How to install a heat exchanger?

Prior planning is very important before the installation of many types of heat exchangers.

- Adequate foundations and supports should be provided to bear the static weight of the exchanger unit, the weight of the units in it, and the dynamic loads due to wind, earthquake, etc. to make sure that the exchanger unit will not settle thus causing strains in piping and stresses in the unit.

- Leave enough space to be able to service the exchanger in a future, such as cleaning, repairs or replacement.

- Piping configuration should allow bypassing of the unit for inspection, cleaning, and repairs. Cooling water piping should be set to allow backflushing to remove deposits.

- Piping should be able to expand and contract freely. It should not transmit fluid pulsations and mechanical vibrations to the unit

- Provide necessary instruments to measure temperatures and pressure next to it.

- Do not pipe drain connections to a common closed manifold, as it makes it difficult to check if the unit has been thoroughly drained or not.

During actual installation of the unit on site take the following steps:

- On receipt of a heat exchanger inspect it for any damage in transit.

- Remove packing and preservative materials if it has been stored prior to installation.

- Set the unit square and level so that the piping connections can be made without forcing.

- Insulate the unit if very hot or cold compared to the ambient temperature.

- Pressure test the heat exchanger before starting operation.

What types of heat exchangers these installation recommendations can be used for?

These installation recommendations can be used for shell and tube, double pipe, finned coil, brazed plate heat exchangers, plate and frame type of exchangers, oil coolers and many other types.

These installation recommendations can be useful not only for industrial and / or commercial installations, but to home improvement installations of heat exchangers as well.

What other factors should be considered during selection and /or installation of the exchangers?

During selection and /or installation of the units another common factors to be considered are fouling, fluid viscosity, thermal performance, etc.

Most heat exchangers selected are thermally correct, but some constructions are not suitable for a specific application and can cause field problems. Constructions having a negative influence on plant operation, maintenance, metallurgy, requirements, cost, handling, shipping, freezing, recirculation, tolerances, manifolding, distribution, noise, availability, and pressure drop, etc. The effect of adjoining non-exchanger related constructions on performance should not be overlooked. The effects of filters, racks, screen rooms, packaging, heat sinks, hot spots, blowers, and ducting also have a great influence on performance of the heat exchangers.

We believe this information can be useful both for training engineering and non-engineering personell.

Replacing Your Furnace Does Not Require That You Replace Your Air Conditioner

So you either want to or need to replace your furnace. Money is tight and you can not afford to replace the air conditioner at the same time. This is no problem and do not allow yourself to be talked into changing them both out. The furnace can easily be changed now and the air conditioner kept intact or replaced at a later time.

Talking with your contractor frankly about what you want is always a good policy. If you have an old furnace that needs to be replaced, or if your furnace develops a cracked heat exchanger, many contractors practically demand that you change everything at once. This is not the truth and you need to know that changing either the heating or cooling sides out independently is very possible.

Now I will say that from a contractors point of view that I would always feel out the customer to see if they were willing to change everything. Hey, while you are in the mess of changing one it does make it easier to do both and the total price of the contract is higher which is always nice as far as the contractor goes. But from a homeowners point of view the money is not always available to do what you would like to do. So you need to just bite off a bit at a time, even if it costs a bit more in the long run.

Find a contractor that is willing to work with you. This may not be the lowest price, but the contractor that will work with you will give you the best job and make you the happiest. If you tell the contractor that you need to make the air conditioning last a year or two longer, but that you want to do it then, he can make provision for that change and make that change easier when the time comes along.

For most systems changing out the furnace just involves installing temporary supports to hold the indoor coil while the furnace is taken out from underneath it and then the coil is just lowered back down onto the new furnace. With a little forethought and care this can happen very easily. I have done this many times and it will work great!

Good communication is the best way to get what you want. If you are talking and the contractor is not listening to what you want, then do not buy from him no matter how good the price is. Find the contractor that is willing to listen to you and mesh his plan with yours to give you the system that you deserve and can afford.

A shell & tube heat exchanger article by Dougles Chan - Search Engine Guru - The best SEO company in Singapore and globally. Contact Dougles Chan @ +(65) 9388 0851 or email to dc@dougleschan.com for more information on how to make your website to be the top in Google.

Solar Heat Exchangers - Heating Your Home With The Power Of The Sun & Stop Your Air Conditioner Leaking Water

If you are interested in harnessing solar power for solar heat in your home, but are not quite in the position to be installing solar panels and a large solar heating system, you should consider using a solar heat exchanger. Solar heat exchangers are great for heating your home in many different capacities. They are also usually quite affordable.

Did you know that heat exchangers are used throughout your home already? They are commonly found in cars, refrigerators, and air conditioners and they regulate the heat that is generated and used in these items. They prevent over-heating and transfer the right amounts of heat to the right places. Solar heat exchangers are essentially the same, but they transfer the sun's heat instead of heat generated by an appliance or engine. They usually use liquid and air to transfer heat to another area, such as your swimming pool or your hot water tank.

One of the most popular types of solar heat exchangers is a swimming pool heater. These are great for any swimming pool owner. As you may know, heating a swimming pool can be expensive and consumes quite a bit of energy. If you don't want to give up your heated pool, but still want to be environmentally friendly, you should look into installing a solar heat exchanger.

Another type of solar heat exchanger is one that works to heat smaller areas, such as hot water heaters and sheds. These heat exchangers are great for those individuals that want to use solar heat, but do not want to spend a lot of money. These come in a variety of styles and sizes, so you can choose one that suits your needs.

Stop Your Air Conditioner Leaking Water

The three most common reasons for water leakage from heat pumps are dirty filters or heat exchanging coils, blocked drains, and a shortage of refrigerant. They are pretty simple to diagnose and repair.

Remember: Turn off the power source to your air conditioner before trying any of the following!

1. Dirty Filters and or Blocked Heat Exchanger
When the filters, or heat exchanging coil, are dirty or blocked, this causes a restriction in air flow. This in turn can then cause the temperature of the coil to drop. If the coil temperature drops below zero, moisture in the air that is condensating on the coil can freeze and form little ice flakes which are then blown out of your air conditioner, causing water leakage.
Check the filters, and if they look dirty, give them a good clean with the hosepipe or shower head. Remove all the dirt and give them a spray with a kitchen or bathroom antiseptic spray to kill any bacteria or mould on them.

Check the aluminum coil behind the filters. If it is covered in dry lint, try vacuuming the coil carefully with the brush attachment on your vacuum cleaner. If it is particularly dirty, you will need to use a garden spray bottle and a strong grease removing kitchen cleaner. Spray it on the coil, allow to work for around 5 minutes then rinse the coil off with the spray bottle. This should remove the dirt and improve the air flow. Please be careful not to spray water near to the electrical panel on the air conditioner.

ALWAYS read the manufacturers' manuals on how to clean your heat pump or air conditioner correctly!

2. Blocked Drains
On a wall mounted ductless air conditioner, a blocked drain can be pretty obvious and easy to diagnose. Water will usually drip down the wall from the back of the unit and may also leak through the air outlet at the front if the drain is blocked.

Stand on a small ladder and look down from the top of the air conditioner. Towards the bottom of the heat exchanger is a little plastic tray which is designed to catch the condensate produced by the cooling mode of the air conditioner. Check that this tray is not full of water or overflowing.

If your outdoor unit is directly behind the wall the indoor unit is mounted on, your drain pipe will likely follow the pipework through the wall and drip into the garden. If this is the case, find the end of the drain pipe outside, wipe the end clean with a cloth then blow as hard as you can into it. This should clear any blockages.

If you cannot clear the blockage yourself, or if it is buried inside the wall, you will need to phone a professional HVAC service company and book a service call.

3. Your Air Conditioner Has A Leak and Has Lost Refrigerant
If your air filters and heat exchanger are clean and you have lots of air flow, your air conditioner should deliver plenty of cool air. If it is struggling to cool the room for a few hours and then starts leaking water from the air vent it may be short on refrigerant.
Set your heat pump to the lowest setting possible and leave it to run for a little while.

Then check the heat exchanging coil underneath the filters. If it is covered in ice, your air conditioner has a leak and requires a professional to service it. If your air conditioner is leaking refrigerant, the leak will need to be found and fixed before it can have additional refrigerant added to it.

If in doubt, or these tips don't work, contact your local air conditioning company for a service.

A shell & tube heat exchanger article by Dougles Chan - Search Engine Guru - The best SEO company in Singapore and globally. Contact Dougles Chan @ +(65) 9388 0851 or email to dc@dougleschan.com for more information on how to make your website to be the top in Google.

How to Clean Your Heat Exchanger Tubes

Heat exchanger tubes are part of a heat exchanger, which is a device used for efficient heat transfer from one area or medium or another in order that the hot fluids never mix when a solid wall separates it or whether the media are in direct contact. This device has various applications such as in space heating, refrigeration, power plants, air conditioning, petrochemical plants, chemical plants, petroleum refineries and for the processing of natural gas.

A typical example of this tool is found inside your cars known as the radiator where it acts as the heat transfer medium transferring hotness from water in the engine to the air flowing through the generator. There are several types of this device and each is crafted to suit the application where each is used.

As an efficient tool that is designed to work for its costumers, it being a scientific invention will also wear out once not taken care of. One best means to augment the working capacities of heat exchanger tubes is by thorough cleaning. There are a number of advantages why these units must be cleaned. One prime reason is it will protect your system from unexpected and sudden failure and this may work to the owners' disadvantage.

 Apart from ensuring that it will work properly, cleaning will also help increase the unit's efficiency. Checking on the unit at least once every three months will also lengthen the life of the unit and will make you have every penny's worth of your investment.

Since cleaning of heat exchanger tubes is beneficial, how does one proceed with it? What are the common methods of cleaning them? Here are some things to remember:

• Disconnect first the unit from the whole system itself to prevent electrocution. This is followed by removal of loose materials found close. This will prevent possible pushing of these materials towards the tube's interior once you start brushing.

• The next thing to do is to remove the materials found inside the tube prior to inserting appropriate sizes of brushes to start cleaning. Brushes with strong nylon bristles are advised to thoroughly clean the interiors of the tube and to remove whatever loose materials still present inside.

• Sometime brushing the interior is not enough so you have to scrape through the walls to remove materials that adhered to the tubes. It is important that you make use of a scraper made of materials that is less hard than the materials that compose your heat exchanger tubes to avoid damaging it.

• After doing the above step, let water rush through the interior to remove other materials not perfectly taken out by scraping. It will also lighten up the interiors.

The Energy Efficiency of a Hydronic Heat Exchanger

The oldest type of hydronic heat exchanger is the one pipe system. This system sends heated water to the radiators and then uses gravity flow to return condensed water back to the boiler for reheating, but the disadvantages are that clanking sound familiar with those old cast iron models from years ago.

The most common hydronic heat exchanger system is the 2 pipe system. This system sends hot water from the exchanger to the radiators to heat the rooms; a return pipe sends the water back to the boiler to be reheated. This system is the most quiet and efficient of the 2 systems, but all of these systems require a bleeding system to remove air from the pipes and a pressure leveling system that helps keep the water level constant to avoid hissing and knocking noises that are common with water and steam heating systems.

The hydronic heat exchanger is also popular in water to air or forced air heating systems. As water is sent to the heat exchanger, it is moved throughout the duct system by an air handler that pushes heated air at the right volume into each room to ensure proper heating within the home. Booster coils can also be utilized to super heat air in large duct systems where a single air handler is used. In situations where space is limited wall mounted heat exchangers can be used to maximize space as well as add reinforcement in larger applications where constant heat or temperature regulation is needed. Stainless steel is commonly used in water tanks and in the bodies of hydronic heat exchangers as they hold heat well and when coupled with copper elements provide excellent heat transfer. Additional advantages of a hydronic heat exchanger is the multiple uses available for homeowners, such as providing hot water for bathing, cleaning clothes and dishes, as well and heating swimming pools, hot tubs and many other domestic needs. Known for their superior heating ability in industrial situations this low cost solution is also commonly used for air cooling and driving commercial refrigeration in larger commercial buildings.

This highly efficient heating solution is considers a popular "Green" energy alternative when coupled with a wood burning furnace, totally eliminating the need for electricity and fossil fuels. There are a number of tax credits and rebate incentives available for using this energy efficient heating solution. This can offset the installation and cost of purchasing a hydronic heat exchanger, making the return of investment rapid, and one of the most popular choices for home, business, and industrial heating and air cooling solutions available.

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Heat Exchanger Fundamentals

Heat Exchanger is the equipment in which heat (thermal energy) is transferred from one fluid to another fluid. These fluids are separated from each other with a metallic wall. To affect the exchange of heat, both the fluids must be at different temperatures. Heat will flow from hotter to the colder fluid.

Heat can be used for different purposes like, heating a colder fluid; cooling a hotter fluid; to condense a gaseous fluid; to boil a liquid and so on.

Type of heat exchangers

Although there are different types of This heat, the construction of That's fall mainly into two categories: 1. Shell and; and 2. Plate

1. Shell and Heat Exchangers

This is the most common type of heat exchanger construction and is suitable for high pressure applications. This type of That's consists of a set of, called -bundle, arranged in a shell (pressure vessel). One fluid flows through the, this fluid is called side fluid; and other fluid flows over the, this fluid is called shell-side fluid. side fluid is separated from the shell side fluid by sheet at the end of the. The are welded or press fitted into the sheet to provide a leak tight joint. In the shell, are supported by plates called baffles. These baffles reduce the vibration and direct the shell side fluid over the for increased heat transfer efficiency. Generally Shell are designed by TEMA standard and local and international codes for pressure vessels like, ASME BPVC, PD 5500, AD Merk blatt, etc.

There are mainly three types of shell and heat:

Fixed -sheet That's: A fixed -sheet heat exchanger has straight that are secured at both ends to sheets welded to the shell. The sheet may be welded to channel also. In this type of That's, bundle is fixed and cannot be removed. Hence it is generally used in clean service. In the event of large temperature differential between and shell material, higher longitudinal stresses will be developed in the shell and To reduce these stresses, a flexible element called expansion joint is used on shell.

U- Heat Exchanger: In this type of That's, one -sheet is stationary and it has a bundle of U-shaped. bundle is removable for cleaning purpose. Hence it is used for dirty service on shell side. Because of U-bends, it is very difficult to clean inside of. Hence it is not suitable for dirty service on -side.

Floating -sheet This: In this type of this, one -sheet is stationary and the other is free to float within the shell axially. bundle is removable for cleaning purpose. As Floating -sheet heat exchanger can be cleaned from both and shell side, it can be used for services where both the shell and side fluids are dirty.

2. Plate type heat exchanger

A plate type heat exchanger consists of plates instead of to separate the hot and cold fluids. Because of the larger surface area of the plate, this type of is capable of transferring more heat than similarly sized shell and. This type of used for medium and low pressure applications.

The Use of Plate Heat Exchangers and Air to Water Heat Exchangers in the Air Conditioning Industry

Heat exchangers are devices specially created for efficiently transferring the heat from a liquid to another liquid over a hard surface. This heat transfer can be absorption or heat dissipation. Heat and cooling exchangers are found every day on all sorts of devices, from boilers, or furnaces, to refrigerators and air conditioning systems.

As a device for heat transfer, it is a purpose of the heat exchanger to transmit heat as efficiently as possible. This allows the selection of the ultimate tool, for example, when it arrives to saving energy by recuperating wasted heat and causing it to be useful. In the case of a misuse of energy or heat flux that is not recovered, a brazed plate exchanger redirects the hidden flow of heat into something that can be used.

Whether for heating, ventilation, air conditioning or cooling, the brazed plate heat exchangers are perfectly suited for all applications. In ventilation, air conditioning and cooling systems, brazed plate heat exchangers ensure clean air and a chilly breeze. The brazed plate heat and cooling exchangers are a piece of equipment preferred for the mechanical industry.



The heat brazed plate exchangers, along with the air to water heating and cooling exchangers are the basic components of any air conditioning system. Without them, this machine would be nothing more than a fan. Companies that manufacture air conditioners are entirely dependent on heating exchanger producers. This dependence reflects highly in the financial statements of the suppliers of heating plate exchangers, since the air conditioner industry has increased at a fast pace.

The heat plate exchangers are widely used for heating, cooling and even refrigeration. Heavy Industries that use this technique are the power plants, chemical and petrochemical, petroleum and refined petroleum, natural gas processing plants and waste water treatment.

Gaskets that connect the disks are the main weakness of this heat plate exchanger's frame. Depending on the speed of the fluid and corrosion, seals can begin to lose, after a period, after the downtime that require maintenance and replacement. Pressure drop in the heat and cooling exchanger is high, and this may require the purchase and operating costs and more efficient pumping system. Although the maintenance is easier for a plate exchanger, it can still become clogged. This leads to long periods of inactivity.

To make sure that your device is properly taken care of, you will need to clean it regularly. Remember that almost all deposits can be moved by chemical means. This cleaning should only be done by a professional, because the improper use of chemicals can damage the device. Also, mechanical removal uses a number of different techniques. There are special scrapping brushes that reach the tiniest corners of the device.

No matter how you choose to clean your heat exchanger, keep in mind that it is recommended to ask for an expert's help. Try and prevent fouling as much as possible.

Compact Plate Fin Heat Exchangers

A plate-fin is a variety of custom shell and tube heat exchangers design that utilizes a plated and finned chamber in order to move heat in between fluids. It is often classified as a compact exchanger of heat to emphasize its relatively high heat conversion surface area to quantity ratio. The plate-fin is widely used in several industries, like the aerospace business for its compact size and light-weight properties, as well as in cryogenics exactly where its ability to facilitate warmth transfer with little temperature differences is required.

Going Deeper Into Plate-Fin Custom Shell And Tube Heat Exchangers Design

A plate fin custom shell and tube heat exchangers design was actually developed by an Italian technician, Paolo Fruncillo. A plate-fin exchanger consists of layers of corrugated sheets divided via flat metal dishes, usually aluminum, to establish a number of finned chambers.

Separate cold and hot fluid streams circulation through alternating levels of the exchanger and are generally enclosed in the sides through bars at the sides. Heat is moved from one stream with the fin interface towards the separator plate and with the next set of fins to the adjacent fluid. The actual fins also serve to boost the structural integrity from the heat exchanger and allow this to withstand high demands while providing a long surface area for the exchange of heat.



A high level of flexibility is present within plate-fin custom shell and tube heat exchangers design as they can operate along with any blend of natural gas, water, as well as two-phase liquids. Heat transfer in between multiple process channels is also accommodated; having a variety of fin levels and types because different entry as well as exit points are readily available for each stream.

The main kinds of fins tend to be: plain, which make a reference to basic directly finned and triangular or even rectangular designs; herringbone, in which the fins are positioned sideways to produce a zig zag path; and serrated and perforated that refer to cuts as well as perforations in the fins to augment circulation distribution and enhance heat transfer.

The drawback to plate-fin custom shell and tube heat exchanger design is that fact that they are susceptible to fouling because of their compact flow pipes. They also can't be mechanically cleaned, as well as require other cleanup methods in addition to proper filtration to eliminate potential fouling streams.

Inside a plate-fin, the fins are often capable of being rearranged. This enables both liquids to result in cross counterflow, counterflow, cross flow or even parallel flow. When the fins were created properly, the actual plate-fin heat exchanger can work in ideal countercurrent arrangement.

The cost of a plate-fin custom shell and tube heat exchangers design is typically greater than conventional warmth exchangers due to a higher level associated with detail required throughout the manufacturing process. However, these types of costs can often be outweighed through the savings made by the added exchange of heat.

Maintenance of Heat Exchangers-Sample of Tender Notice

Sub: Maintenance of Heat Exchanger– Additional Work

Sealed tenders are invited from registered contractors with HOCL, Kochi for Maintenance of Heat Exchangers – Additional Work

General Scope of Work for Maintenance of Heat Exchanger & Pressure Safety Valves

·         Once the equipment is ready for maintenance, isolation of equipment by putting blinds/spectacle blinds in feed and out let nozzles and all other nozzles indicated for the purpose and fix blind number tags.

·         Preparation for man entry ie. provide necessary hose connections for draining, purging, steaming and water washing and airing of the equipment as the case may be.

·         Fixing and operating eductors for airing the equipment.

·         Record in the blind tag Nos. in the blind register and obtain signature in the register by Engineer-in-Charge.

·         Pressure safety valves on the equipment and connected pipe lines shall be in the scope of work of the respective equipment in the schedule of rates unless otherwise mentioned separately.

·         Assisting the inspecting team engaged in the inspection of column / pressure vessel.

I.          Heat Exchanger Maintenance

·         Open channel head cover

·         Open channel head

·         Open shell cover and floating head cover if the exchanger is floating head type.

·         Pull out the tube bundle (not applicable if exchanger is fixed tube type).

·         Clean the tubes and shell, channel head and channel head shell and floating head cover and offer the parts for hydroblasting and cleaning.  If hydroblasting is required for cleaning, the same will be arranged by HOC at their cost.

·         Assemble the tube bundle, channel head shell and covers in required sequence and stages suitable for Hydrotest of tube side and shell side separately..

·         Hydrotest the exchanger on shell side and tube side.

·         Hydrotest should be got witnessed by Engineer-in-Charge/3^rd Party Inspector.

·         Test rigs should be used for testing floating head type exchangers tube bundle.

·         Test pressure should be as per the inspection of the Inspector/Engineer-in-charge.

·         Leaking tubes if any noticed during hydrotest should be plugged using CS/SS/Brass plugs as per the instruction of Engineer-in-charge.  Required plugs will be supplied by HOC at free of cost.

·         Removal of isolations ie. blind, spectacle blinds, blind tags.

Note : 50% of the quoted rate only will be paid to the party if the tube bundle is not pulled out and brought to the ground (ie. only hydro testing of the tube and shell side and plugging of the leaking tube is done.)

II.         Maintenance of Pressure Safety Valves

·         Removal of PSV from the location, which are mounted on vessel/column/Heat Exchanger and or its connected piping.

·         Blinding inlet/outlet nozzle of the PSV immediately and put blind tags without disturbing the flare system and record in the blind register.

·         Dropping the PSV to the ground level.

·         Transportation of PSV from site to Central Workshop.

·         After overhauling, testing and third party inspection by HOCL, collect the valves from Central Workshop and transport it to the respective locations.

·         Remove the blinds, blind tags and fix the PSVs at respective locations using new gaskets and fasteners.

·         Cost of these works shall be absorbed in the quoted rate for the maintenance of columns, Heat Exchanger, Vessel.

Taxes & Duties

Your quoted rate shall be inclusive of all taxes and duties whatever applicable to this job except service tax.  Service tax will be paid extra if the party produces service tax registration and other relevant documents to HOC.

Liquidated Damages

In the case the party fails to complete the work within the stipulated period, there shall be a penalty at the rate of ½% (half percent) of the value of the contract per day of delay to a maximum of 5% of the total contract value.

Defect Liability Period

Contractor shall guarantee the work for a period of one year from the date of issue of completion certificate.  Any damage or defect that may arise or lie undiscovered at the time of issue of completion certificate, connected in any way with the workmanship should be rectified by the contractor at his own expense as deemed necessary by the Engineer-in-Charge.        

Initial Security Deposit

Initial security deposit @ 2.5% of the contract value shall be remitted with HOCL, Kochi within 10 days from the date of receipt of this work order.

Agreement

You have to execute an agreement with HOC in the prescribed format on a non judicial stamp paper for Rs. 100/- given in the GCC within 10 days from the date of work order.

Scope of Supply

·         HOCL shall issue pipe fittings, hoses, gaskets, fasteners, tube plugs, air, water, electricity at one point free of cost to the contractor.

·         HOCL shall permit the contractor to hire the HOCL’s Forklift and mobile crane on chargeable basis if it is available and the rate shall be Rs. 1000/hr. for mobile Crane of capacity 18T and Rs. 600/hr. for Forklift + service tax.

·         Contractor shall bring necessary tools and tackles, chain pulley blocks, D-shackles, slings and any other equipments required for the work at his own risk and cost.

·         HOC will provide only the gaskets and fasteners for the final box up work.  Temporary gaskets for blinding/isolation should be made by the contractor.  However, gasket sheets for the same will be provided by HOCL at free of cost.

Testing & Inspection

HOCL shall inspect the equipments during the work in progress along with the 3^rd party inspection arranged by HOCL.  All the necessary assistance shall be provided by the contractor to the Inspectors during inspection of the equipments.  Contractor has to follow all the instruction given by HOCL Engineer-in-Charge, Inspection Engineer & 3^rd party Inspector.

Payment Terms

·         90% payment will be released after completion of work and certification by Engineer-in-Charge.

·         Balance 10% payment will be made after defect liability period of one year or on production of PBG for the said amount.

Completion Period

The completion period shall be 20 days from the date of clearance to start the job and deviations shall be permitted as per the work permits issued by HOCL

ESI, PF Requirements

Please see the Annexure – A attached.

Note:

1.                  This tender aims for already enlisted contractors for this work with HOCL Kochi Unit.  Any new contractor who wish to empanel for this type of work may submit the credentials as detailed below so that they will be evaluated and pre-qualified and shall be considered for similar future work.

Credentials to be submitted for the pre-qualification.

1.      Details of the Organization and the works carried out

2.      Work Order copies of the work executed showing the order value for the last 3 years.

3.      Man Power Organogram

4.      Solvency Certificate from a Nationalized Bank

5.      Annual Turn over for the last 3 Years.

Solar energized Liquid Desiccant Air Conditioning – A review (Part I)

Abstract

A review on Liquid Desiccant based cooling technologies with special focus on advances in
liquid desiccant materials and configurations of heat and mass exchangers have been
discussed. Performance comparison and energy saving potential of a hybrid liquid desiccant
cooling system based on vapour compression based sensible cooling and liquid desiccant
based dehumidification in comparison to conventional vapour compression system has been
reviewed. Hybrid liquid desiccant cooling system has enormous energy and cost saving
potential especially in hot and humid regions like India. The ability of Liquid Desiccant
cooling technology to be energized by Solar thermal makes it an attractive alternative to high
electrical energy intensive conventional vapour compression based cooling for residential and
commercial HVAC applications.

Keywords: Liquid Desiccant, Dehumidification, Vapour Compression, Solar Thermal.

1. Introduction

India is a tropical country and more than 80% of Indian Sub continental area falls under
Warm humid or Composite Climatic zone [1]. These climatic zones are characterized by high
annual average temperatures and high humidity. With rapid urbanization and industrialization
in India, there is sharp rise in air conditioning load in Industrial, commercial as well as
residential buildings.

 The Air conditioning load could be broadly classified as sensible load and latent load.
Conventional vapour compression Air conditioners (VAC) meet the total air conditioning
load by cooling the air below the dew point temperature and thus condensing the moisture.
These systems require evaporator temperatures to be maintained much lower than required to
achieve sensible cooling alone. The dew point temperature is much below the set temperature
level and hence process air requires further heating to bring its temperature to set temperature
level. This requirement increases the capacity rating of the compressors and requires high
electricity and consequently operates at reduced coefficient of performance (COP) [2].

There is a necessity to separate the latent cooling load and sensible cooling load and handle
them separately so as to improve the COP of the air conditioners. The desiccant cycles can be
used to reduce the moisture content of air by partially converting latent cooling load to
sensible cooling load and then meeting the load by VAC’s. These systems with vapour
compression cycle for meeting sensible cooling load and liquid – desiccant cycle for latent
cooling load are called hybrid systems.

2. Liquid desiccant dehumidification and air conditioning

A desiccant material has a strong attraction for water vapour. Desiccants are commonly used
in industrial applications where low dew-point air is needed. The strength of a desiccant can
be measured by its equilibrium vapour pressure (i.e., pressure of water vapour that is in
equilibrium with the desiccant). This equilibrium vapour pressure increases roughly
exponentially with the temperature of the desiccant/water system. It also increases as the
desiccant absorbs water (a dilute liquid desiccant will have a higher equilibrium vapour
pressure than a concentrated liquid desiccant). When the absolute humidity of air that has
come into equilibrium with a liquid desiccant of fixed concentration is plotted on a
psychometric chart, the equilibrium line closely follows a line of constant relative humidity
and the Fig1. illustrates this behaviour for solutions of lithium chloride.


As shown in the Fig 2., the brine-bulb temperature for a 43% solution of lithium chloride and
air at 30.0/25.6°C dry-bulb/wet-bulb will be 47.8°C. With an ambient wet-bulb temperature of
25.6°C, a typical cooling tower might supply water at29.4°C. It’s impractical to cool the
ambient air using this cooling water in a conventional heat exchanger, because the cooling
water is only one degree below the air temperature. However, a strong cooling effect could be
achieved by wetting the surfaces of the heat exchanger with the 43% lithium chloride. Of
course, one does not get this enhanced cooling for free. If the cooling process is to be
continuous, energy must be expended to regenerate the desiccant back to its original
concentration. If ambient air from the preceding example is brought into equilibrium with
43% lithium chloride at 85°F (29.4°C), the air will have a dew point of 33.5°F (0.8°C), a wetbulb
of 57.8°F (14.3°C), and its enthalpy will be reduced from 41.5 Btu/lb (96.3 kJ/kg) to
24.9 Btu/lb (57.8 kJ/kg). This large cooling effect, both in terms of latent cooling and total
cooling, and low dew point—both of which are achieved without a compressor—demonstrate
the potential for liquid desiccants to become an important part of HVAC systems. Liquid
desiccants have been successfully used to produce dry air for a surprisingly long time. Dr.
Russell Bichowsky, working for the Frigidaire Division of General Motors, first used
solutions of lithium chloride to dry air in the 1930s. Also in the 1930s, the Niagara Blower
Company introduced a liquid desiccant technology that used glycol solutions to prevent frost
from forming on low-temperature evaporators. Both lithium chloride and glycol continue to
be used today in liquid-desiccant dehumidifiers, but their use is limited primarily to industrial
applications[3].

3. Hybrid configuration: desiccant de-humidification and vapour compression based
cooling

An example of desiccant cooling application is represented in fig. 3 [4].


Figure 3.Schematic of Hybrid Liquid Desiccant aided Vapour compression air conditioning

Here, the cool strong desiccant solution is sprayed onto the top of the dehumidifier through
spraying nozzles. By gravitation, it trickles through the structure of the dehumidifier where it
gets contact with the process air stream blown perpendicularly to its trickling flow direction.
Since, the cool and strong desiccant solution vapour pressure is less than that of the air vapour
pressure, water vapour migrates from the air stream to the desiccant solution and condenses
therein. Consequently, the heat of condensation and mixing are liberated causing an increase
in the solution’s temperature. The process air stream is slightly cooled down due to its contact
with the cold desiccant solution. The dehumidified and rather warm process air stream then
passes successively through the evaporative cooler and the evaporator of the traditional
refrigerant vapour compression air conditioner, before being delivered into the conditioned
space. The diluted desiccant solution, exited from dehumidifier, is circulated through the
regenerator where it is heated and the moisture absorbed in the dehumidifier is now lost to the
scavenger air stream. In order for the system to keep functioning continuously and effectively,
an equal amount of water vapour absorbed from the humid air and condensed to the desiccant
solution in dehumidifier must be evaporated from the desiccant solution in the regenerator.
The hot and strong desiccant solution is thereafter cooled down in the pre-cooler and then
cooled further in the heat exchanger (HX) before being ready again to dehumidify the
incoming process air.

The lowest limit temperature attainable by the evaporative cooler is the process air wet bulb
temperature which decreases with the decrease of the relative humidity and increases with the
elevation of the dry bulb temperature. The essential role of the desiccant solution in this example is to lower the relative humidity of the incoming air stream in order to enable the
evaporative cooler to function more effectively.
Here, the desiccant assisted evaporative cooling is associated with the traditional vapour
compression air conditioning to reduce its size and enhance its coefficient of performance.
Because the latent load is handled independently by the desiccant dehumidifier, the need of
cooling the ventilation air below its dew point is obviated. The temperature of evaporation can
thus be lifted up to 15 °C from its generally practiced level of 5 °C for the traditional vapour
compression system. The increase in evaporation temperature will entail the increase of the
system’s coefficient of performance (COP).

This assemblage can be useful in humid climates where the wet bulb temperature is fairly
high. In such climates, a significantly downsized vapour compression air conditioner can be
supplemented with a desiccant assisted evaporative cooler in order to reach the desired indoor
temperature, thus enabling costs and energy savings and improving the indoor air quality.

4. Liquid desiccant materials

Liquid desiccants such as Glycols and solutions of halide salts are routinely used in industrial
de-humidifiers. Commonly used liquid desiccant materials include lithium chloride, lithium
bromide, calcium chloride, triethylene glycol and mixture of salts etc. The choice of desiccant
will have a profound effect on the design of desiccant de-humidifiers.

The desirable properties of liquid desiccants include large saturation absorption capacity, low
regeneration temperature, Low Viscosity, Good heat transfer, non volatile, non – corrosive,
odourless, non toxic, non flammable, stable and inexpensive. Surface Tension of liquid
desiccants is an important parameter of liquid desiccants as it plays important role in static
hold up and wetting of the surface of heat and mass exchanger of Liquid desiccant system.
Halide salts such as lithium chloride and lithium bromide are very strong desiccants. A
saturated solution of lithium bromide can dry air to 6% relative humidity and lithium chloride
to 15% but halide salts are corrosive in nature. Lithium Chloride has good desiccant
characteristics and does not vapourize at ambient conditions but droplet filters are necessary
to prevent any mixing of the liquid droplets with process air. Cost of halide salts are relatively
high except calcium chloride whose cost is comparatively low compared to LiCl, LiBr and
TEG. Another advantage of Calcium chloride is its low viscosity which reduces the pumping
power. But the CaCl2 salt is highly corrosive in nature and can be used in non metallic
systems only [5].

The least expensive alternative to lithium chloride is calcium chloride. Unfortunately, calcium
chloride is a relatively weak desiccant. A 42% solution, which is about as strong as can be
used without encountering crystallization, will dry air to about 35% rh. (For comparison, a
43% lithium chloride solution can dry air to a 15% rh.).

Glycols are the second class of liquid desiccants now used in industrial equipment. Both
triethylene and propylene glycol have low toxicity, and their compatibility with most metals
has led several researchers to use them in LDACs designed for HVAC applications. However,
all glycols have one undesirable characteristic that they are volatile and any evaporation into
the supply air makes it unacceptable for air conditioning for occupied buildings [6]. Salts of weak organic acids, such as potassium or sodium formate and acetate, have been explored as less corrosive alternatives to halide salts that are also not volatile. Although it is a significantly weaker desiccant than lithium bromide or lithium chloride, the ability to dry air below 30% relative humidity could make potassium formate a good alternative desiccant in some applications. Another less expensive alternative is potassium acetate. While potassium acetate could dry air to about 25%, its viscosity becomes very high. At 70% concentration and 27°C, a potassium acetate solution has a viscosity of about 28 cp. This is almost twice has high as a 43% lithium chloride solution at the same temperature. Water at 27°C has a viscosity of close to 1.0. [3].

Studies were also conducted on mixtures of calcium chloride and lithium chloride solutions to
take the advantage of good desiccant properties of LiCl and low cost CaCl2 [7].

4.1 Advantages of using liquid desiccants include

1. Lower air pressure drop in process air stream.
2. Liquid desiccants are capable of providing equivalent dehumidification as solid desiccant
systems with lower regeneration temperature(mostly 70 - 80°C) due to the internal cooling
provided by cooling tower water or chilled water and allowing utilization of solar heat or
waste heat.
3. Pumping of liquid desiccants is possible makes it possible to connect several small
desiccant dehumidifiers to a larger regeneration unit which is especially beneficial for
large multi zonal commercial buildings.
4. Liquid desiccants have high COP’s as highly efficient liquid-liquid exchangers could be
employed.
5. Simultaneous air dehumidification and desiccant regeneration is not necessary as it is
possible to store dilute saturate liquid until regeneration heat is available.
6. Liquid desiccants are highly beneficial for their ability to filter microbial contamination,
bacteria, viruses, and moulds from process air stream.

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