Pool in the park - Hornsby Aquatic Centre

Sunday, 29 September, 2013

Pool+Spa has been following the development of the new aquatic centre at Hornsby in Sydney’s north. Raymond Huzij, Project Manager, Major Buildings at Hornsby Council, talks about the team’s progress.

P+S: Last time we checked in on the team’s progress, ADCO had just poured sections of the car park floor slab and the formwork for the northern end of the pool was being erected. What has happened in the past two months and where is the project at now?

RH: The floor of the 50 m pool has been completed in three sections. The starting block wall at the northern end of the pool has been poured and the side walls of the pool are progressively being constructed. There is a lot of attention to detail to ensure that there is adequate concrete cover to the reinforcement and that the waterstops are being correctly installed at all of the pour breaks. The beginnings of the terraced seating plats have been formed up.

The overall structure for the 50 m pool is now quite evident and it’s context can now be appreciated. With the western side of the pool being bushland and the eastern side being Hornsby Park, the feeling of the ‘pool in the park’ can now be appreciated.

P+S: Can you please provide details of the pump/filtration etc

RH: Geoff Ninnes Fong and Partners - Structural, Aquatic and Civil Consultants has advised on the following:

Due to difficult site access, chlorine production is based on on-site hypogeneration from a brine solution using a ProMinent Chlorinsitu system that provides weak, very pure sodium hypochlorite with low TDS.

The basic process is removal of soiled surface water (maximum pollution zone) with wet deck gutters and longitudinal pool grating to balance tanks. Soiled water passes through precoat filters (Atlas) which also have reverse flow cleaning as required to an approved 30 m3 backwash tank that encourages sedimentation.

Advanced oxidation and chloramines are controlled by high-intensity, medium-pressure Prominent UV.

Return of treated/filtered water is via a floor returning piping system with adjustable nozzles (additional wall return system for the 50 m pool) designed to create a conventional surflo mixing pattern.

Management of the process is through ProMinent automatic water chemistry controls that monitor key parameters.

Layout of the balance tanks is to Geoff Ninnes Fong & Partners (GNFP) requirements so that all reticulation connecting the pools to the centrally located plant room is protected and installed within accessible concrete balance tank structures. This is a preferable, cheaper and safer option than disparate plant spaces for each pool.

To contain costs, a combined pool water treatment plant is being used for the learn-to-swim (LTS) and leisure pool being at the same temperatures. The choice of water treatment plant was the stainless steel Atlas precoat filter system for all pools. The Atlas system is simple and very efficient and uses minimal water flow to effectively backwash the filters without complex valve settings and vibration/bumping systems. The spacing of elements within the filters gives very effective filtration and a long life for components. Regeneration cycles optimise the life of the filter media.

Compared to a normal sand filtration system, the saving of water for the Atlas precoat water treatment plant for the centre gives a total water saving of some 2000 m3 (which allows for total dissolved solids (TDS) control) and this is a substantial saving of water, heat and chemicals.

The chosen brine to chlorine system gives a very mild but very pure form of sodium hypochlorite and minimises TDS. A chlorine truck delivery access is not required.

The plant for the 25 and 50 m pool, and the combined leisure and LTS pools use the same size filters, providing added efficiencies in purchasing the plant and especially in maintenance and plant control. Each plant uses PCT460 Atlas filters, each filter with 46 m2 of filter area.

The plant filters to 2 micron (sand is 12 micron) giving exceptionally clean water. The filters have the ability to filter out Cryptosporidium and Giardia. The exceptional water quality optimises the effectiveness of the UV, which destroys the chloramines and pathogens in the water and especially the trihalomethane group, which can be absorbed through skin, ingested or inhaled.

There is no change in the chemical composition of the water (pH, colour, TDS and odour) by the use of UV advanced oxidation and it cannot be overdosed, nor is there a chemical residue.

All the water treatment plants on this project use ProMinent high-intensity, medium-pressure UV which breaks down the chemical bonds (chlorine/nitrogen) in chloramines. It also kills all the pathogens.

The pools in the centre are as follows:

  • 50 m pool: 1030 m2, average depth 1.52m, T/O 3.28 hours, fully tiled. Filters - 3 x Atlas PCT 460.
  • Leisure pool with spa, water features, children’s area and LTS pool with disabled ramp: 262 m2, average depth 0.73 m, T/O 1.18 hours, fully tiled. Filters - 1 x Atlas PCT460.
  • 25 m LTS pool with disabled ramp: 238 m2, 1.1 m, T/O 1.84 hours, fully tiled. Filter - 1 x Atlas PCT460.

P+S: What heating system has been selected and why?

RH: George Floth from Sustainable Building Consultants has advised that the heating system selected is a combination of several systems: high-efficiency, gas-fired boilers (2 x 500 kWt) and a reciprocating gas engine cogeneration plant (1 x kWt). This combination of systems was selected as the optimal solution to satisfy multiple discordant goals:

  • Achieving a reduction in greenhouse gas emissions of 30% over equivalent facilities.
  • Minimising noise pollution to nearby neighbours.
  • Working within the project budget.
  • Providing adequate redundancy in the system to ensure continuous operating capabilities.

The selected systems have the additional benefit of providing a diversity in their energy source (electricity and gas), allowing Hornsby Aquatic Centre to minimise its risk of exposure to volatility in the price of these commodities.

P+S: Have there been any obstacles or challenges that needed to be tackled in the past two months - if so, what were they and how were they overcome?

RH: The structural steel for the main pool hall is being constructed in Young. The structural engineer has designed the main trusses with a camber so that when all of the elements of the roof and ceiling are installed the structure will deflect to a straight profile. To verify that the trusses will perform as designed a special load test will be undertaken in the factory to confirm expectations.

P+S: What are the next steps - what are you preparing for at the moment? Is the team on schedule?

RH: The car park slabs are continuing to be constructed to the south allowing the pool structure above to follow. The leisure pool will be the next element to be constructed - this will be a challenge given that most of the pool is formed of curved surfaces.

The overall program has been adjusted to take into account inclement weather and the overall project is tracking in accordance with the program.

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