How it Works
Conventional air conditioners have two main problems:
"Every one in a while,
a revolutionary product comes along that changes everything"
- Steve Jobs
A Revolution in
Unlike most desiccant systems, the patented AirGreen multi-stage process produces supply air at 70°F and below. This allows AirGreen units to be a direct replacement for RTU and AHUs in many applications. In other applications, AirGreen units may be added to pre-treat air.
Learn more about the applications of AirGreen units here.
"Matching the Sensible Heat Ratio of Air Conditioning Equipment with the Building Load SHR", November 2003, TIAX LLC Acorn Park, Cambridge MA
Typical indoor RH levels with conventional equipment are 60 to 65%, which accounts for the "clammy" feel of the air.
The AirGreen Method
The patented AirGreen process delivers superior performance at revolutionary 130°F hot water and 60°F chilled water. These can be provided by a heat pump, waste heat, or geothermal cooling. No other competitor can match this performance or efficiency.
The AirGreen liquid desiccant air conditioning unit effectively replaces the air handler or fan-coil and removes the condensate problem completely by absorbing all the moisture required and simultaneously cooling. The regenerator reconcentrates the desiccant for reuse.
It is important to understand how the AirGreen approach to air conditioning differs from conventional cooling and from other desiccant systems.
Desiccant systems remove humidity without cooling the air to the dew point. They thus save the energy required for cooling below the desired supply air temperature.
Conventional systems remove heat and moisture on large air coils cooled by refrigerant flowing through them. If there is sufficient moisture in the air and the coils are cold, moisture will condense and restrict the airflow through the coil. The condensation of moisture requires cold for removing the latent heat of condensation as well as for cooling the air. The amount of latent energy that normal coils can remove is normally restricted to about 20% of the energy supplied to the coil. In most parts of the US there is much more than 20% latent energy in outside air in summer.
Most desiccant systems struggle to remove the latent energy and so deliver supply air at “room neutral” conditions or higher when there is much latent energy in the air. Many need large cooling devices following the dehumidification.
Most liquid desiccant systems are limited in the level of drying the air that they can do unless they use a high temperature for regenerating the desiccant. Thus, they cannot use low temperature waste sources.
About the diagram
The left hand zig-zag line shows the treatment of Outside Air to Supply Air through the AG Air Conditioner with 4 sectors. The graph is plotted on a psychrometric chart with humidity on the vertical axis and temperature on the horizontal axis. In each sector the air is dried by the desiccant (diagonal line) and then cooled by the 60°F chilled water (producing 65°F cooled air).
The right hand zig-zag line should be read from bottom upwards. The air used for regenerating the desiccant is first pre-heated using exhaust air and then evaporates moisture from the desiccant in 4 stages. Satisfactory concentrated desiccant can be produced using a hot water source of 130°F or less for certain applications.
AirGreen products remove the humidity in multiple stages. During each stage of dehumid-ification the heat is removed from the liquid desiccant by pumping it through a plate heat exchanger with a high capacity for removing heat to the cooling fluid. Plate heat exchangers are very cost-effective for removing heat from a liquid and have a very long life compared with coils.
AirGreen products are designed to carry out net cooling to the air after removing the humidity. They can also dry the supply air to around 30% relative humidity at the same time. The importance of this will become apparent when we move on to the energy savings estimation.
The Air Conditioner takes 100% outside air and dehumidifies and cools it in summer and humidifies and heats it in winter.
The Regenerator takes return air from the building and uses it to reconcentrate the liquid desiccant for reuse. The return air may be only 60% of the supply air to the building.
In addition there is a storage unit for the liquid desiccant. This balances the desiccant flows to each unit and also acts as a reserve supply of desiccant.
Each air handler has a supply of heated or cooled water to control the air temperature.
The conventional system cools the air down to the super-cooling temperature of 50 or 55F to reduce moisture and then reheats it to the comfort level. The energy to do this is shown on the vertical axis. Note that conditioning outside air requires much more energy than for recirculated air.
AirGreen only has to cool to the comfort level plus the cooling needed for the building. The amount of outside air is the same volume in each case. The actual energy used is proportional to the shaded areas. According to Department of Energy figures the reduced energy is 61% lower than the conventional system.
The air from a conventional system comes from the coils almost saturated. As it heats up to 70 or 72°F the relative humidity drops to 60 or 55%. Since moisture is being added to the room by people breathing, cooking, etc. that is the lowest RH that can be achieved and it will sometimes rise to 70%, which is an unhealthy level. Often the temperature is kept lower and the relative humidity is even higher.
AirGreen systems are designed to deliver air at 30%to 35% RH and 65 to 70°F. This enables the room to be kept at 40% RH, which is the optimum comfort level. Because of this lower humidity you may notice on the diagram that the return air energy is lower and closer to the comfort level. The comfort level is in reality determined more by the relative humidity than the temperature since it is the ability to remove moisture from the skin without perspiring that determines comfort.
Although the diagram is drawn in total energy units, you can imagine that the AirGreen system is providing air at lower humidity and therefore lower energy level. Thus, if AirGreen equipment supplies air with a lower humidity level than the required comfort level the amount of airflow required to do the same total ‘energy’ reduction will be less. More accurate figures are needed to show how much less, but it can amount to 50% or less airflow needed, and at the same time the comfort level is being increased!
Suppose the Outside Air is at 95°F, 55% RH with an enthalpy of 45 Btu/lb. The Supply Air is at 55°F, 100% RH and 15% Outside Air is used for ventilation. The building latent and sensible loads are 10% and 15% respectively (modern insulation).
The Supply Air must be reheated to 67°F to reduce the RH to 55%, which negates 40% of the cooling. The latent load in the building could increase the RH to, say, 60%, which is far from ideal, and the sensible load increases the temperature to 78°F. This requires about 400 cfm per ton of cooling.
The AirGreen equipment would require about half the cooling tonnage and only 200 cfm per ton. Thus the air volume circulated would be only one-quarter that needed conventionally. The indoor conditions would be an ideal 40% RH and a temperature of between 70°F Supply and 78°F Return Air.
We say that 61% of energy is saved. That is if you compare AirGreen with a conventional system burning even more energy to produce a more comfortable condition approaching that produced by AirGreen. The added problem with conventional systems is that an up-market system producing modest comfort costs more than a system with AirGreen as well as using 61% more energy on average.
Health & Comfort
The first aspect of health is the control of relative humidity (RH). It is well-known that conventional air conditioners produce air that is more humid than they should do and transmit and nurture of air borne diseases. Air from wet coils at 55°F is almost saturated and contains at least 9 parts per thousand of moisture, and occupants increase that to around 10 parts. At 72°F this is a relative humidity of 60%, which borders on unhealthy. In humid climates it can often reach 70%, which is unhealthy.
AirGreen systems can control the humidity of the supply air between 30% and 50% as needed. The building can be kept at around 40% RH or at a level set by the building control system. The absolute humidity of the supply air can be reduced to around 4 or 5 parts per thousand. This removes moisture (in the exhaust air) so that additional cooling can be done using conventional systems running with dry coils, which increases their efficiency. (see applications)
In winter, the humidity in buildings is usually too low. Low relative humidity causes breathing difficulties and bleeding in airways. Heating reduces relative humidity and moisture should be added to keep it above 30%. The AirGreen system adds moisture to the air via the liquid desiccant. This method ensures that the air is always sterilized of microbes.
AirGreen products clean the air to remove dust, mold, and mildew spores all year round. Since condensate is completely removed, there is no danger of diseases like legionella breeding in the air conditioning system. The cleaning is done by a liquid washing process that is more effective than most filters and also less restrictive on the airflow. Thus, less energy is used by the fans than with Hepafilters. The air is so clean that asthma sufferers will be delighted.
Dust and other deposits do not accumulate as they do on filters because they are washed into the sump and then filtered out in a cartridge filter that can be easily changed.
The liquid desiccant is a natural biocide and disintegrates all known bacteria and viruses that are a danger to humans. It does this by removing the water from their molecules – that is desiccating them. Now the AirGreen system is treating mainly outside air and thus bringing very clean air into the building. AirGreen can also add up to 40% of recirculated air when extra purification is needed. The AirGreen desiccant solution has been tested and used operationally to clean the air in a SARS hospital ward. The military have tested it on anthrax!
The solution to the cross-infection problem in hospitals is believed to lie in a larger volume of clean outside air. AirGreen can provide that economically and effectively.
Clean & Healthy
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