Engineering Plant to Suit the User or Policy?

I had an interesting chat with an engineer over the weekend; an engineer responsible for managing boiler plant for landlords. Among other schemes he is responsible for the hot water plant on one of HTA’s recently completed schemes. This is a scheme where we did the working drawings, but didn’t do the original design.

His summary of the plant performance was startling. The scheme has four gas boilers and a gas-fired CHP. All installed to meet planning targets. So far so good. I asked him whether the CHP had been switched on yet, and he shook his head, and said, “and neither has three of the boilers”!

We are well into cold weather and this scheme hasn’t needed more than 20% of the available heating plant turned on to meet its entire hot water and heating demand. This suggests to me and him that there is something rather wrong in the process when this can happen. If we over-designed in any other dimension by 80% it would be obvious to everyone, but in heating plant it is somehow invisible?

The engineers view is that M+E design codes and practice hasn’t caught up with modern fabric standards, or modern living patterns. We are routinely designing for heating demands that aren’t there. Solar gains and equipment gains are often enough to heat modern apartments and most people in dense apartment schemes never actually need to turn the heating on. meanwhile we have built a boiler too big, with circulation pipework that is too wide, and radiators that are not needed.

He points out that many ‘design’ engineers are involved early on in the process to specify systems, and these are then handed over to a M+E installer who will usually value engineer down the system as much as possible, but will still install it to meet the performance targets specified at the design stage. This is at least partially about insurance, as the design risk will remain with the design engineer. So the final design may have little to do with the performance of the actual building, or the actual energy use of the occupants.

None of this is sustainable. Sustainability is not just about the standards of the things that you do, it is also about assessing properly whether you need to do it at all.


One thought on “Engineering Plant to Suit the User or Policy?

  1. This is nothing but bad engineering. If an engineer can’t navigate around codes to produce the right solution for their client then it looks from here negligent. No CIBSE guide suggests ignoreing the performance of building fabric, building form or occupant behaviour. Employ an engineer who can design based on first principles rather than follow old fashioned rules of thumb. It might cost you more up front but ‘lean design’ costs a lot less to install and operate.
    I’ve never seen this done in my career but have come accross over sized plant many times.

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