Bigger is not better
The Association of Hydraulic Services Consultants Australia NSW is looking to undertake real life testing to enable economical designs through correctly sized pipes and pumps. Warren Smith & Partners hydraulic engineer Jonathan Mousdell explains.
The sizing of potable water supply systems is a common task for hydraulic engineers and despite it being common knowledge within the industry that pipes are generally oversized, it would be detrimental personally and commercially to venture from the Australian standards.
Therefore, the Association of Hydraulic Services Consultants Australia (AHSCA) NSW has formed a sub-committee to undertake testing to improve the industry, with a view to eventually updating Australian standards.
The sub-committee has been formed on the back of growing knowledge within the industry that potable water supply pipes are based on conservative, outdated methods. The loading unit method currently referenced in AS3500.1:2015 Plumbing and drainage – Part 1: Water services is extended from information gathered in the 1940s. This is an era when fixtures used 50% more water and the average time spent doing laundry was six hours per week.
Who is currently on the team?
The sub-committee consists of several industry experts from various backgrounds, including both manufactures, supply authorities and building service engineering firms. Currently represented along with hydraulic services consultants are: NSW Fair Trading, Enware, Itron, All Valve and Rheem, while Sydney Water is offering resources. Additionally, the AHSCA NSW is in discussions with other industry experts.
What will be the benefits of the investigation?
The current practice of routinely oversizing potable water supply pipes disregards sustainable development, compromises public health and misuses valuable space.
Aside from the embodied energy associated with unnecessarily larger pipes, the larger pipes have increased heat loss which consequently leads to ongoing energy costs over the design life of the system. Also, a rare peak flow rate which meets the most efficient point of the selected pump curve effectively means that the pumps will not be operating efficiently.
The risk to public health comes from low velocities through the system as low velocities encourage the growth of bacteria and allow biofilms to form on the pipework.
Finally, there can significant space savings within risers, ceiling space and plant rooms. This potential lettable area will be valuable for architects, building operators, developers and other services.
What are the desired results of the investigation?
The overall outcome is to update the Australian standards to cover multiple sectors rather than just residential. This would enable moving away from performance solutions when designing buildings, such as hospitals, which are currently not covered under AS3500.1.
The research is also looking for the conversion to peak demand to come from a full flow calculation rather than loading unit calculation. This future-proofs the conversion against unforeseeable industry changes that are certain over time, e.g. changes to tapware flow rates, increased use of vacuum toilets and new technologies. This would look similar to the example shown in Figure 1.
We also think that some serious thought needs to be put into the velocity that is recommended to be designed to. Designing the very rare peak to 1.5m/sec generally leads to low and non-cleansing velocities for all other times. It may be beneficial designing a ‘daily peak’ to 1.5m/sec while ensuring that the ‘annual peak’ is within 3m/sec.
What is the strategy to achieve the results?
Initially, the testing is likely to be undertaken in Sydney with a focus on residential. It is proposed to split a large building up to treat it as multiple, various sized buildings, with continuous flows such as cooling towers to be separated. Figure 2 indicates the strategy at a high level.
Over time it is proposed to cover various sectors ranging from stadiums to shopping centres. It is also deemed required to assess a range of geographical areas, assessing and comparing the effect of the climate i.e. how does the incoming water temperature and duration of shower affect peak flows between Hobart and Cairns?
The amount of buildings tested per each sector will depend on the variance observed between similar sized buildings. Ideally, after say five similar sized buildings within the same sector, there will be strong enough correlation to be confident that the data is true and correct. If not, the process will need to continue until correlation is evident.
The occupancy levels in the buildings will need to be known and the peak demand will relate to that occupancy level. For example, the results of a 100-bed residential building with 80% occupancy will effectively be the results of an 80-bed residential building.
What is next?
There are potentially more questions than answers still at this stage. The committee will continue to meet up, firm up a strategy and decide how to action it. As the process is still in the early stages, resources, funding and ideas are all welcome so please do not hesitate to get in touch with the team at firstname.lastname@example.org.
*This article was originally published in the summer 2018 edition of Plumbing Connection. Click here to subscribe.