1-4 basic water systems

8/18/2019 1-4 Basic Water Systems

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PART 1

Module 1/4

Basic Water Systems


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Objectives:

• To defne basic heating, chilled waterand condenser water systems

• To defne their components• To understand how they are used


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ITRO!"#TIO TO MO!"$%

• The commissioning o watersystems requires a basicknowledge o heating, chilledwater and condenser watersystems.

• In this module we will look at the

dierent types o systems thatyou will see, the equipment usedin them and their saety aspects.


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1& '%ATI( S)ST%MS • Heating is normally carried out by either low, medium or high temperature

hot water systems.

• ater is used because it is one o the most e!cient "uids or heat transer.

• #ou will oten fnd that low temperature hot water is abbre$iated to %TH,medium temperature to &TH and high temperature to HTH.

• 'lso, the word pressure is sometimes used in place o temperature, gi$ingthe abbre$iations %(H, &(H and H(H.

The dierent types o system are classifed by their "ow temperature asshown in the table below)

T)P% *$OW T%MP%RAT"R%

%TH&THHTH

*p to +-+- to +/-0reater than +/-


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$o+ Tem,erature 'ot Water -$T'W / $P'W.

• %ow temperature hot water is mainly usedor the heating o houses, ofces and otherbuildings o that nature.

• hen low temperature hot water is used,

the temperature o the water is belowatmospheric boiling point, normally at about1/- with the return temperature normally++ - lower 23+-4.

• 5ometimes a /- temperature dierencebetween "ow and return is used, which hasthe eect o reducing pipe si6es. 2Thereason or this will be e7plained in latermodules4


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8igure below shows a schematic drawing o a typical %THsystem consisting o a boiler, eed and e7pansion tank, pumpset and a distribution pipe work. Two secondary circuits areshown, a constant temperature circuit ser$ing an air handlingunit heater battery and a $ariable temperature circuit ser$ingsome radiators.

%et us look at each part o the system in turn.

Figure 1 - Schematic Drawing of a Low Temperature Hot Water Heating System.



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Boiler:• The boiler plant pro$ides heat or the

water in the system.

• 9oilers are normally oil or gas fred: coalfring is not used $ery oten nowadays.



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*eed ad e0,asio ta:

• 'ny heating system will leak $ery slightly through pump and $al$eglands, no matter how tight they are.

• The eed and e7pansion tank pro$ides make;up water to oset thisloss.

• The tank also ser$es another purpose. 's the water in the system is

heated, it e7pands 2increases in $olume4. I the eects o thise7pansion were not allowed or, the additional $olume o waterwould try to orce its< way out o any weak points in the system andcould cause bad leaks.

• Two pipes run between the eed and e7pansion tank and the heatingsystem. The cold eed pipe is taken rom the bottom o the tank and

pro$ides make up water to the system.• This pipe is normally $al$ed between the tank and the system, so

that i it is necessary to drain a system down, the cold eed will nottry to fll it up again.

• The o,e vet runs rom the system to terminate o$er the tank. This pipe is open ended and must ne$er be $al$ed.



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Pum,s:

• ' pump is used to circulate the heated water aroundthe system rom the boiler through the pipe worksystem to ser$e radiators, heater batteries and othertypes o heat emitters.

• #ou will oten fnd not one but two pumps on asystem 2as shown in the schematic4. In this case, onepump will be used as a duty pump. The other one willbe used as a standby in case the duty pump ails. This means that i a pump does break down, the

whole heating system is not put out o action.• here duty and standby pumps are installed, it isusual to swap o$er the duty and standby pumps atera period o running, to pre$ent the standby pumprom sei6ing.



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Pi,e+or:• The pipework system is used to distribute

the heated water rom the boiler to therespecti$e heat emitters.

• *sually a two pipe system is used: the "owpipe taking the water rom the boiler to theheat emitters and the return pipe returning

the water to the boiler.



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3ariable tem,erature circuit:

• The schematic diagram also shows a secondary circuit being taken rom the mainpipework system to ser$e a number o radiators.• #ou can see a three way $al$e at the start o the circuit. This $al$e keeps the

amount o water to the radiators constant by mi7ing main "ow water .with returnwater rom the radiators. Howe$er, because the radiator return water is at a lowertemperature than the main system, the secondary "ow temperature is $aried. Thisis known as a constant volume, variable temperature circuit .

• The three way $al$e is called a mixing valve. In fgure +, a three way $al$e isshown in the return rom a Heater 9attery 2the secondary return4. In thisapplication, the $al$e is termed a mixing valve in a diverting application. In$ariable temperature circuits, the three way $al$e is located in the secondary "ow.hen a three way $al$e is used in this manner it is known as a mixing valve in amixing application.

• The amount o main "ow water that the $al$e mi7es with the secondary circuitreturn water is determined by comparing outdoor temperature with eithersecondary circuit return temperature or room temperature. #ou should be able torealise that as outside temperature alls, more heating will be required 2a higher

secondary "ow temperature4 so the $al$e will open to allow more main "ow waterthrough to the secondary circuit until the $al$e is ully open and the secondary"ow temperature is the same as the main "ow.

• 's the outside temperature rises, the $al$e will close, allowing more secondaryreturn water and less main "ow water to be mi7ed, creating a lower secondarycircuit "ow temperature.

• This type o system is also known as a compensated circuit because itcompensates the secondary circuit "ow temperature to suit the outsidetemperature.



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#ostat tem,erature circuit:• The schematic diagram shows a sub;circuit being taken rom

the main pipework system to ser$e an air handling unitheater battery.

• #ou can see a three way $al$e at the heater battery. This$al$e will normally be controlled to maintain the air comingo the heater battery at a certain temperature. This is done

by opening the $al$e to $ary the amount o return water romthe heater battery. It ollows that by doing this, the amount o"ow water to the heater battery is also $aried. Howe$er, the"ow temperature is kept constant. This is known as aconstant temperature, variable volume circuit .

• hen a three way $al$e is used in this type o application it

is termed a mi0i valve i a diverti a,,licatio.• This type o circuit is only usually used to ser$e heat emitters

where the heat content o the water is passed to an airstream "owing o$er the emitter or to a secondary watersystem, or e7ample a calorier ser$ing a domestic hot watersystem.



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Air 5adli uit 5eater battery ad Radiators :

• These are both types o heat emitters. They aredescribed later in this section.



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• &edium temperature hot water is mainly used or theheating o actories and other buildings o that nature.

• 's you saw rom the chart at the start o this section, thetemperature o the water in an &TH system is abo$eboiling point, normally at about +/- with the returntemperature normally +- lower 2++-4 is achie$ed bypressurising the system with a pressurisation unit. Thistype o system is known as a pressurised or sealedsystem.

• ith medium and high temperature hot water systems,as the boiler raises the temperature o the water, thepressure in the system must also be raised. This is toensure that the system pressure is always abo$e thepressure at which water boils 2saturated $apourpressure4. I this was not done, the water would $eryrapidly boil and turn to steam 2also known as >"ashinginto steam>4 and the system would not unction as it wasdesigned to. 8or this reason you will ne$er fnd an &THor HTH system with a eed and e7pansion tank.

Medium Tem,erature 'ot Water -MT'W /MP'W.


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The schematic drawing below shows a typical &TH system

containing a boiler, pressurisation unit, pump set and adistribution pipework circuit ser$ing some unit heaters.

e ha$e already discussed boilers, pumps and pipeworkcircuits under %TH systems. *nit heaters are a type o heatemitter. These are discussed later in this section. %et us look atthe pressurisation unit.


FIGURE 2 - SCHEMATIC

OF AN MPHW SYSTEM


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(ressurisation *nit

• a pressurisation unit is used to maintain the system pressure highenough to allow the system temperature to be raised abo$e atmosphericboiling point.

• ?ormally, a pressurisation unit will be made up o a eed tank, pressurecylinder, water make up pump and high and low pressure controls. Thepressure cylinder usually is partly flled with nitrogen: the rest o thecylinder is flled with system water. The nitrogen is separated rom the

system water by a rubber diaphragm. 5ometimes air is used instead onitrogen, howe$er this is normally when pressurisation units are used on%TH heating and chilled water systems. The pressurisation unitoperates in the ollowing way)

@ 's the temperature o the water in the system rises, it will e7pand. The e7panded water will enter the pressure cylinder and compressthe nitrogen cushion until the nitrogen is compressed to the pressureneeded in the system to pre$ent the water rom boiling. I the

pressure in the system drops 2due to leaks at $al$e and pump seals4,a pressure sensor will start the pressurisation pump. This will takewater rom the make;up tank and pump it into the system until thesystem working pressure is reached again.

@ The amount o nitrogen 2or air i used4 in the pressure cylinder issu!cient so that in its< compressed orm it will equal the systemworking pressure.



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• High temperature hot water is used mainly as a transportation medium to pro$ide

a primary heating source or medium and low temperature hot water systems inlarge industrial comple7es and district heating systems. That is, it replaces an%TH or &TH boiler.

• 's you saw rom the chart at the start o this section, the temperature o thewater in an HTH system is normally at about +A- with the return temperaturenormally /- lower 2+/-4. 'gain, a pressurisation unit is used to pre$ent thesystem water rom boiling.

• The schematic drawing below shows a typical HTH system containing a boiler,pressurisation unit, pump set and a distribution pipework circuit ser$ing a

calorifer that pro$ides heating to a low temperature hot water system.

• The boilers and pumps used in a HTH system are similar to those alreadydescribed or low temperature and medium temperature hot water systems. Thepipework, $al$es, pipe fttings and heat emitters used in this type o system are ostronger construction to allow them to cope with the ar higher systemtemperature and pressure.

'i5 Tem,erature 'ot Water Systems

FIGU! " - T#$I%&L S%H!'&TI%

(F & HTHW S#ST!'


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• %ow temperature hot water systems can be, and normally

are, balanced and commissioned at operating temperatures.• &edium and high temperature systems must be balanced

when they are cold.• 's already e7plained to you, these systems are pressurised

so that the system temperature can be raised abo$e boilingpoint. This is potentially $ery dangerous.

• I, or e7ample, you are balancing a medium temperaturesystem and one o the connections should break, at yourwater meter, the system water will be allowed to escape. 'sthe system water temperature is abo$e boiling point, it will"ash o to steam as soon as it is e7posed to normalatmospheric pressure. This can cause se$ere burns.

If ever you are working on an MTHW or HTHW systemand you are asked to work with the system at normaloperating temperature, refuse ! This point cannot beemphasised enough

SA*%T) ASP%#TS


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'eat %mitters

Ty,e !escri,tio

'ir handling unit heaterbattery or rost coil

These are used to heat air at an air handling unit. They are normallymade up o copper tube with copper or aluminium fns. The air ispassed o$er the fns. ontrol is by a sensor in the air stream and athree port control $al$e. They can be used in %TH, &TH andHTH systems. They are normally ser$ed by constant temperaturecircuits.

Badiators Cespite the name, 3D o the heat gi$en rom radiators iscon$ecti$e.

Two basic types are used, column and panel. olumn radiators areusually made rom cast iron whilst panel radiators are made rompressed steel. olumn radiators are not used $ery requently todaycontrol is usually by a thermostatic radiator $al$e and a $ariabletemperature circuit. Badiators are normally used in %TH systemsonly.

?atural con$ectors ?atural con$ectors are normally made up o a fnned tube containedin a cabinet, howe$er they can be built into architectural eaturesunder windows or hand rails. ontrol is sometimes by a $ariable

temperature circuit. They are used in %TH, &TH and HTHsystems without the casing becoming dangerously hot.

5kirting heating element 5kirting element is normally made up o fnned tube, eithercontained

in a cabinet or embedded in a "oor and co$ered with a grille. ontrolis by a $ariable temperature circuit. They are normally used on %THsystems only.


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'eat %mitters

Ty,e !escri,tio

8an con$ectors 8an con$ectors are made up o fnned tube and a an, contained in acabinet. The fnned tube is normally located near to the top o thecasing. 'ir is drawn in through an opening at the bottom o thecasingby the an, then blown across the heating element and dischargedthrough a grille at the top. ontrol is usually by a local thermostatswitching the an on and o. They are used on constant temperature

circuits on either %TH, &TH or HTH systems.

*nit heaters *nit heaters are a type o an con$ector used or industrialapplications.

They are again made up o fnned tube and a an in a casing,howe$er,air is normally drawn in at the back o the heater and discharged atthe ront. ontrol is by a local sensor switching the an on and o.

They are used in constant temperature circuits on %TH, &TH

or HTH systems. They discharge higher $olumes o air at higher$elocities and are usually located at high le$el.

Badiant panelsEstrip Badiant panels and strips consist o a pipe attached to a radiantsurace. The back o the radiant surace is normally insulated topre$ent heat loss, howe$er, it can be let open to gi$e a degree o con$ecti$e heating. ontrol is usually by a local sensor and control$al$e ser$ing a 6one o panels or strips. They can be used on %TH,&TH and HTH systems.


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1& #'I$$%! WAT%R S)ST%MS • hilled water is produced by heat e7changer o a $apour compression cycle

system, also known as the mechanical rerigeration process.• The technical aspects o the mechanical rerigeration process will be looked at in

another module.

• hilled water is usually controlled to a "ow temperature o F or G- and a returntemperature o G- higher, that is ++ or +/-. I the "ow temperature were muchlower, there would be a danger o the water in the system ree6ing.

• hen chilled water pipework has to be run outside or through cold areas, rostprotection is required to pre$ent the system water rom ree6ing. This can take theorm o electric trace heating tape wrapped around the pipework running throughthe cold area. I the system is o the closed type, a mi7ture o water and ethyleneglycol 2anti;ree6e4 can be used in the system.

IMPORTAT OT%:

All c5illed +ater circulatio ,i,e+or is isulated +it5va,our sealed isulatio& W5e balaci orcommissioi a c5illed +ater system it is im,ortat toesure t5at t5e va,our seal is ot damaed i ay +ay& I6t5e va,our seal is damaed7 codesatio may occur+5ic5 +ill i tur cause damae to t5e ,i,e+or7

,i,e+or 8ttis ad valves&


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1& #'I$$%! WAT%R S)ST%MS The schematic drawing below shows a typical chilled watersystem. The system is made up o a chiller, a pump set andpipework distribution system ser$ing an air handling unit coolingcoil and a secondary circuit ser$ing a number o an coil units.

e ha$e already looked at pumps and pipework in the lowtemperature hot water system section o part + o this module.

The remaining items are described below.

FIGU! ) - T#$I%&L

%HILL!D W&T! S#ST!'


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#5iller The chiller is the heart o a chilled water system. It contains thee$aporator, compressor, condenser and e7pansion $al$ecomponents o the mechanical rerigeration process. 9asically,the chiller operates in the ollowing way.

@ 5ystem water is passed o$er tubes containing rerigerantin the eva,orator section o the chiller.

@ Heat rom the system water is transerred to thererigerant by a heat e7change process, ha$ing the eecto cooling the system water.

@ The heated rerigerant is compressed by a com,ressor then passed through the codeser. ondensers can be

either water or air cooled.

@ 't the condenser, a urther heat e7change takes placerom the rerigerant to the condensing medium. The cooledrerigerant is then passed back to the e$aporator throughan e0,asio valve to pick up more heat rom the chilled

water system.


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#5iller • Air cooled codesers are made up o a fnned tube coil and a an,

housed in a cabinet. The rerigerant runs through the fnned tubecoil. 'ir is drawn across the coil by the an, causing a heat e7changebetween the rerigerant and the air. That is, the heat taken rom thechilled water system and being passed onto the rerigerant at thechiller, is fnally reected to outside air by the condenser.

• Water cooled codesers are ser$ed by a condenser watersystem. The rerigerant passes through tubes in the condenser.ondenser water is passed across the tubes. This causes a heate7change to take place between the rerigerant and the condenserwater. The condenser water is then pumped around a pipeworksystem and passed through a urther heat e7changer. 't the heate7changer, the heat in the system is fnally reected to outside air.(art o this module looks at condenser water systems and thedierent types o heat e7changers.

• ondensers are usually remote rom the chiller. Howe$er, in somesystems a chiller, compressor, e7pansion $al$e and an air cooledcondenser are combined in one casing. These are known as

packaged chillers.


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Mae ", ad %0,asio Ta • In the same way as heating systems, any chilled water

system will leak $ery slightly through pump and $al$e glands,no matter how tight they are. The make up and e7pansiontank pro$ides make;up water to oset this loss. The tank isnormally installed at the highest internal point in the building.

• I the water in the system is not being cooled, it e7pands

slightly. I the eects o this e7pansion were not allowed or,the additional $olume o water would try to orce its< way out

o any weak points in the system and could cause leaks. Toa$oid this, a $ent pipe is again taken rom the system to themake up and e7pansion tank.

• The arrangement and operation o the tank is e7actly thesame as that described or a low temperature hot waterheating system. ' pressurisation unit and e7pansion $esselmay be used instead o a make up and e7pansion tank. The&TH section o part one o this module gi$es an o$er$iew o

a pressurisation unit.


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Secodary #ircuit• hilled water is usually circulated at a constant temperature,

howe$er, when the system includes an coil units, they are normallyser$ed by a secondary circuit taken o the main or primary circuit.

• ' chilled water secondary circuit is e7actly the same as a heatingsystem secondary circuit e7cept that it ser$es an coil units instead

o radiators. The temperature o the water in the secondary circuit

is again compensated to outside temperature.• The amount o main "ow water that the $al$e mi7es with the

secondary circuit return water is determined by comparing outdoortemperature with either secondary circuit return temperature orroom temperature, #ou should be able to realise that as outside

temperature rises, more cooling will be required 2a lower secondary

"ow temperature4 so the $al$e will open to allow more main "owwater through to the secondary circuit until the $al$e is ully open

and the secondary "ow temperature is the same as the main "ow.

• 's outside temperature alls, the $al$e will close, allowing more

secondary return water and less main "ow water to be mi7ed,

creating a higher secondary circuit "ow temperature.


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Air 'adli "it #ooli #oil

• ooling coils are used to cool air at an airhandling unit.

• They are normally made up o copper tubewith copper fns. The air is passed o$er the

fns.• ontrol is by a sensor in the air stream and

a three port control $al$e on a constant

temperature circuit.


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*a #oil "it

•8an coil units are a type o an con$ector unit,howe$er, they contain a flter and separate fnnedtube heating and cooling coils as well. I theyha$e been designed or a cooling only application,they will not contain a heating coil.

• ontrol is usually by a local sensors and a ourport control $al$e at each unit. They are used onchilled water and %TH systems.

• ontrol can also be with constant water through

the heating and cooling coils with a damper2acting under the dictates o the room sensor4di$erting the air o$er either the heating or coolingcoils as required.


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9& #O!%S%R WAT%RS)ST%MS

's stated in part /, a condenser water system is used as the

method o heat reection or a water cooled chiller. The drawingbelow shows a typical condenser water system. The system is

made up o the condenser section o a water cooled chiller, apump set, a pipework distribution system and a cooling tower 2themethod o heat reection4.

e ha$e already looked at pumps, pipework and make up ande7pansion tanks in this module. The remaining part o a condenser

water system is the heat e7changer. There are two main types inuse at present: the cooling tower and the dry cooler. They are

described below.

FIGU! * - S%H!'&TI% (F &

%(+D!+S! W&T! S#ST!'


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#ooli To+er• ' cooling tower comprises a matri7 o packing material, a

water sump and a an all located in a casing.

• The an is normally located at the top o the casing.ondenser water, containing heat reected rom the chilled

water system, is sprayed o$er the matri7 and allowed tocollect in the sump. The an draws air up through the tower

and across the matri7. 'ny heat contained in the condenserwater is reected to the air passing o$er the matri7.

• ater is taken rom the sump and returned to pick up more

heat rom the chilled water system. The cooling towercontains moisture eliminators to pre$ent water being blown

out o the tower by the an.• Cue to the operating temperature o condenser water

systems, the water in the sump o cooling towers can assistin the ormation o the bacteria causing %egionnaires

Cisease. ooling towers, are used less requently nowadays

or this $ery reason.


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4& 3%TI( O* S)ST%MS

• It is a act o lie that when water systems are flled orthe frst time, or ha$e been drained down and reflled,pockets o air become trapped in the system. Thismeans that the system is not completely ull o water.

• hen the circulation pumps in the system are switchedon, the pockets o air will be circulated around the

system. This will cause a reduction in the e!ciency othe system. This is because air is not as good a heattranser medium as water. 'ir in a system can also aectpump impellers. The impeller is designed to mo$e wateronly. ith air pockets in the system, the impeller will bemo$ing a mi7ture o water and air bubbles instead. Theair bubbles will scour the impeller as they hit it and itwill cause noise at best or cause $ery erraticunrepeatable readings at worst.

• 8rom a commissioning $iewpoint, air trapped in a watersystem will drastically aect the readings taken by awater meter, causing the meter to indicate a lower

water "ow rate than there actually is.


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4& 3%TI( O* S)ST%MS

• In the longer term, air mi7ed with water can createhydrogen, which, being the basis o all acids can corrodeany metal parts o the system, such as pipework. 'nyhydrogen contained within the system will escape when$enting is carried out.

• 'ir $ents should be installed in all water systems to allow

the air in the system to be remo$ed. They are installed atall high points in the system and at e$ery item oequipment such as heat emitters, an coil units andcooling coils. 'ir $ents come in two types: manual andautomatic. 'utomatic air $ents 2''J


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Met5od o6 3eti+. Knsure that the system is completely switched o. That means all

boilers and pumps i it is a heating system, all chillers and pumps i it isa chilled water system and all cooling towersEdry coolers and pumps i it

is a condenser water system. The system should be allowed to stand orat least minutes to allow any pockets o air in the system to rise tothe high points o the system.

/. Identiy the location o all manual air $ents in the system rom thelayout drawings and a $isual inspection. This includes all $ents atradiators and coils.

. =pen the $al$e at the each $ent until all air is released and water "ows.'ir $ents built into radiators and coils require a special key called a $entkey.

Knsure air is being discharged rom the $ent point and not being suckedin. This can happen especially at the higher points o the system i thesystem is not su!ciently pressurised to o$ercome the height o thesystem.

I this is the case, it could be why there is air present in the systemanyway, being drawn by the negati$e pressure through $al$e glands,''J


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%%R#IS%S

+. hat are the design "ow and return water temperatures or)

a4 %ow temperature heating systems

b4 &edium temperature heating systems

c4 High temperature heating systems

/. hy is $enting o a system so importantL

. Cescribe a secondary chilled water circuit and pro$ide a schematic

diagram.

A. Cescribe a an con$ector


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ASW%RS TO %%R#IS%S

+.

a4 1/- 8low3+- Beturn

b4 +/- 8low

++- Beturn

c4 +A- 8low+/- Beturn

/. Beduction in e!ciency

Camage to pump impellers'ect readings during commissioning %ong term aect causescorrosion


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ASW%RS TO %%R#IS%S. hillerEs

(umps (rimary

(rimary ircuit &ain ommissioning station(umps 5econdary5econdary ircuit &ain commissioning station port mi7ing $al$e 2di$erting application49ypass Couble Begulating Jal$e5econdary circuit compensated to outside temperatures8an coil units

ontrol $al$es on 8an coil units(ossible ommissioning de$ice on an coil unit or 0roups o units

A. Beer to Cescription contained in the table in the pre$ious slide.

1-4 basic water systems

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