Thermal fluid systems often can be used where other heating systems such as hot water or steam cannot. The hot oil systems usually are nonpressurized, indirect heating systems with a primary source of energy -- gas, fuel-oil or a waste product -- to heat thermal fluid that passes through the system. According to Joe Richardson, managing director of Thame Energy Systems Ltd., Thame, Oxon, England, the principal advantages of thermal fluid heaters are:
  • High thermal efficiency and economical operation.
  • Temperatures up to 716°F (380°C), depending on thermal fluid type.
  • Water treatment not required.
  • Internal corrosion and scale eliminated.
  • Freezing risk during winter eliminated.
  • Pipe corrosion prevented.
  • Nearly maintenance-free operation provided because bellows-sealed valves and simple burner components typically used.
According to Richardson, today's advanced controls provide operation flexibility and the ability to supply fluid at precise, independently controlled temperatures. If the process requires some portion of the heat load to be steam or hot water, it can be provided by an unfired steam generator or calorifier, he says.

All conventional fuels can be used as well as combustible waste products in solid, liquid or gaseous form, Richardson says, noting that electrical power is the only other external service required. In addition, thermal fluid systems are compact, so they can be placed close to where the heat is needed, minimizing the need to alter the building and shortening installation time.

Modern thermal fluids offer good thermal stability and heat transfer characteristics to ensure long life and low viscosity for good circulation. The thermal fluid typically circulates through the heater coils via a low-pressure circulating pump selected for high temperature operation. Three-way control valves regulate temperature while safety systems monitor the flow and return temperatures, and automatically adjust burner firing, Richardson says.

Thermal fluid heaters use an expansion tank that allows thermal fluid expansion during operation, and the release of water vapors and gases during startup and throughout the life of the system. Pipework to and from the system should be carbon steel with suitable expansion devices and cast iron bellows-sealed valves, which are welded in position to eliminate gasket joints. This reduces the risk of leakage at flanged joints, which should be kept to a minimum, Richardson says. After installation all pipework should be insulated and clad. For more information, visit