Energy Saving by ESCO (Energy Service Company) Project in Hospital

Transcription

1 7th International Energy Conversion Engineering Conference 2-5 August 2009, Denver, Colorado AIAA Tracking Number: Energy Saving by ESCO (Energy Service Company) Project in Hospital Satoru Okamoto * Shimane University, 1060 Nishikawatsu, Matsue, Shimane , Japan The combined production of electrical, heating and cooling energy is becoming an increasingly important technology. It has several advantages: including a lower consumption of primary energy, reduction levels of air pollution, and less expenditure. Simultaneous production of heat, cold and power gives us higher efficiency of whole system. Depending on the conditions, this combined system can be the most economical solution for a building by an ESCO (Energy Service Company) project. The requirement is that the system is located where there is a high consumption of electrical, heating and cooling energy throughout the year. An example of the type of consumer that has such conditions is a hospital. This paper constitutes a work starting from an analysis of typical energy demand profiles in a hospital and technical criteria to assess the feasibility of cogeneration plants are proposed by an ESCO project. A feasibility analysis performed for a non-optimized CGS (Cogeneration System) predicts a large potential for primary energy savings. Planned CGS of hospital is a future autonomous system for the combined generation of electrical, heating and cooling energy in the hospital. The driving cogeneration units are two high-efficiency gas engines; this is used to produce the electrical and heat energy. A Miller cycle gas engine is used as a driving unit because of high needs for electrical and heating energy. The natural gas-fuelled reciprocating engine is used to 735kW of power. In our case, electrical energy will be used in the only Hospital. A deficit in electricity can be also purchased from the public network. The generated steam will be used to drive three steam-absorption chillers and delivered to individual consumers of heat. An additional peak-time waste heat boiler will cover the need for additional heat during the winter period. We can thus affirm that in large hospitals major opportunities for CGS applications exist, because of the higher required capacity and the more regular demand profiles. The simulation was performed for a gas engine CGS system with a heat recovery boiler and three absorption chillers. The simulation was carried out in the hypothesis to strictly follow the sum of electrical demand for direct users and for feeding the absorption chiller. The primary energy saving ratio was 16.5 %. In this work the technical viability of CGS system for energy supply in the Hospital was discussed by an ESCO project, starting from an analysis of energy consumption data available for the Hospital; no obstacles were recognized for the technical feasibility of CGS. The average ratio between electric and thermal load in the Hospital is suitable to make CGS system operate. A feasibility analysis performed for a non-optimized CGS system predicted a large potential for primary energy savings. Nomenclature C = generated electricity, heating and cooling energy by CGS CGS = cogeneration system GJ = giga-joule h, hr = hour RT = ton of refrigeration T = total primary energy consumption of conventional system t = ton * Professor, Department of Mathematics and Computer Science, 1060 Nishikawatsu, Matsue, Shimane , Japan, Member 1 Copyright 2009 by the, Inc. All rights reserved.

2 T I. Introduction HE combined production of electrical, heating and cooling energy is becoming an increasingly important technology. It has several advantage: these include a lower consumption of primary energy, reduction levels of air pollution, and less expenditure. Simultaneous production of heat, cold and power gives us higher efficiency of the overall system. Depending on the conditions, this combined system can be the most economical solution for a building. The requirement is that the system is located where there is a high consumption of electrical, heating and cooling energy throughout the year. An example of the type of consumer that has such conditions is a hospital. It can happen that in a certain period of the year this type of system is not profitable because of the relative costs of gas and electricity. For this reason it is always important to make a detailed analysis of any planned system and to look at the various possible operating regimes 1, 2. The basis of a cogeneration energetic system (CGS) is the electrical, heating and cooling device. There are, however, different kinds of cogeneration systems, which can be distinguished by the type of driving unit and the type of cooling device. The driving unit of a cogeneration module can be a steam turbine, a gas turbine, a reciprocating engine or a fuel cell. The cooling energy from cogeneration system is mainly produced in one of two ways, i.e., with a turbo- chiller or with an absorption chiller. The decision about which variant to choose depends on the required output power and the operating regime 3, 4. CGS for the commercial use at the end of March 2006 in Japan is shown in Fig Figure 1 (a) indicates the distribution of the total number of sites (4,638) to the various activities of the tertiary sector, with hospitals being 16 % of the sites. Figure 1 (b) indicates the distribution of the total capacity (1,646 MW) to the various activities of the tertiary sector, with hospitals having 16 % of the capacity. (a) Ratio of sites (total number of sites: 4,638) (b) Ratio of capacity (total capacity: 1,646MW) Figure 1: CGS for commercial use as the end of March Figure 2: ESCO project 6. 2

3 An ESCO (Energy Service Company) project is an energy-saving business activity on a private basis offering energy-related services to clients shown in Fig. 2. Those who undertake ESCO projects are referred to as ESCOs. For example, in the projects under the shared saving contract, ESCOs provide their clients with comprehensive services for factories, buildings and other establishments encompassing audits for energy saving performance, design and implementation of conservation measures, maintenance, operation and management of the introduced facilities and procurement of project funds. ESCOs accomplish energy conservation without damaging the environment, while guaranteeing the expected energy savings. In this work the technical viability of CGS system for energy supply in a Hospital by an ESCO project was discussed. Starting from an analysis of energy consumption data available for a specific Hospital, no obstacles were recognized for the technical feasibility of CGS. The concept of CGS is an original autonomous system for the combined generation of electrical, heating and cooling energy in the hospital. The adopted cogeneration units have the higher efficiency (40.7 %) of the gas engine generator than the other conventional driving units; this is the Miller cycle gas engine, which is novel technology and is very little driven about the cogeneration systems in order to produce the electrical and heat energy efficiently. The average ratio between electric and thermal load in the Hospital is suitable to make CGS system operate. A feasibility analysis performed for a non-optimized CGS system predicted a large potential for primary energy savings. II. Energy Demand in Hospital Energy demand in hospitals can vary widely year by year, depending on eventual variations in the number of patients and facilities: Most hospitals are growing much faster than the economy as a whole, and this requires large efforts to forecast demand and frequent increases in the energy supply as well. Because of the large differences in energy demand among hospitals, a feasibility study should be performed for each case study with ad hoc considerations. However, in this work some outlines on CGS applications in hospitals are proposed, starting from a statistical distribution of available energy consumption data. Energy demand in hospitals is correlated to many factors; among these, heat losses by infiltration and losses through windows and roofs (and thus related to the heated or air-conditioned surface and volume) are prevalent. The examined Hospital belongs to Shimane University Faculty of Medicine in Japan. The Hospital is an eightstories building and was completed in 1977, and therefore the facilities of the Hospital of University are superannuated ones. The heated and air-conditioned areas are 42,203 m 2. The number of the sickbeds is 616. Despite this quantitative analysis of energy consumption in the Hospital, a qualitative analysis is needed to assess whether a CGS system can comply with energy requests. The Hospital is provided with central system for hot or warm water production (heavy oil fuelled boilers; 16 t/h x 2 and 5 t/h x 1) and for cooling (three absorption chillers; 600 RT and turbo-chiller; 400 RT) indicated in Fig. 3. Power is usually purchased from the electric utility electricity. All-air system are mainly adopted, with air- treatment units where temperature and humidity are adjusted; a typical range of temperature for the heat exchanger in such units is o C. Figures 4 and 5 show the energy consumption profiles in the only Hospital of University on annual and monthly basis respectively. In Fig. 4, bars in gray, in slant-striped, in white and in black respectively represent the electric consumption for feeding an absorption chiller covering the whole cooling demand and the lighting system etc., the hot water and the sterilization demand, the cooling, and the heating consumption. The electric consumption monthly profile, represented in Fig. 5, is also very regular because electric load is related to quite constant activities 12 months a year. Figure 6 shows the comparison between the heat ratio of Hospital of University and the averaged heat ratio of the other hospitals in Japan 6. The heat ratio is defined as the ratio of heating demand and cooling demand to annual energy consumption by ECCJ 6. The ratio of Hospital of University is 0.32, and is lower than the averaged value of the other hospital in Japan, that is 0.4. Heat ratio is defined in Appendix 1. A feasibility study is performed and predicts a large potential for primary energy savings. The typical daily consumption represented in Fig. 7 for electric loads and heating and cooling loads are about constant in summer, autumn and winter, respectively. The typical hourly consumption profiles represented in Fig. 8 for heating and cooling are quite regular, with little increase during morning or afternoon, depending on the weekday or the holiday. The electric load hourly profile is characterized by regular power requests during the daytime, with a demand leap of the lighting system and the elevators. Obviously, some electric loads require a very high safety of supply; hence, dedicated engines or inverter groups are usually available for energy supply in case of power grid failures. 3

4 (a) Detailed diagram (b) Block diagram Figure 3: Conventional system of hospital. Figure 4: Annual energy consumption of hospital. Figure 5: Monthly energy consumption of hospital. Source 1) : Shimane Prefectural Central Hospital 7 Source 2) : ECCJ Energy Conservation Center, Japan 6 Figure 6: Comparison of the heat ratio 6. (a) One week in summer Figure 7: Daily energy consumption of hospital. (b) One week in autumn (c) One week in winter 4

5 (a) Weekday in summer (b) Holiday in summer (c) Weekday in autumn (d) Holiday in autumn (e) Weekday in winter (f) Holiday in winter Figure 8: Hourly energy consumption of hospital. III. Technical Potential of CGS in Hospital A. Description of Cogeneration System in Hospital The Shimane University Hospital is a large consumer of electrical, heating and cooling energy. For this reason the installation of a system for the simultaneous generation of electrical, heating and cooling energy would be the best solution if we want to reduce investment and operating costs and meet ecological requirements. Several studies have been done for design of cogeneration systems in hospitals 8. They showed different technical possibilities and also tried to identify economic benefits. In this paper, there is a design challenge to determine the optimal size of CGS for the load fluctuations 8. From actual needs for electric, heating and cooling energy, the gas engine and chillers were selected. For such system we tried to find the best operation throughout the year. This study will look at the possibility of installing a cogeneration system, i.e., the simultaneous generation of heating, cooling and electrical energy. Figure 9 shows the concept of a future autonomous system for the combined 5

6 generation of electrical, heating and cooling energy in the hospital. The driving cogeneration units are two highefficiency (40.7 %) gas engines; this is the Miller cycle gas engine, and used to produce the electrical and heat energy efficiently. The mechanism inside the Miller cycle engine cylinder is as follows. The volume of the Miller cycle before compression is reduced compared to the conventional type by opening the inlet valve and discharging some of the mixed air in the cylinder. However, the expansion ratio is the same as the conventional type. In other words, the amount of energy that can be taken out is the same, but the efficiency of the engine is improved since the energy used during compression is reduced 9. Gas engine is used as a driving unit because of high needs for electrical and heating energy. The natural gasfuelled reciprocating engine is used to generate 735kW of power. Figure 10(a) shows the consumption of the natural gas throughout the year. In our case electrical energy will be used only in the Hospital. A deficit in electricity can be also purchased from the public network shown in Fig. 10(b). Figure 10(b) shows the utility electricity of the conventional system and the generated electricity by the planned cogeneration system. The generated steam will be used to drive three steam-fired absorption chillers (600 RT x 3) and delivered to individual consumers of heat shown in Fig. 10(c). Figure 10(c) shows the generated steam throughout the year. An additional peak-time waste heat boiler will cover the need for additional heat during the winter period. This system is capable of doing simultaneous heating and cooling shown in Fig. 10(d). Figure 10(d) shows the heating load during the winter period and the cooling load during the summer period. In order to increase the reliability of the cooling-energy supply it is necessary to install an additional absorption chiller. The choice of the cogeneration system was based on the monthly heating load and cooling load, and its consumption is showed in Fig. 10(d). Normally, the heat-energy needs in the winter are too high to plan a cogeneration system on the maximum amount of heating energy required. The requirements for electrical, heating and cooling energy vary within certain limits. The generated electrical energy throughout the year is approximately 17,716 GJ, and the predicted cooling energy is 9,443 GJ, which are the energy contents of CGS described in Table 1 of Appendix 2. By considering the needs for electrical and heating energy we chose a cogeneration module on the basis of the peak cooling load. For cooling purpose we chose three absorption chillers, one with a cooling power of 600RT. Water temperature in the cooling jacket circuit of reciprocating engines typically exceeds these values, being sufficient for feeding the air-heating system. Depending on the cooling demand levels, a double effect lithium bromide absorption chiller can be installed, producing 5-7 o C chilled water for the air-treatment units. A double effect absorption chiller require super-heated feeding water at o C or low pressure steam (typically kpa); only high temperature heat recovery from exhaust is compatible with the temperature required by absorption chillers. Figure 9: Cogeneration system of hospital. 6

7 (a) Consumption of natural gas (b) Electricity (c) Generated steam (d) Heating load and cooling load Figure 10: Energy contents of planned cogeneration system. B. Feasibility of CGS in Hospital The heat ratio is defined as the ratio of heat demand to electricity demand. From Fig. 6, the heat ratio of Hospital of University is 0.32, and is lower than the averaged value of 0.4 from the other hospitals in Japan. When designing a CGS plant for Hospitals a modular approach should be adopted, like in most of CGS installations in hospitals all over the world which usually consist of several smaller modules to cover the growing heat demand. In the meantime, a modular approach enhances the reliability of supply, which is a main concern for hospitals. Based on our experience, we can thus affirm that in large hospitals major opportunities for CGS applications exist, because of the higher required capacity and the more regular demand profiles. CGS applications in small hospitals usually lead to longer payback periods. When retrofitting a conventional plant shown in Fig. 3 with a CGS system, the existing components and equipment must be integrated with the new ones. In this section a typical energy system for the Hospital and required system are examined. Fig. 9 shows the new components or major changes which are two gas engine generations and heat recovery boiler. When the conventional system is converted into the CGS, the existing boilers and chillers can be used as auxiliary systems. As concerns the infrastructures, the same pipelines as the centralized all-air system for heating and cooling can be conserved. In order to confirm all the above consideration, a brief analysis is performed for the Hospital, with known monthly loads of electric, heating and cooling. This analysis is much more general; the purpose of this section is to show the enormous potential for energy saving by cogeneration in the Hospital, where interesting results may be achieved even by a non-optimized plant design and operation. The simulation was performed for a gas engine CGS system with a heat recovery boiler and three absorption chillers in the hypothesis to strictly follow the sum of electrical demand for direct users and for feeding the absorption chiller. The primary energy saving ratio was calculated by T C 100 =16.5 %. T 7

8 Here T represents the total primary energy consumption of the conventional system, and C represents the energy consumption of CGS with utility electricity. T is equal to the sum of fuel consumption in the local energy system and in a power plant eventually supplying the Hospital with electricity. The detailed energy contents are indicated in Appendix 2. When comparing the cogeneration system with the conventional system, care must be taken in properly evaluating the unit energy costs of each case. With cogeneration, the electric utilization class and the contractual power are generally lower, thus imply higher electricity costs. Moreover, the value of heat depends on the user s characteristics. Taking for example a business and commercial use, such value is simply given by the heat demand times the unit cost of the fuel used in the conventional system; in turn, such fuel cost can either be the same as the cogeneration plant, or lower, or higher. In order to account for the user s characteristics, the computer program requires a value of the cogenerated heat which must take into account the differences in fuel costs and efficiencies between various fuel streams used for the cogeneration and the conventional case 8. ESCOs raise their revenues from fees paid by clients using a part of the financial gain achieved through energy savings. ESCOs and their clients enter into a performance contract (on a piecework basis) to guarantee the effect of energy conservation. Clients pay fees for the comprehensive services provided by ESCOs. On the other hand, supplemental power costs, which are defined as the cost of power which is purchased from the utility on a regular basis, and supplemental fuel costs, which is the cost of fuel required for the conventional boiler and the duct burner, were evaluated. The payback periods through cost saving derived from the efficiency of the cogeneration system are estimated in the Hospital. The incremental costs of operating the cogeneration system are contained in the evaluations. The capacity of the cogeneration system should be designed in the lower range of electric power supply per maximum demand. CGS in the Hospital was planned under a fifteen year contract to guarantee the effect of energy conservation and cost saving provided by ESCOs. IV. Conclusions In this work the technical viability of CGS system for energy supply in Shimane University Hospital by an ESCO project was discussed, starting from an analysis of energy consumption data available for the Hospital of University; no obstacles were recognized for the technical feasibility of CGS. The average ratio between electric and thermal load in the Hospital is suitable to make CGS system operate. A feasibility analysis performed for a nonoptimized CGS system predicted a large potential for primary energy savings. Acknowledgments The author gratefully acknowledges the contribution of the staff of the Shimane University Hospital. References 1 Bizzarri, G., and Morini, G. L., Greenhouse gas reduction and primary energy savings via adoption of a fuel cell hybrid plant in a hospital, Applied Thermal Engineering, Vol. 24, 2004, pp Szklo, A. S., Soares, S. J., and Tolmasquim, M. T., Energy consumption indicators and CHP technical potential in the Brazilian hospital sector, Energy Conversion and Management, Vol. 45, 2004, pp Santoyo, J. H., and Cifuentes, A. S., Trigeneration: an alternative for energy savings, Applied Energy, Vo. 76, 2003, pp Bilgen, E., Exergetic and engineering analyses of gas turbine based cogeneration systems, Energy, Vol.25, 2000, pp Japan Cogeneration Center, 6 ECCJ Energy Conservation Center, Japan, 7 Shimane Prefecture, 8 Bizzarri, G., and Morini, G. L., New technologies for an effective energy retrofit of hospitals, Applied Thermal Engineering, Vol. 26, 2006, pp

9 Appendix 1 Heat includes both heating and cooling, then Heat ratio is defined as the ratio of heating demand and cooling demand to annual energy consumption by ECCJ Energy Conservation Center, Japan 6. Heating + Cooling Heat ratio = Annual energy consumption In Fig. 6, the heat ratio for the University Hospital is given as 0.32, which agrees with the results obtained in 2008 year. Appendix 2 The energy contents of conventional system and CGS are described in Table 1. Nomenclature: CE : generated electricity by CGS (kwh) CG : consumption of natural gas (m 3 ) CO : cooling load (kcal) CT : operating time of CGS (h) HE : heating load (kcal) HO : heavy oil = 1,112.9 (kl/year) HW : hot water (kcal) ST : steam (kg) TE : utility electricity of conventional system (kwh) Dimensions: 1 kcal = J = x 10-3 kwh 1 J = x 10-7 kwh 1 kwh = kcal = 3.6 x 10 6 J Heating value of heavy oil = 9,300 kcal/l = GJ/l Heating value of natural gas = 9,800 kcal/m 3 = GJ/m 3 Efficiency of CGS generator = 0.41 T = TE + HO C = = 17,274,380 = 62,187.8 = 105,590.9 = ( TE CE) ( kwh) ( kl) ( GJ ) + 43,403.1( GJ ) ( GJ ) + CG 3 ( 17,274,380 4,921,090)( kwh) + 1,065,792( m ) = 44,471.8 = T C 100 T ( GJ ) + 43,697.5( GJ ) ( GJ ) 105, (%) = 100( %) 105,590.9 = 16.5( %) Table 1: Energy contents of conventional system and CGS. 9