HVAC System
General Requirements
The essence of design should be simplicity and reliability in order to give long continuous services with high economy and low maintenance cost. Particularly attention should be paid to internal and external access in order to facilitate inspection, cleaning and maintenance.The design, dimensions and materials of all are to be that they will not suffer damage as a result of stresses under the most severe service conditions.
Fully detailed specifications of the parts of the plant are to be submitted with the tender describing particularly the materials to be used.
Workmanship and general finish are to be of the highest class throughout.
All similar parts of the plant are to be interchangeable.
All equipment is to operate without undue vibration and with the least possible amount of noise and is not to cause a nuisance.
All equipment is to designed to minimize the risk of fire and any damage which may be caused in the event of fire.
The equipment is also to be designed to prevent ingress of all vermin, accidental contact with live parts and to minimize the ingress of dust and dirt. The use of materials which may be liable to attack by termites or other insects is to be avoided.
Compliance with Manufacturer’s Specification
The Contractor shall ensure that all equipments and accessories used in the installation shall be suitable for the work to be performed and that the loading of equipment shall not exceed the maximum capacity specified or agreed in writing by the Manufacturer.The Contractor shall be responsible for the inspection of all equipment and accessories before their incorporation in the Work and to ensure that they comply fully with the requirements of the specification and that they are not defective in any way as regards to materials or workmanship. Should any such non-compliance and defects be found in the course of the works, the Contractor shall correct or cause to be corrected such non-compliance to the specifications and/or the defects all at his own expense and to the satisfaction of the S.O.
Tropicalisation
The Contracts Works shall be installed in tropical conditions below 1000 metre altitude and shall be suitable for continuous operation at maximum rating in the situations described and under site conditions with an ambient air temperature of 40 deg centigrade and a relative humidity of up to 100 per cent . The frequency of thunderstorms is also high and the iso ceraunic level is between 150 to 200 days per annum.All the equipment and materials offered shall be fully tropicalised and suitable for continuous trouble free operation under adverse climatic conditions of heavy thunderstorm and rain, high humidity, intense sunlight and ambient air temperature of up to 40 deg centigrade.
In choosing materials and their finishes due regard is to be given to the humid tropical conditions under which the equipment is to work. Some relaxation of the following provisions may be permitted where equipment is hermetically sealed but it is preferred that tropical grade materials should be used wherever possible.
i. Materials - Iron and steel shall be painted or galvanized as appropriate.
Indoor parts may alternatively have chromium or copper-nickel plated or other approved protective finish.
Steel iron and steel parts (other than rustless) of all instruments and electrical equipment, the cores of electro-magnets and the metal parts of relays and mechanism shall be treated in an approved manner to prevent rusting.
Cores etc. which are built up of lamination or cannot for any other reason be anti-rust treated, shall have all exposed parts thoroughly cleaned and heavily enameled lacquered or compounded.
Where it is necessary to use dissimilar metals in contact, these shall, if possible, be so selected that the potential difference between them in the electro chemical series is not greater than 0.5 volt. If this is not possible, the contact surfaces of one or both of the metals shall be electroplated or otherwise finished in such a manner that the potential difference is reduced to within the required limits, or if practicable than two metals may be insulated from each other by an approved insulating material or coating of approved varnish compound.
ii. Screws, Nuts, Springs, Pivots, etc.
The use of iron and steel shall be avoided in instruments and electrical relays whenever possible.
Steel screws, when used shall be chromium plated or when plating is not possible owing to tolerence limitations, shall be of stainless steel.
All wood screws shall be dull nickel plated brass or of other approved finish.
Instrument screws (except those forming part of a magnetic circuit) shall be of brass or bronze.
Springs shall be non-rusting materials e.g. phosphor-bronze or nickel silver, as far s possible.
Pivots and other parts for which non-ferrous materials is unsuitable shall be of an approved rustless steel where possible.
iii. Fabrics, Corks, Paper, etc.
Fabric, cork, paper and similar materials, which are not subsequently to be protected by impregnation shall be adequately treated with an approved fungicide. Sleeving and fabrics treated with linseed oil or linseed oil varnishes shall not be used.
iv. Wood
The used of wood in equipment shall be avoided as far as possible. When used, wood work shall be thoroughly seasoned teak and other approved wood which is resistant to fungal decay and shall be free from the shales and warp, sap and wane, knots faults and other blemishes.
Woodwork shallbe suitably treated to protect it against the ingress of moisture and from the growth of fungus and termite attack, unless it is naturally resistant to those causes of deterioration.
All joints in woodwork shall be dove-tailed or tongued and pinned as far as possible.
Metal fittings where used shall be non-ferrous materials.
v. Adhesives
Adhesives shall be especially selected to ensure the use of types which are impervious to moisture, resistant to mould growth and not subject to the ravages of insects. Synthetic resin cement shall be used for joining wood. Case in cement shall not be used.
Chromium Plating
The chromium plating of those, components of the plant where offered by the Subcontractor shall comply with the requirements of B.S. 1224.Cleaning and Plating
Metal work which is normally painted in the factory before dispatch shall be prepared by filling in or wire brushing and rubbed down to smooth finish and then given one priming coat, one or more undercoats and one or more top coats of approved paints. The second top coat shall be of the different shade of colour.Metal work which is normally painted on site shall be prepared as above and given one coat of approved preservation paint before leaving the factory.
Metal work which will be erected in the open shall be given top coats of bitumastic based paint with appropriate approved primer and undercoat.
Where aluminium paint is specified the paint used for the undercoat shall be of the same quality as the top coat but slightly coloured by the addition of washing blue.
The inside of control cubicles, cabinets, etc. where condensation is liable to occur shall be coated with anti-condensation composition.
All bright metal parts shall be covered before shipment with an approved protective compound and protected adequately during shipment to site.
Means of Fixing
Unless otherwise stated, all fixing of brackets and hangers shall be done by means of rawplugs of rawbolts as recommended by the Rawplugs Company of London.All rawplugs used shall be of the soft metal (white bronze or similar) type. Where receiving holes must be cut, suitable masonry drills shall be used for sizes up to and including 13 mm diameter. For larger sizes ‘Star’ drills or other means of percussion drilling may be used.
An acceptable alternative to above means of fixing, would be the used of ‘Philips Readheads’ or stud guns in which case the manufacturers recommended procedures of operation shall be strictly adhered to.
Rating Name Plates
Each main and auxiliary item of plant is to have permanently attached to it in a conspicuous position a rating of non-corrodable material upon which is to be engraved an identifying name, type or serial number, together with details of the loading conditions under which the item of plant in question has been designed to operate and such diagram plates as may be required by the S.O.All items of plant are to be provided with a nameplate or label designating in the English Language the service of the particular equipment. The inscriptions are to be approved by the S.O. or as detailed in the appropriate sections of the Specification.
Bases
All angle iron or other bases or supports of metal work are to be constructed in such a manner so as to provide clearance for easy cleaning after the machine is installed.Nuts, Bolts, Studs & Washers
Nuts and bolts are to be treated with a non seizing compound on the threads.Fitted bolts shall be a driving fit in the reamered holes they occupy and shall have the screwed portion of such a diameter that it will not be damaged in driving.