What about something like this?

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Permalink Reply by Jim Martin on August 27, 2008 at 10:47am

What you propose has some potential. As I understand it, there would need to be an energy input to heat the boiler. If that energy is used only for creating flow in the building and generating power at the top of the air "chimney," the question would be whether it generates much electricity for the energy input.

If the energy input to the boiler is used for another purpose, such as generating electricity as in a coal-fired power plant, and the heat being extracted in the air-to-air exchanger would otherwise be wasted, this scheme may create more usable energy with no extra fuel. The problem then is that the removal of heat by the exchanger reduces the chimney effect, which is needed to keep the pressure low at the exhaust of the boiler system. If the boiler creates hot water used for building heat or domestic hot water, and the exhaust to the exchanger is only the combustion exhaust, the heat removed at the exchanger might not make much difference.

This system has similarities to two others. The Solar Tower uses solar heated air to create an upward flow to turn a turbine. The Solar Windmill uses both solar heat and wind to create upward flow. One option being considered for the Solar Windmill is to attach it to a tall building or exhaust stack, in which case heat from the building or exhaust stack would increase the upward flow. More information is available by clicking on my name.

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Permalink Reply by JohnG on August 27, 2008 at 6:44pm

Jim,

Thanks for your reply. The boiler in most large buildings is used for heat, either steam or hot water. Typical they are fueled by natural gas or fuel oil, I'm proposing to use the stack exhaust heat to superheat the air entering the chimney. Most high rise buildings struggle to control a natural stack effect, this just amplifies the effect. Also, buildings typically exhaust waste air through the roof, I'm proposing to redirect the exhaust to the bottom of the chimney further priming the stack effect. What I'm not sure of is if you can create enough CFM of air to spin a turbine generator of sufficient size to power the building. The biggest objection I've heard is it would take up too much income producing square footage. I think tenants would flock to a building where the electric power is free.

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Permalink Reply by SJC on September 20, 2008 at 9:43pm

You would not get a large amount of energy recovered because of the lack of density of air. You could recuperate the heat and drive an organic rankine turbine using a fluid that boils at lower temperature than water, but you might only recover 10% of the waste heat, which might be 10 times the recovery of this method.

There are many very efficient building heaters these days. Most of them involve phase change of water to steam and back to water. They can be 90% efficient. The best way is combined heat and power. You generate electricity and use the waste heat to heat the building. We have been very wasteful with energy all these years and years from now hopefully this will be a just a mistake made in the past that we have learned from.

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Permalink Reply by Curt Rothman on January 18, 2009 at 4:22pm

Direct Contact Inc has a patented technology for capturing waste heat that is proven, highly efficient, and typically pays for itself in less than 3 years. The units have a lifespan greater than 10 years with minimal maintenance . The typical fuel savings is 7-10% per unit installed. By burning less fuel, the Green impact is also meaningful.

The company has now successfully installed similar systems throughout the US which are currently recovering heat (and water) in several different applications, including:

* Natural gas boiler exhaust
* Wood fuel boiler exhaust
* Municipal Steam
* Food Processing

For more information, please see www.dciheat.com

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Permalink Reply by Earl the Energy Explorer on February 3, 2009 at 7:33pm

There is other effort going on along these lines. See MIT news release on thermoelectric systems research.

www.energyinfoforyou.com

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Permalink Reply by RWC1972 on February 3, 2009 at 9:40pm

No property developer is going to sacrifice that much space out of their building to be non-billable, just accept it.

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