Abstract
Vapor cooling systems are comparatively more efficient than mechanical cooling systems. This system will use low-cost fuels and waste energy, and COP does not reduce with load. It is composed of a compressor, condenser, expansion valve, and evaporator. This report will provide a design and analysis of a Lithium-bromide cooling system. The Lithium-bromide cooling system will require low maintenance. It is suited for operation under high temperatures. The design uses calculations and information from pre-designed systems. It aims to develop an energy-efficient and cost-effective system. More so, it will provide clean air in the building.
Introduction
Cooling demand in buildings is expected to increase over time. Vapor cooling systems are economical and efficient to establish cooling systems that eliminate the need for mechanical air-conditioning mechanisms (Bryne et al., 2018). Findings by the International Energy Agency on the Energy in Buildings and Communities program support the practicality of passive ventilative cooling control in controlling internal building parameters (O’Donovan et al., 2021). An absorption chiller cooling system uses heat energy in a refrigeration cycle to control room temperatures. Lithium-bromide provides an efficient cooling mechanism under high temperatures and unfriendly environmental conditions such as dust (Bongotra, 2017). This paper provides a design mechanism for an absorption cooling system for a CSET building under summer conditions in Ningbo. Building parameters such as flow rate, the theoretical center of pressure, and heat dissipation rate influence the calculation of calculation for volume, size, and types of components in the system. This Lithium-bromide system is targeted to provide desirable room conditions under extreme weather conditions.
Methodology
This design report will utilize data from coursework references, peer-reviewed journals, and calculations. The coursework reference provided information on the system functioning, desirable properties of refrigerant absorbent mixtures, and practical assemblies for the proposed building size. Peer-reviewed journals have been incorporated in this report to provide reference to practical cooling systems designed in the world. They have been used to provide insights into the success of passive cooling technologies in effectively controlling room temperatures. This report borrows journals on existing cooling technologies and focuses on their drawbacks and areas that require improvement. Finally, the report used calculations on the anticipated room parameters to determine the system component specification, sizes, and operation conditions. Calculations were crucial in establishing the fluid flow rates, cooling loads, inlet/outlet heating coil temperatures, and evaluation of overall performance.
Results
This cooling machine will use a Lithium-bromide solution as absorbent and water as the refrigerant. The calculations in the system will assume a steady state and flow, pure refrigerant in the generator, zero pressure drop due to friction, and negligible changes in kinetic and potential energies across the components. This design sample will operate generator inlet/outlet heating coil temperatures of 20 to 110 degrees Celsius.
Flow rate is the amount of fluid passing at a point at a specific time. This cooling machine will serve a room area of 1500 meters squared. The cooling system will require a mass flow rate of 0.5 Kg/s for the refrigerant and solution to effectively cool the building (Vazhapilly et al, 2013). The room will require a massive cooling system to deliver the desired flow rate.
Figure 1 shows the operation cycles of the Lithium-bromide cooling system. It is designed to operate in summer conditions at Ningbo, which are average 30 degrees Celsius temperatures and 1013 millibars. The work at the compressor will be obtained from the difference between h2 and h1. It is represented by Wc = h2- h1. Work at the evaporator will be obtained by the difference between h4 and h1. Here; Q0= h1 – h4’. Assuming a 0.5 HP air conditioner can work for a 15 square meter house, this CSET building will require a 50 HP air conditioner to regulate the room temperatures efficiently.
Figure 1 Lithium-bromide cooling machine operation diagram
Discussion
Vapor absorption refrigeration systems will comprise a compressor, evaporator, condenser, and an expansion valve. It contains fluid that serves as a refrigerant. This fluid, when subjected to compression and expansion, absorbs and releases heat to and from the surrounding environment depending on room parameters. This cooling system will use water-lithium bromide, which is practical for large buildings (Lecture 16). More so, it is effective since the temperatures at the Ningbo are above zero degrees Celsius. Since the room area of 1500 meters square is immense, the design will require a multi-stage water-lithium bromide design to maintain room temperatures continuously. The Lithium-bromide has a desirable temperature difference with water, which qualifies the duo for refrigerant and absorbent in the system. It aims to maintain a temperature of 23-28 degrees Celsius.
The Lithium-bromide system will comprise a thermal compression system, which will include a solution pump, heat exchanger, absorber, and generator. This system will use a shell and tube condenser. The refrigerant will flow outside the minute tubes through the honeycomb structure, while the absorbent will flow in the tubes. The system will be effective due to the easy availability of water. They will be crucial for summer temperatures that may exceed 30 degrees Celsius. Moreso, these liquid cooled condensers are relatively cheap to acquire. Figure 2 shows a design of the shell and tube condenser. The shell and tube structure will be 0.45 meters in diameter and 2 meters in length.
Figure 2 Shell and tube condenser
This system will also use a recirculation evaporator, which will help conserve the fluid levels in the cooling system. It will have an electronic expansion valve, which will be more effective in controlling and regulating flow around the cooling system. EEV will provide better responsiveness. An EEV is illustrated in Figure 3. The system design will also use solar energy for heat supply to the generator. These are environmentally friendly. The design will filter ambient air before delivery to the system.
Figure 3 An Electronic Expansion Valve
Figure 4 Lithium-bromide system design
Conclusion
This report has established the design of a vapor cooling system for the CSET building. It has borrowed from peer-reviewed journals, coursework material, and peer-reviewed journals. The water-elium-bromide fluids will be practical in this system, which is set to operate under high room temperatures during the summer period. Components in the systems have been selected specific to the environmental conditions in Ningbo. Although the Shell and Tube condenser displays inefficiencies when exposed to contamination, it is best suited for high summer temperatures. The Electronic Expansion Valve will provide swift control of the fluid flow among the components. More so, the recirculation evaporator will enhance fluid circulation for efficient cooling. This system design will sufficiently provide cooling for the CSET building.
References
Bangotra, A. (2017). Design-analysis of generator of vapour absorption refrigeration system for automotive air-conditioning. Int. J. Eng. Res. Technol, 6, 121-125. https://www.academia.edu/download/60729208/design-analysis-of-generator-of-vapour-absorption-refrigeration-system-for-automotive-air-conditioning-IJERTV6IS06007420190928-52151-bo8.pdf
Byrne, P., Ghoubali, R., & Diaby, A. T. (2018). Heat pumps for simultaneous heating and cooling. https://hal.science/hal-01990466/
O’Donovan, A., Murphy, M. D., & O’Sullivan, P. D. (2021). Passive control strategies for cooling a non-residential nearly zero energy office: Simulated comfort resilience now and in the future. Energy and Buildings, 231, 110607. https://www.sciencedirect.com/science/article/pii/S0378778820333934
Vazhappilly, C. V., Tharayil, T., & Nagarajan, A. P. (2013). Modeling and experimental analysis of generator in vapor absorption refrigeration system. International Journal of Engineering Research and Applications, 3(5), 63-67. https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=2cbca7be10bffd0397c900361ff914e8a51c7516
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