Psychrometric Analysis of an Open-Loop Batch-Type Heat Pump Drying Process


Published: 2023-07-20

Page: 61-68

Arachchige Jayaruwani Fernando *

Department of Agricultural Engineering and Soil Science, Faculty of Agriculture, Rajarata University of Sri Lanka, Sri Lanka and Postgraduate Institute of Agriculture, University of Peradeniya, Peradeniya, Sri Lanka.

Kahawaththage Sanath Priyantha Amaratunga

Department of Agricultural Engineering, Faculty of Agriculture, University of Peradeniya, Peradeniya, Sri Lanka.

*Author to whom correspondence should be addressed.


Psychrometric processes are vital in agriculture and food processing as they contribute to storage and preservation, drying and dehydration, quality control, cold chain management, process optimization, food safety, and the maintenance of sensory attributes. By effectively managing temperature and humidity, these processes ensure product quality, extend shelf life and enhance the safety of agricultural and food products. Further, the psychrometric equations can be applied to study the drying behavior of hot-air dryers. Therefore, this study aimed to develop models to analyze the psychrometric properties of batch-type, open-loop heat pump drying systems for coffee beans. Coffee beans (370 kg) at 70.01±1.26% (w.b.) moisture content were dried in an open-loop batch-type heat pump dryer. The weight reduction of coffee beans in the drying chamber and the amount of condensed moisture at the evaporator were measured. Two models for condensation and evaporation processes were developed and validated with experimental data. The models indicated that the humidity ratio is essential in developing models for condensation and evaporation processes in heat pump dryers.

Further, the model-validated results showed that the developed models could be used to analyze the air properties in an open-loop heat pump drying system, especially in the drying chamber and the evaporator. These models would support researchers and engineers in making informed decisions to optimize system design, improve energy efficiency, and implement measures that contribute to more effective and environmentally sustainable drying operations.

Keywords: Condensation, drying, evaporation, heat pump, humidity ratio, psychrometric

How to Cite

Fernando , A. J., & Amaratunga, K. S. P. (2023). Psychrometric Analysis of an Open-Loop Batch-Type Heat Pump Drying Process. Asian Journal of Agriculture and Allied Sciences, 6(1), 61–68. Retrieved from


Download data is not yet available.


Chua KJ, Chou SK, Ho JC, Hawlader MNA. Heat pump drying: recent developments and future trends. Drying Technology. 2002;20(8):1579–1610.

Toledo RT. Fundamentals of Food Process Engineering. New York: Van Nostrand Reinhold; 1991.

Chua KJ, Chou SK, Yang WM. Advances in heat pump systems: A review. Applied Energy. 2010;87(12):3611–3624.

Fayose F, Huan Z. Heat pump drying of fruits and vegetables: Principles and potentials for Sub-Saharan Africa. International Journal of Food Science; 2016.


Goh LJ, Othman MY, Mat S, Ruslan H, Sopian K. Review of heat pump systems for drying application. Renewable and Sustainable Energy Reviews. 2011;15(9): 4788–4796.

Minea V. Overview of heat-pump - assisted drying systems, part ii: Data provided vs results reported. Drying Technology. 2015;33(5):527–540.

Patel KK, Kar A. Heat pump assisted drying of agricultural produce—An overview. Journal of Food Science and Technology. 2012;49(2):142–160.

Yuan Y, Lin W, Mao X, Li W, Yang L, Wei J, Xiao B. Performance analysis of heat pump dryer with unit-room in cold climate regions. Energies. 2019;12(16): 3125.

Shallcross DC. Preparation of psychrometric charts for water vapour in martian atmosphere. International Journal of Heat and Mass Transfer. 2005;48(9): 1785–1796.

McLaughlin CP, Magee TRA. The determination of sorption isotherm and the isosteric heats of sorption for potatoes. Journal of Food Engineering. 1998;35(3):267– 280.

Lewicki PP, Lukaszuk A. Changes of rheological properties of apple tissue undergoing convective drying. Drying Technology. 2000;18(3):707–722.

Wang J, Sheng K. Far-infrared and microwave drying of peach. LWT-Food Science and Technology. 2006;39(3):247–255.

Sosle VR., Raghavan GSV, Kittler R. Low temperature drying process for heat sensitive agri-food products. In 2000 ASAE Annual International Meeting. American Society of Agricultural Engineers. 2000; 1–9.

Fernando AJ, Amaratunga KSP, Madhushanka HTN, Jayaweera HRYS. Drying performance of coffee in a batch-type heat pump dryer. Trans ASABE. 2021;64:1237–1245.

ISO. Green coffee – determination of water content – basic reference method. Technical report, 11520-2:2001 (R2018); 2001.

C'esar LVE, Lilia CMA, Octavio GV, Isaac PF, Rogelio BO. (). Thermal performance of a passive, mixed-type solar dryer for tomato slices (Solanum lycopersicum). Renewable Energy. 2020147:845–855.

Yuan Y, Lin W, Mao X, Li W, Yang L, Wei J, Xiao B. Performance analysis of heat pump dryer with unit-room in cold climate regions. Energies. 2019:12(16):3125.

Liu H, Yousaf K, Chen K, Fan R, Liu J, Soomro S. Design and thermal analysis of an air source heat pump dryer for food drying. Sustainability. 2018;10(9):3216.

Yousaf K, Liu H, Gao X, Liu C, Abbas A, Nyalala I, Ahmad M, Ameen M, Chen K. Influence of environmental conditions on drying efficiency and heat pump performance in closed and open loop drying of paddy. Drying Technology. 2019;33(5):1–14.

Ceylan I, Aktas M, Do˘gan H. Energy and exergy analysis of timber dryer assisted heat pump. Applied Thermal Engineering. 2007;27(1):216–222.