Heat Loss & Gain Flashcards
What is heat loss?
the ability to loose heat from different surfaces
What factors determine the amount of energy you need to heat a house?
- temperature difference
- resistance to heat flow (insulation)
- ventilation losses
- internal gains
- external gains
What is the ideal room temp?
20-25 degrees
What comes under fabric heat losses/gains?
heat lost or gained through the roof, walls, windows
What comes under ventilation heat losses/gains?
heat losses through air temperature
What is the total heat loss equation?
total heat loss from a space/building is the sum of fabric losses + ventilation losses
What are the 3 main methods of heat loss?
conduction, convection and radiation combined
What is conduction?
heat transfer through a sold body (e.g a wall)
What is convection?
heat transfer between a solid surface and the surrounding fluid (air/water)
What is radiation?
heat transfer between the surfaces of remotely located solid bodies
What is Q in terms of heat loss?
the rate at which heat is lost in a building (a measure of energy) in watts W - HEAT TRANSFER
Why is it important to control heat loss?
greater thermal comfort reduced operational cost reduced carbon emissions meet international emissions standards important element of design
What is the mechanism of heat loss by conduction?
through solid materials, resistance of layers (each solid layer has a resistance to heat loss)
What is the total resistance for heat loss through conduction in a solid material?
total resistance = sum of resistances of all individual layers
What is the total resistance for heat loss through conduction in a material with an air gap?
total resistance = sum of resistances of all individual layers + resistances for air gap
What is the U-value?
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)
How do we minimise building fabric heat losses?
- 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
What are typical U values for roofs, walls, windows and floors?
roofs - 0.13
walls - 0.18
windows - 1.4
floors - 0.13
What does a high U value mean?
highest potential of heat loss
Why is glazing a big issue in terms of heat loss?
large glass facade takes in lots of heat
Conclusions
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
