published by: Jake Yu, HVAC Applications Engineer


While free cooling with direct outside air is extremely efficient for cooling remote cell sites and small equipment rooms, care must be taken in locations where air contamination is an issue. Due to the risk of clogged filters causing diminished cooling capacity and high temp alarms, free cooling is often entirely disabled for these locations. On an average site with 10kW load, a potential saving on the order of $2,000/yr/site is lost when relying solely on compressors for cooling. This issue can be resolved by setting up Intelligent Free Cooling (IFC), a 2 layer approach to maximize energy saving while protecting the building from air contaminates:


1.  Air Filter Protection Device
This AIRSYS patented device is field installed and communicates airborne contaminate density to the AIRSYS Lead/Lag controller. The controller immediately shuts the outdoor air damper when the contaminate density exceeds the predefined threshold.


2.  Air Pressure Switch
The air pressure switch is standard on all AIRSYS units and allows the user to set maximum primary air filter dirtiness. If this threshold is exceeded, Free Cooling (FC) is disabled until the filters are replaced. Even in the worst case scenario, mechanical cooling capacity will be maintained.

Benefits of Intelligent Free Cooling (IFC)

  • Compared to relying solely on compressors for cooling, enabling IFC can easily save $1,000-$2,000/yr for each medium sized (10kW) site. The ROI is less than 6 months from utility cost savings alone.
  • Depending on the climate, IFC can offset compressor run time and turn-ons by 40-90% throughout the year. This eases the wear on the compressor and related components such as switches, contactors, and condenser fan motors. This significantly extends system life expectancy and reduces maintenance cost.
  • Having another form of cooling provides a safety layer in temperature control of remote sites. IFC can offset the entire heat load during colder months and nights while providing emergency ventilation during the hotter times.


Reasons to Deploy


Efficiency: For locations where air contaminates quickly clog the air filters, FC with no protection will initially yield better energy efficiency. However, as the filters clog, the savings quickly diminishes.  IFC provides better long-term HVAC system efficiency.


Filter Life: The Air Pressure Differential Switch provides a adjustable limit on how dirty the air filter can get before the system automatically disables FC.  This helps ensure normal cooling capacity can be maintained under all circumstances.  IFC enhances this standard configuration of the AIRSYS HVAC systems by extending air filter life.

 

Return on Investment


The ROI analysis below is based on energy savings alone. Higher utility costs and indoor setpoints will yield better results. Capital cost estimates include material costs and 3 hours of labor for installation and testing.

 

10 kW Heat Load

 

Baseline, FC Off Due to Environment

IFC, Standard Sensitivity

IFC, Max Sensitivity

Annual Utility Cost

$2300

$600

$700

Annual Utility Saving

Baseline

$1700

$1600

Capital Cost

Baseline

$600

$600

ROI (years)

Baseline

0.35

0.38

 

3 kW Heat Load

 

Baseline, FC Off Due to Environment

IFC, Standard Sensitivity

IFC, Max Sensitivity

Annual Utility Cost

$700

$200

$250

Annual Utility Saving

Baseline

$500

$450

Capital Cost

Baseline

$600

$600

ROI (years)

Baseline

1.20

1.33

Note: Weather data for Cleveland, OH is used along with $0.10/kWh utility cost and 79°F indoor temperature setpoint.

Please contact us at ASNSupport@air-sys.com for any questions regarding install, configuration, and testing of Intelligent Free Cooling.