district heating. Fuel utilization has been increased from 33 to 80%.
 District heating also has other benefits for the urban communities
 that should be considered. A significant amount of the sulfur dioxide
 and suspended solids in the urban environment originates from small,
 predominately oil-fired boilers supplying the heating needs of com-
 mercial buildings, industrial facilities, and urban housing. A major
 advantage of installing district heating is to replace a large number
 of small boilers with a large centralized cogeneration plant, municipal
 incinerator, or renewable heat sources. Such central sources burn less
 fuel and are better maintained than small boilers. This results in a
 significant reduction in the amount of pollutants being discharged into
 the atmosphere. Also, large centralized plants include pollution control
 equipment and discharge emissions through high stacks. The improvement
 in urban air quality with district heating has been demonstrated in
 European cities and cited as a major advantage of district heating.
 District heating with cogeneration also has the potential to conserve
 water resources, reduce thermal pollution of our waters, and reduce the
 adverse environmental impact of cooling tower drift because of the
 significant reduction in heat rejected to the environment from the
 central generation plant.


 RESEARCH AND DEVELOPMENT NEEDS

 One of the key factors common to district heating and waste heat
utilization is the large investment in the piping transport and distribution
system. The large capital investment is the main component of delivered
energy cost. If the cost of piping could be substantially reduced, the
economic feasibility of using low-temperature thermal energy from central
facilities would be greatly enhanced.
 Significant progress has been made on plastic and concrete conduit
technologies in the past decade. They have the potential to greatly reduce
the cost of piping materials and pipe installation. However, there are
significant temperature and life expectancy limitations for these new
materials. A materials testing and research program is needed to develop
piping systems that are lower in cost, cheaper to install, and serviceable