ENERGY EFFICIENCY | DESIGN FOR PERFORMANCE If we are designing a sophisticated building which most air conditioned offices are why not run it virtually in advance of constructing it, and check that its going to work? Software used in Australia including IES and EDSL, which, ironically, is made in the UK is set up to enable this to be done relatively easily. However, the capacity of the model to do that isnt used in this country, says Cohen, who adds that the model can be used to commission the building and fine-tune it in operation. The modelling we currently do is all about the fabric of the building, says Cohen, while advanced simulation requires the full detail of the heating, ventilation and air conditioning (HVAC) system including the ducts, fans, pumps, chillers, boilers to be entered into the model, and modelling to be done at least hour by hour. On a time-step by time-step basis, you work out: how much heating or cooling is required in each zone of the building; how the HVAC system is going to provide that heating or cooling; how much air will be going down the ducts; what is the pressure drop in those ducts; and what the fan efficiency is, given the pressure drop, he says. You have a power curve in your model to describe how efficient your fan is for example, depending on what load its working at and you work out the amount of energy used for the fan at every time-step, so it gets accumulated to the figure for the whole year. As well as getting the model to create the right conditions in the virtual building, the control systems are defined, Cohen adds. This definition can be written into a draft description of operations, which is used by engineers to design the buildings controls. The model can also be used by commissioning agents to check that the real building is being controlled in the same way as its virtual counterpart. You end up with a building that should operate the same as it does in its virtual twin, says Cohen. If you allow the market to drive the scheme, it can be very effective in getting the market to compete for higher levels of performance And it can be done; one of the pilot studies carried out high-quality advanced simulation work on an existing building and the corroborated model represented the real operation of the building. We were able to verify that the model could reflect what was happening in the real building, says Cohen. Reaching goals As soon as you assign a rating to a building, it changes the conversation, adds Cohen, because you dont need to be an engineer to understand that if a five-star building is using three times less energy than a twostar building its a better building. Setting a minimum standard tends to become a race to the bottom, says Ratcliffe. If you allow the market to drive the scheme by setting its own goals, it can be very effective in getting the market to compete for higher levels of performance as Australia has proven. We want people to get confidence and experience with the pioneers project by testing the water carefully, setting fairly conservative targets without penalties for not achieving those targets, so contractors dont have to price it into the risk perspective, says Cohen. Nabers has had a long journey to get to the point where disclosure is mandatory, starting off as a voluntary initiative. It achieved market coverage by reducing, gradually, the size of the assets that needed to disclose, says Ratcliffe, who hopes the UK will follow a similar trajectory, but in a much shorter timeframe. Its not just possible its a very exciting prospect, says Cohen. The industry will warm to this because it will help M&E engineers attract and keep the best talent, as its going to make their job a lot more interesting. CJ The best buildings in Melbourne are using five or six times less energy than on average in the UK 26 December 2018 www.cibsejournal.com CIBSE Dec18 pp24-26 DfP.indd 26 23/11/2018 16:00