The challenge to deliver net zero all-electric buildings is a formidable one. And no-one knows that better than an ESD consultant.
Victorian based AECOM principal sustainability consultant Sian Willmott is well familiar with the task. Her remit in all-electric projects stretches from education to healthcare and the commercial sector.
When it comes to office buildings, she says, the first variable to consider in designing a fossil fuel-free office building is the climate in its location. So many of the outcomes depend on that.
In colder climates, office buildings rely heavily on gas for heating and hot water. That’s because the electric alternative to gas boilers, heat pumps, become less efficient as the temperature starts to drop (moving heat from a very cold area to a warmer one takes a lot more energy than the inverse).
In Melbourne, a heat pump might struggle to warm the building up on a chilly winter morning, when the mean minimum temperature can hover around 5-7 degrees Celsius.
Willmott says a heat pump working under these conditions is typically operating at less than 300 per cent efficiency, falling short of the 500 per cent efficiency it needs to be operating at consistently to be as carbon efficient (in Victoria) as a traditional gas boiler.
“This means an investment in energy efficiency is needed elsewhere in the design to reach the same carbon targets until the grid decarbonises” she explains.
Warmer climates are easier because buildings don’t need as much heating, and airconditioning has always been an electric solution.
The sticking point for warmer climates is usually hot water, but Willmott says this is typically a low energy portion for a large commercial building.
The real challenge is transitioning existing office buildings to all-electric.
First barrier is the issue of space: heat pumps equal to the task of meeting the same peak demand for heating and hot water as a gas boiler, need up to five times more space in the plant room.
The second is location. Heat pumps need generous ventilation to reject heat efficiently. Compared to gas boilers, which only need minimum ventilation for combustion and to meet gas code requirements, heat pumps aren’t particularly flexible on location.
“This means a heat pump solution is easier when you have more space; which is unfortunately rare when you’re looking at high rise developments – as they’re usually in a tight CBD infill, not the suburbs,” Willmot says.
In these situations, developers may face less net lettable area, with impact on income.
“Heat pumps are generally easier in homes, schools, and other places that have more space to work with.”
Heating and hot water are the big gas users but in some commercial buildings there might also be cooking facilities, with food and beverage tenants particularly attached to gas.
The final hurdle is backup generators, which are commonly diesel. Willmott says there’s currently no viable carbon neutral alternative.