Direct And Reverse Return Systems

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閉ループシステムはさらに、直接リターンまたは逆リターンに分類できます。

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ダイレクトリターン

ダイレクトリターンシステムにより、配管を最も直接的な経路で実行でき、配管コストを最適化できます。

欠点は、通常、各ファンコイルユニットまたはエアハンドラーでの流れのバランスをバランシングバルブを使用して調整する必要があることです。

各ファンコイルまたはエアハンドラーへの供給および戻り配管を通る水回路の長さは、直接戻り配管では異なります。バランスが取れていない限り、ポンプに近いファンコイルは、遠くにあるファンコイルよりも大きな流量を受け取ります。

などの開ループシステムコンデンサー水システム冷却塔を使用する場合は、個別のターミナルが存在せず、バランスをとるのが比較的簡単であるため、常に直接リターンされます。

逆戻り

逆戻りシステムは、各ファンコイルまたはエアハンドラーへの供給および戻り配管を通る水回路の長さが本質的に同じになるように配管されています。したがって、圧力損失は基本的に等しいです。同一の流れを備えた複数の同一ファンコイルユニットを備えたホテルなどの建物は、リバースリターンシステムの優れた候補です。

逆戻りの場合、パイプの長さが長くなり、コストがかかります。ただし、ダイレクトリターンシステムを使用して各ファンコイルにバランシングバルブを追加するコストは、追加された逆リターン配管の追加コストを相殺できる可能性があります。

個々のファンコイルまたはエアハンドリングユニットの水圧降下が互いに適度に近接していない場合、エンジニアは配管の配置に関係なく、バランシングバルブを指定することがよくあります。

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.