Chiller - Absorption

Chiller:Absorption

Used in:   Chilled water loop, supply side

The Absorption Chiller is nearly identical to the more sophisticated Absorption indirect chiller model. Since these absorption chiller models are nearly identical (i.e., the performance curves of the enhanced model can be manipulated to produce similar results to the Absorption Chiller model), it is quite probable that the Absorption Chiller model will be deprecated in a future release of EnergyPlus.

Note: Absorption Chillers and their associated performance curve objects are developed using performance information for a specific chiller and should normally be used together for an EnergyPlus simulation. Changing the object input values, or swapping performance curves between chillers, should be done with caution.

General

Name

The auto-generated name of the chiller can be edited.

Chiller template

Use this browse option to select a chiller from the EnergyPlus chiller database whose performance data you wish to copy to your chiller.

Chiller type

The type of chiller can be one of these options:

• 1-Constant CoP - a simple model with constant efficiency and no performance curves.
• 2-Chiller EIR- a more detailed model using 3 performance curves to determine cooling capacity and CoP from the chiller load and outside air temperature.
• 3-Reformulated EIR - an empirical model similar to the EIR model
• 4-Absorption - the basic absorption chiller model as described on this page.
• 5-Indirect absorption -a more advanced absorption chiller model with more flexible performance curves and ability to model the effect of varying evaporator, condenser, and generator temperatures.

Note: The Chiller type cannot be edited directly. To help you to ensure that appropriate performance curves are used, you must either load a new chiller template of the type required or add a new chiller, selecting the appropriate type from the drop list.

Nominal capacity

This numeric field contains the nominal cooling capability of the chiller (in W or Btu/h).

Nominal pumping power

This numeric field contains the nominal pumping power of the absorber (in W or Btu/h).

Chiller flow mode

This choice field determines how the chiller operates with respect to the intended fluid flow through the device’s evaporator. There are three choices for specifying operating modes for the intended flow behaviour:

• 1-Constant flow is the default option for constant volume chilled water loops and is useful for constant speed pumping arrangements where the chiller’s request for flow is stricter and can increase the overall loop flow.
• 2-Leaving setpoint modulated is the default option for variable volume chilled water loops and changes the chiller model to internally vary the flow rate so that the temperature leaving the chiller matches a setpoint at the evaporator outlet. For the absorption chiller, this mode also affects the flow rate on the generator connection.
• 3-Not modulated is useful for either variable or constant speed pumping arrangements where the chiller is passive in the sense that although it makes a nominal request for its design flow rate, it can operate at varying flow rates. This flow mode does not impact the condenser loop connection.

In all cases the operation of the external plant system can also impact the flow through the chiller - for example if the relative sizes and operation are such that flow is restricted and the requests cannot be met.

For variable flow chilled water loops these options are available: 2-Leaving setpoint modulated and 3-Not modulated.

For constant flow chilled water loops these options are available: 1-Constant flow and 3-Not modulated.

The type of loop (variable/constant flow) can be changed by modifying the Plant loop flow type on the Chilled water plant loop dialog.

Note: When the 2-Leaving setpoint modulated option is selected then you must add an extra Setpoint manager immediately downstream of the chiller chilled water outlet to define the temperature of the water supplied.

Sizing factor

This optional numeric field allows the user to specify a sizing factor for this component. The sizing factor is used when the component design inputs are autosized: the autosizing calculations are performed as usual and the results are multiplied by the sizing factor. For this component the inputs that would be altered by the sizing factor are: Nominal Capacity, Nominal Pumping Power, Design Chilled Water Flow Rate, Design Condenser Water Flow Rate and Design Generator Fluid Flow Rate. Sizing factor allows the user to size a component to meet part of the design load while continuing to use the autosizing feature.

Condenser

Condenser type

The condenser type determines what type of condenser will be included with this chiller. Valid condenser types are:

• 1-Air cooled,
• 2-Water cooled,
• 3-Evaporatively cooled

The default is 2-Water cooled which requires the full specification of the Condenser loop and its associated equipment. 1-Air cooled and 3-Evaporatively cooled do not require a Condenser loop to be specified.

Note: Condenser type cannot be edited directly. To help you to ensure that appropriate performance curves are used, load a chiller of the correct type from the Chiller template.

Temperatures

Reference entering condenser fluid temperature

This numeric field contains the lower limit for the evaporator outlet temperature (in °C or °F). This temperature acts as a cut off for heat transfer in the evaporator, so that the fluid doesn’t get too cold.

Leaving chilled water temperature limit

This numeric field contains the absorption chiller’s condenser inlet design temperature (in °C or °F).

Flow Rates

Design chilled water flow rate

For variable volume chiller this is the maximum flow and for constant flow chiller this is the design flow rate. The units are m3/s or gal/min.

Design condenser water flow rate

This numeric field contains the absorption chiller’s design condenser water flow rate (in m3/s or gal/min).

Note: For water cooled chillers, EnergyPlus sets the condenser fluid flow rate to the maximum value whenever the chiller is operating. The Chiller flow mode only affects the chiller evaporator flow rate.

Part Load Settings

Minimum part load ratio

This numeric field contains the absorption chiller’s minimum part load ratio. The expected range is between 0 and 1. The minimum part load is not the load where the machine shuts off, but where the amount of power remains constant to produce smaller loads than this fraction.

Maximum part load ratio

This numeric field contains the absorption chiller’s maximum part load ratio. This value may exceed 1, but the normal range is between 0 and 1.1.

Optimum part load ratio

This numeric field contains the absorption chiller’s optimum part load ratio. This is the part load ratio at which the chiller performs at its maximum COP.

Generator Heat Input Part Load Ratio Curve

The Generator Heat Input Part Load Ratio Curve is a quadratic equation that determines the Ratio of the generator load on the absorber to the demand on the chiller. The defining equation is:

GeneratorInputRatio=C1*PLR+C2+C3∗PLR

The following three fields contain the coefficients for the equation.

Coefficient 1 of the generator part load ratio curve

C1 in the Generator Heat Input Part Load Ratio Curve. This value is obtained by fitting manufacturers’ performance data to the curve.

Coefficient 2 of the generator part load ratio curve

C2 in the Generator Heat Input Part Load Ratio Curve. This value is obtained by fitting manufacturers’ performance data to the curve.

Coefficient 3 of the generator part load ratio curve

C3 in the Generator Heat Input Part Load Ratio Curve. This value is obtained by fitting manufacturers’ performance data to the curve.

Pump Electric Use Part Load Ratio Curve

The Pump Electric Use Part Load Ratio Curve is a quadratic equation that determines the Ratio of the actual absorber pumping power to the nominal pumping power. The defining equation is:

ElectricInputRatio=C1+C2∗PLR+C3∗PLR2

The following three fields contain the coefficients for the equation.

Coefficient 1 of the pump electric use part load ratio curve

C1 in the Pump Electric Use Part Load Ratio Curve. This value is obtained by fitting manufacturers’ performance data to the curve.

Coefficient 2 of the pump electric use part load ratio curve

C2 in the Pump Electric Use Part Load Ratio Curve. This value is obtained by fitting manufacturers’ performance data to the curve.

Coefficient 3 of the pump electric use part load ratio curve

C3 in the Pump Electric Use Part Load Ratio Curve. This value is obtained by fitting manufacturers’ performance data to the curve.

Generator Hot Water Supply

Hot water plant connection

Check this checkbox if there is a hot water plant connection.

Design generator hot water flow rate

This numeric field contains the absorption chiller’s design condenser fluid flow rate (m3/s or gal/min).