U.S. patent application number 10/158745 was filed with the patent office on 2002-10-24 for ventilator system and method.
This patent application is currently assigned to Building Performance Equipment Inc.. Invention is credited to Haglid, Klas C..
Application Number | 20020153133 10/158745 |
Document ID | / |
Family ID | 22694299 |
Filed Date | 2002-10-24 |
United States Patent
Application |
20020153133 |
Kind Code |
A1 |
Haglid, Klas C. |
October 24, 2002 |
Ventilator system and method
Abstract
The ventilator system and method use a isolating heat exchanger
to selectively transfer heat between exhaust air leaving an
enclosed space and outside air entering the enclosed space. The
system operates in three basic modes, under the control of a
microprocessor-based controller which is responsive to the
temperatures inside and outside of the enclosed space. In the
heating mode, heat is transferred from the exhaust air to the
outside air when the enclosed space requires heating. In the
cooling mode, heat is transferred from the outside air to the
exhaust air when the outside air temperature is higher than that in
the enclosed space. In the supplemental cooling mode, heat transfer
between the exhaust and outside air is reduced or eliminated when
the outside air temperature is below the desired temperature in the
enclosed space and cooling is required. In the heating mode, the
heat exchanger is selectively heated when necessary to defrost it.
A by-pass is provided for the introduction of outside air in order
to avoid heating of the outside air by the exhaust air during the
supplemental cooling mode of operation, and/or provide fresh air to
the enclosed space without cooling the heat exchanger while it is
being defrosted.
Inventors: |
Haglid, Klas C.;
(Wilmington, DE) |
Correspondence
Address: |
Attention : Gregor N. Neff, Esq.
Kramer Levin Naftalis & Frankel LLP
38th Floor
919 Third Avenue
New York
NY
10022-3852
US
|
Assignee: |
Building Performance Equipment
Inc.
|
Family ID: |
22694299 |
Appl. No.: |
10/158745 |
Filed: |
May 20, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10158745 |
May 20, 2002 |
|
|
|
09579739 |
May 26, 2000 |
|
|
|
09579739 |
May 26, 2000 |
|
|
|
09188729 |
Nov 9, 1998 |
|
|
|
6176305 |
|
|
|
|
Current U.S.
Class: |
165/231 ;
165/248; 165/250; 165/254; 165/292; 165/294; 165/54 |
Current CPC
Class: |
Y02B 30/56 20130101;
F28D 9/0081 20130101; F24F 5/0035 20130101; F28F 2250/102 20130101;
F24F 2012/007 20130101; F28F 21/065 20130101; F24F 12/006 20130101;
F28D 5/00 20130101; Y02B 30/545 20130101; Y02B 30/563 20130101;
F24F 2006/146 20130101 |
Class at
Publication: |
165/231 ;
165/248; 165/250; 165/254; 165/292; 165/294; 165/54 |
International
Class: |
F24H 003/02; F28F
017/00; F25D 021/00; F25B 029/00; F24F 011/04; G05D 023/00 |
Claims
What is claimed is:
1. A method of ventilating an enclosed space using an air handling
system including an isolating heat exchanger for conducting exhaust
air from said enclosed space and outside air into said enclosed
space and exchanging heat between said exhaust air and said outside
air while isolating the flows of said outside and exhaust air from
one another, an enclosed space air temperature sensor, an outside
air temperature sensor, a first fan to move said exhaust air
through said heat exchanger, a second fan to move said outside air
through said heat exchanger, and a programmed controller for
controlling the flow of said exhaust air and said outside air and
the heat transfer therebetween, said method comprising: (a) during
a first cooling mode, causing heat to be transferred from said
outside air to said exhaust air when the outside air temperature is
greater than a desired enclosed space temperature; (b) during a
second cooling mode, reducing or eliminating the transfer of heat
from said exhaust air to said outside air through said heat
exchanger when said outside air temperature is lower than said
desired enclosed space temperature, and said space temperature is
greater than said desired space temperature.
2. A method as in claim 1 including the step of, during a first
heating mode, utilizing said controller in causing heat to be
transferred from said exhaust air to said outside air when said
outside air temperature is at a temperature which is below said
desired space temperature by at least a pre-determined amount.
3. A method as in claim 2 in which said air handling system
includes a sensor for detecting freezing conditions in said heat
exchanger, and including the step of utilizing said controller in
causing the heating of said heat exchanger to alleviate said
freezing condition.
4. A method as in claim 3 in which the heat exchanger heating step
includes reducing the flow of sub-freezing outside air through said
heat exchanger.
5. A method as in claim 3 in which the heat exchanger heating step
includes re-circulating said exhaust air through said heat
exchanger in the path otherwise taken by said outside air.
6. A method as in claim 3 in which the heat exchanger heating step
includes one or more steps selected from the group consisting of;
reducing the flow of outside air through said heat exchanger while
maintaining the flow of exhaust air therethrough; recirculating
said exhaust air through said heat exchanger; and applying heat
from a heat source to said heat exchanger.
7. A method as in claim 1 including the step of using evaporative
cooling during said first cooling mode to cool said exhaust air
prior to its entering said heat exchanger.
8. A method as in claim 7 in which said evaporative cooling
comprises one or more steps selected from the group consisting of;
spraying water into said exhaust air; wetting a membrane with water
and contacting said exhaust air with said membrane; and spraying
water into said exhaust air and onto a membrane contacting said
exhaust air.
9. A method as in claim 1 in which said air handling system
includes a by-pass duct and fan for selectively introducing outside
air into said enclosed space without flowing through said heat
exchanger; and including the step of operating the by-pass fan to
introduce outside air into said space during said second cooling
mode.
10. A method as in claim 9 including the step of operating said
by-pass fan during defrosting of said heat exchanger.
11. A method as in claim 1 in which the step of substantially
eliminating the transfer of heat during said second cooling mode is
performed by reducing or eliminating the flow of exhaust air
through said heat exchanger while flowing said outside air
therethrough.
12. A method of ventilating an enclosed space using an air handling
system including an isolating heat exchanger for conducting exhaust
air from said enclosed space and outside air into said enclosed
space and exchanging heat between said exhaust air and said outside
air while isolating the flows of said outside and exhaust air from
one another, an enclosed space air temperature sensor, an outside
air temperature sensor, a first fan to move said exhaust air
through said heat exchanger, a second fan to move said outside air
through said heat exchanger, and a programmed controller for
controlling the flow of said exhaust air and said outside air and
the heat transfer therebetween, said method comprising: during a
heating mode, causing heat to be transferred from said exhaust air
to said outside air when said outside air temperature is at a first
temperature which is below a desired space temperature by at least
a pre-determined amount, and during a cooling mode, reducing or
eliminating the transfer of heat from said exhaust air to said
outside air through said heat exchanger when said outside air
temperature is above said first temperature but below said desired
temperature, and said space temperature is greater than said
desired space temperature.
13. A method of ventilating an enclosed space using an air handling
system including an isolating heat exchanger for conducting exhaust
air from said enclosed space and outside air into said enclosed
space and exchanging heat between said exhaust air and said outside
air while isolating the flows of said outside and exhaust air from
one another, an enclosed space air temperature sensor, an outside
air temperature sensor, a first fan to move said exhaust air
through said heat exchanger, a second fan to move said outside air
through said heat exchanger, and a programmed controller for
controlling the flow of said exhaust air and said outside air and
the heat transfer therebetween, said method comprising: cooling
said enclosed space by substantially eliminating the transfer of
heat from said exhaust air to said outside air through said heat
exchanger when said outside air temperature is below a desired
space temperature but above a temperature at which heating of the
enclosed space is required, and said space temperature is greater
than said desired space temperature.
14. A method as in claim 13 in which the transfer of heat from said
exhaust air is reduced or eliminated by one of more of the steps
consisting of: by-passing outside air around said heat-exchanger;
and reducing or eliminating the flow of exhaust air through said
heat exchanger
15. A system for ventilating an enclosed space, said system
including an outside air duct, an inside air duct, an inside air
temperature sensor, an outside temperature sensor, a heat exchanger
with two sets of isolated air flow passages, one of which
communicates with said outside air duct, and the other of which
communicates with said inside air duct, an inside air fan
positioned to force inside air through said inside air duct and
said heat exchanger, an outside air fan positioned to force said
outside air through said outside air duct and said heat exchanger,
and a control circuit including a programmed processor for
selectively operating said air fans and the exchange of heat
between said inside air and said outside air in response to
temperature signals received from said temperature sensors.
16. A system as in claim 15 including an evaporative cooler for
selectively cooling said inside air before it passes through said
heat exchanger.
17. A system as in claim 15 in which said evaporative cooler
includes a membrane in the flow path of said inside air and a water
sprayer to supply water to wet said membrane.
18. A system as in claim 15 including a sensor for sensing freezing
conditions in said heat exchanger, said processor being programmed
to cause said heat exchanger to be heated when the freezing
conditions are detected.
19. A system as in claim 18 in which said processor is programmed
to cause said heat exchanger to be heated by reducing the flow of
outside air through said heat exchanger while maintaining the flow
of inside air therethrough.
20. A system as in claim 15 including a by-pass conduit and a fan
for introducing outside air into said enclosed space without
passing said outside air through said heat exchanger, said
processor being programmed to cause outside air to flow through
said by-pass in response to signals indicating that the outside air
temperature is below a desired air temperature in said space and
above a temperature at which heating in said space is needed.
21. A system as in claim 15 in which said processor is programmed
to cause heat to be transferred from said inside air to said
outside air in said heat exchanger when said inside air temperature
sensor indicates that heating is needed in said enclosed space, to
cause heat to be transferred from said inside air to said outside
air when said inside air temperature sensor indicates that cooling
is needed in said enclosed space and said outside air temperature
sensor indicates that said outside air temperature is higher than
the inside air temperature, and to cause no heat to be transferred
between said inside air and outside air when cooling in said space
is needed and said outside air temperature is below said inside air
temperature.
22. A system as in claim 15 in which said heat exchanger is made of
crossed plastic conduits assembled together.
23. A system as in claim 20 in which said by-pass conduit has an
outlet into said outside air duct, and including gravity louvers
normally covering said outlet of said by-pass conduit, said louvers
being opened by air pressure from said by-pass fan.
24. A system as in claim 18 in which said inside and outside ducts
have inlet sections, and including louvers at the inlet sections
and another louver between said sections, said louvers being
selectively operable to recirculate inside air through said heat
exchanger and reduce or eliminate outside air flow in response to
the detection of freezing conditions in aid heat exchanger.
Description
[0001] This invention relates to ventilator systems and methods,
and particularly to ventilator systems and methods using isolating
heat exchangers to exchange heat between exhaust air leaving an
enclosed space, and outside air entering the building.
[0002] It is increasingly common to make modern homes and
commercial buildings very air-tight in order to reduce heating and
cooling costs. As a result, it has become increasingly necessary to
bring fresh air into the building in order to avoid an extreme
reduction of oxygen in the building, which can cause the illness or
even death of the occupants.
[0003] Prior ventilator systems have been designed to use heat
exchangers to transfer heat from the exhaust air to the outside air
to pre-heat the outside air before it enters the building, thus
saving energy and heating costs. This is useful in cold weather
when the building must be heated.
[0004] In order to protect the health of the occupants, it is very
desirable to prevent the air being exhausted from the enclosed
space from mingling with the incoming outside air. Thus, often the
heat exchangers which are used are those in which the flow of
exhaust air is isolated from the flow of outside air through the
heat exchanger. These are sometimes called "isolating" heat
exchangers.
[0005] Other ventilator systems provide for heat transfer from the
outside air to the exhaust air when the outside air temperatures
are higher than the desired temperatures in the enclosed space.
This cools the incoming air before it is further refrigerated to
provide the ultimate desired temperature, thus reducing the load on
the refrigeration system and reducing the cost of cooling.
[0006] Applicant has discovered a problem in that it is believed
that prior ventilator systems are not efficiently operable
throughout a complete range of outside and inside air temperature
conditions. This reduces the utility of the prior ventilator
systems and makes them less cost-effective than they might be.
[0007] Accordingly, it is an object of the present invention to
provide a ventilating system and method in which the foregoing
problems are eliminated or alleviated.
[0008] More particularly, it is an object of the invention to
provide a ventilator system and method which can be utilized for
essentially all ventilating conditions, and at essentially all
times of the year.
[0009] It is an object of the present invention to provide a
flexible ventilator system and method in which the mode of
operation can be changed readily in response to changing climactic
and interior space conditions.
[0010] It is a further object of the invention to provide such a
system which is relatively inexpensive to manufacture, simple in
construction, inexpensive to install and use, and reliable for
long- term operation.
[0011] In accordance with the present invention, a ventilating
system and method are provided in which an isolating heat exchanger
is used for recovering energy while supplying outside air to an
enclosed space during all weather conditions, by the use of inside
and outside air temperature signal.
[0012] The invention also provides a ventilating system and method
using an isolating heat exchanger in which two different modes of
cooling are available; one in which the heat exchanger transfers
heat from the incoming outside air to the cooler exhaust air, and
another in which heat transfer between the incoming and outgoing
air is temporarily eliminated in order to provide supplemental
cooling when the inside air temperature is below the inside air
temperature.
[0013] Additional cooling is provided by evaporatively cooling the
exhaust air before it reaches the heat exchanger so as to greatly
increase the temperature drop of the incoming outside air before it
enters the enclosed space.
[0014] A further feature of the invention is the provision of a
ventilating system and method using an isolating heat exchanger
with supplemental cooling, without heat transfer between incoming
and outgoing air, as well as heat transfer from the exhaust air to
the incoming outside air during cold weather.
[0015] Another feature of the invention is the provision of a mode
of operation to defrost the heat exchanger. This operation is
accomplished by any one or more of the methods of reducing outside
air flow; by-passing outside air flow around the heat exchanger;
and heating the outside air before it reaches the heat
exchanger.
[0016] The preferred ventilator system and method use a isolating
heat exchanger to selectively transfer heat between exhaust air
leaving an enclosed space and outside air entering the enclosed
space. The system operates in three basic modes, under the control
of a microprocessor-based controller which is responsive to the
temperatures inside and outside of the enclosed space. In the
heating mode, heat is transferred from the exhaust air to the
outside air when the enclosed space requires heating. In the
cooling mode, heat is transferred from the outside air to the
exhaust air when the outside air temperature is higher than that in
the enclosed space. In the supplemental cooling mode, heat transfer
between the exhaust and outside air is reduced or eliminated when
the outside air temperature is below the desired temperature in the
enclosed space and cooling is required. In the heating mode, the
heat exchanger is selectively heated when necessary to defrost it.
A by-pass is provided for the introduction of outside air in order
to avoid heating of the outside air by the exhaust air during the
supplemental cooling mode, and/or provide fresh air to the enclosed
space without cooling the heat exchanger while it is being
defrosted.
[0017] 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
[0018] FIG. 1 is a schematic side-elevation and cross-sectional
view of a ventilating system constructed in accordance with the
present invention;
[0019] FIG. 2 is a perspective view of a heat exchanger used in the
system shown in FIG. 1;
[0020] FIG. 3 is a perspective, broken away enlarged and partially
schematic view of a portion of the heat exchanger shown in FIG.
2;
[0021] FIG. 4 is a schematic diagram of a control circuit for
controlling the operation of the system shown in FIG. 1; and
[0022] FIG. 5 is a perspective, partially exploded view of a
roof-top installation of the ventilator of the present
invention.
GENERAL DESCRIPTION
[0023] FIG. 1 shows the ventilating system 10 of the present
invention in schematic form.
[0024] The ventilating system 10 is in use to provide ventilation
to an enclosed space indicated schematically by the dashed line 12.
This enclosed space can be a residence, a business office, a
skyscraper or other type of enclosed space.
[0025] The ventilating system 10 includes a housing 14 in which is
mounted a heat exchanger 16, an exhaust air fan 28, and an outside
air fan 26.
[0026] The heat exchanger 16 is mounted in the housing 14, tilted
as shown in FIG. 1, with its upper and lower edges 42 and 44 sealed
to the top and bottom walls of the housing, respectively, and with
the other corners of the heat exchanger attached with sealing
members 38 and 40 to the side walls of the housing, also so as to
provide an air seal between adjacent sides of the heat
exchanger.
[0027] The unit described so far is supplied as a free-standing
module. Attached to it, as in a typical installation, is an outside
air inlet duct 18 and an exhaust air outlet duct 20. Both of the
ducts 18 and 20 communicate with the ambient air outside of the
enclosed space 12.
[0028] Attached at the other end of the housing 14 are an exhaust
inlet duct 22 and an outside air outlet duct 24. The mounting of
the heat exchanger 16 in the housing, with the seals at its four
corners, provides two isolated air flow paths through the heat
exchanger.
[0029] One path is shown by arrows 46 and 48 extending from the
outside air inlet duct 18 downwardly and to the right and out
through the duct 24, in the direction shown by the solid arrows
through the heat exchanger 16.
[0030] The other flow path is from the exhaust inlet duct 22
through the heat exchanger 16 in the direction of the arrow 52 and
out through the exhaust outlet duct 20, as shown by the dotted
arrows passing through the heat exchanger in FIG. 1.
[0031] The flow paths taken by the outside air and the exhaust air
through the heat exchanger 16 are isolated from one another so that
the two air streams do not intermingle, thus helping to protect
against contamination of the incoming outside air.
[0032] The outside air flowing through the duct 24 flows through
other ducts (not shown) and usually is delivered to one of three
locations. Either it is mixed with return air entering the system
at 30 and delivered to a heating/refrigeration unit 32 to either
heat or cool the air, or it is delivered directly into the enclosed
space 12, as indicated by the arrow 49.
[0033] It should be understood that in ventilating some spaces,
such as in hospitals and other critical environments, it is desired
to use 100% outside air for heating or cooling in the enclosed
space, thus maximizing the protection against air contamination. In
such circumstances, the outside air is not mixed with the return
air.
[0034] Temperature sensors are provided at 84 and 86, the inlet to
the exhaust duct 22 and the inlet to the outside air duct 18,
respectively, or at other suitable locations. The temperature
sensor 84 senses the actual indoor temperature, and provides a
corresponding electrical signal. Similarly, the temperature sensor
86 senses the outside air temperature and provides a corresponding
signal.
[0035] These signals are delivered to the microprocessor-based
controller shown in FIG. 4, which uses the temperature signals to
control the operation and to selectively control the exchange of
heat between the exhaust and outside air streams and other
functions to be described below.
[0036] FIG. 5 is a perspective view of a typical installation of
the ventilating system 10 and a heating/refrigeration unit 32 on
the roof 47 of a building. The unit 10 is shown separated from the
unit 32 for the sake of clarity in the drawings.
[0037] Return air from the building returns to the unit 32 through
the duct 43 and part or all of it flows through the exhaust conduit
22, through the, eat exchanger (not shown in FIG. 5) and out
through the exhaust outlet.
[0038] Outside air enters the unit 10 and flows either through the
heat exchanger along path 46, or through a by-pass 66 and gravity
louvers 76 (to be described below) to the outside air duct 24,
which is connected to the unit 32 through a fitting 45.
HEATING MODE
[0039] The first mode of operation to be described is one in which
heating of the enclosed space is required by a furnace or other
heating means. Usually, the outside air temperatures are below
50.degree. F. when heating of the interior space in most commercial
buildings is required. However, the outside air temperature at
which heating is first needed can be considerably lower, e.g.,
35.degree. F., for buildings with large internal heat sources, such
as large banks of computers or intense lighting, or solar
energy-absorbing surfaces, etc. Of course, this temperature also
can be higher, where the internal heat generation is at a low
level.
[0040] In residential buildings, the temperature at which heating
is first required usually is considerably higher, say 60.degree. F.
or 65.degree. F., because internal heat generation usually is lower
than in most commercial buildings.
[0041] As it will be described below in connection with FIG. 4, the
operation of the ventilating system is controlled by a programmed
microprocessor 96. The heating mode is started when the outside air
temperature reaches a pre-determined level which can be different
for each building or space within a building. For this reason, the
microprocessor is of the field-programmable variety so that the
heating mode start point can be set independently for each
building.
[0042] The fans 26 and 28 are variable-speed fans. During the
heating mode of operation, preferably the fans 26 and 28 operate at
or near maximum speed, thus providing pre-heating of the outside
air entering the enclosed space so as to reduce the cost or heating
the space.
[0043] Of course, the speeds of the fans 26 and 28 can be varied as
desired to increase or decrease the corresponding air flows as
required by the enclosed space.
SUPPLEMENTAL COOLING MODE
[0044] In accordance with the present invention, a supplemental
cooling mode of operation of the ventilating system is provided in
which outside air is taken in but heat transfer between the exhaust
air and the outside air is reduced or eliminated so that the cool
air will not be heated substantially by the exhaust air and will be
supplied at or near the outside temperature for use in cooling the
interior of the enclosed space.
[0045] Usually, this mode of operation occurs when the temperature
in the enclosed space, as sensed by the temperature sensor 84, is
above a desired level, e.g., 70.degree. F., so that cooling is
needed, while the outside air temperature is below the desired
level. Typically, the supplemental cooling mode will most often be
desired when the outside air temperature is in the 50.degree. F. to
70.degree. F. range.
[0046] By this means, the natural cooling potential of the outside
air can be used to cool the enclosed space, either with or without
the use of refrigeration or other cooling.
[0047] This mode of operation is particularly advantageous because
many commercial buildings require cooling when outside temperatures
are relatively low. For example, because of the use of substantial
amounts of heat-generating computers or other office machines,
indoor lighting, groups of people, solar heating through building
windows, etc., many commercial buildings have a heat build-up which
is not dissipated by only moderately cool outside temperatures, so
that cooling is required.
[0048] During this mode of operation, heat exchange between the
exhaust air and outside air is reduced or eliminated by one of
several different methods. Only the simplest one will be described
here. That is to simply slow or stop the exhaust fan 28 so that
either less or no exhaust air will pass through the heat exchanger
and heat the incoming outside air. Other methods will be described
below.
COOLING MODE
[0049] This mode of operation is used when the outside air
temperature is above that desired for the enclosed space. When the
weather outside is hot, and the air exhausted from the enclosed
space is cooler than that coming in from outside, the exhaust air
cools the outside air in the heat exchanger 16 before it enters the
enclosed space. If necessary, the outside air then can be sent to a
refrigeration unit 32 to be cooled further. This can significantly
reduce the load on the refrigeration unit and reduce the cost of
hot weather air conditioning. Some de-humidification of the outside
air also is accomplished.
[0050] As during the heating mode, preferably, both fans 26 and 28
are operated at maximum speed.
OUTSIDE AIR BY-PASS
[0051] In accordance with another aspect of the present invention,
a by-pass conduit 66 is provided for introducing outside air into
the enclosed space 12 under selected conditions. By-pass conduit 66
also has its own independently operable variable speed fan 68 for
delivering outside air into the outside air duct 24.
[0052] One of the conditions in which the by-pass duct is useful is
during the supplemental cooling mode of operation described above.
During this mode, heat transfer between the exhaust air and the
outside air can be prevented without stopping the exhaust fan 28
simply by slowing or stopping the fan 26 and running the fan 68.
This allows warm interior air to be exhausted and cool outside air
to be introduced, with less or no heating of the outside air.
[0053] Another advantage of the invention is that the by-pass can
be used for two different functions; it can be used as a
supplemental cooling mode by-pass, as described above, and in
defrosting the heat exchanger.
LOUVER SYSTEM
[0054] The optional louver system for use in conjunction with the
by-pass, and also for other functions, now will be described.
[0055] A set of gravity-type louvers is provided at 76 at the exit
of the by-pass 66 into the duct 24.
[0056] A set of motorized louvers 70 is provided in a septum or
wall 36 separating the ducts 18 and 20.
[0057] Two other motorized louvers 72 and 74 are provided,
respectively, at the entrances to the ducts 18 and 20.
[0058] Additional gravity-operated louvers 78 are provided at the
outlet from the housing 14 into the duct 24.
[0059] Gravity-operated louvers open in response to an air pressure
differential in one direction, but close either under gravity or
pressure in the opposite direction. In general, it is preferred to
use gravity-type louvers instead of motor-driven louvers, wherever
possible because they tend to operate smoothly over long periods of
time without significant maintenance and also are less complicated
and expensive. Gravity louvers work either in a vertical or
horizontal orientation.
[0060] The operation of the louvers during various different phases
of the operation of the system will be described below.
DEFROST MODE
[0061] The exhaust air from the enclosed space during the cooling
mode has a certain level of humidity, say, 55% or thereabouts. When
the warm, humid air from the interior of the enclosed space passes
through the cold heat exchanger, moisture condenses from the air
and condensate and water runs downwardly out of the heat exchanger
and through holes in perforated floor panels 54 and 56 of the
housing 14 to drip pans 58 and 60 with drains 62 and 64 for
removing the accumulated water. The drip pans are isolated from one
another by a septum or wall 59 in order to preserve the isolation
of the outside air path from the exhaust air path.
[0062] When the outside air temperature is very low, the water
accumulating in the heat exchanger starts to freeze and clog up the
passages in the heat exchanger. This reduces the heat exchange
efficiency of the heat exchanger, increases the pressure drop
across the heat exchanger, and can totally disable it. Therefore,
means are provided for defrosting the heat exchanger when freezing
conditions are detected.
[0063] Freezing conditions are detected preferably by means of a
temperature sensor 88 mounted near the lower portion of the heat
exchanger where ice tends to accumulate first. When the temperature
sensed by the sensor 88 reaches freezing (32.degree.
approximately), the temperature sensor sends a signal to the
control system which starts the defrost operation.
[0064] In its simplest form, the defrost operation comprises simply
reducing the speed of the outside air fan 26 while leaving the
speed of the exhaust fan 28 at its original maximum speed, thus
reducing the cooling of the heat exchanger and allowing the warmth
of the exhaust air to melt the ice in the heat exchanger and bring
its temperature up to above the freezing level. When the
temperature sensed by the sensor 88 rises to the desired level
again, the speed of the fan 26 is restored to its previous
level.
[0065] This operation is repeated as often as necessary to prevent
icing of the heat exchanger.
[0066] The simple defrosting method described above is adequate in
many circumstances. However, more heating of the heat exchanger may
be required in order to defrost it. If so, the intake of outside
air can be stopped completely for a time until the temperature of
the heat exchanger rises.
[0067] In accordance with another aspect of the invention, if it is
desired to maintain the flow of outside air into the enclosed space
at a steady level, even during defrost, then the fan 68 in the
by-pass duct 66 can be turned on to bring in outside air without
passing it through the heat exchanger, to either supplement the air
brought in by the slowed fan 26, or to replace it entirely.
[0068] It is possible that further heating of the heat exchanger
beyond that provided by the means described so far would be
necessary. In such cases, by closing the louvers 72 and 74 and
opening the louvers 70, the exhaust air is re-circulated back
through the outside air flow passages and into the enclosed space,
thus using the residual heat in the exhaust air for further heating
and defrosting. Thus, exhaust air exiting the heat exchanger can
pass upwardly from conduit 20 into conduit 18, through the outside
air passages in the heat exchanger, and out through the duct 24
back into the enclosed space.
[0069] Even further heating of the heat exchanger can be provided
by other means such as the introduction of steam into the inlet 91
in the duct 18 so as to preheat the outside air before it reaches
the heat exchanger. Of course, this requires additional energy and
should be restricted to uses in which it is considered most
beneficial, such as in hospitals and other institutions. Other heat
sources also can be used to supply the necessary supplemental
heat.
[0070] When the by-pass fan 68 is operated, the air pressure it
produces lifts the louvers 76 and allows air to pass into the duct
24. If there is no air flow created by the fan 26 through the
louvers 78, the back pressure produced by the fan 68 closes the
louvers so that outside air does not flow backwardly through the
heat exchanger.
[0071] Means other than a temperature sensor can be used to detect
freezing conditions. For example, air pressure sensors to detect
the change in pressure caused by ice formation are known in the
prior art can be used, if desired.
EVAPORATIVE COOLING
[0072] During the cooling mode of operation, it is preferred to use
a relatively low-cost method of further reducing the temperature of
incoming outside air so as to decrease the cooling load on the
refrigeration system. This is provided by an evaporative cooling
system including a spray nozzle 94 (FIG. 1) and a solenoid-operated
valve 92 selectively supplying pressurized water from the supply
line 90 to the spray nozzle 94. The spray 94 sprays water into the
exhaust air before it enters the heat exchanger 16.
[0073] Preferably, the water from the spray nozzle 94 is sprayed
onto an air-permeable membrane 82 which covers the exhaust air
entrance to the heat exchanger.
[0074] FIG. 2 is a perspective view of the heat exchanger 16
showing the membrane 82 (broken away). The membrane 82 preferably
comprises a thin mat of synthetic fibers such as those used in
ordinary air filters so as to enhance the evaporation of the water
in the exhaust air stream to give evaporative cooling of the
exhaust air. Such a mat is made of fibers which do not deteriorate
due to prolonged contact with water and the air which impinges on
the membrane.
[0075] Alternatively, as shown in FIG. 2, water can be dripped from
one or more pipes 83 with holes 85 in it to drip water onto the
membrane. The water migrates downwardly through the membrane under
the force of gravity.
[0076] Any water which accumulates in the heat exchanger due to the
water spray will drain out through the bottom of the heat exchanger
and into the drip pans 58 and 60, the same as condensate.
[0077] Evaporative cooling can reduce the temperature of the
incoming air by a very significant amount, and is not very costly
in terms of either materials or energy required. Therefore, it is a
very cost-effective way of preconditioning the outside air to
reduce the energy requirements of the refrigeration system. Again,
as with other operations of the system, the evaporative cooling
equipment preferably is turned on in response to the detection of
an outside air temperature which is greater than the desired inside
air temperature by a certain minimum amount.
[0078] For example, the minimum temperature difference in question
might be 3 to 10 degrees Farenheidt. Thus, if the outside
temperature were 72 degrees and the desired space temperature is
70.degree. F. and the minimum differential is 10 degrees, the
evaporative cooling system would not operate. When the outside air
temperature reaches 80 degrees, the evaporative cooling system will
turn on and operate continuously until the outside air temperature
drops below the desired level.
CONTROL SYSTEM
[0079] FIG. 4 shows schematically the control circuit of the
ventilation system of the present invention. A microprocessor 96 is
provided and programmed so as to control both the turning on and
off and the speed of each of the fans 26, 28 and 68 in response to
the signals sent to the microprocessor by the temperature sensors
84, 86 and 88. Operating signals are sent by the microprocessor
also to the louver motors 71, 73 and 75 to operate the powered
louvers and the solenoid valve 92 to start and stop the water spray
for the evaporative cooling system described above.
[0080] As noted above, it is preferred that the microprocessor be
field-programmable to allow the variation of set-points, etc. for
each installation.
[0081] The microprocessor also is programmed to have certain
"dead-bands" around the various control points to prevent excessive
"hunting". Preferably, the dead-bands also are field-programmable
in order to enable the customization of the system for a particular
enclosed space.
[0082] For example, a dead-band of 3.degree. F. to 5.degree. F. or
more around each set-point can be beneficial. Manual over-ride also
can be provided to enable adjustments for special circumstances.
Automatic control of some set-points also can be provided. For
example, the switch-over from supplemental cooling mode to heating
mode can be delayed, even though a sudden cold-snap reduces the
outside air temperature to below the heating mode set-point, if the
inside air temperature is still high enough to require cooling.
HEAT EXCHANGER
[0083] The heat exchanger 16 has a rectangular shape and preferably
is made of plastic. It is preferred that the heat exchanger be of
the type shown in U.S. Pat. No. 4,820,468 to M. J. Hartig, which is
sold by the Hartig Company, Wilmington, Del.
[0084] The structure of this heat exchanger is illustrated in FIGS.
2 and 3, and particularly in FIG. 3. The heat exchanger structure
comprises a plurality of plastic extrusions 100 with closely spaced
parallel passageways 104 separated by square extruded channel
members 102 extending perpendicular to the direction of the
passageways 104. Although only two of the extrusions 100 and a pair
of channel members are shown in FIG. 3, for the sake of simplicity
in the drawings, it should be understood that there are many
extrusions and channel members in the typical heat-exchanger.
[0085] Each extrusion 100 comprises a solid top sheet 101 and a
solid bottom sheet 103 with multiple vertical walls forming the
passageways 104. Thus, crossed air flow paths are formed by the
passageways 104, on the one hand, and the spaces 106 between the
channel members and the hollow interiors of the members 102. These
crossed flow paths are isolated from one another by the solid
sheets 101 and 103. The extrusions 100 and 102 are heat-welded
together to form a strong, lightweight corrosion-resistant heat
exchanger.
[0086] The exhaust air preferably flows through the larger
passageways 106, as indicated by the arrow 50, and the outside air
flows through the passageways 104. This arrangement is preferred
because the exhaust air may have entrained water droplets and
condensation and ice may form in the exhaust air passageways so
that the larger passageways will remain operative for heat transfer
over a wider range of operating circumstances than if the smaller
passages were used. Although condensation also will occur when hot,
humid outside air is cooled in the heat exchanger, it is believed
that the larger passageways will better suit the conduct of exhaust
air.
[0087] The material of which the heat exchanger 16 is made
preferably is polyethylene or polypropylene, or other plastic
materials which also are impervious to deterioration under
prolonged contact with water and flowing air.
[0088] Equivalent heat exchangers also can be used in the practice
of the invention. For example, isolating heat exchangers made of
various metals can be used, as well as heat pipes whose ends are
isolated from one another with one end in the outside air flow and
the other in the exhaust air flow. Hydronic heat exchangers with
liquid working fluids also can be used.
[0089] The plastic heat exchanger described above is advantageous
over the usual metal heat exchanger, even though the heat
conductivity of the plastic is considerably lower than that of the
metal. The plastic lasts a very long time without corroding and is
considerably less expensive than metal. Also, the plastic heat
exchanger is less expensive to manufacture than metal heat
exchangers. The added volume required for the plastic heat
exchanger to exchange the same amount of heat as a metal heat
exchanger is more than offset by the foregoing advantages.
[0090] The plastic heat exchanger is believed to be particularly
advantageous when used with evaporative cooling because any scale
which forms from the water spray can be broken free relatively
easily by flexing the heat exchanger.
[0091] The above description of the invention is intended to be
illustrative and not limiting. Various changes or modifications in
the embodiments described may occur to those skilled in the art.
These can be made without departing from the spirit or scope of the
invention.
* * * * *