• Vol 10, No 6 (2019)
  • Mechanical Engineering

The Application of U-shape Heat Pipe Heat Exchanger to Reduce Relative Humidity for Energy Conservation in Heating, Ventilation, and Air Conditioning (HVAC) Systems

Aliefka Satria Kusumah, Imansyah Ibnu Hakim, Ragil Sukarno, Fadhil Fuad Rachman, Nandy Putra

Corresponding email: nandyputra@eng.ui.ac.id


Cite this article as:
Satria Kusumah, A., Ibnu Hakim, I., Sukarno, R., Fuad Rachman, F., Putra, N., 2019. The Application of U-shape Heat Pipe Heat Exchanger to Reduce Relative Humidity for Energy Conservation in Heating, Ventilation, and Air Conditioning (HVAC) Systems. International Journal of Technology. Volume 10(6), pp. 1202-1210

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Aliefka Satria Kusumah Applied Heat Transfer Research Group, Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia
Imansyah Ibnu Hakim Applied Heat Transfer Research Group, Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia
Ragil Sukarno Applied Heat Transfer Research Group, Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia
Fadhil Fuad Rachman Applied Heat Transfer Research Group, Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia
Nandy Putra Applied Heat Transfer Research Group, Department of Mechanical Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia
Email to Corresponding Author

Abstract
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Hospitals consume large amounts of energy, especially in their heating, ventilation, and air conditioning (HVAC) systems due to the special requirements for ensuring healthy, comfortable, and safe environmental conditions. The use of a Heat Pipe Heat Exchanger (HPHE) is recommended as a means of minimizing electricity consumption with no loss of comfort while also improving indoor air quality. An experimental study was conducted to investigate the performance of a U-shape HPHE in recovering exhaust air heat from an indoor room included in an HVAC system. The U-shape HPHE consists of several tubular U-shape heat pipes with water as a working fluid and arranged in a staggered configuration. Tests were carried out to determine the impact of the inlet air temperature, air velocity, and the number of heat pipes on its effectiveness. The experiment revealed that the higher the temperature of the inlet air, the more effective the U-shape HPHE. The results show that the temperature of the air entering the cooling coil decreased by 1.73 °C with an effectiveness value of 7.64 %. This result was achieved using 12 U-shape HPHEs, which had a staggered arrangement, an air velocity of 1.5 m / s, and an air temperature entering the evaporator of 45 °C. The highest amount of heat recovery, 2190.43 kJ/hour, was achieved when the air velocity was 2.5 m/s.

Effectiveness; Heat Recovery; HVAC; U-shape Heat Pipe

Introduction

Hospitals and health facilities are responsible for excessive energy demands. Increasing energy demand, in the context of limited availability of fossil energy resources, is encouraging people to find alternative energy sources (Elfani, 2011) and more efficient ways in which to use energy (Vakiloroaya et al., 2014). Research from the Energy Star program shows that energy consumption per m2 in hospitals greatly exceeds that found in many other types of buildings (World Health Organization, 2014). The air quality in every hospital operating room must be kept sterile; thus, special places such as operating rooms in hospitals usually require air temperatures in the range of 20 oC–24 oC, relative humidity between 50 % and 60 %, and for positive air pressure to be maintained (Leung & Chan, 2006). As the ASHRAE Standard states, “Relative humidity in inhabitable spaces should be maintained between 30% and 60%, to minimize the growth of allergenic or pathogenic organisms” (ASHRAE Standard, 1981).  

The use of a conventional cooling coil to obtain relative air humidity following the standard demands a process for reheating air from the dew point prior to its distribution to the conditioned room, which requires an external energy source (Bearg, 1992).

The Heat Pipe Heat Exchanger (HPHE) may offer a solution to this problem. Warm air from outside is recovered by the HPHE to reheat the cold air at the dew point, thereby saving reheating energy. The evaporator section of a U-shape HPHE can serve as a precooler of warm air before it is cooled by a cooling coil device, thus increasing the capability of the cooling coil.

McFarland et al. (1996) and Abtahi et al. (1988) conducted experiments to determine the effect of using an HPHE on the performance of conventional air conditioning systems. In their experiments, three configurations of the system were applied: a system with HPHE installed, a system without HPHE, and the use of a damper system. The results showed that the utilization of HPHE in conventional air conditioning systems has a significant effect in terms of controlling humidity and reducing energy consumption (Abtahi et al., 1988) (McFarland et al., 1996). An experimental study on the use of an HPHE to cool the fresh air inlet in a heating, ventilation, and air conditioning (HVAC) system was also conducted by El-Baky and Mohamed (2007). Their results revealed that effectiveness of up to 48 % could be achieved when the temperature of the fresh air was 40 oC. In addition, they found that heat recovery could be increased to 85 % with a higher temperature of fresh air entering the inlet (El-Baky & Mohamed, 2007).

The heat pipe is thus a beneficial device within energy recovery systems (Srimuang & Amatachaya, 2012). Several types of heat pipes have been applied, such as straight heat pipes (Putra et al., 2017), thermosyphon (Jouhara & Merchant, 2012), oscillating heat pipes (Winarta et al., 2019), and a wraparound loop heat pipe (Jouhara & Meskimmon, 2018). An HVAC system with an HPHE installed provides the benefit of acting as heat recovery equipment, mainly when used in the operating room of a hospital (Shabgard et al., 2015). Therefore, this recent research aims to investigate the thermal performance and energy recovery associated with the use of a U-shape HPHE in an HVAC system.

Conclusion

The chamber structures used in this analysis were modified to the standard conditions found in a hospital. Previous studies have used only a straight-type HPHE configuration, while in this study, a combination of straight-type HPHEs and U-shape HPHEs were used. The use of the U-shape HPHE in this study was found to create an energy consumption saving in the hospital of up to 608.45 W or 2190.42 kJ/hour. Applied to actual conditions where the value of Te, i is less than 45 oC, such as in Indonesia, which experiences daily ambient temperatures ranging from 28 to 32 oC, the potential savings to be made are in the range 200–350 W. The effectiveness of the U-shape HPHE increases as the number of U-shape HPHEs increases and the air inlet temperature in the evaporator increases, while it falls as the air velocity increases. The value for HPHE heat recovery rises as the number of U-shape HPHEs increases, the evaporator inlet air temperature increases, and the air inlet velocity increases. The highest effectiveness of the U-shape HPHE is 7.64 % and the lowest HPHE effectiveness is 0.30 %. The highest HPHE heat recovery is 608.45 W, and the lowest HPHE heat recovery is 117.21 W.

Acknowledgement

The authors are grateful for the financial support from Kemenristek Dikti RI through the PDUPT Scheme 2019 with contract number NKB-1651/UN2.R3.1/HKP.05.00/2019.

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