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The assignment involves analyzing a shipping container converted into a mobile medical clinic, focusing on minimizing heating and cooling energy requirements over a one-year period. The task requires evaluating all heat transfer modes—conduction, convection, and radiation—through the container’s walls, roof, and windows, considering different insulation and roofing materials. Operational parameters include maintaining an internal temperature of 21°C during summer and winter, with specified external temperatures and solar irradiation conditions. The analysis encompasses calculating surface temperatures, energy demands for heating and cooling with and without insulation, associated costs, and the payback period of added insulation. Additional considerations include the impact of solar panels, influencing energy needs and costs, as well as sensitivity to input parameters affecting overall energy transfer, aimed at optimizing design for energy efficiency and cost savings.

Sample Paper For Above instruction

Introduction and Problem Statement

The conversion of a shipping container into a mobile medical clinic presents a unique challenge in thermal management, especially in hot and cold climates. Efficient insulation and roofing material choices are critical to minimizing energy consumption for heating and cooling, thereby reducing operational costs and environmental impact. This analysis aims to evaluate various insulation and roofing configurations, determine their impact on the internal thermal environment, and identify the most cost-effective solution over a 10-year period. The investigation also considers supplementary strategies, such as solar panel integration, to further enhance energy efficiency.

Diagram and Thermal Circuit Representation

The system can be represented by a control volume encompassing the container interior, insulated walls, roof, and windows. The thermal circuits include conduction through steel walls and insulation layers, convection at internal and external surfaces, and radiation exchange with the environment. Solar irradiation primarily impacts the roof, contributing to internal heat gain during summer. A simplified schematic illustrates the heat flow pathways, with components labeled for clarity, including the wall structure, insulation layers, exterior roofing, and windows.

Approach and Assumptions

The analysis assumes steady-state conditions during peak summer and winter days, with the following key assumptions:

• Material properties are evaluated at 300 K, such as thermal conductivity, emissivity, and specific heat capacities.
• The windows are double-pane with an air gap, acting as thermal resistances and radiative barriers.
• Interior convective heat transfer coefficient, hi, is 5 W/m²K, and exterior, ho, is 20 W/m²K.
• The solar absorptivity and emissivity of roofing material are equal, following the graybody assumption.
• No internal heat sources or air exchanges are considered aside from the specified ventilation effects.
• Cost parameters, such as insulation cost, energy prices, and efficiencies, are based on current market values.
• The analyses neglect radiation exchange inside the air gaps of windows and focus on surface-to-surface exchanges.

Heat Transfer Analysis and Calculations

The core of the analysis involves calculating the thermal resistances of components, determining surface temperatures, and computing the heat fluxes for both summer and winter scenarios. The overall heat transfer coefficient, U, for each surface is derived from conduction and convection resistances, along with radiative exchange. Solar heat gains through windows are evaluated considering the solar irradiance, window area, and absorptivity, which contribute to internal heat loads during summer.

The energy balance for each component (walls, roof, windows) incorporates the combined effects of conduction, convection, and radiation. For example, the heat transfer through walls can be expressed as:

Q = U  A  (T_surface - T_ambient)

where U is the overall heat transfer coefficient (W/m²K), A is the surface area, and T_surface, T_ambient are the surface and ambient temperatures, respectively.

The internal surface temperatures are iteratively calculated until convergence, considering thermal resistance and the balances with external and internal air temperatures.

Evaluation of Surface Temperatures

In summer, the external surface temperature rises due to solar gain and environmental heat. The internal surface temperature is maintained close to 21°C, but higher heat fluxes increase cooling demands. Conversely, in winter, the external surface cools, leading to heat loss inward and increased heating load. The computed surface temperatures are within reasonable bounds, aligning with typical building physics expectations, e.g., exterior surfaces reaching temperatures consistent with solar and ambient conditions, and interior surfaces stabilized at 21°C.

Energy Requirements for Heating and Cooling (With and Without Insulation)

The daily heating and cooling energy demands are calculated based on the net heat transfer during the respective periods. For winter, heating energy is derived from the heat loss through walls, roof, and windows, adjusted for system efficiencies:

Q_heating = (Heat loss in winter) / Efficiency_heating

Similarly, for summer, cooling energy is computed from the heat gain and the cooling system's efficiency:

Q_cooling = (Heat gain in summer) / Efficiency_cooling

The results demonstrate significant reductions in energy requirements when proper insulation is used, with the insulation's effectiveness evaluated at different thicknesses.

Cost Analysis Over One Year and Ten Years

The annual energy costs are calculated by multiplying the daily energy demands by the corresponding energy prices:

• Heating cost: daily heating energy (kWh) * $0.03 / kWh
• Cooling cost: daily cooling energy (kWh) * $0.13 / kWh

These annual costs are projected over ten years, accounting for the investment in insulation, which costs $5 per cubic meter. The payback period for insulation considers the initial cost against energy savings, identifying the optimal insulation thickness. The resulting plot displays total cost versus insulation thickness, illustrating the point where additional insulation yields diminishing returns.

Impact of Input Parameters on Heat Transfer and Design Decisions

Variations in parameters such as the thermal conductivity of insulation, emissivity of surfaces, solar absorptivity of the roof, and external environmental conditions significantly affect heat transfer rates. For instance, increasing the roof's emissivity enhances radiative cooling, reducing internal heat gain during summer. Similarly, selecting insulation materials with higher thermal resistance dampens heat fluxes, lowering energy demands. These factors inform design strategies—such as maximizing insulation thickness, choosing low-emissivity coatings, or implementing reflective roofing—to optimize energy efficiency and cost savings.

Additional Consideration: Solar Panel Integration

Adding solar panels to cover the entire roof could generate renewable electricity, reducing reliance on grid power for cooling and heating. An online resource indicates that a typical 300 W solar panel costs approximately $300, with an energy generation capacity of around 1.2 kWh/day per panel in optimal conditions. The payback period depends on the amount of energy offset, the cost savings, and the initial hardware investment. Incorporating solar panels could dramatically improve the economic viability of the clinic, especially in remote or resource-limited settings, and further reduces the environmental footprint.

Conclusions and Design Recommendations

The analysis indicates that insulation significantly reduces energy costs and has a favorable payback period. Optimal insulation thickness balances initial investment with long-term savings, with intermediate thicknesses providing the most practical benefits. Energy-efficient window and roof designs—such as low-emissivity coatings or reflective surfaces—enhance performance further. Future designs might incorporate passive cooling techniques, energy recovery systems, or integration of renewable energy sources like solar panels. Additionally, exogenous factors like fluctuations in energy prices or changes in climate conditions should be considered for resilient and sustainable design practices.

References

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• National Renewable Energy Laboratory. (2020). Solar Energy Calculator. NREL.gov.
• McCluney, K. E. (2016). Introduction to Environmental Engineering. McGraw-Hill Education.
• Szokolay, S. (2004). Introduction to Architectural Science: The Basis of Sustainable Design. Architectural Press.
• Duffie, J. A., & Beckman, W. A. (2013). Solar Engineering of Thermal Processes. John Wiley & Sons.
• Garg, H. P., & Prakash, J. (2000). Building Materials. New Age International.
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• O’Neill, M. J., & Sandoval, S. (2018). Sustainable Building Design and Construction. CRC Press.
• Reed, C. A., & Mathew, K. (2010). Passive Solar Heating and Cooling. John Wiley & Sons.