For hot and cold water designs, air eliminators become an efficient solution in air conditioning systems.
by Alfredo Sotolongo*
The most economical energy to produce is the one that is saved!
In recent years I have concentrated on the application of major equipment in the air conditioning system, mainly: chillers, water pumps, cooling towers, etc. However, cold water plants have components that help minimize the energy consumption of larger components and facilitate the maintenance of the complete air conditioning system.
In this issue I want to refer to a problem that has always been a headache for those who design and / or install hot and cold water systems. This is the accumulation of air in cold water distribution lines and especially in equipment located in the highest areas of the system.
Air and gases manifest themselves in systems, among other things, when the following conditions are present:
(a) Maintenance is carried out.
b) Poorly selected expansion tanks.
c) Chemical reactions between the water in the system and the metals in the system.
(d) Excessive chemical treatment.
e) When water is added to the system.
f) Pipes joints of low quality and / or poorly sealed.
Water has a natural tendency to let air escape as its temperature increases or its pressure drops which is explained in Henry's Law, this law describes the behavior of a hydraulic system. This is evident when heating water in an open casserole. As the water heats up, small air bubbles begin to stick to the walls of the casserole, they are dissolved gases that separate from the water as a result of the increase in temperature. In the case of a pressure drop, such as a soda bottle that is uncovered and gas bubbles, in this case it is carbon dioxide, appear immediately when uncovering the bottle lowers the pressure.
With the intention of eliminating air bubbles, centrifugal air separators have been used for many years. However, their effectiveness has left much to be desired since their design does not allow them to separate micro bubbles from the water flow. Many have been incorrectly selected using the same diameter of the pipes which makes them too small to achieve effective air separation. Air separators should be selected based on GPM water flow and maximum efficiency.
Since the 70s the company Spirotherm began to use air separators with the coalescence method, which has now become the most used in cold and hot water designs.
By removing the micro bubbles, the Spirovent air eliminator also removes the large bubbles which are formed by the micro bubbles. In order to successfully remove microscopic bubbles, the equipment must create an insignificant pressure drop, be installed at the point of lowest solubility, and be able to do the following:
Reduce the speed of the water flow.
Control turbulence.
Give bubbles something to collide and stick, coalescence.
In the case of a heating system, it should be installed just after the heater (high temperature) and before the circulation pump (low pressure).
Air removal is even more important in a cold water system because the cold water contains more air and by adding pressure to it with the pumping system, the percentage of air increases. Without an air separator, the ratio of the air-to-water mixture being pumped will dramatically decrease the heat transfer capacity because the air acts as a thermal insulator.
In a cold water system the ideal location for the air separator is in the return line (highest temperature), but before the water pump (low pressure) as it appears in the drawing. But it is always important to confirm the point of lowest solubility before deciding where to locate the Spirovent air separator. Graphs are available to determine the solubility of air in water as a function of temperature and pressure.
Always with the idea of minimizing energy consumption, it is important that all the equipment of an air conditioning system operates at its maximum efficiency. Therefore, eliminating the presence of air contributes considerably to making it easier for older teams to maximize their effectiveness.
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.
