Abstract
• A novel and verified model of a run-around heat recovery system. • Optimization of liquid flow rate in run-around heat recovery system. • Influence of circuitry arrangement and glycol concentration. Heat recovery technologies are used to reduce the energy use and the operating costs for ventilation systems in buildings. Run-around heat recovery systems for ventilation are commonly used in buildings when cross-contamination between the air streams is not acceptable, in buildings with complex ducting and in retrofit projects with space limitations. The design and operation of run-around systems are rather complex, especially in ventilation systems with variable air flow rates since the coupling liquid flow rate must be adjusted with respect to the air flow rate. This paper presents a mathematical model of a run-around heat recovery system. The model is validated with lab measurements and used further in parametric studies to evaluate how the overall thermal effectiveness of a system is influenced by different heat exchanger configurations, coupling liquids and operating conditions. Important findings suggests that the thermal effectiveness is highly sensitive to the coupling liquid flow rate, particularly for systems designed for high thermal effectiveness and for variable air volumes. The optimum liquid flow rate cannot only be determined by the air flow rate as it is influenced by the heat exchanger configuration and the liquid properties and not always found within the turbulent flow regime.
Highlights
Buildings accounted for 30% of final energy use in 2019, and were responsible for 28% of global carbon dioxide emissions in 2019 [1,2]
The aim is to determine the effect of the coupling liquid flow rate on the thermal effectiveness at different air flow rates and the effect of ethylene glycol concentration and circuitry arrangement on the results
This study used correlations available in the open literature to find the convective heat transfer coefficients on the air side. Some of these correlations are developed for larger fin pitch and fewer tube rows than what is common in run-around heat recovery systems
Summary
Buildings accounted for 30% of final energy use in 2019, and were responsible for 28% of global carbon dioxide emissions in 2019 [1,2]. The largest share of the carbon dioxide emissions from buildings can be attributed to space heating, accounting for 12% of the total energy use and carbon emissions globally in 2019 [3]. Different heat recovery technologies are used to decrease the energy use of buildings’ ventilation systems. Technologies that adjust air flow rates such as variable-air-volume (VAV) systems have been installed in many build ings to reduce energy use in buildings. Due to the coronavirus outbreak, measures such as increased air flow rates and operating time have been proposed by various HVAC organizations, which will increase energy use in ventilation systems [4,5]
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