Passive annual heat storage principles in earth sheltered housing, a supplementary energy saving system in residential housing

Passive annual heat storage principles in earth sheltered housing, a
supplementary energy saving system in residential housing
Akubue Jideofor Anselm
*
Green Architecture Department, School of Architecture and Urban Planning,
Huazhong University of Science and Technology, Wuhan 430074, China
Received 7 July 2007; accepted 3 November 2007
Abstract
This paper looks through the many benefits of earth not only as a building element in its natural form but as a building mass, energy pack and
spatial enclosure which characterized by location, unique physical terrain and climatic factors can be utilized in developing housing units that will
provide the needed benefits of comfort alongside the seasons. Firstly the study identifies existing sunken earth houses in the North-west of China
together with identifying the characters that formed the ideas behind the choice of going below the ground. Secondly, the study examines the
pattern of heat exchange, heat gains and losses as to identify the principles that makes building in earth significant as an energy conservation
system. The objective of this, is to relate the ideas of sunken earth home design with such principles as the passive annual heat storage systems
(PAHS) in producing houses that will serve as units used to collect free solar heat all summer and cools passively while heating the earth around it
and also keeping warm in winter by retrieving heat from the soil while utilizing the free solar heat stored throughout the summer as a year-round
natural thermal resource.
# 2007 Elsevier B.V. All rights reserved.
Keywords: Passive annual heat storage; Earth shelter; Earth homes; Energy saving design; Building with earth
1. Introduction
Earth sheltered homes, refers to structures built within or
with the support of earth as superficial material, and mostly
built in functional styles devised to meet the needs of common
people in their time and place. These structures in the past were
built by people not schooled in any kind of formal archit ectural
design or with identifiable building techniques rather they
depended on the cover the very structure of the earth could
provide them for purposes of shelter, warmth and security.
However, recent quest for energy saving and efficiency in
buildings has redirected the eyes on the earth material not only
as support, but also as massing for passive energy utilization

indoors.
1.1. Characteristics and significance of earth as resource
for energy in buildings
Carmody and Sterling [12] suggested that even at very
shallow depths and given normal environmental conditions, the
ground temperatures seldom reaches the outdo or air tempera-
tures in the heat of a normal summer day, thereby conducting
less heat into the house due to the reduced temperature
differential. Most researchers on earth supported housing are in
agreement with the idea that building underground provides
energy savings by reducing the yearly heating and cooling loads
in comparison with known conventional structures. In his own
case, Carpenter [6] views earth sheltered buildings as having
the best potential for energy savings in any design. Not only is
the temperature difference between the exterior and interior
reduced, but the fact yet remains that the building is also
protected from the direct solar radiation. In the case of colder
climates, according to Kumar et al. [17], it was noticed that
during winters, the rate of heat loss in bermed (earth supported)
structure was less in comparison to that in on-grade structures,
indicating through results that the floor surface temperature
increased by 3 8C for a 2.0 m deep bermed structure due to
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* Correspondence address: Apartment 512, Friendship Apartments, Huaz-
hong University of Science and Technology, Hubei Province, Wuhan 430074,
China. Tel.: +86 27 87550793; fax: +86 27 87547833.
E-mail address:

0378-7788/$ – see front matter # 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.enbuild.2007.11.002
lower heat transfer from the building components to the ground.
Thus indicating the passive heat supply from the ground even at
the extreme cold temperatures of winter, hence is a factor for
energy saving in earth shelter buildings.
Apart from the energy values which the subsurface climate
of the earth provides, the other significant characters beneficial
to earth shelters includes a major goal of recycling surface
space by relocating functions to underground, by this earth
shelters liberates valuable surface space for other functional
uses and improves ground surface visual environment, open
surfaces for landscaping and thus a more greener atmosphere.
In order to achieve the maximum benefits from earth sheltered
housing, its application could be examined also at an entirely
community scale rather than simply at the scale of individual
housing. While contemporary use of earth sheltering is confined
to individual homes built on single plots of land or a small cluster
of houses which will absolutely be affected by surrounding
conventional structures around, the traditional use encompassed
entire communal design or villages that will stay within the same
conditions the micro-environment provides as a few isolated
earth sheltered houses do not really reach the scale needed for
sustainable development as asserted by Dodd [13],earth
sheltered mass-housing may become the general concept for
design and building with earth as Moreland [2] envisioned in his
book for entire communities enjoying dual land use by locating
all housing underground. If a single case of earth sheltering is
found to have significant advantages, these advantages can only
increase in magnitude if applied to whole communities.

1.2. From the prehistoric to the modern earth shelter
principles
Earth sheltered ho mes have provided shelter, warmth and
security for mankind since the beginning of recorded history. In
Japan was discovered the oldest human habitation in a layer of
earth about 600,000 years old in Kamitakamori, Miyagi
Prefecture (Japan times, 24 October 2000). Archaeologists
from the Tohoku Paleolithic Institute, Tohoku Fukushi
University and other institutes said they believe that the
finding may be one of the oldest in the world. There are only a
few remains of human dwelling struct ures from the early
paleolithic period in the world, as early humans such as the
Peking-man lived in caves. Researchers believed the dwellings
were built by primitive man, or homo erectus, who appeared
some 1.6 million years ago and likely reached Japan 600,000
years ago at the latest, according to the archaeologists. The
buildings could have been used as a place to rest, a lookout for
hunting, a place to store hunting tools or to conduct religious
rites.
In China, however, the modern underground habitats (earth
shelters) are commonly called cave dwellings as shown in
Fig. 1, even though they are entirely man-made earth sheltered
environments and its culture were dated back to before 2000
B.C. It is believed that underground housing preceded above
ground housing in this area. From study on the existing Chinese
earth habitats were discovered analytical data on the climatic
and topographical relations hips to the unique design elements
utilized to attain living comfort by the cave shelter dwellers.
Such analysis as the rain, wind, sun and seasonal weather
conditions that exist in these areas where these dwellings were

located according to Golany [8], possibly necessitated the
advantage of its existence in these locations.
Analysis on each location also provided results and findings
in terms of climatic effects, design styles and residential
activities of the dwellers. In the North-west of China, variety of
structures existed, ranging from striking examples of hidden
opulence to humble subterranean cubbyholes where its people
immerse themselves in nature’s simplicity. Golany’s [8]
Fig. 1. A typical earth shelter plan in North-western China.
A.J. Anselm / Energy and Buildings 40 (2008) 1214–1219 1215
research also provided analytical data on climatic and
topographical relationships to the structural design styles.
With single unit design solution, multi unit designs and finally
Urban planning initiatives on how to achieve a sunken city that
exists beneath rather than above ground level as seen in Fig. 2
below. Also fascinating in discovery included methods and
techniques of ventilating the building units natu rally without
the necessary use of mechanical ventilation options. Such
natural ventilation alternatives provided a cost efficient and
energy efficient value to the whole process.
2. The concept of passive annual heat storage system
PAHS a method of collecting heat in the summertime, by
cooling the home naturally, storing it in the earth’s soil naturally
and then afterwards returning that heat to the contact structure
(earth home) in the winter was originally introduced by Hait [4]
in his book published in 1983. It includes extensive use of
natural heat flow methods, and the arrangement of building
materials to direct this passive energy from the earth to the
building, all without using machinery.
According to this concept, there exists cooling actions when

one climbs down basement structures or caves. This cooling
action experienced in these enclosed environments is a resu lt of
the heat being drawn away from the body to the surrounding air
which then transfers this thermal energy into the surrounding
structures whose heat content is less than that of the adjacent air
mass. The dynamics behind this concept is that heat always
flows from a warmer system to a cooler system (as in the case
mentioned above with the human body as the warm system and
the surrounding air and walls as the cooler system). By this
action if you are warmer than the surrounding air, the heat of the
body will escape to the surrounding air until temperature
equilibrium is attained. Likewise, in the case the air inside the
room is warmer than the surrounding walls, heat will be drawn
out of the air into the walls, thus cooling the air and warming the
walls. On the other hand, if the air temperature inside the room
is cooler that the surrounding walls, heat will be drawn out of
the walls into the air by this warming the air and cooling the
walls. Passive annual heat storage (PAHS) uses this thermo-
dynamic principal in conjunction with bare earth to aid control
the micro-climate within the building, in the case of the earth
sheltered dwelling, it utilizes the surr ounding earth to regulate
its temperature throughout the year.
Globally, the earth receives electromagnetic radiation from
the sun which is typically defined as short-wave radiation and
emits it at longer wavelengths known typicall y as long-wave
radiation. Fig. 3 below shows an analysis of the earth’s short-
wave and long-wave energy fluxes produced with details from
Bonan [1] .
Fig. 2. Aerial view of an earth shelter neighborhood in Lian Jiazhuang, Shanxi
Province, North-western China.

Fig. 3. Earth’s energy budget diagram showing the short-wave (a) and long-wave (b) energy fluxes.
A.J. Anselm / Energy and Buildings 40 (2008) 1214–12191216
This absorption and re-emission of radiation at the earth’s
surface level which forms a part of the heat transfer in the earth’s
planetary domain yields the idea for the principle of PAHS. When
averaged globally and annually, about 49% of the solar radiation
striking the earth and its atmosphere is absorbed at the surface
(meaning that the atmosphere absorbs 20% of the incoming
radiation and the remaining 31% is reflected back to space).
3. Thermal analysis (concept and application in earth
shelter design)
There exist two major concepts in earth shelter construction;
the Bermed shelter and the Envelope or True underground earth
shelter. In this case, this study considers the two major styles of
Bermed earth shelter construction which are:
(a) Elevational or slope design.
(b) Atrium or courtyard design.
Using PHOENICS-VR fluid- flow simulation environment,
the study calculates the thermal flow pattern in the different
earth shelter designs whilst identifying the different effects of
the earth’s PAHS on the slope and atrium designs as shown in
Figs. 4 and 5 below.
3.1. Analysis
An architectural 3D model was developed imputing the
ordinary concrete wall module for the boundary wall materials,
while observing other necessary EARTH Envir onment para-
meters. The model was then subjected to two cases of
simulation tests; one with the case of the Earth shelter Slope
design parameter where only about 50% of the structure’s
exterior fac¸ade is in direct contact with the earth mass and

the other case of the Earth shelter Atrium design with 80% of
the exterior fac¸ade in contact with the earth mass. The
temperature ‘Attributes’ assigned to the earth mass was taken
from an assumption of winter and summer variations in the
annual earth temperature values at below 5–10 m depth and the
surface-air temperature likewise which values was assigned as
same for the two design cases.
3.2. Results and discussion
The simulation experiment expresses the thermal systems of
the fluid-flow around and within the indoor environment of an
earth shelter structure in context with the PAHS concept. After
running the ‘Earth Solver’, the result from the experiment is
presented in Figs. 4 and 5 above. The difference in the two cases
(the slope design and the atrium design), suggested that the
effects of PAHS and the passive cooling effects on the buildings
indoor comfort was influenced much by the orientation of the
structure (in this case the placement depth of the building below
the grade).
The Atrium design which has 80% of its exterior fac¸ade in
contact with the earth mass presented better indoor conditions
(i.e. passive cooling and heating needs) for both the summer
and winter temperatures more than the slope design that has just
Fig. 4. Effects of PAHS and passive cooling on earth shelter indoor space in summer: (a) elevational or slope design and (b) atrium or courtyard design.
A.J. Anselm / Energy and Buildings 40 (2008) 1214–1219 1217
about 50% of its fac¸ade in contact with the earth. From this
result, it could be deduced or assumed that the greater the
percentage of fac¸ade in contact with the earth the better the
passive annual heating and cooling gains.
Although this assumption seems rightly beneficial to the
energy saving concepts in homes, it is also right to consider

other detrimental factors like the normal heat and cooling losses
due to thermal transmittance factors. As Klaus [5] stated, that
earth shelters are subjected to heat and cooling losses partly via
the soil to the external air, via the soil to the groundwater below
or directly to the groundwater. Klaus presented the quantity of
loss as calculable in this case and the equation is as follows:
Q
T
¼ A
total
#i À #OT
RAL
þ
#i À #GW
RGW
½W
where WOT = mean outside temperature, %0to
À5 8C % (We + 15 K), ROT = Ri + RlA+R lB+Re = equiva-
lent resistance to thermal transmission room-outside air,
RlA = equivalent resistance of the soil to thermal conductivity,
RlB = resistance of building component to thermal conductiv-
ity, RGW = Ri + RlB+Rls = equivalent resistance to thermal
transmission room-groundwater. Rls=T/ls = thermal conduc-
tivity resistance of soil to groundwater, D = depth of ground-
water, ls = thermal conductivity coefficient of soil, %1.2 W/
mK and WGW = groundwater temperature = 10 8C.
Also to further evaluate the performance in the long-term of
subsurface environment and accurate environmental informa-
tion on the boundary conditions necessary for achieving an
efficient design, one of which is the temperature of the

surrounding soil, accurate data regarding diurnal and annual
variation of soil temperatures at various depths is necessary to
accurately predict the thermal performance of earth sheltered
structures. Although actual data on soil temperatures is not
usually abundant, research has facilitated the evaluation of the
underground climate in order to assess the suitability of earth
sheltered structures. Algorithms for this calculation of the soil
temperatures at various depths have already been developed
based on existing field measurements in different regions of the
world and by this, the annual pattern of soil temperatures at any
depth can be accurately considered as a ‘sine’ wave about the
annual average of the ground surface temperature, Labs [15].
Accordingly, a mathematical method was developed by Labs to
predict the long-term annual pattern of soil temperature
variations as a function of depth and time for different soils and
soil properties that are stable over time and depth. This method
is sufficiently accurate in the case certain thermal and physical
characteristics are accurately estimated.
The equation for estimating subsurface temperatures as a
function of depth and day of the year is as follows (with the unit
of cosine expressed in rad):
T
ðx;tÞ
¼ T
m
À A
s
e
Àx
ffiffiffiffiffiffiffiffiffiffi

p
365a
r
cos

2p
365

t À t
0
À

x
2

ffiffiffiffiffiffiffiffi
365
pa
r

(1)
where T
(x,t)
= subsurface temperature at depth x (m) on day t of
the year (8C), T
m
= mean annual ground temperature (equal to
steady state) (8C), as the annual temperature amplitude at the
surface (x =0)(8C), x = subsurface depth (m), t = the time of
Fig. 5. Effects of PAHS and passive cooling on earth shelter indoor space in winter: (a) elevational or slope design and (b) atrium or courtyard design.

A.J. Anselm / Energy and Buildings 40 (2008) 1214–12191218
the year (days) where January 1 = 1 (numbers), t
0
= constant,
corresponding to the day of minimum surface temperature
(days) and a = the thermal diffusivity of the soil (m
2
/day).
Following this assessment of subsurface climate, the
calculated soil temperatures can then be used in calculating
the heat flux through the building surfaces. The energy
efficiency of each wall in contact with the earth at varying
depths can thus be investigated for local climatic conditions in
the buildings.
4. Conclusion
With the information available so far on means of assessing
the performance of earth shelters and PAHS effects on these
structures, it is then possible for designers and planners in
different regions to have access to a simple framework for
assessing its efficiency at the initial planning stages. The
resulting outputs can then be used for the heat transfer and
energy consumption simulations within the building units.
Results from these simulations will provides insight into the
degree of passive heating and cooling or reduction in heat flow
that the soil climate can provide as compared to the surface
climate as well as suggesting para meters for dept h placement of
earth shelter buildings for more efficient results.
Acknowledgements
This paper was inspired by the author’s doctorate research
work which is based on the use of alternative passive heat

storage systems in achieving indoor comfort in hot summer-
cold winter regions. Special recognition and appre ciation goes
to the Dean of the School of Architecture and Urban planning
Prof. Baofeng Li, for his support. The author also wished to
acknowledge the support by the National Natural Science
Support Fund (Contract No. 50578067) and the Special
Research Support Fund for Doctorate Degree research
programme (Contract No. 20060487008) for the Changjiang
River Districts (Huazhong and Huadong) of China. The author
wishes to appreciate the efforts and cooperation received from
the Ecology department of the school in providing data and the
assurance of assistance on further work.
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