060301-sea water cooling - march 2006-islamabad

7/27/2019 060301-Sea Water Cooling - March 2006-Islamabad

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Sea-Water CoolingFor Air-Conditioning SystemsBY

Fahim I. SiddiquiPartner / Principal Mechanical ConsultantFND Consulting Engineers

13th Annual ConferencePakistan HVACR Society

March 2006


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You cannot discover oceans

unless you have the courage toleave the shore.


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Fahim I. Siddiqui Paper At 13th Annual Conference Pakistan HVACR Society March 2006

What is Sea Water?

Thermal Impacts

Environmental Concerns

Materials of Construction

Presentation Overview:

Sea-Water Cooling


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Sea-Water Cooling

How can sea-water be used for cooling?

Using sea-water as make-up water in

sea-water cooling towers.

OR

Using sea-water to remove condenser heat.OR

Using cold sea-water to directly cool

buildings (SWAC).

Presentation Overview:



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Why sea-water cooling?

Because-

An air-conditioning system uses a lot of fresh water, which is

a very expensive resource today,

&

Using fresh water is not a adopting a policy of environmentsustainability.

&

Using sea-water reduces operational expenses

Sea-Water Cooling



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What is Sea Water?

Seawater is water and various

dissolved salts.

Six elements and compounds

comprise about 99% of sea

salts.

The quantity of these salts is

constant in all seawater,however the amount of salt will

vary due to runoff and

precipitation.

3.7, 4%

55, 54%

7.7, 8%

30.6, 31%

Na

CI

SO4

Mg

Ca

K

Minor Salts



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What is Sea Water?

Seawater is typically defined in terms of salinity.

Salinity is defined as the total amount of solid material dissolved

in a kilogram of seawater when all the carbonate has been convertedto oxide, all bromide and iodine replaced by chlorine, and all organic

matter is completely oxidized. Average Seawater - Salinity is 35,000 ppm, Alkalinity of 115 ppm, and

a pH of around 8.

For Cooling Towers, Sea Water is Circulating Water with a Salinity of

10,000 ppm or greater.

Since the circulating water is typically concentrated, the cooling

tower could also be exposed to salt water service even if the makeupwater has a salinity below 10,000 ppm.



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Sea-Water Cooling

Towers


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Sea-Water Cooling Tower Schematic



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Impacts on Thermal PerformanceSalt has Four Physical Effects Upon Water That Impacts Thermal

Performance.

1. Increased Density - Average Seawater Density is 2.8% Greater than Fresh

Water (1,028 vs. 1,000 kg/m3)- Use caution when specifying cooling tower flow rates (1 m3/hr is not equal to

1 ton/hr)

2. Lower Vapor Pressure - Average Seawater Vapor Pressure is 0.5% to 2.0%

Lower than Fresh Water.

-The increased density and lower vapor pressure result in a decreased Latent

Heat transfer

-Latent Heat transfer, or the energy of evaporation, accounts for most of the

temperature drop in a cooling tower.



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3. Seawater Provides Less Surface Tension, Which Effects Water Film

- This will have a minor impact if film fill is used

4. Reduced Heat Capacity - Seawater Heat Capacity at 38C is 7.1% Less than

Fresh Water

- This increases the Sensible Heat transfer, or the energy of a temperature change,

within the cooling tower

- Reduced heat capacity actually serves to increase the performance of a salt water

cooling tower, however it is not enough to offset the other physical effects

Impacts on Thermal Performance



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The Result is Reduced Thermal Performance

10,000 ppm Salinity 1% Reduction



Due to Decreasing Thermal Performance, the Practical Limit of

Salinity is ~70,000 ppm

Two Cycles of Concentration Maximum for Typical Seawater

Reduced Performance Must be Offset with a Larger Footprint for the

Cooling Tower and/or Increased Fan Motor Power

Impacts on Thermal Performance



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Environmental Impacts

Evaporation is Pure Water - No Environmental Concern

Drift

Salt May Collect on Nearby Facilities - Buildings, Power Lines, Cars - Corrosion is

Major Concern Majority (99%) of Drift Droplets will be 20 Microns or Smaller for Atmospheric

Distribution

Less than 5% are 10 Microns or Smaller

Cooling Tower Should be Placed Downwind from the Rest of the Plant/ Building

Blowdown - Depending on Concentration and Return Location,

Blowdown May be a Concern



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Materials of Construction-1

Due to the Corrosive Environment, Special Consideration Must be

Given to all Materials that will be in Contact with the Water

Structure

Hardware / Reinforcement

Fill

Distribution System

Fan Stacks

Mechanical Equipment & Supports



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Structure:

Structure Can be Wood, Fiberglass, or Concrete

With proper treatment, the use of Douglas fir or redwood is possible. However, if

the tower is to be used for intermittent service problems could arise from thecontinual wetting and drying of the wood. If a fire protection system is required, a

wood tower is more expensive than a fiberglass tower.

Fiberglass has a high resistance to corrosion and drying, a long service life, and

lower cost than concrete. However, the cost of fiberglass may exceed that of

concrete when freight is considered.

Concrete is the best overall option for saltwater towers in India & Pakistan.

Longest service life of all materials, and could be cheaper too in Pakistan due to low

labour cost.




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Structure Concrete:

Additional Performance Impacts due to Increased Air Blockage from Larger

Support Beams - 3 to 5%

Longest Service Life Lower maintenance requirements than wood or fiberglass

Installation Requires More Man-Hours

Typically offset by low labor rates in India & Pakistan

Concrete Materials Selected to Reduce Chance of Water Penetration

Emphasis on American Concrete Institute (ACI) Design Codes




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Hardware: For Wood and Fiberglass Structures the Connecting Hardware is a Concern

Silicon Bronze or is recommended unless high levels of sulfides are present

Silicon bronze hardware is 2X the cost of 316SS.

Titanium, Monel or another nickel alloy can also be used Titanium hardware is 6X the cost of 316 SS.

High molybdenum metals such as Super Duplex (254SMO) or Super Austenitic

Stainless Steel (AL6XN UNS S31254 and N08367) are also acceptable.

In Concrete Towers Exposed Hardware and Reinforcement Bars are aConcern

Exposed hardware should be silicon bronze, titanium, monel, or a high

molybdenum metal

Rebar should be stainless steel or epoxy coated carbon steel




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Fill:

Depending on Water Source and Treatment, Suspended Solids Levels May be

High - Sand, Debris, Oil, Biological TSS levels will impact fill selection

TDS has no effect on fill selection

Circulating Water Temperature

PVC Sheets - Temperatures < 60oC

Polypropylene Sheets - Temperatures < 77oC




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Fill:

Film Fills

Low TSS Levels (


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Water Distribution:

The Distribution System is the Same For Salt Water and Clean Water Towers

Materials are inert and will not be harmed by salt water

Headers - Fiberglass

Laterals - PVC

Spray Nozzles Polypropylene

Care should be taken when selecting the connecting hardware




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Fan Stacks: Velocity Recovery Design

Can be Made of Fiberglass or Concrete

Fiberglass Fan Stacks

Segmented - 15 to 20 segments

Bolting hardware should be 316 SS, Silicon

Bronze, or Monel

316 SS is Recommended - Hardware is not

in contact with water and Silicon Bronze

tends to gaul easily Concrete Fan Stacks

Can be cast-in-place or pre-formed

Lower Maintenance

Higher Cost




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Mechanical Equipment:

Standard motor, gearbox, and fan hub can be used, but at least one layer of

epoxy coating should be applied

Fan blades should be fiberglass, but marine grade or epoxy coated aluminumcan be used

Drive shafts are typically a carbon composite material. The couplings should

be 316 SS or monel

The mechanical supports should be epoxy coated carbon steel. Severallayers are recommended. Stainless steel supports can be used, but are cost

prohibitive.




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Sea-Water Condenser

Cooling


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Sea-Water Condenser CoolingSchematic



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Problems of direct & indirect

cooling Piping and equipment blockage by marine animals and semi-floating

debris.

Growth of small marine organisms on condenser tubes, piping and HX

surfaces.

Erosion, corrosion, pitting and cracking associated with the quality of sea

water



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A sea-water intake piping.

Intake water filtration system.

Sea water supply pumps, pipeline, and discharge pipeline.

Heat exchangers transferring heat from the fresh water

circulation loop to the seawater.

A fresh water circulation network, including pumps. This

network provides chilled water that circulates through each

building.

Because of the economy of scale, the seawater A/C system is

most appropriate for large or multiple buildings in coastalareas.

Sea-Water Air-ConditioningSystem Components



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Sea Water Intake,Filtration& Pumping Station


k l


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Sea Water Intake,Filtration& Pumping Station


S W t I t k


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Sea Water Intake


S W t I t k


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Sea Water Intake



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Sea Water Intake



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Sea Water Intake



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Sea Water Intake



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Sea Water Intake



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Sea Water Intake



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Sea Water Intake



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Sea Water Intake



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Sea Water Intake



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Sea Water Intake



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Sea Water Intake



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Sea Water Intake



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Sea Water Intake



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Sea Water Intake-backwash


k


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Sea Water Intake



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Prevent the ingress oflarge floating debris only

Low cost

Frequent maintenance

required

Hi down time

Rapidly clogged by

seaweed, jellyfish, plasticbags and other fibrous

materials Clogging restricts the flow

and increases pump powerconsumption

Bar Screens



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Traveling Band Filter



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Traveling Band Filter

Intake Works & Filtration iscritical to the success of sea-watercooling.

Band screens are equipped with aback-washing spray systemdischarging all removed debris intobaskets for collection / removal orinto a tough to be sluiced away fordisposal.


D Filt


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Drum Filter


D Filt


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Drum Filter


Pl H E h


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Preferred Material is Titanium.

Easy to maintain as the whole heatexchanger can be opened up plate byplate.

The Natural Energy Laboratory of

Hawaii has conducted years of testingon heat exchangers.

This long-term testing has shown that

fouling is not a problem with deepseawater, and corrosion can beeliminated with either titanium oraluminum.

Plate Heat Exchanger



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Sea-Water Cooling

(SWAC)

S W t C li g


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Central air conditioningsystems circulate water attemperatures of 40F to 50F.

These temperatures are

commonly found in the deepocean at about 1000ft to1500ft depth, even in tropical& sub-tropical climates.

The use of this cold water for

direct cooling of buildings waspreviously hindered by lack ofknowledge on deep-waterpipelines,& heat exchanger

fouling and corrosion.

During the last decade,

research has provided therequired knowledge for itsapplication.

Sea-Water Cooling


Depth wise Temperature in Ocean


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Depth-wise Temperature in Ocean

Generally, water at 42Fcan be found between1800ft- to 2100ft depthsand water as cold as39F can be obtained at2500ft.

For applications on the

coastline, an unlimitedsupply of cold water is

often a few kilometersoffshore.


S W t C li


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An experts comment:

The sing le mos t ef fect ive measure for reducingcarbon d ioxide em issions on a global basis would

be the subst i tut ion of deep ocean water air

condi t ion ing and indus t r ial cool ing w herever and

whenever i t is feasib le.

Sea Water Cooling


S W t C li g


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Deep, cold seawater has long been recognized as a valuableocean energy resource.

Over the past 20 years research and experimentation has

been conducted on ocean thermal energy conversion

(OTEC).

Out of this research, one clear economic winner emerged:

Sea-Water Air-Conditioning (SWAC).

It is technically and economically feasible today;

Once installed, the energy is inexhaustible and

There are no adverse environmental impacts.

Sea Water Cooling


Sea Water Cooling Design


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Sea-Water Cooling DesignConsiderations

Location and layout of site (survey and investigate the hydraulic andhydrographic conditions at the proposed site).

Sea water intake level and tidal& storm level considerations.

Intake sump and pump model test: important as the screens, intake

channels, penstocks, etc. affect the smooth flow of the water to thepumps.

Environmental and local regulations.

Structural costs.

The sea-water intake must be designed to catch & remove jelly

fishes, plastic bags and other floating and semi-floating debris .



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Seawater A/C is suitable for coastal developments with large airconditioning demand and reasonable access to deep, cold seawater.The main factors that influence the economic viability of a seawater

air conditioning system are:

Distance offshore to cold water in the 38F to 48F range,

Size of the A/C load,

Percent utilization of the A/C system,

Local cost of electrical power,

Size of the onshore distribution system,

Local seafloor bathymetry,

ContinuedFahim I. Siddiqui Paper At 13th Annual Conference Pakistan HVACR Society March 2006


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Wave and storm data,

Local climate,

Existing vs. new buildings,

Environmental requirements,

Secondary uses of the seawater.

Larger seawater A/C systems are more economical than

small systems. In general, a system smaller than 1.000tons is not economical


Economic Viability


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Economic Viability


Economic Viability


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Savings afforded by the seawater airconditioning system are defined as thevalue of chiller energy demand in aconventional air conditioning systemminus the value of electrical demand forthe seawater pumping in a seawatersystem.

The savings are typically 80 percent or

better, resulting in payback periods of2.5 to 5 years, depending on specificfactors.

The payback values only provide a general

guideline relative to the economic merits ofseawater air conditioning. The constructionand application benefits and challenges ofthe cold seawater system are very site-specific.

Economic Viability


Site Specific Analysis


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Utilizing the seawater air conditioning system can be very attractive forlarge users needing a base load system and with adequate access todeep, cold seawater.

The economic payback period can be quite small, specially for new

structures, where credit can be taken for not installing conventionalchillers, the payback is significantly better.

Energy savings with the seawater system can be as large as 80 percent,

so there is less dependence on conventional fuels and energy-cost

increases. Coastline of Pakistan is a suitable candidate for cold sea water

application.

Site Specific Analysis


Alternate usage of cool


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In some locations the seawater available may not be sufficiently coolto completely lower the freshwater to its optimal temperature.

In these cases, a chiller unit can be installed with the cold sea-water

cooling the freshwater first, followed by chiller units.

Alternately the cool sea-water can cool the condensers of chillers,

maintaining a high efficiency at low condensing temperatures.

Alternate usage of coolsea-water



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Power savings realized by seawater air

conditioning can be significant, and studies

show that a saving of about 80% are possible

against a conventional electric operated system.


Sea Water Piping Material


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The preferred material for the sea-water pipeline is high-molecular-weight polyethylene.

This material is ideal for cold water pipelines as it is:

rugged,

Flexible,

Completely inert in seawater,

Its flexibility allows for fast and easy installation,

Expected lifetimes of 20 to 30 years.

Capitalizing on polyethylene's flexibility, these pipelines can be safely deployed to depthsreaching 3,000ft, and for the maximum polyethylene pipe diameter available5ft.

Pipelines have been buried, bolted to the bottom, gravity weighted, pendant-supported,and floated over the bottom in long, continuous buoyant spans.

Combinations of these techniques can be used to reliably deploy polyethylene pipelinesover a wide variety of bottom and environmental conditions.

Sea Water Piping Material



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Sea-Water Treatment

Most practical procedure for sea water treatment.

Minimizes maintenance.

Most reliable, economical and efficient method for

preventing the growth of mussels and other marine

organisms.

CHLORINATION:



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Sea-Water Treatment

Hypochlorite Generation by Electrolysis of Sea Water

Most popular method.Higher initial cost.

Sodium Hypochlorite is generated on site by electrolysis of

sea water.No problem of supply, storage and transport.

NaOCL Solution Dosing Simple method. Lowest capital outlay

Cost is comparatively higher than other methods.

NaOCL solution is not stable at higher temperatures.

Gas Chlorination

Traditional method. Hazardous to personnel and environment in bottle gas

storage and injection room.

Permission and approval are required from the dangerous

goods division of explosives / fire service department.


Costs


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As with most alternative energy systems, the heaviest expenses forseawater air conditioning system would occur in the initialcapitalization.

Total capital costs include the cold water intake pipe, the pumping

station, the onshore heat exchangers, the onshore distribution system,and the effluent pipeline.

The largest cost is in the seawater supply system (intake pipe, pumps,

effluent pipe). This segment typically represents 45 to 75 percent ofthe total capital costs. On average, approximately half the capitalcosts is in the seawater supply system, 15 percent is in the heatexchanger, and the last 35 percent, in the distribution system.

Costs


Project References


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Project References1. In 1975, the US Department of Energy funded a program entitled "Feasibility of a District Cooling

System Utilizing Cold Seawater." The two most favorable sites identified were Miami/Ft. Lauderdaleand Honolulu.

2. In 1999, the Cornell Lake Source Cooling Projectinstalled a 63 diameter pipeline into nearby LakeCayuga. This pipeline was 10,000ft in length and installed to a depth of 250ft. Cold water from thispipeline, at approximately 4C, provides 20,000 tons of air conditioning for the Cornell UniversityCampus.

3. Two Buildings known as Purdys Wharf are cooled by cold sea-water at Halifax, Nova Scotia.

4. The Lake Water Supply Project, New York State: establishing a cold-water district as part of a

proposed lake water supply project for the town of Webster New York along the shores of LakeOntario. This project would require 3- 63 HDPE pipelines, each 3miles in length. Estimated cost ofthis project is $120 million.

5. Deep Water Cooling Project, Toronto, Ontario, Canada: The city of Toronto, Ontario, Canada is

developing a district cooling plan that will utilize cold water from Lake Ontario to provide airconditioning to Toronto. Construction has already begun for the cold water distribution systemthroughout the city.

6. In 1995, Stockholm Energy started supplying properties in central Stockholm with cooling from its newdistrict cooling system, using cold water from the Baltic Sea.7. Ontario, Canada is developing a district cooling plan that will utilize cold water from Lake Ontario to

provide air conditioning to Toronto. Construction has already begun for the cold water distributionsystem throughout the city.

8. In 1995, Stockholm Energy started supplying properties in central Stockholm with cooling from its newdistrict cooling system, using cold water from the Baltic Sea.

http://www.makai.com/p-ACpipes.htmhttp://www.makai.com/p-ACpipes.htm


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ThankYou

060301-sea water cooling - march 2006-islamabad

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