Determining U-values of Wall and Roof

Objective:

To calculate the U-value ( w/m²K) of different materials used in a different climatic zones

U value: Thermal transmittance (U value) is the heat transmission in unit time through unit area of a material or construction and the boundary air films, induced by unit temperature difference between the environments on either side. Unit of U value is W/m2 .K. U value for the wall/roof/glazing indicates its ability to transfer heat through conduction. 

Outcome:

Students will learn about thermal properties of building materials used in India

Requirements:

Energy Conservation Building Code (ECBC) documents, Suggestive research papers based on building materials and their thermal properties

Prerequisites:

Students should have knowledge about materials used in Walls and Roofs in different climatic zone, both vernacular and contemporary materials 

Procedure:

Step 1: Create 5 groups out of the class and each group takes up one climatic zone. A brief introduction on the ECBC document be given before the groups start with the activity. 

Step 2:  Students should list down the building materials used and specification of different layers while assembling for roof, and wall through research for the identified climatic zone. For eg: 

Wall for Hot dry climates (Vernacular) – External lime plaster, Clay bricks, Internal Lime plaster;

Wall for Hot dry climates (Contemporary) – External plaster, AAC blocks, Internal plaster, Ceramic tiles.

Step 3: Each group should list down such layers and assemblies as shown in the example below used in particular climatic zone along with the thickness, in the table below. 

Step 4:  Students should calculate the U – value for roof, and wall to understand the heat transfer of different materials

Table: Wall Assembly U-value Calculation

Sr. No	Materials	Thickness (m)	Thermal Conductivity (k) (W/m.K)	Specific Heat capacity (kJ/kg.K)	U-value W/m².K	ECBC U-Value Requirement for Wall Assembly W/m².K	Climatic Zone – City/State
Assembly 1 (Vernacular) for Hotdry climate
1	Internal Lime Plaster	0.015
2	Clay Block	0.25
3	External Lime Plaster	0.015
Assembly 2
Assembly 3

Table: Roof Assembly U-value Calculation

Sr. No	Materials	Thickness (m)	Thermal Conductivity (k) (W/m.K)	Specific Heat capacity (kJ/kg.K)	U-value W/m².K	ECBC U-Value Requirement for Wall Assembly W/m².K	Climatic Zone – City/State
Assembly 1 (Vernacular) for Hotdry climate
1	Wooden frame	0.075
2	Thatch	0.25
Assembly 2
Assembly 3

Step 5:  The lower the U value, better Thermal conductivity. Discuss and Reflect on the findings. 

References:

Bureau of Energy Efficiency – beeindia.gov.in – https://beeindia.gov.in/sites/default/files/Residential%20Code_Building%20Envelope_Draft_rev4.pdf