Solar Heating Systems

1. Solar Heating Systems

2. Solar Heating Systems
A New Idea?
•The Greeks faced severe fuel shortages in fifth
century BC, resorting to arranging their houses
so that each could make maximum use of the
sun’s warming rays. A standard house plan
emerged, with Socrates noting, “In houses that
look toward the south, the sun penetrates the
portico in winter.”
•The Romans picked up on this technique, and
improved it by adding windows of mica or glass
to better hold in the heat.
•In the Americas, the Anazazi took advantage of
solar insolation in their cave dwellings in
1220AD

3. Early Passive Solar Designs
•Montezuma
Castle, Arizona,
1200AD
•Direct gain
construction
•South facing
•Overhang
•Stone is a good
thermal mass

4. Passive and Active Solar Heating
Passive Solar Heating
–The sun’s radiation heats a house without having to do
any work
Active Solar Heating
–Work is used to pump solar heat into a house (usually
with a pump or a fan)
Direct Gain Solar Heating
–Incoming sunlight is used to heat the floors of the actual
living space directly
Indirect Gain Solar Heating
–Incoming sunlight is converted to heat and circulated to
the rest of the house through convection

5. Elements of Passive Solar Design

6. Elements of Passive Solar Design
Aperture (Collector)
•The large glass (window) area through which
sunlight enters the building.
•Typically, the aperture(s) should face within 30
degrees of true south and should not be shaded
by other buildings or trees from 9 a.m. to 3 p.m.
•The amount of solar gain transmitted through
glass is affected by the angle of the incident
solar radiation.
•Sunlight striking glass within 20 degrees of
perpendicular is mostly transmitted through the
glass, whereas sunlight at more than 35 degrees
from perpendicular is mostly reflected.

7. Elements of Passive Solar Design
Aperture (Collector)
•Low-emissivity (Low-E) coatings are
microscopically thin, virtually invisible, metallic
oxide layers deposited on a window surface
•Low-E coatings are transparent to visible light,
and opaque to infrared radiation.
•In typical insulated glazing, the low-e coating is
found on one of the interior faces of the glass.
•A simple low-e coating helps to reduce heat loss
but allows the room to be warmed by any
sunshine.

8. Elements of Passive Solar Design
Absorber
•The hard, darkened surface of the storage
element.
•This surface—which could be that of a
masonry wall, floor, or partition (phase
change material), or that of a water
container—sits in the direct path of
sunlight.
•Sunlight hits the surface and is absorbed
as heat.

9. Elements of Passive Solar Design
Thermal Mass
•The materials that retain or store the heat
produced by sunlight.
•The difference between the absorber and
thermal mass, although they often form the
same wall or floor, is that the absorber is an
exposed surface whereas thermal mass is
the material below or behind that surface.
•Masonry materials, like concrete, stones,
brick, and tile, are commonly used as
thermal mass in passive solar homes. Water
also has been successfully used.

10. Elements of Passive Solar Design
Distribution
•The 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 three
natural heat transfer modes—conduction,
convection, and radiation—exclusively.
•An active design uses fans, ducts, and
blowers may help with the distribution of
heat through the house.

11. Elements of Passive Solar Design
Control
•Roof overhangs can be used to shade the
aperture area during summer months.
•Other elements that control under- and/or
overheating include electronic sensing
devices, such as a differential thermostat
that signals a fan to turn on; operable
vents and dampers that allow or restrict
heat flow; low-emissivity blinds; and
awnings.

12. Elements of Passive Solar Design
Landscaping
•Evergreen trees planted in back (North Side)
•Deciduous trees planted in front (South Side)
•Partial earth sheltering in back

13. Modern Passive Solar Design
•Note Evergreen
trees and
partial earth
sheltering.
•What side
(north or south)
of the house
are you looking
at?

14. Modern Passive Direct Gain
Solar Design

15. Modern Passive Direct Gain
Solar Design
•South Facing,
double pane
windows serve
as the
aperature
•Ceramic floor
tile acts as the
absorber and
thermal mass,
storing solar
heat

16. Trombe Walls
•Trombe walls
are an indirect
gain system
because the
heat from the
wall is
circulated to
the house
through
convection

17. Trombe Wall - Outside View

18. Trombe Wall – Inside View

19. Trombe Wall
•The Trombe wall distributes or releases heat into
the home over a period of several hours.
•Solar heat migrates through the wall, reaching
its rear surface in the late afternoon or early
evening.
•When the indoor temperature falls below that of
the wall's surface, heat begins to radiate and
transfer into the room.
•For example, heat travels through a masonry
wall at an average rate of 1 hour per inch.
Therefore, the heat absorbed on the outside of
an 8-inch-thick concrete wall at noon will enter
the interior living space around 8 p.m.

20. Thermosiphoning Air Panels
•Panels are attached to
wall that allow air to be
heated by sun
•Indirect gain because
air is circulated to
house by convection

21. Solar Heating with
Greenhouses
•Heat from solar radiation is stored in water drums
or concrete floor
•Convection circulates heat to rest of house

22. The Greenhouse Effect
•Glass will transmit
visibly light but not
infrared light (i.e. the
radiation given off by
room temperature
objects)
•Solar radiation enters,
but heat cannot escape
as infrared radiation
•Heat is trapped and
temperature rises

23. Solar Heating with
Greenhouses

24. Passive Solar Water Heaters I
•A batch solar water
heater consists of
black water tanks set
in the sunlight
•Glazing (glass panel)
partially prevents heat
from escaping
•Must be covered with
insulation at night

25. Passive Solar Water Heating II
•In a thermosiphoning
solar water heater
water is circulated
through a solar
collector by natural
convection
•Tank must be placed
above the collector

26. Thermosiphoning Hot Water
System

27. Active Solar Heating
•In active solar heating, a fluid or air is first heated
by the sun
•Pumps or fans are used to distribute heat to
storage or direct use

28. Flat Plate
Collectors
•Most common
type of domestic
solar collectors
•Solar radiation is
absorbed by a
metal plate
•Glass covers
prevent heat from
escaping

29. Flat Plate Collectors
•Heat from a flat
plate collector is
exchanged with
fluid in metal
tubes
•Water can also
trickle down
corrugated metal
sheets

30. Solar collector for
heating water
A home in California in 1906

31. Flat Plate Collectors
•Collectors
mainly used
to heat water.
•5% are used
for Domestic
Hot Water.
•95% used to
heat water for
swimming
pools.

32. Orientation of the
Collector Plates
•Since more heat is
required in winter,
collector plates should
face more towards the
winter sun
•A good rule is to angle
the plate halfway
between the noon
height of the sun in fall
and winter

33. Calculating the Tilt of a
Collector Plate
•The optimum angle in spring or fall is
angle
fall
= your latitude
•The optimum angle in winter is
angle
winter = your latitude + 23.5°
•Thus optimum angle = (angle
fall
+
angle
winter
)/2

34. Calculating the Tilt of a
Collector Plate
•What is the optimum angle for a solar
collector in Peoria (40° N)?
–angle
fall
= 40°
–angle
winter
= 40° + 23.5° = 63.5°
–optimum angle = (40° + 63.5°)/2 = 51.7°
51.7°

35. Size of Collector
Q = I x e x A
I = insolation
e = efficiency
A = area of
collector

36. Insolation
•Insolation is the
amount of useful
radiation that can be
collected on a
horizontal surface
•Insolation can be
increased by tilting a
surface towards the
sun (i.e. south)
Here insolation is in Btu/ft
2
/day

37. Calculating the Size of Collector
•How large a collector is required to heat
a home that requires 100,000 Btu/hr?
Assume the insolation is 1300 Btu/hr/ft
2

and the collector is 50% efficient.
•Answer: Q = I x e x A
I = insolation, e = efficiency, A = area of
collector
Rearrange equation to obtain A = Q/(I x e)
= 100,000/(1300 x 0.5) = 154 ft
2

38. Calculating the Size of Collector
•How much heat could you obtain with a 30
x 50 ft solar collector in Peoria (assume
30% efficiency)
•In Peoria, the average insolation is 1200
Btu/ft
2
/d
•Area x Insolation = Btu’s per day
•Including efficiency: 0.30x(30x50)x1200
= 540,000 Btu/day = 22,500
Btu/hr

39. Domestic Hot Water Systems
•Some active systems are used only to heat water
•Antifreeze solution is pumped through the collectors (to
prevent freezing in winter)
•Heat from the antifreeze is exchanged with water

40. Domestic Hot Water Systems

41. Domestic Heating Systems
•Active systems can be used to heat the house as well
•Some heated water is circulated through pipes in the
floor, which heats the house

42. Domestic Heating Systems

43. Hot Air Heating
•Air is heated in a flat
plate collector and
circulated with fans
•Some heat from the
air is stored in a bin
full of rocks, the rest
is used to heat the
house
•Cold water is heated
by circulating
through the heated
rocks