FARBER ENERGY DESIGN

 

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ENERGY-EFFICIENT DESIGN

(Ideas on exceeding Title 24 efficiency requirements)

 

ENERGY EFFICIENCY – EXCEEDING CODE MINIMUMS

 

The Title 24 energy code sets a minimum level of energy efficiency, which applies to most new and remodeled buildings in California.  However, the Title 24 efficiency requirements are not necessarily the “optimum” level of efficiency for many projects.  Given rising energy costs, concern about global warming, and the desire to become less reliant on non-sustainable energy sources, there are many good reasons to consider exceeding the Title 24 efficiency requirements.  Some developers see energy efficiency as a selling point.  And some owners are interested in making a statement about creating less impact on the environment.

 

Many government agencies are requiring their new buildings to exceed Title 24 and/or meet the LEED “green building” requirements (which requires energy-efficient building design).  Some cities are requiring stricter “sustainable resource” design requirements for new private sector buildings, or giving incentives to do the same.  Both private and public building owners are encouraged to exceed Title 24 by incentive programs offered by utilities and government agencies (see the Energy Efficiency Incentive Programs page of this web site for more information).

 

ENERGY-EFFICIENT DESIGN STRATEGIES

 

The following are some key design considerations for energy-efficient buildings:

 

¡  Building orientation

For all types of buildings, in all climate zones, orienting the building on an east-west axis, so that larger exterior wall areas are facing north and south, is desired because it maximizes the potential for glazing on the south and north, while decreasing the potential east and west-facing glazing areas.  East and west-facing fenestration is less desired because it is subject to high solar loads in summer, and is difficult to shade due to the low morning and afternoon sun angles that strike east and west facades (see Apparent Motion of the Sun on the Fenestration page of this site).  East and west-facing glazing also transmits very little winter solar heat that is desired in smaller (mainly residential) buildings.

 

 

 

NONRESIDENTIAL BUILDINGS

 

In most nonresidential buildings, where occupants, lighting and equipment result in large internal cooling loads, solar heat is not desired (except in cold climates in winter).  Therefore, north-facing glazing is best.  South-facing glazing is superior to either east or west-facing glazing, as it receives less summer solar heat, and is easier to shade. 

 

 

 

RESIDENTIAL BUILDINGS

 

In residential buildings (and very small-scale commercial buildings), solar heat is desired in winter, but is not wanted in the warm summer season.  Therefore, maximizing south-facing glazing (with modest overhang to shade the summer sun) is best.

 

 

 

 

 

¡  Daylighting

Building designs can take advantage of natural daylight to light interior space, while reducing electric lighting energy through automatic controls.  The best designs bounce daylight onto and off a white ceiling, while also partially shading the glazing.

 

 

 

¡  Renewable Energy

Passive and active solar systems can be incorporated into buildings for space heating and domestic hot water needs.

 

 

PASSIVE SOLAR HEATING & COOLING

 

 

ACTIVE SOLAR HEATING & PV

 

 

Passive solar systems rely on direct solar heating of the space, by “collecting” solar heat through south-facing windows.  Passive solar heating performs best when designed with interior thermal mass to soak up excess solar heat during the daytime, which is released as the space cools at night. Passive cooling can be achieved by use of thermal mass inside the occupied space, which can be cooled on summer nights with open windows and/or forced ventilation systems, helping to keep buildings cooler during warm days.

 

 

Active systems rely on solar collectors to collect heat , to be used for domestic hot water, space heating and pool heating. Photovoltaic (PV) panels produce electricity.  A storage medium (usually water for thermal systems, the electric utility or batteries for electric systems) is employed to have access to the energy when needed.  Both types of collectors are usually mounted on south-facing roof surfaces, unshaded by neighboring structures and trees.

 

 

Description: SolarPassive602-2

 

 

 

¡  Other energy efficiency options to consider      (for more ideas and applicability to specific projects, contact F.E.D.)

®  Fenestration

For most building types and climate zones, Title 24 sets fairly stringent efficiency requirements for windows, glass doors and skylights.  Low-E glazing is typically required in order to achieve the “baseline” requirements both the SHGC and U-factor.  For low-rise residential buildings, non-metal frames are the norm.  For nonresidential and high-rise residential projects, thermally-broken frames are sometimes required in order to meet energy code efficiency requirements.

 

For nonresidential buildings, where mechanical cooling is often running throughout the year in order to achieve indoor comfort, low SHGC glass (and/or well-shaded glass) is essential.  And because automatic daylight controls are required by the energy code, and reducing electric lighting saves lighting and AC energy, specifying Low E glass with high visible light transmittance is also important.  In fact, the 2013 energy code for the first time regulated glazing daylight transmittance.  The good news:  There are now many Low E glass choices that offer both low SHGC and high VLT.  However, all but the very lightest tint glass models reduce daylight significantly compared to clear Low E glass.

 

For residential buildings, where cooling is more seasonal, and where space heating is often a greater energy concern than space cooling, the most efficient designs will use higher SHGC glazing combined with shading designs that let in direct winter sun, but shade glazing from unwanted direct sun in summer. 

 

®  External window shading systems

Horizontal projections are effective at south windows, less so at east and west-facing windows – where a combination of horizontal and vertical projections can be quite effective.  Windows with integral blinds are also helpful in blocking solar heat.  Interior blinds are much less effective.  Note that adjustable shading systems cannot receive credit under Title 24 compliance rules.

 

®  Insulation

For the most part, Title 24 sets fairly stringent requirements for building insulation.  While batt insulation between wood framing can often be adequate, the energy code has increased insulation requirements to the point where, for both residential and nonresidential buildings, insulative sheathing is usually required on wood frame walls in order to meet the prescriptive insulation requirements!  And metal frame walls (including even demising walls in the 2016 code) usually can’t meet mandatory minimum insulation requirements without insulative sheathing. 

 

Adding as little as R-4 insulative sheathing to a metal frame wall can make a dramatic improvement in energy efficiency.

 

Title 24 is still fairly lax for raised concrete floors above unconditioned space (such as parking).  An uninsulated floor will result in less occupant comfort and greater energy usage.  This is especially a concern for apartments.  Insulating all raised floors is highly recommended.

 

®  Cool Roof

Cool Roof (CR) keeps roofs, and the conditioned spaces below them, cooler.  CR is prescriptively required for nonresidential and high-rise residential buildings in all climate zones, and for low-rise residential buildings in most climate zones.  Where a specified CR product exceeds prescriptive minimum values, it will yield a “credit” towards performance energy compliance.  CR is always recommended in warmer climate zones.

 

®  High efficiency cooling and heating systems

High SEER air conditioners, high AFUE condensing furnaces, high-efficiency “split” heat pumps, economizers, evaporative coolers (swamp coolers), geothermal heat pumps.  For low-rise residences in warmer climate zones, whole house cooling fans became a prescriptive requirement in the 2013 code.

 

®  AC fan system efficiency.

Variable speed supply fans, and for nonresidential buildings: larger ducts or raised floor air distribution to reduce the static pressure.

 

®  Thermal recovery ventilation systems

Exhaust air tempers fresh ventilation air by use of a heat exchanger, thus reducing cooling and/or heating energy.

 

®  Efficient lighting

The energy code requires many automatic controls, such as daylighting, occupant vacancy, and sweep shut-off.  However, while LED lighting has become almost standard in the past few years, the energy code’s lighting energy efficiency requirements do not explicitly require LED lighting.  Given that LED lighting is more efficient than fluorescent, and is said to be cost-effective as compared to fluorescent when automatic control system costs, longevity, and energy savings are factored in, LED lighting is highly recommended.

 

®  High efficiency water heating systems

Tankless water heaters only use energy when there is demand.  Point-of-use in-line electric water heaters are suitable for small demand situations (such as office and retail).  Tankless gas-fired water heaters are often an excellent alternative to storage-type gas water heaters.  For large demand situations, consider solar water heating systems with tankless gas-fired water heaters as back-up.  Hot water delivery time a concern?  Install multiple water heaters, or use an “on-demand” type pumped recirculation system.

 

®  Operable windows on nonresidential buildings

Especially effective if flow-through ventilation can be achieved.  In larger buildings, consider tying window operation to HVAC system control by use of sensors.  In fact, such controls become a prescriptive requirement in the 2016 code.

 

 

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