Month: June 2025
Why Damper Placement Shouldn’t Be Overlooked in Low-Temp Reheat Design
A Closer Look at Terminal Unit Performance
In HVAC system design, details matter, especially when your goal is high efficiency with low-temperature reheat systems.
For decades, most single-duct VAV terminal units have placed the damper upstream of the reheat coil. While this configuration is familiar and still widely used, when applied to low-temp hydronic systems (120°F and below), it can introduce performance losses that aren’t always obvious at the design stage.
One recent innovation, the Price SDV-Vantage, takes a different approach by relocating the damper downstream of the coil to improve efficiency and airflow performance.
New to single-duct systems? Price Industries has a quick overview:
Damper position vs. coil performance
Recent third-party studies and testing show that placing the damper upstream of the coil can lead to:
- Uneven airflow across the coil face at part-load
- Up to 13% loss in heating capacity, even at steady airflow
- Temperature stratification in the discharge duct
- Reduced accuracy of zone control and sensor feedback
These issues are especially problematic when working with condensing boilers or heat pump systems, where water temperatures are lower and thermal performance margins are tighter.
Downstream damper placement option
Moving the damper downstream of the coil helps maintain uniform airflow across the heat exchanger. Testing has shown this approach can lead to:
- Improved heat transfer across all damper positions
- Reduced fluid flow requirements, lowering pump energy use
- More consistent discharge air temperatures
- Fewer issues with sensor control logic due to stratified temperatures
This configuration addresses a common but often-overlooked efficiency gap in low-temp reheat design.
Price Industries Vantage cross section showing the downstream damper.
Is this relevant to your next project?
If you’re designing HVAC systems for schools, offices, or healthcare facilities, here are a few questions to consider:
- Are you specifying VAV terminal units to perform using 100–120°F hot water supply conditions?
- Do your system sequences depend on accurate downstream temperature sensing or stable airflow control?
- Is your team trying to reduce pumping energy, system air pressure drop, or improve boiler return temps?
If so, damper placement should be evaluated just like any other critical component.
It’s not a replacement, It’s a design option
Upstream damper configurations still have their place. They’re well-understood, reliable, and appropriate for many conventional hydronic designs.
This isn’t about replacing one standard with another, it’s about aligning the terminal unit design with the performance goals of today’s low-energy systems.
How Havtech Supports the Engineering Process
Our team helps engineers:
- Evaluate VAV unit specifications for part-load and low-temp performance
- Review airflow measurement and control strategies
- Support submittal review, mockups, and performance modeling
- Provide insight into how real-world configurations impact operation and energy goals
Want to Evaluate Your Current Approach?
Our engineers are available to discuss current specs, provide sample data, or walk through test results in more detail.
Overview
Originally built in the 1930s for the U.S. Department of Agriculture’s Cotton Division, the long-vacant Cotton Annex in Washington, D.C. was transformed by Carmel Partners into a modern office-to-apartment building—preserving its character while meeting today’s performance and energy standards through a thoughtful HVAC retrofit for this historic building.
JCM Associates led the HVAC design and coordination for the project, involving Havtech early to ensure the system approach was aligned with the building’s complex retrofit needs.
Challenge
The project required a flexible, energy-efficient HVAC system that preserved leasable space and met strict design and code requirements. Challenges included limited space for equipment and ductwork, aging infrastructure, and the need to comply with D.C.’s Building Energy Performance Standards (BEPS), while maintaining cost efficiency.
Details
| Developer | Carmel Partners |
| Mechanical Design Build Partner | JCM Associates |
| Building Type | Office-to-Residential |
| Square Footage | 510,708 total, (~80,423 repurposed) |
| System Installed | Daikin VRV + Rebel Rooftop Units |
| Completion | 2025 |
Solution
Havtech recommended a hybrid system combining Daikin Emerion VRV units and Rebel rooftop units. The VRV system’s modular layout and small-diameter refrigerant piping allowed for flexible zoning and installation within the building’s existing framework. Daikin Rebel rooftop units delivered high-efficiency air handling in a compact footprint, eliminating the need for extensive structural changes or mechanical rooms. Additionally, native controls simplified BAS integration reducing the need for third-party coordination during commissioning.
“Havtech was instrumental in helping us navigate the unique challenges of retrofitting a historic structure. Their support and system expertise made it easy to meet our performance targets without compromising space or design intent.”
Wesley D. Goodemote, P.E.
Director of Engineering, JCM Associates
Results
Space & Design Efficiency
Space Saving
Compact components minimized ductwork and eliminated large mechanical rooms preserving valuable interior square footage.
Simplified Installation
Modular VRV and Rebel rooftop units fit the building’s structure, avoiding major layout or envelope changes.
Energy & Cost Savings
Low Operating Costs
The all-electric, high-efficiency system significantly reduces energy use and supports BEPS compliance, minimizing long-term utility expenses.
Future-Ready Infrastructure
The design supports electrification goals and positions the building for LEED certification and future upgrades.
Comfort & Performance
Zoned Comfort
Quiet, individually controlled
HVAC systems enhance tenant
satisfaction and comfort.
Simplified Maintenance and BAS Integration
Fewer moving parts and native
controls make maintenance
easier and integrate directly with
building automation system for
long-term ease of operation.
Conclusion
The Cotton Annex project demonstrates how a well-executed HVAC strategy can overcome retrofit challenges and deliver long-term results. The system preserves space, lowers energy and maintenance costs, and enhances tenant comfort while supporting code compliance and future-ready infrastructure.
Planning a retrofit or redevelopment?
Havtech can help you align HVAC design with your goals for efficiency, compliance, and occupant experience.
