ZEB - Zero Energy Buildings explained
Tuesday, October 16, 2007 at 09:57PM
Toby Considine in Background, Microgrids and Distributed Systems

All the ideas in Zero Energy buildings have been around in some form for a while. The problem is the key elements, such as demand-response, have been centrally controlled. Sign up for this program months in advance, and then the Power Company controls your [water heater]. But what if I want to stay home today? Too bad. Consumers do not want loss of control. This limits participation.

New initiatives are getting closer to changing this. There are now a couple web services protocols for building controls: oBIX and WS-Devices. The newest Windows now is able to discover such services automatically. Soon there will be software to let your PC discover and operate building systems much as they discover printers today. It is not hard to imagine an agent talking to the power spot market, talking down to the systems, reading the electric meter live…

Some of the so-called “Zero Energy” initiatives envision each building supported by multiple on-site energy collection and generation systems. Based upon the building’s operating posture, and the mix of energy sources available, such a building would pull 35% or less of its total energy budget from the grid. If the facility includes local buffering and storage of electrical energy, whether this buffering is in the form of souped-up traditional batteries or new-fangled hydrogen storage, this become viable.

Power comes over the grid as Alternating Current (AC). Power is stored in batteries as Direct Current (DC). Power from the grid must be converted from AC to DC for storage. Before it is used in your home of office, it must be converted back to DC. Power is lost with each conversion. Power from most on-site generation is DC. On-site DC power generation can be stored in those batteries without the losses you expect converting from the AC grid to DC.

If future houses support DC distribution for internal use, then the batteries can become the primary source for the house. Because this removes the loss from converting the DC battery to AC, this effectively increases power stored in the battery with no new storage technology required. Most devices in modern houses are DC anyway. Those little bricks and wall-warts, the rectangular boxes attached to the plug or in the middle of some power cords convert power from AC to DC. This conversion is very inefficient; a third of the power may be converted to heat before it goes any further. The Galvin Power Initiative (www.galvinpower.org) is a good source for the engineering behind this. With appropriate local buffering (batteries), an awful lot of power consumption can be shifted to off hours without loss of occupant autonomy.

Zero Energy Buildings, then, are engineered to be efficient, make some of their power on-site, and shift energy use to when it is cheaper and more plentiful.

Next – Zero Energy Buildings and Shifting Power Consumption

Article originally appeared on New Daedalus (http://www.newdaedalus.com/).
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