JPH0339839A - Heat insulating structure for bottom of tank - Google Patents

Abstract

PURPOSE:To produce an enough heat insulating effect by a method wherein a frame body is mounted to the bottom of a tank body, a space part surrounded with the frame body and the bottom is filled with a heat insulating material, and a shield member is attached on the under surface of the frame body to shut off the space part, filled with the heat insulating material, from the outside of the frame body. CONSTITUTION:A heat accumulating tank is securely supported and fixed to three lines of base concrete 8 through a support frame 9. A base plate 11 made of stainless serving as a shield member having approximately the same diameter as that of the support frame containing an upper flange part 9e is placed on the support frame 9, and a frame body 12 is placed on the base plate 11. A space part formed in the frame body 12 with a chord part 13b on the body side and a reinforcing part 13c on the body side is filled with a heat insulating material 14 made of foamed styrene resin. The space part, formed with an oblique piece 21b, a bottom plate 15, and a peripheral edge part 13a on the body side, of the support plate 21 is filled with a heat insulating material 22 made of foamed styrene resin. Since the space part is filled with the heat insulating material, heat accumulated in the heat accumulating tank is difficult to escape through the space to the outside, and a heat insulating effect can be improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a heat storage tank used as a heat storage tank for large-scale air conditioning equipment such as office buildings and hospitals. This relates to a heat retention structure.

[Conventional technology]

Traditionally, this type of air conditioning equipment has consisted of an ice maker that takes in water and produces ice, a heat storage tank that serves as a tank to store the ice, and the ice stored in the heat storage tank or hot water generated from the ice maker. The ice storage tank is equipped with a heat exchanger that performs heat exchange by sending ice stored in the heat storage tank to the heat exchanger to perform a cooling effect, and hot water generated during ice making by the ice maker to the heat exchanger to provide a heating effect. I try to do the following.

[Problem to be solved by the invention]

However, since the heat storage tank is partially formed of concrete in the basement of a building, etc.,
The problem is that sufficient heat insulation measures have not been taken to begin with.

In particular, since the bottom of the heat storage tank, which is the bottom of the tank, is shared with the floor of the building, it is not thick enough to provide a sufficient heat retention effect.

Therefore, an object of the present invention is to provide a heat retaining structure for the bottom surface of a tank that can obtain a sufficient heat retaining effect.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a frame on the bottom of the tank body, fills a space surrounded by the frame and the bottom with a heat insulating material, and also provides a shielding member on the bottom of the frame. A means is employed in which the space filled with the heat insulating material is isolated from the outside of the frame.

[Effect]

The bottom of the tank body is provided with a space that is isolated from the outside of the frame by the frame and the shielding member, and the space is filled with heat insulating material, so that the heat stored in the heat storage tank is It is difficult for the heat to escape through this part to the outside, and the heat retention effect is the same as above.

Furthermore, the heat retention effect is further improved by using wood with low thermal conductivity as the frame and partitioning the frame into a plurality of spaces.

〔Example〕

An embodiment embodying this invention is shown in FIGS. 1 to 18 below.
This will be explained according to the diagram.

First, to explain the outline of the air conditioning equipment of this embodiment, as shown in FIG.
It is equipped with a heat storage tank 1 as a tank for storing this ice R, and an air conditioner 3 that takes in the ice R stored in the heat storage tank 1 and exchanges heat. Heat storage tank 1
A water suction pipe 4 for taking water therein into the ice maker by a pump (not shown) and a discharge pipe 5 for sending ice produced by the ice maker 2 back into the heat storage tank are connected to each other. A supply pipe 6 for taking in ice from the heat storage tank 1 is connected to the heat storage tank 1 and the air conditioner 3 by a pump (not shown), and the air conditioner 3 receives high temperature water after heat exchange. A water pipe 7 is connected to return the water to the heat storage tank 1.

As shown in FIGS. 3 and 4, the heat storage tank 1 is formed into a cylindrical shape with a planar cross-sectional shape in the inside of the tank, and is attached to a three-strip basement concrete 1 installed in the roof of a building. - 8 are supported and fixed via support frames 9 and 7.

As shown in FIGS. 1 and 7, the support frame 9 is placed on the squonk 1.1-)=8,,,)- and is provided with an upper flange portion 9e and a lower flange portion 9f.・
i-ta cross section horizontal channel! A peripheral edge part 9a made of a steel material having a cylindrical shape as a whole, and - within this peripheral edge part 9a.
- A plurality of guard parts 9b made of a steel material with an n-shaped cross section are constructed at regular intervals, and a guard part 9 is installed between these arc parts 9b.
It is composed of a plurality of reinforcing parts 9C having a reverse cross section and installed at regular intervals so as to be orthogonal to It is designed to form a flat surface. The peripheral edge portion 9a is divided into four parts, and the ends are butted against each other and a reinforcing member is applied from the inside, and the four parts are integrated by the pole 1- and a nut. A plate-shaped fixing portion 9d extending inward in the axial direction of the peripheral edge portion 9a is attached to a portion of the peripheral edge portion 9a, which is approximately in the middle of the abutting portion, between the rows of the lower flange portion 9f; The support frame 9 is secured by nuts to the foundation bolts 10 protruding from the base concrete 8 at this fixing portion 9d.
is supported and fixed to pace concrete l.8.

As shown in FIGS. 1 and 8, a stainless steel substrate 11 serving as a shielding member is placed on the support frame 9 and has a diameter that is approximately the same as the diameter including the upper flange portion 9o. , a frame 12 is placed on this substrate ll. The frame body 13 has a wooden body-side peripheral part 13a that is concentric with the upper flange part 9e of the peripheral part 9a, and a position within the main body-side peripheral part 13a that corresponds to the monitoring part 9b and the reinforcing part 9C. A main body side string part 13b and a main body side reinforcement part 13c, also made of wood, are arranged orthogonally to each other.
Each of these is made of quadrangular prism-shaped wood. In the frame 12, a space defined by the main body side chord part 13b and the main body side reinforcement part 13c is filled with a heat insulating material 14 made of expanded styrene resin. , the upper end surfaces of the main body side reinforcement part 13c and the main body side technical part 13b form the same plane.

A stainless steel bottom plate 15 is placed on the frame 12 and has a regular dodecagonal shape.
, a space surrounded by the frame 12 and the base ville is cut off from the outside of the frame 12.

A cylindrical stainless steel tank body 16 is placed at a predetermined distance inwardly from each side 16a constituting the outer edge of the bottom plate 15. As shown in FIG. 5, the tank body 16 is formed by stacking a total of four stainless steel cylinders with the same diameter and the top one being half the height of the other three cylinders. . The flange parts 17 of each cylinder that contact each other are welded with wedges at equal intervals on the outer surface of the tank body 16, which is the joint part thereof, and the abutting parts are welded and fixed on the inner surface of the tank body 16. has been done.

The lower end of the tank body 16 is fixed to the bottom plate 15 by welding, and a fixing member 18 having a cross-section extending outward in the axial direction is welded to the outer periphery of the lower end. The heat storage tank 1 is connected and fixed to the support frame 9 by passing a bolt 19 through the space between the support frame 18 and the upper flange portion 9e and fastening the napht 20 thereto. Although not shown, the fixing member 18 is provided with reinforcing ribs at regular intervals.

As shown in FIG. 1, a support plate 21 is provided between each side 15a constituting the outer edge of the bottom plate 15 and the outer edge of the substrate 11.
are connected. The support plate 21 consists of a vertical piece 21a extending upward from the side 15a and a diagonal piece 21b extending diagonally downward from the side 15a.
The distal end portion b is clamped and fixed between the substrate 11 and the main body side peripheral portion 13a. Diagonal piece 21b of the support plate 2 construction
The space surrounded by the bottom plate 15 and the main body side peripheral portion 13a is filled with a heat insulating material 22 made of expanded styrene resin. Furthermore, on the inside of the vertical piece 21a of the support vi21, that is, on the side corresponding to the tank body 16, there is a heat insulation panel 23, which will be described later.
The lower end of the lowest heat insulation panel 23 is positioned and supported.

As shown in FIGS. 1, 3, and 4, a lagging layer 24 made of foamed styrene resin is sprayed along the shape of the tank body 16, and a plurality of lagging layers 24 are formed on the surface of the tank body 16. Heat-insulating panels 23 made of stainless steel are attached to cover the entire side surface of the tank body 160. As shown in FIGS. 11 and 12, the heat insulation panel 23 is formed into a regular square shape in the front having the same length as each side 15a of the bottom plate 15, and has an approximately hemispherical shape in the center. A convex portion 23a is formed. Both left and right edges of the heat insulation panel 23 are bent inward at acute angles, and as shown in FIG. The trajectory drawn by 23 is approximately circular. As shown in FIGS. 1, 9, and 10, on the inside of the heat-retaining panel 23 facing the tank body 16, there is a foamed polyethylene resin plate that is curved to follow the side shape of the tank body 16. A heat insulating member 25 is fitted to form a space between the tank body 16 and the heat insulating panel 23 that is shut off from the outside. The heat retaining panel 23 is fastened to a mounting bolt 23b protruding from the side surface of the layer body 16.

As shown in FIGS. 2 to 6, the water suction pipe 4 connected to the ice maker 2 and the supply pipe 6 connected to the air conditioner 3 are installed through the lower side of the tank body 16. A lower inspection port 26 with a double glass structure for inspecting the inside of the tank is provided at a height that can be recognized by the operator. Similarly tank body 16
The discharge pipe 5 extending from the ice maker 2 passes through a position above the water suction pipe 4 and the supply pipe 6 on the lower side surface of the ice maker 2 .

As shown in FIG. 4, the discharge pipes 5 are composed of four pipes with closed ends, and are arranged parallel to each other in the fitted heat storage tank 1. A plurality of upward elongated holes 27 are formed at regular intervals in the direction.

In order to prevent turbulence in the lower part of the tank due to the flow rate of the ice R being discharged, the long hole 27 is designed so that when the ice R discharged from the long hole 27 rises by 1 m, the influence of the flow rate on the surrounding area disappears. The hole portion is formed to the calculated size.

Incidentally, in this example, the cross-sectional area of the vibrator is set to 50-1.
The flow rate Q of ice R in the pipe is 140t/mln, and the pipe has a width of 2a11. Three elongated holes 27 each having a length of 50,011 mm are provided. Therefore, the area A of the discharge hole constituted by the elongated hole 27 is calculated as A-(0,5XO,02)x3-=0.03rrf, and the initial flow velocity vO of ice R from the discharge hole is Vo- Q
/A, it is calculated as 0.078 m/s. From here, assuming that the powder flow constant in the stationary fluid is 3.5 (experimental value), the flow velocity of ice R at a position where the distance χ from the discharge hole is 1 m is Um
When asked for, Um-(3,5XUo)/Su 71-01-2.73X
10 m/s Therefore, the ice R discharged from the elongated hole 27 becomes a laminar flow that does not affect the surroundings inside the tank due to its flow velocity at a position 1 m higher.

Note that the discharge pipe 5 is fixedly supported in a horizontal state by a support rod 28 having a tip end of each vibrator erected from the bottom plate 15.

As shown in FIGS. 13 and 14, the tip of a first fall prevention member 29 is welded and fixed to the intermediate side of the tank body 16, and the base end of the first fall prevention member 29 is fixed to the concrete beam A. It is bolted on.

The tip of a second fall prevention member 30 is welded and fixed to one side of the tank body 16 180 degrees opposite to the first fall prevention member 29 near the upper end of the tank body 16. The base end of the member 30 is bolted to the concrete beam B. Since the beam B is provided farther away from the outer peripheral surface of the tank body 16 than the beam A, the arm of the second anti-overturn member 30 is more distant than the arm portion 29a of the first anti-overturn member 29. 30a is formed longer.

As shown in FIGS. 3, 5, and 6, an upper inspection port 31 similar to the lower inspection port 26 is provided on the upper side surface of the tank body 16, that is, the uppermost cylindrical portion. Photosensor windows 32 are provided at two positions where a straight line extending horizontally through the approximate center point of the planar section of the main body 16 intersects with the upper side surface of the main body 16 . The uppermost cylindrical portion is penetrated by a water supply pipe 7 disposed from the air tank 3 and a refrigerant water supply pipe 33 for sending water after heat exchange.

A top plate 34 having an umbrella-shaped cross section is fitted onto the upper edge of the tank body 16, and its peripheral edge is welded and fixed to the tank body 16. As shown in FIG. 6, on the upper surface of the top plate 34, the upper end of a post 35, which will be described later, is exposed at the center, and manholes 36 as internal inspection entrances are provided on all sides around the post 35.

On both sides of the manhole 36 on the upper surface of the top plate 34, a thermovibrator for detecting the hot water temperature in the tank and a preliminary hole 38 for detection have their upper ends exposed. Although not shown, a lagging layer made of expanded styrene resin is applied to the upper surface of the top plate 34 in the same way as the side surface of the tank body 16, and a covering plate 39a made of stainless steel is coated thereon as shown in FIG. has been done. A handrail 39 is provided on the periphery of the upper surface of the covering plate 39a, and a handrail ladder 40 connected to the handrail 39 extends downward along one side of the tank body 16. There is.

In addition, the central part of the heat storage tank l is shown in Figures 4, 5, and 15.
As shown in the figure, a cylindrical support 35 is erected from the bottom plate 15 to pass through the top plate 34. A vibrator 37 for detecting the temperature inside the tank is erected on one side of the heat storage tank 1 in parallel with the support column 35, passing through the bottom plate 15 and the top plate 34. A ventilation hole 4 is provided at the upper end of the support column 35 exposed above the top plate 34.
1 is provided, and an opening 43 is formed at the lower end of the support column 35 at a joint portion with a support member 42 that fixedly supports the support column 35 with respect to the bottom plate 15.

In the heat storage tank 1, the upper part of the support column 35 has a structure shown in FIG.
As shown in FIG. 18, a main water sprinkling plate 44 is attached which closely fits into the inner peripheral surface of the tank body 16 in a horizontal state.
Further above, a multi-number water plate 45 having a tray-shaped cross section and a smaller diameter than the main water spray plate 44 is attached at its center. The main water sprinkling plate 44 is above the installation position of the upper inspection port 31 and the optical sensor window 32 provided on the upper side of the tank body 16, and is also located above the installation position of the water supply pipe '33.
and located below the penetration position of the water pipe 7, and the tank body 1
It is spot welded onto an angle 46 installed between the inner circumferential surfaces of 6. Above the numerical water plate 45, a water inlet 7a of a water pipe 7 branched into two in the heat storage tank 1 is arranged so as to be able to inject water.

An overflow hole 47 is provided between the main water spray plate 44 and the differential water plate 45 in the support column 35 . In this embodiment, it is provided at a position above l0C11 from the main water sprinkling plate 44. A communication hole 48 is provided in the support column 35 at a position immediately below the main water sprinkling plate 44 . The ventilation hole 41, overflow hole 47, communication hole 48, and opening 43 are in communication with each other, and the support column 35 also functions as an overflow vibe and a vibe for regulating negative pressure inside the tank body 16. It has become. The pillar 3
5, an inner cylinder 49 is provided between the communication hole 48 and the opening 43.
The gap between the inner circumferential surface of the support column 35 and the outer circumferential surface of the inner tube 49 is filled with foamed polyurethane resin 50 to form a double structure.

The main sprinkler plate 44 is formed by dividing the planar shape of the heat storage tank 1 and is composed of ten punching boards 51, and the joint surface between each punching board 51 and the joint surface with the inner circumferential surface of the tank body 16 are Spot welded.

In addition, 52 is a support through hole for passing the support 35 through, 53 is a through hole for a thermovib for temperature detection,
54 is a preliminary through hole. Further, 55 is an inspection hole located below the manhole 36.

Each punching board 51 constituting the main water sprinkling plate 44 has a main drip hole 5 formed from above in a tapered cross-section with a small diameter.
G is provided. This main pilot hole 56 is a hole for uniformly dropping water onto the water surface in the heat storage tank 1, and the water that is injected from the water pipe 7 onto the main water spray plate 44 via the multi-number water plate 45 and stagnant therein is The size and number of holes are calculated to maintain the water level between 4fi and 10cs and ensure uniform dripping.

Incidentally, in this embodiment, the diameter of the main water spray plate 44 is 3.55.
0 m, the diameter of the main drip hole 56 is 6 countries, and the water sprinkling amount Q is set to a maximum of 22001/ml n and a minimum of 44011/min, and the drip hole 56 for uniform dripping is arranged as follows. are doing.

That is, assuming that the flow coefficient C is 0.76 (experimental value), the area A of the main drip hole 56 is 2.83×10 ♂, and the water level height H on the main water spray plate 44 is 0.1 m, the amount per unit of the main drip hole 56 is The water sprinkling amount Q is determined from Q, -CAa1 ear, and then the number N of main drip holes 56 is determined from N-Q/Q. The result of that calculation is Q + = 1,
8071/min-N-1217 pieces. Then, the pinch P in the arrangement pattern as shown in FIG. 17 is determined using D="1.15PN, and
The pinch P between them is 901m.

In addition, the number of holes that can be calculated as described above is 1222.
each punching board 5 pieces but spot welded
Considering leakage from one gap, 1096 main drip holes 56 are actually provided.

Further, in the numerical water plate 45 provided on the main water sprinkling plate 44 , an opening hole 57 having a tapered cross section is used to drip water that has been injected from the water inlet 7 a of the water pipe 7 and stagnated onto the main water sprinkling plate 44 .
Twelve opening holes 57 are provided, and the opening holes 57 are formed to have a larger diameter than the main drip hole 56.

Next, the functions and effects of the air conditioning equipment configured as described above will be explained.

First, water supplied from the water supply pipe 33 and stored in the heat storage tank 1 is sent to the ice maker 2 via the water supply pipe 4. Ice maker 2
The ice R generated is discharged into the lower part of the heat storage tank 1 through the elongated hole 27 of the discharge pipe 5.

When the projected ice R rises 1 m from the elongated hole 27, its flow velocity becomes almost 0, and thereafter it flows upward in a laminar flow due to the difference in specific gravity between the water and the ice R. Therefore, no turbulence occurs in the lower part of the heat storage layer 1, and since the ice R flows upward, cold water is always stored below the discharge pipe 5.

At this time, the discharge pipe 5 has elongated holes 27 facing upward in the elongated direction at regular intervals on the upper side of the circumference of the pipe whose tip is closed, so that the ice R remains at the mainstream velocity from the tip of the discharge pipe 5. Since the ice R is discharged upward from the elongated hole 27 without being blown out while suppressing the main flow velocity, the ice R can be caused to flow upward in a laminar flow without causing turbulence in the heat storage tank 1.

Therefore, it is possible to prevent mixing of the high-temperature part and the low-temperature part in the tank and maintain an appropriate temperature distribution, and since cold water can always be stored below the discharge pipe 5, heat usage efficiency can be increased.

From this state, the cold water in the lower part of the heat storage tank 1 is sent to the air conditioner 3 via the supply pipe 6. At this time, since the heat storage layer 1 has a cylindrical shape inside the tank, the ice R and cold water in the tank flow as a whole and no part of it stagnates, making the tank internal capacity 100% effective. can be used. Moreover, by making it cylindrical, if the volume is the same, the installation area can be reduced by increasing the height of the tank body structure 6, and the temperature distribution inside the tank can be divided into upper and lower high-temperature parts and low-temperature parts, so there is no uneven temperature distribution. Good heat exchange can be achieved.

Moreover, when the cold water in the lower part of the heat storage tank 1 is sent out of the tank via the water suction pipe 4 or the supply pipe 6, the water level in the tank decreases accordingly. Then, the space above the water surface in the tank becomes negative pressure, but the air vent 4
1 and communication hole 48, and is communicated with the outside air to adjust the negative pressure.

When the heated water passes through the air 11 machine 3 and is injected onto the differential water plate 45 through the water inlet 7a of the water pipe 7, the water flows from the sub-groove lower hole 57 onto the main water sprinkler plate 44. At the same time as being dripped, the water that has accumulated on the main water sprinkling plate 44 is dripped uniformly over the entire surface of the tank from the main dripping holes 56. At this time, the numerical water plate 4
5 and the main water spray plate 44, the water can be dripped more stably and uniformly over the entire water surface in the heat storage tank 1, and as a result, the water is dripped with the ice R at the top of the tank. It is possible to uniformly, efficiently and quickly exchange heat between the heated and warm water.

When the water remaining on the main water spray plate 44 reaches a predetermined height (10 cm in this embodiment) that exceeds the dripping capacity, overflow water passes through the overflow hole 47 of the support post 35 and into the heat storage tank. Since the cold water flows out through the opening 43 to the cold water side in the lower part of the interior of the water bottle 1, an appropriate dripping state can be maintained at all times through the main water sprinkling plate 44.

When all the water on the main water sprinkling plate 44 is dripped, the main drip hole 56 is blocked by a curtain of water due to the surface tension of the remaining water. At this time, since the main drip hole 56 has a tapered cross section with a small diameter at the top, only the small diameter portion above the main drip hole 56 is blocked, and as a result, cold air from below inside the tank is blocked. When frozen, only the upper part of the main drip hole 56 in the depth direction is frozen. Therefore, when water whose temperature has newly become higher is dripped onto the main water spray plate 44, the freeze is easily released.

When the water level in the heat storage tank 1 rises to the level immediately below the main water spray plate 44, that is, when the volume of ice R increases too much, the optical sensor detects this through the optical sensor window 32, and the ice maker 2 restrict the operation of

Heat storage P! The bottom plate 15 of l has the bottom plate 15 and the frame 12
A space is provided which is shielded from the outside of the frame body 12 by the substrate 11, and a heat insulating material 1 is provided in the space.
4, it becomes difficult for the heat stored in the heat storage tank 1 to escape to the outside through this part, and the heat retention effect is improved. Further, by using wood with low heat conductivity as the frame 12 and partitioning the inside of the frame 12 into a plurality of spaces, the heat retention effect can be further improved,
Wood is a more flexible material than concrete, so it absorbs shock and has a vibration-proofing effect.

The heat insulation panel 23 protects the tank body 16 from external shocks.
At the same time, the lagging layer 24 of the tank body 16 and the heat insulation member 25 provided inside the heat insulation panel 23 prevent the heat stored in the heat storage tank 1 from being released to the outside, thereby achieving a heat retention effect. can be improved. Furthermore,
Since an air layer is provided between the heat retaining member 25 and the lagging N24, the heat retaining effect is further improved.

Note that the present invention is not limited to the above embodiments,
For example, it is also possible to make changes as shown below.

(1) The number of the main body side string parts 13b and the main body side reinforcement parts 13C can be arbitrarily changed.

(2) Changing the material of the heat insulating material 14 to glass wool or the like other than the foamed polyethylene resin of this embodiment.

〔effect〕

As described in detail above, according to the present invention, in the heat insulation structure of claim 1 characterized by the following specific effects, there is a space on the bottom surface of the heat storage layer that is shielded from the outside of the frame by the frame and the shielding member. Since the space is provided with a heat insulating material and the heat insulating material is filled in the space, it becomes difficult for the heat stored in the heat storage tank to escape to the outside through this part, thereby improving the heat retention effect.

In the heat retaining structure of claims 2 and 3, the heat retaining effect can be further improved by using wood with low heat conductivity as the frame and partitioning the frame into a plurality of spaces.

[Brief explanation of drawings]

Figure 1 is a sectional view of the bottom of the heat storage tank showing the main parts of the present invention, Figure 2
The figure is a schematic diagram of an air conditioning equipment embodying the present invention, Figure 3 is a front view of a heat storage tank, Figure 4 is a sectional view taken along line A-Ai in Figure 3,
Fig. 5 is a front view from Fig. 3 with the exterior such as a heat insulation panel removed, Fig. 6 is a plan view of Fig. 5, Fig. 7 is a plan view of the support frame, Fig. 8 is a plan view of the frame body, 9 is a front view of the heat insulation member, FIG. 10 is a plan sectional view of FIG. 9, FIG. 11 is a front view of the heat insulation panel, FIG. 12 is a plan sectional view of FIG. 11, and FIG.
The figure is a schematic side view showing the installation position of the fall prevention member.
The figure is a plan view of Fig. 13, Fig. 15 is a partially cutaway sectional view of the heat storage tank, Fig. 16 is a plan view showing the main water sprinkling plate and the numerical water plate in Fig. 15, and Fig. 17 is the main water sprinkling plate. Plan view, No. 18
The figure is a partially enlarged sectional view of FIG. 17. Substrate 11 as a shielding member, frame 13, main body side peripheral part 1
3a, main body side string part 13b, main body side reinforcement part 13C1 heat insulating material 14, bottom plate 15 as a bottom surface, tank main body 16°

Claims (1)

[Claims] 1. A frame (12) is provided on the bottom (15) of the tank body (16), and a heat insulating material ( 14), and a shielding member (11) is provided on the lower surface of the frame (12) to isolate the space filled with the heat insulating material (14) from the outside of the frame (12). Features a heat-retaining structure on the bottom of the tank. 2. The frame (12) has a main body side peripheral portion (13a) having a size approximately equal to the outer diameter of the bottom surface (15), and a main body side peripheral portion (13a) arranged in a grid pattern within this main body side peripheral portion (13a). String section (1
3b) and a main body side reinforcing portion (13c). 3. The tank bottom heat retention structure according to claim 1, wherein the frame body (12) is made of wood.