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A Free Energy Desiccant based make-up
air drier and heat exchanger system


 FIG 1: FREE ENERGY Desiccant-Based Fresh Make-Up Air Drier and Heat Exchanger System Shown Installed On An Attic Floor!

Inspect Fig 1 very carefully. It shows the typical "Don't Walk On It, Or You Will Fall Through! (please, kindly, keep your feet on the walkway) "type of attic floor with ceiling/floor joists and pink fiberglass insulation between them.

The light blue box contains a cylinder filled with six compartments containing desiccant!

We have intentionally selected a desiccant that is a safe chemical that is hydroscopic (water loving) at low temperatures, but hydrophilic (water hating) at higher temperatures.

The light yellow box contains a heat-pipe fresh-air (make-up air) heat exchanger.

The idea is to bring in fresh make-up air to avoid "Sick House" syndrome in our well insulated and otherwise "airtight" alternative energy powered home.

In Fig 1, There is an energy efficient compact florescent work light and a quad electrical outlet box on the tan exterior wall at the top left in this illustration.

Plugged into the quad box are two shrouded, and louvered duct fans that blow air outward to remove air from the home.

Fig 1a. Version Showing The Individual Components By Callout Number.

The fan connected to the red hose (1) exhausts hot (160ºF or so in summer) attic air through the top four desiccant cartridges (2) inside the light blue box, thus using the attic's waste heat to dry the desiccant. The other well-insulated red hose (3) simply gathers up the very hot air high up at the attic roof's apex and transfers it into the desiccant dryer inlet.

The hot attic air thus removed, is then continually replaced by fresh cooler air from the soffet vents under the eaves, thereby cooling the attic space, and also reducing the temperature difference across the attic floor and the cool space below.

Meanwhile, via the green hose, (4) fresh, but too-humid and too-warm air is sucked in from outdoors and passes through the previously dried desiccant chambers (5) where it becomes dried, (but still too warm) thus giving up its large amount of latent-heat of vaporization to the desiccant, as the desiccant chemically grabs the moisture from the incoming fresh air

Then, via the middle green hose (6) , the now dry, but still too-warm fresh air passes into the yellow box and through heat pipe counter-flow heart exchanger inside (7) .

In the yellow box's heat-pipe heat exchanger (7) , the cool but stale air about to be exhausted adsorbs the sensible heat from the incoming dried fresh (make-up) air thus cooling and conditioning the make-up air before it is mixed into the cool space air via the final green hose (8) that runs from the yellow heat exchanger box to the fresh air register in the ceiling below.

The other exhaust fan, via the brown hose (9) , sucks stale (and now warmed) air from the stale air exhaust side (10) of the yellow box's heat exchanger and directs it outside.

The remaining brown hose (11) removes stale but still cool air from the cool conditioned space, into the inlet of the yellow box's heat exchanger by using the partial vacuum created by the brown hose, (9) and the exhaust fan at the heat exchanger box (10) outlet.

Note that there is no actual mixing of the incoming fresh air (7) and the outgoing stale air in the yellow heat exchanger box (10) . The two counter-flowing air streams are kept completely isolated and separate. Only the heat is efficiently cross-transferred!

Likewise, the hot attic air (2) never mixes with the fresh incoming air (5) in the blue desiccant unit. The hot attic air is simply used to dry the desiccant just before being instantly exhausted.

Every few minutes, an tiny ultra low power DC motor just rotates the desiccant drum exactly 120 degrees of arc, thus moving two new, previously dried, fresh desiccant canisters into the incoming fresh make-up air stream.

Simultaneously, two of the now wetted (from humidity previously removed from the incoming fresh but humid air stream) desiccant canisters, are moved into the hot dry attic air exhaust air stream to begin anew, the desiccant's drying/reconditioning cycle.

By using otherwise unused attic waste heat to a thermodynamic advantage, we both reduce the attic temperature, and thus also reduce the Air Conditioning heat load demand!

In addition, we save energy in another important and "ghostlike" and "phantom"! way

We simultaneously, by chemically drying the air, remove very large amounts of "hidden heat" ..the "latent heat of vaporization"(the reason steam feels so hot on your hand!).

By never having to run the electric heat pump compressor or Air Conditioning compressor to remove this large latent heat of vaporization, from the incoming make-up air (or the re-circulating cooled air) enormous savings in Air Conditioning power consumption are realized!

This pictorial illustration is meant primarily to be educational. The black box illustration, conveys the principles of operation, of such a desiccant air conditioning scheme, that works in humid climates.

For clarity purposes, it is not fully optimized in these drawings, and therefore is not intended to be used, without further refinements, as an actual construction plan.

In the real world, we would package the yellow box and the blue box together, in the same housing, together with a series of cascaded particle and air pollution removal filters, and a fresh Make-Up Air/Re-Circulated Air proportioning control damper to create a single, fresh air ventilation system, to use with our alternative energy homes.

Now let us take a peek inside the light blue desiccant box!

Inside the light blue box is a slowly rotating :

And, what's inside the yellow box?

Heat Pipe Heat Exchangers

Heat pipe heat exchangers are sometimes used for air-to-air energy recovery systems. These devices involve three fluids: the two air streams between which heat is being transferred and a third fluid sealed within the multitude of heat pipes making up the unit.

In a typical application exhaust air and fresh air are flowing in opposite directions, i.e., in a counter-flow arrangement, in adjacent ducts with the unit spanning the cross-section of both ducts. In the winter (as seen above in the schematic) heat transferred from the warm air being exhausted provides the energy to evaporate the working fluid in the sealed heat pipe. That vapor flows to the other end, where it condenses, giving up the heat to the incoming fresh air. The condensed liquid flows back to the warm end to complete the cycle. In the summer the operation is reversed. The warm, but fresh, air entering the building is pre-cooled by transferring heat through the heat pipes to the cool, but stale, exhaust air leaving. To compensate for the low heat transfer coefficients with gases, the outside surfaces of the heat pipes are aggressively finned.

What's a heat pipe anyway?

Heat Pipe Structure

A traditional heat pipe is a hollow cylinder filled with a vaporizable liquid.

A. Heat is absorbed in the evaporating section.

B. Fluid boils to vapor phase.

C . Heat is released from the upper part of cylinder to the environment; vapor condenses to liquid phase

D. Liquid returns by gravity to the lower part of cylinder (evaporating section).

heatpipestructure.JPG (27525 bytes)

We have already shown you some FREE ENERGY tricks, that can be used by you to get cool, and dehumidified air for free, by simply recycling the otherwise wasted energy from a hot attic.

Now, we will show how to modify a conventional compressor-based air conditioning system to get more dehumidification without increasing the operating cost or energy consumption of the compressor!

Enhancing Dehumidification with Heat Pipes
Product Review - Environmental Building News June 1998

Compressor-based Air conditioners cool air in two ways: they reduce air temperature directly (removing sensible heat) and they remove moisture from air, reducing its latent heat. In some cases the relative balance between these two functions is acceptable, but there are also many applications for which additional dehumidification is needed.

The traditional approach to these situations has been to overcool the air (thereby extracting more moisture), and then to reheat it to the desired temperature with gas or electricity. This approach wastes energy twice: once for the additional cooling and again for the reheating.

There are several ways to increase the dehumidification capability of an air conditioner (AC) that are not as wasteful.

One of the best ways for many situations was adapted from NASA technology by inventor Khanh Dinh. Dinh's heat pipes precool the air before it reaches the evaporator coils (or chilled water coils) of the AC unit, which increases the amount of moisture that those coils extract. The heat pipes also reheat the outgoing air, which leaves the system just slightly warmer than it would have been had the heat pipes not been there at all.

This reheated air is also significantly drier than it otherwise would have been. The amazing thing is that both the pre-cooling and reheating are totally passive-requiring no added energy or moving parts.

The heat pipes work because they contain a refrigerant that evaporates as the warm incoming air passes by the pipe, which removes heat from that air. The refrigerant, now a gas, then rises up along the pipe to the other side of the cooling coil. On this side it encounters the chilled air, condenses into a liquid, and runs back down to where it started. As the refrigerant condenses, it returns the heat that it had extracted from the air before the cooling coil (see schematic).

While heat pipes are widely used in mechanical systems to reclaim energy from exhaust air in preconditioning incoming fresh air the amazing thing is that they can also be used to achieve enhanced dehumidification.

For example, some of their heat pipes are configured in a loop rather than a single pipe, so that the gas rising up the pipe is not moving against the liquid running down.

In engineering lingo, the sensible heat ratio (SHR) is the amount of sensible cooling an AC unit provides as a fraction of the total cooling. Thus, an AC unit with a typical SHR of 0.75 removes 75% sensible heat and 25% latent heat (moisture).

That ratio may be appropriate in some cases, but there are many situations, especially in the hot-and-humid Southeast, when more latent heat removal is desirable.

In general, the need for enhanced moisture removal depends on factors such as the outdoor humidity, the amount of outdoor air coming into the building, the amount of humidity generated indoors, and the desired indoor humidity level.

One method by which enhanced de-humidification can be achieved, is by cleverly arranging some passive heat pipes, to straddle th3 air conditioner's evaporators coil. No additional compressor power is needed as this additional passive heat pipe based de-humidifier is powered solely by the temperature differentials.

usingheatpipe.JPG (29961 bytes)

The heat pipes may be described as having two sections: pre-cool and reheat .

The first section is located in the incoming air stream. When warm air passes over the heat pipes, the refrigerant
vaporizes, carrying heat to the second section of heat pipes, placed downstream. Because some heat has been removed
from the air before encountering the evaporator coil, the incoming air-stream section is called the pre-cool heat pipe.

Air passing through the evaporator coil is assisted to a lower temperature, resulting in greater condensate removal.
The "overcooled" air is then reheated to a comfortable temperature by the reheat heat pipe section , using the heat
transferred from the pre-cool heat pipe.

heatpipeinac.JPG (50390 bytes)

Forced Air heating and air conditioning are inherently energy inefficient.

Water, with its large heat capacity is, by volume, 3550 times more efficient in transporting heat than air is!

So water heating and cooling transport, called "hydronics" should be used as much as possible in alternative energy

The "Forced Air Handler's" big problem, is the attempt to force air to flow down a long tube using pressure from the
supply end.

That is inherently an extremely inefficient process.

Take a soda straw and try to blow air through it without puffing your cheeks out!

Very little air flows because of turbulence creating a high back pressure.

Now try sucking on the same straw.

Notice how the airflow increases and is smooth with little effort.

When you suck air out nature abhors a vacuum and replacement air rushes in!

The air flow is now laminar, smooth and turbulence free!

By design, "forced Air" heating is extremely wasteful of blower power. In addition air is a terrible heat transport medium
for any real hest over a distance.

So by using local zone units, many of which have a couple of small 12 volt DC muffin fans that use suction to move more air
over the heat exchanger, and thus take only a couple of watts.

Using proper small suction fan design, coupled with local zone heat exchangers, and combined with the awesome heat
transport capacity of hydronics, we can heat and cool a local zone without huge energy penalty incurred with ridiculous
"Forced Air" inefficient supply end blowers trying to push turbulent air down long ducts.

Since all the I 2 R losses from 1-3 KW of blower motor heat end up canceling out 1-3KW of cooling, there is a double
whammy, since now an additional 1-3 KW of cooling must be re-supplied to meat the original cooling demand. Now the
blower losses increase slightly more. Forced Air Handlers" are a needless, tail-chasing, energy wasting vicious-circle scheme.
They are a poor design, a holdover from the cheap energy heyday of the 1940's and 1950's that presumed cheap energy, that
now really needs to be avoided!

Unlike the large and extremely energy inefficient "Forced air Handlers" in common use, such a alternative energy home's
"Unforced Make-Up Air Handler" is

designed to be smaller and far more energy efficient.

It is said to be an "Unforced" air handler because small fans suck air and create a partial vacuum wherever air movement
is desired.

Because Mother Nature "Abhors A Vacuum" She kindly and benevolently rushes in to do almost all the air-moving work for free !


Q. If outside air is hot and humid and the attic is vented. Wouldn't the hot attic air be humid and not dry the
desiccant, and not be hot enough to drive the H2O from the desiccant?

A: That's a very good question!

Look at the Mollier Diagram below.

Observe that air that contains 100% humidity (fog point) at 23 degrees centigrade (72°F) temperature becomes air with just 20% relative Humidity by heating to just 122°F! Attics on a summer Solar day often reach about 150°F-160°F.

So even if it is a sweltering, muggy 110°F outside with 90% relative humidity, that hot attic air will become a very DRY 20-30% when heated. This is why you can successfully use a attic heat powered desiccant dryer to slash your air conditioning costs!

Mollier Diagram

The Mollier diagram is a very useful tool to solve HVAC-problems graphically. It includes all humidity functions in one chart.

Fig. 4a: Mollier diagram: curves of constant relative humidity . The region below 100% (fog region) is not valid because
condensation occurs.

Fig. 4b: Curves of constant enthalpy are added to Fig.4a . Also example 1 is included below.

Example 1:
To warm up air from 20 °C to 25 °C and humidify the air from 40 %RH to 60 %RH 20.2 kJ/kg would be needed.

With Best regards,


Patrick Ward

Richmond, VA


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