We often have requests to provide coolers such as “My oil is at 80 °C, I need it to be 60 °C, please quote me a cooler doing 80 °C down to 60 °C from 100 L/min”. This almost always results in a cooler larger than required. Your system doesn’t go from 60 °C up to 80 °C in one pass so the cooling doesn’t have to remove it in one pass either.
Maintaining an operating temperature is about balancing the heat generated by the system with a cooler removing the same amount at an ideal operating temperature.
Say your system goes from ambient (25 °C) to 80 °C over two hours from start up, and the total oil volume in the system is 500 L. Using heat transfer equations this is calculated to be a heat load of 6.8 kW, versus the initial enquiry of 59.5 kW.
The actual cooler required is an ACX400, where the cooler requested is an ACX800 costing three times as much.
Hydraulic systems often run at very high pressures, much higher than standard coolers will handle. Our ACX units will handle up to 30 bar constant pressure but even this is dwarfed by system pressures. Sure we can build you a custom unit to withstand any pressure but it’s much more economical if you can locate the cooler in a line that sees minimal pressure such as the return line or have a separate cooling circuit, sometimes known as “offline cooling”. We can supply our coolers with integral oil pumps that run off the fan motor so you do not need to purchase or wire up extra equipment.
When specifying the ambient temperature, make sure to advise the actual ambient required. We put safety factors into the performance of our coolers already so if you add margin without telling us, the cooler will be oversized. Also, if your site only gets to maximum ambient for a few hours several days a year, consider whether your system will accommodate slightly elevated oil temperatures for that period. A few degrees less in design ambient could save you thousands.
These points are also applicable to water cooled units such as shell and tube oil coolers.
We have calculation software available on our Cooler Selection Program to help with these calculations and more, you can even select the cooler for your application and download drawings and specification sheets. Click here if you would like to sign up.