Chiller (Water Cooled)

A Chiller (Water Cooled) operates by circulating water through coils, absorbing heat from the building's air. The heated water is then directed to a cooling tower, where the heat is released into the atmosphere. The cooled water is recirculated, and the cycle repeats.

System

Chiller Type

Chiller Type is shown for information only. It is not editable and shows that the Energy Plus object model used is the Chiller Electric EIR object.

Sizing

Cooling - Rated CoP

Specify the Chiller's Coefficient of Performance (COP), a numeric field representing the chiller's efficiency. This value should exclude energy consumption from pumps or cooling tower fans and must be provided at the reference temperatures and water flow rates defined below. Include evap-cooled or air-cooled condenser fans unless the Condenser Fan Power Ratio input field is used with a value greater than 0. If condenser fan power is modelled separately, avoid duplicating this energy use, as the calculated condenser fan energy is reported on the same electric meter as compressor power.

Ref. Leaving Chilled Water Temp.

Specify the Chiller's Reference Leaving Chilled Water Temperature in Celsius. This numeric field represents the temperature of the chilled water leaving the chiller at reference conditions.

Sizing Factor

Specify an optional sizing factor for this component, a numeric field that influences the autosizing of certain design inputs. When autosizing, the calculations are performed as usual, and the results are multiplied by the sizing factor. The affected inputs include Reference Capacity, Reference Chilled Water Flow Rate, and Reference Condenser Water Flow Rate. This feature enables sizing a component to address part of the design load while still leveraging the autosizing capability.

Sizing Method

Specify the Sizing Method by choosing between Autosize or Manual. Manual sizing necessitates completing all numerical fields with valid entries.

Leaving Chilled Water Lower Temp. Limit

Specify the Lower Limit for the Leaving Chilled Water Temperature in Celsius. This numeric field serves as a cut-off for heat transfer in the evaporator, preventing the fluid from reaching excessively low temperatures. As of now, this input field is unused, and the default value is set to 2 degrees Celsius.

Reference Capacity

Specify the Reference Cooling Capacity of the chiller in Watts. This numeric field represents the chiller's capacity at the reference temperatures and water flow rates defined below.

Ref. Chilled Water Flow Rate

Specify the Water Flow Rate for the chiller. For a variable flow chiller, this represents the maximum water flow rate, while for a constant flow chiller, it denotes the operating water flow rate through the chiller's evaporator. The units are in cubic meters per second, and the minimum value for this numeric input field must be greater than zero.

Min. Part Load Ratio

Specify the Minimum Part Load Ratio for the chiller. This numeric field contains the chiller's minimum part-load ratio, with the expected range between 0 and 1. Below this part-load ratio, the compressor cycles on and off to meet the cooling load. Ensure that the Minimum Part Load Ratio is less than or equal to the Maximum Part Load Ratio. The default value is set to 0.1.

Optimum Part Load Ratio

Specify the Optimum Part Load Ratio for the chiller. This numeric field contains the chiller's optimum part-load ratio, representing the point at which the chiller performs at its maximum coefficient of performance (COP). Ensure that the Optimum Part Load Ratio is greater than or equal to the Minimum Part Load Ratio and less than or equal to the Maximum Part Load Ratio. The default value is set to 1.0.

Max. Part Load Ratio

Specify the Maximum Part Load Ratio for the chiller. This numeric field contains the chiller's maximum part-load ratio, with a value that may exceed 1, although the normal range is between 0 and 1.0. Ensure that the Maximum Part Load Ratio is greater than or equal to the Minimum Part Load Ratio. The default value is set to 1.0.

Min. Unloading Ratio

Specify the Minimum Unloading Ratio for the chiller. This numeric field contains the chiller's minimum unloading ratio, representing the point at which the chiller capacity can no longer be reduced by unloading and must be false loaded to meet smaller cooling loads. A typical false loading strategy is hot-gas bypass. Ensure that the Minimum Unloading Ratio is greater than or equal to the Minimum Part Load Ratio and less than or equal to the Maximum Part Load Ratio. The default value is set to 0.2.

Chiller Flow Mode

Specifythe chiller operating mode for the intended fluid flow through the evaporator. Three options are available:

Not Modulated: Suitable for variable or constant speed pumping arrangements where the chiller makes a nominal request for its design flow rate but can operate at varying flow rates.

Constant Flow: Useful for constant speed pumping arrangements where the chiller's request for flow is stricter and can increase the overall loop flow.

Leaving Setpoint Modulated: Alters the chiller model to internally vary the flow rate, matching the temperature leaving the chiller to a setpoint. External plant system operation can also impact flow. Adjust as per system requirements; the default is Not Modulated.

Ref. Condenser Fluid Flow Rate

Specify the chiller's operating condenser fluid flow rate in cubic meters per second. If Condenser Type is Air Cooled or Evaporatively Cooled with Heat Recovery, this field is also used for entering the air flow rate. When autosized for Air Cooled or Evaporatively Cooled condensers, the airflow rate is set to 0.000114 m3/s/W (850 cfm/ton) multiplied by the chiller's Reference Capacity. This flow rate is essential for setting condenser outlet air node conditions and calculating water use rate for evaporatively-cooled condensers.

Ref. Condenser Fluid Flow Rate

Ref. Entering Condenser Fluid temp.

This numeric field contains the chiller’s reference entering condenser fluid temperature in Celsius. The default value is 29.4 degrees Celsius. For water-cooled chillers, this is the water temperature entering the condenser (e.g., leaving the cooling tower). For air- or evap-cooled condensers, this is the entering outdoor air dry-bulb or wet-bulb temperature, respectively.

Chilled Water Loop Pump Rated Power Consumption

Specify the chiller's reference entering condenser fluid temperature in Celsius. For water-cooled chillers, this is the water temperature entering the condenser (e.g., leaving the cooling tower). For air- or evaporatively-cooled condensers, this is the entering outdoor air dry-bulb or wet-bulb temperature, respectively. The default value is 29.4 degrees Celsius.

Chilled Water Loop Pump Rated Flow Rate

Specify the pump's design maximum volume flow rate in cubic meters per second. This parameter is crucial for ensuring optimal pump performance within the HVAC system. Define the maximum flow rate according to system requirements and specifications.

Chilled Water Loop Pump Min. Flow Rate

Specify the minimum volume flow rate for variable flow capacity operation in cubic meters per second. If set to autosize, utilize the Design Minimum Flow Rate Sizing Factor to scale this value as a fraction of the Design Maximum Flow Rate. Ensure accurate sizing to optimize pump efficiency and system performance during variable flow conditions.

Chilled Water Pump

Pump Speed Control

Specify the pump operation mode: Constant Speed or Variable Speed. Tailor the choice to meet specific system demands and efficiency goals.

Pump Rated Head

Specify the pump's design head pressure in kiloPascals. Set this value to align with system requirements and ensure efficient pump operation. The default is 350 kPa.

Pump Design Min. Flow Rate Fraction

Specify the pump's minimum volume flow rate during variable flow capacity, in cubic meters per second. When autosized, use the Design Minimum Flow Rate Sizing Factor to scale it as a fraction of the Design Maximum Flow Rate. Ensure it's below 99% of the Design Maximum Flow Rate for a variable speed pump to avoid warnings.

Pump Motor Efficiency

Specify the efficiency of the pump motor as a numeric value. This represents the ratio of the pump motor's useful power output to its total power input.

Pump Control Type

Specify either Continuous or Intermittent operation for the pump. In Continuous mode, the pump runs continuously, adjusting its flow rate based on demand. In Intermittent mode, the pump may shut down during periods of no load on the loop, conserving energy. The pump operates intermittently during other conditions, adjusting its flow between the minimum and maximum limits to meet demand.

Pump Frac. Motor Inefficiencies to Fluid Stream

Specify the fraction of power loss to the fluid caused by the pump motor. This numeric input reflects the proportion of power lost to the fluid stream in the pump system.

Pump Design Power Sizing Method

This field is optional. Choose between Power Per Flo and "Power Per Flow Per Pressure for pump sizing. If Power Per Flow, the Design Power Consumption is calculated using the sizing factor from Design Electric Power per Unit Flow Rate. If Power Per Flow Per Pressure is chosen, the Design Power Consumption uses the sizing factor from Design Shaft Power per Unit Flow Rate Per Unit Head. The default method is "Power Per Flow Per Pressure" if unspecified.

Pump Design Elec. Power / Flow Rate / Pressure

Specify the pump's design electric power per unit flow rate per unit pressure. This input, applicable when designing power consumption, is set to autosize, and the sizing method is Power Per Flow Per Pressure, which determines the efficiency of the impeller and drive assembly for calculating pump power consumption at the design flow rate, considering motor efficiency and pump head. The default is 1.282051 W/((m³/s)-Pa).

Condenser Water Pump