J. Ward MacArthur

A moving-boundary formulation for modeling time-dependent two-phase flows

Abstract A mathematical model describing the transient interactions in one-dimensional two-phase flows with heat transfer is presented. A moving-boundary refrigerant model is used to predict the position of the two-phase/vapor interface. A boundary immobilization technique is used to predict the temperature profile along the heat-exchanger wall. Typical results of an evaporator model, in terms of interface position and discharge superheat, are presented for inlet flow disturbances. The model is then used in an overall heat-pump simulation to predict cyclic performance. The results compare favorably to those obtained with a high-fidelity spatially dependent heat-pump model, but require significantly less computational effort.

Theoretical analysis of the dynamic interactions of vapor compression heat pumps

Abstract A detailed mathematical model of vapor compression heat pumps is described. Model derivations of the various heat pump components are given. The component models include the condenser, evaporator, accumulator, expansion device, and compressor. Details of the modeling techniques are presented, as is the solution methodology. Preliminary simulation results are also illustrated. The model developed predicts the spatial values of temperature and enthalpy as functions of time for the two heat exchangers. The temperatures and enthalpies in the accumulator, compressor and expansion device are modeled in lumped-parameter fashion. Pressure responses are determined by using continuity satisfying models for both the condenser and evaporator. The discussion of the solution methodology describes the combined implicit/explicit integration formulation that is used to solve the governing equations. The summary provides a list of future work anticipated in the area of dynamic heat pump modeling.

Application of numerical methods for predicting energy transport in earth contact systems

Methods for analysing conductive heat flow with applications to underground earth contact systems are reviewed. A discussion and comparison of both the finite difference and finite element methods are presented. The effect of domain discretisation on accuracy for both methods is presented. One- and two-dimensional models are derived and used to solve selected problems. The results for various discretisation domains are compared and constrasted. The application of both the finite difference and finite element approaches to the analysis of heat transfers in an underground building is given. Recommendations are made to aid in the selection of the numerical techniques that are the most appropriate for analysing conductive heat flow problems. Finally, a statement is made on the analysis of the three-dimensional heat and moisture transport problem associated with underground earth contact systems.

Reducing residential fuel consumption through cost-effective interseasonal energy transfer☆

Abstract Energy savings obtainable through effective interseasonal energy transfer are explored by means of a detailed dynamic computer simulation. The mechanism of interseasonal energy transfer is the solar assisted Annual Cycle Energy System (ACES). The operational concept of the ACES is discussed and the modeling methodology used in evaluating the system is presented. Annual energy consumption and associated costs are investigated for the Full, Minimum and Cost Optimized ACES in a variety of U.S. climates. The energy and economic effectiveness of the ACES is evaluated by comparing the ACES to four conventional heating and cooling systems. Results show that the ACES can be three to four times more energy efficient than the conventional systems investigated in this study. Under prototype equipment cost constraints, the residential ACES are not, in general, cost competitive with the conventional systems. However, with realistic projections on the cost of mature components, the residential ACES are far superior to the conventional systems.

A regional evaluation of the annual cycle energy system

The Solar Assisted Annual Cycle Energy System (ACES) is evaluated by means of a dynamic computer simulation. The operational concept of the ACES is discussed and the methodology used in evaluating the system is presented. Annual energy consumption and associated costs are investigated for the full, minimum and cos-topimised ACES in a variety of US climates. The energy and economic effectiveness of ACES is evaluated by comparing ACES with four conventional heating and cooling systems. Results show that ACES can be three to four times more energy efficient than the conventional systems investigated in this study. Under prototype equipment cost constraints, residential ACES is not, in general, cost competitive with the conventional systems. However, with realistic projections on the cost of mature components, residential ACES is far superior to conventional systems.