Energy Consumption Reduction of AHU using Heat Pipe as Dehumidifier

Transcription

1 Energy Consumption Reduction of AHU using Heat Pipe as Dehumidifier Rohit R. Parab Mechanical Engineering Department Vishwakarma Institute of Technology, Pune, India Laxmikant D. Mangate Mechanical Engineering Department Vishwakarma Institute of Technology, Pune, India ABSTRACT A Heat Pipe is a simple device which is used to transfer heat from one location to another, using evaporation condensation cycle. It combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two interfaces. Heat pipe are used in number of applications ranging from electronics equipment cooling to HVAC. In current project performance characteristics of heat pipe as dehumidifier are experimentally investigated. A heat pipe dehumidifier is designed and tested at various inlet conditions of temperature and relative humidity. The energy-saving ratio with the heat pipe dehumidifier ranges from 6.4 % to 14.4 % according to the performance testing. Also effect of change in ADP (Apparatus Dew point ) also studied.the dehumidification capacity and the cooling coil power increases, but the energy saving ratio is reduced with the increase of air relative humidity, dry bulb temperature and air quantity. Keywords Heat Pipe, AHU, Dehumidifier, Energy consumption NOMENCLATURE Cp Specific heat h Enthalpy h fg Latent heat of vaporization Q Heat transfer rate Q L Latent heat Q S Sensible heat m a mass of air R Gas constant ρ Density K Thermal conductivity AHU air handling unit(s) ASHRAE American society of heating, refrigerating and air conditioning engineers SHR Sensible heat ratio V Velocity P Pressure CFM cubic feet per minute DBT Dry-bulb temperature WBT Wet-bulb temperature ADP Apparatus dew point RH Relative humidity h Coefficient of Convection Re Reynolds Number Pr Prandtl Number. INTRODUCTION One of the key global challenges which we are facing today is depletion of natural resources. Scarcity of these resources has led to increase in cost energy in exponential manner. Thus expected surge in prices is much more compared to other commodities. In addition, in order to curb carbon dioxide emissions certain protocols climate change convention Kyoto protocol have been imposed on all nations. As manufacturing industries worldwide have been focusing on reduction in costs, reduction 26 Rohit R. Parab, Laxmikant D. Mangate

2 in energy costs is one of key strategy for manufacturing organizations Humidity control is essential for material processing, space conditioning of habitable buildings, and industrial air-conditioning consumes significant quantities of electrical energy. Two methods for reducing humidity are either to increase size of air conditioners to over cool the air and remove moisture and then again heat the air before circulating it,.another method is using desiccant system to capture moisture in one area and release it in another by applying heat. Both these method consume considerable amount of energy thus increasing energy bills. Heat pipe eliminates the need for reheat or desiccant systems and increases the dehumidifying capacity of an air conditioner by as much as 70%. The technology uses about 40% less energy than electric reheat systems and approximately 25% less energy than other types of reheat methods. Reducing humidity is vital from health conditions perspective.it helps in prevention of growth of mold, mildew, fungus, and dust mites all common allergy agents. Heat pipe as dehumidifier can help cure sick building problems with conditioned fresh air and, as a result, can improve employee productivity M/s Flash Electronics (India) Pvt. Ltd. is one of the established unit in Indian market and a trusted supplier to major Indian two and three wheeler manufacturers. Annual energy cost of the M/s Flash Electronics (India) Pvt. Ltd., is to the tune of Rs Lacs. With spiraling energy costs, FEIPL is keen to trim down energy consumption and cost. The present assignment is for checking levels of energy efficiency at the FEIPL plant 1. The energy audit was conducted which aimed at recording and quantification of the energy consumption at this unit. Subsequently, it also tries to explore the possibilities of conserving energy through better production practices and employment of latest technologies. As FEIPL is into manufacturing of Electrical and Electronic component for automobile sectors,maintaining temperature and humidity is crucial.as per guidelines temperature to be maintained is C and Humidity to be maintained in % RH.same temperature is required in Office area from human comfort perspective.for maintaining the same AHU (Air handling unit) provided to Electronics and Sensor department Table 1 :Increase In Electrical load year over year Machine Load Utility Load Plant load Before After Data shows that there is nearly 16.6 % increase in machine load whereas whopping 108% increase in Utility load.utility load which was 28 % of plant before has increased significantly to 41 % of plant load PERFORMANCE STUDY OF AHU The AC plant has 2 nos. (2 x 20 HP) AHU s for supplying air to the aforementioned areas (electronic section, reception and ignition coil section etc). Table below gives the rated and actual measured air flow rates and power consumption for the blowers. Table 2 :Performance Study of AHU (Shop floor) No. Particulars Value 1 Supply air velocity m/sec Supply air DBT, C 19 3 Supply Air WBT, C 16 4 Supply air Enthalpy, kj/kg Return air temp, DBT, C Return air velocity, m/sec Return air WBT, C Return air Enthalpy, kj/kg RH % at served area AHU 1, blower -1, kw AHU 1, blower -2, kw Rohit R. Parab, Laxmikant D. Mangate

3 Sr.No Table 3: Performance Study of AHU (Office ) Particulars value Supply air DBT C 17.1 Supply air WBT C 16.1 Supply air Enthalpy KJ/Kg Return Air temp DBT C 22.2 Return air Velocity m/s 4 Return air WBT C 18.9 Return air enthalpy KJ/Kg RH at served area % 74 Density of supply air kg/m mass flow of air (kg/hr) As it can be seen from data is that air is overcooled in AHU and then humidification process followed due to which is increase in Electric energy consumption and electric energy cost EXPERIMENTAL SETUP AND MEASUREMENTPROCEDURE The test section consists of two air ducts of 0.15 X 0.15 m 2 section areas connected together by heat pipe heat exchanger. Heat pipes were installed by drilling holes in the duct A refrigeration machine consisting of; Blower, cooling coil along with the measuring instruments were used to supply the return cold air to the condenser Side of the heat pipe. A blower of variable speed installed before the cooling coil. The refrigeration unit was charged with chilled water and the evaporator was made from cooling coil, installed in the duct of 0.15 X 0.15 m 2 inside dimensions. The return cold and fresh warm air ducts were insulated with glass wool of 25 mm thickness to minimize the heat transfer to surrounding The air temperature and relative humidity at inlet and outlet of the two ducts were measured with Hygrometer steady state conditions were ensured before taking measurements during experiment. The refrigeration unit was operated and after enough time, the temperatures and humidity of fresh and return air before and after heat pipe heat exchanger were recorded, when they reached steady state i.e. nearly constant. The ratio between return cold and fresh air mass flow rates was obtained. The recorded data of the air were represented on the psychometric chart. Fig. 1: Experimental set up to measure heat pipe performance The air parameter range provided by the test system is: Room temperature -18~35, Relative humidity 50%~85%, Air quantity 25 CFM The heat pipe dehumidifier is tested at different dry bulb temperature and different wet bulb temperature (relative humidity). The working conditions and the results about the parameters, such as, dehumidification capacity, cooling coil power, heat pipe saving and energy saving ratio are listed in table The air parameters captured in the dehumidifier at different points. Point 1 is the state of high temperature wet air, point 2 is low temperature wet air after pre-cooling in evaporation side of heat pipe, point 3 is low temperature dry air after passing through cooling coil to low temperature and dehumidification, point 4 is dry air after passing through heat pipe condensation side to increase temperature Wet air and reheat low temperature dry air, 1-2 and 3-4 show the processes and the energy saving ratio. Point 5 is point after low temperature and dehumidification in the similar power condition of cooling coil with heat pipe, it can be indicated that point 4 has a higher air temperature and a lower relative humidity than point Rohit R. Parab, Laxmikant D. Mangate

4 RESULTS Graph was plotted for cooling coil power required with and without heat pipe and energy saving shown on the graphs the temperature of experimental cooling coil can also be varied by varying temperature Of water circulated through it.this temperature difference obtained by adding ice at inlet water and recording The temperature.for varying inlet temperature and humidity humidifier was used Readings were taken at various inlet DBT i.e at 25,26,27,28,29,30 degcelsius and graphs were plotted,results indicated that there is almost linear variation observed in the outlet temperature w.r.t. changing cooling coil temp Fig. 2: Variation of cooling coil power with and without heat pipe with respect to Variation in inlet DBT and RH 1. The cooling coil power reduced greatly with the using of heat pipe. 2. Heat pipe heat exchanger tested for various inlet and outlet temperature conditions and 3. results show that there is significant drop in energy consumption Energy saving ratio observed during experiments from 8.4% to 14.4 %.Thushas substantial potential of saving electrical energy consumption required for cooling coil Graph was plotted for Specific humidity at inlet and outlet conditions.specific humidity indicates mass of water vapor present in air w.r.t. dry air.difference in specific humidity would indicate that there is substantial amount of moisture removed from the process Fig. 3:Variation of Humidity ratio with and without heat pipe with respect to Variation in inlet DBT and RH Fig. 4:Effect of changing cooling coil ADP CONCLUSIONS The test indicates that: 1) Heat pipe has a good operating effect, the air temperature has a great change after passing through heat pipe, the energy saving effect is marked. The cooling coil power with using heat pipe has been greatly reduced, the energy saving ratio of heat pipe is range from 6.4 to 14.4 % 2) Air relative humidity is linearly proportional to the dehumidification capacity and increase cooling coil power but the energy saving ratio of heat pipe is reduced. 3) Under constant relative humidity, dehumidification capacity and cooling coil power decrease along with the decrease of dry bulb temperature, but the energy saving ratio of heat pipe dehumidifier increase. 4) Under condition of the same dry and wet bulb temperature, dehumidification capacity and cooling coil power reduce along with the reduction in airflow quantity but the energy saving ratio increases. 29 Rohit R. Parab, Laxmikant D. Mangate

5 ACKNOWLEDGMENTS The authors are grateful to Vishwakarma Institute of Technology, Pune, India for providing space for experimentation. The authorsalso want to thank Mr.AjyakumarAmbike,LaxmanPawashe,AtulTotade,SunilShirgave for their immense support for the Project REFERENCES [1] Parkcheol-woo et.al. Energy consumption reduction technology in manufacturing-a selective review of Policies, Standards, andresearch, InternationalJournal of precision engineering and manufacturing Vol.10, no.5, (2009) [2] Wan J.W et.al, The effect of heat pipe air handling coil on energy consumption in central air conditioning system,journal of Energy and building (2007) [3] MostafaA.Abd El-baky,MousaM.Mohamed, Heat pipe heat exchanger for heat recovery in air conditioning Journal of Applied Thermal Engineering 27 (2007) [4]AliakbarAkbarzadeh Application of heat pipe heat exchanger to humidity control in Air-conditioning systems Applied Thermal Engineering Vol. 17, No. 6,(1997) , [5] Senthilkumar, R., et.al., Thermal Analysis of Heat Pipe Using Self Reweting Fluids, Journal of Thermal Science,, Vol. 15, No. 3, (2011 ) [6] Senthilkumar, R., et.al, Thermal analysis of heat pipe sing Taguchi Method International Journal of Engineering Science and Technology Vol. 2,No.4, (2010), [7] Xiaobao Zhao et.al. Performance test and Energy saving analysis of heat pipe dehumidifier Journal HVAC Technologies for Energy Efficiency Vol.4 (2006) 4-5 [8] Nemec Peter et.al., Thermal Performance Measurement of Heat pipe Global Journal of Technology and Optimization Vol.2 (2011) [9] Sivaraman B. and Krishna.N Experimental analysis of heat pipe solar collector with different L/di ratio of Heat pipe,journal of scientific and Industrial research Vol.64, (2005), [10] DharP.L.,SinghS.K, Studies on solid desiccant based hybrid air-conditioning systems, Applied Thermal Engineering Vol.21 (2001) [11] Dr.Niu.L.J., Technology options for humidity control for hotels in Southeastern China Climate Journal of HKIE Transactions, Vol 8. No2, (2001) 20-24, [12] AhmadzadehtalatapehM,Yau Y.H, The application of heat pipe heat exchangers to improve the air quality and reduce the energy consumption of the air conditioning system in a hospitalward A full year model simulation, Journal of Energy and Building Vo.43 (2011), [13] Heat Pipes Theory, Design, Applications by David Reay and Peter Kew [14] Refrigeration and Air conditioning by R.K Rajput [15] Refrigeration and Air conditioning by P.L.Anantnarayan 30 Rohit R. Parab, Laxmikant D. Mangate