Solar Gain

Question 1

What happens to a particle when it absorbs short wave radiation.

Answer 1

They emit it as long wave radiation.

Question 2

Explain refraction

Answer 2

As radiation is absorbed through a particle the angle it leaves the particle is different to the incident angle. Beam radiation is the part of the radiation that reaches the earth without reflection of refraction. So it is in the same angle.

Question 3

What is the effect of the atmosphere on solar radiation.

Answer 3

It eliminates almost all of the uvc (which is below 290nM). And some of the uva (280-315nM). Carbon dioxide and water vapour cause scattering of the shortwave radiation.

Question 4

What determines the extent of diffuse and beam radiation received on the earths surface.

Answer 4

Extend of cloud cover, dust and smoke concentration, water vapour.

Question 5

Why does the type of light received from the sun change depending on time, location and season

Answer 5

Because the greater the angle of incidence the more of the atmosphere the light beams will be filtered through.

Question 6

At what ttimes of year is the sun closest and furthest from the earth?

Answer 6

Closest jan the 3th Furthest jan the 4th

Question 7

What is the definition of the equator and the north and south poles.

Answer 7

It is the plane that is perpendicular to the earths axis of rotation with the highest circumference. The latitude is 0 at the equator. The latitude at the north and south poles are +90 and -90 degrees.

Question 8

Explain latitude and longitude

Answer 8

Latitude is the angle from the equator to a given point on the worlds surface. Latitude lines are known as parallels.

Question 9

Define solar altitude

Answer 9

It is the angle of the sun relative to the tangent of a particular point on the earths surface.

Question 10

Explain the solar azimouth? And what is it used for

Answer 10

The solar azimouth (greek letter alpha) It is the angle of the sun measured on the horizontal plane relative to true south. It is negative before mid-day and positive after midday. This is used for calculating the angle of a wall relative to the path of the suns radiation during the day.

Question 11

What is the formula for total radiation reaching the earths surface

Answer 11

Beam radiation + diffuse radiation.

Question 12

What is the sunrise angle

Answer 12

It is the solar bearing and sunrise

Question 13

What radiation is received by a vertical plane

Answer 13

the direct beam radiation, the atmospheric diffuse radiation, the ground reflected radiation.

Question 14

What is the formular for direct beam radiation incident on a surface

Answer 14

The strength of the beam times the cosine of the incident angle x cosine of the bearing angle.

Question 15

What are the ways of reducing solar gain in a building?

Answer 15

Smaller windows, designing the angle of the building and the windows to avoid the worst of the solar gain, high reflectance glazing, highl absorbtion glazing, use of internal blinds, use of double glazing, use mid pain blinds with double glazing, external projections like solar lourves,

Question 16

Explain the proccess of solar gain on non glass building surfaces.

Answer 16

A variety of wavelengths will land on the building surface. Some will be incident on thermally massive materials and heat them up, the heat will conduct through the building fabric and reach the inside envelope some time later night. Some of this heat will also be emmitted to the surroundings through convection and radiation. Low angled surfaces like flat and to a lesser extent pitched roofs will absorb far more radiation than vertical walls due to the cosine rule.

Question 17

Explain solar gain through windows

Answer 17

Radiation will land on the windows some will be reflected back depending on the relfectivity of the glass. Some of the radiation will be absorbed by the outer layer of glass, this will be emmitted as long wave infra red both inside and outside of the building. In the case of double and triple glazing, some of the heat will transfer in the inner pain through conduction and convection, argon is used because it convects heat less effectively than air. some of the radiation will pass through the glass and land on room surfaces where it will re-radiate as long wave radiation and convective heat.

Question 18

what is the solar gain ratio?

Answer 18

It is the ratio of radiation incident to the glazing to the radiation that transmits through the glazing

Question 19

What is the effect of blinds on solar heat gain?

Answer 19

The short wave radiation passes through the window and lands on the blind where it is reflected back towards the window as long wave radiation. It bounces back and forth until it is all converted into convective heat. Very little heat is reflected back out of the glass, but because convective heat is easier to remove through ventilation and air conditioning it does help in some way.

Question 21

Explain what is meant by the (thermal) time lag and decreement factor of a structure

Answer 21

It is the time between the peak of incident radiation on opaque surfaces of a building and the peak of temperature within a building. Decreement factor is the ratio of the change in indoor temperature (within a 24 hour period) to change in outdoor temperature. High thermal mass on the external walls promote a high lag. High thermal mass on outside and inside walls promote a high decreement factor.

Question 22

In what circumstances is high thermal mass useful. In climates where there is a big difference between night time and daytime temperatures such as some deserts.

Question 23

Explain the concept of sol-air temperature.

Answer 23

This is the equivalent air temperature that would result in the same level of heat transfer (in the absence of solar gain) as the actual air temperature and the incident solar radiation.

Question 24

With regards ti heat gain calculations explain T_eo and Delta(T_eo0)

Answer 24

It is the average 24 hour outside air temperature

Delta T_eo is the difference between the average 24 hour air temperature and the instantaneous outside air temperature

Question 25

What is tei

Answer 25

It is the environmental temperature in the space

Question 26

What is the formula for beam irradiance on a wall?

Answer 26

Question 28

Explain solar irradiance through glass

Answer 28

Question 29

Explain how wall protrusions effect the U value

Answer 29

Question 30

explain the formula for convection

Answer 30

Question 31

What are the convection coefficient numbers

Answer 31

Question 32

Explain the formula for adaption to outside conditions

Answer 32

Question 33

What are the external surface resistance figures

Answer 33

Question 34

How do you calculate the u value for a sloping roof?

Answer 34

Question 36

How is the solar gain factor calculated?

Answer 36

Question 37

explain the concept of sol air temperature

Answer 37

Question 38

Explain the solar gain factor

Answer 38

Question 39

explain time lag and decrement factor of a building?

Answer 39

Question 41

explain the G value of a window of the solar heat gain coefficient

Answer 41

A windows G value is the ratio of solar radiation onto a window to what gets inside through conduction, convection and radiation.