TECHNICAL FEATURE This article was published in ASHRAE Journal, July 2015. Copyright 2015 ASHRAE. Posted at www.www.burnsmcd.com .org. This article may not be copied and/or distributed electronically or in paper form without permission of ASHRAE. For more information about ASHRAE Journal, visit www.ashrae.org. District Energy Enters The 21st Century BY STEVE TREDINNICK, P.E., MEMBER ASHRAE; DAVID WADE, P.E., LIFE MEMBER ASHRAE; GARY PHETTEPLACE, PH.D., P.E., MEMBER ASHRAE The concept of district energy is undergoing a resurgence in some parts of the United States and the world. Its roots in the U.S. date back to the 19th century and through the years many technological advancements and synergies have developed that help district energy efficiency. This article explores district energy and how ASHRAE has supported the industry over the years. District Energy’s Roots along with systems serving groups of institutional build- District energy systems supply heating and cooling ings, were initiated and prospered in the early decades to groups of buildings in the form of steam, hot water of the 1900s and by 1949 there were over 300 commercial or chilled water using a network of piping from one or systems in operation throughout the United States. Of more central energy plants. The concept has been used course, systems in the major cities of Europe also gained in the United States for more than 140 years with the favor in Paris, Copenhagen and Brussels. In many cases first recognized commercial district energy operation district steam systems were designed to accept waste originating in Lockport, N.Y. circa 1877. The Nov. 19, 1881, steam from urban electric production and became a reve- issue of Scientific American featured a front page story with nue center for growing electric utilities in the United States. illustrations describing the commercial venture in New After World War II, economic conditions changed in York City associated with production and distribution of the United States and steam district heating systems steam for building heating, motive power and cooking. lost favor for several reasons, including population The New York Steam Company installed a network of shifts to the suburbs, electric generation plants being pipes to distribute steam produced in boilers as well as constructed remotely from downtown areas, and rapid waste steam from electric production (Figure 1). growth of the natural gas distribution industry. Since The district heating concept grew in urban areas and was the electric side of the utility business seemed to have preferred where in-building boilers needing attendants unlimited growth potential, the steam district heating and fuel deliveries could be avoided. Commercial systems, business in many cases were neglected or abandoned. Steve Tredinnick, P.E., is senior project manager at Burns & McDonnell, Downers Grove, Ill. David Wade, P.E., is president of RDA Engineering Services, Atlanta, and is a member and past chair of TC 6.1, Steam and Hot Water Systems. Gary Phetteplace, Ph.D., P.E., is president of GWA Research, Lyme, N.H., and lead author of the ASHRAE District Heating Guide and District Cooling Guide. All authors are members and past chairs of TC 6.2, District Energy. Tredinnick is Handbook subcommittee chair of TC 6.2. 48 ASHRAE JOURNAL ashrae.org JULY 2015 TECHNICAL FEATURE Institutions where a profit motive was not dominant but FIGURE 1 November 19, 1881 Scientific American magazine cover showing steam pip- continued customer service was dominant continued ing installation in New York City. Image courtesy of David Wade, RDA Engineering operation and expansion of district systems, seeing clear life-cycle advantages. In Europe, a tradition of hot water district heating began early and was continued after World War II as part of major reconstruction efforts. European designers recognized the benefits of hot water distribution com- pared to steam with regard to lower heat loss, less main- tenance requirements and synergistic interface with combined heat and power (CHP). Other factors contrib- uting to widespread adoption in Europe are planned communities, lack of natural gas distribution, air quality concerns, and reduced reliance on imported fuels. District cooling, in the form of chilled water service, was first offered as a utility in Hartford, Conn., in 1963. The system was developed by the Connecticut Natural Gas Company as a way to use natural gas for air con- ditioning. Similar systems were developed within five years in Pittsburgh and Tulsa. Those systems continue operation through the present day. Interest in district energy systems in the United not a coherent U.S. energy policy to incentivize develop- States was renewed after the Energy Embargo of 1973 ment of district energy systems. when the U.S. Department of Energy (DOE) undertook Even the most efficient buildings require a grid to bal- a series of programs to evaluate community energy ance annual energy production and use. Many think of systems using district heating and cooling through the grid as only electricity; however, the possibilities for interface with power plants. DOE also explored the energy efficiency expand greatly when a district energy potential to provide low grade heat to large metropoli- thermal grid is available. tan areas from nuclear plants located nearby. This pro- European countries that are committed to reduction gram encouraged new hot water district heating sys- of greenhouse gases have made district energy systems a tems in St. Paul, Minn., Piqua, Ohio, and Jamestown, major component in their national energy strategies and N.Y. The program was terminated in the early 1980s, policies. They recognize that a thermal grid gives them and subsequent fuel price uncertainties reduced (but the most flexibility and energy independence when did not eliminate) interest in district heating and cool- integrating conventional fossil fuels, nuclear energy, ing as a commercial venture. biomass, wind, solar and geothermal energy. Many The reason district energy is not more widely used in systems there are base loaded with heat generated by the U.S. is largely institutional, rather than technical.1 municipal refuse incineration and waste heat recovery Most U.S. buildings are conceived, designed and con- from electric generation. Low temperature hot water structed by individuals who rarely consider the energy systems* can interface directly with heat from solar characteristics of surrounding buildings. U.S. codes and energy collectors or heat from heat pump systems. design protocols deal with energy use at a single build- ing, rather than on a community scale. Private utili- Concept of District Energy ties in the U.S. reinforce this approach through their District energy is not for everyone. It is a very tech- focused marketing of electric or natural gas service. nical and economic decision that requires a detailed Furthermore, unlike other places in the world, there is analysis (see 2012 ASHRAE Handbook—HVAC Systems and * Low temperature hot water district heating is defined as having a supply temperature equal to or lower than 250°F (121°C); however, it should be noted that many systems, especially in Europe, operate at much lower temperatures and often they also use seasonal temperature modulation, i.e., temperature reset based on outdoor temperature. JULY 2015 ashrae.org ASHRAE JOURNAL 49 TECHNICAL FEATURE Equipment, Chapter 12) looking at the alternatives in down the equipment for removal or installation. both a quantitative and qualitative manner. For most, Longer paybacks are palatable (government facilities, this decision is similar to whether one drives your car airports, college and universities, hospital campuses, etc.). or take public transportation to work. On public trans- Architectural features of a significant or historic portation, for example, one can work or sleep or stay building would be adversely affected by cooling towers productive in lieu of focusing your efforts on fighting or boiler stacks. traffic and driving yourself. On the other hand, using Conversely, district energy does not work well when your personal car, one can go from place to place at the buildings are too small or too far apart from one your own schedule and convenience, albeit at a prob- another (increasing distribution costs); have newer able higher cost. Of course, pros and cons exist for each highly efficient existing HVAC systems; or when the sys- method, and many factors affect your decision such as tem developer requires rapid payback on their invest- whether you live close to a bus or train line or not. ment. Many times several of the previously listed factors must occur for a project to germinate. Where to Apply District Energy District energy for heating or cooling works well as an Expected Benefits alternative to boilers and chillers in each building when As highlighted in ASHRAE’s District Cooling Guide2 and the the following factors are present. 2012 ASHRAE Handbook, when a net present value (NPV) High load-density facilities (i.e., short distances of analysis is conducted comparing the costs of connecting distribution piping can interconnect several buildings of to a district cooling system to constructing a building spe- reasonable size) such as airports; college and university cific cooling plant, the results are extremely competitive campuses; large hospital complexes; large office and and most times financially equivalent or superior. With industrial complexes/campuses; casinos; sports stadi- comparable,