A Feasibility of Geothermal Cooling in Middle East

Transcription

1 A Feasibility of Geothermal Cooling in Middle East ASAD SALEM & HAFIZ ELSIR MIRGHANI HASHIM Department of Mechanical Engineering Rochester Institute of Technology Rochester Institute of Technology, Dubai Campus UNITED ARAB EIMERTES, DUBAI Abstract: - Over percent of the energy in Dubai commercial buildings is used for Ventilation and Cooling (HVAC). The preponderance of this energy is utilized to building cooling. The goal of this project is to explore the feasibility of geothermal coupled cooling system in Dubai. Ultimately it was concluded that geothermal cooling is technically feasible and economical option in Dubai. The vertical; open-loop shallow geothermal system has the most potential. This was determined by conducting multiple cost-benefit, simulation and analysis comparing three different options with current system and the possible economic costs of installation with the potential economic, and environmental benefits. The Ground Couple Heat Pump (GCHP) option was compared with other cooling systems options linked to the same building and operating under similar loads and climatic conditions. All systems were fully analyzed throughout one year also a life cycle of 20 years were evaluated to see how much of an impact it will have. Results showed that by choosing the geothermal option savings up to 198 million KWh in energy, $27 million in the operating cost, and a total savings of more than $14 million could be achieved with a simple payback time of about 8 years along with a reduction of 148,448 tonne and 545 tonne in CO 2 and NO X respectively. Key-Words: - Geothermal, Wet Cooling Tower, Air-Cooled, Energy Savings, CO 2 Emission 1. Introduction Ground Coupled Heat Pump (GCHP) is a well-known technology that has been used for over 50 years. However its market penetration, in particular in Middle East, is still small. In countries such as Japan, South Korea and China in which GCHP are very popular, climatic conditions are such that by far most of the demand is for space heating, whereas air conditioning is rarely required. Therefore, the experience with GCHP in East, Europe and North America refer mostly to heat pumps operating in heating mode. However, with the ongoing proliferation of GCHP technology into Middle East in particular in UAE, the use for cooling is becoming increasingly important. In this sense, implementation of this technology to cooling dominated applications in hot climates is still in the early stages. The aim of this work is to gain an insight into the technical and economical viability of the GCHP technology for commercial applications in the Dubai. In this direction, we present the performance analysis of an indirect vertical open-loop ground source heat pump system installed in Dubai, (UAE) operating in cooling mode. The details of various type of geothermal will not be discussed here; the interested reader is referred to (Geothermal HAVC, 2010) for recent overview [1]. In the scoop of this study three options were considered in order to establish a comparison the efficiency improvement and energy savings: 1. Wet-cooled chillers system combined with geothermal systems. 2. Wet-cooled chillers system combined with cooling towers. 3. Replacement of the existing air-cooled chillers system with alternative more efficient chillers. The main objective is the development of a commercial size, economic, energy efficient and environmentally friendly, fully integrated turnkey ground source heat pump system for cooling, targeted specifically at commercial applications in the Dubai region. ISBN:

2 2. Geothermal Background There is significant increase in the number of research related to GCHP, reflecting the rapidly increasing activity worldwide. This section will present several situations at different geographical areas and countries. Curtis,.et.al...[2] proposed one of the largest geothermal systems in Europe that provided heating and cooling by a geothermal energy storage to a building area of close to m 2 in Nydalen, Oslo an output of 9MW of heating and 7.5MW of cooling was achieved by 180 wells at a depth of 200 m (Each well provided 4-10 kw) while the annual energy was reduced by 60-70%, compared to traditional oil or gas systems. Andrew Chiasson [3] proposed an open loop GHP system at a Middle School in Lapwai. Approximately 300 gpm of ground water 58 o F where required for both heating and cooling. A separation distance of 300ft was estimated between the supply and rejection well. The total capital cost of an open loop was about $115 K, the GHP system operated with an annual energy saving of about $18 K furthermore; the system showed that a 50 years life-cycle cost that is 33% lower than the conventional alternative with a simple payback period of about 7 years. Leslie Johns,.et.al...[4] proposed a GHP shallow system that covered a 6000 tons of cooling capacity at Tulane University s. A 2000-ton capacity chiller was required extracting humidity from the building. The GHP system capital cost was $32 million. Tulance would saved at least $400 K or 33% of the previous HVAC maintenance costs, reduced energy consumption by 2700 million kwhs, reduced energy expenditures by $189.5 million,reduced emission by 26% or 14,175 metric tons/year. A life span of around 50 years was estimated for the system with a payback time of 7 years (Net present value of about $90 million). Regie Goforth.[5].modified a governmental.facility was provided with Ground water open loop which served by one well capable of 600 gpm of 70 o F water. Within weeks of the geothermal heat pump system began experiencing extremely high and totally unacceptable levels off corrosion. The first solution was to eliminate the open holding tank that was allowing oxygen to enter the system. The second was to isolate the geothermal fluid loop from the inbuilding distribution loop. That was done through addition of plate and frame heat exchangers. The third solution design change was to add a variable speed. that would minimize turbulence at start up and eliminate the problem of brining sand up from the production zone. Edward Brendt.[6] presented an open loop, central and water source heat pump system in the Parkview Apartment in Winchester, Massachusetts. The system was served by three wells. The depth is estimated to be 80 use of only one well with the second in reverse except during peak demand period. A plate and frame heat exchanger separates the well from the in-feet. The two wells provided approximately 1500 gpm of 54 o F water. Operating of the system requires the building circulation system. Water, after passing through the heat exchanger, and finally drains into a nearby stream. Toni Boyd.[7] proposed two basic geothermal resources utilization options for supplemental heating at the Utah Transit Authority (UTA) Warm Springs Facility in Salt Lake City, UT. Under option 1 (a) it was estimated that UTA would avoid about $17 K annually in natural gas cost, with a simple payback of 11 years, option 1(b) it was estimated that UTA could avoid much more in natural gas costs than the first option but at the expense of electrical energy consumptions for the heat pump, thus the net annual energy saving for this option of about $31 K with a simple payback of 12 years. Under option 2 it was estimated that an annual energy saving to UTA would be similar to option 1(b), but slightly less at $29 K at a simple payback of 10 years. Hamstra,.et.al..[8].proposed.a.single loop. geothermal systems have been promoted and applied at a college campus building located in Indiana. In this configuration, a single pipe is routed in a circular fashion with primary circulation pumps that vary flow rates with fluid temperature differentials measured at multiple points. Load and performance data are monitored and subsequently controlled via a central control system. Each building is connected to the loop to dedicated geothermal heat exchangers which can take multiple forms such as vertical, horizontal, or slinky closed loops; deep-earth horizontal directional bored loops; and pond/lake loops. Dragi. Antronijevica,.et.al...[9].proposed.a.comprative analysis of six different vapor compression cycles of ground heat pump to be used as fossil fuel boiler retrofit in a high temperature radiator heating system of a building at new Belgrade Municipality. ISBN:

3 Thermodynamic evaluation has been based on the comparison of seasonal coefficients of performance of the heat pump systems, calculated with respect to the actual heating load requirements and achieved coefficients of performance on a statistically rendered ambient boundary condition and ground water temperature. Also, the energy analysis of the system has been performed. The final selection of the groundwater heat pump included detailed economic analysis of the heat pump layouts with the best thermodynamics characteristic. James.Minges [10] proposed a geothermal heating and cooling system in The Exchange which located in Farmington Connecticut. A 55 o F geothermal source was provided by 4 wells. The system uses a shell and tube heat exchanger between the wells and the circulating fluid that supplies the heat pump. All of the pumps are submersibles. The water is then disposed of into a creek at a maximum of 85 o F. James system has been in operation for 28 years (extremely reliable,) an energy analysis on the building was performed, which had saved up to $600 K as compared to a conventional system and the total electrical load for the building in 1997 was 5 million kwh. This amounts to about 18 kwh/squ.ft/ys. Based on the number presented the heat pump system uses 7 kwh /squ.ft/ys. for the load. The existing system has operated very successfully for over 5 years (10h/day), and has severed the needed cooling loads perfectly. At this point, maintenance is however, becoming a problem and the system reliability is coming more and more into questions. The answer is the system will definitely show its age, because usually the estimated life-time for air-cooled chiller is between years. One of the main concerns is to explore the amount of life-time and money put into the new system compared with coming maintenance problems, bearing in mind that the current system are not fitted with variable speed diver compressors. According to the existing dewatering system at the site Fig.1 there is also a huge potential of underground water due the high water-table in the area. Thus, the motivation for conducting this project originated from an interest of increasing the efficiency at commercial buildings in Dubai city. 3. Building Characteristics Dubai Silicon Oasis Headquarter is a commercial building strategically located in the center of Dubai silicon oasis (DSO) and will be a taken as an example for this study. The integrated free zone technology park was built in This business center is one of the largest in the United Arab Emirates providing fully serviced offices, meeting rooms and virtual offices, catering for everything from a single workstation to an unlimited number of offices. The building consist of six wings (A, B, C, D, E and F) each wing contain (2- basement floors - 1 ground floor - 10 typical floors) On each floor, there are 9 offices in different sizes (total of 82 offices in the whole building).the existing cooling system at the building used a total of 14 screw compressor air-cooled chillers at two different model and capacities refer to Table.1. In order to find the best solution an energy study was performed to compare three different options as mentioned before with the original air-cooled used system. The estimated cooling loads were determined using ASHRAE guidelines based on them, specific heat pump models were selected that best suited the needs Figure 1: Dewatering System ISBN:

4 5. Wet-Cooled Geothermal System Option The proposed wet-cooled geothermal heat pump option consists of three water-cooled 650-ton units connected in series. Only two of the chiller can cover the building load (operating condition) while the third chiller will be at the standby condition refer to Fig.2. The proposed system consists of two loops separated by (shell & tube) heat exchanger of a suitable material plus non-metallic piping, to isolate groundwater from the heat pump equipment. This chosen configuration reduces potential scale or corrosion to one piece of equipment. Routine maintenances and cleaning of the (shell&tube) heat exchanger usually results in a trouble-free system. An open discharge method will be used for this option. Water will be extracted from an underlying aquifer from an open loop at 69.8 o F passing through the heat exchange that protect the closed-loop within the building from the water quality issues such as dissolved mineral, acidity,etc, and then wastewater will be discharge at 84.2 o F on an evaporation ponds/lakes few meters far from the site. Figure 2: Wet Cooled Geothermal Option Schematic 6. Wet Cooling Tower Option The proposed Wet Cooling Tower heat pump option consists of three water cooled 650-ton units connected in series same chillers type and model used in option1. Only two of the chiller can cover the building load (operating condition) while the third chiller will be at the standby condition refer to Fig.3. Each chiller consists of its own three cell cooling tower at a capacity of 1, Ton and 5520 (GPM) Flow rate, variable speed compressor, shell-and-tube type condenser. Figure 3: Wet Cooling Tower Option Schematic 7. Highly Efficient Air-Cooled Option The proposed Air Cooled option heat pump plant consists of seven Air-cooled variable speed diver type 220-ton units connected in series. Only six of the chiller can cover the building load (operating condition) while the chiller 7 will be at the standby condition refer to Fig.4. The design offers a lighter, smaller and quieter package that minimizes the installed cost and maximizes usable building space. Each chiller is custom-matched to meet the individual building wings load and energy requirements which perfectly meet with chosen building strategy. Also a variety of standard heat exchangers and pass arrangements are available to provide the best possible match. The chosen design will minimize the quantity of refrigerant used in the system. The highest portion of green house gases is carbon dioxide generated from electric power plants. HVAC systems are one of the largest consumers of electricity in commercial buildings. Variable speed drives are provided in these chillers to ensure that these chosen air-cooled are more efficient than the existing Air-cooled chillers which discussed earlier. Figure 4: Highly Efficient Air-Cooled Option Schematic ISBN:

5 8. Estimation of investment: Economical Analysis The installation costs of the studied options are difficult to estimate with high degree of certainty without more design specifics. However, reasonable assumption was made according to the building estimated cooling loads, estimation of investment including heat pump units, heat exchangers, pumps, chillers, piping, and design fees management and other fees. In the water-cooled cooling tower chiller system, the cost of the lost water relates to about 8% of the loop water evaporating in the cooling tower (and needing replacement constant replacement). $4,000,000 $3,500,000 $3,000,000 $3,395,010 $3,007,868 $800,000 $700,000 $600,000 $714,926 $2,500,000 $2,000,000 $1,500,000 $1,804,913 $500,000 $400,000 $300,000 $279,420 $1,000,000 $500,000 $0 $200,000 $100,000 $0 $144,414 Water-Cooled Geothermal Air cooled Water-CooledCooling Tower Figure 5: Capital Costs According to Fig.5 the capital costs for air-cooled system and the water-cooled cooling tower system are likely to be less than the cost of the water-cooled geothermal system (since the ground open-loop isn t needed). However, the chiller cost still contributes significantly to the total equipment costs. Note the amount of savings only include the cost of the chillers and doesn t include the fixture needed to support the chillers. The proposed options will use electricity as it fuel.current standard cost for electricity used in the calculation is 0.11$/kWh The analysis presented in Fig.6 shows that the yearly electricity cost for the geothermal-cooled heat pump option will save up to $300 K compared to the air-cooled option, will saved up to $150 K compared to the water-cooled cooling tower option and will save up to $800 K compare to the existing system. At this point the geothermal option is clearly the most efficient using less than half Existing System vs Geothermal Air-Cooled vs Geothermal Cooling Tower vs Geothermal Figure 6: Annual Electricity Bill Savings the electricity of the other options. One of the primary benefits of most geothermal heat pump option relates to the reduced operating cost, which is based mostly on the reduced energy consumption. The systems are expected to last 20 years without replacement. Thus, it is important to look again at a 20-years life cycle for each option. The life cycle of 20 years will be used to appropriately weigh the estimated operating costs and Energy usages Fig.7 display the operating cost and Energy usages lifecycle. An effective rate of return of (3% for Energy) and (5% for the Operating Cost) is used to account for both interest and inflation rates annually. Also Fig.8 presented the total savings for the three studied options. A life cycle of 15 years is chosen for existing system because the system has already operated for 5 years. ISBN:

6 Figure 7: Annual Operation Costs, Annual Energy Usages 20 years life cycle savings for the three used options compared with the existing system $16,000,000 $14,000,000 $12,000,000 Total Savings $11,579,280 $14,143,597 $10,000,000 $8,000,000 $6,995,183 $6,000,000 $4,000,000 $2,000,000 $0 Air Cooled vs Water-Cooled (Cooling Tower) Air-Cooled vs Geothermal Water-Cooled (Cooling Tower) vs Geothermal Figure 8: Total Savings Comparisons for the three used Options ISBN:

7 Comparing the geothermal option with conventional cooling systems indicates that the water-cooled geothermal-cooled option will reduce the operating (annual) system costs, but will also increase the capital cost. Since the operating costs are lower, the geothermal-cooling system would clearly be the best option in Dubai. Fig.9 below shows an estimated breakdown of the payback periods for the three proposed options. production associated with providing cool for the Dubai commercial building. Figure 9: Payback Periods Comparison Clearly we can see that, the geothermal-cooled system will have a payback period of about 8-9 years, the water-cooled Cooling Tower option will have a payback period of 5-6 years, and the Air-Cooled option will have a payback period of 2-3 years. This indicates that providing the absence of funding would have a major impact on the payback period of the project, especially as the rate of return increases. 9. Environmental Impacts One of the major impact issues with this project deals with the CO 2 production associated with the DSO energy consumption. It is estimated that 1.44 lbs of CO2, and Ib of NOx is produced in delivering 1 kwh of electricity [11]. Based on these relationships, Fig.10 displays the CO2 and Nox production comparing the three discussed options. Based on this figure above, clearly we can notice that the Geothermal-cooled option has the best performance in minimizing the CO 2 and NO x Figure 10: CO 2 and No x Emission savings Comparison 10. Conclusion Commercial buildings in Dubai have relatively high occupancy, fluctuating demands, and widely vary cooling requirements within individual zones that are difficult to meet efficiently with conventional systems. The selected options at this project will be successful in providing comfort conditions at reasonable first and continuing operational costs. Comparison between the three options at 20 years life cycle clearly showed that there is a potential for the efficient use of GCHP in Dubai commercial building leading to significant savings up to 198 million kwh in energy usage and $27 million in operating cost. Finally, total savings of more than $14 million were achieved with a simple payback period less than 8 years with reduction of 148,448 tonne and 545 tonne in CO 2 and NO x respectively). ISBN:

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