Canadian Consulting Engineer

A Physical Affair

"Green building" and "sustainable building" have become buzzwords much in vogue these days, but the meaning of these terms is starting to be diluted and they are being misapplied for marketing purposes. On one hand, these marketing efforts are lau...

March 1, 2004  By Geoff McDonell, P.Eng.

“Green building” and “sustainable building” have become buzzwords much in vogue these days, but the meaning of these terms is starting to be diluted and they are being misapplied for marketing purposes. On one hand, these marketing efforts are laudable — persuading society to think about the impact of buildings on the environment, to reduce, re-use, and recycle. But are people getting the right message?

Recent examples have struck a chord with me. An architectural publication listed many new building projects, including award-winning single-family dwellings and “resort homes” (part-time occupancy). Some of these projects were promoted and judged in terms of their “sustainable aspects” and environmentally sensitive approaches to the building project and site.

Can someone please explain to me what is “environmentally friendly” about a 600+ square metre, two-person home, occupying a large plot of land, far from an urban centre and reachable only by a long drive in a sport utility vehicle? The heating and ventilating systems of these “prize homes” were also monuments to technology. They had complicated geothermal heat pump air-conditioning systems, outdoor heated swimming pools, energy gobbling domestic hot water heating systems to serve the high demand of the plumbing fixtures and kitchen gadgets, and near-commercial grade ventilation systems to allow the near-commercial grade kitchen cooking appliances to operate. Yet these projects were being promoted for their “sustainable design aspects.” Green-washing at its highest level, and conspicuous consumerism at its worst.

The projects described above will be used for marketing purposes by the winning teams to promote further creations of their “environmentally sensitive” design businesses. The owners will show off their neat gadgets and complicated house systems to their pals and perpetuate the cycle. I’m being cynical, yes, but in a world with natural resources being consumed at an exponential rate, one has to question the lifestyle of such owners and the designers who pander to them.

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Lead instead of follow

True sustainable design means taking a minimalist approach and trying one’s best to avoid the use of complex technology. Remember, it’s “reduce, re-use and re-cycle.” Traditionally, engineers design building systems to react to the architectural design. The promotional material for a sustainable building design guideline recently published by a large technical association contains the words, “this guide will help answer the question ‘what do I do now?'” Note the reactive nature of the approach.

I believe the correct approach is for building engineers to become more proactive in order to create really sustainable buildings. Being more proactive means using an integrated design process and working with the architects to fully explore the building physics in order to reduce the need for complex HVAC and electrical lighting solutions. Lead instead of follow!

Traditionally the engineers designing the building HVAC and lighting systems are educated about how these systems work and how to apply them. The equipment manufacturers assist (trying to sell their products) by providing packaged solutions of bundled technology, making the building engineers’ job easier and relegating many of these design folks to being catalogue shoppers and “equipment specifiers.”

But I believe consulting engineers should be experts about the building systems they design and that they should be leading the industry towards reducing the impacts of buildings on the environment. After all, most of the engineering associations’ codes of ethics have some sort of verbiage about maintaining the utmost regard for public safety and minimizing environmental impact. The “commodification” of the consulting engineering business over the last two decades has contributed to the erosion of these ethical concepts, resulting in an industry that, too often, has become a drafting service, doing whatever the owner/developer wishes, at the lowest fee, using packaged off-the-shelf solutions. Granted, some owners and developers are demanding more energy efficient and environmentally sensitive projects, but they are rare, with much of the building industry devoted to lowest first cost, low fees, and low risk/low effort designs.

Building physics

The solution? We building services engineers have to become better educated about building physics and understand how a building acts within the environment. Do so-called “climate adapted” buildings cost any more to build? Not really. It’s just a matter of reorganizing the traditional line item costs on the building budget spreadsheet in order to spend money where it counts.

The building systems engineer has to know how the building envelope design affects the indoor climate, both in terms of thermal comfort and lighting quality. The idea is to help the architects design better buildings that don’t require high degrees of technology to be habitable. Simple, passive, low impact solutions must be striven for, and they require an integrated design team approach. A short definition of a sustainable building would be that, in addition to being very energy efficient, it uses less material, uses simple passive low maintenance systems, has recycled and recyclable material as part of its content, provides a very comfortable and stable indoor climate for the occupants, and hopefully does not have an impact on the local environment and green space. The extreme case of a sustainable building is no new building at all, where we rely on buildings that may have multiple uses and occupancies over their long lifetimes, measured in hundreds of years.

From a building systems engineer’s point of view, the integrated building design approach means learning about building orientation and passive solar heat gain in the winter, and balancing that with reduced solar heat gain in the summer, while satisfying the desire for good natural daylighting to save artificial lighting cost and energy. It means making sure the glazing has high thermal resistance to reduce and even eliminate the need for perimeter heating and perimeter thermal control systems. An intimate knowledge of glazing system properties, glass performance and specifications is required, which is not normally part of the typical HVAC engineers’ toolkit.

Radiant temperatures

Another aspect is improving our knowledge of human comfort parameters. Typically HVAC engineers are concerned about air temperature, air velocity and relative humidity as comfort parameters. But mean radiant temperature and the operative or “resultant” space temperature must also be considered for a complete measure of human comfort.

The importance of mean radiant temperature can be found in the design of glazing systems. In a generally cold climate like Canada, a typical office building uses some type of double glazing, and the framing system may or may not have a thermal break to help reduce thermal bridging from the outside to the inside. In winter, the interior surface temperature of the glass and frame becomes a cold radiant cooling panel, which requires a great deal of warm air supply to overcome. Conversely, in summer time, the window becomes a radiant heating panel, requiring lots of cool air supplied to maintain some degree of comfort.

There are many examples of perimeter offices in the winter having a thermostat that indicates the ambient air temperature is 75F, but the occupant has a supplemental electric heater plugged in under the desk, and he or she still “feels” too cold. That situation is a result of the radiant cooling effect of the glass creating a “resultant temperature” of around 66F. The typical HVAC design reacts to conventional glazing by providing high-peak capacity perimeter thermal control systems. They use lots of cold or warm air that reacts quickly to the high, rapidly changing thermal loads of solar gain, as well as to transmission heat losses and gains. The radiant effect of the glass isn’t normally considered by most HVAC engineers, but yet it can be up to 50% of the human comfort equa
tion!

Building thermal mass and the “enertia” (thermal time lag) aspect of high mass buildings must be considered in the overall study and in calculating the size and type of occupant comfort control systems. High mass buildings can retain stable temperatures and virtually eliminate day to night temperature swings — a common approach in pueblo structures and Middle Eastern architecture. This is building physics in action! Building systems engineers must understand how the building envelope and structure react to the local climate. The knowledge is especially critical when using natural ventilation schemes. The conventional approach has been to calculate and size main HVAC plant equipment for the highest peak loads and then carry on to add various controls to allow the system to operate at part loads for much of the time. By accounting for thermal mass storage, and the time delay of the building thermal loads in relation to occupancy times, they can eliminate significant amounts of the peak heating and cooling loads, saving material, energy and operating costs.

Natural ventilation — not a panacea

Natural ventilation systems have the potential to provide low energy, comfortable fresh air movement in a building, provided the system has been very carefully modeled and designed with respect to the building shape, and external and internal characteristics. Even then, the effectiveness of the natural ventilation system is subject to the whims of nature — wind speed (or lack of), wind direction, ambient air temperature and humidity, buoyant plume generation within the building, air flow paths through the building, and the quality of the ambient air. Again, the proper application of natural ventilation systems requires a great deal of building physics knowledge, as well as sophisticated computational fluid dynamics computer modeling, if there is any hope of the reality matching the theory of the design.

And don’t forget that “natural ventilation” is raw, unfiltered outdoor air containing whatever airborne material is in it, at whatever ambient humidity level it is, being wafted through the inside of a building. The ambient outdoor air quality must be clearly ascertained for a natural ventilation system to be applied as an option for a building system.

If I sound cautionary about natural ventilation, I am. There are many who believe in natural ventilation as a requirement for a low energy building system, but the track record leaves a lot to be desired. Some naturally ventilated buildings have higher than anticipated heating loads, poor airflow in certain areas, significant temperature gradients, uncontrolled drafts, etc. Personally, I am on the controlled dedicated outdoor air supply (DOAS) bandwagon since it has many advantages over natural ventilation, for very little additional cost and energy differences.

A concept that leads to very good energy efficiency as well as improved occupant comfort, is to separate the temperature control function from the ventilation air function and to heat and cool the space with hydronic radiant systems. Conventional building HVAC systems use air to heat, cool and ventilate the occupied space. Consider that fan energy can be up to 70% of an HVAC systems’ energy use, and that air has a very light thermal mass which requires a very high peak load to be able to counteract changes in thermal loads in a space. Water, with its higher thermal mass can hold over 3,400 times as much energy per unit mass compared to air, so transporting energy around a building with a hydronic system is inherently more energy efficient. If the temperature control in a space is provided by hydronic radiant panels, applied capillary tubes, or radiant slab systems, then the air system can simply be reduced to a constant temperature DOAS ventilation system that supplies only the air needed for healthy ventilation and make-up air for exhaust air systems. This type of system can result in significant energy and operating cost savings, and it uses less material for sheet metal ductwork, fan equipment, and mechanical plant equipment. The reduced plenum space requirements for systems like this can also allow the building designers to use less floor- to-floor height, reducing the size of the building and saving building structure and envelope costs.

The key to better building design is expanding the knowledge base of the design team as a whole, particularly about the effects and interactions of building physics. This approach also means looking at building component costs differently. A well integrated building design can still meet an aggressive capital cost budget, provided the owner allows the detailed cost allocations to suit non-conventional approaches for specific building components and systems. An example is high performance glazing. It can be easily shown that for every dollar increase in the cost for better glass and framing performance, a dollar can be saved from the HVAC system costs — provided HVAC system designers can move away from the “all-air” system approach.

A big challenge will be to overhaul professional fees, which, for building services engineers, have traditionally been based on a percentage of construction cost. In a “whole building/integrated design” process the engineers must be compensated using some other formula, since there may likely be more effort required to design a low energy use building system that also has very low capital costs.

Geoff McDonell, P.Eng., is a senior mechanical engineer with Omicron Consulting Group of Vancouver, and is a LEED-accredited professional

References

http://projects.bre.co.uk/natvent/reports/barrier/nlbar.pdf

http://erg.ucd.ie/EC2000/EC2000_PDFs/natural_ventilation.pdf

http://fire.nist.gov/bfrlpubs/build03/PDF/b03001.pdf

http://doas-radiant.psu.edu/

http://www.buildingsgroup.nrcan.gc.ca/projects/idp_e.html

http://www.ggashrae.org/documents/Olesen_Radiant_Cooling.pdf

http://www.hydronics.org/articles/Radiantcooling/radiant_cooling.htm

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