A definition of the mirage

 

Average energy use of multi-unit residential buildings in Canadian city of Vancouver in 1990 was 315 kWh /m2 and declined, reaching 250 kWh /m2 in 2002. This would be considered all right, if not that someone found that the average energy use in similar buildings in 1920s was the same. So, the masonry building without any insulation built 80 years before, consumed as much energy as a shiny, glass-clad building constructed in 2002. This of course says nothing about the increased functions that current modern buildings are fulfilling compared with what was the state of the art in 1920s.

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In contemporary office buildings, the office equipment and computers use 10% of total energy but energy for lighting uses 28%. For a layman, who believes that 1920 people also used lights (and probably less efficiently than now) and who knows that today we now, have thermal insulation, air barriers and many other energy saving measures it is difficult to understand why we do not use less energy than used in the 1920’s. Furthermore, someone observed that from 1920s to 2000s there has been a 3-fold increase in emissions attributable to buildings.

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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 come back to the carbon neutral new construction, last seen on this continent in the mid 19th century. To see how this can be accomplished we need to review the changes in building construction that took place over the last 60 years.

 

Buildings in 1920

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The construction of a masonry building took a long time. As the load bearing function required thick masonry walls on lower floors that became and much 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. Excellent, heavy, and typically oil painted wood of double windows were integrated with the masonry walls. Windows area was small. From building physics point of view the building was airtight, massive and well integrated. Because of its inefficient and periodic heating sources, the indoor temperature varied between periods of comfort and discomfort.

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Improvements of heat, air and moisture controls in the cold climates

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A number of significant developments took place in the 1930’s. Use of building paper weather barriers, as distinct from roofing materials, became the rule. The building paper was placed on the external side of the wall sheathing, impeding the movement of air and rain while permitting some moisture to permeate to the outdoors. To improve thermal comfort, wall cavities were filled with insulation -- first using wood chips and other available materials, sometimes stabilized with lime, then shredded newsprint and eventually mineral fiber and fiberglass batts. 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 that, in turn, was detrimental to the durability of the wall.

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Vapor barriers were introduced to reduce the flux of vapor coming from the warmer indoor environment alleviating the condensation. 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).

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Following WWII, wood boards were replaced first by the plywood sheathing, later by wafer board and subsequently by Oriented Strand Board (OSB). Use of paper faced gypsum panels for the interior finishes emerged during this evolution, driven by the need to reduce construction time.  Incidentally, use of polyethylene vapor retarders continued this trend disallowing wall drying towards the interior. Moisture tolerance of modern walls declined. Despite use of materials that are progressively were more susceptible to moisture, these materials still performed adequately when properly used. Nevertheless, to perform adequately drying capability to the outside became critical.  

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More recent increase in levels of thermal insulation and requirements for air barriers to eliminate air leakage through the building enclosure, however, reduced the outward drying capability of walls so much so that deficiencies, such as leaks at windows or cladding penetrations, may now more easily result in moisture-originated damage.

 

In summary, the following major changes in wall design have taken place over the last 60 years.

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1) Increased levels of thermal insulation

2) Increased level of water vapor resistance

3) Increased air tightness of the walls

4) Reduced moisture buffer capability

5) Introduction of more moisture sensitive materials

 

Each and all of these can dramatically reduce the moisture tolerance of residential walls.

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Before the 1970’s our society was not concerned with cost of energy. Excessive air leakage and associated heat losses were more of an inconvenience than a serious problem. Introduction of energy conservation as a means of reducing the impact of oil imports, first started in the 1970’s and then accelerated in the last decade caused the requirement of mechanical ventilation in houses.

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As we introduced high efficiency heating devices that eliminated the need for chimneys, we introduced a new concern – 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 builder’s design framework and the phrase such as “building as the system” describes it best.

 

As for the large buildings, building physics tells us each floor must be separated from the others so the problems of small and large buildings are alike.

 

Interim summary

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One can see that innovation involves different material improvements all centered around improvement product manufacturing but these trends coalescence around improved indoor environment and individual occupant comfort in particular.

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From building physics point view the common for those improvements is fragmentation. Each of the changes, while positive in itself, may produce unpredicted effects for the building. E.g. elimination of wood strapping under exterior plaster and replacing lime with cement increased cracking and affected moisture management strategy; elimination of interior plaster or introduction of simplified methods of window mounting, both dramatically increases air leakage of the walls etc.

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Increased comfort caused increase of the energy use; so the second observation is a relation between energy consumption and occupant comfort.

 

To alleviate the problem, one must examine means of retaining comfort while reducing consumption of energy. While the media talk glibly about using more and more of the renewable energy, they do not realize that renewable energy is like an icing on the cake. You cannot talk about icing before you have the cake. Renewable energy sources still represent a drop in the bucket in comparison to the gross energy inefficiency of today’s buildings.

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The need for air pressure control in buildings

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As long as buildings were leaky and poorly insulated, the effect of HVAC systems on air pressure and on the durability of the enclosure was not significant. There was no need to understand air movements in the building other than providing a necessary supply of fresh air. That is not the situation today. Now we require well-insulated, airtight buildings in which potential health problems (mold/ microbial contamination) are minimized.

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Today, understanding air movements in a building is a necessity. The determination of air pressure differences, however small and difficult to measure, is needed to establish the performance of the building as a system.  This is probably one of the key reasons for a fundamental revision to many assumptions that have developed over the years.  Air transport control is now recognized as the most critical issue in design of building enclosures. While the need for air tightness is now well recognized, achieving it in practice is still a challenge.

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Air barrier systems are needed for the proper performance of building enclosures in all climates. Ensuring continuity of the air barrier plane over 100% of the surface is required. Air barrier continuity must be checked both during the design and during the construction.

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Evaluation of systems not materials

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It is important to analyze performance of assemblies not on the materials. Dealing with materials is easier. 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 retarder, air barrier, thermal barrier (fire protection), rain-screen etc, and functions are mentally coupled with materials. But some materials may have different functions, e.g. closed-cell polyurethane foam, can be an insulation, a rain-screen, water vapor retarder or air barrier.

 

The outcome of an architectural design is modified by interactions between different materials and the trades involved in installing them in an assembly.  Architectural design and construction processes are holistic and involve highly specialized people – how should they collaborate during this process? This aspect of design is so important that we stress the importance on mock-up evaluation and continuous commissioning as the separate activities in the construction process.  This is to ensure that the design concept is buildable and that all the trades learn what they must do to satisfy the building objectives.

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Finally, we have established that the future belongs to green buildings.  What are the considerations that make the complex called the “green value” of a building?

 

Key components of “green value” of the building

 

The list of key components of “green value” during the design and construction of buildings includes the following considerations:

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1. Design for durability

2. Design for energy efficiency and efficient use of materials

   1. Separation of ventilation/air distribution and heating/ cooling systems

   2. Instantaneous gas heaters or solar integrated domestic hot water systems

   3. Possible increased use of day lighting

   4. Analyze indoor environment with view to occupant health and productivity

   5. Flexibility, i.e., lower costs associated with changing space configurations

   6. Possible re-use of materials in building enclosure systems

   7. Design from cradle to cradle i.e., considering if the existing components can be used in the next generation buildings

3. Design to be efficient enough for use of renewable resources now or later

   1. control of inter-zonal and interstitial air flows

   2. evaluation of building enclosure performance under service conditions

   3. provision of extending use of renewable resources when they become economically justified

4. Building and testing the mock-up of building enclosures for commercial buildings

5. Using the commissioning process as a part of the design and construction process (from statement of building objectives through the construction and occupancy tests)

1. Trouble shooting study of design drawings is the first step in commissioning

2. Testing air leakage as a QA means during construction

3. Testing air quality of occupied space after occupancy

 

Number one in the green value complex is the durability. If one can extend the service life of a building, say by 20% longer than a typical construction, one reduces the annual costs; save materials that would be used in the replacement building so that materials and energy can be used for other productive means. In this process the direct savings on replacement materials and energy provide a multiple effect that may be compared to injecting 3 to 5 times more money into the local economy.

 

The second critical consideration is to apply all passive measures before progressing to the renewable energy generation. The passive measures that are often neglected, even though they offer the most value for the money, are:

 

1. Simple building shape and mass placement that respects the climate (saves the cost and reduces energy use in adaptable systems)

2. Increase airtightness (cost little, saves lots)

3. Increase insulation and reduce thermal bridging (costs but saves energy)

4. Improve selection of windows (increases costs but saves operating cost)

 

Translating this list into more specific requirements one may give examples, as follows:

 

1. use free geothermal pre-cooling or solar air pre-heating

2. use solar support to hot water system (often leased)

 

These examples are followed by more complex technical measures ranked for their energy saving potential:

1. use dedicated ventilation air system

2. use radiant ceiling of floor cooling

3. use heat and energy recovery ventilators

4. use diagnostics for malfunctioning of a system component

5. use brushless DC motors

6. use small centrifugal compressors

7. use micro-channel heat exchangers

 

In short, we stress that high performance building enclosures are a pre-requisite for the next generation of HVAC and lighting systems. Efficient energy management can dramatically reduce thermal loads which in turn encourages use of distributed HVAC systems.

 

One can also observe a trend for building enclosures to become multi-functional. Dynamic envelopes can be used to pre-heat or pre-cool indoor air; and by using filters and dehumidifiers on supply air these enclosures can also modify the indoor environment. Advances in window technology permits use of increased day lighting. With reduced thermal loads several technologies previously discarded in research are becoming more economically viable. Those include effects of thermal mass and phase change materials – even though these effects are climate dependent – they are coming back as significant improvements in the technology mix.

 

In a nut shell- designing building as a system produces a better and less expensive building than traditional material selection to a preconceived building.