3.1 General
This section describes the basic elements of district heating and cooling (DHC) systems and compares the environmental benefits of DHC systems with conventional (i.e. non-district) systems.In general terms, DHC systems can be defined as the production of heating (hot water or steam) and cooling (chilled water) energy at one or more sources, and subsequent distribution of the thermal energy via pipelines to "district" users. A typical DHC system is therefore comprised of three subsystems:
The concept of DHC is similar to potable water distribution or electric power generation and distribution systems. A combination of residential, commercial and industrial users may be involved with varying uses of the thermal energy including space heating and cooling, domestic hot water hating, plant process heating and cooling, etc.
- thermal energy generation; where steam or hot water in the case of district heating, and chilled or cold water in the case of district cooling, are produced,
- thermal energy distribution: where the thermal energy medium (steam or water) is distributed via pipelines from the production sources to the network of users, and
- incorporation of the thermal energy at the user's (customer's) location.
A district heating and/or cooling system differs fundamentally from a conventional system in that, in the case of the latter, thermal energy is produced and distributed at the location of use. Examples of conventional systems include home heating and cooling with, respectively, furnaces and air conditioners, electric heating of offices, package boilers/chillers providing heating/cooling of apartment complexes, and a dedicated boiler plant providing heat to an industrial facility.
There are many factors regarding DHC systems which must be considered in determining whether or not implementation of a particular system is preferred. These include economic criteria, viability of competing systems, local climatic conditions, user characteristics such as load density, total load requirements, characteristics of the heating and cooling systems currently in place, developer's perspectives, local utility considerations, local and global environmental impacts, and others. All of these factors will likely have a bearing on decisions made regarding the viability of a particular DHC system.
The description which follows provides a conceptual overview of DHC systems, with emphasis on those components which have an environmental impact. Other components, (i.e., do not have significant environmental impact) which would have to be considered in an overall system analysis, such as types and costs of equipment used, heat distribution medium proposed (water, steam), operating temperatures and pressures, system control characteristics, user prerequisites, etc., are only briefly discussed, as these aspects are not the focus of this report.
Section 3.2 provides a discussion of the basic equipment that is associated with DHC systems.
Section 3.3 identifies potential environmental benefits of DHC systems compared to conventional systems. These benefits are illustrated through actual case studies and examples in Section 4.0.
| District Heating and Cooling System Components |