Lecture Notes Unit 2

Sustainable Design Modified for Student Use

Autodesk Sustainable Design Curriculum

Sustainable Design Education Curriculum Modified for Student Use

Sustainable Design Curriculum

Education Curriculum

Unit 2) Process Change and Sustainable, Carbon Neutral Buildings

Learning Goal: Understand the definition of carbon neutrality and the process for designing carbon neutral buildings. This unit focuses on two items:

1. Developing the knowledge necessary to use carbon as sustainability metric for buildings in general and the design of new buildings in particular. 2. Understanding why it is necessary to change the traditional design process if policy goals associated with reducing green house gas emissions are to be

achieved. It is valid to evaluate the carbon footprint to each component, material or operation associated with the built environment. However, this unit focuses on the carbon footprint associated with the operating energy of a building, primarily because over the life of a building, the carbon emissions associated with operating a building are much greater than the embodied carbon emissions associated with the components of the building. In addition, it is exceedingly difficult to quantify the carbon footprint of all the components that make up a building. Carbon is the primary metric emphasized in unit 2, but it can be treated as a proxy for energy consumption. Carbon is emphasized because climate change has become an urgent issue in recent years and the built environment is responsible for a larger portion of the United States’ carbon emissions than either the transportation or industrial sectors. In this chapter, students will learn how to evaluate and reduce the carbon footprint of their building designs. Students will also be introduced to other performance evaluation metrics including water and energy consumption, site-based renewable energy potential, natural ventilation potential, daylighting potential and more.

Carbon Neutrality and Buildings The definition of what constitutes a carbon neutral building is in flux, with no uniform definition existing among the regulatory or design community. Regions of the US and of the world that utilize large amounts of hydro power for example, are in favor of a definition that takes into account the low carbon emissions of their regional power grid. Others feel it is more appropriate to utilize national averages for carbon accounting.

1 Finally, the use of carbon credits and offsets are

allowed by some carbon accounting systems and not by others. A carbon neutral building, as defined by the Autodesk® Green Building Studio

® web service

accounts for regional differences in the carbon footprint of the regional electric grid, and mandates that any fossil based electricity and fuel use be eliminated through efficiency gains or offset by onsite non-fossil based energy sources such as PV or wind energy. In addition, the carbon footprint can be reduced by purchasing biofuels or carbon offset credits. Applying this definition, if the regional electricity grid is 60% fossil fuel and 40% hydroelectric, reducing grid electricity use by 60% relative to a code minimum building and eliminating/offsetting on-site fuel use will make the project carbon neutral. Any combination of efficiency, natural ventilation, renewable energy, carbon credits and biofuels can be used to reach this goal. This definition assumes all calculations are based on annual energy use, generation and offsets. Carbon neutrality is often used interchangeably with net-zero energy consumption. A net-zero energy project is defined as a project/building that consumes only what it produces with respect to energy, on an annual basis. Renewable non-carbon sources are required to meet the typical definition of a net-zero energy building. Non-carbon renewable sources include wind energy, solar energy, biofuels and in some cases partial renewable energy “credits” are assigned for certain technologies such as geothermal heat pumps which utilize the earth as a heat source/sink. In principle the definitions could be quite different. For example, a building which uses only nuclear or hydro based electricity could be carbon neutral, even if it used a large amount of energy, but it would never be net-zero on an energy basis. It is more difficult under this definition to design and operate a carbon neutral building in a region that relies heavily on coal or other fossil fuels to generate most of its electricity.

1 Among the governmental, corporate and trade groups that are attempting to define rules for estimating carbon footprints are: The US Environmental Protection Agency, numerous electric utilities, municipal and state governments including Seattle and California, the Association of Heating Refrigeration and Air Conditioning Engineers (ASHRAE) as part of their Standard 189 Committee, and undoubtedly others.

Why is a Process Change Essential for Design of Carbon Neutral Buildings? Prior to the availability of BIM tools, estimating a building’s carbon and energy performance would require the use of a specialized consultant. The energy consultant would manually measure and/or count the surfaces, windows, light fixtures, piping, etc from the architect’s paper plans and enter the project data in an engineering software tool or spreadsheet. This process would take days to weeks and was very costly and time consuming. Evaluating the carbon footprint of multiple schemes early in the design process was out of the question for both cost and time reasons. Additionally the architect did not receive feedback on how their design decisions impacted the energy consumption and carbon footprint of the project until many important decisions had been finalized. Without feedback on how their design was performing, architects and owners were forced to rely upon intuition, MEP engineers and specialized consultants to reduce the energy consumption by specifying highly efficient lighting and mechanical equipment. Any analysis, if it occurred, was typically carried out relatively late in the design process. BIM tools such as Revit Architecture, allow architects to analyze their schematic designs using various software tools which can carry out robust analyses in minutes. This process of submitting schematic designs for energy analysis can, and must be repeated as a design progresses to compare results and minimize resource use for various configurations of building form, product selection and environmental response. This iterative approach and the need to begin analyses early in the design process is a fundamental departure from traditional approaches that involve specifying efficient components late in the design process. The responsibility for designing carbon neutral buildings requires the input of many parties, but the designing and advocating for a superior schematic design rests squarely upon architects’ shoulders. This curriculum is designed to help students successfully meet the challenge of designing carbon-neutral buildings. For the sake of presenting ideas to the students in a meaningful way, concepts are introduced in a linear fashion. However, it must be emphasized that the design process is iterative, repeating design process steps as the team moves ever-closer to an optimal carbon neutral design. Residential vs Commercial Buildings: A Brief Primer Designing a carbon-neutral single family home requires different strategies compared to designing carbon neutral commercial buildings. While many professionals

and even non-professionals may believe they intuitively understand what makes a “good building”, this intuition should be informed by energy-use data studies of existing buildings and whole building simulation results that are carefully examined and understood. The graph illustrated compares the percentage of energy end use for residential buildings in the U.S. compared to commercial buildings in the U.S. As you can see, in residential buildings the largest percentage of energy is devoted to space heating—nearly 35%; however in commercial buildings space heating comprises only about 16% of the total building energy end-use. This tells us that measures that reduce heating loads (passive solar design, increased levels of insulation, windows with a lower u-value) play a larger role in designing carbon-neutral houses than in designing carbon neutral commercial buildings. It is very common for the core of commercial buildings to require cooling, even in the winter in places like Minnesota—most commercial buildings have large cooling loads from the heat given off by people, lights, and equipment. The heating loads in commercial buildings typically occur early in the morning before the occupants arrive—or can even be the result of certain types of cooling systems that over-cool a space and require re-heating. This tells us that a passive solar design for a commercial building may not be beneficial; it may lead to increased energy use because the solar gain may not be useful for most hours. Another interesting energy-use to compare is lighting: this is the largest energy end-use in commercial buildings at around 28% of total energy compared to around 13% for houses. Again this tells us that one of the most important

Figure 1: Comparison of % of Energy End-Use

0%

5%

10%

15%

20%

25%

30%

35%

% of Total Building Energy Use

Space Heating

Lighting

Space Cooling

Water Heating

Refrigeration

Electronics

Cooking

Ventilation

Computers

Other

Comparison of Energy End Use

Residential

Commercial

Source: 2005 Buildings Energy Data Book, 2003 data

factors to consider in a commercial building is how to reduce the lighting load (which also reduces the unwanted heat produced by electric lights). Daylighting is probably the single most beneficial feature to incorporate into a carbon-neutral commercial building. Not only will the reduction in electric lights save on lighting energy, the reduction of the heat generated by the electric lights will also reduce the cooling energy required in the building. The table below compares the energy consumption characteristics of typical residential and commercial buildings.

Your Home (“skin-dominated”) Commercial Building (internal-load dominated)

Loads The loads on the heating and cooling systems are primarily dominated by the weather on the building’s envelope or “skin”. Internal loads play a smaller role.

The heating and cooling loads are driven by both internal gains (the energy required provide lighting and to supply cooling to offset the heat given off by people, lighting, and equipment). HVAC loads may or might not be very dependent on weather depending on building type.

Space Cooling

Driven by the weather and can be controlled to some extent with higher levels of insulation, shading to the building and windows, and overhangs.

Depending upon location and internal loads, many commercial buildings will typically need cooling, even in the winter, to counteract the internal loads. Higher levels of insulation are not always beneficial. However better windows (lower SHGC) and shading are important to minimize solar radiation and increase comfort.

Space Heating

Space heating is typically the largest energy-end use for residential projects. Increased insulation, improved windows (double-pane with good (lower) u-value) and careful attention to reducing infiltration are beneficial.

Often heating needs occur either early in the morning before occupants arrive, or as a result of re-heating needs for a space that is over-cooled.

Windows

If the design goal includes passive solar heating, use windows with a higher SHGC value on equatorial facing facades to allow solar gain in the winter months, but be sure to design overhangs to shade the unwanted heat gain in the summer. Use lower SGHC value glass on the east and west orientations—unwanted summer solar gain cannot be controlled with overhangs on these orientations.

Use windows with low SHGC value on all orientations (although the north is not as critical) to lower the cooling load. Similarly to insulation, windows with low u-values in high internal gain buildings in warm climates may lead to increased cooling loads by trapping internal loads within the space. Perform whole building simulations to determine the impact on your design.

Infiltration

Often the single largest contributor to heating energy consumption, especially for older homes in cold climates. Air changes typically range from 0.4 air changes per hour (ACH) for newer homes to 1.5 ACH for older homes. Infiltration values below approximately .35 ACH require mechanical ventilation systems.

Infiltration is typically not an issue in larger commercial buildings which are pressurized and leak air out of the building rather than in. Smaller commercial buildings may behave like residential buildings.

Lighting Lighting is a smaller percent of energy end-use for homes, but it is always important to incorporate fluorescent lamps (or other more efficient light sources) in place of incandescent wherever possible.

The single largest energy end-use in typical commercial buildings. Very important to design for daylighting, occupancy controls, and ultra efficient lighting systems. Not only consumes lighting energy, but the heat given off also increases the cooling energy requirements.

Operable windows and controllable openings

Almost always present and a critical part of ventilation, cooling, and general comfort.

Rarely available but should always be considered if the weather and building end-use allow. Ventilation and cooling are nearly always mechanized with no individual user-control. Can be a key factor in increasing occupant satisfaction while reducing energy use. Issues include noise and interactions with HVAC system.

Insulation Levels

Increased insulation is nearly always beneficial for skin-dominated loads.

Its importance depends upon many factors such as location (Fairbanks, AK versus Palm Springs, CA); internal loads (such as server farm vs warehouse). Usually construction capital is better invested in daylighting controls and/or more efficient lighting systems. In some cases increased insulation can even result in an energy penalty by trapping internal loads within the space and putting increased loads on the air-conditioning.

Table 1. Design Considerations: Your Home vs. Commercial Buildings

The Design Process Overview – Steps to Carbon Neutral Design The traditional method for designing a new building forces the architect to design his or her building in a vacuum: there are no energy savings targets established up front, and no method for the architect to evaluate design decisions against the target. If architects hope to design a carbon-neutral building it is critical to overhaul the established design process with the following steps:

1. Set Savings Target 2. Optimize Site and Building Form & Openings

a. Form/Footprint – Sun is primary source of heat and light. Once built, the form is typically fixed for the life of the building. b. Envelope – Openings and mass primary source of cooling and fresh air for ventilation. Location of openings for light and cooling/ventilation.

3. Minimize Internal and External Loads a. Electric lighting – Only use in spaces where the natural light is insufficient and during hours where there is no sun. Design efficient task/ambient

lighting systems with occupancy and daylighting controls. b. Specify Energy Star or other efficient equipment and appliances. c. Evaluate glazing and envelope options to minimize external loads.

4. Select HVAC System a. Natural ventilation – Replace or offset mechanical cooling and ventilation with natural ventilation b. Mechanical Ventilation – Use in conjunction with natural ventilation when natural ventilation is not sufficient. c. Mechanical Cooling – When natural ventilation and mechanical ventilation are not sufficient. Utilize systems that are efficient and provide comfort

in the occupied portion of the space. Stage system operations by using fans and economizers first, then efficient compressorless (evaporative, thermal mass, heat exchanger) options where possible, then compressors. Discussions regarding displacement vs. radiant vs. overhead supply should occur only after the first items are addressed.

d. Mechanical Heating – Use when form/footprint does not allow sufficient passive solar heating. Heat recovery where possible. 5. Onsite Renewables

a. Generate Energy - Power what remains with on-site non-carbon source (such as photovoltaics, air and water panels, wind, and other renewable sources.)

6. Commissioning a. Ensure building is functioning as designed and sustainability goals will be achieved. Daylighting and window controls if any must be included in

commissioning, not just HVAC. 7. Purchase Green Power & Carbon Credits

a. To offset what remains of your building’s use after applying rigorous efficiency measures. Never use as a “free-pass” for excessive CO2 emissions. 2

Set Savings Target How will you know if your design has “arrived” if you don’t first determine a destination? Without the establishment of an energy savings target, the architect is “working blindly.” There are many Fossil Fuel Reduction Goals established by prominent organizations, including the following:

• A carbon neutral building, as defined by ASHRAE Standard 189, the US EPA (draft only) and others. Autodesk Green Building Studio web service defines carbon neutral as a design which eliminates or offsets fossil based electricity and fuel use. For example, if the electricity grid is 60% fossil fuel and 40% hydroelectric, reducing grid electricity use by 60% and eliminating/offsetting on-site fuel use will make the project carbon neutral. Use any combination of efficiency, natural ventilation, renewable energy, carbon credits and biofuels to reach this goal.

• A net-zero energy project annually consumes only what it produces. Renewable source are beneficial to produce net zero energy buildings: wind, solar, biofuels etc. This is different than a Carbon-Neutral building, which uses no fossil fuel or CO2 source to operate.

• American Institute of Architects “Promote integrated/high performance design including resource conservation resulting in a minimum 50% or greater reduction in the consumption of fossil fuels used to construct and operate new and renovated buildings by the year 2010 and promote further reductions of

2 See graphic of carbon neutral design process

10% or more in each of the following 5 years.” —High Performance Building Position Statements ©2005, The American Institute of Architects, Washington, DC.

• Architecture 20303 “All new buildings and major renovations reduce their fossil-fuel GHG-emitting consumption by 50% by 2010, incrementally increasing

the reduction for new buildings to carbon neutral by 2030.” • U.S. Green Building Council All new commercial LEED projects are required to reduce CO2 emissions by 50 percent when compared to current emission

levels. • U.S. Conference of Mayors Adopted the “2030 Challenge” for City Buildings and calls on the Conference of Mayors to increase the fossil-fuel reduction

standard for all new buildings to carbon neutral by 2030

EPA Target Finder The US EPA has performance targets for automobiles that everyone is familiar with, but less familiar is the EPA Target Finder for buildings. This tool helps designers set aggressive, realistic energy targets and rate a building design’s estimated energy use based on data from the U.S. Department of Energy (DOE) Energy Information Agency's 2003 Commercial Buildings Energy Consumption Survey (CBECS). Local climatic conditions of the building and energy fuel mix typical of the region (reflected by including the ZIP code) are used to generate the energy use intensity (EUI) for a project. Optimize Site, Building Form & Openings Building forms with no potential to become carbon neutral will become a liability to owners and may have to be torn down because they will not meet future sustainability targets and will be too expensive to operate. This is analogous to vehicles with poor fuel economy losing value during times of high fuel prices. No amount of mechanical or electrical engineering wizardry can create a carbon-neutral building from a bad form. Powering a poor building form with renewable energy (PVs) is too expensive. As a comparison, using 2009 cost values, it would cost approximately $8,000 to power a typical hair blow dryer using PV panels

4.

Similarly with buildings, powering an inefficient building with an expensive renewable energy system does not make sense. A simple example is harvesting daylight from openings rather than powering light fixtures with PV panels. It is more cost effective to utilize openings for light, and then power lights during dark hours with PVs.

3 The 2030 Challenge (http://www.architecture2030.org/) is a global initiative stating that “all new buildings and major renovations reduce their fossil-fuel GHG-emitting consumption by 50% by 2010, incrementally increasing the reduction for new buildings to carbon neutral by 2030.” 4 Assumes $8/Watt installed for PV power and a 1,000 Watt hair dryer.

Floor Plate Decisions How did architects address the design problem prior to the availability of air-conditioning and electric lighting? They had to ensure that the form of their building

allowed for two major features: 1. Fresh air - windows that opened to allow natural ventilation. 2. Natural light - Placement of windows, clerestories and skylights to allow natural light to

penetrate far into the occupied space. And what happened to the typical commercial building footprint after the advent of air-conditioning? Architects felt free to ignore the constraints of the outdoor environment. Deep rectangular shapes allowed owners to maximize the real estate on their lots. However; this big box form means the majority of the spaces are in the interior of the building without access to windows, which in turn means this design must rely strictly upon electrical lighting and mechanical air-conditioning. Because it is easier for the mechanical engineers to properly design the heating and cooling system when the environment is controlled, the windows are now sealed shut. These building’s are not habitable without electrical lighting and HVAC systems. Pay attention to orientation: Depending upon a building’s location, shape, size, and/or distribution of glass, changing the orientation can have an impact on amount of solar gain and other aspects of weather interacting with the envelope of the building, which will affect the heating and cooling loads. The modern glass box design is not a sustainable building form in most climates. Unless combined with multiple skins and significant amounts of natural ventilation, it is completely dependent on intensive engineering to make it habitable. It is critical that building massing look at climate, prevailing winds, availability of natural light by season and harvesting of rainwater by season. There are many examples of buildings that use massing to address the climate and function of the building. And/or use materials from the site.

Site Considerations A design that responds to the bioclimatic conditions will require less mechanical intervention, less electric lighting and possibly less fresh water consumption. Orient the structure to take advantage of passive heating, cooling, and lighting. Include methods to harvest rainfall for irrigation or other non-potable uses. Carbon-neutral design will require you to understand the weather data for your project location. One easily accessible source of climate data is the Autodesk® Green Building Studio® (GBS) tool, which provides a complete year of weather data, including dry bulb temperature, dew point temperature, relative humidity, wind speed and wind direction, direct normal radiation, global and diffuse horizontal radiation, total sky cover and many more. Many areas of the United States have micro-climatic conditions where the weather at your actual site may differ considerably from the nearest weather stations, which is typically located at the airport. The Autodesk Green Building Studio web tool provides virtual weather stations no further than 14 km (8.8 miles) from any given project within the mainland United States. The climate study portion of a design process should include, at a minimum, dry bulb temperature and humidity studies and prevailing wind patterns for natural ventilation strategies. The graphic above is from the GBS weather data and presents a wind rose for Salt Lake City, UT for the summer season from 8am-6pm. This suggests that if a design goal is to allow wind-induced natural ventilation in the summer during daytime hours, and if external temperatures allow, the most-effective use of building openings would be on the northwest and south-southeast facades. Envelope Considerations Material Choices

• Metal Framing: While valued for its structural benefits and recycled-content, metal framing has the drawback of a lower assembly insulation value than a wood framed component because of the high conductivity of the metal. Also wood has a greater ability to buffer moisture than metal. It is critical to ensure that metal framed buildings utilize thermal breaks, both for energy and moisture reasons.

• Wood Framing: Wood construction offers a better overall insulation quality than steel, but it is not suitable for high-rise construction. Also wood is

vulnerable to insect damage and rot.

• High Mass Construction Materials: The use of concrete/brick/stone and other high mass materials for building facades is typically limited to low rise buildings for cost and structural reasons. In climates with large diurnal temperature swings, high mass buildings may be able to store energy IF the building’s interior temperature is allowed to float and if the mass is “charged” during the warm or cool hours.

• Insulation (R-Value). Does your project need a low conduction (High R-value) roof and/or walls for high performance? It depends on the building type,

climate, and occupancy schedule. You need to perform whole building energy analysis on your project to answer the question. For example a house in a winter-dominated climate will benefit from higher R-value constructions while a retail store in a warm climate with large diurnal temperature swings will probably show increased energy use with higher R-value constructions. This is because improved insulating qualities will trap heat from the internal loads within the building, it will reduce heating demands but may lead to increased cooling energy requirements

• Continuous Insulation. Insulation that covers the framing members and thereby provides a greater insulation value. This is especially important for metal

framing to control condensation.

• Cool Roof . The use of reflective roofing materials or cool roof systems is one means of keeping solar heat out of buildings and increasing energy savings. Cool roofs (generally white) stay as much as 70 degrees F cooler at peak times than traditional asphalt roofs

[1], offering important benefits to building

owners and also protect the environment from the negative effects of urban heat islands. The magnitude of energy savings depends upon building type, level of roof insulation and ventilation rate. The “cool roof” effect can be achieved by specifying a reflective, high emissivity single ply elastomeric membrane, or coating the roof with a certified cool roof coating. Typical rolled roofs, built-up roofs, and composition roofs absorb between 70-90% of incident solar radiation. Cool Roofs can absorb as little as 20% of incident radiation (three-year aged performance)

[2]. Asphalt shingles are cheap &

prevalent and all roofers know how to install them. BUT, they are a very poor choice for reflecting incoming solar radiation. The solar reflectance of all commercial asphalt shingles is low (premium white shingles are only about 30% reflective, and other colors reflect less.)

[3] In addition to reducing the heat

gain within a building, cool roofs may also benefit the immediate surroundings by reducing the heat island effect—the result of many dark surfaces within an urban environment that can actually increase the ambient air temperatures by as much as 2-8 degrees F

[4].

Non-Traditional Construction Materials and Methods

• Structural Insulated Panels (SIPs) are rigid panels of foam insulation joined to oriented strand board (OSB). Typically used as floors, walls, and roofs on smaller buildings. Benefits of using SIPS in construction generally include lower labor cost, less job site waste, shorter construction time, and better-insulated buildings. SIPS are prefabricated in the factory with window openings and electrical/plumbing chases. Especially in the case of larger projects, the use of SIPS should be considered based on economies of scale. Outside finishes can be customized to meet whatever “look” is desired. More information about this technology, including links to suppliers, can be found at www.sips.org.

• Insulated Concrete Forms (ICFs) s are forms/molds or hollow blocks with built-in insulation. These are stacked and filled with reinforcing bar and concrete.

[1] Lawrence Berkeley National Laboratory Heat Island Group. (http://eetd.lbl.gov/HeatIsland/CoolRoofs/) [2] Cool Roof Rating Council Product Directory (http://coolroofs.org/index.html) [3] ibid [4] Environmental Protection Agency, ENERGY STAR Cool Roof Products (http://www.energystar.gov/index.cfm?c=roof_prods.pr_roof_faqs)

Both SIPS and ICFs have a typical insulation value of approximately R5 per inch. ICFs also have thermal mass benefits. Both also reduce infiltration/noise.

• Straw Bales. Many factors can affect the insulating quality of a straw bale wall, including moisture content, bale size and bale orientation. Autodesk Green Building Studio has adopted the California Energy Commission’s default assumption insulation value of R-30 for Straw Bale construction.

• Radiant Barriers. Radiant barriers consist of shiny “foil” like materials that lessen the ability of a hot surface to transfer heat by radiation to adjacent

surfaces. Many of these materials look like the shiny mylar inside a potato chip bag or like aluminized “bubble wrap” used to insulate HVAC ducts. Consider specifying a layer of radiant barrier film to the underside of the roof decking for those areas with plenums and foil faced insulation for those areas where the insulation is at the roof deck. This measure effectively cuts down the radiant heat entering the space directly below the roof, which means mechanical systems face lower cooling loads.

Windows, Openings and Skylights Properly placed windows and other openings are indispensable for both daylighting and natural ventilation strategies. Natural ventilation cooling strategies must be complemented by effective control of solar gains. Typically, light from a window is able to penetrate a depth of approximately 15 feet into a space for daylighting purposes. In at least one country (Germany), new buildings are required to be designed so that each occupant is within 7 - 10m of an exterior view/window. Some important definitions relating to glass and windows are:

• U-value or U-factor indicates how well a window resists conduction. The rate of heat conductivity is indicated by the U-value (inverse of the R-value) of a window assembly. The lower the U-value, the greater a window’s resistance to conductive heat flow and the better its insulating value. The definition of “good” U-value depends on the climate, the building type and the amount of glass. For example, in a warm climate like Los Angeles, the U-value doesn’t matter much. However, in cold climates a low U-value is beneficial – 0.25 - 0.40 would be preferable. It is VERY important for skylights in cold climates to have low U-value to deal with condensation issues.

• SHGC measures a window's ability to block radiant heat transfer, typically from sunlight. The SHGC is the fraction of incident solar radiation admitted

through a window. SHGC is expressed as a number between 0 and 1. The lower a window's solar heat gain coefficient, the less solar heat it transmits.

The definition of Good SHGC depends on the climate, the building type and the amount of glass. For example in hot climates like Tucson, Miami, or Dallas a low SHGC is Good – 0.20 - 0.35. In a cold climate like Fairbanks, AK or a situation where you want to take advantage of the sun for passive heating, High is Good – 0.5-0.7. A low SHGC is VERY important for windows/skylights in hot climates.

• Visible light transmittance (Tvis or VLT) measures the transmission of visible light. The visible transmittance is an optical property that indicates the

amount of visible light transmitted. Most VLT values are between 0.3 and 0.8. The higher the VLT, the more light is transmitted. A high VLT is typically desirable to maximize daylight, however too much light transmission can cause glare.

The definition of Good VLT depends on the climate, the building type and the amount of glass. For example, glare can become a problem if the VLT is too high and the glass area is large. On the other hand, if the VLT is too low and the glass area is too small, you have spent money on glass and didn’t get the benefit of natural daylight light. Selective coatings allow high Tvis and low SHGC – you don’t need mirrored glass to get low heat gain. New glass can have 65% visible light transmittance, 30% solar heat gain, and 0.30 U value.

Skylights and Roof Glazing How much roof glazing is enough? For 100% daylighting from traditional skylights – approximately 5% of roof area should be in skylights, (5% Skylight-to-Roof Ratio or SRR). This value obviously depends on the illuminance desired in the space, the ceiling height and the VLT of the skylights. In general a high VLT/SHGC ratio is desirable, but the ideal skylight specification depends on climate. All climates should have high visible transmittance (Tvis or VLT). Hot climates should have low SHGC. It is almost always cheaper to use skylights to light a space than Photovoltaic panels to generate renewable electricity which in turn power electric lighting.

• How to Size a Rectangular Skylight. Area of one skylight = (Floor to Ceiling Height x 1.5)

2 x SRR. Choose a size that is appropriate. Start with 5% SRR

and modify depending on climate and building use. For example with a 12' ceiling and 5% skylight to roof ratio the right size skylight would be approximately: (12 x 1.5)

2 x 5% = 16.2sf. Therefore the project should use evenly distributed 4'x4' or 8'x2' skylights for good light distribution.

5

• Tubular skylights require a much lower SRR than traditional skylights, approximately 1-2%.

• U value is more important in cold climates and has energy and condensation implications—the lower the U-value the greater the insulation value.

• Dampers (to darken space) are available with most skylights.

• Tubular Skylight spacing guidelines.

6 The following spacing criteria (from a tubular skylight manufacturer) is intended as a guide to provide uniform

distribution of daylighting. MH refers to the mounting height of the diffuser above the work plane. o Enclosed and Open Plan Spaces:

From Walls: Spacing ≥0.5 x MH (1.0 x MH = Maximum) Between Units: 1.0 x MH < Spacing < 1.3 x MH (Max. Spacing = 1.5 x MH)

Open Ceiling Spaces: From Walls: Spacing ≥0.5 x MH (0.8 x MH = Maximum) Between Units: 0.8 x MH < Spacing < 1.3 x MH (Max. Spacing = 1.5 x MH)

Minimize Internal Loads Daylighting It may come as a surprise to some that lighting is typically the largest regulated energy use in a non-residential building—approximately 25 – 35% of the total depending on the building type, location and hours of operation. The design goal should be to create a lighting system which uses daylighting with electric lighting as a backup. Daylighting is affected by quality of sunlight, glazing materials, adjacent surfaces and overhangs, and adjacent ground reflectance. A good daylighting design will require coordination with the lighting designer, a controls consultant, possibly the structural engineer if numerous roof penetrations are present, and of course the architect who will be leading the effort. The ideal daylighting design provides proper light to the work plane without glare. It is important to provide adequate light while minimizing the cooling load from solar gain. The design needs to start with the consideration of the building orientation and structural composition. A general rule of thumb is that the daylighting zone may be considered to be a depth of about 1-1/2 to 2 times the window head height. For example if a space has windows with a head height of six feet, it may be feasible to daylight up to about 12 feet deep into the space (assuming no internal partitions would block the light). A narrow building will have a greater proportion of its interior in the usable daylight zone. Daylight penetration can be increased to up to 2.5 times the window head height by using light shelves or other means of reflecting the light farther into the space. Ideally, one should combine the light shelf with shading devices to block glare and direct solar gain. In addition, separate daylighting glass can be used above the lightshelves. This glass can have different optical properties than the vision glass that is lower. A light shelf is generally a horizontal element positioned above eye level and divides a window into a view area on the bottom and a clerestory area on the top. It can be external, internal, or combined and can either be integral to the building, or mounted upon the building. The orientation, position in the façade (internal, external, or both), and depth of the light shelf are critical factors in the design. For instance, an internal or exterior light shelf redirects the light but will also reduce the amount of light received on the interior for some hours of the day and year.

5 Communications with Jim Blomberg, Sunoptics Prismatic Skylights, Inc. http://www.sunoptics.com/ 6 http://www.solatube.com/

Light shelves are most effective on the south orientations and can be effective on north orientation for controlling glare (but will not function to bounce light further back into the space). Light shelves on east and west orientations may not bounce light that much further into the spaces, but are an effective means of reducing direct heat gain and glare during the times of the year when the sun is higher in the sky. For south-facing rooms it is recommended that the depth of the internal light shelf be approximately equal to the height of the clerestory window head above the shelf.

Figure 2. Light Shelves simultaneously shade and reflect incoming daylight (Source http://www.arch.hku.hk/~kpcheung/teaching/b4link/b4-link1.htm)

Exterior light shelves reduce daylight near the window but improves the light uniformity. The recommended depth of an external light shelf is roughly equal to its height above the work plane. To reduce cooling loads and solar gain, an exterior light shelf is the best compromise between requirements for shading and distribution of daylight.

Light shelves may be constructed of many materials, such as wood, metal panels, plastic, fabric, or acoustic ceiling materials. Considerations that affect the choice of material will include structural strength, ease of maintenance, cost, aesthetics, etc. Lighting Efficiency Don’t use the energy code lighting power density (LPD) maximum as your lighting goal—it’s easy to reduce the LPD by at least 15% below the code maximum. For example the California and ASHRAE Energy Codes stipulate a prescriptive maximum of 1.5 watts per square foot for retail buildings however a large retail chain account recently committed its projects to an LPD of 0.95 watts per square foot—a 30% reduction. High efficient lamp/ballast combinations provide a 15% savings in electricity consumption without reducing light output. Careful design with efficient light fixtures, indirect-direct fixtures and strategies incorporating lower ambient light levels with appropriately placed task lighting can further reduce the LPD. Lighting research suggests that the human eye perceives cooler temperature lighting (lamps rated at 5000 K or greater) to be brighter than standard warmer temperature lamps (3500 K or less). The lamps containing more blue in the spectrum (5000 K or greater) will be more visually efficient than lamps with less scotopic content (white light with a higher bluish content) even if they have the same lumen and efficacy values. The use of scotopically enhanced lighting can therefore be used at lower energy levels while maintaining equal visual effectiveness. Additional technologies that are ready for use in the market place include LED lighting, induction lighting for outdoor uses, and fiber optic lighting for decorative purposes. Scotopically enhanced lamps have an energy savings potential of 17-24% compared to 835 lamps (lamps with a Color Rendition Index of 85%, and a color of 3500K) and 22-30% compared to 735 lamps (lamps with a Color Rendition Index of 78%, and a color of 3500K). An additional advantage of utilizing 5000 K lamps is the integration of the lamp color with natural daylight. Daylight, in general, is cool in color temperature, which gives it a bluish-white appearance. Noontime sunlight has a color temperature of approximately 5000 K, this compares to incandescent lighting at 2800 K, warm fluorescent at 3000 K, and cool fluorescent at 4100 K. 5000K or 6500K lamps may be too “blue” or “cold” for some applications, but proportional savings can be achieved by using 3500K or 4100K lamps in place of 3000K lamps. Occupancy Controls The simplest way to reduce the amount of energy consumed by lighting systems is to turn lights off whenever they are not required. Manual light switches are not used as often as they could be. One solution to this problem is occupancy sensors, which sense the presence of people in a space and respond accordingly. These switches are appropriate in spaces where people pass in and out of often, such as private offices; restrooms, storage areas, and conference rooms. Other internal loads. Always specify Energy Star equipment and account for this reduction in internal loads in any analysis of cooling loads. Select HVAC System If the project goal is a carbon-neutral building, an HVAC system should be included and/or sized for a project only after all other features of the building have been optimized. Design the building form, mass, and openings to take full advantage of natural ventilation and daylighting opportunities. Use electric lighting only in spaces where the natural light is insufficient and during hours without sun. If possible, make use of ceiling fans--with an air movement of about 150 fpm (1.7 mph), a person will experience the same level of comfort with the air temperature 3-5°F higher than a space without air movement. Incorporate thermal mass and evaporative cooling if appropriate for the weather and building use, and only use compressor cooling as a back-up or on design days. Finally, similar to daylighting design, this effort requires coordination between the architect, the mechanical engineer, possibly a controls contractor if window sensors are included, and very importantly the owner if the definition of comfort is to be explained and discussed. This does not mean that the mechanical engineer has less work to do, rather the reverse is true. It is more challenging to predict and design for comfort in a mixed mode or naturally ventilated building than it is to specify rooftop units that are sized to keep a space at 74 degrees F. Ideally, the steps to HVAC design should follow these steps—each are covered in more detail below:

1. Investigate if Natural ventilation is sufficient as the sole means of providing cooling. 2. Mechanical Ventilation – Use in conjunction with natural ventilation when natural ventilation is not sufficient.

3. Mechanical Cooling – When natural ventilation is not sufficient. Typically mixed mode systems which use both mechanical and non-mechanical means are worth investigation. The first stage fans (economizer), then compressorless systems where possible, followed by chilled/hot water and compressors. Talking about displacement vs. radiant vs. overhead supply should be after the first items are addressed.

4. Mechanical Heating – Use when form/footprint does not allow sufficient passive solar heating. Heat recovery where possible. Natural Ventilation. Building form and opening design must allow for stack effect and/or cross-ventilation. Stack effect ventilation occurs whenever there is a difference in height between an inlet and the outlet opening, and when there is a temperature difference between the indoor and the outdoor temperature. Because warm air rises without any mechanical intervention, the cooler fresh air enters the lower inlet while warmer stale air exits from the upper opening. Of course this presumes the free movement of the air without obstructions. Fan-assisted ventilation may be necessary in some cases. An increase in temperature difference or increased heights between the inlet and outlet area cause an increase in stack effect ventilation. Why consider natural ventilation in your projects? Studies have cited many benefits in addition to energy efficiency, including improved air quality and increased productivity

7. While it is typical for residential buildings to open windows and doors for cooling during mild weather, it is less common for non-residential buildings.

Typical non-residential buildings have greater internal heat gains, therefore a greater cooling load, plus a smaller ratio of envelope surface to internal volume compared to homes. However, unlike mechanical air-conditioning, natural ventilation is unable to reduce the humidity of air entering a building. Careful analysis of the weather is critical for natural ventilation feasibility studies. The climatic elements important to natural cooling in buildings are: temperature, wind, humidity and radiation. The Autodesk Green Building Studio web service will calculate the natural ventilation potential for your project, including an estimate of the total hours per year that mechanical cooling will be required, and the total hours per year that natural ventilation may be possible. These estimates assume natural ventilation during hours when cooling is needed and when using natural ventilation will not increase heating loads. Air changes per hour are limited to 20 using natural ventilation. In order to realize the potential your building form and opening design must be able to allow stack effect or cross-ventilation. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) defines a reasonable comfort zone for ventilation cooling between 68°F to 78°F. The use of a ceiling fan will allow the air conditioner to be set at a higher thermostat setting than usual, since the air movement created by a fan produces a cooling effect on the body. Studies have shown that people prefer higher temperatures when subjected to air motion and that at 60% relative humidity, 90% of people would be just as comfortable if the air dry bulb temperature were raised from 79.2° F to 82.5° F, if air speed was also increased from still air at 20 feet per minute to 150 feet per minute (fan on high). At 80% relative humidity, 90% of people would also be as comfortable if set points were raised from 77.9° F to 81.8° F while similarly increasing air speeds

8. Note that if ceiling fans are employed and the thermostat setting is not changed, energy use will actually increase because of

the electricity use associated with the ceiling fans. Natural Ventilation from Wind. The following equations are simplified and applicable to residential and light commercial buildings exposed to relatively unobstructed air flows. Natural ventilation in dense urban settings follows the same principles, but is complicated by adjacent buildings and structures. Regardless of the specific details of air flow in and around a building, it is critical to recognize that a building with no openings has no potential for being naturally ventilated. Openings do not have to be windows, they can be louvered openings, operable skylights or sliding partitions that are manually or mechanically operated. It is critical to have an understanding of prevailing wind directions before investigating natural ventilation potential. Wind creates a positive pressure on the windward side of a building and negative pressure on the leeward side. Air seeks to equalize this pressure by entering openings on the windward side and exiting through openings on the leeward side. In order to promote this cross-ventilation it is important to avoid obstructions between the windward and leeward openings.

7 Fisk, William J. “Health and Productivity Gains from Better Indoor Environments and their Relationship with Building Energy Efficiency” Indoor Environment Department, Environmental Energy Technologies Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720; 8 James, Patrick W. (1996). Are Energy Savings Due to Ceiling Fans Just Hot Air? Paper presented at the ACEEE Summer Study on Energy Efficiency in Buildings. http://www.fsec.ucf.edu/bldg/pubs/pf306/

The volume of airflow resulting from wind can be estimated by using the following formula:9

Qs = 88 * MPH * Cv * A * U where

Qs = ventilation due to wind, cubic feet per minute (CFM) 88 = a constant that converts wind speed from miles-per-hour (mph) to feet-per-minute (fpm) Cv = effectiveness of openings (assumed to be 0.5 to 0.6 for perpendicular winds and 0.25 to 0.35 for diagonal winds) A = free area of inlet openings, square feet is reduced from rough opening area by screens and window geometry, A is typically 10 – 30% of the opening area depending on window type. U = wind speed, mph

Natural Ventilation from the Stack Effect. The stack effect occurs when there is a difference in height between the inlet and the outlet opening, and when there is a temperature difference between the indoor and the outdoor temperature. If the indoor temperature is warmer than the outside, the warmer indoor air will rise out through top opening, being replaced with cooler air from outside. If the indoor air is cooler than the outdoor air, the cooler indoor air will sink out through low opening, being replaced with warmer air from outside. A “solar chimney”, heated by solar energy can be used to drive the stack effect without increasing room temperature in situations where cooling is desired but the outdoor temperatures are greater than the indoor, such as on a hot summer afternoon. The flow rate caused by the stack effect can be calculated by the following (or you can visit this website for a handy online calculator http://chuck-wright.com/calculators/stack_effect.html ): Qs = 60 * Cd * A * square root (2g * (Hn - Hb) * ((Ti - To) / Ti)) where Qs = flow rate in cubic feet per minute (cfm) Cd = discharge coefficient for opening, use 0.65 for unobstructed openings A = opening area, square feet Ti = indoor temp (Rankine) To = outdoor temp (Rankine) Hn = height of "neutral pressure point" (for simple systems, assume 1/2 way between top and bottom openings) Hb = height of bottom opening g = gravitational constant, 32.2 ft/s

2

Knowing the ventilation flow rate, and the temperature difference between the indoors and the outdoors, you can calculate the effective heating or cooling rate.

Qs = 1.1 * Q * ∆T Where

Qs = sensible heat load in BTU per hour (for reference, air conditioners are sized in "tons" of cooling capacity, one ton equals 12,000 BTU per hour. Rule of thumb ranges for cooling capacity requirements are roughly 400-600 square feet of conditioned space per ton of air conditioning.) 1.1 = constant, air density and specific heat of air ∆T = difference between the indoor and outdoor temperature, F

The total natural ventilation flow rates for wind plus stack effect = square root (wind flow rate squared + stack effect flow rate squared). Natural Ventilation Design Guidelines. The following guidelines are based upon recommendations from The 2001 ASHRAE Fundamentals Handbook and the National Renewable Energy Laboratory Whole Building Design Guideline

10. Keep in mind there is no one-size fits all approach for a successful natural ventilation

9 2005 California Residential Alternative Calculation Method (ACM) p 4-16, taken from the 2005 ASHRAE Fundamentals Handbook chapter 27.11. 10 2001 ASHRAE Fundamentals Handbook and http://www.wbdg.org/resources/naturalventilation.php?r=minimize_consumption

design and some strategies for optimal natural ventilation may conflict with strategies for controlling solar heat gain, such as building orientation or use of shading devices.

• In order to provide the maximum benefit, naturally ventilated buildings should be narrow. • When trying to maximize natural ventilation from wind, site the building with openings perpendicular to the prevailing summer winds. Autodesk Green

Building Studio web service provides climate data that includes hourly wind speed and direction. • Each naturally-ventilated space should have a minimum of two openings: one for entering supply air and one for and exhaust air. Locate the exhaust

openings high above inlet to maximize stack effect. Ideally the openings should be oriented on opposite sides of the room with minimal obstructions that may inhibit the airflow within the room. Using equally sized inlet and outlet openings maximizes the air flow for a given opening area.

• Window openings should be operable by the occupants. • Install ridge vents (openings at the highest point in the roof). Such vents are a good air outlet for both stack-effect and wind-induced ventilation. • Design for airflow between the rooms of the building as well as in and out of the building. Strategies include interior doors designed to be open and/or high

louvers or transoms. • Clerestories or vented skylights provide an air outlet for stack-effect ventilation strategies. Because air in skylight wells is typically warmer than the air

within the habitable space, the wells act as a solar chimney to increase the air flow. In order to complete the ventilation system routing of the air, openings lower in the structure must be provided. For security and noise reasons, locating the lower openings is often a more difficult design challenge, especially if the openings are to be used to pre-cool the building when it is unoccupied.

• If the building has an attic, it is critical to ventilate it. Ventilated attics are about 30°F cooler than unventilated attics.11

• Ceiling fans, as mentioned earlier, provide the same level of human comfort with air temperatures 3-5°F higher than a space without air movement. See ASHRAE Standard 55 for details on how human comfort is perceived.

• Whole building fans pull in cooler outdoor air through openings and exhaust the air out through an opening in the upper portion of the building. According to the Whole Building Design Guide, ceiling and whole-building fans can provide up to 9°F effective temperature drop at one tenth the electrical energy consumption of mechanical air-conditioning systems.

12

• Nighttime ventilation works well in hot, dry climates where there is a large variation in temperature from day to night. The building is ventilated at night, then, closed in the morning to retain the cool temperatures without introducing hot outdoor air. Nighttime ventilation can be designed with security in mind by use of multiple smaller openings. This type of strategy requires the use of a high-mass material capable of holding the “coolth.” For example concrete and masonry construction works well, even doubling up the layers of gypsum board, or using a concrete veneer within the spaces can be beneficial for adding mass. High mass walls and floors can serve to dampen temperature swings within a space by absorbing heat when indoor temperatures rise and slowly releasing it when the indoor temperatures drop

• Open staircases can be an effective way of providing for stack effect ventilation; however in most regions fire codes prohibit the use of any openings in enclosed stairway wells.

Mechanical Ventilation. Proper ventilation is necessary for human comfort and health. Ventilation provides fresh air, controls odors, and removes excessive CO2 and other contaminants from the indoor environment. When natural ventilation by itself cannot provide sufficient ventilation and/or cooling for the building, ventilation actively managed through fan-powered distribution systems should be considered. While the fans use energy, there is still energy savings compared to systems requiring compressors. Mechanical Cooling. Utilize mechanical cooling only when mechanical ventilation and natural ventilation are not sufficient. The use of mechanical cooling systems should be staged as follows:

1. Enable fans and economizers. Economizers, as the name implies, economize by saving on cooling energy costs. If the thermostat calls for cooling and the outdoor air is cool enough the economizer brings in the cooler outdoor air to circulate through the system without requiring the air conditioning compressors to be used. Newer integrated economizers will continue to operate the building on 100% outside air if the outside air temperature/enthalpy is lower than the return

11 ibid 12 ibid

temperature/enthalpy. However economizers, if not properly programmed or functioning, can also waste a great deal of energy. If the outdoor temperatures are quite high, for example 95F, and the economizer dampers are fully open, the air conditioning compressor will expend unnecessary energy to cool down the 95F air.

2. Examples of cooling without compressors include evaporative cooling, dessicant cooling and in some locations air pulled through an underground culvert. An evaporative cooler provides cooling by combining water evaporation and moving air. Fresh outside air is drawn through a moist medium; the air is cooled by evaporation and:

• circulated through the space directly (direct evaporative cooling); • used as a secondary air stream to pre-cool an air-conditioning system (indirect evaporative cooling); • or a combination of the two, called indirect-direct or IDEC evaporative cooling.

The temperature of the outside air can be lowered by up to 30F.13

Evaporative coolers are very effective as long as the outside air is dry enough. However, the ability for evaporative cooling decreases as the humidity of the outdoor air increases. Newer two-stage, or indirect/direct evaporative cooling systems can provide cooling well beyond the thresholds of the traditional “swamp coolers” used in the past.

3. The cooling stage of “last resort” is use of air-conditioning compressors. The supply air cooled by the compressors can be distributed in ways that will also impact the energy consumption of the building. Fans can use a great deal of energy and some distribution systems minimize the fan energy better than others. This includes underfloor and displacement systems that take advantage of the buoyancy of warm air and in some cases provide occupants with control over the air flow in their own space.

13 California Energy Commission. Consumer Energy Center. http://www.consumerenergycenter.org/home/heating_cooling/evaporative.html

Mechanical Heating. Use when form/footprint does not allow sufficient passive solar heating. Use heat recovery where possible and provide heat in a form that is most useful to occupants. Can include radiant, convective or a combination. Heating Equipment

• Furnaces (air heaters) • Boilers (water heaters/steam) • Infra-red Radiant Heaters (gas/electric) – electric radiant heaters can be very expensive unless the climate is mild. • Electric Heaters • Heat Pumps • Solar Collectors

Cooling Equipment

• Direct Expansion (DX) units, typically called RTUs (rooftop units) or packaged units depending on the region. • Chillers. In large buildings, the equipment used to produce cool water are called chillers. The cool water is pumped to air handling units to cool and

dehumidify the air. • In the US, the capacity of cooling equipment is typically measured in tons. One ton of cooling is equal to the amount of cooling that occurs when one ton

of ice melts in 24 hours. One ton of cooling = 12,000 Btu/hr. A window wall air conditioner provides approximately one ton of air conditioning.

Heat Rejection Equipment

• Condensers or Cooling Towers are heat exchangers that are required for chillers to reject heat that has been removed from the conditioned spaces. Can be either air-cooled or water-cooled. Water-cooled condensers usually rely on rooftop cooling towers for rejecting heat into the outdoor air; however, it is possible to reject the heat into the ground or a river or body of water.

Air Distribution Equipment The conditioned air is typically delivered with fans pushing the air through duct work or under the floor and through diffusers. Moving a large mass of air at low speed is a far more efficient than pushing air through small ducts at high speed. For example – Cutting a given fan’s speed to 50% of full speed will cut the power required to (0.5 x 0.5 x 0.5) = 12.5% of full load power, while the air flow will only be cut in half (not including parasitic loads associated with the variable speed drive). Supplying only as much air as is needed to condition or ventilate a space through the use of variable-air-volume systems is more efficient than supplying a constant volume of air at all times.

• Constant Air Volume systems deliver a constant flow of air while varying the temperature of the supply air • Variable air volume (VAV) systems vary the amount of air supplied to a zone while holding the supply air temperature constant. • Under floor air distribution delivers air low in the space, at low velocity and pressure drop, and relatively high temperature compared to traditional ceiling

delivery systems that deliver a blast of 55F air from above. This system type has the potential to save energy with both reduced fan energy and warmer supply air (reduced HVAC loads) and to provide a high degree of individual comfort control.

• Displacement Ventilation relies primarily on the buoyancy of warm air rather than fans to move air. • Radiant Heating provides space heating by circulating heated water or steam through radiators in the room or tubing embedded in the floor • Chilled Beams provide space cooling by circulating cool water through exposed tubes in the ceiling.

Typical HVAC Central Plant or Built-up Systems

� Typically utilize chilled water (CHW) and hot water (HW) instead of refrigerant to move heat to central air handlers which contain the fans, economizers, cooling and heating coils and dampers.

� Chillers supply the chilled water � Cooling towers which supply condenser water (CW) to the chiller are used instead of the air condensers as found on most DX equipment. � Boilers typically supply the HW or steam (can be steam from district heating) � Typically contain CHW, HW and CW loops, along with piping, pumps and controllers.

Cogeneration is a process that takes advantage of waste heat generated on site and uses it to produce service hot water, process heat, or absorption cooling in addition to the electricity that is typically produced by these systems. Typical HVAC efficiency metrics:

� EER (energy efficiency ratio) is a measure of how efficiently a cooling system will operate. EER is most commonly applied to window units and unitary air conditioners and heat pumps. The EER is the ratio of Btu/hr of cooling at 95Fdivided by the watts used at 95F.

� SEER (seasonal energy efficiency ratio) measures how efficiently a smaller residential air conditioner or heat pump will operate over an entire cooling season, as opposed to a single outdoor temperature. As with EER, a higher SEER reflects a more efficient cooling system. SEER is the ratio of the total amount of cooling Btu’s the system will provide over the entire season divided by the total number of watt-hours it consumes.

� HSPF (heating seasonal performance factor) is the measurement of how efficiently heat pumps operate in heating mode over an entire heating season. The higher the HSPF, the more efficient the system. HSPF is calculated by dividing the total number of Btu’s of heat produced over the heating season by the total number of watt-hours of electricity required to produce that heat.

� AFUE (annual fuel utilization efficiency) measures how efficiently a gas furnace or boiler operates. AFUE is the percentage of energy consumed by the system that is converted to useful heat. For example, a 90% AFUE means that for every Btu of gas used the system will provide 0.9 Btu of heat. The higher the AFUE, the more efficient the system.

� kW/ton is most often used to determine chiller efficiency and measures the energy input in kW over the tons of cooling provided. The lower the ratio, the more efficient the chiller.

Onsite Renewable Energy Photovoltaic modules convert between 5% and approximately 20% of the incident solar energy into electricity. For most projects, the remaining portions of the system convert the direct current electricity from the panels into alternating current that can be used in most buildings, synchronize the PV power to the grid power, and in remote locations can include a battery storage system. It does not typically make sense to store energy in batteries if the project is in an urban or suburban location. While it is obvious to the casual observer that a project with photovoltaic panels on the roof is interested in sustainability, addition of onsite renewable energy to your project should be considered only after all the less glamorous work has been completed. Minimize external & internal loads and select HVAC system before considering onsite renewables.

– Incorporate PVs as part of the shading systems of the building. – Use wind when available and appropriate to the site – As an example, it is almost always cheaper to use skylights to light a space than photovoltaic panels to power an inefficient lighting system.

Building-integrated photovoltaic materials serve the dual purpose of producing electricity and serving as construction materials. They can replace traditional building components, including curtain walls, skylights, atrium roofs, awnings, roof tiles and shingles, and windows. The cost of the PV system is partially offset by the cost of avoided construction material and the PV panels require no additional support. These materials are unbreakable and do not require roof penetrations or racks to install. Solar modules now also come in a variety of styles, colors and sizes, making it easy to integrate into a building design. There are modules made of thin film that can be rolled out in between the seams of standing seam roofs, modules integrated into curtain wall glass and solar modules that resemble traditional roof shingles. For more information, visit the US Department of Energy’s photovoltaic site at http://www.eere.energy.gov/RE/solar_photovoltaics.html . Commissioning Commissioning a green building is analogous to buying an expensive sports car that is promised to go from 1-60mph in 2 seconds, but you have to first have a mechanic tune it up before it will perform correctly.

14 Green building measures cannot achieve their goals unless they work as intended. The best way to determine

14 Source of analogy: California Integrated Waste Management Board. http://www.ciwmb.ca.gov/greenbuilding/Basics.htm

if a building is working as intended is by a process called “commissioning.” Building commissioning includes testing and adjusting the envelope, mechanical, electrical, and plumbing systems to ensure that all equipment works and operates according to design criteria. What Do You Get Without Commissioning?

� A study of 60 commercial buildings found that more than half suffered from control problems. � 40% had problems with HVAC equipment � 1/3 had sensors that were not operating properly. � 15% had missing specified equipment � Approximately 1/4 of them had energy management control systems (EMCS), economizers, and/or variable speed drives that did not run properly.

Source: U.S. DOE, “Building Commissioning: The Key to Quality Assurance” A DOE summary of five case studies examined the energy savings goals versus actual energy savings and found the actual energy savings in all five of the cases were lower by a range of about 8 to nearly 40% compared to the goal. (http://eetd.lbl.gov/emills/PRESENTATIONS/Commissioning_Cost-benefits.pdf ) Benefits

� Increase in Energy Efficiency � Improved Performance of Building Equipment & Systems � Improved IAQ, Occupant Comfort, and Productivity � Decreased Potential for Building Owner Liability related to IAQ problems � Reduced Operation and Maintenance Costs

The American Council for an Energy Efficient Economy investigated 38 energy-saving strategies, and found that commissioning is one of the greatest potential energy saving tools. For existing buildings, commissioning typically yields an energy savings of 5-20%, depending upon the size and complexity of the building and the extent of the commissioning.

15

Further references: http://eetd.lbl.gov/emills/PUBS/Cx-Costs-Benefits.html and http://www.fypower.org/bpg/module.html?b=offices&m=Commissioning http://www.ggashrae.org/meetings/2006-2007/Green_Building_Confessions.pdf Purchase Green Power & Carbon Credits To offset what remains of your building’s use, purchase green power. There are three general options, but the only one available everywhere in the U.S. is the third one, the other two depend upon the utility and market serving your project.

1. Utility Green pricing. An option that allows utility customers to pay a premium on their electric bills in order to support investment in renewable energy projects and technologies. Currently about 750 utilities nationwide offer this pricing.

2. Green power marketing. This is the sale of green power through competing vendors. Unlike Green Pricing, you actually switch electricity providers. 3. Renewable Energy Certificates. (RECs or green tags). RECs represent an investment in the production of renewable energy, even though the

electricity flowing into your project may not come directly from these renewable energy projects. Customers can purchase RECs independently of their electricity provider.

According to the Union of Concerned Scientists, “The overall environmental benefit of purchasing a green pricing or green marketing product versus RECs is exactly the same.” (http://www.ucsusa.org/clean_energy/renewable_energy_basics/buy-green-power.html ) For more information on green power options offered in your location, visit the U.S. Department of Energy http://www.eere.energy.gov/greenpower/about/index.shtml .

15 Thorne, Jennifer, and Nadel, Steven. June 2003. Retrocommissioning: Program Strategies to Capture Energy Savings in Existing Buildings. American Council for an Energy Efficient Economy (ACEEE). Report Number A035. page 10. http://www.aceee.org/pubs/a035full.pdf

Carbon credits or offsets can be purchased to offset the CO2 emissions for which individuals and businesses are responsible. Typically the carbon offset providers invest in renewable energy, energy efficiency, and tree planting. Carbon offsets are in no way a “free pass” and should never replace efforts to avoid generating the CO2 emissions in the first place. For a list of providers visit Ecobusinesslinks.com http://www.ecobusinesslinks.com/carbon_offset_wind_credits_carbon_reduction.htm. Since 2003, the Chicago Climate Exchange has provided a marketplace for trading greenhouse gas emissions in the same way that commodities are traded. This marketplace is in its infancy, but represents a method for providing transparent GHG allowance trading in the marketplace. Water and Energy Efficiency While climate change awareness has lead to an important movement toward more energy efficient buildings, it is essential that an energy efficient design also incorporate water conservation measures. Why? Although it may not be front-page news, there is a critical relationship between water, energy, and global warming. We are all familiar with efficient water-using appliances such as washing machines. However even toilets and irrigation systems consume electricity, but because that usage doesn’t show up on the electric meters in our homes and offices it’s easy to ignore. Based on recent research done in California, it is estimated in that arid state that approximately 19% of the state’s electricity and an even higher percentage of its natural gas is used to acquire, treat and convey water to end-users. Clearly saving water also saves energy, although the connection is not intuitive to most people.

16

Water and Climate Change. There is growing evidence that global warming will have a negative impact on water availability and hence water energy intensity in many regions. A study recently published in the journal Science, has predicted a permanent drought in the Southwestern United States by the year 2050. Some even speculate that this drought, likely the result of global warming, has already begun. California is particularly vulnerable to water shortages; the State relies upon the Sierra snowpack for much of its water and studies indicate that a warming climate means more rainfall and less snow. In addition to a reduced snowpack, warmer temperatures will result in earlier snowmelt as well. The snowpack accounts for about one-third of the State’s surface water, and global warming could feasibly reduce the spring snowpack by 90%. 1. Zarembo, Alan, Bettina Boxall. April 6, 2007. A permanent drought seen for Southwest. Los Angeles Times. http://articles.latimes.com/2007/apr/06/science/sci-swdrought6 2. Anderson, Leonard. Apr 5, 2007. California snowpack melt stirs water worries. Reuters. http://www.reuters.com/article/environmentNews/idUSN0526172720070405?feedType=RSS 3. Global Warming and California’s Water Supply: A Fact Sheet of the Union of Concerned Scientists. Union of Concerned Scientists. Berkeley, CA Water Conservation Examples might include: waterless urinals, high efficiency toilets (1.3 gallons per flush compared to 1.6 for low-flow toilets), rainwater catchment for non-potable irrigation uses, and xeriscape (drought-tolerant plants) landscaping. Current plumbing and other codes often prohibit or place unreasonable restrictions on greywater systems, but some municipalities are beginning to adopt dedicated “purple pipe” systems that distribute recycled water for irrigation purposes. Some conservation measures involve trade-offs between energy and water: for example evaporative cooling and cooling towers improve energy efficiency but increase water use. The Autodesk Green Building Studio web service estimate the typical water usage for your project, based upon standard efficiency appliances and typical occupancy loads. You have the ability to change assumptions within the tool and estimate potential water savings.

Practicum

Hands on:

Workbook Exercises

There are no prepared exercises for this unit. 16 Stein, Marjorie and Bailey, Patrick. March 2007. Supply and Demand Side Water-Energy Efficiency Opportunities Final Report. Prepared for Pacific Gas and Electric. Page 11.

Additional exercises

1. Submit your BIM model to Autodesk Green Building Studio. Review the following results: a. What is the carbon-neutral potential for this project? b. What is the wind energy and the photovoltaic energy potential for this project? c. What is the natural ventilation potential for this project? d. What is the prevailing wind direction for this project for the year? How about for just the summer?

Note: In order to run the Revit model through Green Building Studio, it needs to be prepared for building performance analysis. For step by step instructions to prepare the model for building performance analysis, refer to the Autodesk’s Revit

® Architecture and Revit

® MEP Tutorial for Green Building

Studio. Unit 7 of the Student Workbook also carries these instructions.

Questions

2. Are there other energy efficiency programs for buildings beyond those already mentioned? 3. How do they compare to carbon-neutral, net-zero, and the 2030 Challenge? 4. Find examples of building forms that have potential to introduce natural ventilation and daylighting and examples of those that do not. 5. Does your electric utility offer green power?

Additional References

Architecture 2030 Toolkit http://www.aia.org/toolkit2030/index.cfm The 2030 Challenge: http://www.architecture2030.org/ U.S. Environmental Protection Agency, Energy Star: http://www.energystar.gov/index.cfm?c=new_bldg_design.bus_target_finder U.S. Department of Energy High Performance Buildings: http://www.eere.energy.gov/buildings/highperformance/ Center for the Built Environment: http://www.cbe.berkeley.edu/ The Weather Underground: http://www.wunderground.com/ Daylighting Collaborative. http://www.daylighting.org/why.php Lawrence Berkeley National LaboratoryWindows & Daylighting: http://windows.lbl.gov New Buildings Institute: http://www.newbuildings.org/ U.S. Department of Energy, Energy Efficiency and Renewable Energy, Building Technologies Program: http://www1.eere.energy.gov/buildings/ Structural Insulated Panel Association http://www.sips.org/ Insulating Concrete Forms (ICFs) Association http://www.forms.org Efficient Windows Collaborative: http://www.efficientwindows.org/ Cool Roof Rating Council: www.coolroofs.org Lawrence Berkeley Heat Island Group: http://eetd.lbl.gov/HeatIsland/