Double Regulating Valve

 

A Double Regulating Valve (DRV) is a type of valve commonly used in heating, ventilation, and air conditioning (HVAC) systems, particularly in hydronic (water-based) heating and cooling systems. It serves two main functions: regulating the flow of water to ensure proper system balancing and allowing for isolation and flow measurement.

Functions of a Double Regulating Valve (DRV)

1. Flow Regulation:

   • The DRV allows precise adjustment of the flow rate through a particular section of the system. This is crucial for balancing the system, ensuring that each part receives the correct amount of water flow to operate efficiently.

2. Flow Measurement:

   • Many DRVs are equipped with ports that allow for the measurement of the flow rate using an external measuring device. This feature helps in accurately setting the flow rate during system commissioning and maintenance.

3. Isolation:

   • The valve can also be fully closed to isolate a section of the system for maintenance or repair, making it a versatile component in hydronic systems.
     
     
     

Key Components of a Double Regulating Valve

1. Valve Body:

   • Typically made of brass, bronze, or cast iron, the valve body houses all the internal components and connects to the pipework.

2. Adjustable Stem:

   • The stem is turned to adjust the valve opening, thereby regulating the flow. It often features a lockable mechanism to secure the valve in the desired position after adjustment.

3. Flow Measurement Ports:

   • These are small ports located on the valve body, allowing connection to a differential pressure measuring device. The flow rate is calculated based on the pressure drop across the valve.

4. Indicator Scale:

   • The valve may include a scale or dial that indicates the position of the valve, assisting in precise adjustment and ensuring repeatable settings.

5. Locking Mechanism:

   • After the desired flow rate is set, the valve can be locked in place to prevent accidental adjustment.

Applications of Double Regulating Valves

1. HVAC Systems:

   • DRVs are widely used in HVAC systems to balance the flow of water in heating and cooling circuits. Proper flow balancing ensures that all parts of the system operate efficiently and that no area is over- or under-serviced.

2. Chilled Water Systems:

   • In chilled water systems, DRVs help maintain consistent temperatures by ensuring that the correct flow of water reaches each cooling unit.

3. Heating Systems:

   • In hot water heating systems, DRVs ensure that each radiator or heating coil receives the appropriate amount of hot water, improving comfort and system efficiency.

Benefits of Using Double Regulating Valves

1. System Balancing:

   • DRVs are essential for achieving hydraulic balance in water-based systems, preventing issues like uneven heating or cooling and ensuring that the system operates as designed.

2. Energy Efficiency:

   • By precisely controlling the flow of water, DRVs help reduce energy consumption, as the system does not need to work harder to compensate for imbalances.

3. Ease of Maintenance:

   • The ability to isolate sections of the system and accurately measure flow rates makes DRVs valuable for routine maintenance and troubleshooting.

4. Improved Comfort:

   • In HVAC applications, balanced water flow leads to more consistent temperatures throughout a building, improving overall comfort for occupants.

Installation and Maintenance

• Installation:
  • DRVs should be installed according to the manufacturer's instructions, typically on the return side of a heating or cooling loop. Proper orientation and connection to measurement devices are essential for accurate flow regulation.
• Maintenance:
• Regular checks should be performed to ensure the valve is functioning correctly, especially during seasonal system adjustments. The measurement ports should be kept clean, and any scale or debris should be removed to maintain accurate flow measurements.

In the realm of HVAC systems, maintaining balanced flow in chilled water lines is crucial for achieving optimal performance and energy efficiency. Double regulating valves (DRV) play a key role in this process by providing a means to control and balance the flow of chilled water within a system. In this article, we explore the significance of double regulating valves and elucidate the process of balancing a chilled water line using one, complete with a sample calculation.

Understanding Double Regulating Valves (DRV)

A double regulating valve is a versatile control valve designed to regulate the flow of water within a system while also providing a visual indication of the set flow rate. These valves consist of two components: a regulating valve and a flow measurement device. The regulating valve allows users to manually adjust the flow, while the flow measurement device, often in the form of a pressure differential indicator, provides a visual indication of the set flow rate.

Balancing Chilled Water Lines with Double Regulating Valves

Balancing a chilled water line involves ensuring that the flow of water through each terminal unit (e.g., air handling units, fan coil units) is proportionate and meets the design specifications. The double regulating valve simplifies this process by allowing for precise adjustment of the flow rate to achieve optimal balance.

Here is a step-by-step guide on how to balance a chilled water line using a double regulating valve:

Determine Design Flow Rates: Understand the design flow rates for each terminal unit in the chilled water system. This information is typically provided in the project specifications or can be obtained from the HVAC design documents.

Install Double Regulating Valves: Install a double regulating valve at each terminal unit in the chilled water line. Ensure that the valves are positioned to facilitate easy access for adjustments and readings.

Initial Valve Adjustment: Initially, set the double regulating valve to a midway position. This allows for a baseline flow rate through the terminal unit.

Measure Pressure Differential: Utilize the pressure differential indicator on the double regulating valve to measure the pressure drop across the valve. This reading provides an indication of the flow rate passing through the valve.

Compare with Design Flow Rates: Compare the measured flow rate with the design flow rate for each terminal unit. Adjust the double regulating valve accordingly to increase or decrease the flow until the desired flow rate is achieved.

Repeat for Each Terminal Unit: Repeat the adjustment process for each terminal unit in the chilled water line, ensuring that each unit is receiving the appropriate flow rate for optimal performance.

Sample Calculation:

Assuming a design flow rate of 500 gallons per minute (GPM) for a specific terminal unit, and a measured pressure drop across the double regulating valve of 10 psi, the flow rate (Q) can be calculated using the valve's characteristic flow curve. This may involve referring to manufacturer-provided data or using flow coefficient (Cv) values.

Q = Cv × √ΔP

Assuming a Cv value of 20:

Q = 20 × √10

Q ≈ 63.25GPM

Therefore, by adjusting the double regulating valve to achieve a pressure drop of 10 psi, the flow rate through the terminal unit can be estimated at approximately 63.25 GPM.

Summary

A Double Regulating Valve (DRV) is a critical component in hydronic HVAC systems, designed to regulate and balance water flow while also allowing for flow measurement and system isolation. Its ability to maintain hydraulic balance, improve energy efficiency, and simplify maintenance makes it a valuable tool in ensuring the optimal performance of heating and cooling systems.