Community based energy services, as the term suggests, provide heating, cooling and renewable energy to more than one building. It is an alternative to the use of individual energy related systems in each building. The services often consist of: (1) Centralised generation and supply of heating/cooling as well as energy from renewable sources; (2) A distribution network to bring heating/cooling to buildings within the community; (3) Other installations (air handling units, and controls) within individual buildings. Community based energy services are often found in two forms – district heating/cooling and combined heat and power (CHP) generation.
District heating/cooling refers to combined heating/cooling at a centralised location, and distribution of heating/cooling to the buildings of a defined community, through a piping network, for space and water heating or space cooling. The energy required for heating/cooling can be tapped from waste heat from nearby industrial processes (if available) and/or renewable sources such as solar thermal and geothermal energy. District heating/cooling may provide higher efficiency for heating/cooling, compared to the use of individual systems in individual buildings. It also provides flexibility to a building’s owners/tenants to purchase and use only the required heating/cooling.
Due to the economy of scale of centralised heating/cooling installations, district heating/cooling systems can apply various forms of energy efficient practices in a cost effective manner. One such practice is the use of thermal ice storage. Ice is generated during off-peak hours and stored for chilled water generation use during peak hours, helping reduce electricity peak load. By shifting a part of the chilling load to offpeak hours, chiller equipment requirements and size can be reduced closer to the average load. This leads to higher chiller operating efficiencies and lower cost per unit of cooling. Another practice is the use of sea water as an indirect source for district cooling systems in tropical coastal regions. The constant cool sea water temperature in these regions can act as a heat sink to cool condenser water-based district cooling systems, reducing electricity load demand.
Combined heat and power generation (CHP) operates with a similar concept to district heating; however, heat is sourced from the heat waste of power generation in the same system. Typically, power generation is on average only 35% efficient with 65% of the energy potential being waste heat. CHP can reduce the efficiency loss by recouping heat waste as a form of thermal energy for space heating/cooling, and as such, can increase plant efficiency to 90% or more (KPMG, 2009). Conventionally, waste heat recovery and power generation of CHP plants is from cogeneration in plants burning fossil fuels.
However, an increasing number of CHP plants are based on renewable sources such as solar thermal, biogas,micro-hydro or cleaner sources such as biomass. Natural gas and fossil fuels can be used only as make up and back up sources. CHP systems are also being integrated with other renewable energy harvesting technologies, forming a hybrid system. For example, a CHP system utilising biogas is suitable for agriculture-based communities. Biogas (usually in the form of methane) is harvested from organic solid waste and manure which has undergone anaerobic digestion. Organic solid waste and manure are dayto- day wastes produced from community and farming by-products. They can be used as resources for CHP to co-generate heat and electricity. The digested manure can also be used as fertiliser for agricultural production.
The availability of various heating-cooling technologies – e.g., compression and absorption chillers – has led to the development of combined cooling and power generation systems. In these systems, waste heat from a CHP process is converted to chilled water and is transmitted to individual buildings in communities for space cooling purpose. Such developments allow wider and more flexible applications of district heating/cooling and combined heating/cooling and power generation in various climatic regions and seasons.
Community based energy services can be grouped into two application categories – high-density and lower density settings. In high-density settings, district heating/cooling is more feasible, as it can serve a large pool of community members in a small serving radius. In the high-density urbanised setting, the implementation of a CHP system is less feasible, due to the fact that: (1) energy generation is less crucial since electricity is readily available from the grid, (2) space constraints for a co-generator in combination with other renewable energy generation facilities such as biogas, and (3) less accessibility to renewable energy sources such as biogas and biomass, which would need to be transported to the site. CHP systems are, however, more feasible in lower density settings at urban fringes or agricultural villages and towns. In these areas, renewable energy sources are more readily available within the community itself, e.g., biogas from farm waste and manure, biomass from farming by-products and gardening waste, etc.
For both district heating/cooling and CHP systems, there are five main application requirements. Four of which are the main components: centralised plants, a heating/cooling distribution network, installation in individual buildings and metering. The fifth requirement is maintenance.
Centralised plants produce heating/cooling through boilers/chillers, recover waste heat through cogeneration, or tap into waste heat from nearby industrial processes or power plants. Solar thermal technology can also be deployed for thermal energy generation. Where heat waste is available but cooling energy is needed, heating-cooling conversion technologies are required. Thermal energy is usually stored and transmitted in the form of hot/chilled water.
Heating/cooling distribution networks transfer thermal energy from a centralised plant to individual buildings within a community. The distribution network includes pipes and pumps. Pipes are often made of steel or copper, and are thermally insulated. They are often run underground to save on-grade land space and receive additional thermal insulation of earth. Leak detection systems and corrosion protections are required for underground piping. Pumps create pressure to circulate the thermal medium in the piping network of individual buildings. Afterward, the thermal medium is circulated back to the centralised plant, where it is recharged with thermal energy. Variable speed pumps are recommended for energy saving. The pumps should have low noise levels to prevent noise transfer through the thermal medium into the buildings.
Installations in buildings. Because thermal energy is generated at a centralised location, installations in buildings are simpler than the use of conventional full heating/cooling systems within individual buildings. The installation requirements include a heat exchanger, piping, valves, and control system. Control systems are similar to those used in conventional individual heating system – i.e., the same type of room thermostats, thermostatic radiator valves, and time switches or programmers. Similar to individual heating/cooling systems, tenants must understand how to use their heating/cooling controls to optimise thermal comfort and energy efficiency.
Metering is essential to monitor and ensure the efficient operation and usage. Data from the meter are useful for any necessary adjustments to the system’s components, in terms of capacity, to allow better operational efficiency. Meters should also be installed at an individual end user’s premises, not only to calculate fees to be charged but also to provide consumers with a direct incentive and to avoid wasting the purchased energy.
Maintenance requirements include preventive maintenance checks (including leakage), monitoring and reporting a system’s performance.
Feasibility for implementation
Key activities leading to expanding implementation of community based energy services include setting up suitable investment and financing mechanisms, research and development, consulting with prospective energy and thermal energy users, and capacity building for maintenance staff.
Investment and financing mechanisms determine the feasibility for implementation, due to the initial large investment cost of a community based energy service system. This is followed by research and development, especially to identify energy sources (e.g., locally available waste heat from industrial processes, biomass and biogas).
User consultation is important to gain common understanding, expectations and co-operation. Consultation can be held in several sections, during a feasibility study, planning and design of a system and the construction and operational stages. The agenda should covers issues such as siting of the centralised plant, choice of equipment and control systems for individual buildings, charging system, procedures to rectify faults and feedback from users.
Capability building is also necessary, especially in developing countries to improve the system performance at minimum cost, and to train a local maintenance workforce with technical skills to install, monitor, identify faults in, and to repair the systems.
As a general observation, district heating has larger market penetration compared to district cooling, due to the more severe impact of cold weather compared to that of hot weather. The main markets for district heating are in Europe (including Eastern Europe) and Northern Asia. As of 2007, district heated floor space reach 108.8 million square metres including 41% of households in the Czech Republic, 8 million square metres in Slovakia, 38.16 million square metres (serving 70% of households) in Latvia, and over 3 billion square metres in China (Euroheat & Power, 2007). Nevertheless, the use of renewable energy resources and waste heat for district heating and implementation of CHP have significant potential to expand. In Slovakia, for example, renewable energy sources account for only 4% of the total installed district heating capacity. The remaining energy sources are coal and coal products (91%), and natural gas (5%) (Euroheat & Power, 2007).
The use of community based energy services can lead to many benefits related to environmental development. District heating/cooling systems can be more thermally efficient compared to that of many isolated small systems in individual buildings. District heating, for example, can provide up to 60% of heating and hot water energy demands for 70% of families in Eastern European countries and Russia (OECD/IEA, 2004). Furthermore, the operation of a centralised plant is more optimal in terms of energy efficiency, renewable energy deployment, and maintenance personnel. The IPCC’s Fourth Assessment Report (Levine et al., 2007) draws attention to examples of district heating system tapping heat sources from:
- Sewage waste heat in Tokyo, Japan and Gothenburg, Sweden
- Geothermal heat in Tianjin, China
- Waste heat from incineration in northern Europe.
CHP, on the other hand, can be operated on biogas, which is sourced from the organic waste generated by the community it serves. The products of CHP include both electricity and its generation’s by-product (heat) and thus makes better use of energy resources. The combination of a biogas anaerobic digester and a CHP co-generator also offers better sanitation solutions for rural communities, reduction of odour and flies, prevention of water pollution due to waste dumping, and improved environmental health. Furthermore, sludge from a bio-gas digester can be used as compost for landscaping or agricultural production.
In social development terms, community-based energy services help create a sense of community and strengthen social coherence within a community. In economic terms, the use of community-based energy services offer owners of individual buildings:
- Savings on capital cost for installing boiler/chiller plants
- Savings on building space and maintenance cost for boiler/chiller plants
- Savings on ongoing capital expenses to upgrade boiler/chiller plants
- Flexibility, monitoring ability and controllability of thermal energy usage
- With these, community based energy services become a form of catalyst for energy conservation behaviour.
The main financial requirements for community based energy services include initial capital/investment cost, operational cost, and maintenance cost. All the cost components are high, due to the large-scale service application of the system. The actual investment cost of CHP and district heating/cooling varies depending on the systems, regions and whether the components are locally available. For example, the cost for a CHP including an anaerobic digester (to feed biogas to the CHP operation) with a capacity of 370kW is approximately US$8.5 million for a US installation in 2002 (North West Community Energy, 2002). A biomass–based CHP with a capacity of 2-3MW cost about Euro 1.2 million in Finland in 2001 (Kuntatekniikka et al., 2001).
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