Buildings contribute significantly, accounting for one-third of global energy consumption and carbon dioxide emissions. Precise humidity control is vital in various applications, including hospitals, manufacturing facilities, pharmaceutical cleanrooms, art galleries, libraries, specialized hotel spaces, and commercial establishments. In subtropical climates, the combination of humid outdoor air and ventilation needs increases the dehumidification load, elevating the energy consumption of air-conditioning systems. The conventional vapor compression system (CVCS) is the preferred technology for space conditioning, managing the latent heat load by cooling air below the dew point temperature.
However, the conventional approach to moisture removal in humid conditions is energy-intensive and not optimally responsive to advancements like inverter systems, which excel in sensible cooling. Addressing this, the hybrid cooling system (HCS) integrates solid desiccants with CVCS, effectively decoupling sensible and latent loads. Yet, reliance on natural gas-fired boilers or electric heaters for desiccant regeneration compromises efficiency and undermines carbon reduction efforts.
This thesis tackles the aforementioned challenge and attempts to improve the performance of HCS by integrating advanced high-temperature heat pump (HTHP) technologies. Acknowledging the pivotal role of refrigerants, the study begins with an in-depth analysis of fourteen refrigerants, spanning hydrofluorocarbons, alkenes, and hydrocarbons. Employing a 4E analysis (energy, exergy, environmental, and economic) and TOPSIS methodology, the study identifies optimal refrigerants for various condensing temperatures from 45 – 130 °C. Considering India's present emission factor, R407C, R1270, R290, R152a, R1234ze(E), and R245fa are found to be the best refrigerants for the condensing temperatures ranging from 45 - 65 °C, 66 – 68 °C, 69 – 77 °C, 78 – 92 °C, 93 – 95 °C, and 96 – 130 °C respectively.
The subsequent study explores the system performance of HTHP integrated in HCS numerically. Heat pumps with condensing temperatures of 80 °C, 90 °C, and 120 °C using synthetic refrigerants and ejector enhanced trans-critical CO2 heat pumps were compared with CVCS and HCS. The 120°C synthetic refrigerant heat pump with R245fa and trans-critical CO2 heat pump demonstrated a system COP of 1.26 and 1.38, respectively, surpassing CVCS with a system COP of 0.62. These setups achieved CO2 emission reductions of 51.25% and 55.18%, compared to CVCS and HCS, respectively.
The final phase focused on developing a 120 °C HTHP system featuring a high temperature scroll compressor due to its non-availability. This system can also generate steam with a stagnation pressure of 1.5 bar, a flow rate of 81.43 kg/hr, and a temperature of 108.52 ℃ and was installed in a canteen replacing a diesel boiler. Data from 31 days of operation were analyzed, revealing a system COP of 2.2 and average daily energy savings of 57.79 kWh with cost savings of Rs. 1125.46. While carbon emissions increased by 20.3% compared to diesel, based on India's emission factor, considering the European Union's emission factor, the system has the potential to reduce carbon emissions by 57.8%.
In essence, this thesis serves as a guide for industries seeking sustainable solutions for industrial process heating and dehumidification systems to meet their energy sustainability goals.