U.S. patent application number 11/941037 was filed with the patent office on 2009-05-21 for trigeneration system and method.
This patent application is currently assigned to The Regents of the University of California. Invention is credited to Gerardo C. Diaz.
Application Number | 20090126381 11/941037 |
Document ID | / |
Family ID | 40640533 |
Filed Date | 2009-05-21 |
United States Patent
Application |
20090126381 |
Kind Code |
A1 |
Diaz; Gerardo C. |
May 21, 2009 |
TRIGENERATION SYSTEM AND METHOD
Abstract
A trigeneration system comprising a cooling loop and a
heat/power loop connected by a heat exchanger. Energy available at
the high side of the cooling loop is transferred from cooling loop
to the heat/power loop by the heat exchanger. This energy is put to
use by the heat/power loop to efficient produce heat and power. The
system can be run transcritical and use environmentally friendly
working fluid, such as carbon dioxide.
Inventors: |
Diaz; Gerardo C.; (Merced,
CA) |
Correspondence
Address: |
FOLEY & LARDNER LLP
P.O. BOX 80278
SAN DIEGO
CA
92138-0278
US
|
Assignee: |
The Regents of the University of
California
|
Family ID: |
40640533 |
Appl. No.: |
11/941037 |
Filed: |
November 15, 2007 |
Current U.S.
Class: |
62/238.1 ;
60/645; 62/235.1 |
Current CPC
Class: |
F01K 25/10 20130101;
F24H 4/02 20130101; F25B 25/005 20130101; Y02E 20/14 20130101 |
Class at
Publication: |
62/238.1 ;
60/645; 62/235.1 |
International
Class: |
F25B 27/00 20060101
F25B027/00; F01K 13/00 20060101 F01K013/00 |
Claims
1. An apparatus for providing cooling, heat and power, comprising:
a cooling loop for providing cooling; a heat/power loop for
providing heat and power; and a heat exchanger connecting the
cooling loop to the heat/power loop such that energy from the
cooling loop is transferred to the heat/power loop by the heat
exchanger.
2. The apparatus of claim 1, wherein the cooling loop is a closed
loop cooling system comprising: cooling loop components; conduit
connecting the cooling loop components; and cooling working fluid
flowing through the conduit and cooling loop components.
3. The apparatus of claim 2, wherein the cooling loop components
further comprise a suction line heat exchanger for increasing the
coefficient of performance of the cooling loop.
4. The apparatus of claim 2, wherein the cooling loop components
further comprise an expander for increasing the coefficient of
performance of the cooling loop.
5. The apparatus of claim 2, wherein the cooling loop is configured
to run transcritical.
6. The apparatus of claim 5, wherein the cooling working fluid
further comprises carbon dioxide.
7. The apparatus of claim 2, wherein the cooling loop components
further comprise: a compressor for compressing the cooling working
fluid; an expansion valve for expanding the cooling working fluid;
and an evaporator for absorbing heat from ambient air into the
cooling working fluid.
8. The apparatus of claim 1, wherein the heat/power loop is a
closed loop system comprising: heat/power loop components; conduit
connecting the heat/power loop components; and heat/power working
fluid flowing through the conduit and heat/power loop
components.
9. The apparatus of claim 8, wherein the heat/power loop is
configured to run transcritical.
10. The apparatus of claim 9, wherein the heat/power working fluid
comprises carbon dioxide.
11. The apparatus of claim 8, wherein heat/power loop components
further comprise: an auxiliary energy heat exchanger for adding
auxiliary heat from an external system to the heat/power working
fluid.
12. The apparatus of claim 11 wherein the external system comprises
at least one solar collector.
13. The apparatus of claim 8, wherein the heat/power loop
components further comprise: a pump for increasing the enthalpy of
the heat/power working fluid; a turbine for producing power from
the heat/power working fluid; and a condenser and a hot water heat
exchanger for heating water from energy extracted from the
heat/power working fluid.
14. The apparatus of claim 1, wherein the cooling loop is a closed
loop cooling system comprising: cooling loop components; conduit
connecting the cooling loop components; and carbon dioxide working
fluid flowing through the conduit and cooling loop components; and
wherein the heat/power loop is a closed loop system comprising:
heat/power loop components; conduit connecting the heat/power loop
components; and carbon dioxide working fluid flowing through the
conduit and heat/power loop components; and wherein the heat
exchanger further comprises a carbon dioxide to carbon dioxide heat
exchanger.
15. A method for producing cooling, heat, and power, comprising:
producing cooling by: compressing cooling working fluid to produce
high pressure/high enthalpy cooling working fluid; rejecting heat
from the high pressure/high enthalpy cooling working fluid to
produce high pressure/low enthalpy cooling working fluid; expanding
the high pressure/low enthalpy cooling working fluid to produce low
pressure/low enthalpy cooling working fluid; and absorbing heat
from ambient air into the low pressure/low enthalpy cooling working
fluid to cool the ambient air; and producing heat and power by:
increasing pressure of a heat/power working fluid to produce a high
pressure/low enthalpy heat/power working fluid; adding the heat
rejected from the high pressure/high enthalpy cooling working fluid
to the heat/power working fluid to produce a high pressure/high
enthalpy heat/power working fluid; using energy from the high
pressure/high enthalpy heat/power working fluid to produce power;
using additional energy from the heat/power working fluid to heat
water to produce heat.
16. The method of claim 15 further comprising adding additional
energy to the heat/power working fluid from an external system.
17. The method of claim 16 wherein the external system comprises at
least one solar collector.
18. The method of claim 16 wherein the additional energy comprises
waste heat generated by the external system.
Description
FIELD OF THE INVENTION
[0001] Embodiments of the present invention relate generally to
heating, cooling, and/or power generation systems. More
particularly, embodiments of the present invent relate to combined
heating, cooling and power generation systems with a transcritical
carbon dioxide cycle.
BACKGROUND INFORMATION
[0002] This section is intended to provide a background or context
to the invention that is recited in the claims. The description
herein may include concepts that could be pursued, but are not
necessarily ones that have been previously conceived or pursued.
Therefore, unless otherwise indicated herein, what is described in
this section is not prior art to the description and claims in this
application and is not admitted to be prior art by inclusion in
this section.
[0003] Ozone layer and/or global warming problems have focused
considerable attention on the nature of refrigerants employed in
refrigeration systems of various sorts. Some such systems,
particularly those that do not have sealed compressor units are
prone to refrigerant leakage. Older refrigerants, HFC 12, for
example, are thought to cause depletion of the ozone layer while
many of the replacements, HCFC 134a, for example, are believed to
contribute to the so-called "greenhouse effect" and thus global
warming.
[0004] As a consequence, a considerable effort is underway to
develop refrigeration systems employing "natural" refrigerants such
as carbon dioxide and/or propane. Carbon dioxide is plentiful in
the atmosphere and may be obtained therefrom by conventional
techniques and employed as a refrigerant in such systems. Should
the systems leak the CO.sub.2 refrigerant, because it was
originally obtained from the atmosphere, there is no net increase
of the refrigerant in the atmosphere, and thus no increase in
environmental damage as a result of the leak.
[0005] As carbon dioxide has a low critical point, systems
utilizing carbon dioxide as a refrigerant usually require the
refrigeration system to run partially above the critical point, or
to run transcritical. Transcritical refrigeration systems operate
at relatively high pressures and require, in lieu of a condenser in
a conventional vapor compression refrigeration system, a gas cooler
for the refrigerant. One of the drawbacks of this cycle is that it
has a lower coefficient of performance (COP) than comparable
refrigeration cycles operating at high ambient temperatures.
[0006] Cogeneration systems are systems which combine cycles to
generate electricity together with refrigeration and/or heat. These
systems offer the opportunity to reduce the cost of electrical
energy for a building complex, factory, hospital, or local group,
and to ensure the continuous availability of electrical energy
during blackouts or "brownouts," while simultaneously providing
cooling and/or heating.
[0007] Today, many standard industrial processes use energy
cogeneration to increase the efficiency of their heating and
electrical generation processes. One application of a cogeneration
systems is to use "wasted" energy, in the form of heat or exhaust,
from a conventional power generation system, to heat or cool a
liquid which, in turn, is used to heat or cool a building. While
cogeneration is useful, much of the heat produced by the electrical
and/or heat generation techniques goes unused. Moreover, many
industrial applications also desire the production of a cooled
fluid to utilize in cooling applications, such as air-conditioning
of buildings. Therefore, there has been effort to utilize
cogeneration waste heat to also generate a cooled fluid. This
energy concept is called trigeneration. While attractive, there are
many hurdles to producing an efficient trigeneration cooling
system.
SUMMARY OF THE INVENTION
[0008] One embodiment of the invention relates to an apparatus for
providing cooling, heat and power, comprising a cooling loop for
providing cooling, a heat/power loop for providing heat and power,
and a heat exchanger connecting the cooling loop to the heat/power
loop such that available energy from the cooling loop is
transferred to the heat/power loop by the heat exchanger. The
cooling loop can be a closed loop cooling system comprising cooling
loop components, conduit connecting the cooling loop components,
and cooling working fluid flowing through the conduit and cooling
loop components. The cooling loop components can include a
compressor for compressing the cooling working fluid, an expansion
valve for expanding the cooling working fluid, and an evaporator
for absorbing heat from ambient air into the cooling working fluid.
The cooling loop components can also include a suction line heat
exchanger and/or expander for increasing the coefficient of
performance of the cooling loop. The cooling loop can be configured
to run transcritical and, in one embodiment, the cooling working
fluid can comprise carbon dioxide.
[0009] In one embodiment, the heat/power loop can be a closed loop
system comprising heat/power loop components, conduit connecting
the heat/power loop components, and heat/power working fluid
flowing through the conduit and heat/power loop components. The
heat/power loop components can include a pump for increasing the
enthalpy of the heat/power working fluid, a turbine for producing
power from the heat/power working fluid, and a condenser and hot
water heat exchanger for heating water from energy extracted from
the heat/power working fluid. The heat/power loop components can
also include an auxiliary energy heat exchanger for adding
auxiliary heat from an external system, for example a solar
collector, to the heat/power working fluid. The heat/power loop can
be configured to run transcritical and, in one embodiment, the
heat/power working fluid can be carbon dioxide. In systems in which
both the cooling and heat/power working fluids comprise carbon
dioxide, the heat exchanger can comprise a carbon dioxide to carbon
dioxide heat exchanger.
[0010] Another embodiment of the invention comprises a method for
producing cooling, heat, and power. Cooling can be produced by
compressing the cooling working fluid to produce high pressure/high
enthalpy cooling working fluid, rejecting heat from the high
pressure/high enthalpy cooling working fluid to produce high
pressure/low enthalpy cooling working fluid, expanding the high
pressure/low enthalpy cooling working fluid to produce low
pressure/low enthalpy cooling working fluid, and absorbing heat
from ambient air into the low pressure/low enthalpy cooling working
fluid to cool the ambient air. Heat and power can be produced by
increasing pressure of a heat/power working fluid to produce a high
pressure/low enthalpy heat/power working fluid, adding the heat
rejected from the high pressure/high enthalpy cooling working fluid
to the heat/power working fluid to produce a high pressure/high
enthalpy heat/power working fluid, using energy from the high
pressure/high enthalpy heat/power working fluid to produce power,
and using remaining energy from the heat/power working fluid to
produce hot water. Additional energy can also be added to the
heat/power working fluid from an external system. The external
system can include solar collectors and/or the additional energy
can comprise waste heat generated by the external system.
[0011] These and other advantages and features of the invention,
together with the organization and manner of operation thereof,
will become apparent from the following detailed description when
taken in conjunction with the accompanying drawings, wherein like
elements have like numerals throughout the several drawings
described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a block diagram of one embodiment of a
trigeneration system according to the present invention.
[0013] FIG. 2 is a graph illustrating pressure-enthalpy diagrams
for one embodiment of a trigeneration system according to the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] Embodiments of the present invention are described as being
useful in the environment of a trigeneration system employing a
transcritical cycle using a refrigerant such as CO.sub.2. However,
it is to be understood that the principals disclosed and claimed
herein may find use in refrigeration systems using nontranscritical
and/or conventional cycles. In addition, refrigerants other than
CO.sub.2 can be employed. Accordingly, no limitation to
transcritical refrigeration systems or CO.sub.2 refrigerants are
intended except insofar as expressly stated in the appended
claims.
[0015] Referring to FIG. 1, one embodiment of a trigeneration
system according to the present invention is generally designated
with reference numeral 100. The system 100 includes a refrigeration
loop 102 and a heating/power loop 104, connected by a heat
exchanger 106. The refrigeration loop 102 includes heat exchanger
106, as well as a compressor 108, an expansion valve 110, and an
evaporator 112. The heat/power loop 104 includes a pump 114, a heat
exchanger 116, a turbine 118, a second heat exchanger 120 and a
condenser 122.
[0016] In the refrigeration loop 102, refrigerant is circulated
through the closed loop system. In one embodiment, the refrigerant
is CO.sub.2. Because CO.sub.2 has a low critical point, systems
utilizing CO.sub.2 as a refrigerant usually require the
refrigeration loop to run transcritical. In this embodiment,
refrigerant at point 1 is compressed above its critical point by a
compressor 108. As a result, high pressure and high temperature
refrigerant exits the compressor 108 at point 2. Heat is rejected
from the high-pressure side of the refrigeration loop 102 to the
heating/power loop 104 by the heat exchanger 106 which produces a
low enthalpy-high pressure working refrigerant fluid at point 3.
The working refrigerant fluid is then expanded in an expansion
valve 110 to produce an expanded low pressure refrigerant at point
4. The refrigerant enters the expansion valve 110 through an
expansion valve inlet 109 and exits through an expansion valve
outlet 111. The expansion inlet 109 can be controlled to regulate
the high side pressure to achieve the optimal coefficient of
performance.
[0017] After expansion, the refrigerant enters an evaporator 112
through an evaporator inlet. In the evaporator 112, the refrigerant
receives heat from ambient air. The ambient air flows through the
evaporator in a direction opposite to, or perpendicular to, the
flow of the refrigerant. A fan can be used to move the ambient air
across the evaporator 112. After exchanging heat with the
refrigerant, the cooled ambient air exits the evaporator. The
refrigerant exits the evaporator 112 at high enthalpy and low
pressure and temperature. The superheated refrigerant then
re-enters the compressor 108, completing the refrigeration cycle.
The environmental working conditions of the refrigeration loop 102
are defined, at least in part, by the ambient air temperature at
the evaporator inlet.
[0018] In the heat/power loop 104, CO.sub.2 can also be used as the
working fluid. A pump 114, can be used to increase the pressure of
the working fluid between points a and b. Heat from the
refrigeration loop 102 can be added at a constant pressure between
points b and z by the heat exchanger 106. In one embodiment, where
CO.sub.2 is used as the working fluid in both the refrigeration
loop 102 and the heat/power loop 104, the heat exchanger 106 can be
a CO.sub.2-to-CO.sub.2 heat exchanger. If solar collectors and/or
waste heat are available, then additional energy can be added by
another heat exchanger 116 to increase the available potential to
generate power at the turbine 118. Power is generated at the
turbine 118 between points c and d. For example, the turbine 118
can include an output drive shaft which drives an electric
generator for producing electricity.
[0019] In one embodiment, the temperature at point d remains high
enough to allow the system 100 to produce hot water. A heat
exchanger 120 and condenser 122 can be used to extract energy from
the working fluid to heat up water flowing through the heat
exchanger 120 and condenser 122. Water flows from outside the
system 100 into the condenser 122 where it is heated from
temperature T.sub.w.sup.in to T.sub.w.sup.out. It then flows
through the heat exchanger where it is heated up from temperature
T.sub.w.sup.out to T.sub.w.sup.HW. The heat exchanger 120 can be
used to extract energy from the working fluid between points d and
e. At point e, the working fluid is generally still in vapor state
so the condenser 122 can be used to reject latent heat and complete
the heat/power cycle.
[0020] The embodiment described above effectively utilizes the
energy available at the high-side of the refrigeration loop 102 to
produce power and hot water. This energy is usually wasted as heat
rejected to the ambient in a standard air conditioning system.
Instead, using heat exchanger 106, this energy is transferred to
and utilized in the heat/power loop 104. By putting this available
energy to use, the power obtained at the turbine 118 in the
heat/power cycle is more than the power used by the pump 114 so the
net COP of the refrigeration cycle can be increased. The system 100
can also be operated in winter as a heat pump. Since in this case
the priority is to obtain very hot water for heating purposes, the
location of the turbine 118 can be modified to be placed downstream
of the heat exchanger 120. The cycle can operate with an
environmentally friendly refrigerant, such as CO.sub.2. In
addition, the system 100 can also take advantage of waste heat or
heat generated from the utilization of optional solar collectors.
The system's COP can be further improved by adding a suction line
heat exchanger and/or an expander in the refrigeration loop. The
cycles can also be optimized in terms of operating pressures and
amount of charge in the system 100 to suit particular
applications.
[0021] FIG. 2 shows a pressure-enthalpy diagram for the combined
refrigeration-heat/power cycles described above. For the
illustrated set of operating conditions, an improvement in COP of
15% can be realized and the heat/power cycle can generate hot water
at 40.degree. C. Of course, performance numbers can vary depending
on the operating conditions. As shown in FIG. 2, a vapor
refrigerant exits the compressor 108 at high pressure and enthalpy,
shown by point 2 in FIG. 2. As the refrigerant flows through the
heat exchanger 106 at high pressure, it loses heat to the
heat/power loop working fluid, exiting the heat exchanger 106 with
low enthalpy and high pressure, indicated as point 3 in FIG. 2. As
the refrigerant passes through the expansion valve 110, the
pressure drops to point 4 in FIG. 2. The refrigerant passes through
the evaporator 112 and exchanges heat with the outdoor air, exiting
at a high enthalpy and low pressure, represented by point 1 in FIG.
2. The refrigerant is then compressed in the compressor 108 to high
pressure and high enthalpy, completing the refrigeration cycle.
[0022] On the heat/power loop 104 side, low pressure-low enthalpy
working fluid, at point a is pumped through pump 114 to produce
high pressure-low enthalpy working fluid at point b. Excess heat
from the cooling loop is passed through the heat exchanger 106 and
is absorbed into the working fluid in the heat/power loop 104 side
raising the temperature of the working fluid at point z. Additional
energy can be added to the working fluid by heat exchanger 116.
This additional energy can be waste heat (if available) or it can
be supplied by solar collectors or other additional heat sources.
This additional energy increases the enthalpy of the working fluid
at point c as shown in FIG. 2.
[0023] The high pressure-high enthalpy working fluid available at
point c can be fed into the turbine 118 to produce power. The
working fluid exiting the turbine 118 at point d is low-pressure,
but high enthalpy fluid which can be used to produce hot water.
Heat exchanger 120 and condenser 122 can be used to extract energy
from the working fluid to produce hot water. Partially heated water
flows into the heat exchanger 120 and exits as hot water. As energy
is extracted from the working fluid by the heat exchanger 120, the
working fluid temperature drops from point d to point e on FIG. 2.
The condenser 122 partially heats the water being fed into the heat
exchanger 120. Latent heat rejected by the condenser 122 is
absorbed by the water further reducing the enthalpy of the working
fluid from point e to point a thus completing the heat/power
loop.
[0024] The foregoing description of embodiments has been presented
for purposes of illustration and description. The foregoing
description is not intended to be exhaustive or to limit
embodiments of the present invention to the precise form disclosed,
and modifications and variations are possible in light of the above
teachings or may be acquired from practice of various embodiments.
The embodiments discussed herein were chosen and described in order
to explain the principles and the nature of various embodiments and
its practical application to enable one skilled in the art to
utilize the present invention in various embodiments and with
various modifications as are suited to the particular use
contemplated. The features of the embodiments described herein may
be combined in all possible combinations of methods, apparatus,
modules, systems, and computer program products.
* * * * *