SEASONAL COLD STORAGE BUILDING AND PROCESS APPLICATIONS: A STANDARD DESIGN OPTION?

Transcription

1 SEASONAL COLD STORAGE BUILDING AND PROCESS APPLICATIONS: A STANDARD DESIGN OPTION? Edward L. Morofsky Manager - Research, Development and Demonstration Public Works and Government Services Canada Technology and Environment Antares Drive Ottawa, Ontario K1A 0M3 Canada Phone: (613) Fax: (613) [email protected] ABSTRACT Seasonal cold storage designs have obvious energy efficiency and environmental benefits. Modern applications of seasonal cold storage in aquifers date from the 1960 s in China. The International Energy Agency s Implementing Agreement on Energy Conservation Through Energy Storage initiated an annex in 1991 entitled, Innovative and Cost-effective Seasonal Cold Storage Applications." The annex collected and analyzed data on 50 projects in four countries up to The primary objective of Annex 7 was to identify, analyze, and document systems and applications that maximize energy savings and environmental benefits from the application of seasonal thermal storage of cooling. The ultimate purpose was to encourage the adoption of thermal storage of cooling as a standard design option. The results of Annex 7 have been comprehensively reported. This paper evaluates data on an additional 52 new projects collected for the period 1993 through 1996 to determine the effectiveness of the Cold Storage Annex in stimulating applications in building and process cooling. The number of projects meeting Annex 7 criteria is increasing, the cost-effectiveness is improving, and projects are attaining commercial sizes. The conclusion is that seasonal cold storage is not yet a standard design option in most countries. Cold aquifer thermal energy storage is fast becoming a standard design option in The Netherlands. 1. INTRODUCTION Annex 7 of the Energy Conservation Through Energy Storage Implementing Agreement of the International Energy Agency dealt with Innovative and Cost-effective Seasonal Cold Storage Applications. The objective was to identify, analyze, and document systems and applications that maximize energy savings and environmental benefits from the application of seasonal

2 thermal storage of cooling in order to encourage the adoption of thermal storage of cooling as a standard design option. Conclusions of Annex 7 included the identification of applications that were competitive with conventional chilling under appropriate geological conditions. Cooling energy sources include ambient air and by-product energy from ground-source heat pumps. Energy can be gathered by cooling tower, air handling unit or heat exchanger. Storage media include aquifers, rock, and soil. Process cooling was seen as a large opportunity, due to the long cooling time period, especially in moderate climates. Good payback is assured with large energy storage (high energy savings) and large cooling capacity (high capital cost savings). 2. ANALYSIS Figure 1 shows the annual number of projects in total - for each of the four Annex 7 countries: Canada, Germany, The Netherlands and Sweden. It indicates that the annual number of projects meeting the Annex 7 criteria of deliberate storage of cold energy for a period of at least three months has achieved a yearly total of approximately 17. Projects already underway for implementation in 1997 and 1998 are expected to maintain the pace. Figure 1 also shows that the increased activity is due predominantly to projects in The Netherlands, where a comprehensive implementation program has been responsible for increasing interest. Seasonal Cold Storage Projects by Year Sweden The Netherlands Germany Canada Figure 1. Seasonal cold storage projects by year and by country There are 75 realized projects in operation in Annex 7 countries for which data on cooling power (kw thermal) and cooling energy (MW hours) are available. The annual power and energy are shown as a bar chart (using the left ordinate) in Figure 2. The cumulative energy and power are shown by the two lines (values read from the right ordinate). Cumulative totals of 50 MW thermal and 75 GWh of stored energy have been achieved over the years 1985 to Projects coming on stream in are forecast to increase the cumulative total to 95 MW thermal and 95 Gwh of stored energy. Figure 2 combined with Figure 1 gives an enhanced view of the annual progress. Variations in numbers of projects sometimes mask a steady increase in cumulative energy and power.

3 Cooling Capacity by Year 45, ,000 40,000 90,000 35,000 30,000 25,000 20,000 15,000 10,000 5, kwth or MWh 1997 kw MWh kw cum MWh cum 80,000 70,000 60,000 50,000 40,000 30,000 Cumulative 20,000 10,000 0 Figure 2. Cumulative cooling power and cold energy by year. While annual energy-to-power ratios vary, the cumulative power and energy totals shown in Figure 2 are essentially equal. Thus the average value of annual equivalent full-load hours of cooling is 1,000. This is not surprising considering the large number of northern European projects having a short annual cooling season and the large proportion of commercial applications with a short comfort cooling season. Cooling power requirements largely determine first cost, while cooling energy requirements determine energy savings due to replacing renewable energy for electrically-driven chillers. Process cooling applications have a greater number of equivalent full-load hours, sometimes approaching the maximum of 8,760 hours. These cumulative energy totals can be compared to the estimated total annual cooling energy stored in Shanghai in 1984 of approximately 300 GWh. By 1984 there were 492 cold storage wells in Shanghai accepting 29 million cubic meters of water annually. Of these wells, 90% were used for both injection and extraction. These cold storage wells supplied textile mills, chemical works and other industrial plants, as well as commercial buildings such as the Shanghai Exhibition Hall where there were five injection wells and one extraction well. Figure 3 plots cooling stored in MWh versus cooling power in kw thermal. It also indicates by various symbols (diamond, square, triangle and circle) the country in which the project is located, whether the project was in the original Annex 7 data (open symbols), or the recent compilation for 1993 to the present (filled symbols). A line of 1,000 hours of equivalent full-load has been added for reference. Projects that fall on this line would provide 1,000 hours of cooling if operated at rated cooling output assuming 100% recovery of stored energy. Lines of 100 and 10,000 equivalent full-load hours have also been added. All projects save one fall between these lines. Of course, 10,000 hours is an obvious maximum as it is greater than the 8,760 hours in a year. Do projects with greater annual equivalent full-load hours exhibit better economics? This is treated below in Table 1 by combining data from Figures 3 and 4.

4 Stored Cold by Cooling Capacity 86 projects MWh cooling 100,000 10,000 1,000 Can Ger Neth Swe 10,000 hours 1,000 hours 100 hours ,000 10, ,000 Figure 3. Stored cold by cooling capacity in 86 energy storage projects. Simple financial payback in years (compared to a conventional design) versus cooling power in kw thermal is plotted in Figure 4. Projects are differentiated as real ( ), inpreparation ( ) or cancelled ( ). Open symbols indicate the original Annex 7 data set and filled symbols ( ) indicate later projects. It can be seen that most recent projects have paybacks of less than or equal to five years. A number of projects have a payback of zero years. Payback does not seem to be dependent on power (kw thermal) alone. However, stored energy (MWh) divided by power (kw thermal) or equivalent full-load hours does seem a better determinant. Table 1 indicates that projects having less than 1,000 equivalent full-load hours have an average eight-year payback, while those having greater than or equal to 1,000 equivalent full-load hours have an average five-year payback. There are 18 realized aquifer projects with greater than or equal to 1,000 equivalent full-load hours with an average 3.3-year payback and an average 3,345 equivalent full-load hours. Table 1. Average paybacks for various types of energy storage projects. Project Criteria kw thermal Number of projects meeting criteria Average payback years Average equivalent full-load hours (EF-LH) < 1,000 EF-LH >= 1,000 EF-LH realized aquifer >1000 EF-LH ,345 Annex 7 realized Annex 7 cancelled Latest realized Realized rock Soil all types Realized aquifer

5 The average payback of realized projects has decreased from 5.8 years for the original Annex 7 projects to 4.1 years for recent projects. The average payback of cancelled old projects is 8.4 years. Realized projects in rock have an average 5.4-year payback. Soil projects have a 21-year payback. Forty-two realized aquifer projects have a 4.1-year payback. Payback by Cooling Power Payback years Real In Prep Canc New Real New Prep New Canc ,000 10,000 kw thermal Figure 4. Payback versus cooling power for realized, in-preparation and cancelled projects. 3. CONCLUSIONS Partial data were gathered on 55 recent projects in Annex 7 countries. Consistent characteristics of size and economics have been achieved. Aquifer storage and rock storage are competitive with conventional chilling designs. There are 18 realized aquifer projects with greater than or equal to 1,000 hours with an average 3.3-year payback and an average 3,345 equivalent full-load hours. The effect of storage energy size can be gauged by projects having less than 1,000 hours that have an average eight-year payback, while those having greater than or equal to 1,000 hours have an average five-year payback. Aquifer projects continue to be more popular and most projects occur in The Netherlands and Sweden. Belgium has collaborated with The Netherlands on several projects and shared geology has assisted in transferring experience into Belgium. The number of projects meeting Annex 7 criteria is increasing, the cost-effectiveness is improving, and projects are attaining commercial sizes. The conclusion is that seasonal cold storage is not yet a standard design option in most countries. Cold aquifer thermal energy storage is fast becoming a standard design option in The Netherlands.

6 ACKNOWLEDGEMENTS This paper is based upon the work of the Annex 7 experts from Canada, Germany, the Netherlands and Sweden. My particular gratitude is directed to those experts who provided data on recent projects. I also congratulate the Canadian Operating Agent, Verne Chant of Hickling Corporation, who guided the Annex to a successful conclusion. REFERENCES Canada-China Aquifer Thermal Energy Storage Technical Exchange 1984, trip report by E. Morofsky, Public Works Canada, Energy Efficiency, Economics and the Environment, E. L. Morofsky (1994) Aquifer Thermal Energy Storage Workshop (the Keynote presentation), pp. 1-8, November 1994, Tuscaloosa, 182 pages. Final Report of Annex 7, Analysis of Economic, Energy and Environmental Aspects; (1994) International Energy Agency, Energy Conservation Through Energy Storage Implementing Agreement (Annex 7), Public Works Canada, PWC/RDD/125E, Ottawa K1A 0M2, March 1994, 49 pages + 40 app. Innovative and Cost-effective Seasonal Cold Storage Applications: Workplan, Morofsky, E. and V. Chant (1991) IEA Energy Conservation Through Energy Storage Annex 7, Thermastock '91, Scheveningen, The Netherlands, May, NOVEM, Utrecht. Overview of Projects with Seasonal Storage for Cooling from Four Countries, Chant, V. and E. Morofsky, in Aquifer Thermal Energy (Heat and Chill) Storage, Jenne, E.A.(Editor), Papers presented at the 1992 Intersociety Energy Conversion Engineering Conference, Pacific Northwest Laboratory, PNL- 8381, November 1992 and in Vol 4 of the Proceedings, ISBN , August, San Diego, , Copyright SAE. State-of-the-Art Review in The Netherlands, Innovative and Cost-effective Seasonal Cold Storage Applications (Annex 7), Leo van Loon and Hans Buitenhuis et al., March 1991, 80 pages, NOVEM, Utrecht. Summary of National State-of-the-Art Reviews, Innovative and Cost-effective Seasonal Cold Storage Applications, International Energy Agency, Energy Conservation Through Energy Storage Implementing Agreement (Annex 7), Public Works Canada, PWC/RDD/96E, Ottawa K1A 0M2, June 1992, 41 pages. Underground Thermal Energy Storage, State-of-the-Art 1994, G. Bakema and A. L. Snijders, International Energy Agency, Energy Conservation Through Energy Storage Implementing Agreement, Annex 8, October 1995, 83 pages, ISBN x. Workshop on Generic Configurations of Seasonal Cold Storage Applications (Proceedings), International Energy Agency, Energy Conservation Through Energy Storage Implementing Agreement (Annex 7), Public Works Canada, PWC/RDD/89E, Ottawa K1A 0M2, September 1991, 89 pages.

7

8

9