Los sistemas de circuito cerrado se pueden clasificar además como de retorno directo o de retorno inverso.
Devolución Directa
El sistema de retorno directo permite que las tuberías corran por el camino más directo para optimizar los costos de tubería.
La desventaja es que el flujo en cada unidad fan coil o unidad de tratamiento de aire generalmente debe equilibrarse mediante una válvula de equilibrio.
La longitud del circuito de agua a través de las tuberías de suministro y retorno a cada fan coil o unidad de tratamiento de aire es diferente en la tubería de retorno directo. Los fan coils cercanos a la bomba reciben un mayor caudal que los más alejados, a menos que se logre el equilibrio.
Los sistemas de lazo abierto como el sistema de agua del condensador con una torre de refrigeración son siempre de retorno directo ya que no existen terminales individuales y el equilibrio es relativamente sencillo.
Retorno Inverso
El sistema de retorno inverso está conectado de manera que la longitud del circuito de agua a través de las tuberías de suministro y retorno a cada fan coil o unidad de tratamiento de aire sea esencialmente la misma. Por tanto, las caídas de presión son básicamente iguales. Edificios como hoteles con múltiples unidades fan coil idénticas con flujos idénticos son excelentes candidatos para sistemas de retorno inverso.
El retorno inverso tiene mayores longitudes de tubería y costos. Sin embargo, el costo de agregar una válvula de equilibrio para cada fan coil utilizando un sistema de retorno directo podría compensar los costos adicionales de la tubería de retorno inverso agregada.
Si las caídas de presión de agua de las unidades de fan coil o de tratamiento de aire individuales no están razonablemente cerca entre sí, los ingenieros a menudo especificarán válvulas de equilibrio de todos modos, independientemente de la disposición de las tuberías.
FREQUENTLY ASKED QUESTIONS
In a direct return system, the flow rate at each fan coil unit or air handler is not uniform. Fan coils or air handlers closer to the pump receive a greater flow rate than those further away, unless balancing is accomplished using balancing valves. This can lead to uneven cooling or heating performance across different areas of the building, highlighting the importance of proper balancing in direct return systems.
Balancing valves are used in direct return systems to ensure that the flow rate at each fan coil unit or air handler is consistent, despite the varying lengths of the water circuit. These valves regulate the flow rate by creating a pressure drop, which helps to balance the flow across different branches of the piping system. By installing balancing valves, HVAC designers and engineers can ensure that each fan coil unit or air handler receives the required flow rate, regardless of its distance from the pump.
A reverse return system is piped so that the length of the water circuit through the supply and return piping to each fan coil or air handler is essentially the same. This design approach eliminates the need for balancing valves, as the flow rate at each fan coil unit or air handler is inherently balanced due to the equal piping lengths. Reverse return systems can provide more even cooling or heating performance across different areas of the building, but may require more complex piping designs and higher upfront costs.
Yes, direct return systems can be used in combination with other piping configurations, such as loop systems. In fact, many modern HVAC systems incorporate a hybrid approach, where direct return systems are used for certain branches of the piping network, while loop systems are used for others. This hybrid approach can help to optimize piping costs, simplify system design, and improve overall system performance.
Direct return systems are often preferred in applications where piping costs are a significant concern, such as in large commercial or industrial buildings with extensive piping runs. They are also commonly used in retrofit projects where existing piping infrastructure needs to be reused or modified. Additionally, direct return systems may be preferred in applications where simplicity of design and installation is a priority, such as in smaller buildings or in areas with limited access.
