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What Is a Single-Duct Hydronic Reheat System?

Posted by Mark Mahon on February 4, 2025 at 9:00 AM
Mark Mahon
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Where Zone Control Meets Design Flexibility

As we discussed in our last blog post, single-duct VAV systems with hydronic reheat are one of the most popular commercial HVAC air distribution systems in North America. These systems provide heating, cooling and ventilation by regulating airflow and hot water.

Woman engineer working on blueprint in office with colleagues on background Healthcare staff walking through a hospital corridor
Staff member using lab equipment Teacher reading her pupils a story at the elementary school
Single-duct hydronic reheat systems benefit many different applications, including offices, hospitals, schools and laboratories

Single-duct hydronic reheat systems contain several components:

  • Air handling units supply conditioned and dehumidified air throughout the building at a constant temperature (typically saturated 55°F).
  • Single-duct VAV terminal units are placed in each zone to regulate the supply airflow with a damper based on room temperature
  • Hydronic reheat coils are positioned within the VAV box and utilize energy from hot water to reheat the air when required.
  • The hydronic system typically uses a boiler, pumps and distribution piping to supply hot water to the reheat coils.
  • System controls such as thermostats, sensors, digital controllers and temperature control valves are used in each zone to calculate the airflow and fluid flow required to make the space comfortable.
Hydronic Reheat System Diagram
A typical single-duct hydronic reheat system showing an air handling unit (A), single-duct terminal unit with hydronic reheat coils (B) and a condensing boiler with pumps and distribution piping (C)

Part of what makes single-duct VAV systems with hydronic reheat so common is that they are suited to a variety of applications. They are an excellent choice for buildings containing spaces that have variable occupancy and thermal loads or that require precise temperature control.

Examples of common applications and the corresponding benefits of employing single-duct VAV reheat can be seen below. These systems help balance energy efficiency, zone control and design flexibility to meet diverse HVAC system requirements.

Application Design Challenge Met by Single-Duct VAV Reheat
Offices
  • Need for individualized occupant control
  • High-load perimeter zones with low-load interior zones
Hospitals and healthcare
  • Strict temperature and humidity requirements
  • Need to prevent overcooling in sensitive areas
  • Diverse zone requirements (operating rooms, patient rooms and labs)
Educational
  • Need for accurate ventilation control for variable occupancy
  • Diverse zone requirements (classrooms, auditoriums and labs)
Laboratories and research
  • Internal load variability from equipment and occupancy
  • Need for accurate control of temperature, humidity and ventilation
Airports and transportation
  • Large spaces with diverse occupancy
Government and institutions
  • Diverse zone requirements (offices, meeting rooms and public service spaces)
  • Desire to balance energy efficiency with thermal comfort

Price’s project and application engineers are ready to assist design engineers, building owners, architects and mechanical contractors with product choices that can optimize air distribution system efficiency.

Click here to find a sales representative or technical expert near you, or reach out to our team at airmovement@priceindustries.com.

 

Mark Mahon Headshot Mark Mahon is Business Development Manager for Fan Coils and Terminals for Price's Air Moving team. He is based out of Price's Progress facility in Lawrenceville, GA. Click here to connect with him on LinkedIn.

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Topics: Terminals, HVAC Fundamentals, HVAC, Engineering, Design Engineering

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