JP2008309382A - Heat pump utilizing groundwater and ground heat - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that a temperature difference of heat to be collected is small since a heat pump may be frozen when the groundwater of a heat pump system utilizing the groundwater is used as a heat source of the heat pump, and further the total length of an underground heat exchanger is increased since the quantity of heat absorbed from the ground is small when the brine is used as heat source water in a heat pump system utilizing ground heat, thus causing a cost increase. <P>SOLUTION: The brine is used as the heat source water of a water heat source heat pump. The brine absorbs heat from the groundwater and the ground in a returning well-groundwater well heat exchanger, and further exchanges heat with the groundwater in a water-water heat exchanger to absorb heat from the groundwater. Further a returning well-groundwater well device constituted by inserting an U-tube heat exchanger into the returning well for returning the groundwater to an original groundwater vein of the groundwater extracted from the groundwater vein, charging a water permeable filler material between the outside of the U-tube and a casing, and holding a cover for preventing the overflow of water from a ground surface is used. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a groundwater-based heat pump system and a ground heat-based heat pump.

The conventional groundwater-based heat pump system pumps up groundwater (well water) and uses it as a heat source for a water heat source (water-cooled) heat pump, and the groundwater after heat exchange is returned to a reduction well to prevent ground subsidence (for example, Non-patent document 1). There are a method of directly using ground water as a heat source of the heat pump and a method of exchanging heat between the ground water and brine with a water-water heat exchanger and using the brine as a heat source of the heat pump.
In addition, the heat pump system using ground heat absorbs heat from the ground using a ground heat exchanger such as a U tube or a coaxial heat exchanger (for example, see Non-Patent Document 2).
“Geothermal” Vol. 39, No. 1, 2002, p. 63 “The Journal of the Geothermal Society of Japan” Vol. 27, No. 4, 2005, p. 263

However, when the groundwater of the heat pump system using groundwater is directly used as the heat source of the heat pump, there is a risk of freezing of the evaporator in the heat pump, so the temperature difference that can be collected is small. For example, the temperature after the groundwater has absorbed heat from the heat pump is normally set to about 5 ° C., and if the temperature is lower than this temperature, there is a risk of freezing in the heat pump due to a sudden power failure or the like. In addition, even in a system that exchanges heat between groundwater and brine, if the brine temperature falls below freezing point, groundwater may freeze due to a sudden power failure. Further, if the capacity of the water-water heat exchanger is increased, the amount of heat that can be used increases, but the cost of the heat exchanger increases accordingly.
In the case of a heat pump system using geothermal heat, brine is used as the heat source water. However, since the amount of heat that can be absorbed from the ground is small, the total depth of the underground heat exchanger is increased, resulting in an increase in cost.

Brine is used as the heat source water for the water-cooled heat pump, and the brine absorbs heat from the groundwater and the ground in a heat exchanger that also serves as a reduction well and a geothermal heat well, and further exchanges heat with groundwater in the water-water heat exchanger. And absorbs heat from groundwater. In addition, in order to return the groundwater extracted from the groundwater vein to the original groundwater vein, a U-tube heat exchanger is inserted into the reduction well having a casing having a mesh in the groundwater vein portion, and water is transmitted between the outside of the U-tube and the casing. The reduction well and the geothermal heat according to claim 2, wherein the heat is absorbed from the ground and the groundwater to be reduced, which is filled with a filler such as silica sand and has a lid that prevents water from overflowing from the surface. The problem is solved by the method of claim 1 in which a heat exchanger that also serves as a well is used.

According to the present invention, by exchanging heat of groundwater with a water-water heat exchanger and further exchanging heat with a heat exchanger that also serves as a reduction well and a geothermal heat well, the heat pump of the heat pump is compared with the conventional heat pump system using groundwater. The amount of heat that can be used as a heat source can be increased, and furthermore, the amount of heat collected per depth of the same underground heat exchanger can be increased as compared with a heat pump system using underground heat.
In the groundwater heat pump system, groundwater extracted from the extraction well needs to be reduced to the ground so that there is no impact on land subsidence. However, according to the present invention, the original groundwater extracted from the groundwater vein by the casing and mesh is used in the reduction well. Groundwater can be returned to the groundwater vein, and a U tube that indirectly exchanges heat is also installed in the reduction well, so forced convection heat transfer between the groundwater reduced water and the U tube and heat collection from the ground It can also be used as a ground heat exchanger having a larger amount of heat collected per unit depth than a conventional ground heat exchanger.
For this reason, the total cost of a reduction well and a geothermal well can be reduced.
In this way, groundwater is heat-exchanged twice with a water-water heat exchanger and further with a reduction and underground heat well to collect heat, resulting in a larger amount of heat collection than a system with only a water-water heat exchanger. .

  As shown in FIG. 1, the invention according to claim 1 of the present invention includes a water heat source heat pump 1, an extraction well 2, a water-water heat exchanger 4, a reduction and underground thermal well 3, groundwater piping and brine connecting them. It is a pipe. When viewed from the groundwater side, the groundwater is extracted from the extraction well 2 by the pump 6, dissipates heat through the water-water heat exchanger 4, is distributed to the plurality of reduction and geothermal wells 3, flows in the casing and It passes through the permeable filler outside the U tube 13 and flows to the original groundwater vein 15. Install a lid so that groundwater does not overflow from the surface part of the reduction and geothermal well 3. When viewed from the brine side, the brine is circulated by the pump 5 and radiated by the heat exchanger 7 in the heat pump, and then distributed and flows to the U tube 13 of the reduction and underground thermal well 3 to absorb heat from the groundwater and underground. The water gathers on the ground, absorbs heat from the groundwater by the water-water heat exchanger 4, returns to the pump 5, and repeats this.

  The invention according to claim 2 of the present invention has a casing 16 in a well, a mesh 17 in a lower portion, a lid 19 in a ground surface portion, and a U tube 18 in the casing as shown in FIG. A reduction well in which the U-tube 18 and the casing 16 are filled with a water-permeable filler 40 to reduce the groundwater, and the U-tube 18 can absorb heat from the groundwater. It can have the characteristics of both geothermal wells, and more heat can be collected per unit depth than a normal underground heat exchanger.

(Embodiments of the invention described in claims 1 and 2 of the present invention)
FIG. 3 shows an embodiment of the invention described in claim 1 and claim 2 of the present invention.
FIG. 3 shows an embodiment when heating and cooling are performed. The brine piping 36 is distributed and connected to a plurality of water heat source heat pumps 25. The number of reduction and underground thermal wells 26 can be adjusted according to the amount of well water reduction.

  First, the heating will be described. Here, the water heat source heat pump 25 is a direct expansion system, and the air conditioner 29 during heating is a condenser.

Considering the groundwater as the center, the groundwater is extracted from the extraction well 27 by the well pump 30, dissipated by the heat exchanger 32, distributed by the groundwater piping 34, enters the reduction and underground heat well 26, and the water permeability in the casing The heat is absorbed from the underground 43 through the filler 35 having the property, and is radiated to the U tube 38, and returns to the original underground water vein 44. At this time, it is preferable that the groundwater well 26 is located downstream from the extraction well 27 with respect to the extraction well 27 so that the groundwater after heat exchange is not extracted again from the original extraction well 27.

  For example, if the underground temperature is assumed to be 10 ° C, the groundwater temperature is considered to be 10 ° C. The groundwater of 10 ° C. is pumped up from the extraction well 27 and radiated to 5 ° C. by the water-water heat exchanger 32, passes through the groundwater piping 34, and further radiated by the reduction and underground heat well 26, and the temperature is lowered. At this time, a part of the heat is absorbed from the underground 43, but the amount of heat released to the U tube 38 is larger. The calculation results will be described later.

Pay attention to the flow rate and the permeability of the filler so that it does not fall below freezing when it is below freezing before it reaches the underground waterway in the casing. In addition, when the well pump is stopped due to a power failure or the like, the brine in the U tube may be below freezing, so the area around the U tube may freeze slightly, but there is a water flow due to groundwater reduction due to gravity. In addition, it is considered that the temperature recovers because heat is absorbed from the ground, and further, since the groundwater circuit is an open circuit, there is almost no influence of expansion due to freezing.

  Considering the brine as the center, the brine is conveyed by the brine pump 31, dissipated heat by the evaporator 42 of the water heat source heat pump 25, distributed by the brine pipe 37, and reduced to the U tube 38 in the geothermal well 26. Then, it returns to the ground, passes through the brine pipe 39, further absorbs heat in the water-water heat exchanger 32, returns to the brine pump 31 and repeats this.

  For example, the brine inlet temperature of the evaporator 42 of the water heat source heat pump 25 is 5 ° C., the outlet temperature is −5 ° C., the heat is absorbed by the U tube 38 to 0 ° C., the heat is absorbed by the water-water heat exchanger 32 and 5 ° C. It becomes.

  Unless heat exchange is performed for the water-water heat exchanger, the water heat source heat pump, the reduction, and the underground heat well in this order, a high heat source temperature cannot be ensured.

  Next, the cooling time will be described. Here, the water heat source heat pump is a direct expansion system, and the cooling air conditioner 29 is an evaporator.

  Considering groundwater as the center, groundwater is extracted by a well pump 30, absorbs heat by a water-water heat exchanger 32, is distributed by a groundwater pipe 34, enters a reduction and geothermal well 26, and is permeable in the casing. The heat is dissipated to the ground 43 through the filler 35 having the heat and absorbed from the U tube 38 to return to the original underground water vein 44.

  For example, when the underground temperature and the groundwater temperature are assumed to be constant 10 ° C. throughout the year, the ground water is pumped up to 10 ° C. from the extraction well 27 and is absorbed by the water-water heat exchanger 32 to 15 ° C. After passing through the groundwater pipe 34, the heat is further absorbed by the reduction and underground well 26 and the temperature rises and returns to the groundwater vein 44. At this time, some heat is dissipated to the ground 43, but the amount of heat absorbed from the U tube 38 is larger. The calculation results will be described later.

  Similarly, considering the brine as the center, the brine is conveyed by the brine pump 31, absorbs heat by the condenser 42 of the water heat source heat pump 25, and is distributed by the brine piping 37, and the U tube in the reduction and geothermal well 26. The heat is radiated at 38, returned to the ground, further radiated by the water-water heat exchanger 32 through the brine pipe 39, and returned to the brine pump 31 to repeat this.

  For example, the condenser brine inlet temperature of the water heat source heat pump is 20 ° C., the outlet temperature is 30 ° C., heat is radiated by the U tube 38 to 25 ° C. on the ground, and the water-water heat exchanger 32 absorbs heat to 20 ° C. .

  Thus, if this invention is used, it is possible to use the water heat source heat pump which can be switched between cooling and heating.

  As for the brine piping, the brine may be water as long as the underground temperature is high and the freezing temperature is not reached.

The reduction of claim 2 and the heat collection effect of the underground heat exchanger are calculated by a simple method.

First, for the purpose of comparison, the amount of heat collected by a normal U-tube underground heat exchanger is calculated.
The U tube is sufficiently long compared to the inner diameter of the tube, and the calculation of the U portion at the tip is ignored. Further, although there are two U tubes, for the sake of simplicity, it is regarded as one virtual tube having the same pipe thickness with the same cross sectional area as the total of the cross sectional areas of the two inner diameters. Further, the temperature of the virtual tube is constant as the average temperature of the inlet and outlet of the U tube.
As shown in FIG. 4, the pipe (thermal conductivity λ1 [W / m · K], a portion from the distance r1 [m] to r2 [m] from the center) and soil (thermal conductivity λ2 [W / m · K], The amount of heat φ [W / m] passing through the cylindrical surface having a unit length of a distance r2 [m] to r3 [m] from the center is expressed by Equation 1 using Fourier's law. Here, the temperature is t1 [° C.] at the pipe inner surface r1, the temperature is t2 [° C.] at the pipe outer surface r2, the temperature is t3 [° C.] at the soil radius r3.

Soil temperature 10 ° C, soil diameter 5.5m, soil thermal conductivity 2.0W / m · K, U tube inner diameter 27mm, U tube wall thickness 3.5mm, U tube thermal conductivity 0.42W / M · K, inlet temperature −5 ° C., outlet temperature 0 ° C., the amount of heat collected per virtual tube per meter was 28 W / m.

ここで、ｒ：中心からの距離、λ：熱伝導率、ｔ：温度
仮想チューブ（ｒ１≦ｒ≦ｒ２、λ＝λ１）
地下水部分（ｒ２≦ｒ≦ｒ３、ｔ＝ｔ２＝ｔ３）
ケーシング（ｒ３≦ｒ≦ｒ４、λ＝λ３）
土壌（ｒ４≦ｒ≦ｒ５、λ＝λ４）
（仮想チューブ内表面ｒ１での温度（＝地中熱温度）はｔ１［℃］、仮想チューブ外表面ｒ２で温度はｔ２［℃］、ケーシング内表面ｒ３で温度はｔ３、土壌半径ｒ５で温度はｔ５［℃］とする） Next, the reduction of Claim 2 and the heat collection effect of the underground heat exchanger are calculated.
The U tube is sufficiently long compared to the inner diameter of the tube, and the calculation of the U portion at the tip is ignored. Further, although there are two U tubes, for the sake of simplicity, it is regarded as one virtual tube having the same pipe thickness with the same cross sectional area as the total of the cross sectional areas of the two inner diameters. Further, the temperature of the virtual tube is constant as the average temperature of the inlet and outlet of the U tube. Up to this point, it is the same as an ordinary U tube.
There is a permeable filler inside the casing and outside the virtual tube, and groundwater flows. Groundwater dissipates heat to the virtual tube and absorbs heat from the ground. In the calculation, 1 m is divided in the depth direction, and the water temperature is assumed to be constant within the section. In addition, the heat transfer resistance between the groundwater and the inner surface of the casing and the heat transfer resistance between the groundwater and the outer surface of the virtual tube are ignored because they are sufficiently small. In addition, the heat conduction of the filler is ignored because heat is transferred to the groundwater. The amount of heat absorbed from the ground and the amount of heat released to the virtual tube are reflected in the water temperature at the next 1 m. By repeating this, the depth of the reduction well is calculated.
The amount of heat obtained from the soil to the groundwater is φs [W / m], the amount of heat given from the groundwater to the virtual tube is φu [W / m], the amount of heat given to the groundwater portion is φw [W / m], and the amount of heat collected from the virtual tube is φ [W / m] is expressed by Equation 2 using Fourier's law.

Here, r: distance from the center, λ: thermal conductivity, t: temperature virtual tube (r1 ≦ r ≦ r2, λ = λ1)
Groundwater part (r2 ≦ r ≦ r3, t = t2 = t3)
Casing (r3 ≦ r ≦ r4, λ = λ3)
Soil (r4 ≦ r ≦ r5, λ = λ4)
(The temperature at the virtual tube inner surface r1 (= ground heat temperature) is t1 [° C.], the temperature is t2 [° C.] at the virtual tube outer surface r2, the temperature is t3 at the casing inner surface r3, and the temperature is at the soil radius r5. t5 [° C])

As with a normal U-tube underground heat exchanger, the soil temperature is 10 ° C., the soil diameter is 5.5 m, the soil thermal conductivity is 2.0 W / m · K, the U-tube inner diameter is 27 mm, and the U-tube thickness is The thermal conductivity was 3.5 mm, the U tube thermal conductivity was 0.42 W / m · K, the inlet temperature was −5 ° C., and the outlet temperature was 0 degrees.
Also, the casing heat transfer rate is 50 W / m · K, the casing inner diameter is 150 mm, the casing thickness is 10 mm, the porosity γ of the permeable filler is 10%, the reduced well water amount Q is 25 L / min, and the well water passes through the casing. The cross-sectional area is a value obtained by subtracting the U-tube outer cross-sectional area (for two single tubes) from the casing inner area. Assuming that the specific heat of the well is 1 kcal / L and the specific gravity is 1 kg / L, the temperature at which the well goes down by 1 m is φw × 0.86 / (60Q) [° C.].
The results of calculating this up to a depth of 100 m are summarized in Table 1, Table 2, FIG. 5 and FIG.
Tables 1 and 2 show the temperature of well water, the temperature difference between well water and geothermal heat (brine), the amount of well water radiated (to the geothermal brine), soil and well water, up to 100 m per depth Temperature difference, well water endotherm (from soil), and temperature drop (well water). It can be seen that the well water temperature decreases as it travels through the casing. When the well water temperature decreases, the temperature difference from the geothermal brine becomes small, so the amount of well water radiated to the geothermal brine decreases. The well water endotherm increases. However, since the well water heat dissipation amount is larger than the well water heat absorption amount, the well water temperature generally decreases as shown in FIG.
The average value of the amount of heat collected from the geothermal brine of the reduction and geothermal well is shown in FIG. When the depth is 100 m, it is 86 W / m. Under these conditions, it has been found that a heat collection amount of three times or more can be obtained as compared with a normal U-tube underground heat exchanger.

  Similar calculations can be made for cooling.

  The water heat source heat pump can be used not only in a direct expansion system but also in a heat pump chiller that generates cold water and hot water.

Since these calculations estimate the steady state and can estimate the state at the maximum load peak, they are useful for designing the heat source capacity of groundwater and underground heat pump systems.

The present invention is useful for air conditioning, hot water supply, floor heating, bathtub heating, pool heating, and snow melting on roads and parking lots.

It shows the groundwater piping and brine piping connecting the water heat source heat pump, the extraction well, the water-water heat exchanger, the reduction and the underground thermal well, and the ground water piping, which is the invention described in claim 1 of the present invention. The invention according to claim 2 of the present invention has a casing in the well, a mesh in the lower part, a lid in the ground part, a U tube in the casing, the U tube and the casing In the meantime, an apparatus (reduction and geothermal well) having both the characteristics of a reduction well and a geothermal well filled with a water-permeable filler is shown. The Example of the invention of Claim 1 and Claim 2 of this invention is shown, The heat pump system in the case of utilizing an air conditioning is shown. In the figure, temperatures not in parentheses are examples of groundwater, brine, and underground temperatures during heating, and temperatures in parentheses are examples of groundwater, brine, and underground temperatures during cooling. The figure for calculating the amount of heat collection of a normal U tube underground heat exchanger. The graph of an example of the result of having calculated the well water temperature in the depth at the time of using the reduction | restoration which is invention of Claim 2 of this invention, and a geothermal hot well. The graph of an example of the result of having calculated the average amount of heat collection according to the depth at the time of using the reduction | restoration and underground thermal well which are inventions of Claim 2 of this invention.

Explanation of symbols

1 Water heat source heat pump 2 Extraction well 3 Reduction and underground heat well (casing)
4 Water-water heat exchanger 5 Brine pump 6 Well water pump 7 Heat exchanger (evaporator or condenser)
8 Groundwater piping 9 Groundwater piping 10 Brine piping 11 Brine piping 12 Brine piping 13 U tube (brine piping)
14 Underground 15 Groundwater veins 16 Casing part 17 Mesh part 18 U tube (brine piping)
19 Lid 20 Groundwater piping 21 Brine piping (out)
22 Brine piping (return)
23 underground 24 groundwater veins 25 water source heat pump 26 reduction and underground thermal well 27 extraction well 28 refrigerant pipe 29 indoor air conditioner 30 well water pump 31 brine pump 32 water-water heat exchanger 33 groundwater pipe 34 groundwater pipe 35 permeability Filling material and groundwater 36 Brine piping 37 Brine piping 38 U tube (brine piping)
39 Brine piping 40 Permeable filler and groundwater 41 Permeable filler and groundwater 42 Evaporator and condenser 43 Underground 44 Groundwater veins

Claims (2)

In the heat pump system, brine is used as the heat source water of the water heat source heat pump, the brine absorbs heat from the ground water and the ground in the heat exchanger that also serves as the reduction well and the underground heat well, and further in the water-water heat exchanger A method of absorbing heat from groundwater by exchanging heat with groundwater.
In order to return the groundwater to the original groundwater vein extracted from the groundwater vein, a U-tube heat exchanger is inserted into the reduction well having a casing with a mesh in the groundwater vein portion, and water is transmitted between the outside of the U-tube and the casing. The reductive well and the geothermal heat well of claim 1 that absorbs heat from the ground and the groundwater to be reduced, having a lid that prevents the water from overflowing from the ground surface, and is filled with a filler having a property. apparatus.

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