Building Envelope Audit

Building Envelope AuditNaufal aulia azizTeknik fisika, institut teknologi bandungWhat is Building Envelope?Bulding envelope consists of those elements of a building that enclose conditioned spaces through which thermal energy may be transferredThe envelope audit should record for each space the size, physical characteristics, Hours of operation and function. The assorted materials of construction, windows, doors, holes, percentage glass, etc. should also be recorded.

InfiltrationLeakage or infiltration of air into a building is similar to the effectof additional ventilation, and it cannot be controlled orturned off at night.It is the result of cracks, openings around windows and doors, and access openings.Formula of Infiltration to heat flow:

Q is heat removal, Btu/Hrcfm is ventilation or infiltration rate, cubic feet per minuteT is the allowable heat rise

Q = 1.08 cfm T

Effect of Door Size and Time Opened on The Average Annual Heat Loss

Reducing InfiltrationTo reduce heat loss for operating doors, the installation of vinylstrips is sometimes used. This type of strip is approximately 90% efficient in reducing heat losses. Vertical shafts, such as stairwells, should be isolated.Poor quality outdoor air dampers are another source of excess infiltration. Replacement with good quality opposed-blade dampers with seals at the blade edges and ends will reduce infiltration losses. Reducing exhaust air by filterizing fitting baffles or a false hood inside existing hood.

Heat Flow Due to ConductionWhen a temperature gradient exists on either side of a wall, a flowof heat from hot side to cold side occurs.

Q is the rate of flow Btuhd is the thickness of the material in inchesA is the area of the wall, ftT is the temperature difference, FU is the conductance of the material-Btu/hr/sq ft/Fk is the conductivity of the materialR is the resistance of the material.

Q = k/d A TU=k/d= 1/R

Heat Flow Due to RadiationRadiation is the transfer of radiant energy from a source to a receiver, The radiation from the source (sun) is partially absorbed by the receiver and partially reflected.

Q = rate of heat, flow by radiation, Btu/hre = emissivity of a body, which is defined as the rate of energyradiated by the actual body. = 1 for a block body. = Stephen Boltzmans Constant, 1.71 109 Btu/ft2 hr T4A = surface area of body in square feet.

Q = A T4

Energy Audits of RoofsTo reduce the HVAC load the U-Factor of the roof is increased by adding insulation.For cooling load considerations the color of the roof is important. Light color roofs, or adding a surface layer of white pebbles or gravel, are sometimes used. The roof temperature can also be lowered by utilizing a roof spray.

Computer ServicesMost manufacturers of roof insulation and window treatments offer computer simulations to estimate savings as a result of using their products. Manufacturers such as 3M offer computer load simulations for their products.

Glass AuditGlass traditionally has poor conductance qualities and accounts for significant heat gains due to radiant energy.To decrease losses due to conductance either the glass needs to be replaced, modified, or an external thermal blanket added. Solar Radiation Considerations: In addition to heat flow due to conduction, a significant heat flow occurs through glass due to the suns radiant energy. To reduce solar loads, there are several common devices:Roller shades (least expensive)Reflective polyester filmVenetian blindsVertical louver blindsExternal louvered screensTinted or reflective glass (most expensive)

Window TreatmentsSeveral types of window treatments to reduce losses have becomeavailable. Solar ControlThermal BarriersInfiltration

Solar ControlSolar Control Films-A range of tinted and reflective polyester films are available to adhere to inner window surfaces to provide solar control for existing clear glazing. Films are typically two or three layer laminates composed of metalized, transparent and/or tinted layers. Fiber Glass Solar Control ScreensMotorized Window Shading SystemExterior Sun Control LouversExternal Venetian BlindsAdjustable Louvered WindowsSolar ShuttersThermal BarriersMultilayer, Roll-Up Insulating Window ShadeInsulating Window ShadeReflective, Perforated Solar Control LaminateSemi-Transparent Window ShadesLouvered Metal Solar ScreensOperable External Louver BlindsLouvered Metal Solar ScreensInsulating Solar Control FilmInterior Storm WindowRetrofit Insulating Glass System

Passive Solar Building DesignsA passive solar system is defined as one in which thermal energy flows by natural means. Examples of solar building design include: Solar greenhouses which are built on the south side of buildings. These can produce 60-100% of heating and cooling requirements. Underground buildings which use ground temperature to provide year-round temperature requirements. Enhanced natural ventilation through solar chimneys or use of Trombe wall.

Reducing Stratified AirOne way of reducing air temperatures near ceilings during theheating season is to use a circulation fan.The result of reducing ceiling temperature is a reduction in conduction and exhaust losses.