A model for the dynamic response of a cooling coil

The purpose of this study is to develop and evaluate simulation models for the dynamic performance of dry and wet cooling coils. The energy consumed by a building air conditioning system is directly related to that in the cooling coil. A dry-area model without consideration of condensation is established with three energy equations, and a wet-area model is developed based on a mass balance equation for moist air and three energy equations for the air, tube/fin, and working fluid. The derivatives with respect to the time variable are approximated using an explicit method, and the upwind approximation is used for the spatial variables. The results of the dry-area model show good agreement with those for the effectiveness method and the dynamic responses have reasonable physical meaning. The wet-area model is first compared to the dry-area model, and then the wet conditions are applied. A new factor called the mass transfer efficiency as a parallel to the total fin efficiency is introduced in the mass balance equation for the wet-area model to produce consistent results. The dynamic responses for several practical operations related to changing inlet conditions are reported. Comparisons indicate that the model predictions show good agreement with experimental data.