Heating, ventilation, and air conditioning (HVAC) systems provide building heating and cooling, and more modern-day HVAC systems are starting to use hydronic piping to provide newly constructed buildings’ heating and cooling needs. For this type of work, two main system configurations are possible: two-pipe systems or four-pipe systems.


●        Two-pipe system - These systems are present when heating and cooling share hydronic piping. Each fan coil has one supply pip and one return pipe (two total pipes).


●        Four-pipe system - These systems are present when heating and cooling have separate hydronic piping. Each fan coil has two supply pipes and two return pipes (four total pipes).


While each system has its advantages and disadvantages, each particular facility can be retrofitted with one of the two systems, depending on various factors.


Two-Pipe HVAC Systems

A two-pipe system requires half the hydronic piping as the four-pipe system, meaning fewer materials are required for build and installation, a shorter installation time, and a lower cost. Because it is smaller, the system also takes up much less space, reducing the space requirements of the building’s mechanical room(s).


Though the two-pipe system is initially less expensive, it does have its setbacks. The two-pipe system’s main limitation is its lack of operating flexibility. Depending on the facility’s needs, the system’s hydronic piping circuit that runs throughout the building must connect to the boiler or the chiller. And because all building areas must operate in the same mode, heating some areas while cooling others is not possible with this system configuration.


Therefore, two-pipe systems are ideal for warm, tropical climates because buildings in these areas rarely every require space heating.


Four-Pipe HVAC Systems

The four-pipe system allows for more flexibility and has more performance options that a two-pipe system does not. For example, the system’s fan coils can more easily deliver simultaneous cooling and dehumidification by using the cold and hot water coils at the same time.


One must also realize that this system uses twice as much piping as the two-piping system because it requires more space to accommodate the circuits that run through the building. This means the required number of fixtures, valves, and connection points is higher. The two-pipe system also takes more time to install and is generally more expensive than its counterpart.


Four-pipe systems are ideally used in multi-climate regions that experience both hot and cold outside temperatures. The reason is because throughout the year, buildings will require both space heating and cooling, making the four-pipe system the more efficient option.


Still not sure of the overall differences of the two- and four-pipe HVAC systems? Gausman & Moore’s engineers will work with your facility’s builders and contractors to determine which system type is optimal for your building. Our goal is to create healthy, indoor environments that are comfortable, energy efficient, and cost-effective. For more information regarding our HVAC and other mechanical engineering services, contact us today.