Low Temperature Radiant Variable Flow Cooling and/or Heating
A Low Temperature Radiant panel is a zone level heating and/or cooling coil mounted in the floor, walls, and/or ceiling of the rooms. The Low Temperature Radiant Variable Flow equipment is zone level equipment that uses water to heat and/or cool a room surface (floor or ceiling). 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.
A Ceiling Radiant Panel must be assigned to a zone that contains rooms with radiant layers in their ceiling construction. An In Floor Radiant Panel must be assigned to a zone that contains rooms with radiant layers in their floor construction.
The heating and/or cooling is controlled by throttling the hot or chilled water flow to the unit. The temperature remains constant while the flow increases or decreases to meet the load. The Low Temperature Radiant Variable Flow equipment uses a water loop from a separate plant and are not themselves directly heated by gas or electric: there are separate library members for Low Temperature Radiant Electric panels and High Temperature Radiant panels.
Control Type
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Default: Mean Air Temperature
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Typical Range: N/A
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Min Max: N/A
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Units: N/A
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This field specifies along with the water temperatures and setpoint temperatures how the user wishes to control the hydronic radiant system. The temperature denoted in the Setpoint Temperature fields 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 user must select from the following options:
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Mean Air Temperature
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Mean Radiant Temperature
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Operative Temperature
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Outdoor DryBulb Temperature
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Outdoor WetBulb Temperature
Note: Operative temperature for radiant system controls is the average of Mean Air Temperature and Mean Radiant Temperature.
Operating Modes
Low Temperature Radiant Variable Flow equipment may be configured as cooling only, heating only, or heating and cooling. The temperature difference is based upon the operating mode. If the unit operates in cooling only or heating only, the heating or cooling temperature range is selected.
Cooling Mode
Nominal Cooling Capacity
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CDefault: Autosize
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Typical Range: Autosize
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Min Max: 0 < x
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Units: Btuh, Mbh, tons, tons/ft2, Btuh/ft2, W, W/ft2, W/m2, kW, % of Clg capacity
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This field specifies the maximum or nominal cooling capacity. 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.
Cooling Range
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CDefault: 0.9
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Typical Range: N/A
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Min Max: N/A
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Units: Delta °F, Delta °C, Delta °R, Delta K
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This field specifies the range of temperature over which the radiant system operates. This range operates with the Cooling Setpoint Temperature Difference field to define the response of the system to various zone conditions.
Cooling Setpoint Temperature Difference
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Default: 1.8
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Typical Range: N/A
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Min Max: N/A
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Units: Delta °F, Delta °C, Delta °R, Delta K
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This field specifies the temperature difference with the zone setpoint. It is used in conjunction with the Cooling Range to define whether or not the system is running and what the current flow rate is. Water flow rate to the system is varied linearly around the setpoint temperature based on the Cooling Range and the maximum cooling flow rate that the program defines.
Heating Mode
Nominal Heating Capacity
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Default: Autosize
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Typical Range: Autosize
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Min Max: N/A
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Units: Btuh, Mbh, tons, tons/ft2, Btuh/ft2, W, W/ft2, W/m2, kW, % of Htg capacity
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This field specifies the maximum or nominal heating capacity. 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.
Heating Range
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Default: 0.9
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Typical Range: N/A
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Min Max: 0 < x
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Units: Delta °F, Delta °C, Delta °R, Delta K
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This field specifies the range of temperature over which the radiant system operates. This range operates with the Heating Setpoint Temperature Difference field to define the response of the system to various zone conditions.
Heating Setpoint Temperature Difference
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Default: 1.8
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Typical Range: N/A
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Min Max:N/A
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Units: Delta °F, Delta °C, Delta °R, Delta K
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This field specifies the temperature difference with the zone setpoint. It is used in conjunction with the Heating Range to define whether or not the system is running and what the current flow rate is. Water flow rate to the system is varied linearly around the setpoint temperature based on the Cooling Range and the maximum cooling flow rate that the program defines.
Condensation
Control Type
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Default: System Off
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Typical Range: System Off, No Moisture Control
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Min Max: N/A
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Units: N/A
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When radiant systems do cooling, there is the possibility that condensation will occur on the surface that is being cooled. This is due to the fact that the surface temperature may drop below the dew-point temperature of the space which causes condensation to accumulate on the surface.
The Control Type field can be set to either No Moisture Control or System Off.
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No Moisture Control – TRACE 3D Plus will nothing other than produce a warning message when condensation is predicted to occur. The program will continue: no moisture will be removed from the zone air and no adjustment will be made to the surface temperature as a result of the condensation.
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System Off – TRACE 3D Plus will predict cases where condensation will occur and shut-off the radiant system to avoid this situation. With this option, the user has the ability to adjust when the system will shut down using the Dewpoint Range field.
Dewpoint Range
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Default: 34°F/1.11°C
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Typical Range: 50 to 59°F / 10 to 16°C
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Min Max: 0 to 100°F/-17 to 38°C
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Units: °F/°C
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This optional parameter is only available when the System Off option is selected for the Control Type. It establishes the difference between the calculated dew-point temperature of the space and the allowed surface temperature to which the surface can drop before the radiant system shuts down. This parameter can be any positive, negative, or zero value. When this parameter is zero, the radiant system will shut down when the surface temperature drops to the dew-point temperature or below. When this parameter is positive, the radiant system will shut down when the surface is the number of degrees above the Dewpoint temperature. This allows some extra safety to avoid condensation. When this parameter is negative, the radiant system will shut down when the surface temperature is the number of degrees below the dew-point temperature. While not recommended, this strategy allows the user to simulate a situation where small amounts of condensation are tolerable.
Hydronic Tubing
Diameter
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Default: 0.51 in/0.13 m
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Typical Range: N/A
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Min Max: x > 0
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Units: ft, in/m, cm, mm
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This field is the inside diameter of the tubes through which water is circulated for the system. The inside diameter is used to determine the convective heat transfer from the water to the inside surface of the hydronic tubing.
Length
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Default: Autosize
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Typical Range: N/A
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Min Max: x > 0
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Units: ft, m
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This field is the total length of pipe embedded in the surface. 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 being transferred to/from the radiant surface to the circulating fluid. This field is auto sizable.
Circuit
Circuit Length Method
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Default: Autocalculate
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Typical Range: N/A
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Min Max: One per surface, Autocalculate
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Units: N/A
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This optional input allows the user to choose between modeling 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 input field Circuit Length. To model as a single circuit choose One Per Surface. To model as multiple circuits choose Autocalculate which is the default option.
Circuit Length
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Default: 350 ft/106.7 m
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Typical Range: N/A
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Min Max: > 0
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Units: ft, in/m, cm, mm
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This field represents the length of each parallel hydronic circuit in a surface. It is only available when the circuit length method is set to Auto calculate.