Performance Modeling of Low Cost Solar Collectors in Central Asia Progress Report Steph Angione, Zach Auger, Adrienne Buell, Suza Gilbert, Emily Kunen, Missy Loureiro, Alex Surasky-Ysasi, Amalia Telbis

Problem Definition Goal: Design a performance model for a solar collector in central Asia Specifications: –Heat water for domestic use –Low cost –Local materials –Efficient –Ease of maintenance –Sustainable

Decision Making Process Background Research: –Region and climate data –Materials and availability –Heat transfer –Testing and modeling process Specified Situation: –Household size: 7 people –Water usage: 25 liters per person –Region: rural, mountainous –Output Temperature: 60 °C –Functionality: year round –Storage tank Capacity: 1-2 days of water –Delivery system: use existing

Geography: Afghanistan Located in Central Asia, on the Iranian plateau at a longitude of 33°00’N and a latitude of 65°00’E. Includes three distinct areas: –Central Highlands –Southern Plateau –Northern Plains

Geography: Tajikistan 93 % of the country is covered in mountains More than half lies above 3,000 meters Contains dense river network

Climate: Afghanistan Highlands similar to lower Himalayas –Temperature range from 50°-60° F Hottest weather in southwest Coldest weather in northern regions Waves of intense cold with temperatures below zero

Lifestyle: Afghanistan ~300 families/village 43 inhabitants/km 2 Life Expectancy: 43.7 male 43.1 female Children per family: ~7 85% water usage is for agriculture Less than 20% have piped water 4% of population has electricity

Housing: Afghanistan –Construction Materials Stone, wood, plaster and straw, brick –Terraced Housing Roof of one in yard of the other 2 stories –cooking and eating on upper floor –windows with hinged shutters Post and beam constructions – coniferous wood used

Lifestyle: Tajikistan 2/3 of population lives in rural areas 44 inhabitants/km 2 Life expectancy: 67 male Children per family: ~6 Natural water system infected with chemicals, bacteria –20% clean water coverage in rural area –90% clean water coverage in urban area 95% of rural population has electricity

Housing: Tajikistan Varies by Region –Urban Areas: Apartments –Flat areas: 1 story, flat roof, covered courtyard –In mountains: Build into the mountain Low ceiling Small openings & rooms Fire place in central room Multifamily/ multistory Construction: –Raw bricks, plaster & cut straw (horizontal layers) –Where available: wood used for roof beams –Cement often used for roof Area: ~51.4 m 2

Materials What to look for when looking for a material: –Thermal Properties –Durability –Availability –Construction Methods –Maintenance –Costs Materials Specified by EWB: –Sheet Metal –Wood –Glass –Black Paint –Horsehair Regional Materials Used: Clay, Cement, Brick, Coniferous Trees Wood, Sheep Wool, Straw, Plaster

Used as a conductor –High heat capacity [ J/kg*K] Variety of metals available –Best heat capacity – Aluminum [903 J/kg*K] –Best conductivity – Copper [401 W/m*K] Durability and Construction Methods: –Cutting tasks only require aviation snips –Small Pieces are easy to bend –Can be fastened to wood using nails –To fasten two sheets pre-drill holes in each, then join using screws or pop rivets Sheet Metal Copper Sheet: Can be shaped into any form easily Doesn’t not crack when hammered, stamped, forged or pressed. Resists corrosion and does not rust Can be recycled Aluminum Sheet: Excellent conductor of heat Light (about 1/3 weight of copper) Easily machined Resists corrosion Withstands wind, rain, chemicals, pollution Excellent durability Can be recycled

Wood Used as Insulator Specific Heat: –Independent of wood species –Dependent of temperature and moisture content of wood Thermal conductivity –Smaller than value for metals –2-4 times better than other insulating materials –Conductivity along the grain is 1.5 to 2.8 times greater Thermal diffusivity is much lower than metal, brick, and stone Durable insulation Easily cut for construction –Hand-tools sufficient

Glass: Used for glazing Thermal properties: –Coefficient of thermal conductivity ~1.0 W/m*K Optical properties: –Soda Lime Glass: Refractive Index (I=435 nm): (I=645 nm): Figure 1 shows optical transmission % versus wavelength Figure 1 Soda Lime Glass: Table 1 Thermal Expansion x /°C (0-300°C)93.5 Strain Point, °C473 Annealing Point, °C514 Softening Point, °C696 Density, g/cc2.47 Young's Modulus x10 10 Pa7.03 Poisson's Ratio0.22 Log 10 Volume Resistivity ohm-cm, 250°C6.4 Dialectric Constant, 1Mhz, 20°C7.2 Refractive Index, nm1.51

Black Paint Used to improve thermal conductivity of material Semi-selective black painted surface –Absorptivity = a = 94% –Emissivity = e = 28% Non-selective coating (matt texture): –Absorbs 90-95% of all solar radiation –Radiates back about 90% of maximum heat energy Cheap but can be ineffective if not used in proper location Easily applied and restored

Horsehair and Sheep Wool Horsehair: Used for insulation Material readily available 0.3 million horses in Afghanistan (FREE) Durable Lasting for over 200 years Insulation used for homes Bousillages – mixture of moss and clay Outer layer is a mixture of horsehair, water, and clay Sheep Wool: million sheep in Afghanistan

Regional Materials Positive Aspects of using regional material: –Cheap –Readily available –Training on how to use materials not needed

What is a Solar Collector? Radiation from the Sun transformed into thermal energy Used for Heating air or water Different types: –Batch –Vacuum –Concentrating –Flat Plate

Heat Transfer Formulas Conduction –Fourier’s Law: dQ/dt=-kA(dT/dx) –Through a material Convection –Newton’s Law of Cooling: dQ/dt=hA(Ts-Tf) –Fluid flowing past a solid Radiation –Stephan-Boltzman Law: dQ/dt=εσATb4 –Heat emitted by an object Hot Material

Before You Pick a System Information Needed: Sunlight Striking Surface –Latitude –Season –Weather Patterns –Sun’s Position Temperature Wind Speeds Humidity Some Basic Questions: Will the Collector Storage System Be in the Same Unit? Will the Liquid Circulate Naturally or Be Pumped? Will Back Up Heating and Storage Be in the Same Tank? What Freeze Protection Method will be Implemented?

Components of a Solar Collector Absorber Plate Absorber Surface Coatings Glazing Insulation Casing

Sample Calculation Assumptions: –Power from Sun: 1kW/m 2 –Input Temperature: 0°C –Output Temperature: 60°C –Household Size- 10 people –Hot Water Per Person- 25 Liters per day –Hours of Sunlight: 5 per day Outcome: –Surface Area of 3.5m 2 Issues of Note: –Based on Maximum Possible Energy Absorption –February Basis

Testing and Modeling Determine All Variables and Constants Visualized Design/Schematic –CAD software: SolidWorks, ProE –Free-hand sketches

Calculations Use of MatLab or Excel Use of possible simulations –F-chart –TRNSYS

F-Chart Advantages –only 2.5 percent error vs. monitored systems –easily determines thermal performance

F-chart continued… Disadvantages –underpredicts system performance in mountainous regions

Solar Heater Types and Designs Passive vs. Active Solar Heaters –Active use pumps to circulate water or an antifreeze solution through heat-absorbing solar thermal collectors –Passive The water is circulated without the aid of pumps or controls Open Loop vs. Closed Loop If the liquid that needs to be heated is also the one being circulated: Open Loop If antifreeze or another solution used in a heat exchanger to heat the water: Closed Loop

1.Active Solar Heaters 1.1 Open Loop Use Pump Direct Water Heating More Efficient Cost Less Drain-Back Freeze Protection UNRELIABLE

1.2 Closed Loop Drain Down One Liquid Unreliable Freeze Protection Drain Back 2 Liquids Antifreeze Solution Good Freeze Protection Heat Exchanger Less Efficient 1. Solar Collector 6. Collector Return Breaker 11. Tank Drain Solar Collector 2. Vent/Vacuum 7. Collector Supply 12. Tank Drain Fitting 3. Hot Water to Taps 8. Drain Down Valve 13. DHW Electric Tank 4. Cold Feed 9. Circulating Pump 14. Immersion Heater 5. Tempering Valve 10. Drain

2. Passive Solar Heaters Batch Simplest Type: One or more storage tanks Heat loss from tank Not reliable in areas That experience Freezing Thermosyphon 2 Liquids: Antifreeze Solution Heat Exchanger: Efficiency Decrease No need for Pumps Storage tank placed Above collector

Recap: Possibilities and their +/- …what we ended up picking Active –Open Loop: (+) cost less (-) pump controlled (-) only possibility for freeze protection: manually draining X Second one OUT !!! –Closed Loop: Drain Down: –(-): not reliable !!! X First one OUT !!! Drain Back: –(+) good freeze protection –(+) can use water/water instead of antifreeze –(-) pump and 2 different storage tanks Passive –Batch (+)easy (can even be a tank painted in black) (+) offers freeze protection because the water is only present in the tanks and the areas are large; the water cools off slowly (-) takes long to heat the amount of water –Thermosyphon (+) no need for pumps (+) offers good freeze protection (-) heavy tank placed above the collector (-) efficiency decreases when using indirect heating We voted between: Drain Back, Batch and Thermosyphon –Systems chosen Group I (Suza, Missy, Emily and Zach): Drain Back System Group II (Stephanie, Adrienne, Alex and Amalia): Thermosyphon

Team Members: Melissa Loureiro Emily Kunen Suza Gilbert Zach Auger Team Drain Back

Drain Back - Description Solar collector located above storage tank 2 liquid system Both can be water 1liquid water and 1an antifreeze solution Active closed loop system Uses pump Pump circulates water through collectors when collectors are warmer than stored water Heat exchanger used in storage tank Heat transfer between circulating fluid and potable water Circulating solution drains to a 2 nd tank when pump shuts off Tank is placed on a tilt for complete drainage

Pros and Cons Positive Aspects: Less likely to freeze Fewer components than other active systems –Less likely to break More reliable than antifreeze system Negative Aspects: Requires Energy for Pump Heat loss during transfer If antifreeze used must be replaced every 3 years

Optimization Excel spread – sheet to model variables Optimization parameters: »Cost »Materials »Temperature into/out of collector »Size of collector »Amount of daily solar power »Time required to heat water »Length of piping system »Efficiency

Team Thermosyphon Amalia Telbis Alex Surasky- Ysasi Steph Angione Adrienne Buell

Thermosyphons Things to address: –Substance for antifreeze –Efficiency of Heat Exchanger in Tank –Pipes in Tank –Flat plate, glazed collector –Liquid Replacement –Storage tank placement & attachment –High Limit Safety Valve

Performance Model Program in MatLab Output –Collector Size –Monthly Expected Performance –Optional Maximum Size- Output is Volume of Water Heat Dissipation in Storage Tank Data in Excel to be Referenced F-Chart

Timeline and Future Plans By Spring Break (3/22) –Gather remaining relevant data –Pricing (in US dollars) and local pricing –Construction techniques –Finalize ideal design to be modeled for each group Week of 4/10 –Incorporate losses into design and model for each group Week of 4/17 –Final model completed for each group May 3 rd –Final presentations due