License to Chill - March 2019
Many years ago, a particular OEM used to offer a packaged air-cooled centrifugal chiller. The chiller was a great piece of technology, because the centrifugal compressor in it was able to operate at rather high ambient conditions. In no time, the aircooled centrifugal chillers were everywhere – on standalone buildings and installed as part of large central chilled water plant.
The benefits of air-cooled centrifugal chillers were enormous, as they made it unnecessary to have condenser pumps and cooling towers, not to mention the cost savings through not having to undertake condenser water treatment, plus not having to worry about condenser tube fouling and scaling. The chillers allowed large chilled water plants to be constructed at much less a cost in comparison to a water-cooled plant, while incorporating the use of centrifugal chiller technology.
I, for one, was, therefore, sad when the OEM discounted the air-cooled centrifugal chiller and moved to screw air-cooled chillers. It was the loss of a great technology for all, and I really was left wanting for someone to reintroduce the technology to the Middle East region.
Well, the wait is over – hey presto, we have a new centrifugal air-cooled chiller ! What’s even more exciting is that the new chiller has an oil-less, magnetic-bearing centrifugal compressor. It can operate at up to 58 degrees C ambient conditions, without the need for any adiabatic condenser for pre-cooling. The new technology is, without question, a game changer for any facility.
As many of the readers of my column know, I am a big supporter of oil-less, magnetic-bearing centrifugal compressor technology, as these compressors installed on chillers provide unrivalled energy efficiency and reliability. For many years, I would visit the North American factory of a chiller manufacturer and request air-cooled chillers with oil-less magnetic centrifugal compressor technology, but the answer was always the same: “Not possible with the high-lift considerations of the centrifugal compressor.” Well, as we all know, nothing stays the same, and I am happy to inform that high-lift compressors were developed and are now available for air-cooled chillers.
The twin turbo high-lift compressor is the world’s first oil-free compressor optimised for high-lift applications. The compressor utilises oil-free magneticbearings, a permanent magnet motor and an integrated variable speed drive. The compressor operates with refrigerants R- 134A, R-513A and HOF-1234ze. Each compressor is sized from 82 to 107 tonnes and is small and lightweight and perfect for air-cooled chillers, as multiple compressors can be utilised for many different tonnage applications. The new hi-lift compressor has received numerous awards, including the 2018 AHR Product of the Year and 2018 AHR Innovation Award for Green Buildings.
The new high-lift centrifugal compressors, with two-stage design, allow the compressor to unload up to 20% with AHRI ambient relief, or up to 28% at constant 35 degrees C ambient. This also allows more accurate water-temperature control for process applications at low-load conditions, as well as reduces frequent compressor starts and stops.
The compressors also have built-in economisers for improved performance.
As I stated, from at the beginning, the technology is a game changer ; you can now have oil-less, magnetic-bearing ! TTH/TGH High Lift Compressor – Robust Design ! TTH/TGH High Lift Compressor – Economizer centrifugal technology on air-cooled chillers. The benefits of this open up so many possibilities for installing air-cooled technology and receiving the efficiencies of water-cooled equipment. Let me list all the benefits of installing oil-less magnetic-bearing air-cooled centrifugal chillers versus water-cooled chillers…
- Same Centrifugal Compressor technology as water-cooled chillers
- No cooling towers
- No cooling tower or condensor water utility costs
- No hazardous chemicals and blowdown water being introduced into the sewer and sewage-treatment plants (improves environmental sustainability) as well as no possibility of Legionella, as no cooling tower water mist is created
- No chemical costs for condensor-water-loop treatment (improves environmental sustainability).
- No storage of hazardous chemicals, thus eliminating over 10 OSHA health and safety requirements
- No lack of water issues
- No condenser pumps and piping
- No cooling tower and condensor tube cleaning and expensive associated condensor-water-side high-maintenance costs
- Saves mechanical room space
- Easier to control (no tower bypass, cooling tower VFD and associated tower controls and control logic)
- In addition to all these, the air-cooled centrifugal chiller has solar-assisted condenser fans, which is another energysaving feature.
The first cost of installing an air-cooled centrifugal chiller plant versus the cost of a water-cooled plant would be exponentially less. Now, let’s consider the operational cost. Let’s look at a watercooled chiller versus a chiller with the new oil-less, magnetic-bearing compressor. The power cost of the water-cooled chiller versus the air-cooled chiller would be close. Now, if you add the cost of the cooling tower water, the cost of the cooling tower chemical water treatment, the cost of the power to pump the cooling tower water (condenser pumps), and the cost to operate the cooling tower fans (not to mention the efficiency loss of the water-cooled chiller due to condenser tube fouling by sludge, scale and biological matter, such as biofilm), you will find that the air-cooled centrifugal chiller/plant will be less costly to operate than the chilled-water plant.
What I am stating is that air-cooled centrifugal solutions might now be the right choice in most selections. The aircooled chillers and plants should not be rejected without consideration, and to assume water-cooled plants are less costly to operate than air-cooled plants is just an incorrect assumption, especially now with the development of the high-lift, oil-less, magnetic-bearing centrifugal chillers. First cost, operational cost, water and power cost, chemical cost and maintenance cost must all be taken into consideration, as well as environmental impact and health and safety (blowdown water and Legionella) before an air-cooled or water-cooled plant is selected; and what you will find is the air-cooled option might just be the better option for your plant, whether it is a stand-alone building or a District Cooling plant.
If a facility already has air-cooled chillers, and replacement is an option, the new high-lift centrifugal chiller would be the only way forward. And if you currently have an aircooled chiller, with either screw or reciprocating compressors, it is possible to engineer and design a field-retrofit, whereby a new control system and new oil-less, magneticbearing centrifugal compressors will be installed, which will allow you to enjoy huge energy savings without a chiller-replacement exercise.
This was not possible in the Middle East region before. Readers, the future is here, and it is decidedly air-cooled centrifugal chillers.