FP7-2010-NMP-ENV-ENERGY-ICT-EeB
TIBUCON
Self Powered Wireless Sensor Network for HVAC System Energy
Improvement - Towards Integral Building Connectivity
Instrument:
Small or medium-scale focused research project - STREP
Thematic Priority:
EeB.ICT.2010.10-2 – ICT for energy-efficient buildings
and spaces of public use
ENERGY HARVESTING STRATEGIES PERFORMANCE
AUTHORS: AUTHORS: DR N. GRABHAM, DR M. TUDOR, J. MABE, P. DYMARSKI
Actual submission date: 30.12.2011
Start date of project: 01.09.2010
Duration: 36 months
Organisation name of lead contractor for this deliverable: UoS
Dissemination level: Public
Revision
Final
TIBUCON
Energy Harvesting Strategies Performance
Introduction
The purpose of this study is to assess the amount of ambient energy available in domestic
and commercial environments that can be harvested using a selected range of energy harvesting
technologies.
Energy Harvester Types
Three primary harvesting technologies were considered for use in the TIBUCON project
and these are:
Photovoltaic Energy Harvesters: These are a well-established, mature, technology.
Specific modules are available that are optimized for indoor use, with their operational wavelengths
optimized for operation under artificial lighting. These devices will also operate satisfactorily under
the lower illumination levels to be anticipated in an indoor environment, as compared to those to be
anticipated if the solar module was deployed outdoors in direct sunlight. An example of an outdoor
specification solar module is shown in Figure 1.
Figure 1 – External Specification Solar Module
Thermoelectric Energy Harvesters: These harvesters are based upon the Seebeck
effect, whereby a temperature gradient across the device provides the energy for the device to
operate. Typical placement of such devices is anticipated to be on the HVAC radiators and
pipework, with the temperature difference between these surfaces and the ambient air temperature
providing the required thermal gradient. Specific energy harvesting devices are now available
which are optimized for use as harvesting modules as opposed to the first generation Peltier
cooling elements, which can be used for harvesting purposes but which are optimized for cooling
operation. An example of a bulk material thermoelectric energy harvester is shown in Figure 2, an
example of a thermal energy harvesting device using a micro-fabricated thermoelectric harvester is
shown in Figure 3.
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TIBUCON
Energy Harvesting Strategies Performance
Figure 2 – Bulk Thermoelectric Energy Harvesting Device
Figure 3 – Energy Harvesting Node with Micro-Fabricated Thermoelectric Harvesting Device
Vibration Energy Harvesters: Commercially available energy harvesters fall into three
modalities: piezoelectric, electromagnetic and electrostatic. Of these three modalities only
piezoelectric and electromagnetic based harvesters have been developed to commercially
available devices and are therefore suitable for consideration in this project. The main limitation of
the available units is that the level of energy that can be harvested is highly dependent on the
frequency of the exciting vibration due to the resonant mode of operation employed by these
harvesters. An example of a piezoelectric-based vibration energy harvester is shown in Figure 4.
Figure 4 – Piezoelectric-based Vibration Harvester
In addition to the three main harvester technologies that are outlined above less well
established and emerging technologies were also considered for their use within the scope of this
project. These devices had limited potential for deployment within the target environments due to
the lack of suitable ambient source energy, or had a device cost which was incompatible with the
financial targets required to permit deployment of a large number of sensor nodes.
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TIBUCON
Energy Harvesting Strategies Performance
Available Energy Sources within Deployment Environments
The TIBUCON project aims to produce sensor nodes that can be deployed into two main
environments: residential properties and office spaces. To this end, surveys of the available
ambient energy sources and the typical levels of these sources were performed for both residential
and office locations.
Residential Environment: Surveys of the available ambient energy were performed for a
number of residential apartments located in San Sebastian, Spain. These measurements were
concentrated on the main living space as this is the target location for the TIBUCON sensors.
Within the apartment living room areas the main ambient energy sources are solar and thermal
energy. There is a lack of significant airflows for wind energy harvesting and vibration for vibration
harvesting. Within the main living spaces the ambient light levels at the approximate midpoint of
the side walls ranged from 70 to 200 lux in rooms with normal lighting levels, within the darker
rooms these levels reduced to around 40 lux, In all cases close to the exterior windows provided
illumination levels in excess of 1000 lux. The use of the HVAC radiators and associated pipework
as a heat source for thermal harvesters does however have the limitation that these are only
heated during the periods of time that the space heating is active, which for the test site is from 12
noon to 10pm daily between the dates 1st of October and 15th of May.
Office Environment: Surveys were performed in a range of indicative office buildings,
with the primary emphasis on office space, as opposed to plant areas. Within the occupied office
spaces surveyed the main source of available ambient energy is solar, with some locations having
exposed HVAC radiators which could be used as heat sources for thermal energy harvesters
however this is limited by the fact that the HVAC radiators are likely to only be active through part
of the year. In common with the residential spaces surveyed there is a lack of significant airflows
for wind energy and vibration for vibration harvesting. Some airflow may be present during periods
when the air conditioning is active but strong airflows are typically avoided for occupant comfort
with diffusers used. A further factor in favour of using solar energy harvesting within the office
environment is that offices are typically well lit to suit the tasks being carried out within them and to
maximise occupant alertness, within the office spaces there were typically illumination levels of 200
lux and above available in the surveyed locations. Some locations had areas with lower
illumination levels but in general this was due to positioning of furniture causing areas to be
blocked from the natural and artificial light sources. In the majority of the office spaces, locations
were available with illumination levels of 500 lux and greater. This level of illumination is
attributable to the level of lighting specified for office working environments.
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TIBUCON
Energy Harvesting Strategies Performance
Selected Energy Harvesting Technologies
The most applicable energy harvesting technology for nodes across both deployment
environments has been found to be solar energy harvesting and a range of commercially available
photovoltaic modules have been identified which are optimised for operation under low level
artificial lighting conditions.
It is anticipated that all the energy harvesting sensor nodes will be equipped with indoorspecification solar modules as their primary energy harvesting technology. There are however
some further options for alternative energy harvesting technologies within specific locations. Within
the residential retrofit environment, and also in some of the surveyed office buildings, there is the
potential to deploy thermal energy harvesters as a secondary energy source where there are
suitable heat sources. In most cases these heat sources are HVAC pipework and radiators, though
in the case of pipework etc. associated with space heating it is to be anticipated that the heat
sources will only be available for parts of the day during applicable seasons and not available at all
during seasons when the space heating is inactive. Where external sensor and/or routing nodes
are required it is possible to add a secondary harvesting module containing an externalspecification solar module which will provide a larger energy budget than that provided by the
indoor-specification
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