Original papersSensitivity analysis of CSGHEAT model for estimation of heating consumption in a Chinese-style solar greenhouse
Introduction
Chinese-style Solar Greenhouses (CSGs) have become popular to grow vegetables without any auxiliary heating or with minimum heating depending on the locations of greenhouses. CSGs are mostly used in China and are also being adopted by many countries including Canada. The adaptation of the CSGs beyond China might require some modification in design and environmental control systems. In northern China (32–43°N), mostly no auxiliary heating is supplied to the greenhouse (Tong et al., 2009), but supplemental heating might be required for extending the growing period in relatively high northern latitudes. The heating requirement in a typical CSG located in Saskatoon (52.13°N) could be about 50% less as compared to a typical gutter connected commercial greenhouse (Ahamed et al., 2016). However, a substantial amount of supplemental heating is still required for year-round production at high northern latitudes.
A few thermal models (Guo et al., 1994, Ma et al., 2010, Meng et al., 2009) have been developed to simulate the microclimates of CSGs. However, almost all of the models are developed for simulation of temperature variation of different components in the CSGs. Ahamed et al. (2018) developed and validated a time-dependent heating simulation model (CSGHEAT) for estimation of the heating requirement in the CSGs. Greenhouse thermal models are usually developed based on some assumptions and approximation of different heat transfer parameters. It is important to analyze the effect of these parameters on the model output with a different value before the developed model is incorporated into a practical application. Also, the variation of some user-defined input variables about greenhouse design and indoor environmental control systems could greatly affect the model output. As some variables have a higher impact than others on heating needs, the identification of highly sensitive variables is important from both a technical and economic perspective and should be handled with utmost care (Lam and Hui, 1996). Sensitivity analysis could identify the most influential parameters of the greenhouse on its overall performance such as heating or cooling demand of greenhouses. It can also be used to assess the set of parameters which has the greatest influence on the building performance and the degree of influence. Accordingly, in order to get the accurate prediction from the heating simulation tool such as CSGHEAT, it is important to understand its sensitivity to the input parameters and building envelope materials, and environmental control parameters.
Several studies can be found in literature about sensitivity analysis performed for greenhouse simulation models to evaluate the effects of technical parameters and physical parameters on the output (Chalabi and Bailey, 1991, Navas et al., 1997, Van Henten, 2003, Vanthoor et al., 2011). Chalabi and Bailey (1991) evaluated the sensitivity of a non-steady state energy and moisture balance model to its parameters for the conventional greenhouses. Van Henten (2003) studied the sensitivity of the greenhouse climate control model to evaluate the impact of the model parameters on the performance. However, the sensitivity of greenhouse heating simulation models has rarely been studied, and moreover, most of sensitivity studies for greenhouse thermal models have involved the conventional-style greenhouses, not the Chinese-style solar greenhouses, which was the main focus of this study.
The objective of this study was to conduct a sensitivity analysis of a recently developed heating simulation model (CSGHEAT) for estimation of the heating energy requirement in a CSG at high northern latitudes. The results could be helpful to understand the degrees of sensitivity of the model to various influential parameters, and also to better understand the energy-efficient design principles and operating strategies of environmental control systems used in cold regions.
Section snippets
Heating simulation model (CSGHEAT)
The CSGHEAT model was developed for simulation of time-dependent heating requirements in the CSGs, and the cooling load was not considered because the greenhouse temperature is usually controlled by opening the vent near the ridge. The model was developed based on the heat balance of indoor greenhouse air, and the heat sources and sinks of the greenhouse were estimated based on the lumped estimation methods. The general heat balance equation of the developed model is given by Ahamed et al. (2018
Sensitivity of CSGHEAT model to default parameters
The thermal model was developed based on some assumptions to reduce the complexity of the model. The sensitivity of the model to some important parameters with default values related to the assumptions in model development was conducted to evaluate their significance on the model output. These parameters include air thermal conductance of double-layer cover, greenhouse floor parameters, and characteristic length of convective surfaces.
Conclusions and recommendations
In this study, the sensitivity of the heating simulation model (CSGHEAT) was conducted to evaluate the performance of the model for different values of the selected default parameters and also the sensitivity of design parameters and environmental control parameters on the heating requirement. The results indicate that the value used for default parameters in model development is reasonably acceptable. The sensitivity analysis also indicates the design parameters including the thermal
Acknowledgment
The authors are highly thankful to the College of Graduate and Postdoctoral Studies (CGPS) at the University of Saskatchewan, and Innovation Saskatchewan for their financial support to the research.
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