High Temperature Radiant
The high temperature radiant system (gas-fired or electric) is a 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 energy (heat) to a building occupants directly as well as the building surfaces (wall, ceiling, or floor). The component does not require the use of a zone thermostat unless the unit is being autosized. 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 supplied to or gas consumed by the unit. This is not intended to simulate low temperature electric or hydronic radiant systems.
Nominal Heating Capacity
|
Default: Autosize
|
|
Typical Range: Autosize
|
|
Min Max: 0 < x
|
|
Units: W, W/ft2, W/m2, Btuh, Mbh, tons, Btuh/ft2, kW, % of Htg capacity, tons/ft2
|
This field is for the maximum amount of electric energy rate (electric power) converted into heat in the high temperature radiant electric unit. This input field is auto sizable. The controls for the radiant system will 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. Note that if the user elects to autosize this field, a standard zone thermostat must be defined as autosizing.
Radiant
|
Default: 50%
|
|
Typical Range: 20 to 80%
|
|
Min Max: 0 to 100%
|
|
Units: %
|
This field specifies what fraction of the power input to the high temperature radiant heater is actually transferred to the space as radiant heat. The fraction should be between 0% and 100%. This is the portion of the total power that is modeled as radiation.
Latent
|
Default: 40%
|
|
Typical Range: 20 to 80%
|
|
Min Max: 0 to 100%
|
|
Units: %
|
This field specifies the fraction of the power input to the high temperature radiant 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.
Lost
|
Default: 10%
|
|
Typical Range: 10 to 20%
|
|
Min Max: 0 to 100%
|
|
Units: %
|
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.
*Note: 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 using the Radiant Incident on people.
Fuel Type
|
Default: Natural Gas
|
|
Typical Range: Natural Gas, Electricity
|
|
Min Max: N/A
|
|
Units: N/A
|
This field denotes the type of high temperature radiant heater: gas or electric.
Combustion Efficiency
|
Default: 100%
|
|
Typical Range: 20 to 80%
|
|
Min Max: 0 to 100%
|
|
Units: %
|
This field is the combustion efficiency for a gas high temperature radiant heater. It is intended to take into account any potential inefficiencies in the combustion process inside the radiant heater. The heater gas consumption is the ratio of heater output over the combustion efficiency. This field is not available when the Fuel Type is “Electricity”.
Radiant Incident on people
|
Default: 10%
|
|
Typical Range: N/A
|
|
Min Max: 0 to 100%
|
|
Units: %
|
This field specifies the fraction of the radiant portion of heat transfer to the zone from the radiant 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 a convective energy (like an internal gain). The basic assumption here is that radiant energy falling on people will most likely be rereleased to the zone air by convection. This is a simplification of reality, but it maintains the overall energy balance.
Temperature Control
Control Type
|
Default: Mean Air Temperature
|
|
Typical Range: N/A
|
|
Min Max: N/A
|
|
Units: N/A
|
This field specifies how the user wishes to control the high temperature radiant system. The user must select from the following options:
● Mean Air Temperature
● Mean Radiant Temperature
● Operative Temperature
● Mean Air Temperature – Detailed
● Mean Radiant Temperature - Detailed
● Operative Temperature – Detailed
Heating Range
|
Default: 3.6
|
|
Typical Range: N/A
|
|
Min Max: 0 <= x
|
|
Units: Delta F, Delta C
|
This field specifies the range of temperature over which the radiant system throttles through the electric resistance from zero heat input up to the maximum specified in the Nominal Heat Capacity field. The Heating Range parameter is used in conjunction with the Setpoint Temperature Type to define the response of the system to various zone conditions. The field Setpoint Temperature specifies the temperature where the power input to the system is at half of the maximum power input. For example, if the Setpoint Temperature is currently 15°C and the heating throttling range is 2°C, the electrical power supplied to the radiant system will be zero when the controlling temperature 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. In between 14°C and 16°C, the power input to the radiant system is varied linearly.
Setpoint Temperature Type
|
Default: Constant
|
|
Typical Range: N/A
|
|
Min Max: Constant, Variable
|
|
Units: N/A
|
This field specifies the type of heating setpoint for the radiant system. Used in conjunction with the Heating Range field, it will define whether or not the system is running and the current power input to the radiant surface. Power input to the system is varied linearly around the setpoint temperature based on the Heating Range and the maximum electrical power parameters. The field Setpoint Temperature specifies the temperature where the power input to the system is at half of the maximum power input. For example, if the Setpoint Temperature is currently 15°C and the heating range is 2°C, the electrical power supplied to the radiant system will be zero when the controlling temperature is at or above 16°C and the maximum power input when the controlling temperature is at or below 14°C. This represents a heating range of 2°C around the setpoint of 15°C. In between 14°C and 16°C, the power input to the radiant system is varied linearly.
Constant Setpoint Temperature / Variable Setpoint Temperature
|
Default: 55°F, 13°C
|
|
Typical Range: N/A
|
|
Min Max: N/A
|
|
Units: °F, °C
|
This field specifies the heating setpoint for the radiant system depending on the Setpoint Temperature type. For a Constant type, the user should enter a Constant Setpoint Temperature. For a variable type, the user can select a setpoint schedule from the menu.