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This paper presents a new air-heating system concept for energy-efficient dwellings. It is a system designed to heat a low-energy building by coupling a heat-recovery ventilation system with a three-fluid heat exchanger located on the chimney of a wood-pellet stove. The proposed work focuses on the heat transfer that occurs between flue gases, the ventilation air and the combustion air within a triple concentric tube heat exchanger with no insulation at its outer surface. The main objective is to predict outlet temperature for the specific geometry of the heat exchanger studied here. Thus, the governing differential equations are derived for a counter-co-current flow arrangement of the three fluids. Then analytical solutions for the steady-state temperature distribution are obtained as well as the amount of heat transferred to the outside. An expression for the effectiveness of the heat exchanger is also proposed. Based on these results, calculations are performed on a case study to predict the fluid temperature distribution along the heat exchanger. Finally, a parametric study is carried out on this case study to assess the influence of the relevant parameters on the effectiveness of the heat exchanger. In addition, computation of heat losses to the outside justifies whether insulation is needed. [ABSTRACT FROM AUTHOR]

In this paper, experimental tests conducted on a new wood-based air-heating system for energy-efficient dwellings are presented. The main objective is to evaluate the resulting outlet temperatures and the amount of heat recovered by the ventilation air in order to assess feasibility and performance of coupling a mechanical ventilation heat-recovery unit and a triple concentric tube heat exchanger integrated into the chimney of a room-sealed wood-pellet stove to heat an entire house. After introducing the context of this work, the three main components of the combined system developed here, the coupling configuration adopted, as well as the protocol used and the sensors implemented on an experimental setup carried out in a laboratory are detailed in turn. Then, the heat transfer rates obtained from measurements for the various fluids as well as the effectiveness of the heat exchangers are presented and discussed. Finally, the resulting outlet temperatures of the three fluids exchanging in the triple concentric tube heat exchanger studied here are compared to those provided by analytical solutions obtained with a mathematical model. It is shown that heat transfer rates are predicted with a relative difference that is lower than 5% compared to experimental values and that such a system enables to cover all or most of heat losses in an energy efficient building. [ABSTRACT FROM AUTHOR]

Abstract: The air-handling units (AHUs) provide complete control of temperature and humidity in air-conditioned spaces. The models of the AHU elements are nonlinear and the controlled variables, temperature and relative humidity, coupled. This paper demonstrates that in the case of sensible heat exchange without moisture removal if the outputs of the electric coils, fluid-filled coils and steam humidifiers of an AHU are considered to be the differences between the air temperature and the humidity ratio of the outlet and the inlet, then the models may be written as the product of a static and a dynamic gain. The parameters of the discrete form of these models are experimentally identified. The dynamics of the elements and of their sensors are very similar. Therefore, the parameter identification of the elements takes into account the model of the sensor, previously identified. This grey-box approach combines theoretical modelling, parameter identification of discrete models and parameter identification of partially known models by using optimization techniques. [Copyright &y& Elsevier]