During and after recent Hurricanes Harvey, Irma, and Maria in 2017, and Hurricane Sandy in 2012, combined heat and power (CHP) enabled a number of critical facilities to continue their operations when the electric grid went down. Time and again, CHP has proved its value as an alternative source of power and thermal energy (heating and cooling) during emergencies, and demonstrated how it can be a cost-effective and reliable choice in making energy infrastructure more resilient in the face of extreme weather events.
CHP can effectively contribute to state and local planning efforts to build resiliency for both critical facilities and microgrids. CHP systems allow facilities to remain functional in the event of a disaster, and for non-critical loads to resume functionality as quickly as possible (e.g. CHP systems with back start capability and that meet other technical requirements, can ensure seamless operation during a grid outage). Key facilities across sectors can be protected from disruptions to the electricity grid through the use of CHP and other forms of distributed energy. Compared to backup generators, CHP systems run daily and are typically highly reliable.
A 2013 report prepared for Oak Ridge National laboratory (ORNL) provides details on the reliability benefits of CHP and how to effectively integrate CHP for reliability purposes. It also highlights key state and local policies designed to promote CHP in CI applications.
Not every CI facility is a good fit for CHP. In order to efficiently and economically utilize the outputs from a CHP system, a facility must have a consistent demand for both electricity and thermal energy. The facility also needs to have reliable access to fuel, usually in the form of pipelined natural gas. CHP is a good fit for critical infrastructure sub-sectors such as hospitals, food sales and food processing facilities, nursing homes, prisons, universities, chemical plants, and water treatment facilities. In some cases, CHP systems may also be appropriate for places of refuge and chemical and pharmaceutical facilities. CHP may not be an ideal solution for smaller facilities with limited thermal demand, such as police stations, emergency responders, telecommunications and office buildings. However, if these buildings are in CI clusters, there may be opportunities for a microgrid that is anchored by a CHP system. Smaller facilities may also want to explore options other generation technologies.
The 2013 “Guide to Using Combined Heat and Power for Enhancing Reliability and Resiliency in Buildings” from DOE and EPA offers a detailed look at the opportunities for CHP to provide resiliency and reliability benefits and the factors determining the successful implementation of CHP at critical facilities. Below is a list of the identified CHP conducive subsectors and brief descriptions for each:
Airports - These facilities are often in NOx nonattainment areas and face significant emissions pressure from both regulators and the community. Airports have large space conditioning and electrical loads with long hours of operation, and are often well suited to add CHP to their district energy systems. Airport CHP installations vary widely in size depending on the size of the airport and the addressable thermal loads, but the most common technology is a reciprocating engine fueled by natural gas.
Chemicals / Pharmaceuticals - Pharmaceutical manufacturing facilities have consistent heating, cooling, and power loads, and typically operate 24/7. They require a reliable power supply for their core business that can be served well by CHP. Most pharmaceutical CHP installations use larger CHP systems and can range from 1 MW to over 100 MW. Combustion turbines and steam turbines are the most prominent prime movers for CHP installations at pharmaceutical facilities, and natural gas is the primary fuel for these systems.
Colleges/Universities - Due to their large thermal loads and desire for reliable power, CHP is a good fit for colleges and universities. A number of college and universities use CHP to provide steam and some power to key campus facilities. Having a heated pool on campus presents an even greater opportunity for CHP implementation. The majority of CHP systems at colleges/universities are natural gas-fired, and most institutions use a boiler/steam turbine or gas turbines. A number of college and university CHP systems have been designed to be able to run independently of the grid. This has enabled colleges and universities to continue many of their normal operations during storm events, and has helped increase interest in the use of CHP in this market sector.
Critical Manufacturing - Critical manufacturing facilities are ideal candidates for CHP due to their conincident power and thermal loads and high number of operational hours per year. Facility and plant managers of critical manufacturing facilities are well equipped to pursue CHP opportunities as industrial facilities currently make up about 86% of existing CHP capacity in the U.S. Like many other industrial applications, critical manufacturing facilities have consistent heating, cooling, and power loads, and typically operate 24/7. They also require a reliable power supply that can be served well by CHP. Combustion turbines and steam turbines are the most prominent prime movers for CHP installations at critical manufacturing facilities, and natural gas is the primary fuel for these systems.
Data Centers - Data centers require high quality, reliable power for extended periods of time and have large thermal loads for space cooling. CHP systems at data centers must be able to easily integrate with other energy generation and storage systems, and they range in size from a few hundred kilowatts up to 10MW. The majority are fueled by natural gas and use microturbines as prime movers.
Distribution Centers - Distribution centers or refrigerated warehouses can incur significant costs in the case of power outages and typically require year-round space cooling and refrigeration from absorption chillers, and consistent, reliable electric power generation. Distribution center CHP system sizes can vary widely depending on the building size, but they are nearly all fueled by natural gas and are reciprocating engines or combustion turbines.
Fire Stations - Fire stations have coincident thermal and electric loads, requiring space heating and cooling, domestic hot water (DHW), lighting, and plug loads. Similar to police stations, fire stations typically have lower capacity requirements than other CHP candidates, so 24/7 operation or on-site housing is typically required for CHP implementation. Currently, there is a limited amount of CHP installations at fire stations, but most utilize small microturbines or fuel cells, no more than 100 kW in size. If located close to other government buildings such as police stations, multiple building loads can be served by a single CHP system, forming a small microgrid anchored by CHP.
Food Processing - Food processing facilities comprise a wide variety of plants and process ranging from local dairies to large wet mill corn processing facilities that resemble chemical plants. Natural gas is the preferred fuel for CHP in this sector unless the plant has processing waste available or is used to handling large amounts of solids in their operations. Expanding markets for CHP include animal/poultry slaughtering, flour and rice milling, breweries, soft drink manufacturing, animal food manufacturing, fruit and vegetable canning, fluid milk, beet sugar, soybean processing and cereal manufacturing.
Food Sales/Supermarkets - Similar to distribution centers or refrigerated warehouses, refrigeration and lighting are the two largest electricity/thermal loads in the supermarket industry, creating a good fit for CHP. Supermarket CHP systems can provide the electricity and chilling needed to satisfy the high energy demands and reliability requirements. CHP systems at supermarkets are typically on the smaller side, with no systems larger than 1 MW, and nearly all are reciprocating engines or fuel cells.
Government Facilities - Most government CHP systems consist of combined cycle/gas turbine configurations or reciprocating engines. Natural gas is used to a lesser extent in these CHP applications as compared to other commercial markets, although the majority of capacity comes from natural gas-fired systems. CHP systems can help meet government objectives such as reducing greenhouse gas (GHG) emissions and can help operations remain up and running during emergency events. Government facilities that operate 24/7 and have coincident thermal and electric loads are good candidates for CHP.
Hospitals/Health Care - Hospitals, nursing homes and other healthcare facilities are good candidates for CHP based on their thermal loads and the need for reliable power. Most hospital CHP systems consist of gas turbines, and reciprocating engines, and 84 percent of existing hospital/healthcare CHP capacity is natural gas. Many healthcare CHP systems are designed so that they can operate independently of the grid, in case of weather events or other incidents that may cause grid outages. Interest in CHP at healthcare facilities, especially in densely populated areas that are more prone to natural disasters, has increased in recent years due mainly to CHP’s reliability benefits.
Hotels/Lodging - Most CHP systems located at hotels are smaller systems typically less than 5 MW and use natural gas-fired reciprocating engines. Nearly all hotel CHP capacity is fueled by natural gas. Hotels have large thermal loads for hot water, and use CHP to provide hot water for guest use and laundry facilities. Larger hotels that have multiple restaurants, provide spa services and have heated swimming pools typically make the best candidates for CHP.
Laundries - Laundries typically consume large amounts of hot water and electricity for their cleaning processes, and also have long operational hours compared to other commercial facilities. Reciprocating engines are primarily used in laundry CHP applications, using recycled heat to produce hot water. CHP systems at laundry facilities are usually on the smaller side at less than 1 MW, while many of the older systems installed at laundry facilities are under 100 kW.
Military Bases - Much like colleges, military base CHP systems are typically installed at sites with large campuses that have a significant power and thermal loads for barracks, office buildings, training facilities, medical centers, and other staff support buildings. Military bases are also often served by a large central plant that enables easier CHP integration. CHP systems on military campuses range in size from a few kilowatts to several dozen megawatts, though most systems are under 20 MW. The majority of systems are natural gas-fired and use boiler/steam turbines or reciprocating engines as prime movers.
Multifamily - Multifamily facilities looking to incorporate CHP require central hot water and space heating systems, and buildings that have no sub-metering. Sized appropriately, CHP systems at multifamily residences such as coop buildings, apartments, and condominiums can meet all of the building’s steam and power needs. Ninety-nine percent of existing CHP capacity located at multi-family residences is fueled by natural gas. The majority of multi-family CHP systems are gas turbines and reciprocating engines.
Nursing Homes - Hospitals, nursing homes and other healthcare facilities are good candidates for CHP based on their thermal loads and the need for reliable power. Most hospital CHP systems consist of gas turbines, and reciprocating engines, and roughly 80% of existing hospital/healthcare CHP capacity is natural gas. Many healthcare CHP systems are designed so that they can operate independently of the grid, in case of weather events or other incidents that may cause grid outages. Interest in CHP at healthcare facilities, especially in densely populated areas that are more prone to natural disasters, has increased in recent years due mainly to CHP’s reliability benefits.
Police Stations - Police stations have coincident thermal and electric loads, requiring space heating and cooling, domestic hot water (DHW), lighting, and plug loads. Because police stations have lower capacity requirements than most CHP candidates, 24/7 operation or holding cell facilities on site are typically required for CHP implementation. The majority of CHP installations at police stations are small reciprocating engines, microturbines, or fuel cells, with the largest systems no more than a few megawatts. If located close to other government buildings such as fire stations, multiple building loads can be served by a single CHP system, forming a small microgrid anchored by CHP. Nearly all police station CHP systems are fueled by natural gas.
Prisons - Prisons and large correctional facilities represent a significant amount of potential for CHP systems because they generally have a significant coincident thermal and electric loads to serve space heating, domestic hot water (DHW), laundry, cooking, space cooling, lighting, and plug loads. Facilities that operate 24/7 and have on-site housing or holding cells present an even greater opportunity for CHP. CHP systems at prisons vary in size from under 100 kW to over 40 MW, depending on the size of the institution. The majority of prison CHP installations utilize reciprocating engines as their prime movers, but larger facilities use combustion or steam turbines.
Schools - CHP systems are increasingly common in schools due to their consistent cooling and electric loads and ability to serve as places of refuge, and most CHP systems at schools required heated pools to make the installation economically viable. These CHP systems are small, less than 1 MW systems and most schools use reciprocating engines as their prime mover. Roughly 80% of school CHP capacity is fueled by natural gas. Since schools often serve as places of refuge for the community during storm events, CHP systems have become increasingly popular due to their ability for the school to have lighting and other essential services during power outages.
Water Treatments Plants - Water treatment plants that have anaerobic digesters and operate 24 hours a day are prime candidates for CHP. Most CHP systems at wastewater treatment plants are between 100kW and 10MW. The majority are fueled by anaerobic digester gas produced on site, or natural gas. Nearly 70% of wastewater treatment facilities use reciprocating engines as their prime mover, with microturbines also making up nearly 20% of the CHP wastewater treatment CHP installations.
The requirements for a CHP system to deliver power reliability, as in a CI facility, are fairly straightforward, but they may add some costs relative to CHP in a non-critical facility. In order to ensure uninterrupted operation during a utility system outage, the CHP system must have the following features:
- Black start capability – The CHP system must have a battery powered starting system.
- Generator capable of operating independently of the utility grid – The CHP electric generator must be able to continue operation without the grid power signal. High frequency generators (microturbines) or DC generators (fuel cells) need to have inverter technology that can operate the grid independently.
- Ample carrying capacity – The facility must match the size of the critical loads to the CHP generator.
- Parallel utility interconnection and switchgear controls – The CHP system must be able to properly disconnect itself from the utility grid and switch over to providing electricity to critical facility loads.
Power reliability is a critical issue for many customers, especially at critical infrastructure facilities where power disruptions represent a significant safety and health risk to their operations. These risks often compel customers to install back-up or emergency diesel generator sets, which can be unreliable in an actual emergency. CHP can be a reliable and cost-effective alternative to installing back-up generators to provide protection against extended outages. A CHP system is typically selected for a facility due to its ability to reduce operating costs and overall emissions. However, power outage protection can also be designed into a CHP system that efficiently provides electricity and thermal energy to the site on a continuous basis. CHP systems can be configured meet the specific reliability needs and risk profiles of various customers, and to offset the capital cost investment for traditional back-up power measures.
Backup generators are seldom used and are sometimes poorly maintained, so they can encounter problems during an actual emergency (Table 1). More information on CHP vs. backup emergency generator sets can be found in the Midwest TAP's (formerly Clean Energy Application Center) CHP Resource Guide for Hospitals.
Table 1. CHP vs. Backup Generation
Designed and maintained to run continuously
Improved performance reliability
|Only used during emergencies
|Natural gas infrastructure typically not impacted by severe weather
|Limited by on-site storage – finite fuel supply
|Transition from Grid Power
|May be configured for “flicker-free” transfer from grid connection to “island mode”
|Lag time may impact critical system performance
Thermal (heating, cooling, hot/chilled water)
Typically natural gas fueled
Achieve greater system efficiencies (80%)
|Commonly burn diesel fuel
CHP systems are a more reliable, cleaner, efficient, and cost effective onsite power supply, which provides electricity and heating/cooling under both emergency and normal operating conditions.
A 2007 EPA report on valuing the reliability of CHP helps potential customers and relevant stakeholders understand how to value the various reliability benefits that CHP can provide compared to traditional backup power generation.
The DOE CHP Installation Database tracks CHP installations across the country, including those at CI facilities. With a focus on national security, health, and public safety, the sub-sectors listed in Table 1 have been flagged as critical infrastructure in the database. This does not include industrial manufacturing facilities (i.e. chemicals and food processing) or some other sectors identified as CI by the Department of Homeland Security. The database does not have information for which installations have black start capability. Data for CHP installations at critical infrastructure facilities is shown in Table 2, with a total of 5.5 GW from 1,023 sites.
Table 2. CHP Installations by Critical Infrastructure Sub-Sectors