Device for accumulation tanks for fluid

Method and device for maintaining and reinforcing in an accumulation tank a stratified condition of fluid caused by the fluid in the tank when a flowing of the fluid is caused by heating the same. The portion of the fluid in the tank that is to be heated is separated from the fluid in the tank prior to the heating and the heated fluid is permitted to ascend through a liquid column separated from the fluid in the tank and is conducted back into the tank at the fluid-layer that has substantially the same temperature as the heated fluid. The device comprises an accumulation tank in which a tube is arranged substantially vertically from the bottom thereof towards its upper part and the tube receives separated heated fluid which is allowed to ascend through the tube. The tube is provided with openings one after the other along the tube constituting outlets for the heated fluid.

The present invention relates generally to accumulation tanks for fluid, 
and more particularly to a device for such tanks for stratified 
accumulation of fluid, where the stratification is determined by the 
varying temperatures in the accumulated fluid. 
Accumulation tanks of the kind to which the present invention relates are 
primarily intended for storing heated water in house heating, which water 
in turn is used for the actual heating of houses, e.g. with common water 
radiators, and for heating household water. Such accumulation tanks are 
primarily meant for storing heat energy, which is obtained intermittently 
and/or with varying intensity and which can be withdrawn rather uniformly. 
The range of application of the invention is, however, not limited to 
heating but can successfully be extended to include other areas, e.g. 
within the process industry where there is a demand for 
temperature-stratified fluid-storing. 
There is presently a desire that solar energy should be usable for heating 
purposes in combination with other sources of energy. However, solar 
energy is provided intermittently as well as with varying intensity, 
whereby the intermittent provision to the greatest extent is dependent 
upon the periodic alternation of day and night, while the varying 
intensity to the greatest extent is dependent upon the relationship 
between sunny and cloudy weather. 
Heretofore all of the supplied energy has been taken up in the form of 
heated fluid, whereby the fluid itself or another material, e.g. sand or 
rock, has constituted the storing material. As long as the solar energy 
has given a higher fluid temperature than the temperature in the storing 
material this energy has been assimilated while the system has been shut 
off if the solar energy has not given such a temperature. 
To improve the heat exchange by the heat transfer from the solar heating 
system to the fluid in an accumulation tank it has recently become more 
and more common to use so called heat pumps. No effort has, however, been 
made in constructing the accumulation tank, and this has simply 
represented a fluid reservoir in which the fluid has been free to 
circulate. The withdrawal of heat from the fluid in the tank has taken 
place at the top of the tank, either through heat exchange or through a 
direct withdrawal of fluid, and this has resulted in that the fluid in the 
tank has been caused to circulate and in that the difference in 
temperature between the upper part of the tank and its bottom has been 
relatively small. The fact that the heated fluid has been fed directly to 
the tank or has been in a heat interchanging relationship with the fluid 
in the tank at the lower part of the tank contributes to the circulation 
in the tank. It has been desired to obtain as high a temperature as 
possible in the hot water that is withdrawn from the tank for use as 
household water or for heating purposes. Preferably the temperature of 
this water must not fall below 50.degree. C. but this has earlier not been 
possible to achieve as the mixing in the tank has lowered the temperature 
of the fluid or water in the tank, which has possibly been heated to a 
high temperature, during its rising in the tank. To remedy this it has 
been common to supply additional heat, e.g. by means of an electrical 
cartridge heater. However, it is advantageous to obtain hot water with a 
temperature preferably above 50.degree. C. without such an arrangement of 
additional heat. For heating purposes it is also advantageous if it is 
possible to withdraw fluid of a relatively high temperature. 
The present invention is intended to eliminate the drawbacks of the prior 
art system and to obtain the objects and advantages mentioned above. This 
is accomplished with a device according to the claims.

The accumulation tank 1 in FIG. 1 consists of an impervious heat-insulated 
container 2, from the bottom 3 of which a tube 4 extends upwardly and 
terminates adjacent to the cover 5 of the tank 1. The tube 4 is provided 
with openings 6 which are arranged one after the other and is open at the 
upper end. A pipe 7 extends from the bottom 3 of the container 2 to a 
solar energy collector 8 and a pipe 9 extends from the solar energy 
collector 8 back to the container 2 and has its orifice at the lower end 
of the tube 4. 
A circulation pump is preferably inserted in either of the pipes 7 or 9, 
but in principle the system also works due to so called thermosiphon 
circulation in which case no circulation pump is needed. 
In the accumulation tank 1 there are furthermore provided outlets for 
heated fluid which are not shown in FIG. 1. The system illustrated in FIG. 
1 preferably contains a so called anti-freezing fluid, as there is 
otherwise a danger of bursting due to frost during winter, and in this 
case the withdrawal of the heat energy stored in the accumulation tank 1 
is accomplished by means of heat exchangers. The system is preferably 
filled with fluid except for a small air-cushion, which is necessary for 
allowing the fluid to expand in relation to its heating. 
In the solar energy collector 8 the fluid that flows from the bottom of the 
tank 2 through the pipe 7 is heated and the heated fluid flows into the 
lower end of the tube 4. It is not necessary that the tube 4 fits tightly 
against the bottom 3 but the heated fluid should be led into the tube 4 
and should not be allowed to flow up around the outer side of the tube 4. 
The accumulation tank should have a relatively large volume so that the 
fluid flow from the tank to the solar energy collector and back does not 
cause any noticable turbulence in the fluid in the tank. 
The tube 4 constitutes an ascending pipe through which the heated incoming 
fluid ascends to the same extent that a corresponding quantity of fluid 
flows out through the pipe 7. The tube 4 is provided with openings 6 
uniformly spaced along its length. The heated fluid ascends in the tube to 
the level of the opening where the temperature of the fluid in the tank 1 
substantially corresponds to the temperature of the ascending fluid, and 
there the fluid flows out through the opening. 
This means that the warmer the fluid is that flows in through the pipe 9 
the higher it ascends in the tube 4 before it flows out through the proper 
opening 6. If cooler fluid enters it does not ascend to the same level and 
the result is that the fluid-layer above this cooler fluid-layer is not at 
all affected by the fluid that enters through the tube 4. Thus it has 
become evident that a fixed stratification is maintained in the 
accumulation tank by a device as presently described, and that this 
stratification is dependent upon the temperature differences in the fluid, 
in which the upper layer is the warmest. 
The accumulation tank illustrated in FIG. 2 consists of a heat-insulated 
container 10, which at the bottom has a chamber 11 from which an ascending 
pipe 12 extends upwardly towards the cover 13 of the container 10. The 
wall 14 of the chamber 11 as well as the pipe 12 are heat-insulated. The 
chamber 11 is in communication with the rest of the interior of the tank 
through an opening 15. 
In the chamber 11 there are two heat-exchanger loops 16, of which one may 
be part of a circuit provided with a solar energy collector, and the other 
may be part of a circuit for a heat pump. In this system the fluid from 
the heating-circuits is insulated from the fluid in the container 10, 
which means that the fluid in the container may be used directly in e.g. 
heating-or hot water-systems. The container is naturally provided with 
discharges (not shown) for the heated fluid and may also comprise heat 
exchangers for the withdrawal of thermal energy. 
The circulation in the container 10 goes on in substantially the same quiet 
way as in the container 2 in FIG. 1. The fluid in the chamber 11 is heated 
through heat exchange at the loops 16 and ascends through the tube 12 to 
the level where the temperature of fluid in the container 10 is 
substantially the same as the temperature of the ascending fluid, and 
flows out through the proper opening 17 in the tube 12. At the same time 
fluid flows into the chamber 11 through the opening 15. 
In principle the openings in the ascending pipe may simply consist of a 
hole in the tube wall. However, FIG. 3 illustrates a preferred embodiment 
of these openings where they are formed as small nozzles 20 which give the 
fluid that flows out of these nozzles a slightly directed movement that 
preferably coincides with the rounded configuration of the container. It 
has appeared that such a movement of the outflowing fluid causes less 
turbulence than a flow directed straight outwardly. 
FIG. 4 of the drawings shows the principles for a heating system for houses 
in which an accumulation tank according to the present invention is 
included. The accumulation tank 1 consists of a vertical section 30 and a 
horizontal section 31, whereby the horizontal section constitutes an 
additional storing section of the tank 1. In connection with the tank 1 
there is provided a solar energy collector 32 and a heat pump 33, and 
outlets to a heating system indicated by a water radiator 34 and a 
hot-water system 35. 
An ascending pipe 36 rises through the vertical section 30 of the tank 1, 
and is provided with openings 37, in the same manner as in the above 
described embodiments. The ascending pipe 37 extends from a chamber 38 at 
the bottom of the tank 1. 
A vertical wall 55 extends from the bottom of the tank and terminates just 
under the horizontal part 31 of the cover of the tank. This wall 55 
prevents the cold fluid in the lower part of the horizontal section 31 of 
the tank from entering into the lower part of the vertical section 30 of 
the tank. Since the heat pump 33 draws heat from the fluid in the 
horizontal section 31 of the tank, the fluid in this section has a 
relativley low temperature, which is advantageous when it concerns a fluid 
that shall be supplied to the solar energy collector 32 for heating, but 
is on the other hand disadvantageous if this cooled fluid should enter 
into the vertical section 30 of the tank where the object is to keep the 
temperature as high as possible. 
It is also possible to have the two sections of the tank completely 
separated from each other as two separate units, which are interconnected 
by pipes. This would hardly give any functional advantages but might on 
the other hand simplify the installing of the set up. 
The circulation system in connection with the solar energy collector 32 is 
closed so that it may contain anti-freeze fluid and also includes a 
circulation pump 39. The fluid is heated in the solar energy collector 32 
and is conducted through a pipe 40 and through a change-over valve 41 to a 
heat-exchanger cell 44 in the horizontal storing section 31 of the tank. 
From the heat-exchanger cell 44 the fluid is then conducted back to the 
solar energy collector 32 through a pipe 45, in which the circulation pump 
39 is arranged. If the fluid from the solar energy collector 32 has a 
relatively low temperature the valve 41 is preferably adjusted so that the 
fluid passes by the heat-exchanger cell 42 in the chamber 38 and is 
conducted directly through the heat-exchanger cell 44 since the fluid, if 
its temperature is not sufficiently high, will counteract the heating 
accomplished through the system that is provided with the heat pump 33. 
The heat pump 33 is thus provided with a loop 46 which leads to a heat 
exchanger cell 47 at the upper part of the horizontal storing section 31 
of the tank. The heat pump 33 absorbs heat from the fluid in the storing 
section 31 of the tank through this heat exchanger cell 47 and emits this 
heat through a heat exchanger cell 48, which is inserted in a pipe-loop 49 
from the heat exchanger 33, in the chamber 38. 
It is true that the temperature of the fluid in the storing section 31 is 
lowered through this arrangement but the temperature of the fluid in the 
vertical section 30 of the tank is raised and it is desired to keep the 
temperature as high as possible in that section. 
As illustrated the fluid in the tank may be used directly for heating 
purposes. A pipe 50 extends from the upper part of the tank 1 and a 
circulation pump 51 inserted in this pipe pumps the hot fluid through 
radiators and the like, which is marked by the radiator 34. The return 
fluid then flows through a pipe 52 back to the storing tank 31. 
The reference number 35 marks a pipe from a heat exchanger 53 for the 
heating of household hot-water, whereby cold water is supplied to this 
heat exchanger through pipe 54. The pipe 54 passes through the storing 
section 31 for pre-heating of the water before it reaches the heat 
exchanger 53, which is positioned in the upper part of the vertical 
section 30 of the tank, where the fluid in the tank has its highest 
temperature. 
The system may comprise various valves and temperature sensors for 
automatic change-over and best possible exchange of heat. There may also 
be additional heating arrangements that are connected when need arises, 
e.g. electrical cartridge heaters or oil-driven heating arrangements. Such 
measures are however evident for anyone skilled in the art and will not be 
discussed further in this connection. 
Through the invention it is achieved that the fluid in the tank is kept 
well stratified dependent upon its temperature, in spite of the fact that 
thermal energy is continuously withdrawn and supplied, which has 
previously resulted in a levelling out of the temperature of the fluid to 
a substantially equal temperature of the fluid in the upper part of the 
tank and the fluid at the bottom of the same. With the present invention 
it has thus become possible to withdraw even comparatively hot water for 
household use, which has previously been difficult to accomplish without 
special measures.