The type of exchanger used for a given service depends on process, safety and operating requirements, and economics. Selection of the most economical heat exchanger in a given service includes the initial cost of the exchanger, installation osts, maintenance costs, incremental pumping and compression costs, and where applicable, utility system investment and energy requirements.
As an example, the initial cost of a water-cooled shell and tube heat exchanger will be much less than an air-cooled heat exchanger for the same service. However, the cost of the cooling water supply, including makeup water, chemical treatment, blowdown disposal, the cooling tower and fans, water circulation pumps, and piping to and from the water-cooled exchanger, often more than offset the lower first cost of the water-cooled exchanger. Operating and maintenance costs for water coolers are also more than for air coolers.
Air cooling is usually more economical than water cooling when the required process fluid outlet temperature is 20°F or more over the design ambient air temperature.
In most cases, a custom designed shell and tube heat exchanger will be the economical choice.
Pre-engineered double pipe or small multitube hairpin heat exchangers compete with custom designed shell and tube exchangers and are usually economical when the required heat transfer surface area is less than about 1000 square feet.
Plate and frame heat exchangers may be economical where weight and space are highly valued, alloy material is required, pressures and temperatures are moderate (less than 200 psig and 250°F), and fluids are compatible with rubber gaskets. Titanium plate and frame exchangers on offshore platforms in sea water/fresh water service are appropriate applications.