Heat Transfer. 2020;1–15. wileyonlinelibrary.com/journal/htj © 2020 Wiley Periodicals LLC | 1 Received: 15 February 2020 | Revised: 4 May 2020 | Accepted: 5 May 2020 DOI: 10.1002/htj.21788 RESEARCH ARTICLE Experimental and theoretical study of waste heat recovery from a refrigeration system using a finned helical coil heat exchanger Bahaulddin K. Roomi | Maathe A. Theeb Department of Mechanical Engineering, College of Engineering, Mustansiriyah University, Baghdad, Iraq Correspondence Bahaulddin K. Roomi, Department of Mechanical Engineering, College of Engineering, Mustansiriyah University. P.O. Box (46049), Bab Al Muadham, Baghdad 10047, Iraq. Email: bahaa.k@uomustansiriyah.edu.iq Abstract This paper is an experimental and theoretical study that aimed at conserving energy by utilizing the waste heat generated from a refrigeration system by calcu- lating the range of condensation after the compression stage for the refrigerant (R410A). A helical coil tube‐ shell heat exchanger was designed as a heat recovery unit to use the waste heat from an air conditioner 1TR (split type) in the outdoor unit between the compressor and the condenser to produce hot water and increase the coefficient of performance (COP) of the refrigera- tion cycle. Two experimental types of the helical coil heat exchanger (conventional and finned) were used in attempts to induce absorption of the rejected heat into tap water. The increase in the COP ranges from 12.5% to 40%, an increase in the water outlet temperatures difference reaches 12°C. A cost–benefit analysis in terms of the net present value and the payback period (PP) has been performed. From the analysis, it has been observed that the use of the designed heat re- covery unit will save electrical consumption to produce the required hot water with a PP of about 11.7 months for the conventional heat exchanger and 17.5 months for the finned helical coil heat exchanger. KEYWORDS COP, cost–benefit analysis, finned helical coil heat exchanger, waste heat recovery