Green Ideas: Cutting Edge Technologies

Photo Voltaics | Climate Façade | Green Roof | Fuel Cells | Wind Power | Geothermal Heat Pumps | Rainwater Collection | Solar Domestic Hot Water Heating | Alternative Fueling Facility (Parking and recharging for electric vehicles) | On-Site Biological Waste Treatment (Living Machine) | Natural Ventilation | Radiant Ceilings or Slabs |

Photo-voltaics
Photo-voltaic cells can be mounted on the building roof or integrated into the building façade. PV can provide portions of the buildings electrical load during daylight hours, shaving peak demand. In remote locations PV's can be combined with storage devices to provide electricity "off the grid."

Climate Façade
An advanced technology used successfully in other parts of the world is something we call the "Climate Façade." The Climate Façade is typically a curtain wall with two layers of glazing separated by a large (12 inches or more width) air space. Automatic sun shades can be installed in the air space to block solar heat gain during warm conditions. The sun shades can be opened to allow light to enter the space during winter, and at times of indirect sunlight. This system allows the curtain wall to have the thermal efficiency of highly reflective insulating glass, yet allow natural lighting into the space in a manner similar to clear glass. The Climate Façade can be integrated with the building HVAC systems to allow wintertime heat recovery from the sun shades and/or direct venting from the air space during times of high cooling load.

Green Roof
Many technologies improve the sustainability of the building roof. The roof can become a "habitat" with plantings of grass and other vegetation. This decreases solar load and winter heat loss, while providing greenspace for birds and other wildlife. Alternatively, the roof can include water features, such as reflecting pools, or fountains, which will evaporatively cool the building during the summer months. See also greenroofs.com for impartial info on green roofs, roofscapes inc. for green roof supplies, and American Hydrotech, Inc. for roofing membranes for green roofs.

Fuel Cells
Fuel Cells produce electricity through a clean chemical reaction. Commercially available fuel cells typically combine natural gas with air to produce electricity. The only waste products are carbon dioxide and hot water, which can be used for other building needs (desiccant or absorption cooling, heating, preheating of domestic HW, etc.) Fuel Cells can be combined with UPS systems to provide high quality, reliable power for applications that might typically require an emergency generator. Small capacity fuel cells for the residential market are available to the public. See also GE's Jenbacher gas engines that run on either natural gas or a variety of other gases (e.g., biogas, landfill gas, coal mine gas, sewage gas, combustible industrial waste gases).

Wind Power A wind turbine can be used to generate electricity for building use. See also DOE Wind Technologies in New England.

Geothermal Heat Pumps
With ground source heat pumps, the earth is used as a heat sink in summer, and a heat source in winter. This eliminates the need for cooling towers and provides some energy savings.

Rainwater Collection
It may be feasible to collect rainwater in a catch basin or other device, for use in the building in a manner similar to gray water systems. This will reduce building water consumption and may reduce storm sewer requirements.

Solar Domestic Hot Water Heating
Solar heat exchangers could be mounted on the roof of the building. When conditions are favorable, these could be used to heat domestic hot water at an energy savings compared to conventional systems. A back-up system for cloudy days and evenings would be required.

In temperate climates solar water heaters are usually employed to support a conventional (i.e. gas or electric) sanitary hot water system by pre-heating the water coming off the mains; due to variations in the availability of solar energy (night / day, summer / winter, clear sky / cloudy) it is normally not advisable to rely completely on solar energy for water heating. The collected solar energy would be used to heat an additional coil in the hot water storage of the conventional system; the calorifier might want to be increased in size to allow the use of the solar energy (peak at lunchtime) with a time lag (user peak morning or afternoon).

The solar energy is collected by so-called solar collectors, which heat up water which is circulating through them, and then in turn heats the above mentioned coil in the calorifier; the collector circuit normally consists of the collector itself, a circulation pump (which can be solar powered, too), and pipework that connects the collector and the calorifier.

The main factors for the collector's efficiency are its heat loss and its absorbtion. The absorbtion capacities of the collector - in simple terms actually just a pipe with water - is increased by either welding the pipe to a plate (increasing the collector area) or focussing the solar irradiation of a larger area onto the pipe; in both cases the pipe would want to be black for increased absorbtion. The heat loss is taken care of by effective insulation; the better the insulation, the more expensive the collector usually becomes. Insulation types range from a simple glass pane on the sun side and some cork on the back side of the collector, over double glazing with low-e coating and polyethylene foam, to vacuum insulation (mostly in form of tubes) and reflector systems.

The peak efficiency of solar water heaters then varies from 40% (normal, good quality flat collector) to over 80% (vacuum tubes), giving a peak harvest of up to 500 W/m² a "normal" household would require about 3 500 W. The choice between high efficiency and normal efficiency (equivalent to high and normal costs) depends mostly on the area available, since the achieved energy cost is roughly the same; if sufficient space is available, a normal efficiency system should be chosen, while a high efficiency system should be used with limited space.

As long as the collectors are installed at an angle of more than 20&#deg; from the horizontal, they are self-cleaning and almost maintenance free; the yearly solar harvest only varies little between a southeast, south or southwest orientation of the collectors. Some construction costs can be saved if the collectors are integrated into the roofing system, rather than supported on an independent system above the roof.

Alternative Fueling Facility (Parking and recharging for electric vehicles)
This would encourage use of other green technologies. Utilities or car manufacturers may be willing to bear the costs of this type of facility.

On-Site Biological Waste Treatment (Living Machine)
On-site biological waste treatment could be used to treat both "gray" and "black" water to local prevailing standards. This would reduce pollution as well as load on waste treatment plants.

Natural Ventilation
In the Northeast US, I see two schemes where natural ventilation would play some role:

1. Seasonal switchover. This is basically what many people do at home. During the winter they use their boiler, or furnace. Come June 15, they take the AC unit out of the Garage and stick it in the window. Spring and Fall, they rely on natural ventilation for cooling. There is absolutely no reason why this shouldn't work in a bigger building, provide we make accommodations to allow this to happen. (I guess part of the key to this is that building residents have to be willing to accept variations in temperature. They would be more willing to do this if they have some control over what is happening.)
2. Night Time Cooling, with Thermal Storage in the Building Mass. This would be more difficult to control, and would only work in a building with a conventional schedule. Basically one would subcool the building at night using the outdoor air. The thermal mass of the building can absorb heat generated in the space during the day, reducing the peak load. There is some potential for condensation and moisture control problems with this scheme.

I also see a real potential for systems that use outdoor air for cooling, but use some fans, making them strictly speaking, not natural ventilation. Maybe we should avoid the term "natural" and think of "low-energy" instead.

Radiant Ceilings or Slabs
Radiant ceiling panels, or chilled floor slabs can used in lieu of conventional systems to provide space conditioning. These systems improve energy efficiency and minimize the architectural impact of HVAC systems. Unfortunately these systems are probably not appropriate if used in conjunction with operable windows in humid areas, due to the possibility of condensation problems during the summer months.

Pros:
- Quiet
- Energy Efficient
- Architectural Impact reduced

Cons:
- Difficult to provide Latent Cooling (Dehumidification). Condensation on radiant surfaces may create indoor rain.
- Limited to spaces with relatively low cooling loads
- Slab type systems may be difficult to control, as they don't "change direction" quickly due to their high thermal mass.

There are several ways around the condensation difficulty. One solution is to use a radiant cooling device with its own condensate drip pan. Edwards Engineering makes a device they call the Valance Heating and Cooling system. They are ugly, but they work very well in the right application. Princeton University has installed them in their Scully Hall Dormitory. They are so happy with them that they are now standard for all new dormitory projects there.