Flashcards in Heat Transfer Deck (26)
a form of energy. Describes the total energy of all particles within an object.
Indicates how hot or cold something is, it depends on how fast the particles are moving and is a measure of the average kinetic energy of particles. The faster the particles moving, the higher the temperature.
The transfer of heat from a hot object to a cooler one by direct contact. The greater the temperature difference the faster the heat flows from one object to another.
insulators and conductors
Conductor: Substances that transfer heat easily.
Insulator: Materials that slow the transfer of heat.
Transfer of heat when hot water/air becomes less dense rises and is replaced by cooler more dense air/water.
Where sweat/water on the surface turns to vapour, the surface is cooled. To evaporate liquid, energy is required, in this instance heat energy.
Occurs when microwaves infrared radiation, visible light or another form of electromagnetic radiation is emitted or absorbed. The hotter an object is the more heat it radiates.
› Example: The warming of the earth by the sun.
› Example: Thermal radiation from the human body.
- Some homes have fireplaces installed in them. Fireplaces require wood to be collected, this can then be burned to release heat energy and warm the house.
- Fireplaces mainly utilise convection to heat the home. As the fire heats the air which then travels in convection currents throughout the home.
burning fossil fuels
- Many homes have gas heaters that burn natural gas and release heat into the home.
- Electricity can be used in air conditioners to warm/cool the house.
- These methods also utilise convection as the main way to heat the home.
how is heating in the home achieved
burning fossil fuels and consumption of energy
passive solar design
passive solar design
- The use of the sun’s energy for the heating and cooling of living spaces by exposure to the sun.
- When sunlight strikes a building material can reflect, transmit, or absorb the solar radiation.
- The heat produces by the sun causes air movement that can be predictable in designed spaces.
elements of passive solar design
The basic responses to solar heat lead to design elements, material choices and placements that can provide heating and cooling effects in a home. These are known as elements of Passive Design and include:aperture/collector
A large glass area through which sunlight enters the building. The apertures should face within 30° of true south and should not be shaded by other buildings or trees from 9 am to 3 pm daily during the heating.
The hard, darkened surface of the storage element. The surface which could be a masonry wall, floor or water container, which sits in the direct path of the sunlight. Any sunlights hitting the surface is absorbed as heat.
Materials that retain or store the heat produced by sunlight. While the absorber is an exposed surface, the thermal mass is the material below and behind this surface.
Method by which solar heat circulates from the collection and storage points to different areas of the house. A strictly passive design will use the 3 natural heat transfer modes (convection, radiation and conduction) exclusively. In some applications, fans, ducts and blowers may be used to distribute heat through the house.
Roof overhangs can be used to shade the aperture area during summer months Other elements that control under and/or over heating include electronic sensing devices, such as differential thermostat that signals a fan to turn on, operable vents and dampers that allow or restrict heat flow, low emissivity blinds and awnings.
Windows facing north. This allows sun in during the winter.
Deciduous Trees on the north. Provides shading during summer, however shed their leaves during autumn allowing sun in during the winter.
Double Glazed Windows. Keeps heat in during the winter and heat out during the summer.
Double Bricking. Keeps heat in during the winter and heat out during the summer.
Insulation. Reduces heat transfer, keeping heat out or locking heat in.
Eaves. Stop radiation entering during summer and allows it to enter during the winter. (The sun is lower in the winter).
two primary elements of passive heating
thermal mass and south facing windows.
passive solar cooling
- Passive solar cooling systems work by reducing unwanted heat gain during the day, producing non-mechanical ventilation, exchanging warm interior air for cooler exterior air when possible, and storing the coolness of the night to moderate warm daytime temperatures.
- Measure of how much work or energy is conserved in a process. In many processes, work or energy is lost, for example as waste heat or vibration.
energy efficiency equation
Efficiency = Energy Out (J) / Energy In (J).
- Power is the best way to compare the cost of running different appliances is to look at power consumption, which is a measure of how much power they use in watts.
- The standard metric unit for power is watt.
- A kilowatt is 1000 watts.
P = E / t
P – Power (watts).
E – Energy (J).
t – Time (seconds).
- One watt is the power when one joule of energy is transferred in one second.
the sun and energy
- The sun is the ultimate source of energy on earth.
› Producers convert this light energy from the sun into chemical energy in the form of glucose through photosynthesis that all life depends on.
› When living organisms die, they have the potential to become fossil fuels, this means that the sun was the original source of energy for fossil fuels.
› The sun also has the ability to produce electrical energy, through the use of solar panels.