Realizing that in design of Zero Net Energy (ZNE) projects, the integration includes not only technology itself, and also the expansion of technologys use and collaboration producing a collective vision by many people of similar minds. Today we see hundreds of American webinars where various companies are teaching the use of their products, however a very few teach principles that govern the selection of the products.
Furthermore, we realized that the third industrial revolution is not only about the energy sources as were the two previous revolutions (with focus on steam or fossil fuels), but about the integrated world of communication and energy. For the use of decentralized and distributed sources of renewable energy we need a strong increasingly international communication network. Information Technology (IT) changed our social life; now we have to learn how to share our experience in the attempt to introduce the principles of ZNE building physics to the process of integrated design.
The average energy use for commercial buildings in North America in 1990 was 315 kWh/m2 . Since 1990, energy use in commercial buildings steadily declined, reaching 250 kWh/m2 in 2002. Note, however, that this was equivalent to the energy use of commercial buildings in 1920. Consequently, a masonry building no insulation built 80 years ago consumed as much energy as a shiny, glass-clad building constructed today! This of course does not address the increased power functions that current modern buildings require as compared to the state of the art in 1920 (Energy Consumption in Mid and High Rise Residential Buildings in British Columbia by Graham Finch, Eric Burnett, and Warren Knowles, in BEST 3; www.thebestconference.org ).
In contemporary office buildings, the office equipment and computers use 10% of total energy but energy for lighting uses 28%. The average person might believe that in 1920, people used less efficient lights in buildings that had no thermal insulation, air barriers or most other energy saving measures. It might be difficult to understand then why we use more energy today than used in the 1920s. The fundamental conundrum is that despite these facts, from 1950 to 2000 there has been a 3-fold increase in emissions attributable to buildings,
This is the energy situation in which we find ourselves and in which we as a society have agreed that by year 2030 we will return to carbon neutral construction last seen on the North American Continent in the mid 19th century. To understand this, we need to review the changes in building construction that have taken place over the past almost century of building development.
The construction of a masonry building took a long time. As the load bearing function required thick masonry walls on lower floors and lighter at the top floors, such a building had a huge thermal capacity. The floors contained steel beams and masonry blocks. The walls were airtight because of exterior and interior lime-based plasters (stucco). Lime develops strength slowly, allowing on settlement and movements of the walls. Heavy and typically oil painted wood of double windows were carefully integrated with the masonry walls. Windows area was small. From a building physics point of view these buildings were airtight, massive and well integrated. Because of inefficient and periodic heating sources coupled with the thermal inertia of massive walls, the indoor temperature varied slowly between periods of comfort and discomfort. Natural daylight facilitated by floor plan to window aperture planning produced mostly daylit buildings with reduced use of inefficient artificial lights.
A number of significant developments took place in the 1930s. Use of building paper weather barriers distinct from roofing materials became prevalent. Building paper placed on the external side of the wall sheathing impeded the movement of air and rain while permitting moisture to permeate to the outdoors. To improve thermal comfort, wall cavities were filled with insulation, with first wood chips, paper and other available materials. These insulations sometimes stabilized with lime included shredded newsprint, mineral fiber and fiberglass batt insulation. Yet, the presence of thermal insulation in the wood frame cavity lowered the temperature on the outer side of the cavity, leading to vapor condensation creating durability problems within the walls.
Paper vapor barriers were added to the warm side of the wall to slow the migration of moisture into the insulation thereby increasing the walls effectiveness. Vapor barriers reduced the flux of vapor coming from the warmer indoor environment, thereby reducing condensation within the wall and insulation layers. A practical unit of permeance describing acceptable level of vapor flow retardation by a wood plank was introduced and named 1 perm (57 ng/m2 s Pa).
Post WWII, slatted wood boards were replaced first by the plywood sheathing, then by wafer board and subsequently by Oriented Strand Board (OSB). More efficient building practices replaced lath and plaster interior walls with paper faced gypsum board panels with polyethylene vapor barriers. However for the wall to perform adequately, drying capability to the outside must be maintained. These plastic vapor barriers disallowed drying within the wall thereby reducing the moisture tolerance within modern walls.
More recent increases in levels of thermal insulation along with the increase of air barriers to eliminate air leakage through the envelope further reduce the outward drying capability of walls. Therefore, even small deficiencies within a building envelope such as leaks in windows or cladding penetrations will likely result in moisture-originated damage.
In summary, the following major changes in wall design have taken place over the last 90+ years.
Each of these collectively dramatically reduces moisture tolerance with walls and building envelopes.
Before the 1970s our society remained unconcerned with the cost of energy. Excessive air leakage and associated heat losses were inconvenient but not a serious problem. As we introduced high efficiency heating devices that eliminated the need for chimneys we introduced new problems, namely the need for air redistribution within the house. Now, interaction of the building enclosure with the heating, ventilation, and air redistribution systems in the occupied space has become part of the builders design framework, considering the “building as the system”.
Building physics tells us each floor must be separated from the others for efficient operations. This principle is applying equally to the challenges of small and large buildings alike.
So far we have talked about buildings in cold climates. What about buildings in warm climates? The situation becomes even worse, protecting the wall from rain with water-proof materials. With vapor barrier protection on the interior side of the wall, we have allowed interior moisture to build within the wall due to the point considerations and air conditioning systems inadequately removing the humidity of indoor air.
Each of the changes, while positive, produced unpredicted effects. For example, the elimination of wood strapping under exterior plaster and the replacement of lime with cement increased cracking and affected moisture management strategies, while eliminating interior plaster simplifying window mounting and sealing dramatically increases air leakage of within the walls.
On the other hand, increased living standards with the resultant increase in the indoor environmental comfort caused dramatic increases of the energy consumption. So construction improvements being fragmented themselves , brought about a tremendous increase in energy use.
While the American media talk glibly about using more renewable energy, they often forget that renewable energy is the icing on the cake. You cannot talk about icing before you have the cake. We must address our fundamental energy consumption, our energy foot print and affect dramatic reductions at the user side before trying to produce more renewable energy to offset todays untenable consumption. Building physics dictates that building systems must be analyzed and altered to use less energy before we produce more energy. Renewable energy sources still represent a drop in the bucket in comparison to the gross energy inefficiency of todays buildings. Before using the expensive renewable energy we must dramatically improve energy efficiency of the buildings themselves. Fortunately, we have the technology to accomplish this today! But change to these many “old” building systems and to designs comes very slowly. A 21st Century Concept of building science, considers buildings as investments in the future of efficiency and energy and not just costs.
As long as buildings were leaky and poorly insulated, the effect of HVAC systems on air pressure and on the durability of the enclosure remained insignificant. There was no need to understand air movements within the building other than providing a necessary supply of fresh air. That is not the situation today. Now we require well-insulated, airtight buildings where potential health problems, sick buildings and mold/ microbial contamination must be eliminated.
Today, understanding air movements in a building have become a necessity. The determination of micro air pressure differences, however incremental or difficult to measure, is required to establish the High Performance (HP) of the building as a system. This understanding of High Performance buildings produced a fundamental revision in design professionals assumptions developed over many years. Air transport control is now recognized as the most critical issue in design of building enclosures. While air tightness in building envelopes is now well recognized and quantified, achieving it in practice remains a universal challenge.
Air barrier systems are needed for the proper performance of building enclosures in all climates. Many architects and design professionals do not realize that cost of space cooling is dramatically higher than that of heating. Designers must therefore ensure thermal comfort in the warm climates more than in the cold ones. Ensuring continuity of the air barrier plane over 100% of the surface is required in all climates. Checking air barrier continuity during the design and construction stages with digital and analog tools becomes critical in all climates.
It is important to place emphasis on performance of the built assemblies as systems instead of separate materials as individual elements. Dealing with materials is frankly easier and has a nice understandable message. Building codes and standards always ascribe a specific function to a specific material because this is the only way that a prescriptive code can work. We have water vapor retarders, air barriers, thermal barriers, fire protection barriers, rain-screens etc, all with functions that are mentally coupled to specific materials. Some materials may have different functions, for example, closed-cell polyurethane foam, can be insulation, rain-screen, water vapor retarder or air barrier.
The outcome of an architectural design is modified by interactions between different materials as well as the trades involved in installing those materials in an assembly. Architectural design and the construction processes must become more holistic, integrating the expertise of highly specialized people. Collaboration, understanding and integration during the design process came to the front of the considerations for producing todays High Performance buildings. Today we stress the importance on mock-up evaluations, digital analysis and predictions, and continuous high level commissioning as separate activities in the construction process. These activities from the designers and the field must become integrated into a holistic design and construction process. This creates two results: (1) To ensure that the design concept is build-able and built as designed. (2) That the trades and subcontractors, the actual builders, integrate and actively participate in satisfying the HP building objectives.
In a nutshell, the entire process of building design and construction is moving rapidly to an integrated delivery approach with considerations of energy efficiency and High Performance building design becoming the new priority and reality.