There are alternatives of air conditioning systems that operate under low enthalpy conditions with optimal performance and remarkable energy savings.
by Alfredo Sotolongo*
The most economical energy to produce is the one that is saved!
I have always referred to our tropical countries which lie between the Tropics of Cancer and Capricorn due to the high moisture content and high temperature in the outside air, which represents very high enthalpy.
However, in many of these countries and south of the Tropic of Capricorn there are also areas with drier and less hot outside air with low enthalpy.
When there are conditions in which the enthalpy is lower than in our most tropical countries, air conditioning systems can be used that represent great savings in energy and at the same time, in water consumption.
The company Aaon has developed and patented chillers and package units with evaporative condensers and refrigerant superheating coolers. Which consume up to 22% less water than conventional evaporative condensers and are much more efficient than air-cooled coolers and package units.
Package units include 100% modulating hot gas reheating. This allows to control the exact amount of humidity to be reduced and thus supply the air consistently to conditions that allow using systems where relative humidity is critical for their proper functioning.
Among these systems where relative humidity is critical, but very efficient, are the Cold Beams and the Under-floor Air Distribution known as DABP. Therefore, in places with low enthalpy and using evaporative condensers, very attractive efficiencies are achieved and water consumption is minimized.
Cold Beams are installed on the roof of the conditioned area, they are supplied with cold water and use two methods of heat transfer. The thermal load heats the air and it rises towards the Cold Beams cooling and descends to displace the hot air creating a natural convection movement. Cold Beams also cool by radiation.
The challenge presented by the Cold Beams is the danger of condensation that in areas of low enthalpy is easier to control. To overcome this challenge, the temperature of the water supplied to them must be at least 2⁰F higher than the dew temperature of the air in the conditioned area.
To use DABP, Under-floor Air Distribution, it is necessary to raise the floor and a full chamber is created between the raised floor and the structural slab of each level of the building. Air is supplied through the raised floor at temperatures between 62⁰F and 68⁰F instead of the 55⁰F of traditional systems.
The theory behind the DABP system is to create a floor-to-ceiling stratified air condition of the conditioned area, relying on the natural flotation of the air to remove heat and pollutants that affect occupants. However, in reality, diffusers on the floor that create turbulence along with the activity in the space slowly mix the air supplied with the air from the conditioned area a few feet above the floor and it ascends to the ceiling. This mixture conditions the air comfortably around 70⁰F to 75⁰F.
The challenge presented by the distribution of air through the floor, DABP, is very similar to that of the Cold Beams, condensation on the floor. It is important to control the air humidity in the air conditioning unit. This is achieved first by extracting water from the cooling coil and then reheating it by modulating the hot gas in another coil versus the cooling coil in order to deliver the air to ideal conditions. Some of the hot gas instead of being sent to the condenser is sent proportionally to the overheating coil.
I think that in areas where the air is drier, you can consider the application of pack units and / or chillers with evaporative condensers that are much more efficient than air-cooled ones. Their most important goodness is that due to Aaon's patent, they consume less water than conventional ones. In addition, they can be combined with Cold Beams and With Under-floor Air Distribution. There are also other combinations with diffusers and handlers of variable volume.
The ideal goal for our industry is to make the three fluids in an air conditioning system, refrigerant, water and air, variable.
If you need more information on any of the topics covered in this column, please contact me at the mail: [email protected]
* President of Protec, Inc., is certified as a professional engineer in Puerto Rico and the state of Florida; has more than 40 years of experience in the application and sale of systems and equipment for energy conservation. He is a member of ASME (American Society of Mechanical Engineers), AEE (Association of Energy Engineers), ASHRAE and was president of the Miami chapter of that association.
