f Sec Recommendations

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A Survey of Solar Water

Heating Systems onFlorida Schools

Findings Conclusions and Recommendations

A Reportby

The Florida Solar Energy CenterFSEC-CR-314-90

Research Reported on Here

Was Supportedby

The Governor s Energy Office

The Florida Department of Education

Spring 1990

Marvin Yarosh - Project DirectorJim Huggins - Principal Investigator

Tom Tiedemann - Co-InvestigatorJoAnn Stirling - Project Secretary

Edited by Mary Freen



CH PTER

Recommendations

Throughout this report describes the findings from our many site visits and the

conclusions that we have drawn from these findings. In this section we

summarize the most important suggestions and recommendations on ways to overcome

the problems we identified. The recommendations are categorized within the

general topic areas of Design and Installation and Operation and Maintenance .

Many of our recommendations we believe can be applied to all LSWH systems but

we claim only that they have particular value for systems on Florida schools.

SYSTEM ESIGN N INST LL TION

The design and installation recommendations made here are not all inclusive.

They reflect primarily those areas of design installation in which we found

errors omissions or problems.

eneral Recomme ndations

0 Solar system designers must produce detailed drawings and specifications

which provide all the essential information for the system installers.

The design drawings and specifications should not omit details assuming

that an experienced installer will fill in the gaps.

0 Designers should follow up to assure that the system is being installed

in accordance with their drawings and specifications.

0 The designer or his or her representative should conduct or witness a final

operating inspection and acceptance test once the installation is complete.

0 School solar systems should carry a full two-year warranty on their

operation and performance.

6.1



ollector ubsystem

0 In Florida schools which have low summer hot water loads, we recommend a

collector tilt of 45° . The collectors, if possible, should face due south.

If there is a very strong reason for them to not face south, the deviation

should never be greater than 45°.

0 The piping on the collector array, as well as the collectors themselves,

must be drainable. The designer should specify pipe slopes and mounting

methods to ensure this. It is best if the array can be drained from ground

level or from the equipment room.

drainage is acceptable.

If this cannot be achieved, roof

0 Avoid air and liquid traps in the system piping. The collector array

piping should be designed so that it can be drained regardless of the type

of system. Pipe slopes should be uniform and constant to permit good

drainage of the system. Collectors mounted with the tubes horizontal

should be slightly canted to encourage tube drainage.

0 The flow through the collector array must be balanced for optimum

performance. This can be accomplished either through a reverse return

plumbing configuration, or through the use of balancing valves. Werecommend the use of reverse return piping since we saw little evidence

of adequate balancing of valve balanced systems. Reverse return is less

expensive, easier and more reliable than balancing valves.

0 The collector array must have a relief valve wherever the collector array

can be isolated valved off . All systems except drainback systems require

an air vent wherever air can collect high points . We recommend automatic

air vents because manual air vents do not seem to receive the attention

they need. All draindown systems require at least one vacuum breaker

usually more to let air back into the system. If the system is not a

draindown system, it should not have a vacuum breaker, especially on a

closed loop system using antifreeze.

6



-

0 All pressure, pressure-temperature, air bleed and vacuum breaker valves

should be located in accordance with good design and installation practice.

Temperature

temperature.

relief valves should be located near points of maximum

0 The collector array should be located as close as possible to the solar

storage tank to reduce heat loss in the connecting piping. Likewise, the

storage tank should be close to the backup tank and the backup tank should

be as close to the load as practical.

0 It is the designers responsibility to assure easy access to the collector

subsystem. For roof mounted systems, permanent stairs or ladders are much

preferable to portable ladders. Multilevel roofs should have fixed ladders

to facilitate access to the different roof levels. The school personnel

should make sure that access to the permanent ladder is not blocked at any

time. Systems which are difficult to reach are often ignored.

0 All pipes on the collector array must be insulated. The insulation used

must be highly resistant to moisture absorption and must be covered to

protect it from ultraviolet radiation (sunlight). We recommend wrapping

the insulation with aluminum tape or with a metal jacket. Elastomeric or

soft foam insulation, even when painted, degrades and must be frequently

recoated with a protective paint.

0 Solar collectors which must be protected from vandalism (glass breakage)

should have plastic (instead of glass) glazing. The use of heavy screening

to protect the glass reduces performance much more than does the use of

a good projectile repellent plastic.

ontrol ubsystem

Most of the problems identified in our investigations were found within this

subsystem.

6



0 Temperature sensors should be carefully located to sense the temperature

desired. The collector sensor should be inside the collector box, on the

absorber plate, near the collector exit. An alternative location (though

not as desirable) is on the collector exit tube directly adjacent to the

collector. The sensor should be in intimate thermal contact with the

copper tube and well insulated from the surrounding air. We strongly

recommend that a spare sensor also be installed and labeled, but not

connected. The can be used if the sensor fails. The

collector temperature should be checked during regular inspections.

0 We suggest that the sensor measuring the coolest liquid in the collector

loop be placed on the storage tank exit pipe, adjacent to the tank bottom.

The exit pipe leads to the pump suction. The sensor location 'should be

accessible for replacement, and a spare sensor should be installed and

labeled for later use.

0 We recommend choosing a controller that displays sensor temperatures. We

also recommend that the controller be equipped with spare input ports so

that the additional theocations be read attemperatures may

controller. This would enable sensors to measure temperatures in the fluid

stream to and from the collector array, and give the system operator

-valuableinf()rmation on system performance.

is very desirable, too.

A pump p()wer~inaicatorlight

0 Most controllers are designed to accept the input from only one sensor on

the collector array and only one sensor on the solar storage tank. The

design/installation drawings should show only one sensor on the collector

array. We recommend that an extra sensor be placed in a collector as a

spare for later use, but it must be labeled as such so the installer knows

what it is for. Controller installation instructions must be followed

exactly 30 of the controllers we examined.e had to rewire

6



Stol aae Subsystem

0 The LSWH system should have two storage tanks -- one for solar heated water

and one for the backup system. A combined tank which services both the

solar system and the backup system is not acceptable.

0 A vertical axis tank is preferable to a horizontal axis tank. The vertical

tank improves the water's stratification, allows the solar collectors to

work with the coldest supply, and thus, improves collector efficiency.

0 The solar stora~e tank should be sized to provide about 65 of a typical

day's load of hot water. Any of several common computer programs can be

used forsiz-rnttFie~soTaf- 'system-. '- -Tf ie--sys6~rn-sFi-6uld-have--a ' rat io of 1- 2

gallons ...of stor.age__per _square ...oot_of collector area. Over- or under-

sizing the solar storage tank reduces the overall efficiency of the solar

system.

0 Insulation on the solar storage tank must meet the SMACNA standard of a

2 loss in 12 hours as describedin the SHR 1988 quipmentHandbook

The distance between the solar storage tank and the backup heating system

should be kept to a minimum. This is particularly true if the load is

intermittent. The intermediate piping acts as a heat exchanger and losses

from the piping-can be significant.

i stribution and Piping Subsystems

These recommendations cover principally-the piping in the equipment room. Of

special concern is the integration of the solar system with the backup system.

0 All pipes which carry heated water must be insulated, even the last few

feet of the cold water supply pipe where it enters the storage tank(s).

This reduces the heat lost by conduction along the pipe. All valves,

c even pumps should be s-eEEe'rs; '-heaF'eXC1-iangers, and perhaps

insulated. It is extremely helpful to the operator and to maintenance

6



0

~- -- -~-

personnel to label the pipes with the fluid (cold water, hot water, solar

collector loop, etc.) and the direction of flow. Check valves and other

active components that are covered by insulation should also be labeled.

Check valves must be installed in the correct orientation and direction.

We have seen check valves installed sideways, upside down, and backwards.

Designers should therientationhow location andhe correct on

installat ion drawings.

Many schools have loops that continuously circulate hot water from the-.- -. - - -- ---

backup system to the building to keep hot water available at the tap. We

recommend avoiding these energy wasting loops by locating the storage tank

equipment room near the When a buildingot water usage point.._ .... .--..-.-. ----- ---.- ---..

circulation loop is used, the return line must not return to the solar

storage tank. Water heated by the backup heating system should never

enter any part of the solar collector loop or solar storage. Operating

these pumps continuously wastes energy. The pumps on building circulation

loops should have timers to limit pump operation to times when hot water

is needed. Also, the timer should have a battery backup so that it does

not have to be reset every time there is a power failure. Removing or

disabling time clocks is extremely wasteful of energy, but we found that

some maintenance personnel had disconnected these timers to eliminate the

need for resetting.

0 Since the solar system occasionally needs to be shut down, it should have

a bypass valve to bypass the solar system and feed cold supply water

directly to the backup heating system. However, this bypass valve must

be labeled so that :itwill not be left in the open posifion. We saw many

systems in which the solar system was collecting energy but very little

was used because the bypass valve was left open.

0 In a closed loop system, the heat exchanger must be sized correctly. The

most common mistake _w..e~~w~s~ undersi3-=~~e ._ex~?aIlger.

the solar system efficiency. From an operating standpoint,

exchanger is better than an undersized one.

This reduces

an overs ized



Instrumentation

Without adequate instrumentation it is often difficult to tell when or how well

an LSWH system is operating.

able to do this.

It is essential, however, for the operator to be

0 The minimum measurements that we require on a large solar system include

the following:

The fluid temperature going to the collector array

The fluid temperature corningfrom the collector array

Themfl uid. fl ow.~rate-_.m..mm_m.m mm m - _m --.-.

A light or other signal that the pump is operating.

If heat exchangers are employed, additional temperatures should be measured

to provide the log mean temperature difference across the exchanger.

Instruments which are locally read thermometers , should be in the fluid stream

that they are measuring and should be easy to read. We recommend that such

instruments be located in an equipment room where they are protected from the

environment. Instrumentation, like the system, must be kept in good operating

condition.

Freeze Protection Methods

As many as one third of the systems visited showed some kind of damage from

freezing. The methods for protecting systems from freezing have been described

and discussed elsewhere in this report; only recommendations are included here.

0 Recirculation freeze protection is an acceptable design only for southFlorida. Because freeze damage to collectors is an extremely costly event,

we recommend that draindown, drainback, or antifreeze systems be used

where recirculation freeze protection isfreez ing may occur. Where

employed, freeze valves should also be used.

7



0 If freeze valves are used, they must be located on the exit side of the

collector array about a foot from any pipe carrying hot water. The hot

wa.terproduced by a solar collector will. damage most freeze valves, causing

their set point to change. A check valve must be located between the solar

storage tank and the freeze valves. There should be enough freeze valves

distributed throughout the array to ensure flow through every collector.

If -..the.~fr ee z e-.p.ro te ct.ion...i s..dr a indown,...the. a utoma ti c..-drain..Yalve s. s hould........._.....

be located in a nonfreezing environment.

0 No new solar systems on schools should be accepted without an O M manual

which describes exactly how the water heating system works. The O&M manual

should not be merely a compilation of component manufacturers' literature,

but must include instructions for operating and maintaining that specific

solar system. The operator at the school must have a copy of this manual.

0 Each school should designate at least one individual as the solar system

operator. This individual should be responsible for proper operation of

the solar system. The individual must be able to determine whether the

When it is not operatingolar system is operating properly or not.

properly, he/she must notify the maintenance department.

0 At a minimum, the operator must know if the solar system is working when

it should be working, and is not working when it should not be working.

Operators can very easily be trained for this responsibility.

0 If drainback or draindown freeze protection is used, the valves and tanks

should be checked periodically to make sure they are working properly.

Al so, the co 11 e ct::Qr.~?._.§hgJ 1.sLl ~_cll~~c;;l<,.g.<L.tQ_I1l?JS.L;:;~£~.J::b.ey. ...?rere fill i ng

completely when normal operation is resumed.

8



~-

..

0 Each school district central office should identify a cadre of individuals

whose function is to become thoroughly familiar with maintenance and repair

procedures for those LSWH systems installed in their county.

0An infrastructure must be established by the school system to ensure that

qualified personnel staffnd maintenance despiteperating are on

personnel changes.

0 The district maintenance office should conduct a thorough inspection of-----

the LSWH system at least once a year preferable every six months .

inspection should include:

This

The collectorarray - -

- All valves

Insulation of piping

- All performance and monitoring instrumentation

- The controller

- All sensors.

An overall efficiency test should also be conducted.

0 The district maintenance office should assume responsibility for assuring

that the designated--sol-arsystem operators are adequately trained to

operate the solar systems.

9

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