Chillers

Published: June 11, 2015 By: McIntosh Perry

In January 2012, changes in legislation banned the use of R11 refrigerant in chillers. The refrigerant of choice is either R123 and R134a, but the catch is R123 will be phased out in 2030. Even though that’s a long way off, building owners and operators should be aware of this date as well as other options.

R123

ChillerR123 was singled out for extended life because it has low ODP (Ozone Depletion Potential) and better GWP (Global Warming Potential) numbers than other HFC’s including R134a. (GWP for R123 is as low as 76 compared to 1320 for the next best alternative). The governing board for LEED accreditation has also recognized the low impact of R123, in that it now gives a point for use in high efficiency centrifugal chillers – similar to R134a.

A definite plus for R123 is that it provides a higher efficiency in converting electrical power to cooling (up to 13.5% extra) which suggests a smaller machine and/or energy savings. Over the past few years several buildings have converted their older R11 based chillers to use R123 by changing the seals and incorporating a full overhaul of the machinery. There should be no problem in maintaining these machines so that they achieve their expected life span and running them without any fear of curtailment due to environmental legislation.

Chiller Room Upgrades

The best course of action for chillers more than 15 years old is replacement. The first step is to contact a consulting engineer to assess the situation and provide a course of action. For those of you planning a chiller replacement, you should also be aware that part of that work will require several upgrades to the chiller from itself to meet the current B52 CSA standard. This includes leak detection and alarms, evacuation exhaust, heating the room, etc.

Chiller Choices

So, what are the choices for chillers? The most common are centrifugal chillers (similar to the R11 based machines), screw chillers and air cooled chillers (maybe with R22 refrigerant). Be aware that air cooled chillers are mounted outside and that there are inherent noise issues with the air flow through the equipment that should be accounted for if you having penthouse dwellers. They are also typically for smaller cooling applications. Screw chillers are particularly useful for buildings with highly variable daily cooling requirements, such as small offices, as they exhibit good high-load and part-load efficiencies. Smaller condominiums and low-rose buildings may also use this screw technology but in sensitive cases the slightly higher pitch noise may be an issue.

For a typical building the centrifugal chiller still appears to be the workhorse of choice, with the screw machine coming in second. Larger chillers may utilize the screw type chiller. In smaller commercial buildings we are still seeing R22 based equipment being installed – but except that to change as the phase out time of 2020 approaches for this refrigerant. Interestingly the suggested replacement for R22 is R410a – which is made of 50% R125, which in itself is made from a feedstock of R123 so that suggests R123 will be around for quite a while.

Variable Speed Drives

With the production of new centrifugal chillers using R123 or R134a there have also been some developments to try to make the machinery more efficient by utilizing a variable frequency drive (VFD) for the compressor motor. Old machines were designed to be most efficient at 100% capacity but in actual fact run most of their lives at 50% – 80% capacity and sometimes even less in the spring and fall where little cooling is actually required. By designing the motor to slow down as dictated by the cooling load requirements a much better efficiency curve is achieved, particularly at the low cooling times – which equates to savings in hydro. Figures suggest that 95% of the C02 emitted that relates to chiller operations is due to the making of the electricity to run them…

If ordering a new chiller you should incorporate this VFD option – but if you are thinking or upgrading your existing chiller compressor motor to a variable speed model, be aware that it is costly to retrofit and pay-back may be a long way away.

Making the Decision

Since there are still many options to review when selecting a replacement chiller it is advisable to get the opinion of your consulting engineer and have specifications drawn up so that you can compare bids in an “apples to apples” fashion. It is also probably a good idea to look at replacing the cooling tower at the same time – and a review of its condition may result in a recommendation to replace or refurbish it. Refurbishing would typically include the wet deck, spray nozzles and changings to a variable speed motor and VFD drive. What tips the scale is often the crane cost. If you are having the expensive ($30,000,000 – $60,000,000) crane it may make sense to use it to also lift off and replace the cooling tower at the same time. Part of the tendering process will also include where to put the crane – if streets can be used, then local municipal approval must be obtained. If the building site lands are to be used then a requirement for shoring the underground parking garage may also need be included in the bid cost.

There are many considerations to be made when undertaking such a project – so don’t forget to call your consulting engineer in the early stages of decision making.

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