REDUCTIONS IN ENERGY CONSUMPTION AND CO 2 EMISSIONS

Transcription

1 REDUCTIONS IN ENERGY CONSUMPTION AND CO EMISSIONS FOR GREENHOUSES HEATED WITH HEAT PUMPS Y. Tong, T. Kozai, N. Nihioka, K. Ohyama ABSTRACT. In the greenhoue indutry, it i eential to ue energy efficiently by operating economically feaible heating ytem intead of the traditional combution-baed heating ytem. In our experiment, a heating ytem with houehold heat pump wa operated at nighttime. Another heating ytem with a keroene heater wa ued a a comparion. We compared the energy conumption, energy utilization efficiency, CO emiion and energy cot of two heating ytem. When the inide air temperature wa maintained at around 16 C while the outide air temperature ranged between -5 C and 6 C, the reult howed that 1) the energy conumption wa 5% to 65% lower in the greenhoue with heat pump (G hp ) when compared to the greenhoue with a keroene heater (G kh ), ) the energy utilization efficiency of the heat pump wa 1.3 to.6 time higher than that of the keroene heater, 3) CO emiion were reduced by 56% to 79% in the G hp when compared to the G kh, and 4) energy cot wa lower in the G hp when compared to the G kh. Thee reult indicate that the heat pump ytem i found more efficient than the keroene heating ytem and economically feaible for greenhoue heating. Keyword. Coefficient of performance, Energy utilization efficiency, Renewable energy. There ha been much reearch on uing energy efficiently ince the firt oil crii in the early 197 when inufficient oil upply caued a ignificant increae in energy price (Byun et al., 6; Bakker et al., 8). Energy cot peaked again in 8 and in 11 (Petroleum Aociation of Japan, 11). Furthermore, the global effort to reduce CO emiion ha led to innovative technologie to improve energy utilization efficiency (Bakker, 9). It i eential for the greenhoue indutry to reduce energy conumption and CO emiion ince foil fuel energy i till ued for heating during the cold winter eaon, and energy account for a ubtantial fraction of total production cot (Diez et al., 9; Aye et al., 1). There are two main way of reducing energy conumption and CO emiion in greenhoue. One i to Submitted for review in June 11 a manucript number SE 97; approved for publication by the Structure & Environment Diviion of ASABE in January 1. The author are Yuxin Tong, Aitant Profeor, (1) Intitute of Environment and Sutainable Development in Agriculture, Chinee Academy of Agricultural Science, Beijing 181, China and () Key Lab of Energy Conervation and Water Treatment of Agricutural Structure, Minitry of Agriculture, Beijing 181, China; (3) Center for Environment, Health and Field Science, Chiba Univerity, Kahiwa-noha 6--1, Kahiwa, Chiba 77-88, Japan; Toyoki Kozai, ASABE Member, Profeor Emeritu; Center for Environment, Health and Field Science, Chiba Univerity, Kahiwa-no-ha 6--1, Kahiwa, Chiba 77-88, Japan; Naoko Nihioka, Staff Member, National Intitute of Advance Indutrial Science and Technology (AIST), Umezono, Tukuba, Ibaraki, Japan; and Katumi Ohyama, ASABE Member, Aociate Profeor, Center for Environment, Health and Field Science, Chiba Univerity, Kahiwa-no-ha 6--1, Kahiwa, Chiba 77-88, Japan. Correponding author: Yuxin Tong, (1) Intitute of Environment and Sutainable Development in Agriculture, Chinee Academy of Agricultural Science, Beijing 181, China; () Key Lab of Energy Conervation and Water Treatment of Agricultural Structure, Minitry of Agriculture, Beijing 181, China ; phone: ; yxtong7@hotmail.com. deign energy-aving greenhoue with le energy demand and/or le energy loe. Another way i to improve the energy utilization efficiency and/or ue renewable energy ource intead of foil fuel that are directly related to CO emiion. One method of improving energy utilization efficiency and employing renewable energy ource i to ue electricity-driven heat pump intead of traditional combution-baed heating ytem (Sami and Tulej, 1994; Hardin et al., 8). Heat pump are widely recognized a highly energy efficient ytem for many application uch a heating, cooling, and dehumidification (Ozgener and Hepbali, 7). Heat pump perform heating by moving heat energy efficiently from one heat energy ource to another (Kulcar et al., 8). Energy ource can be renewable energy ource including air, ground water, ground oil, and olar energy, which are clean, inexpenive, ever preent in large quantitie, and eay to acce by uing heat pump technologie (Chen and Lan, 9). Therefore, heat pump technologie are economical, utainable, and without producing harmful emiion on ite. The heat pump technologie are being improved every year. Coefficient of performance (COP), indicating how much heat energy i gained or removed by the heat pump compared with that conumed by their compreor, i an important performance index of heat pump. In Japan, the COP for heating of houehold heat pump increaed from around 4.3 in 1998 to 7.1 in 11 under the Japanee indutrial tandard condition of C indoor and 7 C outdoor, reported by Mitubihi Company (11). The COP i expected to increae to around 8 a heat pump technology further improve (Kozai, 9). Thu, great potential reduction in energy conumption and CO emiion exit when employing the recently developed heat pump for heating. Applied Engineering in Agriculture Vol. 8(3): American Society of Agricultural and Biological Engineer ISSN

2 In the recent year, there are many report about greenhoue heating by uing heat pump, uch a ground-ource heat pump (e.g., Benli and Durmu, 9; Cai et al., 1; Benli, 11), olar aited ground-ource heat pump (e.g., Ozgener and Hepbali, 5; Ozgener, 1), and airource heat pump (e.g., Aye et al., 1; Tong et al., 1). However, few tudie have been publihed on the economic analyi and potential reduction in energy conumption and CO emiion when uing houehold heat pump with high COP for greenhoue heating. Therefore, the objective of our experiment were to: 1) analyze the energy conumption and the energy utilization efficiency of the heat pump and a keroene heater, ) analyze the CO emiion of the heat pump and the keroene heater, and 3) invetigate the energy cot for the heat pump and the keroene heater. MATERIALS AND METHODS EXPERIMENT SETUP Two North-South oriented, ingle-pan, addle-roof greenhoue built of teel pipe and located in Kahiwa, Japan (35 87 N and E) were ued during thi experiment. Both greenhoue were 1 m long, 7. m wide and 3.7 m high. The roof and ide wall were covered with polyethylene terephthalate (PET) and polyvinyl chloride (PVC) film, repectively. The internal thermal creen of the roof and ide wall were made of polyeter-woven cloth and polyolefin film, repectively. The thermal creen of the ide wall were cloed during the experiment, while thoe of the roof were opened during the daytime (8:- 17:) and cloed during the nighttime (17:-8:) by uing a timing device. Ten air-to-air heat pump (MSZ-SV88-W, Mitubihi, Co., Tokyo, Japan; heating capacity:.8 kw each; COP: 5.4, for heating at the Japanee Indutrial Standard condition of C indoor and 7 C outdoor), were intalled along the wall of one greenhoue (G hp ). The internal unit of the heat pump were intalled on upporting pole at the height of 1.5 m above the ground, while the external unit were intalled on upporting pole of.5 m above the ground and near to their internal coil. In another greenhoue (G kh ), one keroene heater (KA-5, Nepon, Co., Tokyo, Japan; heating capacity: 3.3 kw), which ha been widely ued for greenhoue heating in Japan, wa intalled at the northern end, and upplied hot air through two platic duct laid on the ground along both ide wall. The experiment wa conducted from 1 January to 1 March 9 during the nighttime (18:-7:) and the inide air temperature wa maintained at 16 C in both greenhoue. Tomato (Solanum lycopericum cv. Momotaro York) plant were grown at a denity of. plant m - during the experiment. In thi experiment, the tomato plant and it culture condition were identical to thoe decribed by Tong et al. (1). MEASUREMENTS The air temperature and relative humidity inide the greenhoue were meaured by enor (SHT-71, Senirion AG, Switzerland; preciion: temperature ±.4 C, relative humidity ±3%). The outide air temperature (T out ) and relative humidity (MT-6, EKO Intrument, Co., Ltd., Tokyo, Japan; preciion: temperature ±.3 C, relative humidity ±%) were recorded in a mall weather tation 3 m from the experimental greenhoue. The electric-energy conumption of each heat pump (W hp ) and the keroene heater (W kh ) were meaured by wattmeter (Clamp on Power Hiteter 3169/3168, Hioki, Co., Nagano, Japan; reolution:.1wh). The keroene conumption of the keroene heater (V k ) wa meaured by weighting the oil tank continuouly during the experiment uing an electric balance (LDS-6H, Shimadzu, Co., Tokyo, Japan; reolution:.1 kg). The heat tranfer at the ground urface in the G hp and G kh were meaured at two point with heat flux plate (MF-18M, EKO Intrument, Co., Ltd., Tokyo, Japan; reolution:.1 mw) in each greenhoue. All the data were recorded every minute. SENSOR CALIBRATIONS The air temperature and relative humidity enor were calibrated by uing Amann apiration pychrometer (Y-511, Yohino, Co., Tokyo, Japan) at air temperature of -1 C, C, 1 C, C. The wattmeter were calibrated by uing a tandard calibration unit (Clamp on Power Hiteter 9796, Hioki, Co., Nagano, Japan). The electric balance wa calibrated by uing it tandard weight (6 kg). The heat flux plate were calibrated by the tandard heat flux plate (MF-18M, EKO Intrument, Co., Ltd., Tokyo, Japan). PERFORMANCE CALCULATIONS Energy Conumption The hourly energy conumption of both greenhoue wa etimated by: hp = W hp λe (1) kh = W kh λ e + V k λ k () where hp and kh = the hourly energy conumed by the heat pump and the keroene heater, repectively, (MJ); λ k = the heat energy generation coefficient of keroene, 36.7 MJ L -1 (Kozai, 9); V k = the hourly keroene conumed by the keroene heater (L); W hp and W kh = the hourly electric-energy conumed by the heat pump and the keroene heater, repectively, (kwh); λ e = the energy conumption rate of the power generation ytem of Tokyo Electric Power Co. Inc., 9.97 MJ kwh -1 (Minitry of Environment Japan, 7). Energy Utilization Efficiency The hourly heat energy generated in the G hp and G kh ( h-hp and h-kh, repectively) wa etimated by the method decribed by Tong et al. (1). The energy utilization efficiency (EUE) of the heat pump and the keroene heater (EUE hp and EUE kh, repectively) wa calculated by: 4 APPLIED ENGINEERING IN AGRICULTURE

3 EUE EUE hp kh = = h hp h h kh CO Emiion The hourly amount of CO emiion of both greenhoue wa etimated by: kh (3) (4) M hp = W hp m e (5) M kh = W kh m e + V k m k (6) where M hp and M kh = the hourly amount of CO emiion generated in the G hp and G kh, repectively, (kg); m e = the CO generation rate of electricity,.45 kg kwh -1 (The Tokyo Electric Power Co., Inc., 7); m k = the CO generation rate of keroene,.49 kg L -1 (Minitry of Environment Japan, 7). The Energy Conumption and CO Emiion Under Different Cop According to the COP value reported by Tong et al., (1), the average hourly COP of 3, 4, 5, or 6 were aumed under the ame air temperature condition a the preent experiment. Since the COP i defined a the ratio of the heat energy generated in the greenhoue ( h-hp ) to the electric-energy conumed by the compreor of the heat pump, the W hp can be calculated by dividing the h-hp by the COP. The hourly energy conumption and CO emiion under different COP of 3, 5, or 6 were calculated by uing equation 1 and 5, repectively. The Cot and the Aociated CO Emiion per Unit Heat Energy Generated The cot and the aociated CO emiion per unit heat energy generated were calculated by: P P = λ M m = λ where P = the cot per unit heat energy generated ($ MJ -1 ); p = energy cot ($ unit -1 ); λ = heat energy generation coefficient per unit energy ource [electricity, 3.6 MJ kwh -1 ; natural ga, 41.1MJ (Nm 3 ) -1 (Kozai, 9)]; M = aociated CO emiion per unit heat energy generated (kg MJ -1 ); m = CO generation rate per unit energy ource (kg unit -1 ). (7) (8) RESULTS AND DISCUSSION THE ENERGY CONSUMPTION AND ENERGY UTILIZATION EFFICIENCY OF TWO HEATING SYSTEMS AS AFFECTED BY OUTSIDE AIR CONDITIONS The hourly energy conumption in both G hp and G kh decreaed with increaing outide air temperature, when the inide air temperature wa maintained at around 16 C (fig. 1). When the outide air temperature ranged between -5 and 6ºC, the hourly energy conumption per floor area in the G hp wa in the range of.-.56 MJ m -, while that in the G kh wa in the range of MJ m -. The energy conumption wa reduced by 5-65% in the G hp compared with the G kh. Thi reduction in energy conumption in both G hp and G kh increaed with increaing outide air temperature. The reduction wa higher than the previouly reported energy aving of 4% by comparing the ground-ource heat pump with coal-fired heating ytem (Cai et al., 1) and 16% by comparing the air-to-water heat pump with LPG (liquefied petroleum ga)-fired heating ytem (Aye et al., 1). The energy conumption of the heat pump and keroene heater i related to the difference between inide and outide greenhoue air temperature and/or the heating load of the greenhoue. Energy conumption increae with increaing inide air temperature et point. To achieve a particular inide air temperature, the heating load increae with decreaing outide air temperature. Accordingly, the energy conumption increaed a outide air temperature decreaed, epecially in the G hp during defrot mode (Hardin et al., 8). Figure 1 how cattered data for energy conumption in both G hp and G kh. Thi wa becaue the heating load of the greenhoue wa alo affected by the outide wind peed, condenation on the cover and/or cloud. A trong outide wind peed increaed the heat energy tranmiion through the cover material and heat tranfer by ventilation (Bailey, 1994). Condenation on the cover reduced the tranmittance and increaed the emiivity of long-wave radiation (Walker and Walton, 1971; Pieter et al., 1995). The heat lo by long-wave radiation from the cover material wa lower on a cloudy day compared to a clear day (Nijken et al., 1984). Larger catter data of energy conumption were oberved in the G kh than that in the G hp probably due to the difference in the control method of air temperature. The heat pump employed proportionalintegral-derivative (PID) control, while the keroene heater employed a imple on/off control that can reult in larger fluctuation of heat load a well a air temperature. The larger fluctuation of heat load may lead to the larger variation of energy conumption in the G kh. The energy conumption of the heat pump i related to their COP which i mainly affected by their working condition and the heat pump technology. To achieve a certain heating requirement, the energy conumption can be reduced by uing heat pump with high COP, epecially under a high outide air temperature and/or a low inide et point temperature (fig. ). The maximum COP can be obtained if the ratio of the heating load of the greenhoue to the total heating capacity of the heat pump i in a range of.6 to.8 (Kozai et al., 9). When the ratio i lower than 8(3):

4 Hourly energy conumption (MJ m - ) COP :3 heater COP :4 COP :5 COP :6-6 T in : 16.8±.4 (ºC) Figure. Hourly energy conumption affected by outide air temperature (T out ) with different COP (coefficient of performance) of the heat pump in the greenhoue with heat pump and the greenhoue with a keroene heater. The olid line how the actual data of thi experiment and the dotted line how the imulated data. the above range, the increae in COP with increaing outide air temperature and/or decreaing inide et point temperature i lowed down by the decreaing heating load. Thu, the reduction in energy conumption of the greenhoue may decreae with decreaing heating load of the greenhoue. The energy utilization efficiency of the heat pump wa 1.3 to.6 time higher than that of the keroene heater (fig. 3). The energy utilization efficiency of the heat pump increaed with increaing COP, while that of the keroene heater wa almot contant. Thu, compared with combution-baed heating ytem (uch a keroene heater), technology improvement are making heat pump increaingly competitive in term of energy aving (Kozai, 9). CO EMISSIONS DUE TO OPERATION OF THE HEAT PUMPS AND THE KEROSENE HEATER AS AFFECTED BY OUTSIDE AIR CONDITIONS Similar to the trend of hourly energy conumption, the hourly CO emiion in both G hp and G kh decreaed with increaing outide air temperature (fig. 4). The hourly CO emiion per floor area in the G hp were in the range of 9.5 to 4 g m -, and in the G kh were in the range of 31 to 55 g m -. Thu, CO emiion were reduced by 56% to 79% in the G hp compared with the G kh. Thi reduction increaed with increaing outide air temperature. EUE T in : 16.8±.4 (ºC) EUE hp EUE kh Figure 3. The energy utilization efficiency of the heat pump and the keroene heater (EUE hp and EUE kh, repectively) affected by the outide air temperature (T out ). Each data point repreent the mean of the energy utilization efficiency with it tandard deviation. Hourly CO emiion (g m - ) y x x R =.66 = y x x R = Figure 4. Hourly CO emiion affected by the outide air temperature (T out ) in the greenhoue with heat pump (G hp ) and the greenhoue with a keroene heater (G kh ). Data collected on 7-11 January, January, 5-6 January, 8-9 February, 19- February, and 6-8 February, 9 are hown a example. Each data point repreent the hourly average. In the G hp, the heat pump were driven by electricity (no CO wa generated on ite), o the CO emiion depended on the following 1) The efficiency of the power generation ytem: the higher the efficiency of producing the ame amount of electricity, the lower the CO emiion, ) The energy ource employed in the power generation ytem: the higher the percentage of renewable energy ource employed, the lower the CO emiion. For example, CO emiion in Norway, where renewable ource uch a hydroelectric power are widely ued, are ignificantly lower than in other European countrie (Jenkin et al., 8; Mancarella and Chicco, 8). Similarly, France, where much power i generated by nuclear power plant, ha relatively low CO emiion (Mancarella and Chicco, 8; Omer, 8), and 3) The COP of the heat pump: the higher the COP, the lower the CO emiion (fig. 5). In the G kh, the heater with the energy utilization efficiency of.8 on average wa driven by keroene (CO wa generated on ite), o the CO emiion were directly related to keroene conumption. In figure 4, the pread of the data i due to the fluctuating energy conumption, a hown in figure 1. Hourly CO emiion (g m - ) T in : 16.8±.4 (ºC) heater COP:3 COP:4 COP:5 COP:6 Figure 5. Hourly CO emiion affected by outide air temperature (T out ) with different COP (coefficient of performance) of the heat pump in the greenhoue with heat pump and the greenhoue with a keroene heater. The olid line how the actual data of thi experiment and the dotted line how the imulated data. G kh = G hp T in : 16.8±.4 (ºC) APPLIED ENGINEERING IN AGRICULTURE

5 Table 1. Cot per unit heat energy of three different energy ource in different countrie. Cot per unit heat energy ($ MJ -1 ) Country Electricity [a] Natural ga [b] Keroene [c] Japan Taiwan [d] -- [d] Korea USA UK France Italy [a] IEA: International Energy Agency (1), Key World Energy Statitic. [b] OECD/IEA (9), Energy Price and Taxe 3rd uarter. [c] IEA: International Energy Agency (9), End-Ue Petroleum Product Price and Average Crude Oil Import Cot. [d] No available data. Baed on the above dicuion, one effective way to mitigate CO emiion in the greenhoue indutry i to ue heat pump with high COP and witch the energy ource from foil fuel to renewable energy ource. Heat pump will be a more attractive option to reduce CO emiion a technologie improve and a the power generation ytem i witched to renewable energy ource without CO emiion. ENERGY COSTS AND CO EMISSIONS BY USING THE ELECTRICITY-DRIVEN HEAT PUMPS AND COMBUSTION- BASED HEATING SYSTEMS WITH DIFFERENT COPS To etimate if one heating ytem i economically feaible and environmentally utainable or not, a real-world analyi i neceary. Therefore, the cot and CO emiion per unit heat energy were calculated by uing the combution-baed heating ytem (taking keroene/natural ga heater a example) and electricity-driven heat pump with different COP. Taking the cot per unit heat energy in Japan a an example (fig. 6 and table 1), for achieving the ame amount of heat energy in a greenhoue: (1) The electricity-driven heat pump would be cot-effective compared with the keroene heater, if their COP wa higher than around.. Thi reult indicate that the heat pump ued in the preent experiment are cot aving ince the COP of the heat pump wa alway higher than.9. () The electricity-driven heat pump would be cot effective compared with the natural ga heater, if their COP wa higher than around 3.9. (3) The cot i much lower when uing the natural ga heater compared to the keroene heater. The energy cot i relatively teady when uing the electricitydriven heat pump ince the price of the electricity remain more contant, while the price of foil fuel fluctuate over time. Figure 6 and table how that the CO emiion were lower uing the electricity-driven heat pump compared to the keroene/natural ga heater in the preent experiment ince the COP of the heat pump wa alway higher than.3. The CO emiion of the natural ga Energy cot ($ MJ -1 ) combution-baed heater heat pump COP Figure 6. The cot and CO emiion per unit heat energy by uing the combution-baed heating ytem (taking the keroene/natural ga heater a example) and electricity-driven heat pump with different COP. Baed on the data in table 1 and, three line were howed a example. heater are lower than that of the keroene heater when delivering the ame amount of heat energy. CONCLUSIONS When the air temperature inide the greenhoue wa maintained at around 16 C and the air temperature outide the greenhoue ranged between -5 C and 6 C, the experimental reult can be ummarized a follow: 1. The hourly energy conumption in the greenhoue with heat pump wa in the range of. to.56 MJ m -, while that in the greenhoue with a keroene heater wa in the range of.4 to.76 MJ m -.. The energy utilization efficiency of the heat pump wa 1.3 to.6 time higher than that of the keroene heater. 3. The hourly CO emiion in the greenhoue with heat pump were in the range of 9.5 to 4 g m -, while that in the greenhoue with the keroene heater wa in the range of 31 to 55 g m During the experiment, the heat pump ued for greenhoue heating were cot effective. Baed on thee reult, it wa concluded that heat pump are energy- and carbon-aving technology, and offer coniderable economic benefit. Moreover, heat pump will become more attractive for efficient multi-purpoe environmental control ytem a their technology improve. Since the greenhoue ued in thi experiment are relatively mall, thermal property in a commercial greenhoue with a larger floor area (e.g., >1 m ) i different from that in thi experiment. To adopt our evaluation method with repect to energy conumption and CO emiion in larger greenhoue, further experiment are needed CO emiion (kg MJ -1 ) Natural ga [b] Keroene [b] Table. CO emiion per unit heat energy from different energy ource. Energy Source France Japan EU-5 United State China Poland Electricity [a] CO emiion per unit heat energy (kg MJ -1 ) [a] Jenkin et al. (8). [b] Kozai (9). 8(3):

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ASAE 14(): NOMENCLATURE Abbreviation COP = coefficient of performance for heating G hp = greenhoue with heat pump G kh = greenhoue with keroene heater EUE = energy utilization efficiency Variable M = amount of CO emiion generated (kg) P = cot per unit heat energy generated ($ MJ -1 ) p = energy cot ($ unit -1 ) = hourly energy conumed or generated (MJ) T = air temperature ( C) W = electric-energy conumption (kwh) V = amount of keroene conumption (L) m = CO generation rate (kg unit -1 ) λ = energy generation coefficient per unit energy ource (MJ unit -1 ) Subcript e = electricity h = heat energy hp = heat pump in = inide greenhoue k = keroene kh = keroene heater out = outide greenhoue = energy ource 46 APPLIED ENGINEERING IN AGRICULTURE