Experimental Investigation of Gas Engine Driven Heat Pump Used in Water Cooling

Transcription

1 The Online Journal on Power and Energy Engineering (OJPEE) Vol (1) No (3) Experimental Investigation of Gas Engine Driven Heat Pump Used in Water Cooling E Elgendy, J Schmidt Institute of Fluid Dynamic and Thermodynamic, Faculty of Process and System Engineering, Otto-Von-Guericke University, Magdeburg, Germany Abstract-Nowadays a sustainable development for a more efficient use of energy and the protection of the environment is of increasing importance Gas engine heat pumps represent one of the most practicable solutions which offer high energy efficiency and environment benefits to heating and cooling applications In this study, the performance characteristics of engine driven heat pump used in water cooling were investigated experimentally without engine heat recovery All of evaporator water inlet temperature, evaporator water volume flow rate and ambient air temperature were changed in a wide range of operating conditions The results showed that primary energy ratio of the system increased by 262% as evaporator water inlet temperature changed from 13 o C to 22 o C On the other hand, raising of ambient air temperature from 218 o C to 277 o C led to decrease in system primary energy ratio by 8% The maximum primary energy ratio obtained was 169 over a wide range of operating conditions Keywords- Gas engine heat pump Experimental investigation - Cooling mode R4a - Energy efficiency I INTRODUCTION Depletion of fossil fuels and environmental pollution are two of main problems in the whole world Fossil fuels represent the main energy source in the world and its depletion is a risk for energy poverty in the future In Europe, more than 5% of the total energy consumption dependence on fossil fuel [1] Also environmental pollution problems increase with consumption of fossil fuels There are two ways to solve these problems (i) Developing alternative energy sources and (ii) Improving energy efficiency of equipments that use fossil fuels Heat pumps (HPs) are a natural choice in areas where there are needs for cooling and heating applications as they can improve the overall energy utilization efficiency and are environmentally friendly [2] Approximately, one third of all single-family homes built in the US were heated by HPs in 1984 [3] There are mainly two types of heat pumps being used today, the vapor compression heat pump with a mechanical compressor requiring mechanical drive energy and the absorption heat pump using thermal drive energy The great majority of heat pumps work on the principle of the vapor compression cycle According to energy sources HPs are divided into many categories, namely electric driven HPs (EHPs), chemical HPs, geothermal energy HPs, solar assisted HPs and/or hybrid power systems etc [4 6] In the case of EHPs, fuel is mainly converted to electrical energy at power plants and the waste heat is discharged to the environment, then electrical energy is transmitted to the HPs and is converted to mechanical energy by the motor of HP In this process, energy has been converted twice and heat loss is high However, energy efficiency can become higher if fuel conversion located closer to heat required In this case, heat released in fuel conversion process can be efficiently used Since engine heat pumps (GEHPs) are harmonious with this concept, they are attracted the investigators with the high energy efficiency, especially in heating [7] Main applications of GEHPs are for space and water heating/cooling purposes However, they can be integrated to industrial applications, especially in drying processes [8] Many researchers focused on the operational rol of GEHP because the optimal rol could reduce the energy consumption effectively Li et al [9] introduced a cascade fuzzy rol strategy for the GEHP system The performance of the cascade fuzzy rol was compared to that of a cascade PI (proportional and integral) rol strategy, and the results proved that the cascade fuzzy rol strategy gave better performance and reduced reaction time and smaller overshoot temperature Yang et al [] published an intelligent rol simulation model for GEHP system in heating mode to research the dynamic characteristics of the system The model consisted of eight models for its components The results showed that the model was very effective in analyzing the effects of the rol system The steady state accuracy of the intelligent rol scheme was higher than that of the fuzzy roller An algorithm was written to model GEHP dynamically in cooling mode by Shin et al [11] The dynamics of the model was established based on conservation laws of mass and energy A good agreement with real system was reached in temperatures, pressures and system coefficient of performance (COP) The effect of both ambient temperature and engine speed on heating performance of GEHP based on steady state model were analyzed by Zahng et al [12] The result proved that engine speed had a remarkable effect on both the engine and heat pump, but ambient temperature had a little influence on the engine performance Many researchers are interested in GEHP used for air heating systems A little publications focused on GEHP used for water cooling Variations of unit parameters like evaporator inlet temperature and its volume flow rate are no more discussed So, the present paper aims to study the performance of GEHP used in water cooling without engine Reference Number: W9-9

2 The Online Journal on Power and Energy Engineering (OJPEE) Vol (1) No (3) heat recovery Effect of both water evaporator inlet temperature and its volume flow rate on the system performance is focused Moreover, effect of ambient air temperature on both engine and refrigeration cycle is presented This paper is only the first part of a widely study carried out by the authors The experimental results and theoretical modelling for water cooling with engine heat recovery will be presented in further publications II EXPERIMENTAL APPARATUS The experimental apparatus use a GEHP (TGMP 28 C1N) produced by AISIN Company in Japan as outdoor unit The nominal cooling capacity is 28kW, while in heating mode the capacity is 34kW While the unit includes water cooling system, split air unit and air handling unit beside the operational and safety rol devices Figure (1) shows a schematic diagram of the experimental apparatus used for water cooling Measuring instruments positions are also indicated The test apparatus consist mainly of three cycles namely, primary working fluid cycle, engine coolant cycle and secondary working fluid cycle R4A is used as primary working fluid while both water and air are used as secondary heat transfer fluids at heat source (evaporator) and heat sink (condenser) In engine coolant cycle both ethylene glycolwater mixture (65% by volume) and propylene glycol-water mixture (45% by volume) are used as working mediums All the measuring instruments have been installed and connected to 64 channels in the data acquisition cards Refrigerant mass flow rate is measured using KROHNE (Optimass, 7C) which is working according to Coriolis principle II-a Primary Cycle Refrigerant (R4A) coming out of compressors (state point 2) flows into outdoor unit (state point 5) after passing through an oil separator and a reversing valve Compressor (1) is equipped with a capacity rol valve (V 1 ) to rol the capacity of compressor by increase or decrease the valve steps The refrigerant in the outdoor unit is condensed (state point 8) using the outside air (state point ) and then distributed into two branches In cooling mode, valve (V 4 ) is maintained closed Therefore all the refrigerant coming out of outdoor unit passes through subcooler The refrigerant in the subcooler is subcooled (state point 9) by transfer its heat to the throttled refrigerant flowing through valve (V 5 ) Mass flow rate of the subcooled refrigerant is measured before passing through electronic expansion valves (V 6 ) and (V 7 ) using flow meter (F 1 ) Now it flows into the unit where it is evaporated (state point 15) using the water coming out from the tanks Evaporated refrigerant coming out from both subcooler (state point 11) and unit (state point 6) are mixed (state point 17) before entering the accumulator and then returning back to the compressors (state point 1) II-b Engine Coolant Cycle Coolant sent from the coolant pump (state point 22) is heated by the heat released from the engine block and exhaust as (state point 23) The heated coolant returns to the coolant pump by making a shortcut via a thermostat valve when coolant temperature is low (lower than 55 o C) at engine startup As coolant temperature increases (higher than 55 o C), coolant flows into the sub heat exchanger (state point ) and heats refrigerant to enhances evaporation efficiency (in heating mode) and then comes back to the pump after its volume flow rate is measured using ultrasonic flow meter (F 4 ) When coolant temperature is very high (higher than 63 o C), coolant flows into sub heat exchanger, heat recovery heat exchanger and radiator (state point 24) to dissipate heat The coolant exit from both heat recover heat exchanger (state point 25) and radiator (state point 26) is mixed (state point 27) and its volume flow rate is measured using ultrasonic flow meter (F 3 ) before returning back to the coolant pump Heat gained in heat recovery heat exchanger is supplied to the water in the tank (1) using propylene-water mixture as a working medium (state points 28 and 29) II-c Secondary Cycle The chilled water coming out from unit (state point ) is pumped to both tanks (1) and (2) using variable speed water pump (WP 1 ) In the case of no engine heat recovery, both tanks are used as heat source for the evaporator A two way valve (V 2 ) is used to rol the percentage of water flowed from tank (1) The warm water coming out from tank (1) and the cold water coming from tank (2) are mixed before their volume flow rate are measured using ultrasonic flow meter (F 2 ) Temperature of air inlet to outdoor unit (state point ) is measured using PT sensors to study the effect of ambient air temperature on the performance characteristics of GEHP III Data Reduction Temperature, pressure and flow rate measuring locations are shown in Figure (1) Pre-calibrated PT sensors are used to measure operating temperatures Digital pressure gauges are used to record the pressure at five locations in the refrigerant circuit of the heat pump The flow rates of engine coolant and water flow are measured using Ultego II flow sensors All the measured data are recorded using DIAdem software and analyzed using an EES program [13] to estimate the system performance Using the measured data of operating pressures and temperatures of R4A, ethylene glycol-water mixture, propylene glycol-water mixture and water the inlet and outlet specific enthalpy values of each component are estimated (h 1 h 31 ) Then, energy and mass balances are carried out for the main components of the GEHP to compute their loads in addition to system overall performance Reference Number: W9-91

3 The Online Journal on Power and Energy Engineering (OJPEE) Vol (1) No (3) Outdoor Unit 7 5 Sub hex 21 V 3 18 V 4 Radiator Heat Recovery R4A Ethylene-Water Propylene-Water Water V 5 F P T Flow Pressure Temperature Subcooler 11 9 WP 1 WP 2 Indoor F5 Unit 31 F1 P3 V 6 V 7 14 P4 F F4 27 F3 Tank (1) Tank (2) Engine WP 3 6 V 2 Reversing Valve 2 P2 3 4 V 1 17 Oil Separator Compressor (2) Compressor (1) 1 P1 Accumulator Figure (1) Schematic diagram of the experimental apparatus with measuring points locations The refrigerant unit cooling capacity ( be written as follows: Q M ref ( h15 h9 ) V w w( h h31) M Q ) can (1) Throttled refrigerant mass flow rate ( sub ) flowing through subcooler can be calculated applying energy balance equation for subcooler (2) Q sub M ref ( h8 h9 ) M sub( h11 h8 ) To estimate the compressor power consumption, it is important to calculate the refrigerant mass flow rate exits from compressors to both outdoor unit ( accumulator ( M M comp, dis ) and ) So, applying mass and energy balances on accumulator yields to the following equation h h 17 1 M comp, dis (3) h1 h4 M and the refrigerant mass flow rate exits from compressor ( M comp, dis ) can be calculated as the following M M M comp, dis ref sub (4) Then the compressor power consumption (P comp ) is (5) P comp M ( h2 h1 ) M ( h3 1) comp, dis h The performance of a GEHP is estimated by means of three main parameters [14,15]: (i) primary energy rate (PER), (ii) Engine consumption Q ) and (iii) Heating/cooling capacity ( Q Q can be expressed as the following Q PER (6) Q Q V LHV (7) ( PER and )Where LHV represent lower heating value of the while volume flow rate ( V ) is measured IV RESULTS AND DISCUSSIONS Stiemle et al [16] reported that water temperature between 6 and 12C is recommended for summer air-conditioning chiller units Hence, evaporator water mass flow rate was selected to obtain water temperature at the evaporator outlet within the above recommended range Figure (2) illustrate the effect of evaporator water inlet temperature and its volume flow rate on the performance of GEHP while the effect of ambient air temperature on the performance of GEHP is presented in Figure (3) Reference Number: W9-92

4 The Online Journal on Power and Energy Engineering (OJPEE) Vol (1) No (3) Compressor power and heat loads (kw)4 Q Q ewo P c omp amb,av =221C =374 m 3 /h =27m 3 /h 4 Evaporator water outlet temperature ( C) Compressor power and heat loads (kw) 4 Q Q ewo P comp =377 m 3 /h amb,av =218C amb,av =277C 4 Evaporator water outlet temperature ( C) (A) dddddddddddddddddddddddddddddddddddd amb,av =221C =374 m 3 /h =27 m 3 /h (A ) =377 m 3 /h amb,av =218C amb,av =277C PER 15 PER Evaporator water inlet temperature (C) (B) Figure (2): Variations of compressor power, heat loads and PER versus evaporator water inlet temperature for different water volume flow rates Evaporator water inlet temperature (C) (B) Figure (3): Variations of compressor power, heat loads and PER versus evaporator water inlet temperature for different ambient air temperatures IV-a Effect of Evaporator Water Inlet Temperature Evaporator water outlet temperature ( ewo ) is also presented in the diagrams It can be seen from Figure (2) that increasing the evaporator water inlet temperature leads to better performance for GEHP system As a result of increasing evaporator water inlet temperature, evaporation temperature increases which leads to increase cooling effect (h 15 -h 14 ) and decreases compressor specific work (h 2 -h 1 ) On the other hand, refrigerant mass flow rate increases as a result of evaporation temperature increases So, both unit capacity and compressor power increase but with different rates The rate of increase in unit capacity (13%) is higher than the rate of increase in compressor power (2%) with respect to high water volume flow rate Gas consumption is decreased by 11% as evaporator water inlet temperature increase among the entire range Primary energy ratio (PER) of the GEHP increases (262%) as a result of changed evaporator water inlet temperature from 13 to 22 o C for constant water volume flow rate The higher rate of increase in unit capacity (12%) and the higher rate of decrease in consumption (11%) leads to the higher rate of increase in PER as showed also in Figure (2B) Reference Number: W9-93

5 The Online Journal on Power and Energy Engineering (OJPEE) Vol (1) No (3) IV-b Effect of Evaporator Water Volume Flow Rate The effect of evaporator water flow rates on the performance characteristics of GEHP is shown in Figure (2) Figure (2A) shows the variations of the compressor power and heat loads with the evaporator water flow mass rate while variations of (PER) versus evaporator water mass flow rate are presented in Figure (2B) Clearly, the evaporation temperature increases as the evaporator flow rate increases So, unit capacity increases with (22%) as evaporator volume mass flow varied from 27 to 37m 3 /h At higher values of evaporator water inlet temperature, compressor power decreases (12%) while it remains constant at the lower ranges As a result of increasing evaporator water volume flow rate, engine consumption is decreased by 22% As evaporator volume flow rate changed from 27 to 37m 3 /h, primary energy ratio (PER) increased with (53%) This is mainly due to the rate of increase in unit capacity and the rate of decrease in engine consumption IV-c Effect of Ambient Air Temperature Figures (3A) and (3B) show the variation of performance characteristics of GEHP related to the ambient air temperature The performance of the heat pump and engine are affected by ambient temperature As the ambient temperature raising from 218 to 277 o C, all of unit capacity, compressor power and consumption increased by 23%, 2% and 15% respectively Since rate of increase in consumption is higher than that in unit capacity, PER decreases as shown in Figure (3B) V CONCLUSIONS The objective of the present work is to estimate the performance characteristics of the engine heat pump working with R4A under various operating conditions All the experimental runs carried out in cooling mode without engine heat recovery and at constant engine speed (175rpm±1%) Based on the experimental results, the following conclusions can be drawn: - Evaporator water inlet temperature has the highest influence on the primary energy ratio of the engine heat pump - Primary energy ratio increased by 262% as evaporator water inlet temperature increases from 12 o C to 22 o C - Higher evaporator water volume flow rate yields lower consumption and higher unit capacity - Ambient air temperature has a significant effect on both coefficient of performance of the heat pump Acknowledgment The Authors are grateful for the installation of testing plant provided by Wärmetechnik Quedlinburg (WTQ) GmbH The financial support of the Egyptian government for the PhD of Mr Elgendy is gratefully acknowledged REFERENCES [1] H Laue, Renewable Energy, Springer Berlin Heidelberg, 6, pp [2] M E Jonsson and E Granryd, Multipurpose heat pump for domestic applications, IIF-IIR- Commission E2 & B2- Linz, Austria, 1997, [3] J M Calm, Heat pumps in USA, Int J Refrigeration, 1987, :19 6 [4] W Wongsuwan, S Kumar, P Neveu, FA Meunier, review of chemical heat pump technology and applications, Appl Thermal Eng, 1, 21: [5] A Hepbasli and L Ozgener, Development of geothermal energy utilization in Turkey: a review, Renewable Sustainable Energy Rev, 4, 8: [6] O Ozgener and A Hepbasli, A review on the energy and exergy analysis of solar assisted heat pump systems, Renewable Sustainable Energy Rev, 7, 11: [7] Z Lian, S Park, W Huang, Y Baik and Y Yao, Conception of combination of -engine-driven heat pump and water-loop heat pump system, Int J Refrigeration 5, 28:8 9 [8] A Hepbasli, Z Erbay, F Icier, N Colak and E Hancioglu, A review of engine driven heat pumps (GEHPs) for residential and industrial applications, Renew Sustain Energy Rev (9), pp85-99 [9] S Li, W Zhang, R Zhang, D Lv, Z Huang, Cascade fuzzy rol for engine driven heat pump, Energy Convers Manage 5, 46: [] Z Yang, Z Haibo, F Zheng, Modeling and dynamic rol simulation of unitary engine heat pump, Energy Conversion and Management, 7, 48: [11] Y Shin, H Yang, CS Tae, CY Jang, S Cho, Dynamics modeling of a engine-driven heat pump in cooling mode, J Mech Sci Technol 6, : [12] RR Zhang, XS Lu, SZ Li, AZ Gu, Analysis of energy consumption and running cost of enginedriven heat pump, J Harbin Inst Technol, 6, 38: [13] SA Klein and FL Alvarado, EES-Engineering Equation Solver, F-Chart Software, Wisconsin, USA, 9 [14] K Taira, Development of a 25-RT multiple-unit engine heat pump, ASHRAE Trans, 98, [15] JT Harmish, DW Procknow and FE Jakob, Residential heat pump design and development, Proc Conf Cogeneration and Energy Conservation for the 9's, Mesa, USA, 1991, pp 111 [16] F Stiemle, Development in air-conditioning, Proceeding of IIF-IIR conference (Commissions B1, B2, E1 and E2), BUCHAREST, ROMANIA, 1996, Reference Number: W9-94