Ben Nakamura ProfPROPOSAL FOR THE UTILIZATION OF GROUND HEAT FOR JAPANESE GREEN BUILDING SYSTEMS

Monotsukuri Institute of Technologist, ben@iot.ac.jp

Koji Morita Dr. Eng
Institute for Energy Technology, AIST, Japan k.morita@aist.go.jp

Keywords: ground-source heat pump, ground heat exchanger, energy piles, air-conditioning, single-family house, eco-campus, semi-transparent solar panel, efficient energy storage

Seiji Miwa.
Sogo Consultant, Japan, miwas@sogo-co.co.jp

Daito Bunka University Itabashi Campus
Designed by: Ben Nakamura
Keisuke Yamamoto
Keiji Hori

Photo1 left : Central Library Building, approached by a huge staircase and equipped with semi-indoor
Spine Space which generates interpersonal communication and interchange

Photo1 center, right : Spine Space of the Lecture/Laboratory Halls, covered by semi-transparent soalar panels

Summary

1. The Potential of Ground Heat and Barriers to Its Promotion in JapanThe ground temperatures at 100m in depth range from 10 to 20 °C in Japan. In winter, these temperatures arequite higher than the ambient temperature, and quite lower in summer. Thus, efficient space heating or coolingcan be achieved using ground heat.
The utilization of ground heat leads to a reduction in fossil fuel consumption and in carbon dioxide emissions.
Also, the utilization of ground heat for space cooling contributes to a moderation of the heat-island phenomenon
which is emerging as a serious issue in urban areas.
However, the utilization of ground heat has not been well promoted in Japan because of high drilling costs andhigh electric power cost. In order to promote ground-source air conditioning systems in Japan, it is essential toreduce construction costs significantly and to achieve substantially higher energy efficiency with the system.
The utilization of energy piles, foundation piles converted into ground heat exchangers, seems to be one effective
way of reducing construction costs. In this report, a ground-source air conditioning system using energy piles
installed at the Itabashi campus of Daito Bunka University is introduced. A newly developed ground-source
air-conditioning system for single-family houses, which has been developed with the aim of reducing construction
costs and improving the energy efficiency of the system, is also introduced.

1.1 Barriers to the Promotion of Ground-Source Air-Conditioning Systems in Japan
風力発電

Wind tower

太陽光発電パネル
通風

排気

太陽光

通風

Semi-transparent
solar panels

屋上緑化

天空光
ライトシェルフ

換気口

二重床チャンバー（蓄熱利用）通風

2. First Approach: The Eco-Campus Scheme
for Daito Bunka University Itabashi Campus

交流の杜

2.1 Outline of the Redevelopment Project of Daito Bunka University, First Phase

給気塔
34℃

沿道緑化

The first phase of the redevelopment project for Daito Bunka University, Itabashi Campus was completed in the year 2003. Over 27
ideas and techniques for comprehensive green building systems are tested and executed, making it a model example for urban
campus green building projects.
Two main concepts for the eco-redevelopment of the campus are as follows; The first is to develop new values by creating
communal spaces for students with a new internal quadrangle courtyard created by rearranging the setting of the buildings.The
second is to create an eco-campus using comprehensively integrated techniques synthesized with architectural design, utility design
and facility management systems.

雨水貯留槽

2.2 Highlights of the eco-campus techniques

Utility-Tunnele Cool/Hot Tube

1. Creation of a semi-indoor Spine Space with minimum artificial air conditioning for un-specified purposes, encouraging students tocommunicate with each other and with the teachers.
2. Minimizing central conditioning. Small amount fresh air is heated or cooled in central system, by newly developed energies andmore efficient systems, then discharged underneath of the rooms floor.

共同溝クールチューブ
地中温度 年間15℃〜20℃

新鮮空気

余冷
32℃

26℃

水蓄熱槽
冷温水

地熱利用中空杭杭内循環水温度
20℃〜25℃

外気処理空調機(地熱を熱源として利用)

Ground heat piles using
hollow construction piles

Fig2, Cross-section of the Lecture-Hall & Laboratory Building, showing the natural energy flow system
2.3 Newly developed energies
1. Semi-transparent Solar Electricity Generating Panels which cover approximately 750m2 of the southern facade and the roof of theSpine Space of Lecture Hall No.3,
2. Efficient utilization of the ground heat, represented by over 4.8 of COP, with a ground-source heat pump system that utilizes
energy piles, i.e., foundation piles converted into ground heat exchangers.
3. Efficient energy storage with rain water storage, using the basement floor of the existing library building which has been
demolished, and above which is created as a central community plaza, and the energy source of which is the efficient usage of theexhaust thermal energy of the gas co-generation system.

01審美感

単位面積当たりの年間ランニングコスト=35.0％減
Running cost cut 35% per year

(％)

03独創性

originality
04象徴性

18維持管理

電気料金-46.2％

50

symbol17ｴﾈﾙｷﾞｰｺｽﾄ

05完成度

energy costcompletion

16ｲﾆｼｬﾙｺｽﾄ

06機能性

15先進性

07効率性

functionefficiency

advance

水道料金-53.8％

0

Air conditioning is limited to specific purpose spaces. An amount of fresh air appropriate for the ventilation is discharged into eachroom via the perimeter of the floor from an underground heat storage pit where humidity and temperature are controlled, wherepre-cooling or heating takes place. Individual thermo-regulation with a GHP heat pump is done only when essential. Advantage istaken of the flow of air and heat created by the draft from above (wind tower effect). As far as possible, unused and ineffectively
used energy are employed.

maintenanceinitial cost

ガス料金
+3.7％

2."Basic low-energy air-conditioning system, adding natural energy to the ventilation"

08利便性

14ﾕﾆﾊﾞｰｻﾙ性

universal

convenience

13地域環境性

09安全性

regional environment

10

safety12資源消費

10先導性

consumption of resources 11環境負荷
leadership
loading environment

3. "External insulation and air tightness capacity of basic body performance"

19.34

18.91

20

単位面積当たりの年間CO2排出量=2.2％減
the amount of CO2 exhausted in each unit area per year
(Kg-C/m2･年)

Ａ.感性軸
sensitivity

Ｃ.社会軸
social-merit

Ｂ.機能軸
technical-merit

Ｄ.経済軸
cost-merit

Evaluation of sensitivity, social-merit,
technical-merit, and cost-merit

Assessment of enviromental and utility design

2.5 Specified Topics from the eco-design ideas
1. "Ground heat pump using hollow piles"

Fig.3 Assessment of environmental and utility design. (in eco-design for the Daito Bunka University)

water-cooled heatpump chiller

See-through type photovoltaic power generator panels enclosing solar battery cells in laminated glass are used on the south façadeof Building No. 3 and on the roof surface. Units of stainless steel pipes are arranged alternately with these, bamboo-blind fashion,
the spine enclosed by a screen. The modular solar battery cells on the wall and roof are sensitised so that each cell knows exactly
when to soften the glare of the south summer sunlight or encourage the warm inflow of winter light. This screen creates a bright andopen architectural space. Moreover, it has the effect of reflecting the movement of the people in the spine as a moire pattern. In
Phase 2 of the construction, when the demolition of the old library is completed, the complete shape of the screen facing thecourtyard will become apparent.

air conditioner
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heat source water

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ground heat exchanger tubes

According to the lighting plan, in Lecture Hall, a skylight is introduced through the north-facing light shelf. By means of a section
form, light from the skylight reflected on the ceiling of the outside terrace is brought inside. Zone lighting control is used as a lighting
energy conservation measure.

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2.6 Specific topics from the eco-design ideas
1. "Utilization of Ground Heat in the Itabashi Campus of Daito Bunka University"(1) Use of Ground Heat with Hollow Piles

Detailed drawing of SGP

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46 sets of high-density polyethylene tubing having a total length of
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Hollow-pile insertion-type heat-exchange tube for use of ground heat

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Cooling capability: 53kw (15RT), Heating capability: 43kw
9
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Terrestrial water-cooled heat pump chiller using ground heat

Countermeasures taken to reduce the impact of solar radiation from the west include deep eaves on the south and east sides ofspine space; wood insulation for the external wall; tree planting on the roof and the fixing of cross-vertical louvers made of polyesteron the west side of the Central Block. During execution, various materials were verified with the wind tunnel experiment, and photocatalyst techniques were used to prevent pollution.

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4. "Load reduction policy"

Mean temperature of circulating water(in degrees Celsius)

60

Mean temperature of circulating waterin air cooling seasons(round trip)

Temperature(℃)

Temperature(℃)

30
25
20
15
10

Mean temperature of circulating water in air-heating seasons(round trip)

5

During Heat pump operation
COP=about 4.8

50

7/31

8/30

9/29

10/29 11/28 12/28 1/27

2/26

3/27

4/26

5/26

Data
Discharge radiation of 73w/m
Heat collection of 52w/m
Operating conditions
Monday to Saturday 9:00-17:00 at full capacity
17:00-9:00 on the following day : shutdown
Sunday all day : shutdown

Fig.5 Estimated thermal transition of circulating ground water

Sapporo
105
4.5
4.1
9.2
7.2
4.4

Sendai
60
4.9
4.5
6.1
5.4
4.7

Tokyo
55
5.3
4.8
4.3
4.0
4.4

Fukuoka
65
5.5
4.9
4.3
4.0
4.3

The estimated COPs of the system, which include power consumption of auxiliary equipment such as a circulation pump and acontrol system, range from 4.1 to 4.9 for space heating. These COPs are higher by 1 compared with the conventional systems. Thus,
the developed system might be much more competitive with the systems burning heating oil than the conventional systems in termsof running costs. The overall COPs of the system which include space heating and cooling were estimated to be 4.3 to 4.7.

40
30
20

3.3 Discussion

10
7/1

An investigation of the developed system was performed by carrying out numericalsimulations to estimate the required length of the ground heat exchanger and toobtain knowledge on the operational performance of the developed system in four
major cities in Japan, Sapporo, Sendai, Tokyo and Fukuoka.
In this investigation, a 150m2 class standardized single-family house which meets
the Japanese next-generation energy saving standard was assumed. The hourlybase air-conditioning loads calculated based on the standard weather data in eachcity were used in the simulations. Assumed temperature profiles in the ground foreach city are shown in Figure 8. A 1.3 W/m・K of effective thermal conductivity of
Fig.8 :
the ground was assumed in each city.
Table 1 shows the required length of the ground heat exchanger for a single-family
Assumed temperature profiles
house, and the estimated COPs of the heat pump system. These estimated lengths
in the ground at the major cities.
are significantly shorter than those of conventional systems. This indicates thatthe construction costs of the heat exchanger can be reduced substantially compared with the conventional systems.
The estimated length for Tokyo is the shortest. This means that construction costs for the system would be cheapest in Tokyo. Until
now, it has been considered that the ground-source air-conditioning system is more practical in colder areas such as Northern
Honshu and Hokkaido. However, this indicates that there is no less of a possibility of realizing practical ground-source
air-conditioning in warmer cities such as Tokyo.
City
Required Length of
DCHE (m)COP of Heat Pump in Heating (-)
COP of System in Heating (-)
COP of Heat Pump in Cooling (-)
COP of System in Cooling (-)
Overall COP of System (-)

0
6/1

Despite high drilling costs and high electric power prices in Japan, our economical analysis of a 4,000m2 class building indicated thata ground-source air conditioning system was more economical than an oil-fired absorption chiller/heater system in the long term.
This indicates that there is a greater possibility for the ground-source air conditioning system to be economical in relatively large
buildings.
In regard to systems for single-family houses, the construction costs and energy efficiency of conventional ground-source systems
have been far from economical, except for the case of groundwater-source systems. The authors have been developing a new
air-conditioning system in cooperation with Kyushu University aiming at achieving a practical system. A prototype of the system wasinstalled in December 2004 in Fukuoka City in a house built for experiments, and the operational data have been collected toevaluate performance of the system.
3.1 Concept of the Developed System
Schematic drawings of the conventional system and the newly developed system
shown in Figure‚55 can be applied to up to 150m2 class single-family houses withup to 5 rooms.
Single or double U-tube heat exchangers have been commonly employed inconventional systems in Japan as they have been abroad. In the developed
system, the Downhole Coaxial Heat Exchanger (DCHE; Morita et al., 1985;
Morita and Tago, 1995) proposed by the authors together with others is utilized.
It is said that the specific heat extraction rate, i.e., heat extraction rate per unit(a) Conventional System
length of the heat exchanger, of the single U-tube heat exchangers is about 20W/m
and the double U-tube heat exchangers about 40W/m. On the other hand, aseasonal average specific heat extraction rate of about 90W/m has been obtained
at 1.25 W/m・K of small effective thermal conductivity of the formation with the
DCHEs in a snow-melting system (Morita and Tago, 2005).
In the developed system, direct expansion/condensing units are utilized. Becauseof this, the system is greatly simplified and the number of component parts can be
reduced significantly. Installation of the air-conditioning refrigerant pipes issignificantly easier than with conventional systems that circulate water oranti-freeze. These factors make the installation of the total system much easier.
Hence, equipment and installation costs can be reduced considerably.
(b) Developed System
Moreover, the necessary pumping power might be less than one half that of theconventional system. This leads to a higher COP of the system. In the developed
Fig.7
system, only one stage of heat exchange is necessary to transfer heat from theComparison of the conventional
refrigerant gas to the indoor air. Meanwhile, two stage heat exchanges are
and developed ground-source
necessary in conventional systems. Thus, the temperature loss in the indoor-side
air-conditioning systems forheat transfer circuit is smaller than with conventional systems. This leads to asingle-family houses
higher COP of the heat pump.

Table 1 Estimated required length of the heat exchanger and COPs.

Fig.4 Layout of Ground Heat Tube Pile

35

3. Second Approach: Development of a Ground-Source Air Conditioning
System for Single-familyHouses

3.2 Estimated Required Length of the Ground Heat Exchanger andPerformances

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Though the ground heat pump using hollow piles has been adopted here experimentally, the result of using 2 U-tubes in 23 piles atabout 25m was a heated (cooled) energy performance of 50-70KWH. Also the cost performance is good, and even in temperatezone monsoon areas, it can be a very effective method of tapping future unused energy. This is explained in detail in the second
chapter.

(2) Utility-Tunnel Cool/Hot Tubebalance19耐久性

durability

As an eco-campus the importance of natural air flow, has been emphasized, and low-tech methods of air flow and heat flow havebeen comprehensively developed, integrating the architectonic cross-section and the utility system. The various techniquesdeveloped numbered 27 items, and successfully synthesised the overall space into one "flow."

We have implemented a method for gathering ground heat by using 23 hollow piles (PHC piles of 20m to 25m), which are structurally
required in the lecture building, and inserting heat-exchange tubes into the hollow part of the piles. Water is circulated in the tubes
through a sealed channel where it gathers ground heat (about 17ºC) that is stable throughout the year, and then the water is
supplied as cooling/heating water through a water-cooled heat pump chiller. The cooling/heating water is supplied to the primary coilof an "air conditioner for treatment of outside air" in the lecture building, where it is used as a heat source for treating outside air.
In order to confirm the responsiveness of ground heat exchange, which is expected to fluctuate according to area, we carried out athermal response test after insertion of the heat-exchange tubes during the construction of the lecture building. As a result of thethermal response test, we determined that a heat radiation load of 73w/m can be obtained during air-cooling seasons, and a heatcollection load of 52w/m can be obtained during air-heating seasons (Fig. 5). These were the predicted results.
According to measured values obtained after the lecture building was completed, it was confirmed that a heat radiation load of
64w/m could be obtained during air-cooling seasons, and a heat collection load of 78w/m could be obtained during air-heating
seasons. Thus, we obtained favorable results that were equivalent to the predicted thermal response values.
As a result of having calculated the equipment efficiency of the water-cooled heat pump using ground heat from the input energy andoutput energy amounts of the same device, we obtained a COP of 3.9 for air-cooling seasons and a COP of 4.8 in air-heating
seasons, both of which were very good values.
Furthermore, from measurement temperature progress graphs for the inside of the pile, the outside of the pile, and the background(part which is not thermally affected) when ground heat is used, we ascertained that the outside of the pile and the background areless affected by the use of ground heat, and that the influence of outside air temperature is observed only slightly at the shallow levelof GL-5m. Although the drop in temperature on the inside of the pile when ground heat is used was a little larger than we originallyestimated, the temperature rise (recovery) after equipment operation was stopped progressed within an estimated period of time.
Therefore, we consider the long-term balance between income and expenditure of energy using ground heat to be valid (Fig. 6).

02調和性

LLC

100

2.4 Eco-Campus Schemes
1. "The eco-campus, a fusion of the architectonic cross-section and the utility system"

Besides using external insulation, wooden sash frames, pair glass insulation and a high basic body of air tightness, use has been
made in the second phase of construction of multi-service tunnels as cool tubes, geothermic availability of ground energy throughhollow piles and a method of thermal storage cogeneration of exhaust heat. Thus has been achieved a fusion of the outside air
introduction type air conditioning method, (a principle of the middle phase), with the architectonic cross-section form. A room
temperature of 12-15°C is maintained even in winter.

aesthetic

20ＬＣＣ

The increase in the number of installed Ground-Source heat pumps (GSHPs) has beenremarkable in the United States, Sweden, Germany, Switzerland etc. In contrast, onlya small number of the GSHPs have been used in Japan. The total number of the GSHPs
functioning in Japan is estimated to be 120 to 200. Most of these are groundwater-source
heat pumps. Thus, the utilization of ground heat has not been well promoted in Japan.
The major reasons for this are as follows:・High drilling costs
Unconsolidated and easily collapsible sedimentary formations are commonly distributed
throughout inhabited areas of Japan. For this reason, drilling costs are approximately 10
and 5 times higher than those in the United States and Switzerland, respectively. Hence,
the total cost of the system is very high in comparison with that of conventional air
conditioning systems.
・High electric power costs
It is said that the target COP (coefficient of performance) of the heat pump in GSHP
systems is about 3 in countries which commonly use these systems. However, in Japan,
the price of electric power per unit heat amount is 3.7 times higher than that of heating oil.
If the COP of the heat pump were at the same level as those of above mentioned countries, Fig. 1
it would be impossible to achieve cheaper running costs than the systems which burn oil.
Groundwater temperatures at 100m in・Low heat transfer performances in formations
depth in Japan (Yamamoto,1983)
Since unconsolidated sedimentary formations are widely distributed in Japan, the effective thermal conductivities of formations are
generally small. The in-situ effective thermal conductivities of the formations measured by the authors range from 1.2 to 1.8W/m･k.
They are quite small compared with those in Northern European countries and Switzerland where formations mainly consist of rock.
For instance, in Sweden, formations of effective thermal conductivities ranging from 2.5 to 4.0W/m･k are widely distributed (Ohtani
et al., 2003). Also, it is said that the effective thermal conductivities of formations are 2.0 to2.6W/m･k in Switzerland (Rybach, 1994).
This indicates that longer ground heat exchangers, and thus higher construction costs, would be necessary in Japan as comparedwith these countries.
Conditions in Japan for applying ground-source air conditioning systems are much more severe than in countries where the GSHPs
use has been rapidly increasing. In order to promote ground-source air conditioning systems in Japan, it is essential to reduce
construction costs significantly and to achieve substantially higher energy efficiency with the system.

0

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Time
(o'clock)Low-temperature side entrance temperature
Low-temperature side entrance temperature
High-temperature side entrance temperature
High-temperature side exit temperature

Fig.6 Temperature of ground water-cooled heat pumpmeasured at the opening

Fresh outside air (54,000m3) introduced into the building is supplied from an air supply tower installed at the "community square"using part of a utility-tunnel (total of 150m) constructed under the building as a supply conduit. Outside air is cooled or heated by the"cool/hot tube effect" in the utility tunnel, which is treated with anti-fungal coating, and is sent to the air conditioner for treatment ofoutside air. According to measured values obtained after the lecture building was completed, it is clear that the amount of outside-air
reduction energy attributable to the cool/hot tube effect could be 1,858MJ/day during air-cooling seasons and 1,805MJ/day during
air-heating seasons. It has been confirmed that the effect is particularly large at the day time of the cooling season and at themorning and evening time of the heating season, and that there is a difference of 5ºC at the cooling season, and 4.4ºC from theoutside air temperature.

Construction costs for conventional ground-source air-conditioning systems are estimated to be about 5 million Yen for asingle-family house. On the other hand, construction costs for the developed system are estimated to be about 3 to 3.5 million Yen in
Sendai, Tokyo and Fukuoka. These construction costs could become even cheaper if the system is promoted. It seems that thepossibility for the promotion of the developed system is not small.
This investigation indicates that the heat charged into the ground is 2.6 times as great as the heat extracted from the ground inFukuoka. This suggests that it is desirable to develop a system which can also supply hot water to improve the annual heat balancein the ground in warmer areas in Japan. Such a system might also improve the economic competitiveness of the system. The
authors are planning to develop such a system.
This project has been carried out with the aim of developing an air-conditioning system for single-family houses. However, it mightalso be realistic to apply the same concept to bigger buildings using greater heat pumps.

4. Conclusions
The utilization of ground heat for air-conditioning should contribute to realise green building. In this report, aground-source air conditioning system using energy piles installed at the Itabashi campus of Daito Bunka
University and a newly developed ground-source air-conditioning system for single-family houses wereintroduced.

2.7 Discussions
The construction costs for the project in Daito Bunka University, which utilized double U-tubes in 23 hollow piles (25m deep), wassignificantly low. The see-through type solar energy generation panel installed on the same building generates 30kw of energy andcost 75 million yen, whereas the piping and the heat pump system utilizing these hollow piles collect approximately 70kw of energy
and cost as little as 18 million yen for 46 sets.
Utilizing the fundamental piles eliminates well-digging cost; therefore simply the piping and the heat pump system accounted for thecosts.
In order to identify how much energy could be utilized, however, the investigation had to be carried out with testing piles, and theheat collection interval and the heat pump capacity had to be decided according to the results.
For the future, the prediction technique by means of ground heat conductivity and the engineering capability to design with lessdrilling surveys in the field should be further developed and improved.

These two systems might be effective in reducing construction costs of the ground source air-conditioning
systems. Also, an investigation of the developed ground-source air-conditioning system for single-family houses
indicated that substantially higher COPs than that of conventional ground source air-conditioning system can beachieved with the developed system.
For further development of the design method, more data of temperature profiles and thermo physical propertiesof formations should be collected in many areas.
Photo2 :left: Vertical cloth louver center : Curved ceiling of the library right : Light-shelfs, for Lecture halls

These approaches may leads to the future promotion of the ground heat utilisation to a popular system.