U.S. patent application number 12/661659 was filed with the patent office on 2010-09-30 for dynamic outside air management system and method.
Invention is credited to Milton Meckler.
Application Number | 20100242507 12/661659 |
Document ID | / |
Family ID | 42782447 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100242507 |
Kind Code |
A1 |
Meckler; Milton |
September 30, 2010 |
Dynamic outside air management system and method
Abstract
An outside air management system in which the air is cooled by a
first refrigeration condenser to a temperature either above or
somewhat below the dewpoint of the incoming air so as to remove
either none of the moisture to be removed, or a significant portion
of it. The air then is sent to a desiccant wheel which removes the
remainder of the moisture to be extracted. The temperature of the
air leaving the wheel is above the desired delivery temperature.
Then a heat exchanger and a second condenser remove sensible heat
from the heated air leaving the desiccant wheel to bring the air to
the desired temperature. Thus, the temperature and humidity are
controlled substantially independently of one another. A heat pump
embodiment of the invention allows the reversal of the flow of
refrigerant in the system, allowing it to be used to either heat or
cool.
Inventors: |
Meckler; Milton; (St.
Petersburg, FL) |
Correspondence
Address: |
Gregor N. Neff, Esq.
14th Floor, 489 5th Avenue
New York
NY
10017
US
|
Family ID: |
42782447 |
Appl. No.: |
12/661659 |
Filed: |
March 22, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61210921 |
Mar 24, 2009 |
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Current U.S.
Class: |
62/94 ; 62/176.6;
62/271; 62/324.6; 62/426; 62/498 |
Current CPC
Class: |
F24F 2203/1072 20130101;
F25B 40/00 20130101; F25B 2313/02541 20130101; F24F 5/0014
20130101; F25B 2313/02331 20130101; F25B 40/04 20130101; F25B 13/00
20130101; F24F 2203/1032 20130101; F25B 2313/02741 20130101; F24F
2203/104 20130101; F24F 3/1423 20130101 |
Class at
Publication: |
62/94 ; 62/271;
62/426; 62/176.6; 62/324.6; 62/498 |
International
Class: |
F25D 17/06 20060101
F25D017/06; F25B 15/00 20060101 F25B015/00; F25B 49/00 20060101
F25B049/00; F25B 13/00 20060101 F25B013/00; F25B 1/00 20060101
F25B001/00 |
Claims
1. An outside air supply management system for a building, said
system comprising (a) first cooling apparatus for cooling incoming
outside air to a variable first temperature, at which a quantity of
moisture is removed from said outside air, said quantity varying
from zero to a substantial quantity, (b) a variable capacity
desiccant wheel controllable for removing from said air
substantially all of the remainder of the moisture designed to be
removed from the air received from said first refrigeration unit
and issuing dehumidified air at a desired dewpoint, and a
temperature above a desired temperature to be maintained at a
utilization location, (c) a second cooling apparatus for cooling
air from said desiccant wheel to a second temperature desired to be
maintained at a utilization location, (d) at least one air mover
for moving said outside air through said first cooling apparatus,
said desiccant wheel, and said second cooling apparatus to said
utilization location, and (e) a programmed controller for
controlling the operation of said cooling apparatus and said
desiccant wheel to achieve the temperatures and dewpoint specified
above and thereby control the humidity and temperature of the air
delivered to said utilization location substantially independently
of one another.
2. A system as in claim 1 in which each of said first and second
cooling apparatus comprises a refrigeration evaporator, and a
single compressor supplying both of said evaporators with
refrigerant, and at least one expansion valve controlled by said
controller to govern the cooling provided by said evaporators, and
a flow re-directing valve operable to convert said system between a
cooling system and a heating system in which said evaporators are
converted into condensers used for heating.
3. A system as in claim 1 including a desiccant regeneration
sub-system comprising an air mover for moving return air from said
utilization location to heating apparatus, said heating apparatus,
including a desuperheater and then to said desiccant wheel to
regenerate the desiccant therein, said programmed controller being
programmed to set said first temperature at a level sufficient to
assure regeneration of the desiccant in said desiccant wheel.
4. A system as in claim 1 in which said cooling apparatus includes
at least two evaporators are connected together in a refrigerant
flow circuit selected from the group consisting of a parallel
connection with a single expansion valve, and a tandem connection
with two separate expansion valves, one for each of said
evaporators.
5. A system as in claim 1 including a conduit for introducing a
portion of said return air into the incoming outside air.
6. A system as in claim 1 including a heat exchanger forming part
of said second cooling apparatus for absorbing heat from the air
leaving said desiccant wheel and delivering heat to said return air
to heat it before reaching said heating apparatus and said
desiccant wheel.
7. A system as in claim 1 including equipment for sensing the
dewpoint of air in said utilization location, a further dew point
detecting equipment for said outside air, said dew point equipment
being connected to provide inputs to said controller, the
performance characteristics of said desiccant wheel being stored in
said controller for use in controlling the speed of said desiccant
wheel, and compressor control equipment for changing the output of
a compressor in said system to modulate cooling in said system.
8. A system as in claim 1 including a thermostat and a CO.sub.2
sensor in said utilization location and delivering signals to said
controller, and a desiccant wheel rotator motor connected to be
controlled by said controller in accordance with the desiccant
moisture reduction needed, a sensible cooling air handling unit
receiving conditioned air outside from said outside air supply
system, said controller being programmed to increase the internal
air temperature design point in response to reductions in outside
air volume requirements.
9. A system as in claim 1 in which each of said first and second
cooling apparatus includes an evaporator, and including a variable
compressor for compressing refrigerant gas and supplying it to both
of said evaporators, a desuperheater, at least one condenser, a
subcooler, and at least one controllable valve for selectively
operating said cooling apparatus to produce variable amounts of
cooling as needed.
10. A system as in claim 9 in which the refrigerant used in the
refrigeration system in which said evaporators are used is R22 or
equivalent.
11. A system as in claim 3 in which said system includes an
evaporator for each of said cooling apparatus, a condenser and a
compressor, and is part of a heat-pump system with at least one
valve for selectively reversing the flow of refrigerant through
said evaporators and condenser and reverse the functions of said
condenser and said evaporators and convert said system from a
cooling mode to a heating mode.
12. A system as in claim 11 in which said desiccant wheel is
operated to transfer moisture from said return air to said incoming
outside air for humidification, with said evaporators converted to
heaters, and said system includes a desuperheater which is
connected for reverse operation as an evaporator.
13. A method of conditioning outside air to cool and dehumidify
said outside air and deliver the cooled and dehumidified air to an
internal utilization location in a building, said method comprising
the steps of: (a) moving outside air into contact with a first
variable cooling device and controlling the temperature produced in
said outside air to a first temperature to remove from zero to a
substantial portion of the moisture to be removed from the air, (b)
moving air from said first cooling device to a desiccant device and
controlling said desiccant device to remove from substantially all
of the remaining moisture desired to be removed therefrom, (c)
removing heat from the air leaving said desiccant wheel by means of
a second cooling device to a temperature desired for said
utilization location, and (d) moving the air leaving said second
evaporator to said utilization location.
14. A method as in claim 13 including the steps of: (e) moving
exhaust air from said utilization location to a heat exchanger to
absorb heat removed from air leaving said desiccant device, (f)
moving exhaust air from said heat exchanger to a desuperheater and
heating said air therein, (g) using the heated exhaust air from
said desuperheater to regenerate the desiccant material in said
desiccant device, and (h) controlling said first temperature so as
to eliminate or minimize the need to supplementally heat said
exhaust air.
15. A method as in claim 13 including using a programmed electronic
controller to control the amount of cooling provided in such of
said cooling steps and the amount of moisture removed from the
outside air by said desiccant device to deliver outside air to a
utilization location at a desired temperature and humidity with
each quantity being controlled substantially independently of the
other.
16. A method as in claim 13 including using a programmed electronic
controller to control the amount of cooling provided in such of
said cooling steps and the amount of moisture removed from the
outside air by said desiccant device to deliver outside air to a
utilization location at a desired temperature and humidity
substantially without reheating said air, and utilizing said
controller to compute the level of operation of each of said steps
to produce said outside air at the desired temperature.
17. A method as in claim 13 including sensing CO.sub.2 levels in
the utilization location and delivering corresponding signals to
control the steps of moving air to provide the amount of
ventilation needed as indicated by said CO.sub.2 levels and
increasing the required temperature level of a conditioned space as
a function of the reduction in outside air volume.
18. A method as in claim 13 including programming a programmable
controller to provide set levels of parameters based on the time of
year and time of day in the location of the building of said
utilization location
19. An air conditioning system particularly well adapted to
condition extremely high-humidity air, said system comprising: (a)
a first DX coil for cooling incoming outside air to a first
temperature, (b) a desiccant wheel for dehumidifying air received
from said wheel, (c) a heat exchanger selected from the group
consisting of a heat pipe structure and a sensible heat wheel
receiving air from said desiccant wheel and transferring said heat
to another location spaced from the path of said air leaving said
desiccant wheel, (d) a second DX coil for cooling air received from
said heat exchanger and delivering the cooled air to a utilization
location. (e) a fan for moving air from said utilization location
through said other location to a desuperheater and then to the
regenerative side of said desiccant wheel to regenerate the
desiccant therein, and (f) a device for controlling the amount of
cooling provided by said first DX coil to reduce said first
temperature to near the saturation level of said outside air.
20. A system as in claim 19 including a condenser, a single
compressor supplying both of said DX coils, at least one expansion
valve, and a valve for selectively reversing the flow of
refrigerant through said DX coils and said condenser to provide for
heating operation of said system, with said desiccant wheel
selectively transferring moisture from return air to said outside
air for humidification.
Description
[0001] Priority for this patent application is claimed from U.S.
provisional patent application Ser. No. 61/210,921 filed Mar. 24,
2009. The disclosure and claims of that patent application hereby
are incorporated herein by reference.
[0002] This invention relates to air conditioning systems and
methods. In particular, the invention relates to dynamic outside
air management systems and methods, in which the humidity, the
temperature and the flow rate of outside air introduced into a
building are controlled.
[0003] A very common prior art approach to reducing the humidity
and/or temperature of mixed outside and return air is one in which
refrigeration equipment is used to cool that air to a temperature
determined by the apparatus dewpoint which is well below that
needed to bring the temperature down to the level desired in the
conditioned space. This is done in order to remove enough humidity
from the air to meet the humidity requirements for air used in the
conditioned space.
[0004] Because the temperature of the refrigerated supply air is
well below that needed to cool the conditioned space to the desired
temperature and humidity, the air may have to be reheated before
delivering it to the conditioned space, at part cooling load,
e.g.
[0005] Such a prior system has at least two major drawbacks; first,
that the capital expenditures for the equipment needed for a new
HVAC system are relatively high, and, secondly, the energy usage
for both a new and a retrofitted existing system is excessive.
These disadvantages increase the capital equipment and operating
costs for using the system.
[0006] In other prior dehumidification systems, desiccant devices
are used to assist in dehumidifying outside air. In such systems,
it is difficult to control the temperature of the air independently
of the desired dewpoint. This often results in the delivery of air
which is wrong in one or both of those parameters; that is, it
often is either the wrong temperature or wrong dewpoint. Additional
equipment suggested to correct the problem is undesirably complex
and of limited utility.
[0007] Accordingly, it is an object of the invention to provide air
conditioning equipment and methods in which the foregoing
disadvantages are eliminated or reduced.
[0008] It is a further object of the invention to provide a dynamic
outside air management system and method in which dehumidification
and cooling of outside air can be controlled substantially
independently of one another without undue complexity and cost.
[0009] In addition, it is an object to provide such a system and
method which is capable of delivering outside air in a "space
neutral" condition in both heating and cooling operating modes with
good efficiency and lower levels of overall HVAC system energy
usage.
[0010] It is another object to provide a dynamic outside air system
and method which can be used for humidification as well as for
dehumidification, and for heating as well as cooling outside air
and also can perform in a free cooling mode in which either
dehumidification or cooling or both can be suspended while
providing adequate ventilation for a conditioned space, thereby
conserving energy which otherwise might be wasted.
[0011] It is another object of the invention to provide automatic
reduction of the quantity of outside air when it is not needed for
ventilation because of the reduced presence of people in the
conditioned space.
[0012] In accordance with the present invention, the foregoing
objects are met by the provision of an outside air management
system and method in which incoming outside air is first cooled to
a first temperature and then dehumidified by a desiccant device to
a predetermined desired dewpoint, followed by cooling the
dehumidified air to a space-neutral temperature, and delivering
that air to a utilization location. Thus, the dehumidification is
performed by the combination of the first cooling means and the
desiccant wheel, and the delivery temperature of the air controlled
independently by a separately controllable sensible cooling
step.
[0013] Preferably, the first temperature is set at a value as high
as possible, so as to use as little energy as possible in cooling,
while minimizing the energy used in regenerating the dessicant in
the desiccant wheel.
[0014] Thus, the cost of the equipment is limited, and the
temperature of the air leaving the desiccant device can be held at
or above the desired delivery air temperature so that further
sensible cooling is all that is needed and heating is not
required.
[0015] Preferably, the system and method operates in three
different modes; cooling mode, when the outside air is hot and
usually humid; heating mode, when the outdoor air temperature and
humidity are relatively low; and "free cooling" mode when one or
more of the dehumidification and cooling functions is disabled
because little or no heating or cooling is unnecessary.
[0016] The operation of the equipment preferably is controlled by a
programmable logic controller (PLC) which senses dry-bulb and
wet-bulb temperatures of the outside air, flow rate of the outside
air, the output of the thermostat in the conditioned space, as well
as dew point or wet-bulb/dry-bulb temperatures in the controlled
space. The PLC controls the desiccant wheel speed and the
variable-output refrigerant compressor to vary the amount of
moisture removed from the air, and controls the refrigeration
equipment to control the amount of temperature reduction it
produces. The PLC controls the fans for outside air and exhaust air
during the different modes of operation, and in response to the
sensing of CO.sub.2 in the conditioned space to reduce the energy
wastage when ventilation can be reduced without harm to the
occupants.
[0017] The system can be configured as a heat pump system,
including reversing valves for converting the system from a cooling
mode to a heating mode in which humidification is provided by
operation of the desiccant wheel to transfer moisture.
[0018] The foregoing and other objects and advantages of the
invention will be set forth in or apparent from the following
description and drawings.
IN THE DRAWINGS
[0019] FIG. 1 is a schematic diagram of a dedicated outside air
conditioning system in accordance with the present invention;
[0020] FIG. 2 is a schematic diagram of a modified system like that
shown in FIG. 1;
[0021] FIG. 3 is a schematic diagram of a programmable logic
controller used in controlling the systems shown in FIGS. 1 and 2
and elsewhere in this patent application;
[0022] FIG. 4 is a schematic diagram of another embodiment of the
invention like that of FIG. 1;
[0023] FIG. 5 is a psychometric diagram used in explaining the
invention;
[0024] FIG. 6 is a schematic diagram of a refrigeration system used
with the system of FIG. 4;
[0025] FIG. 7 is a temperature-entropy plot used in explaining the
system of FIG. 4;
[0026] FIG. 8 is a schematic diagram of a heat-pump system like
that of FIG. 6, in a cooling mode of operation;
[0027] FIG. 9 is a schematic diagram of the heat-pump system of
FIG. 8 in a heating mode of operation.
[0028] FIG. 10 is a schematic diagram of the heat pump system as in
FIG. 9, but with mechanical components added as in FIGS. 1 and
2.
[0029] FIG. 11 shows an improved version of the FIGS. 9 and 10
system; and
[0030] FIG. 12 is a schematic diagram of the FIG. 8 system, with
modifications as in FIGS. 10 and 11.
GENERAL DESCRIPTION
[0031] FIG. 1 shows a system 20 in which air from outside of a
building ("OSA") is drawn into a building at inlet 22 by a fan 34,
processed by the system 20, and delivered at an outlet 36 to a
utilization location ("UL") 24.
[0032] The utilization location 24 can be an indoor building space
to be conditioned, or the junction with another conditioning system
which is used together with the dynamically controlled outside air
system 20.
[0033] The system 20 preferably has three possible modes of
operation, depending upon the climate at the location of the
building in which the air is used.
[0034] The three modes of operation are:
[0035] 1. Cooling mode
[0036] 2. Free cooling mode
[0037] 3. Heating mode
[0038] In some climates, only one of the three modes of operation
maybe used. For example, in climates which are constantly hot and
humid only the cooling mode might be necessary. In more temperate
zones, all three modes may be needed, each at different time of the
year.
[0039] Certain buildings may have internal heat and humidity loads
which render its conditioning needs substantially independent from
the external climactic environment. For example, computer data
centers which are located around the world develop so much internal
heat from the computing equipment and lights, in addition to the
heat and humidity generated by people working inside the building,
that such buildings may need cooling and dehumidification almost
all the time.
[0040] Office buildings in which a substantial number of people
work and office equipment and lighting are used have similar
needs.
Cooling Mode
[0041] FIG. 1 shows the system 20 as it is configured for operation
in the cooling mode.
[0042] The outside air is delivered to a first set of evaporator
coils DX2 at 26. The first evaporator DX2 is set to cool the
incoming outside air to a temperature which is substantially higher
than that used in the ordinary system in which refrigeration is
used entirely for dehumidification. The air preferably is cooled
only to a temperature sufficiently low to advantageously use it
with a desiccant device such as a desiccant wheel, and the
desiccant device is used to remove the majority of the moisture to
be removed from the outside air. Therefore, the first evaporator
DX2 is set to reduce the temperature only as low as needed to avoid
or minimize supplemental heating of the desiccant wheel
regeneration air. Thus the first temperature will be set at a level
which may produce from zero to a significant amount of the moisture
to be removed.
[0043] The outside air leaves the evaporator 26 and flows to a
desiccant wheel 28 which removes the remainder of the moisture to
be removed. Thus, the desiccant wheel removes moisture until the
air has the desired humidity. Then, the air then flows through a
heat exchanger 30 such as a sensible heat wheel, heat pipes, etc.
This cools the air leaving the desiccant wheel which has been
heated in the process of drying the air.
[0044] The somewhat cooled air from the sensible wheel 30 then is
delivered to a second set of evaporator coils DX1 at 32 which
further sensibly cools the air received from the sensible wheel to
a desired temperature for use at the utilization location 24.
Because the desiccant wheel is operated so as to deliver air at
temperatures at or above the desired temperature, only sensible
cooling is needed; heating is unnecessary.
[0045] If, for example, the utilization location is a space to be
conditioned, the air delivered at the outlet 36 preferably will be
at a "space-neutral" temperature and humidity; that is, at the
temperature and humidity desired for the air to enter the
conditioned space.
[0046] Alternatively, at the utilization location 24, the air
delivered at 36 can be mixed with return air conditioned by the
main refrigeration system, or otherwise, as desired.
[0047] It is notable that the air delivered at 36 is delivered at
the desired temperature and humidity without requiring reheating,
thus saving substantially in equipment and operating costs compared
with prior systems using only refrigeration for
dehumidification.
[0048] Also included in the system 20 is a return duct 38 which
delivers return air to one side of the sensible wheel 30 to heat
the return air for use in regeneration of the desiccant wheel
28.
[0049] Heated air leaves the wheel 30 and moves to a desuperheater
40 which heats the air further.
[0050] Next, the air travels to a supplemental heater 42 which can
be used if and when necessary to further heat the air delivered to
the desiccant wheel 28 to regenerate the desiccant. The air pulled
through the return system by the exhaust fan 44 then exits the
system at 46.
[0051] Thus, heat extracted from the refrigeration system and the
desiccant wheel is used to regenerate the desiccant, and make
maximum utilization of the energy available in the system.
[0052] Optionally, return air can be added to the outside air, as
indicated by the dashed line RA, in the amount of 10% to 15%, to
somewhat reduce the amount of dehumidification required.
Refrigeration System
[0053] The refrigeration subsystem is shown in the lower portion of
FIG. 1. It includes a variable output compressor 48, a condenser
50, a subcooler 52 and a single expansion valve 54. In the system
shown in FIG. 1, the two evaporators, DX1 and DX2 are connected and
parallel to one another and are both controlled by the single
expansion valve 54. This is possible where both DX1 and DX2 operate
in the same temperature range. The subcooler 52, as it is well
known, exchanges heat between the heated and cooled gases and
liquids flowing into the subcooler.
[0054] The advantageously smaller than conventional condenser uses
outside air introduced at 22 for cooling its coils with the aid of
a fan 56.
[0055] The desuperheater 40, as it is well known, receives hot
compressed gas from the compressor 48, uses the heat to heat the
return air flowing through it, and sends the gas to the condenser
50.
[0056] The system shown in FIG. 1 thus operates in a highly
efficient manner whereby the system operates so as to control the
dewpoint of the air discharged and its temperature.
[0057] FIG. 2 shows a dynamic outside air management system 60
which is the same as the system shown in FIG. 1 except that a
modified refrigeration subsystem 23 is provided.
[0058] The subsystem 23 is the same as subsystem 21 shown in FIG. 2
except that it has a separate expansion valve 58 for the evaporator
DX1, in addition to the expansion valve 54, and the evaporators DX1
and DX2 are not connected to one another in parallel. Thus, the two
evaporators can be operated independently of one another, and in
different temperature ranges.
Control System and Method
[0059] FIG. 3 is a schematic circuit diagram showing a programmable
logic controller ("PLC") 72, together with the sensors from which
it receives information, and the operating devices which it
controls.
[0060] The PLC 72 can be any one of a number of commercially
available programmable logic devices which can be programmed,
within the skill of the art, to perform the functions to be
described below.
[0061] The sensors are shown in two separate groups, group 74 and
group 76. The sensors in group 74 usually will be located so as to
detect the characteristics of the incoming outside air.
[0062] The sensors in group 76 normally are positioned in or near
the conditioned space or elsewhere where convenient in the
building.
[0063] The outside air sensors include a flow sensor 78 detecting
the flow rate of the incoming outside air, a dry-bulb thermometer
80 and a wet-bulb thermometer 82 to detect the dry-bulb and
wet-bulb temperatures of the incoming outside air.
[0064] The detectors 76 include a conventional space or return duct
mounted thermostat 84, a CO.sub.2 sensor 92, and a dewpoint
detector 94. If desired, the dewpoint detector 94 can be replaced
by a dry bulb and a wet bulb sensor, such as the thermometers 80
and 82. In the case in which dry bulb and wet bulb temperatures are
sensed by separate units and delivered to the PLC, the PLC is
programmed to compute the dew point and control additional
equipment as described below.
[0065] The equipment controlled by the PLC includes the outside air
fan 34, the exhaust fan 44, the supplemental heater 42, the speed
of the desiccant wheel motor 88 and the speed of motor 86 of the
compressor to control its output.
[0066] Also, the valves of the refrigeration system, indicated
collectively at 90, also are controlled by the PLC.
[0067] Further, the PLC controls the main air handling system 99,
to control the desired temperature in that space, as it will be
described below.
[0068] It should be understood that when the system of FIG. 1 or
FIG. 2 operate in a heat pump mode, either for cooling or heating,
the additional valves needed for such operation are included within
the group indicated at 90.
[0069] In addition, the sensible heat wheel drive motor 96 can be
controlled, if needed or desired, so as to increase or decrease the
sensible wheel speed if and when necessary.
[0070] An additional device 98 supplies calendar and clock
information. Actually, such information normally would be provided
internally within the PLC, but it is shown as a separate input, for
the sake of explanation.
[0071] By using the calendar and clock inputs, the PLC can set the
system 20 or 60 for operation in accordance with the time of year
and time of day, and whether the building zone occupied or not,
thereby conditioning the system for use in various different
seasons of the year, and times of day, so as to reduce the
unnecessary usage of energy when few or no people are occupying the
buildings, and for selecting among the three different operational
modes of the system.
[0072] Similarly, by use of the CO.sub.2 sensor 92, the ventilation
needs of people in the thermostatically controlled zones of the
building at a particular time can be determined. This can allow the
outside air flow as detected by the flow detector 78 to be reduced
significantly by reducing the speeds of fans 36 and 44 because the
CO.sub.2 detector detects the reduced CO.sub.2 output by reduced
numbers of people. This can reduce the need for ventilating air
when demand is very low, thus further saving energy and/or improve
operation of separate secondary systems as described below. In
addition, energy is saved in the main air conditioning system in an
existing building, which uses refrigeration for dehumidification,
because the temperature at which the air must be maintained can be
raised (e.g., from 55.degree. F. to 57.degree. F.) because there is
less outside air entering, and more recirculated air which needs
less cooling and dehumidification.
EXAMPLE
[0073] Assume a 1400 cfm conventionally designed AHU (air handling
unit) zone cooling requirement at a 55.degree. F. supply air
temperature and 25% OSA (or 350 cfm) for occupant ventilation
needs. Therefore, at zone design conditions, [1400-350] or 1050 cfm
of space would by mixed with 350 cfm OSA return air upstream of the
AHU cooling coil, discharging supply air at 55.degree. F. Assuming
an apparatus dewpoint of 52.degree. F. for a conventional AHU
cooling coil with a 55.degree. F. leaving air temperature requiring
a constant 25% OSA or 350 OSA to satisfy peak zone occupant
demands, the AHU should provide both sensible and latent cooling to
maintain a conditioned building space at 75.degree. F. and 50%
RH.
[0074] Assume the combined cooling load with OSA at peak design
cooling load is 58,590 BTU/hr computed as follows:
1400.times.4.5.times.9.3 BTU/#BDA (delta h). Building occupants
tend to move around during a typical work day, as part of their
normal activities, particularly where current "hotelling" company
practices allow more of their employees to work at home and come
into their offices only when necessary. Therefore, a more realistic
OSA CFM rate=0.7.times.350=245 cfm would seem advisable,
particularly when the present dynamically managed pre-conditioner
is employed at design cooling day conditions. Accordingly, the
corresponding recirculated return air flow rate equals [1400-245]
or 1155 cfm.
[0075] Assume that either a new or existing conventional AHU is
required to provide sensible cooling only. Therefore, its leaving
coil temperature can be reset by the programmed PLC and OSA flow
rate sensor located in the room return air duct could be
automatically reset to 57.degree. F. from 55.degree. F. (by the
following ratio [1050/1155].times.25 delta T=18.degree. F. delta T.
Furthermore, employing lower 18.degree. F. delta T with the same
AHU cfm supply air rate would still provide an equivalent and
sensible cooling effect with a [75.degree. F.-18.degree. F. delta
T]=57.degree. F. AHU supply air temperature to meet required
temperature of 75.degree. F. at a 1155 cfm return air rate to the
AHU.
[0076] Since the retrofitted or new sensible cooling only secondary
AHU discharge temperature can be automatically reset by our PLC to
57.degree. F. (from 55.degree. F.), the net energy saved by the AHU
amounts to 4% of input to a chiller (or equivalent refrigeration
compressor energy saving) from the resulting 2.degree. F. rise in
AHU supply air temperature. It is believed that a benefit of 2% per
1.degree. F. rise in AHU cooling coil discharge will be
obtained.
[0077] Finally, assuming a 0.7 KW/ton input chiller (or equivalent
refrigeration compressor) energy savings, based on the stated
requirement, 58,590/12000 Btu/ton or 4.88 tons;
4%.times.4.88.times.12,000=2342 Btu/hr savings; therefore, total
net energy saved=10,042 Btu/hr reduction in energy use achieved
through the use of the dynamic OSA management system:
[58,950-48,908] or 10,042 Btu/hr+[350-245] (or 595 cfm OSA at
0.0875 Btu/#BDA delta h) or 2342 Btu/hr]}/58,590=21% net energy
saving.
[0078] The dew point detector 94 detects the dew point of the
conditioned space or other system at the utilization location 24
and delivers this information to the PLC 72. The PLC also computes
the dew point of the outside air in response to signals from the
dry bulb and wet bulb thermometers 80 and 82.
[0079] By comparing the dew point of the outside air with the
desired dew point, the PLC determines how much, if any, moisture is
to be removed by the first evaporator DX2, and determines the
necessary speed of the desiccant wheel, and controls the desiccant
wheel motor 88 accordingly.
[0080] The performance characteristics of the desiccant wheel at
different wheel speeds, air flow rates and moisture contents and
moisture balance characteristics, are stored in the memory of the
PLC, or in software used to operate the controller, so that the
operational parameters to produce air with a desired output are
developed and used to control the air temperature produced by DX2,
wheel speed, etc.
[0081] Preferably, the exit temperature from the first condenser,
DX2 is not substantially lower than that necessary to limit the
desiccant wheel operation to a level which requires either no or
minimum of supplemental heating of regeneration air.
[0082] By minimizing the cooling required from the first evaporator
DX2, its size and operating cost can be minimized, and the
temperature of the air leaving the desiccant wheel will be
relatively high, creating a consistent need only for sensible
cooling in the last stage of processing. No moisture removal is
required from the evaporator DX1.
[0083] If the system shown in FIG. 2 is used, the second expansion
valve 58 is adjusted by the PLC to give a variable but desired
amount of cooling, so as to produce the desired temperature at the
utilization location 24.
[0084] Based on the amount of moisture being removed by the
desiccant wheel, based on the dew point outputs and the speed of
the wheel, the supplemental heater 42 is turned on when the heat
provided by the desuperheater 40 is insufficient to regenerate the
desiccant material.
[0085] In either case, essentially no dehumidification is provided
by the second evaporator, DX1; it, instead, provides only sensible
cooling. Thus, the control of temperature and humidity are
basically independent of one another, and the need for heating the
air delivered is avoided.
[0086] By delivering air in a "space neutral" condition, the air
can be introduced into different heating/cooling/dehumidification
zones at a temperature and dewpoint close to that needed in that
zone. Thus, the air is best adapted to the needs in each of many
different zones.
FURTHER EMBODIMENTS
[0087] Further embodiments of the invention are shown in FIGS. 4-9
of the drawings. These drawings show a sustainable and energy
efficient outside air desiccant--assisted pre-conditioner or
conditioner system particularly suitable for use in microclimates
with high prevailing seasonal humidities in excess of 100 grains/lb
bone dry air (gr/#BDA).
[0088] The system, when used in the cooling mode as a
preconditioner, also can serve to provide dehumidified outside air
to new or existing package rooftop or interior air conditioner (AC)
or (HVAC) heat pump unit. It may be configured as an integral
component of either type of unit or installed to supply
dehumidified air to one or more existing air conditioner or heat
pump units either by direct ducted connection or connection in
parallel when ducted to a common return plenum or supplied directly
into conditioned space at a space neutral or variable discharge
temperature. When interconnected with a new or existing heat pump
it can be also be employed to maintain a minimum % relative
humidity (% RH) during HVAC "heating" mode, for example.
[0089] One can practice the invention by using the system and
method of the invention in any of several different configurations.
For example, the system can be operated as a stand-alone rooftop
unit, or as a package fully integrated and self contained (or split
system configured) rooftop air conditioner or heat pump system.
Alternatively, the system can be used as the preconditioner
component of a system where separate secondary means is provided
for sensible cooling to deal with both seasonal and internally
generated cooling requirements. When required, in such a system,
supplemental space heating or cooling can be provided when
operating in a re-circulating OSA, return and exhaust constant
volume or VAV air distribution system.
EXAMPLE
[0090] Assume that one wishes to condition 4,000 scfm of outside
air in a 100% OSA dedicated outside air system as shown in FIG. 4.
It is used in the cooling mode in a climate requiring much
dehumidification and little or no heating year-round.
[0091] The components of the system shown in FIG. 4 are the same as
those shown in the upper halves of FIGS. 1 and 2, except that
heat-pipes HP are used as a heat exchanger instead of the sensible
wheel 30, and the supplementary heater 42 is not shown in FIG.
4.
[0092] In FIG. 4, the air streams of principal interest are
individually numbered 1 thru 11. The system parameters in each of
those air streams for a 4,000 SCFM flow is shown in the table
below:
TABLE-US-00001 # SCFM DB (.degree. F.) W (Gr/lb) H (Btu/lb) 1 4,000
95 145 45.6 2 4,000 68 100 31.9 3 4,000 111 47 34.1 4 4,000 86 47
28.0 5 4,000 73 47 24.2 6 4,000 75 47 24.7 7 3,400 75 65 28.2 8
3,400 100 65 34.3 9 3,400 147 65 45.7 10 3,400 11 3,400 Note:
desiccant wheel cassette of 1220 mm dia. X 200 mm depth, rotating
at 40 RPH
[0093] Total process (1-5)
Q.sub.Total=4000.times.4.5.times.(45.6-24.2)=385,200 Btu/hr=32.1 RT
[0094] DX2 (1-2) Q.sub.2=4000.times.4.5.times.(45.6-31.9)=246,600
Btu/hr=20.6 RT [0095] DX1 (4-5)
Q.sub.1=4000.times.4.5.times.(28.0-24.2)=68,400 Btu/hr=5.7 RT
[0096] DX2+DX1 Q.sub.REFRIG.=Q.sub.2+Q.sub.1=20.6+5.7=26.3 RT
[0097] In the foregoing table;
[0098] "SCFM" is the outside air flow rate, in standard cubic feet
per minute;
[0099] "DB" is the dry bulb temperature of the air, in degrees
F.;
[0100] "W" is the humidity ratio, in grains per lb;
[0101] "H" is the enthalpy, in Btu/lb; and
[0102] "Q" is the cooling capacity required, in tons.
[0103] As it can be seen, outside air enters at 95.degree. F. dry
bulb and 145 grab humidity corresponding to an enthalpy of 45.6
Btu/lb, a condition (or state) also represented in the psychometric
diagram of FIG. 5 by the same designated air flow arrow
numbers.
[0104] In the table above, Qtotal corresponds to the mechanical
refrigeration needed in tons (RT) to condition the 4000 scfm of OSA
to obtain the desired air stream 5 conditions of 73F and 43 gr/lb.
or 32.1 RT. Therefore to maintain conditioned space parameters of
75.degree. F. and 50% RH, the preconditioned OSA would need to
enter the space independently or via another means at air location
6, or at a space neutral DB temperature (75.degree. F.) after
adjustment for fan reheat and any ductwork distribution, sensible
heat gain (assumed for our purposes to be 2.degree. F.) and have
enough latent heat capacity at 47 gr/lb to maintain 50% RH in the
conditioned space. This assumes that any sensible heat gain due to
people, lights, equipment and associated peak building envelope
sensible transmission heat gains would be removed by independent
cooling means dedicated to removing only sensible heat gains.
[0105] The comparable mechanical refrigeration capacity (shown
above as Qtotal) is believed to be reduced by 5.7 RT or a total
Q1+Q2 or approximately 18% by use of the invention.
[0106] FIG. 5 is a psychometric chart of air stream flow state
points showing the results of the above. The large numbers
correspond to the air stream numbers in FIG. 4.
[0107] It should be understood that although not shown in FIG. 4, a
supplemental heater 42 as shown in FIG. 1 is provided in the
regeneration air stream immediately preceding the desiccant wheel
DH whenever the heat available from the desuperheater DSH falls
below 147.degree. F., at the conditions given above for this
example, so as to maintain the humidity at 47 gr/lb, or whenever
the compressor cycles off, for example, when both the thermostat 84
and dewpoint detector 94 indicate a need for dehumidification.
[0108] Additionally, although not shown in the drawings, if it is
advantageous to do so, other cooling equipment such as indirect
evaporative coolers can be used to cool the outside air before
dehumidification. Also, enthalpy wheels or other heat exchangers
can be used to exchange heat between the outside air and the
exhaust air before the outside air is de-humidified.
[0109] FIG. 6 is a refrigeration system schematic diagram for the
system of FIG. 4. The components shown in FIG. 6 are the same as in
FIG. 1, except that the heat exchanger HTHX and the two valves "CV"
have been omitted from FIG. 1 as being unnecessary. The heat
exchanger "LTHX" in FIG. 6 is the same as the subcooler 52 shown in
FIG. 1. Liquid flow paths are shown as solid lines and gas or
gas-liquid flow paths are shown as dashed lines. The air flow at
location numbers 1-2, 4-5 and 8-9 are the same as in FIG. 4. The
valves "DV" are air-coil discharge sensor-activated three-way
temperature control valves for air cooling coils DX1 and DX2.
[0110] The lower case letters in FIG. 6 indicate refrigerant
temperature-pressure-state conditions as identified on the
schematic Temperature-Entropy or TS diagram of FIG. 7.
[0111] FIG. 7, as noted above, is a TS diagram describing the
refrigeration cooling cycle of the FIG. 6 system, and using the
same lower case letters identifying refrigerant state conditions or
state points at the corresponding points in FIG. 6. In FIG. 7, it
should be noted that the process, between points e and f, is
assumed to be isentropic expansion (i.e., with constant
entropy).
Heat-Pump Embodiments
[0112] FIGS. 8 and 9 show operation of the system shown in FIGS. 4
and 6, and those of FIGS. 1 and 2 when operating in heat-pump
mode.
[0113] This mode of operation is preferred for use in northerly
temperate climates such as that in Boston, New York, Chicago, USA,
or wherever operation in both heating and cooling (and
free-cooling) modes is needed or desired.
Cooling Mode
[0114] FIG. 8 shows the system of FIG. 6 modified for operation as
a heat-pump in the cooling mode. FIG. 8 is the same as FIG. 6 with
the exception of the insertion of a 4-way solenoid valve (shown at
lower left hand corner of FIG. 8) used to switch the heat pump from
the cooling and de-humidification mode to the heating and
humidification mode by redirecting refrigerant flows as shown FIG.
9. This reverses the functions of the condenser and evaporators DX1
and DX2 and by-passes flow to the desuperheating coil DSH as well,
when used in the heating mode.
[0115] The valves CV shown in FIGS. 8 and 9 are optional bypass
valves. They can be used for re-directing the flow of refrigerant
to enable the use of a fixed-output compressor to give variable
output, or for the purposes of enabling alternative
interconnections.
Heating Mode
[0116] FIG. 9 shows the system of FIG. 8 in the heating mode.
Refrigerant flow is reversed from that shown in FIG. 8 by the 4-way
solenoid valve so that DX1 now serves as a low temperature (LT)
condenser and DX2 now serves as a high temperature (HT) condenser
and the former condenser now becomes the evaporator. The evaporator
extracts heat from ambient air and/or exhaust air to provide heat
for humidification and tempering of the OSA to deliver air at
approximately 72.degree. F., partially humidified. Thus, there is
provided improved comfort and static electricity-free air but at a
humidity below that needed to result in moisture condensation on
exterior glass.
[0117] For example, humidification occurs by enabling the DH wheel
to operate with the desuperheater DSH by-passed thus, in effect,
transferring moisture from the return air to the OSA air. The air
then is heated by LT condenser DX1 to the desired delivery
temperature.
[0118] Operation of the motor-driven DH wheel will be cycled by
humidity detected either in the OAS supply duct or the dew point
controller 94 located in conditioned space to maintain safe
humidification levels and avoid condensation on exterior envelope
wall or glazing.
[0119] FIG. 10 is a schematic diagram of the heating-mode heat-pump
system 100, of FIG. 9, with the mechanical components added, as in
FIGS. 1 and 2.
[0120] The 4-way solenoid valve 101 has two different flow paths
102 and 104. When the valve 101 is in the state shown in FIG. 10,
refrigerant flows through path 102 from LTHK (Low Temperature Heat
Exchanger) 52, which is the same as the subcooler shown in FIGS. 1
and 2, to DX2, which now has been connected to become a condenser
to be a heater instead of a cooler.
[0121] The HTHX (High Temperature Heat Exchanger 106) is
interconnected with the LTHX and other components as shown in FIG.
9.
[0122] The desuperheater 40 is disconnected and inactive, as is the
supplemental heater 42. The sub-system 108 is for heating, and is
not a refrigeration sub-system as is the system 21 in FIGS. 1 and
2.
[0123] The valves CV shown in FIGS. 8 and 9 have been omitted from
FIGS. 10-12.
[0124] FIG. 11 shows a system 110 that is the same as that in FIG.
10, except that the desuperheater is connected by lines 112 and 114
to receive refrigerant and thus become a second evaporator unit to
supplement the unit 50 and increase the output of the system.
[0125] FIG. 12 shows the heat-pump system 120 used in the cooling
mode. The system 120 is the same as shown in FIG. 8, except that
the mechanical components have been added, as in FIGS. 1 and 2.
[0126] The valve 101 now has changed state to direct the flow
through path 104 to create the cooling mode of the heat-pump
operation. The desuperheater 40 now is connected to heat the
regeneration air, as in FIGS. 1 and 2. The units DX1 and DX2, and
the condenser 50 have again reversed the functions they have in
FIGS. 9-11 to be used in cooling and dehumidification.
[0127] The introduction of 10% to 15% return air at the outside air
inlet is eliminated.
[0128] There are numerous HVAC air distribution options for
removing conditioned space sensible (only) heat and provide heating
as discussed above where required.
[0129] Mention was made above of numerous means of incorporating
the active 100% OSA preconditioner as a component of one of the
following 8 air distribution types or as integral part of any of
the air distribution system where both indoor and outdoor latent
humidity requirements for conditioned building spaces are
controlled independently, thereby permitting sensible heat gains to
be removed by the following supplemental sensible cooling only
downstream companion separate systems; namely: [0130] (1) fan coil
air distribution units, [0131] (2) mini-split ductless air
conditioning units, [0132] (3) air handlers operating at higher
temperature to achieve a more energy efficient DX evaporator coil
operation [0133] (4) chilled water cooled coil air handlers with
either: [0134] (4a) a fixed OSA ventilation rate or [0135] (4b) a
constant volume air distribution system, with OSA, return and
exhaust air streams, or [0136] (4c) variable air volume (VAV) air
distribution system, with OSA, return and exhaust air streams
[0137] (5) 100% OSA DOAS type distribution systems also
incorporating chilled water [0138] (6) mini-split ductless fan
powered terminals [0139] (7) series fan powered terminals for
secondary space sensible (only) cooling needs all of which can be
controlled from zoned thermostats while also resulting in improved
indoor IAQ at all part load space occupant cooling [0140] (8)
parallel fan powered terminals for secondary space sensible (only)
cooling needs all of which can be controlled from zoned thermostats
while also resulting in improved indoor IAQ at all part load space
occupant cooling and heating requirements [0141] (9) heat pump unit
heated and humidified exterior space heating conditions all of
which have been shown in FIGS. 8 and 9.
[0142] In operation, in the cooling mode, the first cooling coils
DX.sub.2 (FIG. 4) receiving OSA are deliberately set to cool
incoming air to a temperature, preferably above the conditioned
space desired temperature, so that little or no dehumidification
takes place.
* * * * *