solar domestic hot water heating systems design, installation and

Solar Domestic Hot Water Heating Systems

Design, Installation and Maintenance

Presented by:

Christopher A. Homola, PE

A Brief History of Solar Water Heating

Solar water heating has been around for many years because it is the easiest way to use the sun to save energy and money. One of the earliest documented cases of solar energy use involved pioneers moving west after the Civil War. They would place a cooking pot filled with cold water in the sun all day to have heated water in the evening.

The first solar water heater that resembles the concept still in use today was a metal tank that was painted black and placed on the roof where it was tilted toward the sun. The concept worked, but it usually took all day for the water to heat, then, as soon as the sun went down, it cooled off quickly because the tank was not insulated.

A Brief History of the American Solar Water Heating Industry1890 to 1930's - the California Era

The first commercial solar water heater was introduced by Clarence Kemp in the 1890's in California. For a $25 investment, people could save about $9 a year in coal costs. It was a simple batch type solar water heater that combined storage and collector in one box.

The first thermosyphon systems with the tank on the roof and the collector below were invented, patented, and marketed in California in the 1920's by William Bailey. One of the largest commercial systems in California was installed for a resort in Death Valley.

Natural gas was discovered in Southern California and cheap natural gas, aggressively marketed by utility companies, ended the solar water heating market. Patents were sold to a Florida company, owned by HM Carruthers in 1923 and the solar hot water industry began in the coastal cities of central Florida and southern Florida.

1930's to 1973 - the South Florida Era

Floridians purchased or shipped to the Caribbean more than 100,000 thermosyphon water heaters between 1930 and 1954 when the industry collapsed. During the second World War (1942 to 1945) copper was reserved for the military and the solar industry was not able to make solar collectors.

After the war, the Florida industry boomed again for about six years. Half of Miami homes had solar water heaters with over 80% of new homes having them installed. In the early 1950's electricity became cheap in Florida and utility companies gave away electric water heaters in an effort to eliminate the solar water heating industry.

By 1973, there were only two full-time solar water heating companies left in the United States both operating out of Miami, Florida.

1973 to 1986 - Oil Embargo and Tax Credits

The oil embargo of 1973 resulted in a rise in fuel prices. A few companiesstarted experimenting with solar water heaters and designing systems but there were really no national solar collector manufacturers with widespread distribution until the late seventies.

The federal government sponsored a few HUD Grants for domestic solar waterheaters in the period just before the start of the 40% Federal tax rebate in 1979.

The tax credit era, 1979 to 1986, started a nationwide boon in solar hot water systems that resulted in hundreds of manufacturers and thousands of contractors and distributors starting new businesses.

Equipment has improved since the 1980’s. Improvements were precipitated by both certification design review and experienced installers.

Today, more than 1.2 million buildings have solar water heating systems in the United States. Japan has nearly 1.5 million buildings with solar water heating. In Israel, 30 percent of the buildings use solar- heated water. Greece and Australia are also leading users of solar energy.

There is still a lot of room for expansion in the solar energy industry. There are no geographical constraints. For colder climates, manufacturers have designed systems that protect components from freezing conditions. Wherever the sun shines, solar water heating systems can work. The designs may be different from the early solar pioneers, but the concept is the same.

Environmental Benefits

Solar water heaters do not pollute.

Solar water heaters help to avoid carbon dioxide, nitrogen oxides, sulfurdioxide, and the other air pollution and wastes created when

the local utilitygenerates power or fuel is burned to heat domestic water.

When a solar water heater replaces an electric water heater, the electricitydisplaced over 20 years represents more than 50 tons of avoided carbondioxide emissions alone.

Long‐Term Benefits

Solar water heaters offer long‐term benefits that go beyond simpleeconomics.

In addition to having free hot water after the system has paid for itself inreduced utility bills, owners could be cushioned from future

fuelshortages and price increases.

Solar water heaters can assist in reducing this country's dependence onforeign oil.

It

is

estimated

that

adding

a

solar

water

heater

to

an

existing

home

raisesthe resale value of the home by the entire cost of the system.Homeowners may be able to recoup their entire investment they selltheir home.

Economic Benefits

Many

home

builders

choose

electric

water

heaters

because

they

are

easy

to

install

and

relatively

inexpensive

to

purchase.

However,

research

shows

that

an

average

household

with

an

electric

water

heater

spends

about

25%

of

its

home

energy costs on heating water.

It makes economic

sense

to

think

beyond

the

initial

purchase

price

and

consider

lifetime

energy

costs,

or

how

much

you

will

spend

on

energy

to

use

the

appliance

over

its

lifetime.

The

Florida

Solar

Energy

Center

studied

the

potential

savings

to

Florida

homeowners

of

common

water‐heating

systems

compared

with

electric

water

heaters.

It

found

that

solar

water

heaters

offered

the

largest

potential

savings, with solar water‐heater owners saving as much as 50% to 85% annually on

their utility bills over the cost of electric water heating.

http://www.fsec.ucf.edu/

Economic Benefits Continued

A solar hot water heater heats the same amount of water for a fraction of thecost.

A solar hot water heating system’s performance is dependent on theintensity of the sun in its location.

The initial expense of installing a solar hotwater

heater

($3500

to

$5500)

tends

to

be

greater

than

installing

an

electric

($450to $650) or gas ($750 to $1000) water heater.

The costs vary from region to region. Depending on the price of fuel sources, thesolar water heater can be more economical over the lifetime of the system thanheating water with electricity, fuel oil, propane, or even natural gas because thefuel (sunshine) is free.


However,

at

the

current

low

prices

of

natural

gas,

solar

water

heaters

cannotcompete with natural gas water heaters in most parts of the country exceptin new home construction. Although you will still save energy costs with asolar water heater because you won't be buying natural gas, it won't beeconomical on a dollar‐for‐dollar basis.

Paybacks

vary

widely,

but

you

can

expect

a

simple

payback

of

4

to

8

years

ona well‐designed and properly installed solar water heater. You can expectshorter paybacks in areas with higher energy costs. After the paybackperiod,

you

accrue

the

savings

over

the

life

of

the

system,

which

ranges

from15 to 40 years, depending on the system and how well it is maintained.


You can determine the simple payback of a solar water heater by firstdetermining the net cost of the system. Net costs include the total installedcost less any tax incentives or utility rebates. After you calculate the netcost of the system, calculate the annual fuel savings and divide the netinvestment by this number to determine the simple payback.

An example: Your total utility bill averages $160 per month and your waterheating costs are average (25% of your total utility costs) at $40 per month.If you purchase a solar water heater for $2,000 that provides an average of60% of your hot water each year, that system will save you $24 per month($40 x 0.60 = $24) or $288 per year (12 x $24 = $288). This system has asimple payback of less than 7 years ($2,000 ÷

$288 = 6.9).

For

the

remainder

of

the

life

of

the

solar

water

heater,

60%

of

the

hot

water

will

be

free,

saving

$288

each

year.

You

will

need

to

account

for

some operation and maintenance costs, which are estimated at $25

to $30

a year. This is primarily to have the system checked every 3 years.

If you are building a new home or refinancing your

present

home

to

do

a

major

renovation,

the

economics

are

even

more

attractive.

The

cost

of

including

the

price

of

a

solar

water

heater

in

a

new

30‐year

mortgage

is

usually

between

$13

and

$20

per

month.

The

portion

of

the

federal

income

tax

deduction

for

mortgage

interest

attributable

to

the

solar

system

reduces

that

amount

by

about

$3

to

$5

per

month.

If

your

fuel

savings

are

more

than

$15

per

month,

the

investment

in

the

solar

water

heater is profitable immediately.

Peak Power Benefit

A typical residential solar water heating system (SWHS) for a family of four delivers 4 kilowatts of electrical equivalent thermal power when under full sun and when the temperature of the water in the storage tank is about the same as the air temperature. Such a system typically has about 64 square feet of solar collector surface area and produces approximately the same peak power as 400 square feet of photovoltaic panels.

Production Capacity Benefit

Ratings of collectors and systems, along with other information specific to the local area, can be used to calculate the specific reduction in a utility’s peak demand. On average, for every solar water heating system that is installed, 0.5 kilowatts of peak demand is deferred from a utility’s load.

Energy Production Benefit

Because peak performance occurs infrequently, a more realistic indication of solar thermal system performance is the rated daily energy output of the collectors or system.

Using this method, a typical solar water heating system contributes 7 to 10 kilowatt-hours per day, depending on the solar resource and type of collector.

Electric water heating for residential applications typically consumes about 12 kilowatt-hours per day, depending on ground water temperature.

Annual site-specific energy savings for domestic water heating systems are available at www.solar-rating.org for all systems certified by the Solar Rating and Certification Corporation (SRCC).

Using this data, a typical solar water heating system produces about 3,400 kilowatt-hours per year, depending on local conditions and type of collector.

http://www.solar-rating.org/

•Atmosphere

•Angle of Incidence

•Geography

•Latitude and Season

•Air Pollution and Natural Haze

What Influences the Amount of Solar Radiation?

Atmosphere

The atmosphere absorbs certain wavelengths of light more than others. The exact spectral distribution of light reaching the earth's surface depends on how much atmosphere the light passes through, as well as the humidity of the atmosphere. In the morning and evening, the sun is low in the sky and light waves pass through more atmosphere than at noon. The winter sunlight also passes through more atmosphere versus summer. In addition, different latitudes on the earth have different average “thicknesses” of atmosphere that sunlight must penetrate. The figure below illustrates the atmospheric effects on solar energy reaching the earth. Clouds, smoke and dust reflect some solar insolation back up into the atmosphere, allowing less solar energy to fall on a terrestrial object. These conditions also diffuse or scatter the amount of solar energy that does pass through.

Angle of Incidence

The sun’s electromagnetic energy travels in a straight line. The angle at which these rays fall on an object is called the angle of incidence. A flat surface receives more solar energy when the angle of incidence is closer to zero (i.e. perpendicular) and therefore receives significantly less in early morning and late evening. Because the angle of incidence is so large in the morning and evening on earth, about six hours of “usable” solar energy is available daily. This is called the “solar window.”

Absorptance vs. Reflectance

Certain materials absorb more insolation than others. More absorptive materials are generally dark with a matte finish, while more-reflective materials are generally lighter colored with a smooth or shiny finish.

The materials used to absorb the sun's energy are selected for their ability to absorb a high percentage of energy and to reflect a minimum amount of energy. The solar collector's absorber and absorber coating efficiency are determined by the rate of absorption versus the rate of reflectance. This in turn, affects the absorber and absorber coating's ability to retain heat and minimize emissivity and reradiation. High absorptivity and low reflectivity improves the potential for collecting solar energy.

Collecting and Converting Solar Energy

Solar collectors capture the sun’s electromagnetic energy and convert it to heat energy. The efficiency of a solar collector depends not only on its materials and design but also on its size, orientation and tilt.

Available solar energy is at its maximum at noon, when the sun is at its highest point in its daily arc across the sky. The sun's daily motion across the sky has an impact on any solar collector's efficiency and performance in the following ways.

1.Since the angle of incidence of the solar energy – measured from the normal (right angle) surface of the receiving surface – changes throughout the day, solar power is lower at dawn and dusk. In reality, there are only about 6 hours of maximum energy available daily.2.The total energy received by a fixed surface during a given period depends on its orientation and tilt and varies with weather conditions, time of day and season.

Insolation

Insolation is the amount of the sun’s electromagnetic energy that “falls” on any given object.

Simply put, when we are talking about solar radiation, we are referring to insolation.

In Florida (at about sea level), an object will receive a maximum of around 300 Btu/ft2hr (about 90 watts/ft2 or 950 watts/meter2) at high noon on a horizontal surface under clear skies on June 21 (the day of the summer equinox).

PV Solar Radiation (Flat Plate, Facing South, Latitude Tilt)—Static Maps

These maps provide monthly average daily total solar resource information on grid cells of approximately 40 km by 40 km in size. The insolation values represent the resource available to a flat plate collector, such as a photovoltaic panel, oriented due south at an angle from horizontal to equal to the latitude of the collector location.

Resource:

National Renewable Energy Laboratory

www.nrel.gov/gis/solar.html

Optimum Performance Considerations

Optimum Tilt:• To latitude for greatest performance or up to latitude minus 5 degrees.

• Optimum Summer Load: Latitude minus 15 degrees (e.g. solar air conditioning).

• Optimum Winter Load: Latitude plus 15 degrees (e.g. solar space heating).

Optimum Azimuth:

• Toward the equator (e.g. Facing south in northern hemisphere).

Figure 1. Sun Path Diagrams for 28º N. Latitude

Seasonal Variations

The dome of the sky and the sun’s path at various times of the year are shown in Figure 1.

Figure 2a And 2b. Collected Energy Varies with Time of Year And Tilt

For many solar applications, we want maximum annual energy harvest. For others, maximum winter energy (or summer energy) collection is important. To orient the flat-plate collector properly, the application must be considered, since different angles will be “best” for each different application.

Actual Collector Orientation Possibilities

Collector Orientation

Collectors work best when facing due south. If roof lines or other factors dictate different orientations, a small penalty will be paid, as shown in Figure 3. As an example: for an orientation 20 degrees east or west of due south, we must increase the collector area to 1.06 times the size needed with due south orientation (dashed line on Figure 3) to achieve the same energy output. The orientation angle away from due south is called the azimuth and, in the Northern Hemisphere, is plus if the collector faces toward the east and minus if toward the west.

Figure 3. Glazed Collector Orientations

Tilt Angle

The best tilt angle will vary not only with the collector’s geographical location but also with seasonal function. Solar water heating systems are designed to provide heat year-round.

In general:

A)Mounting at an angle equal to the latitude works best for year- round energy use.

B)Latitude minus 15 degrees mounting is best for summer energy collection.

C)Latitude plus 15 degrees mounting is best for winter energy collection.

Various Collector Tilt Angles

Solar water heating systems include storage tanks and solar

collectors.

There are two types of solar water heating systems: Active, which

have circulating pumps and controls, and Passive, which don’t.

Most solar water heaters require a well‐insulated storage tank.

Solar storage tanks have an additional outlet and inlet connected

to and from the solar collector.

In two‐tank systems, the solar water heater preheats water

before it enters the conventional water heater.

In one‐tank systems, the back‐up heater is combined with the

solar storage in one tank.

Solar Water Heating System Basics

Electric Back-Up

Solar systems with single tanks are designed to encourage temperature stratification so that when water is drawn for service, it is supplied from the hottest stratum in the tank (i.e. top of tank).

While a solar system tank in the United States normally contains a heating element, the element is deliberately located in the upper third of the tank.

The electric element functions as back-up when solar energy is not available or when hot water demand exceeds the solar-heated supply.

Natural Gas Back-Up

Natural gas back-up systems may use passive (thermosyphon or integral collector system) solar preheating plumbed in series for proper operation.

Or two separate tanks may be used for active solar systems with natural gas back-up heating systems.

The solar storage tank is piped in series to the auxiliary tank sending the hottest solar preheated water to the gas back-up tank.

Solar Collectors

Four types of solar collectors are used for residential

applications:

Flat‐plate collector

Integral collector‐storage systems

Batch system

Evacuated‐tube solar collectors

Flat‐Plate Collector

Flat plate collectors are designed to heat water to medium

temperatures (approximately 140 degrees Fahrenheit).

Flat plate collectors typically include the following components:

1.Enclosure: A box or frame that holds all the components together.

2.Glazing: A transparent cover over the enclosure that allows the sun’s rays to pass through to the absorber. Most glazing is glass but some designs use clear plastic.

3.Glazing Frame: Attaches the glazing to the enclosure. Glazing gaskets prevent leakage around the glazing frame and allow for contraction and expansion.

4.Insulation: Material between the absorber and the surfaces it touches that blocks heat loss by conduction thereby reducing the heat loss from the collector enclosure.

5.Absorber: A flat, usually metal surface inside the enclosure that, because of its physical properties, can absorb and transfer high levels of solar energy.

6.Flow Tubes: Highly conductive metal tubes across the absorber through which fluid flows, transferring heat from the absorber to the fluid.

Integral Collector Storage (ICS) Systems

In other solar water heating systems the collector and storage tank are separate components. In an integral collector storage (ICS) system, both collection and solar storage are combined within a single unit. Most ICS systems store potable water inside several tanks within the collector unit. The entire unit is exposed to solar energy throughout the day. The resulting water is drawn off either directly to the service location or as replacement hot water to an auxiliary storage tank as water is drawn for use.

Cutaway of an ICS system

Batch solar water heater

Batch System

The simplest of all solar water heating systems is a batch system.

It is simply one or several storage tanks coated with black, solar-absorbing material in an enclosure with glazing across the top and insulation around the other sides.

It is the simplest solar system to make. When exposed to sun during the day, the tank transfers the heat it absorbs to the water it holds.

The heated water can be drawn directly from the tank or it can replace hot water that is drawn from an interior tank inside the building.

Evacuated Tube Solar Collectors

This type of system features parallel rows of transparent glass tubes.

Each tube contains a glass outer tube and metal absorber tube attached

to a fin. The fin’s coating absorbs solar energy but inhibits radiative heat

loss. These collectors are used more frequently for commercial

applications.

Evacuated-tube collectors generally have a smaller solar collecting surface because this surface must be encased by an evacuated glass tube. They are designed to deliver higher temperatures (approximately 300 degrees Fahrenheit). The tubes themselves comprise the following elements:

1.Highly tempered glass vacuum tubes, which function as both glazing and insulation.

2.An absorber surface inside the vacuum tube. The absorber is surrounded by a vacuum that greatly reduces the heat loss.

Active Solar Water Heating Systems

There are two Solar Water Heating System types: Active and Passive

There are two types of Active Solar Water Heating Systems:

Direct Circulation Systems

Indirect Circulation Systems

Direct Circulation Systems

Pump

circulates

domestic

water

through

the

collector(s)

and

into

the

building. This

type

of

system

works

well

in

climates

where

it

rarely

freezes.

Direct Pumped System

Direct System with Photovoltaic‐Powered Pump

Direct System with Automatic Drain-down system configuration

The direct pumped system has one or more solar energy collectors

installed on the roof and a

storage

tank

located

somewhere

within

the

building. A

pump

circulates

the

water

from

the

tank

up

to

the

collector

and

back again. This

is

called

a

direct

(or

open

loop)

system

because

the sun’s heat is transferred directly to the potable water circulating through the collector and

storage tank. Neither an anti‐freeze nor heat exchanger is involved.

This

system

has

a

differential

controller

that

senses

temperature

differences

between

water

leaving

the

solar

collector

and

the

coldest

water

in

the

storage

tank. When

the

water

in

the

collector is about 15‐20°F warmer than the water in the storage tank, the pump is turned on by

the controller. When the temperature difference drops to about 3‐5°F, the pump is turned off.

In this way, the water always gains heat from the collector when

the pump operates.

A

flush‐type

freeze

protection

valve

installed

near

the

collector

provides

freeze

protection.

Whenever

temperatures

approach

freezing,

the

valve

opens

to

let

warm

water

flow

through

the collector.

The

collector

should

always

allow

for

manual

draining

by

closing

the

isolation

valves

(located

above the storage tank) and opening the drain valves.

Automatic recirculation is another means of freeze protection. When the water in the collector

reaches

a

temperature

near

freezing,

the

controller

turns

the

pump

on

for

a

few

minutes

to

warm the collector with water from the storage tank.

Direct System Advantages

• Service water used directly from collector loop.

• No heat exchanger – more efficient heat transfer to storage.

• Circulation pump (if needed) needs only to overcome frictionlosses – system pressurized.

Direct System Disadvantages

• Quality of service water must be good to prevent corrosion, scaleor deposits in components.

• Freeze protection depends on mechanical valves.

• Recommended in climates with minimal/no freeze potential, and good water quality.

Indirect Circulation Systems

Pump circulates a non‐freezing, heat transfer fluid through the collector(s)

and a heat exchanger.

This heats the water that then flows into the home.

This type of system works well in climates prone to freezing temperatures.

Indirect Pumped System Using Anti‐Freeze Solution

This

system

design

is

common

in

northern

climates,

where

freezing

weather

occurs more frequently. An anti‐freeze solution circulates through the collector,

and

a

heat

exchanger

transfers

the

heat

from

the

anti‐freeze

solution

to

the

storage tank water. When toxic heat exchanger fluids are used, a double‐walled

exchanger

is

required. Generally,

if

the

heat

exchanger

is

installed

in

the

storage tank, it should be located in the lower half of the tank.

A

heat

transfer

solution

is

pumped

through

the

collector

in

a

closed

loop. The

loop includes the collector, connecting piping, the pump, an expansion tank and

a

heat

exchanger. A

heat

exchanger

coil

in

the

lower

half

of

the

storage

tank

transfers

heat

from

the

heat

transfer

solution

to

the

potable

water

in

the

solar

storage tank. An alternative of this design is to wrap the heat

exchanger around

the tank. This keeps it from contact with the potable water.

The

differential

controller,

in

conjunction

with

the

collector

and

tank

sensors,

determines when the pump should be activated to direct the heat transfer fluid

through

the

collector. The

photovoltaic

panel

located

on

the

roof

supplies

the

power to operate the circulating pump.

Indirect Pumped System Using Anti‐Freeze Solution

and Wrap Around Heat Exchanger

A fail‐safe method of ensuring that collectors and collector loop piping never freeze

is to remove all the water from the collectors and piping when the system is not

collecting heat. This is a major feature of the drain back system. Freeze protection

is provided when the system is in the drain mode. Water in the

collectors and

exposed piping drains into the insulated drain‐back reservoir tank each time the

circulating pump shuts off. A slight tilt of the collectors is required in order to allow

complete drainage. A sight glass attached to the drain‐back reservoir tank shows

when the reservoir tank is full and the collector has been drained.

In this particular system, distilled water is recommended to be used as the collector

loop fluid‐transfer solution. Using distilled water increases the heat transfer

characteristics and prevents possible mineral buildup of the transfer solution.

When the sun shines again, the circulating pump is activated by a differential

controller. Water is pumped from the reservoir to the collectors, allowing heat to

be collected. The water stored in the reservoir tank circulates

in a closed loop

through the collectors and a heat exchanger at the bottom of the

storage tank.

The heat exchanger transfers heat from the collector loop fluid to the potable water

located in the storage tank.

Indirect System Advantages

• Freeze protection provided by antifreeze fluid or drainback.

• Collector/piping protected from aggressive water.

Indirect System Disadvantages

• Must account for reduced heat transfer efficiency through heat

exchanger.

• Added materials = added cost.

• If not using water, fluids require maintenance.

• Most designs require added pumping cost.

Passive Solar Water Heaters

Passive solar water heaters rely on gravity and the tendency for water to naturally circulate as it is heated.

Passive solar water heater systems contain no electrical components, are generally more reliable, easier to maintain, and possibly have a longer work life than active solar water heater systems.

The two most popular types of passive solar water heater systems are: Integral-Collector Storage (ICS) andThermosyphon systems.

Integral Collector Storage System

In an integral collector storage system, the hot water storage system is the collector.

Cold water flows progressively through the collector where it is

heated by the sun.

Hot water is drawn from the top, which is the hottest, and replacement water flows

into

the

bottom. This

system

is

simple

because

pumps

and

controllers

are

not

required.

On

demand,

cold

water

from

the

building

flows

into

the

collector

and

hot

water

from the collector flows to a standard hot water auxiliary tank within the building.

A flush‐type freeze protection valve is installed in the top piping near

the collector.

As

temperatures

near

freezing,

this

valve

opens

to

allow

relatively

warm

water

to

flow through the collect to prevent freezing.

In

areas

of

the

country,

the

thermal

mass

of

the

large

water

volume

within

the

integral collector storage collector provides a means of freeze protection.

Thermosyphon System

As

the

sun

shines

on

the

collector,

the

water

inside

the

collector

flow‐

tubes

is

heated. As

it

heats,

this

water

expands

slightly

and

becomes

lighter than the cold water in the solar storage tank mounted above the

collector. Gravity then pulls heavier, cold water down from the

tank and

into the collector inlet. The cold water pushes the heated water through

the collector outlet and into the top of the tank, thus heating the water

in the tank.

In

a

thermosiphon

system

there

is

no

need

for

a

circulating

pump

and

controller. Potable

water

flows

directly

to

the

tank

on

the

roof. Solar

heated

water

flows

from

the

rooftop

tank

to

the

auxiliary

tank

installed

at ground level whenever water is used with the building.

The

thermosiphon

system

features

a

thermally

operated

valve

that

protects

the

collector

from

freezing. It

also

includes

isolation

valves,

which

allow

the

solar

system

to

be

manually

drained

in

case

of

freezing

conditions, or to be bypassed completely.

Typical Components of a Direct Flat Plate Collector System

AIR VENT

Allows air that has entered the system to escape, and in turn prevents air locks that would restrict flow of the heat-transfer fluid. An air vent must be positioned vertically and is usually installed at the uppermost part of the system. In active direct systems supplied by pressurized water, an air vent should be installed anywhere air could be trapped in pipes or collectors. Indirect systems that use glycol as the heat-transfer fluid use air vents to remove any dissolved air left in the system after it has been pressurized or charged with the heat-transfer fluid. Once the air has been purged in these indirect systems, the air vent mechanism is manually closed.

TEMPERATURE-PRESSURE RELIEF VALVE

Protects system components from excessive pressures and temperatures. A pressure- temperature relief valve is always plumbed to the solar storage (as well as auxiliary) tank. In thermosiphon and ICS systems, where the solar tanks are located on a roof, these tanks may also be equipped with a temperature-pressure relief valve since they are in some jurisdictions considered storage vessels. These valves are usually set by the manufacturer at 150 psi and 210° F. Since temperature pressure relief valves open at temperatures below typical collector loop operating conditions, they are not commonly installed in collector loops.

PRESSURE RELIEF VALVE

Protects components from excessive pressures that may build up in system plumbing. In any system where the collector loop can be isolated from the storage tank, a pressure relief valve must be installed on the collector loop. The pressure rating of the valve (typically 125 psi) must be lower than the pressure rating of all other system components, which it is installed to protect. The pressure relief valve is usually installed at the collector.

PRESSURE GAUGE

Is used in indirect systems to monitor pressure within the fluid loop. In both direct and indirect systems, such gauges can readily indicate if a leak has occurred in the system plumbing.

VACUUM BREAKER

Admits atmospheric pressure into system piping, which allows the system to drain. This valve is usually located at the collector outlet plumbing but also may be installed anywhere on the collector return line. The vacuum breaker ensures proper drainage of the collector loop plumbing when it is either manually or automatically drained. A valve that incorporates both air vent and vacuum breaker capabilities is also available.

ISOLATION VALVES

These valves are used to manually isolate various subsystems. Their primary use is to isolate the collectors or other components before servicing.

DRAIN VALVES

Used to drain the collector loop, the storage tank and, in some systems, the heat exchanger or drain-back reservoir. In indirect systems, they are also used as fill valves. The most common drain valve is the standard boiler drain or hose bib.

CHECK VALVES

Allow fluid to flow in only one direction. In solar systems, these valves prevent thermosiphoning action in the system plumbing. Without a check valve, water that cools in the elevated (roof-mounted) collector at night will fall by gravity to the storage tank, displacing lighter, warmer water out of the storage tank and up to the collector. Once begun, this thermosiphoning action can continue all night, continuously cooling all the water in the tank. In many cases, it may lead to the activation of the back-up-heating element, thereby causing the system to lose even more energy.

FREEZE-PROTECTION VALVES

Are set to open at near freezing temperatures, and are installed on the collector return line in a location close to where the line penetrates the roof.

Warm water bleeds through the collector and out this valve to protect the collector and pipes from freezing. A spring-loaded thermostat or a bimetallic switch may control the valve.

TEMPERATURE GAUGES

Provide an indication of system fluid temperatures.

A temperature gauge at the top of the storage tank indicates the temperature of the hottest water available for use.

Temperature wells installed at several points in the system will allow the use of a single gauge in evaluating system operation.

Selecting a Solar Water Heating System

Investigate local codes, covenants, and regulations.

Consider the economics of a solar water heating system.

Evaluate the site’s solar resource.

Determine the correct system size.

Estimate and compare system costs.

Building Codes, Covenants, and Regulations for Solar Water Heating Systems

Before installing a solar water heating system, you should investigate local building codes, zoning ordinances, and subdivision covenants, as well as any special regulations pertaining to the site. A building permit will probably be required to install a solar energy system onto an existing building.

Not every community or municipality initially welcomes renewable energy installations. Although this is often due to ignorance or the comparative novelty of renewable energy systems, compliance with existing building and permit procedures to install a system is unavoidable.

The matter of building code and zoning compliance for a solar system installation is typically a local issue. Even if a statewide building code is in effect, it's usually enforced locally by the city, county, or parish. Common problems owners have encountered with building codes include the following:

Exceeding roof load Unacceptable heat exchangers Improper wiring Unlawful tampering with potable water supplies.

Potential zoning issues include the following:

Obstructing sideyards Erecting unlawful protrusions on roofs Siting the system too close to streets or lot boundaries.

Special area regulations—such as local community, subdivision, or homeowner's association covenants—also demand compliance. These covenants, historic district regulations, and flood-plain provisions can easily be overlooked.

Building Codes, Covenants, and Regulations for Solar Water Heating Systems Continued

Renewable Energy Funding Sources

The Database of State Incentives for Renewables & Efficiency (DSIRE) is a comprehensive source of information on state, local, utility, and federal incentives that promote renewable energy and energy efficiency. The website is http://www.dsireusa.org.

http://www.dsireusa.org/

Federal Level Funding

Federal Incentives for Renewable Energy

U.S. Department of Treasury - Renewable Energy Grants

Eligible Renewable Technologies:

Solar Water Heating, Solar Space Heating, & Photovoltaic Systems

Energy Efficient Mortgages

Federal Housing Authority (FHA) & Veterans Affairs (VA) programs


Solar Water Heating, Solar Space Heating, & Photovoltaic Systems

State Level Funding

State of Ohio Incentives for Renewable Energy

Ohio Department of Development - Advanced Energy Program Grants- Multi-Family Residential Solar Thermal Incentive


Solar Water Heating & Solar Space Heating Systems

Applicable Sectors: Multi-Family Residential, Low-Income Residential

Ohio Department of Development - Advanced Energy Program Grants- Non-Residential Renewable Energy


Solar Water Heating, Wind, & Photovoltaic Systems

Applicable Sectors: Commercial, Industrial, Nonprofit, Schools, LocalGovernment, State Government, Agricultural, Institutional

Site Assessment

Solar Path Finder

http://www.solarpathfinder.com

Collector Positioning Flat-plate collectors for solar water heating are generally mounted on a building or the ground in a fixed position at prescribed angles. The angle will vary according to geographic location, collector type and use of the absorbed heat. Since residential hot water demand is generally greater in the winter than in the summer, the collector ideally should be positioned to maximize wintertime energy collection, receiving sunshine during the middle six to eight daylight hours of each day. Minimize shading from other buildings, trees or other collectors. Plan for lengthening winter shadows, as the sun's path changes significantly with the seasons.

Ideally, the collector should face directly south in the northern hemisphere and directly north in the southern hemisphere.

However, facing the collector within 30° to 45° either east or west of due south or north reduces performance by only about 10 percent.

A compass may be used to determine true south or north.

The closer to the equator, the less the need to maintain the orientation and direction of the collector, but be aware of the seasonal position of the sun in the sky and how it may affect the seasonal performance of the system.

The optimum tilt angle for the collector is about the same as the site's latitude plus or minus 15°. An inexpensive inclinometer will aid in determining tilt angles. If collectors will be mounted on a sloped roof, check the roof's inclination to determine whether the collectors should be mounted parallel to the roof or at a different tilt. In general, collectors should be mounted parallel to the plane of a sloped roof unless the performance penalty is more than 30 percent. The mounted collector should not detract from the appearance of the roof.

Total length of piping from collector to storage should not exceed 100 feet. The longer the pipe run, the greater the heat loss. If a greater length is necessary, an increase in piping diameter or pump size may be required.

If the collectors will be roof-mounted, they should not block drainage or keep the roof surface from properly shedding rain. Water should not gather or pool around roof penetrations. Roof curbs may be require.

To Estimate Shading of a Rooftop/Pole Mount on the Future Site

To Estimate Needed Pole Height to Avoid Shading

To Estimate How Much to Crop Tree to Avoid Shading

During the site visit, the assessor should provide:

A basic analysis of the project’s energy needs.

Recommendations for energy efficiency in order to reduce the

size and cost of the proposed renewable energy system.

Provide an evaluation of the renewable energy resource at the

site.

Information regarding the best place to site the solar system.

Additionally, the assessor should follow‐up with a written report

detailing the site assessment information.

Site Assessment Benefits

A renewable energy site assessment conducted by a certified

assessor provides an opportunity to discuss with an experienced,

objective third party about the characteristics of the property and

learn about a variety of equipment and options.

A site assessment is essential when considering a solar project.

The site assessors report can be used to present a summary of

information and options to decision makers for their approval.

Cost of a Renewable Energy Site Assessment

Certified assessors establish their own fees for their services.

On

average,

the

full

cost

of

an

assessment

is

between

$300

and

$500. The

cost

varies

depending

on

the

number

of

technologies

being

assessed

and

the

complexity

of

the

system,

as

well

as

the

assessor’s travel costs.

When

arranging

for

a

site

assessment,

discuss

with

the

assessor

your

expectations

so

that

you

can

receive

an

accurate

cost

estimate.

Sizing the Solar Hot Water Heating System

Just

as

you

have

to

choose

a

30‐,

40‐,

or

50‐gallon

conventional

water

heater,

you

need

to

determine

the

right

size

solar

water

heater

to

install.

Sizing

a

solar

water

heater

involves

determining

the

total

collector

area

and

the

storage

volume

required to provide 100% of your household's hot water during the

summer.

Solar‐

equipment

experts

use

worksheets

or

special

computer

programs

to

assist

you

in

determining how large a system you need.

Solar storage tanks are usually 50‐, 60‐, 80‐, or 120‐gallon capacity. A small (50 to 60

gallon)

system

is

sufficient

for

1

to

3

people,

a

medium

(80‐gallon)

system

is

adequate

for

a

3‐

or

4‐person

household,

and

a

large

(120‐gallon)

system

is

appropriate for 4 to 6 people.

A rule of thumb for sizing collectors: allow about 20 square feet of collector area for

each

of

the

first

two

family

members

and

8

square

feet

for

each

additional

family

member if you live in the Sun Belt. Allow 12 to 14 additional square feet per person

if you live in the northern United States.

Sizing the Solar Hot Water Heating System

Continued

A

ratio

of

at

least

1.5

gallons

of

storage

capacity

to

1

square

foot

of

collector

area

prevents the system from overheating when the demand for hot water is low.

In

very

warm,

sunny

climates,

experts

suggest

that

the

ratio

should

be

at

least

2

gallons of storage to 1 square foot of collector area.

For example, a family of four in a northern climate would need between 64 and 68

square feet of collector area and a 96‐

to 102‐gallon storage tank.

(This assumes 20 square feet of collector area for the first person, 20 for the second

person, 12 to 14 for the third person, and 12 to 14 for the fourth person.

This equals 64 to 68 square feet, multiplied by 1.5 gallons of storage capacity, which

equals 96 to 102 gallons of storage.)

Because you might not be able to find a 96‐gallon tank, you may want to get a 120‐

gallon tank to be sure to meet your hot water needs.

Resources

Analysis Tools

Preliminary

Screening:

To

determine

if

a

project

is

a

possible

candidate for solar hot water heating, try using the Federal Renewable

Energy Screening Assistant (FRESA) software. This is a windows based

software tool which screens projects for economic feasibility. It is able

to

evaluate

many

renewable

technologies

including

solar

hot

water,

photovoltaics, and wind.

Another

and

somewhat

more

detailed

screening

tool,

Retscreen,

is

provided

by

Natural

Resources

Canada.

Go

to

http://www.retscreen.net/

to download the simulation software.

http://www.retscreen.net/

Resources Continued

Analysis Tools

Detailed

Performance:

Once

preliminary

viability

has

been

established,

it

will

eventually

be

necessary

to

evaluate

system

performance

to

generate

more

precise

engineering data and economic analysis. This can be accomplished based upon hourly

simulation

software

or

by

hand

correlation

methods

based

on

the

results

of

hourly

simulations. Two software programs which are available include:

FCHART,

a correlation method available from the University of Wisconsin. Go to

http://www.fchart.com/


TRNSYS,

software available from the University of Wisconsin. Go to

http://sel.me.wisc.edu/trnsys/


http://www.fchart.com/

http://sel.me.wisc.edu/trnsys/

FCHART can be used with the following:

Collector Types Flat-Plates Evacuated Types Integral Collectors

System Types Water Storage Heating Building Storage Heating Domestic Water Heating Integral Collector-Storage DHW Indoor and Outdoor Pool Heating

FeaturesLife-cycle economics with cash flow Weather data for over 300 locations Weather data can be added Monthly parameter variation 2-D incidence angle modifiers English and SI units Approved for use in California Versions for Mac, DOS, and Windows

F-ChartExample Input

Parameter Input Screen for Flat-Plate Collector

F-ChartExample Input

Parameter Input Screen for General Solar Heating System

F-ChartExample Output

F-ChartExample Output

Graphical Output Screen showing Solar vs. Month

Installation

Installation of the Solar Hot Water System

The proper installation of solar water heating systems depends on many

factors.

These factors include solar resource, climate, local building code requirements,

and safety issues.

Wind Loading

A mounted collector is exposed not only to sunlight and the rigors of ultraviolet light but also to wind forces. For example, in parts of the world that are vulnerable to hurricanes or extreme wind storms, the collector and its mounting structure need to be able to withstand intermittent wind loads up to 146 miles per hour. This corresponds to a pressure of about 75 pounds per square foot. Winds, and thermal contraction and expansion may cause improperly installed bolts and roof seals to loosen over time. As always, follow local code requirements for wind loading.

Example of a Collector mounted down from roof ridge to reduce wind loading and heat losses

Roof Mounting Considerations

Do not mount collectors near the ridge of a roof or other places where the wind load may be unusually high. The figure below shows a desirable location for a roof-mounted collector. Mounting collectors parallel to the roof plane helps reduce wind loads and heat loss.

Ground Mounting

In an alternative to roof mounting, the collector for a solar water heating system may be mounted at ground level. The lower edge of the collector should be at least one foot above the ground so it will not be obstructed by vegetation or soaked by standing water.

Example of a Rack-mounted collector

Roof Mounted Collectors

There are four ways to mount flat-plate collectors on roofs:

1. Rack Mounting. This method is used on homes with flat roofs. Collectors are mounted at the prescribed angle on a structural frame. The structural connection between the collector and frame and between the frame and building, or site must be adequate to resist maximum potential wind loads.

Example of a Standoff-mounted collector

2. Standoff Mounting. Standoffs separate the collector from the finished roof surface; they allow air and rainwater to pass under the collector and minimize problems of mildew and water retention. Standoffs must have adequate structural properties. They are sometimes used to support collectors at slopes that differ from that of the roof angle. This is the most common mounting method used.

Example of a Direct- or flush-mounted collector

3. Direct Mounting. Collectors can be mounted directly on the roof surface. Generally, they are placed on a waterproof membrane covering the roof sheathing. Then the finished roof surface, the collector's structural attachments, and waterproof flashing are built up around the collector. A weatherproof seal must be maintained between the collector and the roof to avoid leaks, mildew and rotting.

Example of an Integral-mounted collector

4. Integral Mounting. Integral mounting places the collector within the roof construction itself. The collector is attached to and supported by the structural framing members. The top of the collector serves as the finished roof surface. Weather tightness is crucial in avoiding water damage and mildew. Only collectors designed by the manufacturer to be integrated into the roof should be installed as the water/moisture barrier of buildings. The roofing materials and solar collectors expand and contract at different rates and have the potential for leaks. A well sealed flashing material allows the expansion and contraction of the materials to maintain a water seal.

Roof Work Considerations

The most demanding aspects of installing roof-mounted collectors are the actual mounting and roof penetrations. Standards and codes are sometimes ambiguous about what can and cannot be done to a roof. Always follow accepted roofing practices, be familiar with local building codes, and communicate with the local building inspector. These are prime roof work considerations:

1. Perform the installation in a safe manner.

2. Take precautions to avoid (or minimize) damage to the roof area.

3. Position collectors for the maximum performance compatible with acceptable mounting practices.

4. Seal and flash pipe and sensor penetrations in accordance with good roofing practices. Use permanent sealants such as silicone, urethane or butyl rubber.

5. Locate collectors so they are accessible for needed maintenance.

Maintenance

Maintenance

Regular

maintenance

on

simple

systems

can

be

as

infrequent

as

every

3‐5

years, preferably by a qualified contractor with experience and knowledge of

solar hot water heating systems. Systems with electrical components usually

require a replacement part or two after 10 years.

Corrosion and Scaling in Solar Water Heating Systems

The

two

major

factors

affecting

the

performance

of

properly

sited

and

installed

solar

water heating systems include scaling and corrosion.

CorrosionMost

well‐designed

solar

systems

experience

minimal

corrosion.

When

they

do,

it

is

usually

galvanic

corrosion,

an

electrolytic

process

caused

by

two

dissimilar

metals

coming into contact with each other. One metal has a stronger positive electrical charge

and pulls electrons from the other, causing one of the metals to

corrode.

The

heat‐transfer

fluid

in

some

solar

energy

systems

sometimes

provides

the

bridge

over which this exchange of electrons occurs.

Oxygen

entering

into

an

open

loop

solar

system

will

cause

rust

in

any

iron

or

steel

component.

Such

systems

should

have

copper,

bronze,

brass,

stainless

steel,

plastic,

rubber components in the plumbing loop, and plastic or glass lined storage tanks.

ScalingDomestic water that is high in mineral content ("hard water") may cause the buildup or

scaling

of

mineral

(calcium)

deposits

in

solar

heating

systems.

Scale

buildup

reduces

system performance in a number of ways. If the system uses domestic water as the heat

transfer fluid, scaling can occur in the collector, distribution

piping, and heat exchanger.

In systems that use other types of heat‐transfer fluids (such as glycol), scaling can occur

on the surface of the heat exchanger that transfers heat from the solar collector to the

domestic water. Scaling may also cause valve and pump failures on the domestic water

loop.

Scaling

can

be

avoided

by

using

a

water

softener(s)

or

by

circulating

a

mild

acidic

solution (such as vinegar) through the collector or domestic water loop every 3–5 years,

or as necessary depending on water conditions.

There

may

be

the

need

to

carefully

clean

heat

exchanger

surfaces

with

medium‐grain

sandpaper.

A

"wrap‐around"

external

heat

exchanger

is

an

alternative

to

a

heat

exchanger located inside a storage tank.

Periodic Inspection ListThe following are some suggested inspections of solar system components.

Collector shadingVisually

check

for

shading

of

the

collectors

during

the

day

(mid‐morning,

noon,

and

mid‐afternoon)

on

an

annual

basis.

Shading

can

greatly

affect

the

performance

of

solar

collectors.

Vegetation

growth

over

time

or

new

construction

on

the

building

or

adjacent

property

may

produce

shading

that

wasn't there when the collector(s) were installed.

Collector soilingDusty

or

soiled

collectors

will

perform

poorly.

Periodic

cleaning

may

be

necessary in dry, dusty climates.

Collector glazing and sealsLook

for

cracks

in

the

collector

glazing,

and

check

to

see

if

seals

are

in

good

condition. Plastic glazing, if excessively yellowed, may need to

be replaced.

Piping and wiring connectionsLook for fluid leaks at pipe connections. All wiring connections

should be tight.

Piping and wiring insulationLook for damage or degradation of insulation covering pipes and wiring.

Roof penetrationsFlashing

and

sealant

around

roof

penetrations

should

be

in

good

condition.

Support structuresCheck all nuts and bolts attaching the collectors to any support

structures for

tightness.

Pressure relief valve (on liquid solar heating collectors)Make sure the valve is not stuck open or closed.

PumpsVerify that distribution pump(s) are operating. Check to see if they come on

when

the

sun

is

shining

on

the

collectors

after

mid‐morning.

If

the

pump

is

not operating, then either the controller or pump has malfunctioned.

Heat transfer fluidsAntifreeze

solutions

in

solar

heating

collectors

need

to

be

replaced

periodically.

If

water

with

a

high

mineral

content

(i.e.,

hard

water)

is

circulated

in

the

collectors,

mineral

buildup

in

the

piping

may

need

to

be

removed

by

adding

a

de‐scaling

or

mild

acidic

solution

to

the

water

every

few years.Storage systemsCheck storage tanks, etc., for cracks, leaks, rust, or other signs of corrosion.

Manufacturers

ACR Solar International Corporation

http://www.solarroofs.com

FAFCO, Inc.

http://www.fafco.com

Velux America

http://www.veluxusa.com

Heliodyne, Inc.

http://www.heliodyne.com

Silicon Solar Inc.

http://sunmaxxsolar.com

Solarhart

http://www.solarhart.com

SunEarth, Inc.

http://www.sunearthinc.com

Solene, LLC

http://www.solene‐usa.com

Thermo Technologies

http://www.thermomax.com

Trade Associations

American Solar Energy Society (ASES)

http://www.ases.org

Florida Solar Energy Center (FSEC)

http://www.fsec.ucf.edu

Solar Energy Industries Association (SEIA)

http://www.seia.org

Solar Rating & Certification Corporation (SRCC) http://www.solar‐rating.org

About the American Solar Energy Society

Established in 1954, the American Solar Energy Society (ASES) is the nonprofit organization dedicated to increasing the use of solar energy, energy efficiency, and other sustainable technologies in the United States

About the Florida Solar Energy Center

The Florida Solar Energy Center (FSEC) was created by the Florida Legislature in 1975 to serve as the state’s energy research institute. The main responsibilities of the center are to conduct research, test and certify solar systems and develop education programs.

About the Solar Energy Industries Association

Founded in 1974, the Solar Energy Industries Association (SEIA) is the leading national trade association for the solar energy industry. The mission of the Solar Energy Industries Association is to expand markets, strengthen research and development, remove market barriers and improve education and outreach for solar energy professionals.

About the Solar Rating and Certification Corporation

In 1980 the Solar Rating and Certification Corporation (SRCC) was incorporated as a non-profit organization whose primary purpose is the development and implementation of certification programs and national rating standards for solar energy equipment.

The End

solar domestic hot water heating systems design, installation and

Documents