IHBC CPD boost: Over-engineered buildings nullify the green benefits, from pbctoday

Alex Hill, managing director at Whitecode Design Associates, offers insight into the smart ways to design building services to ensure they perform as designed and maintain a thermally comfortable environment for occupants, without being over-engineered, from pbctoday.

Alex Hill writes in pbctoday:

While achieving technical compliance and meeting building codes is one thing, designing a building’s M&E systems to have more electrical, heating and cooling capacity than is needed will ultimately cost more and drive higher energy consumption.

Over-engineering has a significant impact on the cost and performance of a building project or scheme, particularly in terms of efficiency. Signs of over-engineering can manifest themselves in a variety of ways, from plant cycling and uncomfortably warm spaces to slow pump speeds and stop-start chillers. These inefficiencies have a draining effect on a building’s performance and occupant comfort, and can also negatively impact a building’s green credentials.

Why do designers over-engineer?

Over-engineering can occur for many reasons but the majority of the time it can be as a result of human behaviour. We are, arguably, predisposed to err on the side of caution when there is a certain degree of risk – think of all the people who stocked-up on household necessities ahead of the lockdown period. Where there are ambiguities, human beings will over-compensate, just to be sure they have shielded themselves against anything that has the potential to cause any damage. The same can be said for construction projects; under-designing is known to affect companies’ insurance claims, so for engineers it is no wonder they give a 20% leeway. If there is a 96m allowance for pipework, for a little bit of luck it will be rounded up to 100m!

Documents such as the 18th edition of the New Wiring Regulations, known as BS 7671 published by the IET, recommends an additional 20% capacity for future uses. This implies the current electrical networks are being designed 20% larger than they need to be based on a potential forecast. While this is all well and good and looking to the future makes sense, by project completion if we apply this principle to all building services, these incremental increases create a massively over-engineered building. This current practice, therefore, is resulting in a high degree of inefficiency.

To challenge this systemic issue, change must come from within. Some degree of commonality needs to be identified so designers can make their calculations with as much reliability and accuracy as possible.

How do we overcome over-engineering?

One of the options that has the potential to combat over-engineering is data. The construction industry’s digital maturity is developing day-by-day, with more and more companies finding they now have the appetite to utilise different technologies.

There is certainly the culture available to make data sharing a viable solution to over-engineering. For the very first time, we are seeing the Greater London Authority request the data capture of metres to accurately benchmark the schemes that are being implemented in a specific area. Should this be successful, the industry will be able to learn from this and see the real-time electrical performance of a building.

The data could be used to learn from previous projects, in order to inform how to improve future ones. Offering visibility and traceability, data sharing will empower engineers to drive towards greater efficiency on their forthcoming projects, especially on programmes where they are not working for the end-user.

Designers will be able to ask themselves what they could have done better; if the electric or heating load is accurate, and whether anything else could have been executed to make a product more efficient. The visibility and traceability that data provides would greatly reduce the likelihood of over-engineering, as engineers are able to gauge the predicted energy usage from data that is shared by the electrical supplier.

In order for this to be delivered across the industry efficiently and professionally, legislation would have to be put in place as opposed to advisories. The data would also, of course, have to be held in a central repository that is secure; either an online library or made accessible through a reputable industry body. Once it is available, the data would have to be listed in the design standards such as CIBSE, IET and the electrical design manuals so the design standards reflect the benchmarks.

While EPCs and performance analyses are a prerequisite in government-led schemes, we need to make sure there is the interest and incentive to roll-out this approach to all areas of the industry. Post-occupancy evaluations are essential for all projects, as they enable designers to learn what they could do better next time – whether it is reducing the size of a heat pump or decreasing the length of a particular pipe.

Let’s take an example of a residential high-rise development comprising 400 flats. From the initial calculations, it is clear the development requires 1000kw of electrics. But what if designers had access to metre data from previous developments? Would this visibility enable them to make more accurate predictions? If there was, for instance, the data to monitor the actual use over the course of three years, it might show us that only 600kw is being demanded. Think of the extent in which this would help designers to anticipate expected loads with greater confidence and reliability! Even the smallest change in pipework length or cable size has a knock-on effect on a building’s entire system; from the insulation to the clips, weight and strength or screws, pump size and standing heat loss. The list goes on. If we make use of data sharing, engineers could design products more efficiently.

While there are many ways to overcome over-engineering, the utilisation of data will undoubtedly enable designers to have more clarity when it comes to ascertaining how a building performs. If the data is able to capture the actual loads once a building is in use, consider the vast difference it will make to the way engineers consider a scheme’s electrical network. It will offer more reliability for the designers and better value for their clients, and will greatly improve the overall efficiency of a building once it is in use.

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