1 Harvesting water from the air
1.1 LP Turbines for domestic or small business use can be housed in an insulated outer box that acts as a condensation chamber. This design can also produce indoor air cooling as a side product.
Figure 1. In a warm humid climate, households could become self-sufficient in meeting their drinking water, electricity and indoor air cooling needs.
The design can be scaled up to meet these needs in larger buildings.
1.2 Moisture can also be harvested from air vented from horticultural glass houses.
Figure 2. Fresh air (filtered to remove insect pests) needs to be continuously fed into the glasshouse in order to provide the plants with carbon dioxide. As a bonus, such glasshouses would provide more electricity per square metre of ground space than solar panels. Some of this electricity could be used for converting atmospheric nitrogen into nitrogen fertiliser.
Nitrogen fertilisers can boost plant growth, but when used outdoors, it can be flushed away to produce ground water and river pollution. Thus, carefully managed food production inside glass houses will also help to protect our natural water supplies.
2 Distillation of sea water
According to existing technology, reverse osmosis is preferred to distillation because it requires significantly less energy. However, LP Turbine based desalination systems swing the energy balance in favour of distillation, because they generate electricity, instead of consuming it.
The following designs are worth considering for the small scale off-grid production of desalinated water.
2.1 The basic concept
Figure 3. This system is primarily a power generator that produces fresh water as a bonus.
It could produce about 0.5 litre of distilled water per hour, for an environmental temperature of 20oC.
The system also produces an output of cooled air that can be used to cool a dwelling or storage space.
It is mechanically simple because it operates at atmospheric pressure. However, its distillation efficiency is low because a large fraction of the heat entering the evaporation chamber is used for warming air, rather than evaporating water.
Sea water corrosion is an issue, especially for the evaporation chamber. The two main solutions are to construct the chamber from glass fused steel or stainless steel.
Stainless steel has fifteen times the thermal conductivity of glass fused steel, allowing heat to flow in through all the chamber walls day and night. But it is also relatively expensive, with an evaporation chamber having 1 m2 upper and lower surfaces costing approximately £500.
A glass fused steel evaporation chamber with a glass or plastic lid could run on solar energy, on sunny days, producing up to 5 litres of water per day.
During the hours of darkness, a modest output of distilled water could be maintained, supplemented by the production of dew on the outer surface of the cover.
2.2 An improved water output design
If we pump the atmospheric air out of the system, all of the heat entering the evaporation chamber can be used to evaporate the brine.
By using atmospheric heat in this more efficient way, a 10 kilowatt LP Turbine will produce approximately 14 litres of water per hour, during the day and on warm) nights.
This output can be obtained, irrespective of atmospheric air temperature, provided that all parts of the system remain above the freezing point of water.
Figure 4 . The lines of ridges and furrows should tilt gently downhill to simplify dew collection.
2.3 A cascade system to multiply distilled water output
This design employs stainless steel partitions, wherever heat flows across the partition is desired, but saves on material costs by using glass fused steel elsewhere.
Figure 5. Several design variations on this concept are possible. These include
- Lagging the evaporation chambers and electrically heating the first stage in the cascade. A second LP Turbine will be required to prime the system and compensate for heat losses.
- The number of stages in the lagged cascade can be increased by raising the temperature in the first evaporation chamber. However, salt water corrosion increases exponentially with temperature. So, higher quality stainless steel may be required for the warmer chambers.
- Distillation systems should be relatively easy to maintain, but are far more bulky than their reverse osmosis equivalent. So for large scale desalination purposes, a reverse osmosis unit powered by an LP Turbine may be your best option.
3 Incorporating clean water production into desert architecture
The aim is to create buildings that have glass roofs that act as lenses for focusing solar energy, then to use this energy for distilling sea water and producing electricity.
In order to minimise the weight of the roof, Fresnel roofing tiles would be used.
This diagram of a vertical Fresnel lens explains the principle involved.
Figure 6. A Fresnel roof would be approximately twice as heavy as a sheet glass roof, but would have ability to focus solar energy.
The advantage of a Fresnel roof, compared with a simple glass roof is that the solar energy can be recycled and used to distil several batches of salt water, before it is finally converted into electricity.
Here are some examples of the new opportunities open to architects.
3.1 A single module design
Figure 7. The roof is made of Fresnel prisms that focus the solar energy along a north-south axis. The line of focused energy moves across the chambers during the day.
The water vapour produced by evaporation in the currently hottest evaporation chamber could reach 100oC.
Successive evaporation chambers reach their highest temperature in turn, throughout the day. Using a system of valves, water vapour from the currently hottest evaporation chamber is fed into the condensation chambers under the cooler adjacent evaporation chambers. A fraction of the vapour condenses out, releasing latent heat that helps to warm the evaporation chambers above them. This recycling of the thermal energy can be repeated several times along the chain, for as long as there is an evaporation chamber at a lower temperature than the vapour in the underlying condensation chamber. After the recycling process has been exhausted, the residual vapour is condensed out on the outer casing of an LP Turbine.
The LP Turbine would produce an output of cold air that could also be used to cool the building interior.
This design could also be used to distil filtered sewage water and produce a liquid fertiliser residue.
3.2 Modular Fresnel roofed buildings
Figure 8. The range of Fresnel roofed buildings that could be created is only limited by architects imaginations.
Today’s prosperous coastal Middle Eastern cities have a skyline similar to New York and other thriving coastal cities. However, their hot arid climate and access to glass making sand offers them the opportunity to be different.
Eyesight benefits of buildings with Fresnel roofs
Worldwide, there has been an increase in myopia (near sight) since the covid outbreak in 2020. Most experts put this down to young people spending more time indoors than before the outbreak.
To reduce their risk of developing myopia, young people are recommended to spend at least an hour a day outdoors. Spending additional time in Fresnel roofed school and nursery buildings could be a good way of increasing this daylight diet by providing strong but diffuse daylight that has been stripped of its potentially harmful UV component by the glass in the roof.
4.1 Repairing coastal freshwater aquifers
Salt water can leak into the aquifers if the local sea level rises or too much freshwater is drawn from them. This problem can be reversed if the aquifer is rested, but salt water just outside the freshwater zone is pumped out, encouraging freshwater to flow in and replace it. In warm climates, where LP Turbines rarely ice up, a simple PL Turbine with no electrical components could act as a mechanical work amplifier, for operating the pumps.
Fig ure 9. The brackish water that is pumped out of the aquifer could be partially desalinated so that the water fed back into the sea has the same salinity as the local sea water.
4.2 Using abandoned deep mine water for irrigation
This basic type of LP Turbine could also be used for pumping water out of abandoned deep coal mines.
Deep mine water can be as warm as 40oC, allowing an LP Turbine to run on thermal energy extracted from the water. Before being used for irrigation, the water would need to be aerated to solidify any dissolved iron and filtered, say by using cyclone filters, to remove the solid iron oxide particles. Both of these operations could be carried out using mechanical work provided by a basic LP Turbine.