An Architect's Guide for Sustainable Design of Office Buildings

4. Energy Use

4.0 Introduction

Energy use is at the centre of the environmental debate and reducing the amount of non-renewable energy needed to operate buildings will remain a key performance issue.

It is estimated that the average yearly cost for energy in Crown-owned facilities is approximately $20/m². Although this down 25% from figures available in 1979, energy costs still represent approximately 30% of the O&M total budget in office buildings. PWGSC will pursue further reductions vigorously and cost effectively with due consideration for the quality of the work environment, as pledged in its Sustainable Development Strategy.

Global Warming

Although price increases and security of supply of a dwindling resource will continue to remain important concerns, the environmental implications of continued fossil fuel use will guide future policy. The current dependence on fossil fuels and nuclear power, and the attendant production of 'greenhouse gases' and other pollutants imposes a critical pressure on natural systems and human health.

Over the millennia the earth's climatic patterns have changed considerably as a result of natural events. Current increases in global warming and attendant climate change derive largely from the greenhouse effect associated with human activities. The principal atmospheric gases which exacerbate the greenhouse effect are carbon dioxide, water vapour, methane, nitrous oxide and ozone. In 1987, human activities released an estimated 8500 million tonnes of carbon in the form of CO₂ primarily from the burning of fossil fuels; 255 million tonnes of methane and 0.772 million tonnes of CFC's.

Emissions of greenhouse gases need to be reduced by 60-80 percent immediately to stabilize their concentrations at current levels and methane would need a 15-20 percent reduction.^[1] Canada, along with 150 nations signed the Climate Change Convention in 1992 requiring that developed countries continue to report on actions with the aim of returning their emissions of CO₂ gases to 1990 levels by the end of 2000. This requirement has been incorporated into the departmental Sustainable Development Strategy.

Local Air Quality

Many air pollutants such as Oxides of Nitrogen (NOx), Oxides of Sulphur (SOx) and Un-burned Hydrocarbons (Methane, etc.,) emitted during the production of building materials and the burning of fossil fuels also have adverse local and regional environmental impacts: urban smog and acid rain. These create health risk to humans, other species, terrestrial vegetation, and marine life.

The efficient and appropriate use of energy has a substantial impact on the environment in terms of conserving fossil fuels, reducing pollutant air emissions and minimizing consumption and waste. The construction and operation of buildings are significant contributors to the emission of greenhouse gases. It has been estimated that fifty percent of atmospheric carbon dioxide, the main contributor to global warming, comes from buildings and related industries.^[2]

Sustainability will require:

• A drastic reduction in the amount of energy required to meet user needs through a significant improvement in the energy efficiency of buildings, their systems and their operation;
• Since our transition to sustainability will parallel our adoption of renewable energy sources, buildings must also be provided with or capable of being modified to accommodate solar and other renewable energy collecting systems;
• A comprehensive view of energy use with the aim of matching the quality of energy to the end-use, and how waste heat from one process can be usefully employed in another.

4.0.1 Life-Cycle Energy Use

Life-cycle building energy use includes the energy required to:

• Produce and transport building materials, components and assemblies and to construct buildings;
• Heat, cool, light and ventilate, run equipment and to maintain and repair buildings;
• Disassembly and demolition at the end of the building or assembly's useful life.

Energy accounting over the past fifteen years has focused almost exclusively on operational energy use in buildings and the development of strategies to reduce it. The energy to produce buildings - their embodied energy - is an emerging environmental concern.

A comprehensive energy and cost analysis includes:

• Evaluating alternative energy strategies and material choices with respect to life-cycle energy use, i.e., operating plus embodied energy use;
• Examining techniques which reduce the recurring embodied energy associated with maintenance, repair and refurbishment over the life of building.

4.1 Reducing Lighting Energy

Lighting in office buildings can represent one of the largest component of energy use. Lighting represents one of the most direct means of achieving energy reductions and improved occupant satisfaction.

Daylight

All existing office buildings have windows and offer some potential for daylighting. However, direct sunlight in the workplace and attendant excessive solar heat gain are undesirable.

De-lamping

De-lamping, under-lighting and similar strategies reduce operating energy and can be effective ways of reducing the existing lighting energy use but, if done insensitively, often can sacrifice productivity and user satisfaction. Lighting quality must also be a prominent goal in energy efficient lighting design.

Lighting Levels

Office lighting standards are specified by the PWGSC Office Lighting.^[3]

Older standards of 700-1000 Lux exceed those in current lighting guidelines. The most appropriate approaches provide 300 to 500 Lux of ambient light, supplemented with user controlled task lighting.

Lighting Energy

ASHRAE/IES 90.1^[4] specifies maximum lighting densities of 1.8 W/ft² (19.4 W/m²) for office uses. A good lighting design should achieve quality lighting of office interiors with lighting densities between 0.9 and 1.3 W/ft² (9.5 - 14 W/m²).

Task/Ambient Lighting

Many lighting strategies in existing buildings would have been premised on the general lighting of the entire office floor. Task-ambient lighting permits a lower overall general lighting and attendant energy reductions.

4.2 Selecting Lighting Equipment

Lamps

Compact fluorescent and full size fluorescent lamps with small diameters (T-5, T-8 and T-10) and triphosphor coatings offer the best of energy efficiency and colour rendering.

Ballasts

In addition to greater longevity and the elimination of flicker, electronic ballasts offer:

• Considerable operational energy savings;
• Ability to dim fluorescent lamps at lower costs than standard ballasts.

The replacing of older fluorescent light ballasts and other electric equipment may require handling Polychlorinated Biphenyls (PCBs), a hazardous material.

Luminaires

Luminaires and lighting systems employing advanced optical systems and efficient reflector materials, such as polished reflectors and parabolics offer significant energy gains.

Using a good quality flat prismatic lens with a sharp cut-off (such as holophane fish eye lens) is much cheaper and more efficient than using deep cell parabolics.

Improved lighting energy efficiency can be achieved by:

• Specifying smaller T-5, T-8 or T-10 lamps with triphosphor coating;
• Specifying high frequency ballasts;
• Specifying low Total Harmonic Distortion ballasts, i.e., 17.5% or less since harmonics can cause interference with electronic equipment, current/voltage surges, overloading of transformers, etc.

4.2.1 Lighting Control

Energy benefits from daylight will only accrue if the electric lighting is reduced at those times when daylighting is making a useful contribution to the interior illuminance. This can be done through zone switching or dimming operated by photosensitive controls.

The quality of lighting control can be improved by:

• Providing a mixed approach to lighting control which combines local, manual switching to meet the needs of the users and automatic 'fail-safe' features such as occupancy sensors, etc., to reduce wasted lighting energy;
• Providing manual switching to users in all rooms;
• Providing separate switching in all days lit zones;
• Using a controlled stepped lighting strategy, e.g., using three tube luminaries wired for two switches allows four lighting settings: off, one tube, two tubes or three tubes;
• Using photocell controlled dimming ballasts to adjust output of fixtures in response to daylight;
• Scheduling each area on its own, with override, (often by pressing a number on the phone which signals the computer to switch lights) can reduce demand on the lighting system;
• Specifying time switches and other systems for turning off lights on a particular floor or the entire building.

4.3 Selecting HVAC Controls

Energy Management Strategies

Introducing more energy efficient technologies and components which depend on regular management involvement and maintenance often leads to an increase in energy use rather than a reduction. This is usually due to failure of occupants and operations management to fully comprehend their operation and sustain their maintenance.

Energy management control systems which are simple to operate, combined with operator training and periodic system evaluation are useful approaches. Such an approach will overcome the problem of increased energy use and, when applied, can demonstrate the savings that will justify the additional investment.

Energy management strategies are best when they:

• Are capable of being operated and maintained simply, efficiently and effectively;
• Have a greater number of HVAC zones with more flexible systems and capable of being reorganized to cover small areas;
• Provide for setback of temperature during unoccupied hours;
• Are designed for optimal heat-up and cool-down strategies prior to building occupancy;
• Accompanied by individual meters or sub-meters within the building;
• Provide continual feedback to users and management on building energy use.

4.4 Selecting Primary HVAC Equipment

Primary systems such as boilers, chillers, cooling towers, etc., convert primary energy sources such as fossil fuels and electricity to thermal transport media such as steam, hot water, and chilled water.

The conversion efficiency of the equipment relative to the thermodynamic loads imposed is a critical issue in plant selection.

Sizing Primary Systems

Although primary systems must have the capacity to meet worst-case or "design" conditions, in most circumstances they are actually operating at output levels well below design capacity and outside their most efficient range. Proper equipment sizing can have much greater performance impact than any intrinsic differences between technologies.

System Flexibility

Offices built in the 1950s and 1960s, with their massive central services designed to operate between 9-5 do not lend themselves to after hours operation on a reduced scale. Energy efficiency and greater operational flexibility will require more flexible HVAC systems with more zoning, capable of being reorganized to cover small areas.^[5]

System Reliability

Equipment durability and cost can become crucial questions. A system intended for 8-12 hour use may not be good enough for 24 hour use. Round the clock space must be more reliable than conventional space since the number of hours where the building can be closed for maintenance will be less.

When designing the primary equipment, energy and operational performance can be improved by:

• Examining the potential for using ground source/ geothermal, solar and other renewable sources of primary energy prior to looking at conventional sources, and evaluating them on a life-cycle basis;
• Carefully considering the conversion efficiency of the equipment relative to the thermodynamic loads and timing imposed;
• Considering "part-load" efficiencies in plant selection since this level of "turndown" severely hampers the efficiency of many types of primary equipment (as well as adding to initial capital costs);
• Making provision for staged or variable output primary equipment which operates at peak efficiency through the bulk of the heating/cooling season, as well as separate supplementary equipment that operates efficiency only at peak design conditions;
• Where building use requires simultaneous heating and cooling of different thermal zones, using secondary mechanical systems such as area heat pumps to transfer thermal energy to meet these needs and minimize additional purchased energy;
• Reclaiming "waste" heat from building exhaust or condensate fluids to reduce overall energy use;
• Employing air and water-side cooling economizers whenever appropriate;
• Providing durable and reliable equipment in those spaces anticipated for round the clock use;
• Providing easy access to equipment by engineers and contractors.

4.5 Selecting Secondary HVAC Equipment

The HVAC secondary systems are the "distribution" portion of the HVAC system, and typically includes fans, pumps, ductwork, heating and cooling coils/devices, and associated control systems. Eliminating reheating and re-cooling of distribution fluids as a control strategy in response to the diverse loads occurring throughout a building is central to improving the energy performance of HVAC systems.

Minimizing Fan and Pump Energy

Minimizing volumes and parasitic losses such as static pressure loss to reduce fan and pump energy, and utilizing water instead of air whenever possible are emerging design philosophies. (Water is a much more efficient energy transport medium than air due to its higher specific heat and better overall controllability.)

Compartmentalization

Secondary system design should address thermal loads, ventilation requirements, and energy transport management on a zone specific basis to minimise parasitic losses and reheating/re-cooling. Decentralization, rather than centralization, is emerging as the prevailing approach to secondary system design.

Secondary System Sizing

Similar to primary systems, appropriate sizing of all secondary systems to the unique characteristics of the project at hand is essential for optimal performance and efficiency.

When designing the secondary equipment, energy and operational performance can be improved by:

• Designing a decentralized, rather than centralized approach to secondary system design;
• Sizing the systems appropriate to the unique characteristics of the area and load;
• Eliminating reheating and re-cooling of distribution fluids as a control strategy in response to the diverse loads occurring throughout a building;
• Minimizing volumes and parasitic losses such as static pressure loss to reduce fan and pump energy, and utilizing water instead of air whenever possible;
• Employing state-of-the-art and emerging strategies to reduce fan and pump energy;
• Using variable speed fan and pump controls to match system load while minimizing energy consumption.

Energy efficiencies and air quality may be gained by:

• Designing an outdoor air economizer cycle to allow the use of outdoor air for building cooling when outdoor weather conditions permit by increasing the proportion of outdoor air mixed with return system air, up to 100%.

When replacing electric motors, energy efficiency can be improved by:

• Specifying that all newly installed electric motors have efficiencies which meet or exceed those specified in clause 5.4.3 of ASHRAE/IES Standard 90.1-1989, "Electrical Motors".

4.5.1 Service Hot Water

Though the supply of hot water is not usually a major component of office building energy use, savings are possible. Low flow fixtures, pipe insulation and recirculating systems are important strategies.

When replacing equipment, energy improvements can be gained by:

• Using conservation devices such as flow limiters, timed valves etc., on hot water supply;
• Specifying that all newly installed domestic hot water equipment, piping insulation, controls and fixtures meets or exceeds the appropriate sections of ASHRAE/IES 90.1-1989 Standard;
• Placing water heaters as close as possible to point of use;
• Specifying that all fixtures using hot water which require more than 25 m of pipe length to connect them to a hot water source be fitted with point-of-use heaters;
• Specifying recirculating systems insulated throughout their entire length;
• Examining solar hot water heating systems a life-cycle basis for their feasibility.

4.6 Commissioning Guidelines

A substantial number of air quality problems in buildings result from inadequate attention paid to ensuring that all equipment is functioning properly before the occupants move in.

Full building commissioning of electrical, mechanical and other building systems and equipment is an important requirement for each new facility or major renovation.

System performance can be confirmed by:

• Provision of commissioning services according to ASHRAE Guideline 1-1989: Commissioning of HVAC Systems.

4.7 Using Thermal Mass

Thermal mass offers the threefold advantages of:

• Moderating the temperature of occupied spaces during conditioned periods and thereby minimizing or eliminating the need for mechanical cooling;
• Allowing free pre-cooling through night-time flushing in some seasons and climates;
• Absorbing useful winter solar gain and thereby offset winter heating requirements.

Mechanical cooling systems can be reduced or eliminated by:

• Reducing solar heat gain into the building through the use of improved solar control devices;
• Using inherent building mass to provide a cooling sink and combine with night-time flushing;
• Providing operable windows to provide effective cross-ventilation of occupied areas;
• Designing sensors linked to the HVAC system so that the terminal serving the zone will adjust accordingly when windows are opened during the heating or cooling season.

4.8 Upgrading Windows

Windows are a key element affecting building energy performance. They significantly influence heat loss, solar heat gain, daylight and visual access to the exterior.

If the windows are to remain, then issues of repair and maintenance for edge leakage, the possibility of changing the solar transmission by the addition of reflective films or the addition of external solar control devices are the most likely options for improvement.

If windows are to be replaced, then the choice of the replacement glazing and frames will be governed by the following considerations:

Heat Loss

The overall U-Value of a window depends on the area weighted effects of the centre of glass component, the edge of glass component that accounts for the higher heat flow rate through the spacer, and the type of frame.

Solar Heat Gain

Window design and its attendant solar control strategy should maximize useful winter solar heat gain and minimise excess solar gain at other times.

Operable Windows

Operable windows provide the opportunity for natural ventilation when outside conditions permit. To minimise conflict with energy efficiency, sensors can be linked to the HVAC system so that the terminal serving the zone will adjust accordingly when the window is opened during the heating or cooling season.

Admission of Daylight

If integrated with the electric lighting strategy, natural lighting can reduce the building's operating energy costs.

Improved performance can be achieved by:

• Specifying high performance glazings, the thermal resistance of which are based on a comprehensive exploration of building energy use;
• Evaluating the overall U-Value of the window system, not just the glazing;
• Specifying window frames which enhance the overall thermal resistance of the glazing system and provide minimal infiltration and leakage;
• Controlling excess solar gain by the combination of effective external devices and occupant controlled internal blinds to control sky glare;
• Matching high performance glazings to the various orientations of the building and carefully assess the solar transmission characteristics of the glazings used on south-facing windows;
• Carefully considering the use of tinted or reflective glasses to reduce excess solar heat gain since these also reduce daylight and obscure visual access to the exterior.

4.9 Upgrading Walls and Roofs

Again, if the walls are to remain, then strategies centre on repairing seals and possibly overcladding.^[6] If major replacement is planned, then the following issues assume importance:

Thermal Resistance

Thermal resistances for walls and roof assemblies of complex buildings should be designed to the most effective performance standards as determined within an overall analysis of building energy use. Due to the complexity of energy use in large office buildings, a simulation may be required to arrive at the best choice.

Thermal Bridging

Thermal bridges should be minimized or avoided by the use of non-conductive fasteners or the addition of thermal breaks such as insulating cladding.

Air Barrier

The total air barrier assembly should be designed to be continuous throughout the building envelope, structurally supported to resist wind load or pressurization without displacement and have a service life as long as the life of the building or, at a minimum, be located such that it may be serviced as necessary.

Weather Barrier

Engineered weather barrier systems such as curtain walls and rain screens should be incorporated where building form and site warrant, e.g., all buildings higher than four stories and on low buildings with little shelter bomb wind exposure.

4.10 References

1. Houghton, J.T., Jenkins, G.J., Ephraums, J.J., (Editors) Scientific report on the intergovernmental panel on climate change. Cambridge Univ. Press, 1990. (back to 1)
2. RIBA, Initial RIBA Policy Statement on Global Warming and Ozone Depletion, Royal Institute of British Architects, May 1990. (back to 2)
3. Pasini, I., Office Lighting, Design Standard RPSB/DGSI 1-4:95-1, Real Property Services, Public Works and Government Services Canada, Ottawa. (back to 3)
4. Stillman, D., Offices Open All Hours, The Architects Journal, Vol. 196, No. 21, 25th November 1992, pp. 47-48. (back to 4)
5. ASHRAE/IES 90.1. (back to 5)
6. Brook, M.S., Renovating Curtain Wall, Canadian Architect, May 1995, pp. 36-38. (back to 6)

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