Christian Westwood, product specialist, Climate Control Products, Rittal, looks into today’s enclosure cooling solutions, and explains how their efficiency can help towards reducing energy consumption and operating costs...
Innovative technological advances continue to improve the energy efficiency of cooling products. However, when a particular climate control solution is providing essential cooling, it is not only the energy consumed that should be considered. The control of such a system can also play an important role in reducing operating costs – after all, why use energy when you don’t have to?
A further consideration is the accuracy of the manufacturers’ information. Not all cooling units are the same; and claimed cooling output and power consumption figures may seldom be achieved in practice. So, how can you be sure that your cooling unit is providing the performance levels both expected and required?
The direct use of ambient air remains the most energy efficient method of dissipating the heat produced by the equipment installed in an enclosure. Should the environment permit the use of such a solution, i.e. the ambient air is of a sufficiently low temperature and free from contaminants, then a fan-and-filter unit, with a combination of fan and dust filter, will provide a means of cooling that has minimal operating costs.
Fan-and-filter units may be fitted with diagonal fans, a hybrid of the more conventional axial and radial variants. This option will provide improved performance against static pressure and, in turn, offer improved energy efficiency and a more constant air throughput, effectively minimising the occurrence of hot spots in the enclosure.
Energy consumption may be reduced further by the introduction of a simple control mechanism. A thermostat or hygrostat may be used to switch a fan-and-filter unit on or off in response to varying temperature and relative humidity inside an enclosure. The same energy-saving philosophy that has resulted in many motors being controlled by inverter drives has resulted in a more sophisticated form of control for the fan-and-filter unit. A speed control device may be used to vary the rate at which the fan rotates and thus the amount of air being provided, in response to the cooling demand, ultimately switching the fan off when it is not required.
Further energy savings from the fan-and-filter unit may be yielded by the adoption of a different type of motor. Developments in energy efficient fan-and-filter units for climate control in enclosures show that upcoming energy efficiency guidelines are not only met but easily exceeded by using electronically commutated (EC) motors, an innovation that utilises direct current (DC) motors. More energy efficient than the conventional alternating current (AC) shaded-pole equivalent, EC motors not only offer energy savings of up to 60% but they also provide intelligent control and fan status monitoring.
Infinitely variable speed control offers a means of conserving energy further by operating the fan at a speed determined by the demand for cooling. A programmable logic controller (PLC) may be used to control the fan motor, via a 0-10V DC or pulse width modulated (PWM) signal. Alternatively, a thermistor that accepts a 10V DC supply, which may be taken directly from the EC motor, may be used to provide a signal, in the voltage range 0-10V DC, to control the speed of the fan. An effective yet simple and inexpensive solution.
A tacho-signal output allows direct monitoring of the fan speed, and therefore a malfunction or failure may be immediately signalled. The operator can react immediately, not just when the temperature inside the enclosure rises above any alarm level, therefore minimising the risk of component failure in the enclosure and reducing system downtime.
There may be applications in which the ambient conditions do not lend themselves to a solution that directly uses ambient air as a means of enclosure cooling. In such instances, either cooling units or air-to-water heat exchangers may be considered. Improvements have also recently been made to this type of cooling technology.
Although by no means new, the door switch is worthy of mention at this point as a fundamental control method. Whatever the type of cooling solution, there is typically no need for the switch to continue operating when the enclosure door has been opened. Should the climate control system remain operational upon opening the door then it is no longer merely maintaining the internal temperature, it is trying to maintain the temperature of the environment around the enclosure as well – a needless use of energy.
Software that employs an intelligent strategy to effectively target the use of energy may be integrated into both cooling units and air-to-water heat exchangers. Such software may, for example, disable the internal fan when the temperature inside the enclosure falls to 10°C below the level desired, enabling it for a period of 30 seconds every 10 minutes to ensure the accuracy of the sensed temperature and adequate air distribution, before permanently enabling again when the temperature rises to 5°C below the setpoint temperature.
Cooling units may incorporate any one or a number of innovative technologies in a perpetual endeavour for manufacturers to further improve their energy efficiency. However, how can they be certain of achieving claimed cooling performance and power consumption figures in practice?
The current DIN EN 14511- 2 standard clearly defines the test conditions to determine the cooling output and energy efficiency of air-conditioners, liquid chillers and heat pumps that use electrically driven compressors with air, water or brine as a heat exchanger. This standard also states that the specified cooling output may not be lower than the measured cooling output by more than 8%. The test is used to determine the total cooling output, its latent and sensible constituents, the electrical power consumption and the energy efficiency ratio (EER) of the cooling device. With this information, the efficiency of the cooling unit in operation may be determined.
Certification of cooling units
Energy efficient cooling products, together with complementary control components, may help in attempts to reduce energy consumption and operating costs. Furthermore, the certification of cooling units guarantees their performance, offering piece of mind that the climate control solution functions just as well in practice as on paper.
Rittal supplies climate control products incorporating all of the energy saving technologies discussed and claims to be the first manufacturer worldwide to have its complete range of cooling units independently certified by the TÜV Nord test centre for refrigeration, air-conditioning and ventilation technology in Essen, Germany. All TopTherm cooling units may now bear the TÜV Nord mark of conformity. In supplying units with this label, Rittal commits to regular product inspections by TÜV Nord and undertakes to report all changes that may affect the performance of the product to the test house, with the devices retested if necessary.