U.S. patent application number 14/775750 was filed with the patent office on 2016-01-28 for multicycle system for simultaneous heating and cooling.
This patent application is currently assigned to Thar Geothermal LLC. The applicant listed for this patent is THAR GEOTHERMAL LLC. Invention is credited to Lalit Chordia, John C. Davis, James Waters.
Application Number | 20160025392 14/775750 |
Document ID | / |
Family ID | 51538051 |
Filed Date | 2016-01-28 |
United States Patent
Application |
20160025392 |
Kind Code |
A1 |
Chordia; Lalit ; et
al. |
January 28, 2016 |
MULTICYCLE SYSTEM FOR SIMULTANEOUS HEATING AND COOLING
Abstract
System that delivers heating and/or cooling to multiple zones
using two or more thermodynamic cycles that are tailored
specifically to the overall load and in so doing provide a heating
or cooling effect at high efficiency using only a single work fluid
and a single accumulator connected to two or more external
media.
Inventors: |
Chordia; Lalit; (Pittsburgh,
PA) ; Davis; John C.; (Pittsburgh, PA) ;
Waters; James; (Concord, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THAR GEOTHERMAL LLC |
Pittsburgh |
PA |
US |
|
|
Assignee: |
Thar Geothermal LLC
Pittsburgh
PA
|
Family ID: |
51538051 |
Appl. No.: |
14/775750 |
Filed: |
March 17, 2014 |
PCT Filed: |
March 17, 2014 |
PCT NO: |
PCT/US2014/030425 |
371 Date: |
September 14, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61789668 |
Mar 15, 2013 |
|
|
|
Current U.S.
Class: |
165/10 ; 165/212;
62/430 |
Current CPC
Class: |
F25B 9/008 20130101;
F25B 2309/061 20130101; F28D 20/00 20130101; F25B 25/005 20130101;
F24D 3/18 20130101; F24D 2220/08 20130101; F25B 25/00 20130101;
Y02E 60/14 20130101; F25B 2400/075 20130101; F24F 5/0017 20130101;
F25B 29/003 20130101; Y02B 30/12 20130101; F24D 2200/12 20130101;
Y02B 10/40 20130101; F25B 2339/047 20130101; F24F 2221/54 20130101;
F25B 29/00 20130101; F24D 2200/11 20130101 |
International
Class: |
F25B 29/00 20060101
F25B029/00; F28D 20/00 20060101 F28D020/00; F24F 5/00 20060101
F24F005/00 |
Claims
1. A method of transferring energy between two or more external
media comprising: providing two or more external media; employing a
single working fluid operating in more than one thermodynamic cycle
simultaneously, wherein each thermodynamic cycle of the more than
one thermodynamic cycle has a common neutral condition of
temperature and pressure and at least two thermodynamic cycles of
the more than one thermodynamic cycle are selected from the group
consisting of: a first cycle wherein (i) the single working fluid
is liquid in the common neutral condition; (ii) impelling the
liquid working fluid from the neutral condition by a first
mechanical device to one of the two or more external media that is
a heat source; and (iii) the liquid working fluid absorbs energy
from the heat source and returning the single working fluid to the
common neutral condition; a second cycle wherein (i) the single
working fluid is liquid in the common neutral condition; (ii)
depressurizing the liquid working fluid from the common neutral
condition to a pressure that is less a pressure of the common
neutral condition; (iii) the liquid working fluid absorbs energy
from one of the two or more external media that is a heat source
and vaporizes; and (iv) compressing the single working fluid by a
second mechanical device to the pressure of the common neutral
condition; a third cycle wherein (i) the single working fluid is
gaseous in the common neutral condition; (ii) impelling the gaseous
working fluid by a third mechanical device from the common neutral
condition to one of the two or more external media that is a heat
sink; (iii) the gaseous working fluid provides heat to the external
media; and (iv) returning the single working fluid to the common
neutral condition; and a fourth cycle wherein (i) the single
working fluid is gaseous in the common neutral condition; (ii)
drawing the gaseous working fluid from the common neutral condition
and compressing the gaseous working fluid by a fourth mechanical
device to a pressure greater than the pressure of the common
neutral condition pressure and a temperature greater than the
temperature of the common neutral condition; (iii) directing the
gaseous working fluid to one of the two or more external media that
is a heat sink; (iv) the gaseous working fluid provides heat to the
external media; (v) depressurizing the working fluid to a pressure
of the common neutral condition.
2. The method as described in claim 1, wherein the single working
fluid at the common neutral condition is a heat source for at least
one thermodynamic cycle of the more than one thermodynamic cycle
while the single working fluid is a heat sink for another at least
one thermodynamic cycle of the more than one thermodynamic
cycle.
3. The method as described in claim 1, wherein at least one
external media of the two or more external media is selected from
the group consisting of earthen ground, indoor air, ventilation
air, outdoor air, water, construction features of a building, and a
heat-transfer fluid.
4. The method as described in claim 1, wherein fluid flow rates
through at least one of the multiple cycles is controlled such that
the common neutral condition is static.
5. The method as described in claim 1, wherein the neutral
condition liquid level, pressure and temperature are allowed to
vary such that the common neutral condition is dynamic.
6. The method as in claim 1, wherein the energy transferred through
one of the external media of the two or more external media is the
net energy of all of the thermodynamic cycles of the more than one
thermodynamic cycle.
7. The method as described in claim 1 wherein the single working
fluid is carbon dioxide.
8. An apparatus for transferring energy comprising: a single
working fluid; a single accumulator to store the single working
fluid and to set a common neutral condition of a plurality of
thermodynamic cycles; a plurality of fluid channels connected to
the single accumulator, wherein the plurality of fluid channels
being exposed to a plurality of external media define a plurality
of zones to transfer energy between the single working fluid and
each external media of the plurality of external media; and at
least one single working fluid driving mechanism disposed in each
fluid channel of the plurality of channels to determine a
thermodynamic cycle of the each zone of the plurality of zones;
9. The apparatus according to claim 8, wherein at least one single
working fluid driving mechanisms is selected from the group
consisting of pumps, compressors, and blowers.
10. The apparatus according to claim 8, further comprising one or
more pressure control devices disposed in the each fluid channel of
the plurality of fluid channels, wherein the one or more pressure
control devices is selected from the group consisting of pressure
regulators, orifices, and capillary tube.
11. The apparatus according to claim 8, wherein two or more
external media of the plurality of external media are selected from
the group consisting of earthen ground, indoor air, ventilation
air, outdoor air, water, construction features of a building, and a
heat-transfer fluid;
12. The apparatus according to claim 8, wherein the single working
fluid is carbon dioxide.
13. The apparatus according to claim 8, wherein the single working
fluid at the common neutral condition is a heat source for at least
one thermodynamic cycle of the plurality thermodynamic cycles while
the single working fluid is a heat sink for another at least one
thermodynamic cycle of the plurality thermodynamic cycles.
14. The apparatus according to claim 8, wherein the common neutral
condition is static.
15. The apparatus according to claim 8, wherein the common neutral
condition is dynamic.
16. The apparatus according to claim 8, wherein the single working
fluid can be simultaneous gaseous and liquid states.
17. The apparatus according to claim 8, wherein at least two
thermodynamic cycles of the plurality thermodynamic cycles are
selected from the group consisting of: a first cycle wherein (i)
the single working fluid is liquid in the common neutral condition;
(ii) the liquid working fluid is impelled from the common neutral
condition by a first single working fluid driving mechanism to a
first external media of the plurality of external media that is a
heat source; and (iii) the liquid working fluid absorbs energy from
the heat source and the liquid working fluid returns to the common
neutral condition; a second cycle wherein (i) the single working
fluid is liquid in the common neutral condition; (ii) the liquid
working fluid is depressurized from the common neutral condition to
a pressure that is less a pressure of the common neutral condition;
(iii) the liquid working fluid absorbs energy from a second
external media of the plurality of external media that is a heat
source and vaporizes; and (iv) the liquid working fluid is
compressed by a second single working fluid driving mechanism to
the pressure of the common neutral condition; a third cycle wherein
(i) the single working fluid is gaseous in the common neutral
condition; (ii) the gaseous working fluid is impelled by a third
single working fluid driving mechanism from the common neutral
condition to a third external media of the plurality of external
media that is a heat sink; (iii) the gaseous working fluid provides
heat to the third external media of the plurality of external
media; and (iv) the working fluid returns to the common neutral
condition; and a fourth cycle wherein (i) the single working fluid
is gaseous in the common neutral condition; (ii) the gaseous
working fluid is drawn from the common neutral condition and
compressed by a fourth single working fluid driving mechanism to a
pressure greater than the pressure of the common neutral condition
pressure and a temperature greater than the temperature of the
common neutral condition; (iii) the gaseous working fluid is
directed to a fourth external media of the plurality of external
media that is a heat sink; (iv) the gaseous working fluid provides
heat to the fourth external media of the plurality of external
media; (v) the working fluid is then depressurized to a pressure of
the common neutral condition.
18. The apparatus according to claim 8, wherein one fluid channel
of the plurality of fluid channels being exposed to an earthen
ground external media with a first single working fluid driving
mechanism of the at least one single working fluid driving
mechanism being a pump, and a second first single working fluid
driving mechanism of the at least one single working fluid driving
mechanism being selected from the group consisting of a compressor
and a blower.
19. The apparatus according to claim 8, wherein one fluid channel
of the plurality of fluid channels being exposed to an earthen
ground external media with a single working fluid driving mechanism
of the at least one single working fluid driving mechanism being a
pump.
20. The apparatus according to claim 8, wherein one fluid channel
of the plurality of fluid channels being exposed to an earthen
ground external media with a first single working fluid driving
mechanism of the at least one single working fluid driving
mechanism being selected from the group consisting of a compressor
and a blower.
21. The apparatus according to claim 8, wherein one fluid channel
of the plurality of fluid channels being exposed to only an earthen
ground external media with a first single working fluid driving
mechanism of the at least one single working fluid driving
mechanism being a pump, and a second first single working fluid
driving mechanism of the at least one single working fluid driving
mechanism being selected from the group consisting of a compressor
and a blower.
22. The apparatus according to claim 8, wherein one fluid channel
of the plurality of fluid channels being exposed to only an earthen
ground external media with a single working fluid driving mechanism
of the at least one single working fluid driving mechanism being a
pump.
23. The apparatus according to claim 8, wherein one fluid channel
of the plurality of fluid channels being exposed to only an earthen
ground external media with a first single working fluid driving
mechanism of the at least one single working fluid driving
mechanism being selected from the group consisting of a compressor
and a blower.
24. The apparatus as described in claim 8, wherein the accumulator
liquid level, pressure and temperature are allowed to vary such
that the common neutral condition is dynamic.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a 35 U.S.C. 371 US national phase
application of PCT international application serial number
PCT/US2014/030425, entitled "MULTICYCLE SYSTEM FOR SIMULTANEOUS
HEATING AND COOLING," filed on Mar. 17, 2014, which claims priority
to U.S. Provisional Application Ser. No. 61/789,668, titled
"MULTICYCLE SYSTEM FOR SIMULTANEOUS HEATING AND COOLING," filed
Mar. 15, 2013, all incorporated by reference herein in their
entirety.
FIELD OF THE DISCLOSURE
[0002] Modern systems for building heating, ventilation and air
conditioning (HVAC) are typically sectioned into one or more zones.
Each zone might be configured with its own independently controlled
HVAC system; or alternatively, the building might be configured
with a single, central HVAC system, with separate controls in
multiple zones to distribute conditioned air as demanded. Zones can
vary in size, and loads within each zone will change depending on
the time of day, building orientation, occupancy, productive
activity and many other variables. At any given time, some zones
could call for cooling, while others could call for heating. For
example, in a building with a strong southern exposure and many
windows, the morning demand might call for cooling on the south
side while the north side still uses heating.
[0003] A common means for dealing with such a variety of loads is
to operate, at the same time, separate cooling and heating systems
running independently of each other. There are times when a zone
were to demand cooling, while a heating system might still be used
to restore air to a comfortable temperature after it has been
chilled for the purpose of dehumidification.
[0004] In the particular case of heat-pump systems wherein both
heating and cooling are provided simultaneously, equipment costs
are high because of the need for multiple sub-systems, each with
its own set of cycle components (typically a compressor,
accumulator, expander and heat exchangers), each one optimized for
the particular mode of air conditioning--heating or cooling--being
applied.
[0005] In any thermodynamic system that causes heat to move from
one location to another, heat exchangers facilitate the absorption
of energy from one location and the expulsion of energy to another.
In the typical room air conditioner, heat is absorbed by a cold
fluid circulating through a coil that is exposed to indoor
conditions, thereby cooling the room air. After compression to a
higher temperature the fluid is condensed in another coil that is
exposed to the outdoors, thereby rejecting heat to an environment
that is outside of the room being cooled. The converse is true in
the case of the outside air being used as a source of heat for
indoor air, in which case the cycle is reversed so that working
fluid vaporizes in the outside coil, is then compressed to a higher
temperature, and then condenses in an indoor coil to release heat
inside a building. The colder the outside air, the harder the
compressor needs to work to provide adequate heat indoors.
[0006] In applications involving multiple zones, the need could
arise for heating in some areas and cooling in others. This is
often the case in large buildings, where southern exposures may
incur enough solar heat to require cooling, even in winter, while
the back of the building is being heated. For situations such as
this, a popular remedy is Variable Refrigerant Flow (VRF) systems.
Such systems employ a variable flow compressor that responds to
changes in the load inside the building. Automated valves in the
system direct fluid to the appropriate subsystem for heating or
cooling. Valve multiplexers facilitate the movement of heat from
one room to another, but overall the system is characterized by a
single cycle driven by the compressor of the outdoor unit. The
heating and cooling potential in various zones is confined to the
limits of temperature and pressure of the cycle.
[0007] One way to improve efficiency is to absorb heat from, or to
reject heat to, the earth. Such systems are commonly called
Ground-Source Heat Pumps (GSHPs). Carbon dioxide can be safely
recirculated though ground loops without fear of environmental
damage in the event of a leak. A conventional system with carbon
dioxide as a working fluid can use a compressor drives the fluid
through the outside medium--be it air, water, soil or other
"environmentally contaminable" medium--to either lose energy or
absorb energy before recycling back to system or transferring heat
indoors. Fluid returns to the indoor system either as a gas or a
liquid, depending on the air-conditioning mode set indoors.
[0008] What is lacking is a system that can deliver heating or
cooling to a zone using a thermodynamic cycle that is tailored
specifically to the overall load and in so doing provide a heating
or cooling effect at high efficiency.
SUMMARY OF THE DISCLOSURE
[0009] To that end, it is an object of this invention to heat and
cool multiple zones simultaneously by operating different cycles of
heating and cooling simultaneously with a single fluid that shares
a common point with all the cycles. More specifically, the common
point in all cycles is the neutral condition.
[0010] It is a further object of this invention, the energy
transferred to one of the external media is the net energy duty of
all the remaining cycles and such external media is ground, air or
water.
[0011] By accumulator is meant any means of storing the working
fluid and containing it within a defined space, at a state
condition known herein as the neutral condition, said space of
which may be in the form of a vessel, a collection of vessels or
closed channels, be they above ground or below ground."
[0012] By compressor and its root derivatives is meant the
impelling of gas to a substantially higher pressure.
[0013] By neutral condition is meant a condition of temperature and
pressure common to each thermodynamic cycle where the liquid and
gas are in equilibrium.
[0014] By pump and its root derivatives is meant the impelling of
liquids.
[0015] By blower is meant a device to drive gas with enough
compression that it will flow at the desired flow rate.
[0016] By working fluid is meant the substance in either liquid or
gaseous state that conveys heat from one point to another within an
apparatus and is impelled by a pump, blower or compressor.
[0017] By heat sink is meant where energy is absorbed.
[0018] By heat source is meant where energy is provided.
[0019] By external medium is meant earthen ground, indoor air,
ventilation air, outdoor air, water, construction features of a
building, liquid or solid phase change material, or a heat-transfer
fluid that further transfers the energy to and from another medium,
with any of which the working fluid exchanges heat.
[0020] By zones is meant external spaces within which there are
different demands for heating or cooling.
[0021] In the present invention energy is transferred between one
or more external media using a single working fluid operating in
more than one thermodynamic cycles simultaneously, wherein there
exists at least one condition of temperature and pressure in common
with each cycle, said condition referred to herein as the neutral
condition. The neutral condition is controlled so as to ensure the
simultaneous existence of both liquid and vapor states of the
working fluid, in thermodynamic equilibrium. In one embodiment of
the apparatus of the present invention the neutral condition is
held in the accumulator. At the location of the neutral condition,
the working fluid can act as a heat source for at least one
thermodynamic cycle while simultaneously acting as a heat sink for
at least one other thermodynamic cycle. Manipulating the neutral
condition, results in an enthalpy change that balances the net
energy change of all the thermodynamic cycles.
[0022] The fluid is contained and pressurized within pipes, tubing
and heat-exchange equipment, collectively referred to as channels,
and is driven through them. One preferred embodiment of a driving
means is a pump, while other embodiments include such means as a
blower or compressor. Heat is transferred through these channels
and external media at points along the flow path where a
temperature differential exists between the working fluid and the
external media.
[0023] In another embodiment of the present invention, one of the
external media is earthen ground. Other embodiments of the external
media include spaces to be cooled or heated. A preferred working
fluid is carbon dioxide, although other working fluids may be used
as well. Earthen ground can be used as either a heat sink or heat
source in case conditions in the accumulator need a decrease or
increase in energy, respectively, in order to maintain the neutral
condition and adequate amounts of vapor and liquid and to keep the
accumulator's liquid level within upper and lower set-point
limits.
[0024] In one embodiment of the present method, any combination of
two or more of the following thermodynamic cycles operates
simultaneously to transfer energy, such as heating and cooling. One
possibility could be a cycle wherein (i) the working fluid in at
least one thermodynamic cycle is liquid in the neutral condition;
(ii) the liquid working fluid is impelled from the location of the
neutral condition by a mechanical means through an external medium
that is a heat source; (iii) the liquid working fluid transfers
energy to the heat source and then (iv) returns to the location of
the neutral condition. A second possibility is a cycle wherein (i)
the working fluid in at least one thermodynamic cycle is liquid at
the location of the neutral condition; (ii) the liquid working
fluid is depressurized from the neutral condition to a pressure
that is less than that of the neutral condition; (iii) the lower
pressure working fluid is impelled from the location of the neutral
condition by a mechanical means through an external medium that is
a heat source; (iv) the working fluid is compressed to a vapor
state by a mechanical means to the pressure of the neutral
condition. A third possibility is a cycle wherein (i) the working
fluid in at least one thermodynamic cycle is gaseous at the
location of the neutral condition; (ii) the gaseous working fluid
is impelled by a mechanical means from the location of the neutral
condition without substantial compression through an external
medium that is a heat sink; (iii) the working fluid then returns to
the location of the neutral condition. A fourth possibility is a
cycle wherein (i) the working fluid in at least one thermodynamic
cycle is gaseous at the location of the neutral condition; (ii) the
gaseous working fluid is drawn from the location of the neutral
condition and compressed to a pressure greater than that of the
neutral condition pressure, thereby increasing in temperature;
(iii) the working fluid is directed through external medium that is
a heat sink; (iv) the working fluid expands to a pressure that is
close to that of the neutral condition; and (v) the working fluid
returns to the location of the neutral condition.
[0025] In another embodiment of the present invention liquid
working fluid from the accumulator is impelled by a pump and is
channeled through a warmer external medium causing the liquid fluid
to absorb heat and evaporate to a vapor within the channel. Liquid
working fluid from the accumulator is expanded to a pressure that
is less than that of the neutral condition, then channeled through
a warmer external medium that causes the liquid fluid to absorb
heat and evaporate to a vapor within the channel, then is
compressed back to the pressure of the neutral condition. Gaseous
working fluid from the accumulator is blown without significant
compression and channeled through a cooler external medium that
causes the vapor fluid to expel heat and become a liquid. Gaseous
working fluid from the accumulator is compressed to a pressure
greater than that of the neutral pressure, from which point it is
channeled through a cooler external medium that causes the vapor
fluid to expel heat and become a liquid, and is then finally
expanded back to the pressure of the neutral condition. After
emerging from the channels that pass through warmer or cooler
external media, the various streams of working fluid return to the
accumulator vessel that is maintained at the temperature and
pressure of the neutral condition. The net result of these cycles
can cause a change in neutral conditions, typically changing the
liquid level, pressure and temperature in the accumulator. In order
to maintain the accumulator at prescribed conditions of
temperature, pressure and liquid level, a separate stream of
working fluid is channeled through one the external media acting as
a heat sink or heat source, depending on need. This external medium
is typically outside air, water, a heat transfer fluid or earthen
ground. In a preferred embodiment, an external medium is earthen
ground. The amount of working fluid diverted to this medium is
sufficient to offset the net difference of the sum of the heat
duties of all the other warm and cool external media traversed by
working fluid. The energy transferred through the external media is
the net energy of all of the thermodynamic cycles. For example, if
the net heat duty from the other external media is positive, i.e.,
an excess of heat, vapor is driven by a blower or compressor from
the accumulator and subsequently condensed while being channeled
through a heat-sink medium, thus expelling heat. As fluid emerges
from the heat sink it is channeled back to the accumulator. If the
net heat duty is negative, i.e., a deficit of heat, liquid working
fluid is pumped from the accumulator and subsequently evaporated
while channeled through a heat-source medium, thus absorbing heat.
It then returns to the accumulator.
[0026] Another embodiment of the present invention is an apparatus
for transferring energy between two or more external media. A
single working fluid operates in more than one thermodynamic cycle.
One or more means of driving impels the single working fluid
through channels to two or more external media. Pressure
regulators, orifices, capillary tube, and other commercially
available valving is used for pressure control of each
thermodynamic cycle. An accumulator maintains the neutral condition
of the thermodynamic cycles. In another embodiment, heat from one
of the external media is transferred to another external media. The
enclosed channels conduct working fluid through heat exchangers for
the purpose of transferring heat to or from external media. Valves
control the lowest and highest pressures of each thermodynamic
cycle operating simultaneously, said valves ensuring that at least
one of the highest or lowest pressure of each of the thermodynamic
cycles is common to all cycles at the neutral condition, which is
held in the accumulator. One or more driving means impels a portion
of liquid working fluid that is close to the neutral-condition
pressure, while one or more driving means impels a portion of vapor
working fluid that is close to the neutral condition pressure. A
driving means such as a compressor drives a portion of working
fluid that is in vapor state regardless of pressure. The
accumulator contains an amount of working fluid in excess of that
used to fill the enclosed flow channels, while being controlled to
a pressure that is close to the neutral-condition pressure, and in
sufficient quantity so as to deliver working fluid in a given
thermodynamic state to two or more of the external media and to
ensure the availability both of liquid at any pump suction and of
vapor for compression. The accumulator connects to channels through
the various external media for the purpose of conveying excess
energy to at least one of the external media, or absorbing energy
from at least one of the external media. This external medium is
typically outside air, water, a heat transfer fluid or earthen
ground. In a preferred embodiment, an external medium is earthen
ground. Channels in the form of pipe or tubing embedded in earthen
ground contain the working fluid as it passes through this medium.
The preferred working fluid is carbon dioxide, although the present
invention is not limited to any one working fluid. Earthen ground
can be used as either a heat sink or heat source in case conditions
in the accumulator need a decrease or increase in energy,
respectively, in order to maintain adequate amounts of vapor and
liquid and to keep the accumulator's liquid level within upper
(maximum) and lower (minimum) set-point limits. Other external
media to which heat is expelled or from which heat is absorbed by
the working fluid, may be but are not limited to room air, fresh
ventilation air or an intermediate heat-transfer fluid such as
water or glycol mixed with water. Liquid pumping and vapor blowing
may supplement the work of compressors, thereby improving cycle
efficiency.
[0027] In the present invention, a single accumulator services the
entire system, no matter what the combination of heating and
cooling zones that may exist within the building. Liquid and gas
are simultaneously fed to the zones. Energy is efficiently traded
among cooling and heating systems by means of the unitary
accumulator. All systems may be located indoors, except for a loop
that is directed outdoors, preferably through earthen ground, for
the purpose of either absorbing heat or expelling heat, as needed
to keep the accumulator liquid level within acceptable limits. This
contrasts with a Variable Refrigerant Flow system wherein a
compressor delivers a gaseous working fluid to the indoor systems,
and, overall, only one thermodynamic cycle that governs the system,
even though a system of valves inside the building redirects both
liquid and gaseous working fluid between zones so as to minimize
waste heat. The present invention, on the other hand, delivers
liquid and gaseous working fluid to the building by different
driving means of compression, pumping or pressure relief through an
expander so that downstream systems undergo different thermodynamic
cycles that are tailored to their particular loads.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] In order that the invention may be more readily understood,
and so that further features thereof may be appreciated,
embodiments of the invention will now be described, by way of
example, with reference to the accompanying drawings in which:
[0029] FIG. 1 represents the pressure-enthalpy relationship of
multiple cycles operating simultaneously;
[0030] FIG. 2 shows a generic layout of equipment in a system of
the type disclosed herein;
[0031] FIG. 3 repeats FIG. 2 but with annotations that related the
various devices to the pressure-enthalpy relationship shown in FIG.
1;
[0032] FIG. 4 expands on FIG. 3 to show the multiplicity of devices
and cycles that is possible in accordance with this disclosure;
and
[0033] FIG. 5 presents a process flow diagram in support of the
Example.
DETAILED DESCRIPTION OF THE DRAWINGS
[0034] The ensuing descriptions of the thermodynamic cycles make
use of a common chart of pressure and enthalpy, the vapor-liquid
envelope of which is denoted by a heavy curved line in FIG. 1. The
multiple thermodynamic cycles of the present invention are
described in this diagram.
[0035] One of the cycles shown in FIG. 1, referred herein as the
"pumped cycle," is represented by the points P.sub.1, P.sub.2,
C.sub.4, P.sub.3, and back to C.sub.4 and finally P.sub.1, in that
order. In this manner, the pumped cycle is providing supplemental
cooling. Working fluid that has been condensed along the return
path of P.sub.3 to C.sub.4 while passing through an external medium
is available to a pump at a suction pressure denoted by P.sub.1. It
is immediately pumped up to pressure P.sub.2, which is still in the
liquid region. In practice, the difference in pressure between
P.sub.1 and P.sub.2 is slight. From the pump discharge, the fluid
traverses a thermodynamic path from P.sub.2 past C.sub.4 to P.sub.3
as it flows through channels that contain it within an external
medium, which could be air, water or ground, where it absorbs heat
and evaporates. For example, the working fluid could absorb heat
from a room, thereby cooling that space. Point P.sub.3 may fall
short of the vapor-liquid equilibrium envelope or run past it into
the superheated vapor state, depending on the amount of heat to be
absorbed and the temperature differential between the fluid and the
medium being cooled, but the pressure will remain nearly the same.
The segment C.sub.4 to P.sub.3 forms a locus of equal temperature
and pressure that is referred to as the neutral condition. The
neutral condition is common to all thermodynamic cycles of this
invention. It is also the condition of temperature and pressure
that exists in the accumulator. From point P.sub.3, the fluid flows
to another heat exchanger, where it is condensed at close to the
same temperature as evaporation. Point P.sub.1 lies at the liquid
edge of the vapor-liquid equilibrium zone, but at a temperature and
pressure that is slightly lower in temperature and pressure from
the neutral condition.
[0036] External air or ground temperature is denoted in FIG. 1 by
the dashed line, which marks an isotherm on the pressure-enthalpy
chart that is cooler than the isotherm C.sub.4-P.sub.3. For
example, a fluid that is evaporated and condensed at 62 F could be
evaporated by a room-air medium at 72 F and then condensed by
ground at 55 F. As the liquid emerges from the condensation medium,
however, it undergoes a slight decrease in pressure at the suction
side of a liquid pump.
[0037] The conventional cooling cycle, referred to herein as
"compressed cooling," can provide much lower temperatures than pump
cooling. This cycle is shown in FIG. 1, where the fluid traversing
point C.sub.4 is expanded to point C.sub.1, which is at a lower
pressure and temperature than the neutral condition. One advantage
of lower temperatures is its ability to dehumidify the air. Once
the fluid is completely vaporized, it enters a compressor suction
at C.sub.2 and moves to a condition of higher temperature and
pressure at C.sub.3. Importantly, the higher pressure is close to
that of the pumped liquid so that the compressed fluid can re-mix
with pumped fluid, in the accumulator.
[0038] Yet another of the cycles shown in FIG. 1, referred to
herein as "compressed heating," starts with vapor from point
P.sub.3, at practically the same pressure as point H.sub.2, that is
sent to a compressor for boosting to condition H.sub.3, from which
the fluid then enters a heat exchanger, located in a different
zone, for purposes of heating, rather than cooling, that zone. The
fluid may be at supercritical pressure, as indicated in FIG. 1,
although it may also pass through a zone of condensation within the
vapor-liquid equilibrium area. In the preferred case of carbon
dioxide, the fluid would most likely be maintained above the
critical pressure, such that it does not change state as it cools.
After emerging from the room-air heater at condition H.sub.4, the
fluid is then expanded to the H.sub.1. Heat is then absorbed
indirectly from higher-enthalpy streams returning from the pumped-
or compressed-cooling coils or the ground itself, in the
accumulator, before the fluid returns to the compressor for
re-circulation in the compressed heating loop.
[0039] It is thus demonstrated that a single fluid can progress
through each of the three aforementioned thermodynamic cycles
simultaneously, and that there is a temperature and pressure in
common in all these cycles known as the neutral condition. Pumped
cooling is denoted by the path
P.sub.1-P.sub.2-C.sub.4-P.sub.3-C.sub.4-P.sub.1. Compressed heating
is denoted by the path H.sub.1-H.sub.2-H.sub.3-H.sub.4-H.sub.1. The
difference in pressure and temperature between lines
H.sub.1-H.sub.2 and P.sub.3-C.sub.4 is not significant. Compressed
cooling is denoted by the path
C.sub.1-C.sub.2-C.sub.3-C.sub.4-C.sub.1. All three of these cycles
pass through at least some portion of the same or common neutral
condition of temperature and pressure exhibited by C.sub.4-P.sub.3.
This condition of temperature and pressure also exists in the
accumulator, and working fluid passes through the accumulator at
some point in all of the cycles.
[0040] For purposes of illustration, the following descriptions may
refer to fluid entering into or emerging from a ground loop of
embedded tubing. The ground represents one of several types of
external media to which heat is expelled, or from which heat is
absorbed. It is the preferred medium for balancing excess or
deficit heat in the accumulator according to this disclosure,
although this disclosure by no means limits this function to
earthen ground. Other media serving this function could be outdoor
air, a heat sink of stored energy, water, a zone of hot or cold
temperature in a manufacturing area or another non-ambient
source.
[0041] A simplified example of such a multi-zone heating and
cooling system is shown in FIG. 2. At the heart of this process is
accumulator vessel 1, which contains an equilibrium vapor-liquid
mixture of working fluid. This working fluid flows through various
devices for heating or cooling zonal air and then back to the
accumulator 1. In the example shown, these devices are shown as
fan-blown air handlers, although it is understood that this
disclosure is by no means limited to devices of this type alone.
Heat can also be exchanged in such devices as water heaters or
coolers, solar collectors, waste-heat recuperators, radiant coils
and even complete indirect cycles for heating or cooling, as will
be explained with subsequent FIGS. 3 and 4. It is further
understood that the number of devices need not be limited to four,
as shown in FIG. 2. There can be any number of devices, in various
combinations of heating and cooling modes, as is typical of a
multi-zone system for conditioning the air in buildings.
[0042] One of the example devices in FIG. 2 is a heater 2, which
can be used to heat room air, and which is serviced by a compressor
3 that heats up the working fluid ahead of it. An expander 4 after
the heater 2 relieves pressure back to the neutral accumulator
pressure. Another heating device 5 is serviced by a blower 6 rather
than a compressor. In this configuration, vapor from the
accumulator 1 could be used to pre-heat outside ventilation air if
that air is substantially cooler than the temperature of the
working fluid in the accumulator. Alternatively, it could be used
to preheat water going to a water heater. In the case of a blower,
fluid is impelled without substantial pressure change. A slight
loss of pressure due to suction at the blower inlet is recovered at
the outlet as the fluid pressure returns to that of the common
neutral condition. This path is denoted by sequent
B.sub.2-B.sub.2-C.sub.4.
[0043] A third device 7 can cool and possibly dehumidify zonal air
in an exchange of heat with liquid working fluid that is first
cooled in expander 8 before reaching air handler 7, where it
evaporates to vapor and moves on to the suction of compressor 9.
This compressor 9 brings the working fluid back to the neutral
accumulator pressure. The fourth device in this example, air
handler 10, exchanges heat with liquid working fluid that is pumped
from accumulator 1 via pump 11. This liquid also evaporates to
vapor in the air handler, but does so at conditions that are close
to the neutral condition. A typical application for this type of
cooling is to pre-cool incoming ventilation air.
[0044] In all of the aforementioned example devices, working fluid
goes back to the accumulator 1. All streams return to the neutral
condition, but with varying degrees of energy, as measured by
enthalpy. The higher the degree of energy, the higher the fraction
of vapor versus liquid. They all combine to a single state point,
denoted by the letter J in FIG. 1, that fits somewhere on the line
of the neutral condition, C.sub.4 to P.sub.3.
[0045] Depending on the heating and cooling loads imposed on the
system by the air handlers, the instantaneous quality at point J is
very likely to differ from the quality of accumulator 1, leading to
a change in equilibrium temperature and pressure in the
accumulator, which also causes the liquid level in the accumulator
1 to rise or fall. In this way, the accumulator 1 acts as a dynamic
heat sink or heat source to balance the overall energy load of the
system. The accumulator 1 can only serve this function so long as
there exists both liquid and vapor in it. To ensure this condition,
and to prevent the liquid level from rising too high or falling too
low, working fluid is sent to an external medium, preferably the
ground loop 12, in the form of vapor to be condensed if energy must
be subtracted from the system, or in the form of liquid to be
evaporated if energy must be added. In either case, fluid emerges
from the external medium at the neutral condition, now adjusted for
proper energy balance. The trigger for moving fluid through the
external medium is a liquid level that has drifted far enough from
upper or lower set-point limits as to cause the equilibrium
temperature to rise or fall enough to provide sufficient
temperature differential with the external medium, preferably the
ground, as to facilitate efficient heat transfer. Specifically,
liquid level is allowed to rise high enough that the equilibrium
temperature in the accumulator 1 falls sufficiently low as to
facilitate efficient evaporation in the ground loop 12, or the
liquid level is allowed to fall low enough that the equilibrium
temperature in the accumulator 1 rises far enough to facilitate
efficient condensation in the ground loop 12. As shown in FIG. 2,
vapor can be driven through the ground loop 12 at moderate pressure
drop by a driver 14, which may be a blower or compressor. Liquid is
typically driven by pump 13 to prepare it for evaporation in the
ground loop 12.
[0046] In a perfectly steady-state condition, wherein the loads on
the air handlers never vary and the ground acts as a perfect heat
sink or source at constant temperature, the accumulator level would
remain constant. Flow through the ground loop 12 would likewise
hold steady, and the neutral condition would be unchanged. Working
fluid would reject heat to the ground, or absorb it from the
ground, so as to correct any net energy gain or loss, respectively
in the combined working fluid leaving the air handlers. For
example, take the hypothetical case of a simultaneous demand
profile of 2.0 kilowatts compressed heating, 3.0 kilowatts of
compressed cooling and 3.9 kilowatts of pumped cooling using carbon
dioxide as the working fluid. The set-point liquid level is 25% of
the accumulator height, and pressure is 55 bar. This condition
would cause a heat and pressure to build up in the accumulator,
leading to the excess being expelled to the ground. Of the total
mass flow of fluid in and out of the accumulator 1, close to 30%
would have to channel through the ground loop 12 in order to
prevent the liquid level from falling further.
[0047] Under conditions of surplus cooling duty, as in the example
above, it is desirable to maintain a liquid level that is low
enough as to maintain a vapor temperature that is sufficiently
higher than ground temperature as to ensure adequate condensation
in the ground loop 12. Conversely, under conditions of surplus
heating duty, it is desirable to maintain a liquid level that is
high enough as to ensure adequate evaporation of pumped liquid in
the ground loop 12. Between these conditions of suitable
temperature differential with other external media, such as the
ground, and the working fluid, the accumulator 1 itself acts as the
heat sink for surplus cooling duty, or heat source for surplus
heating duty, as manifested by changing temperature, pressure,
liquid level and enthalpy within its confines.
[0048] FIG. 3 takes the example presented in FIG. 2 and annotates
it with state points as labeled in FIG. 1. Points C.sub.4, P.sub.3
and H.sub.4, which correspond to the condition of the working fluid
at the outlets of the air handlers, are all at the temperature and
pressure of the neutral condition. Meanwhile, a blower or
compressor 14 pushes accumulator 1 vapor into the ground loop 12
for condensation, or a pump 13 pushes liquid into the ground loop
12 for evaporation, in such manner as to return working fluid to
the accumulator 1 at the neutral condition. Under steady state in a
properly controlled system, the stream of the working fluid
resulting from the mixture of fluid coming from the ground loop 12
with fluid from the air-handling devices will be not only of the
same temperature and pressure as the accumulator 1, but also the
same vapor-liquid quality, thereby maintaining a steady liquid
level. Under transition conditions caused by varying heating and
cooling loads, however, the mixture of working fluids from the
ground loop 12 and the devices will actually be of a higher or
lower quality as the accumulator 1--at the same temperature and
pressure--so as to correct the liquid level in the accumulator 1
toward the set point level. Whenever the liquid level remains at a
pre-determined level (the "set point"), the system is said to be
"static," i.e., the pressure and liquid level in the accumulator is
constant and the liquid level is allowed to change only when net
enthalpy changes of the multiple cycles is not zero. To accomplish
this, fluid flow rates through the multiple cycles are controlled
so as to maintain constant temperature and pressure. The liquid
level is accumulator 1 is monitored by a gauge (not shown). When
the liquid level exceeds the maximum level of the set point, pump
13 is actuated to pump liquid from accumulator 1 through ground
loop 12 to evaporate the fluid (as discussed above). When the
liquid level drops below the minimum level of the set point, blower
or compressor 14 is actuated to push vapor from accumulator 1
through ground loop 12 to condensate the fluid (as discussed
above). The alternative is to allow the temperature and pressure
within the accumulator to change. The liquid level within the
accumulator may also change, but it is not a requirement. Under
this condition, the system is said to be "dynamic."
[0049] The pumped cycle may serve to boost the efficiency of either
compressed cooling or compressed heating by pre-cooling or
pre-heating incoming ventilation air, respectively. For example, if
the outside air is cooler than ground temperature, pumped liquid
from the ground can be used to pre-heat ventilation air to a
temperature close to that of the ground. Conversely, if the outside
air is substantially hotter than ground temperature, pumped liquid
from the ground can be used to pre-cool ventilation air. The same
principle applies to a secondary working fluid, such as water,
which may be used as an intermediate between the primary working
fluid pumped or compressed through the ground loop 12, and the
external medium of room air. Such a fluid may be heated or cooled
by blown vapor or pumped liquid, respectively. Ventilation air can
only be pre-cooled or pre-heated at any particular time, depending
on the temperature of outside air. But it may still be possible to
run both blown vapor and pumped liquid cycles at the same time, so
long as they exchange heat with different media. An example could
be pre-cooling warm outdoor air with pumped CO.sub.2 liquid while
pre-heating water with blown CO.sub.2 vapor.
[0050] As was noted above in the discussion of FIG. 2, there can be
any number of devices, in various combinations of heating and
cooling modes, as is typical of a multi-zone system for
conditioning the air in buildings. This is now demonstrated in FIG.
4, which shows a multiplicity of devices in both heating and
cooling modes. For simplicity, each of the four basic modes
described by FIG. 2 is shown with a pair of zonal cycles, although
the actual number of such sub-loops can be greater or fewer, even
none. FIG. 4 is annotated with cycle labels in accordance with FIG.
3. Multiplexing junctions 15 are denoted as parallel lines and
represent a piping arrangement that directs the fluid to the
appropriate indoor system, which may be either direct, as described
by subset 16, or indirect, as described by subset 17. A similar
multiplexing array follows the indoor system so as to direct the
working fluid back to the accumulator 1 via either a compressor,
expander or unobstructed pipe, as used by the particular mode of
heating or cooling being exercised. In direct heating or cooling
(subsets 16), the working fluid from the accumulator 1 exchanges
heat with the space being so conditioned, typically a room in a
building. The simplified depiction of the multiple cycles shown in
FIG. 2 is representative of such direct heating and cooling. In
indirect heating or cooling (subsets 17), the working fluid
exchanges heat with a second working fluid, which then undergoes a
vapor-liquid compression cycle of its own. It is this secondary
fluid that exchanges heat with the space being conditioned, rather
than the working fluid from the accumulator 1. Such systems of
indirect heating and cooling are in fact quite common. Thus, FIG. 4
presents a more generalized picture of a multi-cycle heating and
cooling system than the simplified version shown in FIG. 2. Whether
direct or indirect, the working fluid of the accumulator 1
eventually comes to the same points labeled as H.sub.4, C.sub.4 and
P.sub.3, which occupy the same positions in both FIGS. 2 and 4.
[0051] Example. A test set up comprises the direct exchange (DX)
geothermal well field employing carbon dioxide (R744) working
fluid, compressor-pump skid, and air-handling unit (FIG. 5).
[0052] The air handing unit (AHU) has two microchannel heat
exchangers (mcHX 20, 22) installed in it. The bottom mcHX 20 is
positioned so that it is the first to encounter the return of
outside air, which is supplied with pumped R744 refrigerant. The
top mcHX 22 encounters air that has passed through (or been
conditioned) by the bottom mcHX 20, which is supplied with
compressed R744 refrigerant. Both supply streams come from the same
accumulator 1. The bottom mcHX 20 is also instrumented with two
coriolis mass flow meters to measure the quality of the R744
refrigerant upon entering and leaving.
[0053] The test started with the compressed cooling alone. After
the system was operating for about 1 hour, pump cooling was
operated simultaneously. After a few hours the pump cooling was
shut off and the compressed cooling system alone was running.
[0054] The average pressure increase across the compressor was 420
psig. Temperature, density and power readings from this test are
given in the Table 1 below.
TABLE-US-00001 TABLE 1 Pump and Compressed Compressed Working fluid
CO2 Units Cooling Cooling Power demand: Compressor kW 2.2 .+-. 0.1
2.1 .+-. 0.2 Pump kW 0.1 .+-. 0.1 Heat exchanger inlet: CO2 Temp
.degree. C. 7.0 .+-. 0.7 8.5 .+-. 2.1 CO2 Density Kg/m.sup.3 254.3
.+-. 10.6 308.8 .+-. 47.0 Heat exchanger outlet: CO2 Temp .degree.
C. 18.1 .+-. 1.3 13.3 .+-. 4.7 CO2 Density Kg/m.sup.3 98.8 .+-. 4.6
109.9 .+-. 14.7 Coefficient of 4.1 .+-. 0.2 7.7 .+-. 1.2
Performance
[0055] While the disclosure has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made therein without departing from the spirit and scope of the
embodiments. Thus, it is intended that the present disclosure cover
the modifications and variations of this disclosure provided they
come within the scope of the appended claims and their
equivalents.
* * * * *