Currently new air conditioning systems for business and commercial use are being applied with good results, variable frequency drives are part of this offer.
by Alfredo Sotolongo*
Increasingly, in the business segment, frequency inverters have been applied not only to modulate the operation of motors in water or air systems, but even to make the hydraulic balance of pumping systems more efficient.
Among the most recent applications are air handlers that serve a specific area without using boxes or diffusers of variable volume. The handler modulates only the amount of air, keeping the supply temperature constant. This represents considerable energy savings and with the added benefit of achieving lower sound levels, which, in turn, contribute to comfort.
These units are used in areas where the number of people or the thermal load varies throughout the day. Such as conference rooms, meeting and meeting spaces, assembly rooms, auditoriums, libraries, supermarkets, department stores, etc.
They are units that can well use cold water coils or direct expansion. In the first case, it is possible to lower the capacity without any risk of the coil freezing as it happens with the direct expansion coils with non-modulating compressors. However, in the case of direct expansion, with the relatively new digital compressors that can reduce up to 10% of the total capacity, modulation is now also achieved without any risk of freezing in the coil when the air flow is reduced.
The control sequence is as follows:
The air flow is modulated by means of a frequency inverter that controls the revolutions of the supply fan motor, based on the difference between the temperature of the conditioned environment and the temperature value to which the thermostat located in the environment is adjusted.
Additionally, the modulating digital compressor is controlled by means of a thermostat located at the outlet of the handler, measuring the temperature of the supply air to determine the mass of refrigerant needed and maintain the constant supply temperature.
Therefore, as we all know, the vast majority of air conditioning systems operate much of the time at partial loads and these single-zone units of variable volume represent many benefits for the user. With modulation capability in both the fan and compressor, these systems can provide precise temperature control and passive humidity control.
Likewise, the compressor's modular capacity avoids start-stop cycles, reducing their wear and tear and allows lower energy consumption than when hot gas overheating is used.
The company that has dedicated the greatest resources in the research and development of these units is AAON, this company has achieved a good combination of components and their respective controls represent great profits at extremely reasonable prices, all this together amply justifies the return on investment.
When these single-zone variable volume units are used, not only is energy saved and the life of the modulating compressor extended, but the initial cost is reduced as variable volume boxes are eliminated achieving the same effect.
I recommend that when you have this type of application, where the thermal load varies during the operating time of the handler, you take into account the use of units of variable volume of a single zone. With the many benefits of these units they will be able to provide great benefits to their customers.
If you need more information on any of the topics covered in this column write to me at the [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.
