U.S. patent application number 11/789252 was filed with the patent office on 2008-10-30 for environmental control unit for harsh conditions.
This patent application is currently assigned to Hunter Manufacturing Co.. Invention is credited to John L. Creed, Robert K. Crowder, Steven G. Skinner.
Application Number | 20080264080 11/789252 |
Document ID | / |
Family ID | 39885393 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080264080 |
Kind Code |
A1 |
Creed; John L. ; et
al. |
October 30, 2008 |
Environmental control unit for harsh conditions
Abstract
A method of controlling an air conditioning system of the type
having a variable capacity compressor circulating refrigerant
through a condenser, an expander, an evaporator and returning to
the compressor. Sensors are disposed to sense a refrigerant
condition selected from one of pressure and temperature on one or
both the compressor high pressure and low pressure side; and, in
the event of an overload condition, the sensors generate a control
signal that effects operation of an actuator for moving a member in
the compressor to vary the compressor capacity to the lowest
capacity output. Alternatively, the generated control signal may
vary the compressor speed.
Inventors: |
Creed; John L.; (Niles,
OH) ; Skinner; Steven G.; (Willoughby, OH) ;
Crowder; Robert K.; (Eagle Rock, VA) |
Correspondence
Address: |
FAY SHARPE LLP
1100 SUPERIOR AVENUE, SEVENTH FLOOR
CLEVELAND
OH
44114
US
|
Assignee: |
Hunter Manufacturing Co.
|
Family ID: |
39885393 |
Appl. No.: |
11/789252 |
Filed: |
April 24, 2007 |
Current U.S.
Class: |
62/132 ;
236/92R |
Current CPC
Class: |
F25B 49/025 20130101;
F25B 2700/1933 20130101; F25B 2700/21151 20130101; F25B 2700/2104
20130101; F25B 2600/025 20130101; F25B 2700/151 20130101; F25B
2700/1931 20130101; F25B 2700/21175 20130101; F25B 2700/21152
20130101; Y02B 30/70 20130101; F25B 2600/111 20130101; Y02B 30/743
20130101; F25B 2600/2525 20130101 |
Class at
Publication: |
62/132 ;
236/92.R |
International
Class: |
F25B 49/02 20060101
F25B049/02 |
Claims
1. A method of controlling cooling rate in an air conditioning
system of the type circulating refrigerant from a compressor with a
variable capacity control mechanism to an outdoor heat exchanger
through an expander to an indoor heat exchanger and return,
comprising: (a) providing an electrically operated actuator and
effecting movement of the compressor variable capacity mechanism;
(b) sensing a compressor high side condition and generating a first
electrical signal indicative thereof; (c) sensing a compressor low
side condition and generating a second electrical signal thereof;
and, (d) connecting said first and second sensor signals in a
circuit and generating an electrical control signal in response to
one of first and second signals and controlling the electrically
operated actuator with the control signal and varying the
compressor capacity.
2. The method defined in claim 1, wherein said step of the
compressor low side condition includes sensing the indoor heat
exchanger discharge temperature.
3. The method defined in claim 1, wherein the steps of sensing a
condition includes sensing one of pressure and temperature.
4. The method defined in claim 1, further comprising sensing
ambient temperature in the area to be air conditioned and
generating a third electrical signal indicative thereof and
changing the control signal in response to said third signal.
5. The method defined in claim 1, wherein the step of connecting an
electrically operated actuator includes connecting a solenoid
operated valve.
6. The method defined in claim 1, wherein the step of connecting an
electrically operated actuator includes connecting an
electromagnet.
7. A method of controlling refrigerant circulating through a
variable capacity compressor, an exothermic heat exchanger, an
expander, an endothermic heat exchanger and return comprising: (a)
sensing a refrigerant condition on the compressor high side; (b)
sensing a refrigerant condition on the compressor low side; and,
(c) reducing the compressor variable capacity when an overload
condition is sensed in one of steps (a) and (b).
8. The method described in claim 7, wherein the step of sensing a
refrigerant condition on the compressor high side includes sensing
one of refrigerant pressure and temperature.
9. The method defined in claim 7, wherein the step of sensing a
refrigerant condition on the compressor low side includes sensing
one of pressure and temperature.
10. The method defined in claim 7, wherein the steps of sensing
include: (a) generating an electrical control signal indicative of
the sensed condition; and, (b) the step of varying compressor
capacity includes disposing a servomechanism receiving the
electrical control signal and moving a control member in the
compressor.
11. The method defined in claim 7, the step of sensing a condition
of the refrigerant on the compressor high side includes sensing a
condition intermediate the expander and the endothermic heat
exchanger.
12. The method defined in claim 11, wherein the step of sensing a
refrigerant condition intermediate the expander and the endothermic
heat exchanger sensing one of temperature and pressure.
13. The method defined in claim 7, wherein the steps of changing
the compressor variable capacity includes: (a) connecting an
electrically operated actuator to the compressor; (b) generating a
low capacity control signal in response to sensing an overpressure
or the compressor high side; and, (c) applying the low capacity
control signal to the actuator and varying the compressor for
lowest capacity.
14. The method defined in claim 13, wherein the step of generating
a control signal includes disposing at least one pressure switch
and changing circuit resistance upon actuation of the pressure
switch.
15. The method defined in claim 13, wherein the step of generating
a control signal includes disposing a thermistor in circuit and
varying the resistance in response to sensed refrigerant
temperature.
16. The method defined in claim 13, wherein the step of generating
a control signal includes sensing the air temperature in the area
to be cooled.
17. The method defined in claim 7, wherein the step of sensing a
high-side condition includes sensing compressor discharge
temperature.
18. The method defined in claim 7, wherein the step of changing the
compressor capacity includes changing the compressor speed.
19. An environmental control unit comprising: a variable output
compressor; an outdoor coil connected to said variable output
compressor via a first conduit; an indoor coil connected to said
variable output compressor via a second conduit; and, a controller
for said variable output compressor compressor, said controller
comprising: a first sensor connected to said first conduit for
sensing a compressor high side condition and generating a first
signal; and, a control circuit for generating a control signal in
response to said first signal in order to reduce a capacity of said
variable output compressor.
20. The unit of claim 19, further comprising: a second sensor
connected to said second conduit for sensing a compressor low side
condition and generating a second signal; wherein said control
circuit generates a control signal in response to said second
signal.
21. The unit of claim 19, wherein said first and second sensors
comprise one of a pressure sensor and a temperature sensor.
22. The unit of claim 19, wherein said first and second sensors are
positioned in series.
23. A method of controlling cooling rate in an air conditioning
system of the type circulating refrigerant from a compressor with a
variable capacity to an outdoor heat exchanger through an expander
to an indoor heat exchanger and return, comprising: (a) sensing at
least one of a compressor high side condition and a compressor low
side condition; (b) generating a control signal indicative sensed
condition; and, (c) varying the compressor capacity in response to
the control signal.
Description
BACKGROUND
[0001] The present disclosure generally relates to methods and
arrangements of components that prevent high-pressure shutdown
during loads that can exceed the design load, or designed saturated
condenser temperature or condenser coil condition of a field
deployable, mobile, Environmental Control Unit (ECU).
[0002] In military applications where transport bulk and weight are
at a costly premium, simply enlarging ECU's for greater capacity is
unacceptable. Heretofore, attempts have been made to reduce the
size and weight of ECU's and produce a lighter, smaller, more
efficient unit. The effort has primarily been focused on known
techniques such as hot gas by-pass and fixed capacity compressors,
in a smaller frame or enclosure.
[0003] ECU's for military use differ from non military air
conditioning systems. An ECU for military service is designed for
withstanding induced vibration from ship, air, and ground
transportation, particularly when stacked with other units.
Additionally, lifting provisions must be provided for helicopter
sling transport; and, the units must withstand dropping, 40 Mph
winds with 4 inches per hour rain, must be able to operate on both
60 and 50 hertz alternating current with limited compressor starts
and must be capable of being operated on un-prepared or rough
terrain. In military service, the operational extremes can vary
from severe cold, snow and freezing rain to above 145.degree. F.
combined ground solar and ambient load. Military service units must
also withstand tropical, desert, and high altitude conditions. Each
ECU intended for military field service is developed for a specific
capacity and application; however, once fielded, will be required
to operate when attached to any tent or hard wall structure. It has
been difficult to match ECU capacity to the load due to the various
field tent and hard wall shelter variations. These structures vary
in insulation factor, fenestration, and the type of air
distribution system employed. Thermal loads and evaporator air flow
can vary to an extent that the known evaporator de-rating
techniques, such as hot gas by-pass and compressor suction cooling
are inefficient. In many cases, it has been found such techniques
cannot provide the range of control necessary to prevent component
degradation or provide consistent ECU operation.
[0004] In such military applications, the ECU can be a split
design, with the evaporator inside the area to be cooled with the
condenser and compressor section outside; or, all components can be
contained within a single enclosure. ECU's for military
applications are generally powered by portable generators, but may
be connected to a local power grid when such is available. Examples
of the range of refrigerants used are HCFC-22, HFC-134a and R410,A
R407C. Current ECU's have compressors with fixed capacity output.
Load capacities of an ECU generally range from about 9,000 BTU to
about 100,000 BTU. The most commonly used ECU's have a capacity of
about 60,000 BTU.
[0005] In an attempt to retain design airflow, ECU condensers and
evaporators are provided with screens and filters to protect them
from debris. Particulate matter encountered in military field usage
can vary from blown organic plant matter, such as grasses or trees,
to foot and vehicle generated sand and dust, to climatic sand and
dust storms. Restriction of condenser airflow from sand and dust is
a frequent field occurrence. The dust that is removed from
condensers and evaporators has the consistency of talc and passes
easily through the screens and filters, clogging coils and reducing
airflow.
[0006] Currently, there is no method of preventing sand and dust
from causing coil airflow restriction in a unit, in a manner that
will meet space volume and electrical power draw requirements. For
operation in high ambient solar temperatures, some manufacturers
have included a sun shield or fly to reduce the solar load on the
ECU, in an attempt to reduce compressor high side system pressures.
Also, coils are being cleaned more frequently; however, with so
many ECU's in the field, this takes time and cannot always be done
in a timely manner.
[0007] Another ECU problem is the cost of providing diesel fuel for
power generation in the field. Fuel cost can easily exceed $30.00
per gallon on site. Current ECU technology uses hot gas bypass, to
de-rate or reduce the efficiency of the evaporator during low load
conditions. The by-pass of gas can be before or after the
evaporator. This fluid by-pass is not used for cooling but uses
compressor energy to pump it. Such non-cooling load on the
compressor is disadvantageous because it results in costly
increased diesel fuel consumption.
[0008] These aforesaid refrigerant management techniques have added
to the complexity of the ECU in view of the requirement for the
additional piping, valves and fittings. They have also resulted in
increased system leaks, inoperable units and increased maintenance.
Furthermore, the gas by-pass approach does not adequately regulate
the system when the condenser is restricted, or during ECU
operation under high ambient conditions when the load exceeds the
design load. This results in frequent nuisance shut downs, due to
overpressure conditions at the compressor discharge.
[0009] One approach to addressing the described problems is
disclosed in U.S. Pat. No. 6,047,557; U.S. Pat. No. 6,601,397 B2;
International Publication Number WO 2006/014079 A1 and U.S. Pat.
Publication 2005/0189888 A1 the disclosures of which are
incorporated herein by reference in their entireties. These patents
show the components of the compressors and how they work. The
solution presented in the above patents is that of using a variable
capacity type scroll compressor that is able to load and unload to
vary the capacity. Other methods use variable speed compressor
drive converters that provide scroll or rotary compressor RPM
controls for changing the capacity output of a compressor. Although
the techniques described in the aforesaid patents have been used in
commercial refrigeration applications and in unitary air
conditioners for the commercial market, such systems have not been
able to meet the special operational, maintenance, and sustainment
cost requirements for a military field deployable ECU.
[0010] U.S. Patent Publication 2005/0189888 A1 refers to a variable
speed drive of compressors; and, U.S. Pat. No. 6,047,557 refers to
a pulse width modulating duty cycle. Each has the ability to be
temperature controlled by an operator selectable thermostat input
with additional pressure and temperature sensor connection
locations.
[0011] It has been proposed to employ an inverter driven compressor
for an ECU application; however, the inverter or variable frequency
drive is complicated to diagnose and creates high levels of Electro
Magnetic Interference. EMI is also costly to shield.
[0012] In military applications, ECU's are often required to
operate in high ambient conditions with blowing sand and dust. In
order to meet recently increased demand for military service
applications, commercially available and modified commercial air
conditioners have been employed in military usage. In desert
environments, the modified commercial air conditioners have
frequently shut down due to over pressure. Such units employed in
desert environments have also experienced high failure rates of
compressors, contactors and function controllers. These failures
have been attributed to prolonged operation at elevated system
pressure and subsequent high compressor motor current draw. The
cost and effort required to provide routine maintenance and repair
has thus been increased. Furthermore, where non-military
contractors are hired to perform maintenance, if their contract
cost is exceeded, maintenance and repair work is stopped until
contract cost issues are resolved, resulting in periods of
inoperation.
[0013] Current ECU and fielded commercial air conditioners do not
have the ability to reduce capacity during excessive high ambient
conditions or when operated with reduced condenser air flow, caused
by sand and dust loading. Loss of cooling and additional
maintenance is created from high-pressure induced short cycling,
i.e., when the compressor overload pressure switch trips on
high-pressure. Some designs will automatically reset, and others
need to be manually reset. High temperature starting and stopping
of the compressor under load also decreases the life of the
compressor. Repetitive starting and stopping of compressors can
also create power line problems when powered by a mobile generator;
and, the loss of cooling can also be life threatening in a field
hospital application.
[0014] It has thus been desired to provide a lighter, smaller, more
efficient ECU that self regulates capacity based on indoor and
outside temperatures, indoor air distribution airflows and
evaporator and condenser coil heat transfer conditions without shut
downs due to overpressure.
[0015] However, when compressor high side capacity is exceeded,
currently the compressor is simply shut down. This is
disadvantageous for the reasons detailed above. Accordingly, it has
been deemed desirable to develop a new and improved environmental
control unit which would overcome the foregoing difficulties and
others while providing better and more advantageous overall
results.
SUMMARY
[0016] The subject matter of the present disclosure integrates a
variable capacity compressor with pressure and temperature sensors
to modulate system capacity based on component condition, ambient
temperatures, and airflows. This variable capacity system control,
self regulates, during over capacity and under capacity conditions,
to the maximum cooling capacity obtainable using less power than
systems currently available in ECU's utilized in military field
service.
[0017] More specifically, the present disclosure relates to the use
of variable capacity compressors and methods to provide voltage
control input to the variable capacity compressor controller or
inverter. This eliminates the need for hot gas by-pass, which is
inefficient during low load conditions, and provides an alternative
to compressor suction side quenching and similar refrigerant
management schemes that have increased the occurrence of
refrigerant leaks.
[0018] The present system maintains ECU operation during
out-of-design tolerance operation such as operation with high
condenser pressure, low evaporator pressure and excessive
compressor inlet temperature. The presently disclosed adaptive
control provides a variable voltage output signal to operate
commercially available compressor controllers that vary the
compressor capacity (such as digital scroll) or the speed of the
compressor (such as variable frequency drive or inverter). This
adaptive input provides automatic ECU balancing when used in an
environmentally severe or military application, matching variable
cooling capacity based on maximum heat transfer of the evaporator
or condenser and protects the compressor inlet temperature.
[0019] This disclosure describes and illustrates a system with the
ability to vary the system high and low side pressures and
temperatures, coupled with providing thermostat input to a digital
or variable speed compressor drive controller. The compressor
capacity can be reduced during low load conditions, caused by cool
ambient conditions or a restricted evaporator coil. The present
system has the ability to lower the compressor capacity to match
the load and prevents frost or evaporator freeze up, and reduces
energy related costs compared to a system employing hot gas
by-pass. By reducing compressor output to match the heat rejection
capabilities of the condenser, where condenser airflow has become
restricted, compressor cut-off due to high pressure is eliminated.
During high evaporator load conditions, when the suction gas
temperature exceeds the manufacturer's design limits, the
compressor capacity can be changed to lower the suction temperature
thereby saving energy. Contrasted with systems which use hot gas
by-pass and quench type refrigerant management resulting in
additional components, associated tubing and fittings with greater
potential leak points, this disclosure presents a system that
reduces generator fuel or electric grid cost, is simple to
understand and repair while using fewer components.
[0020] In one embodiment, the sensors may generate a signal to a
controller which operates an actuator for effecting movement of a
member in the compressor for varying compressor capacity. In
another embodiment, the sensors may generate a signal to a
controller which effects compressor speed changes to vary the
capacity. In a sensed overload condition, the generated signal
effects varying the compressor capacity to the lowest capacity
output condition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a system schematic of a known ECU system
configuration;
[0022] FIG. 2 is a schematic of several different known ECU system
configurations;
[0023] FIG. 3 is a system schematic of an ECU system in accordance
with the present disclosure;
[0024] FIG. 4 is a system schematic of an ECU according to the
present disclosure employing discrete voltage increasing and
decreasing;
[0025] FIG. 5 is a system schematic of an ECU of the present
disclosure with variable voltage;
[0026] FIG. 6 is a block diagram of the cooling control in
accordance with the present disclosure; and,
[0027] FIG. 7 is a block diagram of the cooling control system in
accordance with the present disclosure alternatively employing a
microprocessor.
DETAILED DESCRIPTION
[0028] Referring now to FIG. 1 a known ECU system configuration is
illustrated with a compressor 1, an exothermic heat exchanger or
condenser 2 and an endothermic heat exchanger or evaporator 3 which
can be disposed within a common enclosure; or, which can be
configured as a split system. In FIG. 1, the compressor 1, the
condenser 2 and the evaporator 3 are in a standard vapor cycle
configuration. The compressor 1 supplies compressed refrigerant to
the condenser 2, which is ambient air-cooled causing the
refrigerant to be cooled and returned to the liquid state. The
condenser supplies liquid refrigerant through a filter dryer 9 to a
suitable expansion device such as a thermal expansion valve 11. The
expansion valve 11 provides a restricted orifice that causes the
liquid refrigerant to undergo a pressure drop and atomize into
liquid droplets that are introduced into the inlet side of the
evaporator 3. Expansion valve 11 is controlled by temperature
sensing bulb 4, which senses evaporator discharge temperature; and,
valve 11 is pressure compensated by a pressure tap 5 of the
evaporator discharge pressure. The evaporator 3 acts as an
endothermic heat exchanger and extracts heat from the surrounding
airflow within the shelter to be cooled, thereby causing
vaporization of the liquid refrigerant droplets in the evaporator
into a gas. The compressor 1 extracts this gas by suction through
return line 7 and again compresses it continuing the cycle.
Diagnostic and service access is provided by a discharge service
access port 18 and suction service access port 17.
[0029] In order to provide the compressor 1 with high temperature
and pressure protection and system safety, additional components
are specified by the compressor manufacture and the military. A
high-pressure switch 27 is typically specified, with a manual
reset, to shut the compressor off in the event of a restricted
filter dryer 9, or insufficient refrigerant cooling of the
condenser 2, that can be created by reduced airflow, such as caused
by sand or dust restriction, or high ambient conditions. The
high-pressure manually resettable switch 27, when tripped, will
shut off the compressor, stopping the ECU from cooling until the
operator manually resets the switch. This is by design, in order to
require human operator maintenance action. The ECU operational
manual usually instructs that, before manually resetting of the
high-pressure switch 27, the condenser condition should be checked
for blockage and cleaned as needed. The usual scenario is that the
high-pressure switch 27 is repeatedly reset until maintenance
personnel can clean the coil with pressurized air or water. A
pressure relief valve 28 located in the compressor discharge line
provides release of excessive system pressure and recloses when a
safe pressure is established. A sight glass 10 between the filter
drier 9 and an expansion device 11 provides a visual observation of
the liquid charge and moisture state of the system and aids during
servicing.
[0030] A low-pressure manually resettable switch 6 is specified to
shut the compressor off, in the event of loss of system charge.
More commonly, it will trip due to a frosted, frozen evaporator
coil, due to airflow loss. Air flow restriction through evaporator
3 can be caused by the conventional air filter (not shown) being
clogged with sand and dust. In many cases such air filter cannot
capture or retain the dust due to its small size. Over time, the
dust will clog the evaporator 3 and restrict the air flow through
the evaporator. If the low-pressure switch 6 trips, the compressor
will stop, preventing the ECU from cooling until the operator
manually resets the switch. This requirement is by design, in order
to require human operator maintenance action. The ECU operational
manual usually instructs that, before manual resetting of the
low-pressure switch 6, the condition of evaporator 3 be checked for
blockage and the evaporator be cleaned, as needed. Also, the inlet
filter and return ducts are checked for blockage or restriction. If
no deficiency is found, gages are attached and the system is
checked for low refrigerant charge level. The low-pressure switch 6
may be repeatedly reset until maintenance personnel can repair the
ECU. The continual resetting of either the low pressure switch 6 or
the high pressure switch 27 results in increased wear of the
compressor. This, in turn, increases the power required to operate
the compressor and creates excessive loads on the power supply
generator. If either pressure switch is left tripped, no cooling is
provided to the shelter.
[0031] In order to match cooling capacity to the load, an indoor
temperature-sensing thermostat 24 cycles the compressor 1 on and
off as required. This is not preferred, and in some cases not
allowed when powered by mobile generators. Indoor thermostat 24 is
then used as an on-off switch operating contactors 23 provided for
compressor control. Contactors 23 may be wired to a soft start
device or be used separately to cycle the compressor 1 on and off.
Frequent compressor starting causes high compressor motor current
draw which overloads the power grid creating line surges and low
voltages.
[0032] Heretofore, it has been common practice in a typical ECU
arrangement to match cooling capacity to the load by using a
refrigerant by-pass system. In the FIG. 1 arrangement, a pressure
or temperature sensor 13 modulates the hot gas by-pass valve 12
between a closed position and a full open position.
[0033] In the FIG. 1 arrangement, high pressure gas from the
compressor 1 is diverted through a tee connection 22 and passes
through an isolation ball valve 19 that is used for diagnostic
function checks. Flow from valve 19 passes through hot gas by-pass
valve 12, as needed, to the tee connection 21 into the compressor
return or suction line 7, thereby reducing the flow through
evaporator 3. This has the effect of lowering the heat adsorption
capacity of the evaporator.
[0034] In addition to using a hot gas bypass valve 12, the prior
art system of FIG. 1 uses a liquid quench valve 14, incorporated to
cool the compressor inlet during very high load conditions in the
evaporator 3. The liquid quench valve 14 is opened when the
condenser 2 has reduced airflow from sand and dirt clogging.
Reduced airflow through the condenser 2 increases the temperature
of high-pressure liquid from condenser 2, which passes through
expansion valve 11 to the evaporator. During high loading added
thermal load to the evaporator 3 increases the evaporator discharge
temperature in suction line 7. A temperature sensor 15 is disposed
in line 7 to react to this temperature. It provides a signal for
effecting opening of liquid quench valve 14, allowing by-passing of
the evaporator 3 with high pressure liquid from tee connection 20
through liquid quench valve 14 to tee connection 21 in line 7. The
by-passed high-pressure liquid cools the refrigerant in suction
side line 7.
[0035] A high inlet temperature will over-heat the compressor 1
degrading its useful life. Temperature sensor 15 can also be
located on the compressor outlet or inside the compressor.
[0036] Providing flow through valve 14 and cooling of compressor 1
prevents the compressor 1 from having to be cycled off, in order to
not exceed the manufacturer's maximum inlet temperature
recommendations. The hot gas bypass 12 and liquid quench valve 14
are shown as common methods of control.
[0037] Known ECU's require the ability to de-rate the capacity of
condenser 2 and evaporator 3, and cool the compressor 1, in order
to prevent compressor 1 from cycling on and off as loads
change.
[0038] In the above described known system example, any time gas or
high pressure liquid is diverted from the basic refrigeration
cycle, efficiency is lost. The efficiency loss is the result of
electrical power required for compressor operation during any
by-pass function. This electrical power required for the compressor
may become greater than the actual cooling effect.
[0039] An ECU employed for a military application is also more
complex in operation than a commercial unit. This is due to the
added field environment of sand and dirt loading on the coils. As
coils experience reduced airflow, the system reacts to provide
premature diversion of gas or high-pressure liquid.
[0040] FIG. 2 illustrates a known system arrangement for plural
shelters with an ECU 327. Various split system ECU's 303, 308, 316
are also shown. A split system is an ECU that has its components
divided into two enclosures, having the indoor coil or evaporator
and related components separated from the outside coil or condenser
with its related components. This type of configuration eliminates
outside ductwork heat losses. Depending on the type of
configuration, it can reduce component weight sufficiently to
eliminate the need for a forklift or similar positioning equipment
and permit manual placement of the components. As is known, the
components can be stand-alone or may be attached to internal air
distribution or duct work as needed.
[0041] FIG. 2 is representative of known basic military
configurations in which refrigerant and electrical connections 302
are passed through the shelter wall 301. The shelter wall 301 can
be a hard or soft wall such as a tent. Indoor coil or evaporator
300 contains the evaporator coil and ventilation blower, with
related refrigerant and electrical controls. Outside coil 303
contains the condenser coil, compressor and related refrigerant and
electrical controls. The related refrigerant and electrical
connections 302 are attached after placement of indoor coil 300 and
outdoor coil 303.
[0042] A shelter 306 is shown in FIG. 2 having a soft wall and is
shown elevated to allow pass-through of connections to an indoor
coil 305. After positioning of the components, the soft wall 306 is
lowered between indoor coil 305 and outdoor coil 308. Indoor coil
305 includes a ventilation blower with related refrigerant and
electrical controls. Outside coil 308 includes a compressor and
related refrigerant and electrical controls. The related
refrigerant and electrical connections 307 are factory attached and
routed to the common bottom frame 310. Both indoor coil 305 and
outdoor coil 308 are mounted to the common bottom frame 310, which
may be suitably configured for ready movement by a forklift.
[0043] Another shelter 313 may have a hard or soft wall with a
first indoor coil 311 and a second indoor coil 312, each containing
a ventilation blower with related refrigerant and electrical
controls. An outside coil 316 includes a compressor and related
refrigerant and electrical controls. The related refrigerant and
electrical connections 314 and 315 are routed through shelter wall
313 and attached after placement of indoor coils 311, 312 and
outdoor coil 316. Indoor coils 311, 312 can be of a window mount
style to provide for fresh air make up flow, mounted to an inside
wall, or can be placed on the floor or an elevated stand.
[0044] Another shelter 326 may have a hard or soft wall. The supply
and return air flow from ECU 327 is connected to the shelter 326 by
flexible or rigid duct work 328, 329.
[0045] FIG. 2 depicts an arrangement using an electrical generator
320 and may comprise a single or plural generators connected to
power distribution box 318 instead of local supply grid power for
illustration of a generator application.
[0046] Generator 320 is connected to a power distribution box 318
by power cable 319. The power distribution box 318 supplies power
through cable 304 to the compressors and fan motors associated with
indoor coil 300 and outdoor coil 303 and power for other uses in
shelter 301, through power cable 321.
[0047] In addition, power distribution box 318 supplies the
compressors and fan motors for indoor coil 305 and outdoor coil 308
through power cable 309. Power for other uses in shelter 306 is
supplied through power cable 322.
[0048] Power distribution box 318 also supplies power to the
compressors and fan motors associated with indoor coils 311, 312
and outdoor coil 316 through power cable 317. Shelter 313 is
supplied through power cable 323 for its other uses.
[0049] Power distribution box 318 also supplies ECU 327 through
power cable 325. Other electrical uses for shelter 326 are supplied
through power cable 324.
[0050] FIG. 3 illustrates an ECU of the vapor cycle type configured
to employ the subject matter of the present disclosure. In contrast
to the systems of the type illustrated in FIG. 1, the system of
FIG. 3 reduces plumbing complexity, the potential for refrigerant
leaks, the skill needed for diagnostics and repair, the number of
spare parts to stock, and the losses created from gas or
high-pressure liquid diversion.
[0051] In FIG. 3, a variable output compressor 101, condenser 102
and evaporator 103 may be disposed within a common enclosure.
Alternatively, it is configured as a split system arrangement, such
as depicted in FIG. 2.
[0052] In the FIG. 3 embodiment, the variable output compressor
101, the condenser 102 and the evaporator 103 are in a common case
configuration. The variable output compressor 101 supplies
pressurized refrigerant gas to the condenser 102, which is ambient
air-cooled to effect condensation of the refrigerant. The condenser
102 supplies liquid refrigerant to a filter drier 109. The filter
drier 109 in turn supplies refrigerant flow through a sight glass
and moisture indicator 110 to a suitable expansion device such as a
thermal expansion valve 111. The expansion valve 111 may be of the
type employing a restricted orifice that causes the liquid
refrigerant to atomize into liquid droplets, which are subsequently
introduced into the inlet side of the evaporator 103. Expansion
valve 111 may be of the type controlled by a temperature sensing
bulb 104 and pressure compensated by connection to a pressure tap
105 connected to receive evaporator discharge pressure. The
evaporator 103 endothermically extracts heat from the surrounding
airflow and effects vaporization of the liquid refrigerant droplets
therein into a gas. The variable output compressor 101 extracts
this gas from the evaporator by its inlet suction and then
compresses it back into a high pressure state. The pressurized
refrigerant is then cooled in the condenser 102, condenses to
liquid and is returned back to the filter drier 109, and expansion
device III where the cycle continues.
[0053] A pressure switch 116 is disposed on the compressor high
pressure or discharge line and shuts off the compressor 101 when
the maximum allowable design pressure is exceeded. Another pressure
switch 106 is disposed in the low pressure or evaporator suction
return line 107 and shuts off compressor 101 when the pressure in
line 107 is below allowable design suction pressure. A pressure
relief valve 108 is set to release excess refrigerant pressure if
maximum allowable design pressure is exceeded, e.g. an over
pressure condition is sensed. Valve 108 automatically recloses when
normal pressure resumes. A service access port 118 is provided in
the compressor high pressure discharge line; and, a suction service
access port 117 is provided in the suction line 107, both for
facilitating diagnostic and refrigerant servicing.
[0054] The prior art system of FIG. 1 employs hot gas by-pass and
liquid quench to manage capacity. In contrast, the presently
disclosed system shown in FIG. 3 does not use these aforesaid
capacity control techniques.
[0055] Instead, the ECU refrigeration system of FIG. 3 employs a
compressor 101 that is of a variable capacity design and is managed
by a control 114 that may be either an inverter that controls the
speed or Rpm of the compressor 101 for changing its capacity.
Alternatively, compressor control 114 may be a digital control that
generates the loaded and unloaded signal, effecting changing the
capacity of compressor 101. Both types of compressor control 114,
by design, provide the lowest capacity when required, while
maintaining sufficient oil flow through compressor 101. A control
signal 113 may be a variable DC voltage which by voltage value
change causes compressor control 114 to change the compressor
capacity output.
[0056] An inverter driven compressor may be employed, but has the
disadvantage of being difficult to fault diagnose and costly to
shield compared to a digitally controlled compressor. If an
inverter driven compressor is employed, the variable voltage
hereinafter described is connected to the variable voltage input
terminals of the compressor inverter drive.
[0057] The following describes an embodiment of the present system
in which an electrical control operates a digital compressor drive
to create a compressor control signal. The variable output signal
is connected to the variable voltage input terminals of the
compressor drive.
[0058] FIG. 3 depicts a compressor 101, managed by a modulating
solenoid 112. Modulating solenoid operated valve 112 is connected
to a tee connection 115 and is operative to supply the pressure
changes needed to move internal components of compressor 101, for
changing the output capacity of the compressor. The compressor
capacity modulation can be any combination of full flow, reduced
flow, or a no flow. Modulating solenoid 112 may be replaced by an
electro magnet that is positioned on or within the compressor. The
electro magnet may be operative to move the internal capacity
control components of the compressor to modulate the flow instead
of using gas pressure. The electro magnet may be controlled by an
electrical control signal and be cycled between an "on" or an "off"
state depending on the capacity requirements of the compressor 101.
Either of the "on" or "off" states of the electrical control signal
may effect movement of the compressor internal capacity control
components for effecting lowest or highest capacity output.
[0059] A sensor 120 is disposed in evaporator discharge line 107
and may be a pressure or temperature source that provides suction
side or evaporator discharge signals. A sensor 121 is disposed in
the condenser discharge line and may be a pressure or temperature
source that provides high-pressure side or condenser discharge
signals. Another sensor 122 may be disposed in the compressor
discharge line and may be a pressure or a temperature source that
provides compressor discharge signals. A thermostat 123 is disposed
to provide conditioned air temperature regulation signals for the
air in the shelter.
[0060] Heretofore, ECU's operated in fielded operational climatic
conditions encountered in military applications have not proven
satisfactory because of component deficiencies. Also, known air
conditioning systems have previously been operated by compressor
on-off cycling.
[0061] In such a known system, the pressure switch 116 and pressure
switch 106 were connected to compressor control 114. Compressor
control 114 turned off compressor 101 during an excessively low or
high-pressure occurrence. In such prior art systems, no provisions
were made to provide variable compressor capacity control based on
high side pressures. As discussed earlier, neither hot gas by-pass,
liquid quench, nor similar hydraulic control devices are used in an
ECU to modulate capacity based on the high-pressure side.
[0062] Referring to FIG. 3, the presently disclosed system
integrates a variable capacity compressor, such as compressor 101,
and compressor control 114 with a single variable voltage signal
that is the sum of a pressure sensor signal, a temperature sensor
signal (such as a signal from the suction pressure or temperature
sensor 120 signal, a signal from the high-pressure sensor 121 and a
signal from the compressor discharge pressure or temperature sensor
122) with a signal from thermostat 123. The present system
accomplishes control without the use of a
proportional-integral-derivative controller (PID) or similar type
controller device. This single variable signal is connected to the
thermostat input of the compressor control 114. The variable
voltage provided to the thermostat is operable to sustain, increase
or decrease the capacity of the compressor 101.
[0063] The benefit of a single control input is that the digital
controller or inverter (depicted as compressor control 114) can be
driven with only one connection that is the summation of many
sensors. A single variable voltage connection is easier to
diagnose. The compressor controller can be made less expensive, as,
the pressure and temperature sensors do not have to terminate at
the compressor controller. In addition, each sensor input requires
software and in this embodiment custom software for operation. Thus
the compressor controller 114 becomes application specific,
resulting in higher cost and decreased availability as compared to
an off-the-shelf readily available compressor controller 114. By
using the single thermostat input, the total system capacity can be
regulated to the maximum coil capacities during extreme high
ambient conditions, such as caused by sand and dust loading of
coils or an improperly sized shelter air distribution system.
[0064] This voltage control is based upon the fact that a condenser
high pressure and a evaporator low pressure will not occur at the
same time. Only one sensor at a time will be operational in the
circuit, except for the thermostat. In the event that a condenser
high pressure and compressor high temperature signal occurred at
the same time, the voltage would modulate between the two or be the
sum of these two inputs further reducing the regulation of the
compressor. If the thermostat is calling for reduced compressor
capacity, it is unlikely that any other sensor would be active.
FIG. 6 shows how the circuit is managed if a sensor becomes active
during a thermostat call for less capacity. An ECU will not have a
high-pressure condenser condition and an evaporator suction
pressure low temperature condition at the same time.
[0065] FIGS. 4, 5, 6 show the details about how a variable DC
voltage can be produced and, by circuit resistance, regulated to
control system capacity.
[0066] FIG. 4 shows an arrangement in which a discrete (stepped)
voltage is employed to generate a variable voltage output. The
voltage applied to input 200 is determined by the compressor
controller voltage requirements and may be, for example, a 5 or a
10 volt dc signal. For this example 0 to 5 volts is used. The
output voltage 205 remains high at 5 volts, for compressor full
capacity output when discharge pressure switch 201, suction
pressure switch 202, thermostat switch 203 and compressor suction
temperature sensor switch 204 are closed. Resistors 206a through
206d are shunt resistors for switches 201-204 and have the
respective resistance values thereof selected to provide the
desired voltage output for effecting the desired compressor
capacity when their respective sensor contacts are open. A reduced
capacity voltage level occurs when the discharge pressure switch
201, senses a predetermined pressure, causing the switch to open
and putting resistor 206a in the circuit. If the value of 206a is
selected to provide 4 volts, a 4 volt output voltage 205 is applied
to the compressor controller thereby causing the controller to move
the compressor control components to effect reducing the compressor
capacity and lowering the discharge pressure, in turn preventing
high pressure switch 116 in FIG. 3 from effecting compressor shut
off. This relatively simple capacity control circuit is not only
reliable, but is simple to diagnose and repair in the field. This
system thus saves electrical operating cost when compared to a hot
gas by-pass system and also reduces capacity during high ambient
conditions and when the condenser coil cooling airflow is
restricted by clogging with sand and dust.
[0067] FIG. 5 shows an embodiment of the present system wherein the
voltage applied to input 210 is determined by the compressor
controller and thermostat voltage requirements. Output voltage 215
is controlled by selection of the values for variable sensor
resistors 216a, 216b, 217c series connected with the high pressure
sensor 214 to provide a control signal. Positive or negative
coefficient temperature and pressure sensors may be employed for
sensors 211-214. A positive temperature or pressure coefficient
resistor may be employed to give an increase in resistance on
increase of pressure or temperature; and, a negative coefficient
resistor may be employed to give a decrease in resistance on
reduced pressure or temperature change.
[0068] For this example, a positive temperature coefficient (PTC)
thermistor 216A employed in discharge side sensor 211 increases in
resistance as the compressor discharge temperature rises. The
increased resistance lowers the voltage of the control signal,
which in turn effects compressor component movement for reducing
the compressor output. The resistance of thermistor 211 continues
to increase until the compressor discharge temperature begins to
lower. As the compressor discharge temperature lowers, the
resistance lowers effecting movement of the compressor components
for increasing the compressor capacity. The sensor 211 may be
placed on the high-pressure outlet of the compressor. This location
and function thus provides the same compressor protection as liquid
quench valve 14 of the Prior Art system of FIG. 1, but is simpler,
less costly and more reliable.
[0069] A negative temperature coefficient (NTC) thermostat is
employed in suction side sensor 212, which has a negative
coefficient thermistor 216b built in. As the temperature decreases,
the resistance of 216b will increase, thereby lowering the output
voltage 215. As the control signal 215 voltage is reduced, the
compressor control components will be moved and compressor capacity
decreased, reducing cooling system capacity. This type of sensor
may be placed at the evaporator discharge location to prevent
evaporator freeze up, due to low airflow caused by a coil or filter
clogged by sand or dust or from shelter ducting which does not
provide adequate airflow.
[0070] Thermostat signal sensor 213 may be of a snap action type.
As depicted in FIG. 4 thermostat 203 may be of the type that uses a
preset resistive value, or may be a commercially available
thermostat that supplies a variable output voltage. Different
styles are available providing many options, for example, from
those using a set point to those providing user choice of degrees
off set point.
[0071] Referring to FIG. 5, pressure sensor 214 is disposed to
sense compressor discharge, or high side pressure. It has a
positive coefficient resistance built in. As the pressure
increases, the resistance increases thereby reducing output signal
voltage 215. This causes the controller to effect movement of
compressor components and reduces the compressor capacity. Sensor
215 may be placed after the condenser and before the filter drier.
Such a location for sensor 215 offers protection from the situation
in which flow through the filter drier becomes restricted. More
importantly, a sensor so located effects a reduction of compressor
capacity during periods of extreme high ambient temperatures, or
when the condenser has experienced reduced cooling airflow from
sand and dust clogging. Reducing the compressor capacity prevents
compressor over pressure and resultant compressor shut-off by the
overpressure sensor 214.
[0072] Referring to FIG. 6, another embodiment is shown wherein
control power at terminals 245, 246 is supplied to a temperature
control device 239. Also, a signal based on a temperature sensor
240 is outputted to the compressor controller 250 through resistor
231 after passing through interface circuitry and passing through a
diode 248. The interface circuit consists of three circuits which
tune the control for various functions.
[0073] The first circuit includes series resistor 231, and parallel
resistor 232, and drops the output of the control device 239 to a
level that is acceptable to the compressor controller 250.
[0074] The second circuit, comprising parallel resistors 233, 234,
235, is brought into effect as required by closure of any of the
individual system condition switches 242, 243, 244, respectively.
These are operative to lower the output signal to the compressor
controller to reduce output capacity of the compressor.
[0075] The first and second circuits comprise the variable capacity
control. In the event a component failure occurs in either of the
first or second circuit and an open circuit is created at diode
248, the third circuit 241 (bottle) switch voltage is applied to
output 250. The third circuit comprises series resistor 236, and
parallel resistors 237, 238. When the switch 241 is in its normal
position as shown in FIG. 6, the circuit uses resistors 236, 237
and is operable to supply a minimum operating signal to diode 247.
As long as the potential at diode 248 is higher, the minimum
operating signal is blocked at diode 247. When the switch is in
bypass mode, shown in dashed line in FIG. 6, the circuit uses
resistors 236, 237 and 238 in circuit and a maximum operating
signal is outputted at 250 to keep the compressor running at full
capacity without regard to the first and second circuit. Diodes 247
and 248 are employed to insure that the highest voltage potential
is always supplied to output 250.
[0076] In one embodiment, it has been found operable, for example,
to connect output 250 to a Copeland Scroll Digital Compressor
Controller part number 543-0024-00. This type of Controller may be
employed in the electronic interface between a Copeland Scroll
Digital Compressor, such as the ZPD series. However, it will be
understood that various types of electronic interfaces may be
employed depending on the type of variable capacity compressor,
i.e. whether rotary, piston or scroll. This circuit, output 250
connects to the connection points for a variable thermostat
voltage. When using the Copeland Scroll Digital Compressor
Controller thermostat input, a voltage below 1.4 volts cycles the
compressor off. A 1.4 volt to 5 volt variable input controls the
compressor capacity from 10% to 100%.
[0077] With further reference to FIG. 6 resistors 233, 234, 235 can
be manually variable resistors to aid in testing. During initial
calibration of the ECU, these resistors may be manually adjusted
for maximum or minimum pressures and or temperatures of the
compressor, condenser, and evaporator. The calibration may be
preformed within a controlled ambient-psychrometric test chamber.
The various climatic conditions that the ECU would be subjected to
when fielded thus may be simulated, including restricted coil
airflows. After calibration, variable resistors 233, 234, and 235
may be potted and left as adjusted. If desired for robustness,
fixed resistors may be used. For increased performance and
efficiency, pressure transducers or temperature thermistor type
sensors may be utilized. Variable type sensors may be ordered with
the resistance curve selected to fit the capacity control needed
for each coil and for compressor discharge temperature protection.
Additional sensors may be employed if desired and different
locations may be used for the sensor as needed within the control
strategy described herein.
[0078] Referring to FIG. 6, other combinations of pressure and or
temperature sensors may be used. For example, if high-pressure
switch 242 is set to close at 240.degree. F., putting resistor 233
in the circuit, the voltage drop, determined by resistor 233,
reduces compressor capacity control signal to a known voltage
value, until high-pressure switch 242 opens for example at
225.degree. F. removing resistor 233 from the circuit. If suction
switch 243 is set to close at 30.degree. F. putting resistor 234 in
the circuit, the voltage drop, determined by resistor 234 reduces
compressor control signal capacity to a known voltage value until
suction switch 242 opens at 40.degree. F. removing resistor 234
from the circuit. The process of increasing and decreasing the
voltage continues with compressor inlet temperature switch 244 set
to close at 65.degree. F., putting resistor 235 in the circuit, the
voltage drop, determined by resistor 235, reduces the compressor
capacity control signal to this voltage value until inlet suction
switch 244 opens at 55.degree. F. removing resistor 235 from the
circuit.
[0079] Thermostat 239 may be a Johnson Control A350P proportional
temperature control that supplies a 10 to 0 volt DC output.
Resistor 231 and resistor 232 fixed values may be selected to lower
the voltage from 10 to 0 to a 5 to 0 volt potential DC for
compatibility with a 5 volt DC compressor electronic interface
control. Thermostat 239 increases or decreases the voltage output
in relation to sensor 240 and the manually selected temperature set
point. When temperature control thermostat 239 calls for maximum
cooling, a 5 volt signal is supplied to output 250. When no cooling
is required, the voltage drops to 0 volts. A 0 volt output signal
250 to the electronic interface turns off the compressor.
[0080] As stated previously it is desirable that an ECU not provide
temperature regulation by cycling the compressor on and off. When
the switch 241 is in the normal position shown in solid line in
FIG. 6, the circuit 236, 237 supplies minimum operating signal to
keep the compressor running at the lowest capacity. A 10 percent
ECU capacity output in most ECU applications will not over cool the
shelter due to heat loss, fenestration, equipment or personnel. The
compressor control 114 of the FIG. 3 embodiment and the compressor
control voltage 250 may be employed to effect operation of an
actuator for moving a member in a mechanically variable capacity
compressor, or operable to effect varying compressor speed in an
electrically controlled variable speed compressor drive. If
desired, an on/off line switch may be incorporated to shut off the
compressor when needed.
[0081] In addition to the circuitry illustrated in FIGS. 4-6, it
should be appreciated that a microprocessor could be employed to
regulate the operation of the variable output compressor 101
illustrated in FIG. 3. Thus, the compressor control 114 could be a
microprocessor which receives the inputs of the various sensors and
switches shown in FIG. 3.
[0082] Referring to FIG. 7, a microprocessor form of circuitry is
shown which may be employed in the present method with the ability
to provide minimum RPM or non-pump time for oil control is that
supplied by the compressor manufacture. Compressor rotor speed or
minimum pump time may also be managed within the program. Values
above the minimum are the available capacity control of the
compressor. The evaporator and condenser load, the ambient
temperature and coil condition may be calculated based on input and
output sensor signals and system reaction to the current capacity
output signal. Information regarding degradation of coils due to
clogging or a restricted evaporator filter may be provided to the
operator for corrective action. In addition, low voltage line
frequency or phase loss may be readily analyzed and the proper
system response provided. Custom microprocessors that have all the
logic functionality and input/output variable control ability to
operate an ECU are commercially available.
[0083] In FIG. 7, microprocessor 312 may be a micro based system
with analog to digital conversion, timer functions, non-volatile
memory, an onboard power supply, watchdog function comparators and
supportive hardware. Microprocessor 312 analyzes the variable
resistance inputs from voltage, current, cycle, pressure and
temperature sensors and provides the maximum compressor capacity
based upon the thermostat set point and component condition, while
providing prognostic and diagnostic functions to the operator. In
addition to operator function status alerts in the event a system
component began to operate outside of its predetermined safe
operation level, a system shut down would occur preventing any
safety issues or component damage and would provide the operator
with the reason for shut down using the control panel 316
diagnostic display.
[0084] Referring to FIG. 7, when the operator first selects
cooling, the microprocessor 312 is supplied with controller power
input 300. Microprocessor 312 will set any internal values and then
perform a pre-start routine consisting of a wire
harness-to-component continuity check to insure key sensors are
functioning, that proper electrical power is available from
compressor phase and current from compressor phase and current
sensor 313 that the wire harness is connected properly. Upon
successful completion of the pre-start, a start routine is
initiated. A reading of the thermostat 302 value is taken; and, if
there is a call for cooling the evaporator blower 317 and condenser
fan 318 are turned on: then readiness of differential pressure 314,
return air 303 and ambient temperature 315 are taken. If the
differential pressure 314 across the evaporator (pressure drop) is
within preset minimums, contactor 311 is energized by the
compressor contactor on/off output 308 through the low-pressure
safety 309 and through the high-pressure safety 310. Compressor
capacity control output 301 starting voltage level is determined by
means of a software look up table, using the ambient temperature
sensor 315 and return air 303 inputs. This is to provide an initial
stabilization capacity to prevent excessive high-pressure upon
first starting with heat soaked components and prevailing
loads.
[0085] The run routine is initiated and compressor inlet outlet
temperature 304, high pressure 307, and evaporator outlet 305
readings are taken. Data derived from testing performed within a
controlled ambient-psychrometric chamber is employed to provide the
operational control and hysteresis of capacity changes of the ECU
vapor cycle. This data provided within a controlled
ambient-psychrometric chamber is employed to provide the operations
control and hysteresis of capacity changes of the ECU vapor cycle.
This data is provided within the memory of microprocessor 312. The
microprocessor 312 is operational to increase or decrease the
compressor capacity voltage 301 to best match the cooling capacity
to component condition and thermostat input 302 set point. The
control panel 316 may present the operator with the on/off status
and any user preferred information such as ambient and indoor
temperature, amperage draw, and the capacity the unit is currently
producing to name a few. In addition to the current ECU status
information on component degradation such as a clogging evaporator
filter or restricted condenser airflow can be provided to the
operator for scheduled maintenance. It will be understood that
variations of the operation sequences, number of sensors, and level
of prognostic and diagnostics may be employed to provide reliable
operation and provide notice of need for repair depending upon the
application.
[0086] The disclosure herein has been described with reference to
the preferred embodiments. Obviously, modifications and alterations
will occur to others upon reading and understanding the preceding
detailed description. It is intended that the disclosure be
construed as including all such modifications and alterations
insofar as they come within the scope of the appended claims or
equivalents thereof.
* * * * *