New guidance on calculating the benefits of CHP for buildings is helping to promote the technology, particularly for commercial buildings in the US. Jan Berry and colleagues explain.
The US Green Building Council’s (USGBC) Leadership in Energy and Environment Design (LEED®) certification process is recognized throughout the US as the standard for ‘green’ building construction. By promoting the market for sustainable design and building practices, the USGBC provides opportunities to ‘effect change in the way buildings are designed, built, operated and maintained.’1
Now, for the first time, the sustainable building market has used its influence to encourage the use of combined heat and power (CHP) technology – a highly efficient, reliable and clean technology.
The Dell Children’s Medical Center of Central Texas was designed with LEED certification in mind
The USGBC has issued guidance on calculating LEED credit for CHP – recognizing the energy and environmental benefits of distributed power generation when the thermal energy is recovered for heating or cooling. The USGBC’s market-based approach to promoting the energy and environmental benefits of CHP is supported by both the government (Department of Energy, through Oak Ridge National Laboratory), and private sectors.
The recently released LEED New Construction (NC) guidance succinctly states: ‘Combined heat and power captures the heat that would otherwise be rejected in traditional fossil fuel generation of electrical power so that the total efficiency of these integrated systems is much greater than from central station power plants and separate thermal systems. CHP systems also produce lower emissions compared with traditional fossil fuel generation. Other benefits include reduction in peak demand, releasing of electrical grid system capacity, and reduction in overall electrical system transmission and distribution losses.’2
Merrill Smith of the US Department of Energy (DOE) explains: ‘DOE analysed the market for CHP and supported development of modular, integrated CHP systems for several commercial and industrial markets. We are excited to work with the USGBC to help develop the market pull for this highly efficient technology.’
THE MARKET FOR CHP IN THE US
Recognizing the pivotal role CHP could have in US energy policy, the US Department of Energy (DOE), the US Environmental Protection Agency (EPA), the United States Combined Heat and Power Association (USCHPA) and others issued the CHP Challenge and signed the CHP Compact in 2000. This partnership established the goal of increasing CHP capacity to 92 GW by the year 2010. This increase in CHP capacity is expected to result in estimated energy savings of 2.4 quadrillion (2.4 x 1015) BTU per year and a reduction of 276 million tons (250 metric tonnes) of CO2 per year compared with separate electricity and thermal energy generation.3 When the Compact was renewed in 2005, much progress had been made toward the goal: 2960 sites were operating and represented over 82 GW of installed capacity.
As the CHP Challenge and CHP Compact were established, the government-private sector team determined that pre-engineered, packaged CHP systems must be developed and demonstrated in a range of commercial market sectors. Beginning in 2001, DOE/ORNL cost-shared projects developed packaged CHP systems that are being tested (see Table 1). These projects demonstrate advanced CHP systems in each commercial and institutional market section where the size of the potential market is significant.4 Case studies documenting lessons learned and the benefits of using packaged CHP systems are being provided to the public.
Figure 1. New site additions, 2000-2005
Figure 2. New capacity additions, 2000-2005
The number and capacity of CHP applications has grown during 2000-2005 in all sectors (see Figures 1 and 2). While commercial applications make up the majority of new CHP sites, capacity (MW) additions are dominated by industrial applications. ‘Other’ applications pertain primarily to agricultural and mining applications (non-manufacturing and non-commercial market sectors). Figure 3 illustrates the breakdown of new site additions by market sector for both commercial and industrial applications, indicating that 7% of new commercial CHP applications are in the hospital market sector. Kim Shinn of TLC Engineering for Architecture expands on this government research by offering his first-hand experience: ‘The hospital and healthcare industry is ripe for integrating energy efficiency into the design of state-of-the-art facilities. CHP is a cost-effective technology for improving efficiency while improving energy reliability, a key consideration for hospital administrators.’
Figure 3. Commercial and industrial site additions, 2000-2005
‘DOE has contributed to this expansion of CHP by working through ORNL to lead a programme that encourages research, development, and deployment of natural gas-fired CHP integrated systems that meet the energy needs of the commercial-institutional arena,’ asserts Patti Garland of ORNL. Packaged systems are now available, and three of the first systems to be deployed are of particular interest:
- The collaboration of United Technology Research Center and UTC Power with DOE and ORNL resulted in the family of PureComfort products: PureComfort 240, 300, 330 and 360. These products are pre-engineered systems that include sets of 60 kW microturbines or an engine to produce power, an exhaust gas-driven, double-effect absorption chiller/heater, and the controls to ensure safe and reliable steady-state and transient operation.
- Honeywell, in conjunction with the US Army and ORNL, completed a new ‘packaged integrated energy system’ at Fort Bragg, North Carolina. The project reduces operating costs while improving energy efficiency and enhancing energy security at the military base. This system includes a Solar 5.7 MW gas turbine with dual fuel capability – it can switch, on the fly, from base operations using fuels including natural gas and No. 2 fuel oil in the event of an emergency. Turbine exhaust directly fires both a Broad absorption chiller that produces up to 1000 tons (900 metric tonnes) of chilled water and a heat recovery steam generator that can produce up to 80,000 pounds (36,300 kg) of steam per hour. Reference designs are available for turbine-absorption chiller/heater systems with electricity and thermal outputs ranging from 1.2 MW/900 tons to 5.3 MW/3300 tons.
- In conjunction with Austin Energy and ORNL, Burns & McDonnell designed, constructed and commissioned a modular CHP plant at the Domain High Tech Park in Austin, Texas during 2004. The Domain system integrates a 4.5 MW Solar combustion turbine with a 2600 refrigeration-ton Broad absorption chiller that is directly fired with the ~900ºF (480ºC) turbine exhaust. Use of pre-manufactured or off-the-shelf components reduces this system’s capital cost as well as the cost of replicating similar on-site generation systems.
A packaged integrated energy system improves energy security for the Fort Bragg military base in North Carolina
These CHP packaged systems are suitable for commercial customers in market sectors such as hotels, healthcare, supermarkets, education and retail with possible adaptation to industrial processes. Since these systems are penetrating the US market for on-site energy, no new projects are planned and projects cost-shared by DOE and ORNL will be completed by 2007. One of these final government-industry collaborative projects is Dell Children’s Medical Center of Central Texas (DCMCCT).
DELL CHILDREN’S MEDICAL CENTER OF CENTRAL TEXAS
In late 2002, Seton Healthcare Network (Seton) decided to construct the healthiest medical facility possible for the children of Central Texas and set the goal of achieving LEED Platinum certification for the new hospital. At that time, the LEED-NC certification process was becoming recognized throughout the US as the standard for ‘green’ building construction. Throughout the planning and budgeting process, hospital management aimed to build DCMCCT in an environmentally responsible manner. Design of the energy-supply system was beginning just as the Domain site (described above) was gaining visibility for successful commissioning. Project participants recognized how successes at the Domain could help DCMCCT achieve aggressive environmental stewardship goals.
Phil Risner of DCMCCT recounts: ‘It was a strategic decision by Seton and the City of Austin to join together in a partnership to build a hospital and energy plant dedicated to serve the hospital that will become a cutting-edge ‘green’ model for future hospital facilities. Seton and Austin Energy (AE), a utility owned and operated by the City of Austin, established a unique agreement by which AE will provide cooling, heating and power as well as emergency power to the Medical Center.’ This strategy – to design the CHP facility to meet thermal and electric loads – will reduce energy costs associated with the production of chilled water and steam because the waste heat from the power generation process will be used to heat and cool the hospital. The medical centre will also benefit from reduced non-energy costs resulting from improved reliability of utilities (power, chilled water and steam). During natural disasters or other events that may cause extended grid power disruptions, the CHP facility will enable the hospital, an important element of Austin’s critical infrastructure, to remain fully operational and capable of serving the community’s healthcare and disaster recovery needs.
The Solar Turbines Mercury-50 gas turbine and the HRSG for the Dell Children’s Medical Center
According to analyses by DOE/ORNL, a cost-share partner in the DCMCCT energy plant project, hospitals are excellent candidates for integrated on-site CHP systems because these facilities have significant coincident electrical and thermal energy demands and operate 24 hours a day, seven days a week. Rod Schwass, representing the Burns & McDonnell design and construction team, states: ‘The AE CHP facility will serve approximately 475,000 square feet (44,100 m2) of hospital building space in this first phase of construction. The system is designed to meet 100% of the facility’s electricity, chilled water and steam loads. Electrical power will be generated by a Solar Turbines Mercury-50, a state-of-the-art combustion turbine with extremely low emissions.’
The medical centre is located within a 709-acre (290 hectare) urban development area less than three miles from downtown Austin – about 70% of the construction was completed by May 2006. This area of Austin is considered a ‘non-attainment zone’ by Texas air quality regulators; however, under the output-based permitting guidelines established by the Texas Environmental Quality Commission, the turbine obtained a permit without the need for any additional emissions control equipment. All the hot exhaust gases from the turbine will be routed through a heat recovery generator, producing steam to meet hospital heating loads and energizing a 1000-ton Trane absorption chiller. The advanced turbine is fuelled with natural gas to produce 4.5 MW of electricity, and will use 100% of the turbine exhaust heat to energize these off-the-shelf technologies to achieve fuel-use efficiency of over 70%. In addition, the facility uses a thermal energy storage tank for up to 8000 ton-hours of chilled water to further reduce fuel usage during peak cooling periods. This combination of low-emission combustion turbine technology, a high degree of waste heat recovery and an innovative thermal storage system will give this CHP plant the exceptional environmental performance that is recognized by LEED.
Methodology for calculating LEED credit For CHP systems
From its inception, DCMCCT management has garnered support for their design approach from USGBC. On 14 April last year, Rick Fedrizzi, President, CEO and Founding Chairman of USGBC, stated: ‘I was fortunate to personally meet with the team from the Austin Energy/Seton Healthcare Network and came away amazed by what I experienced. In particular, the low emissions and the high energy conversion efficiencies predicted for the … combined cooling, heating and power plant, make it quite possible for this project to be awarded the maximum … points allowable under Credit EA-1.’
The thermal energy storage tank reduces fuel usage during peak cooling times
Energy and Atmosphere (EA) Credit 1 allows up to 10 LEED points for achieving ‘increasing levels of energy performance above the baseline in the prerequisite standard to reduce environmental and economic impacts associated with excessive energy use.’2 LEED credit is based on operational cost savings as prescribed by ASHRAE 90.1-2004 Performance Rating Method. After applicants calculate energy cost savings for the Design Building (i.e. the building applying for LEED credit, or Design) as compared to the ASHRAE baseline, they submit their calculations to LEED for a Credit Interpretation Review. LEED credit is typically earned for a single building with dedicated heating and cooling equipment and electricity provided by renewable or grid sources. Equipment configurations for CHP systems are varied, and many CHP systems provide energy for multiple buildings through district energy systems.
The convergence of market interest in obtaining LEED credit, DOE technology development initiatives, and USGBC interest in recognizing the benefits of CHP resulted in formation of an interdisciplinary committee to develop an EA-1 credit calculation methodology for CHP systems. As the committee dealt with the various configurations of CHP systems, deliberations focused on how ownership of the energy system and the building could vary to influence cost transfers occurring between building owners, CHP system operators, and local gas and electric utilities. The committee realized that the complexity of ownership and operational cost-transfer relationships would cause confusion among those who apply for LEED EAc1 credit. To clarify and simplify calculations, a methodology was developed and organized according to potential cases that vary the ownership of the CHP system with ownership of the building and operational cost-transfers (see Table 2).
Ownership of the building and the predicted performance of the CHP system must be understood to determine how energy costs were reduced within the framework of ASHRAE 90.1-2004. Mark Spurr of FVB Energy explains that building ownership is important to understand, but once the relationships are understood, ownership becomes irrelevant to addressing the ultimate goal – meeting building energy requirements with reduced use of fossil fuels. ‘The rates charged to a building by a CHP developer or operator for electricity and thermal outputs typically include factors for capital recovery, maintenance and other non-energy costs,’ remarks Spurr. ‘Since these types of costs are not included in ASHRAE calculations for other energy-efficiency equipment and measures within the design, they must also be excluded for the CHP calculation regardless of the ownership of the system.’
To determine energy cost savings as compared to the ASHRAE baseline, the energy used by the design is calculated for each hour of the year. Hourly CHP performance is also determined either directly or through simulation of the system. The 8760 hour/year calculation captures hourly effects of load coincidence and electrical demand reduction, and any declining block or time-of-day utility rate structures. Generally, the net design hourly energy use is calculated after the CHP contribution(s) and then the prevailing conventional utility rates are applied. In all cases, the method describes how to allocate costs if electricity generated by the CHP is sold to the grid or an external customer, with the design realizing the benefit of thermal outputs resulting from electricity generation.
Case 1: Same ownership, CHP inside building
When all electricity and thermal outputs (heating or cooling) of the CHP are used within the design, the electricity produced is considered ‘free,’ as is the produced thermal energy. The input fuel for the CHP and any additional purchased energy is charged to the design.
Case 2: Different ownership, CHP inside the building
The CHP system in Case 2 is essentially treated the same as Case 1, with the input fuel charged to the design (at the prevailing utility rate as it applies to the design) for all CHP outputs used within the building.
Cases 3 and 4: district CHP
In principle, Cases 3 and 4 are analogous to Cases 1 and 2, except that the design utilizes a ‘virtual’ CHP system within the building with the same performance/efficiency characteristics as the district plant. The calculation of the CHP benefit only considers energy inputs and outputs and ignores all other non-energy cost factors.
Recognition of the efficient fuel use by CHP systems is consistent with the mission of the USGBC: ‘reduce environmental impacts associated with excessive energy use’ by recognizing building environmental performance through the LEED credit process. To ensure that LEED credit awarded for CHP systems is consistent with the goal of USGBC, the committee established four qualifying conditions. The first condition ensures that the CHP system is more efficient than alternative sources of energy by requiring a minimum fuel-use efficiency of 60%. Secondly, the environmental performance of district CHP systems must be validated by a discussion of emission reduction. Meeting the ASHRAE/IESNA 90.1-2004 Energy Standard for Buildings, as specified in EAc1 Prerequisite 2, is the third qualification criteria. Finally, for Case 4, there must be a long-term commitment from the building owner to purchase CHP thermal output from the district CHP system, and the building must be reliant on the district system for 90% of its thermal energy.
EFFECT OF LEED ON CHP MARKET DEVELOPMENT
With many campuses and industrial centres moving into the green building arena, rewarding district CHP systems with LEED credit creates additional market pull for these technologies. Says Robert Thornton, President of the International District Energy Association: ‘LEED is driving building design issues on campuses and in cities. … It is important for LEED scoring to encourage efficient district energy use and, where appropriate, recognize the source efficiencies and environmental benefits.’
The headquarters of renewable energy company NRG in Vermont received a LEED certificate for its green building design, incorporating on-site PV and wind (NRG Systems)
Before the new guidance was issued, the Performance Rating Method of LEED-NC was based solely on ASHRAE/IENSA Standard 90.1 and gave no credit at all to efficient systems outside the building boundary. This narrow scope of analysis for energy-efficient buildings did not include the use of district CHP, benefiting more than a single building, in the overall building analysis. As a result, situations arose where buildings were not connected to district systems or upgrades of district systems were not accomplished in order to ensure more LEED credit for the building – undermining the goal of USGBC to promote energy efficiency. Allowing credit for district CHP systems broadens the scope of the energy analysis and rewards these technologies. District CHP technologies foster sustainability in concert with the USGBC’s overall goals of designing buildings that are environmentally responsible, profitable, and healthy places to live and work.
Donald Fournier, of the University of Illinois at Urbana/Champaign, describes the next steps: ‘The USGBC is also considering how to reward existing buildings connected to district CHP and registered under the LEED-Existing Building rating system. This will further expand the market demand and pull for district CHP technologies.’
The US adopted a market-based approach to promoting highly efficient, distributed power systems that produce cooling and heating. Market interest in obtaining LEED credit, DOE technology development initiatives, and USGBC recognition of the benefits of CHP converged to foster this strategy. Government and the private sector collaborated to complete a market analysis, develop and deploy technology, and establish a national consensus regarding LEED-NC credit. CHP technology, in the form of packaged systems, has become available to commercial and institutional markets just as guidance for earning LEED credit has been released. The coincidence of technology readiness and market incentive should foster the penetration of CHP systems in the commercial building marketplace.
Jan Berry is R&D Program Manager and Patti Garland is CHP Program Manager, both at Oak Ridge National Laboratory. Don Fournier is Program Manager of Smart Energy Design Assistance Center at the University of Illinois at Urbana/Champaign. Phil Risner is Network Engineer/Senior Project Manager at Seton Healthcare Network/Dell Children’s Medical Center of Central Texas. Rod Schwass is Senior Project Manager at Burns & McDonnell. E-mail: email@example.com
- US Green Building Council. (2005). Leadership in Energy and Environmental Design for New Construction (LEED-NC), Reference Guide, Version 2.2, First Edition.
- U.S. Green Building Council. (2006). LEED-NC CHP Calculation Methodology for LEED-NC v2.2 EA Credit 1. Available at https://usgbc.org/ShowFile.aspx?DocumentID=1384
- Discovery Insights, Oak Ridge National Laboratory, U.S. Department of Energy, and Energetics. (2005). CHP Action Agenda: Innovating, Advocating, Raising Awareness, and Delivering Solutions. Prepared for the 6th Annual CHP Roadmap Workshop in New York, New York. Available at https://files.harc.edu/Sites/GulfCoastCHP/Publications/
- Resource Dynamics. (2003). Draft Cooling, Heating and Power for Buildings: A Market Assessment. Available at www.eere.energy.gov/de/pdfs/
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