U.S. patent application number 10/458536 was filed with the patent office on 2004-05-06 for integrated micro combined heat and power system.
Invention is credited to Anson, Donald, Coll, John Gordon, Hanna, William Thompson, Stickford, George Henry JR..
Application Number | 20040083732 10/458536 |
Document ID | / |
Family ID | 26977925 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040083732 |
Kind Code |
A1 |
Hanna, William Thompson ; et
al. |
May 6, 2004 |
Integrated micro combined heat and power system
Abstract
An integrated system to provide both heat and electric power.
The integrated, or cogeneration, system operates with an organic
working fluid that circulates in a Rankine-type cycle, where the
organic working fluid is superheated by a heat source, expanded
through an involute spiral wrap (scroll) expander such that the
organic working fluid remains superheated through the expander,
cooled in a condenser, and pressurized by a pump. Heat exchange
loops within the system define hot water production capability for
use in space heating and domestic hot water, while the generator is
coupled to the scroll expander to generate electricity.
Inventors: |
Hanna, William Thompson;
(Gahanna, OH) ; Anson, Donald; (Worthington,
OH) ; Stickford, George Henry JR.; (Dublin, OH)
; Coll, John Gordon; (Somerset, OH) |
Correspondence
Address: |
NIXON & VANDERHYE P.C./G.E.
1100 N. GLEBE RD.
SUITE 800
ARLINGTON
VA
22201
US
|
Family ID: |
26977925 |
Appl. No.: |
10/458536 |
Filed: |
August 18, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10458536 |
Aug 18, 2003 |
|
|
|
09998705 |
Nov 30, 2001 |
|
|
|
6598397 |
|
|
|
|
60311514 |
Aug 10, 2001 |
|
|
|
Current U.S.
Class: |
60/651 ;
60/671 |
Current CPC
Class: |
F24H 2240/00 20130101;
Y02E 20/14 20130101; F01K 25/08 20130101; F01K 17/02 20130101 |
Class at
Publication: |
060/651 ;
060/671 |
International
Class: |
F01K 025/08; F01K
025/00 |
Claims
We claim:
1. An indirectly-heated micro combined heat and power system
comprising: a heat source; an interloop heat exchanger in thermal
communication with said heat source; a first fluid-circulating loop
with at least a portion thereof passing through a first channel of
said interloop heat exchanger, said first fluid-circulating loop
comprising: an organic working fluid; a scroll expander; a
generator operatively responsive to said scroll expander to
generate electricity; a condenser in fluid communication with said
scroll expander, said condenser adapted to establish a heat
exchange relationship between said organic working fluid and an
external heat exchange fluid for space heating within a dwelling;
and a pump for the circulation of said organic working fluid; and a
second fluid circulating loop with at least a portion thereof
passing through a second channel of said interloop heat exchanger
such that said second fluid circulating loop is in thermal
communication with said first loop, said second fluid circulating
loop comprising: a first sub-loop comprising: piping to circulate a
heat exchange fluid disposed in said second fluid-circulating loop,
at least a portion of said piping in thermal communication with
said heat source; a domestic hot water heat exchanger; and at least
one pump to circulate a portion of said heat exchange fluid through
said domestic hot water heat exchanger; a second sub-loop
comprising: piping to circulate said heat exchange fluid such that
it is in heat exchange relationship with said organic working fluid
in said interloop heat exchanger; at least one pump to circulate a
portion of said heat exchange fluid through said interloop heat
exchanger, wherein said heat source, said heat exchanger, said
first loop and said scroll expander are configured such that, upon
application of heat from said heat source to said organic working
fluid via said interloop heat exchanger, said organic working fluid
becomes superheated to an extent that said organic working fluid
remains superheated at least through said scroll expander.
2. An indirectly-heated micro combined heat and power system
according to claim 1, further comprising an exhaust duct in fluid
communication with said heat source such that products from said
heat source may be removed from said micro combined heat and power
system.
3. An indirectly-heated micro combined heat and power system
according to claim 2, further comprising a heat exchanger in
thermal communication with said exhaust duct.
4. An indirectly-heated micro combined heat and power system
according to claim 1, further comprising a space heating loop
preheat device placed in heat exchange communication with said
second fluid circulating loop.
5. An indirectly-fired cogeneration system comprising: a heat
source; a passive heat transfer element in thermal communication
with said heat source; a first circuit disposed adjacent an end of
said passive heat transfer element such to accept heat transferred
therefrom, said first circuit comprising: an organic working fluid
that becomes superheated upon receipt of heat from said passive
heat transfer element; a scroll expander configured to receive said
superheated organic working fluid; a condenser in fluid
communication with said scroll expander, said condenser configured
to transfer at least a portion of the excess heat contained in said
organic working fluid to an external heating loop; and a pump
configured to circulate said organic working fluid through said
first circuit; a generator coupled to said scroll expander to
produce electricity in response to motion imparted to it from said
scroll expander; and a second circuit configured to transport a
heat exchange fluid therethrough, said second circuit in thermal
communication with an end of said passive heat transfer element
such that heat transferred therefrom increases the energy content
of said heat exchange fluid, said second circuit comprising: a
combustion chamber disposed adjacent said heat source; at least one
external loop heat exchanger; and conduit to transport said heat
exchange fluid between said combustion chamber and said at least
one external loop heat exchanger.
6. An indirectly-fired cogeneration system according to claim 5,
wherein said passive heat transfer element is a heat pipe.
7. An indirectly-fired cogeneration system according to claim 5,
wherein said combustion chamber is defined by: an exhaust duct in
combustion communication with said heat source; an exhaust fan
coupled to said exhaust duct to facilitate the removal of exhaust
gas; and an exhaust gas recirculation duct in exhaust communication
with said combustion chamber.
8. A cogeneration system comprising: a heat source; a passive heat
transfer element in thermal communication with said heat source; a
first circuit disposed adjacent an end of said passive heat
transfer element such to accept heat transferred therefrom, said
first circuit comprising: an organic working fluid that becomes
superheated upon receipt of heat from said passive heat transfer
element; a scroll expander configured to receive said superheated
organic working fluid; a condenser in fluid communication with said
scroll expander, said condenser configured to transfer at least a
portion of the excess heat contained in said organic working fluid
to an external heating loop; and a pump configured to circulate
said organic working fluid through said first circuit; and a
generator coupled to said scroll expander to produce electricity in
response to motion imparted to it from said scroll expander.
9. A cogeneration system according to claim 8, wherein said passive
heat transfer element is a heat pipe.
10. An cogeneration system according to claim 8, wherein said
combustion chamber is defined by: an exhaust duct in combustion
communication with said heat source; an exhaust fan coupled to said
exhaust duct to facilitate the removal of exhaust gas; and an
exhaust gas recirculation duct in exhaust communication with said
combustion chamber.
11. A method of producing heat and electrical power from a
cogeneration device, the method comprising the steps of:
configuring a first circuit to transport an organic working fluid;
superheating said organic working fluid with a heat source that is
in thermal communication with said first circuit; expanding said
superheated organic working fluid in a scroll expander such that
said organic working fluid is maintained in a superheated state;
turning a generator that is coupled to said scroll expander to
generate electricity; cooling said organic working fluid in a
condenser such that at least a portion of the heat in said organic
working fluid passing through said condenser is transferred to an
external heating loop; using at least a portion of said heat that
has been transferred to said external heating loop heat to provide
space heat; returning said organic working fluid exiting said
condenser to a position in said first circuit such that it can
receive additional heat input from said heat source; configuring a
second circuit to transport a heat exchange fluid, said second
circuit defined by a piping loop in thermal communication with said
heat source and heat exchange communication with at least one
domestic hot water loop; heating said heat exchange fluid with said
heat source; and using at least a portion of said heat that has
been transferred to said heating exchange fluid to heat a fluid in
said domestic hot water loop.
Description
[0001] This application is a Divisional of U.S. patent application
Ser. No. 09/998,705 filed Nov. 30, 2001 (non allowed), which claims
the benefit of U.S. Provisional Application No. 60/311,514 filed
Aug. 10, 2001.
BACKGROUND OF THE INVENTION
[0002] The present invention generally relates to a cogeneration
system for the supply of electrical power, space heating (SH) water
and domestic hot water (DHW), and more particularly to a small
scale Rankine-type cogeneration system that utilizes a scroll
expander and an organic working fluid.
[0003] 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. Most present-day CHP systems tend to
be rather large, producing heat and power for either a vast number
of consumers or large industrial concerns. Traditionally, the
economies of scale have prevented such an approach from being
extrapolated down to a single or discreet number of users. However,
increases in fuel costs have diminished the benefits of
centrally-generated power. Accordingly, there is a potentially
great market where large numbers of relatively autonomous,
distributed producers of heat and electricity can be utilized. For
example, in older, existing heat transport infrastructure, where
the presence of fluid-carrying pipes is pervasive, the inclusion of
a system that can provide CHP would be especially promising, as no
disturbance of the adjacent building structure to insert new piping
is required. Similarly, a CHP system's inherent multifunction
capability can reduce structural redundancy.
[0004] 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 single-family
residential and small commercial sites provide heat for both SH
(such as a hydronic system with radiator), and DHW (such as a
shower head or faucet in a sink or bathtub), via demand or
instantaneous system. Existing combination units are sometimes
used, where heat for DHW is accumulated in a combination storage
tank and boiler coil. In one configuration, SH water circulates
through the boiler coil, which acts as the heating element for the
water in the storage tank. By way of example, since the storage
capacity required for instantaneous DHW supplying one to two
showers in a single family residence (such as a detached house or a
large apartment) is approximately 120 to 180 liters (roughly 30 to
50 gallons), it follows that the size of the storage tank needs to
be fairly large, sometimes prohibitively so to satisfy thermal
requirements of up to 25 kilowatts thermal (kW.sub.t) for stored
hot water to meet such a peak shower demand. However, in newer and
smaller homes there is often inadequate room to accommodate such
storage tank volume. In addition to the need for instantaneous DHW
capacity of up to 25 kW.sub.t, up to 10 kW.sub.t for SH is
seasonally needed to heat an average-sized dwelling.
[0005] Furthermore, even in systems that employ SH and DHW into a
single heating system to consolidate spacing, no provision for CHP
is included. In the example given above, it is likely that the
electrical requirements concomitant with the use of 35 kW.sub.t
will be between 3 and 5 kilowatts electric (kW.sub.e). The
traditional approach to providing both forms of power, as
previously discussed, was to have a large central electricity
generating station provide electricity on a common grid to
thousands or even millions of users, with heat and hot water
production capacity provided at or near the end-user on an
individual or small group basis. Thus, with the traditional
approach, the consumer has not only little control over the cost of
power generation, as such cost is subject to prevailing rates and
demand from other consumers, but also pays more due to the inherent
inefficiency of a system that does not exploit the synergism of
using otherwise waste heat to provide either additional electric
generation or heating capacity.
[0006] Large-scale (in the megawatt (MW) range and up) cogeneration
systems, while helpful in reducing the aforementioned
inefficiencies of centrally-based power generation facilities, are
not well-suited to providing small-scale (below a few hundred kW)
heat and power, especially in the small-scale range of a few
kW.sub.e and below (micro-based systems) to a few dozen kW.sub.e
(mini-based systems). Much of this is due to the inability of the
large prime mover systems to scale down, as reasonable electrical
efficiency is often only achieved with varying load-responsive
systems, tighter dimensional tolerances of key components and
attendant high capital cost. Representative of this class are gas
turbines, which are expensive to build for small-scale
applications, and sacrifice efficiency when operating over varying
electrical load requirements. Efficiency-enhancing devices, such as
recuperators, tend to reduce heat available to the DHW or SH loops,
thus limiting their use in high heat-to-power ratio (hereinafter
Q/P) applications. A subclass of the gas turbine-based prime mover
is the microturbine, which includes a high-speed generator coupled
to power electronics, could be a feasible approach to small-scale
cogeneration systems. Other shortcomings associated with
large-scale CHP systems stem from life-limited configurations that
have high maintenance costs. This class includes prime movers
incorporating conventional internal combustion engines, where
noise, exhaust emissions, lubricating oil and spark plug changes
and related maintenance and packaging requirements render use
within a residential or light commercial dwelling objectionable.
This class of prime mover also does not reject a sufficient amount
of heat for situations requiring a high QIP, such as may be
expected to be encountered in a single family dwelling. Other prime
mover configurations, such as steam turbines, while generally
conducive to high Q/P, are even less adapted to fluctuating
electrical requirements than gas turbines. In addition, the
steam-based approach typically involves slow system start-up, and
high initial system cost, both militating against small-scale
applications.
[0007] In view of the limitations of the existing art, the
inventors of the present invention have discovered that what is
needed is an autonomous system that integrates electric and heat
production into an affordable, compact, efficient and distributed
power generator.
BRIEF SUMMARY OF THE INVENTION
[0008] These needs are met by the present invention, where a new
micro-CHP system is described. In micro-CHP, a compact prime mover
can provide both electric output, such as from a generator coupled
to a heat source, as well as heat output to provide warm air and
hot water to dwellings. What distinguishes micro-CHP from
traditional CHP is size: in the micro-CHP, electric output is
fairly small, in the low kW.sub.e or even sub-kW.sub.e range. The
system of the present invention can provide rapid response to DHW
requirements, as the size of tanks needed to store water are
greatly reduced, or possibly even eliminated. The size of the
micro-CHP system described herein can be adapted to particular user
needs; for example, a system for a single-family dwelling could be
sized to produce approximately 3 to 5 kW.sub.e, 10 kW.sub.t SH and
25 kW.sub.t DHW. For small commercial applications or
multi-dwelling (such as a group of apartment units) use, the system
could be scaled upwards accordingly. The heat to power ratio, Q/P,
is an important parameter in configuring the system. For most
residential and small commercial applications, a Q/P in the range
of 7:1 to 11:1 is preferable, as ratios much lower than that could
result in wasted electrical generation, and ratios much higher than
that are not practical for all but the coldest climates (where the
need for heating is more constant than seasonal). Since the
production of electricity (through, for example, a generator or
fuel cell) is a byproduct of the prime mover heat generation
process, no additional carbon dioxide and related atmospheric
pollutants are generated, thus making the system of the present
invention amenable to stricter emission control requirements.
[0009] According to a first aspect of the present invention, a
cogeneration system configured to operate with an organic working
fluid is disclosed. The system includes a heat source, a first
circuit configured to transport the organic working fluid, and a
generator operatively coupled to a scroll expander to produce
electricity. The first circuit includes a scroll expander
configured to receive the organic working fluid, a condenser in
fluid communication with the scroll expander, and a pump configured
to circulate the organic working fluid. The first circuit is in
thermal communication with the heat source such that heat
transferred therefrom converts the organic working fluid to a
superheated vapor. The use of organic working fluid, rather than a
more readily-available fluid (such as water) is important where
shipping and even some end uses could subject portions of the
system to freezing (below 32.degree. Fahrenheit). With a
water-filled system, damage and inoperability could ensue after
prolonged exposure to sub-freezing temperatures. In addition, by
using an organic working fluid rather than water, corrosion issues
germane to water in the presence of oxygen, and expander sizing or
staging issues associated with low vapor density fluids, are
avoided. The organic working fluid is preferably either a
halocarbon refrigerant or a naturally-occurring hydrocarbon.
Examples of the former include R-245fa, while examples of the
latter include some of the alkanes, such as isopentane. Other known
working fluids and refrigerants, despite exhibiting attractive
thermodynamic properties, are precluded for other reasons. For
example, R-11 is one of a class of refrigerants now banned in most
of the world for environmental reasons. Similarly, R-123, much less
environmentally objectionable (for now) than R-11, is the subject
of decomposition concerns under certain micro-CHP operating
conditions. The need to operate the condenser at a high enough
temperature to allow useful hydronic space heating and the need to
have a substantial vapor expansion ratio (of 5 to 7 or 8) limits
the number of fluids with useful properties. In addition, the need
to have a substantial vapor density at the expander inlet has a
direct impact on the fluid choice and the diameter of the scrolls,
both of which impact scroll cost. With many fluids, the condensing
temperature and need for significant expansion result in very high
scroll inlet pressures (increasing pumping power) or super critical
conditions at the inlet, resulting in difficulties in evaporator
design operation and control. These same conditions are of concern
when one considers other natural (hydrocarbon) fluids. For example,
while pentane, butane, and propane were all considered as potential
working fluids, the inventors determined that, of the
naturally-occurring hydrocarbons, isopentane offers superior fluid
properties for micro-CHP applications.
[0010] According to another aspect of the present invention, a
cogeneration system is disclosed. The cogeneration system includes
an organic working fluid, a heat source capable of superheating the
organic working fluid, a first circuit to transport the organic
working fluid, and a generator to produce electricity. At least a
portion of the first circuit, which includes a scroll expander, a
condenser and a pump, is in thermal communication with the heat
source. The pump circulates the organic working fluid through the
first circuit. 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
evaporator to become superheated. 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" (discussed below) is meant to cover the more
specific relationship between direct, adjacent heat exchange
components designed specifically for that purpose. By the nature of
the organic working fluid, it remains in a superheated state from
prior to entering the scroll expander to after it exits the same.
The high vapor density and heat transfer properties of the
superheated organic working fluid ensure that maximum heat and
power can be extracted from the fluid without having to resort to a
large expander.
[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 part of
the organic working fluid-carrying conduit such that the part 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
heat exchange fluid could be water, a mixture of water and a
freeze-inhibiting additive (such as propylene glycol), or an
organic, such as that of the organic working fluid of the first
circuit. The first loop of the interloop heat exchanger is fluidly
connected to the organic working fluid-conveying first circuit,
while the second loop is fluidly connected to the heat exchange
fluid-conveying second circuit. Preferably, the interloop heat
exchanger is situated between the pump and the scroll expander of
the first circuit so that it acts as an evaporator for the organic
working fluid. The latter configuration may also include a space
heating loop preheat device that is in heat exchange communication
with the condenser second loop such that a portion of the heat
still present in the heat exchange fluid after giving up a portion
of its heat to the organic working fluid in the interloop heat
exchanger can be used to preheat fluid in an external SH loop.
[0012] Also, as with the former configuration, the burner can be
disposed within a container. In both configurations, the container
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. In the
former configuration, the heat picked up by the exhaust gas heat
exchanger can be routed to various places within either the first
circuit or the space heating loop to provide additional preheat of
the organic working fluid or space heating fluid, respectively. In
addition, either configuration may be adapted to exchange heat with
an external DHW loop. The heat exchange may further take place in a
heat exchanger configured similar to the condenser, such that two
individual loops are placed adjacent one another to facilitate the
transfer of heat between the respective fluids flowing
therethrough, or in a storage tank (such as a hot water storage
tank) such that the fluid stored therein (preferably water) is kept
at an elevated temperature to have a readily-available supply of
hot tap, bath and shower water. In the case of a storage tank-based
approach, additional heating of the liquid in the tank can occur by
a heating element that receives its power from the generator. Where
no tank is present, the heat to the DHW loop can be taken from a
connection to the first circuit condenser (in the directly-fired
configuration) or the heat exchange fluid flowing through the
second circuit (in the indirectly-fired configuration).
Furthermore, in either of the directly-fired or indirectly-fired
configurations, if it is desired to preserve the ability to provide
DHW while maintaining an overall simplistic, low-cost system, an
oversized or multiple-staged burner may be used. This prompt
heating can reduce the size of or even obviate the need for a large
storage tank while still capable of providing substantially
"instant" hot water when required.
[0013] The operating conditions, including maximum temperature and
pressure, of the cogeneration system's first circuit are configured
to be within the design range of the organic working fluid. A
controller can be incorporated to monitor and, if necessary, change
operating parameters within the system. Switches, sensors and
valves can be incorporated into the system to help the controller
carry out its function. For example, to protect the expander from
overspeeding during startup or shutdown transients, or low (or no)
grid load, the controller can direct block and bypass valves to
actuate, thereby forcing the superheated organic working fluid to
bypass the expander. The controller may also integrate with
user-determined conditions through the thermostat.
[0014] According to another aspect of the present invention, an
indirectly-heated micro-CHP, including a heat source, first and
second fluid circulating loops and an interloop heat exchanger, is
disclosed. The indirectly-fired micro-CHP is advantageous in terms
of system flexibility and maintainability. Multiple
fluid-circulating loops are employed such that the heat source (for
example, a burner) is provided to a second fluid circulating loop
that is in thermal communication with, but fluidly isolated from, a
first fluid circulating loop. The second fluid circulating loop
includes piping used to convey a heat exchange fluid. This piping
is preferably coiled and finned to maximize heat transfer between
the heat source and the heat exchange fluid. At least one pump is
used to circulate the heat exchange fluid. The second fluid
circulating loop further contains a parallel set of sub-loops, one
of which passes through a DHW heat exchanger to heat up municipal
water, while the other passes through the interloop heat exchanger
as an intermediary between the heat source and the organic working
fluid flowing through the first fluid circulating loop. In addition
to passing the organic working fluid through the interloop heat
exchanger, the first fluid circulating loop includes a scroll
expander connected to a generator, a SH heat exchanger, and a
circulation pump. Upon the application of heat, the organic working
fluid becomes superheated, then gets expanded in the scroll
expander to turn the generator, thereby producing electrical power.
The lower pressure, but still superheated organic working fluid
leaving the scroll expander enters the SH heat exchanger, where
another fluid, typically air or water, can be passed through and
heated by the organic working fluid. This SH fluid is then
circulated to radiators or similar space heating devices within a
dwelling. The circulation pump returns the condensed organic
working fluid to the interloop heat exchanger, where it can repeat
the process.
[0015] Optionally, a preheat device for the SH loop can be placed
in heat exchange communication with the second fluid circulating
loop such that additional SH may be effected. In addition, as with
the previous aspect, the heat source may include a burner disposed
within a combustion chamber-type container. The container may
include an exhaust duct, an exhaust fan, and an exhaust gas heat
exchanger disposed adjacent the exhaust duct. The exhaust gas heat
exchanger can further include an exhaust gas recirculation device
to further improve heat transfer from the exhaust gas. Residual
heat that would otherwise be vented out the duct and to the
atmosphere can be captured and rerouted to other parts within the
system. For example, the exhaust gas heat exchanger may be
integrated into the first sub-loop of the second fluid circulating
loop in order to provide additional heating to the DHW heat
exchanger.
[0016] According to yet another aspect of the present invention, a
directly-fired cogeneration system configured to circulate an
organic working fluid is disclosed. The directy-fired micro-CHP is
advantageous in terms of system cost and simplicity. The system
includes a piping loop that defines an organic working fluid flow
path, an organic working fluid disposed in the piping loop, an
evaporator disposed in the organic working fluid flow path, a
burner in thermal communication with the evaporator such that heat
transferred to the evaporator superheats the organic working fluid,
a scroll expander disposed in the organic working fluid flow path
such that the superheated organic working fluid passing through the
scroll expander remains superheated upon discharge from the scroll
expander, a generator operatively responsive to the scroll expander
to generate electricity, a condenser, and a pump disposed in the
organic working fluid flow path between the condenser and the
evaporator. The condenser comprises a primary loop disposed in the
organic working fluid flow path such that the primary loop is in
fluid communication with the scroll expander, and a secondary loop
in heat exchange relationship with the primary loop, where the
secondary loop is configured to transfer at least a portion of the
heat contained in the organic working fluid passing through the
primary loop to an external loop, such as a space heating
device.
[0017] Optionally, the directly-fired micro-CHP system includes a
controller, valves, combustion chamber and exhaust features similar
to that of the previous aspects. Also, as with the previous
aspects, the organic working fluid is preferably either a naturally
occurring hydrocarbon (such as isopentane) or a halocarbon
refrigerant, such as R-245fa. In addition, the heat source, which
can be a burner, may be oversized to provide additional heat in
variations of the system that do not employ a storage tank for DHW
purposes. In this situation, the burner can be either larger, or a
multi-staged device such that each stage is dedicated to a
particular part of the external heating circuits, such as the SH or
DHW circuits. Furthermore, the external heating circuits can be
coupled to the cogeneration system from a single connection on the
condenser such that bifurcated paths corresponding to the SH and
DHW loops can both be accommodated.
[0018] According to still another aspect of the present invention,
a micro combined heat and power system is disclosed. The micro
combined heat and power system comprises an electricity generating
loop and a connection to an external heating loop. The electricity
generating loop includes a burner for raising the temperature of
the organic working fluid such that the organic working fluid
becomes superheated, a scroll expander to receive the superheated
vapor such that the working fluid remains in a superheated state
after passing therethrough, a generator operatively coupled to the
scroll expander to produce electricity, a condenser disposed in
fluid communication with the scroll expander and a pump to
circulate the organic working fluid. The connection is disposed in
the condenser, and is configured to place the external heating loop
in thermal communication with the condenser. This external heating
loop can be either a DHW loop, an SH loop, or both. As with the
previous aspects of the invention, similar controller, combustion
chamber and related features may be incorporated.
[0019] According to an additional aspect of the present invention,
a system for the production of domestic hot water, space heat and
electricity from a Rankine-based cycle with an organic working
fluid is disclosed. The system includes a substantially closed
circuit fluid path configured to transport the organic working
fluid therethrough, a burner configured to provide sufficient heat
to superheat the organic working fluid, and a controller to
regulate the operation of the system. The substantially closed
circuit fluid path is at least partially defined by a coiled
conduit configured to act as a heat transfer element for the
organic working fluid, and includes as components a scroll
expander, a generator, a condenser and a pump. The term "tube" can
be used interchangeably with "conduit", as both describe a closed
hollow vessel used for the transport of fluids. The burner is in
thermal communication with the substantially closed circuit fluid
path's coiled tube. The scroll expander is configured to accept the
superheated organic working fluid. The condenser is configured to
extract at least a portion of the heat remaining in the organic
working fluid after the organic working fluid passes through the
scroll expander. The pump pressurizes and circulates the organic
working fluid.
[0020] According to yet an additional aspect of the present
invention, an indirectly-fired cogeneration system comprising a
heat source, a passive heat transfer element in thermal
communication with the heat source, a first circuit, a generator
and a second circuit is disclosed. The first circuit is configured
to transport an organic working fluid, and is disposed adjacent an
end of the passive heat transfer element such that heat transferred
from the passive heat transfer element increases the energy content
of the organic working fluid. The first circuit is made up of at
least a scroll expander configured to receive the organic working
fluid, a condenser in fluid communication with the scroll expander,
and a pump configured to circulate the organic working fluid. The
condenser is configured to transfer at least a portion of the
excess heat contained in the organic working fluid to an external
heating loop. As with the previous aspects, the generator is
coupled to the scroll expander to produce electricity in response
to motion imparted to it from the scroll. The second circuit is
configured to transport a heat exchange fluid therethrough, and is
disposed adjacent an end of the passive heat transfer element such
that heat transferred therefrom increases the energy content of the
heat exchange fluid. The second circuit is made up of at least a
combustion chamber disposed adjacent the heat source such that
exhaust gas can be removed. Details relating to the combustion
chamber are similar to those discussed in conjunction with the
previous aspects, with the exception that one end of the passive
heat transfer element (which is preferably a heat pipe) is disposed
inside the combustion chamber so that such end absorbs heat from
the heat source.
[0021] According to still another aspect of the present invention,
a cogeneration system comprising a heat source, a passive heat
transfer element in thermal communication with the heat source, and
a first circuit is disclosed. The first circuit is configured to
transport an organic working fluid, and is disposed adjacent an end
of the passive heat transfer element such that heat transferred
from the passive heat transfer element superheats the organic
working fluid. The first circuit is made up of at least a scroll
expander configured to receive the organic working fluid, a
condenser in fluid communication with the scroll expander, and a
pump configured to circulate the organic working fluid. A generator
is coupled to the scroll expander to generate electricity in
response to the expansion of the organic working fluid in the
scroll. The condenser is configured to transfer at least a portion
of the excess heat contained in the organic working fluid to an
external heating loop. As with the previous aspect, the passive
heat transfer element is preferably a heat pipe, and its
integration into the combustion chamber is similar.
[0022] According to another aspect of the present invention, a
method of producing heat and electrical power from a cogeneration
device is disclosed. The method includes the steps of configuring a
first circuit to transport an organic working fluid, superheating
the organic working fluid with a heat source that is in thermal
communication with the first circuit, expanding the superheated
organic working fluid in a scroll expander, turning a generator
that is coupled to the scroll expander to generate electricity,
cooling the organic working fluid in a condenser such that at least
a portion of the heat in the organic working fluid passing through
the condenser is transferred to an external heating loop, using at
least a portion of the heat that has been transferred to the
external heating loop heat to provide space heat, and returning the
organic working fluid exiting the condenser to a position in the
first circuit such that it can receive additional heat input from
the heat source.
[0023] Optionally, the method includes maintaining the organic
working fluid in a superheated state through the expanding step. As
an additional step, the method can selectively use at least a
portion of the heat that has been transferred to the external
heating loop to heat a domestic hot water loop. An alternative set
of steps can be used to configure a second circuit to transport a
heat exchange fluid to a DHW loop where the DHW loop is decoupled
from the SH loop that is thermally coupled to the condenser. The
second circuit is defined by a piping loop flow path that is in
thermal communication with the heat source. The second circuit is
in heat exchange communication with at least one domestic hot water
loop, such as a heat exchanger or a water storage tank, for
example. The second circuit is configured such that at least a
portion of the heat that has been transferred to the heat exchange
fluid will go to heat a fluid (such as water) in the domestic hot
water loop. Preferably, the organic working fluid is superheated to
about 10 to 30 degrees Fahrenheit above its boiling point in the
superheating step, and is pressurized to a maximum pressure of
about 200 to 450 pounds per square inch in the returning (pumping)
step. In addition, the superheating step produces a maximum
temperature of between about 250-350 degrees Fahrenheit in the
organic working fluid. Moreover, the expanding step is conducted
such that the electrical output of the generator is up to 10
kilowatts, while the cooling step is conducted such that the
thermal output transferred to the external heating loop is up to 60
kilowatts. The heat source can either directly or indirectly fire
the organic working fluid. An additional step may further include
operating a set of valves configured to permit the organic working
fluid to bypass the scroll expander upon a preset condition, which
can be a grid outage, startup transient or shutdown transient.
[0024] According to another aspect of the present invention, a
system for the production of electricity and space heat through the
expansion of an organic working fluid in a superheated state is
disclosed. The system comprises an organic working fluid, a flow
path configured to transport the organic working fluid, a
combustion chamber disposed in the flow path, a scroll expander
disposed in the flow path to receive and discharge the organic
working fluid in the superheated state, a generator operatively
coupled to the scroll expander to produce electricity, a condenser
in fluid communication with the scroll expander, and a pump to
circulate the organic working fluid through the flow path. The
combustion chamber comprises a burner, a heat transfer element
adapted to convey the organic working fluid adjacent the burner,
and an exhaust duct to convey combustion products produced by the
burner to the atmosphere. As with previous aspects, coupling
between the condenser and an external heating loop can be used to
effect heat exchange with an SH loop. In addition, system
regulating devices, such as a controller, switches and valves may
be employed, as can additional heat exchange devices that couple to
the exhaust duct or the condenser, also discussed in conjunction
with the previous aspects.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0025] 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:
[0026] FIG. 1 shows a schematic diagram of an integrated micro-CHP
system according to an embodiment of the present invention showing
an indirectly-fired configuration with a storage tank and both SH
and DHW capability;
[0027] FIG. 2 shows a schematic diagram of an integrated micro-CHP
showing an indirectly-fired configuration with no storage tank and
both SH and DHW capability;
[0028] FIG. 3 shows a schematic diagram of an integrated micro-CHP
showing a directly-fired configuration with no storage tank and
both SH and DHW capability;
[0029] FIG. 4 shows a schematic diagram of an integrated micro-CHP
showing a directly-fired configuration with a storage tank and both
SH and DHW capability;
[0030] FIG. 5 shows a schematic diagram of an integrated micro-CHP
showing a directly-fired configuration with no storage tank and SH
capability;
[0031] FIG. 6 shows the integration of a heat pipe into an
indirectly-fired embodiment of the present invention, further
highlighting a common heat exchanger for both SH and DHW;
[0032] FIG. 7 shows the integration of a heat pipe into a
directly-fired embodiment of the present invention, further
highlighting a common heat exchanger for both SH and DHW; and
[0033] FIG. 8 shows the details of an exhaust gas heat exchanger,
including details of an exhaust gas recirculation device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] Referring initially to FIG. 1, one embodiment of the
micro-CHP system 1 is an indirectly-heated, dual-loop system that
includes a first (or primary) circuit 100 and a second circuit 150.
An advantage of the indirectly fired system is that first circuit
boiler (or evaporator) conduit overheating and subsequent bum-out
is avoided. First circuit 100 includes a expander 101, a condenser
102, a pump 103 and one portion of interloop heat exchanger 104. An
organic working fluid (such as naturally-occurring hydrocarbons or
halocarbon refrigerants, not shown) circulates through the loop
defined by the fluidly-connected expander 101, condenser 102, pump
103 and interloop heat exchanger 104. Piping 110 is used to connect
the various components of first circuit 100, whereas the pump 103
provides the pressure to supply the organic working fluid to the
interloop heat exchanger 104, thereby completing the first circuit
100. A generator 105 (preferably induction type) is coupled to
expander 101 such that motion imparted to it by expander 101
generates electricity. While the expander 101 can be any type, it
is preferable that it be a scroll device. The scroll expander can
be a conventional single scroll device, as is known in the art. An
oil pump 108 is used to provide lubricant to the scroll. The
presence of oil helps to establish a seal between the intermeshed
stationary and orbiting wraps that make up the scroll's
crescent-shaped chambers (not shown). A level indicator switch 120
with level high 120A and level low 120B indicators is placed at the
discharge of condenser 103. Controller 130 is used to regulate
system operation. It senses parameters, such as organic working
fluid temperatures, at various points within the first circuit and
level information taken from the level indicator switch 120.
Through appropriate program logic, it can be used to open and close
valves (not presently shown) in response to predetermined
conditions, such as an electric grid outage. The generator 105 is
preferably an asynchronous device, thereby promoting simple,
low-cost operation of the system 1, as complex generator speed
controls and related grid interconnections are not required. 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, 50 or 60 Hz, while
staying within close approximation (often 150 or fewer revolutions
per minute (rpm)) of synchronous speed (3000 or 3600 rpm).
[0035] An external heating loop 140 (shown preferably as an SH
loop) can be coupled to first circuit 100 via connectors (not
shown) on condenser 102. As an option, a preheat coil 145 can be
inserted into the external heating loop 140 such that the hydronic
fluid (typically water) flowing therethrough can receive an
additional temperature increase by virtue of its heat exchange
relationship with heat exchange fluid flowing through second
circuit 150 (discussed in more detail below). The hydronic fluid
flowing through external heating loop 140, is circulated with a
conventional pump 141, and is supplied as space heat via radiator
148 or related device. As an example, hydronic fluid could exit the
condenser 102 at about 50.degree. Celsius and return to it as low
as 30.degree. Celsius. The capacity of the system 1 is up to 60
kW.sub.t; however, it is within the scope of the present invention
that larger or smaller capacity units could be utilized as needed.
Inherent in a micro-CHP (cogeneration) system is the ability to
provide heat in addition to electricity. Excess heat, from both the
heat source and the expanded working fluid, can be transferred to
external DHW and SH loops. The nature of the heat exchange process
is preferably through either counterflow heat exchangers (for
either or both the DHW and SH loops), or through a conventional hot
water storage tank (for a DHW loop). 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.
[0036] Second circuit 150 includes two parallel sub-loops 150A,
150B. Heat to the two parallel sub-loops 150A, 150B is provided by
a burner 151, which is supplied with fuel by a gas train 152 and
variable flow gas valve 153. Piping 160 (which makes up the
parallel sub-loops) passes through a combustion chamber 154, which
is where the heat from the combustion of fuel at burner 151 is
given up to the heat exchange fluid (not shown) that flows through
piping 160. Piping 160, which includes a finned tube portion 161
disposed inside the combustion chamber 154, branches out into the
first parallel sub-loop 150A, which transports the heat exchange
fluid that has been heated in combustion chamber 154 to interloop
heat exchanger 104 in order to give up the heat to organic working
fluid flowing through first circuit 100. Block valves (not shown)
could be used to regulate flow between the sub-loops; 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 150B transports the heat exchange fluid to
DHW heat exchanger 180 in order to heat up domestic hot water. One
side of domestic hot water heat exchanger 180 (which can be a water
storage tank) includes coil 180A configured to transport the heat
exchange fluid, and another side, the shell 180B, to transport
domestic hot water (not shown) from a cold water inlet 191A, past
coil 180A and to DHW outlet 191B. Typically, the cold water comes
from either a well or a city/municipal water supply. Similarly,
temperature sensor 171B can detect the temperature of the DHW
coming out of the DHW heat exchanger 180. This sensor can also be
linked to a controller 130 (discussed in more detail below).
Combustion chamber 154 includes an exhaust duct 155, an exhaust gas
recirculation device 156 with exhaust duct heat exchanger 157, and
fan 158. It will be appreciated by those skilled in the art that
although the fan 158 is preferably shown as an induced-draft fan,
it could also be a forced-draft fan, if properly located relative
to the combustion chamber 154. Temperature sensor 171A is placed at
the combustion chamber 154 outlet for the second circuit 150 to
measure the temperature conditions of the heat exchange fluid, in a
manner similar to that of temperature sensor 171B. Second circuit
pumps 185A, 185B are used to circulate heat exchange fluid through
the second circuit 150, with pump 185B circulating heat exchange
fluid through DHW heater 180 and pump 185A circulating heat
exchange fluid through interloop heat exchanger 104. The exhaust
duct heat exchanger 157 and an exhaust gas recirculation (EGR)
device 156 accept hot exhaust gas from the burner 151 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 158. The heat given up by the
exhaust gas in the exhaust gas heat exchanger 157 is used to
provide additional heat to other parts of the system 1. In the
present figure, this additional heat is used to increase the
temperature of the heat exchange fluid flowing in second circuit
150.
[0037] A controller 130, which could be a programmable logic
controller (PLC) or conventional microcomputer (not shown), can be
used to provide detailed system control. All of the pumps can be
configured to be variable-speed, and are responsive to input
signals from controller 130. Upon receipt of a signal for heat, the
burner 151 ignites the fuel, while the proper circulating pump 185B
or 185A is energized. For DHW, flow switch 190, in conjunction with
temperature sensor 171B, provide inputs to controller 130. Flow
switch 190 selects DHW mode, where the DHW set point is coupled to
temperature sensor 171A. The burner gas flow and DHW pump 185B flow
are regulated to provide the desired temperature at 171B according
to the temperature preset by the user on the DHW thermostat (not
shown).
[0038] When the system is operating, heated heat exchange fluid is
moving past sensor 171A, which is able to provide a valid signal to
the controller 130 so the burner 151 firing rate and pump 185B flow
can be adjusted for both safe operation and the needed output.
However, when the system is just starting, the controller 130 must
be given some initialized state which can be used as a safe
operating condition until such time as heat exchange fluid is
flowing past temperature sensor 171A. It is desirable to have a
minimum amount of heat exchange fluid flow during startup, so that
the fluid heats up as rapidly as possible. However, some flow is
needed to prevent local overheating of the fluid in the combustion
chamber 154, and to provide the controller 130 with an indication
that the burner 151 is indeed firing. The gas rate is set to
provide the longest possible run time for the system, consistent
with measured outdoor temperature and rate of change of indoor
temperature. Pump 185B operates to keep the combustion chamber 154
supplied with the heat exchange fluid at the factory-preset value
for temperature sensor 171A. When temperature sensor 171A gets to
about 50% of the thermostat set point, the pump 185B speed is
increased until the temperature reading in temperature sensor 171A
reaches its set point, at which time the burner 151 and pump 185B
modulate for constant values of temperature sensors 171A and 171B.
When the flow switch 190 indicates zero flow, the burner 151 and
pump 185B cease operation. A small expansion tank (not shown) can
be placed in the second circuit 150 to allow for differential
thermal expansion at moderately high pressures of the heat exchange
fluid.
[0039] When the user desires heat, as indicated by the room
thermostat (not shown) the burner 151 comes on to about 50% of its
capacity to warm up system 1. Pump 185A comes on to a speed
predetermined to coincide with the flow requirements established by
the initial burner firing rate and the design response of the
system. The controller 130 responds to the user demand for heat,
and the owner selected set point for room temperature. Burner 151
firing and pump 185A flow are controlled in part, and
conventionally by room temperature and its set point, as well as
outdoor temperature (sensor not shown). The first circuit pump 103
runs fast enough to keep the organic working fluid liquid level
between level low 120B and level high 120A switch settings. The
controller 130 instructs the pump 103 to start or speed up when the
organic working fluid liquid level rises above the level 120A, and
stopping when the level goes below level 120B, for example.
[0040] The length of finned tube portion 161 of piping 160 that is
inside the combustor 154 can be minimized by carefully selecting
pumps, control points, and conduit size. Referring now to FIG. 8 in
conjunction with FIG. 1, details of the EGR device 156 for
micro-CHP system 1 is shown. In essence, the EGR device 156
functions in conjunction with the exhaust duct 155 and is an
integral part of exhaust gas heat exchanger 157. The hot exhaust
gas stream is directed axially through EGR device 156, which is
preferably placed between burner 151 and exhaust duct 155. An
annular recirculation duct 156B, passes some of the exhaust gas in
a counterflow fashion until it is reinjected at inlet 156A. The
walls of the EGR device 156 are cooled by the heat exchange fluid
that passes through the duct heat exchanger 157, and as a result,
the recirculation gas entering at inlet plane 156A is partially
cooled. This tempered gas stream leaving at plane 156B enters the
second heat transfer section defined by finned tube portion 161 of
second circuit piping (not presently shown), in which additional
cooling of the gas occurs. In a more compact arrangement, the inner
annular duct of the EGR device 156 would be replaced by an array of
fine tubes (not shown), each having a flow inducer for hot gas at
the inlet end. While such an approach would involve the use of a
larger amount of fluid, which would increase the response time of
the system, significant benefits could be realized, including the
application of the EGR device 156 to an evaporator where an organic
working fluid is used such that the fluid is never exposed to the
full temperature of the exhaust gas, and the final heat recovery is
not reduced by any form of added flue gas dilution, especially cool
air. The primary benefit of the EGR device 156 is that levels of
harmful gaseous by-products (such as NO.sub.x) are reduced. An
additional benefit of the EGR device is that by reducing the
highest temperature that the finned tube portion 161 is exposed to,
simpler components that will have lower cost yet which can attain
the same long life of more costly materials can be used.
[0041] Referring next to FIG. 2, an alternate embodiment of the
indirectly-fired micro-CHP system 2 is shown. Here, the second
circuit 250 does not encompass parallel sub-loops. Instead, a
single loop is routed directly from combustion chamber 254 to
interloop heat exchanger 204. DHW capability, which was provided by
second sub-loop 150B in the embodiment shown in FIG. 1, is now
integrated into the external heating loop 240. This external loop,
that services both DHW and SH, can be bifurcated after coupling to
the condenser 202, with valves 247A, 247B operating to supply SH
radiators 248 or DHW heat exchanger 280 as needed. DHW heat
exchanger 280 can be either a water tank to store hot water (as
discussed in conjunction with the previous aspect), or a dual-pass
counterflow heat exchange device. After the fluid (typically water)
passes through either or both SH and DHW heat exchangers, it is
circulated through heating loop 240 back to the condenser 202 to
start its cycle again. Prior to entry into the condenser 202, the
fluid can be preheated by passing it thermally adjacent second
circuit 250 in a preheat device 245.
[0042] Referring now to FIGS. 3 and 4, a directly-fired micro-CHP
system is shown. This system has the advantage of being simpler in
construction, with attendant lower cost. In the present embodiment,
the system 3 does not include a second circuit. The interloop heat
exchanger of the previous embodiments, which acted as the heat
source for the previous embodiment first circuits, is replaced by a
combustion chamber 304, where both the burning of fuel, through gas
train 352, valve 353 and burner 351, and the evaporation of the
organic working fluid takes place. As with the previous
embodiments, the organic working fluid is superheated. Generator
305, as with the previous embodiments, is asynchronously tied to a
load, preferably on the customer/user side of the electric meter,
which is typically the power grid. The load on the scroll expander
301 imposed by the grid ensures that mechanical speeds in the
scroll 301 are kept within its structural limits. Block valve 307A
and bypass valve 307B are situated in the organic working fluid
flow path defined by piping 310 (of which conduit 361 is part).
These valves respond to a signal in controller 330 that would
indicate if no load (such as a grid outage) were on the system,
allowing the superheated vapor to bypass around the expander,
thereby avoiding overspeed of scroll 301. In this condition, the
rerouted superheated vapor is fed into the inlet of condenser 302.
Under normal operating conditions, where there is a load on the
system, the superheated vapor enters the scroll expander 301,
causing the orbiting involute spiral wrap to move relative to the
intermeshed fixed involute spiral wrap. As the superheated vapor
expands through the increasing volume crescent-shaped chambers, the
motion it induces in the orbiting wrap is transferred to the
generator 305, via a coupled shaft or an integral rotor/stator
combination on the scroll 301. Depending on the type of oil used in
the system (such as whether the oil is miscible or immiscible with
regard to the organic working fluid), scroll 301 may preferably
include an oil pump 308 to circulate oil present in the scroll from
the superheated vapor. The workings of the exhaust duct 355 and fan
358 are similar to that of the previous aspect; however, the
present EGR device 356 and exhaust duct heat exchanger 357, rather
than providing additional heat to a heat exchange fluid flowing
through the second circuit 150, 250 of the previous embodiments,
can be used to provide supplemental heat to various locations
within the system 3. For example, additional heat can be added to
the organic working fluid coming out of pump 385, shown at point A.
Similarly, it can be used to add heat to the external heating loop
340 at points B or C. Precise location of the heat exchange points
A, B or C would be determined by the nature of the organic working
fluid and its properties. Note that DHW heat exchanger 380 can be
configured as a conventional dual-pass counterflow heat exchanger,
or as a water storage tank, as discussed in the previous aspects.
In situations where no (or a small) storage tank is being used
(such as, for example, when space is at a premium), then in order
to provide fast-responding DHW, additional heat generation may be
required. One approach is to use a larger or multiple-stage burner
(not shown). This could provide rapid response times to the instant
or near-instant demands associated with DHW uses (such as showers,
baths and hot tap water). Referring with particularity to FIG. 4, a
variation on the directly-fired micro-CHP of FIG. 3 is shown. In
this case, the system 4 specifically includes a storage tank 480.
This approach allows the inclusion of DHW capability without having
to resort to increased burner capacity. In addition, power to a
storage tank heating element 480C can be provided directly off
generator 405. In addition, trade-offs between the size of the
storage tank 480 and the size or number of burner 451 can be made
to best suit the functionality and packaging/volume requirements of
the system.
[0043] Referring now to FIG. 5, a directly-fired micro-CHP system 5
is shown. This represents the most simplistic system, in that it is
geared toward the exclusive generation of electricity and SH. By
not including DHW capability, a storage tank can be avoided without
sacrificing system functionality or requiring augmented burner
capacity. In other respects, this system is similar to that of the
previous directly-fired embodiments, including operation of the
heat source componentry 551, 552 and 553, exhaust componentry 555,
556, 557 and 558, organic working fluid flow path componentry 501,
502, 503, 504, 507A,B and 508, generator 505, and sensing a
controlling apparatus 520, 530.
[0044] Referring now to FIGS. 6 and 7, a variation on the
indirectly-fired and directly-fired cogeneration systems of the
previous aspects is shown. Referring with particularity to FIG. 6,
a passive heat transfer element, preferably in the form of a heat
pipe 675, can be disposed between the first circuit 600 and the
second circuit 650 to effect heat exchange between those circuits
and the heat source. Referring with particularity to FIG. 7, heat
pipe 775 is disposed within the flow path of the first circuit,
which also includes scroll expander 701, condenser 702 and pump
703. In either configuration, the heat pipe is an evacuated and
sealed container that contains a small quantity of working fluid,
such as water or methanol. When one end of the pipe (typically
referred to as the evaporator end) is heated, the working fluid
rapidly vaporizes, due in part to the low internal pressure of the
fluid. The vapor travels to the lower-pressure opposite end
(typically referred to as the condenser end), giving up its latent
heat. Preferably, gravity or capillary action allows the condensed
fluid to move back to the evaporator end, where the cycle can be
repeated. When the fluid has a large heat of vaporization, a
significant amount of heat can be transferred, even when the
temperature differences between the opposing ends is not great. In
other regards, the operation of the systems is similar to that of
the previous aspects.
[0045] Referring now to FIG. 8, details of the exhaust duct heat
exchanger 157 and the exhaust gas recirculation device 156 are
shown. The combustion chamber 154 (not presently drawn to scale)
encases enough of the heat source apparatus, including burner 151)
to ensure that the exhaust gas and related combustion products are
entrained into the exhaust duct 155 such that they can be vented to
the atmosphere. An induced draft fan (shown elsewhere) can be used
to ensure thorough venting of the combustion products. The exhaust
gas recirculation device 156 is a co-annular duct that takes the
exhaust gas leaving the region around burner 151 through the inner
annulus 156A, and doubles back a portion of the gas to flow in the
outer annulus 156B. During the time that the portion of the gas
that is recirculating through the outer annulus 156B, it is giving
up some of its heat to the exhaust duct heat exchanger 157, which
is shown as a coiled conduit. From here, the coiled conduit of the
heat exchanger 157 can be routed to other locations (shown
elsewhere) in the system, where it can then be used to provide
supplemental heat.
[0046] 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.
* * * * *