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HVAC key to top building ratings

A review of international building energy performance assessments has shown HVAC design can have a massive impact on overall ratings.

The study by Integrated Environmental Solutions (IES) compared the LEED, BREEAM and Green Star schemes – developed respectively in the United States, the UK and Australia.

To see the report in full click here

It was undertaken to assist comparison between international assessment schemes and help integration of approaches.

Comparing the systems using a theoretical eight-storey office building in Dubai – which does not currently have its own assessment scheme - showed different issues influenced ratings under each scheme, but heating, ventilation and air conditioning was the most 'heavily weighted factor'.

The report was presented to this week's International Building Performance Simulation Association Conference and Exhibition in Glasgow.

The report noted: “It is worth mentioning that the simulation of the HVAC system is of great importance to the energy rating in the three schemes. In the Green Star scheme the HVAC system counts for 65 per cent of the total energy consumption.

'Little changes or improvements that are made in the system will bring a direct effect on the final score. In addition, both the LEED and the Green Star schemes promotes innovative HVAC technologies and detailed HVAC networks to be simulated, therefore, a well-designed and highly efficient HVAC system will be rewarded in these energy ratings.”

The report conclusions included:
* The energy performance of a building and the corresponding energy rating obtained are strongly dependent on the assessment scheme used as they are based on different energy assessment methods and performance criteria. This meant the case study office building received a high energy rating score in the Green Star scheme, a low energy rating in the BREEAM scheme and failed to be certified in the LEED scheme.

* The HVAC system is the most “heavily-weighted variable in the energy assessment of the three schemes.” As both LEED and Green Star require the full configuration of the HVAC network to be simulated this allows assessors to recognise the specific areas of the model or variables of the system that can be improved despite the complications involved with modelling.

* The LEED and BREEAM schemes take into account quite a large number of parameters for assessing the building energy performance based on two comparable building models while Green Star scheme predicts direct energy consumption from one single building model based on fewer parameters to be assessed

Ya Roderick who led the research said: “The purpose was not to say which is best, but to help people to choose the appropriate scheme which is suitable for their location.”

IES director,David McEwan, who also contributed to the research, pointed out low carbon HVAC design needed to focus in on the details of equipment alongside the overall system.

He said:  “In the United States they are very focused on HVAC and this study does raise the question in the UK over whether BREEAM should have the option of going into more detail particularly as we move towards low carbon and zero carbon building. That is something I think people should be looking at.'

Model used:
The building model created for the model was  an eight-storey building with open-plan offices. The building also included a three-storey car parking area that ties into its main structure. The building had multi-thermal zones comprising office space, data centre, changing and shower areas, toilet, storage, service/plant areas, elevators, circulation areas and car parking areas.

The total floor area of the building was 31291.8 m sq and the Net Lettable Floor (NLA) area was 9,500 m sq. The total building height was 36.7m and the floor-to-floor height was 3.8m including a ceiling void of 0.45m deep.
The HVAC system that was proposed assumes a fully air conditioned plant for the building. The air conditioning system is based on a typical centralised Variable Air Volume system.