U.S. patent application number 10/145685 was filed with the patent office on 2003-11-20 for organic rankine cycle micro combined heat and power system.
Invention is credited to Anson, Donald, Hanna, William T., Yates, Jan B..
Application Number | 20030213245 10/145685 |
Document ID | / |
Family ID | 29418667 |
Filed Date | 2003-11-20 |
United States Patent
Application |
20030213245 |
Kind Code |
A1 |
Yates, Jan B. ; et
al. |
November 20, 2003 |
ORGANIC RANKINE CYCLE MICRO COMBINED HEAT AND POWER SYSTEM
Abstract
A micro combined heat and power system includes at least a heat
source, an expander, a condenser, a pump, recuperator and conduit
for circulating a working fluid. After the working fluid is
expanded, its thermodynamic properties allow it to remain in a
superheated state so that it selectively can give up at least a
portion of its excess heat first to the recuperator and then to the
condenser, which can then subsequently exchange heat with a
circulating air, water or related loop to provide space heat or
domestic hot water that can be used, for example, to heat a
dwelling. The amount of heat exchange in the recuperator can be
adjusted to allow the output ratio of heat to electricity to be
varied while maximizing overall system efficiency. Additional
componentry, such as an accumulator, enhances system operability by
smoothing out working fluid flow rates during transitional
operation, such as start-up and shut-down.
Inventors: |
Yates, Jan B.;
(Reynoldsburg, OH) ; Hanna, William T.; (Gahanna,
OH) ; Anson, Donald; (Worthington, OH) |
Correspondence
Address: |
Killworth, Gottman, Hagan & Schaeff, L.L.P.
Suite 500
One Dayton Centre
Dayton
OH
45402-2023
US
|
Family ID: |
29418667 |
Appl. No.: |
10/145685 |
Filed: |
May 15, 2002 |
Current U.S.
Class: |
60/651 ;
60/671 |
Current CPC
Class: |
F01K 17/02 20130101;
Y02E 20/14 20130101; F01K 25/08 20130101 |
Class at
Publication: |
60/651 ;
60/671 |
International
Class: |
F01K 025/08; F01K
025/00 |
Claims
We claim:
1. A cogeneration system comprising: a heat source; a working fluid
circuit comprising: conduit configured to transport an organic
working fluid through said working fluid circuit, at least a
portion of said conduit disposed adjacent said heat source such
that said organic working fluid disposed in said portion of said
conduit is superheated during operation of said heat source; an
expander in fluid communication with said conduit such that said
organic working fluid received therefrom remains superheated after
expansion in said expander; a condenser in fluid communication with
said expander; a pump configured to circulate said organic working
fluid through at least said conduit, expander and condenser; and a
recuperator coupled to said conduit and configured to selectively
increase the temperature of said organic working fluid entering
said portion of said conduit disposed adjacent said heat source;
and at least one energy conversion circuit operatively responsive
to said working fluid circuit such that upon operation of said
cogeneration system, said at least one energy conversion circuit is
configured to provide useable energy.
2. A cogeneration system according to claim 1, wherein said
recuperator comprises: a first heat exchange passage disposed
between said expander and said condenser; and a second heat
exchange passage disposed between said pump and said part of said
conduit adjacent said heat source.
3. A cogeneration system according to claim 1, wherein said at
least one energy conversion circuit comprises: a generator coupled
to said expander to produce electricity; and a circulating fluid
medium in thermal communication with said condenser such that at
least a portion of the heat given up by said organic working fluid
in said condenser provides increased thermal content to said
circulating fluid medium.
4. A cogeneration system according to claim 3, wherein said
expander is a scroll expander.
5. A cogeneration system according to claim 3, wherein said
circulating fluid medium is configured to transport a space heating
fluid.
6. A cogeneration system according to claim 5, wherein said space
heating fluid is water.
7. A cogeneration system according to claim 5, wherein said space
heating fluid is forced air.
8. A cogeneration system according to claim 3, wherein said
circulating fluid medium is configured to transport domestic hot
water.
9. A cogeneration system according to claim 1, wherein said heat
source is a burner.
10. A cogeneration system according to claim 1, further comprising
an accumulator responsive to pressure differences within said
working fluid circuit such that under a first operating condition,
said accumulator adds excess working fluid to said working fluid
circuit, and under a second operating condition, said accumulator
removes excess working fluid from said working fluid circuit.
11. A cogeneration system according to claim 10, wherein said
accumulator is intermediate said condenser and said pump.
12. A cogeneration system according to claim 10, wherein said
accumulator is situated at a higher elevation relative to said pump
to promote the gravity flow of said additional working fluid from
said accumulator to said pump during said first operating
condition.
13. A cogeneration system according to claim 10, further comprising
a warming device thermally coupled to said accumulator such that
during at least a portion of the period that said cogeneration
system is not in operation, said accumulator is maintained at a
higher temperature than the remainder of said working fluid
circuit.
14. A cogeneration system according to claim 10, further comprising
a valve configured to selectively fluidly isolate said accumulator
from the remainder of said working fluid circuit.
15. A cogeneration system comprising: a heat source; a working
fluid circuit comprising: conduit configured to transport an
organic working fluid through said working fluid circuit, at least
a portion of said conduit disposed adjacent said heat source such
that said organic working fluid disposed in said portion of said
conduit is superheated during operation of said heat source; an
expander in fluid communication with said conduit such that said
organic working fluid received therefrom remains superheated after
expansion in said expander; a condenser in fluid communication with
said expander; a pump configured to circulate said organic working
fluid through at least said conduit, expander and condenser; and an
accumulator responsive to pressure differences within said working
fluid circuit such that under a first operating condition, said
accumulator adds excess working fluid to said working fluid
circuit, and under a second operating condition, said accumulator
removes excess working fluid from said working fluid circuit; and
at least one energy conversion circuit operatively responsive to
said working fluid circuit such that upon operation of said
cogeneration system, said at least one energy conversion circuit is
configured to provide useable energy.
16. A cogeneration system according to claim 15, wherein said
accumulator is intermediate said condenser and said pump.
17. A cogeneration system according to claim 15, wherein said
accumulator is situated at a higher elevation relative to said pump
to promote the gravity flow of said additional working fluid from
said accumulator to said pump during said first operating
condition.
18. A cogeneration system according to claim 15, further comprising
a warming device thermally coupled to said accumulator such that
during at least a portion of the period that said cogeneration
system is not in operation, said accumulator is maintained at a
higher temperature than the remainder of said working fluid
circuit.
19. A cogeneration system according to claim 15, further comprising
a valve configured to selectively fluidly isolate said accumulator
from the remainder of said working fluid circuit.
20. A Rankine cycle cogeneration system comprising: a heat source;
a working fluid circuit comprising: conduit configured to transport
an organic working fluid through said working fluid circuit, at
least a portion of said conduit disposed adjacent said heat source
such that said organic working fluid disposed in said portion of
said conduit disposed adjacent said heat source is heated during
operation of said heat source; an expander in fluid communication
with said conduit such that said organic working fluid received
therefrom remains superheated after said expansion in said
expander; a condenser in fluid communication with said expander; a
pump configured to circulate said organic working fluid through at
least said conduit, expander and condenser; a recuperator coupled
to said conduit and configured to selectively increase the
temperature of said organic working fluid entering said portion of
said conduit disposed adjacent said heat source; and an accumulator
intermediate said condenser and said pump; and at least one energy
conversion circuit operatively responsive to said working fluid
circuit such that upon operation of said cogeneration system, said
at least one energy conversion circuit is configured to provide
useable energy.
21. A cogeneration system according to claim 20, wherein said
accumulator is responsive to pressure differences within said
working fluid circuit such that under a first operating condition,
said accumulator adds excess working fluid to said working fluid
circuit, and under a second operating condition, said accumulator
removes excess working fluid from said working fluid circuit.
22. A cogeneration system according to claim 21, wherein said
accumulator is situated at a higher elevation relative to said pump
to promote the gravity flow of said excess working fluid from said
accumulator to said pump during said first operating condition.
23. A Rankine cycle cogeneration system comprising: an organic
working fluid; an evaporator capable of superheating said organic
working fluid, said evaporator comprising: a burner; and conduit
adjacently spaced relative to said burner such that during burner
operation heat transferred therefrom is sufficient to superheat
said organic working fluid disposed in said conduit; a
substantially closed-loop working fluid circuit in thermal
communication with said burner, said substantially closed-loop
working fluid circuit configured to transport said organic working
fluid therethrough, said substantially closed-loop working fluid
circuit comprising: an expander in fluid communication with said
conduit such that said organic working fluid received therefrom
remains superheated after expansion in said expander; a condenser
in fluid communication with said expander; a pump configured to
circulate said organic working fluid through at least said conduit,
expander and condenser; a recuperator coupled to said conduit and
configured to selectively increase the temperature of said organic
working fluid entering said evaporator; and an accumulator fluidly
responsive to pressure differences within said working fluid
circuit such that under a first operating condition, said
accumulator adds excess working fluid to said working fluid
circuit, and under a second operating condition, said accumulator
removes excess working fluid from said working fluid circuit; and
at least one energy conversion circuit comprising: a generator
coupled to said expander to produce electricity; and a circulating
fluid medium in thermal communication with said condenser such that
at least a portion of the heat given up by said organic working
fluid in said condenser provides increased thermal content to said
circulating fluid medium.
24. A dwelling configured to provide at least a portion of the heat
and power needs of occupants therein, said dwelling comprising: a
plurality of walls defining at least one room therebetween; a roof
situated above said plurality of walls; at least one ingress/egress
to facilitate passage into and out of said dwelling; and a
cogeneration system in heat and power communication with said at
least one room, said cogeneration system comprising: a heat source;
a working fluid circuit comprising: conduit configured to transport
an organic working fluid through said working fluid circuit, at
least a portion of said conduit disposed adjacent said heat source
such that said organic working fluid passing through said portion
of said conduit disposed adjacent said heat source is superheated
during operation of said heat source; an expander in fluid
communication with said conduit such that said organic working
fluid received therefrom remains superheated after expansion in
said expander; a condenser in fluid communication with said
expander; a pump configured to circulate said organic working fluid
through at least said conduit, expander and condenser; and a
recuperator coupled to said conduit and configured to selectively
increase the temperature of said organic working fluid entering
said portion of said conduit disposed adjacent said heat source;
and at least one energy conversion circuit operatively responsive
to said working fluid circuit such that upon operation of said
cogeneration system, said at least one energy conversion circuit is
configured to provide useable energy.
25. A dwelling according to claim 24, further comprising a
controller to control at least the flow rate of said organic
working fluid.
26. A dwelling according to claim 25, wherein said controller is in
signal communication with an outdoor sensor.
27. A dwelling according to claim 25, wherein said controller is
responsive to occupant input.
28. A dwelling according to claim 27, wherein said controller
responsive to occupant input is a thermostat.
29. A dwelling according to claim 24, further comprising an
accumulator responsive to pressure differences within said working
fluid circuit such that under a first operating condition, said
accumulator adds excess fluid to said working fluid circuit, and
under a second operating condition, said accumulator removes excess
working fluid from said working fluid circuit.
30. A micro combined heat and power system comprising: an electric
production subsystem comprising: an organic working fluid; a burner
for superheating said organic working fluid; a scroll expander
configured to receive and expand said organic working fluid in a
superheated state; a generator operatively coupled to said scroll
expander to produce electricity; a condenser disposed in fluid
communication with said scroll expander; a pump to circulate said
organic working fluid through said electricity generating loop; a
recuperator in thermal communication with said expander such that
during operation of said micro combined heat and power system, said
superheated organic working fluid exiting said expander selectively
gives up at least a portion of its excess heat to increase the
temperature of said organic working fluid entering said burner; and
an accumulator intermediate said condenser and said pump; and a
heat production subsystem comprising an circulating fluid medium in
thermal communication with said condenser.
31. A method of producing heat and electrical power from a
cogeneration device, the method comprising the steps of: providing
a heat source; configuring a first circuit to transport an organic
working fluid adjacent said heat source; superheating said organic
working fluid; expanding said superheated organic working fluid to
generate electricity; maintaining said organic working fluid in
said superheated state at least until said organic working fluid
enters a recuperator; giving up at least a portion of the excess
heat from said superheated organic working fluid in said
recuperator; exchanging at least a portion of the excess heat from
said organic working fluid that has passed through said recuperator
in a condenser with a circulating fluid medium such that after
passing through said condenser, said organic working fluid is no
longer in a superheated state; adding heat to said organic working
fluid that is no longer in a superheated state in said recuperator;
and returning said organic working fluid such that it is adjacent
said heat source.
32. A method according to claim 31, wherein said circulating fluid
medium is configured to transport a space heating fluid.
33. A method according to claim 32, wherein said space heating
fluid is water.
34. A method according to claim 31, wherein said space heating
fluid is forced air.
35. A method according to claim 31, wherein said circulating fluid
medium is configured to transport domestic hot water.
36. A method according to claim 31, further comprising adjusting
the flow rate of said organic working fluid through said
recuperator in response to a set point condition in said
circulating fluid medium.
37. A method according to claim 36, wherein said set point
condition is a hydronic fluid temperature in said circulating fluid
medium.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention generally relates to improvements in
operability of a Rankine cycle cogeneration system using an organic
working fluid, and more particularly to the integration of one or
more components into such a system to increase flexibility in
system start-up, output heat-to-power ratio and hot water
production.
[0002] The concept of cogeneration, or combined heat and power
(CHP), has been known for some time as a way to improve overall
efficiency in energy production systems. With a typical CHP system,
heat (usually in the form of hot air or water) and electricity are
the two forms of energy that are generated. In such a system, the
heat produced from a combustion process can drive an electric
generator, as well as heat up water, often turning it into steam
for dwelling or process heat. Traditionally, CHP systems have been
large, centrally-operated facilities under the control of the state
or a large utility company, sized to provide energy for many
thousands of users. If the region being served by the CHP has as
part of its infrastructure adequate heat transporting capability,
the centrally-generated heat and electric power model of the large
CHP system can, within limits, function reasonably efficiently and
reliably. In the absence of adequate heat transport capability,
however, while the region's electric power needs would continue to
be met by the central generating station, the heat needs would need
to be fulfilled separately and remotely from the electricity
production, often near or within the building housing the end-user.
This latter configuration typically includes the presence of one or
more boilers that could generate hot water or steam to provide most
or all of the localized building heating requirements. While either
configuration works well for its intended purpose, inefficiencies
arise. In the former system, much of the heat generated at the
central generating station is, after being transported over long
distances, unavailable for remote use. In the latter system, the
lack of CHP capability necessitates the consumption of additional
energy at the remote location to satisfy heat requirements.
[0003] Recent trends in the deregulation of energy production and
distribution have made viable the concept of distributed
generation. With distributed generation, the large, central
generating station is supplemented with, or replaced by numerous
smaller autonomous or semi-autonomous units. These changes have led
to the development of smaller CHP systems, called micro-CHP, which
are distinguished from traditional CHP by the size of the system.
By way of contrast, the electric output of a generating
station-sized CHP could be in the tens, hundreds or thousands of
megawatts (MW), where the electric output of a micro-CHP is fairly
small, in the low kW.sub.e or even sub-kW.sub.e range. The
inclusion of a distributed system into dwellings that already have
fluid-carrying pipes for heat transport is especially promising, as
little or no disturbance of the existing building structure to
insert new piping is required. Similarly, a micro-CHP system's
inherent multifunction capability can reduce structural redundancy.
Accordingly, the market for localized heat generation capability in
Europe and the United Kingdom (UK), as well as certain parts of the
United States, dictates that a single unit for residential and
small commercial sites provide heat for both space heat (SH), such
as a hydronic system with radiator, and domestic hot water (DHW),
such as a shower head or faucet in a sink or bathtub, via demand
(instantaneous) or storage systems.
[0004] As with all energy production devices that rely on
non-renewable sources, such as natural gas, coal or oil, a more
efficient system consumes lower quantities of fuel to generate the
same energy output as its less efficient counterpart. A key factor
in keeping micro-CHP system efficiency high over a wide range of
operating conditions is how much thermal output is required at the
heat source, such as a natural gas burner. Unfortunately, the
nature of micro-CHP system operation, where both electric power and
heat are generated from the same combustion process often under a
fixed heat to power (Q/P) ratio, is such that when thermal output
is reduced to minimize fuel consumption, the electric power
production often drops even more quickly. As such, these systems
cannot operate efficiently when climatic changes and user
energy-consumption habits deviate significantly, over the course of
a day or the year, from the rated Q/P. With a fixed Q/P heat-led
system, because the electric power output follows heat production,
a significant turndown in thermal load results in a concomitant
loss in electric output, and because maximizing system efficiency
is typically a corollary to maximizing electric output, such part
power operation severely limits the benefits associated with
cogeneration systems.
[0005] What is needed is a micro-CHP system that can operate at
high efficiencies regardless of the Q/P requirements. The present
inventors have recognized that with modulation, the system
continues to operate over a longer period of time such that its
duty cycle is relatively large and that the variable heat output
need not encroach on maximizing electrical output. They have
further recognized that by modulating the system, Q/P is improved
at all conditions, especially at part power conditions. They have
also recognized that a modulation approach that varies the mass
flow of the working fluid to match the heat load while
simultaneously varying the fuel flow to the heat source in order to
keep the inlet temperature of the working fluid heated by the heat
source at a constant temperature results in a thermal output that
can be closely tailored to a user's needs while keeping electrical
power output at a maximum. They have moreover recognized that the
inclusion of various system componentry, such as recuperators and
accumulators, can improve the efficiency of modulating a system by
the aforementioned approach. They have additionally recognized that
in countries where emission requirements are stringent, modulating
can lower burner output at certain system operating conditions more
effectively than by cycling the system such that fuel consumption
to achieve the same amount of energy output is reduced.
BRIEF SUMMARY OF THE INVENTION
[0006] These needs are met by the present invention, where a new
micro-CHP system is described. According to a first aspect of the
present invention, a cogeneration system is disclosed. The system
includes a heat source, a working fluid circuit and at least one
energy conversion circuit operatively responsive to the working
fluid circuit such that upon operation of the cogeneration system,
the energy conversion circuit is configured to provide useable
energy. In the present context, the term "useable energy" includes
that which a user can put to practical use, rather than waste or
incidental energy. This is consistent with the concept of
cogeneration, which is frequently considered to be the
thermodynamically sequential production of two or more useful forms
of energy from a single primary energy source. The most notable
examples of useable energy arising out of the operation of a
cogeneration system are electricity (preferably alternating current
electricity, derived from the mechanical turning of a generator),
and heat in the form of SH and DHW. The working fluid circuit is
made up of conduit, an expander, condenser, pump and recuperator.
The conduit is configured to transport an organic working fluid,
where at least a portion of the conduit is disposed adjacent the
heat source such that during heat source operation, the heat
transferred to the conduit is sufficient to superheat the organic
working fluid disposed in that part of the conduit. The organic
working fluid passing through the expander remains superheated
after expansion, while the condenser is in fluid communication with
the expander to extract some of the heat still extant in the
working fluid after the expansion process. The pump is configured
to circulate the organic working fluid through at least the
conduit, expander and condenser. The recuperator is coupled to the
conduit and is configured to increase the temperature of the
organic working fluid entering the portion of the conduit disposed
adjacent the heat source.
[0007] The thermodynamic properties of some organic working fluids
are ideally suited to the temperature and pressure regimes
encountered in micro-CHP operation. Of particular interest is that
such fluids remain superheated even after giving up a significant
portion of their energy in the expansion process. This is in
contrast to other working fluids, such as water, that typically
condense to a saturated condition after expansion. Furthermore, the
use of organic working fluid rather than water is important where
shipping and even some end uses could subject portions of the
system to freezing temperatures (below 32.degree. Fahrenheit,
0.degree. Celsius). With a water-filled system, damage and
inoperability could ensue after prolonged exposure to sub-freezing
temperatures, whereas an organic working fluid-based system would
be impervious to temperature extremes encountered by dwellings and
related buildings incorporating such a system. In addition, by
using an organic working fluid rather than water, corrosion issues
germane to water in the presence of oxygen are avoided. The organic
working fluid is preferably either a halocarbon refrigerant or a
naturally-occurring hydrocarbon. Examples of the former include the
refrigerant known as R-245fa, while examples of the latter include
some of the alkanes, such as isopentane. Another advantage
associated with organic working fluids is that their high vapor
density and heat transfer properties in the superheated state
ensure that maximum heat and power can be extracted from the fluid
without having to resort to a large expander. To handle the
expansion loads of the superheated organic working fluid, the
expander is preferably a scroll expander.
[0008] Optionally, the energy conversion circuit comprises a
generator coupled to the expander to produce electricity and a
circulating fluid medium in thermal communication with the
condenser such that at least a portion of the heat given up by the
organic working fluid in the condenser provides increased thermal
content to the circulating fluid medium. In the present context,
the term "thermal communication" is meant to broadly cover all
instances of thermal interchange brought about as a result of
coupling between system components, whereas the more narrow "heat
exchange communication" is meant to cover the more specific
relationship between direct, adjacent heat exchange components
designed specifically for that purpose.
[0009] The recuperator preferably includes a first heat exchange
passage disposed between the expander and the condenser and a
second heat exchange passage disposed between the pump and the
portion of the conduit adjacent the heat source. In the present
context, a component in a fluid circuit is "between" other
components in the same circuit when the fluid in the circuit can
flow through the between component on its way from one to the other
of the surrounding components. A recuperator bypass valve can be
included so that, with proper control, the amount of fluid flowing
through the recuperator can be varied, allowing concomitant
variation in Q/P. Preferably, the circulating fluid medium is
configured to transport either or both an SH fluid, such as water
or forced air, or DHW. Preferably, the heat source is a burner in
thermal communication with an evaporator such that heat provided by
the burner causes the organic working fluid that flows through the
conduit in the evaporator to become superheated. Also, the burner
can be disposed within a container (of which the evaporator may
form an integral part) which may include an exhaust duct to carry
away combustion products (primarily exhaust gas), an exhaust fan to
further facilitate such product removal, as well as an exhaust gas
heat exchanger disposed adjacent (preferably within) the exhaust
duct so that residual heat present in the exhaust gas can be used
for supplemental heating in other parts of the cogeneration system.
The exhaust gas heat exchanger can further include an exhaust gas
recirculation device to further improve heat transfer from the
exhaust gas.
[0010] Additionally, an accumulator responsive to pressure
differences within the working fluid circuit can be included. Under
a first operating condition, the accumulator adds excess working
fluid to the working fluid circuit, and under a second operating
condition, the accumulator removes excess working fluid from the
working fluid circuit. The accumulator is preferably disposed
intermediate the condenser and the pump, and is situated at a
higher elevation relative to the pump to promote the gravity flow
of the additional working fluid from the accumulator to the pump
during the first operating condition. In addition, a warming device
can be thermally coupled to the accumulator such that during at
least a portion of the time the cogeneration system is not in
operation, the accumulator is maintained at a higher temperature
than the remainder of the working fluid circuit. A valve configured
to selectively fluidly isolate the accumulator from the remainder
of the working fluid circuit can also be included. When open, this
valve allows the accumulator to be charged before starting so that
during system warm-up, the accumulator can return the extra charge
to the system.
[0011] The cogeneration system can be configured such that the
organic working fluid is directly-fired or indirectly-fired. In the
former configuration, the relationship between the burner and the
organic working fluid-carrying evaporator is such that the flame
from the combustion process in the burner directly impinges on
either the conduit carrying the fluid or a container (alternately
referred to as a combustion chamber) that houses at least a portion
of the organic working fluid-carrying conduit such that the portion
of the conduit where the organic working fluid becomes superheated
is considered the evaporator. In the latter configuration, the
flame from the combustion process in the burner gives up a portion
of its heat to conduit making up a secondary circuit, which in turn
conveys a heat exchange fluid to an interloop heat exchanger. The
indirectly-fired system is advantageous in terms of system
flexibility, due in part to its ability to minimize temperature
excursions in the evaporator, and maintainability, as
heat-sensitive components (such as the conduit used to carry the
working fluid) are not directly exposed to the combustion process
in the case of a burner for a heat source. The directly-fired
system is advantageous in terms of system cost and simplicity.
[0012] According to another aspect of the present invention, a
cogeneration system including a heat source, a working fluid
circuit and at least one energy conversion circuit is disclosed.
The working fluid circuit is made up of conduit, an expander,
condenser, pump and accumulator. As with the previously-described
aspect, the conduit is configured to transport an organic working
fluid, where at least a portion of the conduit is disposed adjacent
the heat source such that during heat source operation, the heat
transferred to the conduit is sufficient to superheat the organic
working fluid disposed in that part of the conduit. Also as before,
the organic working fluid passing through the expander remains
superheated after expansion, while the condenser is in fluid
communication with the expander to extract some of the heat
remaining in the working fluid after the expansion process.
Similarly, the pump is configured to circulate the organic working
fluid through at least the conduit, expander and condenser. The
accumulator is responsive to pressure differences within the
working fluid circuit, and is configured to add excess working
fluid to the working fluid circuit during a first operating
condition while removing excess working fluid from the working
fluid circuit under a second operating condition. The accumulator
is preferably disposed intermediate the condenser and the pump, and
is situated at a higher elevation relative to the pump to promote
the gravity flow of the additional working fluid to the pump during
the first operating condition. In addition, a warming device can be
thermally coupled to the accumulator such that during at least a
portion of the time the cogeneration system is not in operation,
the accumulator is maintained at a higher temperature than the
remainder of the working fluid circuit. A valve configured to
selectively fluidly isolate the accumulator from the remainder of
the working fluid circuit can also be included. When open, this
valve allows the accumulator to be charged before starting so that
during system warm-up, the accumulator can return the extra charge
to the system.
[0013] According to yet another aspect of the present invention, a
Rankine cycle cogeneration system is disclosed. The cogeneration
system includes a heat source, a working fluid circuit and at least
one energy conversion circuit operatively responsive to the working
fluid circuit such that upon operation of the cogeneration system,
the energy conversion circuit is configured to provide useable
energy. The working fluid circuit includes conduit configured to
transport an organic working fluid, an expander in fluid
communication with the conduit, a condenser in fluid communication
with the expander, a pump to circulate the organic working fluid, a
recuperator coupled to the conduit and configured to increase the
temperature of the organic working fluid entering prior to the
working fluid encountering the heat source, and an accumulator
intermediate the condenser and the pump. As with the previous
aspect of the invention, at least a portion of the conduit is
disposed adjacent the heat source such that, during operation of
the heat source, the organic working fluid passing through that
portion of the conduit is heated to a superheated state, and
remains in such state after passing through the expander. Also as
previously discussed, the accumulator is preferably responsive to
pressure differences within the working fluid circuit such that
under a first operating condition, the accumulator adds excess
working fluid to the working fluid circuit, and under a second
operating condition, the accumulator removes excess working fluid
from the working fluid circuit. The accumulator is preferably
situated at a higher elevation relative to the condenser to promote
the gravity flow of the excess working fluid resident in the
accumulator to the condenser during the first operating
condition.
[0014] According to still another aspect of the present invention,
a Rankine cycle cogeneration system is disclosed. The system
includes an organic working fluid, an evaporator made up of a
burner and conduit adjacently spaced relative to the burner, a
substantially closed-loop working fluid circuit in thermal
communication with the burner, and at least one energy conversion
circuit. Heat generated during burner operation is sufficient to
superheat the organic working fluid disposed in the adjacent
conduit. The closed-loop working fluid circuit includes an expander
that in operation maintains the organic working fluid in a
superheated state after expansion in the expander, a condenser in
fluid communication with the expander, a pump configured to
circulate the organic working fluid, a recuperator configured to
increase the temperature of the organic working fluid entering the
evaporator, and an accumulator fluidly responsive to pressure
differences within the working fluid. The accumulator adds excess
working fluid to the working fluid circuit under a first operating
condition (such as during system start-up), and removes excess
working fluid from the working fluid circuit under a second
operating condition (such as during steady state operation). The
energy conversion circuit includes a generator coupled to the
expander to produce electricity, and a circulating fluid medium in
thermal communication with the condenser such that at least a
portion of the heat given up by the organic working fluid in the
condenser provides increased thermal content to the circulating
fluid medium. The circulating fluid medium is preferably an SH or
DHW circuit, including conduit, one or more pumps and related
valving, control and heat exchange equipment.
[0015] According to another aspect of the present invention, a
dwelling configured to provide at least a portion of the heat and
power needs of occupants therein is disclosed. The dwelling (which
can be, for example, a house, apartment or commercial, industrial
or office building) includes walls, a roof situated above the
walls, at least one ingress/egress (such as a door) to facilitate
passage into and out of the dwelling, and a cogeneration system in
heat and power communication with at least one room formed within
the dwelling. The cogeneration system includes, at a minimum, a
heat source, a working fluid circuit and at least one energy
conversion circuit. Optionally, the dwelling further comprises a
controller (such as a thermostat) that is signally connected to a
measuring sensor, such as an outdoor temperature sensing device.
The sensed outdoor temperature can form the basis for the
controller to set a desired hydronic fluid temperature. In
addition, the controller can be responsive to occupant input. In
addition, an accumulator (if present) is configured to be
responsive to pressure differences within the working fluid circuit
in a manner similar to that discussed in the preceding aspect of
the invention.
[0016] According to yet another aspect of the present invention, a
micro combined heat and power system is disclosed. The micro
combined heat and power system includes an electric production
subsystem and a heat production subsystem. The electric production
subsystem includes an organic working fluid, a burner for
superheating the organic working fluid, a scroll expander
configured to receive and expand the organic working fluid such
that the organic working fluid remains in a superheated state, a
generator operatively coupled to the scroll expander to produce
electricity, a condenser in fluid communication with the scroll
expander, a pump to circulate the organic working fluid through the
electricity generating loop, a recuperator in thermal communication
with the expander, and an accumulator intermediate the condenser
and the pump. The heat production subsystem comprises a circulating
fluid medium in thermal communication with the condenser.
[0017] According to still another aspect of the present invention,
a method of producing heat and electrical power from a cogeneration
device is disclosed. A first working fluid circuit with conduit,
expander, condenser, pump and recuperator, and an energy conversion
circuit (both circuits of which are similar to that discussed in
the first aspect) are used in the present method to achieve
cogeneration. Steps in the method include providing a heat source,
configuring the first circuit to transport an organic working fluid
past the heat source, superheating the organic working fluid that
flows adjacent the heat source, and expanding the superheated
organic working fluid to generate electricity. The organic working
fluid in the first circuit is maintained in a superheated state at
least until the organic working fluid enters a recuperator,
whereupon it exchanges at least a portion of its excess heat with
organic working fluid that has already passed through the
condenser, exchanging at least a portion of excess heat from the
organic working fluid that has passed through the recuperator in a
condenser with a circulating fluid medium. The organic working
fluid is returned via the recuperator such that after picking up
additional heat therein, it passes adjacent the heat source.
Optionally, the circulating fluid medium is configured to transport
an SH fluid, such as water or forced air. Similarly, the
circulating fluid medium can be configured to transport DHW.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0018] The following detailed description of the preferred
embodiments of the present invention can be best understood when
read in conjunction with the following drawings, where like
structure is indicated with like reference numerals and in
which:
[0019] FIG. 1 shows a schematic diagram of a directly-fired
cogeneration system according to an embodiment of the present
invention having a connection to both SH and DHW capability;
[0020] FIG. 2 shows a schematic diagram of an indirectly-fired
cogeneration system configuration with connections to separate SH
and DHW capability; and
[0021] FIG. 3 shows that electrical output is maximized when a
cogeneration system is modulated according variable heat loads as
compared to that of maintaining a constant heat load.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Referring initially to FIG. 1, a micro-CHP system 100
capable of providing electric current and heated fluid is shown.
The system 100 includes a working fluid circuit and an energy
conversion circuit. The working fluid circuit includes an expander
101, a condenser 102, a pump 103 and an evaporator 104. These four
components define the major components that together approximate an
ideal Rankine cycle system. That is, the evaporator 104 acts as a
constant pressure heat addition, the expander 101 allows efficient,
nearly isentropic expansion of the working fluid, the condenser 102
acts to reject heat at a constant pressure, and the pump 103
provides efficient, nearly isentropic compression. The evaporator
104 can be a stand-alone device, or part of a larger heat source.
In such a configuration, the heat (shown in the figure being
produced by a combustion process where a fuel, such as natural gas,
is transported via gas line 152 past gas valve 153 to a burner 151)
in the evaporator 104 is transferred to an organic working fluid
being transported through conduit 110 (alternately referred to as
piping). In the present micro-CHP system 100, the energy produced
by the expansion of the organic working fluid is converted to
electricity and heat as the two useable forms of energy. An exhaust
gas recirculation (EGR) device 156 functions in conjunction with
the exhaust duct 155 as part of exhaust gas heat exchanger 157. The
hot exhaust gas stream is directed axially through the EGR device
156 and heat exchanger 157. The primary benefit of the EGR device
156 is that levels of harmful gaseous by-products (such as
NO.sub.x) can be reduced. An optional fan 158 to pull away heat
source byproducts is shown downstream of the heat source as an
induced-draft fan, although it could also be a forced-draft fan if
located upstream relative to the burner 151 and its ancillary
componentry.
[0023] The energy conversion circuit takes the increased energy
imparted to the working fluid in the working fluid circuit and
converts it into useable form. The electrical form of the useable
energy comes from a generator 105 (preferably induction type) that
is coupled to expander 101. The hot fluid form of the useable
energy comes from a circulating fluid medium 140 (shown preferably
as a combined SH and DHW loop) thermally coupled to condenser 102.
Hydronic fluid flowing through circulating fluid medium 140 is
circulated with a conventional pump 141, and can be supplied as
space heat via radiator 148 or related device. As an example,
hydronic fluid could exit the condenser 102 at about 112.degree. F.
(50.degree. C.) and return to it as low as 86.degree. F.
(30.degree. C.). The nature of the heat exchange process is
preferably through either heat exchangers 180 (shown notionally for
the DHW loop, but equally applicable to the SH loop), or through a
conventional hot water storage tank (for a DHW loop). Isolation of
either the SH or DHW loop within circulating fluid medium 140 is
accomplished through valves 107E and 107F. It will be appreciated
by those of ordinary skill in the art that while the embodiments
depicted in the figures show DHW and SH heat exchangers in parallel
(and in some circumstances being supplied from the same heat
exchange device, shown later), it is within the spirit of the
present disclosure that series or sequential heat exchange
configurations could be used. It will also be appreciated that the
heat exchanger 180 depicted in FIG. 1 could be in the form of the
aforementioned hot water storage tank, where the hot fluid
circulating through circulating fluid medium 140 gives up at least
a portion of its heat to incoming domestic cold water coming from
water supply 191A, which is typically from a municipal water
source, well or the like. Once heated in the tank, the domestic
water can then be routed to remote DHW locations, such as a shower,
bath or hot water faucet, through DHW outlet 191B.
[0024] The organic working fluid (such as naturally-occurring
hydrocarbons or halocarbon refrigerants, not shown) circulates
through the working fluid circuit loop defined by the
fluidly-connected expander 101, condenser 102, pump 103, evaporator
104, and conduit 110. The embodiment of the micro-CHP system 100
shown in FIG. 1 is operated as a directly-fired system, where the
fluid that passes adjacent the heat source is also the working
fluid passing through the expander 101. The condenser extracts
excess heat from the organic working fluid after the fluid has been
expanded such that circulating fluid loops hooked up to the
condenser can absorb and transfer the heat to remote locations.
While the expander 101 can be any type, it is preferable that it be
a scroll device. For example, the scroll expander 101 can be based
on a conventional single scroll device, as is known in the art. A
scroll device exhibits numerous advantages over other
positive-displacement systems. For example, since they are made in
very high production volume in dedicated modern facilities, its
cost is inherently low. Furthermore, the modification to an
existing production line to convert from making scroll compressors
to making scroll expanders is considerably simpler than to modify
an existing reciprocating compressor production line, as the
changes to valves and actuation are minimized. Additionally, by
operating with very few moving parts, it can go long durations
between service or component failure. Moreover, when operating in
expansion mode, once the fixed volume of working fluid is captured,
the nature of the working fluid-containing chamber is such that the
volume of the chamber is always expanding. This also promotes long
component life as it avoids the possibility of trapping and
attempting to compress (such as upon a return stroke) a working
fluid that could, under certain pressure and temperature regimes,
include an incompressible liquid phase condensate. An optional oil
pump 108 may be used to provide lubricant to the scroll.
[0025] An optional level indicator switch 120 is placed at the
discharge of condenser 102, while controller 130 is used to
regulate system operation. Sensors connected to controller 130
measure key parameters, such as fluid level information taken from
the level indicator switch 120, and organic working fluid
temperatures at various points within the organic working fluid
circuit. Through appropriate program logic, it can be used to vary
pump speed, gas flow rate and evaporator output temperature, as
well as to open and close valves.
[0026] Referring next to FIG. 3, a comparison between two ways to
mimic the modulation of a boiler to achieve maximum system
efficiency is shown. In many conventional boiler applications,
where the set point of the system 100 is determined by a single
parameter, such as an outdoor temperature, controller 130 (not
presently shown) can be used to provide primary control input to
the evaporator 104 (not presently shown). By operating the
evaporator in a variable-capacity mode, where the gas valve 153 on
the burner 151 (neither of which are presently shown) can be
modulated, the SH or DHW portions of the circulating fluid medium
can be maintained at the desired set point. Such modulation permits
quasi-steady state system operation that is responsive to heat
needs that are keyed to a specified hydronic supply temperature set
point, which is preferably the hydronic temperature coming off the
condenser 102 (not presently shown). For example, the ambient
outdoor temperature is measured and sets the desired hydronic
supply temperature. A single measuring point is used, preferably
positioned on the North side of the building (in the Northern
hemisphere), to avoid the influence of direct sunlight on cold
days. A linear variation of the hydronic set point is used, so that
on very cold days the hydronic set point is at or near its maximum
setting (shown in the figure as 75.degree. C.), while on warm days
the set point is at or near its minimum (shown in the figure as
25.degree. C.). The hydronic pump 141 (not presently shown)
operates continuously so there is always a flow through the
system.
[0027] Similarly, for the micro-CHP, a single measurement of
outdoor ambient temperature can be used to establish the hydronic
supply set point temperature. The working fluid mass flow is then
controlled by the controller to maintain the actual supply
temperature at this set point. Either an inverter drive or a
separate input on the pump 103 would be sufficient to adjust the
displacement of the pump 103 at constant motor speed to vary flow
rate. The gas valve 153 is modulated to maintain the desired set
point for the evaporator 104 outlet temperature of the working
fluid into the expander 101. Properties of the working fluid, as
well as of optional fluids, such as lubricants, may dictate maximum
operating temperatures of the fluid coming out of the evaporator
104. For example, if the working fluid is the refrigerant known as
R-245fa, the temperature set point at the evaporator 104 exit is
about 310.degree. F. (154.degree. C.).
[0028] By operating the system such that the temperature of the
working fluid at the evaporator 104 outlet is at or near its
maximum value, good overall system efficiency results, regardless
of system load. This can include very low thermal loads; for
example, if the thermal load falls much below about 30 to 40% of
full load, it is appropriate to shutdown the system and cease
making both heat and power. Since the hydronic pump is kept running
at all times, even at a low flow rate, the controller 130 can
continuously monitor the error signal between the hydronic actual
and set point values. When this error is large enough, (i.e., the
actual temperature is below the set point by a preselected value)
the controller 130 can start the system for another on-cycle. As
the system 100 operates it may find that even at the minimum system
mass flow, the actual supply temperature begins to exceed the set
point. When this occurs, the system 100 is again shut down. Under
this approach, the system 100 will operate for as many hours as
possible during the colder heating season by running just often
enough to maintain the hydronic supply temperature at the right
value for the nominal heating load. When the system 100 operates at
less than the maximum hydronic supply temperature, more power is
generated than at the maximum temperature, so the controller 130
automatically and passively maximizes the electric power, which can
be produced. Thus, as shown in the figure, the net electrical
output goes up (at the same working fluid mass flow rate) as
hydronic fluid supply temperature requirements goes down, while
variations in working fluid flow rate and can be used in
conjunction to vary electric output under a given thermal load.
This inherent flexibility promotes overall energy (electrical and
heat) system efficiency.
[0029] Referring again to FIG. 1, the generator 105 is preferably
an asynchronous device, thereby promoting simple, low-cost
operation of the system 100, and reducing reliance on complex
generator speed controls and related grid interconnections. An
asynchronous generator always supplies maximum possible power
without controls, as its torque requirement increases rapidly when
generator 105 exceeds system frequency. The generator 105 can be
designed to provide commercial frequency power, for example, 50 or
60 Hz, while staying within close approximation (often 150 or fewer
revolutions per minute (rpm)) of synchronous speed (3000 or 3600
rpm). Block valve 107A and bypass valve 107B are situated in the
organic working fluid flow path defined by conduit 110. These
valves respond to a signal in controller 130 that would indicate if
no load (such as a grid outage) were on the system, or if a high
Q/P were desired, thus allowing the superheated vapor to bypass the
expander, thereby transferring a majority of the excess heat to the
heat exchange loop in the condenser 102 (for high Q/P operation),
as well as additionally avoiding overspeed of expander 101.
[0030] A recuperator 109 is placed between expander 101 and
condenser 102 in order to selectively extract additional heat from
the working fluid once the fluid has been expanded. To achieve Q/P
that varies depending on the heat and electric loads, the burner
151 is capable of modulation, while the condenser 102 is
simultaneously responsive to fluctuating thermal content in the
working fluid and capable of transferring enough heat for hydronic
SH needs (as well as DHW needs). The recuperator 109 is central to
providing a balance between these often diverging requirements. To
meet the heat requirement of the circulating fluid medium, varying
amounts of working fluid can be diverted around the recuperator to
feed the condensed working fluid directly into evaporator 104.
Bypass valve 107C can be a three-way modulating valve to effect
such diversion. For example, if the hydronic fluid requirements of
the circulating fluid medium are substantial (such as on a very
cold day), the bypass valve 107C can be set to largely or entirely
bypass the secondary loop in recuperator 109 to enable maximum heat
transfer to condenser 102. Alternately, if the heat load on the
system 100 is reduced (such as on a relatively mild day), then
bypass valve 107C can be set to permit a significant portion of the
working fluid leaving condenser 102 to pass through the secondary
loop of recuperator 109 to absorb some of the heat from the
just-expanded working fluid, thereby reducing heat input
requirements from burner 151 to the working fluid entering the
evaporator 104. One of the basic approaches to controlling the
temperature at the evaporator outlet is to vary the mass flow out
of the expander. By way of example, when the working fluid is
R-245fa, the outlet temperature can be fixed, or set, to about
310.degree. F. (154.degree. C.). By selecting a corresponding pump
capacity and speed to control the mass flow of working fluid into
the evaporator, coupled with the ability of the expander to accept
a concomitant amount of vapor flow, the evaporator outlet pressure
tends to be typically between 380 and 400 psia (2.62 MPa and 2.76
MPa, respectively), with a preferred pressure of 392 psia (2.70
MPa) at full load. The outlet temperature of 310.degree. F.
(154.degree. C.) leaves about 30.degree. F. (17.degree. C.) of
superheat above the saturation temperature for the fluid, thereby
simplifying the control system and its ability to adjust the burner
firing rate to maintain the set outlet temperature. Then, as the
thermal output capacity to meet lower loads is reduced, which could
be due to cool or warm weather, the pump flow and the pressure
changes accordingly to a lesser value. In an alternative approach,
the same superheat temperature (30.degree. F., 17.degree. C.) can
be maintained, while allowing the evaporator outlet temperature to
fluctuate. Of the two approaches, it is preferable to run the
evaporator outlet at a constant 310.degree. F. (154.degree. C.)
from an efficiency stand point and for simplicity of the
controller, as calculating the proper superheat temperature
requires measuring, in some way, the evaporator outlet pressure.
Because the constant temperature mode results in a higher
efficiency and the expander is robust enough for constant
temperature operation, it is the preferred mode of operation for
the system 100.
[0031] An accumulator 111 is connected intermediate condenser 102
and pump 103. Insofar as the term "intermediate" is construed in
the present context to describe the positioning of the accumulator
111 relative to condenser 102 and pump 103 more broadly than the
aforementioned "between" (which was used to describe the relation
between the expander 101, recuperator 109 and condenser 102), such
use is meant to cover the connection of the intermediate component
(the accumulator 111) to its upstream and downstream component
neighbors (the condenser 102 and pump 103, respectively) to enable
(although not necessitate) fluid communication between two or more
of the components at any given time. A warming device 113 can be
placed adjacent the accumulator 111 to keep the working fluid
inside slightly warmer than the remaining circuit during periods of
system inoperation. Heat for the warming device 113 can be, for
example, from an electric (resistive) supply. Accumulator 111 can
be isolated from the remainder of the organic working fluid circuit
by accumulator isolation accumulator isolation valve 107D, and is
situated vertically above at least the pump 103 such that fluid
flowing from accumulator 111 can be gravity-fed to the inlet of
pump 103. The accumulator 111 acts as a working fluid storage
device in that during periods of low fluid flow rates (such as
during system startup), it can provide an additional charge of
fluid into the working fluid circuit to minimize, among other
things, cavitation of pump 103. Once the system has reached its
normal operating condition, excess fluid in the working fluid
circuit can return to the accumulator 111, which being slightly
cooler than the remainder of the organic working fluid circuit will
allow the excess fluid to condense inside. The accumulator 111
serves as a source of additional working fluid during startup when
liquid working fluid typically accumulates in the crankcase of
expander 101 and potentially in the recuperator 109. The additional
working fluid from the accumulator 111 insures sufficient liquid
working fluid to avoid or minimize cavitation of pump 103. The
warming device 113 can be used if necessary to provide the pressure
needed to force the liquid working fluid out of the accumulator 111
and into the working fluid circuit. Once the system has reached its
normal operating condition, any liquid working fluid in the
crankcase of expander 101 and (if applicable) recuperator 109 will
vaporize and return to the working fluid circuit. If the warming
device 113 is turned off, the normal pressure and temperature of
the working fluid will exceed that of the accumulator 111, causing
excess working fluid to be forced back into the accumulator
111.
[0032] The return of the liquid to the accumulator 111 lowers the
liquid level in the condenser 102. This allows the condenser 102 to
operate more efficiently. Without the accumulator 111, a working
fluid charge that is sufficient to prevent cavitation of pump 103
during startup may result in a flooded condenser 102 during normal
operation. This excess liquid in the condenser 102 will result in
higher condensing pressures and reduced efficiency and performance.
Accumulator isolation valve 107D serves to control the passage of
liquid working fluid into and out of accumulator 111. Accumulator
isolation valve 107D would be opened when the system is off to
allow the liquid working fluid to enter the active working fluid
circuit. At startup, accumulator isolation valve 107D would be
closed to prevent return of the working fluid liquid back into the
accumulator 111 until the system 100 was fully warmed up and the
liquid working fluid had been driven out of the crankcase of
expander 101 and (if applicable) from recuperator 109. Accumulator
isolation valve 107D would then be opened to allow the working
fluid liquid to return to accumulator 111.
[0033] Other means of controlling the flow of liquid working fluid
into and out of accumulator 111 are also possible. In one
embodiment, warming device 113 could be energized to raise the
temperature and pressure in the accumulator 111 above that of the
working fluid during startup. The accumulator 111 would thus remain
full of vapor only until the warming device 113 was turned off and
the accumulator 111 began to cool off. Alternatively, a check valve
with an orifice could replace accumulator isolation valve 107D. The
check valve could allow the liquid to quickly transfer from the
accumulator 111 while the system is off. During startup, the check
valve would restrict flow back into the accumulator 111 except as
metered through the orifice.
[0034] Referring next to FIG. 2, an indirectly-fired cogeneration
system 200 is shown. A second loop 250 in cogeneration system 200
includes two parallel sub-loops 250A, 250B, while a first loop,
which includes an expander 201 coupled to generator 205, condenser
202B, pump 203, recuperator 209, conduit 210 and accumulator 211
with warming device 213, is configured similarly to, although not
necessarily identical to, the system shown in FIG. 1. The most
significant difference of the first loop over the system of FIG. 1
is that the evaporator 104 of the former system is now replaced
with an interloop heat exchanger 202A, thus acting as a heat source
for the first loop. Controller 230 is similar to that of the
previously described system, but now with enlarged functionality to
additionally control some or all of the operations of the second
loop 250. It will be appreciated that circulating fluid medium 240
is, while notionally depicting only an SH component that includes a
pump 241 and radiator 248, is understood to be similar to that of
FIG. 1. Also as before, valve 207C can be used to bypass the
recuperator 209 in order to achieve variable Q/P, while pump 208 is
used to circulate oil or related lubricant through the
expander.
[0035] Heat to the two parallel sub-loops 250A, 250B is provided by
a burner 251, which is supplied with fuel by a gas train 252 and
variable flow gas valve 253. Piping 260 (alternately referred to as
conduit, and which makes up the parallel sub-loops) passes through
a combustion chamber 254, where the heat from the combustion of
fuel at burner 251 is given up to the heat exchange fluid (not
shown) that flows through piping 260. Piping 260 branches out into
the first parallel sub-loop 250A, which transports the heat
exchange fluid that has been heated in combustion chamber 254 to
interloop heat exchanger 202A in order to give up the heat to
organic working fluid flowing through the first loop, which as
previously described, save the presence of the interloop heat
exchanger 202A in place of the evaporator 104, is similar in
construction to the directly-fired cogeneration system 100 shown in
FIG. 1. Block valves (not shown) could be used to regulate flow
between the sub-loops 250A and 250B; however, by idling the pump of
the inactive sub-loop, significant flow in that sub-loop is
prevented without the need for additional valving. The second
parallel sub-loop 250B transports the heat exchange fluid to DHW
heat exchanger 280 in order to heat up domestic hot water. One side
of DHW heat exchanger 280 (which can be a water storage tank)
includes coil 280A configured to transport the heat exchange fluid,
and another side, the shell 280B, to transport DHW (not shown) from
a cold water inlet 291A, past coil 280A and to DHW outlet 291B. As
with the system shown in FIG. 1, the cold water preferably comes
from either a well or a city/municipal water supply. Similarly,
temperature sensor 271B can detect the temperature of the DHW
coming out of the DHW heat exchanger 280. This sensor can also be
linked to a controller 230 (discussed in more detail below).
[0036] Combustion chamber 254 includes an exhaust duct 255, an
exhaust gas recirculation device 256 with exhaust duct heat
exchanger 257, and fan 258. Temperature sensor 271A is placed at
the combustion chamber 254 outlet for the second loop 250 to
measure the temperature conditions of the heat exchange fluid, in a
manner similar to that of temperature sensor 271B. Second loop
pumps 285A, 285B are used to circulate heat exchange fluid through
the second loop 250, with pump 285B circulating heat exchange fluid
through DHW heater 280 and pump 285A circulating heat exchange
fluid through interloop heat exchanger 204. The exhaust duct heat
exchanger 257 and an EGR device 256 accept hot exhaust gas from the
burner 251 and recirculate it in an internal heat exchange process,
thereby lowering the temperature of the exhaust gas that is pulled
away and vented to the atmosphere by fan 258. The heat given up by
the exhaust gas in the exhaust gas heat exchanger 257 can be used
to provide additional heat to other parts of the system 200. For
example, this additional heat can be used to increase the
temperature of the heat exchange fluid flowing in second loop 250,
or to increase the heat content of the organic working fluid in the
first loop.
[0037] Having described the invention in detail and by reference to
preferred embodiments thereof, it will be apparent that
modifications and variations are possible without departing from
the scope of the invention defined in the appended claims. More
specifically, although some aspects of the present invention are
identified herein as preferred or particularly advantageous, it is
contemplated that the present invention is not necessarily limited
to these preferred aspects of the invention.
* * * * *