zone equipment that is intended to model any “high temperature” or “high intensity” radiant system where electric resistance or gas-fired combustion heating is used to supply heat directly to building occupants, as well as to the zone surfaces (wall, ceiling, or floor).
In cases where no other systems are serving the zone in which this system resides, it will use 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 by the user for the radiant system.
The control is accomplished by varying the electrical power or gas consumed by the unit. It is not intended to simulate low temperature electric or hydronic radiant systems. Those devices are handled by Radiant surfaces and other types of Radiative-Convective Heater data
This field is a unique pre-defined user name for this high temperature radiant system.
Select the fuel from:
1-Natural gas - the radiant surface is heated by burning gas with a combustion efficiency defined below.
2-Electricity - the radiant surface is heated by electric elements
This option, along with the throttling range and heating setpoint, defines how the 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
For setpoint control strategies options 4-6, i.e. those ending in "setpoint" above, EnergyPlus calculates the correct heater output to meet the heating setpoint temperature through iteration and interpolation. This method will more closely match the operation of an actual thermostat, but it will require significantly longer execution time. For more information on the standard piecewise linear control algorithm used by the Mean Air Temperature, Mean Radiant Temperature, and Operative Temperature control types (the “non-Setpoint” controls),
See the throttling range and control temperature schedule fields below for more information.
Select the schedule that denotes whether the high 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 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 input power (electricity or gas) converted into heat in the unit (in W or Btu/h).
The controls for the radiant system vary the amount of power supplied to the unit 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 unit. The program calculates the heating capacity from the floor area of the zone served by the 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 unit 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.
This is the combustion efficiency of the gas burner (when Fuel type is set to 1-Natural gas). It should be greater than 0 and less than or equal to 1. The heater gas consumption is the heater output divided by the combustion efficiency.
This field specifies the fraction of the power input to the heater is transferred to the zone as radiant heat. The fraction should be between 0 and 1. In conjunction with the next two parameters, it defines the breakdown of how the power input to the heater is distributed to the zone. The sum of these fractions must be less than or equal to 1. If the fractions are less than one, the remaining energy is added to the zone as convective heat transfer. The radiant heat transfer from the heat is distributed to people and surfaces using the distribution fractions listed below.
This field specifies the fraction of the power input to the heater that is converted to a latent heat gain within the space. This may be appropriate when a combustion process produces moisture that is transferred into the space. The latent heat addition from a high temperature radiant heater is handled as any other latent heat gain within the space, affecting the moisture balance on the zone air.
This field specifies the fraction of power input to the high temperature radiant heater that is “lost”. This energy is a loss term, and this fraction of the input power has no effect on the zone heat balances.
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 heater. Power input to the system is varied linearly around the setpoint temperature based on the throttling range and the maximum power input 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 from the setpoint 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 heat input 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 throttles heat input (via the electric resistance wires or gas burner), from zero up to the maximum defined by the Maximum power input field described above. The throttling range parameter is used in conjunction with the zone setpoint temperature to define the response of the system to various zone conditions. The heating setpoint specifies the point where the power input to the system is at half of the maximum power input. For example, if the heating control temperature setpoint is currently 15°C and the heating throttling range is 2°C, the power supplied to the radiant system will be zero when the controlling temperature (Mean Air Temperature, Mean Radiant Temperature, or Operative Temperature; 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. When the zone temperature is between 14°C and 16°C, the power input to the radiant system is varied linearly.
This setting specifies the fraction of radiant heat output that is incident directly on the people within the space. This has an impact on the predicted thermal comfort of the zone occupants. Note that this energy is accounted for within the heat balance as convective energy, directly affecting the zone air heat balance. The basic assumption here is that most radiant energy falling on people will most likely be convected to the surroundings. This is a simplification of reality, but it maintains the overall energy balance.