Genset canopy RFQ checklist

An unstated target is a target the supplier gets to choose

"Soundproof canopy, 125 kVA, MS, painted" produces three quotations that differ by 40% and none of which can be compared, because each supplier has chosen a different panel build, a different louvre and a different paint system. The canopy is a system of four functions competing for the same panels: weather exclusion, airflow, noise attenuation and service access. Every one of them changes the steel, and the RFQ has to state which one wins where.

Acoustic target and measurement point

A number without a measurement condition is not a specification. "75 dB(A)" could mean at 1 m from the nearest panel, at 7 m, at the boundary fence, or sound power level in the room. The spread between those readings on the same canopy is 10–20 dB.

The clean way to write it is: sound pressure level in dB(A), at a stated distance and height, on a stated number of sides, in free field, with the set at a stated load — or sound power level to ISO 8528-10, which measures airborne noise by the enveloping surface method and removes the room from the answer. A set tested indoors without a correction is not comparable with one tested outdoors.

The attenuation has to hold at every opening, not just in the panels. A sealed 50 mm panel wall with an unsealed door and an open cable gland is a 78 dB(A) canopy.

Louvre free area and airflow

The engine has to breathe and the radiator has to reject heat. Both are satisfied by free area, not by the size of the louvre frame.

A_free (m²) = Q (m³/min) / (60 × v (m/s))

A weather louvre at 45° blade angle and 100 mm pitch gives about 50% free area, so 1.0 m² of free area needs 2.0 m² of gross opening. Acoustic louvres with splitter blades give 30–40% and need a third more frame. Above about 6 m/s through the free area the pressure drop and the recirculation rise, and the set derates.

Separation matters as much as size. A hot exhaust discharging into its own intake raises intake air temperature and costs more output than a slightly undersized louvre. State the exhaust direction and the minimum distance to any wall or adjacent canopy.

Base frame and skid

The base carries the engine, the alternator, the radiator and the canopy, and it is the part that fails first when it is underspecified.

A canopy frame welded square on the fixture and then distorted by a heavy tank in the base will not close its doors at the site. Base design comes before panel design, not after.

Door sealing

Doors are the largest moving opening and the most common acoustic leak. Specify the gasket type, the compression, the number of hinges, the lock type and the swing direction. A single EPDM bulb gasket compressed to 25–30% on a three-point lock is the usual build; a foam strip on a two-hinge door will not hold 75 dB(A) for a season. Cable entry needs a gland plate with a removable section, sealed after the cables are pulled.

Access is part of the acoustic design

A canopy that needs a side panel unbolted for an oil change will be run with the panel off, and the noise target goes with it. State which doors open for daily checks, which panels are removable for major service, the clearance needed in front of each, and whether the control panel is viewed through a window or an opening door. Every one of those is a hole in the acoustic envelope, and each needs a gasket and a latch rather than a cover plate.

Cable entry deserves the same treatment. A 300 × 300 mm gland plate with a removable centre section seals after the cables are pulled; a torch-cut slot in the base does not, and it is the path that shows up as a 3 dB shortfall at commissioning.

Coating specification

State the category, the colour, the gloss and the DFT range. "Painted" is not a specification, and a seven-year life claim without a category is a guess.

Generator data the canopy has to fit

Rating and duty (prime or standby), voltage and frequency, engine and alternator model, radiator airflow in m³/min, exhaust outlet diameter and direction, fuel tank capacity, control panel position and cut-out size, cable entry side and size, set weight and overall dimensions, and the ambient design temperature. Without the radiator airflow and the set dimensions, the louvre and the frame are being designed from a catalogue picture.

What Ganesh runs

Canopies, acoustic enclosures and base frames are built on the same cut-form-weld-coat route: 12 kW fibre laser with a 40 ft × 16 ft bed, 200 T brake with a 4,450 mm bed, three CLOOS robotic MIG cells and 30+ manual stations, seven-tank pretreatment and an 18 ft × 14 ft powder booth. Ganesh builds canopies and base frames for Mahindra Powerol.

See the DG set canopy and genset parts page, the genset and canopy guides, bending for genset canopies and panels and the powder coating cost estimator.

How to fill the form

• Acoustic target with distance, height, sides, load condition and standard.
• Radiator airflow and the free area you expect, or the louvre drawing.
• Base type, tank, lifting points and anti-vibration requirement.
• Door size, swing, gasket and lock.
• Coating category, colour and DFT.
• Annual quantity and delivery location, because the frame is usually shipped assembled.

Two RFQs for a 125 kVA prime-rated set, 415 V, with a front-mounted radiator and a stated airflow of 300 m³/min.

Incomplete: "125 kVA soundproof canopy, MS, painted, 5 nos." Each supplier chooses its own build. One quotes 25 mm infill and reaches about 80 dB(A). One quotes 50 mm infill with an unsealed door and also reaches about 78 dB(A). The third quotes a weatherproof skin and calls it acoustic. All three are defensible against the text, and the buyer cannot tell them apart on price alone.

Complete: "125 kVA prime, 415 V, 50 Hz. Target 75 dB(A) at 1 m, free field, four sides, at 75% load, measured to ISO 8528-10 by the envelope method. Radiator airflow 300 m³/min, front-mounted; intake louvre free area minimum 1.00 m², exhaust louvre 0.90 m²; hot air discharge away from the intake. Base: skid with integral 200 L tank, four marked lifting points, anti-vibration mounts at 5 mm deflection, flatness 1 mm/m. Doors 700 × 1,200 mm, EPDM gasket, three-point lock. Coating: polyester RAL 7035, 80–100 µm, ISO 12944 C3. Annual 60, delivery Pune."

Now the louvre can be checked. At 300 m³/min and 5 m/s the free area needed is 1.00 m²; at 50% free area that is a 2.0 m² gross opening. A supplier who fits a 1.4 m² gross louvre gives 0.70 m² free, which puts face velocity at 300 / (60 × 0.70) = 7.1 m/s. The pressure drop roughly triples, the set pulls hot air, and the derating shows up as reduced kVA on a hot day — with the noise target still met, so nobody suspects the louvre.