Heat Loss & Gain

Question 1

What is heat loss?

Answer 1

the ability to loose heat from different surfaces

Question 2

What factors determine the amount of energy you need to heat a house?

Answer 2

• temperature difference
• resistance to heat flow (insulation)
• ventilation losses
• internal gains
• external gains

Question 3

What is the ideal room temp?

Answer 3

20-25 degrees

Question 4

What comes under fabric heat losses/gains?

Answer 4

heat lost or gained through the roof, walls, windows

Question 5

What comes under ventilation heat losses/gains?

Answer 5

heat losses through air temperature

Question 6

What is the total heat loss equation?

Answer 6

total heat loss from a space/building is the sum of fabric losses + ventilation losses

Question 7

What are the 3 main methods of heat loss?

Answer 7

conduction, convection and radiation combined

Question 8

What is conduction?

Answer 8

heat transfer through a sold body (e.g a wall)

Question 9

What is convection?

Answer 9

heat transfer between a solid surface and the surrounding fluid (air/water)

Question 10

What is radiation?

Answer 10

heat transfer between the surfaces of remotely located solid bodies

Question 11

What is Q in terms of heat loss?

Answer 11

the rate at which heat is lost in a building (a measure of energy) in watts W - HEAT TRANSFER

Question 12

Why is it important to control heat loss?

Answer 12

greater thermal comfort
reduced operational cost
reduced carbon emissions
meet international emissions standards
important element of design

Question 13

What is the mechanism of heat loss by conduction?

Answer 13

through solid materials, resistance of layers (each solid layer has a resistance to heat loss)

Question 14

What is the total resistance for heat loss through conduction in a solid material?

Answer 14

total resistance = sum of resistances of all individual layers

Question 15

What is the total resistance for heat loss through conduction in a material with an air gap?

Answer 15

total resistance = sum of resistances of all individual layers + resistances for air gap

Question 16

What is the U-value?

Answer 16

the U-value of building element is the reciprocal of the total resistance of that element - U = 1/ΣR (U is the thermal transmittance of an element such as a wall, in units of Wm^-2K^-1)

Question 17

How do we minimise building fabric heat losses?

Answer 17

• minimise ventilation heat losses by using natural ventilation and infiltration
• site and orientation: looking at microclimate, landscape and shelter (e.g terraced houses)
• green roofs
• orientating glazing
• control any energy consuming plant so that it operates only when required and to the level required: boilers, TVs, water, heaters

Question 18

What are typical U values for roofs, walls, windows and floors?

Answer 18

roofs - 0.13
walls - 0.18
windows - 1.4
floors - 0.13

Question 19

What does a high U value mean?

Answer 19

highest potential of heat loss

Question 20

Why is glazing a big issue in terms of heat loss?

Answer 20

large glass facade takes in lots of heat

Question 21

Conclusions

Answer 21

Conclusions:

• heat gain as well as heat loss can affect buildings
• early stage design considerations essential
• consider options surrounding site and micro climate
• think of city centre locations and potential