EvaporativeCooler:Indirect:ResearchSpecial
Used in:
- Air Handling Units
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Used in:
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The EnergyPlus Indirect Research Special is similar in principal to the Indirect CelDekPad and Indirect WetCoil evaporative coolers, but it provides some additional flexibility. The model differs in that it gives the user more flexibility to specify the source of secondary air. The cooler effectiveness with respect to wet-bulb depression is allowed to go beyond 1.0. Using the Research Special input object also allows the cooler to control the amount of cooling based on node setpoints (controlled by Setpoint Managers). This avoid problems from over cooling when conditions are such that loads are low and cooling power is high. Fan power is assumed to vary linearly when the cooler is operating at less than full capacity.
The indirect evaporative cooler research special calculation procedure allows accounting for dry and wet effectiveness value variation with flow fraction. Two effectiveness modifier curves are included as optional user inputs for this purpose. Effectiveness modifier curves operate on the design dry and wet effectiveness values. The flow fraction is calculated as a ratio of the sum of current primary and secondary air flow rates to the sum of the design flow rates. Model also accounts for fan and recirculation water pump power variation with secondary air flow rates using pump power modifying curve. The fan power is calculated by multiplying the design fan power using fan power modify curve value evaluated at current secondary air flow fraction. Similarly, recirculating pump power is calculated by multiplying the design pump power by pump power modifier curve value evaluated at current secondary air flow fraction. If the secondary air fan and recirculating pump power modifier curves are not specified, then fan and pump power are assumed to vary linearly with part load fraction.
The cooler effectiveness with respect to wet-bulb depression is allowed to go beyond 1. Fan power is assumed to vary linearly when the cooler is operating at less than full capacity.
A unique name for an instance of an evaporative cooler which is predetermined by DesignBuilder.
Select the type of evaporative cooler from the list of options:
This autosizable setting is the primary air design air flow rate (in m3/s or ft3/min). If the evaporative cooler is on main air loop branch, the design flow rate is the same as branch design flow rate, or else if it is on outdoor air system it will be the maximum of the outdoor air design flow rate and the half of the primary air flow rate on the main air loop branch.
This setting specifies the design effectiveness that is applied to the wet-bulb depression to determine the conditions leaving the cooler. This effectiveness is a complicated function of the efficiency with which heat and mass are transferred on the secondary side and the efficiency of heat exchange between the secondary and primary flows. The model assumes that the effectiveness a function of flow fraction. The flow fraction is the ratio of the sum of primary air and secondary air current flow rates and the sum of the primary air and secondary air design flow rates.
Check this option to allow the Cooler wet-bulb design effectiveness specified above to be modified by a curve based on flow fraction. If this option is not checked then the wet-bulb effectiveness is assumed to be the constant value entered above.
Wet-bulb effectiveness flow ratio modifier curve
This curve modifies the wet-bulb effectiveness design value specified above by multiplying it by the result of this curve. The modifying curve is a function of flow fraction, which is the ratio of the sum of the primary and secondary flow rates divided by the sum of the design flow rates. Any curve with one independent variable can be used. Select a curve from one of these categories:
Enter the dry-bulb design effectiveness of the evaporative cooler. This is the nominal design dry bulb effectiveness with respect to dry bulb temperature difference, i.e., dry operation and at design air flow rates, and no water evaporation or spraying on the secondary side.
Check this option to allow the Cooler dry-bulb design effectiveness specified above to be modified by a curve based on flow fraction. If this option is not checked then the dry-bulb effectiveness is assumed to be the constant value entered above.
Dry-bulb effectiveness flow ratio modifier curve
The dry-bulb effectiveness entered in the previous field can be modified by multiplying by the result of this curve. The curve is evaluated using flow fraction as the independent variable. The flow fraction is the ratio of sum of the primary and secondary flow rates divided by the sum of the design flow rates. Any curve with one independent variable can be used. Select a curve from one of these categories:
This field specifies an effectiveness that is applied to the dew-point depression to determine a bound for the conditions leaving the cooler. The model uses the warmer of the two temperatures determined from wet-bulb depression and dew-point depression.
This field is optional and can be used to model additional water consumed by the cooler from drift. Drift is water that leaves the cooling media as droplets and does not evaporate into the process air stream. For example, water may get blown off the evaporative media by winds and escape the air system. The value entered here is a simple fraction of the water consumed by the cooler for normal process evaporation. The amount of drift is this fraction times the water evaporated for the normal cooling process. This field can be left blank and then there will be no added water consumption from drift.
This autosizable setting is the recirculating pump electric power at Secondary design air flow rate (in W). It is the nominal design pump power water recirculation and spray for evaporation at design secondary air flow rates and cooler design effectiveness.
This numeric input field value is recirculating water pump sizing factor (in W/(m3/s) or W/gpm). This field is used when the previous field is set to autosize. The pump design electric power is scaled with Secondary Design Air Flow Rate. The default value is 90.0 W/(m3/s), i.e. Pump power / Primary air design flow rate = 90 W/(m3/s). Typical values range from 55.0 to 150.0 W/(m3/s).
Select this option to apply a Water pump power modifier curve. If this option is not checked then the pump power is assumed to be constant.
Select a dimensionless normalized pump power modifying curve. The pump electric power is modified by multiplying the design power by the result of this curve. The normalized curve is a function of the secondary side flow fraction as independent variable. The curve generates a value of 1.0 at a flow fraction of 1.0. The flow fraction is the ratio of the primary air during current operation divided by Primary design air flow rate. Any curve with one independent variable can be used. Select a curve from one of these categories:
This field is used to specify the secondary air fan flow rate and is specified (in m3/s or ft3/min). This flow rate would typically be similar in magnitude to the flow through the primary side. The flow rate is used to determine parasitic fan energy and cooler effectiveness. The flow rate (and fan power) is effectively reduced by cycling when the amount of cooling needs to be restricted for control purpose. This field can be autosized. When this input is autosized, the program calculates it by scaling the Primary design air flow rate using secondary air scaling factor specified in the input field below.
This setting is used to scale the secondary air design flow rate and is dimensionless. It is used when the previous field is set to autosize. The Primary design air flow rate is scaled using this factor to calculate the secondary design air flow rate.
This autosizable setting is the fan electric power at Secondary design air flow rate. It is the nominal design electric power at full speed of the secondary air fan.
This input field value is secondary air fan sizing specific power (in W/(m3/s) or W/gpm). It is used when the previous field is set to autosize. The fan power is scaled with Secondary design air flow rate.
The Secondary air fan design power above can be modified by a curve using the secondary side flow fraction as the independent variable. Check this option to modify the secondary fan power in this way. If this option is unchecked then the fan power is assumed to be constant.
The Secondary air fan design power above can be modified by multiplying by the result of this dimensionless normalized curve. The curve is a function of the secondary side flow fraction as the independent variable. The curve generates a value of 1.0 at a flow fraction of 1.0. The flow fraction is the secondary air flow rate during operation divided by Secondary design air flow rate. Any curve with one independent variable can be used. Select a curve from one of these categories:
To define a dry-bulb temperature lower limit for evaporative cooler operation check this checkbox. Otherwise, if this option is unchecked then there is no dry-bulb temperature lower limit for evaporative cooler operation.
Minimum limit dry-bulb temperature
This setting defines the evaporative cooler inlet node dry-bulb temperature minimum limit (in °C or °F). The evaporative cooler will be turned off when evaporator cooler air inlet node dry-bulb temperature falls below this value. The typical minimum value is 16°C.
To define a wet-bulb temperature upper limit for evaporative cooler operation check this checkbox. Otherwise, if this option is unchecked then there is no wet-bulb temperature upper limit for evaporative cooler operation.
Minimum limit dry-bulb temperature
This setting defines the evaporative cooler air inlet node air wet-bulb temperature maximum limit (in °C or °F). When the evaporative cooler air inlet node air wet-bulb temperature exceeds this limit, then the evaporative cooler is turns off. The typical maximum value is 24°C.
To define a dry-bulb temperature upper limit for evaporative cooler operation check this checkbox. Otherwise, if this option is unchecked then there is no dry-bulb temperature upper limit for evaporative cooler operation.
Maximum limit dry-bulb temperature
This setting defines the evaporative cooler air inlet node dry-bulb temperature maximum limit (in °C or °F). The evaporative cooler will be turned off when the evaporative cooler air inlet node dry-bulb temperature exceeds this value. The typical maximum value is 28°C.
This field is used to specify the secondary fan flow rate and is specified in m3/s or ft3/min.
This field is used to specify the total efficiency of the fan and is used to calculate the power consumed by the evaporative cooler secondary fan. Input values should be between 0 and 1.
This field is used to specify the delta pressure across the secondary stage of the evaporative cooler (in Pa or in H2O).
Select this option to model additional water consumed by the cooler from blowdown. Blowdown is water that is intentionally drained from the cooler’s sump to offset the build up of solids in the water that would otherwise occur because of evaporation.
The value entered here is dimensionless. It can be characterized as the ratio of solids in the blowdown water to solids in the make up water. Typical values are 3 to 5. The default is 3.0.
Schedule that defines when the coil is available, i.e. whether the evaporative cooler can run during a given time period. A schedule value greater than 0 (usually 1 is used) indicates that the unit can be on during a given time period. A value less than or equal to 0 (usually 0 is used) denotes that the unit is off.