What is Free Cooling?
Free cooling can be defined as using ambient cooling where mechanical
cooling is being used. Ambient
cooling (Evaporative Cooling Towers, Evaporative Fluid Coolers, Dry Fluid
Coolers) can be used to replace mechanical cooling (Chillers) giving you
“Free” cooling because you are using the outdoor ambient air to
provide low cost cooling.
Cooling reduce my operating
Ambient cooling can use as little as 10% of the energy required to operate
mechanical cooling. The key is identifying the operating temperature of the
process and the coolant temperature required to maintain the process.
What is the payback?
There are many factors that determine the payback in applying a “Free
Cooling” system. The costs can vary with each application based on the
period free cooling can be applied, the local energy costs, and the cost to
adapt the current system to free cooling.
What is the limitation?
The limitation for free cooling is based on the required cooling water
temperature required and the geographical location of the facility. The
lower the cooling water temperature required, the smaller the period of time
available to take advantage of ambient cooling.
The following are some
indicators of what your increased capacity based on these factors
This chart demonstrates that as the temperature approach
increases (the difference between leaving water temperature
and ambient wet bulb temperature), the potential cooling
capacity increases. For example, a
Cooling Tower that has a temperature approach of 27ºF (58ºF
wet bulb) would have double the cooling capacity of the same
cooling tower at 7ºF approach (78ºF wet bulb). That is why,
given the same cooling water temperature, the cooling tower
becomes more efficient in cooler weather.
This chart demonstrates that as you increase the
Cooling Tower water temperature range, the cooling tower
becomes more efficient. Other benefits in increase range is
lower water flow, which would decrease the pump HP required
resulting in more energy savings.
This pump curve is important when determining free cooling
opportunity. If the approach is maintained the same (leaving
water temperature vs wet bulb temperature), the
Cooling Tower efficiency reduces as you reduce your leaving
water temperature when the outdoor wet bulb temperature
decreases. For example, operating your Cooling Tower at 60ºF
leaving water temperature when the ambient wet bulb
temperature is 53ºF, will result in having your Cooling
Tower provide only 2/3 of the cooling capacity at 85ºF
leaving water temperature at 78ºF wet bulb. You would have
to add 50% more cooling capacity to your Cooling Tower in
order to provide the same cooling at the lower temperature.