Terminal Devices
The Terminal Devices tab contains properties on airflow and equipment in the terminal device. Each system is required to have one and only one terminal device. Terminal devices can be changed for different zones on the same system in the Configure Zone Equipment tab in the project.
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Diffuser (no properties)
The Diffuser represents a diffuser into a zone that has no VAV damper, fan, or coil.
CV Terminal Reheat
The Constant Volume with reheat terminal device is used in constant volume systems in order to reheat the supply air before it enters the zone.
Reheat Coil Type: This is the heating coil library sub category which also defines the energy type that is used to heat the coil.
Reheat Coil: This is the specific heating coil library that will be used as the heating coil.
Maximum Reheat Air Temperature: This is the maximum temperature to which the supply air can be heated by the reheat coil. If this field is left blank, there will be no upper limit to the supply air temperature.
VAV Terminal
The VAV Terminal is used to control the supply air of a VAV system using a VAV damper but has no coil or fan.
Damper Heating Action: There are three different options for how the supply airflow can be controlled when the system is in heating mode.
Normal: During heating mode the damper will always remain at the minimum position and the supply air temperature will be increased as the heating load increases. The equipment will be sized so the peak heating load can be satisfied at the minimum heating supply airflow and maximum heating supply air dry bulb.
Dual Maximum: During heating mode, the damper will remain at the minimum position and the supply air temperature will be increased as the heating load increases. Once the supply air temperature reaches a maximum, the VAV damper will start to open, increasing the supply airflow at the maximum supply air temperature. The maximum heating supply airflow will be less than the maximum cooling supply airflow. This control type is only used for hot water reheat coils.
Dual Maximum 100% in Heating: During heating mode, the damper will remain at the minimum position and the supply air temperature will be increased as the heating load increases. Once the supply air temperature reaches a maximum, the VAV damper will start to open, increasing the supply airflow at the maximum supply air temperature. The maximum heating supply airflow will be equal to the maximum cooling supply airflow. This control type is only used for hot water reheat coils.
Clg VAV min Type
The cooling VAV minimum can either be set to a constant value or the VAV minimum can vary. According to a schedule.
Clg VAV min
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Default: 30% Clg Airflow
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: % Clg Airflow; cfm; cm3/s; m3/s; m3/hr
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When the Clg VAV min type is set to constant, this is the minimum supply air flow rate for the VAV system in terms of a percent of the maximum design air flow rate or as an airflow rate value.
When the Clg VAV min type is set to variable, a schedule can be chosen in this field that defines the changing VAV minimum.
VAV w/Reheat
The VAV with reheat terminal device is used to control the supply air of a VAV system using a VAV damper. The terminal box also contains a reheat coil to heat supply air before it enters the space.
Clg VAV min type: The VAV with reheat terminal device is used to control the supply air of a VAV system using a VAV damper. The terminal box also contains a reheat coil to heat supply air before it enters the space.
Clg VAV min
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Default: 30% Clg Airflow
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: % Clg Airflow; cfm; cm3/s; m3/s; m3/hr
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When the Clg VAV min type is set to constant, this is the minimum supply air flow rate for the VAV system in terms of a percent of the maximum design air flow rate or as an airflow rate value.
When the Clg VAV min type is set to variable, a schedule can be chosen in this field that defines the changing VAV minimum.
Reheat coil type: This is the heating coil library sub category.
Reheat coil: This is the specific heating coil library that will be used as the heating coil.
Damper Heating Action: There are three different options for how the supply airflow can be controlled when the system is in heating mode.
● Normal: During heating mode the damper will always remain at the minimum position and the supply air temperature will be increased as the heating load increases. The equipment will be sized so the peak heating load can be satisfied at the minimum heating supply airflow and maximum heating supply air dry bulb.
● Dual Maximum: During heating mode, the damper will remain at the minimum position and the supply air temperature will be increased as the heating load increases. Once the supply air temperature reaches a maximum, the VAV damper will start to open, increasing the supply airflow at the maximum supply air temperature. The maximum heating supply airflow will be less than the maximum cooling supply airflow. This control type is only used for hot water reheat coils.
● Dual Maximum 100% in Heating: During heating mode, the damper will remain at the minimum position and the supply air temperature will be increased as the heating load increases. Once the supply air temperature reaches a maximum, the VAV damper will start to open, increasing the supply airflow at the maximum supply air temperature. The maximum heating supply airflow will be equal to the maximum cooling supply airflow. This control type is only used for hot water reheat coils.
Maximum Reheat Temperature
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: °F; °C
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This is the maximum temperature the heating supply air is allowed to reach.
Htg VAV max
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Default: Autosize
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Typical Range: N/A
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Min Max: -infinity to infinity
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Units: % Clg Airflow; cfm/sq•ft (floor); (m3/s)/sq•m (floor); (m3/hr)/sq•m (floor)
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This field is only used if the Damper Heating Action is set to “Dual Maximum Control”. This value indicates the maximum supply airflow during heating when the VAV damper increases from the minimum value as the heating load increases. This can be input as a percent of the total cooling supply airflow or as an air flow rate per floor area.
VAV Fan Assisted Reheat
The VAV with fan assisted reheat terminal box contains a VAV damper to control airflow into the space as well as a heating coil in series with a variable speed fan. The fan controls the amount of supply air entering the zone and is commonly found in UFAD systems.
Clg VAV min
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Default: 30% Clg Airflow
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: % Clg Airflow; cfm; cm3/s; m3/s; m3/hr
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This is the minimum supply air flow rate for the VAV system in terms of a percent of the maximum design air flow rate or as an airflow rate value.
Heating Coil Type: This is the heating coil library sub category.
Heating Coil: This is the specific heating coil library that will be used as the heating coil.
Fan Type: This is the fan library sub category.
Variable Volume Fan: This is the specific fan library that will be used as the fan in this system.
Parallel Fan Powered VAV
The parallel fan powered VAV boxes contain a VAV damper to control airflow into the zone as well as a heating coil in parallel with a constant volume fan that recirculates air from the zone. Only the recirculated air passes through the fan but both the recirculated and supply air passes through the heating coil. The air entering the zone is equal to the sum of the supply air and the recirculated air.
Clg VAV min
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Default: 30% Clg Airflow
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: % Clg Airflow; cfm; cm3/s; m3/s; m3/hr
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This is the minimum supply air flow rate for the VAV system in terms of a percent of the maximum design air flow rate or as an airflow rate value.
Heating Coil Type: This is the heating coil library sub category.
Heating Coil: This is the specific heating coil library that will be used as the heating coil.
Fan Type: This is the fan library sub category.
Constant Volume Fan: This is the specific fan library that will be used as the fan in this system.
Fan Flow Fraction
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Default: Autosize
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Typical Range: 0–1
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Min Max: 0–1
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Units: dimensionless
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The secondary fan in the terminal box doesn’t always need to run. The fan flow fraction represents the ratio of the current supply airflow to the maximum design supply airflow. When the current flow fraction is above this value, the secondary fan will not run. When the fan flow fraction is below this value, the secondary fan will run. For example, a fan flow fraction of 1 means the secondary fan will run all the time. If the fan flow fraction is 0.7, the secondary fan will only operate when the supply airflow is at 70% or less than the design supply airflow.
Series Fan Powered VAV
The series fan powered VAV boxes contain a VAV damper to control airflow into the zone as well as a heating coil in series with a constant volume fan that recirculates air from the zone. Both the recirculated and supply air pass through the fan and the reheat coil. The air entering the zone is equal to the sum of the supply air and the recirculated air.
Clg VAV min
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Default: 30% Clg Airflow
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: % Clg Airflow; cfm; cm3/s; m3/s; m3/hr
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This is the minimum supply air flow rate for the VAV system in terms of a percent of the maximum design air flow rate or as an airflow rate value.
Heating Coil Type: This is the heating coil library sub category.
Heating Coil: This is the specific heating coil library that will be used as the heating coil.
Fan Type: This is the fan library sub category.
Constant Volume Fan: This is the specific fan library that will be used as the fan in this system.
Dual Duct CV (no properties)
The dual duct constant volume terminal device is only available in the Dual Duct system category. Dual duct systems have separate air paths for hot and cold air. These air streams are mixed in this terminal device in order to adequately condition the space. Different proportions of the hot and cold air may be mixed but the sum of the airflows will be constant.
Dual Duct VAV
The Dual Duct VAV terminal device is only available in the Dual Duct system category. Dual duct systems have separate air paths for hot and cold air. These air streams are mixed in this terminal device in order to adequately condition the space. Different proportions of the hot and cold air may be mixed and the total supply airflow may vary.
Clg VAV min
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Default: 30% Clg Airflow
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: % Clg Airflow; cfm; cm3/s; m3/s; m3/hr
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This is the minimum supply air flow rate for the VAV system in terms of a percent of the maximum design air flow rate or as an airflow rate value.
Four Pipe Induction
The Four Pipe Induction terminal device comes with a water cooling coil and water heating coil. Centrally conditioned air is forced through this terminal unit through a nozzle, inducing room air to flow over these terminal coils. The unit has two inlets and two outlets so the unit can do cooling and heating simultaneously. This terminal device is only available in the Chilled Beam and Induction category.
Induction Ratio
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: dimensionless
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The induction ratio is the ratio of the induced airflow through the unit to the primary supply airflow rate.
Heating Coil Type: This is the heating coil library sub category.
Heating Coil: This is the specific heating coil library that will be used as the heating coil.
Cooling Coil Type: This is the cooling coil library sub category.
Cooling Coil: This is the specific cooling coil library that will be used as the cooling coil.
Chilled Beam (Active) and Chilled Beam (Passive)
The Chilled Beam terminal device is used to do sensible cooling on centrally conditioned and dehumidified supply air. This terminal device includes a cooling coil. The chilled beam can be set to active or passive in the terminal device properties. This terminal device is only available in the Chilled Beam and Induction category.
Chilled Beam Type: Either active or passive chilled beams can be modeled. An active chilled beam supplies air through the unit in order to induce room air to pass over the beam. A passive chilled beam however uses only natural convection to cool the air.
Number of Beams
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: dimensionless
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This is the number of chilled beams in the zone. This can be autosized based on the design load of the zone.
Beam Length
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: ft; m
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This is the length of each individual beam. This can also be autosized based on the design load in the zone.
Design Inlet Water Temperature
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: °F; °C
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This is the inlet water temperature as it enters the chilled beam.
Design Outlet Water Temperature
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: °F; °C
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This is the outlet water temperature as it leaves the chilled beam.
Coil Parameters
The advanced parameters can be used to define information to characterize the performance of the chilled beam using these equations.
Beam cooling output per unit length [W/m]
Coil heat transfer coefficient [W/(m2K)]
Room air mass flow rate across coil [kg/(m2s)]
Room air volumetric flow rate across coil per unit length [m3/(s•m)]
Where:
ΔT is the room air – water temperature difference (average water temperature is used) in degrees C.
ω is the water velocity in m/s.
qpr is the supply air flow rate per unit length [m3/(s•m)]
Coil Surface Area per Coil Length
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: m2/m
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Coefficient in the above equations
Coefficient a
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: dimensionless
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Coefficient in the above equations
Coefficient n1
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: dimensionless
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Coefficient in the above equations
Coefficient n2
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: dimensionless
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Coefficient in the above equations
Coefficient n3
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: dimensionless
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Coefficient in the above equations
Coefficient a0
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: m2/M
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This is the free area of the coil in plan view (for the air flow) per unit beam length.
Coefficient K1
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: dimensionless
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Coefficient in the above equations
Coefficient n
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: dimensionless
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Coefficient in the above equations
Induction Ratio
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Default: blank
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Typical Range: N/A
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Min Max: 0 to 4
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Units: dimensionless
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Coefficient in the above equations. This value is sometimes known as the coefficient of conduction or Kin.
Leaving Pipe Inside Diameter
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Default: blank
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Typical Range: N/A
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Min Max: 0 to infinity
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Units: m
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This is the inner diameter of the leaving pipe.