Ventilation – Workstation ventilator – Covered workbench chamber
Reexamination Certificate
2001-08-14
2003-04-01
Boles, Derek (Department: 3749)
Ventilation
Workstation ventilator
Covered workbench chamber
C454S056000, C454S066000, C454S239000
Reexamination Certificate
active
06540603
ABSTRACT:
The present invention relates to a method as defined in the preamble of claim
1
. Furthermore, the invention relates to a system as defined in the preamble of claim
12
.
The regulation systems used in welding workshops are used to adjust the temperature and amount of air blasted into the workshop. The main purpose of ventilation in welding workshops is to remove the impurities produced in welding work from the workshop in a manner as energy-efficient as possible, yet without compromising on the quality of indoor air.
A commonly used method is a ventilation system based on constant air flow, in which the ventilation in a welding workshop is operated with a constant air flow. Ventilation regulation systems also often employ an expedient whereby the air flow is halved on the basis of outdoor temperature. The air flow, i.e. typically the fan speed, is reduced e.g. to half the design value when the outdoor temperature falls below a set limit, a typical limit being −15° C.
Another common practice is to provide the system with a timing feature, allowing the user to set the operating times of the ventilation system according to the working hours observed in the workshop. As for regulation, conventional ventilation systems also comprise temperature regulation equipment, and they may comprise regulation equipment for heat recovery.
The above-described conventional solution for the regulation of ventilation systems in welding workshops consumes energy in heating the air and in operating the motors of the supply and extract air fans.
The design of ventilation in a welding workshop is based on a theoretically pre-estimated impurity load produced in the workshop in a maximum load situation. In defining the ventilation, the designer has to use various coefficients to achieve a sufficient level of ventilation. The ventilation is designed by considering the factors affecting the quality of air in the working area, including: geometry of welding hall, welding methods, materials to be welded, number of welders, possible independent arrangements, method of supply air blasting, possible local extraction and its type. Another factor affecting the design is whether recirculation of air is employed or not. /Work Safety Fund (Työsuojelurahasto), Report, Workshop-specific ventilation instructions, workshop II, Methods for the solution of ventilation in a welding workshop ZT-05311-08; 1983-08-11, page 26/. Designed on these principles, the air flow is guaranteed to be right in respect of impurities in the worst case, but absolutely too large when the extent of welding activities is lower than in the design situation. In literature, the design rule used for air renewal in welding workshops is a coefficient of 2-6 times per hour.
In conventional systems, air is renewed uniformly regardless of the actual need for ventilation, i.e. the amount of impurities produced in welding work. This leads to a standard fan motor power and excessive energy consumption by the fans and the air heating system during periods when the impurity load is smaller than in the situation for which the air flow was designed.
As stated above, in prior-art ventilation systems for welding workshops, the constant level of general ventilation is always designed for the worst possible situation. For example, the impurity load produced when stainless steel is being welded is heavier than usual, and if stainless steel is welded in a welding workshop, the designer assumes that stainless steel may be welded at all welding stations in the workshop, which further increases the volume of general ventilation. In practice, however, it is not nearly in all situations that the maximum level of general ventilation is needed; instead, in many cases the required volume of general ventilation may be only half the maximum volume. Prior-art solutions have led to an excessive consumption of electric and thermal energy.
Especially in welding workshops where there is considerable variation in the amount of welding work, the above-described system wastes energy as the volume of ventilation is larger than necessary, and thus it increases the environmental stress via emissions in energy production. It can be stated that in many cases ventilation consumes the largest amount of heating energy, and sometimes the fans needed for ventilation are responsible for a significant proportion of the total electricity consumption. Therefore, there is a significant energy saving potential.
For the regulation of ventilation in welding workshops, there are also systems provided with equipment for the measurement of air contamination. Measuring systems based on air contamination can be used to control e.g. the efficiency of ventilation in a welding workshop. However, these systems have not been favored in the regulation of ventilation in welding workshops. This is due to their unreliable operation in demanding conditions, e.g. in welding workshops in metal industry. The reflection density measurements used to measure air contamination have the drawback that they do not detect all the gaseous impurities produced in welding.
When air contamination in a welding workshop is measured using a separate sensor, one of the problems encountered is how to decide which is the right place for the sensor in the welding workshop in respect of air contamination. Sensors measuring air contamination are also very expensive and have a poor performance, which is why they are very seldom used. Because of the large investment costs involved, these systems are economically usable in only very rare cases where the savings achieved via regulation of ventilation are large enough to guarantee a reasonable period of repayment of the investment.
As an example of prior-art technology, reference is made to specification DE 34 34 519 A, which concerns a method and system for extracting welding fumes from the welder's protective mask by means of a suction hose via a funnel placed on the front side of the protective mask. A suction fan or check valve placed in the suction hose is turned on and off on the basis of the start or end of the flow of welding current or wire feed. The suction intensity can be varied on the basis of the magnitude of the welding current. In this specification, the extraction suction from the welding mask is regulated and the welding current, i.e. the current supplied from the welding machine to the welding gun, is measured. Usually the welding current is direct current, which involves the problem that measuring direct current is difficult and the required measuring equipment is very expensive. Moreover, measurement based on wire feed is naturally not applicable to any other welding method. In the specification, the welding current (d.c.) of one machine is measured. The current may be hundreds of amperes for each welding machine, which is why building a measuring system is expensive and difficult especially in the case of a welding workshop containing several welding machines.
The object of the invention is to disclose a control engineering solution which makes it possible to eliminate the drawbacks of prior-art technology economically as profitably as possible.
The method and the system of the invention are characterized by what is presented in the claims below.
According to the method of the invention, the load imposed on the electrical power network by the electric welding equipment is determined and, based on this determination, the volume of supply air and/or extract air is adjusted so as to achieve a level of ventilation proportional to the impurity load.
Correspondingly, the system of the invention comprises measuring equipment for generating a measurement signal corresponding to the load imposed on the electric power network by the electric welding equipment, and a set of control equipment has been arranged to adjust the volume of supply air and/or extract air on the basis of the measurement signal so as to achieve a level of ventilation proportional to the impurity load.
In the solution of the invention, the load imposed on the electric power network by a welding ma
Boles Derek
Young & Thompson
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