On October 11 of this year, I had the privilege of being on two panels at the DC Dialogue conference, in Saudi Arabia. One of them was a discussion – debate, actually – probing the merits of chilled water plants and air-cooled plants. I was the only panellist siding air-cooled technology. Now having said that, I am still, and will remain, a proponent of water-cooled chilled water plants. I will add that many considerations have been overlooked, as of recently, regarding the implementation of new technology air-cooled chillers, especially in the Gulf region, where at one point in time, air-cooled technology dominated the landscape. I would say that over the last two decades, water-cooled technology has made enormous inroads, especially in the District Cooling industry.

Without question, water is a precious and expensive commodity in the Gulf region. This fact cannot be overlooked; however, the industry shifted towards water-cooled technology due to chillers operating more efficiently when water is cooled. Over time, we have been witness to mandates and recommendations in the Gulf for District Cooling Plants (DCPs) with water-cooled chillers to operate on Treated Sewerage Effluent (TSE). Now, although this water comes at a much lower “perceived” cost, it does come with many drawbacks and additional costs. In my next column, I will cover the many additional costs and measures required when using TSE; for now, in this column, I would like to focus on the many benefits of the new technology air-cooled chillers available for us today in the Gulf region versus chilled water plants, using either potable water or TSE.

Dan Mizesko

The first aspect that must be understood is that in this region, most chilled water DCPs operate over 0.75 kW per ton. The vast majority is in the range between 0.85 and 1.0 kW per ton. You see, the thing is when you read all these claims relating to efficiency, no one informs you what their definition of “Chilled Water Plant” is. Is it just about the chillers, condenser water pumps, primary chilled water pumps, secondary chilled water pumps, cooling towers, condenser water makeup pumps and the RO/plant to pre-treat the condenser water? Are these the only pieces of equipment required to generate and deliver the chilled water to end users? Or, is it all of the above, plus indoor lighting, exterior lighting, elevators, office equipment, plug loads, domestic water, and everything and anything that consumes water and power? Oh, and one last thought – it seems the industry has forgotten to include the cost of water when reporting how efficiently the plant operates.

I did not want to get off on a different tangent; however, what is needed is a reporting system that reports how much it takes a plant to produce a Ton/Hr of cooling. That would be the real reporting standard to report how “efficiently” a plant operates. That would include all costs the plant incurs, including utility costs – the cost of total plant electricity and water costs. That total cost would be applied to the total ton-hour production and that would provide a true plant efficiency. That would allow a fair and honest comparison of a DCP’s efficiency. It would also help the end users to understand which DC companies are truly most efficient versus those that just claim they are.

Okay, having established the fact that there does not exist a fair comparison of a DCP’s efficiency, I am going to try to explain why the new air-cooled chiller technology makes a great case for utilisation, especially in the Gulf region, where we can agree water is scarce and very expensive to produce, as it is mostly generated through desalination.

I have been saying for years I am a big supporter of oil-less magnetic bearings centrifugal compressor technology, as these compressors installed on chillers provide unrivalled energy efficiency and reliability. Still to this day, I have not seen many, or any DCPs, with this technology, which in my view is a huge missed opportunity for the huge efficiency gains this technology provides. As I wrote way back in 2019, this technology is also available in air-cooled chillers made for the climate of this region.

The Twin Turbo High Lift Compressor is the world’s first oil-free compressor optimised for high-lift applications. The compressor uses oil-free magnetic bearings, a permanent magnet motor and an integrated variable-speed drive. The compressor operates with refrigerants R-134A, R513A and HFO1234ze. Each compressor is sized from 82 to 107 tons, is small and lightweight and is perfect for air-cooled chillers, as multiple compressors can be used 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 compressor, with a two-stage design, allows the compressor to unload to 20% with AHRI ambient relief or 28% at a constant 95F/35C ambient. This also allows more accurate water temperature control for process applications at low-load conditions as well as reduces frequent compressor start/stops.

The compressor also has an in-built economiser, which improves performance by sending the liquid refrigerant to the evaporator and the refrigerant gas the intermediate stage of compression. The benefits of having the economiser include an increase in capacity (TR) and an improvement in efficiency.

Broadly speaking, the compressor opens up so many possibilities for installing air-cooled technology and receiving the efficiencies of water-cooled equipment. In other words, there are better efficiencies to be had than the vast majority of water-cooled chillers installed throughout the Gulf.

During the DC Dialogue conference, I had a selection of two air-cooled chillers engineered for the OEM; both were selected at 44 degrees C condenser air temperatures. One chiller was of 200 TR capacity, and the other was of 400 TR capacity. Both had average design efficiencies of below 0.567 kW per ton. The figure is less than most water-cooled chillers in the region. Let me list all the benefits of installing oil-less, magnetic-bearing air-cooled centrifugal chillers versus water-cooled ones…

• Same centrifugal compressor technology as water-cooled chillers
• No cooling towers
• No cooling tower or condenser water utility costs
• No condenser water piping network
• No condenser water storage tanks
• No condenser water make-up pumps and piping network
• No blowdown piping and network
• No condenser water filtration system
• No water condenser water treatment equipment
• No hazardous chemicals and blowdown water being introduced into the sewer and sewage treatment plants, which improves environmental sustainability
• No possibility of Legionella bacteria, which instigates Legionnaires’ Disease, as there is no cooling tower water mist being created
• No chemical costs for condenser water loop treatment, which improves environmental sustainability
• No storage of hazardous chemicals, which factors out over 10 OSHA health and safety requirements
• No concerns or uncertainties involving the availability of water
• No cooling tower and condenser tube cleaning and expensive associated condenser water side high maintenance costs
• Plenty of potential for saving mechanical room space
• Easier to control – no tower bypass, cooling tower VFD, and associated tower controls and control logic

In addition to the above, the air-cooled centrifugal chiller has solar-assisted condenser fans, which is another energy savings 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 water-cooled 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 biologicals, 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 suggesting is that air-cooled centrifugal solutions might be the right choice in most selections. Indeed, air-cooled chillers and plants should not be rejected without consideration; it would be incorrect to assume that water-cooled plants are less costly to operate when compared to air-cooled plants, 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 the 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 that the air-cooled option might just be the better option for your plant, whether a stand-alone building or a District Cooling plant. In this region, this option should, without question, be part of the conversation!