Note: Descriptions are shown in the official language in which they were submitted.
~2S~
APPARATUS AND METHOD ~OR BURNING A COMBUS~BLE GAS
_
This invention relates to fln apparatus and snethod for burning a combustible
gas. This invention also relates to a heating ~pparatus useabl~ for ~pac~ heating.
Because of the r~pidly rising cost of naeural gas (methane), in recent years
much effort has been directed to improving the efficiency of gas ~urnaces for
05 residential and other consumers. Most modern gas furnaces use electronic ignition
rather than ~ pilot light to avoid the inevitable waste of g~s which a pilot light
involves. Also, very high efficiency gas furnaces have been introdu-ed; some of
these furnaces use a puLse syseem in which pulses of a g~s and air mixture are
ignited within ~ eombustion chamber, while others rely upon relaSively ~omplicated
iO heat exchangers to extract the maximum amount of heat from the combustion
products produced by burning n~tural gas. The latest furnaces are considerably
more efficient than the older, pilot ignition gas furnaces; a typical p~ot ignition gas
furnace might have a steady state efficiency of about 75% and a seasonal efficiency
of about 65%, while repla~ing the pilot light with either direct spark ignition or
15 intermittent pilot ignition increases the seass)nal efficiency to about 70%. Cert~in
of the high-efficiency g~s furnaces previously mentioned have seRsonal efficieneies
of about 80-90%.
Although much ~ttention has thus been directed to improving the efficiency of
gas furnaces, many residential gas consumers have both a gAS furnace for space
20 heating and 1 g~s water hellter, and relatively little research appe~rs to haYe been
performed to improve the efficiency of gas water heaters. The design of residential
gas water heaters has changed relatively little over the last few years. Most
residential gas water hedters comprise a cylindrical water tank provided with aninsulating jacket and a gas burner which impinges upon the base of the wflter tank;
25 to allow escape of combustion products produced by the burning gas, a vertical
conduit carrying the exhaust products extends vertic&lly upw~rdly ~long the axis of
the cylindrical tank, this vertic~l conduft serving to eîfect additional heat exchan~e
between the combustion products and the water in the tarJk. ~The ste~ state and
seasonal efficiencies of such gas water heaters are only about 709S and 55%
30 respectively, considerably lower thun those of the high-efficiency types of gas
furnaces previously described. Thus, the overall efficiency of gas consumption by
most consumers is markedly diminished by the relative inefficiency o~ ~onventional
gas water heaters. In fact, when appropriate weighting is given to the relQffve
1 1258411
amounts of gas used by the furnace and water heater in a typical household,
the combined seasonal efficiency of gas usage is only about 66%. There is
thus a need to improve the efficiency of gas water heaters in order to
increase the overall efficiency of ~as use.
The use of separate furnace and water heating units has other
disadvantages in addition to the relatively low overall efficiency of gas
use. The separate furnace and water heater require a relatively large
amount of space and also require two separate pilot lights or other ignition
systems, and separate gas lines, thus increasing installation costs.
In order to overcome the aforementioned disadvantages of gas
furnaces and gas water heating units, it i9 desirable to provide a single
unit which functions both as a gas furnace for space heating and as a gas
water heater. This invention provides a heating apparatus which uses a
novel form of heat exchanger to increase the efficiency of the space heating
system.
This is a division of commonly assigned Canadian Patent
Application Serial No. 459,013 filed July 17, 1984.
In one aspect the invention of the parent application provides
apparatus for burning a combustible gas, the apparatus comprising a housing
having within its interior a liquid chamber capable of holding liquid, a
hollow, liquid-impervious combustion chamber member disposed within the
liquid chamber and having within its interior a combustion chamber, an
exhaust conduit having an inlet connected to the combustion chamber and an
- outlet through which combustion products can leave the apparatus, and a
hollow gas burner disposed within the combustion chamber, this gas burner
having walls surrounding an internal chamber and apertures passing through
these walls, thereb~ establishing fluid communication between the internal
chamber' of the gas burner and the combustion chamber outside the gas burner.
This apparatus is characterized in that it further comprises an impeller for
passing a combustible mixture of the combustible gas and air under pressure
into the internal chamber of the gas burner, the impeller having mixture
control device for controlling the ratio of gas an air ln this mixture.
Also, the apertures in the gas burner are sized such that combustion of the
combustible mixture within the combustion chamber outside the gas burner
will not cause ignition of the combustible mixture within the internal
chamber of the gas burner. The apparatus is also characterized in that the
LCM~
12584~L1
exhaust conduit comprises a heat exchanger for effecting heat exchange
between the combustion products produced by combustion of the combustible
mixture and liquid in the liquid chamber, this heat exchanger comprising a
riser section extending upwardly from the combustion chamber and a helical
section extending downwardly from the upper end of the riser section.
The invention of the parent application also provides a method for
burning a combustible gas comprising passing the gas into the hollow
interior of a gas burner, allowing the gas to pass through apertures in the
walls of the gas burner into a liquid-impervious combustion chamber disposed
within a liquid chamber capable of holding liquid, burning the gas within
the combustion chamber and passing the resulting combustion products through
an exhaust conduit at least part of which is disposed within the liquid
chamber and which connects the combustion chamber to the exterior of the
apparatus. This method is characterized in that the combustible gas is
mixed, prior to its entry into the hollow interior of the gas burner, with a
predetermined amount of air at least sufficient to burn completely the
combustible gas, the resultant mixture of combustible gas and air within the
combustion chamber outside the gas burner will not cause ignition of the
mixture within the interior of the gas burner, and the exhaust conduit has a
riser section, which passes the combustion products upwardly from the
combustion chamber, and a helical section extending downwardly from the
upper end of the riser section, so that heat is transferred fro~ the
combustion products through the walls of the combustion chamber, riser
section and helical section to liquid in the liquid chamber.
The present invention, on the other hand, provides a heating
apparatus comprising a tank having within its interior a liquid chamber
capable of holding liquid, a hollow, liquid-impervious combustion chamber
member disposed within the liquid chamber and having within its interior a
combustion chamber, an exhaust conduit having an inlet connected to the
combustion chamber and an outlet through which combustion products can leave
the apparatus, a portion of the exhaust conduit within the liquid chamber
being arranged to serve as the first heat exchanger for effecting heat
exchange between combustion products leaving the combustion chamber and
liquid in the liquid chamber 9 a gas burner disposed within the combustion
chamber, a second heat exchanger disposed outside the liquid chamber and
LC~I:mls
iL2S84~1
3a
arranged to supply heat to the environment to be heated by the heating
apparatus, the second heat exchanger having a liquid inlet and a liquid
outlet, a liquid supply conduit having an inlet disposed with the liquid
chamber and an outlet connected to the liquid inlet of the second heat
exchanger, the liquid supply conduit being arranged to supply
LCM~ Q ,
:1~5~
--4--
liguid from the liquid chamber to the second hent exchanger, ~2d a liquid return~onduit having ~n inlet connected to the liquid outlet of the second heat exchflnger
and an outlet disposed within the liquid chamber, the liquld return conduit being
arr~nged to return wdter from the second heat exchanger to the liquid chamber.
05 This hesting ~pparatus is eh~racterized in that a section of the liquId return conduit
is arrenged Hdjscent to part o~ the exhsust conduit lying outside thc liquld chamber
so th~t combustion products passing ~long the exhaust conduit flow countercurrent
to liquid returning via the liquic) return concluit from the second heat exchanger to
the liguid chamber nnd he~t transfer occurs from the combustion products to the
10 returning liquid. By this means, the returning liquid is partially reheated before it
reenters the liquid ch~mber using heat whi~h would otherwise be wasted in the
combustion products leaving the app~rAtus via the exh~ust concluit.
The apparatus ~nd method of this invention for burning combustible g~s differ
from eonventional gas furnaces in which the combustible gas ~nd ~ir ~re mixed. In
15 conventional g~s furnaces pure g~s flows out of one or more g~s no~zles, thereby
becoming mixed with ~lir to form a combustible mixture which burns immediately
adjacent the gas nozzle. In the apparatus and method of this invention, the
combustible g~s ~nd the air are pre-mixed to form a combustible mixture which isthen forced into the internal chamber of the gas burner (in saying that, in the
20 instlmt method, the combustible mixture is passed "under pressure" ~nto the internal
ch~mber of the g~s burner, we mean only that the combustible mixture enters thisintern~l chAmber at 8 pressure greater than the pressure existing immediA~ely
outside the gdS burner, so that the combustible mixture will flow out oî the g~sburner YiA the apertures therein). The apertures in the gflS burner are sized so that
25 combustion of the gas around the gas burner will not c~use ignition of the
combustible mixture within the gas burner thus, preventing the occurence of ~ny
~lashbflck and/or explosion within the burner or impeller. The pre-mixing of gas and
eir achieved in the apparatus flnd method of this invention enQbles the g~s/air r~tio
to be precisely controlled, in contrast to a conventional furnace in which, because
30 only combus~ible gas flows from the nozzle, only limited control can be exercised
over the gas/air ra~io. Control of the gas/air ratio is importsnt in achieving
msximum efficiency of gas usage, since any excess of ~ir ovel ~hat reguired for
combustion of the g~s simply dilutes the combustion products, reducing the
temper~ture thereof ~nd, thus reducing the efficiency of heat exch~nge between the
35 combustion products and Qny heat exchanger which serves to ramove he~t from the
combustion products ~nd supply it to where it is needed. Those ski~ed ln this field
~LZ5841~1L
--5--
are flware th~t conventional gQS furnaces and water heaters draw past the gas
nozzles ~onsiderably more ~ir than is required for proper combustion of the gas~ but
hitherto it hrs not been possible to exercise effeceive con~rol over the gas/air ratio
in order to avoid dilution of the combustion products by excess ~ir, and this is one of
05 the factors which reduces the efficiency o~ convention~l g~s furnaees ~nd water
heaters. While we do not absolutely e~clude the possibility that the design of the
combustion ehamber in our ~ppar~tus may allow for th~ entry of some additional air
thereinto, in ~ddition to the combustible mixture issuing from the gas burner, we
very much prefer that the combustion chamber have no gas inlet other then the gQS
10 burner and no outlet other than the exhaust conduit so that sll the air reguired for
combustion is mixed with the combustible gas prior to its entry into the gQS burner.
As already mentioned, in the Qpparatus of this invention the impeller forces a
mixture of combustible gas and air into the gQS burner. The admixing of the
combustible gas and ~ir may be effected either upstream or downstream of the
15 impeller; i.e. the combustible gas may be admixed with air upstream of the impeller
~nd the resultant mixture passed through the impeller, or alternatively only air may
pass through the impeller and admixing of the air with the combustible gas be
effected between the impeller and the gas burner. In the former case it is of course
essential that the impeller be of a type which will not ~enerate sp~rks or the like
20 capable of igniting the combustible mixture of gas and air passing through it; in the
l~tter case, no such restriction on the type of impeller exists.
In theory the amount of air mixed with the combustible gas before entry into
the gas burner should be equal to the theoretical Qmount reguired for complete
combustion of the combustible gas. However, in pr~ctice it is desirable to provide a
25 small excess of Qir in order to allow for transient fluctuations in the gns/air ratio
due to fluctu~tions in gas pressure and the like. Thus, the ~mount of air mixnd with
the combustible gas to form the combustible mixture is desirably from l to about 1.2,
snd preferably about l.l, times the amount of air or other oxygen~ontaining gas
stoichiometric~lly required for complete combustion of the combustible gas.
It has also ~een discovered that the geometric shape of the gas burner is
important in the apparatus and method of this invention. Very desirably, the
combustion and the gas burner of the apparatus have substantially the form of a pQir
of co-~xial cylinders ~nd the Qpertures in the gas burner are disposed in the
cylindric~l w~ll of the g~s burner, thereby permitting combustion of the combustible
35 mixture on Q cylindrical fl~me front surrounding the gQS burner. This cylindric~l
fl~me front allows for very good heat transmission ~rom the fl~me to the cylindrical
~2S~
--6--
wall of the combustion chamber which, when the apparatus is in use, is immersed in
liguid hsld in th~ liquid eh~mber, and thus promotes very efficient heat transfer
from the name to the liquid. Whe~ the cylindlic~l burner has an end wall, this end
wall may or may not be provided with apertures i.e. the cylindrical burner may have
05 apertures in the side walls only or in both the side walls snd the end wall. Other
shapes of gAS burner may also be emploged; for ex~mple, th~ burner may be conical,
frusto~onicQl or hemispheric~l or have the form of a hemisphere truncated by a
plane parallel to its ba~e.
However, it ha~ been found that a cylindrical gRS burner having apertures only
10 in the side walls is the most efficient form To ensure good heat transfer to the walls
of the combustion chamber, desirably the part of the combustion chamber surround-
ing the gns burner hAs substantially the same form as the burner. It will be
appreciated, OI course~ that the cylindrical name front which can be achieved in the
instant apparatus using a cylindrical gas burner caMot be achieved by a convention-
lS al gas burner in which pure combustible gas issues from the nozzle, since the flamefront produced by such a gas burner is slways substantially conical. In a particularly
preferred form of the invention described in more detail below with reference to the
accompanying drawing, the combustion chamber has the form of a cylinder
surmounted by an upwardly-tapering frustum of a cone, the inlet of the exhaust
20 conduit is connected to the narrow end of the frusto-conical porffon of the
combustion chamber, the gas burner has the form of R cylinder substantially co-axial
with the cylindrical portion of the combustion chamber and the apertures of the gas
burner are disposed in the cylindrical wall of the gas burner, thereby permitting
combustion of the combustible mixture on a cylindrical flame front surrounding the
25 gasburner.
The apparatus and method of the invention also use a special type of exhaust
conduit to promote very efficient heat transfer from the combustion products to
liquid in the liquid chamber. The part of the exh~ust conduit which acts as a heat
exchanger has a riser section extending upwardly from the combustion chamber and30 a helieal section extending downw~rdly from the upper end of the riser sèction. It
has been found that this form of exhaust conduit provides very efficient heat
transfer îrom the eombustion products to liquid in the liquid chamber bec~use the
downward slope of the helical section contributes to a higher coefficient of
convective heat transfer ~since the coolest downstre~m section of Ule heat
35 exchanger is in cont~ct with the coolest water lying in the lower part of the liquid
chamber~ and therefore to higher efficiency of heat exchange. Desirably, the lower
~258~1~
7-
end of the helicsl section of the exhQust conduit is disposed ~djscent the lowest psrt
of the liquid chamber; since wster hested by the exhnust conduit tends to rise within
the Uguid ch~mber, it is desir~ble thnt the lower end of the hest exch~nger extend
sdjscent the lowest p~rt of ~he liquid ~hsmber in order to ensure th~t ~ l~rge m~ss
D5 of cold ligui~ is not le~ below the heat exch~nger and rem~ins unhented thereby.
The cooling of the eombustion products whch occurs in the heQt exch~nger in
the exh~ust ~onduit may c~use condensstion of liquid from the combustion products.
For obvious ressons, it is desir~ble to provide some w~y of draining such condens~te
- from the exhsust conduit. Accordingly, in the sppsratus of the invention, the
10 exhaust c0l2duit is desirably provided with ~ condensate trnp ~or drAining condensnte
produced by cooling of the combustion products in the hent exchdry~er, this
condensQte trsp comprising a first conduit extending downwsrdly from the lower end
of the helicsl section of the exh~ust conduit, a second conduit extending upwardly
frorn the low~r end of the first conduit, ~nd ~ dr~in conduit extending downwardly
15 from adjflcent the ~unction of the first and second conduits, this dr~in conduit
incl~ling a ~end to trap a~ water and prevent the exit of ~bustion
products through the drain conduit.
The npp~ratus of the invention will, of course, normally incorp~>r~te a li~uid
supply line ehrough which liquià csn be supplied to the liquid ch~mber. Desirably, a
20 portion of the liquid supply line is in contsct with the exhflust conduit so that he~t
tr~nsfer cnn occur from the combustion products pRssing s~ong the exh~ust conduit
to liquid in the liquid supply line.
The presently preferred embodiment of the epp~rstus of the invention will now
be described, though by w~y of illustration only, with reference to the ~ccomp~nying
25 dr~wing, which shows a vertic~l section through the npparstus.This drawing shows nn
spp~rntus of the invention (generfllly designsted 10) which comprises a substsnti~lly
cyUndricQl housing or wster tsnk 12 gener~lly similnr to the tQnk of ~ conventional
- w~ter henter except that ~t lscks the normal centr~l, verticnl exhsust conduit. As
in u conventiondl ggs w~ter he~ter, the tank 12 is surrounded by ~n outer cylinder 14
30 nnd ~n annulQr insulating jacket 16 is disposed between the tnnk 12 ~nd the outer
cylinder ~4 to reduce hest loss from the tnnk 12. The upper end of the outer ~ylinder
14 is closed by Rn end plate 18; the insulnting jncket 16 also fills the space between
the end plQte 18 und thc adjacent upper end wQll of the tank 12 In order to reduce
heQt loss from the end w~ll of the tnnk 12. The lower end of the outer cylinder 14
35 cx~ends downwnrdly beyond the lower end of the tnnk 12 Qnd is closcd by ~ bnsc
plnte 20 which rcsts upon n floor or other suitnblc support surfnce nnd thlls Sup~or~s
~5~
--8--
the entire apparatus. A pad 22 of the s~me insulating material as the jacket 16 is
disposed above the base plate 20 to reduce heat loss via the baseplate.
The lower end wnll 24 of the tar~c 12 has fixed thereto Q drain tube 26 providedwith a manu~lly-oper&ble val~re 28 which is normally closed but which can be opened
05 when it is desired to drain liguid from the tanlc 12. When the apparatus is in normal
oper~tion, the tank 12 is completely filled with water. The central portion of the
lower-end wall 24 is nat and has a central circular aperture cut therein. This
circulsr aperture surrounded by a planar flange 30 which forms part of the lowerend-wall of a combustion ~hamber member 32. This combustion chsmber member
lû 32, lies wholly within the tank 12, is cylindro-conical in forrn having the circular
plate 30 8S part of its base, a cylindrical side wall section 34 extending upwardly
from arounà the periphery of the pl~te 30 and an upper, upwardly tapering frusto-
conical section 36 surmounting the upper end of the cylindrical section 34. The
various sections of the combustion chamber member 32 enclose a cylindro-conical
15 combustion chamber 33. Within this combustion chamber 38 is a gas burner 40
hsving the form of a hollow cylinder closed at its upper end but open at its lower
end. The gas burner 40 extends downwardly through the central circular aperture in
the lower-end wall 24 and has a flange 42 extending radially outwardly below theflange 30. The cylindricnl wall of the gas burner 40 has a multitude of small
20 ~pertures passing therethrough, thereby establishing fluid communication between
the internal chamber within the hollow cylindrical gas burner 40 and the combustion
chamber 3~ lying outside the gas burner 40.
When the apparatus is in operation ~ combustible mixture of nntutal gas and
air is fed under pressure to the internal chamber of the gas burner 40 from an
25 impeller 46 located between the lower end wall 24 of the tanlc 12 and bRseplate 20.
To secure a gas-tight connection between the impeller 46 and the interior of the gas
burner 40, ~he impeller 46 is provided, at i~s outlet end, with a flange 47 for
attachment to flange 42 on the gas burner 40. The flange 30 is provided with four
eguRlly-spQced ~hreaded studs 44 which extend downwardly through bores tnot
30 shown) provided in the flanges 42 and 47 on the gas burner 40 and the impeller 46.
Nuts 45 are screwed on to the lower ends of the studs 44, thereby securing the
flanges 30, 42 ~nd 47 together and establishing a gas-tight connection between the
impeller 46 and the interior of the gas burner 40. Gaskets (not shown) may o course
be provided between lldjacent pairs of the flanges 30, 42 and 4~ to assist in ob~ining
35 gooà seals.
The impeller 46 may be of any convenient type and could b~, for ex~mple, a
I ~Z584~l
vane pump or a fan. Since, as described in more detail below, the impeller 46 isrequired to pump a combustible mixture of n~tur~l gas and air, the impeller must in
prsctice be of a type which can pump such combustible gas without any risk of
explosion, but it is believed that those skilled in this fieid will have no difficulty in
05 providing an impeller which meets these requirements. (AlternatiYely, if mixing of
the natural gas and ~ir is arrunged to take place downstream of the impeller, the
impeller need not be of any specific type.) The impeller 46 is driven by an electric
motor (not shown).
The impeller 46 draws its air from an air-inlet tube 48. The inlet end (not
10 shown~ of this tube 48 is preferably located externally of the building in which the
apparQtus is inst~lled in order that the air dr~wn into the impeller will be
unconditioned, external air and not air which is ~lready conditioned. The portion of
the tube 48 adjacent the main part of the apparatus 10 comprising a horizontal limb
which terminates above the upper endplate 18, Q vertical limb which extends
15 vertically downwardly between the cylindric~l walls of the tank 12 and the outer
cylinder 14 within the insulsting jscket 16, snd a second horizontal limb which
extends to the intake of the impeller 4B. (The shspe of the tube 48 is of coursedictated solely by the type and position of air intake port with which the ~pparatus
10 is intended to be used and may vary alrnost indefinitely. Indeed, in principle tube
20 48 could terminate flush with the upper surface of the endplate 18 but such an
arrangement would have the obvious disadv~ntage of drawing combustion air from
within the building rsther than using unheated outside air. Also, the tube 48 could
be replaced by a simple horizontal tube extending outwardly from the impeller 46i.e. by a horizontal tube which is in effect an extension of the second horizontal
25 limb shown.) This pIacement of the tube 48 is designed so that none of the tube 48,
which is made of polyvinyl chloride, protrudes from the cylindrieal wall of the outer
cylinder 14, since any protruding parts of the tube would be susceptible to damage
during transit (if in place during such transit), or damage after install~tion caused
by, for example, children, household pets, or careless handymen. A mixture control
3û device in the orm of a mRnually~operable butterfly valve 50 is disposed in the
second horizontal limb of the tube 48 (but may alternatively be disposed in the
ver$ical limb of the tube 48); this valve permits adjustment o the natural gas/Air
ratio in the mixture provided by the impeller 46 to the gas burner 40 and is
accessible via a removable psnel (not shvwn) in the outer cylinder 14; naturally, ~
35 corresponding aperture is provided in the insulating jacket I6 adjacent this remov-
able panel. The placement of the valve S0 is designed to permit ready adjustment of
i~84~1
--10-
the vQlve 50 by the person installing the ~pparatus but to render later access by
other persons difficult in order to ensure, as far QS possible, that untrained persons
do not ett~mpt to adjust this v~lve setting, since improper adjustment could result
in incomplete combustion of the n~turQl gas or other undesirable consequences.
05 Natural gas is supplied to the impeller via ~ gas line 52 provided with ~ gas valve 53;
the line 52 intersects the second horizontal limb of the tube 48 immediately
adjacent the inlet of the impeller 46.
Besides the gas burner 40, the combustion ch~mber 38 contains ~n electrical
ignition device 54 which c~n be of any conventionsl type and which is used in the
10 conventional maMer to ignite the combustible gas/air mixture emerging from the
gQS burner 40, and Q flame sensor 56 which is also of a conventional type and which
serves to check that the gQs/air mixture emerging from the gas burner 40 hfls been
correctly ignited by the ignition device 54. The purpose of the flame sensor 56 will
be described in more detail below. (The eleetrical ignition device 54 and the flame
15 sensor 56 may alternatively be combined into a single device which performs both
functions).
The combustion products produced by burning of the gfls/air mixture within the
combustion chamber 38 pass through an exhaust conduit including a heat exchangercomprising ~ riser section 58 which is connected to the upper, n~rrower end of, and
20 extends vertically upw&rdly from, the frusto-conical section 36 of the combustion
chamber member, and a helic~l section 60, which extends downwardly from the
upper end of the riser section 58. The riser section 58 lies along the axis of the tank
12 and the axis of the helicQl section 60 coincides with the axis of the tank 12. It has
been found that this form of he~t exchanger provides Q very efficient heat transfer
25 from the combustion products to water in the tank 12, because the downward slope
of the helical section 60 contributes to a higher coefficient of convective heattransfer (since the coolest downstream section of the he~t exchanger is in contact
with the coolest water adjacent the base of the tank 12~ and therefore to higherefficiency of the heat exchanger. It should be noted that the lower end of the
30 helical section 60 lies adjacent the base 24 of the tank 12; since water heated by the
heat exchanger tends to rise within the tank l2, it is desirable that the lower end of
the heat exchanger extend adjacent the base OI the tank l2 in order to ensure that a
large mass of cold water is not left below the heat exchanger and remains unheated
thereby. The combustion products le~ving the lower end of the helical section of35 the heat exchanger pass through a further portion of the aforementioned exhaust
conduit which ~cts as Q condensate trap, this further portion, including a first
~2S84~l
vertical ~ection 62 extending ~ertically downwardly from the lower end of the
helienl section 60 ~hrough the base 24 of the tank 12, a short horizontRl section 64
which extends into the insulating bl~nket 16, and a second, long vertical section 66
which extends vertically upwardly from the horizont~l section 64 through the
05 insulating blanket 1~ ~nd through sn aperture provided in the upper end plate 18.
~rom the upper end of the second vertical section 66, ~ horizsntal section 68 c~rries
the combustion products out of the building in which the apparatus is installed. tThe
form of the section 68 may vary for the reasons already st~ted in relQtion to the
corresponding section of the inlet tube 48, and similarly the vertical section 66
10 and/or horizontal section 68 may be omitted entirely.) The placement of the second
vertical section 66 within the insulating blanket 16 serves to prevent accidental
damage to the second vertical section, as already described in relation to the air
inlet tube 48.
A water supply line 70 used to supply water to the tank 12 pRsses through an
15 aperture provided in the upper endplate 18 and then passes vertically downwsrdly
within the second vertical section 66 of the exhaust conduit, along the first
horizontal section 64 of this conduit and then vertically upwardly through an
aperture provided in the base 24 of the tank 12 into the interior of that tank. The
disposition of the water supply line 70 within the sections 66 and 64 of the exhaust
20 conduit allows countercurrent flow between water passing along the line 70 and
combustion products passing along the section 66 and 64, and allows heat exchsnge
to take place between the combustion products passing along the exhaust conduit
and the water entering the tank via the water supply line, thus pre-warming the
water entering the tank 12 and further cooling the combustion products, thereby
25 increasing the efficiency of the apparatus. At the point where it enters the exhaust
conduit, the water supply line is provided an U-bend 72; this U-bend reduces thetendency for water warmed by heat transfer from the combustion products passing
~long the exhaust conduit from rising into the portion of the water supply line 70
lying aboYe the upper endplate 18. Such back-flow o water into the part of the
30 water supply line 70 lying above the plate 18 is obviously undesirable since it leads to
heat loss from the apparQtus, thus reducing the eIficiency thereof. In additionl the
resuttant leakage of hot water into the cold water system may produce undesir~ble
changes in tempersture therein.
The cooling of the combu~tion products which occurs in the heat exehanger 58,
35 60 by heat transfer to water in the tank 12, an~ in the exhaust conduit by heat
transfer to the water in the water supply line 70, causes condens~tion of liquid from
S~
--12--
the combustion products, and the resultant condensate passes into the first hori-
zont~l section 64. Thus, the U-shape formed by the sections S2, 64 and 66 serves as
a condensQte trap. A drain conduit 74 extends downwardly from the irst horizontal
section S4 and serves to drain condens~te therefrom. The drain ~onduit 74 is
05 provided with ~ bend below tbe first horizontaI section 64; this U-bend rapidly
becomes filled with condensate whell the app~ratus is in operation, and the
condensate filling the lowest part of the U-bend acts RS a liguid seal to prevent
gaseous combustion products flowing out through the drain conduit 74. The outletend (not shown) of the drain conduit 74 is connected to a suitable drain line.
As already mentioned, ehe apperatus 10 serves ~s both a w~ter he~ter and a
spsce heater or furnace. A water outlet line 76 extends from within the t~nk 12
through the upper end wall of the tank and through the upper endplate 18. This
water outlet tube 76 serves to supply hot water for domestic use, as indicated
schemRtically by n branch line. ~nother branch line 80 leQves the water output line
15 7~ a short distRnce above the upper endplflte 18 and acts as a water supply line to
supply hot water from the tank 12 to a water inlet of a space heating assembly
comprising R second heat exchanger in the form OI a coil 82 disposed within ~ duct
84, which forms part of the ductwork of R conventional forced-air domcstic spaceheating system. Air is forced over the coil 82 by means of ~ thermostatic~Lly-
20 controlled fan 86 (shown only schematically~. W~ter from a water outlet of the coil82 is returned to the tank via a water return line 88, which intersects the water
supply line 70 a short distance aboY~ the upper endplate 18. Thus, water returning
from the coil 82 to the tank ilows through the section of the liquid supply line 70
lying within the sections 66 ~nd 64 of the exhaust conduit, thereby causing the
25 returning water to flow countercurrent to, and receive heRt from, the combustion
products passing along these sections of the exhaust conduit. As will be apparerlt to
those skilled in this field,the apparatus 10 csn also be used in con~unction with a
baseboard radiator or other type of hot wnter spacc heating system.
The dimensions of the Yarious parts of the apparatus 10 c~n of course vflry
30 considerably depending up~n various factors, and in particulRr upon the desired
thermal output of the apparatus. However, a typical 100,000 Btu/hr. (2~200
KCal/hr.) appQratus for domestic use mAy have a tank 12 having a capacity of about
40 U.S. gallons ~151 liters~ and approximately 16 inches (45 cm.~ in diameter. In
steady state operRtion, such a unit would use lûO cubic ft. (2.83 m3) of naturel g~s
35 per hour and approximately 11,000 cubic ft. (311 m ) of air per hour, assuming that
the amount of air is set at the optimum value of approximately 10% ~bove that
12S8411
-13-
stoichiometric~lly required for combustion of the gas. This gas/air mixture will be
forced by the impeller 46 ~t a pressure of approximately 4 inches (l0 cm.) w~tergauge pressure into the internal chamber of the gas burner 40; it should be noted
th~t this operating pressure is considerably greater than that employed in supplying
05 air to most g~s furnaces since the resistance to flow provided by the apertures In
the gas burner and by the he~t exchQr~ger 58, 60 reguires a consider~bly ~reateroperating pressure. The cylindrical portion of the gas burner 40 has Q length of appro2ci~nately 4 inches (10 cm ) and a diameter of approximately 2.2 inches (5.5
cm.). The uppermost 3 inches (7.5 cm.) of the cyIindrical wall of the gas burner 14 is
10 pierced by apertures ha~ing Q diameter of 0.033- 0.036 inches (0.84-0.91 mm.) (though
the apertures could vary within the range of 0.020-0.062 inches (0.50-1.57 mm.) if
desired) spnced on ~3 square grid at intervals of approximfltely 0.070 inches (1.78
mm.); the lines within this grid run parallel to the axis of the cylindrical gas burner
40 and on circles runn~ng llround the gns burner. The helical section 60 of the heat
15 exchanger is formed of a stainless seeel tube of diameter not greater than 2 inches
(~ cm.) and has a total length of ~pproximately 30 ft. ~9.1 m.).
It has been found th~t El 100,000 Btu/hr. (25,200 KCnl/hr,) unit constructed
having the foregoing dimensions hns a steady-state efficiency in excess of 95% snd
experiments indicaee that the seasonal efficiency or service efficiency of the
20 apparatus will be about 90%. Due to the simpIicity of the design, the apparatus is
significantly less expensive to construct than other high effici~ncy gas furnaces ~nd
gas water henting systems presently av~ilable, being comparable to the total
instnlled cost of Q convention~l gas furnace ~nd gas water heRter. The combustion
products leaving the apparatus have Q low nitrogen oxide content, probably due to
25 the near stoichiometric combustion conditions within the combustion chamber 38
made possible by the control of the gas/air ratio which the apparatus provides. The
apparatus does not need a chimney or a class A or B vent; the outlet from the
exhsust conduit may be discharged through corrosion resistant tubing through anyconvenient externel surface of the building in which the apparatus is instnllad. It
30 should be no~ed that the eombined stendy-state efficiency of water and space
heating of about 95% is greater than ~hat of any combined system available.
It will of course be appreciated th~t if desired the heating coil 82, the duct 84
and the fan 86 could be replaced by one or more conventional wnter-filled radi~tors
for spnce heating purposes, a forced-air system being shown in the drswing simply
35 because this is the most common type of system used in domestic space heating.
Obviously, if w~ter-filled radi~to~s are to be used in space heating, it will be
~25~
--14-
necessary to provide the wAter outlet line 76 or the return line 88 with ~ circulnting
pump to effe~t cir~ulstion of water through the radiators. (In practice, ~lthough not
shown in the accompanying drawing, a circul~ting pump will in practic~ usuQlly be
necessary in forced-sir systems ~Is~)
05 All the essentlal features of the appar~tus 10 have already been described.
However, in order to ensure the sQfest possible operation under domestic conditions,
it is desirable that ~ number of safety devices be incorpor~ted into the Qpparatus to
cope with possible equipment failures and unusual operating conditio~s. As already
mentioned, the flame sensor 56 is provided within the combustion chamber 38 to
10 detect an absence of name due either to failure of the ignition device 54 or to
failure to supply proper quantities of gas because of improper operation of the
impeller 46. When the flame sensor detects an absence of fl~me while the impeller
46 should be operating, the name sensor 56 is arranged to close a switch (not shown)
which shuts down the impeller 46. Also, the air inlet line 48 is provided with 815 pressure sensor (not shown) adjacent the inlet to the impeller 46. When the impeller
is operating normally, significant suction exists in the ~ir inlet conduit 48 and if
inadequate suction exists in this line, the impeller is not operating correctly and
accordingly the pressure sensor is arranged to shut the impeller down. The pressure
sensor is also arranged to shut the impeller down if excessive suction exists in the
20 line 48 as a result of, for example, obstruction of the air intake to this line by debris
or other materials.
Those skilled in this field will appreciate that, although the specific embodi-
ment of the invention described ~bove is intended for use as a combined water/space
heating system, the appQratus of the invention may also be useful as a high-
25 efficiency water-heating system without space-heating capability, especially in
commercial water heating systems.
