Heat storage means for solar heating system

An improved pebble bed heat storage means is provided for a solar heating system using air as the heat transfer medium. The pebble bed is confined in a crib or bin contained in an outer housing. The sides of the bin are air pervious and are spaced from the side walls of the housing to define enlarged plenum chambers. Baffles or partitions divide each of the plenum chambers into upper and lower plenum spaces. An upper warm air inlet is provided for the upper plenum space at one side of the pebble bed and is connected by a duct to the outlet from the solar collector panels. An upper warm air outlet is provided at the upper plenum space at the opposite side of the pebble bed and is connected through a conventional furnace with the room space to be heated. A lower cool air inlet is provided for the lower plenum space at the same side of the pebble bed as the upper warm air inlet and is connected to the room space by a cool air return duct. A lower cool air outlet is provided at the lower plenum space at the same side of the pebble bed as the upper warm air outlet and is connected by a blower and a duct to the inlet of the solar collector panels.

This invention relates to a novel and improved solar heating system. More 
particularly, the invention relates to a novel and improved means for heat 
storage and air circulation in a solar heating system using air as the 
heat transfer medium. 
A conventional solar heating system of the type using air as the heat 
transfer medium has roof mounted collector panels and a heat storage 
means, usually a large bin of pebbles or rocks at ground level or in the 
basement of the building. An arrangement of ducts and blowers or fans 
provides for flow of heated air from the collectors either to the storage 
bin or directly to the interior space of the building being heated, and 
cooled air is then recirculated to the collectors. The usual hot air 
furnace is connected into the system to supplement the solar heat source. 
The principal objects of the present invention are to improve the 
efficiency and reliability of operation of such heat storage means and to 
provide enhanced operating flexibility of the same in order to meet the 
varying requirements imposed on the heating system. As will be seen 
hereinafter, these objects are achieved in the present invention by a 
unique structural arrangement in the heat storage means, particularly with 
regard to the air inlets and outlets.

Referring first to FIG. 1, a building structure 10 is shown having a roof 
portion 11, interior room space 12, and a basement 13. An inclined portion 
of the roof 11 is provided with flat plate collector panels 14. Any type 
of collector panel suitable for solar heating of air may be used, but a 
preferred construction is disclosed in my co-pending application Ser. No. 
773,801, filed Mar. 3, 1977, now U.S. Pat. No. 4,099,513, issued July 11, 
1978. 
In the basement area 13 the heat storage means of the present invention is 
provided in the form of a pebble storage bin 16 which is described in more 
detail below. A duct 17 supplies heated air from the collectors 14 through 
a gravity back draft damper 18 to an air inlet 19 at the upper portion of 
the pebble bed 16 at one side thereof. An air outlet 21 from the upper 
portion of the pebble bed 16 is provided at the opposite side thereof. A 
duct 22 supplies heated air through a gravity back draft damper 84 to an 
auxiliary air heater such as a conventional forced air furnace 23 having a 
blower 24 and a burner 26. The heated air then passes through a duct 27 to 
the room space 12 to be heated. When the warm air from duct 27 is forced 
into the room 12 by the blower 24, cooled air flows from the room 12 
through a return duct 28 to another air inlet 29 in the lower portion of 
the pebble bed 16 at the same side of the bed as the inlet 19. Another air 
outlet 31 is provided at the opposite lower portion of the pebble bed 16 
and is connected by a duct 32 containing an air filter 33 to a 
recirculating blower 34. Air is recirculated by the blower 34 through a 
duct 36 having a gravity back draft damper 37 to the solar collectors 14. 
A control system is provided consisting of a conventional house thermostat 
41 located in the room space 12, a thermostat 42 which senses and is 
responsive to the temperature in the upper portion of the pebble bed 16 
adjacent the outlet 21, and a differential thermostat 43 which senses and 
is responsive to the temperature adjacent the outlet from the collectors 
14 and in the lower portion of the pebble bed 16 adjacent the outlet 31. 
The dashed line 44 illustrates the connection between the thermostat 42 
and its sensor or probe in the pebble bed 16, and the dashed lines 46 and 
47 illustrate the connections between the differential thermostat 43 and 
its sensors or probes at the collectors 14 and the pebble bed 16, 
respectively. As also seen in the schematic drawing of FIG. 1, the house 
thermostat 41 has an output connection indicated by dashed line 48 for 
effecting operation of the furnace blower 24 when the temperature in the 
room 12 falls below a predetermined minimum. Thus, air is withdrawn from 
the pebble bed 16 through the outlet 21 and the duct 22, is forced by the 
blower 24 from the furnace 23 through the duct 27 into the room 12, and is 
returned to the pebble bed 16 through the duct 28 and the inlet 29. The 
thermostat 41 has another output connection 49 in series with the 
thermostat 42 which in turn has an output connection 51 for energizing the 
burner 26. Thus, when the temperature in the pebble bed 16 falls below a 
predetermined minimum, which is sensed at 44, and the house thermostat 41 
senses that the room temperature is below its predetermined minimum 
setting, the burner 26 is then activated and the furnace 23 operates in 
the usual manner. 
The differential thermostat 43 is arranged so that when a predetermined 
temperature differential, say 20.degree. F., between the pebble bed outlet 
31 and the outlet of the collectors 14 is exceeded, the blower 34 is 
activated. In other words, when the temperature at the outlet of the 
collectors 14 is at least 20.degree. F. higher than the temperature at the 
pebble bed outlet 31, air is withdrawn by the blower 34 from the pebble 
bed 16, passed through the duct 36 to the collectors 14, and is then 
returned by the duct 17 to the pebble bed 16. In order to prevent loss of 
heat from the pebble bed 16, the gravity back draft dampers 18 and 37 
close automatically when the blower 34 is not operating but open 
automatically in response to air flow when the blower 34 is in operation. 
Likewise, the gravity back draft damper 84 closes automatically when the 
furnace blower 24 is not operating but opens automatically when blower 24 
is in operation. 
Referring to FIGS. 2-5, the heat storage means 16 is contained in a housing 
structure comprising a rectangular enclosure having elongated side walls 
61 and 62 and transverse end walls 63 and 64 supported on a base 66. The 
housing walls may be constructed of any convenient material such as 
ceramic or concrete block or wood frame, and one or more outer layers of 
insulating and finishing material are preferably provided, as shown in the 
drawings, so that the housing is substantially air impervious. For 
example, a suitable wall construction consists of eight inch concrete 
blocks with two inch foamed plastic insulating panels and one-half inch 
gypsum board finishing panels. Removable cover panels 67 are provided at 
the top of the rectangular enclosure to complete the housing structure. As 
an example, the cover panels may conveniently be a composite of one-half 
inch gypsum board and glass fiber or rock wool insulation encased in a 
peripheral wood frame. 
Within the housing structure, a container in the form of a steel framed 
storage bin or crib is provided which comprises a rectangular steel 
framework 71 supported on the base 66 and extending lengthwise between and 
abutting against the housing end walls 63-64. The elongated sides of the 
framework 71 are covered with air pervious panels of expanded metal or 
mesh, as indicated at 72 and 73, and the mesh walls are spaced inwardly 
from the housing side walls 61-62 to provide air plenum chambers at each 
side of the housing. The top of the framework 71 is open so that when the 
cover panels 67 are removed the confined space between the mesh walls 
72-73 and the housing end walls 63-64 can be filled with a mass of 
subdivided solid heat retention material 74, e.g. washed rocks, gravel, or 
pebbles. The plenum chamber between the housing wall 61 and the adjacent 
mesh wall 72 is divided by solid partition or baffle 75 to form an upper 
plenum space 76 and a lower plenum space 77 (FIG. 5). Similarly, the 
plenum chamber between the housing wall 62 and the adjacent mesh wall 73 
is divided by a solid partition or baffle 78 to form an upper plenum space 
79 and a lower plenum space 81 (FIG. 5). The upper and lower air inlets 
indicated schematically in FIG. 1 at 19 and 29 are designated by the same 
numerals in FIGS. 2-5 which show that the inlets 19 and 29 are mounted in 
the housing structure so as to communicate with the segregated plenum 
spaces 76 and 77, respectively. The upper and lower air outlets 21 and 31 
are similarly mounted to communicate with the segregated plenum spaces 79 
and 81, respectively. The partition or baffle 78 also extends inwardly 
into the pebble bed 74 beyond the mesh wall 73, as designated at 78', in 
order to minimize short circuit flow between the plenum spaces 79 and 81, 
as hereinafter described. In certain cases, if desired, a plurality of 
open tubes or pipes 82 may be provided through the lower portion of the 
pebble bed 74 between the sides 72 and 73 of the storage crib in order to 
reduce the resistance to air flow from the plenum space 77 to the plenum 
space 81, as also described hereinafter. 
A heat transfer pipe 83 (FIGS. 2-5) is imbedded in the upper portion of the 
pebble bed 74 and may be connected to the customary hot water supply 
system to supplement the same. 
Referring now to FIGS. 6-8 the several operating modes of the heat storage 
means 16 will be described in conjunction with FIG. 1. 
FIG. 6 shows the operating mode wherein thermal energy is being added to 
the heat storage means 16, as might be the case, for example, during a 
bright sunny day when the heating demand by the room space 12 is at a 
minimum. When the temperature in the room space 12 is above the minimum 
setting of the house thermostat 41, the blower 24 and the burner 26 will 
not be operating and the damper 84 will remain closed. However, the high 
temperature at the collectors 14 causes the differential thermostat 43 to 
place the blower 34 in operation, and heated air is drawn from the 
collectors 14 through the duct 17 into the inlet 19 and the plenum space 
76. The heated air is then drawn transversely and downwardly through the 
pebble bed 74 into the plenum space 81, as shown by the arrows in FIG. 6, 
thereby giving up heat to the pebble bed 74 which is at a lower 
temperature. The cooled air is drawn from the plenum space 81 through the 
outlet 31 and the duct 32 and is recycled through the duct 36 to the 
collectors 14. 
FIG. 7 shows the operating mode wherein thermal energy is being dispensed 
from the heat storage means 16, as might be the case, for example, at 
night when the heating requirements of the room space 12 are greater. 
Since the temperature at the collectors 14 will be much lower than in the 
daytime, the differential thermostat 43 will allow the blower 34 to remain 
in non-operating condition with the dampers 18 and 37 closed. However, 
when the temperature in the room 12 falls below the minimum setting of the 
house thermostat 41, the blower 24 becomes operative and cool air is drawn 
from the room 12 through the duct 28 and the inlet 29 into the plenum 
space 77. The cool air flows upwardly and transversely through the pebble 
bed 74 into the plenum space 79, as shown by the arrows in FIG. 7, and 
heat is given up by the pebble bed to the air which is at a lower 
temperature. The heated air is drawn from the outlet 21 and passes through 
the furnace 23 and duct 27 into the room space 12. If the heat stored in 
the pebble bed 74 is not sufficient to meet the demand called for by the 
setting of the house thermostat 41, the burner 26 will be turned on 
automatically to supply additional heat as air passes through the furnace 
23. 
FIG. 8 shows the operation wherein both modes of FIGS. 6 and 7 are 
operative simultaneously. This might be the situation, for example, during 
a sunny day when the room temperature is such that the house thermostat 41 
causes the furnace blower 24 to operate and when the temperature at the 
collectors 14 is high enough to cause the blower 34 to operate. In such 
case, heated air is drawn by the blower 24 from the plenum space 79 and 
the outlet 21 and is circulated through the duct 27 to the room space 12, 
and cooled air is returned to the plenum space 77 through the inlet 29. In 
this operating mode, however, the cooled air may pass in the path of least 
resistance from the plenum space 77 through the optional by-pass pipes 82 
to the plenum space 81 and is then drawn by the blower 34 from the outlet 
31. The cool air is then circulated through the duct 36 to the solar 
collectors 14 where it is heated and returned by the duct 17 to the inlet 
19 and the plenum space 76 of the heat storage means. During this mode of 
operation, when air is flowing from both outlets 21 and 31, the baffle 
extension 78' functions to reduce or minimize any tendency for short 
circuit flow of warm air from the plenum space 79 to the plenum space 81. 
From the foregoing description, it will be seen that the invention provides 
a highly efficient, reliable, and low cost pebble bed heat storage 
arrangement in which the cool air inlet and outlet and the warm air inlet 
and outlet are located at oppositely disposed vertical surface areas of 
the pebble bed in such manner that air must always flow unidirectionally 
through the pebble bed so as to obtain maximum heat transfer efficiency 
between the air and the storage means. Moreover, the arrangement permits 
complete flexibility in mode of operation with a simple and inexpensive 
control system and without the necessity of providing for reversal of air 
flow through the pebble bed for different operating modes and without the 
need for a plurality of expensive power operated dampers and associated 
controls. 
Although the invention has been described with particular reference to the 
illustrated embodiment, it is to be understood that various modifications 
may be made without departing from the scope of the invention as defined 
in the appended claims.