Evaluation of CCHP systems performance based on operational cost, primary energy consumption, and carbon dioxide emission by utilizing an optimal operation scheme

Combined heating and power (CHP) and combined cooling, heating, and power (CCHP) systems generate electricity and usable heat on-site from one fuel source while organic Rankine cycles (ORC) generate power from low-temperature heat sources. During the operation of CHP and CCHP systems, there are many instances when the recovered exhaust heat is greater than the required thermal load of the building. In these situations, an ORC can be used to capture the excess heat in order to produce additional electricity. Therefore, combining an ORC system with a CHP system (CHP-ORC) or a CCHP system (CCHP-ORC) can further increase the fuel utilization of the system, thereby reducing the operational costs, primary energy consumption (PEC), and carbon dioxide emissions (CDE). This article examines the economic, energetic, and environmental performance of CHP-ORC and CCHP-ORC systems under the operational strategies of follow the electric load (FEL) and follow the electric load with the option of turning off (FEL/OFF) for the city of Boulder, Colorado. Their performance is compared to a stand-alone CHP and CCHP system, respectively, between systems, and to a reference building. Results show that under the FEL operation, the addition of an ORC to either the CHP or CCHP system lowered the operational costs, PEC, and CDE by about 12 per cent, 13 per cent, and 17 per cent, respectively, from the standalone system. In addition, only when the systems operate FEL/OFF strategy minimizing cost or PEC, the cost and PEC could be reduced below the levels of the reference building.

Combined cooling, heating, and power (CCHP) systems use waste heat from on-site electricity generation to meet the thermal demand of the facility, which includes cooling, heating, and hot water. When compared with traditional set-ups of grid-generated electricity and an on-site boiler for heat, CCHP systems are capable of improving fuel utilization and lowering emissions. One of the critical components affecting the performance of CCHP systems is the prime mover. The objective of this investigation is to study the effect of the prime mover size and operational strategy on the energy, economical, and environmental performance of CCHP systems under different pricing structures. Three different sizes for the prime mover, a natural gas engine, are simulated under different operational strategies such as: following the electric demand of the facility, following the thermal demand of the facility, and following a constant load. The results obtained for the CCHP system will be compared with a reference building operating under conventional technologies to determine the advantages or disadvantages of the CCHP system's operation. In addition, a simple optimization of the system's operation determines the best engine load for each hour during the simulation that minimizes cost, primary energy consumption (PEC), or carbon dioxide emissions (CDEs). For this study, three locations in different climate zones that have different electricity rate structures were chosen: one with a constant flat rate; one that uses seasonal rates; and one that incorporates block charges. Historical monthly natural gas rates were also used. Since most authors perform cost analyses using a fixed constant rate for both electricity and natural gas, a comparison is made between the cost results from using the actual cost data to those that use an average fixed rate. In general, among the three engine sizes that were simulated, the smallest engine yielded the lowest costs and lowest PEC; but, no such trend was found with regard to the CDE. The results also showed that the performance of the evaluated CCHP system can be improved by optimizing the system based on cost or primary energy.

Evaluation of a turbine driven CCHP system for large office buildings under different operating strategies

Optimal design and operation strategy for integrated evaluation of CCHP (combined cooling heating and power) system

CCHP (combined cooling, heating and power) systems have good performance as black-start units. It is the most important black-start unit in areas which do not have hydro power units. In this paper, the CCHP system is designed and planned under extra consideration of it serving as a black-start unit. It puts forward an optimized planning (allocation) model for CCHP systems with the consideration of CCHP systems being black-start units. Based on the regional black-start units, black-start schemes and load conditions, the reliability of black-start, outage cost and investment on construction are calculated. Aiming to minimize outage cost and investment on construction, setting simulation results as constraints, building the optimized model and finally applying the Particle Swarm Optimization (PSO) method to attain the best solution. The analysis of example case indicates that the optimized planning proposed here is effective. It gives important reference for the design and planning of CCHP system.

Analysis and optimization of CCHP systems based on energy, economical, and environmental considerations

Combined Cooling Heat and Power (CCHP) attained significant attention among energy professionals and academicians recently due to its superior thermal, economic and environmental benefit in comparison with conventional energy producing systems (internal combustion engine (ICE), micro-turbine, etc). Despite the abundance of literature on CCHP, only a few studies emphasized on the selection of appropriate prime mover for an economically sustainable CCHP system. Furthermore, the effect of part load efficiencies is commonly neglected during CCHP analysis. We had introduced these two new concepts of economic sustainability of specific prime mover and part load effects on efficiency to CCHP system in our previous paper. An algorithm based on hybrid load following method was utilized to determine the optimum prime mover for a particular location and weather type. No studies explored the effects of efficiency parameters and the selection strategies of prime mover in different building types for any particular location using this newly developed algorithm. Since building types dominates the electric, heating and cooling demand extensively, it is imperative to extend the prime mover selection analysis for building types for efficient CCHP operation. Economic, energy, and emission performance criteria have been utilized for the prime mover selection systems in different building types. Computer simulations were conducted for five different building categories (primary school, restaurant, small hotel, outpatient clinic and small office buildings) for each of three different types of prime movers (reciprocating internal combustion engine (ICE), micro-turbine and phosphoric acid fuel cell) in a cold climate zone (Minneapolis, MN). The simulation results of different prime movers were compared with the outcomes of a reference case (for each building in the same climate zone) that has a typical separate heating and power system. The cold climate zone (Minneapolis, MN) helped to explore the heating load effects on economic, energy, and emission performance of the buildings in comparison to other energy demands (i.e. electric and cooling demand). A hybrid load following method was executed, using improvements shown in our previous article. Performance parameters and other outcomes of this study showed that economic savings were observed for the ICE in all building types, and the micro-turbine in some building types. Internal rate of returns of ICE are 22.4%, 14.7%, 20.5%, 14.6% and 6.5% for primary school, restaurant, small hotel, outpatient clinic and small office respectively. ICE also shows highest energy savings among all three prime movers with an energy savings of 20%, 17.2%, 25.7%, 23.8% and 9.7% for primary school, restaurant, small hotel, outpatient clinic and small office respectively. For all types of prime mover based CCHP systems, lower CO2 emission was observed for all building types. However, unlike ICE, which is preferable in terms of economic and energy savings, emission analysis shows that micro-turbine poses better emission characteristics compared to other types of prime movers. CO2 emission for micro-turbine savings are 67.1%, 62.2%, 82%, 43.2% and 81.4% for primary school, restaurant, small hotel, outpatient clinic and small office respectively. The relationship between the power and thermal demand of the different buildings was determined to be a significant factor in CCHP system performance. A sensitivity analysis determining the effects of heat exchanger and heating coil efficiencies on the performance of CCHP systems shows that the economic performance was most sensitive to the heat exchanger efficiency, while energy consumption and emissions was most sensitive to the heating coil and boiler efficiency.

Energy matching and optimization analysis of waste to energy CCHP (combined cooling, heating and power) system with exergy and energy level

As the energy shortage and environmental problems gradually deepened, the Combined Cooling, Heating and Power (CCHP) system has gained attention for its high efficiency and low emission. In this paper, we compare the CCHP system with the conventional separate supply system, and considered the cost saving as the objective function of the multi-objective optimization. In order to show the energy conservation and environmental protection advantages of CCHP, we set the Green House Gases emission reductions and energy savings as constraint conditions. At last, we determined the optimal economic effect of CCHP and conventional separate supply system by case study. It is indicated that the emission reduction of CCHP system is better than the conventional separate supply system in the study, and when the electric price is higher than 0.11 times of gas price, the cost of CCHP system is smaller.

Heating and cooling energy requirements for buildings are usually supplied by separated systems such as furnaces or boilers for heating, and vapor compression systems for cooling. For these types of buildings, the use of combined cooling, heating, and power (CCHP) systems or combined heating and power (CHP) systems are an alternative for energy savings. Different researchers have claimed that the use of CCHP and CHP systems reduces the energy consumption related to transmission and distribution of energy. However, most of these analyses are based on reduction of operating cost without measuring the actual energy use and emissions reduction. The objective of this study is to analyze the performance of CCHP and CHP systems operating following the electric load (FEL) and operating following the thermal load (FTL), based on primary energy consumption (PEC), operation cost, and carbon dioxide emissions (CDE) for different climate conditions. Results show that CCHP and CHP systems operated FTL reduce the PEC for all the evaluated cities. On the other hand, CHP systems operated FEL always increases the PEC. The only operation mode that reduces PEC and CDE while reducing the cost is CHP-FTL. Copyright © 2009 John Wiley & Sons, Ltd.

Over the past decade, rising energy demand and cost have created a surge of interest in alternative methods of power generation. As a result, the implementation of combined cooling, heating, and power (CCHP) systems has become a potential candidate for substitution in conventional power generation. The evaluation of a CCHP system must be based on its potential for savings in cost and primary energy reduction. In general, a CCHP system includes several components to satisfy the electric and thermal demands of the facility. These components include the prime mover, heat recovery system, auxiliary boiler, absorption chiller, heating coil unit, and hot water system unit. In practice, the most common prime mover used in CCHP technology is the internal combustion engine, which is limited by low thermal efficiency and poor emissions. Hence, this paper proposes the use of a Stirling engine prime mover that makes use of waste wood chips for fuel. In addition to the standard CCHP components, the Stirling engine houses heat exchangers to aid heat addition and rejection processes. These heat exchangers must be considered along with the other components when analyzing energy requirements. The goal of this study is to determine how the operational characteristics of a constant output biomass-fired Stirling CCHP system are affected by the performance of the individual CCHP system components. The results of this sensitivity analysis are useful in determining the most important parameters to be considered when implementing and designing the system. Results suggest that fuel cost, engine efficiency, engine size, chiller efficiency, and the Stirling engine’s hot side heat exchanger play the most important roles in the CCHP system operational cost. For example, the results show that increasing the engine size leads to increases in primary energy. In addition, an optimum engine size is suggested for cost savings, with smaller and larger engines both leading to increases in operational cost.

Combined cooling, heating, and power (CCHP) systems generate electricity at or near the place of consumption and utilize the accompanying waste heat to satisfy the building’s thermal demand. CCHP systems have often been cited as advantageous alternatives to traditional methods of power generation and one of the critical components affecting their performance is the power generation unit (PGU). This investigation examines the effect of the PGU on the energy, economical, and environmental performance of CCHP systems. Different size PGUs are simulated under the following operational strategies: follow the building’s electric load, follow the building’s thermal load, and operate at constant load. An internal combustion engine is used as the PGU in the CCHP system to meet hourly electric, cooling, heating, and hot water loads of a typical office building for a year. Annual operational cost, primary energy consumption (PEC), and carbon dioxide emissions (CDE) are found for two cities and compared to a conventional building. Finally, a simple optimization is performed to determine the best engine load for each hour during the simulation. Among the results, the smallest engine generally yielded the lowest costs and lowest PEC; but, no such trend was found with regards to CDE.

Because of the performance of the power generation equipment is almost perfect, how to integrate the thermally-activated technologies and use the waste heat deeply are a critical issue for CCHP (Combined cooling heating and power) system. According to the characteristics of a typical end user’s demands, a CCHP system with the flue gas and geothermal energy is proposed. The system is composed of an internal combustion engine, a soil source absorption heat pump driven by the flue gas, and other assistant facilities, such as pumps, fans, and end user devices. In the winter, the flue gas is used to drive absorption heat pump to recover the waste heat of the soil source and the condensation heat of the flue gas simultaneously, and in the summer, the waste heat of the flue gas is used to drive absorption heat pump to cooling, and the heat sink is the soil. In the paper, the energy analysis of the system is done. Compared with the conventional CCHP system, the operation cost is lowered greatly and the increased investment could be returned within one year. It is show that the system is the efficient integration of clean energy, renewable energy, the discharge of the flue gas could be reduced to below 30°C, and the water steam could be catch to avoid the white smoke of the stack.

Due to the soaring costs and demand of energy in recent years, combined cooling, heating, and power (CCHP) systems have arisen as an alternative to conventional power generation based on their potential to provide reductions in cost, primary energy consumption, and emissions. However, the application of these systems is commonly limited to internal combustion engine prime movers that use natural gas as the primary fuel source. Investigation of more efficient prime movers and renewable fuel applications is an integral part of improving CCHP technology. Therefore, the objective of this study is to analyse the performance of a CCHP system driven by a biomass fired Stirling engine. The study is carried out by considering an hour-by-hour CCHP simulation for a small office building located in Atlanta, Georgia. The hourly thermal and electrical demands for the building were obtained using the EnergyPlus software. Results for burning waste wood chip biomass are compared to results obtained burning natural gas to illustrate the effects of fuel choice and prime mover power output on the overall CCHP system performance. Based on the specified utility rates and including excess production buyback, the results suggest that fuel prices of less than $23/MWh must be maintained for savings in cost compared to the conventional case. In addition, the performance of the CCHP system using the Stirling engine is compared with the conventional system performance. This comparison is based on operational cost and primary energy consumption. When electricity can be sold back to the grid, results indicate that a wood chip fired system yields a potential cost savings of up to 50 per cent and a 20 per cent increase in primary energy consumption as compared with the conventional system. On the other hand, a natural gas fired system is shown to be ineffective for cost and primary energy consumption savings with increases of up to 85 per cent and 24 per cent compared to the conventional case, respectively. The variations in the operational cost and primary energy consumption are also shown to be sensitive to the electricity excess production and buyback rate.

The challenges during the aftermath of natural disasters in remote locations, such as unreliable power supply from the grid during crucial times, coupled with ever-increasing energy needs, demand new and innovative solutions to limited energy production. Local, on-site power generation, such as combined cooling, heating, and power (CCHP) systems, may safeguard against grid fluctuations, outages, and provide additional security through grid independence. CCHP systems can provide more reliable and resilient energy supply to buildings and communities while also providing energy-efficient, cost-effective, and environmentally sustainable solutions compared to centralized power systems. Biomass-driven CCHP systems have been recognized as a potential technology to bring increased efficiency of fuel utilization and environmentally sustainable solutions. Biomass as an energy source is created through agricultural and forestry by-products and may thus be efficiently and conveniently transported to remote rural communities. This paper presents a design and implementation analysis of biomass (primarily wood pellets)-driven CCHP systems for a rural community across the United States. The U.S. Department of Energy Climate Regions map was used to determine areas of interest. For this study, all three climates moist, dry, and marine as well as all major climate zones (2–6) were included. To effectively compare small towns across the U.S., the selection process was based on certain criteria: A population of approximately 1,500 people, the existence of a rural hospital, two kinds of schools (E.g., an elementary and a high school), and small businesses. The following places meet those conditions and are located in differentiating climate zones: (2A) Keystone Heights, FL, (3A) Ackerman, MS, (3B) Quincy, CA, (3C) Mariposa, CA, (4A) Hardinsburg, KY, (4C) Coupeville, WA, (5A) Alma, NE, (5B) Lovelock, NV, (6A) Colebrook, NH, (6B) Choteau, MT. Each location was investigated based on the merits of on-site CCHP systems and potential grid independence. The viability of wood pellets (WP) as a suitable fuel source is explored by comparing it to a conventional natural gas-driven and grid-connected system. To measure viability, three performance parameters — operational cost (OC), primary energy consumption (PEC), and carbon dioxide emission (CDE) — are considered in the analysis. The results demonstrate that in many climate regions wood pellet-fueled CCHP systems create significant economic and environmental advantages over traditional systems. Additionally, on-site energy production and the potential for grid independence, especially in the aftermath of natural disasters provide critical services and added upsides of traditional systems. The main factors in increasing the viability of CCHP systems are the appropriate sizing and operational strategies of the system and the purchase price of biomass with respect to the price of traditional fuels.