Micro-CHP System Generates Heat and Power

Say "micro-CHP" and it sounds like something very familiar in our modern digital world, the microchip. But micro (or small-scale) combined heat and power (CHP) systems for residential applications are, in fact, a different technological breakthrough — and one that's getting a lot of attention from green-conscious builders.

Micro-CHP systems use an internal combustion engine, most efficiently fueled by propane, to generate heat and power a small internal electrical generator.

All engines produce heat, but a micro-CHP system captures it and transfers it to a conventional central-air blower for space heating or to a water supply and delivery pipes for use by various appliances and plumbing fixtures. Meanwhile, the unit generates electricity to help offset what is supplied by the utility grid.

A typical micro-CHP system, similar in size to a conventional outdoor air-conditioning condenser, produces a thermal (or heating) output of approximately 12,000 Btu per hour, and an electrical output of about 1,200 watts. That's plenty of heat to serve a home's hot water needs (especially if tankless propane units are installed) and enough electricity to supplement the power grid or, even better, electricity generated by a photovoltaic (PV) array.

The electricity generated by a micro-CHP unit can also be used to recharge a PV's battery bank if that system is not tied to the meter.

In that case, when the battery voltage drops to a preset level, the propane generator starts automatically to stabilize the energy source and supply DC power to the house. Any power output that exceeds that load demand is absorbed by the battery bank until it is adequately charged and/or the solar collectors are able to take over again. When that happens, the generator turns off and may remain dormant for several hours or even days until it is needed again, making even more efficient use of energy resources.

While micro-CHP systems currently command a small fraction of the housing market, they have been successfully employed as whole-house heating equipment for small homes or zones of larger homes in northern states and Canada, with their electrical generation serving to supplement the power grid, similar to how solar panels are now being employed. They also can be used as more energy-efficient pool and spa heaters, perhaps serving as a backup to a solar thermal collector.

However they are deployed, micro-CHP systems are one component within a sea change of how energy is used and generated in the residential realm — specifically, the optimization (and therefore efficient use) of several of energy sources serving each house and community. The result extends the availability of finite or legacy energy sources while offering alternative solutions.

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