Performances of a heat exchanger and pilot boiler for the development of a condensing gas boiler

The present study is focused on the design and modelling of a novel Combustion Heat Exchanger (CHE), used for heating and hot water supplies in residential buildings. System design includes a combination of an efficient porous burner and heat exchangers. Combined with an Organic Rankine Cycle (ORC) and a Heat Pump (HP), it is meant to deliver higher energy efficiency as well as reduced greenhouse gas emissions. A numerical model has been developed in STAR-CCM+ to evaluate the design. Furthermore, system level heat transfer calculations were acquired to assist with the design process. A step by step approach was undertaken to investigate physical and chemical phenomena in the system. System dimensions, exchanger location and geometry, air/fuel ratio, porous media models, radiation and combustion were investigated along with different exchanger geometries. A novel spiral heat exchanger was introduced in addition to the common coil designs to exhibit both convection and radiation heat transfers. The results indicated that the exhibition of spiral heat exchanger would result in significantly enhanced heat transfer. Overall heat transfer coefficients of 4-5 times higher in comparison to coils could be expected for spiral exchangers. It was shown that radiation heat transfer accounts for a prominent share in the total heat transfer. Furthermore, the CHE could operate at a wide range of lean air/fuel ratios, enabling further decrease in greenhouse gas emissions. As the last part of the study, further investigations on the regular coil exchangers indicated that these exchangers could still be used with the design, but heat transfer enhancement is required to reduce the dimensions. Such enhancements were tested through shell geometry designs with improved results. Overall, the system shows a promising solution for further reduction of CO2 emissions while improving thermal efficiency.

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“…Similar figures have been reported in Ref. [7]. The thermal efficiency of a condensing boiler is around 90% [8].…”

Section: Introductionsupporting

confidence: 89%

Design and Modelling of a Novel Combustion Heat Exchanger for Household Heating

Yadollahi¹,

Ritchie²,

Karimi³

et al. 2018

World Congress on Mechanical, Chemical, and Material Engineering

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“…The exhaust gas temperature is approximately 120e160 C and the efficiency is approximately 82e84%. Existing CB has sensible and latent heat exchangers, providing an efficiency of 86e88% because the exhaust gas temperature is relatively low, approximately 60 C [8]. Lastly, WHR CB, used in some industrial and residential applications, has a waste heat recovery heat exchanger to recover the waste heat from the exhaust gases in addition to the sensible and latent heat exchangers.…”

Section: Introductionmentioning

confidence: 99%

An analysis of the thermodynamic efficiency for exhaust gas recirculation-condensed water recirculation-waste heat recovery condensing boilers (EGR-CWR-WHR CB)

Lee

2015

Energy

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“…Fully premixed burners are widely used in modern household gas boilers [3,4]. To maximize the heat efficiency and reduce CO and NOx emissions, it is important to control the combustible mixture equivalence ratio at all operating conditions including the transient states.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, too much excess air causes flame detachment, prone to CO production as well, and the heat efficiency is also compromised due to higher heat losses in the flue gases [6]. A compromise is therefore sought and the equivalence ratio should be maintained within an optimized range [4]. The current boiler control strategy assumes a fixed natural gas composition but this paradigm is not valid anymore.…”

Section: Introductionmentioning

confidence: 99%