Take care when reviewing technical datasheets and brochures. Cooling capacities are often stated at a nominal condition. In North America, nominal conditions are considered as 45°F leaving water temperature, 55°F inlet water temperature and 95°F Ambient temperature. Some companies, particularly those targeting the European market, may display the cooling capacities at a very different set of conditions. In Europe, nominal conditions are defined as 15°C (59°F) leaving water temperature, 20°C (68°F) inlet water temperature and 25°C (77°F) ambient temperature. So, what’s the difference? Consider that a 10.8 kW chiller rated at 59/68/77 conditions, would perform at only 7.9 kW when rated at 45/55/95 conditions. That’s approximately a 25% difference!
As ambient temperature increases, the cooling capacity decreases. Referencing the example above, changing from 68°F to 95°F ambient results in a 15% derating of the cooling capacity. If the cooling capacity were calculated at a higher ambient temperature of 113°F, there would be an additional 10% derating. Inversely, when ambient temperatures are lower, the conditions at the refrigeration condenser are more favorable. This allows for reduced head pressure and increased efficiency in the refrigeration circuit, thereby increasing the available cooling capacity.
It is also important to note that the ambient temperature is not necessarily referring to the outdoor temperature. It is possible to have an 80°F outdoor air temperature, but a higher indoor air temperature. Taking this to an even more localized position, it is possible to have an average indoor air temperature that is within specification but a condition at the inlet of the condenser coil sufficient to cause a fault. This is especially true if the hot exhaust air from the chiller is re-circulated.
The desired water supply temperature also affects the cooling capacity of the chiller. As the water temperature increases, the cooling capacity will also increase. That means if a unit is rated 10 tons at 45/55/95 conditions, and the desired water temperature for the application is 40°F, the 10 ton unit will now only have 90% of the original rated capacity. This also works to a limited extent in the opposite direction. If a 10 ton unit is operated at 70°F water outlet instead of 45°F, the capacity increases by 20%.
Outdoor installations with low ambient conditions require the use of glycol for its capability to depress the freezing point of the coolant. Many industrial glycols also include a blend of corrosion and/or biological inhibitors, which make these solutions popular for indoor applications. What many people don’t realize is that the cooling capacity of the chiller is directly affected by the use of a glycol based coolant. Due to glycol having a lower specific heat than water, a water/glycol solution is not as effective at heat transfer as plain water. While the negative effect of glycol is only about 1% capacity derating per 10% glycol solution, it is still important to factor in when sizing a chiller.
While you won’t find a chiller installed atop Mount Everest, it is not uncommon to find a chiller installed in Denver, Colorado or Toluca, Mexico. In the aptly named Mile High City, a chiller operating at 45/55/95 conditions will be working at roughly 17% lower capacity than if it were operating at the same 45/55/95 conditions at sea level. Even higher in altitude is Toluca, Mexico. The city is just shy of 9,000 ft above sea level. At such a condition, a chiller would perform at only 72% of its nominal capacity.
Parker’s Hyperchill process water chillers, offer a variety of easily configurable options for all environments.
Parker Hyperchill and Hyperchill Plus chillers deliver safe and reliable operation under varied working conditions like those typically found in the brewery and distillation industry, helping owners and operators maintain the integrity of the final product and reduce cost of ownership.
Design features on the Parker product can deliver significant benefits to the end-users in industrial applications.
Key features and benefits include:
For help in sizing a chiller to fit your specific application needs, please contact Parker’s highly knowledgeable engineers at FAFquotes@parker.com.
This post was contributed by Garrett Rusin, chiller product manager, and Jennifer Fiorello, compressed air and gas treatment technology blog team member, Parker Industrial Filtration and Gas Generation Division.