.Buildings.Fluid.Chillers.BaseClasses.Carnot

Information

This is the base class for the Carnot chiller and the Carnot heat pump whose coefficient of performance COP changes with temperatures in the same way as the Carnot efficiency changes.

Set use_eta_Carnot_nominal=true to specify directly the Carnot effectiveness η_Carnot,0, in which case the value of the parameter COP_nominal will not affect the simulation. If use_eta_Carnot_nominal=false, the model will use the value of the parameter COP_nominal together with the specified nominal temperatures to compute the Carnot effectiveness as

η_Carnot,0 = COP₀ ⁄ (T_use,0 ⁄ (T_con,0 + T_app,con,0 - (T_eva,0-T_app,eva,0))),

where T_eva,0 is the evaporator temperature, T_con,0 is the condenser temperature, T_app,eva,0 is the evaporator approach temperature, T_app,con,0 is the condenser approach temperature, and T_use,0 is the temperature of the the useful heat. If COP_is_for_cooling=true, then T_use,0 is the condenser temperature of a heat pump plus the approach temperature, otherwise it is the evaporator temperature minus the approach temperature of a chiller.

The COP is computed as the product

COP = η_Carnot,0 COP_Carnot η_PL,

where COP_Carnot is the Carnot efficiency and η_PL is the part load efficiency, expressed using a polynomial. This polynomial has the form

η_PL = a₁ + a₂ y + a₃ y² + ...,

where y ∈ [0, 1] is either the part load for cooling in case of a chiller, or the part load of heating in case of a heat pump, and the coefficients a_i are declared by the parameter a.

Implementation

To make this base class applicable to chiller or heat pumps, it uses the boolean constant COP_is_for_cooling. Depending on its value, the equations for the coefficient of performance and the part load ratio are set up.

Revisions

• February 3, 2023, by Michael Wetter:
  Changed parameter binding etaCarnot_nominal(unit="1") = COP_nominal/(TUseAct_nominal/(TCon_nominal+TAppCon_nominal - (TEva_nominal-TAppEva_nominal))) to etaCarnot_nominal(unit="1") = 0.3 to avoid a circular assignment.
  Improved documentation.
  This is for Buildings, #3226.
• April 14, 2020, by Michael Wetter:
  Changed homotopyInitialization to a constant.
  This is for IBPSA, #1341.
• September 12, 2019, by Michael Wetter:
  Corrected value of evaluate_etaPL and how it is used. This correction only affects protected variables and does not affect the results.
  This is for #1200.
• June 16, 2017, by Michael Wetter:
  Added temperature difference between fluids in condenser and evaporator for computation of nominal COP and effectiveness.
  This is for #698.
• March 28, 2017, by Felix Buenning:
  Added temperature difference between fluids in condenser and evaporator. The difference is based on discussions with Emerson Climate Technologies.
  This is for #698.
• January 2, 2017, by Filip Jorissen:
  Removed option for choosing what temperature should be used to compute the Carnot efficiency. This is for issue 497.
• January 26, 2016, by Michael Wetter:
  First implementation of this base class.