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Member questions: cold water storage tanks, failure modes and energy usage estimatesNovember 2017

Maria Thanigasalam, Information Officer

Written by Maria Thanigasalam, BSRIA Information Officer

Q. We have been advised by our water treatment contractor that we need to change all of the cold water sectional storage tank roof supports. We’re concerned about creating areas of stagnant water within the tank and the risk this poses. Could you tell us if there are statutory requirements to change supports in existing tanks?

There are a couple of different ways of approaching this question – a Legionella risk assessment perspective and a water regulations compliance perspective.

Looking at this from a Legionella risk assessment perspective, there are no legal requirements beyond the fairly generic ones in regulations such as COSHH. However, there is a code of practice (L8) which is supported by HSE guidance documents including HSG 274-2. It states “a well-designed system should… all parts of the system including storage tanks… are designed to avoid water stagnation by ensuring flow through all parts of the system”. Ultimately it’s up to you as a building owner how you assess and address risks, but in this case the guidance is pretty clear and you’ve also had a contractor advise you to replace these supports.

From a water regulations compliance perspective, the Water Supply (Water Fittings) Regulations 1999 state that “no water fitting shall be installed, connected, arranged or used in such a manner that it causes or is likely to cause… contamination of water supplied by a water undertaker”. Furthermore, it says “every storage cistern shall be so installed as to minimise the risk of contamination of stored water… and to prevent areas of stagnant water from developing”. There’s nothing specific about internal supports in there. Even though these regulations primarily apply to new installations; water undertakers (e.g. Thames Water) do have powers to enforce improvements to older installations, although usually they only do that if they suspect that backflow prevention isn’t adequate.

Q. We’re looking for information about Failure Codes, Failure Modes, FMECA etc. Do you know if there is a standard set of codes?

While we don’t know of any published built environment data, reliability centred maintenance is popular in industrial applications and there is a lot online resources to help you here such as the following:

“Most traditional lists of failure modes incorporate failures caused by deterioration or normal wear and tear. However, the list should include failures caused by human errors (on the part of operators and maintainers) and design flaws so that all reasonably likely causes of equipment failure can be identified and dealt with appropriately. It is also important to identify the cause of each failure in enough detail to ensure that time and effort are not wasted trying to treat symptoms instead of causes. On the other hand, it is equally important to ensure that time is not wasted on the analysis itself by going into too much detail. (Flynn, C. et al, Applicability of Reliability-Centered Maintenance in the Water Industry, 2009, AwwaRF).”

Fluke 345 Power Meter - available from Instrument Solutions

Q. I deal with energy procurement and I have a client who is moving into new premises in London. They have previously paid for electricity via a set service charge and have no idea as to previous usage or likely levels of future usage.

The new property is five stories, 15,000 sq foot and will hold about 100 staff. This will be used as an office running computers and other office equipment during normal office hours. Energy suppliers want an estimate of electricity usage before providing pricing. Is there a way to come up with a very rough estimate of usage based on size and numbers of staff?

If you want to know the total consumption then the best solution is to use a power meter at the electrical feeder (if the tenant has already moved in). This will capture all the plugin equipment as well as the hard wired ones such as hand driers, lighting etc.. to get a break down then use different power meters for each branch at the feed level (where access is available).

If the tenant has not moved in then estimations can be carried out based on information taken from the light fixture and other equipment. The load can be calculated taking into account the hours of occupancy and number of equipment onsite.

The publications mentioned in the questions above are all available for members to borrow from the BSRIA library, open 8.30 - 5.00 pm Monday to Thursday and 8.30 - 4.30 pm on Fridays.
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