11 April 2013 – Books: It’s the burning question: how green are green buildings? Do they live up to they hype? What is their actual energy consumption, as opposed to their promised energy consumption? And what about water?
Author and keynote speaker on green buildings, Jerry Yudelson says these were the questions he set out to achieve in his latest book, The World’s Greenest Buildings, (£29.99 from UK publisher Routledge).
Yudelson teamed up with co-author Professor Ulf Meyer of Berlin to compile what he belies is the “most extensive research to date on the measurable performance of LEED Platinum or equivalent buildings.”
With 55 case studies from 18 countries, Yudelson could well have delivered on the promise.
The book examines only buildings constructed since 2003, whose owners were willing to release a year’s worth of energy use data and, where possible, water use data, Yudelson says.
“In order to be included in this green building book, buildings had to have a LEED Platinum or equivalent top rating from a national green building rating program, represent a non-residential type, and be at least 4645 sq m (or 50,000 square feet) in size.
“We were aiming at the top-rated green buildings built in the past 10 years, with the goal of giving guidance to future projects in terms of best-practice energy and water performance, but also to refute the claims that green buildings don’t perform.
“In fact, the average building we profile uses almost two-thirds less energy than the 2003 average of U.S. commercial buildings.”
Following is the first of four extracts from the book, from Chapter 8.
Chapter 8 focuses on the measured water and energy use of 49 high-performance buildings.
Water use intensity is heavily dependent on whether the building has a cooling tower for air-conditioning.
In Chapter 2, we introduced some expected energy performance results, shown in Table 8.1, above. Of course, energy performance will vary by building type, (e.g. research laboratories and healthcare facilities typically use three to five times [or more] the energy used in office buildings), but it’s important to set some markers in the ground. The best marker is energy and water-use intensity, measured per unit building area. Based on the case-study data, we provide the following table as a guide for future projects.
|Energy Use Intensity||Water Use Intensity|
|Western Europe||100 –200 kWh/sq.m./year||150 – 200 liters/sq.m./year|
|North America||10 – 20 kWh/sq.ft./year,31,000 – 65,000 BTU/sq.ft./year||10 – 20 gallons/sq.ft./year|
|Australia||100 – 200 kWh/sq.m./year||300 – 600 liters/sq.m./year|
To measure carbon-emission reductions, we need to be concerned with the source energy use (such as the energy consumed and carbon emitted at the power plant).
Since about 70 per cent of large non-residential building energy use comes from electricity, its source energy that will ultimately drive carbon-neutral design considerations.
So the power source also matters; in countries where most power comes from hydroelectric plants, the ratio of source to site energy could be nearly one-to-one. In regions where coal-fired electricity is the norm, the ratio can be as high as three to one. So designers also need to take into account regional differences in power supplies in determining what really constitutes a “zero-carbon” building.
By producing on-site solar power equivalent to a building’s annual energy use, one can get pretty close to a zero-carbon building (excluding the carbon content of the building materials).
|End Use||Energy Use (kWh)||Percentage of Total Load(With Space Heating)||Percent of Electrical Load Only|
|Space Heating (steam) @ 10,553 million BTU||3,092,001||14.6||—|
|Fans – Interior||3,339,364||15.7||18.3|
|Fans – Parking Garage||903,701||4.3||5.0|
|Service Water Heating||1,378,486||6.5||7.6|
|Receptacle Equipment (Plug Loads)||4,847,612||22.8||26.6|
|Elevators & Escalators||2,206,647||10.5||12.2|
Reviewing estimates of building electrical energy requirements, organized by end uses, is a very practical way to look at low-energy building design. Figure 8.1, above, shows the split between various energy uses at a large office building, One Shelley Street, in Sydney, Australia.
You can see that lighting is 22 per cent; air movement and space conditioning total nearly 40 per cent; with the remaining energy in other uses. Trying to design a low-energy building requires considering all uses, including perhaps 25 to 33 per cent devoted to miscellaneous uses and “plug/process loads” from all types of equipment.
To these totals must be added an additional energy demand for direct thermal applications (typically representing 25 to 30 per cent of total building energy consumption) such as water heating, and even cooking, a demand that will vary greatly by building type.
Examining a high-performance new building in China, the World Financial Center in Beijing (profiled in Chapter 9), one can see that the projected distribution of energy end uses shows dramatically different characteristics. Table 8.2 shows that the largest single energy use is plug loads.
In this high-performance building in a temperate climate, the largest end uses are, in order: plug loads, ventilation fans, space heating, interior lighting, water heating, and space cooling. These together account for more than 77 per cent of the total projected energy use. In this climate, heating is relatively more important than in Sydney. Interestingly, plug loads are significantly impacted by occupant behaviour, and many building science researchers are beginning to study how to persuade occupants to become more engaged in reducing building energy use.
One can also look at the difference between the lower-rise Sydney (10 stories) building and the higher-rise (22-storey) Beijing building, with elevators representing a more important load in the Beijing building, and pumps a much smaller load, whereas in Sydney the building employs direct cooling from Sydney Harbour, requiring considerable pumping energy.
Energy Use in Case-Study Projects
Figure 8.2, Projected Annual Energy End Uses for World Financial Center, Beijing, China, above, shows the measured site energy use intensity for case-study buildings, organized by region. Operating data is from the individual case studies in Chapter 7. There was simply neither data nor time to calculate the primary (source) energy use for each building, but this can be done by interested researchers. The reader can also readily see from Figure 8.2 that certain building types such as research laboratories and healthcare facilities have much higher energy use intensities than office or academic buildings.
|Americas||163 kWh/sq.m./year||18 examples|
|Europe||150 kWh/sq.m./year||15 examples|
|Asia Pacific||124 kWh/sq.m./year||12 examples|
What one can see in Table 8.3, Median Energy Use Intensity, by Region, above, and Graphs 8.2a, Energy Use Americas, b, Energy Use Europe, and c, Energy Use Asia Pacific, also below, is that most projects’ site energy use exceeded 100 kiloWatt hours/square metre/year, although about 20 per cent were able to reduce that number to 50 or 60, or even lower.
To reach a truly “stretch” goal of 100 kWh/sq m/year of primary (source) energy use would require most projects, with such technologies as ground-source heat pumps or free cooling from a nearby cold-water body, to reduce total onsite energy use to nearly 50 kWh/sq m/year (energy use intensity of 16,000 Btu/sq.ft./year), an achievable number in theory, but not yet widespread in practice.
Of course, with on-site solar-power generation (or in the case of one building, a neighbouring forest set aside for permanent conservation and carbon-fixing), it’s possible to have a zero-carbon building with an EUI (base building plus tenant load) of 30–35 Btu/sq ft/year [95-110 kWh/sq.m./year], as we saw for the NREL RSF I building in Colorado and the Zero Energy Building in Singapore.
So, for designers, there are now clear targets: achieve at least the median energy use of similar LEED Platinum, BREEAM Excellent/Outstanding, 6-Star Green Star buildings in your region. Of course, many projects now aim at the low end of the energy-use range and have a clear goal to match the “best in class” results already obtained in that region.
|Building Type||Energy Use Intensity(1000’s of Btu/sq.ft./year)||Energy Use Intensity (kWh/sq.m./a)|
|Healthcare – Inpatient||91||287|
|Office, 10,000 to 100,000 sq.ft.||36||113|
|Office, greater than 100,000 sq.ft.||42||132|
Beyond actual results, it’s useful to look at what projects should achieve to meet the [US] “2030 Challenge” goals introduced in Chapter 1. Table 8.4, the final table above, shows what these goals would be for 2010, representing a 60 per cent reduction in energy use from US national averages in 2005.
Recall that by 2015 new buildings should be performing 16 per cent lower than these levels, to meet the 2030 Challenge goal of a 70 per cent reduction (by 2015).
One can see that the median energy use of the world’s greenest buildings barely misses the target in Europe and the Americas, but exceeds it by about 15 per cent in Asia/Pacific, region, demonstrating that in some places the best buildings are on a path toward carbon-neutral energy use by 2030, but that in other places, designers, builders and operators still have a way to go, to meet even interim energy demand targets.
See below for more graphs
And buy the book