Ask the Energy Experts: District heating system feasibility depends on many factors

Are there examples of district heating systems providing heat to new housing developments? A local developer of large luxury homes is incorporating conservation and renewable technologies, and wants to investigate district heat using ground-coupled heat pumps or biomass-fueled boilers.

District heating projects involve many variables, such as the cost of energy, the installed cost of the system, possible revenue from each part of the system, maintenance costs and more. Local climate and regulations, access to funds and available renewable resources must be considered as well when evaluating the feasibility of an individual project. Finally, each proposed system should be planned and designed as a long-term investment. That being said, the technology is a highly efficient means of delivering heat, and a new development offers the best-case payback for installing a district heating system.

Heat, electricity
Where houses are close together and a source of otherwise wasted energy is available, combined heat and power (CHP) systems can provide cost-effective heat to large numbers of customers. In lower-density areas, installing and maintaining piping—especially underground systems—is often prohibitively expensive.

Your development may be a good candidate for a CHP system. These systems use a turbine or diesel engine to generate electricity for on-site use and for sale to the local electrical utility. Most of the waste heat from the process is captured for use by a district heating system to heat homes and domestic hot water. Several college campuses around the country have installed CHP district heating systems. The International District Energy AssociationRedirecting to a non-government site has case studies of some of these projects.

Biofuels such as wood, agricultural waste, garbage, or nearly anything else that will burn are a potential low-cost source of energy for CHP district heating systems. The feasibility of using any fuel depends on several factors – cost (including transportation), volume of fuel available, heating and electrical loads, construction and operating cost of the facility, and the value of the electricity produced.

Direct geothermal
If you have a source of geothermal hot water available, it can be used in a non-CHP district heating system. Boise, Idaho, boasts the first commercially successful geothermal district heating system in the United States, installed in 1897. The system provides 4,000 gallons per minute of geothermal water at 179 degrees Fahrenheit to city businesses and residences. Other locations, mostly in the West, have installed similar district heating systems since then.

The Oregon Institute of Technology Geo-Heat CenterRedirecting to a non-government site (GHC) offers a brief overview of several existing direct-use district geothermal heat systems throughout the Western United States.  The GHC website also contains a list of consultants experienced in all phases of implementing geothermal heating systems, as well as other valuable resources for planners and designers considering this technology.

You also expressed an interest in using geo-exchange (geo-x) heat pumps to supply heat for a district heating system. In a district heating application—regardless of how large or small the system—the greater efficiency of heat pump technology might offset the high first cost of system installation.  Normally, district heating systems are considered an option when the developer has access to a renewable heating resource, such as hot springs or other geothermal resources.  However, the feasibility of adding geo-x heat pumps to each home and business to heat water should be carefully evaluated.

The benefits of integrating technologies and incorporating innovative design into your system depend on your overall goals for the housing development, financial and otherwise. It would be worthwhile to compare the cost of different options:  building a district heating system, installing individual geo-x heat pumps with a desuperheater (heat exchange unit for water heating) or integrating the two technologies. You may be surprised at which option is most cost-effective.

Additional Information Resources
A search of the Energy Solutions DatabaseRedirecting to a non-government site yields several resources on the topic of biofuels. The DOE Office of Energy Efficiency and Renewable Energy has a comprehensive Biomass website.

Here are some more case studies you might find useful: