Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
202877i
INTEGRATED HOT ~ATER SUPPLY AND
SPACE ~BATING 8Y8TBM
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This invention relates generally to an integrated system for
space heating and for heating water for general service use.
Specifically, the invention relates to a heating system
having a water heating module employing the latent heat of
condensation of the hot gases of combustion from the system
burner to preheat fluids entering the relatively small fluid
heating volume of the module and thus achieving a high
thermal efficiency.
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Conventional space heating systems using a central furnace
all operate on the same general principles. Air for a space
to be heated is circulated through and is heated by a heat
exchanger. The heat exchanger may be in contact with the
burning fuel and its hot gases of combustion or in contact
with a secondary fluid which has been heated by a burning
fuel. Such systems are usually either of the forced air or
hydronic type, but may be a combination of both. Most such
systems in general use have indirect furnaces, in which the
air being heated is not in direct contact with the burning
fuel or its gases of combustion.
In a conventional forced air heating system, the furnace has
a combustion chamber in which a flame generates heat and
gases of combustion. The heat and combustion gases rise
through an attached heat exchanger before exiting through a
flue or chimney. Air from the space to be heated is
circulated around the exterior of the heat exchanger where
it is heated by convection and conduction from the heat
exchanger.
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In a conventional hydronic heating system, a fluid is heated
in a heat exchanger in contact with burning fuel within a
furnace. The fluid heat exchanger is in a closed loop by
which heated fluid is circulated to radiators located in the
space to be heated. The air in the space is usually heated
by convective flow around the radiators.
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In a combination system, a fluid is heated as in a hydronic
system, but then circulates through a closed loop to a heat
exchanger, where forced air passes over the heat exchanger
to be heated before being circulated as in a conventional
forced air heating system.
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Convection water heaters used to supply hot water for
general domestic and other uses in houses and other
buildings usually consist of a relatively large hot water
storage tank. Cold water enters the tank, where it is
heated by a flame burner located at the bottom of the tank.
A flue generally passes from the combustion chamber at the
bottom of the tank through the tank to carry gases of
combustion produced by the burner to an external flue or
chimney. In most residential and commercial installations,
the system for heating water is separate from the system for
space heating.
Both space heating furnaces and hot water heaters of
conventional design exhaust the gases of combustion to the
atmosphere through flues or chimneys while the gases are
still relatively hot (sometimes in excess of 500F),
resulting in relatively low thermal efficiencies, as much of
the energy contained in the burning fuel is lost "up the
flue" without heating air or water. Ambient heat losses
from the relatively large volume of water in conventional
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2028771
hot water heaters contribute to the degradation of
efficiency in those systems.
The relatively low thermal efficiency of conventional space
and hot water heating systems result in higher operating
costs over the life of such systems. In addition, those
systems are relatively costly to install, because of the
cost of the chimney or flue required, and, as is usually the
case, the necessity to provide separate fuel lines and
separate chimneys or flues for each of the separate space
heating and water heating systems.
Economic and environmental considerations have led to
increased interest in improving the thermal efficiency and
eliminating energy waste in the design and construction of
space and water heating systems. There is also interest in
producing compact heating units which will occupy a minimum
of space within buildings. Generally, however, an increase
in furnace efficiency does not necessarily result in a
reduction of size, because the structure of the furnace is
determined by the requirement for relatively large heat
exchanger surface areas to transfer heat from the burning
fuel and hot combustion gases to the space air or heat
transfer fluid. Similarly, hot water heater size has not
decreased, but in some modern, more energy efficient
designs, it has actually increased.
There is, therefore, a continued, demonstrated need for a
compact, yet highly efficient integrated system for space
and water heating.
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An object of the present invention is to combine, in a
single integrated system, the functions of both space and
water heating.
Another object of the present invention is to achieve hiqh
thermal efficiency in a compact system for both space and
water heating.
A further object of the invention is to attain the
capability, in a compact system, to supply instantaneous and
continuous hot water service and simultaneously to heat a
space or spaces yet, at the same time, to minimize burner
cycling during periods of lower intermittent demand for hot
water.
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These and other objects of the invention are attained in an
integrated system having a heating module which supplies
heated fluid to a fluid flow loop. The fluid is circulated
in the loop to a space heating heat exchanger by a
circulating pump. The module also supplies heated water for
general domestic or other use. The heating module is of the
high thermal efficiency condensing type and contains storage
for a small volume of heated water to supply small
intermittent hot water demands. The system may be
configured to operate on an open loop principle, in which
space heating and water heating subsystems are combined and
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share common lines, or a closed loop system, in which the
space heating subsystem is isolated from the water heating
subsystem.
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The novel features embodied in the invention are pointed out
in the claims which form a part of this specification. The
drawings and descriptive matter describe in detail the
advantages and objects attained by the invention.
The accompanying drawings form a part of the specification.
Throughout the drawings, like reference numbers designate
like or corresponding elements.
FIG. 1 is a schematic representation of one embodiment of
the present invention, in which the system operates on an
open loop principle, i.e. the entire system is filled with
potable water and service hot water is drawn directly from
the same source that supplies hot water to the space heating
heat exchanger.
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FIG. 2 is a schematic representation of another embodiment
of the present invention, in which the system operates on a
closed loop principle, i.e. the loop subsystem supplying
heated fluid to the space heating heat exchanger is closed
and separate from the subsystem for heating service hot
water.
FIG. 1 depicts schematically one preferred embodiment of the
~`'JI invention, in which the system operates in an open loop
principle, i.e. the entire system is filled with potable
water and service hot water is drawn from the same source
~ that supplies hot-water to the space heating heat exchanger.
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202877i
In FIG. 1, heating system 21 includes an integrated heating
module 22, space heating heat exchanger 23 and a circulating
fluid loop. Space heating heat exchanger 23 typically may
be a plate fin heat exchanger or a radiator having air
flowing through it in the direction of the large arrow into
the space 32 to be heated. Air in space 32 may circulate
through heat exchanger 23 by convection or be forced through
by a fan. Heat exchanger 23 receives hot water from heating
module 22 through inlet pipe 25. Water circulates from
space heating heat exchanger 23 through outlet pipe 26 to
circulating fluid pump 24, then is returned to heating
module 22 through pump discharge pipe 27. Expansion tank 31
is connected to pump discharge pipe 27 to provide volume for
expansion of water as it is heated and to dampen any
pressure surges in the system.
Heating module 22 includes burner 41 in burner cavity 45
supplied with combustible gas 42 through regulator 43. The
burner may be a conventional ribbon type, a jet or "inshot"
burner or preferably, a radiant infrared burner. Ignition
device 44, which initially lights the burner on start-up of
the module, is a conventional furnace control not discussed
in detail here. In such a control, a spark ignition or hot
surface igniter system ignites the burner and a flame
detector senses whether combustion actually occurs.
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Within heating module 22 are heater tank 51 and preheater 52
separated by partition 57. Partition 57 may be insulated.
Water in heater tank 51 is heated by heat from burner 41 and
tank flue 53. The volume of heater tank 51 is sized to
provide a small amount of stored hot water to reduce burner
cycling during periods of low demand on the system.
Pressure relief valve 55 protects heater tank 51 from
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overpressure. Tank flue 53 extends from burner cavity 45
through heater tank 51, partition 57 and preheater 52.
Induction draft unit 56, such as a fan, draws on tank flue
53, causing a flow of gases of combustion from burner cavity
1 45, through tank flue 53 and out of the module to external
vent flue 54 from which the gases are exhausted to the
atmosphere. Gas flow through burner 41, burner cavity 45,
tank flue 53 and vent flue 54 may also be effected by use of
a blower upstream in the gas flow path. Heat is transferred
to water in heater tank 51 and preheater 52 from the hot
gases of combustion in tank flue 53.
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Cold makeup water is supplied to the system via cold water
inlet 61 from a source of water such as a potable water
supply line. A check valve (not shown) may be installed in
the potable water supply line upstream of cold water inlet
61 to prevent back flow into the line from system 21. Cool
water returning from space heating heat exchanger 23 through
pump discharge pipe 27 mixes with makeup water, if any, from
cold water inlet 61 and enters preheater 52. In preheater
52, the cool water is preheated by hot gases of combustion
in tank flue 53 before entering heater tank 51 via
preheater-to-heater tank water transfer line 63. The
preheating process also serves to condense combustion gases
in tank flue 53, increasing the thermal efficiency of the
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Hot water is drawn from heating module 22 via heater tank
hot water outlet 64 on demand from either space heating heat
exchanger 23 or from hot water service line 65. A
thermostatic control device, not shown, is set to control
the temperature of the hot water in heater tank 51. If the
set temperature at heater tank hot water outlet 64 is
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202877i
greater than that desired in hot water service line 65,
optional tempering valve 72, controlled by a thermostat (not
, shown), and tempering water supply line 71 can be provided
; to mix cold water from cold water supply 61 with hot water
from heater tank hot water outlet 64 to achieve the desired
water temperature in hot water service line 65.
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FIG. 2 is a schematic representation of another of the
;, preferred embodiments of the invention, in which the system
operates on a closed loop principle, i.e. the loop supplying
heat transfer fluid to the space heating heat exchanger is
closed and separate from the subsystem for heating service
A hot water. The heat transfer fluid in the space heating
loop may be water, but preferably a mix of water and glycol.
A number of elements of the closed loop embodiment of the
present invention are common or have like function to
similar elements of the embodiment disclosed.in the above
description of the open loop system. Features that are
common to the two embodiments and function similarly have
the same reference numbers in the closed loop embodiment
depicted in FIG. 2 as in the open loop embodiment depicted
in FIG. 1. The major differences in the two embodiments are
in the internal configurations of the heating modules and
~ the connections of the modules to the remainder of the
;i, system made necessary by the requirement, in the closed loop
embodiment, to isolate the space heating subsystem from the
hot water service subsystem.
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Referring to FIG. 2 and the above description of the open
i loop system shown in FIG. 1, heat transfer fluid for space
:~^ heating is heated within heating module 22 by fluid heater
83 which is immersed in the water volume of heater tank 51
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of heating module 22. Heat transfer fluid circulates from
heating module 22 through a closed loop from heater tank hot
liquid outlet 67 through heat exchanger inlet pipe 25, space
heating heat exchanger 23, where heat is transferred to air
to be heated, heat exchanger outlet pipe 26, circulating
fluid pump 24 and pump discharge pipe 27 before returning to
heating module 22. There is no mixing of the heat transfer
fluid with water from cold water supply 61. Within
preheater 52 of heating module 22 is fluid preheater 81,
immersed in the water volume of preheater 52. When system
21 is operating, the water volume in preheater 52 will
generally be at a higher temperature than the returning heat
transfer fluid in fluid preheater 81. The water volume will
therefore preheat the heat transfer fluid in fluid preheater
81, thus reducing the temperature of the water volume in
preheater 52 and enhancing the condensation of the gases of
combustion in tank flue 53. From fluid preheater 81, the
heat transfer fluid flows to fluid heater 83 in heater tank
51 of heating module 22 via fluid preheater-to-fluid heater
transfer line 82. Water to be heated for hot water service
is taken from cold water supply 61 and flows through
preheater 52, where it is preheated by and condenses the hot
gases of combustion in tank flue 53. The preheated water
then flows through preheater-to-hèater tank water transfer
line 63 into heater tank 51, where it is heated by heat from
burner 41 and tank flue 53. Hot water is drawn from heating
module 22 via heater tank hot water outlet 64 on demand from
hot water service line 65. If necessary optional tempering
valve 72, controlled by a thermostat (not shown), which
mixes water from cold water supply 61 with hot water from
heater tank hot water outlet 64 via tempering water supply
line 71, can be provided to achieve the desired hot water
service supply temperature.
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The physical size and operating parameters of the system
embodying the invention are variable and depend on the
specific application to which the system is put. For use in
a typical residential application, the heating module would
have a heating capacity of approximately 110,000 BTU/HR. In
,s such an installation, the volume of the heater tank 51 in
the heating module 22 would be about six U.S. gallons.
Satisfactory space heating performance should be attained
with heater tank outlet temperatures in the range of 120-F -
200-F. If that range is greater than that desired in the
hot water service line, the heater tank output can be
tempered to attain the desired service line water
temperature.
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The open loop embodiment offers the advantages of reduced
cost and less complexity over the closed loop embodiment.
However, the closed loop system may have advantages in
certain applications, such as where local building or
plumbing codes prevent the use of open loop systems.
While two preferred embodiments of the present invention are
shown and described, those skilled in the art will
appreciate that many variations may be constructed and yet
remain within the scope of the invention. As discussed
above, the system of the invention may be made in a wide
range of sizes and heating capacity for use in a variety of
applications. The drawings show a single space heating heat
exchanger while the system may be configured with more than
one such heat exchanger. The system could be used as solely
a hydronic space heating system or solely as a water heating
system. It is intended, therefore, that the scope of the
present invention be limited only by the scope of the below
claims.
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