By Henry Townsend, senior mechanical engineer, WSP Group Africa
All images by © RACA Journal | Benjamin Brits
This luxury residential development known as the ‘Jewel of Hyde Park’, comprises 1, 2 and 3 bedroom apartments, sophisticated security, and a lifestyle centre that offers residents the perfect synergy between work and recreation.
This project – by award-winning Legaro Property Development – is said to be the definition of exclusive urban designer living and is located in the sought-after, beautiful and tranquil Hyde Park suburb of Johannesburg. Its positioning enables quick commute to Rosebank, Sandton and surrounds, and is in walking distance from Hyde Park Corner – that itself offers a combination of high-end shopping, dining and entertainment options.
The Emerald further offers residents exclusive and convenient use of services such as a concierge, fibre and DStv ready connections, and the generously spaced Lifstyle Centre is home to many on site facilities too.
The construction of the Lifestyle Centre and HVAC installation took place between February 2020 and mid 2021, although the complete site development was ongoing at the time of publishing – with phase 3 in the process of selling and further phases under construction or being completed in the greater development.
For this project, the focus for WSP was to meet the HVAC requirements for the Lifestyle Centre, basement parking, laundromat and future provision for a dedicated IT room (also located in the basement).
The Lifestyle Centre, that takes up a significant portion of the site footprint, comprises the following elements to which considerations around the appropriate HVAC solutions were an influence:
- Meeting rooms
- 25 metre indoor heated pool
- State-of-the-art technogym
- Steam room
- Hot yoga studio
- Ice recovery bath
- Administration area
The Lifestyle Centre also includes an outdoor heated pool and relaxation area on the first floor deck.
Client brief and considerations
For this project, WSP received the architectural plans from the client and the expectation was that we would come up with the best design and system components as experts in this discipline. The design methodology had to take into account a number of factors that would suitably service the needs of the occupants in each space – given the particular function.
Consideration of the aesthetics was also a very important part of the client brief and therefore it was vital to not only put an apprpropriate design on the table, but co-ordinate extensively with the client, architectural team and interior designers to make sure to achieve a win-win solution in terms of necessary climate control and having a pleasing visual outcome.
The design brief naturally then included compliance to building standards in terms of ventilation rates, and so on, and would further still maintain all best engineering practices. The systems that were therefore proposed for this project included a dedicated air handling unit (AHU) solution for the pool area and then a variable refrigerant flow (VRF) and direct expansion (DX) solution for the other spaces in the centre.
“Design methodology had to take into account a number of factors that would suitably service the needs of the occupants in each space.”
The VRF system consists of two separate heat recovery type systems serving the ground floor and first floor level units respectively, with a total installed cooling capacity of 91kW. The majority of the indoor units being hide-away type units concealed in the ceiling voids.
The dedicated AHU unit serving the indoor pool area consists of a DX cooling coil connected to three condensors, each with variable-speed driven compressors. The AHU, with a total cooling capacity of 145kW, contains a 1.7 metre diameter rotor type heat recovery wheel, and EC plug fans for controlling and maintaining the supply air and return air flows from the unit. The unit furthermore provides for an internal humidifier with humidity sensor, all communicating to the unit’s controller to assist with relative humidity (RH) control for the space. The AHU unit supplies full fresh air to the pool space at 3.2 m³/s, while also extracting the air from the space and exhausting directly to atmosphere.
HVAC system and selections
For this project it just made sense to select a VRF system because of the location of the rooms and the limitations that would exist in terms of condenser placements – being a high-end center with neat finishings. Daikin was the system of choice for WSP as they successfully won the appointment of the equipment tendering due to cost, specification compliance and quality.
When it came to the selections around the pool area, it is considered good practice to have a dedicated stand-alone system serving such an area. Since the rest of the system would comprise a refrigerant driven system, it was logical to also then include a refrigerant driven type unit providing the cooling to the pool AHU. This was achieved by a unit set supplied by Ecoaire through the same fair tendering process.
The DX coil is needed to control both temperature and assist with achieving acceptable humidity levels within the space. The American Society of Heating, Refrigerating and Air-Conditioning Engineering (ASHRAE) – HVAC Applications – Chapter 6 that specifically relates to natatoriums or indoor swimming pools, documentation provides significant insights and guidance towards the engineering required in these applications in terms of specifications and sizing of units – particularly when heated pools are involved. These standards also provide substantial guidance on humidity control, ventilation requirements, air distribution, duct design, pool water chemistry and evaporation rates.
The basement parking area contains a simple extract ventilation system in the form of jet fans under soffits that operate as an on/off solution linked to various CO sensors located in the space. These sensors continuously monitor the CO levels and once they reach a certain pre-set value, the fans switch on and run until the space reaches a certain level of CO that is again acceptable – which then triggers the fans to switch off automatically.
The laundry area (also located in the basement) includes a simple extract ventilation system to assist in removing the heat generated from the tumble dryers and ironing stations. A split unit is also installed to help with overall space cooling and for comfort of the laundry staff.
The shower/changeroom/toilets (located on two levels), as well as the café kitchen include standard air extract systems. The reception area and upstairs offices are provided fresh air through a slim design diffuser and split wall unit respectively.
The future provision for the dedicated IT room included installation of two mid wall split units.
The air terminal selection was through co-ordination with the architects where the preference was linear slot diffusers or small diffusers in order to ensure the aesthetics aspects were met.
Project challenges and solutions
As it happens with any project of such scale, challenges arise that must be overcome. One such challenge was the limited plantroom space that was allocated. Essentially there was no way of increasing this area purely because of the perimeter location of the building, so we had to make the design work with what was available. Needless to say it was quite a tight squeeze. We had to spend time on the exact positioning of the equipment in the plantroom and to make sure our model was perfectly to scale. The modelling had to match precisely to the suppliers’ dimensions of the AHU, condensing units and ducting before placement on site. Here we worked closely with the suppliers to communicate the space limitations and matching of equipment to fit.
The most significant challenge of this project, however, was definitely the dynamics involved in the gym/indoor pool area that shares the same climatic conditions as a double volume space. What essentially happens here is that this space experiences both heat and a lot of added humidity from the pool water (that is heated) which in turn is rejected into the air. The gym area, being located on the upper mezzanine level above the pool, shares the same volume while it is served by its own multiple VRF-connected diffuser units.
What was experienced shortly after commissioning the systems was that because of the very high humidity in this area, condensation formation occurred on the diffusers in the gym because of the the difference between the supply air temperature from the individual units versus the dewpoint temperature of the shared pool room space. Finding ways to modify the air terminals and system control settings to reach a point where the dewpoint temperature and supply air temperature in these spaces don’t create condensate was the biggest technical challenge by far.
Having developed a personal natural liking for leasure and lifestyle type projects, these usually each have a unique application to start off with and are fun to be involved in – particularly when you get to take on the challenge of projects including high-end facilities and finishes such as this site.
Here the unique elements were directly linked to the purpose and function of the overall development and facilities, including the designing and correct system sizing related to an indoor heated pool area. This is definitely not something one gets to participate in every day, and I will add is also an exercise that you can easily burn your fingers on.
I would strongly advise other engineers taking on applications of this nature to really do your homework properly. One needs to make sure you know the background and all factors of influence. There are a number of guidelines through ASHRAE and other literature sources to consider to ensure adequate knowledge of best practices and how heated pools can have an impact in other systems’ functions.
Impact on energy efficiency
In terms of energy efficiency, the VRF system in itself is a very good, energy efficient system compared to conventional split units as a solution.
Another element of additional efficiency that was included in this project was that the pool system, which is a very large capacity AHU, has a heat recovery wheel which assists with dropping the load on the capacity of the unit itself, because the heat wheel pre-cools the incoming fresh air to the system and this is especially important in this case where the pool unit is a full fresh air unit bringing in a lot of air. This addition definitely reduces the load on the coil which creates better efficiency.
|Project name:||The Emerald – Lifestyle Centre|
|Name of company|
|Architect / Designer||Daffonchio + Associates Architects|
|Project manager||LEGARO Properties|
|Consulting engineer||Electrical||RWP Taemane consulting engineers|
|Mechanical||WSP Group Africa|
|Wet services||N/A (in house by client)|
|Contractors||Main building||LEGARO Properties|
|HVAC & R||Blue Hemisphere|
|Wet services||LEGARO Properties|
|HVAC and associated product suppliers||Ecoaire|