More on Net-Zero Buildings
Earlier in 2009, I wrote on the topic of Net-Zero Energy buildings. During this pas year, there has been much discussion at both the print and online media as well as personal encounters at meetings and seminars regarding this effort. As I discussed last year, the term net zero is used to describe a building in terms of being able to, either through the use of Renewable Energy, or a combination of renewable energy and conservation efforts, use no more energy from the electric grid or any other energy source than it is able to generate on-site. As such, a net energy building WILL almost always purchase energy from outside sources, use it during certain time frames and then regenerate new energy on site to "pay back" what it has purchased.
In most cases, if net-zero energy is achieved, it will almost always be done in the context of a single story building with plenty of roof exposure to the sun. Solar Voltaic Panels are the most common renewable energy source used in this effort, as they are the easiest to incorporate into a building and site plan design. Wind Energy is also possible, but the need for large open spaces as well as land-use and zoning prohibitions and the proximity to other neighboring sites has been a limiting factor in the use of this excellent energy source in many cases. HOWEVER, a U. S. DOE - Pacific Northwest National Lab study in last year, quoted in the August, 2010 issue of Environmental Building News (page11) shows that in five different scenarios when Chicago (a high wind area) and Phoenix ( a high sun area) wind energy actually did better in Phoenix. In addition, achieving net-zero can be VERY costly and is NOT always possible in many buildings due to energy needs per square foot far exceeding the renewable energy generation capability in the space available.
The paragraph above states the major issues working against the goal of net-zero energy buildings in so many cases. The fact that we need such a large roof area to total interior building area makes achieving this goal more and more difficult as the number of stories of the building increase. In fact, an article written in the August, 2010 issue of Environmental Building News quotes a National Renewable Energy Lab (NREL) study done as early as 2007. At that time, it was found that with a one-story building could reasonable achieve net-zero 88% of the time, while at two floors, it dropped to 48%. By the time we get to four floors, it was found that only three percent of the buildings were capable of achieving net zero.
In addition, site issues can also preclude the use of solar energy in areas where the building is shaded by significant trees, or cannot be oriented to face the best exposure to the sun on the given lot dimensions. In the case of trees, it is often far better from an environmental point of view NOT to clear the trees, as to do so, creates the unwanted effects of increased storm water and heat island effect.
This gives reason to suspect that a net zero building can have unwanted environmental side effects, the worst being the contribution of Urban Sprawl. Urban sprawl results when large amounts of land are cleared and built up with buildings often containing just a one or perhaps two stories. In this case, unlike major cities such as New York, the utilization density per square foot of space becomes so small, that the amount of energy saved by the net zero building could be offset by the negative impacts on the loss of open space and the attendant issues of storm water management and traffic. Speaking of traffic, and the need to build more roads and parking facilities, we have another issue -- that of additional energy consumption on the part of single occupancy vehicles needing to commute to a remote site where public transportation is not readily available. While we all realize that it is NOT possible or even advisable to ban all single occupancy vehicle use, its effect on a net zero energy building could offset the energy savings, as well as generate more environmental issues. Version 2 of the Living Building Challenge takes on this issue, by advocating attempting to design to the creation of car-free living. The Living Building Challenge is yet another sustainable building and design rating system, and is more stringent than that of LEED.
Given these concerns, a growing school of thought now encourages designers to take these potential negative side effects into account. One alternative is to take net zero to a broader, and larger level -- Net-Zero Neighborhoods or Communities. In this effort, rather than trying to beat ourselves to death in making each and every building totally net-zero, we will take the entire surrounding area, or neighborhood into account and aim for net-zero energy on an overall basis. This effort has many advantage, but also disadvantages. One of the main advantages is cost savings per building, as each building can pursue the most cost-efficient project in its design as space and orientation permits. The second advantage deals with the ability of being able to pool efforts by having buildings that are more able in terms of orientation to the sun (or perhaps amenable to wind power) build these efforts into the total plan, while other buildings in the community that are not able to do so, would contribute other environmentally sustaining efforts such as storm water as well as waste-water management, and pocket parks.
Another possible energy efficient design tool made available by community based efforts is the use of District Energy Systems. The idea of district energy systems is not new; many colleges, universities and multiple building campuses have employed this design for decades. In this application, a centralized heating and/or cooling plant is used. This plant is then designed to operate in stages as the need of the total campus dictates. In such a manner, during mild periods, only perhaps 30% of the total equipment will be used, allowing the remainder to be taken off-line. This 30% is now operating at peak efficiency, with automatic savings being seen. Short-cycling of compressors is minimized or eliminated, and full AFUE is seen in combustible heating equipment. Another clear advantage can be less initial building costs, as less total capacity is needed, as each building has access to the total capacity of the central plant, eliminating the need for each and every building to design for unusually large and rarely seen load capacity. This means smaller total equipment size for the overall plant. Cornell University in Ithica, New York did this with their cooling plant. I wrote on this in an entry last year.
One main disadvantage of the community or neighborhood based attempt at net-zero is financing. A second issue is that of ownership of the entire set of systems involved. Who will actually pay for the full build-out of the system? Each stake-holder is now sharing a central plant that they do not have true and full ownership of. Also, we see problems when just one building of perhaps several dozen is completed, and ready for occupancy well before the central plant can be brought on line. In this case, a temporary plant may need to be built during this time, creating the effect of consuming more raw materials and thus, not being as green or carbon-footprint friendly as intended.
I do NOT mean to say that we should abandon our quest for net-zero. Rather, we need to focus our design energies into determining what is REALLY best for the individual project that we are involved in. As net-zero can be VERY difficult and often cost-prohibitive to achieve, it may be best to concentrate our efforts in these case on doing more with an inclusive overall design that includes building massing, envelope, lighting, HVAC systems, water efficiency, open space, and storm-water management where applicable for the individual site. In other words, we would be best to do what we can do best for each site, and NOT try to conquer the impossible. It is far better to do something that results in substantial overall savings in one or more areas than not achieve a satisfactory level in the total combined project. That said, net-zero should and must be the initial design goal; this serves to challenge the design team to "put their thinking caps on" and not leave any opportunities available unused.
In most cases, if net-zero energy is achieved, it will almost always be done in the context of a single story building with plenty of roof exposure to the sun. Solar Voltaic Panels are the most common renewable energy source used in this effort, as they are the easiest to incorporate into a building and site plan design. Wind Energy is also possible, but the need for large open spaces as well as land-use and zoning prohibitions and the proximity to other neighboring sites has been a limiting factor in the use of this excellent energy source in many cases. HOWEVER, a U. S. DOE - Pacific Northwest National Lab study in last year, quoted in the August, 2010 issue of Environmental Building News (page11) shows that in five different scenarios when Chicago (a high wind area) and Phoenix ( a high sun area) wind energy actually did better in Phoenix. In addition, achieving net-zero can be VERY costly and is NOT always possible in many buildings due to energy needs per square foot far exceeding the renewable energy generation capability in the space available.
The paragraph above states the major issues working against the goal of net-zero energy buildings in so many cases. The fact that we need such a large roof area to total interior building area makes achieving this goal more and more difficult as the number of stories of the building increase. In fact, an article written in the August, 2010 issue of Environmental Building News quotes a National Renewable Energy Lab (NREL) study done as early as 2007. At that time, it was found that with a one-story building could reasonable achieve net-zero 88% of the time, while at two floors, it dropped to 48%. By the time we get to four floors, it was found that only three percent of the buildings were capable of achieving net zero.
In addition, site issues can also preclude the use of solar energy in areas where the building is shaded by significant trees, or cannot be oriented to face the best exposure to the sun on the given lot dimensions. In the case of trees, it is often far better from an environmental point of view NOT to clear the trees, as to do so, creates the unwanted effects of increased storm water and heat island effect.
This gives reason to suspect that a net zero building can have unwanted environmental side effects, the worst being the contribution of Urban Sprawl. Urban sprawl results when large amounts of land are cleared and built up with buildings often containing just a one or perhaps two stories. In this case, unlike major cities such as New York, the utilization density per square foot of space becomes so small, that the amount of energy saved by the net zero building could be offset by the negative impacts on the loss of open space and the attendant issues of storm water management and traffic. Speaking of traffic, and the need to build more roads and parking facilities, we have another issue -- that of additional energy consumption on the part of single occupancy vehicles needing to commute to a remote site where public transportation is not readily available. While we all realize that it is NOT possible or even advisable to ban all single occupancy vehicle use, its effect on a net zero energy building could offset the energy savings, as well as generate more environmental issues. Version 2 of the Living Building Challenge takes on this issue, by advocating attempting to design to the creation of car-free living. The Living Building Challenge is yet another sustainable building and design rating system, and is more stringent than that of LEED.
Given these concerns, a growing school of thought now encourages designers to take these potential negative side effects into account. One alternative is to take net zero to a broader, and larger level -- Net-Zero Neighborhoods or Communities. In this effort, rather than trying to beat ourselves to death in making each and every building totally net-zero, we will take the entire surrounding area, or neighborhood into account and aim for net-zero energy on an overall basis. This effort has many advantage, but also disadvantages. One of the main advantages is cost savings per building, as each building can pursue the most cost-efficient project in its design as space and orientation permits. The second advantage deals with the ability of being able to pool efforts by having buildings that are more able in terms of orientation to the sun (or perhaps amenable to wind power) build these efforts into the total plan, while other buildings in the community that are not able to do so, would contribute other environmentally sustaining efforts such as storm water as well as waste-water management, and pocket parks.
Another possible energy efficient design tool made available by community based efforts is the use of District Energy Systems. The idea of district energy systems is not new; many colleges, universities and multiple building campuses have employed this design for decades. In this application, a centralized heating and/or cooling plant is used. This plant is then designed to operate in stages as the need of the total campus dictates. In such a manner, during mild periods, only perhaps 30% of the total equipment will be used, allowing the remainder to be taken off-line. This 30% is now operating at peak efficiency, with automatic savings being seen. Short-cycling of compressors is minimized or eliminated, and full AFUE is seen in combustible heating equipment. Another clear advantage can be less initial building costs, as less total capacity is needed, as each building has access to the total capacity of the central plant, eliminating the need for each and every building to design for unusually large and rarely seen load capacity. This means smaller total equipment size for the overall plant. Cornell University in Ithica, New York did this with their cooling plant. I wrote on this in an entry last year.
One main disadvantage of the community or neighborhood based attempt at net-zero is financing. A second issue is that of ownership of the entire set of systems involved. Who will actually pay for the full build-out of the system? Each stake-holder is now sharing a central plant that they do not have true and full ownership of. Also, we see problems when just one building of perhaps several dozen is completed, and ready for occupancy well before the central plant can be brought on line. In this case, a temporary plant may need to be built during this time, creating the effect of consuming more raw materials and thus, not being as green or carbon-footprint friendly as intended.
I do NOT mean to say that we should abandon our quest for net-zero. Rather, we need to focus our design energies into determining what is REALLY best for the individual project that we are involved in. As net-zero can be VERY difficult and often cost-prohibitive to achieve, it may be best to concentrate our efforts in these case on doing more with an inclusive overall design that includes building massing, envelope, lighting, HVAC systems, water efficiency, open space, and storm-water management where applicable for the individual site. In other words, we would be best to do what we can do best for each site, and NOT try to conquer the impossible. It is far better to do something that results in substantial overall savings in one or more areas than not achieve a satisfactory level in the total combined project. That said, net-zero should and must be the initial design goal; this serves to challenge the design team to "put their thinking caps on" and not leave any opportunities available unused.
Posted by Alan L. Englander at 9/25/2010 7:50 PM 
Categories: Net Zero Energy Neighborhoods, Solar Voltaic Panels, Energy Conservation, Urban Sprawl, District Energy Systems, Building Envelope, Transportation, Living Building Challenge, Renewable Energy, National Renewable Energy Lab, Net-Zero Energy Buildings
Categories: Net Zero Energy Neighborhoods, Solar Voltaic Panels, Energy Conservation, Urban Sprawl, District Energy Systems, Building Envelope, Transportation, Living Building Challenge, Renewable Energy, National Renewable Energy Lab, Net-Zero Energy Buildings
Comments