Knowledge base
Sizing a radiator for a generator set is not guesswork and not a catalogue lookup: it is a calculation from a handful of inputs that the engine maker, the site and the customer provide. Get those inputs right and the radiator is right; leave one out and the unit is either too large and too dear or too small and the engine derates on the first hot afternoon. This guide lists the inputs, where they come from and what each one does to the result.
What The Engine Maker Gives: Heat, Flow, Temperatures, Limits
The engine cooling data sheet is the starting point. For each circuit - one for a small engine, a high-temperature (HT) and a low-temperature (LT) circuit for a large one - it states the heat to be rejected in kW at the site rating, the coolant flow in m³/h or l/min, the coolant temperature leaving the engine and the maximum temperature it may return at, and the maximum external pressure drop the engine pump can serve. The LT circuit also carries the charge-air temperature the engine needs for its rating and its emissions, which is why its return temperature is the tightest figure of all.
These are not negotiable. The radiator must reject the stated heat at the stated flow, return the coolant at or below the stated temperature on the design day, and do so with a pressure drop that, together with the pipework, stays under the limit. A rating at another ambient or altitude means another data sheet; ask the engine maker for the site rating.
What The Site Gives: Ambient, Altitude, Humidity, Air
The design ambient temperature is the single most powerful input: it sets the temperature difference the coil works with. The rule is the temperature at which the engine must still deliver its full site rating - a 50 °C design for the Gulf, 40 to 45 °C for southern Europe, 35 °C for the north - and a radiator sized for 40 °C is simply too small at 50 °C. Altitude thins the air, about 10 % less density per 1,000 m, so the fans move less mass and the coil needs more airflow or surface. Humidity changes the air's heat capacity and density a little and must be stated as the basis of the calculation.
The site also says what the air carries - dust, sand, seeds, salt - which sets the fin pitch and the fin material, and where the radiator can stand: on the ground, on a roof, beside the building, with or without a wind that could push the hot discharge back into the intake.
What The Customer Gives: Coolant, Sound, Space, Power
The coolant and its glycol percentage change the heat capacity, the viscosity and the pressure drop - a radiator for 50 % glycol needs 10 to 20 % more surface than one for water - so the mixture is an input, not a detail. A sound limit, with its distance and whether it applies to one unit or to the plant, decides the fans, their number and their speed, and often the length of the unit. The available space and any transport limit cap the length and the height; the power supply - voltage, frequency, EC or AC - fixes the fan family.
From these the design finds the coil surface, the rows and the fin pitch, the circuiting that meets the pressure drop limit, and the fans that deliver the airflow against the coil's resistance at the site density. The result is the datasheet: required and calculated capacity per circuit, flows, temperatures, pressure drops, airflow, fans, power, sound levels, dimensions and weights - all at the stated conditions.
A Checklist For The Enquiry
An enquiry that carries the engine cooling data sheet at the site rating, the design ambient, the altitude, the coolant mixture, the sound limit with its distance, the space and the power supply can be answered with a design and a price in days. One that carries only a kilowatt figure gets a question list first. TECS sizes radiators for generator sets of any make - single circuit or LT/HT, horizontal, vertical or V-type - and returns the datasheet, the dimensional drawing, the fan curve and the acoustic data with the offer.
In Short
- The engine data sheet fixes heat, flow, temperatures and the pressure drop limit per circuit
- The design ambient sets the temperature difference; altitude and humidity change the air
- Glycol percentage, sound limit, space and power supply shape the unit
- The LT return temperature is the tightest figure on a hot site
- The datasheet states every figure at the conditions it belongs to
- TECS sizes radiators for any engine make and returns a full design with the offer
What To Send With An Enquiry
- Engine cooling data sheet at the site rating
- Design ambient, altitude and humidity of the site
- Coolant mixture and percentage
- Sound limit and the distance it applies to
- Installation, space and transport limits
- Power supply: voltage, frequency, EC or AC fans
Questions We Are Often Asked
Can a radiator be sized from the engine's kW alone?
Roughly, for a budget. A real design needs the heat rejection per circuit, the flow and the temperatures from the engine data sheet; two engines of the same output can need radiators that differ by half.
What if the engine data sheet is for sea level and 25 °C?
Ask the engine maker for the data at the site ambient and altitude - the heat rejection and the rating change with both. TECS can estimate the derating, but the maker's figures are the ones to design to.
How much margin should a radiator have?
Enough to cover fouling, uncertainties in the site data and the humidity basis - a few percent on capacity, more on a dusty site. The margin is stated in the design; an unstated margin is no margin.
Does the radiator size change with EC fans?
The fans do not change the heat; they change how the airflow is delivered. EC fans allow slower speeds for a sound limit, which may need a longer coil, and they save power at part load. The coil surface for the design day is the same.
How long does a radiator design take?
With a complete enquiry, days. The thermal and acoustic design, the drawing and the fan curve are produced together; the time goes into the questions when inputs are missing.
Contact Us
Send us the heat duty, the fluid temperatures and flow rates, the ambient conditions and the installation limits. We answer with a design proposal - or write to us on WhatsApp.
