An innovative benchmark testing to quantify saving by retrofitting geyser with Hotspot device Stephen Tangwe, Michael Simon and Sandiswa Qayi
Abstract— Electrical geysers (high -pressure geyser, solar geyser or combinational geyser) are inefficient but widely used in the production of sanitary hot water in the residential sector. The focus of the study is to demonstrate that by installing the hotspot device on the electric element in the geyser a potential demand and energy saving can be achieved by virtue of sanitary hot water production. In this study, a 150 L, 3kW high-pressure geyser without a hotspot device and a 150 L, 3kW high-pressure geyser with a hotspot device were setup in the horizontal configuration at the Fort Hare Institute Research Center at Alice. Controlled volumes of hot water (150 L, 100 L and 50 L) were drawn off from each of the geyser cylinders while the elements were switched off. After completion of the specific hot water withdrawal from both cylinders, the electric elements were simultaneously switched on, and both geysers were allowed to heat up the water to its set point temperature of 55oC. It should be alluded that for each scenario of the withdrawal, the experiments were conducted for one month and in three periods of a day (morning, afternoon and evening) which concurs with the period of hot water demand. A data acquisition system was designed and build to monitor the power and energy consumption of the both hot water systems. The preliminary results depicted that the average demand reduction due to installation of the hotspot device on an existing geyser was 0.14 kW and the average saving on the energy consumed over the three heating scenarios was 0.27/kWh, respectively. Key words— Hotspot device, Geysers, Retrofitting, data acquisition system, saving. 1
INTRODUCTION
Eskom is the primary supplier of electricity in South Africa; more than 90% is generated from coal. The global warming potential because of greenhouse gasses, primarily carbon dioxide, is 510 million tons of which 45% emanates from the generation of electricity from coal [1]. In South Africa, domestic electrical energy consumption is typically allocated according to the proportion of various residential energy utility (water heating, 43%, washing machine, 12.3%, stove, 10.2%, heater, 9.9%, fridge 8.6% and small appliances, 11.2%) [2]. It can be confirmed that the contribution of electrical energy consumption by sanitary hot water production in the domestic sector ranges between 40 to 60% depending on climatic conditions [9]. Sanitary, water heating in South Africa is the largest residential use of electrical energy with up to 50% of monthly consumption used for this purpose [3]. It is worth mentioning that most of the hot water devices are the convectional heater (electric geysers) with an average
We acknowledge Department of Science and Technology, and also CSIR for their financial supports in the acquisition of the equipment used for the conduction of the research.
Stephen Tangwe, Adhoc Eskom UFH M&V Engineer, South Africa and now with Sunderland University, Faculty of Engineering and Advanced Manufacturing, United Kingdom
energy factor of 0.92 [4]. Both, solar water heaters and air source heat pump water heaters are renewable and efficient technologies for sanitary hot water production, but with a reasonably high capital cost that hinders the ease of purchase by a low income level family. Solar water heater harnesses solar energy through its collector and converts it to thermal energy which is transported from the collector to the storage tank (where hot water is stored) by the heat transfer fluid via the process of thermosiphon [10]. The ASHP water heater is a renewable energy device capable of heating water with the majority of the useful thermal output energy derived from ambient aero-thermal energy [5]. It can provide energy saving in the range from 5070%, as the ASHP unit has a co-efficient of performance ranging from 2 to 4 [6], [7]. The type of hot water storage tank for the ASHP water heater is a real challenge to the hot water temperature inside the tank. Heated water by ASHP of similar volume is at much higher temperature in a dual tank than a single tank system, but heat losses are higher [8]. The study focusses on both analytical and statistical comparisons of electrical energy consumption of both 3kW, 150L high-pressure geysers without and with a hotspot device under controlled volumes of hot water drawn off. A two-way analysis (ANOVA2) was used to test for significant difference of the energy consumption with respect to the specific volume of hot water drawn off (column test), the types of geyser configuration (row test) and the interaction effect due to replication (both column and row test) [11],[12],[13].
(e-mail:
[email protected]). Michael Simon, Fort Hare Institute of Technology, University of Fort Hare, South Africa (e-mail:
[email protected]). Sandiswa Qayi, AET Africa, South Africa (e-mail:
[email protected]).
2.
Materials and methods
The two water heating systems under investigation were 3 kW 150-liter high-pressure geysers as depicted in Fig 1. The one of the geyser was without the hotspot device, and consists of a 3 kW heating element fitted in a 150-liter storage tank. The other geyser was with the hotspot and also comprised of a 3 kW heating element encapsulated with the hotspot device creating a cavity within the tank whereby only a small volume of water is heated at a time. Also, two power and energy meters with inbuilt logging capabilities were configured to log every five-minute interval the active power and energy consumption of the two systems under the various controlled volumes of hot water drawn off throughout the performance monitoring period. Geyser without hot spot
Geyser with hot spot
Power meter for geyser without hot spot Power meter for geyser with hot spot
Calibrated drum for volume measurement
Fig 1: Systems installation setup and DAS
3. Results and discussion The performance of the both systems was assessed from March to May 2017 on the basis of power and energy consumption under three distinctive scenarios of hot water drawn off. (50 L, 100 L and 150 L). Each of the specific volumes of hot water drawn off was conducted for a month and in three precise times of the day [morning (were drawn off from 7:00 and start up time of water heating at 8:00), afternoon (were drawn off was from 13:00 and start up time of water heating at 14:00) and evening (were drawn off from 17:00 am and start up time of water heating at 18:00 )]. 3.1 Power consumption of the both systems Table I shows the average power consumed by the geyser without and with the installation of the hotspot device under the controlled volumes of hot water drawn off for
morning, afternoon and evening performance monitoring duration.
throughout
the
Table I: Power consumption for both systems under different withdrawals Geyser type/ Time Morning/ Without Hotspot Afternoon/ Without Hotspot Evening/ Without Hotspot Morning/ With Hotspot Afternoon/ With Hotspot Evening/ With Hotspot
Power consumed by specific draws 50 L 100 L 150 L 2.27
2.28
2.34
2.31
2.26
2.24
2.24
2.26
2.24
2.19
2.25
2.13
2.11
2.10
2.10
2.15
2.10
2.10
It can be observed from Table I that the average power consumed was higher in the geyser without the hotspot installed as opposed to the case with the hotspot with respect to the corresponding specific volume of hot water drawn off. It can be depicted that the average power consumed during the 50 L of hot water drawn off was 2.27 kW for the geyser without hotspot installed and 2.15 kW for the geyser with the hotspot device. Also, the average power consumed for the geyser without the hotspot during the 100 L and 150 L were 2.27 kW and 2.27 kW, respectively, while for the geyser with the hotspot, the average power was 2.15 kW and 2.11 kW, respectively. Finally, throughout the entire heating up process for the different scenarios, the average reduction in the demand owing to the retrofit of the geyser element with the hotspot was 0.14 kW. 3.2 Energy consumption of the both systems Table II shows the average energy consumed by the geyser without and with the installation of the hotspot device under the controlled volumes of hot water drawn off for morning, afternoon and evening throughout the performance monitoring duration.
Table II: Energy consumption for both systems under different withdrawals Geyser type/ Time Morning/ Without Hotspot Afternoon/ Without Hotspot Evening/ Without Hotspot Morning/ With Hotspot Afternoon/ With Hotspot Evening/ With Hotspot
Energy consumed by specific draws 50 L 100 L 150 L 2.4100
6.8700
8.8700
3.2800
7.5800
8.3100
2.8500
7.2800
8.6400
1.7000
4.7400
6.5600
1.9900
5.2600
6.4400
1.8500
5.4300
6.5400
It can be depicted from Table II that the average energy consumed was greater in the geyser without the hotspot installed, in contrast to the one with the hotspot under all the corresponding specific volumes of hot water drawn off. The average energy consumed during the 50 L of hot water drawn off was 2.85 kWh for the geyser without hotspot installed and 1.85 kWh for the geyser with the hotspot device. In addition, the average power consumed for the geyser without the hotspot during the 100 L and 150 L was 7.22 kWh and 8.61 kWh, respectively while for the geyser with the hotspot, the average energy consumed were 5.14 kWh and 6.51 kWh, respectively. The entire heating up process for the different scenarios taking into consideration that the total daily volume of hot water drawn off was 300 L that was achieved over three specific volumes of hot water drawn off (50 L, 100 L and 100 L), resulted in energy consumption of 18.68 kWh and 13.50 kWh for the geyser without hotspot and geyser with hotspot, respectively as shown in the subplot in Figure 6. The difference in the average week and the average month energy consumption was 36.26 kWh and 155.40 kWh, respectively as determined from Fig 2.
Fig 2: The subplots of the average day, week and month energy consumption for both systems 3.3 Performance of two-way ANOVA test of the energy consumption of the both systems The two-way analysis of variance (ANOVA) was conducted for the two systems based on the energy matrix shown in Table II whereby the columns represent the controlled volumes of hot water drawn off, and the rows represent the time and geyser types. The two-way ANOVA test checks for significant difference between the columns, rows and as well as the interaction effect (significant difference owing to the combination of the columns and rows). It should be noted that if the p-value for either the columns, rows and interaction is between 0.00 and 0.05, then there exists a significant difference between the columns, rows and interactions. The ANOVA test treats all the dataset as normally distributed and that null hypothesis test is not rejected. Table III shows the two-way ANOVA test for the energy consumptions under the different volumes of hot water drawn off for the two systems.
Table III: Two-way ANOVA test of the energy consumption of the two systems under the different volume drawn off Sum Squares SS 87.68
ANOVA TABLE Degree Mean F statistics Freedom Square df MS F 2 43.84 478.38
Rows
13.49
1
13.49
147.14
0
Interac tion
1.20
2
0.60
6.56
0.019
Errors
1.1
12
0.09
Total
103.48
17
Source
Colum ns
Fig 3 shows the multiple comparison test of the columns using two-way ANOVA for the energy consumed by both systems.
Prob > F
0
It can be observed that there exist a significant difference between the columns (controlled volumes of hot water drawn off; 50 L, 100 L and 150 respectively), since the pvalue was 0. It was also observed that there exist a significant difference between the rows (Geyser without hotspot and geyser with hotspot) as the p-value was 0. The multiple observations also known as replication that give rise to the interactions, shows a significant difference as the p-value was 0.019. 3.4 Multiple comparison test for the columns using the two-way ANOVA test of the energy consumption of the both systems The multiple comparison test for the columns using the two way ANOVA test was illustrated to show that there exist a significant different in the group energy mean between either any two of the specific volume of hot water drawn off.
Fig 3: Multiple comparison test of the columns using twoway ANOVA It can be observed from Fig 3 that none of the group energy means of the 50 L, 100 L and 150 L hot water drawn off for both geyser without and with hotspots shown by horizontal lines do overlapped. Hence, a significant difference exists between any two of the columns. The average energy for the group energy means represented by the circle marker on each of the horizontal lines were 2.3467 kWh, 6.1933 kWh and 7.5600 kWh for the 50 L, 100 L and 150 L drawn off. It can also be demonstrated that the mean difference between the 50 L drawn off and the 100 L drawn off was 3.85. The mean difference between the true mean of the 50 L drawn off and the 95% confidence level was -4.31. The mean difference between the true mean of the 100 L drawn off and the 95% confidence level was -3.38. Since, in between the both intervals [-4.31 and -3.38], the value 0 is not included, it implies between both columns existed a significant difference. It can also be demonstrated that the mean difference between the 50 L drawn off and the 150 L drawn off was 5.21. The mean difference between the true mean of the 50 L drawn off and the 95% confidence level was -5.67. The mean difference between the true mean of the 150 L drawn off and the 95% confidence level was -4.75. Since, in between the both intervals [-5.67 and -4.75], the value 0 is not included, it implies between both columns there exist a significant difference.
It can also be shown that the mean difference between the 100 L drawn off and the 150 L drawn off was -1.37. The mean difference between the true mean of the 100 L drawn off and the 95% confidence level was -1.83. The mean difference between the true mean of the 150 L drawn off and the 95% confidence level was -0.90. Since, in between the both intervals [-1.83 and -0.90], the value 0 is not included, it implies between both columns there exist a significant difference. 3.4 Multiple comparison test for the rows using the two-way ANOVA test of the energy consumption of the both systems The multiple comparison test for the rows using the two way ANOVA test was provided to show that there exist a significant difference in the group energy mean between either of the two types of geysers (without and with hotspot). Fig 4 shows the multiple comparison test of the rows using two-way ANOVA for the energy consumed by both systems.
4
Conclusion
Hotspot device is a low cost and energy efficient retrofit device to reduce demand and energy consumption of hot water heating by geyser. It can be confirmed that the energy consumption of geyser with hotspot installed shows a significant difference in comparisons to geyser without the hotspot under the 50 L, 100 L and 150 L drawn off. Also, there was a significant difference due to interaction effect of both the various drawn off scenarios and the geyser types as demonstrated by the two-way ANOVA test of energy consumption of the both systems under investigation. 5
Future work
Extension of performance monitoring of the geyser without and with hotspot device installed in a vertical configuration. Also, both laboratory and existing residential homes performance monitoring of the geysers without and with hotspots for different tank sizes and heating element power rating under real time drawn off scenarios. Further study to be conducted on geysers with timers and isotherm blankets. 6
References
[1] Donna Bryson (2011), "Eskom key reason South Africa is a big polluter", Association Press 24 November 2011 [2] Sustainable energy society South Africa. (www. Waterlite.co.za, 2013) [3] Meyer, J.P., and M. Tshimankinda (1998), “Domestic Hot Water Consumption in South African Townhouses”, Energy Conversion and Management, 39:7, 679-684 [4] B.J Haung, F.H. Lin, (1997), Compact and fast temperature response heat pump water heater, American Society of Mechanical Engineers (paper) 97-AA-26 [5] G.L. Morrison, T. Anderson, M. Behinia, Seasonal performance rating of heat pump water heaters, Solar Energy 76 (2004) 147-162 Fig 4: Multiple comparison test of the rows using twoway ANOVA It can be observed from Fig 4 that the group energy means of the two types of geyser (without and with hotspot) shown by horizontal lines do overlap. Hence, a significant difference exists among the two rows. The average energy for the rows energy means represented by the circle marker on each of the horizontal lines were 6.23 kWh and 4.50 kWh for the geyser without hotspot and geyser with hotspot, respectively. Furthermore, since the p-value between the rows was 0, then it is sufficient to confirm that there exists a significant difference between the two types of geysers.
[6] Levins, W.P. 1982. Estimated Seasonal Performance of a Heat Pump Water Heater Including Effect of Climatic and In-House Location. Oak Ridge National Laboratory, Oak Ridge, TN [7] Bodzin, S. (1997), “Air-to-Water Heat Pumps for the Home”, Home Energy Magazine Online, July/August 1997 [8] Carl C. Hiller, (1996), Dual tank water heating system options, ASTAE Transactions 102 part 1 (1996) 10281079 [9] Tangwe, S., Simon, M. and Meyer, E., 2015, March. Quantifying residential hot water production savings by retrofitting geysers with air source heat pumps. In Domestic Use of Energy (DUE), 2015 International Conference on the (pp. 235-241). IEEE.
[10] Barry, E.J., Ervin T Brown, 1940. Solar water heater. U.S. Patent 2,213,894. [11] Wu, C. F. J., and M. Hamada. Experiments: Planning, Analysis, and Parameter Design Optimization, 2000. [12] Neter, J., M. H. Kutner, C. J. Nachtsheim, and W. Wasserman. 4th ed. Applied Linear Statistical Models. Irwin Press, 1996. [15] Hogg, R. V., and J. Ledolter. Engineering Statistics. New York: MacMillan, 1987. AUTHORS BIOS AND PHOTOGRAPHS Principal-author: Stephen Tangwe is a certified CMVP professional. He holds a B.Eng (Hons) and M.Eng degree in Electrical Engineering from AIU, Honolulu, Hawaii. And an expected PhD graduate by existing published works from the University of Sunderland in Engineering and Advanced Manufacturing. He is an IEE, AEE, SAEE and also an IEE Power and Energy society member. At present, he is a graduate student member in the South Africa Institute of Electrical Engineers and his an adhoc Eskom M&V Engineer with the UFH team. He is also an energy efficiency researcher affiliated with Fort Hare Institute of Technology and a MATLAB application Engineer. He is a seasoned author and reviewer in accredited peer review Journals. Tel:0783076922; Email:
[email protected]
Co-author: Prof Michael Simon is a certified CMVP professional. He holds a PhD degree in Physics from the University of Fort Hare. He is presently the University of Fort Hare Energy Manager and Head of the Energy Efficiency Group in Fort Hare Institute of Technology. He is also a certified Eskom M&V professional. He is a Photo Voltaic & an Energy Efficiency Specialist. He is a seasoned author and reviewer in accredited peer review Journals. Tel:072546721; Email:
[email protected]
Co-author: Sandiswa Qayi is the young African woman Managing Director and shareholder of AET Africa Pty Ltd innovation and Energy Efficiency Company based in Eastern Cape, South Africa. She holds a post graduate certificate in Business Management at Regenesys and Systems Engineering Approach and platform-based manufacturing at Massachusetts Institute of Technology (MIT) in Boston. She is a Social Science graduate in Industrial Sociology and Organizational Psychology from Rhodes University with Masters in Development studies from Nelson Mandela University. She is currently mentoring youth in innovation and science and women in business and serve as science ambassador and grass roots innovator in partnership with Department of Science and Technology (CSIR, TLIU) using her business management and social science skills. Tel: +27617596428; Email:
[email protected]
Presenting author: The paper will be presented by S Tangwe
