SOLAR THERMAL ENERGY

Transcription

1 SOLAR THERMAL ENERGY by John Canivan

2 SOLAR THERMAL ENERGY March 2004 Sunny Future Press, Wantagh, NY Copyright John Canivan 2003 ISBN $50.00 All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means electronic or mechanical without the express permission of the publisher. On line support is available from If you have any questions or comments about this book feel free to publish them on the JC Solar Collector Forum or join the Solar Energy group or send to If you find this book helpful you may also appreciate How to Build a Solar Hot Water System, Energy Independence or How to Build a Solar Thermal Roof. Special thanks are extended to my patient wife, Patricia, who helps clarify concepts and tolerates my chaotic desk. Professor Dathatri, coordinator of the Solar Energy Department at the New York State University of Farmingdale, also deserves special thanks for his support and numerous suggestions. And let s not forget my favorite editor, Mel Riddick, the critic. May the sun help you live long and prosper? John Canivan 1

3 SOLAR THERMAL ENERGY This solar thermal energy study guide is designed to be used in conjunction with the STE multimedia interactive slide show. There are over 39 questions generated from the show and this book. The best way to learn about solar thermal energy in the shortest period of time is to view the show with this book at your side, and work out the problems as they re presented. When you feel like taking a break or when you need time to do a calculation hit the pause button. When you re ready to move on hit the pause button again, and the program will resume. To run the slide show effectively you ll need to turn off your PC screen saver. Do this by going to CONTROL PANEL. Click on the DISPLAY icon. Under DISPLAY choose the screen saver tab. For your screen saver choose none. Now turn up the volume on your speakers and load the slide show file. Click the STE icon and then click the start icon to start. You should be able to master all the material contained in this book and all the material on this slide show in a short time. The book and slide show are copy right protected. It is illegal to copy or distribute either the book or the slide show, but the information they contain is yours to keep forever and use to transform the world and bring us one step closer to a Solar Age of peace, tranquility and discovery. Hope you can find the time to visit my website John Canivan at 2

4 OVERVIEW 1. Heat Gain demonstrates how energy available from sunlight may be calculated and converted into a fuel oil equivalent. p4 2. Heat Loss demonstrates how heat loss from a dwelling may be calculated. These calculations help determine how much fuel oil or solar energy would be needed to maintain a dwelling at a set temperature throughout the heating season. p12 3. Heat Theory answers questions like: p16 a. What is heat? b. What is temperature? c. How is heat transferred? d. How does a multi-tank heat storage system work? 4. Solar Power explores the past present and future uses of sunlight used to run pumps and generators. p25 5. Solar Home Heating explores the history of solar heating as well as some home designs based on the greenhouse concept. p30 6. Solar Hot Water demonstrates: p34 a. History of solar hot water. b. Solar collectors c. Solar hot water systems 7. Energy Independent Housing explores: p52 a. Hydronic heating b. Massive heat storage vault details 3

5 c. Super insulation methods d. Zoning e. Integrated heating, electric and living systems e. Overall design considerations 8. Solar Thermal Roof is a futuristic solar thermal design concept that utilizes the entire surface area of a roof for heat gain. P65 9. Solar Thermal Concepts clarifies the basic principles of solar thermal energy application. P Answers to Questions p92 4

6 HEAT GAIN Heat gain from the sun varies from place to place and depends upon weather conditions time of the day and season of the year. On an hourly basis we will assume that one KWH is available to every square meter of direct sunlight unhampered by weather conditions. For local average daily radiant energy availability we will refer to the National Solar Radiation Maps. In this chapter we will be calculating the annual solar radiant energy available for the Long Island area in fuel oil equivalents. December radiant energy will also be calculated. These calculations will be done for latitude tilt angle and latitude tilt angle + 15 degrees. To do these calculations we ll need to convert KWH (kilowatt hour) energy into BTU energy. From this result fuel oil equivalents will be derived. You may refer to the following equivalents while working on heat gain problems. ONE HOUR OF SUNLIGHT = 1 KWH 1 KWH = 3,400 BTU s 1 gallon #2 fuel oil = 150,000 BTU s 1 square meter = 10.6 sq ft one 4X8 collector = 3 m 2 5

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9 Let s begin with a few questions? 1. What is a BTU? 2. How many BTUs are in a gallon of fuel oil? 3. What is the energy equivalent of one square meter s worth of sunlight over the period of one hour in KWH? 4. What is the fuel oil equivalent of one hour of direct sunlight on one square meter? 5. What effect does collector position have on collector efficiency? The average daily radiant energies derived from the National Solar Radiation Data maps have been calculated for your convenience. See how close these approximate values are to the values you derive for the Long Island area? 8

10 6. Use a National Solar Radiation Map to calculate the average annual solar energy available in KWH from one square meter of Long Island real estate at latitude tilt angle over the period of: A. a day = 4.5 KWH/day B. a year? C. Calculate the fuel oil equivalent per year? HINT use annual latitude map KWH/day X days in year = KWH/yr KWH/yr X BTU s/kwh = BTU/yr BTU/yr X BTU/ BTU per gallon = GAL/yr 7. Use a National Solar Radiation Map to calculate the average annual solar energy available in KWH from one square meter of Long Island real estate at latitude tilt angle plus 15 degrees over the period of: A. a day? = 4.3 KWH/day B. a year? C. Calculate the fuel oil equivalent per year? HINT use annual latitude map 9

11 8. Use a National Solar Radiation Map to calculate the average solar energy available during December in KWH from one square meter of Long Island real estate at latitude tilt angle over the period of: A. a day? = 2.5 KWH/ day B. a month? C. Calculate the fuel oil equivalent for the month of December? HINT use December latitude map 9. Use a National Solar Radiation Map to calculate the average solar energy available during December in KWH from one square meter of Long Island real estate at latitude tilt angle + 15 degrees over the period of: A. a day? = 2.8 KWH/day B. a month? C. Calculate the fuel oil equivalent for the month of December? HINT use December latitude map 10

12 10. What is the advantage of tilting a collector at a steep angle? 11. How is a greenhouse able to trap heat? 12. How much solar heat energy will be available for two 4X8 foot collectors in a year at latitude tilt angle? Give answer in fuel oil equivalents. (HINT a 4X8 collector has a surface area of 3 m How much solar heat energy will be available for two 4X8 collectors at latitude tilt angle during the month of December? 14. How much heat energy will two 4X8 collectors harvest at latitude tilt angle + 15 degrees during the month of December? 15. Name two devices used to concentrate the radiant energy of the sun? The solar heat gain of a system is always less than the available energy from the sun. Heat transfer efficiency will of course depend on collector efficiency and the heat exchange process within the storage vault. Heat gain from fossil fuel oil burners depends on the combustion process as well as the heat extraction system. Typical fossil fuel heating systems lose much of their heat during the combustion process of venting hot exhaust gasses. Heat gain efficiencies are important factors that must be considered for both fossil fuel and solar heating systems. To simplify heat loss calculations we will assume an oil burner heat transfer efficiency of 100% although this number is usually much closer to 50%. 11

13 HEAT LOSS 1. What are some factors that contribute to home heating loss? Low outside temperature is something we don t have much control over. Degree days are used to measure the extent and duration of low outside temperature. They are the average daily temperature differences between the inside temperature and 65 0 F. DEGREE DAYS are used to determine how much fuel will be needed to heat a building in a given area. Individual degree days are calculated by subtracting the average outside temperature from the 65 o F. 2. Calculate the degree days for January 5, 2003 when the average outside temperature is 25 degrees F. All degree days in which the outside temperature is colder than the inside temperature are added together to arrive at the annual degree days (DD/year). The temperature difference between the inside and outside of the building is the primary cause of heat loss in the winter months. Other factors include insulation, surface area and air infiltration. 12

14 HEAT LOSS CALCULATIONS In order to calculate the annual heat loss of a building we must first know the number of degree days per year for the area. Next we will have to examine the insulation factors (U) and the surface areas (A) in question. The following abbreviations are used in heat loss calculations. DEGREE DAYS: HOURLY HEAT LOSS: YEARLY HEAT LOSS: DD = (T i - T a )/day Q = U A (DD)/hr E = U A (DD)/yr. 24hr E Energy needed per year BTU Q Hourly rate of heat loss (Btu/hr) U Heat transfer coefficient (Btu/hr-ft 2 - F) = 1/R A Heat transfer area (ft 2 ) T i Inside design temperature ( F) (65 o standard) T a Outside average temperature ( F) DD Degree Day (T i - T a ) F 13

15 3. Calculate the heating needs of a simple shed roof house 12 feet wide, 20 feet long and eight foot high with one 3 X 6 foot air tight door. The average yearly degree days for this house are 5,000. Do not consider the heat loss from the floor or air infiltration. R for walls = 5 U =? R for ceiling = 10 U =? R for door = 2 U =? REMEMBER E = U A (DD)/yr. 24hr E = U A 5, E = U A 120,000 POORLY INSULATED SHED A R U U A (DD)/yr. 24hr WALLS sq ft BTU CEILING sq ft BTU DOOR sq ft BTU TOTAL GALLONS BTU gallons of oil 14

16 4. Now let s calculate the heat loss for the same shed in the same place after adding insulation. Let s give the walls an R factor of 15, the ceiling an R factor of 30 and then let s add a storm door to give our entry way an R factor of 4. WELL INSULATED SHED A R U U A (DD)/yr. 24hr WALLS sq ft BTU CEILING sq ft BTU DOOR sq ft BTU TOTAL GALLONS BTU gallons of oil Notice the value of insulation. 15

17 HEAT THEORY Solar thermal energy is concerned with gathering, transferring and storing heat energy from the sun. 16

18 If you answered a tub of ice water you are correct. Any substance that has a temperature higher than absolute zero contains heat. Absolute zero is 0 0 Kelvin or C or F HEAT is defined as the product of temperature and mass. To calculate the number of BTU s something contains, simply multiply its absolute temperature by its mass. Since ice water is 428 degrees F hotter than absolute 0 we should multiply the weight of the ice water by 428 to find the heat contained in the bathtub full of ice water. A bathtub full of ice water would weigh about 300 lbs so the product of 300 lbs times 428 would give us 128,400 BTUs. A cup of boiling hot coffee is 630 degrees F hotter than absolute zero and it weighs a half of a pound so the heat contained in a cup of coffee would be 315 BTU s You are justified in believing that a tub of ice water is not a good heat source even though it contains more heat than a cup of hot coffee. A useful heat source should be hotter than the item being heated. Heat gain is measured from a reference temperature. The difference between the starting temperature and the ending temperature times the mass is equal to heat gain. To better understand this concept, calculate the heat gain for the tank of water in the next problem. 17

19 Questions: 1. If town water enters your heating system at 55 degrees F how much energy would be required to bring your 80 gallon tank of water at 55 degrees F up to 155 degrees F? Hints: One gallon of water weighs 8 lbs. A BTU is the amount of energy required to raise one pound of water one degree F. 2. How many hours of direct sunlight would it take a 4 collector system to bring this tank of water up to 155 degrees F? HINT The four collectors are each 4 feet long and 8 feet wide. One 4X8 collector has a surface area of 3 m 2 18

20 HEAT is the product of temperature and mass. It is the sum total of molecular motion. Temperature measures the average kinetic state of molecules. Fast moving molecules are hot and slow moving molecules are cold. If we multiply the average kinetic state of molecules by its mass we are measuring heat. CONDUCTION: Solid objects transfer their vibrating molecular motion by conduction. Some substances conduct heat better than others. Aluminum, Copper and Silver are excellent conductors of heat. Collectors convert radiant energy into heat and then transfer that heat to absorber plates, flow tubes and collector fluid by the process of conduction. CONVECTION: Liquids and gases transfer heat by convection currents. Hot molecules rise and cold molecules fall. This is how a passive solar greenhouse is able to heat a house. The funnel like shape of a solar greenhouse actually concentrates hot air molecules before they enter living quarters. HEAT STORAGE There are many kinds of heat storage facilities. Some systems use hot greenhouse air to transfer heat to concrete slabs. Moist hot air condenses on the cold concrete slab to support mold and bacterial growth so we will not consider this method of heat transfer. Instead we ll focus our attention on Hydronic or water heating systems. 19

21 SOLAR HOT WATER A simple closed loop solar hot water system uses a fossil fuel backup heating tank for hot water storage. This arrangement may be simple and inexpensive, but it s not very practical. Heat can only be transferred while there s a difference in temperature. As collector temperature approaches storage tank temperature, heat exchange is minimal. By separating the fossil fuel heating system from the solar hot water storage facility the efficiency of heat transfer is greatly enhanced. To increase efficiency more heat storage tanks should be connected in series. 20

22 Collector fluid is circulated through the carrier pipes and transferred into the storage vault through heat transfer coils near the bottom of each tank. Once inside the vault heat is transferred to and concentrated near the top of the vault. This top layer of hot water is where heat is transferred into domestic hot water system. The rate of heat transfer is affected by the conductive and convective medium as well as temperature differences. Objects with large temperature differences transfer heat faster than objects with low temperature differences. If only one tank was used to transfer heat the transfer rate would approach 0 as the storage tank approached collector temperature. To increase heat gain we should use a multi tank heat storage system. 21

23 Tank 1 is the warmest because this is the first tank used to transfer collector heat. Tank 2, the warmer tank, will receive heat left over from tank 1 s transfer process. Tank 3, the warm tank, is designed to suck the last bit of heat from the already cooled collector fluid. This cooled fluid is then returned to hot collectors to gather more heat from the sun. If we used only one tank to transfer collector heat we d soon be sending hot collector fluid back to the hot collector and the heat gain process would soon end. This is how heat is transferred into a multi-tank heat storage system. HEAT EXTRACTION Heat is extracted from the tops of these tanks where hot water is concentrated. Notice that cold water first enters the heat extraction tubes of tank 3. Tank 3 is used to preheat water before tank 2 s heat extraction. Tank 2 preheats water for tank 1 s heat extraction. If sufficient tanks and sufficient collectors are used a back up heating system would be unnecessary. 22

24 MULTI TANK HEAT STORAGE If we carry this concept of multi tank heat storage to the extreme we might think of using 20 or fifty or even a hundred tanks of water rather than one or two. Heat transfer is simplified by cementing heat transfer tubes from the collectors to the bottoms of 55 gallon tanks. The hot water that concentrates near the top of these tanks is transferred into a heating system by heat extraction tubes cemented to the tops of the tanks. Water never flows into or out of these tanks they are only used for heat transfer. A few more questions 3. How is the sun s energy transferred to the collector? 4. How is heat from the absorber plates transferred to the domestic hot water? 23

25 5. What is heat? 6. What are the advantages and disadvantages of a multi-tank heat storage system? 24

26 SOLAR POWER Our dependence on fossil fuel threatens our economic and ecological livelihood. To avoid further destruction of life sustaining resources we should implement a rational policy of solar application research based on past discoveries and present high tech capabilities. The old saying that necessity is the mother of invention is true. As early as 500 BC, Greek citizens cut down thousands of trees to heat their homes. When the forests were gone they were forced to seek an alternative home heating method. The Greeks use of sundials reinforced their awareness of the suns seasonal position and paved the way for some clever solar passive designs that predate the birth of Christ. In 500 AD Romans used mica and a crude form of glass to trap the sun s heat. Around that same period of time the Anasazi Indians of Southern Colorado used the direct gain system of south facing canyon walls to stay warm. A millennium passed without significant developments in the field of solar thermal energy. 25

27 In 1760 Horace de Sausssure observed that a room covered with glass gets hotter when sunlight passes through it. He determined the effectiveness of trapping heat in this manner by building an insulated class covered pine box. When exposed to sunlight he observed the interior temperature exceeded the boiling temperature of water. In 1860 Auguste Mouchout began work on the first known solar powered motor. His invention called a HOT BOX involved a glass enclosed iron cauldron connected to a steam engine with a copper tube. Incoming solar radiation was trapped by the glass enclosure and was able to bring water to a boil, but the low temperature of this boiling water was incapable of producing a practical power output from a steam engine. In1885 Charles Tellier began his work with a flat-plate collector filled with ammonia instead of water. He decided to use ammonia because ammonia has a lower boiling point than water. In1904 Henry E. Willsie developed the concept of thermal storage. His choice of a vaporizing liquid was sulfur dioxide because of its low boiling point and high specific gravity. The exhausted gas was then reused by liquefying it inside a condensing tube and pumping it back into the boiler. 26

28 In 1875 William Adams decided to make use of flat mirrors that were inexpensive and would not tarnish. He arranged these mirrors on the inside of a cone and focused them on a blackened stationary boiler. To follow the sun s movement the entire assembly could be rotated about a semicircular track. Adams had proved the feasibility of his invention that achieved temperatures in excess of 1200 degrees F and could power a 2 ½ horsepower steam engine. In 1880 John Ericsson, a Swedish born designer developed the parabolic trough for producing solar power. Erickson s parabolic trough collection system has become a solar power standard for modern solar power plants because of their engineering efficiency and ease of operation. In 1895 Aubrey Eneas built a huge parabolic dish to boil water and generate steam. Its reflector spanned 33 feet in diameter and contained 1,788 individual mirrors. Its boiler, which was about 13 feet in length and a foot wide, held 100 gallons of water. After exposure to the sun, Eneas's device boiled the water and transferred steam through a flexible pipe to an engine that pumped 1,400 gallons of water per minute from a well onto an arid California landscape. In 1906 Frank Shuman, a dedicated dreamer and hardheaded businessman decided to build the largest, most cost effective solar powered machine ever conceived. He double insulated his collectors and added reflectors and a tracking device to achieve a higher boiler temperature. The extra investment paid off and his machine was installed just outside of Cairo, Egypt, in 1912, to power a 55 horsepower irrigation pump. 27

29 Some people continued to experiment with solar heating systems through the 40 s 50 s and 60 s but it wasn t until the 1970s oil shortage that the solar industry gained support. A population outraged by the inconvenience of an oil embargo and high utility rates brought solar energy to the nation s attention. The solar manufacturing business picked up and jobs were created for installers. From this point in time until the early 1980 s the solar industry grew. Hazel Henderson, President Carter s economic advisor, believed that the eighties would be the dawn of a Solar Age for Americans. The possibilities of a sustained yield culture based on the diffuse energy from the sun seemed real. Jimmy Carter initiated our nation s first Sun Day He had a solar hot water heater mounted on the White House roof. He set up a Corporate Average Fuel Economy which has saved millions of barrels of fuel oil. Despite President Carter s efforts the US government is still the largest user of energy with the Department of defense as the worst offender. Carter made great contributions toward the solar movement, but his efforts were soon forgotten. Among the first official acts of the Reagan administration were to remove the solar water heater from the roof of the White House. Reagan felt the solar hot water heater was a sign of weakness and poverty so he removed it as a sign of American Prosperity. The price of this prosperity was massive tax breaks for the fossil fuels industry intended to encourage more fuel consumption. Operation Desert Storm was fought to preserve an inexpensive source of foreign oil. Former oil company owner, President Bush did little to encourage solar energy research. Since 1980 there has been an obsession with increasing US fuel consumption at any cost. Oil barons grew powerful as the rest of us became more dependent on a non-renewable resource. 28

30 It would be nice if our government took a leadership position in developing a more comprehensive economy that increased the natural resources of our environment and gave us a sense of purpose, but it appears that we must do these things for ourselves. With the sun as our ally we shall not only have clean, affordable energy, but also have something far more important, the freedom of choice. QUESTION Why is the Solar Energy industry taking so long to develop in America? 29

31 HISTORY OF SOLAR HEATING The history of heating homes with sunlight should extend to those times when cavemen chose south facing caves for additional warmth years ago the Greeks built their houses with south facing windows to gain needed winter heat. The Romans improved on the Greek design by using mica and glass in their windows. Anasazi Indians: Around 800 AD the Anasazi Indians of Southern Colorado found a way to capture the oblique rays of a winter sun. They simply built their stone houses against south facing canyon walls. This is a good example of a passive direct heat gain system that takes advantage of the canyon walls heat retention ability. The remains of the Anasazi Indians are still with us today. Unfortunately we all can't live at the base of south facing canyon wall, however if we re located in the South West we might decide to dwell in an alternative passive solar home called the Adobe. ADOBE: These are houses made from mud bricks that have tremendous heat absorption ability. Solar radiation is absorbed directly during the day and released gradually during the cold nights. Adobe style housing is very popular in New Mexico; as a matter of fact this type of housing is mandatory in Santa Fe and many other areas. The process of heating a south facing, wall is improved with glazing so that this method of heating may be used in less favorable climates. 30

32 The Trombe Wall: Late in the 1950 s a French inventor by the name of Felix Trombe devised a method to improve on the adobe. His invention called for a glazed wall installed on the south side of a building used to trap heat. Cold dense air from the inside of the building is allowed to flow inside the hot, glazed Trombe cavity. The heated air is then returned to the living quarters. Solar Wall: A derivation of the Trombe Wall is the Solar Wall made by the Solar Wall Company. It consists of a blackened corrugated metal fixture attached to the south side of a building. A fan is used to pump the heated air from the sun into the house. 31

33 DIAGONAL GLAZING: Diagonal glazing provides another method for home heating. What advantages might diagonal glazing have over vertical glazing? The Solar Greenhouse: The Solar Greenhouse is very much like the Trombe wall except that it serves the dual purpose of providing a growing environment for plants during a cold winter. Notice also that the diagonal glazing creates a sort of funnel that concentrates heat. Ultraviolet and visible light from the sun is transformed into long-wave IR radiation when it strikes the darkened wall inside the greenhouse. This trapped IR radiation heats the surrounding air which rises to the top of the greenhouse and exits into living quarters. Notice that the heat collection area is separated from the living quarters. This is done to prevent heat loss at night. 32

34 1. Give an example of a direct heat gain dwelling? 2. How does a Solar Greenhouse trap heat? 3. How does a Solar Greenhouse concentrate heat? 4. Why should a Solar Greenhouse be isolated from living quarters? 33

35 SOLAR HOT WATER A BRIEF HISTORY Hot Box 1760: A noted Swiss naturalist by the name of Horace de Saussure observed that a room covered with glass gets hotter when sunlight passes through it. He determined the effectiveness of trapping heat in this manner by building an insulated class covered pine box. When exposed to sunlight he observed the interior temperature exceeded the boiling temperature of water. This simple Hot Box has become the prototype of today s solar collector. Bare Metal Tank: Nineteenth century people heated their water on cook stoves. To facilitate the process farmers placed blackened water tanks on their roofs. By the end of a warm, summer s day these farmers had enough hot water to bathe and wash a few dishes. A Practical Solar Water Heater: In 1891 Clarence Kemp of Maryland patented a way to combine the old practice of exposing metal tanks to the sun with the Saussure hot box system. He called his water heater the Climax, the world s first commercial solar hot water heater. Today this type of collector is called a bread box or batch heater. It became popular in warm sunny southern areas where freezing was not a major problem. Hot water collected during the day stayed hot for awhile after the sun went down, however it never lasted through the night. 34

36 Day and Night Hot Water: To improve on Kemps design William J. Bailey decided to separate storage tanks from collectors. He let rising hot water convection currents do the work of heating the storage tanks. By 1918 Bailey had sold over 4,000 Day and Night Solar Hot Water Heaters, however demand for the Bailey heating system slackened when the price of oil dropped. Countries other than the United States like Israel have always had problems with fuel procurement. They pay two or three times as much for fossil fuel products as we do. In 1960 using the sun to heat water was a novel idea. Today more than 90% of the population uses solar heated water. 35

37 MODERN SOLAR HOT WATER SYSTEMS Closed-Loop & Drain-Back: Closed-loop and drainback solar water heating systems are popular today because they allow more choice in the placement of the storage tanks. They also transfer heat more efficiently than passive bread-box systems. Since freezing is not a problem they can be used year round even in cold climates. The initial cost for an installed cold climate solar hot water system is still too high for most people to consider. As long as the price of oil is low and tax incentives are minimal cold climate solar domestic water heating systems will be scarce. Solar Heaters for Pools: Swimming pool heaters are the most successful solar application today. They often have payback periods less than three years. Since the swimming pool is the heat storage tank plumbing is simplified. A pool s own circulator pump is used to circulate pool water through the collectors. Inexpensive plastic collectors are used because swimming pools never have to get hotter that 90 degrees F. In the United States alone, solar swimming pool heaters gather the energy output equivalent to ten nuclear power plants. 36

38 3 Collector Types Collectors transform light energy into heat energy and transfer that heat to the domestic hot water system. This diagram demonstrates a simple closed loop system used to transfer heat from collector heat storage tank. Notice that hot collector fluid enters the heat transfer coil at the bottom. Why is that? Why is domestic hot water extracted from the top of the tank? 37

39 A CONCENTRATING COLLECTOR consists of a mirrored parabolic trough and an absorber tube. Fluid is pumped through the absorber tube to harvest the sun s energy. A tracking system keeps the rays of the sun focused on the flow tube, but a lot of heat is wasted with this system. Parabolic concentrators are best suited for the production of super heated steam used in power plants. 38

40 BATCH COLLECTOR or BREAD BOX: The batch collector doubles as a storage tank. This type of collector works best in warm climates where freezing is not a problem and there s a plentiful supply of sunlight. 39

41 PARALLEL FLOW FLAT- PLATE COLLECTOR consists of an insulated box covered with one or two layers of glazing. The inside of the collector is lined with a darkened absorber plate bonded to a network of flow pipes. Trapped heat from the sun is transferred from the absorber plate to the flow pipes and then to the collector fluid. 40

42 SERPENTINE FLAT PLATE COLLECTOR is similar to the parallel type collector except that there is only is one long continuous flow tube. The flow tube in this design is over 60 feet long and has only two solder connections. EVACUTED-TUBE with flow tubes: Incased inside a glazed, insulated box for additional heat gain. Collector fluid is circulated through small flow tubes to harvest the heat. 41

43 EVACUATED-TUBE without flow tubes. Heat trapped within the evacuated tube is transferred to collector fluid by means of a low boiling point liquid. This liquid is sealed inside an inner copper heat pipe. The portion of the tube exposed to sunlight heats up and boils the liquid inside. The vapor formed fills the tube and condenses at the top junction where it changes back into a gas. This evacuated tube collector is made in China by the Focus Technology Company. Individual evacuated tubes may be replaced if damaged. 42

44 Hot Water Systems Direct Connect: This is an inexpensive direct solar heated, hot water system. Well water or town water flows directly through the collectors of this system to become domestic hot water. Indirect Connect: The indirect system transfers heat to the domestic hot water system through heat transfer tubes. Fluid that flows through indirect connect collectors never comes in contact with the domestic water supply. DIRECT CONNECT SYSTEMS BATCH HEATERS are simple inexpensive systems best suited for mild climates where freezing temperatures and limited sunlight are not a problem. 43

45 SOME BATCH HEATERS use a sophisticated passive thermo siphoning system to store hot water in an elevated tank. SOME BATCH HEATER SYSTEMS have auxiliary tanks for storing water. SOME BATCH HEATERS systems even have freeze protection, but the one thing they all have in common is the absence of a circulator pump. DIRECT CONNECT POOL HEATING SYSTEMS are the most cost effective simple solar heating system available today with paybacks between three and four years. 44

46 DRAIN DOWN SYSTEMS don t need a batch tank to store hot water because they have a circulator pump that circulates hot water directly through a remote heat storage tank. If temperatures approach freezing an emergency drain down takes place. This drain down system uses sensor control. 45

47 INDIRECT CONNECT: The indirect system transfers heat to the domestic hot water system through heat transfer tubes. The fluid that flows through the collectors never comes in contact with the domestic water supply. Two basic types of indirect systems are the Drain Back and the Closed Loop. DRAIN BACK: Drain-Back systems allow collector fluid, typically distilled water to drain back into the heat storage tank when the collectors are done collecting heat. This simplified sketch of a drain back system demonstrates how hot water is isolated from the collector fluid. When the sun goes down and the collector cools off the pump stops and the collector fluid drains back into the heat storage tank. 46

48 DRAIN BACK with internal heat transfer coil: This drain back system transfers heat indirectly into a heat storage tank with a heat transfer coil. When the pump stops, collector fluid drains back into a small holding tank. This particular drain back system is using an evacuated tube collector. 47

49 CLOSED LOOP SYSTEMS require antifreeze to prevent freezing. The advantage of a closed loop system has to do with the small amount of energy needed to keep the collector fluid circulating, and the assurance that the collector fluid will never freeze. The drawbacks of this system have to do with the difficulty of adding antifreeze and the difficulty of keeping air out of the system. 48

50 CONVENTIONAL COLLECTORS have a network of parallel flow tubes bonded to the absorber plate. Multiple solder joints are required where the flow tubes meet the input and output carrier pipes. One bad solder joint spells disaster for this type of collector. PARALLEL FLOW DYNAMICS: This parallel collector is designed to transport collector fluid from the bottom of the collector to the top via a network of parallel pipes. Notice that the top and bottom pipes are larger than the vertical pipes. There is a reason for this. Fluid mechanics favors an increased flow rate for the end pipes. This is because incoming fluid pressure is greatest at the base of the first pipe and outgoing fluid pressure is smallest at the top of last pipe. If the top and bottom pipes are large the pressure difference is moderated and the flow rate in each of the parallel pipes is more uniform. These collectors may be connected in series because the top and bottom carrier pipes are large. It s unfortunate that flow rate is minimal at the center of the collector where most of the heat is concentrated. 49

51 SERPENTINE FLOW DYNAMICS The serpentine collector consists of one long continuous tube so there is no problem with uniform flow rate. The size of this flexible tubing is an important consideration. 3/8 inch tubing is easily bent, but its flow rate restriction places an excessive burden on the circulator pump. This problem may be overcome by hooking two or four serpentine collectors in parallel. 50

52 Four serpentine collectors hooked in parallel 1. Why should serpentine collectors be hooked in parallel? 2. What does the batch collector have in common with the drain down collector? 3. Name three basic types of collectors? 4. What are the advantages and disadvantages of a closed loop system? 51

53 Energy Independent Housing By understanding of the concepts of heat gain, heat loss, heat transfer and heat storage we should be able to design an energy independent house for a cold climate. Such a house will require more than a passive solar heating system and an array of photovoltaic panels. 52

54 If we do a good job with the collector installation, use thermo pane glass for greenhouse and 8 inches of Styrofoam insulation around the heat storage vault we should be able to collect and use the fuel oil equivalent of 100 gallons of fuel oil during the month of December for the Long Island area. A back up wood stove used to burn household trash could be used to supplement the heating needs of this house. We ll need to conserve energy so our solar home must be well insulated. The old saying: A house is only as good as its foundation is very true, so let s start here. FOOTING: It would be nice to insulate the footing and basement floor with Styrofoam, but the weight of the house would soon crush this material. Instead we should spread a mat of #1 stones, a foot deep, under the footings and under the basement floor. The stones not only provide a solid base for construction, but also provide insulation. As long as the stones are kept dry they act like insulators. To prevent cement from seeping into the stones we will cover them with a tarp before pouring the cement. 53

55 FOUNDATION: The foundation is typical except for the addition of a vault chamber located directly under the solar greenhouse. INSULATION: Let s cover the exterior foundation wall with four inches of poly-styrene foam to give them an R factor of 20. FERO CEMENT: We ll need to protect the insulation with a thin layer of Ferro-cement. MAIN CARRIER BEAM: Supports the foundation as well as the first floor. 54

56 VAULT TANKS: The four heat storage tanks that make up the heat storage vault have a capacity of 4,000 gallons. We ll place an additional 4 inches of poly-styrene foam insides of these tanks to bring our vault insulation factor up to an R40. 55

57 FLOOR JOISTS: 2X10 floor joists are framed in a standard manner. Let s put a lid on the heat storage vault so we don t fall in it while sheathing the first floor. FIRST FLOOR WALLS: First floor walls might look something like this. 56

58 SECOND FLOOR WALLS: Notice how space next to south roof is used as a closet. SOUTH ROOF FRAME: Space normally used for an attic can now be used for living space with the same amount of construction materials. 57

59 NORTH ROOF FRAME: A 2x12x16 roof frame is used to make the shed roof. 58

60 HEAT STORAGE VAULT: A reinforced concrete floor is poured over the polystyrene insulation. This floor is supported at the ends so the insulation will nor be crushed. 59

61 SOLAR GREENHOUSE: side view of solar greenhouse which rests on top of the heat storage vault. 60

62 Sixteen collectors supply the heat for four 1000 gallon heat storage tanks: 61

63 RADIENT HEATING SYSTEM: consists of a network of polyethylene tubes hooked in series and cemented to the first floor. RADIANT HEATING SYSTEM: for first floor, top view. Notice the large surface area of the system. Since we are using the low temperatures of stored hot water we ll need to spread this low temperature over a large surface area to heat the house. A warm first floor helps heat the entire house, but we ll still need to run a standard baseboard heating system for the other floors. To conserve heat each floor should be on a separate heating circuit or zone. 62

64 This concludes our tour of an Energy Independent House. It s a rather large house with a capacity for eight bedrooms and three bathrooms not to mention a full basement. You may have a different design in mind. Understanding the concepts of heat gain, heat loss and heat storage should help you to design a practical solar home of your own. Quiz time 1. Do you think sixteen 4X8 flat-plate solar collectors on the front of the house would be enough? 2. Calculate the amount of energy available to sixteen collectors at latitude tilt angle during the month of December? 3. How much insulation would this house need? Calculate the average R factor ( for walls, ceiling and floor) with a heat loss surface area of 6,000 sq ft necessary to maintain the inside temperature of this house at 65 0 F. The windows and doors have R values of 2 and occupy a surface area of 600 sq ft. The degree days for this house are 5,000. The actual solar heat gathered during the heating season is 80,000,000 BTU. 4. How can zoning reduce heat loss? 5. How much heat gain can we expect form 300 sq. ft. of greenhouse glazing during the month of December? Assume that the efficiency of the heat transfer from the sun is 50%. 63

65 6. Copper transfers heat better than polyethylene so why are polyethylene tubes used in radiant heating systems? 7. A 1000 gallon 4X8X4 heat storage tank is filled with water at F. It s insulated with 8 inches of polystyrene foam with an R factor of 40. The external temperature is 60 0 F. How long will the insulation of this tank be able to maintain the water temperature of the tank above F? 64

66 A SOLAR THERMAL ROOF It is now possible to build a practical renewable energy system that everyone can afford by using the entire surface area of a roof for collecting the sun s energy. A solar thermal roof is 65

67 a practical method for gathering large quantities of heat energy at minimal cost. Unfortunately, since most roofs are not optimized for solar heat gain a radical roof reconstruction would be necessary to make most solar thermal roofs practical. This roof reconstruction could be accomplished during the process of dormer conversion. A solar thermal roof dormer conversion is perhaps one of the best investments a home owner can make for the following reasons: 1. Every dwelling needs a roof. With a little planning that roof could become an asset rather than a liability. Did you know that most roofs have a life expectancy of 20 years or less? This solar roof could easily outlast conventional roofs. 2. A solar thermal dormer adds two additional floors rather than the one typical of most dormer conversions. 3. A solar thermal dormer makes better use of construction materials and takes about the same time to build as a conventional dormer. 4. The north facing shed roof of the solar thermal dwelling could be used to mount photovoltaic panels. 5. A solar thermal roof system could easily pay for itself in less than eight years without government, state and local incentives. With these incentives a solar thermal roof might easily pay for itself in less than four years. Question 1. What is the annual radiant energy available to a 1000 sq ft roof at latitude tilt angle for Long Island in BTU s? Convert this to a fuel oil equivalent value. 66

68 A 50 foot long 20 feet wide roof would require 1000 sq ft of glazing, 1000 sq ft of aluminum absorber plates, 60 sheets of ½ inch isocynate insulation and 1,900 linear feet of ½ inch copper flow tubes. The retail cost of these materials is less than $4000. $4000 is the approximate value of the energy available to a roof like this during the period of one year in a location like Long Island. It s also the energy requirement of a typical family of four for this area. A 4,000 gallon heat storage facility would involve additional expense, but I believe that the entire system could be installed by two men in less than three days. A solar thermal dormer adds two additional floors of living space. My wife believes that this kind of house is too ugly to live in. I told her: Ugliness is the price we have to pay for progress. Maybe I should have said: Beauty is in the eye of the beholder. 67

69 I have a firm belief that form should follow function so I continued to add things that would enhance the dwellings relation with the sun. This is what I came up with: By adding a solar greenhouse on the front I hoped to increase the solar heat gain as well as the esthetic appeal. Other shape houses might also benefit from the solar thermal roof, but I believe this type of house is most capable of energy independence not to mention the additional benefits of an attached greenhouse. 68

70 To achieve high heat gain we should first do all we can to prevent heat loss. The underside of the solar thermal roof should be insulated with six inches of fiberglass insulation. The roof itself should be sheathed with 4X8 isocynate sheets. Isocynate is a standard insulation used by many siding installers. 69

71 After the isocynate insulation is nicely tacked down interlocking absorber plate sections may be installed. Notice the 28 absorber plate columns. If each absorber plate section were 10 feet long it would take 56 absorber plate sections 20 inches wide to cover a roof this size. The horizontal grooves of the absorber plates should be spaced about 6 inches apart to optomize heat absorption at a reasonable construction and material cost. 70

72 The plumbing layout for a solar thermal roof would look something like this. Notice how two sections of half inch copper tubing are joined in parallel. This is done to minimize the expense of the copper tubing and maximize flow rate. To hold the flow tubes in position 1X2 inch supports should be fastened into the roof rafters spaced 16 inches apart. Sheets of fiberglass reinforced plastic four feet wide and 20 feet long should then be placed on top of these supports. The fiberglass glazing could be held in place with 1X2 s. 71

73 Now that we understand how to build a solar thermal roof let s see if we can figure out how to build the necessary absorber plates. The absorber plate is simply a sheet of 20 inch wide aluminum flashing with grooves every six inches used to transfer the sun s heat to flow tubes. The sections are designed to overlap and interlock. The underside of the absorber plate is bonded with strips of half inch isocynate insulation for support. When pressure is applied from above on the copper flow tubes the insulation holds the absorber plate grooves tightly against the copper. Notice the copper tubes that will later be inserted into the grooves of the aluminum flashing. 72

74 Since the fabrication of absorber plates is essential, a jig capable of cranking out absorber plates in a short period of time would be necessary to make the solar thermal roof concept practical. Standard 20 inch wide aluminum flashing can be purchased in fifty foot rolls. If we had a machine to impress grooves onto the flashing every six inches our manufacturing problem would be solved. A rotary press consisting of two drums could be used to make these horizontal grooves. 73

75 If we can t afford labor saving bending machines we could always do it the old fashion way with a hand made pounding jig. This kind of jig can be made with 1X6 pine boards. Notice the slots. For ½ inch copper tubing I ve found that ½ inch slots work best. As you know ½ inch tubing has an outside diameter close to 3/4 of an inch. After bending, the aluminum springs back to a groove that nicely fits the outside dimension of the copper tube. After the jig is finished you can lay in a piece of aluminum flashing between the guide boards. The guide boards keep the aluminum straight. Don t make the guides too tight. If you do the aluminum will bind as you pound in the grooves. Next you can lay in the 9/16 inch steel rods and adjust the position of the aluminum. Start by pounding the end rod. This will pull the sheet of aluminum forward. 74

76 Once the first rod is pounded flush with the top of the aluminum you can place a pounding board over it. Keep pounding. Finish the bend and then pound in the next steel rod. Repeat the process until all the grooves are installed. Remove the rods and remove the absorber plate. It should look like this when you re done. Don t forget to paste some insulation strips on the bottom of the absorber plate to support the groove. 75

77 Cost effective manufacturing techniques and effective use of standard construction materials could easily transform the possibilities of solar energy theory into the practical reality of solar energy applications. A 3,000 gallon multi-tank heat storage system should be included with every 1000 sq ft solar thermal roof. Although the technology for power generation from a storage vault like this has not yet been developed the potential for such a development is very real. Before jumping into a discussion about a possible futuristic solar thermal generator that could be used in conjunction with the solar thermal roof I d like to spend a little more time discussing the benefits of a multi-tank heat storage system as it pertains to heat transfer. 76

78 HEAT TRANSFER How is heat transferred? Heat is transferred by conduction and convection. When a pot of water is boiled kinetic energy is transferred by conduction to water molecules at the bottom of the pot. These fast moving molecules spread their thermal energy to adjacent molecules by conduction and tend to occupy more space than the cold slow moving molecules above them. Since hot water occupies more space than cold-water, hot water will rise and the cold water above will sink to the bottom of the pot. This convection process is how heat is transferred uniformly into a pot of water. Uniform heat transfer in a pot of thick soup is more difficult. Solid soup particles interfere with the convection process and insulate above layers from heat transfer. Mom must stir thick soup because the convection process is not working. She also does this to avoid burning the pot. So Heat is transferred from the absorber plates of the collector into the collector fluid by the process of conduction. From here the collector fluid is circulated through the carrier pipes to the heat transfer vault. Once inside the vault heat is transferred to and concentrated near the tops of tanks. This top layer of hot water is best suited for transferring heat into the domestic heating and hot water system. 77

79 Well that makes sense I guess. I was just wondering why you recommend many separate tanks. Don t you think one would be enough? Good question. The answer to this question has to do with heat transfer rate. The rate of heat transfer has to do with the conductive and convective medium and it also has a lot to do with the temperature differences. Objects with large temperature differences will transfer heat faster than objects with low temperature differences. If one tank is used to transfer heat the transfer rate would diminish as storage tank approaches saturation. In other words if the storage tank temperature is the same as or close to the temperature of the collector little or no heat will be transferred. A multi-tank heat storage system can improve the heat collection capacity. MULTI TANK CONCRETE HEAT EXCHANGE SYSTEM Heat from the solar roof is transferred into a series of 55-gallon drums of water. Notice the set of ½ inch copper heat exchange tubes imbedded inside the cement base on top of the insulated platform. This is where heat from the collectors is exchanged. 78

80 55-gallon drums are pressed into the wet cement for heat transfer. Next the drums are filled with water and sealed. These drums are only used to store and transfer heat, only. Water never flows into or out of them. How is heat transferred out of these tanks? I thought you d never ask. Heat is extracted out from the tank tops where heat is concentrated. Water for heating the house or DHW is circulated through this top set of tubes from the coldest tank to the hottest tank to provide the hottest water available while making efficient use of the heat storage facility. 79

81 To be effective all the tanks inside the heat storage vault must be well insulated with R13 insulation or better. A neat vault like this has a nice table top area that could be used for other things. You could design and build you own concrete tanks if you like. Details of a concrete heat storage vault may be found in my book Energy Independent Housing. 80

82 Futuristic Solar Thermal Home Power The transformation of residential solar thermal heat into residential electricity is more involved than placing grooves in aluminum, and assembling an array of tanks. A large surface area for collecting the heat and large tanks for storing heat are just the tip of the iceberg. We ll need an engine that can use the low temperatures of flat plate collectors. In 1904 Henry E. Willsie did design such an engine. He called it the Day and Night Generator because it was able to generate electricity day and night from the low temperatures obtained from flat plate collectors. Willsie used a lethal gas, SO 2, for his low boiling point liquid so his invention never became very popular. We should learn from Willsie s accomplishments as well as his failures to design a new and improved solar thermal engine fit for the 21 st Century house. REMEMBER THE: 81

83 The concept of a residential solar power system is commonly associated with photovoltaic panels rather than hot water collectors. Conventional photovoltaic panels operate at efficiencies less than 20% and become less efficient with time and temperature. These expensive, high tech systems have pay back periods less than their life expectancy, and although photovoltaic panels do provide an elegant method of producing electricity that s becoming more cost effective every day, I believe there are other avenues of alternative power research worth consideration. Modern solar power plants concentrate the sun s energy to produce the same kind of super heated steam at 1000 degrees F that s used in coal, oil or nuclear power plants. Specially designed blades are used to drive the turbines that produce electricity. Residential solar thermal power plants would use lower temperatures and lower pressures than commercial power plants, but the principles of thermal conversion remain the same. Steam at high pressure, allowed to expand results in a pressure drop and an increase in steam velocity. This high velocity steam, applied to properly shaped turbine blades causes the turbine shaft to rotate. A pinwheel windmill is a practical example of a simple low pressure turbine engine used to pump water from wells before electric pumps were invented. 82

84 A simplified low pressure turbine engine used to generate electricity might look something like this: INSIDE A SOLAR THERMAL TURBINE ENGINE Notice how steam is used to drive the turbine or (pinwheel). Remember how a drop in pressure causes the steam to increase in velocity. By placing holes at the perimiter of the pinwheel to create a low pressure area high velocity steam is created to push the pinwheel counterclockwise. Let s put a lid on this contraption and take another look: 83

85 OUTSIDE A SOLAR THERMAL ENGINE Looks pretty simple, dosen t it? Well the concept is simple enough to demonstrate. To design a practical pinwheel or turbine generator is another story. As you re looking at the steam inlet you re probably wondering where the steam outlet is. We must have a pressure drop on the other side of the turbine otherwise the shaft will never turn and we won t be able to generate electricity. Vented steam would give us the necessary pressure drop, but then we d lose our precious steam. At this time you re probably saying to yourself things like: Vent the steam. Water s cheap. Lose the steam.. Turn T the generator. What you re saying sounds logical enough, but you should know that we won t be able to use ordinary water to generate steam. Flatplate collectors don t normally get hot enough to boil water. We need a safe liquid that boils at a low temperature. We could use Sulfur Dioxide like Wilsie used in 1904, but I doubt that it would be approved. Sulfur Dioxide is a toxic gas that turns into 84

86 Sulfuric Acid when it comes in contact with the mucus membrains of the lungs. Let s use something less toxic.. How about Carbon Dioxide? CO 2 boils at -79 deg. C at atmospheric pressure so there should be no problem associated with bringing it to a rolling boil. CO 2 liquifies when kept under pressure. Since CO 2 is highly soluble in water a water/co 2 mix would provide an ideal non toxic low boiling point mix. Let s call it the seltzer engine.the optimum mix and pressure of the water/ CO 2 mix would need to be determined. OK. We have our safe low boiling point liquid. Now lets go back to our drawings and see if we can figure out a way to cause a pressure drop to drive the turbine and still hold onto that precious CO 2. 85

87 If those holes used to vent the water/co 2 mix lead into a large tank a temperory pressure drop could be achieved. We ll need a condenser pump to recycle the condensed low boiling point liquid back into the heat exchange coils of the hot water storage vault. This creates the low pressure area necessary to drive the turbine blades. 86

88 Since the condensor pump won t be able to condense the low boiling point liquid fast enough we ll need a little help from some external heat transfer coils. Cold water is circulated through the heat transfer coils to help condense the low boiling point liquid. Heat collected from the heat transfer coils would be used for domestic hot water and home heating. Once the hot water storage tank approaches saturation the condensing advantage of the heat transfer coils would cease. To extend the time of electrical generation and heat collection a multi-tank heat storage system would be used. 87

89 When the proportions of a thermal roof double the heat collection abilities quadruple. This proposed five story school building is 100 feet long and 40 feet wide with a surface area of 4,000 sq ft. In one year the south facing solar thermal roof might easily harvest the energy equivalent contained in 10,000 gallons of oil as well as generate 10 MWH of electricity. The north facing roof could be lined with photovoltaic panels facing south. An array of 600 KW panels on the north roof could harvest an additional 32 MWH of electric power. Don t take my word for it. Do the math. The advantages of a solar thermal roof need not be confined to residential housing. Apartments, schools and of course government buildings could also take advantage of this practical alternative energy system. Hopefully our government will soon take a leadership roll in bringing us closer to a sustainable future based on sunshine. 88

90 SOLAR THERMAL CONCEPTS Temperature: The average kinetic energy of molecules. Heat: The product of temperature and mass. BTU: The energy required to raise 1 pound of water 1 degree F. Solar Constant: The solar constant is the average rate of solar energy arriving at the outer edge of the earth's atmosphere, before any losses, about 430 BTU per hour per square foot. The actual rate of radiation varies about 3 percent either way from the average. If all of this energy could be collected and used, it would take about three hours to collect all the energy used on earth for a full year. Wavelength Conversion: Solar radiation, mostly in the form of visible light, is of short wavelengths. When it is absorbed, it becomes thermal energy and has been converted to wavelengths about ten times longer. Greenhouse Effect: Many transparent materials will pass visible and UV light freely, but will not freely pass the longer wavelength of thermal heat energy. Greenhouses and many solar collectors use this effect by applying glass or plastic covers to prevent the re-radiation of the thermal energy. 89

91 Black Body: A "black body" is any material capable of absorbing radiant energy, and transforming it into heat. Selective black body type coatings are used on absorber plates to reduce the reradiation ability without appreciably reducing energy-absorption ability. Carbon black and chrome black coatings are examples of selective coatings used today. Absorber: In a solar heating collector, the absorber is that portion of the collector which receives the radiant energy from the sun and converts it to heat and IR radiation. Flat Plate Collector: The flat-plate solar collector is one of many possible types of solar collectors. It is the most efficient type of collector for use with temperatures between the freezing and boiling points of water. Flat plate collectors are normally used with the flat surface facing south and tilted to an angle appropriate to the intended use. : Diffuse radiation is light energy arriving by reflection or scattering from some direction other than directly from the sun. Diffuse radiation is accepted by flat plate collectors but not by concentrating collectors. Therefore flat plate collectors will produce heat on cloudy days while concentrating collectors will not. Concentrating Collectors use parabolic reflecting surfaces to concentrate radiation into small areas. They track sunlight and are prone to mechanical failure. Although higher temperatures are achieved with concentrators they operate at a diminished efficiency. 90

92 HEAT IS TRANSFERRED BY: Conduction: Heat is transferred between solid materials due to temperature difference. Convection: Heat is transferred between liquids or gasses by subtle differences in density. Hot molecules occupy more space and are lighter than cold molecules. More cold, dense molecules are pulled down by gravity than hot molecules. The natural convection process may be used to separate the cold molecules from the hot ones. Radiation: Radiation transfers energy through empty space. When solar collectors are operated at higher temperatures, the radiation losses increase rapidly. At lower temperatures, radiation losses are small; conduction and convection losses are the main sources of loss. Conduction losses are proportional to temperature differences and insulation factors. Radiation losses are due to poor or no glazing. 91

93 HEAT GAIN ANSWERS TO QUESTIONS 1. A BTU (British thermal unit) is the heat energy needed. to raise one pound of water one degree Fahrenheit. 2. A gallon of number 2 fuel oil contains the energy equivalent of 150,000 BTUs 3. An hour of direct sunlight on one square meter has the energy equivalent of about 1KWH. 4. The fuel oil equivalent of one hour of sunlight on one square meter is 3,400/150,000 or.02 gallons. 5. Maximum heat transfer from the sun occurs when the glazing surface is perpendicular to the rays of the sun. The maximum annual heat gain is achieved a latitude tilt angle. That angle is 41 0 for Long Island. Latitude tilt angle is used to maximize heat gain during the heating season. 6. The average daily solar energy available at latitude tilt angle on one m 2 of long Island real estate is: A. For a day 4.5KWH/day B. For a year 4.5KWH X 365 = 1,642 KWH C The fuel oil equivalent/yr 1,642 KWH X 3,400 BTU/KWH = 5,584,500 BTU 5,584,500/150,000 = 37 gallons 7. At latitude tilt angle per year A. 4.2 KWH/day B KWH/yr C. 35 gallons 92

94 8. At latitude tilt angle for December A. 2.5 KWH/day B KWH/ Dec. C gallons/dec 9. At latitude tilt angle for December A. 2.8 KWH/day B KWH/ Dec. C. 2.0 gallons/dec 10. To gain additional heat during the heating season collectors are sometimes tilted at latitude tilt angle Greenhouse glazing allows visible and ultraviolet light in. Once these short waves strike a darkened surface they are transformed in to long wave IR heat radiation. This IR radiation is reflected back into the greenhouse by the glazing. 12. Two 4X8 collectors occupy a surface area of 6 square meters. The annual energy available to these collectors is the energy equivalent found in 6 X 37 gallons or 222 gallons gallons gallons 15. Parabolic troughs or parabolic mirrors are used to concentrate the suns energy. Convection heat inside a solar greenhouse may also be concentrated. 93

95 HEAT LOSS = 40DD 2. walls 11,712,000 BTU ceiling 2,888,000 BTU door 1,080,000 BTU TOTAL 15,672,000 BTU GALLON EQUIVALENT 104 gallons gallons HEAT THEORY 1. 64,000 BTU / 150,000 BTU =.43 gallons. This is the energy required to bring 80 gallons of water from 55 degrees F up to 155 degrees F. 2. Four collectors occupy a surface area of 12 square meters. 12 KWH of energy are available to these collectors for each hour of direct sunlight. That s 12 X 3,400 BTUs = 40,800 BTUs or.27 gallons. If collector and oil burner are operating at the same efficiency it would take (.43/.27) or 1 hour and 36 minutes of direct sunlight to bring the 80 gallons of water up to F. 3. by the greenhouse effect and by convection 4. by conduction 5. Heat is the product of temperature and mass. 6. The advantage of a multi-tank heat storage system has to do with heat transfer efficiency. One heat storage tank separate from the fossil fuel heating system could supplement hot water requirements but a multi-tank heat storage system should be used for efficient heat transfer. Multiple tanks take up a lot of space and increase the cost of a system but the added expense is justified. 94

96 SOLAR POWER The low price of oil has lulled us into a state of complacency. Solar Energy research funding is minimal. Solar Energy tax incentives and rebates are insufficient to motivate the masses. HISTORY OF SOLAR HEATING 1. A dwelling built into the side of a south facing canyon wall. An Adobe. 2. Greenhouse glazing allows visible and ultraviolet light in. Once these short waves strike a darkened surface they are transformed in to long wave IR heat radiation. This IR radiation is reflected back into the greenhouse by the glazing. 3. Heat is concentrated inside a solar greenhouse by taking advantage of natural convection currents. Hot air rises because it s lighter than cold air. The hot air is concentrated at the funnel like top of the greenhouse before it enters the living quarters. 4. A Solar Greenhouse should be isolated from living quarters to prevent heat loss at night or at times when the sun is not shining. 95

97 SOLAR HOT WATER 1. Serpentine collectors should be connected in parallel to increase the flow rate of the collector fluid and lessen the demand on the circulator pump. 2. Batch collectors and drain down systems are best suited for warm climates. They both work without the use of a circulator pump. 3. Three types of collectors include the concentrating collector, the flat-plate collector, and the evacuated tube collector. 4. Closed loop systems require antifreeze to prevent freezing. The advantage of a closed loop system has to do with the small amount of energy needed to keep the collector fluid circulating, and the assurance that the collector fluid will never freeze. The drawbacks of this system have to do with the difficulty of adding antifreeze and the difficulty of purging air from the lines. ENERGY INDEPENDENT HOUSING 1. A back up heating system should be considered for this energy independent house. 2. 3X16X2 = 96 gallons 3. Heat loss from windows and doors = ½ X 600 sq ft X 120,000 or 36,000,000 BTUs Heat loss from (walls ceiling and door) = 80,000,000 BTU 36,000,000 BTU = 44,000,000BTU 44,000,000 BTU = UA X 120, = U X 6,000 sq ft.061 = U 16.4 = R 96

98 4. Zoning reduces heat loss by selectively heating only those areas where heat is required sq ft of glazing occupies a surface area of 30 m 2. During the month of December 30 m 2 would harvest the equivalent energy found in 30 gallons of fuel at a heat transfer efficiency of 50%. 6. To solve this problem we should first calculate the average heat loss per hour which is: Q = UA(DD)/hr A = 160 sq ft The average temperature of the tank during the heat loss process will be DD = = 100 DD, U = 1/R =.025 Q = UA(DD)/hr 400 BTU/hr =.025 X 160 X 100 The heat loss of 1000 gallons of water going from F to F is 40 0 X 8,000lbs or 320,000 BTU. It would take 320,000/400 or 8,000 hours for this storage tank to lose this much heat. 97

99 about the author John Canivan is a small time self employed home improvement contractor with a dream about a world less dependent on fossil fuels. He believes the human spirit will set us free when placed inside a nurturing environment. Founder of the Adirondack Solar Association of Plattsburgh, NY that organized solar home tours, workshops and sunspace constructions, John continues to believe in the possibilities of a solar age. He s a science teacher, writer, and multi-media artist with a do it yourself attitude. Send him at canivan@optonline.net. You can also visit his website at and preview books like: How to Build a Solar Hot Water System & Energy Independent Housing. 98