Energies 2021, 14, 5956. https://doi.org/10.3390/en14185956 www.mdpi.com/journal/energies Article A Time-Dependent Model for Predicting Thermal Environment of Mono-Slope Solar Greenhouses in Cold Regions Shuyao Dong 1 , Md Shamim Ahamed 2 , Chengwei Ma 3 and Huiqing Guo 1, * 1 Department of Mechanical Engineering, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada; shd491@mail.usask.ca 2 Department of Biological and Agricultural Engineering, University of California, Davis, CA 95616-5270, USA; mahamed@ucdavis.edu 3 Key Laboratory of Agricultural Engineering in Structure and Environment of Ministry of Agriculture, China Agricultural University, Beijing 100083, China; macwbs@cau.edu.cn * Correspondence: huiqing.guo@usask.ca; Tel.: +1-306-966-5350 Abstract: Most greenhouses in the Canadian Prairies shut down during the coldest months (No- vember to February) because of the hefty heating cost. Chinese mono-slope solar greenhouses do not primarily rely on supplemental heating; instead, they mostly rely on solar energy to maintain the required indoor temperature in winter. This study focuses on improving an existing thermal model, entitled RGWSRHJ, for Chinese-style solar greenhouses (CSGs) to increase the robustness of the model for simulating the thermal environment of the CSGs located outside of China. The mod- ified model, entitled SOGREEN, was validated using the field data collected from a CSG in Mani- toba, Canada. The results indicate that the average prediction error for indoor and relative humidity is 1.9 °C and 7.0%, and the rRMSE value is 3.3% and 11.5%, respectively. The average error for pre- dicting the north wall and ground surface temperature is 4.2 °C and 2.3 °C, respectively. The study also conducted a case study to analyze the thermal performance of a conceptual CSG in Saskatoon, Canada. The energy analysis indicates the heating requirement of the greenhouse highly depends on the availability of solar radiation. Besides winter, the heating requirement is relatively low in March to maintain 18 °C indoor temperature when the average outdoor temperature was below –4 °C, and negligible during May–August. The results indicate that vegetable production in CSGs could save about 55% on annual heating than traditional greenhouses. Hence, CSGs could be an energy-efficient solution for ensuring food security for northern communities in Canada and other cold regions. Keywords: Chinese solar greenhouse; thermal model; north wall; cold regions; heating requirement 1. Introduction The extreme cold outdoor temperature is a major barrier to greenhouse production in cold regions. Supplemental heating and dehumidification have been commonly prac- ticed in Canadian greenhouses. The heating cost could be around 70% to 85% of the total operating cost of crop production in greenhouses in high latitudes, excluding the cost as- sociated with labor [1]. The heating cost in the Canadian greenhouse accounts for 10–35% of the total production cost [2,3]; therefore, most greenhouses in the Canadian Prairies shut down during the coldest months. The demand for local produce has increased over the last decade as more and more people acknowledge the health benefits of fresh vege- tables and the need to reduce carbon emissions caused by long-distance transportation of fresh vegetables. Research indicates that the vegetables lose 15% to 77% of their vitamin C within a week of harvest [4]. Chinese solar greenhouses with a south mono-slope (CSGs) do not primarily rely on supplemental heating; instead, they are designed to max- imize solar energy gain and minimize heat loss to maintain suitable indoor temperatures. Citation: Dong, S.; Ahamed, M.S.; Ma, C.; Guo, H. A Time-Dependent Model for Predicting Thermal Environment of Mono-Slope Solar Greenhouses in Cold Regions. Energies 2021, 14, 5956. https://doi.org/10.3390/en14185956 Academic Editor: Donato Morea Received: 28 August 2021 Accepted: 17 September 2021 Published: 19 September 2021 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims in published maps and institu- tional affiliations. Copyright: © 2021 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (http://crea- tivecommons.org/licenses/by/4.0/).