THE CLIMATIC CHAMBER THAT RESPECTS THE ENVIRONMENT
Abstract
The concept of sustainable development sanctions the buy-now mandatory need to calibrate human behaviours and consumption on the basis of the planet's load capacity through a wise management of natural resources (especially exhaustible ones) in order to avoid their waste and impoverishment.
In view of this goal, a series of climatic chambers have been developed through which it has been possible to achieve the following results:
- up to 50% reduction of electricity consumption
- up to 70% noise reduction compared to traditional chambers
- use of eco-compatible materials, such as water-based paints, polyurethane-free thermal insulation and recyclable or easily disposable packing materials
Introduction
The climatic chamber is a machine that permits the conducting of tests on samples in environments (test volume) with controlled temperature and humidity. The temperature of the air is usually raised using electric heaters, the humidity is increased using electric humidifiers, and low temperature or humidity values are maintained by heat exchangers connected to a cooling system.
The control system, generally equipped with PID controllers, measures out the various powers available in order to keep the controlled variables within the tolerance limits required by the test, tolerances that are generally lower than 0.5°C for temperature and 3% for relative humidity.
In a climatic chamber the powers necessary for its functioning vary greatly depending on the type of test to be carried out. This means that all the systems installed must be dimensioned for the worse case conditions, event if they will mostly be used for very limited loads.
In any case, the cost increase of the system is not the only negative aspect; to it must be added the management cost, meant essentially as electricity consumption.
The electric heaters used to heat and humidify the air do not pose particular energy problems, since they can be part loaded and their electricity consumption is proportional to the power distributed; the same cannot be said for the cooling system. Unlike many applications, in a climatic chamber, the cooling system cannot have an on-off function, but must be kept constantly turned on, otherwise there would be an unacceptable decline in the performance required. In other words, it would be impossible to keep the controlled parameters, i.e. temperature and humidity, stable.
In a conventional climatic chamber, it is frequent to see cases where the cooling power required is lower than 10% of the maximum, This fact, together with the characteristics of a classical cooling system, not only means that the electricity absorption is always close to the maximum values, but that the climatic chambers is equipped with devices capable of destroying the excess cold produced.
This can be accomplished in various ways. With climatic chambers, the solution adopted is that of a by-pass, i.e. a line connecting the delivery side to the suction side of the mechanical compressor, thus reducing the flow rate of the coolant in the cooling circuit without, however, any reduction in electricity consumption. Figure 1 shows a general diagram of the by-pass technical solution.
The above considerations formed the starting point for the project, which led to the introduction onto the market of a climatic chamber that is extremely mindful of energy consumption and, in general, to environmental impact, during both the construction and the utilization phases.
Word Green Climatic Chamber
Energy savings
It is impossible to modulate the cooling power of a system because the electric motor of the mechanical compressor, connected directly to the electrical supply, turns at a constant speed; the new chamber whose name is "flower"®, is equipped with a static inverter through which it is possible to vary the rotation speed of the electric motor of the cooling system [1], [2], [3].
Fig. 1 Cooling system of a conventional climatic chamber
Fig. 2 Cooling system of "flower"® climatic chamber
Since both the cooling power and electricity consumption are proportional to this parameter, through the inverter, managed by the climatic chamber's control system, it is possible to reduce the cooling power on the basis of the real needs, obtaining an immediate benefit in terms of electricity consumption savings.
Not to be overlooked is the fact that when the compressor is in minimum speed conditions, all the heat exchangers of the cooling system, calculated for the worst case working condition, are oversized, resulting in an increase of the efficiency of the cooling cycle.
The use of the static inverter not only makes it possible to reduce electricity consumption, but, making it possible to power the electric motor at a frequency of 65 Hz, it makes a significant contribution to the increase of the maximum cooling power available, and this is particularly useful in those tests where the performance of the climatic chamber is directly connected with the maximum power deliverable by the cooling system itself.
In any case, the inverter alone is not able to optimize the energy savings, since in many tests, where the cooling power required is very low, it would be necessary to descend to a rotation speed lower than that allowed to guarantee the correct lubrication of the compressor. In accordance with the above, the inverter allows the modulation of the cooling power, varying the compressor rotation speed between around 600 rpm and 1600 rpm.
For this reason, "flower"® chamber has been equipped with a cold sink consisting of a mixture of water and glycol having a solidification temperature of around -20°C. Inside the cold sink are two heat exchangers, one acting as an evaporator and the other as a supercooler.
When the cooling powers required are very low, the control system of "flower"® chamber keeps the rotation speed of the mechanical compressors at the minimum allowed values, and the excess coolant evaporated in the evaporator situated inside the cold sink. This way the cold sink cools down and at the same time a correct compressor suction pressure is guaranteed. If this functioning mode continues for a long time, the cold sink reaches temperatures close to -40°C.
The cold stored is made available in the situations where the maximum cooling performance is required, typically in the phases where it is necessary to lower the temperature inside the climatic chamber very rapidly. In this condition the coolant coming out of the condenser is sent to the supercooler situated in the cold sink, thus reducing its temperature; it is possible to reach supercooling of greater than 40°C, with substantial improvements of the system's performance.
In short, we can stat that, in addition to the free performance increase described above, with the innovations made there is a reduction in the energy consumption of the cooling system, which turns out to be around 50% of that of a conventional system.
| Useful Volume | 250 | 600 | 1200 |
| "flower"® Chamber | 1500 | 2200 | 3300 |
| Conventional Chamber | 2500 | 3900 | 5400 |
Table 1. Average electrical power measured in watts
| Useful Volume | 250 | 600 | 1200 |
| "flower"® | 6 | 58 | 7 |
| Conventional Chamber | 3.5 | 4 | 4 |
Table 2. Temperature variation speed in °C/minute
Table 1 shows the average electrical powers absorbed by three models of "flower"® chambers compared with those of the equivalent conventional climatic chambers. The fact that the electrical consumption reduction is lower than 50% does not contradict what has been stated above.
In fact, the figures in the table refer to total consumptions, and we must consider that all the equipment present has the same absorption in the "flower"® chamber and the conventional chamber, except for the cooling system, which in any case is the element that influences consumption the most.
Table 2 compares the maximum temperature variation speeds during the cooling phases. The test was carried out by varying the temperature of the air inside the test volume from 180°C to -40°C; the values shown in the table indicate the average temperature variation in reference to the time unit which, in this specific case, is the minute.
The best performances of "flower"® chamber are the result of the possibility to power the compressor at 65 Hz, but especially of the possibility to sub-cool the coolant.
Noise Reduction
With a view to reducing the environmental impact, particular attention was paid to the noise produced by "flower"® chamber in work environments.
The operation focused on the main sources of noise, i.e. the compressor of the cooling system and the cooling fans of the condenser that is installed on the machine. Since the noise of these parts depends on their rotation speed, an attempt was made to limit it. In the case of the compressor, the work done on the speed control, aiming to reduce energy consumption, had a direct effect on the noise reduction also. On the other hand, the condenser fans were equipped with easy-to-find electronic devices that maintain their speed at the minimum value compatible with the condenser's cooling needs in the various utilization modes of "flower"® chamber.
| Useful Volume | 250 | 600 | 1200 |
| "flower"® | 54 | 57 | 60 |
| Conventional Chamber | 59 | 64 | 65 |
Table 3. Noise measured in Db(A)
We can summarize by stating that the final result was a noise reduction by about 5 Db(A) for all those climatic chamber operating conditions in which the compressor rotates at a minimum speed, a condition which is present in a climatic chamber for at least 90% of its utilization time.
Table 3 shows the noise data for different models of "flower"® chamber compared with the equivalent conventional types.
Environmental Impact
The aspects already examined constitute a significant contribution toward reducing environmental impact. In particular, the increase in energy efficiency determines a significant percentage reduction of the emissions of carbon dioxide into the environment.
In addition to this, a specific study was conducted on the material used for construction, in order to identify those characterized by low pollution and easy disposal.
Significant results were obtained in this direction. In particular a water-base paint was used instead of one containing chemical solvents, chemical type insulation materials were eliminated in favour of natural materials, and recyclable or easily disposable materials were introduced as standard packing materials.
In conclusion, we can state that "flower"® climatic chamber is certainly innovative and unique, since it manages to reduce environmental impact. It is intended for all those who, having to use a climatic chamber, want to make a contribution toward preserving our planet and improving the quality of life of future generations.
Bibliographical References
- T.Q. Qureshi, S.A. Tassour, Variable-speed capacity control in refrigeration systems, Applied thermal Engineering 16 (2) (1996)
- P. Binneberg, J. Fhilipp, W.E. Krauss, Variable speed hermetic compressor in a household refrigerator, 20th international congress of Refrigeration, Sydney Australia, 19-24 September 1999, paper code 109
- S.A. Tassou, T.Q. Qureshi, Comparative performance evaluation of positive displacement compressors in variable speed refrigeration applications, International Journal of Refrigeration 21 (1) (1998) 29-41
Summary
Environmental protection and preservation are among the world's highest priorities.
The new "flower"® climatic chamber is the product of Angelantoni Industrie research, a truly innovative step forward in the field of climatic test chambers. An energy consumption of about 50% can be ensured during the stabilization phases thanks to a unique and patented system consisting of an inverter that controls compressor speed and allows the adaptation of the compressor power to different working needs, and a cold sink to increase the cooling efficiency.
A noise reduction of about 70% is obtained thanks to the inverter on the compressor, which reduces the rotation speed to about 40% of its nominal value depending on the working conditions, and an automatic control system that reduces the condenser blower rotation speed on the basis of ambient temperature and cooling power.
These advantages are combined with the use of environmentally friendly materials during production phases such as water based paints, no polyurethane in the insulation materials, and recyclable ore easy disposable packing materials.
Maurizio Ascani
Angelantoni Industrie S.p.A.
