Farmers Co-Op

In the 53,000 square foot Main Office are two HVAC chilled water systems:

#1 includes a 90-ton Carrier air-cooled chiller with a chilled water pump (7.5HP), three constant volume air handlers (7.5HP, 5HP, 15HP), and an accompanying return fan (1.5HP).

#2 includes a 60-ton air-cooled chiller with a constant GPM chilled water pump (5HP) and one constant volume air handler (25HP).

We installed Eaton variable speed drives (VFDs) on all the above designated items, and an Energy Control System. A central controller resides wirelessly on the customer’s internet router, enabling remote access and communication with the VFDs via a Modbus network.

VFDs, when added to constant volume air handling fans, create a hybrid variable volume air handler system. Fan VFDs operate at full speed when the outside air temperature is at or near summertime design conditions. The speed is reduced via an algorithm as the outside air temperature reduces throughout the year. This saves energy and improves dehumidification. 



The Energy Control System includes an Unoccupied Off status on a daily and weekend schedule. During Unoccupied Off, air handlers are off, but start hourly to create air flow to monitor room temp, and change to Unoccupied On status if the room temperature rises above 80 or below 60. AHU’s run at 50% speed during this condition. 

CHWP-1,2: These pumps reduce speed based on chilled water supply and return water temperature differential.

Sensor inputs:  Supply Water Temperature, Return Water Temperature.

AHU-1,2,3,4: Air Handlers reduce speed as outside air temperature falls.

Sensor Inputs: Outside Air Temperature (provided by an API from a weather website and updated every 3 minutes), Room Air Temperature.

RF-4:    Return fan associated with AHU-4

Return fan to track AHU-4 at the same speed output less 5%

The chart below depicts how the required power is decreased dramatically as the motor speed is reduced, resulting in significant savings.

For example, when the Motor Speed is reduced to 75%, the necessary power decreases to 42%, resulting in a 58% energy savings.

March 2017 through March 2018

Cost to Farmers Co-Op   $45,000

ROI   72.3 %

Simple Payback   17 Months

There are 8,300 out of 8,760 hours per year below 90 F degrees.

The system is saving energy 95% of the year.

HVAC Optimization kWh Usage and Savings (August 2018 – May 2020)