What does "Sustainable" mean - it means that you are using far less energy produced from fossil fuels that have to be yielded from the earth by drilling, or mining for them. And if you have to use materials that you have to mine and refine that those materials remain preserved and can be re-used at the end of life so that they do not have to be mined again. For example most of the world's aluminium need can be satisfied with aluminium re-processed from scrap. Low load bearing foundations and walls can use crushed concrete for ballast when available. There are many crushing and concrete re-cycling services available today which can easily be found when searching for "recycled crushed concrete". You can also use Recycled Asphalt Pavement and Crushed Concrete as backfill for Mechanically Stabilized Earth Retaining Walls.
In the context of "Green Sustainable Architecture" this can mean correct positioning of a building versus the prevailing wind direction, run-off water management on the property, wall and roof insulation and avoiding roof penetrations. Those are some of the passive measures that can be taken at the design stage of a new building to make it more sustainable.
In the context of "Heating and Cooling" there are slightly different requirements on a sustainable Heating and Cooling Systems depending on the climate-region. There are also significantly different Systems that can be deployed which will have significantly different requirements for the infrastructure the building has to provide.
The most significant factors for both heating and cooling are loss of heat or cool through walls, windows and ceilings. This has to be addressed architecturally by designing with good or very good insulation materials and the really good ones may not be from re-cycled materials but are end of life recyclable as ballast. In preference of performance; Aerogel, Styrene and Two Component Esther Foams. In preference of price; Foams, Styrene, Aerogel.
The plenum between floors should be well insulated to the outside walls and contain the infrastructure for water-loops rather than air ducts (or both) as well as a 48V-DC electrical distribution system which allows the use of 48V-DC based heat pumps and 48V-DC based lighting equipment.
The reason for using DC based systems is that:
LED lighting running of DC can run with an efficiency of 98% while
AC based LED lighting systems run with an efficiency of 85%.
Any Watt in heat generated requires a Watt to pump it out of the building, in the case where the air space needs to be cooled. The energy wasted by lighting has a direct and significant impact on the energy required to cool a building that is well insulated.
The same applies to the heat exchanger when the heat pump itself is located in the building.
DC based systems can use Solar and Wind Generators to charge Batteries for storage,
the Grid or a Generator can supplement the batteries.
The highest loss of efficiency of conventional air conditioning systems for heat or cool is in the air duct. Therefore for highest efficiency and sustainability heat exchangers should be in each room. The heat exchangers may include heat pumps which for noise reasons may use solid state heat pumps which require little or no maintenance other than air-filter maintenance. This is the most efficient way to cool or heat the air in the room.
Any air-cooling system will have condensate at one time or another. This requires the use of heat-exchange / heat-pump systems with built-in condensate pumps or gravity-fed condensate removal and cater for condensate disposal pipes within each floor level of heat-pumps. The disposal pipes should have the usual grade for gravity-fed pipes. The condensate should be guided to one location where it can be re-used by re-introducing it into the environment via the chiller or may be collected in a cistern for other uses.
The in-house water loop can and should be water based as it is the most efficient energy carrying and storage medium on the planet. The only challenge is that you must not allow the water to freeze so the lines carrying the water have to be well insulated where they leave the building to the outside heat exchanger, underground tank or chiller. A heater of some sort has to be introduced into the water transport loop for locations where temperatures can fall below freezing. This can be hidden in a closet integrated into the structure of the building but accessible from the outside so that heating equipment can be maintained and replaced without affecting the living or working space.
I am often asked why not use anti-freeze in the loop? Well it would have to be non-toxic anti freeze which is expensive and not easy to replenish in case of a leak or a repair. If toxic anti-freeze is used, which is cheaper, the piping needs to run inside a bigger pipe that is drained into an outside tank that can take the whole system's anti-freeze without contaminating the environment. So de-ionized or de-mineralized water and measures to keep it from freezing are more attractive and in case a pipe leaks definitely more friendly to the environment.
The most effective way to create heat at the lowest cost is using natural gas or propane or from bio-mass when and where available. So for all winter applications except in near equatorial regions, a gas heater is most appropriate. This is based on the assumption that the time of the year that heat is needed there is insufficient sun or reliable wind to produce sufficient energy for heating when temperatures fall below freezing. Of course an electric heater could be used driven from the electric grid but that would be the least sustainable way of doing things.
There is one additional way to be even more energy-efficient and that is using a generator that is natural gas and/or propane driven where the cooling loop of the generator can be selectively heating the air-conditioning loop in the winter and the generator charging the batteries at the same time, basically using all the energy (in the winter) the generator produces, electricity and heat. In the summer the generator has to be automatically de-coupled and have its independent chiller when operated.
Another aspect is fresh air, where new structures should accommodate the delivery of fresh air to living and working spaces via a selective and controlled system that uses CO2 sensors to determine the level of human activity and O2 use. This means air ducts that can deliver fresh air from the outside selectively. Such systems should have pollen filters that are easily maintainable and have the ability to email or warn the parties responsible for building maintenance to replace or clean the filters.
Different climate regions require different approaches, in equatorial regions (+/- 10° off the Equator) insulation, positive pressure and dehumidification of fresh air are the key factors for climate control. There are no heating requirements and all cooling can be mostly supplied by solar and wind energy.
In the regions between 20° and 40° North and South, where ambient temperatures can fall below or rise above human comfort, heating and cooling are key requirements. Here, significant efficiencies can be achieved by exchanging air in the plenum of the structure with outside air depending on the outside ambient temperature.
In the regions above 45° heating and occasional cooling as well as controlled heating of the fresh air brought into the building are the key requirements. Underground or above ground tanks can greatly assist in balancing during most of the year except in the winter season.
In the region above 60° insulation and heating are the only requirements for both the area to be heated and the fresh air brought into the building.
For the regions of 20° to 55°, during the transition times of the year, the sun can heat the roof space yet the outside air can be cold. If for cost or other reasons the roof fabric can not be insulated sufficiently, at least the building infrastructure should offer a set of fans that can replace the roof plenum air with outside air. The intake should be on the North side of the building and the outlet(s) on the South side or on both east and west side. Intake fans should also have pollen filters that are accessible and can warn that they need changing.
Water heating systems can consist of solar heated vacuum tubes as well as a propane, natural gas, bio methane or other combustible materials or liquids as a backup for prolonged periods of no sun or at night.
Underground or above ground closed system storage tanks that require sufficient insulation above ground to not freeze in cold environments and if below ground are just below the freezing line of the region. Deep underground tanks are not recommended as the surroundings in hot climates will just make them get hotter and hotter, the system should be able to relieve heat to the environment by being in surface proximity but below the freezing line.
Klaus Bollmann is a 30 year veteran in energy conservation, resource saving innovative products for a sustainable environment. Click the link If you are interested in Ringdale DC Systems high performance 48V-DC products or ActiveLED 48V-DC capable lighting systems, 48V-DC air conditioning systems using Solid State heat pumps and controls.