Compiled by Benjamin Brits
Not only did the team on this project have to pull a rabbit out of the hat with a 16-working-day turnaround, but it is also said to now be home to the largest VRF air handling unit on the continent.
As a plant replacement project, the original plant located at William Moffett shopping centre in Gqeberha (formerly Port Elizabeth), was estimated at about 1 400kW supplied by two water-cooled chillers in a sort of back-to-back installation in the sense that the chiller plant room was located adjacent to the coil arrangement with very short pipe runs.
When the team from VMG Consultants (VMG) visited the site the first time, it was very clear that the old plant was in a bad way and had experienced trouble for some time with certain components being disassembled and one compressor removed and lying on the plant room floor. From the plant layout and modifications, VMG assumed that compressor short-cycling and re-circulation of cooling tower air, were two of the likely culprits.
The original plant layout included a plant room housing the two water-cooled chillers, a plant room housing the coils and two backward curved centrifugal supply air fans, a plant room housing the filters and a manually set fresh air damper, two cooling towers set in a deep outside plant area constrained by high walls on three sides and interconnecting chilled water and condenser water piping between these elements. The total length of the chilled water piping was not more than about 20m. There was no buffer tank, and this almost certainly was a contributing factor for the degradation of the original plant installation because chillers require a minimum water quantity in order to avoid short cycling. The pipe runs were suspected to be far too short. Chiller-suppliers would advise that this is often a common fault with installations using this type of equipment.
The effect of this would be likened to starting and switching your car engine off continuously where it would obviously not last very long. Without sufficient water in the system there is accelerated wear on the compressors. The compressor will start, it will cool down the minimum amount of water in the system very quickly, and then switch off, repeating continuously.
Providing an appropriate current-day solution
Having been involved for some time in assisting this supermarket chain to develop and upgrade their store specifications, so much has changed from the “old days when we used a calculator, a standard one-page calculation sheet, and a few well used data sheets and tables” according to VMG’s managing member Nigel Pengelly.
With any plant replacement that is considered nowadays, there is never simply a “like-for-like replacement”. From the start, VMG would redo the heat load. In this, VMG has often discovered that older plants are considerably oversized.
Historically with old plants such as this one, the heat load calculations were cautiously concluded at best because energy and water were very cheap – quite the opposite in today’s environment. In those days with the information and technology available, a water-cooled plant was perceived to be more energy efficient, because it uses water to cool itself rather than the air and adding to that was the fact that being in Africa already involves higher average temperatures.
With that said, VMG notes that this could still also be a misconception because being in Africa, energy production and water scarcity are real issues that must be on the table. Having previously made use of water-cooled plants, over the last fifteen years they have moved away from this technology. Even though there are several new technologies, and old and new systems up and running with water cooling, their view is that because water has become such a scarce commodity, to waste it on something like air conditioning contributes to depriving someone, somewhere, access to water as a life preserving resource, and further where responsibility and moral boundaries have come into question.
Carrying on, supermarkets are very different to an office for example. In an office, there are a certain number of people, each requiring 7.5 litres of fresh air per second, so your calculations and setup tends to be quite simple. Supermarkets on the other hand have a continuously changing occupancy. Sometimes there are fewer than ten people shopping and sometimes you may have hundreds of shoppers simultaneously, so always accommodating for maximum occupancy is a complete waste of energy. Accommodating for often high infiltration rates through public entrances and receiving doors need to be considered, as well as the numerous extraction systems and extraction canopies which need to be included too.
New technology accommodates for things like CO₂ sensing, advanced controllers, computer software and loggers to create and maintain optimal conditions. However, old plants and buildings don’t usually have these functions, and it may not be cost-effective to retrofit to existing systems.
The new system and installation
The primary brief of this project was that the landlord essentially wanted to ensure that the whole store including the refrigerated area was air conditioned for as much of the summer as possible. As the supermarket had not had air conditioning for some time, and summer was fast approaching, the landlord was faced with a tough decision whether to repair the existing system as a ‘quick-fix’ and then replace the entire system the following winter, or replace the entire system now in a similar time frame to that which the costly repairs would take.
Additionally, the supermarket chain wanted the requirements of their latest specifications to be adhered to as far as possible. The supermarket chain also wanted the facility to, sometime in the future, control the air conditioning and to use it in some sort of dehumidification process. The subsequent upgraded controls included in the project would allow VMG to easily achieve this and would include off-site monitoring and control. So, the system can be monitored and controlled from anywhere and all data can be recorded and analysed at will.
Generally, with the advancement of technology, the heat load and checks against what is installed within a facility – and further making sure that the new heat load is correct, there is invariably a significantly lower requirement to what was originally installed – and with that, obviously energy savings, capex savings and operational savings. For this project, VMG’s heat load calculation ended with a 960kW system – a big difference from the estimated 1 400kW of the original system. And further, the new system uses about half the energy the original system did, and of course, absolutely no water!
Chillers were not considered for this installation replacement as variable refrigerant flow (VRF) systems provided a far more efficient solution and were immediately available. This equipment also forms part of this supermarket’s standard air-conditioning specification. Using readily available equipment, VMG quickly realised that indeed an entirely new plant could be installed in a slightly longer period than repairing the existing installation. With an assurance that a new plant could be up and running by 22 December 2020, the landlord gave the go-ahead.
The cooling towers that were on piers in the outside plant area of the building were removed. The piers were then adjusted, waterproofed, and used to create a platform to install the new VRF condensing units.
VMG selected the LG brand specifically because all the condensing units already meet coastal conditions – in other words black-fin coated condenser coils and the casings are very high spec – (in fact you can’t buy a lower spec unit for inland applications). This saves having to do any additional corrosion treatment to units and was considered a big plus.
Again, in accordance with the supermarket’s specification, EC plug fans were selected as they offer huge savings, not just in running costs, but also maintenance costs. There are no belts to replace or adjust – besides that, this skill is one that has not survived well into modern times – some technicians just don’t know how to carry out the correct tensioning. Incorrect tensioning can accelerate wearing on bearings and create all sorts of other challenges.
The existing plant had two very large backward curved centrifugal fans (see accommodating photos). The outer shells were kept and essentially the new EC plug fans were mounted onto the casings. This itself generated further savings for the client as fan walls were not required. This also meant no need to modify the ducting because the ducting was already connected to the original fans.
The old coils were also removed and replaced. The LG electronic expansion valves (EEV) and controlling kits were added to the system. According to all participants to this project and having obtained general feedback from various suppliers, it is said that this installation is now the largest single VRF air handling unit in the country, and possibly the continent – sized at 45 cubic meters per second or 960kW.
The existing plant at this site ultimately required substantial repairs (a few hundred thousand Rands in reality) and so the recommendation of replacement was a better end result. Had repairs been undertaken, it would have been a case of throwing good money after bad in VMG’s view.
From the quoting phase already, everyone was under pressure and was required to work under short timelines. Part of the process was getting contractor quotes from local companies; however local suppliers could not be utilised as their pricing was substantially more than quotes from companies based in Gauteng. The contracting was awarded to Elmecair for this reason and because VMG had worked with the team on a prior project. When the green light was given, teams would also need to be on site the very next day.
The challenge then continued immediately with the requirement of a 16 working day deadline to be ready for the late December 2020 festive season shoppers. The deadline included to strip out everything, install the new plant, and get everything up and running within that time. The completion of the plant in terms of painting and aesthetic was only completed later in February this year (2021), however the deadline was met with everything complete from a functional point of view. The extreme timeline also meant that a chiller-solution was already excluded as generally it can take up to 15 weeks to get units to site, whereas the VRF units could just be ordered and delivered almost immediately.
What ensued as Pengelly described it, was an “extremely well-orchestrated delivery” that was fantastic to witness while everyone took the challenge very seriously knowing the stakes were very high and not wanting to fail. At times, visiting the site you would see so much happening at the same time and the teams on this project really deserve recognition for what they achieved as the client was well impressed with the delivery being met as well as the quality of work delivered.
Frikkie Kleyn, director at Elmecair noted that they have done several of these types of plant replacements but each one is unique. This one however was marked as the largest of its kind completed to-date. With projects like these, all hands are required and himself and his team, he says, worked hard on-site to complete all the tasks which included building work, manufacturing, installation of the LG MultiV condensing units, piping, and commissioning with LG.
Douglas Scott, mechanical engineer at HCM Contractors adds that “HCM and Elmec have been collaborating on a number of plant room builds and we have developed “a successful formula” that seems to work well. “Before the rooftop concept became popular, the plant room method was quite prevalent for large scale HVAC systems. It’s not really practical to replace these plant rooms after the fact, but they do require service and updating,” says Scott.
HCM Contractors was tasked with the implementation of the AHU equipment into the existing plant room. Due to the age of the previous installation, this required some special planning and site fabrication to integrate the newest air-conditioning technologies into the traditional plant room layout. This included implementing HCM’s now “signature plug fan in-barrel solution” to make use of EBM’s range of EC plug fans. HCM Contractors was also involved in the PLC integration, control, and commissioning of the plant room in collaboration with LG and Elmecair.
The quick turnaround required on this project offered many challenges to be overcome according to Scott. As with any successful endeavour, hours of careful planning and coordination were involved. Keeping on top of suppliers to make sure delivery times were met, components such as switchgear panels and fan adaptor hardware were fabricated up in Johannesburg and then shipped down to PE.
“The deadline on this project was no small task and loads of planning was required, as Douglas mentioned, to complete partial work that in the end, would tie up together and complete the system. The LG equipment arrived on site with the DX coils only arriving two days after. This left the team with only six days to install, pressure test and evacuate the system accordingly for LG to commission by the deadline. LG extended their full co-operation in quickly delivering the equipment on site and their field engineers were always beside the team to ensure that the quality of installation is at par with their standards. It was only possible with the co-operation between all parties to complete this project in the designated time,” says Kleyn.
Scott adds, “A special mention goes out to the dedicated site-work teams who went over and above to complete the installation, as they inevitably are the ones who need to pick up all of the slack. Together, the team overcame each one of the challenges and more to meet the deadlines.”
As the quality of the work was highly praised, Kleyn says, “My father has taught me so much in life and about this industry but one important thing I will never forget is that every job is a self-portrait of the people that do the work. We have so much passion for the industry, we really enjoy what we do and with great engineers like VMG Consulting and partners like LG and HCM how can you not autograph your work with excellence. There is a well-known saying: You’re only as good as your last job, and if you can put a smile on your client’s face and make them feel satisfied, what more motivation does one need?”
Scott adds that quality starts on day one, “HCM endeavours to keep each one of our staff involved in projects from the beginning. This way the staff feel like they ‘own’ the project and this brings a newfound culture of respect. Respect for our team and staff ultimately leads to respect for our customers and therefore quality workmanship. This philosophy allows the quality we ‘autograph’ as Frikkie has mentioned to stand the test of time, no matter what the application.”
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VRF condensing units and EEV