Pre-Commissioning Flushing
This blog will focus on preparing for pre-commissioning flushing of one of the LTHW and CHW systems at Battersea. As a means of introduction and for those that aren’t sure, flushing is the cleaning of pipework to ensure that it is free from debris, settled solids, suspended solids and certain bacteria. This is to ensure that sensitive equipment isn’t damaged (plate heat exchangers and terminal units) when incorporated into the system, that commissioning valves can operate correctly and that microbiologically induced corrosion doesn’t occur.
The contractors involved are:
Skanska Rasleigh Weatherfoil (SRW)- Main MEP contractor
Price Building Services (PBS) – Pipework trade contractor
PH Water & Air Technologies (PH) – Flushing trade contractor
Wyse Power (WP) – Temporary services
When looking at flushing a system there are four basic elements that need to be in place (I’ve annotated who is responsible for each element):
1. A water supply – Down to Carillion to supply
2. Electrical supply (for pumps to get up to required flushing velocities) – Carillion to supply
3. Drainage – Carillion and SRW to supply
4. A complete system – SRW to supply via PBS
I have been managing the preparation for flushing from Carillion’s point of view. This has meant ensuring that points 1 to 3 are in place to meet SRW’s requirements and also ensuring that the approach SRW will take complies with the employer’s requirements which essentially means complying with BSRIA’s BG 29/2012. In reality my main focus hasn’t been on the technical detail and has been on the simple task of trying to prevent SRW from flooding 6 floors of semi-fitted out apartments. The following is worth noting:
Water supply – The permanent Boosted Cold Water Supply (BCWS) on site was not yet installed, therefore a temporary supply was required. This was fairly simple to sort out. I gained confirmation from PH on what their requirements were (a 50mm supply) and then arranged for WP to install a spur from our site temporary supply (50mm) into the plant room where flushing would be taking place with a double check valve fitted to the end for PH to connect onto. If I’ m honest this was a bit of a gamble on my part. As I’ve come to learn this is just a game. Points 1 to 3 above were down to me to sort out. The target start date for flushing the system was 17 Aug 15 therefore in order to avoid a relevant event occurring (JCT term for something which causes delay) and delay notice being issued by SRW I has to ensure we had a water supply. The reason why this was a gamble is that although I was tapping into a 50mm site supply, this supply comes from 2no 5000l break tanks which back in Aug were supplied by a 25mm pipe. PH had a discharge license for 10000l a day and therefore there was a risk that PH’s activities could disrupt the water supply to site. Why did I take this gamble? I knew SRW would not have their system complete in August and I knew a larger water supply was coming to site in the near future. By putting my supply in I protected Carillion contractually – it’s much harder to prove a supply isn’t up to the job than it is to highlight that there isn’t a supply in place at all. What is more frustrating is that I needn’t have taken this gamble at all. I have subsequently read BSRIA’s BG 29/2012, which gives clear guidance on the size of supply required in Table 3.
An extract from Table 3 of BSRIA’s BG 29/2012:
less than 2000l system = 25 mm supply
2000 to 10000l system = 40mm supply
greater than 100000l system = 50mm supply
PH were simply asking for the largest supply they could possibly need, without looking in detail at the size of the system, in order to cover their bases. Assuming that our riser pipework remains at it’s largest diameter and the horizontal distribution pipework is the same as the largest size then the volume of the system comes out at 1959l – I only needed to provide a 25mm pipe which would have been met by our 25mm site supply leaving 10000l a day for site use (more than enough). An easy lesson learnt.
That’s just over 700 words, so I’ll leave it there for this blog and provide comment on my part in confirming SRW have completed the system (visual inspections, air test witnessing and NCRs) at a later date.
As an aside I’ve only got two weeks left on site. If anyone on phase 1 knows that they are coming to Battersea Power Station Phase 1 let me know and there may be scope to arrange a visit to site before I depart and switch focus to phase 3.
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Rich,
Is your CHW system completely installed throughout all 6 floors and therefore are you using the pumps in the plantroom for the flushing?
I ask as we had to conduct flushing in bit-part and therefore use a separate flushing rig as we couldn’t use the plantroom main pumps as the system couldn’t be opened until flushed to avoid possible contamination.
Also, are you involved in witnessing of the flushing results? This is something I was involved with to reassure the client that the particular plantroom was ready and safe to open to the main system risers.
Fran,
To answer your question – no the system isn’t complete, but we are using the system pumps. We’re bypassing the heat exchangers and pressurisation units. The sequnce will be to flush the plantroom, then the risers, then floors. The reason the system isn’t complete is that we are trying to get a programme advanatage and make some money from an employer’s instruction – a bit too long winded to explain on here in full. But essentially we are looking to provide temporary heat to half the apartments up to level 6. To do this SRW have placed isolation valves on the riser flow and return at level 6. This will allow the system to be flushed up to level 6 using the system pumps. For level 7 and up we’ll need to run a temporary supply up to level 7 and then use additional pumps to get the required flushing velocity – this will be done at a much later date. I’d love to be able to witness the flushing as my experience of witnessing to date is that you can’t trust the sub-contractors,however, I doubt it will happen. As mentioned above this was supposed to start on 17 Aug, this was revised to 19 Oct and we’re now towards the end of Nov and it hasn’t begun.
Rich
What is the reason for the temporary heat, beneficial occupancy? Sounds like we are trying to do something similar on my site. I will probably do another blog on it, but in short our client wants us to supply heating early to two of the greenhouses. What this means to us is a redesign of the heating system to incorporate additional heat exchangers and getting an additional boiler up and running. Who would have thought tomato’s would be worth so much.
Matt,
Not for beneficial occupancy. Basically our specification states that some of the finishes being installed need to be kept within certain environmental conditions and therefore temporary heating and cooling needs to be provided – else there maybe a requirement to replace a few floors that distort. This load was supposed to be met by an energy centre seperate to phase 1, this was then instructed late into phase 1 which means the energy centre won’t be available in time. Which in turn means temporary heating and cooling are now required. The client has decided that they don’t want to carry the risk of reworks to finishes and have therefore decided to instruct CCL to provide temporary heating and cooling. As part of the JCT we can only apply our usual 1.5% profit margin to this instruction, however there is a further opportunity. About 50% of the cost associated with the instruction is the fuel bill associated with running the plant. If CCL decide not to run the plant and accept the risk that we may have to replace a few floors that distort we can potentially pocket a considerable amount of cash. Risk seems to be where the money is.
Thanks Rich for an interesting read.