Fluid coolers (aka dry coolers) are used to reject heat from condenser loops in a similar way to cooling towers but with much reduced water consumption. The Fluid cooler is modelled as a cross flow heat exchanger (both streams unmixed) with either single-speed or two-speed fans (induced draft configuration).
Fluid cooler performance is defined through one of the two methods: design heat transfer coefficient-area product (UA) and design water flow rate, or nominal fluid cooler capacity at a specific rating point. Regardless of which method is chosen, the design airflow rate and corresponding fan power must be specified.
The fluid cooler seeks to maintain the temperature of the water exiting the fluid cooler at (or below) a set point. The set point schedule value is defined by the SPM downstream of the condenser supply sub loop.
The single-speed model assumes that part-load operation is represented by a simple linear interpolation between two steady-state regimes (i.e., fluid cooler fan on for the entire simulation timestep and fluid cooler fan off for the entire simulation timestep). Cyclic losses are not taken into account.
The two speed model first runs at low speed and calculates the fluid cooler exiting water temperature. If the exiting water temperature based on “low speed” is at or below the set point, then the fluid cooler fan runs at this speed or below this speed. If the exiting water temperature remains above the set point after “low speed” is modelled, then the fluid cooler fan runs at high speed to reduce the exiting water temperature. The model assumes that part-load operation is represented by a simple linear interpolation between two steady-state regimes (i.e. fluid cooler fan at high and low speeds for the entire simulation timestep). Cyclic losses are not taken into account.
This alpha field contains the identifying name for the Fluid Cooler.
This numeric field contains the heat transfer coefficient-area product (UA) (in W/K or Btu/h-F) corresponding to the design air and water flow rates specified above. If the Performance input method (above) is specified as 2-UA and design water flow rate, then a UA value greater than zero but less than or equal to 300,000 must be defined, or the field can be autosized. If autosized, the Plant sizing data is used and the design fluid cooler UA value is derived from the design load to be rejected by the condenser loop and the design loop delta T. The fluid cooler inlet air dry-bulb and wetbulb temperature are taken from the input. If Performance input method is specified as 1-Nominal capacity then this field is not available since the model automatically calculates the fluid cooler UA based on the fluid cooler capacity and nominal conditions specified below.
This numeric input field contains the “nominal” heat rejection capacity of the fluid cooler (in W or Btu/hr), Nominal conditions i.e. entering air dry-bulb temperature, entering air wet-bulb temperature and Entering water temperature should be provided in the input.
This numeric field contains entering water temperature at nominal conditions (in °C or °F). This field must be specified for both the performance input methods. The design entering water temperature must be greater than the design entering air temperature.
This numeric field contains entering air dry-bulb temperature at nominal conditions (in °C or °F). This field must be specified for both the performance input methods. The design entering air temperature must be greater than the design entering air wet-bulb temperature.
This numeric field contains entering air wet-bulb temperature at nominal conditions (in °C or °F). This field must be specified for both the performance input methods. The design entering air wet-bulb temperature must be less than the design entering air (dry-bulb) temperature.
This numeric field contains the design water flow rate through the fluid cooler (in m3/s or gal/min). This value is the flow rate of the condenser loop water being cooled by the fluid cooler. A water flow rate greater than zero must be defined or the field can be autosized. If autosized the sizing data on the Plant loop dialog is used and the design water flow rate is derived from the design load to be rejected by the condenser loop and the design loop delta T.
Select the method to be used to specify fluid cooler performance:
Single-speed fan
This numeric field contains the design air flow rate induced by the fluid cooler fan (in m3/s or ft3/min). A value greater than zero must be defined regardless of the fluid cooler performance input method. Alternately, this field can be autosized.
This numeric field contains the fan power (in W) at the design air flow rate specified in the previous field. A value greater than zero must be specified regardless of the performance input method, or this field can be autosized. See Engineering ref. for fluid cooler autosizing.
Two-Speed Fan
This numeric field contains the fluid cooler air flow rate at high fan speed (in m3/s or ft3/min). A value greater than zero must be defined regardless of the fluid cooler performance input method. Alternately, this field can be autosized. See Engineering ref. for fluid cooler autosizing.
This numeric field contains the fan power (in W) at the high-speed air flow rate specified in the previous field. A value greater than zero must be specified regardless of the fluid cooler performance input method, or this field can be autosized. See Engineering ref. for fluid cooler autosizing.
This numeric input field contains the “nominal” heat rejection capacity of the fluid cooler (in W or Btu/h) under high-speed fan operation, with nominal (design) inputs entering water temperature, entering air temperature and entering air wet-bulb temperature. The design water flow rate is also provided in the input.
This numeric field contains the heat transfer coefficient-area product (UA) (in W/K or Btu/h-F) corresponding to the high-speed air flow rate and design water flow rate specified above. If the Performance input method is specified as 2-UA and design water flow rate then a UA value greater than zero but less than or equal to 300,000 must be defined, or the field can be autosized. If autosized the sizing data from the Plant loop is used and the fluid cooler UA value at high fan speed is derived from the design load to be rejected by the condenser loop and the design loop delta T. Fluid cooler water inlet temperature, fluid cooler inlet air drybulb and wetbulb are provided in the input. If Performance input method is specified as 1-Nominal capacity, then this field is not available since the model automatically calculates the fluid cooler UA based on the High speed nominal capacity and nominal conditions specified below.
This numeric field contains the fluid cooler air flow rate at low fan speed (in m3/s or ft3/min). This value must be greater than zero, less than the value specified for the field “Air Flow Rate at High Fan Speed”. This field may be autocalculated, in which case it is set to a fraction of the “Air Flow Rate at High Fan Speed” determined in the following field.
This numeric field contains the sizing factor to use when calculating the Low Fan Speed Air Flow Rate. The default is 0.5.
This numeric field contains the fan power (in W) at the low-speed air flow rate specified in the previous field. This value must be specified greater than zero or the field may be autocalculated, in which case it is set to set to a fraction of the High speed fan power.
This numeric field contains the sizing factor to use when calculating the Low fan speed fan power (above). The default is 0.16.
This numeric input field contains the “nominal” heat rejection capacity of the Fluid cooler (in W or Btu/h) under low-speed fan operation, with nominal (design) inputs entering water temperature, entering air temperature and entering air wet-bulb temperature. The design water flow rate is also provided in the input. The value specified for this field must be greater than zero but less than the value specified for the field High speed nominal capacity. This field may be autocalculated, in which case it is set to a fraction of the High speed nominal capacity.
This numeric field contains the sizing factor to use when calculating the Low speed nominal capacity. The default is 0.5.
This numeric field contains the heat transfer coefficient-area product (UA) (in W/K or Btu/h-F) corresponding to the design water flow rate and low-speed air flow rate specified above. If the Performance input method is specified as 2-UA and design water flow rate, this value must be greater than zero but less than or equal to 300,000, less than the value specified for High fan speed U-factor times area value. This field may be autocalculated, in which case it is set to a factor of the High fan speed U-factor times area value. If Performance input method is specified as 1-Nominal capacity, then this field is not available since the model automatically calculates the fluid cooler UA based on the Low speed nominal capacity and nominal conditions specified below.
This numeric field contains the sizing factor to use when calculating the Low Fan Speed U-factor Times Area Value. The default is 0.6.
Note: There are some restrictions with autosizing Fluid coolers with E+ v8.3 and v8.4. For more information on this please contact the DesignBuilder Support Desk.