Evaporative Cooler Units
The zone evaporative cooler unit is a compound object made up of a fan and one or two evaporative cooler components. This unit serves a single thermal zone as a forced-convection, cooling-only unit with supply fan. It always draws 100% of its supply air from the outside, passes the air through a supply fan and evaporative cooler(s) and then into the zone. The fan can be positioned upstream of the cooler(s) for a blow through placement. Or it can be positioned downstream of the cooler(s) for a draw through placement. If there is more than one evaporative cooler, then should be in series with the first cooler immediately upstream of the second cooler. There is an option to include a relief zone exhaust node to balance the air in the zone.
The unit can have either constant or variable speed fans. This zone unit differs from other constant speed forced-air zone units in that its controls are not based on a part-load formulation with averaged air flow rates. Instead the unit is completely on or off during the entire time-step. This means that it is beneficial to use relatively short time-steps. However for variable speed fans, the unit can modulate fan speed to just meet cooling loads and therefore operates similar to other zone HVAC units.
Note: Standard TRACE library members cannot be modified or deleted but they can be copied and edited.
Nominal Cooling Capacity
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Default: Autosized box checked
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Typical Range: N/A
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Min Max: 0 to 1,000,000,000,000,000 (this field cannot be left blank)
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Units: % Clg Capacity; W; kW; W/m2; W/ft2; tons; MW; Btuh; MBh
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This checkbox indicates whether or not the capacity used for the selected fan will be auto sized by the program or referenced from the user defined input.
Supply Fan
Supply Fan Placement
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Default: Blow Through
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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 selectable input field defines how the supply fan is arranged. There are two choices, Blow Through or Draw Through. The Blow Through choice indicates that the fan is located upstream of the evaporative cooler(s). The Draw Through choice indicates that the fan is located downstream of the evaporative cooler(s). These are the only configurations that are available and the HVAC system nodes used as inlets and outlet in the components must be arranged consistent with the flow path.
Fan Control
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Default: Cycling Fan - Load Setpoint
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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 is used to determine how the unit is to be controlled. There are three possible choices:
1. Cycling Fan – Zone Air Temperature: This control method determines whether or not to operate the cooler based on the thermostat setpoint and the zone air temperature. This thermostatic control method uses a throttling temperature range, defined in the Throttling Range input field, to model hysteresis-type control to avoid excessive short-cycling. If the zone air temperature is warmer than the cooling setpoint temperature plus one-half of the throttling range, then the unit is operated for the entire time-step at the design air mass flow rate. If the zone air temperature is cooler than the cooling setpoint temperature minus one-half of the throttling range, then the unit is off for the entire time-step. When the zone air temperatures are within the throttling range, then the unit will stay off if it was not running during the previous time-step and will stay on if it was already running. This control method does not usually behave in a smooth manner and zone conditions will tend to oscillate considerably during periods of low load.
2. Cycling Fan – Load Setpoint: This control method determines whether or not to operate the cooler based on the predicted zone load to cooling setpoint. If there is a cooling load (and the unit is available), then the unit is operated for the entire time-step at the design air mass flow rate. If there is no cooling load, then the unit is not operated at all. The magnitude of the cooling load that will trigger the unit to operate can be controlled using the input Cooling Load Setpoint value. This control method does not usually behave in a smooth manner and zone conditions will tend to oscillate considerably during periods of low load.
3. Variable Speed Fan – Load Setpoint: This control method determines whether or not to operate the cooler based on the predicted zone load to cooling setpoint. If there is a cooling load (and the unit is available), then the unit is operated for the entire time-step at a fan speed that is controlled to meet the sensible cooling load (if possible). The magnitude of the cooling load that will trigger the unit to operate can be controlled using the input Cooling Load Setpoint value. This control method requires a variable speed fan and cannot be used with the Constant Volume fan type.
Supply Fan Type
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Default: Constant Volume
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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 is the type of supply fan that is associated with the library member. Two options are available: Constant or Variable Volume.
Supply Air Fan
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Default: Direct Drive Plenum Fan
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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 input selection refers to the name of the fan library member that is used in this object.
Fan Full Load Energy Rate
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Default: 0.0002 kW/(cfm); Auto Size box is unchecked
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Typical Range: 0.0001 to 0.0004 kW/(cfm)
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Min Max: 0 to 1,000,000,000,000,000 (this field cannot be left blank)
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Units: W; kW; W/(m3/sec); W/(m3/sec)-Pa; W/(cfm); W/(L/sec); W/(L/sec)-in H2O; kW/(cfm); kW/(L/sec); kW/(cfm)-in H2O; kW/(L/sec)-in H2O; W/(cfm)-in H2O; bhp
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This checkbox indicates whether or not the full load energy rate used for the selected fan will be auto sized by the program or referenced from the user defined input.
Pressure Rise
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Default: 4 inches H2O
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Typical Range: 0.25 to 5 in H2O
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Min Max: 0 to 1,000,000,000,000,000 (this field cannot be left blank)
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Units: in H2O; lb/ft2; psig; Pa; kPa; mm Hg; mm H2O; bar; in Hg; atm; mm CE; m CE; m H2O; mbar
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The value will be populated by default based on the fan library member selected. You can override this value and the units of measure.
Dead Band Airflow
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Default: Auto Size box checked
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Typical Range: 0 to 25,000 cfm
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Min Max: 0 to 1,000,000,000,000,000 (this field cannot be left blank)
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Units: m3/sec; cfm; cfm/ft2; (m3/s)/m2; % Clg Airflow; % Htg Airflow; m3/hr-m2; L/s; m3/hr
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Cooling Load Setpoint
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Default: 0.028 tons
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Typical Range: N/A
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Min Max: 0 to 1,000,000,000,000,000 (this field cannot be left blank)
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Units: W; kW; tons; Btuh; MBh
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This input field defines the magnitude of a significant zone cooling load to use with zone-load-to-setpoint based control. This value is used when the unit’s control method is Cycling Fan – Load Setpoint or Variable Speed Fan – Load Setpoint. This is a sensible cooling load that is used as a threshold to determine when the cooling load is significant. When the predicted zone load to cooling setpoint is less than this threshold, the cooler unit’s control will consider the load to be too small to trigger operation.
Evaporative Cooler
Evaporative Cooler Type
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Default: Direct Evaporative
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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 selectable field defines the type of evaporative cooler used in the unit. The zone evaporative cooler unit can have one or two separate cooler components and this field is for the first cooler. There are two types of evaporative cooler types to choose from: Direct Evaporative and Indirect Evaporative.
Evaporative Cooler
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Default: Test: East Data Center DEC
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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 input selection refers to the cooling coils library member that is used for this object.
Cooling Design Airflow
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Default: Auto Size box checked
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Typical Range: N/A
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Min Max: 0 to 1,000,000,000,000,000 (this field cannot be left blank)
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Units: m3/sec; cfm; cfm/ft2 (Floor); (m3/s)/m2 (Floor); % Clg Airflow; m3/hr-m2 (Floor); cm3/sec; m3/hr
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This input refers to the design cooling airflow value associated with the evaporative cooler library member selected. This input can be used to scale the capacity of the evaporative cooler as well.
Optional Evaporative Cooler
Secondary Evaporative Cooler
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Default: Blank
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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 input selection refers to the cooling coils library member that is used for this object.
Secondary Evaporative Cooler Type
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Default: None
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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 selectable field defines the type of the second evaporative cooler used in the unit. The zone evaporative cooler unit can have one or two separate cooler components and this field is for the second cooler. There are 3 options to choose from. The types of evaporative cooler types to choose from: Direct Evaporative and Indirect Evaporative. None is the third option.