Private healthcare-group’s corporate office HVAC gets another life

By Riekert Pretorius, member at Coldfact Projects and Carl Coetzee, director at Lombard Consulting Engineers

This client required a new system that was reliable, energy efficient and that could further be scaled to eventually meet the HVAC needs of the entire building.

Mediclinic Southern Africa operates a range of multi-disciplinary acute-care private hospitals and day clinics in South Africa and Namibia. Their focus is on providing value to patients through safe, quality care in a patient-friendly environment.

The Mediclinic story that began in 1983 with a feasibility study on private healthcare in the Western Cape province of South Africa, resulted in a network today of over 50 facilities across South Africa and Namibia.

The Mediclinic corporate office building is located in Stellenbosch, Western Cape. The building had an aging HVAC system that consisted of a mixture of Daikin VRV 2, 3 and 4 systems, in conjunction with heat recovery wheels on the ventilation side.

While some heat recovery was implemented using these systems, there was still much to be desired in terms of energy efficiency. The building layout and large size further made it ideal for a central chilled water plant where leverage of economy of scale was possible.

A central plant would optimise heat recovery and Lombard Consulting Engineers (LCE) was able to reduce the required plant size using the building’s intrinsic load diversity profile to their advantage. This project was initiated in December 2020 and was completed in June 2021.

Design considerations/client brief

As mentioned, Mediclinic wanted a system that ticked multiple boxes such as reliability, energy-efficient and scalability to eventually meet the heating, ventilation, and air conditioning (HVAC) needs of the entire facility.

There were VRV plants located all over the building and the client thus primarily wanted to reduce their environmental impact, as well as address the time and money spent on constantly maintaining these end-of-life systems.

The maintenance of existing HVAC equipment was an extensive exercise and sourcing spare parts for some of the older units was becoming more and more difficult. The refrigerant networks of the VRV systems were at the end of their lifespan and were becoming problematic.

The new HVAC system and installation solution

The new central chilled water plant was designed in such a way to facilitate a phased approach. The four-pipe, variable primary flow chilled water/heating hot water system, makes use of two state-of-the-art Carrier chillers operating in unison to provide comfort conditions year-round.

The system is able to meet peak loads during winter and summer, but the real advantage of this system is during intermediate seasons when both heating and cooling is required. The system moves energy around to where it is needed in a very efficient manner. One of the units was selected with full heat recovery allowing ‘free heating’ for the cold side of the building while providing cooling to the other warmer side.

The central chilled water plant greatly reduces the amount of refrigerant required to condition the building and all the refrigerant is contained in the two chillers on the roof. With no refrigerant gas circulating through the building and intelligent leak detection on the chillers, this greatly reduces the chances of having a leak and eliminates the risk of leaks going unnoticed.

To further enhance energy efficiency of the HVAC system, air-to-air plate heat exchangers were added into the new air handling units (AHU). The heat exchangers were also specified with bypass-dampers to allow an economy cycle when outside conditions permit.

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Elements of difficulty in the project

Working in a partially occupied building is always difficult and required open lines of communication with the occupants. All parties had to ensure a seamless, covid-friendly transition from occupied space to site and back to occupied space in a very short period.

Limited availability of existing as-built drawings made pre-contract planning of vital importance to ensure everything would fit as was intended. The ceiling void was designed for small refrigerant pipes, not larger chilled water pipes. With some clever engineering, the team could optimise riser locations to keep the pipes in the ceiling void to the smaller diameters.

The type of composite pipe specified for use in the void was crucial to this project’s success as it required no hot works or welding, does not sag under warmer temperatures, and increased the speed of installation ultimately enabling the team to meet the very tight deadline.

The limited plant space on the roof also proved difficult to navigate, however, with the aid of Revit and AUG (Augmentecture) the LCE and Coldfact Projects (CP) team was able to install a 1200kW plant with two large air handling units in the same space that was previously fully occupied by a 250kW VRV system and two heat recovery wheels.

The same plant footprint now has sufficient capacity to supply the entire building and not only two of the six wings.

Additionally, the severe impact of Covid on the shipping industry meant each piece of imported equipment was delayed. CP flew in what they could with the assistance of the suppliers but could not arrange this for the larger pieces of equipment. With close co-ordination between Lombard Consulting Engineers and Coldfact, they were able to minimise the impact of these delays by shifting available units around into a temporary arrangement while eagerly awaiting the rest of the plant.

Sectional handover of areas was critical for the client to maintain their operation and therefore temporary solutions worked well to achieve a sectional handover on time.

Selection of products, system impact on electrical usage and efficiency

The Carrier chillers were selected among many other suppliers due to their optimal performance at both full and part load conditions as well as an economical price tag.

The Trox air handling units were purpose built for this site due to spatial constraints while also ensuring they fit into the project budget. Energy meters have been installed on the main distribution boards (DBs) to track the plant power usage and convert this into a measurable plant coefficient of performance (COP). The CP team is looking forward to report on this in future.

Calculations have shown that energy savings will be achieved due to the superior energy efficiency (EER and COP) of the Carrier units when compared to the old VRV system. The bulk of the energy saving will occur in the intermediate season while heating and cooling at the same time. The combined energy efficiency of the system (cooling kW + heating kW/input kW) is a huge improvement over the old two-pipe (heat pump) VRV system.

The team did not opt to go for any specific green ratings at this stage although the use of best practices and green principles are always a priority to ensure the most economical and cost-effective solutions for the client.

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What made this project special or unique?

To refurbish an entire building of this size is no small task. Especially having to do this in a phased approach to ensure the client could still use most of the building to meet their business needs.

What stands out on this project in particular is that the combined chiller refrigerant volume required to condition the entire building is only slightly more than the refrigerant removed from only two of the six wings of the building. With each subsequent phase more and more refrigerant gas will be removed, which in the long run, is great news for the environment and contributes to improving the client’s carbon footprint.

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