e problems associated with the consumption of air and safety in laboratories when using air suction systems such as hoods, provided the motivation for the Mazzola Company, back in 1987, to analyse and resolve most of these problems.
The costs for running a conditioning system are high and can increase notably when air ejection systems are used. When using a tradition air suction hood without the use of a control system, the air that is ejected from the location to the outdoors is set on the value necessary for containment with the maximum opening of the front rise and fall.
By lowering the rise and fall the front speed rises proportionally with the open surface of the hood according to the following formula:
V = P
Where V is equal to the air speed on the hood's front; P is equal to the flow measured in m3/h; S is equal to the surface of the open front.
This leads to a situation in which the flow is constant, while the front speed rises when the surface decreases leading to several problems for the operator and a useless consumption of the conditioning system.
If we consider, for example, a location with dimensions equal to 10 x 5 x 4 and 3 hoods with a flow of 13000 m3/h, we obtain the following:
10 x 5 x 4 ? 200 m3 volume of the location
3 x 1300 = 39000 m3 flow of the hoods
3900 / 200 = 19.5 changes/h air changes in the facility each day.
Thus, about 20 changes/hour against the necessary 10. The problem was brilliantly resolved and subsequently perfected in 1987 with the V.A.P. control system (automatic flow changer).
The use of a sensor apt to measure the speed in few metres a second, with a precision of 0.03 m/sec, enabled the front speed V to be made constant when the surface S changes, making the flow P change, thanks to several different solutions, leading to notable savings for the conditioning of the location. For example, a hood with a width of 1800 mm and a front rise and fall at 40 cm consumes 1300 m3/h without the V.A.P. control
If we keep constant the front speed, we can calculate the air consumption using the following formula:
P (m3/h) width (m) x (opening (m) x speed (m/sec) x 3600 (sec.) x 1 (h)
width = 1.8 m
opening = 0.005 m
speed = 0.5 m/sec
We obtain: 1,8 x 0,05 x 0,5 x 3600 = 162 m3/h
The consumption decreases to 162 m3/h with a savings of: 1300 = 162 = 1138 m3/h.
Considering the use of the V.A.P. for 8 hours a day for 200 working days we obtain an annual savings of:
8 x 220 x 1138 = 1.820.800 m3
Referring to graph 1, you can immediately evaluate the effective savings that you obtain with our V.A.P. control for the different modes and periods of use. The graph shows the consumption in cubic metres of conditioned air for a year using hoods with width of 1200 mm, 15000 mm and 18000 mm, for 8 and 16 hours a day for 200 working days and for 24 hours a day for 360 days.
To keep the speed constant, two adjustment methods are used indifferently, depending on the type of suction system of the hoods. The V.A.P. control system with a valve of MGV 3300 type is used in the case in which there is an only fan for more than one hood. The control logic receives a signal that is proportional to the speed present on the front of the hood from the sensor and adjusts a throttle valve using an actuator. Opening or closing the front or the side rise and falls the system immediately responds and does not allow the fumes to escape towards the operator and, within a few seconds, the speed is set to the new value.
The MG 3300 V.A.P. control system is used in the case in which there is a fan for every suction hood. The control logic receives a signal that is proportional to the speed present on the front of the hood from the sensor and adjusts the speed of the fan using a frequency converter. In both types, the speed on the front is displayed on a display with three digits found on the control panel.
To maintain constant the depression inside a location containing some chemical hoods, it is necessary to compensate the ejected quantity of air using an appropriate inlet system. To resolve this problem it is possible to use a control system with a suction valve placed above the hood that regulates the front speed,the air suctioned by the conditioner is compensated for by a second valve that inlets the same quantity of air that is suctioned into the facility. With the V.A.P., the functioning of the hoods in different safety categories according to the working being done, is resolved with the use of a small board and a selector. In this way, the front speed can be set to one of the three available speeds, enabling additional air savings when performing non toxic workings at low speed and a high degree of containment when working with more hazardous for the operator materials.
All the V.A.P. controls are available with an alarm that can have an adjustable intervention threshold. The intervention of the alarm, signalled by the lighting of a LED, controls a small exchange relay. Thus, you can connect, with the addition of a power relay, any safety device such as a solenoid valve that blocs the flow of gas if the front speed should fall below the set safety threshold. The operator only works in front of the hood, at a distance of 40 cm, for a brief time during the day normally, the V.A.P. system enables both the operator and the inlet system to work in optimal conditions both in physical and economical terms. The reduction of the front speed decreases the problems arising from high speed above all with low openings, leading to several advantages:
The blocking of the filters used to filter the air inlet into the location, or of any filters fit onto the hood, is immediately compensated for. The quantity of ejected air is reduced and the life of the filters themselves is notably increased. Consequently, maintenance is reduced to minimum levels.
A low front speed avoids draughts of air in the back of the operator that otherwise would have an effect in the long term. The filling of the hood improves noticeably, the whirls caused by high speed are completely eliminated.
Any flames inside the hood are not continuously burnt out interrupting the underway reactions, and forcing you to repeat the experiment.
The V.A.P. controls are made according to the electric standards in force and are fit on waterproof containers with IP 55 degree of protection. High reliability is guaranteed by the elevated number of V.A.P. controls installed in Italy and abroad both in small laboratories and in large national institutions. We remain at your complete disposal.
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