Generator sets are normally furnished with a skid-mounted cooling system, where the radiator is installed in front of the engine, and the cooling fan is mechanically driven by the engine. Skid-mounted radiators are designed for 40°C ambient air conditions (optional 50°C-ratings are also available), and the fans are selected to perform under a maximum external static restriction of 0.50″H2O. These radiators work well when the engine room has sufficient fresh-air ventilation, and when the exhaust air can be easily vented to the exterior. If, however, space and ventilation are restricted, you may find that a remote cooling system is the best solution. This article will assist you in understanding the main components of a remote cooling package, and will outline the information required to specify a reliable system.
A remote cooling system consists of:
- an air-cooled radiator assembly that includes the radiator core, a cooling fan, an electric motor (to drive the fan), and an expansion tank. If the engine has two separate cooling circuits (see this related article), the radiator assembly may consists of two independent cores, which can be stacked or laid out side-by-side within the radiator assembly.
- a liquid-to-liquid heat exchanger(s), required when the engine-mounted water pump(s) are not capable of circulating coolant to the remote radiator’s location. For engines that utilize two separate cooling circuits, two separate heat exchangers are required. These heat exchangers are installed near the engine and their function is described below.
- auxiliary pump(s), required when heat exchangers are used between the engine and the remote radiator. An auxiliary pump consists of a skid-mounted centrifugal pump driven by an electric motor. These pump-skids are installed near the engine and their function is also described below.
- piping between the engine and the remote cooling system. This includes flexible connectors at the engine connections, black iron pipe for the main piping, and insulation (the hot water circuit can carry temperatures exceeding 200°F).
Due to the many variables that exist in these types of installations, a remote cooling system must be designed specifically for each project. You can expect the radiator vendor to have questions about the physical installation, the site conditions, and the technical details for the proposed engine. Answers to these questions will allow the radiator vendor to design a system with the right performance criteria.
About the installation…
- Will the radiator’s airflow need to be directed vertically, or horizontally? A radiator assembly can be designed for vertical installation (with horizontal airflow) or horizontal installation (with vertical airflow). Here are some examples of a vertical remote radiator, and a horizontal remote radiator.
- Are there space limitations for the radiator? What is the maximum footprint available? Does your project require multiple remote radiators to be installed adjacent to each other? If so, be sure to account for sufficient spacing between them.
- What is the expected maximum temperature of the ambient air at the radiator? Be sure to account for all temperature rise due to roofing materials, adjacent equipment, etc.
- Will the radiator’s exhaust airflow be affected by restrictions, such as those caused by mechanical louvers, noise barriers, or other structures? If so, what is the estimated external static restriction?
- Will the radiator be close enough to the engine to allow the engine-mounted water pump(s) to circulate water to the radiator? You can answer this question by calculating the pressure drop across all piping elements, adding a 3-5psi estimate for the radiator, and comparing the total to the maximum friction head of the engine’s cooling system. If the radiator will be elevated above the engine, be sure to also consider the engine’s maximum static head allowance. The performance limits of the engine’s water pump are published in the generator manufacturer’s technical data sheets. Here is an example:
What happens if you exceed the engine water pump limits? You will need a “dual loop” remote cooling system arrangement if your total friction head and/or static head exceed the maximum engine allowances. This is explained below.
Single Loop or a Dual Loop Arrangement? A “single loop” system relies on the engine-mounted water pump to circulate the coolant to the radiator. A “dual loop” system is used when the engine-mounted pump cannot circulate the coolant to the remote radiator. In this scenario, liquid-to-liquid heat exchangers are required. The heat exchangers are placed near the engine, with the “hot side” of the heat exchanger connected to the engine’s water pump (this circuit carries the hot coolant that circulates through the engine, and is the “first loop”). The “cold side” of the heat exchanger is connected to an auxiliary pump. This pump is responsible for circulating coolant to the remote radiator’s location, and represents the “second loop”.
Who does all of this?
It is important that the radiator, heat exchangers and any auxiliary pumps be sized to perform as a system. It may seem a bit complicated, but don’t worry! Given the information listed below, a capable vendor can perform the necessary calculations to help you specify all system components. Here is what you will need:
- Determine the required radiator configuration (i.e.: vertical frame or horizontal frame)?
- Gather engine data sheets listing values for “heat rejection to jacket water” (and aftercooler, if applicable), engine pump flow rates, etc. This information can be found in the generator’s technical data sheets, under the “Cooling System Performance” heading.
- Calculate the estimated piping pressure drop and static head.
- Gather environmental factors such as the maximum expected ambient air temperature at the radiator’s location, external static restriction to the radiator’s exhaust airflow (if any), and any space constraint issues.
- Determine whether there is a maximum allowance for the parasitic load associated with the electric motor on the remote radiator?
Now that you are armed with this information, reach out to your preferred radiator vendor to finalize the product selections. At a minimum, you should now be able to obtain technical performance data for the cooling system components, as well as product data sheets complete with construction details, dimensional data, and electrical characteristics (when applicable).
Some final design tips
- For installations in coastal areas, I recommend that the radiator frame be of galvanized steel construction for corrosion protection. The core itself should be protected against corrosion by specifying solder-coated fins. This process involves immersing the fins in solder and then baking, for a 100% uniform surface coverage.
- Cooling systems are designed specifically for a given engine. Be sure to consider competing engine manufacturers if your project involves a public bid with multiple potential engine vendors.
- Avoid hot air re-circulation when laying out multiple radiators in close proximity to each other. The spacing between adjacent radiators should be 1.5-times the fan diameter (i.e.: three radiators with 6′ fans should have 9′ of spacing between them).
Specifying a remote cooling system may require some additional work, but it should not be perceived as overly complicated. If you are struggling with an application for a remote cooling system, post a question or message, and I will try to help you move forward with your design.