Modelo de propagación

The design of battery room ventilation system shall fully comply with the requirements of DIN 57510/VDE 0510.

Battery systems considered here are as follows.

Trickle charge 1.4 – 1.45 volts/cell Nickel Cadmium

Boost charge 1.6 – 1.65 volts/cell Trickle charge 2.23 volts/cell Lead Acid

Boost charge 2.4 volts/cell

All cells in which the electrolyte is in aqueous solution give off hydrogen and oxygen during charging, the major gassing occurring towards the end of the charging or during boost charging. Typical boost charging cycles are for 8 hours every 6 months. An explosive mixture is formed when the hydrogen concentration, by volume, in air exceeds 3.8%.

A safe dilution (20% of the above) will be maintained using the following formula.

Q = 0.055 x N x I

Where,

Q = Airflow in m³/h

N = Number of battery cells. (Number of blocks x cells/block) I = Charging current at the end of the boost charge, in amps (For design purposes, 25% rated charger current in amps)

Battery rooms should be airconditioned to maintain an average room temperature of 10 – 30⁰C, to give best battery performance and service life, and to limit electrolyte temperature rises during charging.

Inlet air should be introduced at low level, from the building airconditioning system, and mechanically exhausted to atmosphere at as high a level as possible, to avoid air pockets.

When ventilation is provided as described above, then the battery room shall be classified as non-hazardous. However, due to possible local concentrations of gas, the exhaust fan should be suitable for a Zone 2 installation and resistant to the electrolyte.

2.16.3.2 Electrical Substations & Switch Houses

Substations and switch houses should normally be designed as completely closed structures, with dust tight construction and cable passages.

The air conditioning design shall include two or more separate installations, which shall be individually electrically supplied and controlled.

The indoor design criteria shall be such that:

During normal operation, the maximum indoor temperature shall not rise above 35⁰C DB.

In the case of breakdown or maintenance to one of the installations, the maximum indoor temperature shall not rise above 40⁰C DB.

The maximum supply air relative humidity shall not exceed 90%.

2.16.3.3 Gas Bottle Stores

Spare and empty gas bottles shall be separated and stored in an upright-chained position and housed in a purpose built, well ventilated, shaded and secured enclosure located at least 20 m from combustible materials. Possible air pockets at high level shall be avoided.

Requirements are normally satisfied by the provisions of a cage of tubular frame, chain link fencing and roof sheeting with an internal separation.

Electrical installations in gas bottle stores shall be suitable for Zone 2.

2.16.3.4 Kitchens

The guidelines given below address commercial catering installations, criteria for domestic kitchens are given in Appendix K.

Often it is not possible to achieve comfort conditions in kitchen cooking areas at all times because of the extremely high expenditure involved. In such cases, it should be sufficient to maintain acceptable working conditions.

Generally air should be extracted from cooking and subsidiary areas through double-skin hoods located over the main cooking and dishwashing equipment. Hoods should be sized to overlap equipment by 100 mm, to have a minimum face velocity of 0.3 m/s and to have a minimum clearance of 1900 mm above finished floor level. The hood volume should suit the equipment covered. 80 – 85% of the replacement air should be provided, as filtered outside air, at the internal perimeter of the hood. If this part of the replacement air is supplied outside the hood, it should be 100% outside air-cooled to plenum conditions, say 25⁰C. Ducted, re-circulating systems should not be used because of greasing problems. The remainder of the replacement air should be drawn from adjacent areas so that a negative kitchen pressure is maintained to contain odours.

Extract ductwork shall be designed for ease of cleaning, with flanged joints and man-size access doors, and shall be constructed of galvanised sheet steel, minimum thickness, 1.0 mm. Air velocities should be a minimum of 9 m/s. Extract fans should be treated for moisture and heat, and attenuators should be avoided.

Comfort air conditioning should be provided by high level fan coil units.

The requirements for fire detection and protection in kitchens are included in SP-1075 Specification for Fire & Explosion Risk Management.

2.16.3.5 Laboratories

Laboratory air conditioning design shall be based on the specific requirements of the laboratory work. However, the following guidelines should apply.

Laboratory working and solvent storage areas should be provided with an 100% outside air system, and should be under positive pressure to reduce dust ingress. In interior Oman, heating should be included for winter morning start up. Ancillary areas, such as offices, should be provided with separate, re-circulating systems such as fan coil units. Mechanical exhaust should be provided for chemical and material storage areas, typically at a rate of 6 – 15 air changes an hour, depending on the items stored.

Fume cupboards for use with hydrocarbons should have an acid resistant 18/12 stainless steel internal fume chamber with integral bench top. The minimum air velocity over a 400 mm deep sash opening should be 0.75 m/s.

Fume cupboards for general use should have 1 mm thick high-pressure plastic laminate on the sides and solid epoxy resin bench tops. The minimum air velocity over a 400 mm deep sash opening should be 0.5 m/s.

All fume cupboards should be provided with airfoil sash opening profiles and high-level by-pass grilles to ensure constant volume airstreams.

Fume cupboard exhaust ductwork shall be constructed of HDPE and shall not contain fire dampers.

The internal fume chamber, exhaust ducting and exhaust fan shall be classified as Zone 1 hazard. The internal light fittings therefore shall be separated from the fume chamber by an airtight glass plate. Solvent and gas bottle stores shall be classified Zone 2.

2.16.3.6 Temporary Buildings

Air conditioning design parameters for temporary buildings, such as transportable units, should be similar to those for permanent buildings. However, due to inferior thermal storage characteristics, electric heating may be required.