Similar to the constant flow heated floor but control of the variable flow heated floor is accomplished by throttling the hot water flow to the unit.
Note An important advantage of the EnergyPlus variable flow heated floor over the constant flow heated floor is that it is fully autosizable.
This is a read-only label that is automatically generated by the software and which incorporates the name of the zone in which the heated floor is located.
There are 3 ways to define the heating capacity of the unit as selected from the following list of options:
This autosizable field defines the convective electric nominal heating capacity (in W or Btu/h). It is only available when the Heating design capacity method is set to 1-Design capacity.
Enter the heating capacity per unit floor area (in W/m2 or W/ft2) of the unit. This data is only available when the Heating design capacity method is 2-Capacity per floor area.
The program calculates the heating capacity from floor area of the zone served by the unit and the heating capacity per unit floor area value specified here.
Enter the heating capacity as a fraction of the autosized heating capacity for convective electric baseboard unit. This data is only available when the Heating design capacity method is 3-Fraction of autosized capacity. EnergyPlus calculates the heating capacity from the design autosized heating capacity and this fraction. The default value is 1.0.
There are two types of heated floor available:
This is the inside diameter of the tubes through which water is circulated (in m or in). The inside diameter should be entered in metres and is used to determine the convective heat transfer from the water to the inside surface of the hydronic tubing.
This is the total length of embedded pipe (in m or ft). The length of the tube is used to determine the effectiveness of heat transfer from the fluid being circulated through the tubes and the tube/surface. Longer tubing lengths result in more heat that will be transferred to/from the radiant surface to the circulating fluid. This data is auto-sizable.
This input allows you to choose between modelling each surface in the radiant system as a single hydronic circuit or to allow the program to divide the surface into multiple parallel hydronic circuits based on the Circuit length (below). The corresponding options are:
It is recommended that 2-Calculate from circuit length be chosen for new models. The default is 1-One per surface for backward compatibility with older versions of DesignBuilder.
The length (in m or ft) of each parallel hydronic circuit in a surface. This data is only used when the Number of circuits (above) is set to 2-Calculate from circuit length. The default is 106.7 meters (350 feet), which is the maximum circuit length allowed in Title 24.
This is the maximum flow rate of hot water through the heated floor (in m3/s or gal/min). The controls for the floor will vary the flow rate of hot water through the surface(s) using zero flow and the maximum flow rate specified in this field as the lower and upper bounds, respectively.
This option is only available when using the 2-Detailed HVAC Detailed HVAC Activity data
Along with setpoint (control) and water schedules, this setting allows you to specify how the heated floor is to be controlled. The temperature denoted in the setpoint schedule can refer to one of five 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. The choice of temperature is controlled by the temperature control type. The user must select from the following options:
Operative temperature for heated floor controls is the average of Mean Air Temperature and Mean Radiant Temperature. See the control temperature schedule settings below for more information.
This option is only available when using the 2-Detailed HVAC Detailed HVAC Activity data
The Heating control temperature schedule specifies the heating setpoint or control temperature for the heated floor (in °C only). Used in conjunction with the Throttling range, it will define whether or not the system is running and the current flow rate. Water flow rate to the system is varied linearly around the setpoint temperature based on the Throttling range and the Maximum heating flow rate parameters (see above). It should be noted that this control schedule will allow different setpoint temperatures throughout the year for heating. The control of the heated floor is based solely on the values in this schedule, and the Temperature control type described above. The heated floor will not use the HVAC zone thermostat that might be used by other systems serving the zone in which the component resides.
This is the range of temperature (°C) which the heated floor throttles from zero flow rate up to the maximum defined by the Maximum hot water flow rate described above. The throttling range parameter is used in conjunction with the control temperature to define the response of the system to various zone conditions. The heating control temperature schedule specifies the setpoint temperature where the flow rate to the system is at half of the maximum flow rate. For example, if the heating control temperature setpoint is currently 15°C and the heating throttling range is 2°C, the water flow rate to the system will be zero when the controlling temperature (see Temperature Control Type below) is at or above 16°C and the maximum flow rate when the controlling temperature is at or below 14°C. This represents a throttling range of 2°C around the setpoint of 15°C. In between 14°C and 16°C, the flow rate to the radiant system is varied linearly.
The minimum throttling range is 0.5°C.
This is the schedule that determines whether or not the component is available for each timestep of the simulation. A schedule value greater than 0 (usually 1 is used) indicates that the unit can be on during the timestep. A value less than or equal to 0 (usually 0 is used) denotes that the unit must be off for the timestep.