Taking control of retrofits
ThermOzone Director Trevor Dann explores the potential benefits of replacing chiller controls.
Developing our well-established ReChill concept, it became apparent that certain projects required just one principal element of the armoury of techniques - controls replacement.
After ~10 years’ service, many chillers become non-supported by the original manufacturers, and controls systems in particular become obsolete long before the chiller equipment itself has expired.
However, invariably modern electronics installed since ~2000 are ‘locked’ to the specific manufacturer. Whereas a closed protocol secures future service business for the manufacturer and prevents unnecessary ‘fiddling’ particularly during warranty, once a manufacturer loses interest the user is left bereft of effective support. Invariably this means a chiller being changed years ahead of its time. This has significant environmental and cost impacts where a chiller is replaced ~10 years early.
Also this leads to all sorts of attempts to keep an older chiller going, but rarely does a maintainer faced with a chiller in this situation consider a complete change of the controls. The mere thought of ripping out all original controls and associated wiring would bring out even an experienced sparky in a rash!
However, controls replacement is a standard feature of every ReChill project. ThermOzone has an increasing portfolio of sites where ‘controls only’ has been the extent of the remedial works. The results are remarkable from a longevity and reliability perspective.
CASE STUDY: Office Suite, Guildford
This building is a suite of serviced office facilities, offering a comfortable working environment for clients using the facilities. This requires reliable air conditioning or results in disgruntled clients.
The air conditioning cooling source for this building has for the past 15 years been provided by two Dunham Bush water chillers situated in an enclosed plant room at the rear of the building. Whereas the chillers were functional as far as the major hardware was concerned, one had suffered failure of the original controls. Thus the clients were faced with a choice of new equipment entirely, or finding a solution to replace the original controls.
Although seemingly daunting, the latter is actually quite straightforward.
The vast majority of chillers are vapour compression type, so from a control perspective essentially a grouping of various compressors, fans, starters, sometimes pumps and ancillary controls such as solenoid valves and refrigeration control valves (expansion valves).
A simple assessment of a chiller allows a list of these various devices to be derived, from which a control strategy and configuration can be determined. Once this is done it is simply a case of assigning a principal controller, for which we use the Magnum controls system.
The base Magnum set-up offers an array of 30 digital and analogue inputs and outputs suitable for most single system chillers, with expansion boards available to expand to 180 i/o points.
Analogue inputs look at a variable data source such as a temperature, pressure or current probe, whereas a digital input is looking at a simple switch signal (on / off).
A group of digital output relays switch the various contactors and other control devices on and off, e.g. compressors, fans, pumps etc.
Analogue outputs allow fine variable control of devices such as compressor and fan Inverters, and accurate electronic expansion valve control.
The base programme of the Magnum provides reliable, accurate chiller control, with many pre-set operating modes available, each of which can be finely tuned to suit the desired operating configuration.
Magnum can control anything from a simple refrigeration system, a multi compressor pack, multi system chillers, inverter screw chillers, and even centrifugal chillers, including Turbocor units.
Magnum also supports alternative logic control for associated fluid flow systems which is useful for plant management of piped or ducted loop systems.
In the case of One Farnham Road deriving the base control mode was straightforward - four hermetic scroll compressor starters operating in two tandem pairs, two condenser fan motors coupled to a single speed control Inverter, and individual system control solenoids.
An array of temperature and pressure sensors are assigned to allow accurate control of the refrigeration systems, with primary control setpoint either chilled water inlet or outlet temperature. Additional sensors provide motor current, ambient temperature, water flow, and power supply monitoring. An emergency stop facility is also provided.
RODEM - Remote Access & Support
Remote access brings an old chiller truly into the 21st Century, providing the ability to not only observe, but fully adjust and reset a chiller from anywhere an internet connection is available. Magnum is fully compatible with RODEM, our unique remote ‘virtual’ access system.
RODEM allows us to continue the ‘set-to-work’ commissioning process after the engineer has left the job site, allowing us to check operation continually throughout the entire first year of service. This establishes a Soft landing, ensuring maximum reliability from the very first start up, and the chiller can be accurately attuned to suit the specific needs of an individual client.
A controls only retrofit will see selective gains. Accurate control of electronic expansion valves can provide gains of 5% alone. Spotting deleterious trends can provide a further 5% or more, seasonal tuning can also contribute 5% savings, as can automated sub-routines such as target adjustment, whereby the chilled water temperature is adjusted to suit the load - warmer in winter, cooler in summer. Cummulative gains over an annual period can exceed 15 -20% by selective attention to the way the control algorithms interact with the specific building’s needs.
New controls are guaranteed for 24 months, and the installation emulates that of a factory produced new chiller, and is also fully compliant with EN 60204-2 ‘Safety of Electrical Machines’.
This means a rugged and reliable installation offered with not only ongoing support, but also training for maintenance providers and on site technicians.
For most projects we now construct the entire new controls onto an enclosure backplate at the factory, then simply replace the original backplate locally at the site. Downtime is reduced to just a few days in most cases for chillers up to two systems. This project saw the chiller back on line after just 3 days at the job site. One further day was spent fine tuning and establishing RODEM remote access.
We have seen nil issues with the controls themselves, indeed they allowed the chiller to operate without trips throughout the exceptional temperatures experienced in July and August (2019).
The controls retrofit itself was a standalone project, however the unit generally was suffering from service neglect so we also thoroughly cleaned the entire chiller as part of the overall works.
To be further reviewed for Carbon Trust re-accreditation, February 2020.
Trevor Dann - ThermOzone Ltd