By Robert “Tripp” Loflin – Chiller Applications Engineer, Daikin Applied
Businesses are increasingly adopting new technologies to reduce environmental footprints and cut costs. HVAC systems are no exception: Daikin Applied’s product and sales teams constantly receive inquiries about which systems do the best job in making heating and cooling more efficient and cost-effective. As we head into the late summer months, and building and facilities managers are turning down temperatures to keep tenants comfortable, what better time to share findings from a recent study my team of engineers and I conducted on an HVAC process known as “free cooling?”
Free cooling systems allow a building load to bypass mechanical cooling and exchange its heat with lower temperature outdoor air. Based on that description alone, it sounds like a promising option for cutting cooling costs. We conducted a detailed simulation to determine if free cooling is as efficient as it sounds, and found that in some cases it can actually cost companies more money without reducing energy consumption.
In our study, we implemented a number of variables to get the most exhaustive results:
- Building load: we evaluated a building environment that represents a light internal load (hospital) and one representative of a high internal load (data center)
- Weather: we factored in temperature data from climates and regions across the U.S. applicable to each building load
- Integrated vs. stand alone: we also looked at two popular approaches to free cooling. Integrated free cooling, which leverages a water coil directly mounted on an air-cooled chiller; and a standalone option, which involves a dry cooler that is separately located from the system’s air-cooled chiller
Findings indicate that each variable above can play an important role in whether a building or campus will realize actual environmental and/or cost-saving benefits from free cooling. Here is why these three variables matter so much:
- If not in free cooling mode, an integrated fluid coil causes air flow restriction and slows chiller performance, potentially resulting in a 10-15% reduction in chiller efficiency. The research shows that integrated free cooling is only sensible when the wintertime building load is large enough, and the climate cold enough, to permit significant savings that will offset the chiller performance penalty.
- In climates where the air is cold enough, and in environments where the number of wintertime run hours is great enough, both integrated coils and separate dry coolers can provide energy savings.
- In most cases, energy savings with standalone dry coolers is greater due to the effects on summertime chiller performance.
If you’re interested in walking through Daikin’s free cooling simulation step-by-step and understanding how we arrived at our conclusion, you can find exhaustive details – charts, graphs, figures and all – here in this article I wrote for FacilitiesNet.com: http://www.facilitiesnet.com/buildingautomation/contributed/--37475