Multi-stage heat-pipe heat exchanger for improving energy efficiency of HVAC system in hospital operating room

The demands of a room with specific requirements related to thermal comfort, such as the temperature, relative humidity, inside air exchange, and other factors required in a hospital operating room, have necessitated the development of energy-efficient heating, ventilation, and air conditioning (HVAC) systems. Energy recovery with a heat pipe that utilises cold air exhaust from a room in an HVAC system can enhance the efficiency and reduce emissions. In this study, experimental and theoretical analyses were performed to develop a more effective and efficient heat-recovery system using a heat-pipe heat exchanger (HPHE) for HVAC systems in hospital operating rooms. The experiment was conducted by using HPHEs having 3, 6, and 9 rows, with 4 heat pipes in each row arranged in a staggered configuration. The fresh-air inlet temperature in the evaporator section was varied between 30, 35, 40, and 45°C, and the air inlet velocity was varied between 1.5, 2.0, and 2.5 m/s. The theoretical analysis was conducted using the ε-NTU method for predicting the effectiveness, outlet temperature of the evaporator side, and energy recovery of the HPHE. The experimental results indicated that increasing the air inlet temperature in the evaporator section and the number of rows increased the HPHE effectiveness but increasing the air inlet velocity reduced the effectiveness. The highest effectiveness of 62.6% was obtained at an air inlet temperature of 45°C with an air inlet velocity of 2 m/s and a 9-row HPHE. The energy recovery of the HPHE increased with the number of rows, air inlet temperature, and air velocity in the evaporator section. The theoretical analysis results obtained using the ε-NTU method were similar to the experimental results. Thus, this technique can be used as a comparison method in the analysis of heat-recovery systems that apply HPHEs.