of 8
8/3/2019 Cooling Tower Guide 2006 1
1/8
8/3/2019 Cooling Tower Guide 2006 1
2/8
Cooling Tower Systems - Guidance for Energy Efficient Operation
Kelcroft E&M Limited http://www.kelcroft.hk page - 1 - version 1.01
Contents
Disclaimer .......................................................................................2 Purpose ..........................................................................................2 About the Author.............................................................................2 Introduction .....................................................................................3
Air Conditioning Basics...................................................................3 Cooling Tower Location ..................................................................3 Condenser Water System...............................................................3
Filtration .......................................................................................3 Pumps..........................................................................................3 Water Treatment ..........................................................................4 Strainers.......................................................................................4
Control Logic...................................................................................4 Condenser Relief .........................................................................4
Multiple Cooling Towers...............................................................4 Measurement and Verification (M&V) .............................................4 Conclusions ....................................................................................5 Feedback Form...............................................................................6
http://0.0.0.0/http://0.0.0.0/http://0.0.0.0/8/3/2019 Cooling Tower Guide 2006 1
3/8
DisclaimerThis guide is provided on an as-is basis, no warrantee isprovided or implied.
Kelcroft believes the facts and suggestions presentedhere to be accurate. However, final design andapplication decisions are your responsibility. Kelcroftdisclaims any and all responsibility for actions taken onthe material presented.
All Rights Reserved. Copyright 2006.
PurposeThis guide is not intended to be comprehensive designmanual or a text book; it is intended to provide a generaloverview of some of the main factors which influenceenergy efficient operation of cooling tower systems. Thetarget audience for this guide could be developers andowners of cooling tower systems.
This guide will be distributed electronically free of charge.
About the AuthorMr John Herbert, founder and director at Kelcroft E&M
Limited Consulting Engineers he was educated in the UKand holds Hong Kong Permanent residency. John hasmore than twenty four years international BuildingServices (E&M) consultancy experience gained overthree continents. He advises government and privatesector clients covering institutional, commercialresidential and healthcare sectors. Contact email:
Kelcroft E&M Limited http://www.kelcroft.hk page - 2 - version 1.01
mailto:[email protected]:[email protected]8/3/2019 Cooling Tower Guide 2006 1
4/8
Cooling Tower Systems - Guidance for Energy Efficient Operation
IntroductionIn 2000 the introduction of the pilot scheme for watercooled air conditioning in Hong Kong offeredopportunities for building owners to lower their airconditioning operating costs through the application ofcooling tower systems for commercial air conditioningsystems. Cooling towers use less energy, lowering theoperating cost they also benefit the environment; theycreate less noise, and the energy savings reducingemissions from power generators.
Fresh water cooling towers were prohibited in HongKong, and the knowledge and experience in the industrywas lost. The result owners have reported new coolingtower systems have fail to meet their low energyexpectations. To overcome this challenge this guideprovides an overview of the primary factors that influenceefficient operation of cooling towers systems.
Air Conditioning BasicsThe air conditioning system for large commercialbuildings, hospitals, etc. typically comprise central airconditioning system. A primary component, and energyuser is the central chiller plant. Using chilled water itcaptures the heat energy from within the environment,
transferring it to the condenser water system. In turn, thecondenser water system rejects heat energy throughcooling tower(s) to the atmosphere, returning cool waterto the chiller for the cycle to be repeated.
To capitalise upon the inherent energy efficiency ofcooling tower systems the condenser water, and coolingtower systems must be properly designed, operatingcorrectly and regularly maintained. These systems needto incorporate the following features for effective energy
efficient operation.
There are several type of cooling towers, including open,closed circuit, and hybrid, each have different air flowoptions, for example natural, induced draft-type andcounterflow.Photo Above: An open type induced draught coolingtower very poorly located.
Cooling Tower LocationThe positioning of every cooling tower is vital for efficientoperation. The cooling tower must be installed inaccordance with the manufacturers recommendedclearances, specifically to avoid short circuiting of theexhaust to the inlet, effectively lowering capacity. Ensurethat the exhaust air cannot be re-entrained (short circuit)to the cooling tower intake.
Cooling tower intakes should not be installed near anysource of pollution. For example gardens, shrubs, car
parks, or the like. Furthermore the outlet must notdischarge within thirty (30) metres of any fresh air intake.
It is important that the design includes safe lockableaccess, including fixed ladders, platforms, walkways andthe like, to permit easy maintenance inspections.
Condenser Water SystemA clean and properly maintained condenser water systemis vital for energy efficient operation of cooling towersystem.
Closed type cooling towers gained popularity becausethey have a separate the condenser water circuit thuspreventing contamination of the condenser water circuitand heat exchanger.Photo Above: Open type induced draught cooling tower,without filtration or blowdown is entirely blocked with mudTower fill required complete replacement
Filtration
ugh the cooling tower fill is not only cooled
HVACtrainer, and once the system is switched off, for example
ntricate
eing the capacity of the
wer and the condenser heat exchanger. Once
venting contamination of theondenser water system. If open type cooling towers are
Condenser water pumps connect to the chiller heatr to the cooling tower basin. If the available
nt
at 3gpm/ton (0.0538 L/ser kW) the design condition. At non peak times of the
In operation cooling towers are efficient air cleaners; airpassing throbut also cleaned. The dirt and debris is entrained into thecondenser water. Unchecked it accumulates in thecooling tower fill causing blockages, in the tower basin,and fouling heat exchanger surfaces and tubing.
Fine particulates easily pass through the standardsovernight, settle out forming sludge and mud.Additionally, the evaporation process decreases thewater volume, increasing the concentration of sludge andmud collected to form solids, typically with the ipathways of the cooling tower fill.
Any contaminant, including sludge and mud, reduces thcooling tower effectiveness, impairtocontaminated the heat exchanger must be dismantled forlaborious cleaning.
Closed type cooling towers have a separate condenserwater circuit thus precchosen then the system must be designed with aneffective filtration system to remove this dirt and debris.
Pumps
exchangestatic head (height of water) between the tower basin andpump inlet is limited no strainer shall be installedbetween the basin and pump.
Typically the condenser pump is rated as a consta
speed pump, and typically sizedp
Kelcroft E&M Limited http://www.kelcroft.hk page - 3 - version 1.01
8/3/2019 Cooling Tower Guide 2006 1
5/8
Cooling Tower Systems - Guidance for Energy Efficient Operation
year, the flow rate may be reduced, lowering pumpingpower consumed.
Water Treatment Water treatment programs must b
e designed for three
on of system components againstcorrosion; and
cal contaminants, such ast
aires disease.
The firslongevi e third ensures
fe operation. Cooling tower systems are a knownagent
Eof
reeding ground for Legionella bacteria to grow and
to
ith the make-up from the tank. To prevent wastage off
on is thelcium content, more commonly known as its hardness.
usedthe maximum permitted concentration of a
nstituent permitted in the condenser water system
always fitted totion systems pump inlet, primarily to prevente pump seal. However, cooling tower /
forrs
requirements:
1. Scale control2. Protecti
3. Control of biologiLegionella Pneumophila, the bacterium thacauses Legionn
t two help to ensure energy efficiency andty of the cooling system, while th
sasource for the Legionella bacterium, the causativeof Legionnaires Disease. As recognised by the EMSDpilot scheme, all cooling tower systems must be fittedwith an effective chemical dosing system, to mitigate therisk of infection associated with this equipment. ASHRAhas published Guideline 12-2000, Minimizing the RiskLegionellosis Associated with Building Water Systems.
In wet areas that are exposed to sunlight, algae andslime grow, unchecked they provide an excellent
bflourish; chemical water treatment solutions are required.
During the heat rejection process, some water is lostthe environment through evaporation; this is replacedwwater treatment chemicals the dosing and introduction ofresh water must be monitored and regulated.
Water contains various dissolved solids, and salts. Ofparticular importance for cooling tower installaticaAs cooling towers operate evaporation occurs, thisincreases the concentration of any water constituent.Therefore the water treatment system needs to counterthe increasing salt content to prevent formation of
calcium deposits on the heat exchanger loweringefficiency.
Cycles of Concentration (CoC) is the technical termto describecobefore the concentrate is discharged to waste. Toaccomplish this, when the limit of concentration isreached a blowdown valve (also known as Bleed) isopened, discharging condenser water to drain andlowering the concentration.
Strainers Typically Y-type HVAC strainers arewater circuladamage to thcondenser water systems are different, strainers must befitted after the pump because there is low static pumphead, will leads to cavitation and early pump failure.Additionally, as a result of the towers air cleaning effect,the condenser circuit strainers require frequent accessinspection and cleaning. Bucket or basket type straine
with a quick release mechanism, provides easy accessfrom above, encouraging regular maintenance.
Photo Above: Y-type HVAC strainer incorrectly locatedon the suction side of pump.
Control LogicThe control philosophy dictates how the combined chiller,condenser water, and cooling towers systems operate.It is often overlooked that how a system operates at thedesign condition (100% load) is not a sensible indicationof the overall annual performance.
The control logic dictates how the systems operatetogether, and is used to optimize chiller, cooling towerand condenser pump system performance throughout theyear.
Condenser Relief It is expected that the chiller plant operates at full loadand at design parameters only at design conditions.
During other periods (99% of the time), we expect thechiller plant to operate at less than design load, whichprovides an opportunity for condenser water reliefstrategy. Basically it means that the condenser watertemperature can be lowered because the cooling tower isno longer at 100% capacity and the ambient wet bulb isnot at design condition. Lowering the condenser watertemperature can provide significant chiller energysavings.
Multiple Cooling Towers The majority of the electrical power consumed by airconditioning systems is used in the chiller. Thereforeeven small improvements are beneficial, reducingrunning costs. The heart of the chiller is the compressor.Its workload is governed by the difference betweenevaporator refrigerant and condenser refrigerantpressure - reduce the differential pressure lowers powerconsumption and saves energy.
The condenser water system and the automatic controlphilosophy must be designed with energy efficiency inmind, operating multiple cooling towers simultaneouslylowers the differential pressure, and that lowers thepower consumed, saving energy.
Cooling towers have mechanical ventilation fans to movethe air through the tower; these motors should be fittedwith variable frequent drives, or alternately two speedmotors.
Measurement and Verification (M&V)Investors are often concerned that the promised energysavings are actually achieved. One tool to assist isindependent Measurement and Verification (M&V). M&Vis commonly employed on energy service contracts toverify that the promised savings have been achieved,and many be applied for cooling tower installations.
It is important to note that accurate M&V requirescomprehensive energy metering instrumentation to beinstalled. However, it is often overlooked in the drive forlowest first cost bidding, moreover value engineered out
Kelcroft E&M Limited http://www.kelcroft.hk page - 4 - version 1.01
8/3/2019 Cooling Tower Guide 2006 1
6/8
Cooling Tower Systems - Guidance for Energy Efficient Operation
in the drive to lower first costs. If you cant measure it -how can you manage it?
ConclusionsCooling towers offer building owners opportunities toreduce energy consumption compared to air cooledchillers, lowering the energy cost and the associatedpower station emissions. This guide highlights some ofthe major opportunities to minimise energy consumption,without affecting the standard or quality of service.
For more information regarding cooling tower installationsvisit:
http://www.kelcroft.com.hk/cooling-towers.htm
Kelcroft E&M Limited http://www.kelcroft.hk page - 5 - version 1.01
http://www.kelcroft.com.hk/cooling-towers.htmhttp://www.kelcroft.com.hk/cooling-towers.htm8/3/2019 Cooling Tower Guide 2006 1
7/8
8/3/2019 Cooling Tower Guide 2006 1
8/8
