Smardt Displaying at 28th West Coast EMC Show, June 15-16

Smardt is bringing their high-efficiency chillers to Seattle to show in the upcoming 28th West Coast Energy Management Congress Expo. Come see the industry leading oil-free compressor chillers and chiller controls systems first hand!



Exposition Hours:

Tuesday, June 15, 2010: 10:00 AM to 4:00 PM
Wednesday, June 16, 2010: 10:00 AM to 2:00 PM

Free tickets to the expo are available here.

The show will highlight energy efficiency products and programs and is supported by local utilities, industry organizations and local industry. It should be a very informative and exciting show, and it is conveniently located at the Washington State Convention and Trade Center in downtown Seattle.



See you there!

Ultra-Low Sound Air-Cooled Chillers

Air-cooled chillers provide significant advantages for many facility operators and owners. The elimination of a cooling tower greatly reduces the complexity of the system and significantly eases the maintenance of the system. For smaller facilities without the resources of large institutional owners, this reduced maintenance can be critical.

Therefore it is very common to see air-cooled chillers on smaller facilities such as public schools and small office buildings. However, this suitability does carry with it some costs--Air-cooled chillers are usually significantly less efficient than water-cooled chillers and, now with the advent of super-low sound cooling towers, often much noisier. The noise problem can be very significant with this sort of equipment in that a large proportion of the facilities that utilize this technology are located near or in residential areas.

In an earlier post I discussed how the Smardt air-cooled Turbocor chillers significantly change the balance between water-cooled and air-cooled chillers with respect to efficiency and sound. However, it is worth investigating the sound issue in more depth.

Recently, manufacturers have spent some effort in addressing the sound issue on their air-cooled chillers. This has generally been approached by providing low sound fans and addressing the compressor noise. Two products that are currently being marketed as low-sound chillers approach compressor sound in different ways. One product utilizes screw compressors with a VSD to reduce compressor sound at low loads. Another utilizes scroll compressors with elaborate compressor sound enclosures. This approach yields published sound data which is excellent at all chiller load conditions. Until recently, this chiller has been considered by many engineers to be the quietest air-cooled chiller n the market.

The Smardt chiller, of course, uses the extremely low-sound Turbocor compressor, and variable-speed ultra-low sound fans. It is reasonable to believe that this combination would make for a very favorable comparisons with these other low-sound chiller options.

And this expectation is borne out by the data. Smardt air-cooled chillers compare extremely favorably against the variable speed screw chillers as this graph illustrates:


Two things should be noted: First, the comparison here is between a 177 ton screw and a 200 ton Smardt chiller, and second that even at 100% load, the Smardt chiller is far quieter than the screw at 25% load. The difference is even more significant in the lower octave bands that carry so well over distance.

Comparing the Smardt Chiller to the acoustically treated scroll chiller also yields an extremely favorable comparison:



This comparison of 120 ton chillers shows that while both approaches yield extremely low sound levels overall, the Smardt chiller beats the competitor in 5 of 8 octave bands. And the advantage for the competitor in two of the other bands is slight. It also shows the significant effect of A-weighting sound data. In this graph, the red line represents the published sound data from the manufacturer. Close reading of this data indicates that it is not bare sound power, but A-weighted sound power. This method of reporting sound data takes very significant credits into effect, especially in the lower octave bands:

Octave band center frequency (hz)	Weighting
31.5	-39
63	-26
125	-16
250	-9
500	-3
1k	0
2k	1
4k	1
8k	-1

The dark blue data show the raw, uncorrected sound data for this chiller.

If acoustics are a design consideration for your air-cooled chiller product, Smardt offers a solution that is unmatched in the industry.

Extra: Audio Comparison of compressor noise

85 dBA screw compressor
73 dBA Turbocor compressor

Both measured at 1.0 m away from compressor. Your speaker volume will affect the output, but the comparison should be clear if the volume is not adjusted between clips.

Extra extra:

This link has sound files that illustrate the amplitude of a decibel, to give perspective to the graphs above.

Rethinking Air-Cooled Chillers

Air Cooled Advantages

Air cooled chillers offer many advantages to owners and designers. The first, and perhaps most compelling for many jobs is lower installed cost. Lower installed costs (compared to water cooled chillers) are driven by the following advantages:

• No Cooling Tower, Tower pumps, Tower and Pump Starters
• No equipment room required for the chillers
• Mounted starters

They also are easier to maintain, since the systems are significantly simpler than water-cooled systems:

• No on site Systems Engineer required
• No water treatment or make up water required
• No leaks on the roof
• No cooling tower, condenser pumps, associated starters

Generally, however, these advantages have come with significant trade-offs: Efficiency and Sound performance.

However, the introduction of Variable Speed oil-free air-cooled chillers by Smardt changes the balance.


First off, the Smardt Chiller is efficient. With IPLV's as low as 0.65 kw/ton, these chillers rival water-cooled system when the parasitic loads of the condenser pumps and cooling tower are considered. These chillers gain their efficiencies both from the inherent efficiency of the Turbocor compressor and the elimination of oil return issues that prevent other air-cooled chillers from capitalizing on the reduced head pressures available at low ambients.

This means these chillers use about 60-65% energy of other air-cooled chillers for the same load, and can nearly eliminate the energy benefit typically provided by moving to water-cooled systems. When you consider the cost of water (nearly $15/1000 gallons in Seattle, including sewer charges) this means the yearly cost of operation of these units is unrivaled. And energy conservation rebates are extremely attractive for these chillers.

The other major traditional trade off with using air-cooled equipment is sound. Screw chillers especially are known for their unfavorable sound characteristics. In most municipalities, sound ordinances are driven by occupancy and time of day. The most stringent criteria must be met during evening hours, typically when the units are not at their peak load. However, with constant-speed systems, the compressor is either on or off. This means it is either putting out its full sound or none at all. At full speed, such compressors can often exceed the evening sound criteria--even if they are on only momentarily. And the staging between on and off can be objectionable in its own right, regardless of sound level.

The Smardt chiller minimizes the problems with compressor sound in two ways. First, the variable speed drive allows the compressor to ramp slowly up and down to match the required output, eliminating the objectionable switching between compressors that constant-speed chillers exhibit. And secondly, they are just extremely quiet to begin with. Since no moving mechanical part is in contact with the chiller casing, very little mechanical noise is transmitted. Ninety-ton Turbocor compressors have been tested at 72 dBa at one meter, compared to screw compressors that can be as high as 80 dBa or higher in the same test. Five of these compressors operating together yield a sound level of 75 dBa at 10’.

More Benefits

But efficiency and sound are not the only benefits from using the Turbocor technology on air-cooled chillers. Other, less obvious ones exist.

Turbocor compressors have only one moving part, yielding un-matched reliability.

Reliability is enhanced by the elimination of oil in the refrigerant system. And the frictionless bearing requires almost no maintenance.

Since Turbocor compressors are variable speed driven, they provide an inherent soft-start on the compressor. Instead of kicking the motor up to full speed when power is applied to the system, the VSD slowly ramps the compressor up to the required speed for the load sensed by the system. This reduces stress on the already greatly simplified system to reduce wear and tear on the components.

But this soft start has another, very important advantage over standard air-cooled chiler systems--the use of the VSD eliminates inrush amperage. When an electrical motor is at rest, there is very little inductive resistance to current flow through the windings. As the motor starts to turn, this inductive resistance increases with the increase in RPM. What this means is when power is applied across the line (or even with a reduced voltage starter) to a stopped motor, there is a spike of electrical current far greater in amplitude than the design amp draw of the motor:

(example graph of inrush on a well pump motor)

This temporary increased amp draw heats the motor beyond where it is designed to operate for extended periods. This forces the chiller designer to provided anti-recycle timers to prevent rapid re-starts that could fatally overheat the motor. In practice, this usually means constant speed compressors cannot be started more often than every half-hour or so.

Additionally, this increased amp draw has effects that need to be addressed electrically. This becomes even more significant if the chillers are being served by emergency power. The emergency generators that serve the chiller must be sized to handle the inrush amperage. This can be a very costly addition, especially since the added amperage is only required for the first 30 second of operation or so.

Generators = $$$

Turbocor compressors on the Smardt air-cooled chillers eliminate inrush and provides a soft-start. This both heightens reliability and reduces electrical costs. For jobs where reliability is a primary concern, like data centers, this technology makes a lot of sense. First, it eliminates the need for increased generator sizing, it is an inherently more reliable compressor, and it frees the cooling system from reliance on a water utility service that could be disrupted.

The Dark Side of Chiller oil

Most compressorized systems operate with oil mixed in with the refrigerant. This oil is required for lubrication of the shaft bearing and, in positive displacement compressors like scrolls or screws, it actually provides the seal that is necessary to effect the compression of the refrigerant. The oil is miscible with the refrigerant, and travels with it throughout the system to provide lubrication and compression sealing. That means the oil is everywhere the refrigerant is—Which can lead to several operation problems that need to be addressed in the design and operation of the system.

The first issue is oil transport. The oil travels with the refrigerant whenever the velocity of the refrigerant is high enough to carry the oil with it. This means that the system must be designed to ensure adequate velocities are met at all times. The biggest obstacle to refrigerant flow occurs, however, at the expansion device between the condenser and the evaporator. This is by design a big restriction on refrigerant flow—the greater the restriction, the greater the pressure drop across it and therefore the larger the temperature difference between condenser and evaporator. Its function is similar to that of a flow restrictor in a shower head or an orifice plate in a commercial piping system. Therefore, in order to ensure an adequate flow rate for oil transport between the condenser and evaporator, the pressure between these components must be kept above a minimum. If the pressure difference falls below this minimum, oil starts stacking up in the condenser and the machine will trip out on low oil pressure.

While there are methods that can be used to minimize this problem, such as oil pumps and eductors that siphon the accumulated oil out of the condenser, these are usually only provided on larger tonnage centrifugal machines, and even then there is a practical limit to the operating environment the compressor is designed for. In practice, head pressure control is used where low condensing temperatures are expected, such as fan cycling on air-cooled condensers or bypass lines on water cooled compressors. And even then, oil transport problems are a major cause of chiller downtime, especially in cool climates.

These head-pressure control mechanisms ensure a minimum condensing pressure to assure oil transport—which is good, because this ensures trouble-free operation. But it does this at the cost of energy efficiency.

See, a compressor is very similar to a pump. The total mass flow of refrigerant can be thought of as analogous to the flow rate of the pump and the pressure difference between the evaporator and condenser is analogous to the static head of the pump. In order to reduce energy use on a pump, you can either reduce the flow rate through the pump, or you can reduce the static head. In a chiller system you have the same options, but remember that the refrigerant mass flow rate is what determines the cooling capacity of the chiller. If you want to reduce energy use, but still provide the same cooling capacity, your only option is to reduce condenser pressure. One of the great advantages of using the ambient air as a heat sink is that for over 99% of the year, you have access to air temperatures (wet bulb or dry bulb, depending on the heat rejection of the system) below your design condition. This is why part load ratings on chillers are so much better than peak load ratings.


Head pressure controls, however, artificially limit how low this head pressure can go. Just when you are really getting efficient, the system kicks in a mechanism to keep your system from getting any more efficient! Without the need to maintain oil flow, a compressor can take full advantage of the available head pressure relief and operate extremely efficiently.

The second major issue with oil in your system is that it actually inhibits heat transfer, reducing the overall efficiency of the refrigeration system. In fact, a nominal 3.5% charge of oil in a chiller system equates to about an 8% loss of efficiency from this insulating effect (from ASHRAE 601).


And this only gets worse with time. An ARI study found that this insulating effect increases for the first 5-6 years of operation reducing chiller efficiency by about 20% due to oil fouling of the heat transfer surfaces in the chiller.

These numbers assume a constant oil charge—which is a big assumption. In practice, chiller oil charges often exceed the recommended oil charge by very significant amounts—since a common method of correcting a ‘low oil pressure’ alarm is to add more oil—despite the fact that the usual cause of this alarm is the stacking of refrigerant in the condenser, not any loss of oil in the machine. The same ASHRAE study above sampled many machines in the field and found that the average charge of oil was nearly 13% which equates to a total efficiency loss of 21%!

The last major issue with oil in the compressor is the chance of motor burnout. If a refrigerant system experiences a small leak in a low pressure location, moisture and air can enter the refrigerant system. Enough moist air can react with the refrigerant and oil to form hydrochloric and hydrofluoric acids which then travel through the system to the motor windings and eat away the insulation, eventually causing massive arcing and a catastrophic failure of the compressor motor. This acidic residue will be deposited throughout they system, requiring extensive flushing of the chiller shells before the system can safely be brought back on line. This is not only very expensive, but amounts to a very long downtime in what may be a critical building component.


Developed in Australia in the mid-90’s, the Turbocor™ compressor was born out of a desire to avoid the energy penalty and maintenance headaches associated with oil in the refrigerant circuit of traditional compressorized cooling systems.


These centrifugal compressors utilize a unique magnetic bearing to completely avoid the need for oil in the refrigerant system. These systems require very little maintenance and provide excellent efficiency both initially and many years down the road.

Smardt manufacturers water-cooled and air-cooled chillers exclusively utilizing these innovative compressors. These chillers avoid all of the drawbacks of oil, and eliminate much of the cost of ownership that is commonly associated with chiller systems. Since the bearings do not wear, traditional scheduled stop-major chiller teardowns are unnecessary, and all of the downtime and cost associated with oil (around 50% of the maintenance cost on these systems) are avoided. Smardt chillers provide an owner with excellent efficiency, reliability and economy.