温水システムのすべてのコンポーネントは、温水システムの制御とパフォーマンスにある程度の影響を与えます。 バルブ これらは熱伝達の重要な領域を制御するデバイスであるため、重要です。

制御弁
  • 温水システムは相互依存性の高いシステムです。
  • 各システム コンポーネントは相互に作用し、パフォーマンスに影響を与えます。
  • バルブは、温水システムの熱伝達を制御する重要なデバイスです。
  • 適切なバルブのサイズ設定と選択には、システム全体を検討する必要があります。
  • バルブのサイズや選択が正しくないと、熱伝達装置だけでなく機械システム全体にも望ましくない結果が生じます。

なぜバルブの特性を意識する必要があるのでしょうか?

バルブ特性

簡単に言えば、それは使用している機器の性質によるものです。 システムの制御には線形な応答と出力が必要ですが、扱っている伝熱デバイスは非線形性が高くなります。 画像 A から、典型的な加熱コイルの特性がわかります。 非常に非線形であることがわかります。 流量が 50% を超え始めるまでは、ハイエンドで流量がわずかに変化しても出力容量は低下しません。

This image has an empty alt attribute; its file name is image-2.pngThis image has an empty alt attribute; its file name is image-3.pngThis image has an empty alt attribute; its file name is image-4.png
コイル、バルブ、コントローラーの特性曲線

コイルを通る流れは、当社の制御バルブと、それらが本質的に保持する特性によって制御されます。 制御システムに望ましい線形応答/出力を得るには、望ましい応答タイプを与えるコイルとバルブの特性を一致させる必要があります。 この場合、等しいパーセンテージのバルブ特性を加熱コイルと一致させて、線形応答システムを生成します。 ただし、これは理想的な状態であり、現実の世界では常にこのように起こるわけではないことに注意してください。

  • イコールパーセンテージ特性
    • 通常、水用途に使用されます
    • 圧力損失の変化が大きいシステムで使用される
    • 総圧力降下のわずかな割合がバルブによって許容される場合に使用されます。
    • 温度および圧力制御ループで使用
  • リニア特性
    • 通常は蒸気用途に使用されます
    • 液面またはフローループで使用
    • 定常状態システムで使用される
    • バルブ全体の圧力降下が総圧力降下の大部分を占める場合に使用されます。
  • クイックオープン特性
    • 頻繁なオン/オフサービスに使用されます
    • 「瞬間的な」大流量が必要なシステム (安全システムなど) に使用されます。

FREQUENTLY ASKED QUESTIONS

What are the key factors to consider when selecting valves for a hydronic system?
When selecting valves for a hydronic system, it’s essential to consider factors such as flow rate, pressure drop, valve authority, and valve rangeability. Valve authority, which is the ratio of valve flow coefficient to system flow coefficient, affects the valve’s ability to control flow. Rangeability, which is the ratio of maximum to minimum flow rates, determines the valve’s turndown capability. Additionally, the valve’s materials, actuation method, and control signal type must be compatible with the system’s requirements and operating conditions.
How do valve characteristics impact the performance of a hydronic system?

Valve characteristics, such as flow coefficient, pressure drop, and valve authority, significantly impact the performance of a hydronic system. For example, a valve with a high flow coefficient can handle higher flow rates, while a valve with a low pressure drop can reduce energy losses. Improperly sized or selected valves can lead to poor system performance, including reduced heat transfer, increased energy consumption, and decreased system reliability. Moreover, valve characteristics can affect the stability and controllability of the system, making it essential to consider these factors during system design and operation.

What is valve authority, and why is it important in hydronic systems?

Valve authority is a dimensionless parameter that represents the valve’s ability to control flow in a hydronic system. It is defined as the ratio of the valve’s flow coefficient to the system’s flow coefficient. A valve with high authority can effectively control flow, while a valve with low authority may not be able to maintain the desired flow rate. In hydronic systems, valve authority is critical because it affects the system’s stability, controllability, and overall performance. A valve with adequate authority ensures that the system operates within the desired parameters, while a valve with inadequate authority can lead to system instability and poor performance.

How do I determine the required valve rangeability for a hydronic system?

To determine the required valve rangeability for a hydronic system, you need to consider the system’s operating conditions, including the maximum and minimum flow rates, pressure drops, and temperatures. Rangeability is typically expressed as a ratio of the maximum to minimum flow rates and should be sufficient to accommodate the system’s turndown requirements. A valve with inadequate rangeability may not be able to maintain the desired flow rate during part-load conditions, leading to poor system performance and reduced efficiency. In general, a rangeability of 10:1 or higher is recommended for most hydronic systems.

What are the consequences of undersizing or oversizing valves in a hydronic system?

Undersizing or oversizing valves in a hydronic system can have significant consequences on system performance and efficiency. Undersized valves can lead to inadequate flow rates, increased pressure drops, and reduced heat transfer, resulting in poor system performance and decreased efficiency. Oversized valves, on the other hand, can cause unnecessary energy losses, increased wear and tear on the valve, and reduced system controllability. In extreme cases, undersized or oversized valves can lead to system instability, reduced reliability, and even premature failure of system components. Therefore, it’s essential to properly size and select valves for a hydronic system to ensure optimal performance and efficiency.

How can I ensure proper valve sizing and selection for a hydronic system?

To ensure proper valve sizing and selection for a hydronic system, it’s essential to consider the system’s operating conditions, including flow rates, pressure drops, temperatures, and control requirements. You should also consult the valve manufacturer’s specifications and performance data to select a valve that meets the system’s requirements. Additionally, it’s recommended to perform hydraulic calculations and simulations to validate the valve selection and ensure that it can operate within the desired parameters. Finally, it’s crucial to consider factors such as valve authority, rangeability, and materials compatibility to ensure that the selected valve can provide reliable and efficient operation over the system’s lifespan.