DOCUMENTATION AND ANALYSIS OF THE INSULATION PROPERTIES OF AN EXTERIOR WALL IN RYDER HALL, NORTHEASTERN UNIVERSITY By Trisha Parekh This report aims to study and analyze the thermal insulation properties of an exterior wall at Ryder Hall in Northeastern University, Boston. The images and temperature data in this report were documented on 10 th October 2018 at 3.30 pm. The study was conducted on a warm day; therefore, the wall’s insulation potential was not fully utilized. The study includes the calculation and analysis of the wall’s insulation on a cold day as well. The tools used to document thermal images of the wall include a FLIR T-420BX camera and the FLIRTools Software. The wall: A wall is one of the most important architectural elements of a building. Its functions include protection from outside climate, privacy and safety. This exterior wall is specially designed to withstand harsh cold exterior temperature, rain, snow and dew. It comprises of several layers, each playing its role in resisting the external conditions from coming inside the building. The sections below show the various layers in the exterior wall assembly at Ryder hall. I.
From the window….
Fig.1: Section 1-1’ through glazing
Glazing consists of 60% of the external wall area in the documented room. This section through glass has only one member in the assembly-a ½” thick double glass-between the outside and inside. The rate of flow of heat between the outside and inside is a function of the resistance of the materials separating the indoor from the outdoor, the area of that material and the temperature difference between the two environments. Below is a calculation of the heat transfer rate - Q (dot) through the glazing. Item Inside Air Film Double Glazing Outside Air Film
Resistance per inch Rtotal = Table.1: Thermal resistance of wall assembly through section 1-1’
R = 1/U
Thickness (inch) 0.5” -
Total Resistance 0.68 1.69 0.17 2.54
| U = 0.39 Btu/hr.ft2.F
Q = U * A * T Q = (1/2.54) * (80% of 90 sq. ft) * (70F - 9F)
On a cold day when the indoor and outdoor temperatures are 70F and 9F respectively
Q = 1729.13 Btu/hr
Glass is a very poor resistor of heat; therefore, it allows high levels of heat transfer. The above value reflects how badly a glass partition performs in insulation. However, spaces need natural lighting and glass is one of the best materials to cover fenestrations/openings while allowing the flow of light, it sometimes just cannot be replaced. One strategy used to increase the thermal resistance of glass (slightly) is to provide several layers of glass with argon/krypton filled air cavities between them.
Fig. 2: Section through a triple pane glass windo
R = 1/ U
| U = 0.39 Btu/hr.ft2.F
Q = U * A * T Q = (1/2.54) * (80% of 90 sq. ft) * (83.7F – 80.6F)
On the recorded day
Q = 87.87 Btu/hr *Note: The outdoor temperature is higher than the indoor temperature and the heat transfer is reversed (from outside to inside)
Members of a wall assembly are held together using metal or wood framework. These are points in a wall assembly where the thermal property of that specific material (metal or wood) changes the overall heat transfer rate at that physical point in the wall assembly and are known as thermal bridges. Below is the calculation of heat transfer rate through the mullions in the window. Item Inside Air Film Aluminum channel Air cavity Outside Air Film
Resistance per inch 1.2 Rtotal = Table.2: Thermal resistance of wall assembly through section 1-1’at the mullion R = 1/ U
Thickness (inch) 0.5” 3.5” -
| U = 0.41 Btu/hr.ft2.F
Q = U * A * T Q = (1/2.45) * (20% of 90 sq. ft) * (70F - 9F)
On a cold day when the indoor and outdoor temperatures are 70F and 9F respectively
Q = 448.16 Btu/hr
R = 1/ U
Total Resistance 0.68 0.6 1 0.17 2.45
| U = 0.41 Btu/hr.ft2.F
Q = U * A * T Q = (1/2.45) * (20% of 90 sq. ft) * (83.7F – 80.6F)
On the recorded day
Q = 22.77 Btu/hr *Note: The outdoor temperature is higher than the indoor temperature and the heat transfer is reversed (from outside to inside)
Fig.3: Sketch of a classroom in Ryder hall II.
‌To the wall
Fig.4: Section 2-2’ through wall This section is through the external wall representing an assembly of members which together act as an insulation unit. The thickness, material and insulation property of each of the materials in the assembly is as follows:
1. Interior wall finish: The innermost layer is a latex paint finish on plaster. This is an aesthetic element which also acts as a coating to protect the wall from dirt, stains and impact. 2. Interior gypsum board: This is in fact the innermost member in the wall assembly and is 5/8” thick. Gypsum boards are one of the most commonly used interior wall members. They are preferred mainly because of their ease of installation, durability and versatility. 3. Fiberglass insulation: Fiberglass is one of the commonly used insulation materials in the building industry. It is made of plastic reinforced by extremely fine glass fibers. Fiberglass slows the transmission of heat and sound from one side to another by trapping pockets of air. Therefore, in any insulation wall assembly, such a high resistance member (R per inch = 3.5 Btu/hr.ft.F) is fundamental. 4. Plywood: Plywood holds the insulation from the outer side and provides stability and strength to the wall. A 1” thick plywood is the thickest grade of commercial ply and is essentially used on the exterior of a drywall. Besides its functional use, plywood also provides a fairly good thermal resistance in the wall assembly. 5. Air cavity: The air gap or cavity between two walls is a very effective way of preventing the inside wall from getting damp from water seepage through the outermost wall but the heat transfer takes place nonetheless. Many modern wall assemblies consist an additional moisture control film stuck on the exterior surface of the plywood. This is to repel any moisture that gets through the external wall, into the air cavity and deposits on the surface of the plywood. 6. Brick wall: This outermost wall is the entity that is exposed to sun, rain, wind, impact, dirt and all kinds of outdoor hardships. Therefore, a hardy material such as brick is used for building an external wall. Brick is a porous material-it is a good conductor of heat and also allows moisture to pass through.
Below is a calculation of the heat transfer rate - Q (dot) through the wall. Item Inside Air Film Gypsum wall board Fiberglass insulation Plywood Air cavity Brick insulation wall Outside Air Film
Resistance per inch 0.9 3.5 1.25 0.2 Rtotal = Table.3: Thermal resistance of wall assembly through section 2-2’
R = 1/ U
Thickness (inch) 5/8” 4” 1” 2” 9” -
Total Resistance 0.68 0.5625 14 1.25 1 1.8 0.17 19.46
| U = 0.051 Btu/hr.ft2.F
Q = U * A * T Q = (1/19.46) * (88% of 60 sq. ft) * (70F - 9F) Q = 165.51 Btu/hr
On a cold day when the indoor and outdoor temperatures are 70F and 9F respectively
R = 1/ U
| U = 0.051 Btu/hr.ft2.F
Q = U * A * T Q = (1/19.46) * (88% of 60 sq. ft) * (83.7F – 80.6F)
On the recorded day
Q = 8.41 Btu/hr *Note: The outdoor temperature is higher than the indoor temperature and the heat transfer is reversed (from outside to inside)
According to the Massachusetts Energy Code, the maximum U value (thermal conductance) requirements of an above grade exterior wall insulation assembly is U 0.080. The exterior wall assembly at Ryder hall has a U value of 0.051. Therefore, this wall performs very well as an insulation assembly.
Below are the calculations of heat transfer through the metal channels in the wall framework.
Item Inside Air Film Gypsum wall board Aluminum channel Air cavity Plywood Air cavity Brick insulation wall Outside Air Film
Resistance per inch Total Resistance 0.68 0.9 0.5625 1.2 0.6 1 1.25 1.25 1 0.2 1.8 0.17 Rtotal = 7.0625 Table.4: Thermal resistance of wall assembly through section 1-1’ at the thermal bridge junction
R = 1/ U
Thickness (inch) 5/8” 0.5” 3.5” 1” 2” 9” -
| U = 0.14 Btu/hr.ft2.F
Q = U * A * T Q = (1/7.0625) * (12% of 60 sq. ft) * (70F - 9F)
On a cold day when the indoor and outdoor temperatures are 70F and 9F respectively
Q = 62.18 Btu/hr
R = 1/ U
| U = 0.14 Btu/hr.ft2.F
Q = U * A * T Q = (1/7.0625) * (12% of 60 sq. ft) * (83.7F – 80.6F) Q = 3.16 Btu/hr
On the recorded day
*Note: The outdoor temperature is higher than the indoor temperature and the heat transfer is reversed (from outside to inside)
THERMAL GRADIENT
Fig.5: Section through wall showing the thermal gradient and dewpoint temperature
The above figure provides the temperature drop at each consequent layer in the assembly. The steepest drop is from 66F to 22F at the fiberglass insulation layer. This slope shows how affective this member is in providing insulation. When the inside of a building is heated to 70F on a 9F winter design day with 50% relative humidity, the dew forms at a point when water vapor in the air passing through the wall condenses into liquid. This is called dewpoint temperature. The dewpoint temperature for indoor air is 51F which occurs in the fiberglass insulation layer of the wall assembly. Fiberglass is an inert material which does not allow the passage of water or moisture through it. Therefore, if dew is formed in the fiberglass layer, it may get stuck in the air pockets for a very long time. This problem can be solved by using vapor barriers just before the fiberglass layer so as to resist moisture in the air from getting into the wall assembly. Vapor barriers are thin films made of materials such as polyethylene.
ANALYSIS OF THERMAL DATA OBTAINED FROM FLIR T-420BX
The FLIR T-420BX camera was used to capture thermal images of the Ryder hall wall from inside and outside. The data represents the temperature of the surface being captured. In the black and white image below, white represents the hottest regions and black represents the coldest regions on that façade. In the colored images, yellow represent the hottest regions and purple represents the coldest regions on that façade.
Ryder Indoor: The indoor dry bulb temperature at Ryder hall at the recorded time was 80.6F and the relative humidity was 60.5%. The glazing appears to be warmer than the wall and ceiling. In the glazing system, the mullions appear to be much cooler than the glass itself. The overall indoor temperature is cool but the average temperature increases due to the humans in the picture.
Ryder Outdoor: The outdoor dry bulb temperature at Ryder hall at the recorded time was 83.7F and the relative humidity was 69.8%. This picture seems much warmer than the previous one because of the high amount of heat being reflected by the glass. The wall appears to be much cooler than the glazing and the average temperature of the image is also slightly lower in spite of the large reflected heat.
Fig. 6: Indoor thermal image of Ryder hall Temperature at specific point 81.7F Emissivity 0.95 Reflected temperature 68F Image Minimum 76F Image Maximum 97F Image Average 82F Table.5: Thermal data of Ryder hall indoors
Fig.7: Outdoor thermal image of Ryder hall Temperature at specific point 82.3F Emissivity 0.95 Reflected temperature 68F Image Minimum 74.4F Image Maximum 89F Image Average 80.8F Table.6: Thermal data of Ryder hall outdoors
Fig. 8: Indoor thermal image of Ryder hall
Fig.9: Outdoor thermal image of Ryder hall
References: https://www.mass.gov/files/documents/2016/09/nc/115-appendices.pdf https://www.a-aservices.com/about-us/news-and-events/21349-triple-pane-double-hung-windowsinformation.html https://en.wikipedia.org/wiki/Heat_transfer https://www.retrofoamofmichigan.com/blog/fiberglass-insulation-material-ingredients https://www.woodsolutions.com.au/wood-product-categories/plywood http://www.gcsescience.com/pen14-cavity-walls.htm https://www.wbdg.org/guides-specifications/building-envelope-design-guide/wall-systems https://constructioninstruction.com/technical-articles/inside-the-slide-dew-point-in-a-wall/ https://www.certainteed.com/insulation/fiberglass-insulation-and-vapor-barriers/ https://buildingscience.com/documents/digests/bsd-controlling-cold-weather-condensation-using-insulation https://www.archtoolbox.com/materials-systems/thermal-moisture-protection/rvalues.html