Heat exchange system for recycling stack heat

A heat exchange system for recycling waste heat leaving a building stack to supply heat to incoming fresh air or temper stored water of the building water storage system, wherein the building has a source of heat at constant temperature, such as a cooking facility, from which air conveying waste heat is drawn and impelled through a stack in which a closed circuit heat generated refrigerant flow type refrigeration system is established including a heat recovery coil in the stack, heat discharge coils in heat transfer relation to the incoming fresh air and the stored water, liquid refrigerant traps that permit free flow therethrough of the refrigerant adjacent the heat discharge coils adjacent their discharge ends, and thermostatically controlled valves for alternately disconnecting the heat discharge coils from the heat recovery coil in accordance with a predetermined ambient air temperature exteriorally of the building.

This invention relates to providing for recycling some of the waste heat 
passing out of a building stack to heat incoming air or temper stored 
water of the building water system, and more particularly, to a 
refrigeration arrangement of the heat generated refrigerant flow type 
which achieves that end. 
Buildings housing restaurant facilities and the like customarily are 
equipped to provide for forced air ventiliation of the cooking facilities 
through a stack or other suitable discharge duct, with fresh air being 
drawn into the building through suitable ducting for ventiliating and air 
replacement purposes. In many instances, and especially in the short order 
field, the cooking facilities, such as griddles and the like, are in 
intensive use for long periods of time each working day. As is common 
knowledge, the discharge from the stack contains much waste heat which is 
therefore lost to the atmosphere. On the other hand, incoming fresh air, 
when outside ambient temperatures are well below room temperature, 
requires heating; the supplying of the requisite heat for the income air 
is one of the greatest items of expense in the operation of such 
facilities. 
Facilities of this type ordinarily include a hot water system supplied with 
water from municipal mains or other suitable source, which, of course, 
must be heated to provide the desired hot water. The requisite heat is 
usually supplied using natural gas fuel or electrical energy type heating 
systems (both involving considerable attendant expense in view of today's 
high energy expense levels). 
A principal object of the present invention is to provide for a simple but 
effective means and method for recycling some of the waste stack heat and 
utilizing same to either heat the incoming fresh air, where outside 
ambient temperatures require this, or alternately temper stored water of 
the facility hot water system. 
Another principal object of the invention is to provide a closed circuit 
heat generated refrigerant flow refrigeration system of the heat pump type 
of recycling stack heat, for purposes of heating incoming fresh air or 
tempering the stored water of the facility, in which the system is free of 
pumps or compressors and is arranged to provide for rapid recycling of the 
refrigerant through the system for maximized efficiency. 
Another object of the invention is to provide for continuous recycling of 
the stack heat with thermostatically operated controls providing for 
supply of the recycled heat to the incoming fresh air when the outside 
ambient temperatures are below a predetermined level, and alternatively 
supplying recycled heat to a water tempering tank when the outside ambient 
temperature is above said predetermined level. 
Other objects are to provide a stack heat recycling system that is of few 
and simple parts, economical to install and operate, and long lived in 
use. 
In accordance with the invention, in facilities of the type indicated, a 
closed circuit heat generated refrigerant flow type refrigeration system 
is established in operative association with the building stack, the 
building fresh air intake duct, and the building hot water system water 
storage tank whereby a heat recovery coil is mounted in the stack and in 
heat exchange relation with the waste heat bearing gases passing through 
the stack, and heat transfer coils are mounted in heat transfer relation 
to the incoming fresh air and the storage tank water. The coils are 
incorporated in a closed circuit heat generated refrigerant flow system 
that includes a receiver or refrigerant collection tank that accommodates 
expansion and contraction of the refrigerant, and also serves as a vacuum 
chamber due to pressure differentials that build up in the flow system 
during its operation. 
A special aspect of the invention is that the conduiting that communicates 
the refrigerant from the heat transfer coils for return to the heat 
recovery coil is formed, at the level of the receiver and heat recovery 
coil, with a liquid refrigerant trap of the gravity induced type which, 
however, is free of any obstructions to free flow of the liquid 
refrigerant through the conduiting involved. 
Operatively associated with the heat recycling system are thermostatically 
operated control valves that are arranged for alternative isolation of the 
respective heat transfer coils from the heat recovery coil, in accordance 
with a predetermined ambient air temperature exteriorally of the building, 
whereby the heat recovered from the stack is supplied to the incoming 
fresh air when the exterior ambient temperature is below the selected 
level, and when the exterior ambient temperature is above the selected 
level, the recovered stack heat is applied to water to be tempered. 
Alternately, the heat transfer system employed may be simplified to have 
the stack heat that is recovered supplied only to the incoming fresh air, 
or only to water to be tempered. 
In any event, the heat transferred to the heat recovery coil, which 
preferably operates in exposure to temperatures in the 300 to 600 degree 
Fahrenheit range or higher, induces the cycling of the refrigerant in the 
system thereabout to go through the vaporization and liquification phases 
in refrigeration cycle manner that brings about the heat pump type heat 
transfer action involved between the heat recovery coil and the respective 
heat transfer coils. The traps that are in the return conduiting of the 
respective heat transfer coils resist reverse flow of the refrigerant so 
that there is a smooth and continuous run-around type movement of the 
refrigerant through the conduiting coils involved in the refrigeration 
system. 
It is an important feature of the invention that, as temperature 
differentials between the heat source in the stack (which is preferably 
constant for any given application) and the heat discharge points of the 
system are increased, recycling of the refrigerant through the 
refrigeration system accelerates without the need for any mechanical 
pumping action on the refrigerant being required. This accelerating effect 
reaches a maximum that will depend on the refrigerant employed in the 
system, the heat input at the heat recovery coil, and the heat outflow 
from the system at the heat transfer coils employed. 
Other objects, uses, and advantages will be obvious or become apparent from 
a consideration of the following detailed description and the application 
drawings in which like reference numerals indicate like parts throughout 
the several views.

However, it is to be distinctly understood that the specific drawing 
illustrations provided are supplied primarily to comply with the 
requirements of the Patent Laws, and that the invention is susceptible of 
other embodiments which will be obvious to those skilled in the art, and 
which are intended to be covered by the appended claims. 
Reference numeral 10 of FIG. 1 generally indicates a building housing a 
cooking facility generally indicated by reference numeral 12 and shown in 
block diagram form, which is intended to represent a griddle or other type 
of open cooking that in use is intended to be in continuous operation for 
a long period of time during the work day. Typically, the building 10 is 
equipped with a stack 14 provided with suitable blower means 16 for 
impelling air outwardly of the stack 14 and through stack discharge 
opening 18 suitably formed in the roof of the building 10, whereby air 
ambient to the cooking facility 12 is drawn into the stack 14 through 
suitable stack intake opening 19 and discharged to the atmosphere through 
opening 18. 
The building 10 is also typically equipped with a fresh air intake duct 21 
having suitable blower 23 mounted therein for impelling fresh incoming air 
into the building for the usual ventilating purposes. 
In accordance with the invention, the building 10 is equipped with the 
closed circuit heat generated refrigerant flow type heat exchange system 
20 shown in FIG. 2, which comprises heat recovery or absorption coil 22 
suitably mounted in stack 14 and cooperatively related by incorporation in 
the system 20 to heat transfer coil 24 suitably mounted in air intake duct 
21 in heat discharge relation thereto and heat transfer coil 26 which is 
suitably mounted in heat discharge relation to the water of water holding 
tank 28 (which is assumed to be the building water storage tank) suitably 
supported in the building 10. The water of tank 28, in accordance with the 
invention, for water tempering or preheating purposes is connected to 
refrigerant receiving water tempering chamber 29 in which coil 26 is 
mounted by suitable inflow and outflow conduits 30 and 32 that are series 
connected to coil 26 for conducting the water flow therethrough. 
In the diagrammatic showing of FIG. 1 the conduiting of the heat exchange 
system is not shown to simplify the drawing, with FIG. 2 being provided to 
show the essentials of the system layout involved. 
The coils 22, 24 and 26 may be of any type suitable for refrigeration or 
heat pump heat exchange purposes. They thus may take the familiar form 
indicated for coils 24 and sinuous 26 and thus comprise lengths of copper 
tubing and in the rounded shaping indicated, that is usually associated 
with heat exchange coils. Coil 22 is shown in another familiar form 
comprising intake end manifold 40 and discharge or outflow end manifold 48 
connected by spaced grid pipes 43 formed from copper or the like. 
The intake or inflow end 40 of coil 22 is connected to refrigerant receiver 
42, at the lower end 44 of same, by supply conduit 46 while the outflow or 
discharge end 48 of the coil 22 is connected to outflow refrigerant 
conduiting 50 for fluid flow communication with the respective coils 24 
and 26 in the alternate manner contemplated by this embodiment of the 
invention. 
Thus, conduit 50 includes branch 52 which is connected to the intake end 54 
of the coil 24, and branch 56 that is connected to the chamber 29 at its 
refrigerant inlet 58. The branches 52 and 56 are coupled together by 
suitable joint 60. 
Refrigerant return conduit 62 connects the upper end 63 of receiver 42 to 
the coil 24 and chamber 29, the conduit 62 having branch 64 connected to 
the discharge end 66 of coil 24, and branch 68 connected to the 
refrigerant discharge or outlet 70 of the chamber 29. The branches 64 and 
68 are suitably connected together by joint 72. 
In accordance with the embodiment of FIG. 2, it is intended that the heat 
recovered at coil 22, from the waste heat leaving stack 14, be released or 
absorbed at either coil 24 or coil 26, depending on temperature conditions 
of the ambient air external to the building 10. For this arrangement, the 
thermostatically operated control arrangement 80 of FIG. 3 (or its 
equivalent) is employed, which is largely block diagram illustrated, and 
for purposes of illustration is shown to comprise a solenoid operated 
off-on valve 82 incorporated in conduit branch 52 and a similar solenoid 
operated off-on valve 84 incorporated in conduit branch 56, with the 
valves 82 and 84 being electrically operated from thermostatically 
operated control box 86 electrically arranged so that when the temperature 
of the ambient air externally of the building 10 is above a predetermined 
level, such as 60 degrees Fahrenheit, the valve 82 closes the heat 
discharge coil 24 off from communication from the heat recovery coil 22, 
while valve 84 maintains the chamber 29 (in which is mounted heat 
discharge coil 26) in open communication with the heat recovery coil 22. 
When the temperature of the ambient air externally of the building 10 is 
below such selected level, the positions of valves 82 and 84 are reversed 
by the operation of box 86. 
The control box 86 may be of any suitable type that includes suitable means 
for sensing or being responsive to the temperature of the ambient air 
externally of the building 10, and that includes suitable means for 
alternatively connecting the valves 82 and 84 to the suitable source of 
electrical energy that is to be made available for this purpose through 
connection thereto by suitable lead lines 90 and 92. 
FIG. 3 shows the condition where the ambient temperature externally of the 
building is above the predetermined temperature level whereby the control 
device arrangement 80 connects the chamber 29 to heat recovery coil 22 to 
expose the refrigerant flow to coil 26 for purposes of tempering the water 
of tank 28. When the ambient temperature level referred to drops below the 
predetermined level, the positions of the valves 82 and 84 reverse to 
disconnect the chamber 29 from coil 22 and connect the coil 24 to the coil 
22 for refrigerant fluid flow thereto for application of the recovered 
heat to the fresh air being taken into the building through conduit 18. 
The valves 82 and 84 each comprise, in the simplified form shown, a 
suitable valve body 100 defining valve chamber or bore 102 and 
reciprocably receives valve stem 104 formed with aperture 106 that is to 
be disposed in the position of valve 84 to permit communication between 
the upstream and downstream portions of the conduit branch 56, and that is 
to be disposed in the position of the valve 82 to block communication 
between the upstream and downstream segments of the branch 52. For this 
purpose, the valve stems 104 are shown operably associated with suitable 
solenoid coils 107 and arranged in the manner indicated for energization 
of the coils 107 to move them to the flow blocking positions indicated 
against the action of biasing springs 108 that, when the coils 107 are 
deenergized, bias the respective spindles 104 such that their apertures 
106 are aligned with the respective conduit branches 52 and 56 for 
permitting fluid flow therethrough. 
In practice the control device 80 and its valves 82 and 84 may take the 
form of any conventional equipment that will provide the functions 
indicated. 
The coil 22 is incorporated in suitable frame 110 which is suitably mounted 
in stack 14 in the path of the fluid flow through the stack 14. 
The coil 24 is suitably incorporated in a suitable frame, for supporting 
purposes, that is shown in block diagram form only at 112. The coil 26 is 
suitably mounted within chamber 29 in a convenient manner for intimate 
heat transfer relation with the water supplied from the tank 28 through 
conduits 30 and 32 that are connected to the intake and discharge ends 111 
and 113 of coil 26. In the form of FIG. 2, the refrigerant flow relative 
to coil 26 is through chamber 29 in heat transfer relation to coil 26 
through which water from tank 28 flows for water tempering purposes. 
Chamber 29 may be in the form of any suitable refrigerant confining 
container or vessel 115 suitably mounted in building 10 and having coil 26 
suitably supported in same for connection with conduits 30 and 32. 
Container 115 is thus hollow for refrigerant fluid flow therethrough 
between inlet 58 and outlet 70 whereby coil 26 is thus immersed in fluid 
refrigerant that bears recovered heat for transmittal through the tubing 
walls defining coil 26 to the water flowing therethrough. 
Receiver 42 comprises a suitable fluid tight vessel 117 and mounted in any 
suitable manner at the level of recovery coil 22. 
The refrigerant circulation system represented by the coils 22, 24, and 
chamber 29 and its coil 26, the receiver 42, and the conduiting 
interconnecting the coils and the receiver 42 is filled with a refrigerant 
that is matched in operating characteristics to the temperature and air 
flow volume within the stack 14. The specific refrigerant applied will 
depend upon the application, with non-toxic and non-flammable refrigerants 
such as halogenated hydrocarbon products sold under the trademarks Freon 
11, 12, 21, 22, 113 and 114 (or combinations of same) being suitable, 
depending on the application. As indicated in the drawings, the system 20 
is of a closed, non-mechanical pump, refrigeration type in which the flow 
of the refrigerant through the system is generated by the application of 
heat to coil 22. Of course, the conduiting, coils and chambers through 
which the refrigerant flows should be fluid tight throughout system 20. 
Further in accordance with the invention, the system conduits connecting 
the liquid refrigerant return (or heat depleted side of the system) to the 
receiver 42 are each formed to define a liquid refrigerant trap. The trap 
for heat discharge coil 24 is indicated by reference numeral 120 while the 
trap for the return from chamber 29 is indicated by reference numeral 122. 
The traps 120 and 122 each comprise a bight portion 124 formed in the 
conduiting involved that is vertically disposed and includes upstanding 
leg portions 126 and 128 connected by a upwardly directed connecting 
portion 130. The conduiting portions forming the traps 120 and 122 are 
fully opened throughout the lengths of same to provide for free flow of 
liquid refrigerant therethrough through the respective coils 24 and 26 
under the head that exists on the liquid refrigerant within the respective 
traps 120 and 122. However, the quantity of liquid refrigerant that is 
retained by the action of gravity within the respective traps resists 
reverse flow tendencies that may occur in the system 20 during operation 
thereof and insures that the refrigerant flow rates and efficiency desired 
for a particular installation are obtained. 
Further in accordance with the invention, the traps employed in the system 
20, represented in the illustrated embodiment by traps 120 and 122, are 
disposed at the horizontal level of heat recovery coil 22, and between the 
uppermost and lowermost horizontal levels of its ends 40 and 48. Also, 
receiver 42 is similarly positioned, and it is a further criteria of the 
invention that the upper end 63 of the receiver 42 and the portions of 
return conduiting 62 that are downstream of the traps 120 and 122 be below 
the uppermost horizontal level of coil 22. 
In operation, assuming that the ambient temperature externally of the 
building 10 is below the selected level, on start up of the system, by 
instituting heat flow out of stack 14 the heat discharge coil 24 is 
connected to the heat recovery coil 22 while the chamber 29 is 
disconnected therefrom by operation of control device 80 (thus isolating 
coil 26 from coil 22). Liquid refrigerant in coil 22 evaporates as heat is 
absorbed from the stack 14, with the gaseous refrigerant passing through 
conduit 50 and its branch 52 to and through heat discharge coil 24 wherein 
the refrigerant condenses to give up its heat that is transferred to the 
incoming air of duct 18. The reliquified refrigerant passes through trap 
120 and returns to receiver 42 through the conduit 62 and its branch 64 
for return to the intake end 40 of coil 22 through conduit 46. For normal 
operation, the heat source for system 20, represented by stack 14 in the 
illustrated embodiment, should be substantially constant for uniform 
operation of the heat pump type refrigeration system involved. The 
temperature in the locale of the heat recovery coil 22 within the stack 14 
is preferably in the range of from approximately 300 degrees F. to 
approximately 600 degrees F. It will be found in practice that the 
refrigerant cycles through the coils 22 and 24 and receiver 42 in a 
run-around type relation, with the recycling accelerating in proportion to 
the differences in temperature at the locales of the coils 22 and 24; this 
acceleration effect reaches a maximum that will depend on the refrigerant 
employed in the system, the heat input to the system at recovery coil 22, 
and the heat outflow from the system at the coil 24. 
More specifically, on start up of the system, liquid refrigerant in the 
coil evaporates as heat is absorbed by it and passes to coil 24, where it 
condenses to give up stored heat and returns through trap 120 to receiver 
42. During the cycling involved, a pressure differential builds up between 
the discharge end 66 of coil 24 and the lower or discharge end of receiver 
42; this pressure differential and the refrigerant cycling involved will 
increase, as the temperature at the locale of coil 22 rises relative to 
the temperature at the locale of coil 24, until a balance point, or 
maximum pressure difference level is reached, to provide the optimum or 
maximum speed of refrigeration cycling within system 20 for a given 
installation. As indicated this balance point will depend on the specific 
refrigerant employed, the amount of heat input to the system 20 (as at 
coil 22), and the amount of heat output provided by the system (as at coil 
24); such balance point is thus generally dependent on the temperature 
differences at the locales of the coils 22 and 24, as well as the specific 
refrigerant employed. 
Consequently, for any given installation, the heat source represented by 
the stack 14 should provide a temperature level in the locale of coil 22, 
relative to the temperature levels to be expected at the locale of coil 
24, such that the maximum refrigerant cycling effect contemplated by this 
invention will be achieved. When this is observed, up to eighty percent of 
the input heat at coil 22, in terms of BTU's per unit of time, can be 
recovered from waste stack heat, depending on the heat draw off available 
to the system. 
As indicated, when the ambient air temperature external to the building 10 
rises to exceed the indicated predetermined level, the positioning of the 
valves 82 and 84 is reversed to disconnect the coil 24 from coil 22 and 
connect the chamber 29 thereto. The system 20 then operates in the same 
manner to supply heat to the water from tank 28 passing through coil 26, 
so long as the temperature of the ambient air externally of the building 
10 remains at a level above the indicated predetermined level. 
Practice of the invention indicates that as cycling of the refrigerant 
through the system 20 accelerates under the conditions indicated, a 
reduced pressure condition is created in receiver 42, apparently due to a 
separation of the refrigerant on the lower portion of the receiver from 
that entering same at its upper end, due to a rapid draw off of the 
refrigerant from the receiver as the heat input to recovery coil heat 
charges the refrigerant for rapid fluid flow to the heat outflow position 
of the system, where fluid flow of the refrigerant is retarded by friction 
and other resistance to fluid flow. In any event, this tendency toward 
reduced pressure or vacuum conditions in receiver 42 reaches a maximum 
coincident with the obtaining of the aforedescribed maximum cycling speed 
of the refrigerant. 
In the simplified system 20A of FIG. 4, the heat recycling arrangement 
involved is arranged only to supply heat to the incoming fresh air, and 
thus to coil 24. Thus, the control arrangement 80 is eliminated together 
with the conduiting connections to tank 28, with the other parts of the 
system remaining the same as described in connection with the showing of 
FIG. 2, as indicated by corresponding reference numerals, except that 
recovery coil 22A is of the same physical construction as coil 24, and 
thus has its intake end 40A connected to receiver 42 and its outflow end 
48A connected to coil 24. Coil 22A is embodied in frame 110A. 
In the embodiment of FIG. 5, the heat recycling system 20B involved 
supplies covered heat only to the chamber 29, and thus to coil 26. Here 
again, the control arrangement 80 is therefore eliminated, as well as the 
connections with coil 24, with the remaining components being the same as 
shown in FIG. 2, as indicated by corresponding reference numerals to the 
extent applicable. In FIG. 5, the water storage tank 130 is illustrated 
where water supply to the tank 130 is through conduit 132 or alternately, 
when the system 20B is operating, through conduit 30 under the impetus of 
suitable pump 134 operated by motor 136, coil 26 and conduit 32. 
It will be apparent that with regard to the water tempering arrangements of 
FIGS. 2 and 5, a heat exchange coil similar to coil 24 and connected 
directly into the refrigeration system may be mounted in chamber 29 in 
place of coil 26, with the water from tank 130 filling chamber 29 and 
flowing therethrough via conduits 30 and 32. However, the arrangement 
illustrated for chamber 29 is preferred because of the concentrated heat 
inflow effect on water flowing through coil 26. 
It therefore will be apparent that the invention provides a heat exchange 
system for recycling stack heat to recover much of the waste heat leaving 
the stack and apply it in an efficient manner to heat incoming fresh air 
or temper water of a water storage tank. The refrigerant flow system 
involved is free of any mechanical pumping or compressor requirements, 
with the refrigerant flow being induced by the heat at the heat source in 
the stack. 
The foregoing description and the drawings are given merely to explain and 
illustrate the invention, and the invention is not to be limited thereto, 
except insofar as the appended claims are so limited, since those skilled 
in the art who have the instant disclosure before them will be able to 
make modifications and variations therein without departing from the scope 
of the invention.