Abstract

Cogeneration, also known as combined heat and power (CHP), refers to a group of proven technologies that operate together for the concurrent generation of electricity and useful heat in a process that is generally much more energy-efficient than the separate generation of electricity and useful heat.

The typical method of separate centralized electricity generation and on-site heat generation has a combined efficiency of about 45 percent whereas cogeneration systems can reach efficiency levels of 80 percent. Cogeneration is widely deployed outside the United States, with Denmark, the Netherlands, and Finland leading the world in cogeneration deployment as a fraction of total national electricity generation. Micro CHP installations use five different technologies:micro turbines,internal combustionengines,stirling engines, closed cyclesteam enginesandfuel cells.

IntroductionCombined heat and power (CHP) is an efficient and clean approach to generating electric power and useful thermal energy from a single fuel source. CHP places power production at or near the end-users site so that the heat released from power production can be used to meet the users thermal requirements while the power generated meets all or a portion of the site electricity needs. Applications with steady demand for electricity and thermal energy are potentially good economic targets for CHP deployment. Industrial applications particularly in industries with continuous processing and high steam requirements are very economic and represent a large share of existing CHP capacity today. Commercial applications such as hospitals, nursing homes, laundries, and hotels with large hot water needs are well suited for CHP. Institutional applications such as colleges and schools, prisons, and residential and recreational facilities are also excellent prospect.

Background

Started in 1998 with Marathon Engine purchase. Engine developed in 1980s as a heat pump, long life power source. Swiss company ecopower needed a robust engine in 2000 for new CHP. Started a European presence in 2001 and then sold to Vaillant 3500 installs. US market started by MES in 2007 with controlled installs to be monitored. Manufacturing facility in Wisconsin, developing the North American market for small scale CHP. Other products relate to remote power with the Marathon engine.Cogeneration is a system of commercially available technologies that decrease total fuel consumption and related GHG emissions by generating both electricity and useful heat from the same fuel input. Cogeneration is often called combined heat and power (CHP), since most cogeneration systems are used to supply electricity and useful heat. However, the heat energy from electricity production can also be used for cooling and other non-heating purposes, so the term cogeneration is more inclusive. Cogeneration is a form oflocal or distributed generation as heat and power production take place at or near the point of consumption.For the same output of useful energy, cogeneration uses far less fuel than does traditional separate heat and power production, which means lower greenhouse gas (GHG) emissions as fossil fuel use is reduced.

While the greatest potential for increasing cogeneration is in the industrial sector, the technology is also increasingly available for smaller-scale applications in residential and commercial facilities. Cogeneration systems appeal to business operations requiring a continuous supply of reliable power such as data centers, hospitals, universities, and industrial operations. District heating and cooling (DHC) in cities and large institutions is one established use of cogeneration (and one widely employed in Europe) in the residential and commercial sectors. District heating can meet low and medium temperature heat demands, such as space heating and hot tap water preparation, by using waste heat from electricity generation to heat water that is transported through insulated pipes.

OverviewIn many cases CHP systems primarilygenerate electricityand heat is a by-product; micro-CHP systems in homes or small commercial buildings are controlled by heat-demand, deliveringelectricityas the by-product. When used primarily for heat in circumstances of fluctuating electrical demand, micro-CHP systems will often generate more electricity than is instantly being demanded.A micro-CHP system is a smallheat engine(power plant) which provides all the power for an individual building;heating, ventilation, and air conditioning,mechanical energyand electric power. It is a smaller-scale version ofcogenerationschemes which have been used with large scale electric power plants. The purpose is to utilize more of the energy in the fuel. The reason for using such systems is thatheat engines, such assteam power plantswhich generate the electric power needed for modern life by burning fuel, are not very efficient. Due toCarnot's theorem, a heat engine cannot be 100% efficient; it cannot convert anywhere near all the heat in the fuel it burns into useful forms such as electricity. So heat engines always produce a surplus of low-temperaturewaste heat, called "secondary heat" or "low-grade heat". Modern plants are limited to efficiencies of about 33 - 60% at most, so 40 - 67% of the energy is exhausted as waste heat. In the past this energy was usually wasted to the environment.Cogenerationsystems, built in recent years in cold-climate countries, utilize the waste heat produced by large power plants for heating, piping hot water from the plant into buildings in the surrounding community.However, it is not practical to transport heat long distances, due to heat loss from the pipes. Since electricity can be transported practically, it is more efficient to generate the electricity near where the waste heat can be used. So in a "micro-combined heat and power system" (micro-CHP), small power plants are instead located where the secondary heat can be used, in individual buildings. Micro-CHP are defined by the EC as being of less than 50kW electrical power output.In a central power plant, the supply of "waste heat" may exceed the local heat demand. In such cases, if it is not desirable to reduce the power production, the excess waste heat must be disposed in e.g.cooling towersorsea coolingwithout being used. A way to avoid excess waste heat is to reduce the fuel input to the CHP plant, reducing both the heat and power output to balance the heat demand. In doing this, the power production is limited by the heat demand. In a traditionalpower plantdelivering electricity to consumers, about 30% of the heat content of the primary heat energy source, such asbiomass,coal,solar thermal,natural gas,petroleumoruranium, reaches the consumer, although the efficiency can be 20% for very old plants and 45% for newer gas plants. In contrast, a CHP system converts 15%42% of the primary heat to electricity, and most of the remaining heat is captured forhot waterorspace heating. In total, as much as 90% of the heat from the primary energy source goes to useful purposes when heat production does not exceed the demand.CHP systems have benefited the industrial sector since the beginning of the industrial revolution. For three decades, these larger CHP systems were more economically justifiable than micro-CHP, due to theeconomy of scale. After the year 2000, micro-CHP has become cost effective in many markets around the world, due to rising energy costs. The development of micro-CHP systems has also been facilitated by recent technological developments of small heat engines. This includes improved performance and cost-effectiveness offuel cells,Skirling engines,steam engines,gas turbines,diesel enginesandOtto engines.TechnologiesMicro-CHP engine systems are currently based on several different technologies: Fuel cell Internal combustion engines Stirling engines Steam engine Micro turbines

All of the technologies described convert a chemical fuel into electric power. The energy in the fuel that is not converted to electricity is released as heat. All of the technologies, except fuel cells, are a class of technologies known as heat engines. Heat engines combust the fuel to produce heat, and a portion of that heat is utilized to produce electricity while the remaining heat is exhausted from the process. Fuel cells convert the energy in the fuel to electricity electrochemically; however, there are still inefficiencies in the conversion process that produce heat that can be utilized for CHP. Each technology is described in detail in the individual technology chapters, but a short introduction of each is provided here: Reciprocating enginesThe technology is common place used in automobiles, trucks, trains, emergency power systems, portable power systems, farm and garden equipment. Reciprocating engines can range in size from small hand-held equipment to giant marine engines standing over 5-stories tall and producing the equivalent power to serve 18,000 homes. The technology has been around for more than 100 years. The maturity and high production levels make reciprocating engines a low cost reliable option. Technology improvements over the last 30 years have allowed this technology to keep pace with the higher efficiency and lower emissions needs of todays CHP applications. The exhaust heat characteristics of reciprocating engines make them ideal for producing hot water.Steam turbine: Today, steam turbines are mainly used for systems matched to solid fuel boilers, industrial waste heat, or the waste heat from a gas turbine (making it a combined cycle.) Steam turbines offer a wide array of designs and complexity to match the desired application and/or performance specifications ranging from single stage backpressure or condensing turbines for low power ranges to complex multi-stage turbines for higher power ranges. Steam turbines for utility service may have several pressure casings and elaborate design features, all designed to maximize the efficiency of the system. For industrial applications, steam turbines are generally of simpler single casing design and less complicated for reliability and cost reasons. CHP can be adapted to both utility and industrial steam turbine designs.Gas turbines It is the same technology that is used in jet aircraft and many aero derivative gas turbines used in stationary applications are versions of the same engines. Gas turbines can be made in a wide range of sizes from micro turbines (to be described separately) to very large frame turbines used for central station power generation. For CHP applications, their most economic application range is in sizes greater than 5 MW with sizes ranging into the hundreds of megawatts. The high temperature heat from the turbine exhaust can be used to produce high pressure steam, making gas turbine CHP systems very attractive for process industries. Micro turbines They were developed as stationary and transportation power sources within the last 30 years. They were originally based on the truck turbocharger technology that captures the energy in engine exhaust heat to compress the engines inlet air. Micro turbines are clean-burning, mechanically simple, and very compact. There were a large number of competing systems under development throughout the 1990s. Today, following a period of market consolidation, there are two manufacturers in the U.S. providing commercial systems for CHP use with capacities ranging from 30-250 kW for single turbine systems with multiple turbine packages available up to 1,000kW. Fuel cell:Afuel cellis a device that converts thechemical energyfrom afuelintoelectricitythrough a chemical reaction withoxygenor another oxidizing agent. Hydrogenproduced from the steammethanereforming ofnatural gasis the most common fuel, but for greater efficiency hydrocarbonscan be used directly such as natural gas and alcohols likemethanol. Fuel cells are different frombatteriesin that they require a continuous source of fuel and oxygen/air to sustain the chemical reaction whereas in a battery the chemicals present in the battery react with each other to generate anelectromotive force. Fuel cells can produce electricity continuously for as long as these inputs are supplied.The first fuel cells were invented in 1838. The first commercial use of fuel cells came more than a century later inNASAspace programs to generate power for probes, satellites and space capsules. Since then, fuel cells have been used in many other applications. Fuel cells are used for primary and backup power for commercial, industrial and residential buildings and in remote or inaccessible areas. They are also used to powerfuel-cell vehicles, including forklifts, automobiles, buses, boats, motorcycles and submarines.

Cogeneration Process:There are two types of cogenerationtopping cycle and bottoming cycle. The most common type of cogeneration is the topping cycle where fuel is first used to generate electricity or mechanical energy at the facility and a portion of the waste heat from power generation is then used to provide useful thermal energy. The less common bottoming cycle type of cogeneration systems first produce useful heat for a manufacturing process via fuel combustion or another heat-generating chemical reaction and recover some portion of the exhaust heat to generate electricity. Bottoming-cycle CHP applications are most common in process industries, such as glass and steel, that use very high temperature furnaces that would otherwise vent waste heat to the environment. The following description of cogeneration systems focus on toppingCycle applications.Each cogeneration system is adapted to meet the needs of an individual building or facility. System design is modified based on the location, size, and energy requirements of the site. Cogeneration is not limited to any specific type of facility but is generally used in operations with sustained heating requirements. Most CHP systems are designed to meet the heat demand of the energy user since this leads to the most efficient systems. Larger facilities generally use customized systems, while smaller-scale applications can use prepackaged units.

Cogeneration systems are categorized according to their prime movers (the heat engines), though the systems also include generators, heat recovery, and electrical interconnection components. The prime mover consumes (via combustion, except in the case of fuel cells discussed below) fuel (such as coal, natural gas, or biomass) to power a generator to produce electricity, or to drive rotating equipment. Prime movers also produce thermal energy that can be captured and used for other on-site processes such as generating steam or hot water, heating air for drying, or chilling water for cooling. There are currently five primary, commercially available prime movers: gas turbines, steam turbines, reciprocating engines, microturbines, and fuel cells.

Steam turbines and gas, or combustion, turbines are the prime movers (heat engines) best suited for industrial processes due to their large capacity and ability to produce the medium- to high-temperature steam typically needed in industrial processes.

Gas TurbinesGas turbines typically have capacities between 500 kilowatts (kW) and 250 megawatts (MW), can be used for high-grade heat applications, and are highly reliable. Gas turbines operate similarly to jet engines natural gas is combusted and used to turn the turbine blades and spin an electrical generator. The cogeneration system then uses a heat recovery system to capture the heat from the gas turbines exhaust stream. This exhaust heat can be used for heating or cooling. About half of the CHP capacity in the United States consists of large combined cycle systems that include two electricity generation steps that supply steam to large industrial or commercial users and maximize power production for sale to the grid.

Figure 2 shows how a simple-cycle gas turbine cogeneration system recovers heat from the gas turbines hotexhaust gases to produce useful thermal energy for the site.Figure 2: Gas Turbine or Engine with Heat Recovery Unit

Steam TurbinesSteam turbines systems can use a variety of fuels, including natural gas, solid waste, coal, wood, wood waste, and agricultural by-products. Steam turbines are highly reliable and can meet multiple heat grade requirements. Steam turbines typically have capacities between 50 kW and 250 MW and work by combusting fuel in a boiler to heat water and create high-pressure steam, which turns a turbine to generate electricity.12 The low-pressure steam that subsequently exits the steam turbine can then be used to provide useful thermal energy, as shown in Figure 3. Ideal applications of steam turbine-based cogeneration systems include medium- and large-scale industrial or institutional facilities with high thermal loads and where solid or waste fuels are readily available for boiler use.

Figure 3: Steam Boiler with Steam Turbine

Reciprocating EnginesIn terms of the number of units, reciprocating internal combustion engines are the most widespread technology for power generation, found in the form of small, portable generators as well as large industrial engines that power generators of several megawatts; however, because of their small size, reciprocating engines account for only a small share (about 2 percent) of total U.S CHP capacity. Spark ignition (SI) engines are the most common types of reciprocating engines used for CHP in the United States. SI engines (available in capacities up to 5 MW) are similar to gasoline-powered automobile engines, but they generally run on natural gas, though they can also run on propane or landfill and biogas.

Reciprocating engines start quickly, follow load well, have good efficiencies even when operating at partial load, and generally have high reliabilities. Reciprocating engines are well suited for CHP in commercial and light industrial applications of less than 5 MW. Smaller engine systems produce hot water. Larger systems can be designed to produce low-pressure steam. Multiple reciprocating engines can be used to increase system capacity and enhance overall reliability.

Micro turbinesMicro turbines are small, compact, lightweight combustion turbines that typically have power outputs of 30 to300 kW. A heat exchanger recovers thermal energy from the microturbine exhaust to produce hot water or low-pressure steam. The thermal energy from the heat recovery system can be used for potable water heating, absorption cooling, desiccant dehumidification, space heating, process heating, and other building uses. Micro turbines can burn a variety of fuels including natural gas and liquid fuels.

Fuel CellsFuel cells are an emerging technology with the potential to serve power and thermal needs with very low emissions and with high electrical efficiency. Fuel cells use an electrochemical or battery-like process to convert the chemical energy of hydrogen into water and electricity. The hydrogen can be obtained from processing natural gas, coal, methanol, and other hydrocarbon fuels. As a less mature technology, fuel cells have high capital costs, an immature support infrastructure, and technical risk for early adopters. However, the advantages of fuel cells include low emissions and low noise, high power efficiency over a range of load factors, and modular design. A variety of fuel cell technologies are under development, with some targeted for small commercial markets, and other technologies focused on larger, industrial CHP applications.

Environmental Benefit / Emission Reduction Potential

Cogeneration offers multiple environmental benefits. Since less fuel is burned per unit of useful energy output, cogeneration reduces GHG emissions and decreases air pollution compared to SHP systems. Currently installed cogeneration systems avoid the equivalent of 1.8 percent of annual U.S. energy consumption and annual CO2 emissions of 248 million metric tons (equal to 3.5 percent of total U.S. GHG emissions in 2007). A recent study by the Oak Ridge National Laboratory (ORNL) calculated that increasing cogenerations share of total U.S. electricity generation capacity to 20 percent by 2030 (which ORNL estimated would require deploying 156 GW of new cogeneration capacity compared to about 85 GW today) would lower U.S. GHG emissions by 600 million metric tons of CO2 .

While the ORNL analyzed an ambitious goal for expanding cogeneration by 2030, a 2009 study by McKinsey& Company sought to estimate the cost-effective potential for expanding cogeneration by 2020 (i.e., the potential to make NPV-positive investments in cogeneration). McKinsey estimated that the potential exists in the United States for an additional 50.4 GW of cogeneration capacity by 2020, which would avoid an estimated 100 million metric tons of CO2 per year compared to business as usual. McKinsey found that the cost-effective incremental cogeneration capacity consisted primarily (70 percent) of large-scale (greater than 50 MW) industrial cogeneration systems. Figure 4 shows McKinseys estimates of the composition of cost-effective cogeneration potential for 2020.

Figure 4: McKinseys Estimates of Cost-Effective Cogeneration Potential for 2020 by Sector

Education

7% Healthcare12%

Energy-intensive industries31%

Office28%

Cost

Current Status of Cogeneration

Cogeneration currently accounts for roughly 12 percent of total U.S. electricity generation and comprises about 9 percent (85 giga watts at about 3,300 sites) of total generating capacity. Figures 5-8 show how existing cogeneration capacity is distributed across different applications, system technology types, and fuel inputs. Only about 12 percent of existing cogeneration capacity is deployed at commercial or institutional facilities (as opposed to industrial or manufacturing facilities). Nearly three quarters of cogeneration capacity uses natural gas for fuel, and gas-fired combustion turbines and combined cycle systems dominate cogeneration capacity even though nearly half of all cogeneration sites use reciprocating engines (the reciprocating engines are much smaller in terms of capacity than the other systems). Large cogeneration systems (100 megawatts or more in capacity) account for roughly 65 percent of total cogenerationCapacity.

Obstacles to Further Development or Deployment of Cogeneration

Capital Constraints

Cogeneration systems are large capital investments. Firms may be unwilling to undertake such significant capital investments even when they may offer positive returns. Another cost consideration for firms is business uncertainty. If a firm is not confident that it will continue operations for many years at a given facility, it may not invest in the high upfront costs of cogeneration since a projects economic viability can depend on cost savings realized over several years. In addition, there can be costs associated with manufacturing downtime and siting and permitting issues. Also, seamless integration of components beyond the basic equipment can necessitate specialized parts and increase the cost of a cogeneration system.41

Utility Business Practices

Many cogeneration systems maintain their connection to the utility grid for supplemental power needs beyond their self-generation capacity and/or for standby and back-up service during routine maintenance or unplanned outages. Utility charges for these services (standby rates) can significantly reduce the money-saving potential of cogeneration. However, cogeneration and other types of distributed energy allow the grid to function more efficiently by reducing base load and peak demand, as well as reducing the need for transmission and distribution upgrades and construction. Pricing arrangements between utilities and cogeneration system operators that fairly account for utilities obligation to supply backup power as well as the benefits to the grid of cogeneration (e.g., avoided costs of building new generation and transmission capacity) can encourage cogeneration investments.

Utility Interconnection

The economic viability of cogeneration systems depends on their ability to safely, reliably, and economically interconnect with the existing grid. Interconnection standards, including technical specifications as well as application processes and fees, between utilities and cogeneration systems are often state mandated and vary regionally. This lack of uniformity makes it difficult for manufacturers of cogeneration technologies to produce modular components and can make cogeneration system deployment more complicated and expensive. Improved interconnection policies could increase deployment of cogeneration systems.43,44

Environmental Permitting Regulations

By generating both electricity and heat onsite, cogeneration can increase a facilitys onsite air emissions even as it reduces total emissions associated with the facilities heat and electricity consumption. Current environmental permitting regulations do not always recognize this overall emissions reduction benefit. For example, the Clean Air Acts New Source Review (NSR) requires large, stationary sources to install best available pollution control equipment during construction or major modifications that increase onsite emissions. In some circumstances NSR requirements can discourage installation of CHP systems even when they would improve environmental outcomes.45The adoption of output-based emission standards, which allows cogeneration systems to benefitfrom their increased efficiency, is one way to encourage more cogeneration systems. Need for Further Research, Development, and Demonstration (RD&D)To improve the performance of cogeneration technologies and reduce investment costs, furtherRD&D is warranted, specifically in the areas of: high-temperature CHP, small-scale systems (e.g., improving the efficiency of micro-turbines and their cost through improved manufacturing techniques), fuel cell research, heat & cold storage system optimization and integration, andmedium-scale systems (e.g., increased demonstration of medium-scale turbines in various industrialsettings).46

Policy Options to Help Promote Cogeneration

Price on Carbon

Policies that set a price on GHG emissions, such as a GHG cap-and-trade program (see Climate Change 101: Cap and Trade), can encourage investment in energy-efficient technology such as cogeneration. Carbon pricing policies (e.g., cap and trade allowance allocation) can be designed so as not to create disincentives for cogeneration.47

Renewable Portfolio and Energy Efficiency Resource Standards

Renewable Portfolio Standards and Energy Efficiency Standards require that energy providers meet a specific portion of their electricity demand through renewable energy and/or energy efficiency measures. Such policies specify eligible energy sources and technologies that count towards the requirements. More than a dozen states allow cogeneration to count toward renewable/alternative energy and efficiency standards.48

Financial Incentives for Cogeneration

Certain states already offer investment tax credits (ITC), which are a form of subsidy to help offset the upfront capital cost of investments, for cogeneration, and the federal government also offers a10 percent ITC for cogeneration (enacted in 2008) and accelerated depreciation.49 Some statesoffer production incentives, which provide a financial benefit based upon the annual useful energy output of the cogeneration system.

Interconnection Standards

Coordination among state and federal regulators, utilizes, and stakeholder groups regarding best practices in cogeneration interconnection with the electric grid can help ensure cogeneration interconnection contributes to a safe and reliable grid and minimize the cost and complexity facing cogeneration technology providers and users designing and deploying systems for interconnection.

Environmental PermittingCogeneration is more readily deployed when environmental regulations do not penalize cogeneration systems that increase onsite air emissions (by using more fuel onsite to generate both electricity and heat) while also decreasing net air emissions by having higher efficiency (and thus less total fueluse) than separate heat and power generation.50

Research, Development, and Demonstration (RD&D)Continued and increased funding for programs such as the Department of Energys Industrial Technologies Program (ITP)51 would support RD&D for cogeneration technologies to improve reliability and efficiency and reduce costs. ITPs public-private partnerships help future deployment of both integrated energy systems and component technologies (for upgrading and retrofits).

Technical Assistance for Potential Cogeneration UsersMany companies (especially small and medium-sized businesses) that would benefit from cogeneration systems are not aware of their financial or technical options. Expanding programs that work with companies such as the U.S. Environmental Protection Agencys Combined Heat and Power Partnership,52 the National Institute of Standards Manufacturing Extension Partnership,53 and DOEs Industrial Assessment Centers and CHP Regional Application Centers54 would help further

promote cogeneration.

Market statusJapanThe largest deployment of micro-CHP is inJapanin 2009 where over 90,000 units in place, with the vast majority being ofHonda's"ECO-WILL" type.Six Japanese energy companies launched the 300W1kWPEMFC/SOFCENE FARMproduct in 2009, with 3,000 installed units in 2008, a production target of 150,000 units for 20092010 and a target of 2,500,000 units in 2030.20,000 units were sold in 2012 overall within the Ene Farm project making an estimated total of 50,000 PEMFC and up to 5,000 SOFC installations.For 2013 a state subsidy for 50,000 units is in place.The ENE FARM project will pass 100.000 systems in 2014, 34.213 PEMFC and 2.224 SOFC were installed in the period 2012-2014, 30,000 units onLNGand 6,000 onLPG.South KoreaInSouth Korea, subsidies will start at 80 percent of the cost of a domestic fuel cell.TheRenewable Portfolio Standardprogram withrenewable energy certificatesruns from 2012 to 2022.Quota systems favor large, vertically integrated generators and multinational electric utilities, if only because certificates are generally denominated in units of one megawatt-hour. They are also more difficult to design and implement than an aFeed-in tariff.Around 350 residential mCHP units where installed in 2012.

EuropeThe Europeanpublicprivate partnershipFuel Cells and Hydrogen Joint UndertakingSeventh Framework Programmeproject ene.field deploys in 2017up 1,000 residential fuel cell Combined Heat and Power (micro-CHP) installations in 12 states. Per 2012 the first 2 installations have taken place.GermanyIn Germany, 3,000 ecopower micro-CHP units have been installed, using the U.S. based Marathon Engine Systems long-life engine. The engine runs on natural gas and propane. The ecopower micro-CHP is also available in the United States. The German government is offering large CHP incentives, includingfeed-in tariffsand bonus payments for use of micro-CHP generated electricity. The German testing project Callux has 500 Mchp installations per nov 2014.North-Rhine Westphalialaunched a 250 million subsidy program for up to 50 kilowatts lasting until 2017.UKIt is estimated that about 1,000 micro-CHP systems were in operation in the UK as of 2002. These are primarily "Whispergen"Stirling engines, and Senertec Dachsreciprocating engines. The market is supported by the government through regulatory work, and some government research money expended through the Energy Saving Trust andCarbon Trust, which are public bodies supporting energy efficiency in the UK.Effective as of 7 April 2005, the UK government has cut the VAT from 20% to 5% for micro-CHP systems, in order to support demand for this emerging technology at the expense of existing, less environmentally friendly technology. The reduction in VAT is effectively a 10.63%]subsidyfor micro-CHP units over conventional systems, which will help micro-CHP units become more cost competitive, and ultimately drive micro-CHP sales in the UK. Of the 24 million households in the UK, as many as 14 to 18 million are thought to be suitable for micro-CHP units.Two fuel cell varieties of mCHP co-generation units are almost ready for mainstream production and are planned for release to commercial markets in early in 2014. With the UK Government's Feed-In-Tariff available for a 10 year period, a wide uptake of the technology is anticipated.DenmarkThe Danish mCHP project 2007 to 2014 with 30 units is on the island ofLollandand in the western townVarde.Denmark is currently part of the Ene.field project. IRD Fuel Cell Dantherm Power(Ballard Power)The NetherlandsThe micro-CHP subsidy was ended in 2012.To test the effects of mCHP on asmart grid, 45natural gasSOFCunits (each 1,5 kWh) from Republiq Power (Ceramic Fuel Cells) will be placed onAmelandin 2013 to function as avirtual power plant.United StatesThe federal government is offering a 10% tax credit for smaller CHP and micro-CHP commercial applications.In 2007, the United States company "Climate Energy" of Massachusetts introduced the "Freewatt,a micro-CHP system based on a Honda MCHP engine bundled with a gas furnace (for warm air systems) or boiler (for hydronic or forced hot water heating systems). Through a pilot program scheduled for mid-2009 in Southern Ontario, the Freewatt system is being offered by Eden Oak with support from ECR International, Enbridge Gas Distribution and National Grid.Summary:Separate heat and power (SHP) refers to the widespread practice of centrally generating electricity at large- scale power plants and separately generating useful heat onsite for applications such as industrial processes or space and water heating. SHP leads to energy losses in both processes. Typical SHP has a combined efficiency of about 45 percent while cogeneration systems that combine the power and heat generation processes can be up to 80 percent efficient. Because cogeneration takes place on-site or close to the facility it also results in less energy lost during the transmission and distribution process (usually about 9 percent of net electricity generation).

How to design a tubular heat exchanger?At HRS Heat Exchangers, designing tubular heat exchangers is our daily business. In this text we would like to describe you the various steps of the design process.Step 1: Analyzing the applicationWhen an enquiry for a heat exchanger is received, the first step consists in analyzing the application. Is it a food industry application? Is it an industrial one? The design engineer must define correctly the type of heat exchanger that is necessary and complies with the requirements of the application. As can be seen in our product portfolio, various types of heat exchangers can be used.The design temperature, design pressure and maximum allowable pressure drop must be defined for the product and service fluids.Step 2: Identifying the fluid propertiesThe next step is analyzing the fluids involved: the product side fluid and service side fluid. In order to do a correct design of a heat exchanger, four important physical properties of the fluids involved need to be known: Density Specific heat Thermal conductivity ViscosityThe correct way to proceed is to obtain values for these four parameters for various temperatures in the heating or cooling curve of the application. The better we understand the physical properties of the fluids involved, the more accurate will be the design of the heat exchanger. Any mistake in the physical properties involved can lead directly to a wrong design of the heat exchanger.Step 3: The energy balanceOnce correctly defined the physical properties, it is time to check the energy balance. Normally the customer defines the products flow rate and the desired entry and exit temperature of this product. He will have to indicate the type of serviced fluid to be used and define two of the following three parameters: service flow rate, service entry temperature or service exit temperature. With two of these known, solving the energy balance, the third parameter is calculated. Completing step 3 fixes the flow rates and entry and exit temperatures of the product and service side fluids.Step 4: Defining the geometry of the heat exchangersIn this step the design engineer defines the geometry of the heat exchanger. He will choose the shell diameter and will define the tube bundle that is placed inside the heat exchanger: nr of inner tubes, inner tube diameter and wall thickness and the length of the inner tubes. Secondly, the dimensions of the shell and tube side fluid connections are defined. At this stage also the choice of materials applied has to be made. By standard HRS Heat Exchanger applies stainless steels for shell and tubes side, but also other alloys can be applied.Step 5: Thermal calculationAt this stage the design engineer performs a thermal calculation. The objective of this calculation is to obtain the shell and tube side heat transfer coefficients. These coefficients depend basically on the four key fluid parameters and the velocity of the fluid. The relation between the parameters and the heat transfer coefficients is defined in a mathematical formula that is specific to the geometry applied (tubular heat exchanger, plate heat exchanger, corrugated tube). HRS Heat Exchangers has derived its own specific mathematics as it works with corrugated tubes.With shell and tube side coefficients known, the overall heat transfer coefficient can be calculated. Knowing this value, it becomes possible to calculate the total heat transfer area needed for the application:Area = Duty / [K x LMTD]Area: Total heat transfer area required, m.Duty: Total heat transferred, kcal/hr (derived from energy balance).K: Overall heat transfer coefficient, kcal/[hr.m.C].LMTD: Log mean temperature difference, C (the average logarithmic temperature difference between shell and tube side fluid over the heat exchanger length).Another important parameter defined is the pressure drop which is calculated for the shell and tube side fluids. The pressure drop is a function of the Reynolds number, the type of flow (turbulent or laminar flow) and the roughness value of the shell and inner tubes.

Step 6: Interpretation of the thermal calculationThe calculated area is compared with the area defined in step four (defining geometry of the heat exchanger) and a check is made to see if the pressure drops are within the design limits. In case the calculated area exceeds the predefined area, the geometry of the heat exchanger needs to be redefined (more length or more inner tubes). The same accounts for the pressure drop: if the calculated value exceeds the maximum defined pressure drop, then a new geometry must ensure a pressure drop reduction. The interpretation of the obtained results and adaptation of the design may cause that various times step four to six have to be repeated, until a satisfactory result is obtained.Step 7: Mechanical design calculationsWith the heat exchanger geometry defined, the mechanical design calculations must be done to ensure that the heat exchanger design is valid for the design pressure and conditions. The typical calculations are: Calculation of shell wall thickness. Calculation of nozzle wall thickness. Calculation of inner tube wall thickness. Calculation of expansion joint dimensions (to compensate for shell and tube side differential expansion due to temperatures differences. Calculation of tube sheet thickness.The mechanical design calculations may result in needed wall thicknesses or other parameters that do not comply with the geometrical design defined in step 4. In this case a new proposal for the geometry must be made and step 4 to 7 must be repeated.

Step 8: Preparation of the manufacturing drawingsWith all dimensions of the heat exchanger defined, the manufacturing drawings can be prepared. This drawing package contains details of the various components of the heat exchanger:

Shell. Inner tubes. Expansion joint. Connections. Tube sheet. Baffles. etc. The Heat Exchanger Design EquationHeat exchanger theory leads to the basic heat exchanger design equation: Q = U A Tlm, whereQ is the rate of heat transfer between the two fluids in the heat exchanger in But/hr,U is the overall heat transfer coefficient in Btu/hr-ft2-oF,A is the heat transfer surface area in ft2,and Tlmis the log mean temperature difference inoF, calculated from the inlet and outlet temperatures of both fluids.For design of heat exchangers, the basic heat exchanger design equation can be used to calculate the required heat exchanger area for known or estimated values of the other three parameters, Q, U, and Tlm. Each of those parameters will now be discussed briefly. Log Mean Temperature DifferenceThe driving force for any heat transfer process is a temperature difference. For heat exchangers, there are two fluids involved, with the temperatures of both changing as they pass through the heat exchanger, so some typeof average temperature difference is needed. Many heat transfer textbooks have a derivation showing that the log mean temperature difference is the right average temperature to use for heat exchanger calculations. That log mean temperature is defined in terms of the temperature differences as shown in the equation at the right. THinand THoutare the inlet and outlet temperatures of the hot fluid and TCinand TCoutare the inlet and outlet temperatures of the cold fluid. Those four temperatures are shown in the diagram at the left for a straight tube, two pass shell and tube heat exchanger with the cold fluid as the shell side fluid and the hot fluid as the tube side fluid. Heat Transfer Rate, QHeat exchanger calculations with the heat exchanger design equation require a value for the heat transfer rate, Q, which can be calculated from the known flow rate of one of the fluids, its heat capacity, and the required temperature change. Following is the equation to be used:Q = mHCpH(THin- THout) = mCCpC(TCout- TCin), wheremH= mass flow rate of hot fluid, slugs/hr,CpH= heat capacity of the hot fluid, Btu/slug-oFmC= mass flow rate of cold fluid, slugs/hr,CpC= heat capacity of the cold fluid, Btu/slug-oF,and the temperatures are as defined in the previous section.The required heat transfer rate can be determined from known flow rate, heat capacity and temperature change for either the hot fluid or the cold fluid. Then either the flow rate of the other fluid for a specified temperature change, or the outlet temperature for known flow rate and inlet temperature can be calculated Overall Heat Transfer Coefficient, UThe overall heat transfer coefficient, U, depends on the conductivity through the heat transfer wall separating the two fluids, and theconvection coefficients on both sides of the heat transfer wall. For a shell and tube heat exchanger, for example, there would be an inside convective coefficient for the tube side fluid and an outside convective coefficient for the shell side fluid. The heat transfer coefficient for a given heat exchanger is often determined empirically by measuring all of the other parameters in the basic heat exchanger equation and calculating U. Typical ranges of U values for various heat exchanger/fluid combinations are available in textbooks, handbooks and on websites. A sampling is given in the table at the right for shell and tube heat exchangers: SummaryPreliminary heat exchanger design to estimate the required heat exchanger surface area can be done using the basic heat exchanger equation, Q = U A Tlm, if values are known or can be estimated for Q, U and Tlm. Heat exchanger theory tells us that Tlmis the right average temperature difference to use.For example preliminary heat exchanger design calculations, see the article, "Preliminary Heat Exchanger Design Example."For Excel spreadsheet templates that can be downloaded to make preliminary heat exchanger design calculations, see the article: "Excel Spreadsheet Templates for Preliminary Heat Exchanger Design." References and Image CreditReferences for Further Information:1. Bengtson, H.,Fundamentals of Heat Exchangers,an online, continuingeducationcourse for PDH credit2. Kakac, S. and Liu, H.,Heat Exchangers: Selection, Rating and Thermal Design, CRC Press, 2002.3. Kuppan, T.,Heat Exchanger Design Handbook, CRC Press, 2000.Image Credit:Straight tube, two pass, shell and tube heat exchanger:http://www.e-steamboilers.com/en/shell_tube_heat_ex.asp

Conclusion CHP is a proven solution for meeting growing energy demand efficiently, cleanly and economically. CHP is a clean energy solution that immediately addresses a number of national priorities including improving the competitiveness of Pk. manufacturing, increasing energy efficiency, reducing emissions, enhancing our energy infrastructure, improving energy security and growing our economy.

CHP - Background Information

What is CHP:

CHP (combined heat and power) are systems that produce electrical and thermal loads at the same time. Until recently the production of the electricity was made in power plants where huge amounts of heat energy were lost in the environment. The principal idea of CHP is to take advantage of the thermal energy from the production of electricity. Thus, CHP are high efficiency systems.

As micro CHP the EU (2004/8/EC)1has defined small scale systems (less than 50 kW). These usually are applied for space and water heating to individual dwellings and small commercial buildings replacing the conventional boilers.CHP provide furthermore fuel savings, reducing as a result emitted gases and the operational cost. The systems can function in parallel to the grid exporting energy or backing it up in case of a break down.Micro CHP seems like a promising new solution with substantial growth and prospects being appreciated worldwide. Governments consider these systems as reliable solutions. Industry is developing new technologies, introducing alternative fuels and making the systems simpler and more accessible to all.

Types of engines and fuels:Micro CHP are simple systems easily installed. They require roughly the same space with a boiler and are sound insulated. The most commercial systems are the ICE (internal combustion engines) while the external combustion engines such as Stirling engines, micro gas turbines and ORC (Organic rankin cycle) systems are aiming for the biggest market share. Fuel cells are still not commercially available.Micro CHP are usually gas or petroleum fueled. However alternatives like biomass have become available maintaining high efficiencies and reducing carbon emissions to minimum levels.

How micro CHP operate:Micro CHP systems are installed more or less as conventional boilers. They have similar volume and noise regulations.External combustion engines:Most of the micro CHP systems are external combustion engines such as Stirling and rankin

cycle engines. These systems are providing higher efficiency, can work with various types of fuel, have low gas emissions, low levels of noise and vibration. External combustion engines are using a part of fuel gas to drive the engine and produce electricity. The fuel (helium, hydrogen, etc) is been preheated in a heater alternator. Due to the external combustion, damages to the engine are limited, but require good isolation to avoid leakage.

Internal combustion engines:These are more popular in bigger scale systems. Currently industry is constructing high efficiency engines also in small scale systems. These engines are applicable to a wide range of usage and their operation can work also with liquid and gas fuels. Their operation is similar to car engines. Their main disadvantage is high maintenance cost and higher level of noise and gas emissions.

Fuel cells:Fuel cells are electrochemical engines that convert chemical energy of fuel to electricity without combustion. The principal operation is that hydrogen and oxygen reacting with an electrolyte produce water electricity

and heat. Main advantages of fuel cells are high electricity efficiency, easy in usage, low level of noise and emissions. Due to the high efficiency and the type of fuel are used the emissions are 10 to 100 times lower than other system. The disadvantages that are limiting their popularity are high cost and low lifetime. Two most common types of fuel cell systems are the PEM (Proton Exchange Membrane) and SOFC (Solid Oxide Fuel Cells).

Commercial status:External combustion engines are more popular in Europe, while in America internal combustion engines prevail. The Japanese market is focused mostly on fuel cells. Generally, fuel cells seem to be a more promising technology due to the advantages over internal and external combustion engines such as the high efficiency in electricity production, low gas emissions, independent of high heat demand and more suitable for future buildings. However, the cost is very high and their lifetime very short.The tables below are showing the efficiencies for different micro CHP systems and their prices.

References1.Access to European Union law(eur-lex.europa.eu)2.Combined heat and power, last update 1 November 2009 - ender day 1 - 15 April 20103. Harrison J.,Micro Combined Heat & Power (CHP) for housing, 3rd International Conference on Sustainable Energy Technologies. Nottingham, UK, 28-30 June 20044.Government cash reward for microCHP, Combined Heat and Power Association, press release 5 February 2010 Images source: Click on the images to see the source

BackgroundCogenerationCogeneration(Combined Heat and Power or CHP) is the simultaneous production of electricity and heat, both of which are used. The central and most fundamental principle of cogeneration is that,in order to maximise the many benefits that arise from it, systems should be based according to the heat demand of the application. Through the utilisation of the heat, the efficiency of cogeneration plant can reach 90% or more.11% of Europes electricity and associated heat requirements today are produced using this proven energy efficiency principle. The estimated growth potential for cogeneration is a further 110-120 GWe which will lead to an improved environment and greater economic competitiveness in Europe. Cogeneration units can be found in different sizes and applications: industry, households and tertiary sector and spans applications with capacities ranging from below 1kw to hundreds of Megawatts. It is a highly efficient energy solution that delivers energy savings and substantial reductions in CO2emissions. When seriously supported by Member States, realising the potential of cogeneration in Europe will contribute significantly to reaching the strategic climate and energy goals, such as security of supply, energy efficiency and reduction of emissions..