Should Net Zero be today’s goal?
Net Zero is the latest buzzword around the green building industry. The implication is that we should strive for buildings that consume only as much energy as they generate on site. The Living Building Challenge has set this target and the 2030 Challenge aims for zero carbon emissions from buildings by 2030. But is this the right end goal? While achieving net zero is laudable, in the Canadian climate it may be a technically unrealistic target or, at best, financially impractical, because of the significant capital investment required in on-site renewable energy generation.
By Stephen Carpenter
Energy Use in Today’s Buildings
So if net zero is not a realistic target, what should today’s goal be? To answer this question, we must first look at where conventional and green buildings are today. Currently the average Canadian commercial/institutional building uses close to 400 ekWh/m2 [1440MJ/m2] on an annual basis. Schools, offices and MURBs are on the low side of this number and hospitals, sports facilities, and retail centres are on the high side.
Looking back at its 100 LEED certified projects, Enermodal Engineering discovered that the actual energy use of the monitored projects is 45% less than the Canadian average, or just over 200 ekWh/m2. For the most part, these savings were achieved by focusing on a few critical areas: airtight envelope, efficient lighting, and high performance mechanical equipment – including ventilation heat recovery.
A Realistic Goal
So if net zero isn’t realistic based on where conventional and most green buildings are today, then what is? We believe a realistic and cost effective target is 100kWh/m2 [360MJ/m2]. There are three reasons why this is a better goal:
1. It’s Achievable
Of Enermodal’s 100 LEED certified projects, 10 would meet this target making it a challenging yet achievable goal for most projects. Choosing a goal of net zero has the real risk of over-promising and under-delivering, thereby calling into question the credibility of the green building community.
2. It’s a Worthy Challenge
It is interesting to note that in the fine print of the 2030 Challenge, that program allows for 20% of energy to be from green energy purchases. In other words, the actual building energy consumption for its net zero buildings needs to be 20% of current values or 80 ekWh/m2 – pretty close to the 100 noted above. In this sense, 100 ekWh/m2 is no less an accomplishment than zero: only a handful of buildings in Canada have achieved this level of performance.
3. Sets building up for Future Net Zero Performance
A building using under 100 kWh/m2 is perfectly set up to meet its energy use by on-site renewable energy generation or by connecting with neighbouring buildings to make use of complimentary heating and waste heat requirements. But 200 ekWh/m2 is just the average. What about the very best performing buildings from an energy perspective?
Achieving 100kWh/m2 energy Consumption
To achieve this energy target requires a different design process that includes four steps that are not part of conventional practice:
• Concept design workshops – integrated design process and a “shopping list” of energy efficiency features created by energy modelling, enabling the design team to make informed decisions on the best building systems to incorporate into the design
• A design team – with experience delivering buildings with low energy requirements [more on this later] - that is committed to elegantly simple design
• Extended commissioning that includes peer review of design and operator training
• Measurement & Verification - to see if you actually achieved your predicted energy and water savings and, if not, correcting the problems.
Superior Performance by Elegantly Simple Design
Just three words: elegantly simple design. The problem is that it is extremely hard to do simple designs. Engineers are prone to over sizing equipment, adding unnecessary control complexity, and using old rules of thumb that were developed when reducing energy use was not a priority.
To achieve designs below 100 kWh/m2 requires a complete re-think about how we design buildings. And not just M/E design but architectural as well: proper orientation, narrow floor-plates, optimum window-to-wall ratio are all important. These are all features of our new headquarters, A Grander View, which is running at 69 kWh/m2. For the record, it cost approximately $250/sf to build and fit-up. Here are three other examples of how elegantly simple design works in practice:
1) Throw out rules of thumb and design from first principles
One of the biggest mindsets holding back sustainable design is the use of outdated engineering rules of thumb and common practices that are not reconsidered from an energy efficiency perspective. For example, it is common practice with rainwater cisterns [used to supply toilets or irrigation] to fill up the empty cistern with city water if the cistern is empty. This requires the city water to be depressurized in the cistern, which uses energy.
On many of our projects, including Waterloo Region Police Service Investigative Services Building, we have the city water bypass the cistern altogether, joining the building plumbing system after the cistern system so the water maintains the correct pressure from source to building.
2) Eliminate as much equipment as possible
If you plug it in, it will use energy. With this motto in mind, we should eliminate as many unnecessary pieces of mechanical equipment as possible. For example, our own office is built into a hill. The slope creates drainage problems, with a typical solution being a sump pump to pump out water. To eliminate the need for an energy consuming sump pump, we decided to re-landscape the site around the building to allow for gravity drainage to storm drains and eliminate the need for a pump.
3) Waste Not
The traditional approach to server rooms is to install a dedicated air conditioner to deal with the incredible amounts of heat generated by the electronic equipment. Not only is this an extra piece of equipment that serves no other purpose, but the heat energy generated by the equipment is wasted.
Instead, at Northlands Park Collegiate in Manitoba, the building’s variable refrigerant flow heat pumps [integrated into the ground loop heat pump] will provide heating and cooling to the computer rooms and server room which have a different load pattern from the rest of the school. Most of the heat removed from these rooms will be used to heat domestic hot water.
Another development at Northlands is to look to the kitchen for energy savings. Commercial kitchens are often overlooked as much of the load is considered ‘unregulated’ and is not incorporated into mandatory modelling for LEED. Yet, the electrical demand in this kitchen exceeded that of the rest of the school. Therefore, Enermodal’s M/E group selected low-flow, variable-speed range hood ventilation, a dedicated high-efficiency tankless booster heat for the dishwasher, thicker insulation panels for the walk-in coolers and freezers, a water-cooled refrigeration plant connected to the ground heat exchanger, higher efficiency defrost and control for the refrigeration, and electronic pilot lights for the gas cooking appliances.
Conclusion
Recent initiatives within the sustainable design industry have set new performance targets that include net zero energy consumption. Realizing the economic parameters under which the vast majority of building projects operate, it is arguable whether such performance goals will have the desired effect as they may be seen as unrealistic or unattainable. More practical would be the goal of reducing energy consumption to around 100, kWh/m2 per annum, a goal now being achieved by the best 5-10% of green buildings [and about 1% of all new buildings]. Rather than targeting an unachievable goal of net zero, this would instead result in a larger number of ‘Net Zero Ready’ buildings – whose modest energy demands could soon be met through a variety of renewable energy options.
Stephen Carpenter is a LEED Fellow and president of Enermodal Engineering, Canada’s largest green building consulting firm. Founded in 1980, Enermodal has offices across the country in Kitchener, Calgary, Edmonton, Winnipeg, Halifax, Vancouver, and Toronto.
