Advanced Liquid Desiccant-Based Air Conditioning Systems


Air Conditioning for comfort is a necessity in many regions of the Earth. It also ranks high on the electric power demand in those regions. And, as income rises, so does demand for comfort air conditioning, and thus, for electric power.
It is our contention that electric power demand for comfort air conditioning can be drastically reduced, without any effects on comfort.

Our arguments, in three cases, follow:

Air Conditioning and its Technologies

  1. — The Thermodynamic Case

    In today's understanding, Air Conditioning encompasses a few operations, that we shall limit here to Air Conditioning for Human Comfort, leaving out applications to industrial processes and all special cases.
    The main operations in the air conditioning process concern the control of
     — temperature,
     — humidity content,
     — particles,
     — VOC,s (Volatile Organic Compounds),
     — germs of all kinds,
     — and, eventually harmful gases present in atmospheric air.

    Most of the power, in any form (mechanical, thermal, ...) necessary to condition air, is required by the operations to change the temperature and the humidity content.
    Now, since power is not equal power, and power generation ALWAYS implies the degradation of natural resources, it is our quest to assert that the power generation for air conditioning operations, ought to minimize resource degradation!

    Conditioning air for comfort requires, mostly, small changes in temperature, to provide supply air (SUP) at around 20 °C, and a change of a few grams of water vapour per kilogram of dry air, in humidity content!

    If adequate resources are chosen to drive the processes, waste and losses are minimized without affecting the final product — the conditioned air.

    Liquid desiccant-based air conditioning systems, for example, can be driven by thermal power at temperatures around 60 °C, and require reduced mechanical power to drive ventilators and relatively small pumps. In contrast, solid desiccant-based air conditioning systems (DEC Systems require driving temperatures in excess of 120 °C.

    Vapour compression-based air conditioning systems, as the extreme case, are driven by mechanical power exclusively.

    Suppose now a fossil fuel (e.g. natural gas) is burnt to provide thermal power to drive a liquid desiccant-based air conditioning device, which requires a temperature level of ~60 °C. The resource fossil fuel is degraded at a thermodynamic efficiency of 12%, when the process follows an ideal thermodynamic cycle, such as Carnot's. The very same resource however, may be degraded at a thermodynamic efficiency of 70%, would it drive a power process along the same cycle at 800 °C! what is more, that resource would drive both the power and the liquid desiccant-based processes, in a cascade, at a combined Carnot thermodynamic efficiency of 81%!

    Furthermore, while the dehydration of the air by liquid desiccants is driven by a mostly small water concentration difference between the air and the desiccant, dehydration of air using vapour compression refrigeration or absorption chillers, relies on contacting the air with a surface at a temperature well below its dew-point (in order to condense the water vapour from the air), requiring a re-heating step afterwards: Obviously, this step implies a double waste of mechanical power, and thus of the most valuable energy resources!

  2. — The Econommic Case

    Degrading a high potential (exergy, work availability) resource, where a lower potential one would do, ought to be economically painful!
    Energy resources are an exception to good — sane would, perhaps, be more adequate — management: most other resources are valued considering their Total Cost of Replacement. Energy resources are not despite all solemn declarations to the contrary! The price of energy resources, and most natural resources for that matter, undercuts their value by an enormous margin!

    The widely propagated theory that the value of goods equals the price as set by "the Markets", is a modern, mercantilistic, and most deceiving, concept. Not everything can be moneterized, and VALUE can, possibly not, be expressed in Market Units. This holds true particularly for all natural resources. The allocation of resources to the various ends in our world requires URGENT rethinking!

    A case in point, the so-called Renewable Energiesa, are in fact not renewable at all: — they are transient, free, disperse energy resources!

    No energy resources are renewable:

    — Yesterday's wind will not blow again tomorrow;
    — The morning tide, is not the evening tide!
    — The solar irradiation that keeps you warm today, will not comeback tomorrow!
    — The waterfall will never reverse by itself!
    — Geothermal heat is not refillable!
    — That giant wave, so dear it might be to the surfers, is in the Energy Nirvana as soon as it hits the beach!

    Thus, extending one of US President WJ Clinton catch phrases, we would rather say,

    It is NOT the economy, stupid! It is the ENTROPY . . .

  3. —  The Ecologic Case

    And now what ?

    It is a law of nature that Entropy (and disorder in general) will ever increase. The interesting thing about Entropy, is that it can be ignored, for a while. You may even create order around you, by generating higher disorder somewhere else, by exporting waste to some far away region of the Earth, for example! Forget not however, that the Earth is a WHOLE, including all the earthlings such as you and us!

    James Lovelock's GAIAb,c,d theory can help us understand why, as part of this WHOLE, we ought to behave and act sensibly in regard to the WHOLE.GAIA can, of course, take care of it all, while we continue our Business as Usual. Are we ready to accept the consequences?

    GAIA is very powerful, and might, soon rather than later, correct the disturbances that we, as earthlings, have come to generate! No kidding! As a species, we claim for ourselves rights we ought not to monopolize, as we depend on all the other species, and on the Earth's resources to survive.

    Husbanding these resources, like a Swabian Housewife, ought to be held as a Commandment!

    And forget not, we are bound to the smallish livable surface on a fraction of our Planet. And, against all inteligent reasoning, out of pure selfish interest, we blindly ignore how limited the resources are in our beautiful azure-green marbel!

    Saving the Planet, a common slogan, is a false understanding of the problem:
    —  The Planet needs not to be saved, but the LIFE on it does!
    For the Planet it does not matter whether it is azure-green or RED!

    This, however, is no alternative for Living Organisms such as you and us!

Notes & References

[a] Renewable energy is a misleading and unfortunate designation. In fact, it seems more a marketing slogan than a correct description of the thermodynamic reality!
[b] Lovelock,J., L. Margulis 1974. Atmospheric homeostasis by and for the biosphere: The GAIA hypothesis, Tellus XXVI, 2 - 10.
[c] Lovelock,J. 2000. GAIA, 3rd ed., Oxford University Press.
[d] Lovelock,J. 2006. The Revenge of GAIA, 3rd ed., Penguin Books Ltd.