GB2070744A

GB2070744A - Hot water storage tanks

Info

Publication number: GB2070744A
Application number: GB8006830A
Authority: GB
Original assignee: Panetta B F
Current assignee: Panetta B F
Priority date: 1980-02-28
Filing date: 1980-02-28
Publication date: 1981-09-09

Abstract

The invention is concerned with dinsulation means for insulating hot water tanks and comprises a heater jacket which surrounds the tank. The heater jacket preferably comprises a pipe 11 coiled around the tank 4 and through which pipe hot water is curculated. There is at least one layer 12 of an insulation material between the heater jacket and the atmosphere and preferably the heater jacket is sandwiched between two layers 10, 12 of insulation material. The invention is particularly suitable for use in food processing plants in which refrigeration apparatus is used, heat given off by such apparatus being used to heat the water in the storage tanks and the water in the heater jacket. <IMAGE>

Description

SPECIFICATION Insulating means for storage tanks The invention relates to a method and means for insulating tanks for the storage of heated liquids.

It is known to insulate hot water storage tanks by surrounding the outer walls of the tank with a layer of an insulating material such as rockwool or a plastics material such as expanded polystyrene. While the heat loss from a tank so insulated will be much less than with an unlagged tank it will nevertheless be quite considerable, for example in the region of 25 to 30 watts per square metre where the insulating layer has a thickness of about 1 50 mm.

It is an object of the invention to provide insulating means for storage tanks of improved insulating efficiency.

According to the invention insulating means for storage tanks comprises a heater jacket surrounding at least a substantial part of the outer wall surface of the tank and at least one layer of an insulating material between said jacket and the atmosphere. Preferably, the jacket is sandwiched between two layers of insulation, a first layer being located between the outer wall surface of the tank and the jacket, and a second layer between the jacket and the atmosphere.

The heater jacket may comprise an electrically heated blanket or an electrically heated element in the form of a cable coiled about the tank. However, in accordance with a preferred embodiment the jacket is of such a construction that a heated fluid can be circulated therethrough. Preferably, the jacket is in the form of a heater coil and may comprise a pipe, for example a plastics pipe, coiled about the tank through which pipe a heated liquid is circulated.

Some embodiments of the invention are hereinafter described with reference to the accompanying drawings, wherein: Figure 1 is a sectional elevational of a hot water storage tank with insulating means according to the invention; Figure 2 is a section one the line 2-2 of Fig. 1 to an enlarged scale; Figure 3 is a sectional view similar to that of Fig. 2 but showing a temperature gradient; and Figure 4 is a diagrammatic illustration of the circuit of a refrigeration system used to supply heat to a storage tank and insulating means.

Referring to Figs,. 1 and 2 of the drawings, a hot water storage tank 1, which may be rectangular in plan, or of cylindrical shape, comprises a top wall 2, a bottom wall 3, and a side wall or walls 4. The bottom wall 3 of the tank rests on an insulated base 5. The base 5 is suitably comprised of an expanded polystyrene material of high compressive strength such as that sold under the trade name "Styrofoam". The tank is provided with an inlet 6 and an outiet 7 which may be connected to a heat exchanger as described hereinafter in relation to Fig. 4.

The tank is also provided with a cold water inlet 8 and a hot water outlet 9.

The insulating means of the invention comprises a first layer of insulation 10 which is wrapped around the side wall 4 and top wall 2 of the tank and is attached thereto by adhesive tape or other suitable means in well known manner. A heater coil 1 7 which suitably comprises heat-resistant flexible plastics piping is wound around the insulation layer 10 in the region of the side wall 4 and forms a flat coil lying on the top wall 2.A second layer 1 2 of insulating material is positioned between the heater coil 11 and the atmosphere such that the heater coil 11 is sandwiched between the layers of insulating material 10 and 1 2. A sheet of suitable cladding material 1 3 is attached to the outer surface of the layer 1 2. The layers 10 and 1 2 suitably comprise rockwool although other insulating materials such as expanded polystyrene, glassfibre wool or cellular glass insulation of the kind sold under the Trade Mark "Foamglas" may be utilised. Where rockwool is used the first insulation layer 10 suitably has a thickness of about 50 mm while the outer layer 1 2 has a thickness of about 1 50 mm.

In use the temperature of the water in the tank 1 is heated to a desired temperature. A fluid, which may be water, and which is at a temperature above ambient temperature, is circulated through the coil 11. Provided that the temperature of the circulating fluid is above ambient temperature then the heat loss from the water in the tank will be less than would be the case if only conventional insulation of the same thickness as the combined layers 10 and 1 2 were used. If the temperature of the circulating fluid in the coil 11 is the same temperature.as that of the water in the tank 1 then the heat loss from the tank 1 will be negligible. This may be illustrated by reference to Fig. 3 which shows the temperature gradient through the insulating means.Assuming that the temperature of the water in the tank and the water circulated in the coil 11 is 65"C and that the ambient temperature is 1 5 C then the heat loss may be calculated as follows: t, = 65"C t2 = 65"C k value for rockwool = 0.067 w/m C External surface coefficient = 3.0 3/m2 "C t4 (ambient) = 15 C Heat loss from heater coil Resistance to heat flow dx R= -) k 0.150 R1= = -- = 2.238 0.067 R2=- = .33 3 RT = 2.568 At 65-15 0 =- = ~~~~ = 19.470 w/m2 RT 2.568 Intermediate temperatures 50 t2-t3 = ---- x 2.238 = 43.57 2.568 ::.surface temperature t3 = 65-43.57 = 21.3to It is within the scope of the invention to omit the first layer 10 of insulation in which case the heater coil 11 is positioned against the outer surface of the walls 2 and 4 of the tank. The insulation obtained with this arrangement is not as good as that obtained with the arrangement where two layers of insulation are used as described above with reference to Figs. 1 and 2.

Nevertheless, it does provide a more efficient form of insulation than with conventional methods. For example, l have found that where the water in the tank and the water circulated in the heater coil 11 is at 65"C and the outer layer 1 2 consists of rockwool of a thickness of 1 50 mm, the heat loss from the tank is of the order of 19.47 w/m2.

The insulation means of the invention is particularly suitable for use in food processing plants, such as meat factories and creameries, where a constant supply of hot water is required, and where large refrigeration units are used. Thus, in accordance with another aspect of the invention, surplus heat from a refrigeration plant is used to heat water in the tank 1 and also water which is circulated through the heater coil 11. This arrangement is illustrated in Fig. 4 which shows the circuit of a compression refrigerator. The refrigeration circuit contains a refrigerant which may be ammonia, ethyl chloride or Freon.The refrigerator operates in well known manner, that is the refrigerant which has evaporated in an evaporator 14 located in a cold room and so absorbs heat from the cold room is passed to a compressor 15 where it is compressed and passed to a condenser 16 where it gives of heat and condenses to the liquid state. The refrigerant in the vicinity of the condensers will typically be at a temperature of between 93 and 1 20'C. Water in the tank 1 is heated by pumping the water, by means of a pump 17, through a heat exchanger 18 positioned at the condenser 1 6. The water circulating in the heater coil 11 is heated by pumping it, by means of a pump 19, through a heat exchanger 20 located on the refrigerator circuit between the compressor 15 and the condenser 1 6.

Preferably, the arrangement is used to heat water in a batch of storage tanks 1 and these can be heated in sequence by using a suitable valve arrangement. In such a case the hot water in one storage tank is maintained in the heated state by the insulating means of the invention while the water in the remaining tanks is being heated.

It will be appreciated that as an alternative to circulating hot water through the heater coil 11, the heat exchanger 20 can be dispensed with and the refrigerant is pumped directly through the heater coil which effectively becomes part of the refrigeration circuit. The fluid used to heat the heater coil 11 need not necessarily be a liquid and in some situations it may be possible to use hot gases such as flue gases.

While the invention is particularly suitable for maintaining large volumes of water at a high temperature, it may also be used to insulate domestic hot water tanks. For such a use the fluid heater coil is replaced by an electrically heated jacket such as, for example, an electrically heated blanket or coiled element.

Claims

1. Insulating means for storage tanks comprising a heater jacket surrounding at least a substantial part of the outer wall surface of the tank and at least one layer of an insulating material between said jacket and the atmosphere.

2. Insulating means as claimed in claim 1, wherein the jacket is sandwiched between two layers of insulation, a first layer being located between the outer wall surface of the tank and the jacket, and a second layer between the jacket and the atmosphere.

3. Insulating means as claimed in either of the preceding claims, wherein the jacket is of such construction that a heated fluid can be circulated therethrough.

4. Insulating means as claimed in claim 3, wherein the jacket comprises a pipe coiled about the tank and through which pipe a heated fluid is circulated.

5. Insulating means as claimed in claim 1 or claim 2, wherein the jacket comprises an electrically heated blanket or an electrically heated coiled element.

6. A method of maintaining the temperature of a heated liquid stored in a storage tank above ambient temperature using insulating means as claimed in either of claims 3 or 4, which comprises circulating through the jacket a liquid which is at a temperature above ambient.

7. A method as claimed in claim 6, wherein the liquid in the storage tank and the liquid in the jacket is heated by means of surplus heat extracted from a refrigeration system.

8. Insulating means as claimed in claim 3 or 4, wherein the jacket is in fluid communication with a heat exchanger connected to a refrigeration circuit.

9. Insulating means as claimed in claim 3 or 4, wherein the jacket is in fluid communication with a refrigeration circuit such that hot refrigerant may be circulated through the jacket.