Ventilation Heat Recovery from Wood-Burning Domestic Flues. A Theoretical Analysis Based on a Triple Concentric Tube Heat Exchanger

Abstract

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.

Improvements to the Heat Transfer Process on a Hydrogen Sulphide Gas Coolers System

“…Despite common references [2][3]12] did not make an assessment of the idealizations incorporated in heat exchanger basic design theory, Peigné et al [10] reported heat transfer rates relative differences lower than 5% when comparing experimental and numerical results. The influence of previous-mentioned simplifications on current research is further discussed (refer to section 3.3).…”

“…Three repetitions for each measurement were made, to reduce the occurrence of random and accidental errors of observation. The cooler #1 gas outlet temperature was determined by means of an energy balance, while the cooler #2 outlet temperature was validated in the same way [10].…”

“…Since two major thermal communications are present, two overall heat transfer coefficients have to be determined: one related to the internal heat exchange, between the tubeside and the shellside fluid; while the other is associated to the external exchange, between the shellside and the jacket fluid. Consequently, separate values of fouling thermal resistances are calculated for each thermal communication surface [2][3][10][11][12].…”

“…Despite the rating and thermal design theory of three-fluid heat exchangers has been formulated, references regarding the study of jacketed shell-and-tube devices were not found in consulted literature. Our review suggests that tripleconcentric-tube is the most studied configuration, as they are simpler in construction and practically straight-forward to evaluate [7][8][9][10][11]. Sekulić & Shah offered a detailed review on thermal design theory of three-fluid heat exchangers [12], although stating that shell-and-tube multi-fluid equipment has complex stream arrangements, which usually cannot be classified within the parallel or cross-flow configurations discussed by them.…”

Research on Energy Saving Potential for Dedicated Ventilation Systems Based on Heat Recovery Technology

“…Mori et al [2] proposed using submarine heat pumps that have a distinct thermodynamic advantage over other thermal stimulation techniques for energy saving potential. Peigné et al [3] designed a system 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 and their case study results showed that heat transfer rates can be predicted with a relative difference lower than 5%. A study by Huang et al [4] fabricated a novel hybrid-structure flat plate heat pipe for a concentrator photovoltaic system and the results indicated that it can reduce thermal resistance by 65% after a supporting structure is added to the heat pipe.…”