Energy transfer and passive solar design (T2)

Question 1

passive definition

Answer 1

• That is acted upon or is capable of being acted upon from outside; that is the object of action; affected by external force; produced or brought about by external agency.
• Of, relating to, or designating a system in which energy for heating or other purposes is obtained by the absorption of natural radiant energy, usually sunlight.

Question 2

typical household energy annual consumption

Answer 2

4,000 kWh = electricity
12,400 kWh = gas
combined energy consumption 16,400 kWh

Question 3

average hourly energy consumption

Answer 3

365 x 24 = 8760 hours in the year

16400/8760= 1.87 kWh

Question 4

factors that determine the energy consumption of a dwelling

Answer 4

• type, size and age of your home
• location and weather
• heating and cooling type
• levels of wall, floor and loft insulation
• external wall area and windows area
• efficiency of the appliances and lighting
• occupancy
• users’ status and lifestyle

Question 5

How is energy consumed

Answer 5

• Space heating (72%)
• Cooling / air conditioning (0.3%)
• Hot water (13%)
• Cooking (3%)
• Refrigeration
• Lighting (9.5%)
• Entertainment / IT
• Other (1%)

Question 6

solar energy potential

Answer 6

typical annual energy consumption of a UK house = 16400kWh
annual global horizontal irradiation for the midland = 950 kWh/m2

How many m2 of solar potential need to be collected to equal the typical annual energy consumption of a UK household?
16400/950 = 17m2

Question 7

why do photovoltaic panels not supply the total energy demand?

Answer 7

• The conversion of solar energy to electricity is less than 100% efficient.
• The cost of photovoltaic panels is still quite high.
• The patterns of availability don’t match the patterns of demand.
• The potential for storing electrical energy is still quite limited.

Question 8

solar thermal

Answer 8

hot water demand can be largely covered by direct heating of watery solar radiation
hot water tank can be an efficient means of storing energy for when it is needed

Question 9

where does the electricity go if it can not be used straight away>

Answer 9

can be few back into the supply grid

Question 10

what is most of the energy go to from PVC panels?

Answer 10

space heating

used to keep warm can be an effective way of reducing overall energy consumption

Question 11

sunlight through windows

Answer 11

direct sunlight radiation through windows can supply several hundreds watts of energy for every square metres of glass

Question 12

Conduction

Answer 12

is the flow of internal energy from a region of higher temperature to one of lower temperature by the interaction of the adjacent particles (atoms, molecules, ions, electrons, etc.) in the intervening space.

Conduction requires physical contact between surfaces.

net flow of heat from the hot body to the cold one

Question 13

what would happen if you material between two conducting elements

Answer 13

The rate of heat flow through material M will depend on the thickness and conductivity of the material between the two bodies and also the temperature difference between those bodies

Question 14

u-value definition

Answer 14

are used to measure how effective elements of a building’s fabric are as insulators. That is, how effective they are at preventing heat from transmitting between the inside and the outside of a building.

higher the u-value the more slowly heat is able to transmit through it

Question 15

what is the equation of rate of heat loss?

Answer 15

u-value x area x temperature difference

Question 16

units of u-value

Answer 16

watts per square metre per degree/ kelvin

Question 17

convection

Answer 17

Convection is the transfer of internal energy into or out of an object by the physical movement of a surrounding fluid that transfers the internal energy along with its mass.

you can stop some convection by putting the radiator under the window

Question 18

Radiation

Answer 18

Heat radiation is the transfer of internal energy in the form of electromagnetic waves.
For most bodies on the Earth, this radiation lies in the infrared region of the electromagnetic spectrum.
kelvin radiates some electromagnetic energy
net transfer of thermal energy depends the hot to the cold body

Question 19

how radiation and defrosting link

Answer 19

car is on the same side as the house some of the car have frozen by the air temp is the same. radiation from the night can be much less than convection air temperature
rear window has a better view of the cold sky because the window is sloped
polystene sheet would have a higher temperature than the temperature of sky = avoids frost damage

Question 20

thermal heat capacity

Answer 20

of a material is the amount of heat required to change a unit mass of a substance by one unit of temperature.

Question 21

thermal mass

Answer 21

describe a building’s capacity to store heat and/or to resist undesirable ‘swings’ in temperature.

Question 22

passive solar design to heat buildings

Answer 22

• Patterns of supply (daily and seasonal) do not always match patterns of demand.
• Making effective use of solar energy to warm the building in winter and the cooler times in spring & autumn.
• Finding ways to ‘store’ the solar heat for later.
• Distributing the heat in the building.
• Avoiding overheating, especially in the summer months.

Question 23

passive solar design factors

Answer 23

• Locale and prevailing climate
• Building form and orientation
• Surrounding context / obstructions
• Building materials and their thermal properties
• Control strategies: passive, active or hybrid?
• Building occupancy

Question 24

maximum sun altitude

Answer 24

At the summer solstice = 90 - latitude + 23.5
At the equinoxes = 90 - latitude
At the winter solstice = 90 - latitude - 23.5