Apparatus for solar hot water system and method of making same

Apparatus for heating and maintaining the temperature of water in a hot water tank of a solar hot water system and method of making same are provided wherein such apparatus comprises a thermally insulating container disposed around and in spaced relation from the tank with the container having a bottom portion defining a sump for a heat transfer liquid employed in the system and a device for maintaining the level of such liquid in the sump beneath the tank during normal system operation to thereby assure maintenance of an air space substantially completely around the tank with the air space cooperating with the insulating container to assure the temperature of water in the tank is maintained with minimum loss; and, the apparatus may also employ a pressure sensitive shut-off device in the cold water supply to the tank which cooperates with the air space to assure operation of the system with substantially no likelihood of contamination of the cold water supply.

BACKGROUND OF THE INVENTION 
Numerous proposals have been made heretofore to provide a solar hot water 
system; however, inherent in such a system is the problem of providing 
efficient heating of the water in a hot water tank of the system and 
maintaining the water heated with minimum heat loss. Another problem 
encountered with a solar hot water system is the necessity of assuring 
that, in the event of failure of system components, a heat transfer liquid 
normally employed in the energy transport subsystem of the overall system 
does not contaminate the cold water supply. 
SUMMARY 
This invention provides an improved apparatus and method of making same 
which basically overcomes the abovementioned problems; and, such apparatus 
provides efficient heating and the maintaining of temperature of water in 
a hot water tank of a solar hot water system comprising a thermally 
insulating container disposed around and in spaced relation from the tank 
with the container having a bottom portion defining a sump for the heat 
transfer liquid and a device for maintaining the level of the liquid in 
the sump beneath the tank during normal operation to thereby assure 
maintenance of an air space substantially completely around the tank with 
the air space cooperating with the insulating container to assure the 
temperature of water in the tank is maintained with minimum loss. 
The apparatus may employ a pressure sensitive shut-off device in the cold 
water supply to the tank which cooperates with the air space to assure 
operation of the system with substantially no likelihood of contamination 
of the cold water supply. 
Other details and advantages of the invention will become apparent as the 
following description of the embodiment thereof in the accompanying 
drawings proceeds.

DESCRIPTION OF ILLUSTRATED EMBODIMENT 
Reference is now made to FIG. 1 of the drawings which illustrates a solar 
hot water system which is designated generally by the reference numeral 20 
and such hot water system employs one exemplary embodiment of a fail-safe 
apparatus of this invention and method of making such apparatus designated 
generally by the reference numeral 21 and as will be described in more 
detail subsequently. The system 20 has a collector subsystem 22, a hot 
water storage subsystem 23 including a hot water tank 24, an energy 
transport subsystem 25 operatively connected between the collector 
subsystem 22 and the hot water storage subsystem 23 and including a heat 
transfer liquid 26. The system 20 also includes the apparatus 21 for 
heating and maintaining the temperature of water 27 in the tank 24 and a 
control subsystem 28 for the collector subsystem 22, the hot water storage 
subsystem 23, the energy transport subsystem 25, and the apparatus 21. 
The various subsystems 22, 23, 25, 28, and apparatus 21 have each been 
designated generally by arrows and each at only a typical location. 
Further, in accordance with standard practice in the art, the control 
subsystem 28 comprises all of the devices and their electrical, pneumatic, 
or hydraulic auxiliaries used to regulate the processes of collecting, 
transporting, storing, and utilizing energy in response to the thermal, 
safety, and health requirements of the building occupants or facility 
employing the system 20. 
The apparatus 21 which may comprise an assembly which will be referred to 
as a tank assembly and designated generally by the reference numeral 29 
comprises a thermally insulating container 30 disposed around and in 
spaced relation from the tank 24 and it will be seen that the container 30 
has a bottom portion 31 defining a sump 32 for heat transfer liquid 26. 
The apparatus 21 also has a device 33 for maintaining the level of the 
liquid in the sump beneath the tank 24 during normal operation of the 
system 20 to thereby assure maintenance of an air space substantially 
completely around the tank 24 even with heat transfer liquid 26 in the 
sump 32 and such air space is indicated generally by the reference letter 
S. The air space cooperates with the insulating container 30 to assure 
that temperature of water 27 in the tank 24 is maintained with minimum 
loss. 
The tank 24 illustrated in FIG. 2 has an inwardly convex bottom wall 35, an 
outwardly convex top wall 36, and a side wall which in this example is in 
the form of a substantially right circular cylindrical side wall 37 
connected between the bottom wall 35 and top wall 36. The bottom wall 35 
is fixed to the side wall 37 by any suitable means such as an annular weld 
40 and similarly the top wall 36 is fixed to the top edge of the side wall 
37 by means such as an annular weld 41 to thereby provide a high strength 
water tight vessel. As is customary for hot water tanks, the tank 24 has 
its inside surface lined with a suitable anticorrosion material such as 
glass or the like and the glass lining is not depicted by cross hatching 
in the drawings but by the single line 42 defining the inside surfaces of 
the walls 35, 36, and 37. 
The apparatus 21 as shown in FIG. 1, also comprises means 43 for 
introducing the heat transfer liquid 26 against the top wall 36 of the 
tank 24 enabling gravity flow of such liquid 26 as a film indicated by 
arrows 44 along the outside surfaces of the top wall 36 and side wall 37 
to thereby provide optimum heat transfer between the liquid 26 and such 
walls and thus optimum heating of the water 27 within the tank 24. The 
introducing means 43 as depicted in FIG. 2, comprises a pan 45 which is 
supported by a pair of brackets 46 having their opposite ends suitably 
fixed to the container 30 and to pan 45 whereby the pan is supported in 
spaced relation above the tank 24 such that upon filling of the pan 45 the 
heat transfer liquid 26 overflows the pan onto the outwardly convex top 
wall 36 and such overflowing is represented schematically at 47 in FIG. 1 
by drops of liquid 26 between the pan 45 and top wall 36. 
The apparatus 21 has a device 33 for maintaining the level of the liquid 26 
in the sump 32 beneath the tank 24 to thereby assure maintenance of the 
air space S completely around the tank 24 as previously mentioned and for 
the purpose previously specified. The device 33 comprises a liquid 
discharge port 50 in the container 30 beneath the bottom wall 35 of the 
tank 24 and the device 33 of the example comprises a transparent sight 
tube 51 made of plastic or glass and tube 51 is in flow communication with 
the port 50. The sight tube 51 has an upper open end 52 which is disposed 
beneath the bottom weld 40 so that in the event of an excessive volume of 
heat transfer liquid 26 in the sump 32 such liquid will flow out of the 
open end 52 and assure the maintenance of the space S completely around 
the tank 24. 
The thermally insulating container 30 of the apparatus 21 in FIG. 2 
comprises an inner fluid tight housing or receptacle 53 which is disposed 
in spaced relation about the entire outer periphery of such tank and an 
outer shroud 54 which is disposed in spaced relation about the entire 
outer periphery of the inner receptacle 53. The container 30 has a 
thermally insulating material 55 disposed between its receptacle 53 and 
shroud 54 and the insulating material is selected such that it provides 
optimum insulation for the hot water 27 in the tank 24. The insulation 55 
cooperates with the air space S (which is essentially a dead air space) to 
provide, in essence, a double insulation for the tank 24. 
The tank assembly 29 has support means which serves as support means for 
the apparatus 21 and tank 24, and such support means comprises a plurality 
of support columns or legs each designated by the same reference numeral 
57. Each support leg 57 has its upper end portion suitably fixed, by 
welding or the like, as shown in FIG. 1 at 58, to a lower portion 60 of 
the cylindrical side wall 37 which extends beneath the bottom wall 35. 
Each support leg 57 shown in FIG. 2 extends in sealed relation through the 
inner receptacle 53 and then through the insulating material 55 and shroud 
54. A fluidtight seal is provided where each leg 57 extends through the 
receptacle and such seal is provided by sealing means such as a 
circumferential weld 61. The welds 61 serve as a means of fastening the 
container 30 to the support legs 57 whereby the entire weight of the tank 
assembly 29 is supported by the support legs 57. Although any desired 
number of legs 57 may be used, a plurality of three legs are used for the 
tank assembly 29 of the example shown in FIG. 2. 
The tank 24 as seen in FIG. 2, the tank 24 has a cold water supply pipe 
section 63 and a hot water discharge pipe section 64 in fluid flow 
communication therewith. The pipe section 63 extends in a fluid tight 
manner through a pipe sleeve 65 fixed by an annular weld 66 to the top 
wall 36 of the tank 24, and section 63 extends a substantial distance 
within the tank 24. Similarly, the hot water discharge pipe section 64 is 
connected in a fluid tight manner to a pipe sleeve 67 which is fixed by an 
annular weld 69 to the top wall 36 of the tank 24. 
The cold water supply pipe section 63 has a controlled pressure device in 
the form of a low pressure shut-off valve 70 suitably fixed to a portion 
thereof which extends outwardly of a top wall 71 of the shroud 30. The 
valve 70 has a suitable connector fitting 72 which is employed to connect 
the valve 70 with a supply pipe 73 from a water source which is to be 
heated. Similarly, the hot water discharge pipe section 64 has a pipe 
sleeve 74 fixed to a portion thereof which extends outwardly of the top 
wall 71. The sleeve 74 has an outer portion which is suitably connected to 
a hot water discharge pipe 75 which supplies hot water from the tank 24 
for use as desired. 
The shut-off valve 70 is of any suitable type known in the art and 
comprises a part of the control subsystem 28; and, the shut-off valve 70 
is set so that it shuts off the flow of cold water into the tank 24 in the 
event of a sufficient drop in low pressure (to 10 psig, for example) in 
the vicinity of the valve 70. 
Thus, it will be appreciated that in the event of a small pin hole or leak 
up stream of valve 70, when during normal operating conditions the 
pressure in the cold water supply pipes, tank 24, and hot water discharge 
pipes is greater than the pressure outside such pipes and outside of the 
tank 24, due to the provision of the air space S completely around the 
tank 24, there can be no back flow of heat transfer liquid 26 into the hot 
water 27. However, in the event of a substantial failure, such as a large 
opening in the tank 24, for example, or a large leak in either the hot 
water discharge pipe system or the cold water supply pipe system, there 
would be a substantial pressure drop downstream of the valve 70. This 
substantial drop would be sensed by the pressure shut-off valve 70 as a 
pressure differential causing automatic shut-off thereof whereby heat 
transfer liquid 26 could not back-up or reverse flow into the hot water 
27, and contaminate same and then be discharged through pipe 75. 
Thus, it will be appreciated that with the apparatus 21 of this invention 
the air space S and automatic shut-off valve 70 cooperate during normal 
operation of the system 20 such that there is substantially no likelihood 
and indeed it is practically impossible for any contamination of the hot 
water 27 by reverse flow of heat transfer liquid 26 to be discharged 
through pipe 75, or to be pulled into the cold water water line due to 
fluid line pressure drops. 
While the controlled pressure device in the described example is a shut-off 
valve 70, such device may be of course embodied by still other forms, such 
as a pressure switch which would operate to shut down energy transport 
subsystem 25, when the pressure in the cold water supply pipe 63 drops 
below a predetermined level. 
The tank assembly 29 may be sold as a self-contained assembly for quick 
installation in an overall solar hot water system which has a collector 
subsystem 22, energy transport subsystem 25, and control subsystem 28 of 
any desired type. To enable easier installation in an existing system 20 
the pipe sections 63 and 64 are illustrated as extending through the 
container 30. It will also be appreciated that other connections are 
provided, as necessary, from the other subsystems of the overall system 20 
to the tank assembly 29; and, although such connections may be made in a 
similar manner as shown in FIG. 2 for pipe sections 63 and 64 so that all 
connections may be made outside of the shroud portion 54 of container 30, 
in this disclosure not all connections are shown made in this manner and 
as will now be described. 
The control subsystem 28 has hot water temperature control means 75 for the 
water 27 in tank 24. The control means 75 includes a temperature sensitive 
device, such as a thermocouple or a termister, such as thermocouple 76 
disposed within the tank 24 having suitable connections extending through 
side wall 37 in a fluid-tight manner to a differential temperature 
controller 77. The controller 77 is also connected to another temperature 
sensitive device, such as thermocouple 80, operatively connected to the 
collector subsystem 22. In operation, the controller 77 compares the 
temperature of the water 27 with that of the collector subsystem 22, and 
if the temperature of the collector subsystem 22 is higher than that of 
the water 27 by some predetermined amount, such as by 10.degree. or 
15.degree. F., the controller activates a pump 79 of energy transport 
subsystem 25 to start circulation of the heat transfer liquid 26 through 
the collector subsystem 22 and through a conduit 81 which discharges into 
the pan 45 as illustrated at 82. In the example illustrated in FIG. 2, the 
terminal discharge end of the conduit 81 is fixed in a fluid-tight manner 
to a sleeve 83 which is welded and thus sealed in a fluid flow 
communication with receptacle 53 by an annular weld 84. Once activated, 
pump 79 will continue to operate until the temperature difference between 
the collector subsystem 22 and the water 27 drops to a second 
predetermined level, such as about 2.degree. or 3.degree. F., at which 
point the controller 77 will operate to shut the pump 79 off. The 
controller 77 may also house an adjustable control dial 78 (schematically 
illustrated in FIG. 1) for setting the difference in temperature between 
the collector subsystem 22 and the water 27 that will activate and 
deactivate the energy transport subsystem 25 as described. 
The conduit 81 in FIG. 1 has air vent arrangement 85, such as a float 
valve, operatively connected to the upper end portion thereof by a conduit 
section 86 and an air line 87 extends between the vent 85 and an assembly 
90, in this case a T-fitting, which has a conduit section 91 connected as 
shown in FIG. 2 in a fluid-tight manner to a sleeve 92 which is fitted to 
tank 24 by an annular weld 93 or other acceptable means. The assembly 90 
in FIG. 1 has a plug 94 or other acceptable means which enables the heat 
transfer liquid 26 to be introduced into the sump 32 by gravity flow 
through conduit section 91. The components 85 and 90 comprise the control 
subsystem 28 and, in the example, vent 85 serves to vent the air space S 
so that it is maintained at ambient pressure. 
The container 30 in FIG. 1 may have a pressure relief valve 96 which is 
part of the control subsystem 28. The valve 96 is connected to a conduit 
section 97 which as shown in FIG. 2 is sealed to a sleeve 98 which is in 
turn sealed by an annular weld 100 to the inner receptacle 53. The 
pressure relief valve 96 provides for relief of pressure within receptacle 
53 in the event there is an excessive buildup of pressure for any reason. 
It will be appreciated, however, that any necessary pressure relief would 
in all likelihood be afforded by the open-end glass 51, described below. 
Thus valve 96 would except in the most extra ordinary of circumstances be 
unnecessary. 
The pump 79 of the energy transport subsystem 25 may be of any suitable 
type known in the art and such pump is operatively connected to sump 32 by 
a pipe section 103 which is connected as shown in FIG. 2 to a tubular 
sleeve 104 which is sealed by an annular weld 105 to the inner receptacle 
53. The pump 79 may be provided as an integral part of the tank assembly 
29 and has a suitable fitting 106 (FIG. 1) provided thereon for connection 
to a conduit 107 comprising the energy transport system. 
It will also be appreciated that sight glass 51 may be supplied as an 
integral part of the tank assembly 29 and such sight glass may be 
connected to the port 50 by a suitable connector assembly 110 shown in 
FIG. 2 extending between the port 50 and the sight glass 51. The assembly 
110 has an inner portion sealed in flow communication with the receptacle 
53 by an annular weld 111 and an outer portion detachably fixed to the 
shroud 54 of the container 30. The outer portion may have a suitable 
fitting 112 for receiving an inner end portion of sight glass 51 in sealed 
and fluid flow relation therewith. 
The heat transfer liquid 26 may be any suitable heat transfer liquid known 
in the art for a solar hot water system. Similarly, a suitable inhibitor 
may be provided in the heat transfer liquid to prevent corrosion of the 
components that such liquid comes into contact with. For example, in 
applications where the liquid 26 is used with aluminum or steel 
components, it will be appreciated that a suitable inhibitor may be 
provided in the heat transfer liquid 26 to prevent corrosion of such 
aluminum or steel components. 
This invention provides an improved apparatus, and method of making same, 
for heating and maintaining temperature of water in a hot water tank of a 
solar hot water system and the water being heated may be tap water that is 
used in the ordinary home for the usual purposes of drinking, cooking, 
bathing, and the like. Similarly, it will be appreciated that this 
invention may be employed to heat a liquid used strictly in a solar space 
heating system, or to heat swimming pool water, and the like. The volume 
of heat transfer liquid 26 in the sump 32 is controlled by the device 33 
in the form of open-end sight glass 51. The volume of heat transfer liquid 
26 in such sump is sufficient to provide all the heat transfer liquid that 
is necessary for the collector subsystem 22 as well as provide a 
sufficient pressure head, indicated in FIG. 1 at 113, to assure proper 
operation of the pump 80. 
This invention takes advantage of the fact that the heat transfer liquid 26 
flows over the tank 24 in what may be considered a turbulent film which 
provides a scrubbing action along the walls of the tank 24 and thus 
provides optimum heat transfer to the walls of the tank and in turn 
creates sufficient convective movement of the water 27 to provide an 
optimum heat transfer to the water 27 within the tank 24. 
While present embodiments of this invention, and methods of practicing the 
same, have been illustrated and described, it will be recognized that this 
invention may be otherwise variously embodied and practiced within the 
scope of the following claims.