A Necessary Low-Carbon Development Strategy for Chinese Buildings
China has, through tradition and frugality, naturally adopted a definition of what constitutes a comfortable indoor temperature that requires less energy to maintain than U.S. ideas of acceptable indoor temperature, which often begin and end with a thermostat set at 72ºF to control a central heating and air conditioning (HVAC) system. Today, China is at a pivot point where it could either move toward the U.S. approach—and dramatically increase energy consumption and harmful emissions—or build upon its existing approach, which can be supported by smaller systems or even passive approaches to thermal comfort, putting the nation on a much faster path to coal peaking and a clean energy future.
China has the opportunity to improve the thermal comfort of building occupants without increasing energy use by designing new buildings (and retrofitting old ones) to have many of the passive features that RMI’s Innovation Center demonstrates. These features require very low levels of energy to fuel them, and deliver thermal comfort that is better than what most Chinese buildings are delivering now. In the U.S., we need to change both occupier definitions of comfort and the approach to building design to drive dramatic change in building energy consumption. In China, we only have to change the approach to building design, and the Innovation Center demonstrates practical pathways to achieving this.
Over the past three years, RMI has been engaged with China- and U.S.-based thought leaders to explore ways to transform China’s energy economy in an intensive research effort, Reinventing Fire: China. (Download the Executive Summary here.) On our many trips across the ocean, we had ample time to think about the performance of buildings on each side of the Pacific. As we looked for ways to make buildings in China more efficient, an important thought kept recurring: the livability of buildings should also be improved. Fortunately, low-carbon design and low-carbon development strategies to achieve better thermal comfort without increasing energy use exist today. This is something our colleagues based in the new Innovation Center in Basalt, Colorado, know well; the center currently operates in subzero temperatures with a very small distributed heating system that requires less energy to run than the building itself generates.
BUILDING ENERGY USE CONTINUES TO GROW IN CHINA
According to the Reinventing Fire: China analysis, China is now the world’s largest market for new construction, building 1.8–2 billion m2 of floor space every year. With rapid urbanization and population growth, China’s building stock is expected to increase by 64 percent in 2050 compared with 2010. If business as usual continues, energy consumption would increase along with it from 770 million tons of coal equivalent (Mtce) to 2,270 Mtce of primary energy consumption by China’s building sector. Energy use for urban residential heating and cooling would grow most drastically of all end-uses, increasing by 100 percent and 600 percent, respectively, in the reference (business-as-usual) scenario (see Figure 1, left).
The main driver behind this projected increase in heating and cooling energy use is the desire to improve thermal comfort. Across China’s multiple climate zones and huge stock of residential buildings, only those in northern regions that benefit from district heating currently meet the internationally accepted standard for thermal comfort. Hundreds of millions of people in China’s south rely on individual heating devices that may provide only marginal thermal comfort. Also, most HVAC systems in buildings in China are manually operated at only some times and in only some spaces, and adjustments are typically made with an eye on energy bills rather than on tenants’ actual level of comfort and preferences.
PEOPLE DESIRE IMPROVED THERMAL COMFORT
China’s design standards for energy efficient residential buildings require main living areas to be heated to at least 18ºC (64ºF) in winter and cooled to around 26ºC (79ºF) in summer. This temperature range is wider than international norms allow—in the U.S. for example, a more acceptable range is 20ºC (68ºF) to 24ºC (76ºF). Likewise, the predicted mean vote (PMV: a thermal scale that predicts the mean response of a large group of people on their thermal comfort level and runs from Cold, -3, to Hot, +3) is internationally recommended to be set between -0.5 and 0.5—in China, a value of -1 to 1 is viewed as acceptable.
Not only are Chinese standards for thermal comfort below international levels, in reality, temperatures can range far beyond the standards. In Beijing, which is among the northern heating regions, rooms can often be 30ºC (86ºF) in some buildings. Because there are no individual control systems, people just open the window when it gets too hot. In some older buildings, people cannot get warm enough due to poor building envelopes and insulation. For residential buildings in Nanning, which is in a hot-summer, warm-winter climate zone, the PMV in January (the coldest month) is only -2.3 to -1.7, leaving residents feeling very uncomfortable. Several causes contribute to the gap: poor building envelope and airtightness, lower-quality materials and construction practice, as well as less efficient equipment and appliances.
People spend nearly 90 percent of their time indoors, and thermal comfort, along with indoor air quality, ventilation, and other environmental factors, has significant impact on people’s health and working efficiency. People also tend to be in better moods in a more livable place. Now millions of people in China desire better comfort. Our team has been engaging with stakeholders in China, such as the Ministry of Housing and Urban Rural Development (MOHURD) and the China Association of Building Energy Efficiency, and in our conversations they all expressed strong interest in and the urgent need for better thermal comfort in buildings in China. Comfort level and building livability are key components and focal elements of green building projects in China. The required improvements do not necessarily mean upgrading to current U.S. standards, which are sometimes excessive. Chinese usually use energy and other resources in a more conservative way, and it is good to keep these good habits.
DOES IMPROVED THERMAL COMFORT MEAN MORE ENERGY USE?
At first glance, this seems like an inevitable trend. To meet international thermal comfort standards, heating and cooling loads will most likely increase substantially over time. Luckily, solutions exist to avoid this.
In the Reinventing Fire: China scenario, thermal comfort can be achieved with no significant load increase (see Figure 1, right). For both existing and new buildings, the approach to realizing this scenario includes: (1) passive strategies to maximize natural ventilation and daylight and improve the thermal envelope to reduce the demand for heating and cooling capacity; (2) efficient equipment that meets the loads using very little energy; and (3) sensing and smart control technologies for continuous optimization of operational energy use. Each of the strategies can achieve improvements in both energy efficiency and thermal comfort.
Fortunately, China has already made good progress toward improving thermal comfort with little to no increase in energy consumption. Realizing the huge potential for energy savings, China has operated a large-scale retrofit program for residential buildings in the north since 2007. Retrofitted buildings showed improved envelope and airtightness and increased indoor temperatures of 3–5ºC in winter, according to MOHURD. The passive-building demonstration project in Qinhuangdao successfully reduced heating energy use by 62 percent and achieved much better indoor air quality. In October 2015, MOHURD released a trial technical guide to passive design for residential buildings, and more pilots and demonstration projects are emerging throughout the country.
Bold innovations can lead us even further. A leading example of extraordinary energy performance and a high level of thermal comfort is RMI’s very own Innovation Center, where our colleagues are enjoying world-class comfort in the coldest climate zone in the U.S. Through passive, integrative design, and beyond net-zero energy status, the building generates more energy than it uses in any given year while delivering and maintaining a functional and comfortable office space for staff, thanks to an innovative approach to thermal comfort. Moving away from traditional approach of blowing hot or cold air into a building through centralized and energy-intensive HVAC equipment to maintain a certain temperature, the design allows for a wider range of indoor air temperatures (actually very close to Chinese standards) with a target PMV range of -0.5 to 0.5.
The Innovation Center’s design and operation consider all six variables that drive occupants’ thermal comfort: air temperature, air velocity, surface temperature, humidity, clothing level, and activity level. Individual occupants have much more control over their own personal comfort levels, thanks to a variety of technologies that use far less energy than central HVAC. These systems include a personal comfort chair, which can provide individually targeted heating or cooling, and fans and windows that all employees can adjust for their own comfort as needed. Plus, staff members are encouraged to dress appropriately for the seasons, which is facilitated by a casual dress code. Integrative and passive design combined with occupant engagement make the Innovation Center a very comfortable net-zero energy pioneer. This approach of using small, targeted, and controllable systems has great potential in China.
As China continues with rapid new construction and China’s people expect more comfort and livability from their buildings, a new low-energy approach is much needed. Proven solutions can improve thermal comfort with little or no increase in energy consumption through integrative design, passive strategies, equipment upgrades, and occupant engagement. And with the country’s ambition to peak carbon emissions early, it is a great time for China to seize these opportunities and realize enormous potential improvements for its buildings.
Download RMI’s Insight Brief, Re-Defining and Delivering Thermal Comfort in Buildings
Download the Reinventing Fire: China Executive Summary
Image courtesy of iStock.