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Building Environments > Thermal Climate > Flashcards

Thermal Climate Flashcards

1
Q

What does CO2e mean?

A
  • It is the “equivalent amount of carbon“ where equivalent means “having the same warming effect over a 100-year period”.
  • tCO2 = tonnes of CO2
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2
Q

What are the units of energy?

A

Energy = kWh = power x time

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3
Q

What effect does CO2 have on temperature?

A

It amplifies changes in average temperature over long periods of time.

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4
Q

What are the causes of natural climate change?

A
  • Astronomical changes - change in orbit/axis of rotation.
  • Geological changes - volcano eruptions.
  • Oceanic changes
  • Atmospheric changes
  • Vegetation
  • Animals
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5
Q

How have CO2 levels changed overtime?

A

CO2 levels fluctuate but have never historically exceeded 290ppm. However, recent trends are rapidly increasing to levels as high as 405ppm.

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6
Q

What is the carbon composition of the Earth?

A
  • 40,000Gt in ocean
  • 3,000Gt in soils
  • 1,600Gt in accessible fossil fuels
  • 700Gt in vegetation
  • 600Gt in atmosphere
  • Surface waters

Each year:

  • 8.4GtC/y are emitted from accessible fossil fuels into the atmosphere (due to human activity).
  • 2.0GtC/y are absorbed from the atmosphere by vegetation.
  • 1.5GtC/y are transferred into surface waters from the atmosphere.
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7
Q

Why is the carbon composition of the Earth not in equilibrium?

A
  • Human activities cause carbon to move from one group to another meaning the carbon composition is not in equilibrium.
  • Roughly half of all emissions of carbon from fossil fuels into the atmosphere remain in the atmosphere and so equilibrium isn’t achieved.
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8
Q

Which factors affect average atmospheric heat?

A
  • Aerosols = cooling effect
  • Greenhouse gases = heating effect
  • Orbital, solar and volcanos = no effect on long term average
  • Combined, these cause the average atmospheric temperature to rise, meaning heat waves will be of a higher frequency and duration.
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9
Q

What do we need to consider when setting targets to limit CO2 emissions?

A

CO2 remains in the atmosphere for 100 years before it is reabsorbed into the natural cycle. Therefore, we must consider cumulative emissions rather than rate of emissions when trying to decide responsibility.

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10
Q

Which two main events effected the worldwide emissions per capita?

A
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11
Q

Which global targets are being implemented to limit carbon emissions?

A

Global targets (Paris Accord):

  • Keep global temperature rise this century below 2’c.
  • Strengthen the ability of countries to deal with the impacts of climate change.

UK targets (Climate Change Act):

  • From the 1990 baseline, reduce GHG emissions by 80% by 2050 and 34% by 2020.
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12
Q

What is the difference between operational and embodied energy?

A

25% of global emissions come from buildings.

Operational energy:

  • Energy used to run buildings.
  • Accounts for 90% of a buildings energy usage.

Embodied energy:

  • Energy used to produce buildings.
  • Accounts for 10% of a buildings energy usage.
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13
Q

What are the biggest contributors to carbon emissions and energy usage in the UK?

A
  • Buildings account for 35% of all carbon emissions.
  • Most of these come from space and water heating.
  • Buildings account for 40% of overall energy usage.
  • Most of these come from the use of lights and appliances.
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14
Q

What are the different types of climate?

A

Climate (Global influences):

  • 2000km range

Macro climate (Regional factors):

  • 500-1000km range

Meso climate (Local features):

  • 1-10km range

Micro climate (Site arrangement):

  • 0.1km range

Building orientation, form and materials:

  • N/A
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15
Q

Which factors affect climate?

A
  • Atmospheric air flow
  • Effect of latitude
  • Obliquity
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16
Q

How does atmospheric air flow effect climate?

A
  1. Cold and dry air in the atmosphere descends at mid-latitudes.
  2. It more readily takes up moisture creating dry conditions.
  3. At the equator, sun heats the ground which then heats the air.
  4. This causes the hot moist air to rise.
  5. As it does so, it cools, which is precipitated as rain leading to wet tropical forests.
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17
Q

How does the effect of latitude effect the climate?

A

Low latitudes:

  1. The sun’s rays are normal to the ground.
  2. Therefore, the sun has a strong warming effect.

High latitudes:

  1. The sun’s rays are oblique to the ground.
  2. Therefore, the same energy as is received over the equator is spread over a much larger area.
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18
Q

How does obliquity effect the climate?

A
  • The angle made by the Earth’s polar axis to the normal of the ecliptic plane is known as obliquity.
  • The ecliptic plane is the plane of revolution of the Earth around the sun.

During summer:

  • Earth is tilted towards the sun, so temperatures are higher.

During winter:

  • Earth is tilted away from the sun, so temperatures are lower.
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19
Q

Which factors affect the macro climate?

A
  • Large bodies of water (a good store of heat)
  • Large continental land masses (a bad store of heat)
  • Mountains (affect precipitation)
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20
Q

How do large bodies of water affect the macro climate?

A
  • Water has a high specific heat capacity so is a very good heat store.
  • There are very large Gulf Stream which heat up all nearby land meaning two countries which are both on the equator could experience two very different climates.
21
Q

How do large continental land masses affect the macro climate?

A

Land heats up quickly during the day and cools down quickly at night meaning there are large variations in daily temperatures.

22
Q

How do mountains affect the macro climate?

A

The Himalayas prevent moist winds from the Indian Ocean from crossing, producing heavy seasonal rainfalls called monsoons.

23
Q

Which factors affect the meso climate?

A
  • Hills
  • Coastal breezes
24
Q

How do hills affect the meso climate?

A
  1. On a sunny day, warm moist air will rise up the hill and form clouds.
  2. During the evening, the cold sky cools the air that flows downhill causing precipitation.
25
Q

How do coastal breezes affect the meso climate?

A
  • In early afternoon, the land heats up warmer than the sea causing conventional currents.
  • In the evening, the land cools down more than the sea causing reverse breezes.
26
Q

Which factors affect the microclimate?

A
  • Urban heat islands
  • Wind flow
  • Urban canyons
27
Q

How do urban heat islands affect the microclimate?

A

Cities made of bricks and concrete mean lots of heat is absorbed during the day which is then released at night meaning cities are warmer in the evenings than rural areas.

28
Q

How does wind flow affect the microclimate?

A

If wind flow is obstructed, ventilation is harder to achieve so it is hotter.

29
Q

How do urban canyons affect the microclimate?

A

In urban canyons light may not be able to reach street level making it cooler.

30
Q

What is the building envelope?

A

The membrane through which energy and mass transfers occur between the indoor and outdoor environment.

31
Q

In which situations should you use northern/southern facades?

A

Northern facade:

  • For even light distribution.

Southern facade:

  • To capture solar energy.
32
Q

Which building designs should be incorporated into a hot desert climate?

A
  • Pool = provides evaporative cooling.
  • Flat roof = radiates to cold sky during the evenings.
  • Small windows = reduce solar insulation.
  • Thick construction = delays transmission of heat.
  • Courtyards = provide shading.
33
Q

Which building designs should be incorporated into a hot and humid climate?

A
  • Ventilated rood voids = allows through ventilation.
  • Veranda = provides shading
  • Floor on a platform = increases ventilation.
34
Q

What are the different scales of interaction with the external environment?

A
  • Skin
  • Clothing (2nd skin)
  • Building (3rd skin)
  • Microclimate
  • Mesoclimate
  • Macroclimate
  • Global climate
35
Q

What is solar radiation?

A
  • The total amount of energy in sunlight.
  • Wm-2
36
Q

Which factors affect solar radiation?

A
  • The amount of time that the sun is above the horizon.
  • The height above sea level.
  • The clarity of the atmosphere (dependent on pollutants and cloud cover).
  • The angular altitude of the sun above the horizon.
37
Q

What is the difference between direct radiation and diffused radiation?

A

Direct (beam) radiation:

  • Direct radiation due to the sun.
  • Accounts for 33-83% of radiation.
  • Harmful.

Diffused radiation:

  • Scattered radiation due to particles in the atmosphere.
  • Accounts for 5-26% of radiation.
  • Not harmful.
38
Q

How is intensity measured?

A
  • Intensity is measured using a pyranometer.
  1. The sun heats up a black absorber player under the glass dome of the pyranometer, to give you the global radiation.
  2. Another pyranometer has a shadow band fitted to allow you to find the diffused radiation by casting a shadow over the pyranometer to cut out direct radiation.
  3. Therefore, you can also calculate the direct radiation using the equation above.
39
Q

What is global radiation?

A

Global radiation (Wm-2) = Direct radiation + diffused radiation

40
Q

How can we measure how long the sun shines for?

A
  • Use a ‘Campbell Stokes sunshine recorder’.
  • Measure the time when irradiance is above 120Wm-2.
41
Q

What are oktas?

A

Oktas are eighths of a sky which are used to describe how cloudy a sky is.

42
Q

What is the difference between dry and wet bulb temperature?

A

Dry-bulb temperature (DBT):

  • The temperature of air measured by a thermometer freely exposed to the air, but shielded from radiation and moisture.

Wet-bulb temperature (WBT):

  • The temperature of air measured by a thermometer with a moistened bulb.
43
Q

How can we measure humidity?

A

Measure of humidity = DBT - WBT

  • A sling hygrometer, containing both temperature probes is swung around.
  1. In a humid climate, the water on the bulb doesn’t evaporate, so the WBT remains the same, and the reading on each probe is similar.
  2. In a dry climate, the water on the bulb evaporates, so the WBT decreases, and therefore a large difference is created between the two readings.
44
Q

What is the mean radiant temperature (MRT)?

A

The average temperature of all of the surfaces inside a room.

45
Q

What is the operative temperature (OT)?

A
  • The mean of the DBT and the MRT.
  • OT = (DBT + MRT) / 2
  • It is the way in which temperatures inside a building are defined, and is said to be the temperature you actually experience.
46
Q

What is the diurnal temperature?

A

The difference between the daily maximum temperature and the daily minimum temperature.

47
Q

What is the relative humidity (RH)?

A
  • The amount of moisture in the air at a particular time, compared to the maximum amount of moisture the air could hold at that temperature.
  • When the air can’t hold any more moisture, it condenses as dew.
  • RH = actual vapour density / saturation vapour density (x 100%)
48
Q

What are ‘Wind-rose Diagrams’?

A
  • Shows direction from which the wind is blowing.
  • Width/colour of bar shows wind speed.
  • Length of each individually coloured bar shows the % of time the wind is blowing from that direction at that speed.

Building Environments (6 decks)

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