Direct And Reverse Return Systems

闭环系统可进一步分为正向回路或反向回路。

Table of Contents

直接返回

直接回流系统允许管道在最直接的路径上运行，以优化管道成本。

缺点是每个风机盘管或空气处理器的流量通常需要使用平衡阀来平衡。

通过供回水管道到达每个风机盘管或空气处理器的水路长度在直接回水管道中是不同的。除非实现平衡，否则靠近泵的风机盘管比远离泵的风机盘管接收更大的流量。

开环系统，例如冷凝水系统使用冷却塔总是直接返回，因为不存在单独的终端并且平衡相对简单。

反向返回

反向回流系统采用管道连接，以便通过供水和回流管道到达每个风机盘管或空气处理器的水回路长度基本相同。因此，压降基本相等。酒店等建筑物拥有多个具有相同流量的相同风机盘管，是反向回流系统的最佳选择。

反向回流具有更长的管道长度和成本。然而，使用直接回流系统为每个风机盘管添加平衡阀的成本可以抵消添加反向回流管道的额外成本。

如果单个风机盘管或空气处理机组的水压降彼此不相当接近，工程师通常会指定平衡阀，无论管道布置如何。

FREQUENTLY ASKED QUESTIONS

What are the main advantages of direct return systems in closed-loop HVAC applications?

The primary advantage of direct return systems is that they allow piping to be run in the most direct path, which can significantly optimize piping costs. This is particularly beneficial in large commercial or industrial buildings where piping runs can be extensive. Additionally, direct return systems tend to be simpler to design and install compared to reverse return systems.

How does the flow rate vary in a direct return system, and what are the implications?

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.

What is the purpose of balancing valves in direct return systems, and how do they work?

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.

How does a reverse return system differ from a direct return system, and what are the benefits?

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.

Can direct return systems be used in combination with other piping configurations, such as loop systems?

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.

What are some common applications where direct return systems are preferred over reverse return systems?

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.