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Active Solar Thermal Energy Applications in Buildings (Part 1)
Yerevan State University of Architecture and Construction
INOGATE Programme New ITS Project, Ad Hoc Expert Facility (AHEF) Task AM-54-55-56
Slides prepared by: Xavier Dubuisson Eng. MSc. XD Sustainable Energy Consulting Ltd.
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Table of Contents
Part 1
• Solar Energy Resource in Armenia
• Systems and Components
• Thermosiphon Systems
Part 2
• Designing Solar Thermal Systems
• Typical System Configurations
• Installation and Commissioning
• Financial Analysis
• Solar thermal applications in Armenia
• Further References
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THE SOLAR ENERGY RESOURCE
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Solar Trajectory
2-3 Solar Resources - Solar Radiation
Summer solstice
90° - latitude + 23 °
Equinox
90° - latitude
Winter solstice
90° - latitude - 23 °
To find out solar position & intensity at your location: http://www.nrel.gov/midc/solpos/solpos.html
Maximum elevation angle (height of the sun at solar noon): ϒS
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Calculating the Sun’s Position
ζ = 900 − α
Source: Pveducation.org
∝: elevation angle ζ: zenith angle 𝜑: latitude 𝛿: declination angle
In northern hemisphere: ∝ = 90 − 𝜑 + 𝛿
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(1)
Where B = 360/365 (d-81) in degrees and d is number of days since the beginning of year
(2)
Local Standard Time Meridian
Equation of time
Time correction factor
Hour angle
Where ∆𝑇𝐺𝑀𝑇 is difference between local time and Greenwich mean time in hours
Calculating the Sun’s Position
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Local solar time
Declination angle
Azimuth
Elevation
Calculating the Sun’s Position
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Source: http://www.gaisma.com/en/location/yerevan.html
Elevation angle Azimuth angle
http://www.gaisma.com/en/location/yerevan.html
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Calculating solar radiation on a tilted surface
Elevation angle
Panel tilt
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Atmospheric Effects – Air Mass Factor
Air mass factor (AM) = 1/sin ϒS (ϒS: Elevation angle)
Sun elevation at noon over the course of one year at lat. 52 °N
Source: Earthscan, 2010
Source: PVEducation.org
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Air Mass / Radiation intensity
Effect of elevation angle on attenuation of irradiation Source: Earthscan, 2010
Id: direct irradiance (kW/m2)
1.353 kW/m2 = solar constant 0.7 (% of radiation incident to atmosphere transmitted to earth) a = 0.14, h = height above sea level (km) 0.678 is an empirical fit to observed data
IG: global irradiance (kW/m2) on a clear day where
diffuse radiation is still 10% of direct radiation
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Direct and diffuse radiation
Direct radiation: 60%
Diffuse radiation: 40%
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Solar irradiation intensity
Irradiance
Definitions: Irradiation (kWh/m2·yr) Sunshine hours (hrs) Irradiance (W/m2) Peak sunshine hours (hrs)
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Solar energy resource in Armenia
• 1720 kWh/m2,yr average in Armenia
• 1000 kWh/yr,m2 in EU
• 2500 hrs of sunshine per year
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Solar energy resource in Armenia
Source: Sargsayan, 2010.
Average daily total (E1) and diffused (E2) irradiation per m2 horizontal area in Yerevan.
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Annual irradiation across the globe
2-11 Solar Resources - Solar Radiation
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Effect of Orientation and Inclination on Solar Irradiation
6-5 Design and Sizing
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Optimal Inclination
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Effect of Shading
Obstacle height Angle and Azimuth
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Assessing Shading
Solar site locator ($90)
Source: http://www.solardesign.co.uk/sss.php
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Assessing shading
Source: Martin Cotterell. http://www.solarpowerportal.co.uk/martins_blog/sun_path_diagrams_and_shade_lines_2356
iPV iPhone solar app: http://www.solmetric.com/solmetricipv.html
SunEye by Solmetric ($2000 + $600 for software). Source: http://www.solmetric.com
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Assessing Shading
http://www.solarpathfinder.com
Approx. $300
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SYSTEMS AND COMPONENTS
Active Solar Thermal Energy in Buildings
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Solar water heater advertisement, 1902,..Source:..http://en.wikipedia.org/wiki/Solar_water_heating
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Solar Thermal System Components
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Flat Plate Collectors
A: Glazing/ Solar Glass B: Copper or Aluminium Absorber sheet
C: Powder Coated Aluminium Frame D: Collector Pipe
E: Mineral Wool Insulation F: Meander Tube
G: Selective Coating H: Bottom Plate (Aluminium)
I: Secure Glass Fixing J: Revolving Groove for Assembly
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Evacuated Tube Collectors Heat Pipe
Source: www.kingspansolar.ie
Tube-manifold connection
Absorber plate
Absorber support clip
Evacuated glass tube
End support bung
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Evacuated Tube Collectors Direct Flow
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Evacuated Tube Collectors Sydney tube with concentrator
“Sydney” double-walled glass tube
Feeder
Outer glass tube Heat conducting plate Return
Inner glass tube w. absorber coating
Reflector
Evacuated space
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Vacuum tubes versus flat plate
Advantages
• Higher operating temperatures than flat plate
• Reduced heat losses
• Higher yield per m2 of collector than flat plate (attractive where space is an issue)
• Compact and sealed construction, high protection of absorber.
Disadvantages
• High stagnation temperatures, causing more stress on pipework, insulation and solar fluid.
• Higher specific costs (€/m2 of absorber area)
• Higher cost (€/kWh) for available solar yield at medium operating temperature range.
• Possible loss of vacuum
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Absorber Coating
Source: SolarPraxis, 2002
Absorption, reflection and useful heat on various surfaces
Absorption/emission spectrum Wave length λ in μm
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Collectors’ reference areas
Source: SolarPraxis, 2002
(1) Absorber area
(2) Aperture area
(3) Gross area
(1) (2)
(3) (1) (2) (3)
(1) (2) (3)
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Energy Balance of Solar Collectors
Conduction
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Collector energy performance
QA: available thermal power (W/m2)
G: incident irradiance on the glass pane (W/m2)
GA: available irradiance at the absorber, converted into heat (W/m2)
QL: thermal losses through convection, conduction and radiation (W/m2)
𝜏: transmissivity of glass, ∝: absorptivity of absorber ∆𝜃: temp difference between absorber and the air k1: linear heat loss coefficient (W/m2,K) – for low absorber temperatures
K2: quadratic heat loss coefficient (W/m2,K2) – for higher temps, increased thermal radiation
η0 : optical efficiecny = α * τ * F; F: absorber efficiency factor
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Efficiency flat plate versus evacuated tube collectors
Source: Kingspan Solar
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Storage Tanks - configurations
Solar tank with fresh water coil & internal stratification device, Source: www.viessmann.de
Standard twin coil cylinder Source: Tisun
One coil cylinder with immersion heater. Source: Tisun
Solar tank part of thermosiphon system.
Heat store with external stratification device, Source: Tisun
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Energy Content of Storage Tanks
Q: heat content (Wh) M: mass of water/fluid (kg) Cw: specific heat capacity of water (1.16 Wh/kgK) Δθ: temperature difference (K) Energy content in this tank, Q: = 100 kg × 1.16 Wh/kgK × 45 K + 100 kg × 1.16 kWh/kgK × 15 K + 100 kg × 1.16 Wh/kgK × 0 K = 6960 Wh
Q = mcwΔθ
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Storage tank – heat loss
BAD BETTER
Equivalent to yield from 2 m2 of solar collectors
0.6 W/K (x2) 36W 0.3 W/K (x6) 54W
1.4 W/K 42W
Total = 132W
Annual losses: 1156 kWh
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Storage tank – heat losses
• Storage losses can be up to 30% of total heating requirement
• Recommended insulation thickness = 20 cm (large tanks) and applied carefully (no air gaps)
• Insulation around pipe connections and fittings important
• Ratio between height/volume: 2 < H/D < 4
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Storage tank - heat losses
Large tank insulation should be at least 20 cm
Multiple storage tanks result in higher heat losses. Source: AEE INTEC
Single, large, well insulated solar tanks reduce heat losses substantially. Source: AEE INTEC
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Storage Tanks - stratification
Solar tank with external stratification device and fresh water coil. Source: Tisun
Illustration of stratification process. Source: Lochinvar.
Stratification by internal lance using water density variation with temperature for layering hot water inlet. Source: Solvis
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Solar Circuit
Source: Viessmann
De-airing device
Pumping station
Pre-cooling vessel
Expansion tank
Collecting vessel
Temp. sensor solar panels
De-airing device
Temp. sensor solar tank
Controller Pressure relief valve
Filling/draining connections
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Pumping Station
44
Source: Bosch Thermotechnik
(1) Ball valve with temperature gauge and integrated gravity brake
(2) Compression fitting
(3) Pressure relief valve
(5) Connection to solar expansion vessel
(6) Fill and drain valve
(7) Solar pump
(8) Flow rate indicator
(9) Air seperator
(10) Control/shut-off valve
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Heat Exchangers
Finned tube heat exchanger
Plain tube heat exchanger
Plate heat exchanger
Tubular heat exchanger
Internal External
Sou
rce:
Ear
thsc
an, 2
01
0
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Expansion Tanks
Source: www.kingspansolar.ie
As delivered (3 bar charge
pressure)
Solar circuit filled
but cool
Max pressure, highest solar fluid temp.
Solar fluid
Nitrogen
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Overheating prevention
Source: http://www.kingspansolar.ie/
Heat dissipation emitter
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De-airing
Source: spirotech.co.uk http://www.avg.net.au
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Control - Forced Circulation
3-49 Components and Subsystems of Solar Thermal Installation
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Control Operating Principle
3-50 Components and Subsystems of Solar Thermal Installation
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Wide range of control strategies
Source: STECA
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Sensors
3-41 Components and Subsystems of Solar Thermal Installation
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Pipework and Insulation
Insulation material specifications: • resistant to water & impermeable to vapour e.g. Armaflex closed cells (when outside) • low-thermal conductivity • Protection against rodents and bird-pecking • UV resistant
Examplary insulation of ball valves, pumps
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Legionella prevention
External plate heat exchanger Source: Tisun
Internal coil heat exchanger Source: Tisun
Instant fresh water heating solutions
German requirements for domestic hot water temperature
Source: AEE INTEC, 2002.
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Examples of system integration
Source: www.viessmann.de
Pumping station pre-mounted on tank
Controller pre- installed
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Examples of system integration
Source: Solvis.de
Burner
Stratification device
Fresh water station
Central heating feed
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THERMOSYPHON SYSTEMS
Active Solar Thermal Energy in Buildings
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System Configuration
4-5 Solar Thermal Installations
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Components
3-4 Components and Subsystems of Solar Thermal Installation
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Control
3-48 Components and Subsystems of Solar Thermal Installation
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Prefabricated Solar Systems
4-2 Solar Thermal Installations
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