Title: Intelligent Buildings Technology
1Intelligent Buildings Technology
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- Introduction-Energy Management
- Energy used in buildings accounts for almost half
of the total amount of energy consumed in the
European Community today. - Almost 85 of the energy used in buildings is for
low temperature applications such as space and
water heating. - Appropriate building designs involving clean and
efficient technologies are already available and
there use may help to reduce future energy
consumption as well as to provide a better
quality of life for citizens.
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- Introduction-Energy Management
- With fossil fuels the primary energy source, the
building sector currently produces 22 of total
CO2 emissions in the EC. This is more than that
produced by the industrial sector. - Intelligently designed buildings are those that
involve environmentally responsive design taking
into account the surroundings and building usage
and involving the selection of appropriate
building services and control systems to further
enhance building operation with a view to the
reduction of energy consumption and environmental
impact over its lifetime.
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- Energy in Buildings
- Buildings are inherently linked to their usage
and surroundings and hence their indoor
environment is the result of a range of
interactions affected by seasonal and daily
changes in climate and by the requirements of
occupants varying in time and space. - The design of buildings in the mid-late twentieth
century has sought to eliminate the effect of
outdoor daily and seasonal changes through the
use of extensive heating, cooling, lighting and
ventilation equipment, resulting in spiraling
energy consumption and environmental impact.
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- Energy in Buildings
- A more climate sensitive approach linked to the
use of advanced control systems allows the
building occupants to control their indoor
environment whilst maximising the contribution of
ambient energy sources to the creation of a
comfortable indoor environment through the use of
a more climate sensitive design approach. - Under almost all circumstances it is necessary at
some point in time to provide some form of
auxiliary heating, cooling, lighting or
ventilation since natural sources cannot always
cover the requirements for thermal comfort,
visual comfort and IAQ that are the prerequisite
for a well balanced, comfortable and healthy
indoor environment.
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- Energy in Buildings
- The purpose of energy management in buildings,
and hence the role of the building energy
manager, is to identify the areas in building
stock where energy is used in excess. - Energy consumption in building is required for
the following uses - Heating
- Cooling
- Ventilation
- Lighting
- Equipment and machinery
- Domestic hot water
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- Indoor Comfort
- Thermal comfort
- Visual Comfort
- Indoor air quality
8Thermal Comfort
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- Thermal Comfort
- Comfort is defined as the sensation of complete
physical and mental well being. - Thermal neutrality, where an individual desires
neither a warmer nor a colder environment, is a
necessary condition for thermal comfort. - The factors affecting comfort are divided into
personal variables - activity
- Clothing
- and environmental variables,
- (air temperature,
- mean radiant temperature
- air velocity
- air humidity
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Thermal Comfort Energy Balance
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- Thermal Comfort Personal Variables
- Clothing describes the occupants thermal
insulation against the environment. This thermal
insulation is expressed in clo units.
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- Thermal Comfort Personal Variables
- Activity The metabolic rate is the amount of
energy produced per unit of time by the
conversion of food. It is influenced by activity
level and is expressed in mets (1 met seated
relaxing person).
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- Thermal Comfort Environmental Variables
- Temperature
- The average air temperature from the floor at a
height of 1.1 m. - Mean Radiant TemperatureThe average temperature
of the surrounding surfaces, which includes the
effect of the incident solar radiation. - Air VelocityWhich affects convective heat loss
from the body, i.e. air at a greater velocity
will seem cooler. - Air HumidityWhich affects the latent heat losses
and has a particularly important impact in warm
and humid environments
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- Thermal Comfort Indices
- Although the four parameters of air temperature,
radiant temperature, relative humidity and air
movement are generally recognized as the main
thermal comfort parameters, indoor environmental
conditions in terms of thermal comfort can
generally be assessed through three classes of
environmental indices, namely - Direct indices
- Rationally derived indices
- Empirical indices
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- Thermal Comfort Indices
- Direct indices
- dry-bulb temperature
- dew-point temperature
- wet-bulb temperature
- relative humidity
- air movement
- Rationally derived indices
- mean radiant temperature
- operative temperature
- heat stress, and
- thermal stress
- Empirical indices
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- Thermal Comfort PMV Index
- The perceived need for both heating and cooling
is to achieve accepted standards of thermal
comfort, usually defined (directly or indirectly)
by temperature limits. - Controversy exists as to what these standards of
thermal comfort are. It has been observed that
there has been an apparent discrepancy between
comfort predictions using models derived from
laboratory experiments, such as those by Fanger
(1970), and subjective assessments of comfort
found in field studies. It has been found in a
compilation of results from field studies in
predominantly in warm and hot climates by
Humphreys (1978) that the preferred comfort
temperature in buildings was a function of the
average monthly outdoor temperature (To is the
mean monthly temperature)
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- Thermal Comfort PMV Index
- The Predicted Mean Vote (PMV) is a widely
accepted mathematical expression of thermal
comfort. This index is a real number and comfort
is obtained if it lies within the specific limits
of the comfort range. Since 1984, the index
which is calculated through a complex
mathematical function of human activity, clothing
and environmental parameters has been the basis
of the international standard ISO-7730. - This PMV is an index which predicts the mean
value of the votes of a large group of people,
and is directly related to the percentage of
people dissatisfied (PPD), on the following seven
point thermal sensation scale 3 Hot, 2 Warm,
1 Slightly Warm, 0 Neutral, - 1 Slightly Cool,
- 2 Cool, - 3 Cold.
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Thermal Comfort PMV Index
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- Thermal Comfort PMV Index
- The result of using Fangers equations seems to
predict the need for much more closely controlled
conditions than are usually found in free running
buildings, in which people still seem to be
comfortable. Some of the possible explanations
for the apparent discrepancy between the
prediction of the Fanger model and the findings
of the Humphreys survey, are - The thermal comfort parameters, air temperature,
radiant temperature and air movement vary
spatially in a room, and the actual values
experienced by an occupant may not be those
described by a "room-average value". - Thermal comfort parameters vary with time whereas
the Fanger model predicts a response for steady
conditions. - The description of clothing level assumed in the
use of the Fanger equation may not be the same as
is actually worn in the real situation. - The insulation value of the clothing may not be
as predicted from the description of the clothing
ensemble. - The metabolic rate as assumed from the
description of the activity may not be the same
as the actual metabolic rate.
20Visual comfort
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- Visual Comfort
- Visual comfort is the main determinant of
lighting requirements. - Good lighting provide a suitable intensity and
direction of illumination on the task area,
appropriate colour rendering, the absence of
discomfort and, in addition, a satisfying variety
in lighting quality and intensity from place to
place and over time. - Peoples lighting preferences vary with age,
gender, time and season. The activity to be
performed is critically important. - Various agencies (ASHRAE, CIBSE, etc.) and text
books list optimal illuminances for different
activities. These are generally based on uniform
and constant levels of artificial light falling
on the working plane.
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- Visual Comfort Illuminance levels
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- Visual Comfort
- Natural light is a fluctuating source of light.
It depends on the hour of the day, the season,
the climate and the latitude of the location. - The objective of a daylight technique consists of
providing the best possible indoor luminous
environment as often as possible. - A luminous environment should be appropriate to
the function of the room there should be enough
light for reading, writing, or filing documents. - Illuminance of 300 to 400 lux on a desk are often
considered as minimum required levels for most of
office tasks. Hallways might require lower
levels, 100 lux, and commercial centres higher
levels, 700 lux. These requirements are defined
by CIE. - Performance does not depend only on these
illuminance levels. The location of the source of
light with respect to the direction of
observation may require higher illuminance, for
instant when the observer faces a window.
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- Visual Comfort
- The luminous environment should be comfortable,
which means that sources of glare should be
avoided. - Oversized glazed windows with clear glazing are
sources of glare, and this can be fought in using
multiple apertures, if possible on different
walls. - Glossy materials and inappropriate shading
devices might bring excessive amount of light in
the field of vision. - Also, psychological aspects such as the quality
of the vision to the outside, the beauty of the
design and the attractiveness of the space are
very important.
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- Visual Comfort
- Natural light comes from three directions
- Direct Sunlight
- Diffuse light from the sky, and
- Light Reflections from the Environment
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- Visual Comfort
- The daylight factor is a measure of the daylight
level at any position indoors as a percentage of
the illuminance levels outdoors. The daylight
factor at any point on a working plane is
calculated in terms of light coming directly from
the sky (the sky component), light reflected from
outdoor surfaces (the externally reflected
component) and light reflected form surfaces
within the room (the internally reflected
component). The average daylight factor in a
space can be calculated from
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Visual Comfort Indoor lighting distribution
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- Visual Comfort
- If a predominately daylit appearance is required,
then the daylight factor should be 5 or more if
there is to be no supplementary artificial
lighting, or 2 if supplementary lighting is
provided. - Discomfort is caused when the eye has to cope
with, simultaneously, great differences in light
levels, the phenomenon we know as glare. Maximum
recommended values for the ratio between
different parts of a visual field, the luminance
ratio, as shown in the following table.
29Indoor air quality
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- Indoor air Quality
- A conflict has always existed between adequate
ventilation and energy costs has long existed. - During the last three decades, decreased
ventilation rates for energy conservation, along
with increased use of synthetic (i.e. man-made)
materials in buildings have resulted in increased
health complaints from building occupants.
However, energy efficiency and good indoor air
quality in buildings need not be mutually
exclusive. - Good indoor air quality is a function of a number
of parameters including the initial design and
continuous maintenance of HVAC systems use of
low toxic emittance building materials and
consideration of all sources of indoor air
pollution such as occupant activities, operation
of equipment and use of cleaning products. - In fact, in 1986 the WHO (World Health
Organisation) reported that "energy-efficient but
sick buildings often cost society far more than
it gains by energy savings". - The result of the reductions in ventilation rates
in buildings have led to the so called "Sick
Building Syndrome" (SBS) and "Building Related
Illness" (BRI).
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- Indoor air Quality Indoor pollutants
- Every building has a number of potential sources
of indoor air contaminants. - Some sources, such as building materials and
furnishings, release contaminants more or less
continuously. Other sources are related to
occupant activities and therefore release
contaminants intermittently. - Such activities include cooking, smoking, use of
solvents, pesticides, paint, and cleaning
products, and operation of office machines and
equipment. - High concentrations of pollutants can remain in
the indoor air for long periods after they are
emitted. Although some sources may be common in
all building types, office and commercial
buildings vary greatly from residential buildings
in terms of design, air handling systems and
occupant activities and therefore certain indoor
air pollutant sources may be more prevalent in
some types of buildings.
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- Indoor air Quality Ventilation
- There are two types of ventilation natural and
mechanical. - Natural ventilation includes the movement of
outdoor air through intentional openings such as
doors and windows and through unintentional
openings in the building shell scuch as cracks
which result in infiltration and exfiltration. - Mechanical or forced ventilation is intentional
ventilation supplied by fans or blowers. These
fans are usually part of the buildings HVAC
system which heats, cools, mixes and filters the
air being supplied to the building.
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Climate
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- Climate
- Climate responsive design in buildings takes into
account the following climatic parameters which
have direct influence on indoor thermal comfort
and energy consumption in buildings - The air temperature,
- The humidity,
- The prevailing wind direction and speed,
- The amount of solar radiation and the solar
path. - Long wave radiation between other buildings and
the surrounding environment and sky also plays a
major role in building performance.
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- Climate
- The outdoor air temperature has a significant
effect on building thermal losses due to
conduction through the walls and roof of the
building, as well as affecting ventilation and
infiltration losses due to either desirable or
undesirable air changes. - In warm climates the relative humidity plays an
important role in determining thermal comfort
levels, since during warm weather the high
pressure of water vapour prevents the evaporation
of perspiration from the body thereby inhibiting
the body from being maintained at a comfortable
temperature.
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- Climate
- Prevailing wind speed and direction affect
significantly the building thermal losses during
the heating season, increasing both convection at
exposed surfaces and hence encouraging envelope
losses and also by increasing the air change rate
due to natural ventilation and infiltration.
During the cooling season, the knowledge of both
the direction and wind speed permits the design
of the building to facilitate passive cooling. - The sun-path and the cloud cover determine the
amount of solar radiation impinging on
differently inclined surfaces and since the
sun-path changes from season to season, so does
the amount of direct solar radiation impinging on
these different surfaces.
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- Macroclimate is a term referring to the general
climatic character of a region in terms of
temperature, humidity, precipitation, wind,
sunshine and cloud cover. An appreciation of the
overall characterisation of the climate of a
region is a fundamental requirement for climate
responsive building design, this affecting the
general design principles which should be
followed. - Regional climatic factors are strongly affected
by the local topography, vegetation and the
nature of the area, resulting in deviations from
the regional macroclimate. The effect of such
factors results in climatic characteristics known
as the mesoclimate. Heavily vegetated or densely
built-up areas have a significant impact on the
climate of a specific location. - The conditions of the climatic parameters of a
specific site or around a building are termed the
microclimate. Temperature, humidity, wind speed,
and solar radiation around a building can be
affected by the deliberate placement of
vegetation, landscaping, water and fountains, and
positioning of constructions
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- Building Climate interaction
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- Building Envelope
- The building envelope responds dynamically to the
impact of the outdoor climate on the envelope
exterior and the effect of the occupancy pattern
and building usage on the interior. - However, the performance of the heating,
ventilation and air-conditioning systems,
artificial lighting, fenestration opening and
shading can be harmonized and optimized in
response to occupancy needs and climatic
conditions through a building energy management
system which allows direct control of the
necessary actuators either manually or
automatically. - In this manner the individual components of the
building can be controlled to produce the best
possible indoor environment with minimum energy
consumption.
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- Heat transfer
- Conduction - C
- Radiation - R
- Convection - C
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- Heat transfer Conduction
- Conductive heat transfer is a process by which
thermal energy is transmitted by direct molecular
communication. - It is the only mechanism by which heat flows in
an opaque solid. Conduction in a translucent
solid is accompanied by radiation, whilst heat
transfer through stagnant gases and liquids takes
place by conduction with some radiation.
Convection enhances the thermal equilibrium
process in moving fluids. The thermal
conductivity k of a substance determines its
ability to conduct heat. - Conductive heat transfer with respect to
buildings concerns the heat losses through the
building envelope the walls, windows and doors. - Heat transfer is caused by a temperature
difference across the envelope, always in the
direction of the temperature gradient, with
energy entering the one surface at a higher
temperature and leaving the other surface at a
lower temperature. Therefore, buildings are
generally affected by envelope losses in the
winter and envelope gains in the summer.
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- Heat transfer Convection
- Convection is a process of heat transfer by the
combined action of heat conduction, energy
storage and mixing motion. - Convection is combined to fluids only and
requires an external force -either forced or
natural (buoyancy)- to be present. - The rate of heat transfer depends on the
temperature difference between the fluid and the
surface and the convective heat transfer
coefficient h. - The convective heat transfer co-efficient is a
function of - 1) the geometry of the system,
- 2) the velocities and mode of fluid flow,
- 3) the physical properties of the fluid and
- 4) possibly on the temperature difference.
- The convective heat transfer is therefore not
constant or uniform over the whole surface,
although for all intensive purposes in building
physics it is often considered to be so.
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- Heat transfer-Radiation
- All bodies emit radiation. Heat transfer via
radiation occurs when a body converts part of its
internal energy (a result of its temperature)
into electromagnetic waves. - In buildings heat transfer due to radiation is
most apparent with transparent elements, where a
large amount of the impinging radiation coming
from the sun is transmitted to the building
material. - Radiative heat transfer can also contribute to
the cooling of external surfaces through exposure
to the night sky, wherin these surfaces emit net
radiation towards the clear sky, or in the effect
of discomfort associated with sitting next to hot
or cold surfaces (i.e. cold windows).
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Heat transfer-Radiation
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- Thermal storage
- The ability of a material to store energy is
characterised by its specific heat (cp, J/kgK).
The specific heat of a material is defined as the
amount of heat necessary to raise a unit mass of
the material by one degree. The heat that is
stored in the mass of the material, m, for a
temperature change, ?T, is given by
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- Energy Management Systems
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- Intelligent Building-Definitions
- EIBG (European Intelligent Building Group) One
that incorporates the best available concepts,
materials, systems and technologies integrating
these to achieve a building which meets or
exceeds the performance requirements of the
building stakeholders, which include the owners,
managers and users, as well as the local and
global community. - Also from EIBG but more often quoted One that
maximizes the efficiency of its occupants and
allows effective management of resource with
minimum life costs
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- Intelligent Building-Definitions
- IBI (The Intelligent Buildings Institute in
Washington DC, US) one that provides a
productive and cost-effective environment through
optimization of its four basic components -
structure, systems, services and management - and
the interrelationships between them.
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- Intelligent Building-Definitions
- An Intelligent Building is one that
- Provides a productive and cost-effective built
environment through optimization of its four
basic components - structure, systems, services
and management - and the interrelationships
between them. (focused on the benefit of the
Owners)Creating Desired indoor environment) - So as to maximize the efficiency of its occupants
(focused on the benefit of the Users) (Influence
of creating desired indoor environment on
occupants) - And to allow effective management of resource
with minimum life costs (focused on the benefit
of the Managers) (Environmental and economic
impact of creating desired indoor environment)
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- Building Energy Management Systems-Definitions
- Building Energy Management Systems aim to
optimise the use of energy in buildings by
maintaining at the same time the indoor
environment under comfort conditions - Practically, a BEMS is a computerised system that
attempts to control all or some of the energy
consuming operations in a building - HVAC systems (Heating Ventilating and Air
Conditioning) - Lighting systems (natural and artificial)
- Indoor climate
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- Building Energy Management Systems-Definitions
- BEMS are now available with a wide range of
building automation facilities and in many
installations BEMS have replaced hardwired
controls, with control strategies implemented in
software - BEMS can combine many technologies
- Passive heating and cooling
- Efficient daylight penetration by using suitable
shading devices - Efficient appliances that reduce the electricity
consumption - High efficiency windows (e.g. electrochromic)
- Natural ventilation for indoor air quality and
passive cooling - Improvements in building services for HVAC
- Building Energy Management and Control
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- Building Energy Management Systems- How much
energy can be saved
55Building Energy Management Systems- Hardware
Intelligent Buildings Technology
- The basic architecture consists of
- Multiple programmable control panels, called
Network Control Units (NCUs) each NCU manages an
area of the building facility - Operator WorkStations (OWSs) that communicate
with each other over a high speed communication
network normally a standard PC - This communication network is called Local Area
Network (LAN) - NCU capacity can be increased with remote panels
called Network Expansion Units (NEUs) - The NCUs and NEUs directly control central plant
equipment, while the management of smaller air
handlers, heat pumps, lighting circuits and other
building services systems is delegated to a
family of Application Specific Controllers (ASCs)
56BEM Systems Software 1
Intelligent Buildings Technology
- Direct Digital Control (DDC) is the major concept
of Building Automation System (BAS) in nowadays - DDC control e.g. loops for damper operation are
available to provide ventilation requirements or
to utilize outdoor air for cooling - Building energy management features are available
inside a modem BAS - e.g. the duty cycle program reduces electrical
energy consumed by the fan by cycling it on and
off - The unoccupied period program, e.g night cycle
program, is a function that can reduce the indoor
temperature of a space by applying night
ventilation
57BEM Systems Software 2
Intelligent Buildings Technology
- The enthalpy program monitors the temperature and
relative humidity or dew-point of the outdoor and
return air and then positions the outdoor air and
return air dampers to use the air source with the
lowest total heat or least enthalpy - The load reset program controls heating and/or
cooling to maintain comfort conditions in the
building while consuming a minimum amount of
energy - The zero- energy band program saves energy by
avoiding simultaneous heating and cooling of air
delivered to spaces - The occupied-unoccupied lighting control is a
time-based program that schedules the on/off time
of lights for a building or zone to coincide with
the occupancy schedules
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- BEM Systems Architecture 3
- The structures of BEMS change with evolution of
technologies and products. - Early BEMS were centralized energy management
systems and first appeared in the 1970s, having
been developed in the USA. The central station
was based on a minicomputer, which contained the
only computing power or "intelligence" in the
system, with "dumb" or unintelligent outstations
which were boxes or cabinets for relays and
connections to sensors and actuators. - Since about 1980, with the rapid development of
technologies, the outstations became as powerful
as the previous minicomputer, if not more so. - Also, the outstations have gained considerably in
processing power giving them "intelligence".