The Town of Avon Colorado and the Eagle River Water and Sanitation District have partnered to design, construct, and operate a mechanical “Community Heat Recovery System” which extracts low-grade waste heat from treated wastewater and delivers this heat for beneficial use. Immediate uses include heating of the community swimming pool, melting snow and ice on high pedestrian areas in an urban redevelopment zone in order to improve pedestrian safety, and space heating for project buildings and an adjacent water plant pump station building. Points of use are located within one mile of the treatment plant. The initial system is sized to extract heat from 170 m 3 /hr (1.08 mgd) of wastewater plant effluent with a 298 kW (400 hp) heat pump. The heat pump will deliver 1,026 kW (3,500,000 BTU/hr) energy to the heat recovery system. A supplemental natural gas boiler provided to meet peak demands will provide an additional 1,026 kW (3,500,000 BTU/hr) energy. The system is expandable allowing the installation of a second heat pump in the future and roof-mounted solar thermal panels. Power for the waste heat recovery system is provided by wind-generated electricity purchased from the local electric utility. The use of wind power with an electric-powered heat pump enables the agencies to fulfill energy needs while also reducing the carbon footprint. The system will achieve a reduction in the temperature of the treated wastewater, which is currently discharged to the Eagle River during low river flow, fish-sensitive periods. The agencies expect to save tax payers and rate payers money as a result of this project as compared to other alternatives or the status quo because it results in a more sustainable long-term operation. At 2008 utility commodities pricing, delivery of heat generated from this system was estimated to cost about one-third less than that from a conventional natural gas boiler system. This facility is the first of its kind in the U.S. and received a “New Energy Community” grant from the State of Colorado. This project shows how local agencies can work cooperatively for mutual benefit to provide infrastructure which accommodates growth and urban renewal and simultaneously demonstrate strong environmental leadership. The potential application of this technology is broad and global. The installed system is expected to cost about $5,000,000; construction will be completed in 2010.

Nowadays the residential central air conditioning systems are being widely used in China, and there are several different system options in the actual applications. Different residential central air conditioning systems will have different initial costs and operating costs. It is quite important for the decision-makers to choose an economical air conditioning system. In this paper six residential central air conditioning systems are introduced, which are the air-source heat pump system, household gas-fired air conditioning system, air-cooled chiller unit/gas-fired boiler system, water loop heat pump system, ground-source heat pump system and solar heat pump system. By using the method of dynamic total annual cost with an example of residential building in Beijing, the total annual costs of chosen six air conditioning systems are calculated and compared, and the sensitivity of total annual cost are analyzed with the rates of electricity and natural gas being used as the sensitive factors. The results show that the total annual cost of water loop heat pump system is the minimum among the six systems, which is the optimal option under the given conditions. The rates of electricity and natural gas will influence the raking of systems.

An experimental study on the effects of secondary combustion on efficiencies and emission reduction in the Diesel engine boiler system has been undertaken. The co-generation concept is utilized in that the electric power is produced by the generator connected to the Diesel engine, and heat is recovered from both combustion exhaust gases and the engine by the fin-and-tube and shell-and-tube heat exchangers, respectively. A specially designed secondary combustor is installed at the engine outlet in order to reburn the unburned fuel from the Diesel engine, thereby improving the system’s efficiency as well as reducing air pollution caused by exhaust gases. The main components of the secondary combustor are coiled Nichrome wires heated by the electric current and Diesel Oxidation Catalyst (DOC) housed inside a well insulated stainless steel shell. The performance tests were conducted at four water flow rates of 5, 10, 15 and 20 L/min and five electric power outputs of 3, 5, 7, 9 and 11 kW. The results show that at a water flow of 20 L/min and a power output of 9 kW, the total efficiency (thermal efficiency plus electric power generation efficiency) of this system reaches a maximum 94.4% which is approximately 20% higher than that of the typical Diesel engine boiler system. Besides, the use of the secondary combustor and heat exchangers results in 80%, 35%, and 90% reduction of carbon monoxide (CO), nitrogen oxide (NO x ) and particulate matter (PM), respectively.