Economizers use cool outdoor air to cool the indoor space of a building. The system consists of dampers and actuators that draw cool outdoor air into the building’s HVAC system.
When the outdoor air temperature is lower than the temperature setpoint indoors, the economizer dampers open to bring in more outdoor air. This cool air passes through the HVAC system and circulates throughout the building, reducing the need for mechanical cooling. The economizer controller monitors temperature and humidity sensors both indoors and outdoors.
The controller modulates the damper position to maintain indoor thermal comfort based on the differential between indoor and outdoor conditions. The economizer can provide 100% of needed cooling on mild days. On hotter days, it provides partial cooling, and the HVAC system’s mechanical cooling handles the rest of the load. This dual operation significantly reduces energy consumption compared to relying solely on mechanical cooling.
Economizer Components
An economizer consists of several key components:
Actuators control the damper position based on signals from the controller.
The controller processes sensor data and sends signals to the actuators to modulate the damper position. It includes control logic to optimize operations.
Motorized dampers mounted in the outside air intake allow outdoor air into the system. Dampers control airflow direction and volumewithin a duct system to maintain a balanced HVAC system.
Intake filters clean the outside air of particulates before circulating it indoors.
Relief dampers exhaust indoor air to balance the influx of outdoor air.
Temperature and humidity sensors monitor conditions indoors and outdoors.
Proper calibration and maintenance of dampers, actuators, and control sensors are critical to economizer performance and energy savings.
Economizer Types
There are two main types of economizers used in HVAC systems:
Air-side economizers bring in cool outdoor air to cool the building directly. This air passes through the HVAC system rather than recirculating indoor air. Air-side units are the most common type.
Water-side economizers cool a building’s chilled water loop by circulating it through a cooling tower or fluid cooler. The outdoor air cools the water, which then circulates throughout the building to absorb heat through cooling coils. Water-side units take up more space but can use “free cooling” at lower outdoor temperatures compared to air-side types.
Applications
HVAC economizers are well-suited to large commercial buildings with sizable cooling demands. Depending on climate and other factors, they can reduce annual cooling energy usage substantially. The most common economizer applications are office buildings, schools, retail stores, data centers, healthcare facilities, and commercial buildings.
Any HVAC system that needs to condition large volumes of air is a good candidate for an economizer. Economizers commonly serve single-zone and multi-zone systems up to 10,000 tons in capacity.
In hot and humid climates, outdoor air often lacks sufficient cooling capacity for economizers. However, data centers located in hot climates can still benefit due to their high internal heat loads.
Energy Savings
By harnessing cool outdoor air, economizers can reduce HVAC energy consumption by 30% to 60% annually. The specific savings depend on several factors:
Large commercial buildings have greater internal heat loads, increasing the need for cooling.
Temperate and dry regions with wide temperature swings allow for wider use of economizers — applications are limited in hot, humid areas.
Larger air handlers generally serve more extensive facilities with higher cooling loads. Economizer savings scale up accordingly.
Wider differentials between indoor and outdoor conditions allow greater use of “free cooling” and higher savings.
Facilities with high occupancy and extended operating hours have greater energy demands. Economizers reduce consumption more in these buildings.
In addition to energy savings, economizers bring ventilation and indoor air quality benefits. Fresh outdoor air dilutes indoor pollutants and replenishes oxygen.
Maintenance
To sustain energy efficiency and proper operation, economizers require periodic preventative maintenance. Key tasks include inspecting dampers and linkages for proper movement and sealing and replacing damaged gaskets, bushings, and bearings. Actuator movement and response to control signals should be tested, and malfunctioning actuators must be replaced. The technician should clean outdoor air intake screens and replace intake filters as needed.
Sensor accuracy should be verified by comparing readings to a calibrated reference, and inaccurate sensors should be replaced. Control sequences must be checked by simulating parameter changes, and controllers may require adjustment.
Loose hardware needs to be tightened, relief dampers must be confirmed open as outdoor air dampers modulate open, and linkages require periodic adjustment. Proper economizer maintenance keeps the system operating efficiently, preventing costly repairs.
Economizers should be checked by a qualified technician at least annually. Neglecting maintenance checks can lead to economizer problems such as stuck dampers, inaccurate sensor readings, and unbalanced airflow, which reduce energy efficiency.
So, Are Economizers in HVAC Systems Worth It?
Installing an economizer is well worth the investment for most large commercial facilities. The energy savings quickly pay back the equipment cost and continue providing benefits year after year. Properly applied economizers also improve air quality by increasing ventilation to enhance building occupants’ health, comfort, and productivity.
Economizers do require regular maintenance and knowledgeable operation to realize their full potential. Their performance and control settings must be monitored for optimal efficiency. For small residential and light commercial systems, the cost of an economizer is more complicated to justify. The energy savings may not offset the initial expense in a reasonable timeframe.
In summary, economizers provide excellent efficiency gains for large HVAC equipment serving sizable facilities like office towers, hospitals, schools, and municipal buildings. Their value comes from significant cooling energy savings that continue throughout the building’s lifetime.
FAQs About Economizers
Can I install an economizer on my home's HVAC system?
Most residential HVAC equipment does not support adding an economizer. Residential units lack the physical space and control integration needed. The energy savings also rarely offset the retrofit cost.
How often does an economizer need maintenance?
Economizers should be inspected at least quarterly. Sensor calibration and functional testing should be performed annually. Critical components like dampers may need repairs or replacement every five to seven years.
What are the disadvantages of using an economizer?
Potential economizer drawbacks include a higher outdoor air intake dragging in dust and pollen, possible added noise from intake fans and dampers, and the need for regular maintenance. However, these issues are usually minor compared to the energy savings.
Can an old HVAC system be retrofitted with an economizer?
It’s often possible to retrofit an existing air handler or rooftop unit with an economizer. An assessment of needed structural and ductwork modifications is needed.
