Is Premature Failure of a Relatively New Chiller Always a Major Issue?

One of our client buildings had an unusual failure in a 7 year old 450 ton conventional, single compressor centrifugal chiller.  The failure was one in which an internal linkage broke, damaging the guide vanes and the compressor.  The failure was such that the compressor needed major repairs or replacement.

Faced with the failure and a fairly urgent need for cooling (mid-rise elevator machine rooms require chilled water year-round), our client had to work quickly to arrive at a timely solution.  Of advantage in this situation was that our client had recognized many years ago the importance of recording and storing operational data in the “cloud” and the benefit of having subject matter expertise available to review and analyze it.  From some 5 years of recorded performance data, Dimax had 5 minute interval data with which to plot the operational load profiles for the chiller during all seasons of the year.  This data provided valuable insight in the face of this failure.

To resolve the need to have cooling back online expediently, our client reviewed the options of repairing the existing compressor, replacing the chiller or replacing the failed compressor.  One potential vendor visited the site and concluded that they could retrofit the existing system with three new variable speed magnetic bearing compressors piped to the existing evaporator and condenser.  Both these latter components had undergone recent maintenance and testing, and were in good shape.

A critical factor in this building was that the chiller room is located in a mechanical penthouse at the roof level, more than 400 feet above grade.  Craning, if required, would be expensive and a significant logistical issue.  This meant that any expedient solution would need to be compatible with using elevators and “brute force” to get the necessary replacement equipment into place.

The three potential solutions which could work without craning were:

  1. Repair the existing 450 ton single compressor
  2. Replace the existing chiller with modular chillers which could be put in place using the building elevators
  3. Replace the existing single compressor with multiple smaller compressors which could be moved to the mechanical room using the elevator

The solution chosen was the third option, which came at a lower cost and provided the quickest delivery of a working system.

Based on experience with the existing chiller, which had difficulty operating stably with the low cooling load in winter, the building had also budgeted to add tower free cooling in the near future.  However, the multiple compressor solution chosen not only provided higher efficiency equipment with better “turn-down”, it came with an “economizer” cycle which works with low temperature cooling tower water to produce chilled water more efficiently than could be done with full mechanical cooling.  This meant that the capital funds that had been set aside for the planned addition of tower free cooling could be used to offset the cost of the new compressors, and the down-time that would have been required for the installation of tower free cooling was eliminated.  Furthermore the economizer set-up with the selected solution would be simpler to operate, which is good for a building with no operational personnel on site.

There were two impressive results from what seemed to be a very unfortunate failure.  The first was that, once the order was placed, cooling was back online and fully operational in 24 days, just in time for the first hot days of the current season.  The second was that, with the higher efficiency equipment and the variable speed drives, energy savings alone would pay the cost of the retrofit in under 7 years.

So, what can be learned from what our customer experienced?

  1. There is a high value in having recorded historical data and subject matter expertise when major failures occur.
  2. It is important to engage with service providers who can think “outside the box” and come up with a sound recommendation which makes sense.
  3. While the failure of a chiller after only 7 years of a potential 20 year life would seem like a very unfortunate situation, the actual outcome points out that sometimes, trying to get the “life expectancy” out of a piece of equipment may not be the best approach to asset renewal. In this case, the replacement reduces ownership cost over the longer term, and the replacement actually increased plant capacity by about 10%.
  4. For a building owner, being in a position to make a decision quickly and having good advisors on the team is a real asset.

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