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. 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 THE SOLAR ENERGY RESOURCE Solar Trajectory Maximum elevation angle (height of the sun at solar noon): ϒS 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 Solar Resources - Solar Radiation 2-3 Calculating the Sun’s Position Source: Pveducation.org In northern hemisphere: ∝ = 90 − 𝜑 + 𝛿 ζ = 900 − α ∝: ζ: 𝜑: 𝛿: elevation angle zenith angle latitude declination angle Calculating the Sun’s Position Local Standard Time Meridian (1) Where ∆𝑇𝐺𝑀𝑇 is difference between local time and Greenwich mean time in hours Equation of time (2) Where B = 360/365 (d-81) in degrees and d is number of days since the beginning of year Time correction factor Hour angle Calculating the Sun’s Position Declination angle Local solar time Azimuth Elevation Elevation angle Azimuth angle Source: http://www.gaisma.com/en/location/yerevan.html Calculating solar radiation on a tilted surface Elevation angle Panel tilt Atmospheric Effects – Air Mass Factor Sun elevation at noon over the course of one year at lat. 52 °N Source: Earthscan, 2010 Source: PVEducation.org Air mass factor (AM) = 1/sin ϒS (ϒS: Elevation angle) 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 Direct and diffuse radiation Direct radiation: 60% Diffuse radiation: 40% Solar irradiation intensity Irradiance Definitions: Irradiation (kWh/m2·yr) Irradiance (W/m2) Sunshine hours (hrs) Peak sunshine hours (hrs) Solar energy resource in Armenia • 1720 kWh/m2,yr average in Armenia • 1000 kWh/yr,m2 in EU • 2500 hrs of sunshine per year Solar energy resource in Armenia Average daily total (E1) and diffused (E2) irradiation per m2 horizontal area in Yerevan. Source: Sargsayan, 2010. Annual irradiation across the globe Solar Resources - Solar Radiation 2-11 Effect of Orientation and Inclination on Solar Irradiation Design and Sizing 6-5 Optimal Inclination Effect of Shading Obstacle height Angle and Azimuth Assessing Shading Solar site locator ($90) Source: http://www.solardesign.co.uk/sss.php Assessing shading iPV iPhone solar app: http://www.solmetric.com/solmetricipv.html Source: Martin Cotterell. http://www.solarpowerportal.co.uk/ma rtins_blog/sun_path_diagrams_and_sha de_lines_2356 SunEye by Solmetric ($2000 + $600 for software). Source: http://www.solmetric.com Assessing Shading Approx. $300 http://www.solarpathfinder.com Active Solar Thermal Energy in Buildings SYSTEMS AND COMPONENTS Solar water heater advertisement, 1902,..Source:..http://en.wikipedia. org/wiki/Solar_water_heating Solar Thermal System Components Flat Plate Collectors A: Glazing/ Solar Glass C: Powder Coated Aluminium Frame E: Mineral Wool Insulation G: Selective Coating I: Secure Glass Fixing B: Copper or Aluminium Absorber sheet D: Collector Pipe F: Meander Tube H: Bottom Plate (Aluminium) J: Revolving Groove for Assembly Evacuated Tube Collectors Heat Pipe Tubemanifold connection Absorber plate Absorber support clip Evacuated glass tube End support bung Source: www.kingspansolar.ie Evacuated Tube Collectors Direct Flow Evacuated Tube Collectors Sydney tube with concentrator Feeder Outer glass tube Heat conducting plate Return Inner glass tube w. absorber coating Reflector Evacuated space “Sydney” double-walled glass tube 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 Absorber Coating Absorption, reflection and useful heat on various surfaces Absorption/emission spectrum Wave length λ in μm Source: SolarPraxis, 2002 Collectors’ reference areas (1) (2) (3) (1) (2) (3) (1) (2) (3) (1) Absorber area (2) Aperture area (3) Gross area Source: SolarPraxis, 2002 Energy Balance of Solar Collectors Conduction 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 Efficiency flat plate versus evacuated tube collectors Source: Kingspan Solar Storage Tanks - configurations One coil cylinder with immersion heater. Source: Tisun Standard twin coil cylinder Source: Tisun Solar tank with fresh water coil & internal stratification device, Source: www.viessmann.de Heat store with external stratification device, Source: Tisun Solar tank part of thermosiphon system. Energy Content of Storage Tanks Q = mcwΔθ 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 Storage tank – heat loss BAD BETTER 0.6 W/K (x2) 36W 0.3 W/K (x6) 54W 1.4 W/K 42W Total = 132W Annual losses: 1156 kWh Equivalent to yield from 2 m2 of solar collectors 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 Storage tank - heat losses Multiple storage tanks result in higher heat losses. Source: AEE INTEC Large tank insulation should be at least 20 cm Single, large, well insulated solar tanks reduce heat losses substantially. Source: AEE INTEC Storage Tanks - stratification Stratification by internal lance using water density variation with temperature for layering hot water inlet. Source: Solvis Illustration of stratification process. Source: Lochinvar. Solar tank with external stratification device and fresh water coil. Source: Tisun Solar Circuit Temp. sensor solar panels De-airing device Controller De-airing device Pressure relief valve Pre-cooling vessel Pumping station Expansion tank Collecting vessel Temp. sensor solar tank Filling/draining connections Source: Viessmann Pumping Station 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 44 Heat Exchangers External Plain tube heat exchanger Plate heat exchanger Source: Earthscan, 2010 Internal Finned tube heat exchanger Tubular heat exchanger Expansion Tanks Solar fluid Nitrogen Source: www.kingspansolar.ie As delivered (3 bar charge pressure) Solar circuit filled but cool Max pressure, highest solar fluid temp. Overheating prevention Heat dissipation emitter Source: http://www.kingspansolar.ie/ De-airing http://www.avg.net.au Source: spirotech.co.uk Control - Forced Circulation Components and Subsystems of Solar Thermal Installation 3-49 Control Operating Principle Components and Subsystems of Solar Thermal Installation 3-50 Wide range of control strategies Source: STECA Sensors Components and Subsystems of Solar Thermal Installation 3-41 Pipework and Insulation Examplary insulation of Insulation material specifications: ball valves, pumps • resistant to water & impermeable to vapour e.g. Armaflex closed cells (when outside) • low-thermal conductivity • Protection against rodents and bird-pecking • UV resistant Legionella prevention Instant fresh water heating solutions German requirements for domestic hot water temperature Source: AEE INTEC, 2002. Internal coil heat exchanger Source: Tisun External plate heat exchanger Source: Tisun Examples of system integration Controller preinstalled Source: www.viessmann.de Pumping station pre-mounted on tank Examples of system integration Burner Stratification device Fresh water station Central heating feed Source: Solvis.de Active Solar Thermal Energy in Buildings THERMOSYPHON SYSTEMS System Configuration Solar Thermal Installations 4-5 Components Components and Subsystems of Solar Thermal Installation 3-4 Control Components and Subsystems of Solar Thermal Installation 3-48 Prefabricated Solar Systems Solar Thermal Installations 4-2
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