Solar Thermal PDF

Solar Thermal Latitudes Parallels Angle north or south of the equator  Important Dates December 21st – winter solstice Sun is directly overhead at 23.5° S latitude Arctic Circle in 24 hours of darkness March 21st – spring equinox Day length is 12 hours worldwide...

Solar Thermal Latitudes Parallels Angle north or south of the equator  Important Dates December 21st – winter solstice Sun is directly overhead at 23.5° S latitude Arctic Circle in 24 hours of darkness March 21st – spring equinox Day length is 12 hours worldwide Sun is directly overhead at the equator June 21st – summer solstice September 21st – fall equinox  Boston ~ Not only 42 °N changes the peak but also changes where rises and sets Bursa, Turkey (~40°N) Solstice to Solstice http://www.astronet.ru/db/xware/msg/ https://www.boston.com/weather/weather/2012/01/27/post/ 1229646 Time and Day https://www.timeanddate.com/sun/usa/san-antonio  Terms of light Diffuse radiation – light from all over the sky (typically room daylight) Direct radiation – straight from the sun on a clear day ~ 1 kW/m2 referred to as 1 sun Both are useful for solar energy but direct is what is used for high temperature generation Flux = amount of energy in electromagnetic wave that passes perpendicularly through a unit surface area per unit time Light energy is more concentrated near the equator. In other words, there is a greater flux per unit area (W/m2) Solar radiation on a horizontal surface (kWh/m 2/day) July January  General Terms Daylighting – making the most of natural daylight Two Low Temperature Categories of Design Passive - Absorption of solar energy directly into a building to reduce the energy required for heating and/or whole process of integrated low energy building design Active – involves a discrete solar collector to gather solar radiation Solar Thermal Engines – extension of active, usually using more complex collectors to produce high temperatures in order to create steam to turn a turbine Desert Air Conditioni ng https://greenpassivesolar.com/wp-content/uploads/2012/02/Evaporative- Cooling.pdf Strategies  Swamp coolers Pros of Swamp Coolers Improving air quality by purifying it of particles, such as dust. Swamp coolers reduce indoor temperatures at an average of 20 degrees, working ideally when the outside temperatures are between 80-93 degrees. Increasing humidity, which is important to maintain indoor air quality. Being an affordable option for cooling indoor temperatures, especially during the summer, compared to traditional AC systems. They are much more energy-efficient than standard air conditioners, capable of cutting energy costs significantly. They are easy to install and have a generally easy level of maintenance. Cons of Swamp Coolers When temperatures reach over 93 degrees, especially with heavy sunlight, swamp coolers will perform less robustly. They do not work ideally in humid climates. The pads within the swamp cooler should be changed at least yearly and can be expensive – with filters commonly costing over $100 each. Thorough cleanings of these units should be done regularly to ensure the lines are clear of dirt and dust to ensure they run properly. If filters are not changed, it can also breed mold and mildew. General passive solar heating building design 1.Well insulated 2.Responsive, efficient heating system 3.Face south (main rooms) 4.Avoid overshading 5.Thermally massive R-values Insulation R = Resistance to heat flow Based on weather, temp, winds, etc Zone 2 Attic = 30-60 (38) 2x4 walls = 13-15 2x6 walls = 19-21 Floors = 13  Passivhaus Design Example: Germany – the 3 litre house Built 1950s Energy remodel in 1990s Insulation, triple-glazed windows, heat recovery, fuel cell heat/power Heating energy decreased by 7x (210 kwh to 30 kWh/m2/year) Pennyland House Example Half as much gas needed for heating as normal houses. Extra cost was 2.5% of total construction with payback of 4 years. Wallesy School of Design Example Heating system was unnecessary and removed a) Conservatory a) Energy store is building b) Habitable solar collector c) Air movement b) Trombe wall a) Thin air space b) Radiative and air movement c) Direct gain a) Simplest b) Thermally massive (concrete) useful gains c) Thermally lightweight (timber) overheating Urban Daylighting Issues Magic of Glass Transmittance – fraction of incident light that passes through it Spectral transmittance of glass  Double glazed window ~16mm thick Conductance rate of flow will depend on: Temperature difference Total area Thermal conductivity Convection minimized by filling with heavier, less mobile gases and limiting gas  Radiati on of an object's Emissivity - the measure effectiveness in emitting energy as thermal radiation (infrared). Most building materials have emissivity values 0.9-0.95. Low-E Windows – emit less thermal radiation. These coatings can halve the rate at which a window loses heat compared to an uncoated glass window. Single pane to double low-e can reduce heat loss by >70% Radiant Barriers – low R-value but good reflectivity  U-val ue Conductance, convection, and radiation effects combined = reciprocal of R-value; expressed as heat flow per m2 = U-value x temperature difference Lower the value the better the insulation performance single glazing = 4.8, basic double glazing = 2.7, fiberglass insulation = 0.05 (R19) Windows in SA should be