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Net zero feasibility study outlines drastic rethink of building cooling design – Refrigeration and Air Conditioning

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Proposed designs for a viable route to meet the UK’s 2025 and 2030 decarbonisation targets consider how office and domestic blocks highlight the potential of combined heat and cooling

Cooling provision in offices and workplaces will need to be drastically rethought to include passive design measures and more integrated HVACR systems in order to realise upcoming decarbonisation targets.

The UK Green Building Council (UKGBC) has published a new feasibility study into how an office building and residential block could be redesigned to meet the country’s 2025 and 2030 decarbonisation targets using already available existing materials and technologies.

The ‘Building the case for net zero’ report considered the base design of both structures to current standards, and looked at how each could be built to meet predicted 2025 and 2030 UK performance targets.

These targets were devised as an example of the scale of change in a building’s energy usage and operational performance that will be required to realistically meet the aim of eliminating all national carbon emissions by 2050.

From the current baseline design, the 2025 and 2030 office block design proposals look at moving away from the use of an electric chiller with a seasonal efficiency of 4.5 to alternative technologies that provide a combined heat and cooling funciton along with passive design measures.

Use of a reversible air source heat pump for both heat generation and cooling was backed in the ‘intermediate’ design plan set out in the study with the aim to meet the 2025 decarbonisation target. This would also have the benefit of curbing the plant required when using both a gas boiler and chiller, according to the researchers.

The study added, “An active chilled beam solution is preferred to fan coil units, with demand-controlled ventilation enabled, to allow fresh air provision to ramp back when CO2 concentrations in the space allow.”

More fundamental change to building design and HVACR systems are considered under the “stretch” design proposals for meeting the 2030 decarbonisation targets.  According to the UKGBC, this includes adopting a mixed mode ventilation system and controls capable of linking the conditions and temperatures of a building’s façade to its HVAC systems so that they can deactivate when external conditions might allow.

A focus on reducing the overall glazing of a building’s façade is among the other measures backed under this design proposal to reduce solar gain and manage thermal comfort against potential issues of overheating.

The stretch target also backs amending comfort conditions in line with allowable standards so that temperatures are reduced to a maximum og 20 deg C in heating mode and 27 deg C in cooling mode.

Researchers in the study said that a decision as also considered to remove cooling altogether in favour of a building using a “free-running, naturally-ventilated design” – a proposal that was ultimately rejected.

The study said, “Dynamic thermal analysis indicated that the stretch design could meet natural ventilation comfort standards based on current climate data, however its ability to provide comfort conditions decreased when considering future climate projections.”

“The lack of thermal mass in the stretch design cross-laminated timber (CLT) slabs is another factor, and a degree of comfort cooling was therefore retained within the stretch design.”

UKGBC said it viewed the costs to meet the 2025 target as relatively marginal. It added that an organisation using the design plan in the study would be able to recoup the costs in the longer-term through operational costs improvements and an anticipated rise in the rental and capital value of more sustainable buildings.

The anticipated costs for the 2030 design plan were estimated at 5.3 per cent in the case of domestic buildings and between 8 per cent and 17 per cent for the office environment, depending on how the construction supply chain can innovate and adapt to better meet demand for the required products and materials.

Julie Hirigoyen, chief executive with the UKGBC, said the study was designed to look at the precise costs and benefits around immediately trying to make buildings greener both in terms of construction and longer-term operations.

She said, “This study provides long-awaited evidence that building today to the standards of energy and carbon efficiency required by 2025 doesn’t have to cost a fortune and is likely to be offset by enhanced value – such as higher rents, reduced running costs, higher sale price, reduced offsetting costs – in due course.”

“But unsurprisingly, when it comes to building to 2030 standards of efficiency, the current capital cost increase on a baseline 2020 design is more challenging to accommodate. To overcome this, we need a long-term consistent regulatory trajectory that tightens standards over time so as to provide the certainty and level playing field required for the supply chain to innovate and costs to come tumbling down.”

The UKGBC said it has co-authored the report with construction and entering specialists JLL and Hoare Lea. It also made use of insights from building specialists including Alinea, Bennetts Associates, Cast, Cundall, EPR Architects, Heyne Tillett Steel, Landsec, Legal & General and Robert Bird Group.

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