By Jennifer Elias

The most recent Real Estate Energy Benchmark (REEB) dataset from the UK shows that typical practice operational energy consumption, measured at the Utility meter, is 233kWh-e/m2 NIA/yr; the LETI Climate Emergency Design guide and Net zero carbon: energy performance targets for offices both call for 70 kWh-e/m2 NIA/yr (55kWh/m2 GIA/yr): In the UK we need to reduce our operational energy demand by 70%.

Tavis’ blog post (Steps to Net Zero: Step 1 – Passive Design Optimisation) details how we need to prioritise passive design principles to bring demand down; but reducing operational energy demand requires much deeper interventions.

As part of my work for LETI, I was able to demonstrate that increasing temperature setpoint bands can save up to 10% of operational energy: this is a measure that applies as much to existing buildings as to new designs. However, this pushes occupants to adapt their clothing accordingly (perhaps this is the end of the tie in the workplace?!). Our internal research suggests that incorporating ceiling or desk fans within the building can maintain occupant comfort with a 3 degree higher internal temperature.

The other big driver of operational energy demand is internal gains from tenants: this has three impacts. Obviously, more equipment uses more energy outright, but in addition the higher internal heat gains drive up air conditioning use, but also results in oversized air conditioning plant that then operates inefficiently throughout the year (and can often create serious controls problems upstream at chiller plant, for example). Reducing internal gains can then also unlock other opportunities, like natural ventilation and free cooling, or can mean that heat demand from domestic hot water can be matched to cooling demand using a heat recovery chiller.

For existing and new buildings alike, reviewing the drivers of energy consumption (rather than relying on Rules of Thumb or standard specifications and guides) can yield substantial energy savings.

Design for Performance, the approach used in Australia to deliver high NABERS rated buildings, is the approach needed to really understand the opportunities available to deliver operational energy savings. Through developing a digital twin of the proposed design, and using a complete HVAC simulation model to test various options for improvement, the optimum tradeoffs can be made to reduce operational energy. Testing the design and controls strategies under multiple different operating modes can also highlight risks and opportunities to inform the controls regime.

Once this digital twin is in place, the optimised controls strategy must be feed directly into the building’s controls strategy. The digital twin can then guide the commissioning process to ensure the modelled performance is delivered in use.

Throughout operation, it’s critical to undertake ongoing monitoring and targeting: using the digital twin simulation model to compare the energy use in operation to the simulated performance helps to identify opportunities to reduce consumption. Ongoing monitoring should continue through the life of the asset.

Finally, at key plant replacement milestones it’s important to review the basis of the design and interrogate whether the original basis of design still holds – are tenant loads lower? Have operating hours changed? Can new technologies provide better efficiency, and can grouping multiple upgrades together deliver better results than by implementing individual initiatives separately.

Only by applying these approaches and optimising every step of the process are we able to achieve the challenging energy intensive targets. Using the same old approaches will only yield the same energy intensive buildings.

21 Moorfields, London

21 Moorfields is a is the regeneration of the Moorgate area on a brownfield site at 21 Moorfields. The development covers 564,000ft² and comprises two office buildings along with retail and improved pedestrian accessibility via a reconfigured Highwalk and a new public square with improved landscaping.

Approaches used 

  • 21 Moorfields is a pioneering project under the Better Buildings Partnership’s Design for Performance Scheme. Cundall developed the Design for Performance energy modelling for the design. The Design for Performance modelling was then used to inform the controls strategy for the project.
  • The simulation model provides a basis to optimise the design further as the tenant fitout design develops. Monitoring post completion closes the loop to ensure the operational performance aligns with the design intention for the project

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Jennifer Elias, Sustainable Cundall, Zero Carbon Energy