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University of Florida Building Envelope What is a Building Envelope? Answer: Everything that separates the interior of a building from the outside environment Foundation or building slab Walls and ceilings Roof Doors Windows Insulation Foundation or Building Slab

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what is a building envelope
What is a Building Envelope?

Answer: Everything that separates the interior of a building from the outside environment

  • Foundation or building slab
  • Walls and ceilings
  • Roof
  • Doors
  • Windows
  • Insulation
foundation or building slab
Foundation or Building Slab
  • Insulating foundations or bldg slabs is important for energy efficiency
  • For new construction, pre-insulated and pre-cast foundation panels or insulating concrete forms:
    • Minimize heat loss through the foundation
    • Protects the foundation from the effects of the freeze-thaw cycle in extreme climates
    • Reduces the potential for condensation on surfaces in the basement

Interior basement insulation

Exterior basement insulation

wall ceiling construction considerations
Wall/Ceiling Construction Considerations
  • Advanced framing techniques help to achieve E efficiency
  • Framing (of ceilings & walls) can also be avoided entirely with Structural Insulating Panels (SIPs):
    • Prefab panels sandwich a foam core between two sheets of plywood
    • Made to precise design specifications
  • Insulated concrete forms, are now also being used to form insulated concrete walls

Ski Lodge in Canada

Constructed w/ SIPs

wall ceiling construction alternative building materials
Wall/Ceiling Construction: Alternative Building Materials

A wide variety of alternative materials is now being used to construct buildings. Many have energy efficiency as well as environmental benefits. These materials include:

  • Adobe (clay and straw)
  • Straw Bale
  • Rammed earth
  • Tires and other recycled materials

Mixing mud and straw

in brick frames

roof considerations
Roof Considerations
  • White or reflective roofing help reflect heat and keep buildings cool
  • Ventilation should be considered to avoid moisture build-up
  • Studs, sills, and other building components can act as thermal bridges, conducting heat past a building\'s insulation

White acrylic elastomeric roof

coating protects the roof of a

chemical manufacturing plant

heat loss through doors
Heat Loss Through Doors
  • Exterior doors generally comprise a small area of the building envelope
  • Even though most door types may not be very well insulated, they usually do not contribute substantially to the overall heat transfer of the envelope
  • The primary source of heat loss related to doors:
    • is through air leakage due to poor fitting doors and weatherstripping
    • and through the door being physically opened for building access
overhead doors
Overhead Doors
  • Overhead doors used for loading and unloading material or vehicle access are often left open for convenience
  • If used frequently, overhead doors can cause excessive air leakage and result in substantial heat loss or gain
  • This can lead to unnecessary cycling of heating and cooling systems as well as reduce comfort in surrounding areas
overhead doors9
Overhead Doors
  • Evaluate loading schedules for frequency of overhead door use and identify problem areas and retrofit potential
  • Loading dock curtains made of plastic strips can be installed to reduce mixing of outside and conditioned air while permitting access to the loading dock
  • Other alternatives include reducing the door size or installing air curtains, radiant heating systems, conveyor belts, and controls to lock out HVAC equipment when the doors are open
  • Overhead doors in conditioned areas should also be insulated and weatherstripped to prevent heat loss when closed
industrial door options
Industrial Door Options
  • Roll-up Doors can effectively block air movement while not slowing down production.
  • Rapid open / close options are available.

http://www.youtube.com/watch?v=XsLkoJIPym0

  • Vinyl strip doors and air curtains
windows
Windows
  • Labels from:
    • ENERGY STAR®
    • National Fenestration Rating Council
  • indicate:
    • Solar heat gain coefficient (SHGC) - roughly equivalent to the solar shading coefficient
    • U-value - which indicates how well the window insulates
    • Visible transmittance - which indicates how well light passes through the window
  • High-tech efficiency options include windows with:
    • Argon between the window panes
    • Low-emissivity (low-e) coatings
energy efficient windows
Energy-Efficient Windows
  • A deposit of microscopically thin, virtually invisible, metal or metallic oxide layers reduces the U-factor by suppressing radiative heat flow
  • Heat transfer in multilayer glazing is thermal radiation from a warm pane of glass to a cooler pane
  • Low-E coatings are transparent to visible light
  • Different types of Low-E coatings have been designed to allow for:
    • high solar gain (for cool climates)
    • moderate solar gain (for temperate climates)
    • or low solar gain (for cooling dominant climates)

Pyrolitic window:

high solar gain, low-e, double glaze / argon fill

effect of building variables and window oriented heating costs
Effect of Building Variables and Window-Oriented Heating Costs
  • By using energy efficient window technologies, the effect of:
    • shading,
    • window orientation
    • window area

is minimized

Top (red): clear, single glaze

through bottom (purple):

low-e, triple glaze

insulation
Insulation
  • Need to insulate indoor thermal sources:
    • Process heating equipment
    • HVAC Ductwork/ piping
    • Steam lines
  • Separate areas with AC from those without with air curtains or strip doors
  • Weatherstripping and caulking
envelope heat loss
Envelope Heat Loss

The ability to hold indoor air temperature at the desired level is affected by all three methods of heat transfer:

  • Conduction
  • Convection
  • Radiation
conduction
Conduction
  • Requires that surfaces touch for solid-solid heat transfer.
  • Because the different materials in an insulated assembly touch each other, conduction heat loss occurs through solid components of the building envelope.
  • For example, heat flows by conduction from warm areas to the cooler areas of concrete slabs, window glass, walls, ceilings, and other solid materials.
conductance
Conductance
  • The unit used for thermal transmittance (heat transfer) or conductance of a single building material or building is often called the U-value.
  • U-values are expressed in Btu’s per hour per square foot of area per degree temperature difference.
  • Windows are commonly described by their U-values.
  • Descriptions of building walls, floors, or ceilings, often use R-values instead of U-values. The two terms are reciprocal.
  • The U-value or conductance flows through a material and the R-value measures the resistance, or how slowly heat flows.
convection
Convection
  • Transferring heat from one place to another by molecular movement through fluids such as water or air.
  • Heat loss by convection commonly results from exfiltration or air leakage.
  • Convective heat loss occurs when warm air is forced out, usually from the building (exfiltration), by cold incoming air, usually in the lower part (infiltration).
  • The rate of transfer is increased when the wind blows against the building or when the temperature difference between the inside and outside increases
radiation
Radiation
  • Radiation is the heat transfer by electromagnetic waves from a warmer to a cooler surface.
  • The transfer of the sun\'s heat to a roof or the warmth of a standing near a glass furnace are examples of radiant heat transfer.
thermally light and thermally heavy buildings
Thermally Light and Thermally Heavy Buildings
  • Thermally light – A building whose heating and cooling requirements are proportional to the weather driven outside temperatures, e.g., most homes and commercial office buildings.
  • Thermally heavy – A building whose indoor temperature remains fairly constant in the face of significant changes in the outdoor temperature, e.g., a plastic injection molding facility, or a building with a high heat generating device or area in it.
thermal weight
Thermal Weight
  • A "rule of thumb" for determining the thermal weight of a bldg:
    • look at heating and cooling needs at an outdoor temperature of 60°F.
    • If the building requires heat at this temperature, it can, too, considered thermally light,
    • If cooling is needed, it is thermally heavy
  • Some areas within a building can be both thermally light and thermally heavy depending on their use.
    • A meeting room, for example, can have significant heat gains from people, equipment, and lights when the room is occupied and not require any heating from the HVAC system on a cold day.
    • The same meeting room, however, may require heat at the same outdoor temperature when the room is vacant
thermal mass
Thermal Mass
  • Thermal mass saves energy by storing and releasing heat
  • For a building to take advantage of thermal mass, there must be a source of free or less expensive energy to charge the mass.
  • The existence of thermal mass, such as concrete walls and floors, can have a substantial impact on the operation of HVAC system\'s but is difficult to analyze.
  • It can affect the HVAC systems ability to quickly respond to rapid changes in load caused by increased occupancy, equipment, or solar gains through windows.
thermal mass23
Thermal Mass
  • The effect of thermal mass on the building systems will vary
    • by climate and type of building
    • by the location of the mass within the structure
  • Thermal mass in exterior walls, for example, will slow down heat flow through the wall allowing a reduction in insulation requirements while maintaining performance levels similar to standard frame construction.
  • High levels of mass located within the building tend to reduce the effectiveness of mass in the outside walls
thermal mass24
Thermal Mass
  • Buildings that most benefit from thermal mass are typically those with substantial cooling loads
  • In this case, the thermal mass can be precooled at night using outside air for free cooling or less expensive offpeak electricity for mechanical cooling.
  • This allows the mass to absorb heat the following day, reducing the need for operation of cooling systems during peak utility demand hours.
thermal mass25
Thermal Mass
  • Generally, thermal mass is part of the integral construction of the building and is not added for conservation reasons
  • Unfortunately, there are no easy rules to determine how thermal mass will affect different buildings
  • It is important to note its existence because it may help you understand behavior of the mechanical systems or reasons for some comfort complaints
solar heat gain
Solar Heat Gain
  • Windows are subject to solar heat gains which can have significant impacts on HVAC operation and occupant comfort
  • The amount of heat gain is a function of orientation, season, time of day, glazing type, and shading by window coverings, overhangs, other buildings and vegetation
  • Solar gains through south facing glass will add heat to the building in the winter
  • East and West surfaces will gain the greatest amount of heat in the early morning and late afternoon hours during summer months
solar heat gain27
Solar Heat Gain
  • Winter heat gains may be desirable in thermally light buildings while any solar heat gains in a thermally heavy building will only contribute to the cooling load
  • East and west facing glass are primarily a problem during the summer. Low sun angles in the morning and late afternoon can result in substantial solar heat gains as well as unwanted glare
  • The problem of excess solar heat gains during the summer can be compounded by the build up of internal heat most buildings experience late in the day.
  • The combination of solar and internal heat gains can greatly increase the energy required for cooling.
building pressure
Building Pressure
  • HVAC system balance can influence the amount of air leakage
  • Buildings can be slightly pressurized by bringing in more intake air than is exhausted to reduce infiltration
  • An easy method of determining if a building is under positive or negative pressure is to hold an exterior door open about 1 inch on a calm cool day and observe which way the air is flowing
  • If air is flowing into the building, that part of the building is under negative pressure and may have problems with infiltration
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