FREE COOLING APPLICATION IN CHILLED BEAM SYSTEMS

FREE COOLING APPLICATION IN CHILLED BEAM SYSTEMS

The Chilled Beam system which is widely used in Europe, particularly in northern countries and which is becoming increasingly popular in U.S.A and other countries is a quite effective system which creates energy efficiency by facilitating reduction of the central conditioning unit without lowering interior air quality. The use of Free Cooling applications in these systems saves more energy than low temperature chiller applications due to higher cooling water temperatures. The Chilled Beam can be defined as a conditioning device which includes a shell and tube water coil and which operates on a different principle than air diffusers used in mainstream applications. In these products, heating is also possible by circulation of hot water in the water installation.

Chilled Beam applications fall in two basic categories which are “passive” and “active”.

  

The Passive Chilled Beam system:

In the system called Passive Chilled Beam, heat transfer is made basically through natural convection and radiation. The Passive Chilled Beam unit consists of a shell and tube heat exchanger (cooling coil) placed within a casing. In applications, aluminium is widely used as fin material, and copper is widely used as tube material. The cold water obtained from the central water cooling unit circulates within the water cooling coil. In the meantime, ambient air flowing between fins moves from the upper portion of the room to the lower portion. The air within the room travels upward upon becoming warmer. The cooling capacity depends on the difference between the temperature of the cooling coil and that of the room.

In the system called the Active Chilled Beam, the unit depends on fresh air feeding channels and the cool water line. The pre-conditioned air provided from the central air conditioning unit is blown from the small air jets within the unit, creating air movement in the room away from the unit. This movement of air causes the air within the room to flow within the unit and it is cooled with heat exchangers. The movement of air within the room also mixes fresh air with the air circulating within the room.

While their large size comes with

higher cost as compared to conventional diffusers, the advantage in operational costs which

it provides, renders this disadvantage unimportant.

Figure 15. The Cative Chilled Beam unit design

In cases where the amount of air needed to carry the required cold energy is greater than the fresh air requirement, the chilled beam system significantly reduces the amount of circulating air, reducing the capacity of central conditioning device. Since these systems provide for the perceptible cooling requirement of the space and reduce the total cooling requirement of the system, separating the cooling requirement from ventilation and moisture control, they enable downsizing of central air conditioning units thus reducing initial investment and operational costs. Since the system has perceptible operation, the chiller group operates at high water temperatures, facilitating Free Cooling and reduction the cost of operation. Another effect of perceptible operation conditions is eliminating the need of a drainage installation.

The following figure shows the effect of the chilled beam system on efficiency by the results of two comparisons.

Uses of Chilled Beam systems:

The use of active chilled beam systems is recommended for the following venues:

·         Partitioned and open office spaces

·         Hotel rooms

·         Hospitals

·         Stores

·         Banks

·         Laboratories

However, these applications are not recommended for spaces like conference halls, meeting rooms, classrooms, etc. where high ventilation loads are required.

Operating range of the Chilled Beam System:

The Active Chilled Beam system can be applied in spaces where the total perceptible cooling requirement is below 120 W/floor space-m². The optimum working range is 60-80 W/floor area-m²’dir. The passive chilled beam system can be applied in spaces where the total perceptible cooling requirement is 40-80 W/floor area-m². The targeted indoor ambient temperature in summer conditions is 23-26ºC.

Free Cooling and the Chilled Beam System

In the chilled beam system, high temperature cooling water is used in order to avoid condensation. The temperature of the water circulating in the coil in order to cool the room is typically 14-18 ºC. (The temperature of the circulating water for heating is 30-45ºC.) High cooling water temperature leads to use of a lower capacity cooling group in the system. In this case, both the initial investment and operational costs are reduced.

Since Free Cooling systems are operated with higher cooling water values than operating at 6/11ºC or 7/12ºC, Free Cooling systems used for cooling water can be installed in places where chilled beam units exist.

Free Cooling application in Chilled Beam systems can be made by various methods, including:

·         Dry Cooler application

·         Cooling Tower application

·         Underground energy storage systems application

 Free Cooling applications in Chilled Beam systems provide additional efficiency.

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