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Total Home Energy System-Heat Recovery


Heating the house is accomplished by recovering the "waste" heat from the ST-5. Operating at full power, the engine rejects about 58,000 BTU's per hour (about a third of the total available heat) which can be recovered from the exhaust stack (the chimney) by placing a one inch coiled stainless steel tube 13 feet long in the stack. Combining the two, you get about 470 gallons of water at 180o F per hour.

This heat is then dumped into a central water cistern for a hydronic heating system either by emptying the water itself into the cistern, or through a heat exchanger (36 feet of 3/4 inch coiled copper tube) if a closed engine cooling loop is desired. If the water is drawn from and emptied into the cistern, a drain-down cooling loop is necessary to prevent freezing. If a closed loop is used, the loop should contain a glycol solution for the same reason. The following shows the two possible means of transferring the heat to the cistern.

Components for hydronic heating systems and installation assistance are available from most heating contractors and provide very even and comfortable home heating. The boiler in conventional heating systems, however, is replaced by a cistern for an ST-5 powered cogeneration system. Once up to temperature, the cistern can hold enough heat for up to 5 days of heating, depending on its size and the heating load.

A further addition to this system could be another water-to-water heat exchanger in the cistern which would enable the pre-heating of domestic hot water. Passing the domestic water through another coil of copper tubing in the cistern is an easy and cost effective way to provide for this heat exchanger. A sufficient length of tubing will bring the domestic water temperature up to the desired level.

Finally, the remaining heat from the burner exhaust stack (about 38,000 BTU's per hour) can be ducted through the fuel storage area to dry the fuel and keep it ready for use.

A combination of a hydronic heating system with battery storage is not the only means of providing all the user's energy needs. The heat could be stored in another medium, such as sand, which could then be used in conjunction with a warm air heating system. Another possibility is running the engine constantly at a low output and not storing the heat at all. Each method has its advantages and drawbacks, and the user should determine the sustainability of the system for his needs.

This Total Home Energy System is a most efficient one, utilizing up to 80% of the fuel energy either in the form of electricity or heat. Because of their high energy utilization, cogeneration systems are seen as the energy systems of the future. The concept is not limited to homes, but can also be applied to greenhouses, dairies and any other application needing both forms of energy.



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