3.3 Heating wall insulation

• Natuurkunde
• Middelbare school
• havo, vwo
• Leerjaar 3

3.3 Insulation

Learning goals

3.3.1 You can explain ways that a house loses heat.

3.3.2 You can explain how a dynamic equilibrium is reached between heat loss and heat production.

3.3.3 You can calculate how much heat flows away through the wall of a house.

3.3.4 You can explain how you can reduce heat loss in a house.

Section 3 — Inulsation

Heat transfer

Three forms of heat transfer:

• Conduction
  
• Convection
  
• Radiation
  

Exercise — Heat transfer

Three forms of heat transfer:

• Conduction
  
• Convection
  
• Radiation
  

Come up with three examples of for each form of heat transfer

Exercise — Heat transfer

Three forms of heat transfer:

• Conduction
  
• Convection
  
• Radiation
  

Come up with three examples of for each form of heat transfer

Conduction

• A radiator
  
• Holding a hot cup of tea
  
• A pan on a stove
  

Convection

• Warm water flowing through a tap
  
• A cold breeze in the summer
  
• Steam coming of boiling water
  

Radiation

• A campfire
• The sun
• Electric heating

Understanding double glass

Types & insulating quality

Quality of insulation

Q: Heat in joules (J)

U: the quality of insulation of the wall W/(m²•ºC)

A: The surface area of the wall (m²)

ΔT = T end  - T start : The temperature difference (ºC)

Q=U⋅A⋅ΔT

The property of a material of it's quality of insulation

Formula info

Exercise example 1

EXERCISE: Ina reads in a brochure that you can save a lot of energy by insulating central heating pipes: about 10 m3 of natural gas per meter of pipe per year. 1 m3 of natural gas provides 32·10^6 J of heat. Ina insulates 20 m of central heating pipe in her house. How much heat does it save per year?

Answ.:

20 × 10 = 200 m3 per year.

200 x 32.10^6 = 6,4.10^9 J

Exercise example 2

A single glazed pane of 1 m2 has a U-value of 5.8 W/(m2•ºC). 

The temperature outside is 2 degrees Celsius, inside it is 19 degrees Celsius. 

What is the heat loss per hour?

Answ.:

1 * 5,8 * 17 = 98,6 J/s

98,6 * 3600 = 354960 (J/h)

Mr Peterson has a corner house. Every year, 435 MJ heat disappears through each 1 m2 cavity wall of his house. The average temperature difference between outside and indoors is 8.0 °C.

Calculate the U-value of the cavity wall.

Exercise example 3

Qwall = U *  A * delta T

U = ... W/(m2•ºC)

Answ.:

Qw = U * A * delta T

435 = U * 1 * 8

U = 54.375 (/31,...)

U = 1,7 W / (m2 C)

Please try the following

C3.3 exercises: 7(f:x) until 9 (d:x)