U.S. patent application number 10/513976 was filed with the patent office on 2006-08-31 for control of air conditioning cooling or heating coil.
Invention is credited to George Sandor Viczena.
Application Number | 20060191677 10/513976 |
Document ID | / |
Family ID | 29421064 |
Filed Date | 2006-08-31 |
United States Patent
Application |
20060191677 |
Kind Code |
A1 |
Viczena; George Sandor |
August 31, 2006 |
Control of air conditioning cooling or heating coil
Abstract
A fluid heat exchange device, comprising a header and a
plurality of interconnecting circuits between an supply port and a
return port, the interconnecting circuits being connected to the
header by a corresponding plurality of connection ports at
different locations along the header wherein the header includes a
blocking control element inside the header, the blocking control
element being positionally adjustable along the header to
selectively block fluid flow from the supply port through the
connection ports of the plurality of interconnecting circuits,
thereby selectively controlling those interconnecting circuits of
the plurality of interconnecting circuits which are subjected to
fluid flow therethrough in dependency on the position of the
blocking control element.
Inventors: |
Viczena; George Sandor;
(Port Dickson, MY) |
Correspondence
Address: |
VIERING JENTSCHURA & PARTNERS
3770 HIGHLAND AVENUE, SUITE 203
MANHATTAN BEACH
CA
90266
US
|
Family ID: |
29421064 |
Appl. No.: |
10/513976 |
Filed: |
May 7, 2003 |
PCT Filed: |
May 7, 2003 |
PCT NO: |
PCT/IB03/01767 |
371 Date: |
January 26, 2006 |
Current U.S.
Class: |
165/260 ;
165/96 |
Current CPC
Class: |
F28F 27/02 20130101;
F28F 27/00 20130101; F24F 11/83 20180101; F28D 1/05316
20130101 |
Class at
Publication: |
165/260 ;
165/096 |
International
Class: |
F28F 27/00 20060101
F28F027/00 |
Claims
1. A fluid heat exchange device, comprising a header and a
plurality of interconnecting circuits between an supply port and a
return port, the interconnecting circuits being connected to the
header by a corresponding plurality of connection ports at
different locations along the header wherein the header includes a
blocking control element inside the header, the blocking control
element being positionally adjustable along the header to
selectively block fluid flow from the supply port through the
connection ports of the plurality of interconnecting circuits,
thereby selectively controlling those interconnecting circuits of
the plurality of interconnecting circuits which are subjected to
fluid flow therethrough in dependency on the position of the
blocking control element.
2. A fluid heat exchange device according to claim 1, wherein the
header is an supply header interconnected between the supply port
and the plurality of interconnecting circuits.
3. A fluid heat exchange device according to claim 1, wherein the
header is a return header interconnected between the plurality of
interconnecting circuits and the return port.
4. A fluid heat exchange device, comprising an supply header
connected to an supply port, a return header connected to a return
port, and a plurality of interconnecting circuits which are
connected to each of the supply header and to the return header by
a corresponding plurality of connection ports at different
locations along each of the supply header and return header,
wherein the supply header and the return header each includes a
blocking control element inside the header, the blocking control
element being positionally adjustable along the header to
selectively block fluid flow through the connection ports of the
plurality of interconnecting circuits, thereby selectively
controlling those interconnecting circuits of the plurality of
interconnecting circuits which are subjected to fluid flow
therethrough in dependency on the positions of the blocking control
elements of the supply header and return header.
5. A fluid heat exchange device according to claim 1, wherein the
blocking control element is a piston assembly which is movable
along the header, thereby separating the header into two chambers
extending along a part of the header dependent on the position of
the piston assembly.
6. A fluid heat exchange device according to claim 5, wherein at
the return port a valve is arranged for controlling the fluid flow
through the return port, wherein the position of the movable piston
assembly in the header is controlled by fluid flow through the
return port.
7. A fluid heat exchange device according to claim 5, wherein the
position of the piston assembly in the header is measured by means
of a ultrasonic transducer placed at one end of the header for
measuring the distance between the piston assembly and said end of
the header.
8. A fluid heat exchange device according to claim 5, wherein the
position of the piston assembly in the header is measured by means
of a multi turn potentiometer located outside of the header,
wherein the potentiometer is coupled to a threaded rod coupled to
the piston assembly.
9. A fluid heat exchange device according to claim 5, wherein the
position of the piston assembly near an end of the header is
measured by means of a system comprising a permanent magnet at the
piston assembly and a cooperating respective magnetic reed switch
at a housing of the header, wherein the magnetic reed switch is
closed if the permanent magnet is in close proximity to the switch
near said end of the header.
10. A fluid heat exchange device according to claim 6, wherein at
the return port a return control element is arranged for
controlling the fluid flow through the return port, wherein the
return control element is controlled by a fluid pressure difference
between fluid return pressure at the return port and a reduced
pressure which is reduced by a reduction valve in proportion to
fluid pressure prevailing at the supply port.
11. A fluid heat exchange device according to claim 5, wherein the
supply port is arranged at one end of the supply header, and the
supply header includes an supply header portion at the other end
thereof, the supply header portion being extended by a tubular
extension portion which is bent at an angle relative to the supply
header portion, and the piston assembly is comprised of a first
piston and a second piston with a plurality of neutral buoyancy
spacer balls therebetween to be movably arranged in the supply
header portion and in the extension portion of the header with the
first piston located in the supply header portion and the second
piston located in the extension portion, wherein the position of
the piston assembly is controlled by the fluid pressure difference
between fluid pressure acting on the first piston in the supply
header and a fluid pressure acting on the second piston in the
extension portion, wherein the fluid pressure is controlled to
maintain the desired differential pressure between the supply port
and return pipe header.
12. A fluid heat exchange device according to claim 5, wherein a
motor is arranged outside that header comprising the piston
assembly and is coupled to a threaded rod which is coupled to the
piston assembly for driving the piston assembly along the
header.
13. A fluid heat exchange device according to claim 5, wherein the
piston assembly in the header is drivingly supported by a flexible
bellows which is fixed at an end of the header, wherein the bellows
is connected to a fluid supply to be filled with fluid or be
released from fluid, thereby extending and retracting the length of
the bellows, respectively and controlling the position of the
piston assembly inside the header in dependency on the length of
the bellows.
14. A fluid heat exchange device according to claim 5, wherein the
piston assembly is comprised of a flexible bellows and a first
piston and a second piston, which are arranged at opposite ends of
the flexible bellows, wherein each piston includes a radially
expandable chamber and a friction ring formed at the circumference
of the chamber which friction ring is adapted to be pressed at the
inner wall of the header for fixing the respective piston, wherein
the flexible bellows and the chambers each are controllably
connected to a fluid supply, from which the chambers or the
flexible bellows may be separately supplied with fluid pressure or
released from fluid pressure, so that, for moving the position of
the piston assembly, the first piston is adapted to be fixed at the
wall of the header by supplying pressure into the chamber of the
first piston, and the second piston is then displaceable along the
header direction by supplying pressure into the flexible bellows,
and in the displaced position the second piston is adapted to be
fixed at the wall of the header by supplying pressure into the
chamber of the second piston, whereafter the first piston is
removable from the wall of the header by releasing of fluid
pressure from the first piston and is displaceable towards the
second piston by releasing of fluid pressure from the flexible
bellows.
15. A fluid heat exchange device according to claim 5, wherein the
header is comprised of a magnetizable material, and the piston
assembly is comprised of a flexible bellows and a first piston and
a second piston, wherein the first piston and the second piston are
arranged at opposite ends of the flexible bellows, wherein each
piston includes an electromagnet and a radially expandable clamp
ring formed at the circumference of each piston, wherein the clamp
ring is adapted to be pressed at the inner wall of the header for
fixing the respective piston, wherein the flexible bellows is
controllably connected to a fluid supply from which the flexible
bellows may be supplied with fluid pressure or released from fluid
pressure, so that, for moving the position of the piston assembly,
the first piston is adapted to be fixed by the clamp ring thereof
to the wall of the header by energizing the electromagnet of the
first piston, and the second piston is then displaceable along the
header direction by supplying pressure into the flexible bellows,
and in the displaced position the second piston is adapted to be
fixed by the clamp ring thereof to the wall of the header by
energizing the electromagnet of the second piston, whereafter the
first piston is removable from the wall of the header by
de-energizing the electromagnet of the first piston and is
displaceable towards the second piston by releasing of fluid
pressure from the flexible bellows.
16. A fluid heat exchange device according to claim 5, wherein the
blocking control element is a diaphragm extending along the header
from the supply port at one end of the header to the other end of
the header along the plurality of connection ports, wherein the
diaphragm is adapted to be filled with fluid, so that the
connection ports located along the diaphragm are closed if the
diaphragm is filled, and the connection ports are subsequently
opened one after another in proportion to a fluid pressure
reduction in the diaphragm beginning from the one end of the header
at the supply port to the other end of the header.
17. A fluid heat exchange device according to claim 5, wherein the
supply port is arranged at one end of the supply header, wherein
the piston assembly is comprised of a piston and a plurality of
neutral buoyancy spacer balls, wherein the neutral buoyancy spacer
balls are located in the chamber opposite to the supply port and
said chamber is connected with a neutral buoyancy spacer ball
reservoir, wherein a transfer means is provided which transfers
neutral buoyancy spacer balls from the reservoir to said chamber or
from said chamber to the reservoir, thereby the position of the
piston is controlled dependent on the number of neutral buoyancy
spacer balls in said chamber.
18. A fluid heat exchange device according to claim 5, wherein at
the supply port a pump is arranged for controlling the fluid flow
through the supply port, wherein the position of the movable piston
assembly in the header is controlled by fluid flow through the
supply port.
19. A fluid heat exchange device according to claim 5, wherein the
blocking control element is a sleeve which is rotatable in the
header and comprising slots at its circumference at locations
corresponding to those of the connection ports, wherein the slots
have different circumferential lengths so that different numbers of
connection ports are in dependence of the rotational position of
the sleeve.
20. A fluid heat exchange device according to claim 1 and connected
as a cooling fluid device.
21. A fluid heat exchange device according to claim 1 and connected
as a heating fluid device.
Description
[0001] This invention relates to improvements in control of part
load capacity of a fluid heat exchange device, especially a chilled
water cooling coil used in air handling equipment and fan coil
units for comfort cooling and industrial application. In the
following the device is described for cooling application, but is
usable for heating application as well.
[0002] With conventional throttle valve controlled cooling coils at
part load the latent capacity is reduced much faster than the
sensible capacity, resulting in an increase in space relative
humidity and decrease in comfort. Sensible heat source up stream of
the cooling coil other than in the conditioned space does not
contribute to effective sensible load from a latent removal
standpoint. The coil needs to be selected at a high water side
pressure drop at full load to ensure turbulent flow in circuits at
partial load. The associated control valve represents equal or
higher pressure drop than the coil, resulting in high pump pressure
head and considerable operating cost. Except for employing a reheat
device, independent control of sensible versus latent capacity is
not available. Effective treatment of high humidity outside air
requires a dedicated air handler. Hot water heating coils exhibit
the same negative characteristics as far as high pressure head and
part load controllability as cooling coils. To measure the energy
used by an air handler requires a flow meter also entering--leaving
water temperature differential measurement and accurate, repeatable
flow metering is difficult and costly. Selecting a cooling coil and
control valve needs considerable experience despite sophisticated
software selection tools to ensure low load performance and
controllability. Water side balancing of a chilled water system is
time consuming and if not performed correctly reflects on system
performance.
[0003] Preferred objects of the present invention include:
[0004] Maintain latent capacity at least in proportion to the
available sensible load during part load operation down to zero
load.
[0005] Utilise sensible heat available in open return air plenum as
an effective sensible load to enhance dehumidification of
conditioned spade.
[0006] Enable low pressure drop coil selection at full load and
replace the high pressure drop control valve with a low
differential pressure alternative.
[0007] Provide near independent means of part load sensible versus
latent capacity control.
[0008] Use the same air handler, the same cooling coil that serves
the conditioned space to effectively treat high humidity outside
air.
[0009] Permit low water side pressure drop heating hot water coil
selection at full load, at the same time ensure controllability at
low loads.
[0010] Provide an accurate water flow metering option.
[0011] Provide optional water system balance indication and a
degree of self balancing ability.
[0012] Reduce pumping power requirements for new system designs
also for retrofit applications.
[0013] Ease of coil selection. Assuming the coil selected is large
enough to meet full load, part load performance and controllability
is ensured.
[0014] The principle of this invention is circuit by circuit
control of fluid flow. At full load all the circuits are active,
thus there is fluid flowing through all the available circuits of
the coil. At part load the flow of fluid is cut off to some of the
circuits, while flow is maintained at or near full velocity in the
active circuits. The number of active circuits at any given time is
determined by the prevailing air side load on the coil. The
effective coil surface temperature around the active circuits
remains constant, so dehumidification is maintained at part load,
while around the inactive circuits no heat exchange to the air
takes place.
[0015] Other preferred objects will become apparent from the
following description.
[0016] In a broad aspect the present invention resides in a control
method for chilled water cooling coils and hot water heating coils
used in comfort and industrial air conditioning applications,
including:
[0017] A movable piston located in the supply header of the coil.
At full load the piston is at it's upper most position and all the
circuits are active, thus receiving full flow of chilled water. The
position of this piston is dictated by the prevailing sensible heat
load on the coil. At partial load the piston is moved down, cutting
off chilled water supply to the circuits above it's location.
[0018] The percent of active circuits being proportional to the
sensible load and the effective coil surface temperature around the
active circuits remaining constant ensures that the latent capacity
of the coil is also proportional to the sensible load.
[0019] During part load operation around the upper inactive
circuits the coil is at return air dry bulb temperature, no heat
exchange takes place, thus any sensible heat source, be it up or
down stream of the cooling coil is an effective source to enhance
dehumidification of the conditioned space. This includes heat
generated by light fittings in open return air plenums.
[0020] The coil water side pressure drop at full load may be
selected at a low value, as at part load there is no substantial
change in fluid flow velocity in the active circuits and the
movable piston presents only minimal resistance.
[0021] Placing another movable piston, this time in the return pipe
header of the cooling coil, will facilitate latent capacity
control. For full latent capacity this piston is at it's lower most
position, below the exit of the lowest circuit. Elevating this
piston the fluid flow is cut off to the circuits below it's
position. For average space conditioning coil entering air
conditions there is condensate on the higher active portion of the
coil. As this condensate runs down and reaches the low inactive
area, it is partly or fully evaporated, resulting in rapid decrease
in latent capacity and due to evaporative cooling an increase in
sensible cooling of the air stream.
[0022] Thus the piston in the supply pipe header controls sensible
capacity by cutting fluid flow to upper circuits and the piston in
the return pipe header, near independently, controls latent
capacity by cutting off fluid flow to the lower most circuits.
[0023] Ducting the outside air within the space serving air
handling unit to the lower part of the cooling coil, the same air
handling unit may be used to effectively treat humid outside air as
well as serve the conditioned space. The natural limit to this
application is having sufficient sensible heat to perform the
necessary dehumidification. Should there be insufficient sensible
heat, some kind of reheat needs to be applied, just as it would in
case of a conventional air handling unit dedicated to treat outside
air only.
[0024] For hot water heating coils the near constant flow in active
circuits permits low coil differential pressure selection at full
load with assured low load performance and controllability.
[0025] One particular embodiment of this invention employs a
weighted piston in the supply pipe header. The weight of the piston
is such as to impose the desired differential pressure across the
coil thus ensure constant flow velocity in the active circuits. The
weighted piston is acting as a pressure relief device, on rising
pressure it moves up to expose more circuit entries, thus relieve
the pressure and visa versa should the differential pressure across
the coil fall. In this instance there is a low pressure drop
external control valve driven by the sensible load, for example a
butterfly valve. The flow velocity in the active circuits being
constant at a fixed differential pressure across the coil, the
number of active circuits thus the position of the piston is
directly proportional to the water quantity flowing through the
coil. Thus monitoring the position of this weighted piston gives an
accurate, repeatable option to monitor the fluid flow quantity.
Addition of entering and leaving water temperature sensors provides
energy monitoring capability.
[0026] Monitoring the water flow quantity via the position of this
weighted free floating piston also facilitates water side balancing
of the system. Keeping the external control valve full open and
throttling the balance valve until the free floating piston just
moves away from it's upper most position, indicates that the coil
is precisely at design water flow. All that remains is to lock the
balance valve at this particular position.
[0027] An optional interlock between the weighted free floating
piston and external control valve will add self balancing
capability. It is a limiting type interlock, when the free floating
piston in the supply pipe header reaches it's upper most position,
the external control valve is prevented from opening up further.
Should the external control valve be wide open at start up, the
same interlock commands the valve to close until the piston drops
just below it's uppermost position, thus restricting the coil to
design chilled water quantity. During normal operation the external
control valve is driven by the sensible load on the coil, however
when the design water flow is exceeded the limiting function takes
preference. This self balancing ability is suitable for chilled and
hot water distribution systems where the pressure change from full
to minimum system load is relatively small. For distribution
systems where large pressure variations are expected, it is
preferred to include manual balancing valves.
[0028] For a new installation the design can incorporate low
pressure drop coils and control valves, resulting in substantial
pumping power reduction. In a retrofit application where the
original coil is retained, pumping power reduction is proportional
to the pressure head reduction due to the removal of the original
high pressure drop control valve.
[0029] Selecting a coil, part load performance need not be
considered as there is near constant flow velocity in the active
circuits, thus transition from turbulent to laminar flow and
subsequent loss of heat transfer can no longer take place. A coil
suitably sized to meet full load will perform and remain
controllable at low partial loads.
[0030] To enable the invention to be fully understood, preferred
embodiments will now be described with reference to the
accompanying drawings, in which:
[0031] FIG. 1 is a schematic view of the first embodiment
highlighting the principle of this invention, operating as a
chilled water cooling coil.
[0032] FIG. 2 shows the application of this coil in an air handling
unit for treating high humidity outside air and also serving a
conditioned space.
[0033] FIG. 3 is a constant differential pressure, thus constant
circuit flow velocity embodiment of this invention, with weighted
free floating piston in the supply pipe header of the coil.
[0034] FIG. 4 an alternative method to detect location of weighted
free floating piston to facilitate water flow measurement.
[0035] FIG. 5 is a simplified way to detect upper most position of
weighted free floating piston for water side balance indication and
self balancing.
[0036] FIG. 6 shows an integral system powered control valve as an
alternative to external control valve.
[0037] FIG. 7 illustrates a system powered method of controlling
pressure differential across the coil to facilitate latent/sensible
capacity ratio control.
[0038] FIG. 8 is a system pressure dependent low cost system
powered alternative for general comfort cooling application.
[0039] FIG. 9 shows a system pressure dependent motorised
positioning of control piston in supply header. Optional
latent/sensible capacity ratio control by additional piston placed
in return pipe header is also illustrated.
[0040] FIG. 10 is a system powered alternative of positioning of
control piston in return pipe header to facilitate latent/sensible
capacity ratio control.
[0041] FIG. 11 illustrates a three stage solenoid valve controlled
approach, where a number of circuits are controlled as a group.
[0042] FIG. 12 details of hydraulic actuated self propelled control
piston.
[0043] FIG. 13 associated control elements of hydraulic actuated
self propelled control piston.
[0044] FIG. 14 hybrid, hydraulic system and electric powered self
propelled piston for pipe headers made of ferrous material.
[0045] FIG. 15 as in FIG. 14 but suitable for ferrous and non
ferrous coil pipe headers.
[0046] FIG. 16 basic hydraulic actuated diaphragm circuit by
circuit control without 100% positive shut off capability.
[0047] FIG. 17 hydraulic actuated diaphragm with near independent
latent and sensible capacity control, also 100% shut off
capability.
[0048] FIG. 18 basic system powered diaphragm control, no 100% shut
off.
[0049] FIG. 19 system powered diaphragm control with modified pipe
connection to supply pipe header. 100% shut off capability.
[0050] FIG. 20 hydraulic actuated diaphragm and external control
valve, near independent sensible and latent control ability.
[0051] FIG. 21 hydraulic actuated diaphragms for circuit by circuit
control and integral throttle valve, near independent sensible and
latent control.
[0052] FIG. 22 mechanical actuated ball driven positioning of
control piston with 100% shut off capability.
[0053] FIG. 23 hydraulic actuated ball driven positioning of
control piston with 100% shut off capability.
[0054] FIG. 24 method of temperature based control piston position
sensing.
[0055] FIG. 25 pneumatic powered diaphragm control with sliding
bottom end clip used on diaphragm, shown under part load
condition.
[0056] FIG. 26 same as in FIG. 25, however illustrated in the 100%
shut off position.
[0057] FIG. 27 hydraulic actuated diaphragm with external, non
system, hydraulic source. Utilising hydraulic fluid of less than 1
specific gravity.
[0058] FIG. 28 high pumping efficiency, low running cost,
configuration with dedicated speed controlled pump.
[0059] FIG. 29 using a slotted cylinder to control coils with
relatively low number of circuits, such as used in fan coil
units.
[0060] Referring to FIG. 1, the chilled water coil 1, has a supply
header 2, return header 3, and interconnecting circuits 4, between
supply end return pipe headers. The plurality of interconnecting
circuits 4 are connected to each header 2, 3 by a corresponding
plurality of connectinc ports 202 at different locations lying in a
row one above the other along the header 2, 3. Fluid flow is
supplied to the supply header 2 through supply port 201 at the
bottom end of header 2 and is supplied from return header 3 through
return port 203 at the top end of return header 3. Sliding piston
5, placed in supply pipe header 2, and equipped with water tight
seals to prevent water flow from the lower to upper part of pipe
header 2. In this illustration piston 5, cuts off the water flow to
the upper three circuits 6, the coil surface temperature in the
region of circuits 6, is the same as of the entering air and no
heat exchange takes place. The circuits 4, below the lower edge of
piston 5, are active, receiving full supply of chilled water and
the coil surface temperature around circuits 4, is at design
temperature. Air traversing this region is cooled and dehumidified.
Moving piston 5, upwards increases both sensible and latent
capacities of the coil. Moving piston 5, downwards reduces both
sensible and latent capacities. The ratio of sensible versus latent
capacity is defined at the coil selection/design stage and this
ratio remains constant at partial load across the whole operating
range. The position of piston 5, is determined by the prevailing
sensible load as sensed by a space or return air dry bulb
temperature sensor. For most comfort cooling applications sensible
heat control is sufficient and piston 5, is the only required
control element. For applications that need reduction of latent
capacity, there is another piston, piston 7, located in the return
pipe header. For maximum latent capacity piston 7, is at it's lower
most position. Elevating piston 7, thus cutting off water flow
through the lowest circuits 8, results in a reduction of latent
capacity. The condensate forming on the cold surface in the region
of active circuits 4, reaching coil surface around inactive
circuits 8, is partly or fully evaporated, thus reducing latent
capacity and increasing the sensible by evaporative cooling the air
passing through the lower portion of the coil. Should it be
desired, by sufficiently elevating piston 7, in return header 3, a
position is reached where the copying coil is doing pure sensible
cooling without effecting the total moisture content of the air
stream.
[0061] Referring to FIG. 2, typical cooling only air handling unit
9, equipped with air filter 10, cooling coil 1, and supply air fan
11. In this illustration only the lower, shaded half of cooling
coil 1, is active. Return air enters at location 12, outside/fresh
air enters at 13, and the supply air leaves the air handling unit
at location 14. The outside air entering at location 13, is guided
by ducting/baffles 15, to the lower, active portion of cooling coil
1, where, depending on it's dry and wet bulb temperatures, it is
cooled and dehumidified. Since the lower circuits of cooling coil
1, will remain active as long as there is sensible load, humid
outside air can effectively be treated without the need for an air
handling unit dedicated to outside air treatment alone.
[0062] Referring to FIG. 3, where one particular method of
positioning of piston 5, in supply pipe header 2, is illustrated.
External control valve 16, is of low pressure drop type when in the
full open position, as for example a butterfly valve. The degree of
opening of this motorised valve is determined by space or return
air temperature deviation from setpoint, thus by the prevailing
sensible load on the coil. The weight of piston 5, is chosen to
equal the design pressure difference between supply header 2, and
return header 3. For this free floating piston 5, to remain
stationary, the supply header pressure acting on it's bottom must
equal the return header pressure acting on it's top plus the weight
of the piston. As the weight of piston 5, is fixed according to the
design pressure drop of the coil, any deviation from design
DIFFERENTIAL PRESSURE will move this piston up or down until a new
balance is reached and the coil DIFFERENTIAL PRESSURE is at design
again. Evidently having the differential pressure constant will
ensure constant water flow velocity in the active circuits,
although the number of active circuits changes according to the
heat load. Let us assume that the differential pressure across the
coil is at design with the illustrated position of piston 5, and
current opening of control valve 16. Should the air side load on
the coil increase, valve 16, is opened some more, thus the pressure
drop at valve 16, is reduced. This pressure drop change at valve
16, shows up as a pressure differential increase across the coil,
piston 5, is no longer in balance at it's current position and
starts to ride up, permitting water to flow through more circuits,
thus reducing the differential pressure across the supply and
return pipe headers. The upward progress of piston 5, stops when
balance is achieved, that is the differential pressure across the
coil has dropped back to it's design value. Should the air side
load decrease, the opposite happens and piston 5, moves down,
closing off circuits until the new balance position is reached.
From another perspective piston 5, is acting as a gravity operated
pressure relief valve.
[0063] The constant differential pressure maintained by piston 5,
ensures constant velocity in the active circuits and the number of
active circuits is dependent on the position of this piston,
knowing the position of piston 5, provides an accurate means of
measuring the quantity of water flowing through the coil. In this
particular embodiment an ultrasonic transducer/receiver 17, is
placed at the upper end of supply header 2. With it's associated
electronic circuitry the ultrasonic transducer/receiver operates as
an echo sounder and measures the distance of piston 5, relative to
the piston's upper most position. The coil manufacturer's data ca
accurately relate the position of piston 5, to water flow rate. The
addition of entering and leaving water temperature sensors will
provide the necessary inputs to compute the energy used by the
coil. Temperature sensors are not illustrated in FIG. 3. Mechanical
stop 18, is to prevent piston 5, from going all the way to the
bottom of supply header 2 and cutting off the entering water supply
connection.
[0064] Water side balancing of the system and providing self
balancing facility, as explained earlier, requires that it is known
when piston 5, is at or near it's upper most position. Evidently
this echo sounder type device is more than capable of providing the
required information and with some additional electronic circuitry
to indicate water side balance and or to interlock control valve
16, to facilitate self balancing action.
[0065] Referring to FIG. 4, where an alternative method of
indicating the position of piston 5, is illustrated. Multi turn
potentiometer 19, is direct coupled to threaded rod 21, which in
turn supported by bearings 20, and 22. Bearing 20, also contains a
water tight seal. Threaded rod 21, passing through piston 5, is
meshed with female thread contained within piston 5, thus any up or
down displacement of piston 5, from it's position causes threaded
rod 21, to rotate. This in turn rotates potentiometer 19, and a
change in resistance indicates the location of piston 5. The pitch
of the thread on threaded rod 21, is high, in the order of a few
turns representing the full travel of piston 5. To prevent piston
5, from turning about threaded rod 21, there is a vertical
protrusion on the inner wall of supply header 2, and a matching
groove in piston 5. This is not illustrated in FIG. 4, as there are
numerous other ways to achieve this.
[0066] Referring to FIG. 5, for water side system balance
indication and or for self balancing only the near and at the
uppermost position of piston 5, is of relevance. This may be
accomplished without monitoring the full travel position of piston
5, thus in a much simplified manner. In this embodiment piston 5,
contains a permanent magnet 23. Magnetic reed switches 24, and 25,
are located on the outside of and near the top of supply pipe
header 2. When piston 5, is at it's illustrated position both reed
switches are in the off/normally open position. As piston 5, moves
up and permanent magnet 23, is in line with reed switch 24, it
closes and indicates full water flow at correct differential
pressure and velocity across the coil. For self balancing when
magnetic reed switch closes it prevents control valve 16, from
opening further. Should control valve 16, already be too far open,
thus permitting excessive water flow, piston 5, rises higher and
reed switch 25, is activated by permanent magnet 23. When reed
switch 25, is in the closed position it commands valve 16, to
slowly close, thus reduce the water flow rate until piston 5, drops
down sufficiently to permit reed switch 25, to open. During normal
operation, that is when piston 5, is away from it's upper position,
control valve opening is set by space or return air deviation from
setpoint. Reed switches 24, and 25, are only acting as an upper
limit to indicate and or to prevent excessive water flow across the
coil, thus facilitating water side system balancing and or actual
balance.
[0067] Referring to FIG. 6, where an integrated system powered
control valve is shown as an alternative to external control valve
16, of FIGS. 3, and 4. This system powered valve consists of piston
26, cylindrical protrusion 27, and valve seat 28, housed in the
upper enlarged portion of return pipe header 3. Small diameter pipe
29, originates in entering water supply pipe and via filter 30, and
solenoid valve 31, can supply high pressure water to space above
piston 26. The water pressure available via solenoid valve 31, is
greater than the pressure in return header 3, thus piston 26, is
forced downwards, restricting the water flow rate and ultimately
shutting it off when the lower lip of protrusion 27, is in contact
with valve seat 28. To move the control valve to a more open
position solenoid valve 33, is opened, relieving the pressure above
piston 26, and discharging the excess water via pipe 34, into the
return water pipe. When solenoid valves 31, and 33, are closed
piston 26, maintains it's position. Pulsed opening of solenoid
valves 31, and 33, moves piston 26, to the desired position, thus
sets the required water flow rate. Protrusion 27, may be shaped
other than cylindrical to facilitate linear valve characteristics.
In normal operation position of piston 26, is set by the prevailing
sensible load, derived from temperature deviation of space or
return air from setpoint for constant volume air handlers. For
variable volume air handlers the supply air temperature deviation
from setpoint is the driver. If equipped with some form of position
indication of weighted free floating piston 5, flow monitoring and
water side system balance are handled as described in conjunction
with FIGS. 3, 4, and 5.
[0068] Referring to FIG. 7, where the "weight" of piston 5 is
variable, thus the differential pressure across the coil and
consequently the chilled water flow velocity in the circuits is
also variable. In this illustration piston 5 does not contain a
weight. Vertical supply pipe header 2, is extended via a 90 degree
bend into a horizontal section 42. Piston 43, is in this horizontal
portion 42, of supply pipe header. Loose fitting balls 44, between
piston 5, and piston 43, act as flexible "push rod" and transfer
force between the two pistons. High pressure system water enters
lower chamber of cylinder 36, via pipe 29, filter 30, fixed orifice
38, and pipe 39. The upper chamber of cylinder 36, is connected to
the return pipe header 3, via pipe 40. There is a weighted free
sliding piston 35, in cylinder 36, separating the lower and upper
chambers. The weight of piston 35, is such that when the
differential pressure between supply and return headers, 2, and 3,
respectively is at design, piston 35, remains in the same relative
vertical position to cylinder 36. Should the differential pressure
increase, piston 35, moves upwards, further exposing pipe entry 41,
which via pipe 34, relieves the excess pressure. The water quantity
entering lower chamber of cylinder 36, is restricted by fixed
orifice 38, and up and down movement of piston 35, governs the
quantity of water leaving via pipe 41. In order for this balance to
prevail, the differential pressure across the coil needs to remain
constant and this is achieved by pipe 39, conveying the same
pressure as in lower chamber of cylinder 36, to horizontal portion
of supply header 42. Thus the same pressure is acting on right hand
surface of piston 43. When the pressure on the right hand side of
piston 43, equals the pressure on lower side of piston 5, the
system is in balance, thus operating at design differential
pressure. Should the differential pressure decrease, due to
downward movement of control piston 26, or a pressure reduction in
the system distribution piping, pilot piston 35, drops down,
closing off water entry to pipe 41, permitting more water to enter
header pipe extension 42. Due to the reduced differential pressure
across the coil pressure acting on lower surface of piston 5, is
less than the pressure on the right side of piston 43,
consequently, piston 43, acting via spacer balls 44, will force
piston 5, to move down. Piston 5, in turn cuts off water flow to
some more circuits, resulting in an increased differential pressure
across the coil. The downward movement of piston 5, stops when the
coil differential pressure is again at it's design value, thus the
new balance point is reached and pilot piston 35, is permitting the
same water quantity to escape via pipe 41, as the quantity entering
via fixed orifice 38. Cylinder 36, is made of non ferrous material
and pilot piston 35, is of ferrous material and solenoid 37,
surrounds the upper portion of cylinder 36. When there is no
current flow in solenoid 37, the weight of pilot piston 35, sets
the magnitude of the coil differential pressure, acting as a
gravity pressure relief valve. Introducing a current into solenoid
37, the magnetic force acting on pilot piston 35, is counter acting
some of it's weight, thus the differential pressure setpoint for
the coil is reduced. Thus different differential pressure setpoints
may be maintained by changing the flow of current in solenoid 37.
The surface temperature of the coil, which in turn depends on
circuit flow velocity, effects the latent capacity of the coil more
than it effects it's sensible capacity. Therefore in this
embodiment the space or return air relative humidity controls the
differential pressure of the coil and the dry bulb temperature is
in command of total flow by positioning piston 26, of the integral
control valve. There is an interlock, not illustrated, when piston
26, is in it's upper most position, thus the control valve is full
open, yet the coil is unable to meet the sensible load, the latent
call for high circuit flow velocity is ignored and more circuits
are made available for sensible cooling. To achieve this the
current flow in solenoid 37, is increased, reducing the coil
differential pressure setpoint, thus more active coil surface area
is presented to the air stream. The foregoing latent versus
sensible capacity ratio control is and alternative to utilising
piston 7, placed in the return header 3, of the coil, as described
in conjunction with FIG. 1.
[0069] Referring to FIG. 8, illustrating a simple low cost
approach, without compensation for system pressure variations,
utilising a system powered control valve. Should the sensible load
decrease, solenoid valve 31, opens, admitting more water into
chamber on right side of piston 43, which in turn forces piston 5,
downwards via ball shaped spacers 44, cutting off water flow in
some more circuits. Keeping solenoid valve 31, open after all the
circuits are cut off, when lower surface of piston 5, reaches valve
seat 45, all water flow through the coil is stopped. This would be
the case when this particular air handling unit is not in service.
Should the sensible load increase, solenoid valve 33, is opened
permitting water to flow out from header 42, on right side of
piston 43. System pressure acting on piston 5, forcing piston 5,
spacers 44, and piston 43, up and to the right and permitting water
to flow from supply header 2, into some of the circuits. When the
coil cooling capacity is matching the air side cooling load,
solenoid valve 33, is closed. Valves 31, and 33, remain in the
closed position, the number of active circuits remain the same,
until there is a change in the air side load. For constant volume
air handlers solenoid valves 31, and 33, are controlled by
deviation from space or return air temperature setpoint, for
variable volume air handlers by deviation from supply air
temperature setpoint.
[0070] Referring to FIG. 9, an alternative method of positioning
piston 5, is shown. Geared motor 45; drives worm screw 21, and
piston 5, is coupled to worm screw 21, by a matching female thread.
When geared motor 45, turns worm screw 21, in one direction, piston
5, is moved upwards, reverse rotation causes piston 5, to move
downwards. When piston 5, is driven all the way down and it's lower
surface contacts valve seat 46, all water flow through the coil is
stopped. There is a vertical protrusion on the inner surface of
supply header 2, with matching groove in piston 5, to prevent
piston 5, to turn about it's axis when it is being repositioned by
worm screw 21. The vertical protrusion and groove in piston 5, are
not illustrated. Bearings 20, and 22, are to maintain axial and
radial positions of worm screw 21, and bearing 20, also contains a
water tight seal. Geared motor 45, is under the control of
prevailing sensible air side load. The optional latent/sensible
capacity ratio control is accomplished by piston 7. The mechanism
to position piston 7, in return header 3, is identical to the one
described above in conjunction with piston 5. Geared motor 47,
positioning piston 7, is under the command of space or return air
relative humidity deviation from setpoint.
[0071] Referring to FIG. 10, where a system powered version of
positioning piston 7, in return header 3, is illustrated. System
water may enter or escape from flexible bellows 48, via small
diameter pipe 32, and bellows 48, in turn moves piston 7, to the
desired position. Control piping arrangement, filter and solenoid
valves are the same as illustrated in FIG. 8. The positioning
signal for piston 7, originates from relative humidity deviation
from setpoint.
[0072] Referring to FIG. 11, illustrating three stage control of
cooling coil by solenoid valves. Dividing plates 49, placed in
supply pipe header 2, create three separate chambers in supply
header 2. The water flow to each chamber is controlled by
individual solenoid valves 50, 51, and 52. In the illustration
valves 50, and 52, are closed and 51, is open thus only circuits 4,
are active and there is no water flow in circuits 6, and 8. The
current operation mode is at reduced sensible capacity also at
reduced latent/sensible capacity ratio. In place of solenoid valves
motorised on/off valves or modulating control valves may be
utilised and the groups of circuits and valves are not limited to
three.
[0073] Referring to FIG. 12, a self propelled hydraulic powered
piston assembly is illustrated. This piston assembly is placed in
the supply pipe header 2, of the cooling/heating coil. The three
chambers 53, 54, and 55, may be pressurised via connecting pipes
56, 57, 58, respectively. Applying pressure to chamber 53, via pipe
56, expands flexible bellows 59, forcing split friction ring 60,
against the inner wall of pipe header 2, thus clamping the upper
part of the piston assembly in place. Pressurising chamber 54, via
pipe 57, will clamp the lower part of this piston assembly in
position. Delivering pressurised fluid to chamber 55, via pipe 58,
moves the upper and lower portions apart, as in illustrations A,
& C. Permitting fluid to flow out from chamber 55, lets the
upper and lower portions to move to close proximity as in
illustration B. If chamber 53, is pressurised and chamber 54, is
not under pressure, the lower portion of the piston assembly will
move down when fluid is delivered to chamber 55, and move up when
fluid is permitted to flow out from chamber 55. The upper part of
the assembly may move up or down when the lower part is clamped in
place in a similar manner. Thus alternate application of fluid
pressure to chambers 53, 54, and 55, enables the piston assembly to
"climb" up or down in pipe header 2.
[0074] Referring to FIG. 13, the pressurised fluid is derived from
the system, flows through replaceable filter 30, fixed orifices 61,
flexible pipes 56, 57, 58, to chambers 53, 54, and 55. When all
three solenoid valves 62, are closed, the three chambers 53, 54,
and 55, are pressurised. Opening one or more of the solenoid valves
relieves the pressure in the respective chamber/chambers. An
electronic controller, not illustrated, generates the sequential
signal to drive the piston assembly up or down according to the
prevailing load on the coil. Alternative to utilising system power,
a dedicated hydraulic or pneumatic pressure source may be used.
Another alternative is to incorporate solenoid valves 62, in the
piston assembly and bring the connecting wires out from header 2,
in place of flexible hydraulic pipes 56, 57, 58.
[0075] Referring to FIG. 14, where the clamping of upper/lower
portions of piston assembly is accomplished by magnetic force. This
is for mild steel pipe headers only. Solenoid 63, is wound around
ferrous bobbin 64. Split rings 65, are made of plastic and ferrite
mixture. When solenoid 63, is energised the magnetic circuit is
completed via ferrous bobbin 64, split rings 65, and steel pipe
header. Split rings 65, expand and clamp the powered end of piston
assembly in place. Fluid at system pressure is admitted to central
chamber 55, via orifice 61, and when solenoid valve 62, is closed,
expands bellows 59, as shown in illustrations A & C. Opening
solenoid valve 62, relieves the pressure in central chamber 55,
thus reducing the distance between upper and lower portions of the
piston assembly, as per illustration B. Flexible wiring loom, not
illustrated, connects the three solenoids to an external electronic
sequencer.
[0076] Referring to FIG. 15, a magnetic clamping arrangement is
shown suitable for non ferrous also for ferrous pipe headers. Split
ring 65, of plastic and ferrite mix is loaded by springs 66, to
expand and clamp against pipe header 2. In this configuration
solenoid 63, is energised to enable free movement of piston
assembly portion within the pipe header. Closed and open positions
of solenoid valve illustrated in A & B. Split ring 65, and
springs 66, details in illustration C.
[0077] Referring to FIG. 16, a long tubular flexible diaphragm 67,
is fitted inside pipe header 2. The upper expanded circular end of
diaphragm 67, is connected to pipe 71, and the lower collapsed semi
circular end is fastened to pipe header 2, at location 70. System
fluid via filter 30, forced by pump 68, via non return valve 69,
and connecting pipe 71, into below 67, extends the circular portion
of diaphragm 67, downwards, closing off additional circuits.
Turning pump 68, off and opening solenoid valve 62, fluid is
permitted to flow out from diaphragm 67, collapsing more of the
circular section into semi circular and permitting water flow
through more circuits of the coil. Illustrations A. & B. show
expanded circular and collapsed semi circular sections of diaphragm
67, respectively. This particular configuration is suitable for
cooling coils in humid tropical climate, where there is always some
sensible and latent load on the coil and positive shut off of the
water flow is not critical.
[0078] Referring to FIG. 17, where an additional tubular diaphragm
75, is placed inside return pipe header 3. Fully inflating
diaphragms 67, and 75, results in positive shut off of water flow
through the coil. As diaphragm 75, shuts off flow through the lower
circuits, during normal operation it is under relative humidity
control, while diaphragm 67, is under sensible heat control.
Running pump 68, and opening solenoid valves 72, 74, will reduce
sensible and latent capacity respectively and near independently.
Opening solenoid valves 62, 73, will result in near independent
respective increase in sensible and latent capacity. Upright pipe
extension 76, is to ensure removal of air trapped in diaphragm 75.
The length of diaphragm 75, may be 1/2-1/3 or less of pipe header
3.
[0079] Referring to FIG. 18, there is a heavy ball 77, inside
diaphragm 67, thus eliminating the need for controls pump 68, as
shown in FIGS. 16, & 17. Opening solenoid valve 72, admits more
fluid into tubular diaphragm 67, and cuts off flow to additional
circuits. Opening solenoid valve 62, permits fluid to scape out of
diaphragm 67, resulting in more circuits made open to flow.
[0080] Referring to FIG. 19, where tubular diaphragm 67, is turned
90 deg. clockwise, looking down supply header 2, end extended all
the way to the bottom of same. Entering pipe connection 78, to
supply header 2, is turned 90 deg. anti-clockwise and split into
two connections to header 2. In this configuration full shut off of
the chilled water flow through the coil is possible, besides
circuit by circuit control of sensible coil capacity.
[0081] Referring to FIG. 20, the pressure inside tubular diaphragm
67, is maintained at a constant differential above the pressure in
return pipe header 3. Control fluid pump 68, takes system fluid via
filter 30, and delivers this fluid to diaphragm 67, via fixed
orifice 61. Pressure relief valve 36, maintains this pressure at a
constant level relative to the pressure in return header 3. The
pressure differential maintained is equal to the design pressure
drop of the coil. The action of diaphragm 67, in this application
is same as of free sliding piston 5, described in association with
FIG. 3. Butterfly valve 16, sets the quantity of chilled water
flowing through the coil and controlled by the sensible load and
diaphragm 67, maintains constant differential pressure across the
coil by exposing more or less circuits to chilled water flow.
Piston 35, of pressure relief valve 36, is made of ferrous
material. Increasing/decreasing current flow through solenoid 37,
the differential pressure setting of relief valve 36, is changed.
The differential pressure maintained across the coil sets the
sensible to latent capacity ratio of the coil, thus it is under
relative humidity control. When there is water flow in all the
circuits, i.e. diaphragm 67, is at minimum inflation, permanent
magnet 23, comes to close proximity to reed switch 24. Contact
closure of reed switch 24, indicates design flowrate across the
coil when operating at design pressure drop. This may be used as an
indication to facilitate water side system balancing or used as an
interlock to prevent butterfly valve to open more, thus limiting
the coil to it's design water quantity.
[0082] Referring to FIG. 21, the function and operation of
diaphragm 67, is the same as described in conjunction with FIG. 20.
The difference is in replacing the butterfly valve with diaphragm
75, and modification of return pipe connection 79. Solenoid valves
72, and 62, when open, will permit fluid flow to or from diaphragm
75, respectively. The solenoid valves are under sensible load
control and diaphragm 75, is acting as a conventional throttle
valve.
[0083] Referring to FIG. 22, free sliding piston 80, of positive
buoyancy is located in supply pipe header 2. Rotating toothed wheel
81, clockwise transfers balls 82, from reservoir 83, to pipe header
2. The balls 82, force piston 80, downwards. Since piston 80, has a
bore through it the pressure above and below the piston are the
same, thus only a little force is required to overcome the the
buoyancy of piston 80. The balls 82, are of slight positive
buoyancy and if any circuit entrance above piston 80, is open to
water flow, this flow tends to move the nearest ball to block the
open circuit entry. Rotating toothed wheel 81, anti-clockwise
transfers balls 82, from supply header 2, to reservoir 83, piston
80, now free to move up and more circuits become open to water
flow. Toothed wheel 80, is driven by a gear motor, which is not
illustrated, and is under the control of prevailing sensible
load.
[0084] Referring to FIG. 23, moving balls 82, from reservoir 83, to
supply pipe header 2, is accomplished by pump 68, supplying
pressurised fluid via non return valve 69, to the space in
reservoir 83, below piston 84. Opening solenoid valve 62, relieves
the pressure under piston 84, in reservoir 83, and permits the
balls 82, to move from header 2, to reservoir 83.
[0085] Referring to FIG. 24, illustrating a temperature based
method of determining % of circuits in operation. Air handling unit
9, consisting of filter 10, cooling coil 1, and supply air fan 11.
Return air enters the air handler 9, at location 12, and supply air
leaves at location 14. Temperature sensor T1, is placed near the
top of cooling coil 1, and temp. sensor T2, is near the bottom of
same. There is also a temp. sensor T3, located in the leaving air
stream. Where temperature sensed by T3, falls between temperatures
sensed by T1, and T2, is proportional to % of coil circuits in
operation, except when 100% or 0% of the circuits are active. At
full and zero load all three temperatures sensed T1, T2, and T3,
are the same, however the full or zero load condition is easily
determined from the actual value of sensed temperatures.
[0086] Referring to FIG. 25, a long tubular elastic diaphragm 67,
is fitted inside pipe header 2. The upper expanded circular end of
diaphragm 67, is connected to pipe 71, and the lower collapsed semi
circular end is fastened to and sealed at sliding guide 70.
Compressed air from air source 85, enters diaphragm 67, when
solenoid valve 72, is open, via connecting pipe 71, extends the
circular portion of diaphragm 67, downwards, closing off additional
circuits. Solenoid valve 72, closed and solenoid valve 62, open air
is permitted to exhaust out of diaphragm 67, collapsing more of the
circular section into semi circular and permitting water flow
through more circuits of the coil. Illustrations A. & B. show
expanded circular and collapsed semi circular sections of diaphragm
67, respectively.
[0087] Illustration C shows detail of sliding guide 70. The
construction of tubular elastic diaphragm 67, is such, that it
exhibits more elasticity along it's length than around it's
circumference.
[0088] Referring to FIG. 26, where the advantage of non uniform
elasticity of tubular elastic diaphragm 67, is illustrated. Once
diaphragm 67, is fully inflated with air of equal pressure to
prevailing pressure in supply pipe header 2, further increase in
air pressure expands diaphragm 67, downwards. Ultimately, reaching
the bottom of supply header 2, and shutting off water flow through
the coil 100%. This full shut off condition is illustrated here,
all other functions are the same as described in conjunction with
prior FIG. 25.
[0089] Referring to FIG. 27, a hydraulic fluid of lower than 1 in
specific gravity is used to inflate the non uniform elasticity
tubular diaphragm 67. The buoyant fluid is to ensure that the
uppermost portion of diaphragm 67, takes up circular shape first,
thus cuts off chilled water flow to the uppermost circuits first.
When more hydraulic fluid is admitted, this circular shape extends
downwards, cutting off water flow to more circuits progressively.
Elevating the hydraulic fluid pressure inside diaphragm 67, above
the prevailing pressure in supply pipe header 2, expands diaphragm
67, downwards and provides 100% water flow shut off. To increase
hydraulic fluid volume and or pressure in diaphragm 67, pump 68, is
started and fluid is pumped from reservoir 86, via non return valve
69, and connecting pipe 71, into diaphragm 67. To reduce the fluid
volume and or pressure in same, solenoid valve 62, is opened and
the hydraulic fluid is free to flow back to reservoir 86. Although
not illustrated, reservoir 86, may be directly pressurised from the
chilled water supply pipe in order to minimise the load placed on
pump 68.
[0090] Referring to FIG. 28, where the same method of positioning
of piston 5, in supply pipe header 2, is illustrated, as described
in conjunction with FIG. 3, except that the butterfly valve is
replaced with a variable speed pump 87. The pump speed is set by
speed controller 88, which in turn is derived from space air temp.
deviation from setpoint, thus from the prevailing sensible load on
the coil. The weight of piston 5, is chosen to equal the design
pressure difference between supply header 2, and return header 3.
For this free floating piston 5, to remain stationary, the supply
header pressure acting on it's bottom must equal the return header
pressure acting on it's top plus the weight of the piston. As the
weight of piston 5, is fixed according to the design pressure drop
of the coil, any deviation from design DIFFERENTIAL PRESSURE will
move this piston up or down until a new balance is reached and the
coil DIFFERENTIAL PRESSURE is at design again. Evidently having the
differential pressure constant will ensure constant water flow
velocity in the active circuits, although the number of active
circuits changes according to the heat load. Let us assume that the
differential pressure across the coil is at design with the
illustrated position of piston 5, and current speed of pump 87.
Should the air side load on the coil increase, controller 88, ramps
up the speed of pump 87, which attempts to force more chilled water
through the currently active coil circuits, resulting in a pressure
differential increase across the coil. Piston 5, is no longer in
balance at it's current position and starts to ride up, permitting
water to flow through more circuits, thus reducing the differential
pressure across the supply and return pipe headers. The upward
progress of piston 5, stops when balance is achieved, that is the
differential pressure across the coil has dropped back to it's
design value. Should the air side load decrease, the opposite
happens and piston 5, moves down, closing off circuits until the
new balance position is reached. From another perspective piston 5,
is acting as a gravity operated pressure relief valve.
[0091] The constant differential pressure maintained by piston 5,
ensures constant velocity in the active circuits and the number of
active circuits is dependent on the position of this piston,
knowing the position of piston 5, provides an accurate means of
measuring the quantity of water flowing through the coil. In this
particular embodiment an ultrasonic transducer/receiver 17, is
placed at the upper end of supply header 2. With it's associated
electronic circuitry the ultrasonic transducer/receiver operates as
an echo sounder and measures the distance of piston 5, relative to
the piston's upper most position. The coil manufacturer's data can
accurately relate the position of piston 5, to water flow rate. The
addition of entering and leaving water temperature sensors will
provide the necessary inputs to compute the energy used by the
coil. Temperature sensors are not illustrated in FIG. 28.
Mechanical stop 18, is to prevent piston 5, from going all the way
to the bottom of supply header 2 and cutting off the entering water
supply connection.
[0092] Water side balancing of the system and providing self
balancing facility, as explained earlier, requires that it is known
when piston 5, is at or near it's upper most position. Evidently
this echo sounder type device is more than capable of providing the
required information and with some additional electronic circuitry
to indicate water side balance and or to interlock pump speed
controller 88, to facilitate self balancing action. While the
embodiment illustrated in FIG. 28, is not a low first cost
solution, however from a standpoint of pumping power, thus
operating cost, it represents the most efficient approach. Also
incorporates optional features ranging from self balancing to
accurate energy measurements of the coil's energy usage.
[0093] Referring to FIG. 29, where a slotted cylinder 89, is placed
inside supply pipe header. The slots 91, on cylinder 89, are
progressively longer going from top towards the bottom. This is to
ensure that the upper circuits are cut off from chilled water flow
prior to progressing sequentially downwards. The opened up and
flattened mantle 90, of control cylinder 89, also shows progression
of length of slots 91. For progressive and sequential circuit by
circuit control, cylinder 89, is rotated through 180 degrees by
modulating motor 92. Cylinder 89, is open at the bottom permitting
supply chilled water to enter the cylinder. The supply water is
admitted from inside cylinder 89, to coil circuits via slots 91.
Reference point being at the coil circuit entry, when cylinder 89,
is at 0 degree position all the circuits are receiving chilled
water, at 180 degree position all the circuits are shut off. This
particular embodiment shows two circuits being switched in or out
of circulation in single steps Evidently this concept is also valid
for individual circuit by circuit control, also for switching of
multiple circuits in single step by arranging slots 91, in an
appropriate manner. The embodiment illustrated in FIG. 29, is most
suitable for controlling chilled water coils with low number of
circuits, such as used in fan coil units and small air handling
units. The modulating motor 92, is a conventional one used in
standard control applications.
[0094] Positioning signal for modulating motor 91, originates from
conditioned space temperature deviation from setpoint for constant
air volume systems and from supply air temperature deviation from
setpoint for variable volume air distribution systems.
[0095] In general, it would be evident to a skilled engineer that
logical combinations of above described embodiments would also
provide functional solutions, exhibiting some or all of the
attributes described in the foregoing. Utilising different
embodiments the principles of this invention remain the same.
Circuit by circuit control, shutting off the upper circuits first
and progressing downwards provides sensible capacity control.
Circuit by circuit control, shutting off lower circuit first and
progressing upwards facilitates latent/sensible load ratio control.
Maintaining different water side differential pressure across the
coil effects circuit flow velocity, thus temperature rise of
chilled water consequently effective coil surface temperature, is
another way of effecting latent/sensible load ratio control. At
fixed differential pressure across the coil the water flow velocity
in the circuits is constant, thus' the number of active circuits is
directly proportional to the water quantity through the coil,
offering an accurate means for measuring water flow rate.
* * * * *