Factors influencing collection performance of near surface interseasonal ground energy collection and storage systems

The influence of surface boundary conditions, varying climatic conditions and engineering material parameters on the collection performance of near surface interseasonal ground energy collection and storage systems are investigated. In particular, the performance of a proposed design of an interseasonal heat storage system which has also been investigated by others as part of a full scale demonstration project is considered. A numerical model is developed and validated against field data. It is then applied to undertake a series of simulations with varying system parameters. It is found that (i) higher values of thermal conductivity of the storage layer result in increased storage of thermal energy and lower peak temperatures, (ii) system heat losses are strongly influenced by the performance of insulation layers, (iii) warmer climatic conditions provide more thermal energy available to be stored; however, changes in the amplitude of seasonal air temperature variations have an effect on the rate of collection of thermal energy and (iv) the use of correct surface boundary conditions is critical in modelling the dynamics of these systems

SOIL TEMPERATURE CONTROL FOR GROWING OF HIGH-VALUE TEMPERATE CROPS ON TROPICAL LOWLAND

Low soil temperature (14℃–20℃) favours growing of high-value temperate crops that are known to have higher return per hectare of land than other widely cultivated crops, thereby presenting increased income to farmer. However, due to high soil cooling load, growing these crops on tropical lowland area is a challenge except through greenhouse farming or on few cool higher altitudes with resemblance of temperate climate. Greenhouse farming involves cooling the entire volume of planting zone and is energy intensive, while few cool highlands are not sufficient to achieve food security in this direction. This study aims at application of chilled water for direct cooling of soil, to create favorable soil conditions for optimal performance of planted temperate crops. However, soil cooling using vapour compression refrigeration system may not be economically viable. Solar thermal chilled water production system is presented in this study to supply the cooling. The system consists of absorption refrigeration system and dimensioned size of soil bed with chilled water pipe network. The study includes modeling of soil cooling load to determine the refrigeration power required to overcome such load. The modeled system matched well with the experiment; having standard deviation of 1.75 and percentage error of 12.24%. Parametric analysis of the soil cooling showed that temperatures of cooled soil were significantly affected by chilled water flow rates. The regression equation developed from the Analysis of Variance (ANOVA) is suitable for predicting cooled soil temperature. The cooling process is technically feasible, with potential for greenhouse gas emission reduction

Exploring the Ability of a Distributed Hydrological Land Surface Model in Simulating Hydrological Processes in the Boreal Forest Environment

Land surface models (LSMs) simulate vertical fluxes, including evapotranspiration, in a rigorous manner, and are included in atmospheric models, including Regional and Global Circulation Models (RCMs and GCMs). Large-scale hydrological models on the other hand simulate the lateral processes that generate streamflow. Coupling of the two models (referred to as a hydrological land surface model) has the potential to combine the strengths of each. The MESH model developed at Environment Canada is such model that combines the Canadian Land Surface Scheme (CLASS) with a distributed hydrological model called WATFLOOD. In this thesis, the performance of the MESH model was explored using two different runoff generation schemes (i.e., elementary and enhanced runoff generation) and with a priori parameter values and with parameter calibration. The model was tested in the White Gull creek Basin located in the boreal forest, central Saskatchewan using meteorology and flux data recorded at two monitoring stations within the basin for driving and validation. Application of the model with a priori parameter values without calibration resulted in poor performance in simulating both streamflow and evapotranspiration while optimization to calibrate the model to the observed streamflow resulted in a good performance. Streamflow simulation with enhanced runoff generation included performed even better. The optimal model configuration was taken forward for a detailed parameter sensitivity analysis. Univariate analysis was used for pre-screening the parameter space to eliminate insensitive parameters, and subsequently multivariate analysis was performed for a subset of parameters. Vegetation parameters were more identifiable when an objective function measuring the fit to observed latent heat flux was used than when measuring the fit to streamflow. Physiographic and topographic parameters were more identifiable when a streamflow objective function was used. Streamflow was more sensitive to parameter variability than latent heat flux. The use of multiple objective functions to simultaneously constrain the model was explored. Selection of objective function had no significant effect on the simulated evapotranspiration but had some influence on streamflow. Using NSE objective function with streamflow was found to be the most effective way of identifying the best model runs. The additional constraints imposed by evapotranspiration had no impact on the results

Evaluation of the energy-based runoff concept for a subalpine tundra hillslope

A major challenge to cold regions hydrology and northern water resources management lies in predicting runoff dynamically in the context of warming-induced changes to the rates and patterns of ground thaw and drainage. Meeting this challenge requires new knowledge of the mechanisms and rates of ground thaw and their implications to water drainage and storage patterns and processes. The study carries out to evaluate the concept of energy-based runoff in the perspective of ground heat flux, soil thaw and liquid moisture content, tortuosity of snow-free area, preferential flow and discharge of the hillslope. Based on field measurements, coupled energy and water flow is simulated in the Area of Interest (AOI) with a half-hour time interval by the distributed hydrological model, GEOtop. In the field, the saturated hydraulic conductivity varies exponentially between the superficial organic layer and the underlying mineral layer. In the simulation, the parameters of the soil physical properties are input by fourteen uneven layers below the ground surface. Starting from the initially frozen state, the process of soil thaw is simulated with dynamic variables such as soil liquid moisture and ice content, hydraulic conductivity, thermal conductivity and heat capacity. The simulated frost table depths are validated by 44-point measurements and the simulation of point soil temperature is also compared to data measured in an excavated soil pit. As a result, the frost table topography is dominated by both the snow-free pattern and the energy fluxes on the ground surface. The rate and magnitude of runoff derived from snow drift and the ice content of frozen soil is greatly influenced by the frost table topography. According to the simulation, the frost table depth is closely regressed with the ground surface temperature by a power function. As soil thawing progresses, ground heat flux reduces gradually and the rate of soil thaw becomes small when the frost table descends. Along with the snow-free area expanding, the average soil moisture of the AOI increases prior to that time when the average frost table is less than 25 cm deep. The snow-free patches expand heterogeneously in the AOI, which causes the spatial and temporal variation of hydraulic conductivity due to the non-uniform frost table depth. According to the simulation, the transit time of the flow through the AOI decreases to the shortest span on May 13 with the average frost table of 10 cm. Before this date, the time lag between snowmelt percolation and slope runoff is about 8-10 hours; while after this date, the time lag is no more than 5 hours. The pattern of the preferential flow in the AOI highly depends on the frost table topography. When the snow-free patches are widely scattered and the average frost table is between 0 and 10 cm, the preferential flow paths are inhibited. With soil thaw progresses, the preferential flow paths are prominent with the largest single contributing area occurring when the average frost table is between 10 cm to 15 cm. When the average frost table reaches 25 cm, the importance of preferential flow is not apparent, and matrix flow prevails

Development and integration of a green roof model within whole building energy simulation

Green roofs are increasingly being employed as a sustainability feature of buildings. The sustainability approach in building designs requires reducing energy consumption and adopting low carbon energy sources without compromising the increasing expectations of comfort and health levels. Given the wide range of building designs, climates and green roof types, it is desirable to evaluate at the design stage the energy saving impact and other potential benefits from the application of green roofs. Currently, the abilities of building simulation programs to simulate the influences of green roofs are limited. For example, they have limitations in representing dynamic inter-layer interactions and moisture infiltration mechanisms. This research aims to develop a new model for the simulation of green roofs based on the control volume approach and to integrate the model within a whole building energy simulation program. The green roof elements consist of special layers such as plants and soil for which the control volume approach is capable of capturing their special characteristics with regards to the thermal and moisture exchanges. The model has been integrated within the ESP-r whole building energy simulation program. Within the ESP-r, the new green roof model alters the boundary condition of a roof surface on which green roof is constructed. The model development is carried out by a series of steps which include a careful selection of governing equations that describe the thermal and moisture balances in various layers of green roof, the numerical implementation for a simultaneous solution of the governing equations for the whole green roof, algorithm and code development and finally developing the interface with ESP-r. After successful integration, the model results were validated on an experimental test cell, which consists of an approximately 2 m2 planted medium on an insulated box with facilities for thermal, moisture and drainage measurements. The results for the thermal validation were promising with the significant boundary temperature values within a root mean square deviation (RMSD) in the vicinity of 0.5 K, whereas the moisture validation results are found to depend on initial conditions, the lower layers showing an RMSD of approximately 0.05 m3/m3 and the top layer nearly 0.12 [m3/m3]. The model is also able to predict the slowing down of water run-off. A methodology for collecting soil and plant properties which are required to be used along with the program has also been described. Based on the current state of the model and also considering the new developments in green roofs, some suggestions are proposed at the end of the thesis as a continuation of this research

Development and integration of a green roof model within whole building energy simulation

Green roofs are increasingly being employed as a sustainability feature of buildings. The sustainability approach in building designs requires reducing energy consumption and adopting low carbon energy sources without compromising the increasing expectations of comfort and health levels. Given the wide range of building designs, climates and green roof types, it is desirable to evaluate at the design stage the energy saving impact and other potential benefits from the application of green roofs. Currently, the abilities of building simulation programs to simulate the influences of green roofs are limited. For example, they have limitations in representing dynamic inter-layer interactions and moisture infiltration mechanisms. This research aims to develop a new model for the simulation of green roofs based on the control volume approach and to integrate the model within a whole building energy simulation program. The green roof elements consist of special layers such as plants and soil for which the control volume approach is capable of capturing their special characteristics with regards to the thermal and moisture exchanges. The model has been integrated within the ESP-r whole building energy simulation program. Within the ESP-r, the new green roof model alters the boundary condition of a roof surface on which green roof is constructed. The model development is carried out by a series of steps which include a careful selection of governing equations that describe the thermal and moisture balances in various layers of green roof, the numerical implementation for a simultaneous solution of the governing equations for the whole green roof, algorithm and code development and finally developing the interface with ESP-r. After successful integration, the model results were validated on an experimental test cell, which consists of an approximately 2 m2 planted medium on an insulated box with facilities for thermal, moisture and drainage measurements. The results for the thermal validation were promising with the significant boundary temperature values within a root mean square deviation (RMSD) in the vicinity of 0.5 K, whereas the moisture validation results are found to depend on initial conditions, the lower layers showing an RMSD of approximately 0.05 m3/m3 and the top layer nearly 0.12 [m3/m3]. The model is also able to predict the slowing down of water run-off. A methodology for collecting soil and plant properties which are required to be used along with the program has also been described. Based on the current state of the model and also considering the new developments in green roofs, some suggestions are proposed at the end of the thesis as a continuation of this research

A numerical and experimental study of near surface ground energy systems including the use of adaptable insulation layer

Unfortunately, the global conventional fuels in reserves are running out while the world energy consumption is increasing unruly. Therefore, innovative methods for providing sustainable heating and cooling through thermal energy storage (TES) have gained increasing attention. This study presents a numerical and experimental investigation of near surface ground energy systems including the use of adaptable insulation layers. The experimental set up involves the development of an innovative technique that is proposed to regulate the transfer of heat energy to the storage regions of the soil mass. Furthermore, a theoretical framework to represent the transient processes of such systems was developed and 1D and 2D numerical models were established to simulate ground energy system behaviour. The finite element method was utilised for spatial discretization and the finite difference method for time-stepping. The resulting model took into account conductive and convective heat transfer between the fluid inside pipe heat exchangers and the surrounding soil. Key additions were introduced to the recent model work which allowed it to take into account surface snow and ground freezing presence in the system, the amount of thermal energy available in the system and the ability to represent porous layer thermal properties of a multi layered system through considering its components (i.e. air, water and solids particles). The proposed new experimental setup was used to investigate the practical implementation of adaptable insulation layers with the experimental data then used to validate the numerical model. Further validation of the modelling of the surface snow and ground freezing was achieved via comparison against an experimental case study performed by others. In the analysis performed, particular attention was given to the energy balance at the soil surface and its impact on the performance of thermal energy storage devices in shallow regions of the ground. Additionally, the developed models were applied to explore the use of the adaptable insulation layer in different systems in comparison to typical designs. Three case scenarios were chosen to represent different type of systems, a comparisons analysis was then introduced which shows the potential effectiveness of using the adaptable insulation layer