Introduction Lesson 1-9

8/13/2019 Introduction Lesson 1-9

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Introduction

Energy from the sun can be tapped to provide a clean source of home energy. This lesson will introduce you to theways we use energy in the home, and how solar energy can be used to meet some, or all, of a homes energy needs.It will also address safety, codes and covenants, and permits for Pennsylvania.

End Uses of Energy in the Home

Energy is used in many ways in the home, including space heating and cooling, water heating, refrigeration,appliances, lighting, televisions, computers, stereos, and more.

Residential energy use follows a typical pattern. Normally, people get up in the morning and get ready for work, andas they get ready for work, they shower, and fix breakfast. The activities surrounding getting ready for work in themorning makes a peak in home energy use, generally from about 6:00 a.m. to about 8:00 a.m. When people areaway from the home during the day, the homes energy use is low, but when they arrive home from work in theevening, energy use in the home goes up again. Preparation of the evening meal, domestic chores, and leisureactivities make a larger peak in home energy use in the evenings. Energy use is lowest at night when people aresleeping.

This graph illustrates atypical energy

consumption pattern inhomes.

Source: National Centerfor Appropriate

Technology.

According to DOEs Energy Information Administration, almost half of the average home's energy consumption isused for heating. Another 17 percent is used for water heating, 6 percent for cooling rooms, and 5 percent forrefrigeration.


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This chart illustrates how energy is used in homes. Dueto rounding, percentages may not add to exactly 100

percent.Source: DOE Energy Information Administration.

Source: Alliance to Save Energywww.ase.org

Fossil fuels account for the nearly all residential energy use. Displacing fossil fuel use with renewable energyresources such as solar can make a significant contribution to reducing harmful emissions that contribute to globalwarming. Using renewable energy resources like solar also can reduce dependence on the utility grid, and reduceenergy costs.

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Energy Efficiency First

Installing energy-efficient systems in a home is more cost-effective than meeting the energy needs of less-efficientequipment with solar energy. Reducing electricity use is the best and least expensive way to save energy and money.

A homeowner interested in solar energy should be made aware that solar energy systems will provide a much higherfraction of the total energy used in the home if energy-efficiency measures are taken first. Although some efficiencymeasures amount to installing and using more energy-efficient equipment, some efficiency measures relate toenergy-use habits.
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Decreasing hot water requirements or electric requirements of the home will decrease the size of the solar water-heating system or solar electric system and, therefore, will reduce the cost of the solar systems to be installed.Decreasing the hot water requirements of the home from 20 gallons of hot water per person per day to 15 gallonsper day will reduce the solar water system cost by about 20%.

Every kilowatt-hour you trim off your projected annual use in a PV-based system will reduce your initial setup cost by$10-$12. Being smart about the appliances and lights you choose will allow you all the convenience of a typical homewhile consuming far less energy. That can shave thousands of dollars off the initial solar energy system cost.

The homeowner should consider these energy-efficiency strategies:

Replace appliances, lighting, heating and cooling equipment, and other products that aremore than 10 years old with an ENERGY STAR model. ENERGY STAR labeled products meetstrict energy use guidelines, using about 30 percent less energy than their conventionalcounterparts. Choosing ENERGY-STAR products can save families about a third on their energybill with similar savings of greenhouse gas emissions, without sacrificing features, style orcomfort.

To find ENERGY STAR product lists, go towww.energystar.gov/.

Switch electric space heating, water heaters and clothes dryers to natural gas or propane.

Replace older full-size fluorescent lamps with newer, more efficient models. Most common full-sized fluorescentlighting fixtures are equipped with T-12 (1-1/2 inch diameter tubes) lamps and magnetic ballasts. This technologystarted to make its way into American homes in the 1940s. Many of these older fluorescent fixtures are still in usetoday. Although this lighting technology is much more efficient than incandescent lighting, new full-sized fluorescenttechnologies are available today that are even more efficient. The new lamps, T-8 (1-inch diameter tubes) and T-5(5/8-inch diameter tubes) produce much better quality light because of better coatings on the inside of the tube andhigher frequency ballasts. The new lamps are more efficient because of their smaller diameter and higher operatingfrequency. T-8 and T-5 lamps use ballasts specifically made for them; do not use the new lamps on the old T-12ballasts.

Replace incandescent lights with compact fluorescent lamps. The most

common lighting in the home is incandescent. This technology basically usesheat to create light. Incandescent lighting is inefficient, converting about 90%of the electric energy to heat, only 10% to light. Most incandescent fixtures canuse compact fluorescent lamps (CFLs). CFLs are small fluorescent lamps thathave the ballast built into the base. Early CFLs (manufactured in the 1990s)used magnetic ballasts and were heavy, relatively large, and flickered whenthey were turned on. Modern CFLs use electronic ballasts, are smaller, lighter,and come on instantly. CFLs use about one-third as much electric energy toproduce the same light as an incandescent lamp. Most CFLs cannot be usedwith dimming, and CFLs in general do not like enclosed fixtures, where they

can get too hot.

Install lighting controls. Lighting equipment in the home is generally controlled by light switches. The biggestproblem with light switches is that they can be left on when not in use. Lighting controls that can be installed include

timers and occupancy sensors. Timers can be installed that will turn off the lights after a set time interval. Timerswork well in places where the use is intermittent and the occupancy of the space is for short periods of time, such asstairways, hallways, and closets.

There are two basic types of occupancy sensors: Passive Infrared Radiation sensors, and Ultrasonic sensors. Bothtypes have their strengths and weaknesses, and some more expensive occupancy sensors include both types.Occupancy sensors sense when a person is in the space controlled, and turn the lights on. As long as the sensorsenses someone is in the room, the lights stay on. After the person leaves the space, the sensor turns off the lightsafter a pre-set time interval. Problems associated with occupancy sensors include false ons (caused by pets, mainly)and false offs (caused when the person in the room does not move enough to keep the lights on). Occupancy

Image: NREL/PIX 07737
http://www.energystar.gov/http://www.energystar.gov/http://www.energystar.gov/http://www.energystar.gov/


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sensors work well in laundry rooms, workshop areas, and kitchens. If using occupancy sensors in bedrooms andbathrooms, an ultrasonic or dual-sensor type occupancy sensor is recommended.

Install low-flow shower heads and faucet aerators. Low-flow shower heads and faucet aerators can significantlyreduce the amount of hot water used in the home. There are many differentstyles to choose from.

Insulate the current water heater, as well as any hot water pipes that you canget to.

Lower the water heater thermostat. If there is no dishwasher in the homeor ifthe dishwasher is equipped with its own automatic water heaterturn the waterheater down to 120F (49C) to save energy and money.

Practice energy-efficient habits. If a family is accustomed to leaving lights andappliances on when theyre not in use, it will take a lot of dedication on the partof family members to change these energy-wasting habits. Its a worthwhile effort, however, as considerable savingscan be achieve simply by turning off lights and appliances when they are not in use.

Eliminate "phantom" loads. Phantom loads are caused by 120VAC to DC chargers such ascell phone chargers, and by appliances that still use power even though they are turned off,such as televisions, computers and audio equipment. These loads may seem small, butbecause they are on all of the time, they can add up. In fact, they can account for as muchas 6% of a homes energy use. To avoid this energy use, plug all of the related appliances(for example, all of the entertainment equipment) into a power strip that has a switch on it.When the appliances are not in use, switch off the power strip switch. Some homes haveelectric outlets that are switched with wall switches. These can also be used to turn offequipment that contributes to phantom loads.

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Using Solar Energy in the HomeSolar energyenergy from the suncan provide the energy needed formany of these uses. In fact, solar energy can provide all the energy needsin a home. However, systems designed to meet all energy loads in a homeare larger and thus expensive.

Zero-energy homesare both energy-efficient and capable of producingenough of their own electricity from solar and other renewable energyresources to offset the amount of energy purchased from the utility. Theresult is a net-zero annual energy bill.

Building Characteristics

Buildings must exhibit certain characteristics to be a good candidate for asolar energy system.

Exposure:The building should provide maximum southern exposure without any substantial shading from 9 a.m. to3 p.m. Although an orientation of due south is best, a deviation of 30 degrees or less from true south is consideredacceptable for most solar energy applications.


Image: Energy Star

This Zero-energy home built by Habitat forHumanity features an integral collector

storage system to provide hot water. Image:NREL/PIX 14164
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Slope:For roof-mounted systems, the preferred roof slope is equal to the latitude at the site, between 39 and 42degrees in Pennsylvania. Roof slopes between 20 and 60 degrees (roughly 4/12 to 20/12 pitch) are acceptable.

This table shows orientation factors for various roof

pitches.Source: U.S. Department of Energy

Structure:Although most roofs can support the added weight of a solar energy system, you should check thecondition of the rafters. The roof must be able to safely support the added dead load of the solar array and mountingrack and the temporary live load imposed by the installation crew. The solar array and mounting rack will addapproximately 3 pounds per square foot of dead load to the roof. A structural engineer should be consulted if there isdoubt that the roof can handle the additional load.

Access to wiring (solar electric) or plumbing (solar water heat): Ideally, the south-facing roof should be near the

main electrical service entrance if you are installing a solar electric system. To minimize wiring runs, the breakerpanel containing the buildings main disconnect switch and then households electrical end-use breakers should beeasily accessible and relatively close to the solar array. The breaker panel should have space available for installing a120/240V breaker; this is the solar systems connection to the electrical grid. If you are installing a solar water-heating system, you will have to have access to the connections to the existing water heater, and there should beroom near the existing water heater for the solar water storage tank.

The further a home is turned from south, the less its ability to collect solar energy in the winter.

Solar energy systems can be designed to heat water or living spaces, or to provide electricity. Solar electric systemscan be connected to the existing utility grid or can be separate, stand-alone systems.

The following information summarizes common types of solar energy systems. Solar water-heating and solar electricsystems will be addressed in more detail later in this course.


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Passive Solar Energy Systems

Passive solar designsare those that collect the suns energy using no moving parts. Passive systems can provideover half the space heating energy by using windows to allow more sun into the home in the wintertime, increasedlevels of insulation to help to keep the house warm, and added thermal masssuch as concrete, tile, or brick.

Windowsalso are an important component of passive solar designs.Effective passive solar designs for most U.S. climates, includingPennsylvania, use windows to maximize solar heat gain in winter andminimize it in summer.

In heating-dominated climates like Pennsylvania, most windows shouldgenerally face south to collect solar heat during the winter when thesun is low in the sky. In the summer, when the sun is high overhead,overhangs or other shading devices, such as awnings, preventexcessive heat gain.

Windows on east-, west-, and north-facing walls are reduced in heating

climates, while still allowing for adequate daylight.

An indirect-gainsystem has its thermal storagebetween the south-facing windows and the livingspaces. Using a Trombe wallis the most commonindirect-gain approach. The wall consists of an 816inch-thick masonry wall on the south side of a house. Asingle or double layer of glass is mounted about 1 inchor less in front of the wall's surface. Solar heat isabsorbed by the wall's dark-colored outside surfaceand stored in the wall's mass, where it radiates into theliving space.

In direct gainpassive design, the sunlight is allowed

to enter the living space directly. Concrete walls andfloor, along with tile, and sometimes water storagefeatures are used to absorb the solar heat gain in thedaytime, and these building elements re-radiate thewarmth at night.

Solar Water-Heating Systems

Solar water-heating systems can reduce the cost to heat domestic water by as much as half. The challenge innorthern climates such as Pennsylvania is freeze protection, but there are a number of systems on the market thatprovide freeze protection.

Solar water heating is addressed in detail later in this course.

Solar Electric Systems

Solar electric systemsalso called photovoltaic (PV) systemsgenerate electricity directly from the sun.

A grid-connectedor net-meteredPV system is connected to the utility grid through a special meter than turnsbackwards when the house produces more electricity than it needs. The utility grid serves as storage, eliminating theneed for batteries. Grid connected PV systems are covered later in this course.

In passive solar designs, the majority of windowsare placed on the south elevation, as shown here.


In passive solar designs, the majority of windows are placed on thesouth elevation, as shown here. Image: NREL/PIX 02778


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Off-gridor remotesystems are those that are completely independent of the utility grid. They require batteries tostorage the energy they collect during sunny times for use at night or when the sun isnt shining. Since off-gridsystems generally provide electricity for the entire home, they require storage batteries and usually have some kindof backup generator. This course covers only the installation of grid-connected solar electric systems withoutbatteries.

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Pennsylvanias Solar Resource

Most residential solar collectors are flat panels that can be mounted on a roof or on the ground. Called flat-platecollectors, these are typically fixed in a tilted position correlated to the latitude of the location. This allows thecollector to best capture the sun. These collectors can use both the direct rays from the sun and reflected light thatcomes through a cloud or off the ground. Because they use all available sunlight, flat-plate collectors are the bestchoice for many northern states.

PVWatts (www.pvwatts.org)is a useful on-line calculator that helps to understand the solar resource at a givenlocation. The table below shows summer, winter, and annual solar resources for Wilkes-Barre, Pennsylvania. PVWattscan help you determine the solar resource available at your specific site, and also help you estimate the size of solar

system needed to provide the necessary solar energy for either solar water-heating or solar electric systems. (Tip: Toconvert from Kilowatt-hours to Btu, multiply by 3413. To convert square meters to square feet, multiply by 10.76).

Average Daily Solar Radiationfor the months of January and July and yearly for various tilts and azimuth angles in Wilkes Barre, PA (kWh/m2/day)

Source: PV Watts Websitewww.pvwatts.org

Tilt Angle Azimuth Angle January July Yearly

25 180 2.50 5.58 4.19

25 210 2.40 5.81 4.12

25 270 1.72 5.52 3.59

40 180 2.81 5.47 4.1940 210 2.66 5.45 4.09

40 270 1.69 5.08 3.37

55 180 2.89 4.82 3.98

55 210 2.79 4.85 3.88

55 270 1.62 4.55 3.09

Codes, Permits and Covenants

Different communities have different restrictions and requirements in place regarding the installation of solar energy

systems. Before installing any solar energy system, contact your local building code officials to learn about requiredpermits, as well as codes and covenants that could affect where and how you install a solar energy system.

Grid-tied PV systems should be interconnected by a licensed electrician in compliance with the National ElectricalCode (NEC). Hot water systems should be installed by a licensed plumber in compliance with the National StandardPlumbing Code. In fact, some municipalities issue permits for such work only to licensed contractors, and othersmight require approval of the system by a committee.
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It is wise to investigate all requirements prior to beginning your project to ensure that installation is fully incompliance.

Lesson 1 Questions

1. Whats the most important step to ensuring that a PV system provides the highest fraction of total energyused in a home?

2. What is a "phantom" load?

3. What building characteristics must be present in a home in order to be a good candidate for a solar energysystem?

4. What is direct gain passive design?

5. Describe a Trombe wall.

6. What is a grid-connected PV system?Solar Hot Water Basics

Overview Solar Water-heating System Types

o Active Systemso Passive Systems

Solar Water-heating System Componentso Solar Collectoro Heat Exchangerso Heat Transfer Fluidso Circulating Pumpso Sensors and Controlso Storage Tanko Check Valveo Expansion Tanko Pressure Relief Valveo Pressure and Temperature Gauges

Questions Answers

Overview
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In this lesson, you will learn about using the sun to provide heat. For this portion of the course, we will emphasizeheating domestic hot water for a building.

In a solar water-heating system, heat collection is the main objective, along with moving the heat from the collectingsurface, transferring it to storage, and ultimately using it to heat the domestic hot water.

The shallow water of a lake is usually warmer than the deep water.That's because sunlight can heat the lake bottom in the shallow areas

which, in turn, heats the water. It's nature's way of solar water

heating. The sun can be used in basically the same way to heat water

used in buildings and swimming pools.

Most solar water-heating systems for buildings have two main parts:a solar collectorand a storage tank. The most common collector iscalled a flat-plate collector. Mounted on the roof, it consists of athin, flat, rectangular box with a transparent cover that faces the sun.Small tubes run through the box and carry the fluideither water orother fluid, such as an antifreeze solutionto be heated. The tubes

are attached to an absorber plate, which is painted black to absorb the heat. As heat builds up in the collector, it

heats the fluid passing through the tubes. Different types of solar collectors are described below.

The storage tank then holds the hot liquid. It can simply be a modified water heater, but it is usually larger and verywell-insulated. Systems that use fluids other than water (usually a propylene-glycol mixture) heat the water bypassing it through a heat exchanger, which transfers the heat from the glycol mixture to the water being heated.

Solar water-heating systems can be either activeor passive. Most common are active systems, which rely onpumps to move the liquid between the collector and the storage tank. Passive systems, on the other hand, rely ongravity and the tendency for water to naturally circulate as it is heated.

Solar collectors are the key component of active solar-heating systems.

Solar collectors gather the sun's energy, transform its radiation into heat,

and then transfer that heat to water, solar fluid, or air. The solar thermal

energy can be used in solar water-heating systems, solar pool heaters, andsolar space-heating systems. There are several types of solar collectors:

Flat-plate collectors Evacuated-tube collectors Integral collector-storage systems

Residential and commercial building applications that require temperaturesbelow 200F typically use flat-plate collectors, whereas those requiringtemperatures higher than 200F use evacuated-tube collectors.

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Solar Water-heating System Types

Active Solar Water-Heating Systems

This home in Nevada has an integral collector

storage (ICS) system to provide hot water.


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Active solar water heaters rely on electric pumps, valves, and controllers to circulate water, or other heat-transferfluids (usually a propylene-glycol mixture) through the collectors. There are the three types of active solar water-heating systems:

1. Direct-circulation systems(or open systems) use pumps to circulate water through the collectors. Thesesystems are appropriate in areas that do not freeze for long periods and do not have hard or acidic water. Thesesystems are not approved by the Solar Rating & Certification Corporation (SRCC) if they use recirculation freezeprotection (circulating warm tank water during freeze conditions) because that requires electrical power for theprotection to be effective.

2.Indirect-circulation systems(or closed systems) pump heat-transfer fluids, such as a mixture of glycoland water antifreeze, through collectors. Heat exchangers transfer the heat from the fluid to the potable waterstored in the tanks. Some indirect systems have overheat protection, which protects the collector and the glycolfluid from becoming super-heated when the load is low and the intensity of incoming solar radiation is high.

3.Drainback systems, a type of indirect system, use pumps to circulate water through the collectors. Thewater in the collector loop drains into a reservoir tank when the pumps stop. This makes drainback systems agood choice in colder climates. Drainback systems must be carefully installed to assure that the piping alwaysslopes downward, so that the water will completely drain from the piping. This can be diff icult to achieve insome circumstances.

Drainback solar water-heating systems are a good

choice for cold climates like Pennsylvania. Illustration:North Carolina Solar Center.

Passive Solar Water-Heating Systems

Passive solar water heating systems are typically less expensive than active systems, but they're usually not asefficient. Passive solar water heaters rely on gravity and the tendency for water to naturally circulate as it is heated.Because they contain no electrical components, passive systems are generally more reliable, easier to maintain, andpossibly have a longer work life than active systems.


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1. Integral-collector storage systemsconsist of one or more storage tanks placed in an insulated box witha glazed side facing the sun. During the winter, they must be drained or protected from freezing. These solarcollectors may be best suited for areas where temperatures rarely go below freezing. They are also good inhouseholds with significant daytime and evening hot-water needs; but they do not work well in households withpredominantly morning draws because they lose most of the collected energy overnight.

2. Thermosyphon systemsare an economical and reliable choice, especially in new homes. These systemsrely on the natural convection of warm water rising to circulate water through the collectors and to the tank(located above the collector). As water in the solar collector heats, it becomes lighter and rises naturally into thetank above. Meanwhile, the cooler water flows down the pipes to the bottom of the collector, enhancing thecirculation. Some manufacturers place the storage tank in the house's attic, concealing it from view. Indirectthermosyphons (that use a glycol fluid in the collector loop) can be installed in freeze-prone climates if thepiping in the unconditioned space is adequately protected.

Solar water-heating systems almost always require a backup system for cloudy days and times of increased demand.Conventional storage water heaters usually provide backup and may already be part of the solar system package. Abackup system may also be part of the solar collector, such as rooftop tanks with thermosyphon systems. Since anintegral-collector storage system already stores hot water in addition to collecting solar heat, it may be packagedwith a demand (tankless or instantaneous) water heater for backup

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Solar Water-Heating System Components

Components: Collectors

1. Flat-plate collectors

Flat-plate collectorsare the most common solar collectorfor solar water-heating systems in homes and solar spaceheating. A typical flat-plate collector is an insulated metal box

with a glass or plastic cover (called glazing) and a dark-colored absorber plate. These collectors heat liquid or air attemperatures less than 180F. (see Figure 1) Liquid flat-platecollectors heat liquid as it flows through tubes in or adjacentto the absorber plate. The simplest liquid systems usepotable household water, which is heated as it passes directlythrough the collector and then flows to the house. Solar poolheating also uses liquid flat-plate collector technology.

Fig 1


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Air flat-platecollectors are

used primarily for solar space

heating. The absorber plates

in air collectors can be metal

sheets, layers of screen, or

non-metallic materials. The

air flows past the absorber byusing natural convection or a

fan. Because air conducts

heat much less readily than

liquid does, less heat is

transferred from an air

collector's absorber than from

a liquid collector's absorber.

Air flat-plate collectors are used for space heating.

2. Evacuated-tube collectors

Evacuated-tube collectorscanachieve extremely high temperatures(170F to 350F), making them moreappropriate for commercial andindustrial application. However,evacuated-tube collectors are moreexpensive than flat-plate collectors,with unit area costs about twice thatof flat-plate collectors. (see Figure 2)

The collectors are usually made ofparallel rows of transparent glass

tubes. Each tube contains a glassouter tube and metal absorber tubeattached to a fin. The fin is coveredwith a coating that absorbs solarenergy well, but which inhibitsradiative heat loss. Air is removed, orevacuated, from the space betweenthe glass tubes and the metal tubes toform a vacuum, which eliminates

Unglazed solar collectors are typically used forswimming pool heating.

Fig 2 | Evacuated-tube collectors are efficient at high temperatures.


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conductive and convective heat loss.

A new evacuated-tube design is available from the Chinese manufacturers, Beijing Sunda Solar Energy TechnologyCo. Ltd. The "dewar" design features a vacuum contained between two concentric glass tubes, with the absorberselective coating on the inside tube. Water is typically allowed to thermosyphon down and back out the inner cavityto transfer the heat to the storage tank. There are no glass-to-metal seals. This type of evacuated tube has thepotential to become cost-competitive with flat plates.

3. Integral collector-storage systems

Integral collector-storage (ICS) systems, also known as batch systems, are made of one or more blank tanks ortubes in an insulated glazed box. Cold water first passes through the solar collector, which preheats the water, andthen continues to the conventional backup water heater.

ICS systems are simple, reliable solar water heaters. However, they should be installed only in climates with mildfreezing because the collector itself or the outdoor pipes could freeze in severely cold weather. Some recent workindicates that the problem with freezing pipes can be overcome in some cases by using freeze-tolerant piping inconjunction with a freeze-protection method.

Components: Heat ExchangerSolar water-heating systems use heat exchangersto transfer solar energy absorbed in solar collectors to the liquidor air used to heat water or a space.

Heat exchangers can be made of steel, copper, bronze, stainless steel, aluminum, or cast iron. Solar heating systemsusually use copper, because it is a good thermal conductor and has greater resistance to corrosion.

Solar water-heating systems use two types of heat exchangers:

1. Liquid-to-liquid heat exchangers

Liquid-to-liquid heat exchangersuse a heat-transfer fluid that circulates through the solar collector, absorbsheat, and then flows through a heat exchanger to transfer its heat to water in a storage tank. Heat-transfer

fluids, such as antifreeze, protect the solar collector from freezing in cold weather. Liquid-to-liquid heatexchangers have either one or two barriers (single wall or double wall) between the heat-transfer fluid and thedomestic water supply.

A single-wall heat exchangeris a pipe or tube surrounded by a fluid. Either the fluid passing through thetubing or the fluid surrounding the tubing can be the heat-transfer fluid, while the other fluid is the potablewater. Double-wall heat exchangershave two walls between the two fluids. Two walls are often used whenthe heat-transfer fluid is toxic, such as ethylene glycol. Double walls often are required as a safety measure incase of leaks, helping ensure that the antifreeze does not mix with the potable water supply. An example of adouble-wall, liquid-to-liquid heat exchanger is the "wrap-around heat exchanger," in which a tube is wrappedaround and bonded to the outside of a hot water tank. The tube must be adequately insulated to reduce heatlosses. Some local codes require double-wall heat exchangers on solar water-heating systems.

While double-wall heat exchangers increase safety, they are less efficient because heat must transfer through

two surfaces rather than one. To transfer the same amount of heat, a double-wall heat exchanger must belarger than a single-wall exchanger.

2. Air-to-liquid heat exchangers

Solar heating systems with air-heater collectors usually do not need a heat exchanger between the solarcollector and the air distribution system. Some solar air-heating systems are designed to heat water if the spaceheating requirements are satisfied. These systems use air-to-liquid heat exchangers, which are similar to liquid-to-air heat exchangers.


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Heat Exchanger DesignsThere are many heat exchanger designs. Here are some common ones:

1. Coil-in-tank heat exchanger

The heat exchanger is a coil of tubing in the storage tank. It can be a single tube (single-wall heat exchanger)

or the thickness of two tubes (double-wall heat exchanger). A less efficient alternative is to place the coil on theoutside of the collector tank with a cover of insulation.

2. Shell-and-tube heatexchanger

The heat exchanger isseparate from (external to)the storage tank. It has twoseparate fluid loops inside acase or shell. The fluids flowin opposite directions to eachother through the heatexchanger, maximizing heattransfer. In one loop, thefluid to be heated (such aspotable water) circulatesthrough the inner tubes. Inthe second loop, the heat-transfer fluid flows betweenthe shell and the tubes ofwater. The tubes and shellshould be made of the samematerial. When the collectoror heat-transfer fluid is toxic,double-wall tubes are used,and a non-toxic intermediarytransfer fluid is placedbetween the outer and innerwalls of the tubes.

3. Tube-in-tube heat exchanger

In this very efficient design, the tubes of water and the heat-transfer fluid are in direct thermal contact witheach other. The water and the heat-transfer fluid flow in opposite directions to each other. This type of heatexchanger has two loops similar to those described in the shell-and-tube heat exchanger.

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Sizing

A heat exchanger must be sized correctly to be effective. There are many factors to consider for proper sizing,including the following:

Type of heat exchanger Characteristics of the heat-transfer fluid (specific heat, viscosity, and density) Flow rate Inlet and outlet temperatures for each fluid.


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Usually, manufacturers will supply heat transfer ratings for their heat exchangers (in Btu/hour) for various fluidtemperatures and flow rates. Also, the size of a heat exchanger's surface area affects its speed and efficiency: alarge surface area transfers heat faster and more efficiently.

Installation

For the best performance, always follow the manufacturer's installation recommendations for the heat exchanger. Besure to choose a heat-transfer fluid that is compatible with the type of heat exchanger you will be using. If you wantto build your own heat exchanger, be aware that using different metals in heat exchanger construction may causecorrosion. Also, because dissimilar metals have different thermal expansion and contraction characteristics, leaks orcracks may develop. Either of these conditions may reduce the life span of the heat exchanger.

Components: Heat Transfer Fluids

Heat-transfer fluids carry heat through solar collectors and a heat exchanger to the heat storage tanks in solar waterheating systems. When selecting a heat-transfer fluid, you should consider the following criteria:

Coefficient of expansionthe fractional change in length (or sometimes in volume, when specified) of amaterial for a unit change in temperature

Viscosityresistance of a liquid to sheer forces (and hence to flow)

Thermal capacitythe ability of matter to store heat Freezing pointthe temperature below which a liquid turns into a solid Boiling pointthe temperature at which a liquid boils Flash pointthe lowest temperature at which the vapor above a liquid can be ignited in air.

For example, in a cold climate, solar water heating systems require fluids with low freezing points. Fluids exposed tohigh temperatures, as in a desert climate, should have a high boiling point. Viscosity and thermal capacity determinethe amount of pumping energy required. A fluid with low viscosity and high specific heat is easier to pump, becauseit is less resistant to flow and transfers more heat. Other properties that help determine the effectiveness of a fluidare its corrosiveness and stability

Types of Heat-Transfer Fluids

The following are some of the most commonly used heat-transfer fluids and their properties:

AirAir will not freeze or boil, and is non-corrosive. However, it has a very low heat capacity, and tends to leak outof collectors, ducts, and dampers.

WaterWater is nontoxic and inexpensive. With a high specific heat, and a very low viscosity, it's easy to pump.Unfortunately, water has a relatively low boiling point and a high freezing point. It can also be corrosive if thepH (acidity/alkalinity level) is not maintained at a neutral level. Water with a high mineral content (i.e., "hard"water) can cause mineral deposits to form in collector tubing and system plumbing.

Glycol/water mixturesThe most common fluid used in closed solar water heating systems is propylene glycol. Glycol/water mixtureshave a 50/50 or 60/40 glycol-to-water ratio. Ethylene and propylene glycol are "antifreezes." Ethylene glycol isextremely toxic and should only be used in a double-walled, closed-loop system. You can use food-gradepropylene glycol/water mixtures in a single-walled heat exchanger, as long as the mixture has been certified asnontoxic. Make sure that no toxic dyes or inhibitors have been added to it. Most glycols deteriorate at very hightemperatures. The pH value, freezing point, and concentration of inhibitors should be checked annually todetermine whether the mixture needs any adjustments or replacements to maintain its stability andeffectiveness.


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Refrigerants/phase change fluidsThese are commonly used as the heat transfer fluid in refrigerators, air conditioners, and heat pumps. Theygenerally have a low boiling point and a high heat capacity. This enables a small amount of the refrigerant totransfer a large amount of heat very efficiently. Refrigerants respond quickly to solar heat, making them moreeffective on cloudy days than other transfer fluids. Heat absorption occurs when the refrigerant boils (changesphase from liquid to gas) in the solar collector. Release of the collected heat takes place when the now-gaseousrefrigerant condenses to a liquid again in a heat exchanger or condenser. Evacuated tube heat pipe solar

collectors use this kind of fluid.

For years chlorofluorocarbon (CFC) refrigerants, such as Freon, were the primary fluids used by refrigerator, air-conditioner, and heat pump manufacturers because they are nonflammable, low in toxicity, stable, non-corrosive, and do not freeze. However, due the negative effect that CFCs have on the earth's ozone layer, CFCproduction is being phased out, as is the production of hydrochlorofluorocarbons (HCFC). The few companiesthat produced refrigerant-charged solar systems have either stopped manufacturing the systems entirely, or arecurrently seeking alternative refrigerants. Some companies have investigated methyl alcohol as a replacementfor refrigerants.

If a refrigerant-charged solar system and it needs servicing, a local solar or refrigeration service professionalshould be contacted. Since July 1, 1992, intentional venting of CFCs and HCFCs during service and maintenanceor disposal of the equipment containing these compounds is illegal and punishable by stiff fines. Although

production of CFCs ceased in the U.S. 1996, a licensed refrigeration technician can still service your system.

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Components: Circulating Pumps

Centrifugal-type circulating pumps are most commonly used in solar

water-heating systems. Centrifugal pumps generally have low power

consumption and low maintenance and are highly reliable. The bodies are

typically made with cast iron, bronze, or stainless steel. For closed loop

systems lower cost, cast iron circulating pumps are adequate. For open-

loop systems, circulating a replenishing supply of water, a bronze

circulating pump is necessary. Stainless steel pumps are used in swimming

pools and other applications where chemicals are present.

Once it is determined that the pump is to operate in a closed loop, openloop, or other particular environment, the solar system head and flowrequirements are used to select the appropriate pump. Head is thepressure the pump must develop in order to create desired flow through the system. The overall pressure a pumpmust create is determined by the height the water must be lifted and the frictional resistance of the pipe.

Static head is pressure resulting from the vertical height and corresponding weight of the column of fluid in a system.The higher a pump must lift the fluid against gravity, the greater the static head it must develop. Dynamic headincludes the frictional resistance of the fluid flowing through the pipe and fittings in the system. The pressure a pumpmust develop to overcome dynamic head varies with the size and length of the pipe, number of fittings and bends,and the flow rate and viscosity of the fluid.

Circulating pumps are typically categorized for low, medium, or high head applications. Low head applications have 3to 10 feet (0.9-3 m) of head; medium head applications, 10 to 20 feet (3-6 m) of head; and high head applications,over 20 feet of head.

Components: Sensors and Controls


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The differential controllertells the pump when to turn on and off. The

controller, via sensors connected to the collector and the storage tank, determines

whether the collector outlet is sufficiently warmer than the bottom of the tank to

turn the circulating pump on.

The sensors are located at the collector outlet, and at the bottom of the solar

storage tank. These sensors are thermistors that change their resistance with

temperature. The differential control compares the resistances of the two sensors.

It turns the pump on when the collectors are warmer (usually 20F) than the

bottom of the solar storage tank to collect useful heat. The controller usually shuts

the pump down when the temperature difference is 3 to 50F.

Components: Storage Tank

A solar water-heating system is generally installed between the cold water coming into the home and theconventional water heater, and is used to pre-heat the water entering the conventional water heater. A storagetankis necessary to hold water heated by the solar water heating system. Adding another storage tank to hold solarheated water is not only more efficient than have just the conventional water heater, but the solar water storagetank acts as a means to keep the solar panels from over heating. This picture shows the 80-gallon storage tank onthe left and the natural-gas fired conventional water heater with the add-on insulation blanket on the right.

For the summer months that can be satisfied with solar hot water alone, you

can install a "bypass valve assembly" between the solar storage tank and the

backup water heater. The solar bypass consists of three valves (or two 3-way

valves), which will allow the house to be supplied with solar heated waterdirectly. A tempering valve should be added when solar heated water is hotter

than normally produced by thermostatically controlled conventional tank. The

tempering valve is installed on the hot water line feeding the home. The

desired maximum temperature of the water delivered to the tap can be

adjusted. Hot water enters one side, cold water, if necessary, enters from the

bottom and mixed water goes out to the homes hot water plumbing.


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Components: Check Valve

A check valvepermits fluid to flow in one direction only. It prevents heatloss at night by convective flow from the warm storage tank to the coolcollectors. Check valves are either the "swing" type or the "spring" type.Swing-type check valves should be properly installed (i.e. not verticallyupside-down which allows them to hang open). A swing-type check valveshould be used with pump powered directly from a PV module. Low sunconditions produce lower flow rates, which may not be strong enough toovercome a spring-type check valve. For systems using AC circulating pumps,spring-type check valves should be installed. The spring resists thermosyphonflow in either direction.

Components: Expansion Tank

An expansion tankallows the fluid in a closed-loop system to expand and contractdepending on the temperature of the fluid. Without the expansion tank, the plumbingwould easily burst when the fluid is heated. Diaphragm-type expansion tanks areconstructed with an internal bladder and a pressurized air chamber. Heated fluidexpands in the closed loop against the bladder and pressurized air chamber. As the fluid

contracts while cooling, the air chamber maintains pressure in the closed loop. The sizeof the expansion tank must be able to handle the expansion based on the volume,coefficient of expansion, and range of temperature fluctuation. The size and number ofcollectors, and the size and length of piping and fittings determine fluid volume.Diaphragm-type expansion tanks are readily found in most plumbing supply houses.

Components: Pressure Relief Valve

Every hydronic heating system must have protection against high pressures due to high temperatures. A pressure

relief valve of 50 psi is usually adequate to protect closed-loop plumbing systems from excessive pressures.Temperature/pressure relief valves are not commonly used in the closed loop because high temperatures arecommon. Pressure-only relief valves are most commonly used. Pressure relief valves should be have a vent tube thatdirects escaping fluid to a bucket or floor drain. Once one of these valves opens, it is wise to replace it, since theyoften do not fully reseat, scale or dirt particles may allow a slow leak.

Components: Pressure and Temperature Gauges

A pressure gaugeshows if the closed loop system is within an acceptable range ofpressure. A typical system pressure is on the order of 10 to 15 psi. A pressure gauge is usedas a diagnostic tool to monitor the state of the glycol charge. A loss of pressure indicates aleak in the system that needs to be located and repaired.

A pressure gauge


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Two temperature gaugesin the closed loop and one in the water loop

are optional, but valuable indicators of the systems function. One gauge

on each side of the heat exchanger in the collector loop shows the

temperature rise across the collectors and the temperature change

across the heat exchanger. A temperature difference of 15 to 20F

indicates effective system operation. One temperature gauge in the

water loop between the exit of the heat exchanger and the entry to thestorage tank will display the current temperature of solar heated water

entering the storage tank. The temperature gauges should have a range

of 0 to 240 or 300F. A hot summer day may produce water

temperatures in the solar loop around 200F, although normally 180F is

the maximum temperature attained.

Lesson 2 Questions

1. Briefly describe the two main types of active solar water-heating systems.

2. In passive solar water heating systems, what drives the fluids circulation from the collector(s) to thestorage tank?

3. What is the most common solar collector type?

4. When is a double-walled heat exchanger required in a solar water-heating system?

5. Why are refrigerant heat transfer fluids, such as chlorofluorocarbon, being phased out of solar heatingsystems?

6. In a typical residential, closed-loop solar water-heating system what type of pump is commonly used?

7. What is the difference between static head and dynamic head?

8. Where should the controllers sensors be placed in a solar water-heating system?

A temperature gauge


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9. Why should a check valve be installed on a solar water heating system? Where should a spring-type checkvalve be installed?

10. What is the main function of the expansion tank in a closed-loop system?

11. Where should temperature gauges be installed to indicate how the system is functioning in an open-loopand in a closed-loop solar water-heating system?

Lesson 3

Solar Water-Heating Systems; Siting and Sizing

Introduction Energy Calculations and Units

Siting a Solar Water-heating Systemo Collector orientationo Collector tilto Shading

Sizing a Solar Water-heating Systemo Collector areao Storage volume

Questions Answers

Introduction

Visible light (insolation) is the main energy source collected by systems that provide space heat, water heat, and

electricity for homes. Because of the Earths axial tilt, the amount of solar insolation incident at any one spot on theEarths surface varies throughout the year. On a daily and a seasonal basis, the amount of light energy incident on asurface varies from sunrise to sunset. The atmospheric conditions and elevation at the site are also factors thatinfluence the amount of light reaching the Earths surface.

For sites above and below the equator, seasonal variations are commonly marked by the spring and fall equinoxesand the summer and winter solstices. The equinoxes are defined as the time of year when the sun crosses theequator (March and September 21/22). At this time there are an equal number of hours of daylight and nighttime.The summer and winter solstices are defined as the time when the sun reaches its highest/lowest latitude. In thenorthern latitudes, the summer solstice in June 21/22 and the winter solstice is December 21/22. The summersolstice is the date when the number of daylight hours is the longest and the winter solstice has the shortest numberof daylight hours. In the southern hemisphere, the solstices are just the opposite.

Before installing a solar water-heating system, you must first consider the site's solar resource, since the efficiencyand design of a solar water-heating system depend on how much of the sun's energy reaches the building site. Youllalso have to properly size the system to ensure that it meets the hot-water needs of the home. In this lesson, youwill learn how to site and size a solar water-heating system.

Energy Calculations and Units
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We have to be able to measure and compare energy and other quantities to be able to estimate the size of solarwater-heating and solar electric systems. We, therefore, need to gain an understanding of the energy calculationsand energy units we use to make these estimates.

Definitions:

Heat:British Thermal Unit (Btu):the amount of energy to raise 1 pound of water 1

degree Fahrenheit

Therm:100,000 Btu

DekaTherm (DKT): 1,000,000 BtuNatural gas contains about 1 DKT of energy in 1000 cubic feet of gas.

Electric Power and Energy1 Watt = 1 Volt*1 Amp in purely resistant circuits

1000 Watts = 1 Kilowatt (KW) (this is Power)

1 KW* 1 Hour = 1 Kilowatt-Hour (this is energy)

Back to Top

Siting a Solar Water-heating System

Geographic orientation and collector tilt can affect the amount of solar

radiation the system receives.

Solar water-heating systems use both direct and diffuse solar radiation. Despite being a colder, northern climate,Pennsylvania still offers an adequate solar resource. Generally, if the installation site is un-shaded from 9 a.m. to 3p.m. and faces south, it's a good candidate for a solar water-heating system.

PVWatts (www.pvwatts.org)is a useful on-line calculator that helps to understand the solar resource at a givenlocation. The table below shows average summer, winter, and annual solar radiation for Wilkes-Barre, Pennsylvania.

PVWatts can help you determine the solar resource available at your specific site, and also help you estimate the sizeof solar system needed to provide the necessary solar energy for either solar water-heating or solar electric systems.(Tip: To convert from Kilowatt-hours to Btu, multiply by 3413. To convert square meters to square feet, multiply by10.76).

Average Daily Solar Radiationfor the months of January and July and yearly for various tilts and azimuth angles in Wilkes Barre, PA (kWh/m2/day)

Source: PV Watts Websitewww.pvwatts.org

Conversion Table
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25 180 2.50 5.58 4.19

25 210 2.40 5.81 4.12

25 270 1.72 5.52 3.59

40 180 2.81 5.47 4.19

40 210 2.66 5.45 4.09

40 270 1.69 5.08 3.37

55 180 2.89 4.82 3.98

55 210 2.79 4.85 3.88

55 270 1.62 4.55 3.09

Collector OrientationCollector orientation is critical in achieving maximum performance from a solar energy system. In general, theoptimum orientation for a solar collector in the northern hemisphere is true south (azimuth of 1800). However,recent studies have shown that, depending on the location and collector tilt, the collector can face up to 90 east orwest of true south without significantly decreasing its performance.

Local climatic conditions can play a significant role in whether to orient the collectors east or west of true south, aswell as in determining the proper tilt angle for the collectors. The buildings roof orientation and slope, shadingfactors, perceived aesthetics, and local covenants also play significant roles in the installation of the solar systemscollection hardware.

You must also consider factors such as roof orientation (if you plan to mount the collector on the roof), locallandscape features that shade the collector daily or seasonally, and local weather conditions (foggy mornings orcloudy afternoons, for example), as these factors also can affect the collector's optimal orientation.

Collector TiltMost residential solar collectors are flat panels that can be mounted on a roof or on the ground. Called flat-plate

collectors, these are typically fixed in a tilted position correlated to the latitude of the location. This allows thecollector to best capture the sun. These collectors can use both the direct rays from the sun and reflected light thatcomes through a cloud or off the ground. Because they use all available sunlight, flat-plate collectors are the bestchoice for many northern states.


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Optimal tilt angle for solar collector is an angle equal to the latitude.

Although the optimal tilt angle for the collector is an angle equal to the latitude, mounting the collector flat on anangled roof will not result in a big decrease in system performance and is often desirable for aesthetic reasons. Youwill, however, want to take roof angle into account when sizing the system.

Shading

As previously mentioned, solar collectors should be installed at a site that is un-shaded from 9 a.m. to 3 p.m. andfaces south. Shading from mountains, trees, buildings, and other geographical features can significantly reduce thecollectors performance. Before installing a solar energy system, you should first complete a sun path diagram toestimate the impact of shading on annual system performance.

Back to Top

Sizing a Solar Water-Heating System

To properly size a solar water-heating system, youll need to determine the total collector area and the storagevolume needed to meet 90 to 100 percent of the household's hot water needs during the summer. One software toolthat is available to calculate solar water heating system sizing is RetScreen (www.retscreen.net/ang/home.php). Ifyou plan on designing a number of solar water heating systems, you can choose to download the Solar Hot Watersoftware fromwww.retscreen.net/ang/t_software.php.This software can be used to size solar water-heating

systems, and we will use it to verify our Rule of Thumb calculation example below.

Sizing Collector AreaA good rule of thumb for sizing collector area in northern climates such as Pennsylvania is to allow 20 square feet (2square meters) of collector area for each of the first two family members, and 12 to 14 square feet for eachadditional person.

Sizing Storage VolumeA small (50- to 60-gallon) storage tank is usually sufficient for one to two people. A medium (80-gallon) storage tankworks well for three to four people. A large tank (120-gallon) is appropriate for four to six people.

For active solar water-heating systems, the size of the solar storage tank increases with the size of the collector

typically 1.5 gallons per square foot of collector. This helps prevent the system from overheating when the demandfor hot water is low.

The Solar Rating and Certification Corporation website has thermal performance results for tested solar collectorsatwww.fsec.ucf.edu/solar/testcert/collectr/tprdhw.htm.The site has performance data within the temperature rangethat is appropriate for picking a collector for heating the hot water demand. The following is a page from this site.Bear in mind that these collectors are certified based upon Florida conditions. A trial and error procedure is necessaryto get to the right collector sizing for Pennsylvania.
http://www.pasolar.ncat.org/lesson03.php#tophttp://www.pasolar.ncat.org/lesson03.php#tophttp://www.retscreen.net/ang/home.phphttp://www.retscreen.net/ang/home.phphttp://www.retscreen.net/ang/home.phphttp://www.retscreen.net/ang/t_software.phphttp://www.retscreen.net/ang/t_software.phphttp://www.retscreen.net/ang/t_software.phphttp://www.fsec.ucf.edu/solar/testcert/collectr/tprdhw.htmhttp://www.fsec.ucf.edu/solar/testcert/collectr/tprdhw.htmhttp://www.fsec.ucf.edu/solar/testcert/collectr/tprdhw.htmhttp://www.fsec.ucf.edu/solar/testcert/collectr/tprdhw.htmhttp://www.retscreen.net/ang/t_software.phphttp://www.retscreen.net/ang/home.phphttp://www.pasolar.ncat.org/lesson03.php#top


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Collector Certification (A)

Education|Environment |Hydrogen |Buildings|Photovoltaics |Solar

Thermal

Solar Energy>Testing & Certification>Collector>Certification

Collector Certification (A)

Collector Glazing Absorber

Gros

s

Area

Thermal

Performance

Intermediate

TemperatureRating

Manufacturer

ModelFSEC#

No.

Type Material CoatingSq.Ft

Btu/Day

Btu/ft

ACR Solar

Internationa

l Corp

Skyline

20-01 00030 1

Clear

rigid

plastic

Copper

tubes

and fins

Selective20.07

14800 736

ACR SolarInternationa

l Corp

Skyline10-01

00212

C1

Clearrigid

plastic

Coppertubes

and fins

Selective10.0

07500 747

AMK-

CollectraAG

OPC 10

MK-III 00083 1

Evacuat

ed glasstube

Copper

tubes

andaluminu

m fins

Selective15.6

712500 800

AlfaCasting

Corp

*AC-

41983128 1 Glass

Copper

tubesand

aluminu

m fins

Nonselecti

ve

18.4

114200 770

Alfa

CastingCorp

*ACC-

41983129 1 Glass

Copper

tubesand fins

Nonselecti

ve

18.4

116400 893

Alternate

EnergyAE-21

00081

N1 Glass

Copper

tubesSelective

20.7

717600 849
http://www.fsec.ucf.edu/ed/http://www.fsec.ucf.edu/ed/http://www.fsec.ucf.edu/env/http://www.fsec.ucf.edu/env/http://www.fsec.ucf.edu/env/http://www.fsec.ucf.edu/hydrogen/http://www.fsec.ucf.edu/hydrogen/http://www.fsec.ucf.edu/hydrogen/http://www.fsec.ucf.edu/bldg/http://www.fsec.ucf.edu/bldg/http://www.fsec.ucf.edu/bldg/http://www.fsec.ucf.edu/pvt/http://www.fsec.ucf.edu/pvt/http://www.fsec.ucf.edu/pvt/http://www.fsec.ucf.edu/solar/http://www.fsec.ucf.edu/solar/http://www.fsec.ucf.edu/solar/http://www.fsec.ucf.edu/solar/http://www.fsec.ucf.edu/solar/index.htmhttp://www.fsec.ucf.edu/solar/index.htmhttp://www.fsec.ucf.edu/solar/testcert/testcert.htmhttp://www.fsec.ucf.edu/solar/testcert/testcert.htmhttp://www.fsec.ucf.edu/solar/testcert/collectr/collectr.htmhttp://www.fsec.ucf.edu/solar/testcert/collectr/collectr.htmhttp://www.fsec.ucf.edu/solar/testcert/collectr/collectr.htmhttp://www.fsec.ucf.edu/solar/testcert/collectr/tprdhw.htmhttp://www.fsec.ucf.edu/solar/testcert/collectr/tprdhw.htmhttp://www.fsec.ucf.edu/solar/testcert/collectr/tprdhw.htmhttp://www.fsec.ucf.edu/solar/testcert/collectr/tprdhwa.htm#flowrate#flowratehttp://www.fsec.ucf.edu/solar/testcert/collectr/tprdhwa.htm#flowrate#flowratehttp://www.fsec.ucf.edu/solar/testcert/collectr/tprdhwa.htm#flowrate#flowratehttp://www.fsec.ucf.edu/solar/testcert/collectr/tprdhwa.htm#flowrate#flowratehttp://www.fsec.ucf.edu/solar/testcert/collectr/tprdhw.htmhttp://www.fsec.ucf.edu/solar/testcert/collectr/collectr.htmhttp://www.fsec.ucf.edu/solar/testcert/testcert.htmhttp://www.fsec.ucf.edu/solar/index.htmhttp://www.fsec.ucf.edu/solar/index.htmhttp://www.fsec.ucf.edu/solar/http://www.fsec.ucf.edu/solar/http://www.fsec.ucf.edu/pvt/http://www.fsec.ucf.edu/bldg/http://www.fsec.ucf.edu/hydrogen/http://www.fsec.ucf.edu/env/http://www.fsec.ucf.edu/ed/


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System

Net EnergyDelivered:

27,300 Btu

Heat Loss

Coefficient:3.7

Btu/hrF

*The flow rate through a solar collector affects its performance, but may or may not affect the

performance of the system in which it is installed. Some of the collectors listed here have beentested at flow rates other than those specified by testing standards. These collector models are

identified with an asterisk (*) immediately preceding the model number.


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Comparing the daily hot water heat demand with the tested collector thermal performance numbers, we want tochoose solar collectors that will produce the 45,081 Btu/day. Looking in the Btu/day column, we see that we willneed two collectors to match our load, each collector being able to provide about 22,541 Btu/day. An AlternateEnergy Technologies AE-32 collector is rated at 27,500 Btu/day. These collectors each have an area of close to 32square feet. This example compares favorably with the general guidelines presented earlier for the number of solarcollectors to install20 square feet of collector area for the first two people and 12 square feet for each additionaloccupant.

For Pennsylvania, the water storage tank to couple to 64 square feet of solar collector should be at least 80 gallons,but a tank with a capacity of 90+ gallons would be better.

Back to Top

Questions

1. Using the RETScreen software, the AET AE-32 collectors will produce .98 MWh from June-August, or 36,347Btu per day. This is short of our design water-heating load, so we need to pick a different collector. Sincewe are short about 8,734 Btu per day, or 24%, we need to pick collectors about 24% larger than ouroriginal estimate. We will try a 40-square-foot collector, the AET AE-40. Using the RET Screen software, we

see that the AE-40 collectors will produce 1.08 MWh from June to August or about 40,055. What happened?Why do we increase the solar collector area by 25% and only get 10% more hot water? The answer lies inthe fact that, as the amount of energy produced gets close to the amount of energy used, the efficiency ofthe system drops because the higher system temperatures result in more heat loss. The system with thetwo AE-32 collectors has a system efficiency of 35 percent, while supplying 86% of the energy needed inthe summertime (the 86% is called solar fraction). The system with the two AE-40 collectors has a systemefficiency of 31% while supplying 95% of the energy needed in the summertime. Remember, we startedout by sizing the system to provide 100% of summertime water-heating energy.

The other system design parameter we need to look at is the size of solar water storage tank. UsingRETScreen, the previous analysis was done assuming a 120-gallon storage tank. What would the efficiencyand solar fraction be if we were to install an 80-gallon storage tank? The RETScreen model predicts thatusing an 80-gallon storage tank, the solar fraction drops to 93%, and the efficiency stays at 31% for thesummer time. A smaller storage tank therefore decreases the system solar fraction.

How does our system perform on an annual basis?

Average Daily Solar Radiation

for the months of January and July and yearly for various tilts and azimuth angles inWilkes Barre, PA (kWh/m2/day)

Source: PV Watts Website

www.pvwatts.org


25 180 2.50 5.58 4.19

25 210 2.40 5.81 4.12

25 270 1.72 5.52 3.59

40 180 2.81 5.47 4.19

40 210 2.66 5.45 4.09
http://www.pasolar.ncat.org/lesson03.php#tophttp://www.pasolar.ncat.org/lesson03.php#tophttp://www.pvwatts.org/http://www.pvwatts.org/http://www.pvwatts.org/http://www.pasolar.ncat.org/lesson03.php#top


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40 270 1.69 5.08 3.37

55 180 2.89 4.82 3.98

55 210 2.79 4.85 3.88

55 270 1.62 4.55 3.09

2. Using the data for Wilkes Barre in the table above, what is the percent difference in the yearly average dailysolar insolation incident on a surface facing true south (azimuth angle 1800) with a tilt of 25 degrees versusthat with a 55 degree tilt? For a 25-degree tilt versus a 40-degree tilted surface?

3. What is the percent difference between the yearly average value for a surface tilted at 25 degrees facingtrue south versus the same surface, same tilt but with an azimuth angle of 210 degrees?

4. What is the percent difference between the yearly average value for a surface tilted at 25 degrees facingtrue south versus the same surface, same tilt with an azimuth angle of 270 degrees? For surfaces with 40and 55 degree tilts?

5. Given the percent differences shown in question 3, which tilt angle is more reasonable to accept if you hadno choice but to install a solar system with an azimuth angle of 270 degrees? Please explain your answer.

6. If you lived in Wilkes Barre and wanted to maximize the collection of solar insolation in the winter, what tiltand azimuth angles would you mount the solar collectors? Conversely, if you wanted to maximize thesummer solar collection, what tilt and azimuth angles would you mount the solar collectors?

7. In the solar system sizing example, the total daily heat energy demand for 80 gallons of hot water wascalculated at 45,081 Btus. What would the total heat energy demand be for 80 gallons with the hot watertemperature set at 1400F with the same cold water temperature?

8. What would the auxiliary energy demand be for 80 gallons of hot water with the hot water temperature setat 1200F and a solar water heating system providing 1000F water to the cold water inlet of the conventionaldomestic hot water heater? Assume the heat losses for the 120 degree set temperature from theconventional heater when making the calculation.


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Lesson 4

Installing Solar Water-Heating Systems

Introduction Installation Steps

o Mount the solar collectors on the roofo Install the solar storage tank and heat exchanger next to conventional water heatero Install the piping and pump for the glycol loopo Install the water pipingo Install the controlso Fill the systemo Insulate water and glycol lines

Questions Answers

Introduction

To say there are a lot of variables in installing solar water-heating systems would be an understatement. As you

learned in Lesson 3, there are a number of different system types, and the components used will vary frommanufacturer to manufacturer. Every home is a little different, and getting the plumbing from the collectors to thestorage tank may require removal of plaster or sheet rock, which then must be replaced. You may be faced withbuilding a pipe chase in which to run the piping.

In this lesson, we will focus on installing a basic closed-loop solar water-heating system. The links below will providemore insight into system installation. Before the actual solar system installation can take place, a site survey must bedone to answer questions such as:

Can the roof support the dead load of the solar collectors and the live load of the installation crew? Is the roof properly oriented with enough un-shaded area and surface that does not need to be replaced in

the near future?

Can the roof work be done safely? Is there room in the building for the storage tank and associated hardware? Can the plumbing lines be installed between the storage tank and the collectors without a significant

remodeling effort?

For a quick review of some of solar water-heating components and their relationship to each other, seeGly-Mod-WB-SND(used with permission from AAA Solar Supply, 2021 Zearing NW, Albuquerque, NM 87104). You will need FlashPlayer 5 or 6 plug-in to view the video.

If you have a Mac computer, go to AAA Solar Supplys website at:www.aaasolar.com/video/#menuto download theMac version.

AAA Solar Supply also granted permission to use itsGlycolModule video,[Windows Media 16.4MB]which illustrates thecomponents and assembly of an antifreeze solar water-heating system and how to sweat-solder copper pipes and

fittings. You will need Windows Media Player to view the video. If you do not have Windows Media Player, you canview the video with Real Player or Quick Time Player at AAA Solar Supplys websiteat:www.aaasolar.com/video/#menu.

The Florida Solar Energy Center (FSEC), University of Central Florida, 12443 Research Parkway, Orlando, FL 32826and the Solar Rating and Certification Corporation (SRCC), c/o FSEC, 1679 Clearlake Road, Cocoa, FL 32922, havegranted permission to use their materials on installing solar water-heating systems.

Section 3 fromSolar Water and Pool Heating ManualDesign and Installation & Repair and Maintenance, producedby FSEC, covers the steps involved in installing a solar water-heating system without a separate solar storage tank.
http://www.pasolar.ncat.org/lesson04.phphttp://www.pasolar.ncat.org/lesson04.phphttp://www.pasolar.ncat.org/lesson04.php#introhttp://www.pasolar.ncat.org/lesson04.php#introhttp://www.pasolar.ncat.org/lesson04.php#stepshttp://www.pasolar.ncat.org/lesson04.php#stepshttp://www.pasolar.ncat.org/lesson04.php#roofhttp://www.pasolar.ncat.org/lesson04.php#roofhttp://www.pasolar.ncat.org/lesson04.php#water_heaterhttp://www.pasolar.ncat.org/lesson04.php#water_heaterhttp://www.pasolar.ncat.org/lesson04.php#glycolhttp://www.pasolar.ncat.org/lesson04.php#glycolhttp://www.pasolar.ncat.org/lesson04.php#pipinghttp://www.pasolar.ncat.org/lesson04.php#pipinghttp://www.pasolar.ncat.org/lesson04.php#controlshttp://www.pasolar.ncat.org/lesson04.php#controlshttp://www.pasolar.ncat.org/lesson04.php#fillhttp://www.pasolar.ncat.org/lesson04.php#fillhttp://www.pasolar.ncat.org/lesson04.php#insulatehttp://www.pasolar.ncat.org/lesson04.php#insulatehttp://www.pasolar.ncat.org/lesson04.php#questionshttp://www.pasolar.ncat.org/lesson04.php#questionshttp://www.pasolar.ncat.org/lesson04.php#answershttp://www.pasolar.ncat.org/lesson04.php#answershttp://www.pasolar.ncat.org/docs/GLY-MOD-WB-SND.exehttp://www.pasolar.ncat.org/docs/GLY-MOD-WB-SND.exehttp://www.pasolar.ncat.org/docs/GLY-MOD-WB-SND.exehttp://www.pasolar.ncat.org/docs/GLY-MOD-WB-SND.exehttp://www.aaasolar.com/video/#menuhttp://www.aaasolar.com/video/#menuhttp://www.aaasolar.com/video/#menuhttp://www.pasolar.ncat.org/docs/GlycolModule%20AAASolar.wmvhttp://www.pasolar.ncat.org/docs/GlycolModule%20AAASolar.wmvhttp://www.pasolar.ncat.org/docs/GlycolModule%20AAASolar.wmvhttp://www.aaasolar.com/video/#menuhttp://www.aaasolar.com/video/#menuhttp://www.aaasolar.com/video/#menuhttp://www.pasolar.ncat.org/docs/Section%203_SolarWaterHeatingSystemInstallation.pdfhttp://www.pasolar.ncat.org/docs/Section%203_SolarWaterHeatingSystemInstallation.pdfhttp://www.pasolar.ncat.org/docs/Section%203_SolarWaterHeatingSystemInstallation.pdfhttp://www.pasolar.ncat.org/docs/Section%203_SolarWaterHeatingSystemInstallation.pdfhttp://www.pasolar.ncat.org/docs/Section%203_SolarWaterHeatingSystemInstallation.pdfhttp://www.pasolar.ncat.org/docs/Section%203_SolarWaterHeatingSystemInstallation.pdfhttp://www.aaasolar.com/video/#menuhttp://www.pasolar.ncat.org/docs/GlycolModule%20AAASolar.wmvhttp://www.aaasolar.com/video/#menuhttp://www.pasolar.ncat.org/docs/GLY-MOD-WB-SND.exehttp://www.pasolar.ncat.org/docs/GLY-MOD-WB-SND.exehttp://www.pasolar.ncat.org/lesson04.php#answershttp://www.pasolar.ncat.org/lesson04.php#questionshttp://www.pasolar.ncat.org/lesson04.php#insulatehttp://www.pasolar.ncat.org/lesson04.php#fillhttp://www.pasolar.ncat.org/lesson04.php#controlshttp://www.pasolar.ncat.org/lesson04.php#pipinghttp://www.pasolar.ncat.org/lesson04.php#glycolhttp://www.pasolar.ncat.org/lesson04.php#water_heaterhttp://www.pasolar.ncat.org/lesson04.php#roofhttp://www.pasolar.ncat.org/lesson04.php#stepshttp://www.pasolar.ncat.org/lesson04.php#introhttp://www.pasolar.ncat.org/lesson04.php


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See also FSECs SDHW System Installation.pdf [internal link], which provides pictures to complement the Chapter 3text file.

Unlike solar water-heating systems installed in Florida, systems installed in Pennsylvania will have to be freeze-protected. What this means is that the freeze-protected system will include a heat exchanger, a non-toxic heattransfer fluid, an expansion tank, and depending on the system installed, another circulation pump may be required.

AAA Solar Supplysinformation on filling a glycol system[PDF /14KB]provides practical information that you will needto install systems in Pennsylvania.

Back to Top

Installation Steps

The basic steps to install a closed-loop solar water-heating system are:

1. Mount the solar collectors on the roof2. Install the solar storage tank and heat exchanger next to conventional water heater3. Install the piping and pump for the glycol loop4. Install the water piping5. Install the controls6. Fill the system7. Insulate the water and glycol lines
http://www.pasolar.ncat.org/docs/GlycolFill-aaasolar.pdfhttp://www.pasolar.ncat.org/docs/GlycolFill-aaasolar.pdfhttp://www.pasolar.ncat.org/docs/GlycolFill-aaasolar.pdfhttp://www.pasolar.ncat.org/lesson04.php#tophttp://www.pasolar.ncat.org/lesson04.php#tophttp://www.pasolar.ncat.org/lesson04.php#tophttp://www.pasolar.ncat.org/docs/GlycolFill-aaasolar.pdf


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This schematic illustrates components of a solar water-heating system.

Step 1: Mount the solar collectors on the roof

When mounting collectors, make as few roof penetrations as possible. In some cases, the collectors can be mountedon a roof and the piping run through a vertical wall instead of through the roof. Seal all roof penetrations with

silicone sealant. Different manufacturers will supply slightly different hardware for mounting the collectors on theroof. Follow the manufacturers directions carefully.

Locate the rafters to which you will be attaching the collectors. You may be able to do this with a stud finder, or youmay have to go inside the attic space and drill a small hole next to a rafter to locate it. Drill the hole, and then run asmall wire out of the hole to help locate it on the outside. Remember to seal the hole with silicone sealant.


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Rafters are usually 16 inches or 24 inches center to center. If you cannot attach the collector mounting hardware tothe rafter itself, you must install a spanner block between the rafters and mount the collector hardware to thesleeper. Do not rely on the roof sheathing to support the solar collectors. Be sure that the collector mountinghardware is securely attached to the framing members.


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Use the manufacturers recommended flashing around piping going through the roof, or use pipe flashing. Install theflashing with roof sealant to be sure it will not leak.


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If you are using sweated copper plumbing fittings, protect the roof from the torch with a flame-resistant mat.

Remember to install an air vent at the top of the collector.

Back to Top

Step 2: Install the storage tank and heat exchange next to the conventional water heaterPlace the solar storage tank near the conventional water heater. If the heat exchanger is internal to the storage tank,make sure that the glycol loop connections to the heat exchanger and the cold and hot water connections areaccessible. If the heat exchanger is external to the storage tank, it is likely that it is supported by the plumbing.Install unions at the storage tank and heat exchanger connections so that the piping will not have to be cut if thetank or heat exchanger ever need to be replaced.


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Solar water-heating systems use both direct and diffuse solar radiation. Despite being a colder, northern climate,Pennsylvania still offers an adequate solar resource. Generally, if the installation site is un-shaded from 9 a.m. to 3p.m. and faces south, it's a good candidate for a solar water-heating system.


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Step 3: Install the piping and pump for the glycol loop

In most systems, the piping for the glycol loop is no bigger than-inch pipe. Assemble the entire glycol loop without solder so youcan be sure the entire loop will go together, and then solder theentire loop. Be sure to install unions at the pump, so if it everneeds to be replaced, it can be replaced without cutting the piping.

The pump should be installed at the lowest part of the glycol loop.The pump outlet is plumbed to the piping leading to the solarcollectors on the roof. A check valve must be installed at the outletof the pump so that when the pump is turned off, the glycol willnot flow backwards around the loop. An expansion tank must beinstalled, and a pressure gauge should be installed to monitor thepressure in the glycol loop. A pressure relief valve must beinstalled in the glycol loop. The outlet from the pressure reliefvalve should be piped to a drain. This pressure relief valve shouldbe a boiler relief valve, and the operating pressure should be nomore than 30 psi. Optional Equipment:

A ball valve or circuit setter may be installed to controlthe flow in the loop A flow meter also may be installed in the glycol loop Thermometers on the inlet and outlet of the heat

exchanger will help to monitor system performance


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Back to Top

Step 4: Install the water pipingPlumb the cold water energy in the house to the inlet of the solar storage tank, and the outlet of the solar storage

tank to the inlet of the conventional water heater. Install valves and unions on the inlets and outlets of the tanks

Documents

Introduction Lesson 1-9