Economizers are designed to improve HVAC efficiency by mixing outside air with return air—reducing compressor use whenever outdoor conditions allow. But the performance of any economizer depends heavily on the integrity of its dampers. When dampers leak, energy savings drop, comfort issues rise, and systems may fail to meet code. This is where Ultra Low Leak Economizers come in.
Why “Low Leak” Matters
Economizer dampers are engineered to keep two air streams—outside air and return air—separate when required. When dampers leak:
- Unwanted outdoor air enters during extreme temperatures
- Pre-conditioned indoor air is lost
- Free Cooling becomes less effective
- Humidity and temperature control are compromised
- Energy costs increase
This is especially critical during unoccupied hours. For example, when outside temperatures drop near zero, even small leakage through a damper can pull in enough frigid air to tax the HVAC system.
The Role of Title 24 and ASHRAE 90.1
MicroMetl’s Ultra Low Leak dampers are engineered to meet the stringent leakage limits outlined in:
- ASHRAE 90.1
- California Title 24 (Sections 120.2 and 140.4)
Title 24 breaks requirements into three categories:
Mandatory Requirements
These must be included on every project.
For economizers, this includes Fault Detection and Diagnostics (FDD), which is achieved through advanced controllers such as the Honeywell W7220 JADE.
Prescriptive Requirements
These outline specific performance criteria including:
- Maximum 10 CFM of leakage per square foot at 1” w.c.
- A 60,000-cycle life test
- Minimum 5-year warranty
Ultra Low Leak economizers meet these prescriptive requirements.
Performance Method (Alternative Path)
Instead of completing each prescriptive item, the performance approach allows a project to show overall energy compliance using approved modeling software.
If the energy budget meets Title 24 performance targets, some prescriptive items can be bypassed.
However, meeting compliance is significantly simpler when the economizer meets both mandatory and prescriptive requirements out of the box.
Return Air Leakage Is Often Overlooked
Most installers focus on the outside air damper, but leakage through the return damper is just as costly. During Free Cooling, return air that leaks into the outside-air path raises the mixed-air temperature, reducing the efficiency of free cooling and increasing compressor run time.
A high-quality return damper is critical to maintain economizer performance and predictability.
Mixing Boxes Count Too
Economizers are commonly built into RTUs, but mixing boxes—which are installed externally and connected via ductwork—are also subject to leakage standards. MicroMetl offers Ultra Low Leak damper options for specific mixing box models to maintain compliance across the system.
The Real Benefit: Energy Savings and ROI
An Ultra Low Leak Economizer isn’t just a compliance item—it ensures your economizer delivers its intended return on investment by:
- Reducing unwanted air infiltration
- Keeping mechanical cooling off when outdoor conditions allow
- Protecting against overcooling/humidity issues during off-hours
- Maintaining performance over the life of the unit
When paired with an intelligent economizer controller and demand ventilation capability, Ultra Low Leak systems maximize free cooling and minimize unnecessary heating and cooling loads.
