U.S. patent application number 12/807018 was filed with the patent office on 2012-03-01 for heat recovery and demand ventiliation system.
Invention is credited to Richard S. Kurelowech.
Application Number | 20120052791 12/807018 |
Document ID | / |
Family ID | 45697889 |
Filed Date | 2012-03-01 |
United States Patent
Application |
20120052791 |
Kind Code |
A1 |
Kurelowech; Richard S. |
March 1, 2012 |
Heat recovery and demand ventiliation system
Abstract
A ventilation system for an air conditioning system includes
dampers, a heat exchange unit, and a control unit. One damper
controls the flow of ambient air into the system. The other damper
controls the flow of relief/exhaust air that is cannibalized from
return air from a room or space being cooled (or heated) by the air
conditioning system. The ventilation system utilizes a control
algorithm in the control unit to calculate, at stepped spaced apart
increasing room ventilation rates, increasing CO2 concentrations in
the air in the room that are below a maximum desired CO2
concentration in a room. The control algorithm permits a control
unit in the ventilation system to open and close the dampers to
maintain a CO2 concentration in the room that is below the desired
CO2 concentration level.
Inventors: |
Kurelowech; Richard S.;
(Phoenix, AZ) |
Family ID: |
45697889 |
Appl. No.: |
12/807018 |
Filed: |
August 26, 2010 |
Current U.S.
Class: |
454/329 |
Current CPC
Class: |
F24F 11/77 20180101;
Y02B 30/70 20130101; F24F 2110/70 20180101; F24F 2011/0006
20130101; F24F 2110/50 20180101; F24F 11/30 20180101 |
Class at
Publication: |
454/329 |
International
Class: |
F24F 7/007 20060101
F24F007/007 |
Claims
1. In combination with a building structure including a room with a
maximum occupancy rating of at least twenty people per 1,000 sq. ft
of occupied space, an air conditioning system including a heat
transfer coil, a first section of duct (D4) leading to the heat
transfer coil to direct supply air from the building structure over
the coil, and a second section of duct (D2) leading away from the
heat transfer coil to carry air from the coil back into the
building, the improvements in the building structure comprising (a)
a ventilation control unit attached to the first section of duct
and including (i) a housing (23), (ii) a heat exchange unit (12),
(iii) a third section of duct (D1) connected to said first section
of duct (D4) to direct a first portion of return air from the room
into said first section of duct, (iv) a fourth section of duct (D3)
to direct a second portion of return air from the room over said
heat exchange unit, (v) a fifth section of duct (D5) to direct
ambient air over said heat exchange unit into said third section of
duct (D1), said heat exchange unit maintaining said second portion
of return air separate from said ambient air and transferring heat
between said second portion of return air and said ambient air,
(vi) a sixth section of duct (D6) to direct said second portion of
return air from said heat exchange unit into the outside
atmosphere, (vii) an outlet damper (16) controlling the flow of
said second portion of return air over said heat exchange unit (12)
and into the outside atmosphere, (viii) an inlet damper (15)
controlling the flow of said ambient air over said heat exchange
unit (12), (ix) a control unit operatively associated with said
inlet and outlet dampers to control the rate of flow of said
ambient air and said second portion of said return air,
respectively, through said dampers, (x) a first flow sensor
operatively associated with said inlet damper to generate signals
to said control unit representing the rate of flow of ambient air
through said inlet damper, (ix) a second flow sensor operatively
associated with said outlet damper to generate signals to said
control unit representing the rate of flow of ambient air through
said outlet damper, (x) a CO2 sensor in the room to generate
signals to said control unit representing the concentration of CO2
in the air in the room; (b) a first fan to direct said ambient air
into said fifth section of duct, over said heat exchanger, and into
said first section of duct; (c) a second fan to direct said second
portion of return air from said fourth section of duct, and through
said fourth section of duct over said heat exchanger, and into the
atmosphere; (d) a control algorithm in said control unit to
calculate, at stepped spaced apart increasing room ventilation
rates, increasing CO2 concentrations in the air in the room that
are below a maximum desired CO2 concentration in the room.
Description
[0001] This invention relates to heating and air conditioning
systems.
[0002] More particularly, the invention relates to a system to
facilitate ventilation air heat recovery and volume management
while maintaining a high indoor air quality for human occupants.
This invention will substantially reduce the energy consumption of
heating and air conditioning systems in commercial and
institutional buildings with high occupant densities (greater than
20 people per 1,000 square feet of occupied space).
[0003] Commercial and institutional buildings have long been
equipped with constant air volume ventilation systems which employ
a means for outside air to enter and leave the building. Recent
technology also employs ventilation air volume control utilizing
CO2 sensors and operable dampers. Such systems are controlled using
a single point CO2 level as the ventilation reference value and the
objective is to prevent objectionable odors and vapors from
accumulating in buildings.
[0004] It has for many years been desirable to provide, when
possible, improvements to such ventilation air systems.
[0005] Therefore, it is a principal objective of this invention to
provide an improved system to ventilate a building in the most cost
effective, energy efficient manner, and meet the requirements of
indoor air quality standards developed by recognized authorities in
the industry, specifically, ASHRAE Standard 62.1-2010.
[0006] This and other further objects will be apparent to those
skilled in the art from the following detailed description thereof,
taken in conjunction with the drawings, in which:
[0007] FIG. 1 illustrates a retrofit module constructed in
accordance with one embodiment of the invention and installed in a
pre-existing air conditioning or heating system;
[0008] FIG. 2 further illustrates the retrofit module of FIG.
1;
[0009] FIG. 3 illustrates an IRV graph prepared in accordance with
the system of the invention;
[0010] FIG. 4 is a block flow diagram illustrating a heat transfer
and ventilation control system constructed in accordance with the
invention; and,
[0011] FIG. 5 is a block flow diagram illustrating a logic sequence
utilized by a controller in the system of the invention illustrated
in FIG. 4.
[0012] Briefly, in accordance with the invention provided are heat
recovery and ventilation improvements in combination with a
building structure. The building structure includes a room with a
minimum occupancy density of 20 people per 1,000 square feet, an
air conditioning system including a heat transfer coil, and a first
section of duct D4 leading to the heat transfer coil of the air
conditioning unit 22 to direct return air from the building
structure over the coil. The building structure also includes a
second section of duct D2 leading away from the heat transfer coil
to carry conditioned (heated or cooled) supply air S1 from the coil
back into the building. The ventilation improvements in the
building structure comprise a retrofit heat recovery and
ventilation control unit (DVHR) connected to the first section of
duct D4. The DVHR unit includes a housing; a heat exchange unit 12;
a section of duct D5 operatively associated with an outside ambient
air source fan 13 to direct ambient air over the heat exchange unit
12 and into the first section of duct D1; an inlet damper 15
controlling the flow of ambient air into duct section D5 and over
the heat exchange unit into the first section of duct D1; a section
of duct D3 connected to the first section of duct to direct a
portion R2 of the return air flowing through the first section of
duct over the heat exchange unit and into the duct section D6
directing the air to the outside atmosphere via exhaust/relief fan
14; an outlet damper 16 controlling the flow of the portion of
return/exhaust air R2 from the first section of duct D1 over the
heat exchange unit and into the outside atmosphere; a control unit
30 operatively associated with the inlet and outlet dampers to
control the rates of flow of ambient and exhaust/relief air,
respectively, through the dampers; a first flow sensor 20B
operatively associated with the inlet damper to generate signals to
the control unit representing the rate of flow of ambient air
through the inlet damper 15; a second flow sensor 21 operatively
associated with the outlet damper 16; and a CO2 sensor in the room
to generate signals to the control unit 30 representing the
concentration of CO2 in the air in the room. The DVHR also includes
a first fan 13 to direct ambient air into the section of duct D5,
over the heat exchanger 12, and into the first section of duct D1;
a second fan 14 to direct return/exhaust air R2 through the first
section of duct D1, through the heat exchanger 12, and through duct
section D6 and into the atmosphere. The ventilation control system
also includes an algorithm in the control unit 30 to calculate, at
stepped spaced apart increasing room ventilation rates
corresponding to increases in room occupancy, acceptable CO2
concentrations below a maximum desired CO2 concentration in the
room, and to increase or decrease the outside air ventilation rate
to achieve the acceptable CO2 concentration.
[0013] In another embodiment of the invention, I provide
improvements in combination with a building structure. The building
structure includes a room with a maximum occupancy rating of at
least twenty individuals per 1000 sq. ft. of occupied space, and an
air conditioning system. The air conditioning system includes a
heat transfer coil; a first section of duct (D4) leading to the
heat transfer coil to direct return air from the building structure
over the coil; and, a second section of duct (D2) leading away from
the heat transfer coil to carry air from the coil back into the
building, The improvements in the building structure comprise a
retrofit ventilation control unit. The unit is attached to the
first section of duct and includes a housing (23); a heat exchange
unit (12); a third section of duct (D1) connected to the first
section of duct (D4) to direct a first portion of return air from
the room into the first section of duct; a fourth section of duct
(D3) to direct a second portion of return air from the room over
the heat exchange unit; a fifth section of duct (D5) to direct
ambient air over the heat exchange unit into the third section of
duct (D1). The heat exchange unit maintains the second portion of
return air separate from the ambient air and transfers heat between
the second portion of return air and the ambient air. The
ventilation control unit also includes a sixth section of duct (D6)
to direct the first portion of return air from the heat exchange
unit into the outside atmosphere; an outlet damper (16) controlling
the flow of the second portion of return air over the heat exchange
unit (12) and into the outside atmosphere; an inlet damper (15)
controlling the flow of the ambient air over the heat exchange unit
(12); a control unit operatively associated with the inlet and
outlet dampers to control the rate of flow of the ambient air and
the second portion of the return air, respectively, through the
dampers; a first flow sensor operatively associated with the inlet
damper to generate signals to the control unit representing the
rate of flow of ambient air through the inlet damper; a second flow
sensor operatively associated with the outlet damper to generate
signals to the control unit representing the rate of flow of the
ambient air through the outlet damper; and, a CO2 sensor in the
room to generate signals to the control unit representing the
concentration of CO2 in the air in the room. The improvements also
include a first fan to direct the ambient air into the fifth
section of duct, over the heat exchanger, and into the first
section of duct; a second fan to direct the second portion of
return air from the fourth section of duct, and through the fourth
section of duct over the heat exchanger, and into the atmosphere;
and, an algorithm in the control unit to calculate, at stepped
spaced apart increasing room ventilation rates, increasing CO2
concentrations in the air in the room that are below a maximum
desired CO2 concentration in the room.
[0014] Turning now to the drawings, which depict the presently
preferred embodiments of the invention for the purpose of
illustrating the use thereof and not be way of limitation of the
scope of the invention, and in which like reference characters
refer to corresponding elements throughout the several views, in a
preferred embodiment of the invention, the EMS (Energy Management
System) serves primarily as a diagnostic tool to provide graphic
user interface (GUI) capability for the entire campus HVAC and
lighting systems. The GUI comprises a computer screen with graph
interface software and includes (1) on screen representation of
ambient air flow in cfm, (2) on screen representation of
exhaust/relief air flow in cfm, (3) on screen representation of
mode of operation i.e. (i) heat recovery heating mode (changeover
function), (ii) heat recovery cooling mode (changeover function),
and (iii) economizer cooling mode (changeover function), (4) on
screen representation of occupied `active` or `inactive` mode, (5)
on screen representation of which segment CO2 concentration limit
is prevailing, (6) on screen representation of room CO2
concentration level, and (7) alarm functions associated with no air
flow when dampers are expected to be in some open position or
registering air flow, open damper position, when no air is to be
moving. Room ventilation control functions and all algorithm
defining characteristics, formulae and changeover functionality are
embedded in the programmable controller hardware control board and
processor. Ventilation control functions include (1) determining if
the DVHR is to operate in the heat recovery mode or economizer mode
based on outside air temperature (changeover functions), (2)
calculating the IRV based on the algorithm, (3) varying the outside
ambient air damper to maintain the proper CO2 concentration limit,
and (4) varying the exhaust/relief air damper position to maintain
the correct volume of air based on the outside/ambient air
quantity. Changeover functions include (1) heat recovery heating
mode (changeover function), (2) heat recovery cooling mode
(changeover function), and (3) economizer cooling mode (changeover
function). Input variables, i.e. room square footage, room
ventilation rate (Va), people ventilation rate (Vp), (Occmax), are
transmitted to the controller from external sources, i.e. plug-in
interface tools, a keyboard or other data input means. It is the
intent of this embodiment of the invention to maintain a maximum
steady state ventilation to achieve less than the 700 ppm CO2 level
exposure limit defined in ASHRAE 62-200. The maximum steady state
ventilation rate is the calculated IRV based on the two independent
ventilation rates of people and area. The steady state feature
defines that the 700 ppm concentration increase in CO2 above
ambient is accounted for in the algorithm in addition to the area
ventilation requirement. Further, the energy recovery principles
employed in this embodiment of the invention transfer a minimum of
60% of the differential dry bulb temperature energy from the high
air stream temperature to the lower air stream temperature.
[0015] During the summer (cooling) months, the higher outside air
temperature is transferred to the lower room relief air
temperature. During the winter (heating) months, the higher room
relief air temperature will transfer its heat to the lower outside
air temperature. During periods of time when free cooling is
available, the heat recovery (temperature transfer) unit is
by-passed. Heat recovery in the cooling mode should be active at
about 80.degree. F. ambient temperatures and higher. Heat recovery
in the heating mode should be active at about 50.degree. F. ambient
temperatures and lower. Economizer cooling should be the
temperatures in between. These temperatures are usually `field`
adjustable so that when extreme conditions exist, the changeover
temperatures can be reset without completely reprogramming the
controller.
[0016] High occupant spaces historically experience transient and
variable occupant loads. Prior to the 2010 version of ASHRAE
62.1-2010, indoor air quality (IAQ) standards defined constant use
ventilation rates which influenced sizing of heating and cooling
systems based on peak occupant loads. ASHRAE 62.1-2010 explains the
intent of the ventilation standards with respect to volatile
organic compound (VOC) dilution ventilation and CO2/physiological
odor management. Two ventilation rates are independently derived to
meet these separate IAQ comprising conditions and the sum of the
two rates are intended to define the stead state rate CO2+VOC
dilution rates to achieve a maximum CO2 exposure of 700 ppm above
ambient.
[0017] The approach discussed below concerns the proper control of
ventilation (ambient) air which is introduced into a room.
The Approach
[0018] ASHRAE 62.1-2010 requires a minimum cubic foot per minute
(cfm) of outside air (Va) per square foot (sf) of occupied space
(i.e., space in a room) for VOC dilution. Additionally, each person
is assigned a ventilation value (Vp) in cfm per person for CO2/odor
management which is based on occupant occupation or activity. All
CO2 ventilation rates have been developed with the intent that a
change of CO2 concentration in an occupied room will not be
objectionable if the CO2 level is kept below 700 ppm above the
outside ambient CO2 level. Since CO2 sensors measure the total CO2
in air, ambient CO2 levels (OSACO2) need to be measured. Ambient
CO2 levels normally are in the range of 300 to 500 ppm. The maximum
desired total CO2 concentration in a room in parts per million
(ppm) is then equal to (OSACO2+700), or 1000 to 1200 ppm. When a
ventilation system operates during periods when a room is occupied,
and when a low occupant count is in the room, the CO2/odor
management dilution rate can be met with the minimum VOC
ventilation rate. The minimum ventilation rate equals (Va)(x),
although this is a logical expression ASHRAE still requires
separate dilution ventilation rates for CO2, even though it appears
the VOC dilution rate can achieve both criteria.
[0019] If priority is placed on meeting the VOC ventilation
requirements independently of the CO2 ventilation requirements,
then upon start of any initial space ventilation sequence, the VOC
dilution ventilation rate will define any minimum ventilation rate
requirement. If the VOC dilution air quantity remains an
independent ventilation air quantity (variable) in the total
required steady state ventilation rate calculation, the resultant
CO2 ppm concentration will always be substantially lower than the
maximum allowable 700 ppm exposure limit, even at full occupancy of
the room. [0020] 1. The control logic for the ventilation set forth
in the approach discussed above requires an algorithm to define and
respond to the rate of change in the occupancy of a room. A minimum
unreduced VOC dilution ventilation air flow rate, (Va)(x) (where
x=the sq. ft. area of a room), remains a constant to the controller
when the room is occupied. ASHRAE 62.1-2010 defines a quantity of
ambient ventilation air, Vp, per person to insure that the CO2
concentration in a room does not exceed a desired maximum
concentration. Presuming that the Vp is calculated to insure that
the CO2 concentration in a room does not exceed 700 ppm above the
concentration, OSACO2, in the ambient air, then the outside air
flow increases in response to an increase in occupant respiration
(i.e., in response to an increase in the number of occupants in a
room or a change in their activity level), and incremental target
CO2 levels or checkpoints, RV, are defined to simultaneously
achieve a constant VOC dilution ventilation rate and respond to
increasing and decreasing occupancy of a room. The controller
ventilation algorithm described below uses increases or decreases
in room occupancy in incremental selected segments, where n is the
number of segments selected, IRV is the size in cfm of each
segment, and IRVpt is the estimated cumulative number of persons in
a reset segment and any preceding reset segment. The number, and
therefor the size, of each segment is adjusted as desired.
[0021] The design airflow of the VOC dilution ventilation (i.e.,
the base ventilation rate of Rb=(Va)(x)) plus the CO2 control
ventilation (i.e., the size of each segment, IRV, times the number
of segments S.sub.(1, 2, 3 . . . n)) is the divisor in the
algorithm. The dampers 15, 16 (FIG. 1) which regulate the amount of
outside air to the space have a defining minimum VOC dilution air
flow, (Va)(x), as the initial open position. The occupied mode is
determined by time schedule stored in the control unit 30 or by an
occupant sensing mechanism operatively associated with the control
unit 30. A velocity sensor utilizing a transducer records the inlet
air flow quantity and adjusts the damper position to maintain a
minimum set point. This is a pressure independent control function
which is employed for air quantity and quality management functions
of all air flow regulating devices in the system. When, as room
occupancy increases, a maximum cfm of incoming ambient ventilation
air, IRVcfm, is reached for a segment, the CO2 limit (i.e., the RV)
for that segment is the upper CO2 limit for the prior segment. The
minimum VOC ventilation rate=(Va)(x). This would suggest that the
CO2/odor management rate is a duplicate of the minimum VOC
ventilation rate. ASHRAE does not recognize this comparative
analysis.
[0022] The control unit 30 achieves this upper CO2 by adjusting the
damper that regulates the flow of incoming ambient air. In
contrast, when the occupancy levels in a room decreases and the CO2
concentration in the room drops, the maximum cfm of a segment,
IRVcfm, must be overshot by a selected amount before the target CO2
concentration is altered. For example, if in the system represented
in FIG. 3, the room occupancy and CO2 concentration are decreasing,
when the CO2 level reaches 668 ppm, coinciding with 228 cfm, the
control unit 30 does not adjust the damper to achieve a CO2
concentration of 668 ppm (at 228 cfm) from 738 ppm (above 228 cfm)
until the value drops to below the IRV cfm quantity of 228 by at
least 10% of the difference of the segment air quantity, which in
this case is 60 cfm.times.10%=6 cfm. This will allow the IRV to
change once the outside air quantity reduces to less than 222 cfm.
This percentage is a field adjustable value based on the normal
occupancy of the space and how quickly it can gain or lose
occupants. Its use is for this example.
[0023] When a building starts in the occupied `inactive` mode, the
ventilation rate is at its minimum. If no one enters the room, the
room CO2 concentration will be essentially the ambient CO2 level.
It is the intent of the control function to move to the first
calculated segment RV upon occupant entry into the room. There is
no way the ambient CO2 level of the room can be maintained once
people enter. Therefore, the RV adjustment takes place once the air
quantity exceeds its segment limit. Using FIG. 3, RV2@550 ppm will
be the first occupied `active` value. At 300 ppm (RV1), the
ventilation rate is in the occupied `inactive` mode.
[0024] The various necessary ventilation criteria set forth below
are incorporated in the control unit 30 (FIG. 1). In one embodiment
of the invention, ASHRAE 62.1-2010 VOC and CO2 management air flow
rates are provided via a handheld plug-in. In another embodiment,
this data is programmed into the control unit 30. When ASHRAE
62.1-2010 ventilation data is revised, a plug-in or any other
desired data entry system is utilized to update the control unit
30.
[0025] Prior art ventilation systems typically have either fixed or
on/off flow rates. Outside air introduced into a room or other
space must be relieved from the space. When a space has no operable
windows or doors which communicate with outside (ambient) air, the
intake and relief systems permit equal volumes of air in and air
out. Gravity air relief systems are most common. Exterior relief
hoods or louvers are connected to a building or space via either a
direct duct and grille in the ceiling, or a return/relief air grill
in the ceiling which communicates with a return/relief air
plenum.
[0026] During any ambient climate temperature condition, when the
outside air can provide a lower temperature source to the air
conditioning system than the set point of the temperature sensor
without over cooling the space, the outside air supply source
should not be tempered to a higher temperature in the heat exchange
unit 12 (FIG. 1). This defeats the cooling process. Instead, in one
embodiment of the invention, in the free cooling mode outside air
is introduced to the return air path in the manner indicated by
arrow A2 in FIG. 2, bypassing the heat exchange unit 12. This
lowers the return air temperature to the air conditioning unit 22,
thereby reducing the amount of compressorized cooling energy
required to maintain the set point temperature in a room or other
space. This is called the partial outside air economizer mode.
Excess air generated by introducing air in a room or other space
during the partial outside air economizer mode is relieved from the
space via a gravity relief air system. The gravity relief air
system has a back draft regulating damper to prevent outside air
from entering into the building when the air conditioner if off.
The back draft damper can be fitted with either a counterbalanced
barometric relief damper or an electronically operated motorized
damper. Either kind of damper will open when the air conditioner is
operating during the partial outside air economizer mode.
[0027] When the ambient climate temperature conditions are not
suitable for either free cooling or reduced compressorized cooling,
the gravity relief air system is disabled and the heat exchange
unit 12 is enabled. The heat exchange unit 12 works efficiently
down to about 20% of the maximum air flow rate. In the system
illustrated in FIG. 3, the maximum air flow rate is 408 cfm.
[0028] In the heat recovery mode of the module 10 (FIGS. 1 and 2)
of the invention, as the ventilation air quality increases and
decreases, dampers 15 and 16 are operated by the control unit 30.
The control unit 30 ordinarily comprises a microprocessor. The
control unit 30 utilizes the ventilation algorithm described below,
along with any other desired algorithms. Ambient air that is
introduced through damper 15 as ventilation air is compensated for
by exhaust/relief air R2 (FIG. 1) that is directed over heat
exchanger 12 and into the ambient atmosphere via damper 16. A
minimum desired flow rate for ambient air through damper 15 is
determined by the potential for trapping air borne particulates in
the heat exchange unit 12 when the air velocity drops to below the
manufacturer recommend air flow. Some manufacturers permit an air
flow rate that is less than 20% of the maximum desired air flow
rate over heat exchanger 12. In FIG. 3, the maximum desired air
flow rate of ventilation air is 408 cfm.
[0029] Where occupied spaces communicate with the outside ambient
air via operable windows and doors, a minor positive air pressure
is maintained to minimize migration of air borne particulates into
a room or other space. Such minor positive air pressures are not
set forth in published standards, but up to 20% of the design
maximum air flow rate (408 cfm in FIG. 3) can be diverted to the
pressurization mode with minimal energy recovery impact at the
design maximum desired air flow rate (i.e., air flow at peak
occupancy). In FIG. 3, the maximum air flow rate is 408 cfm. It is
recommended that no more than 10% of the maximum air flow rate
(i.e., in the system of FIG. 3 this would be 40.8 cfm) be relieved
for ventilation air flow up to 50% of the maximum air flow rate,
and that the 20% maximum pressurization air flow quantity should
not be exacted on the system until 80% of the design maximum
desired air flow rate is in use.
[0030] The heat recovery operation mode requires verifiable air
flow measurements for proper application of the ventilation
algorithm. In order to maximize the reduction in energy required to
operate the system, the flow rates of the incoming ambient
ventilation air and of the exhaust/relief air stream should be the
same or nearly the same. Toward this end, each air inlet (or
outlet) is provided with a velocity sensor 20A, 20B, 21. It may be
possible to use a common sensor for dampers 15 and 17 because these
dampers will not open together. Each sensor is preferably
calibrated and can operate to within 2% accuracy at velocity
pressures as low as 250 fpm (0.03'' velocity pressure) at sea
level.
[0031] During low occupant loads in a room or other building space,
only a minimal amount of exhaust air, R2, may be available for heat
recovery. During such periods of low ventilation air flow, however,
the outside air cooling load on the room air conditioning system is
also low, resulting in a minor increase to the cooling load of the
air conditioning equipment above minimum (no outside cooling load).
Algorithm calculated indoor air quality (IAQ) conditions are
continuously maintained regardless of the quantity of exhaust air,
R2, utilized.
[0032] The combination of heat recovery and demand ventilation
control enables a substantial reduction in energy use, enables
increased sustained IAQ, and enables enhancements in sustainable
system performance. Enhancements include: [0033] a. Reduction of AC
unit sizes based on the reduction of the cooling load [0034] b.
Reduction of electrical service size based on smaller electrical
loads of the smaller AC units [0035] c. Energy reduction of HVAC
system energy use of 25%-40% [0036] d. Improvements of indoor air
quality (IAQ)] [0037] i. Stable CO2 levels [0038] ii. Adequate VOC
dilution [0039] iii. Reduction of space temperature variations
[0040] iv. Noise reduction [0041] e. Reduction of the carbon
footprint with the reduction of required utility generation [0042]
f. Air conditioning system benefits [0043] i. Reduction of entering
air temperatures to the evaporator and the resultant high
differential pressures at the compressor [0044] ii. LEED compliance
for all refrigerant systems if the normal size refrigerant charge
is compared with the reduced unit size charge [0045] iii.
Minimizing excess outside air into the building when occupancy is
not at maximum [0046] iv. Partial outside air economizer use (not
available with conventional heat recovery modules) [0047] v.
Operable in all ambient temperatures from -10.degree. F. to
120.degree. F. [0048] g. Hydrocarbon power generator emitted
pollution reduction at generating plants [0049] h. Water use
reduction for cooling of utility generator equipment [0050] i.
Reduction of global warming [0051] j. Refrigerant volume leakage
reduction in package air conditioning equipment [0052] k. Reduction
of water chemical treatment at industrial cooling towers of utility
generating plants [0053] l. Reduction of ozone depleting and global
warming refrigerant leakage.
[0054] Use of an occupant sensor(s) to manage IAQ and energy
consumption is complimentary to a lighting control system. A
lighting control system is an energy management tool required by
the International Energy Conservation Code as an alternative to
time clocks which use space occupant overrides for the light
control system. One presently preferred occupant sensor utilizes
infrared temperature sensor technology to determine the number of
occupants in a room. Any human entry in to the sensor zone is
detected and turns on light fixtures. EMS systems can control space
lighting and HVAC during present hours of operation. Substantial
energy and cost savings are realized if the sensor determine the
presence of occupants and turn energy consuming systems on or off.
Such an occupancy sensor can be furnished with an auxiliary contact
to enable independent functioning of the lighting system from the
HVAC system. The auxiliary contact determines if a ventilation
adjustment is in order. The occupancy sensor also enables the
"occupied" mode temperature sensor set point to be changed in
response to an "active" status versus an "inactive" status. If, for
example, during a scheduled "occupied" mode of the HVAC unit, the
room sensor detects no human presence for a selected time period of
five minutes, the HVAC unit serving the room can change to
"occupied-inactive" status. This changes the room people and
ventilation set points to zero outside air. When the room sensor
detects human presence, the operating sequence for the DVHR (Demand
Ventilation Heat Recovery) unit 10 of the invention begins. The
first stage of the ventilation air management mode is utilized when
a room is not occupied and is based on the outside ambient air
temperature and includes the base ventilation rate, Rb=(Va)(x).
Since the room is not occupied, (Vp)(Occact)=0. An outside air
source temperature sensor determines if unit 10 operates in the
Cooling-Heat Recovery (CHR) mode, the Heating-Heat Recovery (HHR)
mode, or the Economizer-No Heat Recovery (EHNR) mode. When unit 10
operates either of the CHR or HHR modes, the occupancy sensor
enables the "occupied-active" mode of the HVAC system. The
ventilation ambient air damper 15 and the exhaust air damper 16
(FIG. 1) are opened, closed, or not adjusted in order to direct
into the room the minimum necessary quantities of ventilation air
as calculated by the ventilation algorithm. The velocity sensors
20A, 20B, 21, the indoor and outdoor temperature sensors, and the
CO2 sensor in the room provide inputs to the EMS (Energy Management
System). The indoor air quality (IAQ) and indoor and outdoor
temperature sensors enable the cooling and heating systems to
operate and the ventilation system algorithm determines calculates
the RV set point of the room.
[0055] When operating in the ENHR mode, the bypass damper 17 (FIG.
2) is opened to its design maximum air flow as sensed by the
velocity sensor 20A. The maximum outside air volume is calculated
by the engineer using the peak air flow of the supply fan 13
divided by the number of DVHR units on its system. During the ENHR
mode, the heat recovery module air pressure drop is excluded from
the system losses because it is bypassed. This allows for the
supply fan 13 to ramp up to a higher air flow because it doesn't
have as much system resistance to overcome. This is a higher air
quantity than the maximum fan capability if the sum of the total
ventilation air flow required for proper IAQ is tabulated. This is
a scheduled value on the drawings usually defined by the
engineer.
[0056] The exhaust/relief damper 16 and the heat exchanger damper
15 are closed. Air is relieved from the room via a gravity relief
system. When the ambient air quantity produces a temperature which
is too cold and the room temperature drops to below the desired set
point, the quantity of ventilation air is controlled based on
readings produced by the room CO2 sensor until the IAQ set point
can not be met and the temperature set point continues to drop.
When this occurs, the HHR mode is enabled. In most cases, the
morning warm-up condition shall enable the HHR mode. After the
system begins operating in the HHR mode, the ENHR mode is enabled
once the outside air temperature reaches 60 degrees F. or reaches
another selected temperature. If at any time the ambient air
temperature exceeds the set point of the room by five degrees F.,
the CHR mode is enabled.
[0057] An infrared sensor in the room or other space determines
when the room is occupied. When the room is not occupied, the
ventilation system of the invention is in an `inactive` mode. When
the room is occupied, the sensor generates and transmits signals to
control unit 30. Control unit 30 places the ventilation system in
the active mode, which triggers use of EQ. 1 (and consequently a
graph comparable to that of FIG. 3) as set forth below.
[0058] Control unit 30 communicates with fans 13 and 14 to turn the
fans on and off and to adjust the speed of operation of the
fans.
[0059] The ventilation unit 10 illustrated in FIGS. 1 and 2
includes a housing 23, heat exchange unit 12 mounted in housing 23,
damper(s) 15, 16, and 17 mounted in housing 23, velocity sensors
20A, 20B, and 21 mounted in housing 23, and a controller 30 mounted
in the housing 23. Fans 13 and 14 can be mounted on housing 23, or
can be mounted at locations separate from housing 23 to direct air
through ducts that are connected to housing 23.
[0060] Duct D5 guides incoming ambient ventilation air A1 over one
side of heat exchange unit 12, out into the duct of D1, and through
duct D4 interconnecting unit 10 and air conditioning unit 22 (FIG.
2). Duct D3 guides a portion R2 of the return air over the other
side of heat exchange unit 12 and out into the ambient air as
exhaust/relief air. The return air comes from the room being
ventilated by unit 10. Dampers 15 and 17 are mounted in duct D5.
Damper 16 is mounted in duct D6.
[0061] Velocity sensors 20A, 20B, 21 are shown mounted in ducts D5
and D6, but that need not be the case. Sensors can be mounted at
any desired location in ventilation unit 10 to obtain an accurate
reading of ventilation air A1 entering duct D5 and of return air R2
exiting duct D6 as exhaust/relief air.
[0062] Velocity sensors 20A, 20B, 21 are operatively associated
with control unit 30 and generate and transmit signals to control
unit 30 defining the velocity of ambient air, indicated by arrow
A1, traveling through ducts D5 and D1 into duct D4, and of return
air, indicated by arrow R2, traveling through ducts D1 and D6.
[0063] Control unit 30 also receives signals from a CO2 sensor (not
shown) in the room or other space being cooled (or heated) by the
air conditioning unit 22. Control unit 30 can also, if desired,
receive signals from a sensor that detects ambient temperature,
from a sensor that detects the temperature in the room being cooled
(or heated) by unit 22, from an infrared or other sensor that
detects when one or more individuals are in the room, and from a
sensor that indicates the desired temperature set point in the
room.
[0064] While the shape and dimension of ventilation unit 10 can
vary as desired, and unit 10 can be installed at any desired
location near to or spaced apart from air conditioning unit 22, the
embodiment of the invention illustrated in FIGS. 1 and 2 is a
preferred embodiment because it is constructed to be inserted after
a portion of ducting that leads to and carries return air to a
previously installed air conditioning unit 22 is removed. After the
portion of the return air ducting leading to the air conditioning
unit 22 is removed, unit 10 is installed in-line to replace the
portion of the return air ducting that was removed. Accordingly,
return air R1 and R2 from the room flows into unit 10, portion R1
flows into ducts D3, D1 and D4 and into air conditioner 22, and
portion R2 flows over or through heat exchanger 12 and out through
duct D6. This, as can be seen in FIG. 2, eliminates or minimizes
the amount of duct which must be utilized to install unit 10
in-line along a return air duct that is connected to air
conditioner 22. In FIGS. 1 and 2, it is assumed that unit 10 is
located outdoors. Unit 10 can also, if desired, be installed in a
duct which is located indoors, or can be installed at any other
desired location. And, as would be appreciated by those of skill in
the art, unit 10 can be utilized and installed when a new air
conditioner is being installed on or adjacent a building structure,
or can be installed as an integral part of air conditioning unit
during the manufacture of a new or refurbished air conditioning
unit. Unit 10 is preferably, but not necessarily, manufactured as a
self-contained module with a control unit 30 designed to receive
necessary inputs from air velocity sensors 20A, 20B, 21, from a
room CO2 sensor, from a room infrared occupancy sensor, from an
ambient air temperature sensor, or from any other desired sensor
that is part of self-contained unit or that is remote from unit 10.
Fans 13 and 14 can be incorporated as a part of unit 10, or can be
omitted from unit 10 and installed in or adjacent ducting that
leads to unit 10. Similarly, dampers 15 to 17 can, as illustrated
in FIGS. 1 and 2, be incorporated as part of unit 10, or can be
omitted from unit 10 and installed in ducting leading to unit 10,
as can control unit 30, velocity sensors 20A, 20B, 21, and heat
exchange unit 12. The compact module configuration, with or without
fans 13 and 14, illustrated in FIGS. 1 and 2 is presently much
preferred in the practice of the invention.
[0065] As is illustrated in FIG. 1, a portion, R2, of the return
air from the room is directed by fan 14 from duct D1 over one side
of heat exchange unit 12 and into the ambient air as exhaust/relief
air. The size, in cfm, of portion R2 is controlled by damper 16.
Another portion R1 of the return air from the room continues
through ducts D1 and D4 to air conditioning unit 22, where it
travels over the cooling (or heating) coils and becomes part of the
supply air, indicated by arrow S1, traveling through duct D2 to the
room.
[0066] As is also illustrated in FIG. 1, ambient air, indicated by
arrow A1, is directed by fan 13 over the other side of heat
exchange unit 12 and into duct D1. This ambient air travels over
the cooling (or heating) coils in air conditioning unit 22 and
becomes part of the supply air, indicated by arrow S2, to the
room.
[0067] When the ambient air is warmer than the desired temperature
of the room, heat exchange unit 12 functions to transmit heat from
the ambient air A1 to return air R2. When the ambient air A1 is
cooler than the desired temperature of the room, heat exchange unit
12 functions to transmit heat from the return air R2 to the ambient
air, A1.
[0068] In FIG. 2, damper 15 is closed. Ambient air A2 entering duct
D5 travels through damper 17, through ducts D1 and D4, and into air
conditioning unit 22. The operational configuration of FIG. 2 is
utilized when the ambient air temperature is sufficiently cool to
provide desired cooling to return air R1.
[0069] In FIGS. 1 and 2, D1 is an air duct integrated with D3 for
return air to air conditioner 22; D2 is an air duct directing
cooled (or heated) supply air S1 from air conditioner 22 back to
the room; D3 is a duct through which return air from the room flows
in unit 10; D4 is a duct that directs return air into the coil/fan
section of air conditioner 22; D5 is a duct that directs ambient
air A1 into unit 10 and over one side of heat exchange unit 12; D6
is a duct that directs exhaust/relief air from heat exchanger 12
into the ambient atmosphere; A1 and A2 are ambient air streams
flowing into duct D5; A1 is a fan induced ambient air stream
directed through or over heat exchange unit 12; A2 is a fan induced
ambient air stream that bypasses heat exchange unit 12 and travels
directing in the return air stream in the manner illustrated in
FIG. 2; R2 is a portion of the return air stream that is drawn over
or through heat exchange unit 12; and S1 is a combination of return
air R1 and outside ambient air A1. FIG. 1 illustrates the heat
recovery mode of the ventilation system of the invention. FIG. 2
illustrates the economizer mode of the invention. In the economizer
mode, the temperature of the ambient air stream A2 permits it to be
added directly to the return air stream R1 and obviates the
necessity of passing an ambient air stream A1 over or through heat
exchanger 12.
[0070] A control system ventilation formula is used to calculate
the CO2 ppm target concentration levels that are required to
maintain in a room a maximum 700 ppm CO2 exposure level for
occupants as defined in ASHRAE 62.1-2010 (and earlier versions).
This maximum 700 ppm CO2 exposure is in addition to the existing
CO2 concentration in the ambient air.
[0071] There are two additive variables required to meet the ASHRAE
standards:
a. One variable is the base "area ventilation rate", i.e., the
ventilation rate required for a room. b. The other variable is the
"person" ventilation rate, i.e., the ventilation rate to compensate
for each person in a room.
[0072] The calculation used below approaches each of the additive
variables to achieve a critical steady state result based on
maintaining a maximum CO2 concentration of 700 ppm above the CO2
concentration in the ambient air.
Variables Used in Conjunction with the Control System Ventilation
Formula [0073] x=square footage of the room [0074] Vp=area (i.e.,
room) ventilation rate requirement in cubic feet per minute
(cfm/sq. ft), as listed in ASHRAE 62.1-2010, Table 6.1. [0075]
Occmax=maximum code or user defined number of occupants in room
[0076] Va="per person" ventilation rate requirement in cfm/person,
as listed in ASHRAE 62.1-2010 Table 6.1. [0077] CRT=rate reset
variable based on outside air temperature during the cooling mode.
This is used in relation to Va. [0078] CRT=1.0 for ambient less
than or equal to 95 F [0079] CRT=0.8 for ambient less than or equal
to 96 F and greater than 95. [0080] CRT=0.6 for ambient temperature
less than or equal to 97 F and greater than 96 F. [0081] CRT=0.4
for ambient temperature less than or equal to 98 F and greater than
97 F. [0082] CRT=0.2 for ambient temperature less than or equal to
99 F and greater than 98 F. [0083] CRT=0.0 for ambient temperature
greater than 99 F. [0084] In other words, if the ambient
temperature is greater than 99 F, ambient air is not utilized to
meet the area ventilation rate requirement, but is still used to
meet the "per person" ventilation requirement. [0085] The CRT
values are adjustable with a plug-in to take into account sensible
cooling excesses associated with extremely high ambient conditions.
Similar adjustments can be defined for very humid locations and
will be based on a relative humidity--dry bulb temperature
measurement which equals a wet-bulb temperature on the psychometric
chart. [0086] HRT=rate reset variable based on outside air
temperature during the heating mode. This is used in relation to
Va. [0087] HRT=1.0 for ambient temperature greater than 25 F.
[0088] HRT=0.8 for ambient less than or equal to 25 F and greater
than 24. [0089] HRT=0.6 for ambient temperature less than or equal
to 24 F and greater than 23 F. [0090] HRT=0.4 for ambient
temperature less than or equal to 23 F and greater than 22 F.
[0091] HRT=0.2 for ambient temperature less than or equal to 22 F
and greater than 21 F. [0092] HRT=0.0 for ambient temperature less
than or equal to 21 F. [0093] HRT values are adjustable using a
plug-in to take into account sensible heating excesses associated
with extremely low ambient conditions. [0094] OSACO2=concentration
of CO2 in ambient air in ppm. [0095] Occact=count of number of
people in room, usually determined by a CO2 concentration that is
in excess of the CO2 concentration in the ambient air. [0096] IRV
graph=a plot of selected spaced apart reset values (RVs). The units
of measure on the vertical axis of the graph are ppm (parts per
million) CO2. The units of measure on the horizontal axis of the
graph are cfm (cubic feet per minute) ventilation air. [0097]
Rb=base ventilation rate for a room in cfm=(Va)(x). [0098] n=the
number of cfm reset segments selected for and represented on size
to other segments, although this is not necessarily the case. IRV
is the size of each segment in cfm. [0099] IRVpt=the cumulative
number of calculated persons in a reset segment and any preceding
reset segments. [0100] IRVcfm=a selected cfm point on the
horizontal axis of an IRV graph at which a reset segment ends, at
which an associated reset value (RV) occurs, and which represents a
cumulative quantity (in cfm) of outside (ventilation) air that is
utilized. The value of such a cfm point is equal to:
[0100] (Vp)(IRVpt)+(Va)(x) [0101] IRV=the size in cfm of each
segment in an IRL graph. IRV equals the maximum outside air
quantity (Vp.times.Occmax) divided by the number of reset segments
(n) selected. If, for example, five reset segments are selected,
the reset values (RV), or check points, occur at 0%, 20%, 40%, 60%,
80%, and 100% of the maximum (Vp.times.Occmax) outside air
ventilation (in cfm) that will be utilized to offset the
concentration of CO2 in the room that is above the concentration of
CO2 in the ambient air. Each segment extends from one RV to an
adjacent RV. For example, one segment extends from the cfm
associated with the RV at 0% to the cfm associated with the RV at
20%. If ten reset segments are selected, the reset values occur at
0%, 10%, 20%, 30%, 40%, etc. of the maximum flow of ambient air
that will be utilized to ventilate the room to offset CO2
concentrations above the CO2 concentration in the ambient air.
[0102] RV=RVd+OSACO2=a reset value on an IRV graph. The number of
RVs presently is one greater than the number, n, of segments. Each
set value (RV) represents a desired CO2 concentration which is
noted on the vertical axis of the graph and which is associated
with a selected cfm point (IRVcfm) on the horizontal axis of the
graph. The value of the selected cfm point (IRVcfm) indirectly
indicates the "actual" number of people (Occact) in the room, i.e.,
the value of the selected cfm points less the base cfm of (Va)(x)
is divided by Vp to give the "actual" number of people in the room.
A reset value (RV) defines a desired total room CO2 concentration
limit at its associated IRVcfm. A velocity sensor 20A, 20B in the
incoming supply stream of ambient air indicates the cfm of the
incoming air stream. As reset value (RV) is used to reset the CO2
maximum allowable ppm value for its associated IRVcfm. The control
system of the invention sends a signal to the outside or ambient
air stream damper motors which modulate the damper blades to adjust
the outside air quantity in response to the CO2 concentration
detected by CO2 sensor(s) and in response to how much the room CO2
deviates from the CO2 concentration defined by the RV. [0103]
RVd=the difference, in ppm, at a selected cfm point on an IRV graph
(IRVcfm) between the RV at that cfm and the ambient air CO2
concentration (OSACO2). Also known as CO2max. [0104] S.sub.(0, 1,
2, 3, . . . n)=a numerical value (0, 1, 2, 3 . . . n) representing
the number of segments used in calculating, with the formula noted
below, both an RV and the amount by which the RV exceeds the
ambient CO2 concentration. For example, when the first set point
RV1 is calculated, a numerical value of 0 is used for S; when the
second set point RV2 is calculated, a numerical value of 1 is used
for S; when the third set point RV3 is calculated, a numerical
value of 2 is utilized, and so on. When S=0, a segment is not
utilized and the RV=OSACO2. [0105] Altcorr=an altitude correction
value. This value increases the IRV values above those established
for sea level and extends the applicable segment maximum CO2 ppm
value to a higher cfm value. This is a multiplier to the IRV
segment values. The value is based on the specific density of air
at sea level divided by the specific density of air at the altitude
of the project site. When the location of a project is at sea
level, the Altcorr is 1.0. [0106] CO2max=the desired maximum CO2
concentration in ppm in a room above the CO2 concentration in the
ambient air. [0107] CO2target=RVd=the target CO2 (above ambient)
for a segment. [0108] Vamb=the cfm of ambient ventilation air
entering the system as measured by a velocity sensor. [0109]
Vexit=the cfm of supply air that exits into the atmosphere after
passing by the heat exchanger as measured by a velocity sensor.
[0110] CO2act=the actual measured CO2 in a room as measured by a
CO2 sensor. [0111] Tact=the actual temperature in a room as
measured by a thermostat.
Control System Ventilation Formula
[0112] Given the above variables, the target CO2 above ambient, or
RVd, for a segment is:
RVd = [ ( CRT or HRT ) ( Rb ) ( OSA CO 2 ) + ( Occact ) ( Vp ) (
OSA CO 2 + CO 2 max ) ] ( Rb ) + IRV ( Altcorr ) ( S ( 0 , 1 , 2 ,
3 n ) ) - OSA CO 2 [ EQ . 1 ] ##EQU00001##
[0113] The following example is presented by way of illustration,
and not limitation, of the invention.
EXAMPLE
[0114] In this example, it is assumed that a room will be occupied
by school children in the age range of 5 to 8. The ambient
temperature is 88 degrees F. The room is located as sea level. The
size of the room is 900 square feet. The CO2 concentration in
ambient air is 300 ppm. Five segments are selected to use in
preparing an IRV graph. The following values are utilized: [0115]
n=5 [0116] No. of RV points on IRV graph=n+1=6 [0117] No. of
occupants in a segment=(Occmax)/n=30/5=6 [0118] x=900 sq. ft. (size
of room) [0119] Va=0.12 cfm/sq. ft (from ASHRAE 62.1-2010: Table
6.1: Minimum Ventilation Rates In Breathing Zone). [0120]
Rb=(Va)(x)=(900)(0.12)=108 cfm [0121] Occmax=30 (maximum number of
children allowed in room per building code) [0122] Vp=10 cfm/person
(from ASHRAE Table 6.1). [0123] CRT=1.0 (ambient temperature is
less than 95 F) [0124] HRT=N/A, because the ambient temperature
requires cooling, and not heating. [0125] OSACO2=300 ppm. [0126]
IRV=(Vp)(Occmax)/n=(10)(30)/5=60 cfm [0127] Occact=number of people
in the room. This number times (Vp) is added to Rb to determine the
maximum airflow in a segment on an IRV graph. The first segment
includes 6 occupants. Six occupants times (Vp)=6.times.10 cfm=60
cfm. 60+108=a maximum airflow of 168 cfm at the upper end of the
first segment in the IRL graph. The second segment would also
include 6 occupants, producing a total room occupancy equal to the
occupancy in the first segment plus the occupancy in the segment or
6+6=12. Twelve occupants times (Vp)=12.times.6=72 cfm. 72+108=a
maximum airflow of 180 cfm at the upper end of the second segment
in the IRL graph, and so on. [0128] Altcorr=1.0. The project site
is at sea level. [0129] CO2max=700 ppm. This value is a constant
for all building types and occupancies. [0130] S.sub.(0, 1, 2, 3 .
. . n)=S.sub.(0, 1, 2, 3, 4, 5) Since CRT and Altcorr are each
equal to 1.0, the control system formula is simplified to:
[0130] RVd = [ ( Rb ) ( OSA CO 2 ) + ( Occact ) ( Vp ) ( OSA CO 2 +
CO 2 max ) ] ( Rb ) + IRV ( S ( 0 , 1 , 2 , 3 , 4 , 5 ) - OSA CO 2
= [ 32 , 400 ) + ( Occact ) ( 10 , 000 ) ( 108 ) + ( 60 ) ( S ( 0 ,
1 , 2 , 3 , 4 , 5 ) ) - 300 [ EQ . 2 ] ##EQU00002##
At the first set point of 0%, Occact=0 (0% of the maximum occupancy
of 30 students=room is not occupied), S.sub.(1, 2, 3, 4, 5)=0, and
the formula is
( Unoccupied condition ) RVd 1 = 32 , 400 108 + ( 60 ) ( 0 ) - 300
= 0 ppm [ EQ . 3 ] RV 1 = 300 ppm . ##EQU00003##
At the second set point of 20%, Occact=6 (20% of the maximum
occupancy of 30 students), S.sub.(1, 2, 3, 4, 5)=1, and the formula
is:
( First occupied segment set point ) Rvd 2 = [ ( 32 , 400 ) ( 6 ) (
10 , 000 ] ( 108 ) + ( 60 ) ( 1 ) - 300 = 250 ppm [ EQ . 4 ] RV 2 =
550 ppm . ##EQU00004##
At the third set point of 40%, Occact=12 (40% of the maximum
occupancy of 30 students), S.sub.(0, 1, 2, 3, 4, 5)=2, and the
formula is:
( Second occupied segment set point ) RVd 3 = [ ( 32 , 400 ) + ( 12
) ( 10 , 000 ) ] ( 108 ) + ( 60 ) ( 2 ) - 300 = 368 ppm [ EQ . 5 ]
RV 3 = 668 ppm . ##EQU00005##
At the fourth set point of 60% the formula is:
( Third occupied segment set point ) RVd 4 = [ ( 32 , 400 ) + ( 18
) ( 10 , 000 ) ] ( 108 ) + ( 60 ) ( 3 ) - 300 = 438 ppm [ EQ . 6 ]
RV 4 = 738 ppm . ##EQU00006##
At the fifth set point of 80% the formula is:
( Fourth occupied segment set point ) RVd 5 = [ ( 32 , 400 ) + ( 24
) ( 10 , 000 ) ] ( 108 ) + ( 60 ) ( 4 ) - 300 = 483 ppm [ EQ . 7 ]
RV 5 = 783 ppm . ##EQU00007##
At the sixth set point of 100%, the formula is:
( Fifth occupied segment set point ) RVd 6 = [ ( 32 , 400 ) + ( 30
) ( 10 , 000 ) ] ( 108 ) + ( 60 ) ( 5 ) - 300 = 515 ppm [ EQ . 8 ]
RV 6 = 815 ppm . ##EQU00008##
With reference to FIG. 3: [0131] 1. The reset values (RVs) or
checkpoints in the IRV graph of FIG. 3 are: RV1=300 ppm CO2;
RV2=550 ppm CO2; RV3=668 ppm CO2; RV4=738 ppm CO2; RV5=783 ppm CO2;
RV6=815 ppm CO2. [0132] 2. In the system, when the room is in the
`occupied-inactive` mode at a zero occupancy count (empty room),
the outside air control damper operates to bring in ambient air at
approximately Rb=108 cfm (900 square feet.times.0.12 cfm/square
foot). This air volume, Rb, is equal to (Vb)(x) and is a constant
ventilation flow rate in the overall equation. If no one is in the
room for 5 minutes or more, the ventilation system goes from the
`occupied-inactive` mode to the `unoccupied` mode and is turned off
so there is no ambient ventilation air flowing into the room. The
five minute time element is adjustable as desired. The minute
someone enters the room, the infrared occupancy sensor (or some
other desired sensor) causes control unit 30 to activate the
`occupied-active` mode and control the dampers 15, 16 to establish
the minimum ventilation value, Rb. As the CO2 concentration rises,
the ventilation rate rises to dilute the CO2 concentration. The
amount that dampers 15 and 16 (or 17) open depends on the
difference between the actual CO2 concentration and the set point
RV2, RV3, RV4, etc. The greater the difference, the more the
dampers open. [0133] By way of example, if after the dampers are
opened to increase the flow rate of ambient ventilation air, the
next reading by velocity sensor 20B indicates a flow rate of 190
cfm (in the second segment in FIG. 3) and the CO2 sensor in the
room reads 400 ppm (in the first segment in FIG. 3), then control
unit 30 begins closing damper 15 to reach an ambient air flow rate
that is in the first segment (108 to 168 cfm) in FIG. 3. The CO2
and velocity readings preferably are made every three to five
seconds, although this can vary as desired. [0134] If in the next
reading sensor 20B indicates a flow rate of 175 cfm and the CO2
sensor in the room reads 425 ppm, the control unit 30 continues to
close damper 15 to reach an ambient air flow rate that is in the
first segment toward the goal of raising room CO2 level to the
segment CO2 set point of 550 ppm. [0135] If in the next reading
sensor 20B indicates a flow rate of 160 cfm and the CO2 sensor
reads 425 ppm, the control unit 30 continues to close damper 15
because the CO2 ppm has not reached 550 ppm at set point RV2.
[0136] If at the next reading sensor 20B indicates a flow rate of
110 cfm and the CO2 sensor reads 560 ppm, then the control unit
begins to open damper 15 to increase the ventilation rate to reduce
the CO2 concentration to 550 ppm or less. [0137] If at the next
reading sensor 20B indicates a flow rate of 140 cfm and the CO2
sensor reads 450 ppm, then control unit 30 begins again to close
the damper 15 since the CO2 concentration is once again less than
550 ppm. When the damper cfm is in the first segment (108 to 168),
the desired CO2 set point is 550 ppm (or less). When the damper cfm
is in the second segment (168 to 228), the desired CO2 set point is
668 ppm (or less). And so on. [0138] If at the next reading, the
CO2 ppm in the room is 740 ppm and the velocity sensor 20B reads
150 cfm, control unit 30 opens damper 15 to increase the flow of
ventilation air. [0139] If at the next subsequent reading, the CO2
ppm in the room is 680 ppm and the velocity sensor indicates an
ambient air flow rate of 240 cfm, then the cfm being utilized and
the CO2 concentration are each in the third segment (228 to 288) in
FIG. 3 and the CO2 set point utilized is the set point for segment
three, namely 738 ppm (or less). In addition, since the CO2
concentration is less than 738 ppm, the control unit 30 begins to
close damper 15 toward the minimum flow rate of 228 cfm for the
third segment. [0140] If in the next subsequent reading, the CO2
room sensor indicates a concentration of 670 ppm, and the velocity
sensor 20B indicates a flow rate of 235 cfm, the control 30
continues to slowly close damper 15 toward the minimum flow rate of
228 cfm for the third segment. As long as the ambient air flow (and
the CO2 concentration) is in the third segment, the cfm measured by
sensor 20B should not drop below 228 cfm. And so on. [0141] 3.
Within a short period of time, the cfm value and CO2 value
stabilize and the system modulates as necessary to meet the
appropriate room CO2 sensor setpoint RV2, RV3, RV4, RV5, RV6. The
initial set point concentration values for CO2 control are
relatively low and the ventilation system responds immediately,
overshooting the appropriate set point value. Very quickly, within
a minute or so, the room sensor combines with the velocity sensor,
in cfm, to determine which segment is in reference for the CO2
control set point reset value. [0142] 4. When an individual enters
the room, a CO2 sensor in the room monitors the increase in CO2
above the initial stable RV1=300 ppm in the room (essentially the
ambient air CO2 level) and begins to open the outside air damper to
increase the amount of ventilation air entering the room. The first
`active` occupied CO2 concentration checkpoint RV2 is 250 ppm above
ambient or 550 ppm total. [0143] 4. As the outside air damper
opens, the velocity sensor in the air stream registers the increase
in air flow and sends the value to the control unit 30 to determine
into which segment air flow value the air quantity registers.
[0144] 5. Since one individual will generate a CO2 amount requiring
approximately 10 cfm of outside air for dilution to 700 ppm above
ambient, approximately 6 students can enter into the room at the
first segment upper CO2 limit RVd2 of 250 ppm above ambient. The 6
student load is coincidental with the first segment maximum air
flow rate of [(Vp)(Occact)+(Va)(x)], as it should be. The total
outside air entering the room at this segment limit is 108 cfm
(area ventilation rate)+60 cfm (people ventilation rate)=168 cfm
total ventilation rate. [0145] 6. During all modes of area
occupancy (when the first person enters the room), the initial
checkpoint or segment target CO2 value RVd2 added to the OSACO2
will be the first segment CO2 limit RV2. The only time the 300 ppm
total RV1 (or 0 ppm above ambient) concentration will occur is when
the room is unoccupied. The minute a person enters, the first
segment value will define the limits until its maximum segment air
flow value in cfm is exceeded. By way of example, the maximum air
flow for segment one is, in the example set forth in FIG. 3, 168
cfm. The maximum air flow for segment two is 228 cfm. [0146] 7. As
additional students enter the room, the CO2 sensor will register a
coincidental rise in the CO2 concentration and the control unit 30
will open the outside air damper 15 further if the CO2
concentration exceeds the set or check point value RV2, RV3, etc.
associated with the segment in which the damper ventilation rate is
operating. When the ventilation rate exceeds the first segment 168
cfm value, which also defines the upper limit of the first segment
CO2 value (i.e., 550 ppm), the measured air quantity enters into
the region of the second segment, which defines an upper air flow
rate of 228 cfm and a CO2 concentration upper limit of 368 ppm
above the ambient air CO2 concentration, or, as is shown in FIG. 3,
a total CO2 concentration RV3 of 668 ppm. [0147] 8. The `five
segment` calculation example created above defines the air flow
rates and CO2 concentration limits of each segment. It does not
control the space CO2. The space CO2 is limited by the CO2 sensor
in the room and the operation of the outside air control dampers.
The calculation accumulates the sensed outside air quantity and
redefines the CO2 sensor set point, nothing more. However, this is
the most critical part of Indoor Air Quality management,
maintaining the proper CO2 limits with a moving occupant
ventilation rate target combined with a fixed area ventilation
rate. [0148] 9. As additional students enter the room and the CO2
concentration rises and the ambient air input damper 15 is opened
further, a greater outside air quantity is measured by the velocity
sensor. As the velocity sensor value in cfm continues to change, it
will register into any one of the segment air value limits. When
the CO2 sensor takes a reading and transmits its value to the
control unit 30, the control unit 30 will look at the air quantity
recorded at the velocity sensor, determine which segment it falls
into, and compare the segment CO2 limit to the CO2 concentration
sensed. The controller will send a signal to the outside air
control damper to increase or decrease the air to the room to meet
the segment set point RV2, RV3, RV4, RV5, RV6. Then, as the sensed
air quantity continues to change, in response to the generation of
CO2 (or to a decrease in CO2 when children leave the room) in the
space, it will redefine which segment is applicable and redefine
the CO2 limit as necessary. This is a dynamic function. CO2
measurements are taken, air flow rates are adjusted, CO2
measurements are taken, all the while, the calculations continue to
reset the CO2 concentration target. [0149] 10. And so on.
[0150] Because measurements are taken constantly, it is not a good
control scenario to make continuous adjustments because the control
dampers will `hunt` for a control point and never achieve it.
Creating segments, where the CO2 target value is fixed for more
than a minute amount of change of air quantity, allows for a more
stable control of outside air quantity and helps prevent rapid
cycling of air conditioning equipment in an attempt to meet a room
temperature set point with a `wild` mixed air temperature entering
the cooling or heating coils or furnace.
Discussion of Formula
[0151] Since actual numbers sometimes aide understanding a
calculation process, the values used in the above example are
referenced in the following discussion.
This particular method of controlling the flow of ventilation air
into a room is to continuously ventilate a room with ambient air at
a base rate equivalent to the Area Outdoor Air Rate set forth in
ASHRAE 62.1-2010: Table 6.1, and to increase the ventilation rate
whenever an individual enters the room, and to decrease the
ventilation rate whenever an individual leaves the room. For each
person entering the room, the ventilation rate is increased to meet
an approximate air quantity based on the People Outdoor Air Rate
set forth in ASHRAE 62.1-2010: Table 6.1. In the above example, the
People Outdoor Air Rate for an individual is 10 cfm. The 10 cfm
value per person was set by ASHRAE 62.1-2010 after completing
several studies which determined that for children 5-8 years of
age, taking into account their volumetric CO2 generation and their
activity levels, that it takes approximately 10 cfm per person to
properly dilute the space CO2 to 700 ppm above ambient. 700 ppm
above ambient CO2 is recognized by ASHRAE as the target CO2
concentration to minimize objectionable odor recognition for 80%+of
occupants newly entering a space who have not become acclimated to
the people generated odors of the space. Therefore, for the sake of
this particular example calculation, it will be established that
for approximately each 10 cfm of air entering the area through the
outside air control damper, one student will be accounted for in
the ventilation calculation. ASHRAE is the American Society of
Heating, Refrigerating, and Air Conditioning Engineers. Stated for
this calculation, the base ventilation rate is (x)(Va), which in
the above example is (900 sq ft)(0.12 cfm/sq. ft)=108 cfm. The
system would, consequently, ventilate an empty room at 108 cfm.
When the first person enters the room, the ventilation rate is
increased by 10 cfm to 118 cfm. When the second person enters the
room, the ventilation rate is increased to 128 cfm, and so on. Each
time a person leaves the room, the ventilation rate is decreased by
approximately 10 cfm. Establishing that this control method
utilizes the formula set forth above to control the ventilation of
a room with ambient air, the formula calculates for set checkpoints
at desired CO2 levels in the room above the CO2 level in the
ambient air. Examining the formula further, each air stream
ventilation rate has its actual or maximum allowable CO2
concentration attribute. The area ventilation rate air stream
contributes to the equation 108 cfm of 300 ppm CO2 concentration.
This would be like comparing 108 gallons of water per minute at 300
degrees F. (under high pressure of course). The people ventilation
rate air stream CO2 contribution to the equation includes the base
300 ppm of CO2 and allows for an additional 700 ppm CO2 increase.
The people ventilation rate contributes 1000 ppm CO2 (total) for
each cfm of air. When we are establishing the maximum allowable CO2
concentration at its specific target cfm limit, we know that the
300 ppm CO2 air stream will dilute the 1000 ppm CO2 air stream. We
are adding the air stream CO2 values to quantify the assimilation
of the total CO2 into the total of the two air streams and
determine the influence of the ambient CO2 air quantity on the room
generated CO2. Once assimilated, the resultant CO2 concentration
should represent the discounted CO2 value, which achieves the
ASHRAE defined individual ventilation air flow rate requirements
for area and people. In general, the formula has to take into
account ventilation air flow into the room for two purposes: [0152]
1. Area ventilation of the room. The area ventilation air flow rate
is determined using the Area Outdoor Air Rate Va set forth in
ASHRAE Table 6.1 and using the size of the room in square feet.
[0153] 2. Ventilation air to compensate for additional CO2 produced
when individuals are in the room. This people ventilation air flow
rate is determined using the People Outdoor Air Rate Vp set forth
in ASHRAE Table 6.1 and the number of people in the room.
A. Area Ventilation Air Flow Rate for the Room
[0154] This ventilation rate is represented in the formula by:
[(CRT or HRT)(x)(Va)
[0155] And, when CRT or HRT and Altcorr each equal one, this
becomes: (x)(Va)
B. Ventilation Air Flow Rate for People
[0156] This ventilation rate is represented in the formula by:
(Vp)(Occmax)
C. Calculation of an IRVcfm.
[0157] The cfm of ventilation air is, as noted, physically measured
to determine the cfm location on the horizontal axis of an IRV
graph. The maximum cfm of a segment (i.e., the IRVcfm) is, on the
IRV graph, associated with an RV. When the IRVcfm of an RV is
reached or exceeded, as determined by the physical measurement of
the incoming ventilation air in cfm, the next IRVcfm is selected.
One method of calculating an IRVcfm adding the base room area
ventilation, Rb, to the ventilation for the number of people in a
room, (Occact)(Vp). These terms are seen in EQ. 1 described above.
A second method of calculating an IRVcfm is to add the base rrom
area ventilation to a calculation in which the total or maximum
people ventilation rate of (Vp)(Occmax) is divided by the number of
segments, n, and multiplied by the number of segments, (S.sub.(0,
1, 2, 3, 4, 5)), which are, when moving from left to right on the
horizontal axis of an IRV graph from the base area ventilation rate
in cfm, required to reach the IRVcfm at issue.
Therefore, an IRVcfm=[(Vp)(Occmax)/n](S.sub.(0, 1, 2, 3, 4, 5))
[0158] Using either the first or the second method of calculating
an IRVcfm gives the same result.
[0159] The block flow diagram of FIG. 4 illustrates an embodiment
of a ventilation system that can be utilized in the practice of the
invention. The system includes a computer which can be utilized in
the control unit 30 of ventilation unit 10. The computer includes
controller 62 and memory 64. The computer can be a digital
computer, analog computer, hybrid computer, or other programmable
apparatus. In practice, the very large majority of computers
comprise digital computers.
[0160] The memory 64 can be any suitable prior art memory unit such
as are commonly used in digital or other computers. For example,
electromagnetic memories such as magnetic, optical, solid state,
etc. or mechanical memories such as paper tape.
[0161] Velocity sensor(s) 62, indoor and outdoor CO2 sensors 55,
and room thermostat 54 input data to memory 64, and can also input
the data to controller 63. An outdoor temperature sensor, room
temperature sensor, and indoor occupancy sensor, or any other
desired sensor or data input means can also be utilized to input
data to memory 64 or controller 63.
[0162] Controller 63 includes IRVcfm calculation sub-routine 50, RV
calculation sub-routine 51, and damper adjustment sub-routine 52.
IRVcfm calculation sub-routine 50 utilizes variables n, Vp, Va, x,
Occmax input 56 from memory. RV calculation sub-routine 51 utilizes
EQ 1 above (Control System Ventilation Formula) and the variables
57 from memory 64 including n, Vp, Va, x, Ocmax, Occact, CO2max,
CRT, HRT, Altcorr, S.sub.(0, 1, 2, 3 . . . n), and OSACO2 to
calculate RV values like those on the graph of FIG. 3. The damper
adjustment sub-routine 52 utilizes variables 58 from memory 64
including Vamb (the desired velocity of incoming air to achieve the
desired ppm CO2 (RV1, RV2, etc.) at the cfm checkpoints (108 cfm,
168 cfm, etc.) on the graph of FIG. 3. Once control 61 utilizes
sub-routine 52 to calculate the desired cfm, control 61 transmits
the necessary signals to damper(s) 54 to achieve the desired cfm of
incoming ventilation air.
[0163] FIG. 5 is a block flow diagram which illustrates a typical
program or logic function which is executed by the controller 63.
The basic control program consists of commands to "start and
initialize" 70, "read memory" 71, and "transfer control" 72
sequentially to one of subroutines 50 to 52. Each sub-routine 50 to
52 includes the steps of "interpret memory" 75, "perform the
sub-routine function(s)" 76 (i.e., determine IRVcfm, RV. etc.),
followed by "return to control program" 77. The sub-routines are
repeated as indicated by the "repeat to last memory step" 73,
followed by an "end" 74 program step which completes the execution
of the program.
[0164] Control unit 30 controls the flow rate in cfm of ventilation
air through unit 10 by opening and closing dampers 15, 16, 17. Fans
13 and 14 increase or decrease their flow volumes based on a static
pressure sensor in the outside air duct or the exhaust air duct. A
variable speed motor controller increases or reduces the fan speed
to maintain a selected static pressure set point. The control unit
30 changes the speed of the fan motors to try maintain a static
pressure level in each duct.
[0165] Having my invention in such terms as to enable those skilled
in the art to make and use the invention, and having described the
best mode thereof, I claim:
* * * * *