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Editor's note: The Energy Services Bulletin features real answers to real questions posed to our staff at the Energy Services Power Line. We hope you find it useful. |
Can you give examples of district heating systems providing heat to new housing developments? A 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 systems are a good way to provide heat to large numbers of customers—especially where otherwise-wasted energy can be used and houses are close together. In areas of lower density, the cost of installing and maintaining the piping, especially if it is installed underground, can be prohibitive. Because of the many variables involved (such as the cost of energy, the installed cost of the piping, revenues from homeowners, maintenance costs, etc.), every system proposed should be evaluated on its economic parameters.
Biofuels are one possible source of energy for the district heating system. To be cost-effective, these systems require a low-cost source of fuel such as wood, agricultural waste, garbage or nearly anything else that will burn. In some parts of the West, large stands of beetle-killed trees could potentially provide fuel for a hot water boiler or a steam boiler as part of a Combined Heat and Power (CHP) system. The feasibility of using this wood depends on several factors: cost of the wood (including transportation costs), volume of wood available, heating and electrical loads, construction and operating cost of the CHP facility and the value of the electricity produced.
A search of the Energy Solutions Database yields several resources on the topic of "biofuels." The DOE Office of Energy Efficiency and Renewable Energy (EERE) has a comprehensive Web site devoted to biomass.
A CHP system may be a possibility for the development. These systems use a turbine or diesel engine to generate electricity for local use and for sale to the local electrical utility. Most of the waste heat from the process is captured and can be used by the district heating system to heat homes and domestic hot water. CHP district heating systems have been installed in several colleges around the country described in several case studies.
If there is a source of geothermal hot water available, it can be easily used in a district heating system. The first commercially successful geothermal district heating system in the United States was installed in Boise, Idaho, in 1897. The system provides 4,000 GPM of geothermal water at 179°F to businesses and residences in the city of Boise.
Since then, many district heating systems have been installed in other locations. The Oregon Institute of Technology (OIT) provides a brief overview of several existing direct-use district geothermal heat systems in the Western U. S. The OIT Web site also contains a list of consultants experienced in all phases of implementing geothermal heating systems, as well as case studies, software, geothermal resource data bases, publication newsletters and lots more.
You also mentioned an interest in using ground-source heat pumps (GHPs) as a source of heat for a district heating system. GHPs are most effective at low operating temperatures—if they are used to raise the temperature above 120° F, the efficiency falls off rapidly. Using a central chiller to heat water to 120° F to distribute to the houses is probably not a cost-effective option—piping and pumping costs increase rapidly for systems using lower water temperatures. Individual ground-source heat pumps serving each house would likely be a much more cost-effective option.
Creating Cellulosic Ethanol: Spinning Straw into Fuel;
BioCycle, April 2005. Article asserts that cellulose ethanol exhibits a net energy content three times higher than corn ethanol and emits a low net level of greenhouse gases.
How Anaerobic Digestion (Methane Recovery) Works
DOE EERE fact sheet of consumer level information on methane and anaerobic digestion.
New reports point way to Northwest biofuels sustainability
Harvesting Clean Energy report on sustainable biofuels; by Patrick Mazza of Climate Solutions.
Oregon Department of Energy - Biomass Energy
Fact sheet and resource list on general information related to biomass energy, biomass use, technology and development.
Producing Bioenergy on the Farm
Harvesting Clean Energy report on sustainable biofuels; by Patrick Mazza of Climate Solutions.
Waste to Energy (WTE) and Biomass in California
California Energy Commission fact sheet highlighting anaerobic digestion, landfill gas to energy and ethanol production.
| January 2009 |
Previous issues
University district-heating project case studies
Oregon Institute of Technology
How Anaerobic Digestion (Methane Recovery) Works
New reports point way to Northwest biofuels sustainability
Oregon Department of Energy – Biomass Energy