ENERGY PERFORMANCE OF DIMMABLE FLUORESCENT LAMPS IN THE INTEGRATED DAYLIGHTINT CONTROL SYSTEM IN COLD CLIMATE Xu L.*, Kim W.U.*, Kim Y.** *
Graduate School of Mechanical Engineering, Korea University, Seoul 136-713, Korea **
Department of Mechanical Engineering, Korea University, Seoul 136-713, Korea
[email protected]
ABSTRACT The objective of this study is to analyze overall energy performance of dimmable fluorescent lamps in the integrated daylighting control system in cold climate. Automated operation of a venetian blind in conjunction with a dimmable electric lighting system could lead to minimize energy consumption for lighting while maintaining comfortable visual environment. It also tends to minimize the cooling load in hot climate and the overall energy consumption of the office decreases. However, in cold climate, as the lamps dim, the lighting system generates lower heat to the office space, resulting in increasing the heating load of the office. The integrated daylighting control system that consisted of a motorized venetian blind and dimmable fluorescent lights was demonstrated in an office located in Seoul, Korea. The energy performance of dimmable fluorescent lamps was investigated.
1. INTRODUCTION The global warming due to the use of fossil fuel has been accelerated rapidly. The Korean government has been made a lot of efforts to reduce the emission of carbon dioxide. In Seoul, approximately 40% of the energy was used in the building sector (Bang, 2009). The retrofit of the energy facilities or redesign of the buildings has been considered to reduce the energy consumption in the building sector. In general commercial buildings, 40% of the total energy consumption in the buildings was used for HVAC systems and 20%∼30% was used for artificial lighting (EIA, 2005). Electric lighting is the largest single-end energy use in office buildings. Several methods to reduce artificial lighting energy, such as efficient ballast, dimming control of lighting devices, have been tried. These methods showed higher net present value and internal return rate than HVAC facilities (Doukas et al., 2009), so the lighting retrofit was preferred to other options. The use of automatically controlled venetian blind to block the direct daylight beam penetration, together with the use of dimmable electronic ballasts could lead to minimize energy consumption for lighting and cooling while maintaining comfortable visual environment. However, in cold climate, as the lamps dim, the lighting system generates lower heat to the office space. Many studies focused on visual performance of the integrated daylighting control system and minimization of the lighting energy (Chaiwiwatworakul et al., 2009; Park and Athienitis, 2005). There were only a few studies which focused on the influence of dimmable fluorescent lamps on the heating load. Therefore, it is necessary to investigate the overall energy performance of the dimmable fluorescent lamps. The integrated daylighting control system that consisted of a motorized venetian blind and dimmable fluorescent lights was demonstrated in an office located in Seoul, Korea. While the venetian blind was controlled to block the direct daylight beam and all lighting fixtures in the office were turned off, daylight illuminance of a day was obtained. Based on this daylight illuminance distribution, light dimming control was simulated to maintain the design work-plane illuminance level. The energy performance of the dimmable fluorescent lamp was evaluated based on the simulation results.
Guard upper-zone floor plenum
C Ceiling plenum
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Figure 1. Schematic of the test office. Window
tan α ) cos γ α : solar altitude angle γ : surface solar azimuth d = tan −1 (
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Figure 2. The profile angle (d), and the blind tilt angle (β).
2. THE INTEGRATED DAYLIGHTING CONTROL SYSTEM 2.1. Configuration of test office A test building was located in Seoul, Korea (latitude 37.58˚N and longitude127.03˚E). There was a private office on the first floor of the test building (seven stories) which was operated for daylighting control under real weather conditions. The interior dimension of the office was width 3.3 m, depth 6.4 m, and height 2.7 m. The office had cream-white painted walls and the windowed facade of the building faced southeast. In the office, there was a glazed window that measures 3.1 m in width and 1.9 m in height, the base of which was 0.8 m above the floor. The test office was conditioned by an air handling unit. 2.2. Illuminance measurement and data acquisition system Figure 1 shows the positions of sensors and equipments installed in the office. Two illuminance transmitters were placed 2 m (31% of room depth) and 3.5 m (55% of room depth) from the window respectively to measure illuminance on the workplane (0.7 m above the floor). The LabVIEW and NI USB 6216 were used for data acquisition and control of blind and dimmable ballasts. All measured data from the sensors and control signals were recorded at 1 minute interval. 2.3. Automated blind system As shown in Figure 2, the blind was mounted in the interior space behind the existing glazed window of the office and d is the profile angle which is the projection of the solar altitude angle on a vertical plane perpendicular to the window, and β is the blind tilt angle. The blind used in the study comprised 0.05 m wide slats of white aluminum sheets. The distance between two adjacent slats was 0.048 m. The angle of the slats of the blind could be adjusted by the LabVIEW through the use of the SOMFY AC motor LS404. The rotation range of the tilt angle was 0 degrees (closed completely) to 180 degrees (closed completely) for 9 steps.
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Figure 3. Electric light correlation of the A lighting fixture. 500
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Figure 4. Electric light correlation of the B lighting fixture. Solar altitude angle and solar azimuth angle were calculated by the correlations proposed by the Global Monitoring Division of the Earth System Research Laboratory (2010).The solar profile angle was used to determine blind tilt angle to allow maximum outside view while blocking direct daylight beam penetration. Due to the separation of the blind slats, the blind slats remained at fully open position when the solar profile angle was greater than 43.8˚. 2.4. Lighting system There were three sets of recessed lighting fixtures, which had three T8 32 W fluorescent lamps, respectively. The dimensions of the lighting fixture were 0.6 m width and 1.2 m length. The analog dimmable electronic ballasts were installed into two lighting fixtures which were placed 1.3 m (A, 20% of room depth) and 3.1 m (B, 48% of the room depth) from the window, respectively. The general electronic ballast was installed in the lighting fixture which was placed 4.9 m (C, 76% of the room depth) from the window. The purpose of the light-dimming control was to complement the target design illuminance level with electric light, hence, to maximize daylight use and save energy. It is necessary to know the workplane illuminance level at a given control signal of the dimmable ballast. The analog dimmable ballast was controlled by 0~10 V signal that could adjust the fluorescent lamp from the darkest illuminable condition to the brightest illuminable condition. To obtain electric light correlation between the illuminance of workplane sensors and voltage
control signal, experiments were conducted at night. The control signals between 0 and 10 V were sent to each dimmable lighting fixture to simulate variable conditions. When only the A lighting fixture was turned on, as the voltage control signal varied from 10 V to 0 V, the illuminance of light meters seemed to vary as an quartic curve (Figure 3). However, in the previous research, the workplane illuminance of electric light was treated as a linear function of the dimmable ballast’s voltage control signal (Verderver et al., 1989; Park and Athienitis, 2005). In this study, light dimming control simulations based on the linear correlations and the quartic correlations were performed, respectively, to evaluate the difference of the energy performance of dimmable lamps. Therefore, a linear correlation and a quartic correlation between the control signal VA and the workplane illuminance (EAL1 , EAL2 ) were obtained as follow for each illuminance transmitter (Figure 3). Coefficients of determination (R2) for eqs. (1)-(4) were 0.9185, 0.995, 0.9192, and 0.9996, respectively. EAL1 = 53.087 ∗ VA − 87.86
(1)
EAL2 = 28.012 ∗ VA − 47.01
(3)
EAL1 = −0.2743 ∗ VA 4 + 4.4587 ∗ VA 3 − 14.49 ∗ VA 2 + 17.653 ∗ VA + 3.9868
(2)
EAL2 = −0.139 ∗ VA 4 + 2.1984 ∗ VA 3 − 6.3846 ∗ VA 2 + 6.0759 ∗ VA + 2.7684
(4)
EBL1 = 38.227 ∗ VB − 59.972
(5)
EBL2 = 39.897 ∗ VB − 63.253
(7)
When only the B lighting fixture was turned on, a linear correlation and a quartic correlation between the control signal VB and the workplane illuminance (EBL1 , EBL2) were obtained for each illuminance transmitter (Figure 4). The quartic correlations were more exact to express the characteristic of the dimmable fluorescent lamp. Coefficients of determination (R2) for eqs. (5)-(8) were 0.9244, 0.9989, 0.9257 and 0.9991, respectively.
E BL1 = −0.2111 ∗ VB 4 + 3.352 ∗ VB 3 − 10.702 ∗ VB 2 + 13.73 ∗ VB + 2.3543 EBL2 = −0.2167 ∗ VB 4 + 3.4293 ∗ VB 3 − 10.794 ∗ VB 2 + 13.855 ∗ VB + 1.5909
(6)
(8)
When only the C lighting fixture, which was equipped with general electronic ballast, was turned on, the illuminance of the L1, L2 were 232.1 lx (ECL1) and 32.2 lx (ECL2), respectively.
2.5. Energy performance of the dimmable fluorescent lamp The electric energy consumption of lighting fixtures was measured by a power meter. As the voltage control signal varied from 10 V to 0 V, the electric energy consumption of the dimmable lighting fixture (A and B) decreased as an s-curve (Figure 5). In most situations, 69% of the electric lighting energy converted to the lighting heat gain of the office space and the left converted to the lighting heat gain of the ceiling plenum (Chantrasrisalai and Fisher, 2006). Therefore, the lighting heat gain of the office space would decrease. The heating load of the office increased because the lower lighting heat gain as voltage signal varied from 10 V to 0 V. Total energy consumption of a lighting tube was defined as the sum of the electric energy consumption and the increase of the heating load. The correlation between the voltage control signal and total energy consumption (ETOT) of the dimmable lighting fixture was developed based on the Figure 5.
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Figure 5. Energy performance of the dimmable fluorescent lamp. 450 400
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Figure 6. Daylight illuminance of the workplane light meters (19/03/2012). ETOT = 0.0004912892 ∗ V 6 − 0.01467906 ∗ V 5 + 0.1523067 ∗ V 4 − 0.6794844 ∗ V 3 + 1.720067 ∗ V 2 − 1.351748 ∗ V + 81.60708
3. SIMULATION RUSULTS AND DISCUSSION
(9)
The venetian blind was controlled as the way described in the automated blind system, while the lighting fixtures were all turned off. Figure 6 shows daylight illuminance of a day. Because the position of the illuminance transmitter L1 was closer to the window than the illuminance transmitter L2, the illuminance of L1 was higher than that of L2. There was a tall building in front of the test office, and the test office was within the shadow of the tall building from 9:40 to 10:40. Therefore, at this period, daylight illuminance of the test office was relatively small. Based on the distribution of daylight illuminance, lighting dimming control was simulated to maintain 500 lx of designed work-plane illuminance level (ESP). The difference between the designed work-plane illuminance and daylight contribution to the work-plane illuminance was the electric light level to be provided. Since the illuminance of the two illuminance transmitters should be maintained at the designed work-plane illuminance, the voltage control signals (VA and VB) could be determined as the solutions of the following simultaneous equations.
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Figure 7. Simulation result of the linear correlation. ESP = EAL1 + EBL1 + ECL1 + EDL1
ESP = EAL2 + EBL2 + ECL2 + EDL2
Where DL1= daylight illuminance of L1, and DL2= daylight illuminance of L2.
(10)
(11)
Because of the geometry characteristic of the office, sometimes the solutions of these simultaneous equations would be not within 0 V and 10 V. Therefore, at that time, voltage control signal of the A lighting fixture was set as 0 V, and the new voltage control signal of the B lighting fixture (VB) could be calculated by substituting it into eq. (11). At this situation, the illuminance of L2 maintained designed work-plane illuminance level. The illuminance of L1 would be a little bigger than designed work-plane illuminance level. 3.1. Simulation results with the linear correlation Substituting linear correlations of eqs. (1), (3), (5) and (7) into simultaneous eqs. (10) and (11), the voltage control signals (VA and VB) were obtained between 0 V and 10 V. Substituting them into eq. (9), total energy consumption of the lighting system for a whole day was obtained as Curve 1 in Figure 7. If the A and B lighting fixtures were all equipped with general electronic ballasts, the total energy consumption of the A and B would maintain at 203.4 W. Therefore, the difference between 203.4 W and Curve 1 was the energy that could be saved by adopting the integrated daylighting control system. Additional simulations with the voltage control signal of the A lighting fixture (VA) maintained above a critical voltage signal were performed to find the critical voltage that can lead to minimize the total energy consumption of the lighting system. At this situation, VA which was below the critical voltage was changed to the critical voltage, and the new voltage control signal (VB,NEW) could be calculated by substituting the critical voltage into the eq.(11) to maintain the designed work-plane illuminance level (500lx) of L2. As a result, the illuminance of L1 would be a little bigger than the designed work-plane illuminance level. It was found that when the critical voltage signal was set as 3.34 V, the total energy consumption of the system was reduced at most by 2.37% in which VA was controlled between 0 V and 10 V. The reasons were as follow. As VA changed from 0 V to 3.34 V, EAL2 increased by 93.56lx, so EBL2 should decrease by 93.56 lx to maintain the designed work-plane illuminance of the L2 (500 lx). As a result, VB which was above 4 V
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Figure 8. Simulation result of the quartic correlation. would decrease by 2.34 V. In figure 5, as VA changed from 0 V to 3.34 V, the total energy consumption increase of the A lighting fixture was small. As VB which was above 4 V decreased by 2.34 V, the total energy consumption decrease of the B lighting fixture was higher than the total energy consumption increase of the A lighting fixture. Therefore, the total energy consumption of the lighting system would decrease. 3.2. Simulation results with the quartic correlation Substituting the quartic correlations of eqs. (2), (4), (6) and (8) into simultaneous eqs. (10) and (11), the control voltage signals (VA and VB) were obtained. The total energy consumption of the lighting system was obtained as Curve 2 in Figure 8. Comparing to the no-dimming system, the total energy consumption of the lighting system for the whole day decreased by 11.1%. When the A and B lighting fixtures were equipped with general electronic ballasts, the total energy consumption of the A and B would maintain at 203.4 W as the line 3 in Figure 8. Therefore, the difference between 203.4 W and Curve 2 was the energy that could be saved by adopting the integrated daylighting control system. Like in the linear correlation simulation, additional simulations with the voltage control signal of the A lighting fixture (VA) maintained above a critical voltage signal were performed to find the critical voltage that could lead to minimize the total energy consumption of the lighting system. When the critical voltage signal was also set as 3.34 V just like in the linear correlation simulation, as the VA changed from 0 V to 3.34 V, EAL2 only increased by 13.7lx and EBL2 should decrease by 13.7 lx to maintain the designed work-plane illuminance of the L2 (500 lx). However, the decrease of VB was much smaller than that in the linear correlation simulation. Therefore, as VA changed from 0 V to 3.34 V, the total energy consumption increase of the A lighting fixture was higher than the total energy consumption decrease of the B lighting fixture. Therefore, the total energy consumption of the lighting system would increase. So, other critical voltage simulations should be performed. It was found that when the critical voltage signal was set as 0.47 V, the total energy consumption of the system could be reduced at most by 0.02% in which VA was controlled between 0 V and 10 V.
4. CONCLUSIONS In this study, an energy performance of dimmable fluorescent lamps in the integrated daylighting control system in cold climate was investigated. Based on the daylight illuminance, the light dimming control was simulated to maintain design illuminance with the work-plane illuminance was treated as the linear function
or the quartic function of dimmable ballast’s control voltage. Because the quartic correlations were more exact to express the characteristic of the dimmable fluorescent lamp, the quartic correlation simulation would be more reliable to maintain the design illuminance. Additional simulations with the voltage control signal of the A lighting fixture (VA) maintained above a critical voltage signal were performed to minimize the total energy consumption of the lighting system. In simulations with the linear correlation, the total energy consumption of the dimmable lamps for the whole day decreased only 2.37%, when voltage control signal of the A lighting fixture was controlled above the critical point (3.34 V). In simulations with the quartic correlation, the total energy consumption of the dimmable lamps for the whole day decreased only 0.02%, when voltage control signal of the A lighting fixture was controlled above the critical point (0.47 V). Therefore, when designing the integrated daylighting control system, the critical point control could be neglected and the voltage control signal of lighting fixture could be adjusted between 0 V and 10 V.
5. ACKNOWLEDGEMENTS This research was supported by Seoul R&BD Program (ST090845).
6. REFERENCES Bang K. 2009, Yearbook of regional energy statistics, Korea Energy Economics Institute. EIA. 2005, Commercial building energy consumption survey: Consumption and expenditure table. Online. Available: http:www.eia.doe.gov/emeu/cbecs/Washington Doukas H, Nychtis C, Psarras J. 2009, Assessing energy-saving measures in building through an intelligent decision support model, Building and Environment. 44(2): 290-298. Chaiwiwatworakul P, Chirarattananon S, Rakkwamsuk P. 2009, Application of automated blind for daylighting in tropical region, Energy Conversion and Management. 50(2): 2927-2943. Park K, Athienitis A. 2005, Development and testing of an integrated daylighting control system, ASHRAE Transaction, 111(PART 1): 218-226. Global Monitoring Division of the Earth System Research Laboratory. 2010, NOAA Solar calculator. Online. Available: http://www.esrl.noaa.gov/gmd/grad/solcalc/ Verderver R, Rubinstein F, Ward G. 1989, Photoelectric control of daylight-following lighting system, LBL 24872: 3-5. Chantrasrisalai C, Fisher D. 2006, Lighting heat gain parameters: Experimental result, HVAC&R Research. 13(2): RP-1282.
