Five-year measurements of thermal performance for a semi-underground test house

Five-year Measurements of Thermal Performance for a Semi-underground Test House H. Yoshino, S. Matsumoto, M. Nagatomo and T. Sakanishi

A b s t r a c t - - I n order to obtain f u n d a m e n t a l data on the thermal performance o f a semi-underground room, a twin-type test house was constructed on the campus o f Tohoku University in September 1984. The test house has two rooms with south-facing windows above the ground surface, a n d a corridor between the two rooms. The floor level is 1.3 m below the ground surface. Thermal insulation 0.1 m deep a n d 1.35 m wide was installed horizontally around the room on the east at a level 0.3 m below the ground surface. The room on the west has no such "horizontal" insulation. Five-year measurements o f air temperatures in both rooms, soil temperatures around the rooms, energy consumption for space heating, a n d so forth were made in four different situations. A n experimental study f o u n d that horizontal insulation was effective in reducing the annual temperature fluctuation o f indoor air, and in reducing the heating load. These effects, which were also analyzed from the viewpoint o f heat balance in the room, were verified by computer calculations based on the two-dimensional finite element method.

1. Introduction n J a p a n in r e c e n t y e a r s , u n d e r ground rooms have been receiving greater attention as a result ofthe need to increase floor area in detached houses located on narrow sites. Utilizing the potential for heat storage in underground soilis desirable for both energy conservation and thermal comfort. However, for semi-underground rooms w i t h windows, t h e r e a r e no d a t a on t h e t h e r m a l e n v i r o n m e n t of a room receiving i n c i d e n t solar r a d i a t i o n or on l o n g - t e r m t h e r m a l behavior. The p u r p o s e of t h i s s t u d y is to obt a i n fundamental data for designing a semi-underground room, focusing especiallyon the effectofthermal insulation placed in the earth around the room. For this purpose, a twin-type testhouse was constructed and itsthermal performance was measured for five-and-a-half years.

I

Present address: Dr. Hiroshi Yoshino, Associate Professor, D e p a r t m e n t of Architecture, Faculty of Engineering, Tohoku University, Aramaki Aoba-ku, Sendai 980, Japan.

This p a p e r r e p o r t s t h e r e s u l t s of t h e t e s t room t e m p e r a t u r e m e a s u r e m e n t s for a room with no s11~liary heating/ cooling system and the energy consumption for the room that used anxqliary heating. The effect of thermal insulation placed in the earth on the t h e r m a l performance w a s a n a l y z e d by calculating h e a t flow t h r o u g h t h e building envelope. The e x p e r i m e n t a l results a r e also c o m p a r e d w i t h calculated results.

2. Description of the Test House and Measurements 2.1. Description of the Test House

I n S e p t e m b e r 1984, a t w i n - t y p e t e s t house for t h e e x p e ~ m e n t w a s cons t r u c t e d on t h e c a m p u s of Tohoku University, in t h e city of S e n d a l in northe r n J a p a n . F i g u r e 1 shows the floor plan. The t e s t house h a s two rooms, each w i t h a south-facing window above t h e g r o u n d surface; t h e r e is a corridor bet w e e n t h e two rooms. The t e s t rooms are 5.4 m deep a n d 2.7 m wide. The room on t h e w e s t side is d e s i g n a t e d as Room C; t h e room on t h e e a s t side, as Room D. The side walls above t h e g r o u n d surface have 0.2 m of foam

Tunnelling and UndergroundSpace Technology,Vol. 7, No. 4, pp, 339-346, 1 9 9 2 . Printed in Great Britain.

Rdsum~ Afindbbtenirdesdonn~fondamentalessurlaperformanae thermique d'une chambre semi-souterraine, un duplex test fur construit sur le campus de l'Universit~ de Tohoku en septembre 1984. La maison comporte deux chambres avec des fe~tres orient~es sud au dessus du so~ et un couloir entre les deux chambres. Le rez-de-chaus~e est ~t l,3 m au dessous de sol. L'isolation thermique ~paisse de 0,3 m e t large de 1,35 m fat installde d l'horizontal autour de la chambre sur la partie est a 0,3 m au dessousdu coL La chambre s i t u ~ ~ l'ouest n'a pas une telle isolation "horizontale". Des mesures, p r ~ l e v ~ sur cinq ans, des teml~ratares de l'air darts les deux chambres, du sol autour des chambres, de la consomm~tion d'dnergiepoar le chauffage de la maison, entre aatres, ont ~t~effectu~sdansquatresituationsdiff~rentes. Une~tudeexp~rimentak a r~v~l~que l 'isolation horizontale ~tefficaoepoarrdduire la fiuctuation de tempdrature annueUe de l h i r int~rieur, ainei que la consommation globale en chauffoge. Ces effets, qui ont dt~ analysds du point de vue de l',kquilibre du chauffizge dans la c]w~bre, [ a r e ~ c o ~ s par sur ordinateu r f o n d ~ sar la r ~ t hode des ~Onents fia is a deux dimensio as.

0886-7798/92 $5.00 + .00 Pergamon Press Ltd

p o l y s t y r e n e i n s u l a t i o n a n d m e t a l sidings for finishing over t h e a i r l a y e r t h a t connects t h e outdoor air. The wall facing t h e corridor a n d t h e ceding of each r o o m a r e also i n s u l a t e d w i t h 0.2 m of foam polystyrene. All windows h a v e double glazing. The south-facing windows a r e 0.8 m h i g h a n d 2.56 m wide. The s m a l l windows on t h e n o r t h wall a r e 0.96 m h i g h a n d 0.8 m wide. W h e n necessary, w e a t h e r s h u t t e r s ins u l a t e d w i t h 0.05 m of foam polystyrene can be u s e d to cover t h e windows. E a c h room h a s a t h e r m o s t a t - c o n t r o l l e d electric space heater. The rooms h a v e no v e n t i l a t i o n systems. The l e a k s in t h e b u i l d i n g envelope were filled w i t h s e a l i n g m a t e r i a l s . The t e s t rooms a r e so a i r t i g h t t h a t t h e a i r l e a k s h a v e not influenced t h e therm a l performance. R e s u l t s of t h e airt i g h t n e s s m e a s u r e m e n t s have been rep o r t e d by H a s e g a w a et al. (1987). F i g u r e 2 shows a section of t h e construction. The floor level is 1.3 m below t h e g r o u n d surface. A portion of t h e concrete walls, a r o u n d t h e ground surface, h a s 0.1 m of insulation. Only Room D is s u r r o u n d e d by "horizontal i n s u l a t i o n ' , 0.1 m deep a n d 1.35 m wide a t a level 0.3 m below t h e ground surface. R o o m C has no such insula-

339

N [

................................................................ '200 2730 20i910200 2730 200~ • ; ~ . . . . . . 1 1"1

i

........

'§ i

~, ]insulation"

,%~;t;oT-.-\! o! o i

.

,~:~! ~

A..... 'I

L~I

~oo~c

~

~

;~

I 'o~OL

~

~11 (West side)

iJ ' qj~'

o

,

; t

~

~

t

.~

ho=,,~,-/~ " ~i~ i

181

_ :'c~', A'

i

io

sc~

area: 14.6m2

,~

,.

JI L -

~Corridor']

285

285 ', 285

285

~ _ i.i ......

shutter (removable)

.'

* ~ "Horizontal Insulation" under the ground surface

" 4!! insulation are polystyrene boards

~_

.o z< c~o

I

t

I

I

~oo, ai,

~20

~

I

~ ,,!~'~..~ .1

.raG:lower line

,.;t

l

~

I

~ t,,-,,"Section~

i~si

measurement poin|s o f~oil temperatures

Results of the Experiments Experiments #1 and #2 Figures 3 and 4a show the temperature fluctuations of outdoor air and 3.

indoor air in both rooms and at four

points in the soil from December 2, 1984, to J a n u a r y 10, 1988. The temperature in each room changes along

Experiment#2 withoutshutters ar~ space heaters

I

1

[

I

SCl uppe, ,no

I

I

I

I

Indoe, air

,iV t ' ~'-'~ ~SOl:lower no , ,~|

% O:oppe, ,,

o! ~l

rooms are surrounded by soil having great thermal capacity, it takes a long time for the soil to become thermally stable. Therefore, the rooms had been heated since J a n u a r y 11, 1988, prior this experiment. E x p e r i m e n t #4 (November 27, 1989, to May 23, 1990): In this fifthyear experiment, both rooms were heated and maintained at a temperature greater t h a n 20°C during the daytime only (7:00 a.n~ to 11:00 p.nL).

E x p e r i m e n t #1 (December 2,1984, to October 8, 1985): Both rooms had insulated weather shutters during the first year in order to avoid disturbing the solar heat gain. No space heater was used. E x p e r i m e n t #2 (November 1,1985, to J a n u a r y 10, 1988): Alter Experiment #1, the weather shutters were not used. No space heaters were used. E x p e r i m e n t #3 (September 10, 1988, to November 26, 1989): During the fourth year, both rooms were heated and maintained at 20°C by electric space heaters. However, when the room air temperature was higher than

I

~

-

20°C without heating, room temperature was not controlled. Because the

Measurements were m a d e for four differentconditions:

I

I

/ ---

Figure 2. A-A' Section of the test house and main positions of thermocouples.

2.3. Experimental Conditions

Experiment#r with shutters, withoutspace heaters I

3O

, ~ o

I

G.L.

refered in Ftgs. 3, 4a, arid 5a.

with analog outlets. The data were integrated and stored in the same way as the temperature measurements.

2.2. Measurement Techniques The temperatures of indoor air, outdoor air, soil, and wall surfaces were measured by copper-constantan thermocouples at 135 temperature measuring points (the main positions of thermocouples are shown in Fig. 2). The data were stored on computer disks at 20-mlnute intervals. The indoor air temperature, a key temperature, was measured at 1.2 m above the floor level, at the center of the room, and at onefourth of the room's depth from the northern wall surface. The energy consumption for space heating was measured by an electric power meter

II

~.

~1 ,

SC1, SC2, SD1, and SD2 are

Figure 1. ~loor plan of the test house and measurement positions of room temperatures (,).

tion. The totalheat transmission rate of each aboveground room per floor areais 1.01 kcal/m2hI~ Moreinformation on the test house is given in Hasegawa et al. (1987) and Yoshino et al. (1990b).

\\

I i ,sc~ i , so~,, ~5: lSe~ i i~85 j910 1~85 L 1585

1

i , _ J_ .~ L . . . . . . .

I~

--r-

i

insulated weather - - - - /

Indoor air

. ~ ~ . . - - . ~

'

~i Concrete -£r

, to'

]

---.~---------------- r ' Horizontal

IndOOr air

; ~!

~;

~ioor .

,,;ii~ .................

......... ~

~,o1' °

(East side} I1~ i

\ . , ~ ,..,..... ~c~j lspace nearer

glazing

~

!o

~oo~o

~

r-~ou01e ~

i 1 _.

•

Ou,'~,

RmC:lower line

1

.......

TRmo:oppo,

I

o, .~! '

I

t

1

- .

~%,,I\',/'L ,Jl . 'i'

,

~ I 0I.-

~, o cO -

~ ~,'~

'

2

)

'~__SC2: lower line SD2: upper line

/

~

'

Oct 9

~

r

IncdentsoarradlationI

I

t

I

I

I

I

I

I

I

DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV 1984 1985 SC 1, SC2, SD 1, and S D2 showt the measurement poimt o / t o i l lemperalure indicated in Fig. 2.

~

~

i

q¢i. C

~

t

i

e

r

r

i

n

p

.

.

~

O ~

,

~ ,

I1.1,,

~ m~ 20

i --20

", .,Jl'l~',l

_lillllitltl,"~=:mi"°°" ~, ...... ,

.... ,iillit, i ii,

I

|

~'-

dlll,l,ll,llUl|mm,", I~'

oci I

~

SD2: upper line

Interruption of data recording (

L- Outd°°rair

4-

/

I

DEC

I

I

I

I

| It

I

II

I

I

JAN £E8 MAR APR MAY JUN JUL AUG SEP OCT 1986 (" 1)Start o/data recording diSC1, SC2, and SD 1 (Jan. 6,1985)

I

~1~

NOV

('2)Start of data recording o f S D 2 (July 14,1985) ('3}Hea W rain (Aug. 4, 1986)

Figure 3. Profiles of daily mean temperature for Experiment #1 and the first half of Experiment #2.

340 TUNNELLINGANDUNDERGROUNDSPACETECHNOLOGY

Volume 7, Number 4, 1992

__ 30 o

-7 ~u ~. rr ~,~20Cl~<"

(Pre-heating period) Experiment #2 without shutters and space heaters ~.~'~repa,'ation period before Experiment ~ t I i J I I I i I I I 1 t l I I 1 I l Indoor air Outdoor air---.~ Indoor air SC2: lower line ~RmC:lower line ii , ~ i ~ !.., , e RmC:lower line. / - - S D 2 : upper line \ R m O:upper line t! | ' ~ i ~ - Rm D:upper , "~ / , ~ \ , I ~i .!,l'!.~fl V " I:i~':':.'Ng"k.. line i,L,2~,,.J::~ ~ ,'~i,

_'

".....

---

......

- I ' ~ ~ l i ' t

>-

0 ~

:5 8

,

6"1, t

.

i

'.1

II

'

~

_. . . .

~

_

I

!!,TLil/IL

~.~':upper,,oe ~

indoor air temp.

~

i

~

, \ , i,i

t

.... , I , i

r~4//7~r,TN

,

m 0

~.~

s ~ t : upperline

,, ,vi

=

~ uulooorair

:tl.illtiit iiii,, <''°'''' ,, ildl -li lltlii lli,lii ,o,

O

~I ik :!. t ,*:i ,i ~

i'

~j .,~.i/I , ~ ~

~

I

"-

!

o_~

-2 ~ O

/ - I n c i d e n t solar radiation

o: ~

2

z < --rr"

(.3 i

I

.-,

ltilil"ll,i/i

.,

-,_-,

ilil

m'~

NO data

i,,.-

~ i I l i I i '-" . t . . i . I . i i i t i v I i t-" i I DE( JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG 1986 1987 1988 SC1, SC2, SD1, and SD2 show the me~L~urementpoints uracil temperature indicated in Fig. 2.

Figure 4a. Profiles of daily mean temperature for the second half of Experiment #2 and the preparation period prior to Experiment #3.

15

I

I

I

I

I

I

I

I

I

I

1

] I

I

II

(.9 >. Z

I

m

I

"7

Start of pre-heating lip

l

[

I

I

I

I

rh ~,, "tI~"t:~A.

<

toad (July 31, 10es)

< 0

I

I

I

I

I

|

DEC JAN FEB MAR APR MAY JUN 1986 1987

I

1

I

I

JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN 1988

JUL

AUG

Figure 4b. Profiles of daily amount of heating load for the preparation period before Experiment #3. the curve like a sine wave, and the annual temperature fluctuation is m u c h smaller than that of the outdoor air. In the case of Experiment #1, the differences between the m u ~ m u m and mln~muzn monthly m e a n indoor temperatures of R o o m C and R o o m D are 0.56 times and 0.50 times as large, respectively, as the difference in outdoor air temperature. In Experiment #2, the differences between Room C and Room D are 0.58 times and 0.52 times as large, respectively, as the difference in outdoor air temperature. The daily fluctuations in Experiment #2 (without the weather shutters) are greater than those in Experiment #1 and are affected by the cbunge in outdoor temperature. The difference between the daily m e a n indoor air temperatures of the two rooms is also shown in Figures 3 and 4a. The air temperature of R o o m D with horizontal insulation is slightlyhigher during the winter; and, inversely, slightly lower during the s11mmer than that in R o o m C. The maximum temperature difference between the two rooms is 1.2°C during the winter in both experiments. During the summer, those values are

Volume 7, Number 4, 1992

0.8°C and 0.6°C in Experiments #1 and #2, respectively. These results show that horizontal insulation is effective in reducing the annual temperature fluctuation of indoor air. Figures 3 and 4a also show the soil temperature fluctuations of the four points indicated by black circles in Figure 2. The soft temperatures at points 3.44 m below the floor level (SC2 and SD2) are stable. The amplitude of the annual temperature swingis about 2°C. Compared with the indoor air temperatures, it seems that the heat flow is downward from May to October and upward during the other half of the year. This means that the soil under the floor contributes to decreasing the fluctuation of indoor temperature, serving as a heat source during the winter and as a cool source during the s~lmmer. Comparing the soil temperatures between the points near Room C and Room D that are 1.6 m below the ground surface (SC1 and SD1), the soil temperature near Room D with horizontal insulation (SD 1) is 2°C to 3°C higher during the winter and I°C to 2°C lower during the summer. The horizontal insulation is effective for protecting the soil itself from the influence of the outdoor temperature.

3.2. Fluctuations of Temperatures and Heating Loads for Experiment #3 From January 11, 1988, to July 31, 1988, before Experiment #3 began, the test rooms were preheated in order to warm up the envelope of the house and adjust the thermostat controllers for the space heaters. The temperature fluctuations of outdoor air, indoor air in both rooms, and four points in the soil du_Hng this period are shown i n Figure 4a; the fluctuations of energy consumption for space heaters are shown in Figure 4b. Soon after beglnn~ng to use space heating in both rooms, the heating load in each room increases sharply and the room temperature is stopped up and fluctuates at a level around 20°C. The influence of space heating also appears in soil temperatures. The soil temperatures at the two points near the walls (SC1 and SD1) decrease before space heating, and increase after space heating. It appears that these transient responses of soil temperatures continue for more than three months, until the end of March. Figure 5a shows the temperature fluctuations in Experiment #3. The room temperatures in both rooms are maintained around 20°C during the

Tt~VELLINOANDUNDERGROUNDSPACETECHNOLOGY341

wlttlout shu:tg~s and with tiitelil!Jlterlt space heat;nr~

O

Z u~

30 . . . . . ~ [ _ _ I _ _ . _ I S O l : lower line SDI: upperline~

l l _I___A Indoor air /RmC:lower line L._..~/'~.f Rm D: upper line

.~v~,,,.,~, .

uJ.uJ

''

I t

'!' / Oo doe a !/~ '-': ,' " , , . ' I !~ ~ , ,,

' "

!

,

~ ,.ii:~

i

11,':,

, ,,'i ~ , ~ 1: I t ,,'~-,

...........

~-

~Tn ,

~

-

~

"V,

,

/'

/

-

- ~ - ......

L,

~,

.... L _

~ ,'?'

~=-"-'-.-----'

\ b~C "2 . u p p e l l , 1e

SD~:lowe,~,ne

SD2:lowerline

.......

(~

i

"

',?!f rt ~.,.~

. . . . . . . . . ~7. . . . . ~ -~

__

1

,' ! ,~' , :, r' '/ , j~.~,,~

L F0

. . . . . . . . ~ /) t, I

"

:?

U :E

4

Z_

ui t-

Z-

z)

0--

m~ i11 m ZZ

I~ ~--2

4/" r'l/ ~'

~

uJ[9

,

y,:=iF,r" ,.

!,

t~,/lJ/,l//~

~-~ ....

,1/'~ ~,,'~1 {/]'

~ /- O u t d o o r a i r

'

I

SC 1 : lower line ,,. . . . . . . ~ u , : upper J,ne


/ SC 1 u p p e r t ~ u

..... Difference of indoor air temp

I, I

-I J ~____I Indoor air R m O : u p p e r line Rr2.D. lower line

1

,/¢t~

r ,

' i ~

nL;.#:,',~,~;t/r~./',

"D,o 6 02E @

r'

::::-~Fi ,~li'li' !

,

LH 10 }--

I

~ . / : . -- - ~ ~ ' J ~ ~ c W ~ ' ~

.... t }

>CE :d u] "l:a.

LU ~0

I~___1.__

1

I

,I I

' l!!!jjl]il'llll I

I

NOV

SEP O C T 1988 SC ~ , SC2.

! '

DEC

I

JAN 1989

I

I

I

I

I

FEB M A R A P R M A Y JUN

I

JUL

,,

/

AUG

I

SEP

I "

I

._,,, I

O C T N O V DEC

I

-q m ~0 I

I

I

JAN FE:::B M A R A P R !990

MAY

show the measurement pomt~ :,/~od temperature

SD1. and SD2

;ndlcatcd m Fig. 2

Figure 5a. Profiles of daily mean temperatures for Experiment #3 and Experiment #4. 15 0

>-,

_z~

___/. I I Occurrence of heating toad (Sept. 28, 1988)

I

__--[

1 __~

1

l

l

l

-1

l

_L

1

I

Rm C-~,

I

I

L

1

Rm C ---x

~ I 0

I'

, ~

t

~

i~i

A

'

Ext,nctmn of heatMg

Occurrence el heating

I ,l~l

"--

<

o

"|

SEP 1988

I

OCT

I

NOV

I

DEC

I

JAN 1989

I

FEB

I

MAR

I

APR

I

MAY

I

JUN

I

JUL

I

AUG

l

SEP

I

OCT

[

NOV

I

DEC

I

JAN FEB 1990

I

|

MAR

I

APR

MAY

Figure 5b. Profiles of daily amount of heating load for Experiment #3 and Experiment #4.

heating season (from September 28, 1988 to July 9,1989). The temperature difference between the two rooms (Room D minus R o o m C) ranged from a maximum of +0.5°C to a minimum of -0.3°C. During the snmmer, from July 10, 1989 to October 6, 1989, the room temperatures float at more than 20°C without heating. The maximum room temperature is about 25°C for Room C and about 24°C for Room D. The room temperature ofRoom D is slightly lower than that of Room C. Figure 5a also shows the fluctuations of soil temperatures at the points indicatedin Figure 2. Because of space heating, the annual mean temperatures of the soil at the two points near Room C and Room D (SC1 and SD1) are 2.0°C higher than those for Experiment #2. The amplitudes of the annual swings of the soil temperatures are smaller than those for Experiment #2. For example, at the point SC1, the amplitude is 6.0°C for Experiment #2 and 3.5°C for Experiment #3. Comparing the soil temperature between point SD1 and point SC1, the soil temperature near Room D with horizontal insulation (SD1) is I°C to 2°C higher during the winter and I°C

to 2°C lower during the summer than the soil temperature near Room C (SC1). The horizontal insulation is effective in protecting the soil itself from the influence of the outdoor temperature in both cases (i.e., with and without space heating). The heating loads for Experiment #3 are shown in Figure 5b. The fluctuation in daily heating load for Room D is more stable than that for Room C. The heating load for Room D with horizontal insulation is almost always smaller than that for Room C. The difference in heating loads between the two rooms is the greatest in January 1989, when the outdoor air temperature fluctuates around 0°C. However, inversely, in July 1989 the heating load for Room C was slightly smaller than that for Room D because of lower soil temperatures around Room D, in comparison with those around Room C. The total heating load through a heating season is 1446 Meal for Room C and 1272 Meal for RoomD. Thetotal load for Room D is 88% of that for Room C. Based on the results of these measurements, it can be said that horizontal insulation was effective in reducing the heating load.

342 ~INNELLINGANDUNDERGROUNDSPACETECHNOLOGY

3.3. Fluctuations of Temperatures and Heating Loads for Experiment #4 Experiment #4 started in November 27,1989, soon after Experiment #3 concluded, and continued until May 23, 1990. For this experiment, indoor airtemperature in each room was maintained at 20"C during the daytime only. Therefore, the daily m e a n temperature of indoor air, which is shown in Figure 5a, was slightly lower than a level of 20°C. The soil temperature fluctuations shown in Figure 5a have characteristics slmilar to those for Experiment #3. The soil temperature near Room D, with horizontal insulation (SD1), is always higher than that without horizontal insulation (SC1) during the period of Experiment #4. The profiles of heating loads for beth rooms are shown in Figure 5b. The difference in heating loads between the two rooms is not very large, compared to the difference in the case of Experiment #3. However, the total heating loads for both rooms are significantly different from one another. The total load during the four months from J a n u a r y to April 1990 is 681 Mcal for Room C, and 636 Mcal for Room D.

Volume 7, Number 4, 1992

•~ 150 o

.c 100-'

Experiment#1 with shutters, without space heaters

~

HG : Monthly heat gain due to incident solar radiation HG~ : Monthly heat gain by space heating

Experiment #2 without shutters and space heaters

<

~Rm D

Rm C ~

~zo

~: 9 -so•"r - 1 0 0 -

HL : Monthly heat lossfrora the room enveropes above the ground surface HI.Z: Monthly heat lossfrom the concrete walls below the ground surface HLf :

-150

Monthly heat lossfrom the floor

DEC I JAhl I F E B I M A R I A P R I M A Y I JUN I JUL IAUG i SEPIOCTINOV~DEC i JAN I FEBIMAR LAPRVMAY ~JUN ~JUL ~AUGISEP I OCT i NOV 1984 1985 1986

Figure 6. Heat balances for Experiment #1 and the first half of Experiment #2.

The total heating load for Room D is 93% of that for Room C. On the other hand, during the same period for Experiment #3, the total load for Room D is 87% of t h a t for Room C. Although the horizontal insulation is also effective in reducing the energy consumption for intermittent space heating, the decrement is smaller than that for continuous space heating.

.4. Analysis of the Effect of Horizontal Insulation with Regard to Heat Balance in the Room 4.1. Analysis Method Based on the results of the experiments, the amount of heat flow through the walls below the ground surface is expected to be different between the two rooms with and without horizontal insulation. The heat flow is measured by heat flux meters and is calculated by the temperature difference between the inside and outside surfaces of the walls. However, there are very few measurement points, and the distribution of heat flow between the upper part and the lower part of the walls is large. Therefore, the heat loss through the concrete walls below the ground surface is estimated on the basis of the

steady-state heat balance in a room. For the calculation, it is assumed that the heat loss per month from the room envelope is balanced with the monthly heat gain due to the incident solar radiation through the glazings and the space heating. Disregarding air infiltration, the heat balance equation is: H L + H I ~ + HLf = H a , + HG h (1)

where HL

= monthly amount of heat loss from the room envelope above the ground surface, Mcal/month HLb~ = monthly amount of heat loss from the concrete walls below the ground surface, Mcal/month HLf = monthly amount of heat loss from the concrete floor below the ground surface, Mcal/month H G = monthly amount of heat gain due to incident solar radiation, Mcal/month

HG h

= monthly

amount

of heat

gain by space heating, Mcal/month The terms of HL and HLf were calculated as follow~." The monthly temperature difference between the

Experiment #2 without shutters and space healers

'~

4.2. Heat Balances for Experiments #1 and #2 Figures 6 and 7 show the calculated

results of heat balance for Experiments #1 and #2. The t e r m of HG h in each month, which means the monthly heat gain by space heating, is always equal to zero and is not included in Figures 6 and 7, because the experiments were conducted under the condition without space heating. For Experiment #1, conducted under the condition with weather shutters, the monthly heat gain as a result of incident solar radiation ( H a ) is always equal to zero; it is not included in Figures 6 and 7. For Experiment #1 with weather shutters, the characteristics of heat balances for both rooms during the winter are quite different from heat balances during the slimmer. During the winter, each test room galn.q heat

Preparation period before Experiment#3

o

O Z

inside and outside wall surface is multiplied by the thermal conductance between them and the area for each wall, and the results are slimmed for all walls. The terms of H G and HG h are obtained by measured data. Therefore, the 1 1 n k n o w n t e r m , H L ~ , c o u l d b e estimated by eq. (1).

zE

--Z" E

LU'7~ -r~ )-if)

~'~

4oo/ . . . . . . 3oo-I Lq

/

-

Rr.o HGh

i!!!i!: !~

!!i!ii! iiii.~i: i;ii!...:

~q

Ouj "

I

|

5O'

'1 DEC } JAN I FEB JMARl APR I MAyI JUN I JUL I AUG I SEP I OCT I NOV I DEC I 1986 1987

-40O

I"

"\\

.,.

I JAN IFEI IMAR IAPR t M A Y I J U N I JUL IAUG 1988

Figure 7. Heat balances for the second half of Experiment #2 and the preparation period before Experiment #3

Volume 7, Number 4, 1992

Tu~mz.L~a ANDUNDERGROUNDSPACETECHNOLOGY343

without shutters and with intermRtentspace healing ~=

Experiment#3 without shutters and with continuousspace heating

Exp rime°t.

>

400 / Rm C--.,

~Rm D

300 _zE < ~

2oo._1 100-4

LU "T" -v ~- -100"T'j -2oo-

OuJ -r - 3 0 0 -400

SEP I O C T I N o v I D E c ] JAN' FEB IMARI APR ~MAYI JUN i JUL ~AUG ~SEP ~OCT JNOVLDEC I JAN I FEB IMARI APR ~ MAY 1988 1989 1990

Figure 8. Heat balances for Experiments #3 and #4. through the walls below the ground surface (HL=,) and the floor (HLf). Conversely, during the summer, each room loses heat through the same walls ( H I ~ and HLf). It can be said that the soil around the rooms acts as a heat source in the winter and a heat sink in the summer. However, the difference in heat balances between Room C and Room D is so small that the effect of horizontal insulation on heat balance is not clear. For Experiment #2, without weather shutters, each room gains heat through the floor during the winter and loses heat through the floor during the summer. The soil below the floor acts as a heat source in winter and as a heat sink in summer. During the year, the rooms lose the heat through the walls below the ground surface. Comparing the term of ilL. between Room C and Room D, HLb, ~or Room D is slightly smaller than HI%, for Room C during the winter. This implies that the horizontal insulation reduces the heat loss through the walls below the ground surface.

4.3. Heat Balances for Experiments #3 and #4 The calculated results of heat balance for Experiments #3 and #4 are

shown in Figure 8. For Experiment #3, the monthly heat losses through the walls and the floor below the ground surface ( H I ~ + I-ILl)during the winter are larger than heat losses occurring during the s, lmmer. The heat losses from the room envelopes above the ground surface (HLaw) show a similar tendency. The heat losses through the floor (I-IL~ have different characteristics from HL~w;they are small and do not change as much during the year. However, they are relatively larger during the snmmer because the soil temperature below the floor slab is a little lower during the s~mmer than during the winter, as shown in Figure 5a. Comparing the monthly heat losses

between Room C and Room D, there is little difference for HL wand HL r However, the terms of H ~ for Room D (with horizontal insulation) were always smaller than those for Room C, except during the summer. The horizontal insulation located in the earth reduces the heat loss through the walls below the ground surface. For Experiment #4, conducted under conditions of intermittent space heating, the effect of the horizontal insulation also appears in the difference in I-IL~ between Room C and Room D. However, the difference is relatively small in comparison with that for Experiment #3. It can be said that the effect of horizontal insulation in reducing heat loss through the walls below the ground surface is greater in the case with continuous space heating.

5. Room Temperatures and Heating Loads: Comparison between Measurement and Calculation 5.1. Calculation Method In order to obtain information to support the results of the experiments, computer calculations were made. The calculation method is based on analysis techniques of unsteady heat conduction by means of the two-dlmensional finite element method with triangular simplex elements. Figure 9 shows a calculation field modelled after the south-north section of the actual test room. For the sake of simple calculation, the ceilings, walls, and windows above the ground surface are not divided into elements, assuming that these room envelopes have no heat capacity. The thermal property of these envelopes is expressed by the total heat transmission rate, disregarding air infiltration. Because the actual test house has a roof over the ce~Hng and metal siding on foam polystyrene walls, incorporating an air layer that is connected to outdoor air, the tempera-

344 rI~NNELLINGANDUNDERGROUNDSPACETECHNOLOGY

ture of the outer model room envelope is assumed to be equal to the outdoor air temperature, disregarding the radiation from the sun and the sky. The calculation field shown in Figure 9 is modeled in such a way. Because the section is regarded as symmetrical, only one side field of the center line is calculated. The bottom of the field, which is 10 m below the floor surface, is assumed to be a water table having a constant temperature of 12 °C, which is equal to the annual mean outdoor air temperature in Sendal. The ground surface is directly exposed to outdoor air, with a sol-air temperature including sky radiation. The incident solar radiation into the room is assumed to contribute to the heating of the room air. For more information on the method, see Hasegawa et al. (1987) and Yoshino et al. (1990a). Figure 10 shows two models for thermal insulation in the earth around the room. Model 1 and Model 4 corresponded to Room C and Room D of the test house, respectively. Conditions for calculation are s, lmmArizedinTable 1. In order to simulate the conditions for Experiments #1, #2, and #3, hourly calculations were done for standard Sendaiweather conditions. Tl~e period of preliminary calculations was four years. The actuallymeasured weather data were not used because the purpose of these calculations was not to examine the accuracy of the calculation method, but rather to obtain information that supports the results ofthe experiments.

5.2. Calculated and Measured Room Temperatures Calculated results of natural room

temperatures under the same conditions as Experiments #1 and #2, are compared with measured results, taking two factors into account: (1) the Annual mean temperature; and (2) the difference between mA~m,~rn and mlnlmum monthly mean temperature.

Volume 7, Number 4, 1992

2700

10000

I

1

Finite elements:542 Nodalpaint~ : 307

G.L.

~

Model 1 G,L, oR

Room

~ , Insulation I~

03

Room

I

Soil

/\/x~ \ A A

\ \ \ ° 0,

Model 4 G.L. i:

:::::::::::::::::::::::::::::::::::::::::::::::: I *

16oo I

\ Isothermal boundary at a constant temperature of 12.0"C

Figure 9. Calculation field modeled after the actual test room.

Figure 11 shows the results. The horizontal axis is the mean indooroutdoor temperature difference over the course of a year, with the exception of October and November (because no data were available for these two months in the first year of measurement). The vertical axis is the ratio of m a x i m u m - m i n i m u m difference of monthly mean room temperature air to the same value in outdoor air. Where the room has incident solar radiation, the calculated results are in

Figure 10. Two forms of thermal insulation for the calculation.

close agreement with the measured results. However, in the case without solar radiant incident, the calculated mean room temperature is about 1.5°C lower than the measured value. One reason for this difference is that solar radiation on the surface of the weather shutters is disregarded in the calculation. However, the effect of the horizontal insulation on the natural room temperature, which is clarified in the experiments, appears in the calculation results.

5.3. Calculated and Measured Heating Loads To compare the heating loads between Experiment #3 and the calculation, measured and calculated heating loads were converted to the heating loads per floor area. Figure 12 shows the measured monthly amount of heating loads for Room C and the calculated loads for Model 1; Figure 13 shows the same information for Room D and Model 4. Although the calculations are

Table 1. Conditions for calculation. Assumed Driving Forces

Assumed Thermal Characteristics

Material or Building Element

Concrete Insulation Soil

Room envelope above the ground surface

Heat Transfer Coefficient (kcaVm2 hK)

Volume 7, Number 4, 1992

Thermal Conductivity (kcal/mhK)

Heat Capacity (kcal/mSK)

1.4 0.03 1.0

476.0 6,0 400.0

Without heat capacity (Total heat transmission rate was used)

Outdoor side: 20.0 Indoor side: 8.0

Internal generation of heat (kcal/h)

Weather Data

Standard weather data for the city of Sendai

Solar Heat Gains through Glazings (kcal/h)

These gains were calculated hourly using the weather data above and assumed to heat indoor air directly

Generation of Heat (kcal/h)

0.0 (disregard)

Air change rate (l/h)

0.0 (disregard)

Air-conditioning Mode

a. Without heating and cooling (natural room temperature) b. With heating to maintain at 20°C (natural room temperature over 20°C is allowed)

TUN~.TJ.~G ANDUND~.P~P~UNDSPATSTECHNOLOGY345

.£ =

I

It} c-

I

I O:

E

I

I

I

Calculated results

I /

O: Measured results

~0.6--

b

Model 1 Room C

I '~

O

"'

~; 0 . 5 - ua rr L.) 111

~.

Model

4

M e,

Room,,, D

conditions ( E x p e r i m e n t s #1-#4), t h e t e m p e r a t u r e of t h e soil covered w i t h i n s u l a t i o n was I°C to 3°C h i g h e r during t h e w i n t e r a n d I°C to 2°C lower during the summer than the temperat u r e of soil w i t h o u t insulation. The horizontal i n s u l a t i o n w a s effective in shielding t h e soil i t s e l f from t h e influence of t h e outdoor t e m p e r a t u r e . 2. I n cases w i t h o u t space h e a t i n g ( E x p e r i m e n t s #1 a n d #2), t h e amplit u d e of t h e a n n u a l fluctuation in room t e m p e r a t u r e w a s 0.5 to 0.6 t i m e s as g r e a t as t h a t of outdoor t e m p e r a t u r e . The a m p l i t u d e of t h e r o o m with horizontal insulation in t h e e a r t h was ab out 10% s m a l l e r t h a n t h a t of t h e other room w i t h o u t such i n s u l a t i o n in both E x p e r i m e n t s #1 a n d #2. This r e s u l t implies t h a t t h e r e d u c t i o n in t h e effect of horizontal i n s u l a t i o n was little influenced by i n c i d e n t solar radiation. 3. I n cases w i t h space h e a t i n g (Exp e r i m e n t s #3 a n d #4), t h e a n n u a l a m o u n t of t h e h e a t i n g load for t h e room w i t h h o r i z o n t a l i n s u l a t i o n w a s about 90% of t h a t for t h e room w i t h o u t such insulation. The horizontal insulation was effective in r e d u c i n g t h e h e a t i n g load. However, t h e effect of horizontal i n s u l a t i o n w a s less significant in the case w i t h i n t e r m i t t e n t space h e a t i n g ( E x p e r i m e n t #4) t h a n in the case w i t h continuous space h e a t i n ~ ( E x p e r i m e n t #3). E3

I

/

Room_O

Without shutters

With ~ u t t e r s LU

o

I

I I I i :3 -' .0 0.0 1.0 2.0 3.0 4.0 5.0 I---..% M E A N INDOOR-OUTDOOR TEMPERATURE DItFFERENCE "°, "C a_ Model 4 and Room D: With horizontal insulation in the earth Model I and Room C: Without such insulation * maximura-minimum difference in monthly mean temperature of indoor air per the same temperature difference in outdoor air "" Mean temperature differences were calculated on basis of the data from December to September for the both experiments. Figure 11. Comparison o f room temperatures between measured a n d calculated results. m a d e ass,, m l n g a two-dlmensional h e a t flow, t h e c a l c u l a t e d m o n t h l y a m o u n t s of h e a t i n g loads a r e not v e r y different from t h e m e a s u r e d a m o u n t s . The calculated monthly heating loads for Model 4 w i t h h o r i z o n t a l insulation a r e a l m o s t a l w a y s s m a l l e r t h a n those for Model 1. However, in J u n e a n d July, t h e m o n t h l y loads for Model 4 a r e slightly l a r g e r t h a n those for Model 1. Such a n effect of horizontal i n s u l a t i o n is also found in J u l y 1989 d u r i n g E x p e r i m e n t #3. I t can be said t h a t t h e calculations s i m u l a t e d well t h e t h e r m a l p e r f o r m a n c e of t h e a c t u a l t e s t rooms. The a n n u a l a m o u n t of h e a t i n g load for Model 4 is 85% t h a t for Model 1; t h e r a t i o for E x p e r i m e n t #3 is 88%. The effect of horizontal insulation in r e d u c i n g t h e h e a t i n g loads also a p p e a r s in t h e calculation results.

a:

2O

E ~__E15" ~'10<:

q z~5 . ul :E

o

6. Conclusions In order to obtain f u n d a m e n t a l information for designing a semi-underground room, and especially for designing t h e r m a l insulation located in t h e e a r t h around t h e room, five-year measurements for t h e r m a l performance of a twin-type semi-underground t e s t house were m a d e for four different conditions (Experiments#I-#4). F u r t h e r m o r e , t h e results of t h e m e a s u r e m e n t s were analyzed from the viewpoint of h e a t balance a n d were verified by computer calculations b a s e d on the two-dlmensional finite element method. The information t h u s obtained m a y be s t l m m a r i z e d as follows: 1. The t e m p e r a t u r e a n d h e a t flux a t a point of t h e soil covered w i t h horizont a l i n s u l a t i o n in t h e e a r t h was v e r y different from those m e a s u r e d a t a point of t h e soil lacking such insulation. I n all cases of t h e e x p e r i m e n t a l xl0

Model 1 and Room C." Without horizontal insulation in the earth * Heating load perfloor area

.z::

2O

References Hasegaw a, F., Yo~hln o, H., and Matsumo to, S. 1987. Optimum use of solar energy technique8 i n a semi-undergrotmd house: first-year measurement and computer analysis. Tunnelling and Underground Space Technology 2:4, 429-435. Yoshino, H., Matsumote, S., Hasegawa, F., and Nagatomo, M. 1990. Effects of thermal insulation located in the earth around a semi-underground room: computer analysis by the finite element method. ASHRAE Transactions 96, Part 1: 103-111. Yoahlno, H., Matsumoto, S., Hasegaw8, F., and Nagatomo, M. 1990. Effects of thermR1 insulatien located in the earth around a semi-tmderground room: a two-year measurement in a twin-type teBt house without auxiliary heating. ASHRAE Transact/ons 96, Part 2: 53--60. xl0

Model 4 and Room D: With horizontal insulation in the earth * Heating load perfloor area

E ~15" ~'10-

~/-- Room C

~

,<:

£

/-

Model 1

!

|

H.I "1!

im

!

i

i

|

!

!

MAY JUN JUL AUG SEF OCTNOVDECJAN FEB MAR APR TOTAL

Figure 12. Comparison o f heating loads between Room C a n d Model 1.

346 r[~..TI~TI'ffI~.T,T,TNC~

UN'DEI~P.OUNDSPACE TECHNOLOGY

o

i MAY

! JUN

i JUL

i-! AUG SEPOCT

I

I NOVDEC

,

!

"! JAN

I ! FEB MARAPR

I

!

TOTAL

Figure 13. Comparison o f heating loads between Room D and Model 4.

Volume 7, N u m b e r 4, 1992