Measuring the energy efficiency of Britomart's buildings

DAVE ANNABLE NABERSNZ was introduced in New Zealand in 2013 and is based on the National Australian Building Environmental Rating System (NABERS). In New Zealand, they only apply to office buildings. They’re a way of measuring energy efficiency of the normal operation of a building. Energy just means any electricity, gas, diesel for generators, etc. The idea is that the ratings make it easy to compare buildings. A four-star building in Wellington will operate just as efficiently as a four-star building in Auckland, even though the building in Wellington might use more energy overall, because it’s colder there. For building owners, it’s a way to show you how your building performs compared to other similar buildings, and a way to track your progress. I don’t know what the latest figures are, but after 10 years in Australia, buildings on average had achieved 30 percent savings. That’s a benefit to landlords and tenants in terms of lower costs, and it also means a reduction in carbon emissions.

DAVE It’s changed since October last year. Until then, NABERSNZ had been measured on the rated area, energy use, hours of occupancy and the location – Auckland, Wellington and Christchurch. That made it quite easy to calculate how much you’d need to reduce energy consumption in order to get a higher star rating. Now the calculation includes an emissions factor, which impacts on the rating, because gas, for example, has a higher emissions factor than electricity.

DAVE Your base building basically relates to everything the landlord needs to provide to create a safe, comfortable building environment. That’s the lifts, HVAC [heating, ventilation, air-conditioning], lighting and power for the access and common areas, and any fire protection equipment. The tenancy rating covers the energy use that the tenants are responsible for. So that’s lighting and power on the tenant floors, and for any supplementary air conditioning they’ve installed – for a boardroom, for example. The whole building rating includes both the base building and tenancy energy. Britomart has whole-building ratings for the Excelsior Stanbeth Building, Australis Nathan Building and the Altrans Quay Building. That’s because there isn’t sufficient metering to be able to accurately separate the tenant’s energy use from the landlord’s energy use.

DAVE Yeah, it doesn’t happen so much now in newer buildings. Although I saw a building recently from 2010 where the metering wasn’t separated. 

DAVE I’m a NABERSNZ-accredited assessor and I have a mechanical building services background. As an assessor, I come in and collect all the information required to do the rating – all the utility and metering data, collect data information on the hours of occupancy, any after-hours occupancy, that sort of thing. What we’ve also been doing here is regular reviews. Every three months we meet to look at how Britomart can reduce the energy consumption in each building. That’s what NABERSNZ is really intended to do – provide a benchmark to help to improve the energy-efficiency of buildings over time – although the reviews are not required to get a rating. And when you have a number of buildings with ratings, you can compare the buildings and say, well, this one’s not performing as well as the others, so what can we do to improve it?

DAVE The biggest thing is making sure that your HVAC is only running when it’s needed. It’s not just making sure that the HVAC isn’t left running all night when nobody’s in the building, but more things like questioning why the boilers are coming on so early, long before people come into work, and leaving them running until 6pm. These days, post-Covid, people don’t really stay in the office until 6 o’clock in the evening, so they don’t need to be on that long. When you ask building managers why their boilers are coming on at 5am, it might be that there were complaints in the past, and they want to avoid more complaints. But there are other ways of thinking about it. You might ask yourself why the building is getting so cold. When you turn the boilers on, are you also starting the ventilation systems and introducing fresh air in to the building. If you’re doing that at 5am when it’s very cold out and the building is unoccupied, you’re just unnecessarily increasing your heating demand. But basically it’s about making sure that everything is only running when it needs to be and when it is running it’s running efficiently. It’s the mechanical systems that drive most of the efficiency gains. You can look at your lighting – make sure you have efficient lights but at the end of the day it’s the mechanical systems that have the biggest impact. In an open-plan office where you’ve got adjustable thermostats for different areas of the office, and people are adjusting it to suit themselves, that can create inefficiencies. You can end up with one area being heated next to an area being cooled, so the fan-coil units will be working against each other. In a lot of larger buildings, to deal with this, building managers set a fixed range the system will cool or heat to, from 21 to 23 or something like that. For Whole Building ratings, a lot of control is taken out of the landlord’s hands. If you have a tenant who occupies half a building but are never in the office and leave the lights on all the time, as a landlord doing a Whole Building rating, you’ll be penalised by that.

DAVE Under the Whole Building and tenancy ratings, the computer count is a factor you take into account. The idea is that everyone in the office will be working on a computer, so you count all the computers in regular use. If you have something like a bank trading floor, you might have people who have multiple computers, and that uses more energy, even though there’s only one person. That’s why you count computers instead of people. 

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