The optimal design for a ground cooling tube in a hot, arid climate

In many hot, arid climates there is a high level of use of domestic air conditioning which can make heavy demands on local electricity generation. A passive strategy which could mitigate this demand is the deployment of ground cooling tubes in which external air is drawn into the building/plant via a tube buried below ground. Whilst this principle has been known of for a considerable time, and many example installations described, there has been no systematic investigation of the influence of the design parameters on the viability of the system. The paper describes a method for carrying out a systematic parametric optimization for a ground cooling tube by coupling a validated numerical model of the system with a constrained optimization method using an evolutionary strategy. Optimizations were based on a thermo-dynamic objective function (minimizing external energy consumption of the whole system) and an economic function (payback time for the tube). Whilst the results are specific to the hot, arid climate of the state of Kuwait, the methodology has universal applicability and illustrates the functional power of combining a performance model with an optimization method in producing optimized designs of energy systems. Practical application: Building and plant simulation programs are becoming increasingly accepted as a design tool: for confirming the performance of a proposed design or for carrying out ‘what if?’ studies to evaluate the effects of varying design parameters or equipment selection. This paper illustrates that, provided the design problem can be modelled in all relevant aspects, linking the simulation program to a constrained optimization can provide significantly more decision support to the designer.