Development of a ground-source heat pump system with ground heat exchanger utilizing the cast-in-place concrete pile foundations of buildings.ABSTRACT Ground-source (geothermal ge·o·ther·mal also ge·o·ther·mic adj. Of or relating to the internal heat of the earth. ge ) heat pump heat pump: see air conditioning. heat pump Device for transferring heat from a substance or space at one temperature to another at a higher temperature. (GSHP GSHP Ground Source Heat Pump GSHP Georgia Society of Health-System Pharmacists ) systems can achieve a higher coefficient of performance The coefficient of performance, or COP (sometimes CP), of a heat pump is the ratio of the output heat to the supplied work or than conventional air-source heat pump (ASHP ASHP American Society of Hospital Pharmacists. ) systems. However, GSHP systems are not widespread in Japan because of their expensive boring costs. The authors have developed a GSHP system that uses the cast-in-place concrete pile foundations of a building as heat exchangers heat exchanger Any of several devices that transfer heat from a hot to a cold fluid. In many engineering applications, one fluid needs to be heated and another cooled, a requirement economically accomplished by a heat exchanger. to reduce the initial boring cost. In this system, some U-tubes are arranged around the surface of a cast-in-place concrete pile foundation. The heat exchange capability of this system, subterranean temperature changes, and heat pump performance were investigated in a full-scale experiment. As a result, the average values for heat rejection were 186-201 W/m (per pile, 25 W/m per pair of tubes) while cooling. The average COP COP In currencies, this is the abbreviation for the Colombian Peso. Notes: The currency market, also known as the Foreign Exchange market, is the largest financial market in the world, with a daily average volume of over US $1 trillion. of this system was 4.89 while cooling, rendering this system about 1.7 times more effective in energy-saving terms than the more typical ASHP systems. The initial cost of construction per unit for heat extraction and rejection is US$0.79/W (approximately [yen]79/W) for this system, whereas it is US$3/W ([yen]300/W) for existing standard borehole bore·hole n. A hole that is drilled into the earth, as in exploratory well drilling or in building construction. systems. Therefore, this system is expected to be commercially viable. INTRODUCTION Ground-source heat pump (GSHP) systems can achieve a higher coefficient of performance than conventional air-source heat pump (ASHP) systems because the ground, which functions as the heat source or sink, is at a higher temperature in winter and lower in summer than the air temperature (Kavanaugh 1992; Kavanaugh and Rafferty 1997). In addition, there will likely be some mitigation MITIGATION. To make less rigorous or penal. 2. Crimes are frequently committed under circumstances which are not justifiable nor excusable, yet they show that the offender has been greatly tempted; as, for example, when a starving man steals bread to satisfy against the effects of the heat island phenomena, as this system does not emit TO EMIT. To put out; to send forth, 2. The tenth section of the first article of the constitution, contains various prohibitions, among which is the following: No state shall emit bills of credit. exhaust heat Exhaust Heat is a Super Famicom game that simulates the season and career of a Formula One superstar. There are over a dozen courses around the world to race and all of them are likenesses of real Formula One tracks (including realistic looking advertisements where the audience into the atmosphere during air conditioning air conditioning, mechanical process for controlling the humidity, temperature, cleanliness, and circulation of air in buildings and rooms. Indoor air is conditioned and regulated to maintain the temperature-humidity ratio that is most comfortable and healthful. . However, GSHP systems are not popular in Japan except for experimental versions. This is primarily due to the high cost of boring to run piping underground. For example, such boring costs average about US$30/m (approximately [yen]3,000/m) in the USA, whereas the same work is about US$100/m ([yen]10,000/m) in Japan. Thus, even if the heat pump performance in GSHP systems is more effective than that of the more common ASHP systems, the GSHP systems are unable to recoup recoup To sell an asset at a price sufficient to recover the original outlay or to offset a previous loss. the initial piping costs within their life cycles. Recently, a GSHP system that uses the foundation piles piles: see hemorrhoids. of buildings as a heat exchanger (so-called energy pile system) was introduced into some buildings in order to reduce the initial boring cost (Hamada et al. 1997; Arup 2002; Presetschnik and Huber 2005). However, an effective and low-cost design method for energy pile systems has not yet been developed. In addition, most energy pile systems have used precast pre·cast adj. Relating to or being a structural member, especially of concrete, that has been cast into form before being transported to its site of installation. , prestressed concrete prestressed concrete Concrete reinforced by either pretensioning or posttensioning, allowing it to carry a greater load or span a greater distance than ordinary reinforced concrete. In pretensioning, lengths of steel wire or cables are laid in the empty mold and stretched. pile or steel pipe pile. Recently, in urban areas in Japan, the cast-in-place concrete foundation piles of buildings have been used for reasons of traffic circumstances CIRCUMSTANCES, evidence. The particulars which accompany a fact. 2. The facts proved are either possible or impossible, ordinary and probable, or extraordinary and improbable, recent or ancient; they may have happened near us, or afar off; they are public or when carrying the piles or for cost reduction. The authors have developed a GSHP system (energy pile system) that uses the cast-in-place concrete pile foundation of buildings. In this research, a full-scale experiment was conducted. The heat exchange capability of this system, subterranean temperature changes, and performance of the heat pump were investigated. Furthermore, the construction costs of this system were also examined. SYSTEM OUTLINE The usual diameters of cast-in-place concrete pile foundations are from 1.5 to 4.0 m. In this system, some U-tubes are arranged around the exterior cast-in-place concrete pile foundations, as shown in Figure 1, as the ideal location. U-tubes are fixed, not directly to the hoops of the main reinforcement reinforcement /re·in·force·ment/ (-in-fors´ment) in behavioral science, the presentation of a stimulus following a response that increases the frequency of subsequent responses, whether positive to desirable events, or of the pile, but to the spacers for preventing eccentricity eccentricity, in astronomy: see orbit. Eccentricity Addams Family weird family, presented in grotesque domesticity. [TV: Terrace, I, 29] Boynton, Nanny travels with set of Encyclopaedia Britannica of the pile. At this location, the U-tubes are positioned outside the diameter of the pile determined by the structural design and the core of the piling (and concrete will be placed around the U-tubes), and will cause no partial loss of area of the piling and no loss in structural strength. The arrangement can also ensure a larger space between U-tubes than in the conventional method of installing U-tubes inside piles, and, thus, the heat interference between U-tubes is smaller. The U-tubes are normally made of high-grade or cross-linked polyethylene For the BitTorrent peer-to-peer protocol feature, see . Cross-linked polyethylene, commonly abbreviated PEX or XLPE, is a form of polyethylene with cross-links. . These U-tubes usually have a 21 to 28 mm inside diameter Inside diameter is the diameter of the addendum circle of an internal gear.1 Notes 1. ANSI/AGMA 1012-G05, "Gear Nomenclature, Definition of Terms with Symbols". . The U-tube used in this system is made of polyethylene polyethylene (pŏl'ēĕth`əlēn), widely used plastic. It is a polymer of ethylene, CH2=CH2, having the formula (-CH2-CH2-)n , which is very steady chemically and is also strong in temperature change. Thus, there is no worry about which polyethylene has deteriorated even if concrete curing (heating, swelling/shrinking) occurs. In the case of the application of 1.5 m cast-in-place concrete pile to the usual office building in Japan, one pile is usually set per 30 to 40 [m.sup.2] floor area each. In this study, the heat extraction/rejection rate for one pile was about 180 W/m. Therefore, if pile length is 30 m (as is very common in Japan), the heat extraction/rejection rate per pile became 5.4 kW. This corresponds to the air-conditioning load for two to three floor areas (i.e., about one-third of the total air-conditioning load of an eight-story office building, which is a very popular building design in Japan). The heat source for air conditioning in office buildings is usually divided into several parts. In this case, geothermal heat from this pile system can be used as one part of the heat source. The other air-conditioning load is supplemented with the usual air-source heat pump. These methods are quite reasonable and applicable. In this paper, basic performance and the construction cost of this system are examined. FULL-SCALE EXPERIMENT Experimental Equipment Outline An experimental institution was built on site at the University of Tokyo “Todai” redirects here. For the restaurant called Todai, see Todai (restaurant). The University of Tokyo (東京大学 in Chiba. Chiba is east of Tokyo, and the average annual air temperature is about 15.4[degrees]C, with the average air temperature in August being about 26.4[degrees]C and in January about 5.4[degrees]C. Accordingly, both heating and cooling functions are necessary. A plan of the experimental institution and the system configuration is shown in Figure 2. The results of this experiment were obtained at a local site. Thus, people should apply these results to other sites carefully. A borehole log at this site is also shown in Figure 2 in order to show the locality 1. locality - In sequential architectures programs tend to access data that has been accessed recently (temporal locality) or that is at an address near recently referenced data (spatial locality). This is the basis for the speed-up obtained with a cache memory. 2. of this experiment. We conducted a thermal response test to measure the ground thermal conductivity thermal conductivity A measure of the ability of a material to transfer heat. Given two surfaces on either side of the material with a temperature difference between them, the thermal conductivity is the heat energy transferred per unit time and per unit in this site, which was 1.40 W/mxK, an ordinary value in Japan. [FIGURE 1 OMITTED] There were two cast-in-place concrete piles (both 1.5 m in diameter, 20 min length) around which eight U-tubes (outside diameter Outside diameter is the diameter of the addendum (tip) circle. In a bevel gear it is the diameter of the crown circle. In a throated wormgear it is the maximum diameter of the blank. The term applies to external gears.1 Notes 1. , 34.0 mm; inside diameter, 28.8 mm) were installed in parallel in this experiment. It is possible to control the number of U-tubes in operation by opening and closing their valves. Before the experiment, an optimum number of pairs of U-tubes was not clarified. Thus, as many pair of U-tubes as possible were arranged, then an optimum number of pairs would be determined by changing the number of pairs operated in this experiment. Opening or closing the valves installed in the tubes can alter the number of U-tubes used. In an actual building, the number of U-tubes to be used will be determined based on pile diameter and heat extraction/rejection ratio. The system used with this experimental equipment consists of a water-to-water heat pump with a reciprocating compressor A reciprocating compressor is a compressor that uses pistons driven by a crankshaft to deliver gases at high pressure.[1] [2] The intake gas enters the suction manifold, then flows into the compression cylinder where it gets compressed by a piston (4.6 kW cooling, 5.7 kW heating). Cold and hot water circulates through a fan-coil unit and a radiation panel in two examination rooms, respectively, as shown in Figure 2. The flow of cold and hot water is 27 L/min (0.00045 [m.sup.3]/s). The flow of the heat source (sink) water is 33 L/min (0.00055 [m.sup.3]/s). This system has two rooms. One has a fan-coil unit installed. The other has a radiation air conditioner conditioner, n 1. an additive substance used to increase the effectiveness of another substance. 2. a substance added to enamel that improves a sealant's ability to adhere. . Thermostat thermostat, automatic device that regulates temperature in an enclosed area by controlling heating or refrigerating systems. It is commonly connected to one of these systems, turning it on or off in order to maintain a predetermined temperature. and electrical valves control the amount of water supplied to the fan-coil unit. [FIGURE 2 OMITTED] Experiment Outline The heat pump in this system operated from 9:00 to 18:00, Monday to Friday, as in typical office buildings. It was not operated on Saturday or Sunday. In summer (from June to September), heat was discharged (sunk) into the ground. Conversely con·verse 1 intr.v. con·versed, con·vers·ing, con·vers·es 1. To engage in a spoken exchange of thoughts, ideas, or feelings; talk. See Synonyms at speak. 2. , in winter (from December to March), heat was extracted (sourced) from the ground. A list of the measurement items is shown in Table 1. COOLING AND HEATING RESULTS IN 2003 Underground Temperature Figure 3 shows the variations in the underground temperature at measuring points A and B and air temperature in 2003. The subterranean temperature was about 20[degrees]C at 1 m below ground level (G.L. -1 m), about 19[degrees]C at G.L. -10 m, and about 17[degrees]C at G.L. -19 m in both measuring points A and B, as shown in Figure 6, at the start of the air-conditioning operation (7/16). The subterranean temperature at each point gradually rose thereafter. The subterranean temperature at G.L. -1 m had reached about 25[degrees]C by the time the air-conditioning operation ended. The subterranean temperature at G.L. -1 m was significantly influenced by the ambient Surrounding. For example, ambient temperature and humidity are atmospheric conditions that exist at the moment. See ambient lighting. air temperature. However, subterranean temperatures only changed a few degrees at G.L. -10 m and G.L. -19 m throughout the year. At the start of the heating operation (12/25), the subterranean temperature at G.L. -10 m was about 19[degrees]C, while that at G.L. -19 m was about 17[degrees]C. The subterranean temperatures at each point fell gradually after the start of this operation. The subterranean temperatures at G.L. -10 m and G.L. -19 m stabilized sta·bi·lize v. sta·bi·lized, sta·bi·liz·ing, sta·bi·liz·es v.tr. 1. To make stable or steadfast. 2. at about 15[degrees]C during the heating operation in February and remained nearly constant until the operation ended (3/28). [FIGURE 3 OMITTED] Heat Source/Sink Water Temperature The air temperature and heat source/sink water temperatures for cooling and heating are shown in Figure 4. The heat sink A material that absorbs heat. Typically made of aluminum, heat sinks are widely used in amplifiers and other electronic devices that build up heat. Small heat sinks are the most economical method for cooling microprocessors and other chips. water temperature at the start of the cooling operation was about 20[degrees]C, rose gradually after that, and reached about 29[degrees]C just before the end of the cooling period. The average temperature of the heat sink water and air during the cooling period were about 24.5[degrees]C and 29.2[degrees]C, respectively. The heat sink water temperature was about 4.7[degrees]C lower than the air temperature on average for the cooling period, and the maximum difference between the water and air temperatures was 12.3[degrees]C for the cooling period. On the other hand, the heat source water temperature at the beginning of heating was about 17[degrees]C and fell gradually after the start of the operation, and remained at about 13[degrees]C from early January until the end of March. The average air temperature during the heating period was about 9.9[degrees]C, while the minimum was about 1.1[degrees]C. The heat source water was about 3.1[degrees]C higher than the air temperature on average for the heating period. The maximum difference between the water and air temperatures was 11.9[degrees]C for that period. Thus, using the groundwater as a heat source or sink was more effective than using ambient air. Accordingly, GSHP is expected to be more effective than ASHP both in terms of cooling and heating. Heat Extraction/Rejection from/into the Ground The averages for the heat extraction and rejection either from or into the ground of the foundation piles A and B at the outset of the cooling and heating periods are shown in Figure 5. The maximum values for heat rejection were 158 W/m (pile A) and 164 W/m (pile B), while the average values for heat rejection were 100 W/m (pile A) and 120 W/m (pile B) while cooling. The heat rejection per paired U-tube was about 12.5-15 W/m during the cooling period. Pile B seems to have higher heat rejection than Pile A. Possible reasons for this finding could be that the local soil thermal properties The thermal properties of soil are a component of soil physics that has found important uses in engineering, climatology and agriculture. These properties influence how energy is partitioned in the soil profile. around pile A and B are different, mass flows in U-tubes around pile A and B are different due to the difference of pipe friction, etc. The maximum values for heat extraction were 119 W/m (pile A) and 124 W/m (pile B), while the average values were 44 W/m (pile A) and 52 W/m (pile B) while heating. Heat extraction per paired U-tube was about 6-7 W/m during the heating period. [FIGURE 4 OMITTED] [FIGURE 5 OMITTED] Coefficient of Performance The coefficients of performance (COP) for this system, the heat sink/source water temperature and air-conditioning load while cooling and heating, are shown in Figure 6. The data were calculated as the total in an hour from values measured at 10-minute intervals. While cooling, the maximum COP was 6.4, while the average was 3.7. When the air-conditioning load was high or the heat sink water temperature was low in August, the COP recorded high values. While heating, the maximum COP was 5.0, while the average was 3.2. When the air-conditioning load was high or the heat source water temperature was high in January, the COP recorded high values. The results showed that COP was affected more by the air-conditioning load than by the source/sink temperature. Although the expected average heat extraction/rejection values were 160 W/m per pile (i.e., 20 W/m per U-tube), the actual value was much less than expected. It is thought that this was due to the low air-conditioning load on this system; therefore, an additional load was installed, and the cooling experiment was repeated in 2004. These results will be described in next section. Figure 6 shows both trends during each day and a seasonal trend. As to a seasonal trend, the results of each month are shown in different symbols in this figure. The plotting with the same symbols shows a trend during each day. The experiment room, where a dummy load A dummy load is a device used to simulate an electrical load, usually for testing purposes. Radio In radio this device is also known as a dummy antenna or a radio frequency termination. of 2.5 kW was placed, was controlled at a constant air-conditioning load. However, the actual load is not maintained at a constant level because it is dependent on outdoor temperature, solar radiation solar radiation, n the emission and diffusion of actinic rays from the sun. Overexposure may result in sunburn, keratosis, skin cancer, or lesions associated with photosensitivity. , and other factors. COOLING RESULTS IN 2004 The cooling results in 2004 are shown in Figures 7-9. Figure 7 shows heat rejection dropping during each day, Figure 8 shows sink temperature increasing during each day, and Figure 9 shows the COP drop during each day. The maximum values for heat rejection were 259 (pile A) and 278 W/m (pile B), while the average values were 204 (pile A) and 220 W/m (pile B) from 6/16 to 8/21. The average values for heat rejection were 186 (pile A) and 201 W/m (pile B) while cooling. These attained the authors' expectations (160 W/m per pile). Here, the COP for ASHP was calculated from the air temperature measured at the experimental site and the performance curve of a typical ASHP. The COPs for this system (GSHP) and the ASHP are shown in Figure 10. The average COPs for this system and ASHPs were 4.89 and 2.90, respectively, while cooling. Thus, this system is about 1.7 times more efficient than the more common ASHP systems. [FIGURE 6 OMITTED] EXAMINATION OF CONSTRUCTION COST A comparison of the construction costs between the usual borehole system and our proposed system is shown in Table 2. Here, a single U-tube is assumed to be used in the usual bore-hole system. The heat extraction and rejection per unit length of a single U-tube is assumed to be 40 W/m. The boring cost is ordinarily or·di·nar·i·ly adv. 1. As a general rule; usually: ordinarily home by six. 2. In the commonplace or usual manner: ordinarily dressed pedestrians on the street. US$100/m (approximately [yen]10,000/m) in Japan. The heat extraction and rejection capabilities of the proposed system are based on the cooling experiment performed in 2004. The construction cost for the proposed system is based on an example introduced in an actual building. The cost of construction per heat extraction and rejection unit of the proposed system is 75% cheaper than that of a borehole system. Accordingly, the proposed system is expected to pay for itself within ten years. CONCLUSIONS 1. The authors have developed a GSHP system using the cast-in-place concrete pile foundations of a building as heat exchangers in order to reduce the initial boring cost. 2. In this system, eight U-tubes are arranged around the outer surface of cast-in-place concrete pile foundations. 3. The heat exchange capability of this system, the subterranean temperature change, and performance of the heat pump were investigated in a full-scale experiment. 4. The average values for heat rejection were 186-201 W/m (per pile, 25 W/m per pair of tubes) while cooling. 5. The average COP for this system was 4.89 while cooling, so this system is about 1.7 times more efficient than the more common ASHP system. 6. The initial cost of construction per heat extraction and rejection unit is US$0.79/W (approximately [yen]79/W) for this system, whereas it is US$3/W (approximately [yen]300/W) for the standard borehole system. 7. This system is expected to be commercially viable. [FIGURE 7 OMITTED] [FIGURE 8 OMITTED] [FIGURE 9 OMITTED] [FIGURE 10 OMITTED] 8. Regarding operational problems related to this approach, the amount of work to connect U-tubes to reinforcing bars cannot be disregarded dis·re·gard tr.v. dis·re·gard·ed, dis·re·gard·ing, dis·re·gards 1. To pay no attention or heed to; ignore. 2. To treat without proper respect or attentiveness. n. . Simplification of the construction method will be examined in future research. 9. The experimental results of this research were obtained at a particular local site. A lot of other research will be required in the future to develop this system to apply generally to real office buildings. REFERENCES Arup Geotechnics Geotechnics (synonymous: Geotechnique) is the application of scientific methods and engineering principles to the acquisition, interpretation, and use of knowledge of materials of the Earth's crust and earth materials for the solution of engineering problems. . 2002. DTI Diffusion tensor imaging (DTI) A refinement of magnetic resonance imaging that allows the doctor to measure the flow of water and track the pathways of white matter in the brain. Partners in Innovation 2002. Ground storage of building heat energy, Overview report. Hamada, Y., K. Ochifuji, K. Nagano, and M. Nakamura. 1997. Study on the heating and cooling by long-term heat storage with underground vertical U-tubes. Proceedings of MEGASTOCK '97 1:37-42. Kavanaugh, S.P. 1992. Field test of a vertical ground-coupled heat pump in Alabama. ASHRAE ASHRAE American Society of Heating, Refrigerating & Air Conditioning Engineers Transactions 98(2):607-15. Kavanaugh, S.P., and K. Rafferty. 1997. Ground-Source Heat Pumps, Design of Geothermal Systems for Commercial and Institutional Buildings. Atlanta: American Society of Heating, Refrigerating re·frig·er·ate tr.v. re·frig·er·at·ed, re·frig·er·at·ing, re·frig·er·ates 1. To cool or chill (a substance). 2. To preserve (food) by chilling. and Air-Conditioning Engineers, Inc. Presetschnik, A., and H. Huber H. Huber was an Italian luger who competed in the early 1980s. A natural track luger, he won a silver medal in the men's doubles event at the 1981 FIL European Luge Natural Track Championships in Niedernsill, Austria. . 2005. Analysis of a ground coupled heat pump heating and cooling system cooling system: see air conditioning; internal-combustion engine; refrigeration. cooling system Apparatus used to keep the temperature of a structure or device from exceeding limits imposed by needs of safety and efficiency. for a multi-story office building. Proceedings of the 8th International Energy Agency, Heat Pump Conference 2005, pp. 4-8. Kentaro Sekine Ryozo Ooka, DrEng Member ASHRAE Mutsumi Yokoi, DrEng Yoshiro Shiba SuckHo Hwang Kentaro Sekine is a research engineer at the Building Engineering Research Institute Technology Center, Taisei Corporation Taisei Corporation (大成建設株式会社 , Kanagawa, Japan, and Mutsumi Yokoi is a senior engineer at Design Division, Taisei Corporation, Tokyo. Ryozo Ooka is an associate professor and SuckHo Hwang is a graduate student at the University of Tokyo, Japan. Yoshiro Shiba is a deputy manager of the Development Department, Zeneral Heatpump Industry Co., Ltd., Nagoya, Japan.
Table 1. The Measurement Items
Measuring Equipment
Measured Item (Permissible Range) Measurement Point
Subterranean T-type thermocouples Depth: 1 m, 10 m, 19 m
temperature ([+ or -]1[degrees]C)
U-bend surface T-type thermocouples Depth: 1 m, 10 m, 19 m
temperature ([+ or -]1[degrees]C)
Heat source/ Platinum measurement In the pipe
sink water resistor
temperature ([+ or -]0.5[degrees]C)
Cold and hot Platinum measurement In the pipe
water resistor
temperature ([+ or -]0.5[degrees]C)
Water flow Flow meter ([+ or -]2%) In the pipe
Electrical Electric power meter Power panel
power used
Outside temperature, relative humidity, wind velocity, wind direction,
quantity of solar radiation, rainfall
Table 2. Comparison of Cost
Proposed System (Cast-in-Place
Borehole Type Concrete Pile Type) (8 Pairs
Form of Heat Exchange (Single U-Tube) of U-Tubes)
Heat extraction and 40 200
rejection per unit
of heat exchange,
W/m
Boring costs, US$/m 100 --
Piping costs, US$/m 20 71
Additional labor costs -- 87
for foundation and
piling work, US$/m
Total cost, US$/m 120 158
Total cost per 3 0.79
extraction and
rejection heat unit,
US$/W
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