119 week 8

Question 1

ways that humans modify small scale climate through surface conditions

Answer 1

albedo
altering geometry
mulching
moisture control

Question 2

ways to alter near surface atmospheric conditions to control frost

Answer 2

preventing heat loss
adding heat
redistributing heat within the system

Question 3

ways that humans modify small scale climate

Answer 3

change surface conditions
control for frost (near surface)
control fog conditions by adding and redistributing heat
control wind with barriers

Question 4

Human modifications change what properties?

Answer 4

Radiative properties (K,L)
moisture properties (water, QE)
thermal properties (conductivity, QH)
Momentum (wind)

Question 5

what does albedo regulate?

Answer 5

K (important for radiation and heat)

Question 6

what does high albedo mean?

Answer 6

high perfection of K is reflected back

Question 7

how can you change geometry to control radiation? what are some examples/

Answer 7

affects shortwave radiation absorption and long wave emission
- ridge and furrow induces multiple reflection, long wave emission reduced because sky view factor is lower (reduces cooling)
- receives energy at a more perpendicular angle

Question 8

Ways that surface geometry affect radiative exchanges

Answer 8

• insolation of a flat surface
• insolation on a sloped surface, angle of incidence and multiple reflection (effective albedo)
• long wave emission from a sloped surface, sky view factor influences total emission

Question 9

how can solar collector be altered to maximize solar energy depending on the season?

Answer 9

in the winter when the sun is low, a more upright solar collector will have a more perpendicular angle of incidence with the solar beam

In the summer when the sun is high, a more horizontally positioned solar collector is best

Question 10

what is aerating?

Answer 10

covering the surface layer with hay, woodchips, gravel, or other material with relatively large amounts of airspace. Air has a lower energy conductivity than bare soil, so air passes less energy to other objects.

Question 11

what are the three ways that mulching controls evapotranspiration and soil warming

Answer 11

aerating
lowering albedo
conductivity

Question 12

how does mulching change the conductivity of soil?

Answer 12

Covering the surface with material that has lower conductivity than the soil (i.e.,
paper). Even paper with similar albedo as bare soil can mediate temperature
fluctuations because it inherently has a lower conductivity than the soil

Question 13

when is mulch laid down? why?

Answer 13

To prevent soil freeze, mulch is laid down in autumn to trap in subsurface heat (QG) throughout the winter. However, it must be removed in spring to allow input of
insolation during the warm season.

Question 14

when does frost occur?

Answer 14

Frost occurs when surface temperature of the ground or plant falls below 0oC. Frost
control aims to keep temperatures at or above freezing

Question 15

two types of frost

Answer 15

Radiative frost – due to radiative divergence.
Advective frost – due to a cold airmass horizontally transporting cold air into
the environment.

Question 16

two ways to control frost

Answer 16

avoidance - do not put cold sensitive plants in cold places (regions where the air stagnates)
modification of the radiation and thermal energy balances

Question 17

When does frost tend to occur?

Answer 17

at night under cold clear conditions (stable)

Question 18

how do you control fog by altering energy conditions?

Answer 18

increasing turbidity
- to slow down energy loss from the system. This includes
Intentionally creating fog, smoke, or mist layers that increase atmospheric
absorptivity and sensible heat released toward the ground
increasing QH
- increasing QH with heat lamps. This is most effective when there is an inversion
layer that keeps warm air from rising and being replaced by sinking cooler air
redistributing QH
- Redistributing QH to the surface with fans. This method creates a vertically
mixed layer of moderate temperature. The rising hot air is brought back down

Question 19

what does creating clouds of fog do?

Answer 19

creating clouds of fog or mist, or smoke reduces nocturnal loss of Lup, especially when the
atmospheric window is wide open. This reduces the sky view factor by placing a “radiative screen”
above the surface that closes the window. This is done using smudge pots, as well as cheesecloth
and glass pots.

Question 20

why do they use heaters on orchards?

Answer 20

Orchards may use heaters to increase QH content. The impact of heating is restricted to the foliage
and fruit due to upward convection of the heated air. To bring QH back down, the use of heaters
may be combined with fans

Question 21

When does Radiative frost occur? The

Answer 21

under inversion conditions.
aim then is to bring the warm air to
the surface by increasing the turbulent mixing and thereby enhancing the QH flux to the surface.
Large fans (i.e., windmills) are useful.

Question 22

fog is created through the ______________ process

Answer 22

condensation

Question 23

how does increasing QH, Mechanical mixing and seeding control fog

Answer 23

with heaters increases the moisture storage capacity of the air and causes the fog to dissipate.

by fans redistributes relatively dry air from higher elevation
down to mix with the fog layer and decrease the moisture concentration in the air

Cold and warm fog may be dispersed by seeding the fog with hygroscopic nuclei,
which promote cloud formation so much that fog droplets grow and fall out as rain.

Question 24

how do barriers effect wind?

Answer 24

barrier obstructs
progression of surface wind,
which causes the wind flowing
over the barrier to sink, as there
is nothing holding it up. This
creates vertical eddies
(turbulence).
Thus, there is a sharp decrease
in windspeed immediately
downwind of the barrier (aka
the ‘cavity’).
The barrier also promotes zero-
plane displacement (top of the
barrier / bottom of the
displacement zone).

Question 25

what are the two main ways that greenhouses modify the environment to make conditions more favorable to plants ?

Answer 25

radiative filters and wind shields

Question 26

how do greenhouses act as a radiative filter?

Answer 26

glass causes attenuation of 15-50% therefore, K inside greenhouse is 85% - 50% of that outside the greenhouse glass absorbs long wave radiation (coming in and going out), so its gets trapped in the greenhouse ---> L* is larger in a greenhouse than outside

Question 27

what happens to K and L at night in a greenhouse

Answer 27

at night, K is negligible outside and L* drops a lot but in the greenhouse K is still negligible but L* remains much larger, escapes at a rate less than 10% of the open air

Question 28

how do greenhouses stay balanced even though they aren't letting out enough L* and therefore have a lot of Q*

Answer 28

must be balanced with large amounts of QH and QE - temp gradients between greenhouse vegetation and the glass is lower than outside vegetation and the sky

Question 29

during the day, where is heat transferred in a greenhouse? at night?

Answer 29

into the soil, At night, when K* and L* decrease and temperatures begin to cool, the soil heat flux is negative (aka heat leaves the soil) and replaces the heat lost via conduction through the glass.

Question 30

ways to cool greenhouses down during the day:

Answer 30

ventilation: fans, windows, Other methods of cooling include painting the glass, putting straw on roofs, and more.

Question 31

is there a strong or weal vertical temperature gradient in a greenhouse? Why?

Answer 31

there is a strong vertical temp gradient because the walls block the wind and cause a zero plane displacement and prevent forced convection. Therefore, the air of a greenhouse does not mix

Question 32

what do builders consider exchanges between when trying to create a comfortable inside environment ?

Answer 32

1. The external climate and the building. 2. The building shell and internal living space. 3. The living space and the occupants.

Question 33

what is the added aspect of climate in a building

Answer 33

QF = anthropogenic heat flux ΔQS is the net change of energy storage by the building and enclosed air. QG (fka soil heat flux) is the energy exchanged between the building and the underlying ground.

Question 34

In the northern hemisphere, ___________ slopes receive less shortwave (K) radiation, and the proportion of diffuse (D) versus direct (S) shortwave radiation is relatively large.

Answer 34

north-facing

Question 35

_________ slopes receive more shortwave energy overall, especially during summer. The proportion of D to S shortwave radiation is relatively low.

Answer 35

South-facing

Question 36

The angle of incidence depends on the ___________ and ____________ angles of the surface.

Answer 36

vertical (zenith), horizontal (azimuth)

Question 37

the temp of a wall is a function of the walls

Answer 37

aspect, which direction the wall is facing time of day, which determines location of the sun and whether the wall is facing it

Question 38

the internal building temp is a function of what?

Answer 38

the walls temp, thus also a function of of aspect and time of day

Question 39

buildings often have negative _________

Answer 39

net longwave radiation fluxes

Question 40

What does QF come from ? What is QF's relationship to external air temp?

Answer 40

QF comes from space heating, metabolic human and animal releases, and more. QF has a direct inverse relationship with external air temperature. QF increases as external temperature decreases, and vice versa

Question 41

characteristics of QH in relation to buildings

Answer 41

QH losses occur convectively and depend on wind speed and the temperature gradient between the building and the surrounding air. QH is almost always directed away from the building. However, some heat is conducted into the building through windows and walls.

Question 42

QE and QG in relation to buildings

Answer 42

QE is usually small, except after rain or if there are indoor plants (moisture release through transpiration). QG depends on each buildings’ ground contact, thermal properties, and temperature gradient between the floor and the ground.

Question 43

energy balance of room depends on

Answer 43

The level of interaction between: o The room’s interior. o The larger building overall, connected by the doors (open vs closed) and uninsulated interior walls. o The building’s exterior, connected by windows that allow greater exchanges of K and L. Rooms facing toward the sun (i.e. southward in Los Angeles) have greater solar heating through the windows and walls.

Question 44

How do places with intense humidity like Madagascar and Polynesia balance indoor climates ?

Answer 44

hut shape made of wood, piling structure, wattle, broad sloped roofs made of leaves provides strong stable structure with abundant air flow

Question 45

how do they build homes in the mediterranean to adjust for the warm, dry summers?

Answer 45

thick brick, stone or. tuff to insulate from the outside white. exterior for high rate of albedo light wood roofs few and small windows to minimize the exchange of heat with the exterior

Question 46

sandy desert environment conditions

Answer 46

extremely low moisture low atmospheric turbidity high surface reflectivity total Q is small QH is dominant strong diurnal cycle - temperature - wind

Question 47

water dominated environment

Answer 47

- high moisture - high atmospheric turbidity - high surface reflectivity Total Q is large - QE is proportionally large - Mild diurnal fluctuations

Question 48

vegetated forest environment

Answer 48

tree canopy creates a new layer (low effective albedo, moisture source) surface level: low K low QH high moisture accumulation zero-plane displacement

Question 49

variable terrain environment

Answer 49

slopes alter solar heating - Perpendicular angle of incidence cause warming. * Aspect is important. Valley * Diurnal wind circulation. * Katabatic vs Anabatic Canyon effect * Low effective albedo. * High QH.

Question 50

indoor greenhouse environment chartcteristcis

Answer 50

greenhouse creates a new layer: - high transmissivity to K low transmissivity to L Q* is large inside Thus, QH/QE is large inside - low wind - accumulation of Q and moisture

Question 51

indoor non-greenhouse environment characteristics

Answer 51

buildings create a new layer - low transmissivity high absorption and emission of L Total Q is regulated inside - QE is low - QH changes with seasons - QF is inverse QH

Question 52

urban environment characteristics

Answer 52

Buildings create a new layer: * Urban canopy with canyons. * Low effective albedo. * Low QE. * High QH. * Zero-plane displacement. * High QF. * High pollution