Utilization of Geothermal Energy for District Heating and Cooling

Transcription

1 Utilization of Geothermal Energy for District Heating and Cooling A.L. POLYZAKIS, C.J. KORONEOS, A.K. MALKOGIANNI, D. C. ROVAS, J. KARMALIS Laboratory of Heat Transfer and Environmental Engineering, Department of Mechanical Engineering Aristotle University of Thessaloniki PO Box 54006, Thessaloniki, Greece Abstract - Renewable energy sources are becoming more and more attractive solutions for clean and sustainable energy needs. The innovation and diffusion of renewable energy technologies can play a major role in the mitigation of climate change. Geothermal energy utilization has a great variety, from residential heating to electricity production, and it is so vast that could supply all the energy needed by humanity. Additionally the geothermal energy in regions close to volcanoes is close to the surface and easy to use economically. Thus, the exploitation of the geothermal hot water sources can eliminate the energy use from hydrocarbons and minimize the environmental impact. The objective of this work is to investigate the potential of the utilization of the existing geothermal potential of Nisyros Island located in the south-east Aegean Sea. Geothermal energy will be exploited in a district heating and cooling system, in a way that all the cooling and heating load of the island, throughout the year, would be covered with no additional use of fossil fuels. The technology for the exploitation of geothermal energy, in cooling mode, is the Single Effect Absorption Chiller. Additionally, the environmental performance of this projected will be presented in terms of CO 2 minimization, due to the avoidance of the fossil fuel consumption. This work is to determine and demonstrate the feasibility of a heating and cooling district system protecting the fragile island environment. Key-Words: geothermal energy, district, heating, cooling, absorption chiller,. INTRODUCTION. General description of the island of Nisyros Nisyros is an island in the south Aegean Sea that belongs in the Dodecanese group of islands. It is located at the south-east edge of the Aegean Sea, facing the shores of Turkey, which are 0 kilometres away. The permanent population of the island is about,000, while during the three summer months is doubled. The island covers an area of 4km 2. The center of the island is dominated by the caldera of the volcano of the island. The major city of the island called Mandraki, is located at the north side of the island, on the seaside. There are two small villages situated on the north-east coastline of the island very close to Mandraki.. 2 Climatic conditions of Nisyros The climate is Mediterranean, that is to say, mild winter and hot summertime. Analytically, climatic statistical data for each month are reported in Table : Table : Nisyros climatic data MONTH BAROMETRIC PRESSURE mmhg AVERAGE AIR TEMPERATURE O C ABSOLUTE MAXIMUM AIR TEMPERATURE O C ABSOLUTE MINIMUM AIR TEMPERATURE O C HOURS OF SUNLIGHT h RELATIVE HUMIDITY % AVERAGE CLOUDINESS (scale of 8), , , , , , , , , , , ISSN: ISBN:

2 2, Average 9. 3, Description of the existing situation The Dodecanese islands electricity system is based on autonomous petrol stations, while the geographic location of the islands has not allowed, till to now, their connection with the continental national network of electric energy. The limited installed power of production units and transport networks of Nisyros electric energy don t ensure sufficiency and stability in cases of peaks. This results in several problems in the network and, in certain cases, provisional interruption in electricity supply, mainly in the summertime period which is the peak tourists season. Nisyros energy demand presents intense fluctuation during the year, because of the change of population. Specifically, the population increases considerably during certain periods throughout the year, especially in the summer tourist period. The autonomous electricity generation stations provide the electricity during both situations of smooth change of demand and peak periods. The procedure which leads to the final heating, cooling, lighting consumption energy and the heating, cooling, lighting power needed, is presented in Table 2. Table 2 presents the different kinds of Nisyros power demand and especially the second column represents the electrical power demand for cooling purposes (air-conditioning). The third one represents the electrical power demand for the other electricity devices except air-conditioning units. The forth column consist of two separate columns representing each one of them the heating power coming from electricity and central heating power respectively. The last column represents the power needed for cooling purposes. Table 2: Nisyros power demand MW 2007 COOLING LIGHTING & OTHER HEATING MW thermal TOTAL POWER MWcooling (MW e ) (MW e ) ELECTR. BOILER (MW) COPaverage=4 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV JAN Other refers to the consumption of any electricity device except air-conditioning units. 2 Assumed 30 days per month According to Greek Government predictions, Nisyros presents low development rates and it has been predicted that in the next five years, the average rate of increase will be approximately %..4 Specifications of Nisyros geothermal field Table 3 shows the specifications of Nisyros geothermal field. The geothermal heat can be used for heating and cooling purposes. Saturated Water 0bar 80 o C 9300kg/h.89kJ/(kg*K) In order to transfer heat Q from the geothermal field, a water-water heat exchanger is used with an effectiveness η =0.85. Then the closed circuit 2 - with the pre-isolated tubes- transfers the heat energy Q 2 to the heat exchanger 2 with an effectiveness η 2 =0.85, just before the desorber of the absorption chiller systems or the heating system. (Fig. ) Table 3: Specifications of Nisyros geothermal field MASS STATE PRESSURE TEMP. FLOW c p ISSN: ISBN:

3 Fig.: Heat transfer system 2. The District Heating System An approximate estimation of the cost of a city district heating system could be derived of an existing case in Greece. The city of Ptolemaida is served by a CHP system with a capacity of 20MW th, with an overall efficiency of The thermal power station is located 4km away from the town and is piping superheated water (20 o C) to the town using pre-isolated pipelines. The total cost of the installation system is estimated about 4 /kw, (2007). [7], [8] 3. The District Cooling System Electricity purchased from utility companies for conventional vapour compression refrigerators can be reduced. The use of heat-operated refrigeration systems help to reduce problems related to global environmental, such as the so-called greenhouse effect from CO 2 emission from the combustion of fossil fuel in utility power plants. Gas absorption systems feature several advantages over conventional vapour compression electric systems: Lower operating costs (operating with waste heat). Non ozone-damaging refrigerants (no use of CFCs or HCFCs). No need for extra electric power (no overcharge of the existing electric power network, especially during the peak hours). Lower-pressure systems with no large rotating components. Low maintenance. Safer operation. High reliability. Smaller total space requirements compared to an electric chiller with separate boiler. Long lifetime, (25-30 years, compare to the 0-5 years of the vapour compression systems). Silent operation. Except for two hermetically sealed pumps, absorption chillers do not have any moving parts. They run more quietly (there are few vibrations) than compression chillers. This difference could be significant in office buildings, hotels or hospitals. Potential financial support from National Government. All water-cooled absorption systems on the market today, use water as the refrigerant and a lithium bromide solution as the absorbent material and they used for medium and large scale applications (3-2,500RTs or 0-9,000kW), while the COP R is between 0.6 and,3. Α typical air-cooled absorption chiller uses ammonia as the refrigerant and water as the absorbent material and they used for rather small applications (3-30RTs or 0-00kW), while the COP R is between 0.6 and 0.7, [],[2],[3],[4],[5]. However, gas absorption systems have three important disadvantages: [2], [3], [4], [5], [9], [0]. Low COP R, the usual range for absorption chillers is depending to the technology used, instead of the of the vapour compression systems. In cases where there is no waste heat available, absorption chillers cost more to operate than electric chillers. They also cost about 50% more to purchase. Water consumption in cooling tower. The single-effect LiBr/Water absorption cycle flow description LiBr/water is used as an absorption working fluid because it is one of the best choices found among hundreds of working fluids that have been considered. The fundamentals of operation of an absorption cycle using aqueous lithium bromide as the working fluid are discussed in this section. To keep the discussion simple, only the most basic cycle is considered. Α block diagram of a singleeffect machine is provided as Fig. 2. The diagram is formatted as if it were superimposed on a Duhring plot [0] of the working fluid. Thus, the positions of the components indicate the relative temperature, pressure and mass fraction. The cycle has five main components as shown in figure 2: the generator (sometimes called desorber), the condenser, the evaporator, the absorber, and the solution heat exchanger. ISSN: ISBN:

4 Figure 2: Single-effect LiBr/Water absorption cycle [66] Starting with state point 4 at the generator exit, the stream consists of absorbent-refrigerant solution, which flows to the absorber via the heat exchanger. From points 6 to, the solution absorbs refrigerant vapour (0) from the evaporator and rejects heat, to the environment. The solution rich in refrigerant () flows via the heat exchanger to the generator (3). In the generator thermal energy is added and refrigerant (7) boils off the solution. The refrigerant vapour (7) flows to the condenser, where heat is rejected as the refrigerant condenses. The condensed liquid (8) flows through a flow restrictor to the evaporator. In the evaporator the heat from the load evaporates the refrigerant, which then flows (0) to the absorber. Α portion of the refrigerant leaving the evaporator leaves as liquid spillover (). The thermodynamic state of every point is summarized in Table 4 Table 4 - Thermodynamic state point summary Point d liquid solution quality set to 0 as assumption 2 led liquid solution culated from pump model 3 led liquid solution culated from solution heat exchanger model 4 d liquid solution quality set to 0 as assumption 5 led liquid solution culated from solution heat exchanger model 6 liquid solution state flashes as liquid passes through expansion valve 7 ated water vapour d to have zero salt content 8 d liquid water quality set to 0 as assumption 9 liquid water state flashes as liquid passes through expansion valve 0 d water vapour quality set to.0 as assumption d liquid water quality set to 0 as assumption In general the Coefficient of Performance of an absorption refrigeration system is obtained from: cooling capacilty obtained at evaporator COP R = heat input for the generator+ work input from the pump () An average of the coefficient of performance value is 4.0. Absorption cooling systems are considerably more expensive than conventional electric compressor chillers (Table 5). In addition, absorption chillers will often require larger cooling towers and larger condenser water pumps, which further increase system costs Table 5: Capital plus installation cost for the electric and absorption chillers of various capacities (2007) Capacity (kw c ) 500,000,800 3,500 5,000 0,000 Installed cost ( /kw c ) Electric centrifugal (0% installation) Single effect absorption chiller (20% installation) Double effect absorption chiller (20% installation) Nisyros conventional case The different costs of energy will be analytically presented, for the conventional namely the present energy situation of the Nisyros Island. The calculation of energy consumption and the power demand is based on the typical day per month (the average day per month). In order to cover the worst case in energy and power, the values referring on a typical day are multiplied by a coefficient.2 (20% increase). Finally, in order to cover future increase in energy use for the next ten years or at least for a period of time exceeding the payment period of the investment, the previous values should be multiplied by a coefficient of. (0% increase). The results are shown in Tables 6 and 7 ISSN: ISBN:

5 . Table 6: Nisyros power demand in MW MONTHS COOLING (MW C ) LIGHTING & OTHER (MW e ) ELECTRIC HEATING MW th BOILERS TOTAL POWER (MW) JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Table 7: Nisyros energy demand MWh MONTHS COOLING (MWh C ) LIGHTING & OTHER (MWh e ) ELECTRIC HEATING MWh th BOILERS TOTAL ENERGY (MWh) JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Electricity Prices The cost of electricity (Table 8) in the conventional case is the same with the proposed case, simply because the utilization of geothermal energy is used only for heating and cooling purposes. Table 8: Electricity prices and percentage of different types of electrical consumption Type of Use Final selling prices ( /MWh), 2007 Percentages % of electric energy Domestic Commercial Cooling Cost The electric compression refrigeration system (conventional air-conditioning), capital cost plus the installation cost is taken to be equal to 00, /MW. Here the MW refer to the maximum value of the cells of coloumn 2, table 6. Operational cost: The electric energy per month supplied from the local grid for cooling (W e,c ), can be calculated as follows: W e, c = MWh / 4[MWh] (2) where MWh are the corresponding values of cells of column 2, Table 7. COP is taken to be equal to 4. Then the operation cost per month is given by the following equation: Operation Cost per month = W e,c x 36,3 x 30 [ /month](3) where 36,3 /MWh is the equivalent electricity price for the entire Island and 30 is assumed the number of days of the month. ISSN: ISBN:

6 The operation cost of the year can easily be calculated as: Operation cost = 2 [ /month] [ /year] (4) which varies accordingly to the inflation rate. Maintenance costs: For absorption chillers cost range is the same as for electric chillers to as much as one-third more (consider: electric chillers maintenance cost 3% of the chiller capital cost). As a result, the maintenance cost (fixed value, for every year) is Maintenance Cost = (Capital cost + Installation cost)x0.90 x 0.03 [ /year] (5) We assume that the maintenance of the cooling system is taking place in January (last week) 5.3 Heating Cost The average capital cost of the heat exchanger is 53 /kwt (2007) with the installation included (0% of the capital cost). The thermal efficiency of the heat exchanger η th, HE varies between On the other hand, the average capital cost of the boilers, which are going to be replaced by a CHP system, is 49 /kwt (2007) plus 0% of that for the installation cost. The thermal efficiency of the boilers η th, b varies between [2], [3], [4]. Heating is coming from two sources: a) from individual boilers using light diesel as fuel and b) from electric inverters, heaters etc, which consume electricity. a) Individual boilers using light diesel as fuel (ρ = 0.86kg/lt, FCV=42.5MJ/kg). Capital cost (fixed value): Capital Cost = [MW]. [ /MW] [ ] (7) where MW is the maximum value among the cells of column 5, Table 6 and /MW is the price of boiler per MW. Installation cost (fixed value): Installation cost = Capital Cost. 0.0 [ ] (8) where factor 0.0. The energy provided from the light diesel per month is calculated as follow: Q COP = L W η th, b = 0.8 in Q f,b = (MWh. 30) / 0.8 [MWh per month] (9) where η th, b is the thermal efficiency of the boilers, MWh are the corresponding values of cells of column 5, Table 7 and 30 is assumed the number of days of the month. The mass of light diesel per month and per year are calculated as follow: m& = [(Q. f, b 3,600) / FCV ] [kg/month] (0) fm,b m fy,b = 2 m fm,b [kg/year] () And so the cost of light diesel per year -which varies accordingly to the international oil prices, can be estimated: Cost of light diesel = (( m& fy, b / 0.86). (30t+70) /.3/59)..9 [ /year] (2) Where 0.86 is the density ρ of the light diesel, COpr=(30t+70)/.3[ /bbl], where t=.45 and represents the exchange ratio ( /$) for the year 2007, while the factor 59 is the capacity of barrel and.9 is due to the isolated consumption area namely Island. Maintenance cost (fix value, for every year): Maintenance Cost = Capital cost [ /year] (4) We assume that the maintenance of the heating system is taking place when there is no need for heating e.g. summer time. b) Electric inverters, heat pumps, heaters etc Capital cost and installation cost and maintenance cost is negligible due to the fact that the majority of them are used for cooling and heating purposes, so the capital cost of them is already calculated in the previous cooling section Operation cost: COP = 2.5 W e, h = [MWh] / 2.5 [MWh] (5) where 2.5 is the assumed average COP of heat pumps heaters, etc, and MWh are the cells of column 4 (Table 7). Operation cost per month = W. e, c [ /month] (6) Operation cost = 2 [ /month] [ /year] (7) (varies accordingly to the inflation rate) 5.4 CO 2 emissions estimation and penalty The electric energy per year supplied from the national grid (PPC) for cooling and heating purposes, is calculated as follow: ISSN: ISBN:

7 Energy per year = 2. values per typical day 30 [MWh/year] (8) where the values per typical day are the cells of columns 2 plus 4 of Table 7 and 30 is assumed the number of days of the month. The island is part of the non-interconnected national grid of Greece. Taking into account the data from Table 9, it can be estimated how many MWh/year is produced from the available kind of power plants, (obviously, renewable excluded) assuming that the total electric energy per year is supplied only diesel power plants: Diesel (medium heating oil): [MWh/year] [MWh/year] Table 9: The installed and the total net power production for the years 2000, 200, 2002 [5] INSTALLED CAPACITY (MW) TOTAL NET PRODUCTION (GWH) 3 December Interconnected System Thermoelectrical Power Plants Lignite Power Plants Oil power Plants Natural Gas Power Plants Total Thermoelectrical Power Plants Hydroelectric Power Plants Wind and other Renewable Power Plants Total Interconnected System Non-Interconnected Islands Thermoelectrical Power Plants Lignite Power Plants Oil power Plants Natural Gas Power Plants Total Thermoelectrical Power Plants Hydroelectric Power Plants Wind and other Renewable Power Plants Total Non-Interconnected Islands Interconnected System & Total Non-Interconn Islands Total Thermoelectrical Power Plants Total Hydroelectric Power Plants Total Wind and other Renew. Power Plants TOTAL Carbon dioxide emissions depend primarily on the type, quality and quantity of the fuel used. To a satisfactory approximation, complete combustion can be assumed, which is very close to reality, when combustion takes place with excess air and the combustion equipment is in good condition and adjusted correctly. Then, the quantity of the emitted CO 2 is calculated by the equation: m& CO = µ CO m& 2 2 f (9) where: µ 44 CO = c 2 2 E m& f = (2) η FCV m& CO 2 : mass of emitted CO 2, µ CO 2 :emissions of CO 2 per unit mass of fuel (e.g. kg CO 2 /kg fuel), c: mass content of carbon in fuel (e.g. kg C/kg fuel), m& f : mass fuel consumption, E: useful energy produced by the system, η: efficiency of the system, based on the lower heating value of fuel, FCV: fuel calorific value (lower) Equations (9)-(2) are applicable not only to cogeneration systems, but to any system burning fuel. For example, when they are applied to a power plant or a cogeneration system, E is the electricity produced and η is the electrical efficiency; η e. typical values of c, µ CO and FCV for various fuels 2 are given in Table 0. ISSN: ISBN:

8 Table 0: Typical properties of fuels for calculation of CO2 emissions. Fuel Carbon content (c 00) % emissions µ CO2 (kgco 2 /kg Natural gas (Russian) Natural gas (Algerian) FCV (MJ/kg) ,002 = = Motor diesel (oil) Light heating oil Medium heating oil y heating oil (residual, m Lignite * * Data are valid for fuel with no moisture and ash. It has to be clarified that if the values of the parameters appearing in Eqs. (20) and (2) change for any reason (e.g. change in efficiency due to partial load, change in quality and consequently in c and H u of fuel), then the total CO 2 emitted during a period of time results as an integral over time (or summation over various times intervals) of Eq. (9). Using the CO 2 calculation method presented above, the m CO2 produced from every type of power plant respectively, can be estimated: Eq. (9) Eq. (20), Eq. (2), (Table 0) m& CO 2 = kgco 2 /y (η DIE =0.36) Assuming that medium diesel power plants exceed the CO 2 emission limit at about 6% then the mass of CO 2, which must be accounted for penalty, will be: m& CO 2,DiM,pen = kgco 2 /year [kgco 2 /year] PPC will pay 80 /additional tone of CO 2 emissions for the period Thus, CO 2 emission cost paid by PPC = m& CO 2,DiM, pen. /,000kg [ /year] (varies with the CO 2 penalty price) The island is using boilers burning only light heating oil. Thus, the electric energy per year produced burning light heating oil will be: Heating energy per year of boilers = 2 MWh. 30 [MWh/year] (22) where the values per typical day are the cells of column 5, Table 7 and 30 is assumed the number of days of the month. Using the CO 2 calculation method presented above, the m CO2 produced by boilers burning light heating oil will be Eq.(9) Eq.(20), Eq.(2), (Table 0) kgco 2 /y (η DIE =0.8) m& CO 2 = Assuming that diesel power plants exceed the CO 2 emission limit at about 3% then the mass of CO 2, which must be accounted for penalty, will be: m& CO 2,DiL,pen = kgco 2 /year [kgco 2 /year] Thus, CO 2 emission cost paid by island. consumers= m& CO 2,DiL, pen ( /,000) = /year (varies with the CO 2 penalty price) where,000 is for units similarity. Total CO 2 emission cost = CO 2 emission cost paid by PPC+CO 2 emission cost paid by island consumers [ /year] 6. Hypothetical Case In this case the thermal and cooling demand of the island is covered by the utilisation of the available geothermal energy at any instant of time, (Fig. 3). Fig. 3: Technical block diagram of the Hypothetical Case Undertaking simple calculations of available geothermal power, we conclude that it is sufficient enough to cover the maximum need in thermal power of the entire island. These calculations are: Q =m. C p,. Τ=0.73MW Q 3 =η 2 Q 2 =η. η 2. Q =0.5MW Q c,available =Q 3 COP R = =0.34MW where m, C p come from Table 3 and Τ is assumed to be 50K and η, η 2 are the effectiveness of the ISSN: ISBN:

9 heat exchanger and 2 respectively. The value 0.34MW is greater than the maximum cooling or thermal month power, needed by the island. Thus, the scenario-case which is studied is realistic. The cost -fixed value- of the two heat exchangers, including the installation cost, is given by the following equation: Heat Exchanger Cost = [MW]. [ /MW]. 2 [ ] (23) where MW is the maximum cell of columns 2 plus 4 plus 5 (Table 6) and /MW is explained above. The heat exchanger maintenance cost -fixed value, for every year- is given by the following equation: Exchanger Maint. Cost = 0.9. [Heat Exchanger Cost] [ /year] (24) where factors 0.9 and 0.02 are explained above: The district heating installation cost -fixed value- is given by the following equation: District Heating Installation Cost = [MW]. [ /MW]. ([MW]/20) [ ] (25) where MW is the maximum cell of columns 2 plus 4 plus 5 (Table 6), /MW is the corresponding price, and the factor 20 is due to the relatively small system (paragraph 2). The absorption chiller cost -fixed value- including the installation cost is given by the following equation: Absorption Chiller Cost = [MW]. [ /MW c ] [ ] (26) where MW is the maximum cell of column 2 (Table 6) and /MW c is the corresponding price. The absorption chiller maintenance cost -fixed value, for every year- is given by the following equation: Absorption Chiller Maint. Cost =0.8. Absorption chiller cost [ /year] [27] where factors 0.8 and 0.03 are explained above. Cost of back up cooling. The electric compression refrigeration system capital cost including the installation cost -fixed value- is given by the following equation: Electric Compression Refrigeration System Capital Cost + Installation Cost = 0.4. [MW]. [ /MW] [ ] (28) where the factor 0.4 is due to the assumption that the back up cooling power is the 40% of the maximum cooling demand power in MW, MW is the maximum value of cells of column 2, (Table 6) and /MW is the corresponding price. The operation cost of electric compression refrigeration system is calculated as follows: Operation back up cooling energy: COP=4.5 W e,c =0.05. [MWh]/4.5[MWh] (29) where W e, c is the electric energy supplied from the local grid for cooling and MWh corresponds to the cooling energy of the whole year (Table 7) and the factor 0.05 corresponds to the possible use of conventional cooling throughout the year due to unpredictable failures of the absorption cooling system. The maintenance cost -fixed value, for every year- is given by the following equation: Maint. Cost=([Capital Cost]+[Installation Cost]) (7/360) [ /year] (30) where factors 0.90 and 0.03 are discussed above, while the factor (7/360) is simulates the relative duration of the operation. We assume that the maintenance of the cooling system is taking place in January (last week). Cost of back up boilers (assume 50% of the maximum heating demand power in MW) using medium heating oil. (ρ =0.92kg/lt, FCV=4MJ/kg) Using the same methodology as in conventional case and especially the part labeled heating. The capital cost (fixed value) and the installation cost (fixed value) can be calculated with the help of Eqs. (7) and (8) respectively, while the maintenance cost (fixed value, for every year) is given by the Eq. (4) with a slight modulation: Maintenance Cost = capital cost (7/360) [ /year ] (3) where the factor (7/360) is due to the fact that operates regularly only 7 days per year. The mass of light diesel per month and per year are calculated as follow: m fm,b = [(Q f, b * 3,600) / FCV ] [kg/month] m fy,b = 2 m fm,b [kg/year] where FCV is given. And so the cost of light diesel per year -which varies accordingly to the international oil prices, can be estimated by Eq. (2): Cost of light diesel = (( m& / 0.86 ) * (2.9t+42.) / fy, b 59) *.9 [ /year] (32) ISSN: ISBN:

10 where 0.86 is the density ρ of the light diesel. Greek government is offering financial support - fixed value- is given by the following equation: Greek Government Financial Support = 0.4 * (Heat exchangers cost + District heating installation cost + Absorption chiller cost + Capital cost of back up boiler + Installation cost of boiler) [ ] (33) 7. CONCLUSIONS The economic results of the economic simulation are presented in Table and Fig.4. Table : Summary of the economic evaluation of the hypothetical case Net Present Case Value (NPV) x 0 3 Conventional Hypothetical Fig. 4a shows the cost distribution of the conventional case. Similarly, Fig. 4b shows the cost distribution of the hypothetical case. Notice that in Fig. b, there are no positive percentages, due to the autonomous local grid of the island. Fig. a, b: Economic distribution a. Conventional Case, b. Hypothetical case It is obvious that the hypothetical case is by far the more attractive solution. This is due to the negligible cost of fuel and CO 2 penalty. The superiority of the hypothetical case is enlarged as the fuel cost and the CO 2 penalty is increased. Finally, the hypothetical case has negligible effect on the delicate island environment. The potential for further work in this field of study is considerable. The future work should be focused on two important guidelines: accuracy and improved complexity. Thus, future work could involve various aspects of concerning: Collection of greater detail and accurate data from the potentials sources. (Creation of detailed energy records for the last 2-4 years would be very useful). The simulation work could be also improved, with fewer assumptions used (namely, accurate compressor and turbine maps, the program could also operate with the turbines unchoked, use of variable geometry, and simulation procedure for every day of the year, etc). Simulation of a double effect absorption cooling system. Consideration of potential emissions penalties (NO x ), other than CO 2. References. McNeely A L., Thermodynamic properties of aqueous solutions lithium bromide, ASHRAE Trans., 85 (), , Energy solution center, Citing Internet resources, http//www. Energy solution center.org, (accessed 2008). 3. Carrier, Citing Internet resources, www. carrier.com, (accessed 2008). 4. Trane, Citing Internet resources, www. trane.com, (accessed 2008). 5. Yazaki, Citing Internet resources, www. yazaki.com, (accessed 2008). 6. Stromberg J., Learning from experiences with Gas Turbine based CHP in Industry, Centre for the analysis and dissemination of demonstrated energy technologies, Caddet analysis support unit, Thermie publication, Basic aspects of application of district heating systems, Journal of Greek electrical and mechanical engineers, vol 3, Northeast CHP Application Center, Economic and financial assessments, CHP Publications &Resources, Herold E. K., Absorption chillers and heat pumps, CRC Press, ASHRAE Handbook, Fundamentals, Amer. Soc. Of Heating Refrigerating and Air-conditiong Engineers, EDUCOGEN, Guide to Cogeneration, SAVE Program contract N XVII/4.03/P/99-59, Ladopoulos G., Energy saving modifications in existing buildings, Journal of Greek electrical and mechanical engineers, vol 377, ISSN: ISBN:

11 3. Thermie publication, Basic aspects of application of district heating systems, Journal of Greek electrical and mechanical engineers, vol 3, Panagiotou G., Performance Investigations of Industrial Gas Turbines for Combined Heat and Power, MSc Thesis, Cranfield University SoE, Academic Year Public Service for Greek Energy Management System (RAE), Public Service for Greek Energy Management System publications, Athens, ISSN: ISBN: