CA 02530861 2013-09-19
TIME COORDINATING ENERGY MONITORING SYSTEM
[0001]
FIELD OF THE INVENTION
[0002] The present invention relates to retrieving energy consumption
information from
monitoring devices. More specifically, the present invention relates to
methods, devices and
systems capable of retrieving time correlated energy consumption information.
BACKGROUND
[0003] In facilities, e.g. buildings or installations, where a significant
amount of power is
used among a variety of units, it would be advantageous to allow the building
owner to
allocate energy costs to the different units, i.e. consumers, within the
facility. For a
commercial office building, these units may include the different tenants
within the building
or the common loads for the facility, such as the elevators or HVAC systems.
For an
industrial facility, these units may include the different production lines,
machines or
processes within the facility. As opposed to allocating costs based on a fixed
or formulaic
approach (such as pro-rata, e.g. dollars per square foot or based on the
theoretical
consumption of a process/machine), an allocation based on actual measurements
using
appropriate monitoring devices may result in more accurate and useful
information as well as
a more equitable cost distribution.
[0004] Both installation and ongoing, i.e. operational and maintenance,
costs for these
monitoring devices are important considerations in deciding whether a
monitoring system is
worth the investment. While monitoring devices may be read manually, which
does not
increase the installation cost, manual data collection may increase on-
going/operational costs.
Alternatively, monitoring devices may be interconnected and be automatically
read via a
communications link. However, typical communication links require wiring to
interconnect
the devices which increases the installation cost.
[0005] Emerging wireless mesh (or ad-hoc) networking technologies can be
used to
reduce the installation costs of monitoring devices while providing for
automated data
collection. Also called mesh topology or a mesh network, mesh is a network
topology in
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which devices/nodes are connected with many redundant interconnections between
network
nodes. Using wireless interconnections permits simpler and cost-effective
implementation of
mesh topologies wherein each device is a node and wirelessly interconnects
with at least some of
the other devices within its proximity using RF based links. Mesh networking
technologies
generally fall into two categories: high-speed, high bandwidth; and low speed,
low bandwidth,
low power. The first category of devices are typically more complex and costly
that the second.
Since energy monitoring does not typically require high speed/high bandwidth
communication,
the second category of devices is often sufficient in terms of data
throughput.
[0006] Energy monitoring devices may include electrical energy meters that
measure at least
one of kWh, kVAh, kVARh, kW demand, kVA demand, kVAR demand, voltage, current,
etc.
Energy monitoring devices may also include devices that measure the
consumption of water, air,
gas and/or steam.
SUMMARY
[0007] The present invention is defined by the following claims, and
nothing in this section
should be taken as a limitation on those claims. By way of introduction,
embodiments described
below relate to an energy monitoring device for reporting energy consumption
over a time
period. In accordance with one aspect of the invention there is provided a
method of
synchronizing a time period over which energy measurements are accumulated for
an energy
monitoring system including a plurality of energy monitoring devices. The
method involves
transmitting a first radio frequency packet from a time reference device via a
network including
at least a first and a second of the plurality of energy monitoring devices to
a third of the
plurality of energy monitoring devices, and transmitting a second radio
frequency packet
containing a current time of the third energy monitoring device to the time
reference device via
at least a fourth and a fifth of the plurality of energy monitoring devices.
The method also
involves calculating a time difference between the current time and a
reference time of the time
reference device, updating the current time of the third energy monitoring
device when the time
difference exceeds a minimum time difference, and accumulating, over the time
period, a
measure of energy consumption by the third energy monitoring device of a load
coupled with the
third energy monitoring device. The method further involves transmitting the
measure of energy
consumption for the time period from the third energy monitoring device via
the network
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including at least the fourth and the fifth of the plurality of energy
monitoring devices to a data
aggregation device, and identifying by the data aggregation device an
aggregate measure of
energy consumption consumed by the load over the time period.
[0008] In accordance with another aspect of the invention there is provided
a system for
correlating energy readings from various loads in a facility. The system
includes a plurality of
energy monitoring devices, first provisions for transferring a radio frequency
packet containing a
time reference from a time reference device via at least a first and a second
of the energy
monitoring devices to a third of the energy monitoring devices, and second
provisions for
adjusting a time register within the third energy monitoring device based on a
measured time
difference included in the packet. The system also includes third provisions
for accumulating
energy consumption over a time period within the third energy monitoring
device, fourth
provisions for transmitting the accumulated energy consumption for the time
period from the
third energy monitoring device via at least a fourth and a fifth energy
monitoring device to a data
aggregation device, and fifth provisions for identifying a measure of energy
consumption
consumed by a load being monitored by the third energy monitoring device over
the time period.
[0009] In accordance with another aspect of the invention there is provided
a method of
synchronizing a local time value maintained in each of a plurality of energy
monitoring devices
with a reference time value maintained in a data aggregation device, the data
aggregation device
and plurality of energy monitoring devices being interconnected by an RF ad-
hoc network. The
method involves receiving time reference data transmitted by the data
aggregation device via the
ad-hoc network by a first energy monitoring device of the plurality of energy
monitoring
devices, the time reference data being communicated via at least a second of
the plurality of
energy monitoring devices, the time reference data being generated based on
the reference time
value. The method also involves determining whether the local time value
maintained in the first
energy monitoring device is synchronized with the reference time value based
on the received
time reference data, and adjusting the local time value maintained in the
first energy monitoring
device based on the time reference data where it is determined that the local
time value
maintained in the first energy monitoring device is not synchronized with the
reference time
value. The method further involves
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acquiring data by the first energy monitoring device, the acquired data being
associated with
a first time period, the first time period being measured based on the local
time value
maintained in the first energy monitoring device, and transmitting the
acquired data to the
data aggregation device via at least a third of the energy monitoring devices
in the ad-hoc
network. The data aggregation device has data associated with a second time
period, further
the second time period is measured based on the reference time value, and the
first time
period is substantially similar to the second time period due to the
adjusting.
[0010] Further aspects and advantages of the invention are discussed below
in
conjunction with the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Fig. 1 depicts a block diagram of a commercial building
incorporating an energy
monitoring system according to one example.
[0012] Fig. 2 depicts a block diagram of the internal circuitry of an
example of an energy
monitoring device for use with the energy monitoring system of Figure 1.
[0013] Fig. 3 depicts a block diagram of an exemplary procedure for time
synchronizing
the energy monitoring device of Figure 2 according to one example.
[0014] Fig. 4 depicts a block diagram of another exemplary procedure for
time
synchronizing the energy monitoring device of Figure 2 according to an
alternate example.
[0015] Fig. 5 depicts a block diagram of another exemplary procedure for
time
synchronizing the energy monitoring device of Figure 2 according to yet
another alternative
example.
[0016] Fig. 6 depicts a block diagram of another exemplary procedure for
time
synchronizing the energy monitoring device of Figure 2 according to yet
another alternative
example.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0017] Herein, the phrase "coupled with" is defined to mean directly
connected to or
indirectly connected through one or more intermediate components. Such
intermediate
components may include both hardware and software based components. Further,
to clarify
the use in the pending claims and to hereby provide notice to the
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public, the phrases "at least one of <A>, <B>, ... and <1\1>" or "at least one
of <A>,
<B>, <N>, or combinations thereof' are defined by the Applicant in the
broadest
sense, superceding any other implied definitions herebefore or hereinafter
unless
expressly asserted by the Applicant to the contrary, to mean one or more
elements
selected from the group comprising A, B, ... and N, that is to say, any
combination of
one or more of the elements A, B, ... or N including any one element alone or
in
combination with one or more of the other elements which may also include, in
combination, additional elements not listed.
[00181 One problem with low speed/low power/low bandwidth mesh networking
technologies is that, although the bandwidth of the network is sufficient for
transmitting energy related data, the overall network, i.e. end to end,
latency or the
variation in latencies over time or over different network paths, may be
significant.
Such ad-hoc transmission paths and resultant latencies may interfere with the
transmission of data which is characterized by, or is sensitive to, a temporal
component or otherwise based on a chronological data component, such as the
time or
sequence of data acquisition. This may result in data being delivered with
significant
delay relative to the time it was acquired and/or relative to the delivery of
other data.
For example, when attempting to measure energy demand, it is desirable to
align the
measurement to certain time boundaries (for instance, a 15 minute boundary).
This
means that all of the data generated/acquired within a given boundary should
be
reported to a central aggregation point where it can be aggregated and
reported as the
demand for that boundary. If the data is time-stamped, then the central
computer can
wait as long as it takes to receive the data and then aggregate the data based
on the
time stamps to determine in which demand window the data belongs. However, if
the
time stamps are inaccurate due to the inaccuracy of the clock in the
monitoring
device, the data from that device may be incorrectly aggregated to the wrong
demand
window resulting in inaccurate reporting. Therefore, time synchronizing either
the
devices themselves, or identifying the demand for given intervals at a central
computer may be necessary. Synchronization of the monitoring devices with a
central time authority may be performed by broadcasting time synchronization
data to
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all of the devices or requiring the monitoring devices to periodically
communicate
with the central time authority to retrieve synchronization signals. However,
if the
data path through the mesh network from the central computer to the monitoring
devices includes delays (for instance lOs of seconds) and the delays between
various
devices are variable, it may become difficult to time synchronize the
monitoring
devices accurately enough for a given desired accuracy. Where the energy data
is not
time stamped by the monitoring device, the data must be received by the
central
aggregation point within a window of time to be properly aggregated into the
demand
for a given period. Network delays may cause difficulties with identifying the
time
period for which any given piece of data from a monitoring device relates.
Further,
packets may arrive out of order due to the fact that each packet may follow a
different
path through the network.
[00191 The following description details various mechanisms for generating
closely aligned/synchronized demand measurements from multiple electrical
monitoring devices which are in communication with a central computer through
a
mesh network. It will be clear to those skilled in the art that the mechanisms
defined
herein are also applicable to monitoring other parameters indicative of energy
consumption. The demand calculation for a given device may be performed
entirely
by the electrical monitoring device, partially performed by the central
computing
device or performed entirely by the central computing device based on energy
readings retrieved from the electrical monitoring device(s).
[0020] In the following description, two relevant time periods will be
generally
referenced. "Monitor time" is the time present in a memory location in a
particular
monitoring device, i.e. the "clock" time known to the monitoring device, also
referred
to as "device time" or "Dt". "Computer time" is the time present in a memory
location in a central computer, i.e. the "clock" time known to the central
computer,
also referred to as "Ct". Computer time will generally be the real or accurate
time to
which it is desirable to reference all measurements and recordings. The
computer
time may be synchronized to time references such as GPS satellites or an
atomic
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clock, or other available time authority. Alternatively, the Dt of any
particular device
may be used as the reference.
[0021] Time within a device may be represented in many formats such as
hours/minutes/seconds, number of seconds since a start time (for instance Jan.
1, 1970
at midnight), or a free running counter value coupled with a conversion
value/function between the free running counter value and real time.
[0022] Figure 1 depicts an exemplary commercial office building 100 for use
with
the disclosed examples. The commercial office building 100 has a number of
floors
110. Each floor may contain an electrical room 130. Alternatively there may be
more than one electrical room 130 per floor or only one electrical room 130
per a
number of floors. Within each electrical room 130 there may be one or more
energy
monitoring devices 120 within an energy monitoring system 101. The energy
monitoring devices 120 communicate among each other to form a mesh network,
depicted in Figure 1 by multiple communications links 140 shown between the
energy
monitoring devices 120. It will be appreciated that fewer or more
communications
links 140 may be used between monitoring devices 120 and that the availability
of a
communications link 140 between any two monitoring devices 120 may fluctuate
depending upon conditions such as interference, etc. Repeaters 155 may also be
provided to facilitate communications between two devices 120 which may not
otherwise be able to communicate due to distance, interference, etc. The mesh
network also encompasses a gateway 150 which facilitates communications with a
computer 160. The computer 160 may communicate energy data and other data over
a LAN 170. The computer 160 and gateway 150 communicate over a serial or other
form of communication link. Alternatively the gateway 150 may interface with
the
LAN 170 directly and the computer 160 may be connected to the LAN 170 in a
different part of the building 100 and communicate with the gateway 150 over
the
LAN 170. The computer 160 may receive a time reference from a GPS satellite
185.
Alternatively, the GPS satellite 185 signal may be received by an energy
monitoring
device 120, gateway 150 or repeater 155 within the mesh network. In this
alternate
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case, the time within the alternate device becomes the reference for the
energy
monitoring system 101.
[00231 A user 190 may transport a portable communication device 180 around the
building 100. This portable communication device 180 may be used as an
alternate
time source to computer 160. In addition, the portable communication device
180
may verify the time in energy monitoring devices 120 within its vicinity due
to the
fact that it will likely communicate directly with energy monitoring devices
120 close
to it and therefore not have a large latency in receiving a packet from the
energy
monitoring devices 120 nearby.
[0024] Figure 2 shows a block diagram of an energy monitoring device 120
according to one example. The energy monitoring device 120 includes electrical
current interface circuitry 210 and electrical voltage interface circuitry
270. The
electrical current interface circuitry 210 and electrical voltage interface
circuitry 270
are operative to interface with power conductors which supply electrical
energy to a
certain load or area of the building 100. This interface may be direct or
through
appropriate current or voltage transformers. In alternative examples, the
energy
monitoring device may lack either the electrical current or electrical voltage
interfaces
210,270 depending upon the implementation and monitoring requirements of the
device 120. The energy monitoring device 120 farther includes an analog to
digital
converter 220, a micro-controller 230 coupled with the analog to digital
converter
220, and RF communications circuitry 240 coupled with the micro-controller
230.
The electrical current interface circuitry 210 and electrical voltage
interface circuitry
270 scale the signals from the power conductors to voltage levels compatible
with the
analog to digital converter 220. The analog to digital converter 220 provides
digital
representations of the voltage and current in the power conductors to
microcontroller
230. Using these signals, the microcontroller 230 calculates at least one
power
parameter such as kWh, kVAh, kVARh, kW demand, kVA demand, kVAR demand,
etc. The microcontroller 230 transmits this power parameter(s) through RF
communications circuitry 240 through the mesh network and gateway 150 to
computer 160. The microcontroller 230 also maintains time for the energy
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monitoring device 100 in a memory register 280 which may be internal to and/or
external to the microcontroller 230. The energy monitoring device 100 also
contains
a power supply 260 which may interface to the same voltage signals as the
voltage
interface circuitry 270 or to an alternative power source. Additional
circuitry 250,
such as wireline communications, I./0 circuitry, etc. may also be provided in
the
energy monitoring device 120.
100251 Several methods for time synchronizing the energy monitoring devices
in
the building 100 to a reference time will now be discussed. It will be
appreciated that
the described methods may be used alone or in combination to create hybrid
time
synchronization schemes without departing from the spirit and scope of the
invention.
[0026] Figure 3 shows a first procedure for time synchronizing the energy
monitoring device 120 with the computer 160, or other alternative time
reference,
according to one example. The procedure may be appropriate when the data
transfer
time of a packet from the energy monitoring device 120 to the computer 160 is
short
and less than the data transfer time of a packet from the computer 160 to the
energy
monitoring device 120. This may be due to the architecture of the mesh
network.
Periodically, the energy monitoring device 120 may determine that time
synchronization is required. The determination period may be based on an
expected
time drift of a crystal or clock within the energy monitoring device 120, etc.
When
time synchronization is required, the energy monitoring device 120 sends its
time into
the mesh network destined for the computer 160 (block 300). When the computer
160 receives the packet, it calculates the difference in time between its time
and the
energy monitoring device 120 time in the packet (block 310). This difference
may be
adjusted by at least the minimum transmission time of the packet. This time
difference is then returned to the energy monitoring device 120 in a
subsequent
packet and the energy monitoring device adjusts its time by the difference
(block
320). In this way, the monitoring device 120 accounts for the transmission
latency in
sending data to the computer 160 and the accuracy in synchronization of the
monitoring device 120 is not dependent on the latency in transmission of a
packet
from the computer 160 to the monitoring device 120.
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[0027] Figure 4 shows a second procedure for time synchronizing the energy
monitoring device 120 with the computer 160 according to one example. This
procedure may be appropriate when the data transfer time of a packet from the
energy
monitoring device 120 to the computer 160 is variable, but at least some
packets will
arrive from the energy monitoring device 120 to the computer 160 within the
desired
time synchronization accuracy. Periodically, the energy monitoring device 120
may
determine that time synchronization is required, as described above. When time
synchronization is required, the energy monitoring device 120 sends its time
into the
mesh network destined for the computer 160 (block 400). When the computer 160
receives the packet, it calculates the difference in time between its time and
the
energy monitoring device 120 time in the packet (block 410). If this
difference in
time is less than any previous difference calculated during the
synchronization
sequence, the difference is recorded in the computer (block 430). The sequence
of
blocks 400-430 may continue for N iterations where N is an integer greater
than or
equal to 1 in order that the chances of a packet having a short transmission
time
through the mesh network is increased. If after the N iterations, the absolute
value of
the minimum time difference recorded is greater than a threshold (block 440),
the
difference is sent from the computer 160 to the energy monitoring device 120
(block
450) such that the energy monitoring device 120 may adjust its time (block
460).
Otherwise, where the difference is already within allowable limits, correction
is not
necessary and the energy monitoring device 120 waits until the next time
synchronization is required (block 470). In this way, synchronization
adjustments are
only made when the time difference between the computer 160 and the energy
monitoring device 120 is more than a given threshold.
[0028] Figure 5 shows a third procedure for time synchronizing the energy
monitoring device 120 with the computer 160 according to one example. This
procedure may be appropriate when the data transfer time of packets within the
mesh
network is variable, but at least some of the time, packets will travel the
network fast
enough to ensure the desired time synchronization accuracy is achieved. The
procedure starts with the computer 160 sending its time (Ti) in a packet to
the energy
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monitoring device 120 through the mesh network (block 500). The energy
monitoring device 120 receives this time (Ti) and compares it to its time at
reception
(T2) (block 505). If these times differ beyond an amount expected within the
network
(for example by more than 5 minutes), the energy monitoring device 120 may
directly
set its time to the time in the packet (Ti) (block 506). This is so that the
energy
monitoring device gets at least a semi-accurate time as soon as possible and
time
differences may be represented in smaller registers (due to the maximum time
difference having an upper bound). The energy monitoring device 120 records
its
time at reception of the packet (T2) and its time at response to the packet
(T3) and
returns these values to the computer 160 through the mesh network (block 510).
The
computer 160 records its time at reception of the return packet (T4) (block
520). The
computer 160 then calculates the round trip delay (Trt=(T4-T1)+(T3-T2)) and
the
difference between the time in the computer 160 and energy monitoring device
120
(Td=[(T1-T2) + (T4-T3)]/2) (block 530). If the round trip delay (Trt) is less
than a
particular threshold, such as double the desired accuracy, the difference can
be
considered useable (block 540) and the difference can be returned to the
energy
monitoring device 120 in a subsequent packet such that the energy monitoring
device
120 may adjust its internal clock (block 550). Otherwise, the procedure
continues
from block 500. Alternatively, this procedure may be initiated by an energy
monitoring device 120.
[0029] Figure 6 shows a fourth procedure for time synchronizing the energy
monitoring device 120 with the computer 160 according to one example. This
procedure may be appropriate when the data transfer time of packets within the
mesh
network is known with a fair amount of accuracy. When it is determined that
time
synchronization is required, as described above, the computer 160 transmits a
packet
onto the network to one or more energy monitoring devices 120 (block 600). As
the
packet transitions through each energy monitoring device 120 on its way to the
destination energy monitoring device 120, each energy monitoring device 120 in
the
path increases a time delay register in the packet by the amount that each
intermediate
energy monitoring device 120 has delayed the transmission of the packet
(blocks 610,
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620). When the packet arrives at the destination energy monitoring device 120
(block
630), the destination energy monitoring device 120 may set its time to the
original
time recorded in the packet by the computer 160 plus the total time delay
through the
intermediate devices (Td) (block 640). In addition, this procedure may take
into
account retries. For instance, an energy monitoring device 120 forwarding a
packet
may increase the time delay register in the packet by the elapse of time
between an
initial attempt to forward the packet and a subsequent attempt. A similar
procedure
can be executed by the gateway 150. For example, if it is known that the
fastest an
energy monitoring device 120 can store and forward a packet is 10ms, it can be
assumed for a message that hopped 50 times that at least 500ms can be
subtracted
from the time offset. Each of the energy monitoring devices 120 that the
packet
transitions through may also accept the time synchronization information
within the
packet for local synchronization.
[00301 Once the computer 160 has received energy measurements from multiple
energy monitoring devices 120 it can correlate the measurements. For instance,
the
computer 160 can add the kWh measurements from more than one energy monitoring
device 120 to provide a combined energy usage value for a given floor,
customer,
section of the building, total building, etc. Alternatively, the computer 160
can
calculate electrical demand over a given time period for a given floor,
customer,
section of the building, total building, etc. This information may be used in
demand
response programs for the entire building or a given section of it. The
computer 160
can also add the total cost of energy for similar sections of the building.
For instance,
the computer 160 can combine at least two of electrical energy usage, gas
usage,
water usage, steam usage and compressed air usage into a total energy usage
value.
[00311 In one example, the energy monitoring device 120 may employ methods to
maintain accurate time keeping between synchronization such as by counting
zero
crossings or cycles of the voltage in the power conductors that are being
monitored.
These cycles may be used as a reference to maintain time between time
synchronization procedures as described above. Since it will normally be known
that
the energy monitoring device 120 is connected to a 50 or 60Hz power system, 50
or
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=
60 cycles respectively of the power system is indicative of the passage of one
second
of time. This may reduce the frequency with which time synchronization
procedures
have to be executed.
[0032] In another example, the mesh networking architecture may provide a
priority messaging system. A time synchronization packet may be sent at a high
priority so that it encounters fewer delays through the mesh network. Using
this
architecture, at least one of the procedures described above may result in
more
accurate time synchronization.
[0033] In another example, the mesh networking architecture may provide for
"quiet times". During these times, general packet traffic is quiesced or
reduced such
that a time synchronization packet can traverse the network with fewer delays
due to
other traffic. These quiet times may be initiated on a periodic basis or in
response to a
command sent from the gateway 150, computer 160, etc. Using this architecture,
at
least one of the procedures described above may result in more accurate time
synchronization.
[0034] In another example, the time synchronization packets within the mesh
network may comprises sequence numbers, keying sequences or other unique
identifiers such that a device receiving the packet can detect a packet
duplication to
prevent duplicate time synchronization sequences. For instance when an energy
monitoring device 120 receives a time synchronization packet, it compares a
sequence
number in that packet to the largest sequence number it has previously
received. If
the new sequence number is not greater than this, the packet is ignored.
[0035] Where appropriate in the above procedures, the procedure may be
initiated
at least a second time before the first execution of the procedure is
complete. This
may allow comparison of the results of the two executions and use of the
results of
the execution that result in the greatest time accuracy.
[0036] Where appropriate in the above procedures, adjustment of the time in a
device may include a discrete adjustment and/or an adjustment to the rate of
change
of time within the device.
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[0037] It will be
noted that changing the time within a monitoring device 120 to
cross a demand interval boundary has historically been a problem. Due to the
fact
that the computer 160 is aware of the amount of time adjustment made in many
of the
above procedures, adjustments to the demand calculations received from the
energy
monitoring devices 120 at the computer 160 can be made by the computer 160.
[00381 When the computer 160 requests energy monitoring data from an energy
monitoring device 120 it may first send packets to the devices 120 that are
furthest
away, either physically/geographically, i.e. furthest floor, or logically,
i.e. in terms of
the number of intermediate devices through which the communications must
travel.
In the illustrated example of Fig. 1, computer 160 would send a request to the
energy
monitoring device 120 on Floor 50 first, then the energy monitoring devices on
Floor
49, etc. Since the request packets take longer (on average) to reach the
energy
monitoring devices 120 that are furthest away, network efficiency is
optimized. This
is due to the fact that in general the requests packets all traverse up the
building
together, each arriving at their respective floor, then all responses are
generated and
traverse back down the building. Of course due to the dynamic nature of the
mesh
network, some packets will get out of order, but in general, data flows in one
direction
through the network and then the other which may optimize the usage of'
available
bandwidth.
[0039] It is
therefore intended that the foregoing detailed description be regarded
as illustrative rather than limiting, and that it be understood that it is the
following
claims, including all equivalents, that are intended to define the spirit and
scope of
this invention.
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