To assist you select the best system for your course of, Cooling Technology is happy to current you with this normal overview of process cooling, together with the various types of evaporative cooling tower systems and chillers, along with essential considerations that should be made when deciding on a cooling system.
Ought to you have any questions or need for further info, please don’t hesitate to contact us.
The Refrigeration Cycle
Forms of Chillers
Types of Compressors
Capacity Control and Heat Steadiness
Water Regulation and Fan Cycling
Non- Corrosive Parts and Safeties
Cooling Tower Theory
Kinds of Cooling Towers
Cooling Tower Systems
Closed-Loop Cooling Tower Systems
Tower Capability Management
The Refrigeration Cycle
Though refrigeration can be achieved by varied means, it is the compression cycle that’s most commonly used. Merely said, when altering the refrigerant’s strain, its state will change to both liquid or vapor. The change in state causes the refrigerant to absorb or discharge heat. So there are two pressures current in a refrigeration system; the evaporating (low pressure) and condensing (high strain).
A thermostatic expansion valve controls the quantity of high-stress liquid refrigerant entering the evaporator. As the refrigerant passes via the orifice of the valve, the pressure is diminished, inflicting it to vaporize and absorb heat. The compressor takes the low-strain vapor and increases each it’s stress and temperature. This hot, excessive-stress fuel is forced out the compressor discharge valve and into the condenser where is it cooled by both air or water. As heat is eliminated, it condenses to a liquid and the cycle starts again.
The primary elements to perform this process are the evaporator, compressor and condenser and thus further explanation of their perform and the sorts of parts available is warranted.Top
Sorts of Chillers
Chillers are often categorized by size (compact or central) and by the kind of condenser (air or water). The classification by condensers will also be discussed right here.
Air Cooled Chillers
Because the title suggests, chillers having air-cooled condensers use air to remove heat from the refrigerant. A fan forces air across small tubes containing the hot refrigerant and discharges that heat into the ambient air. In comparison with water, air is a poor conductor of heat and therefore air-cooled chillers are larger and fewer efficient. The everyday condensing temperature for an air-cooled chiller is 120°F versus a 105°F in a comparable water condensed chiller. Air-cooled chillers also operate at higher compressor ratios which suggests much less cooling per watt energy consumption.
For the smaller, portable chillers, the air-cooled condenser is built-in within the chiller cabinet and so it’s heat is ejected into the realm around the chiller. This heat could be reclaimed to complement a building’s heating system within the winter.
Nevertheless, in the summer time, this can trigger a further load on the building’s air conditioning system except the chiller and/or condenser is situated outdoors. There two kinds of air-cooled chillers- split or integrated programs. With a cut up system or “remote condenserthe chiller is indoors and the condenser outdoors. For the integrated unit, you’ll be able to put a small unit indoors since the load on the air-conditioner will not be a lot. Or you need to use the PCA indoors that allows the heated air to be ducted outdoors. You may at all times put the complete chiller outdoors (if it is designed that manner).
Water Cooled Chillers
Water-cooled condensers are of three basic designs; tube in tube, shell in tube or brazed plate. The tube in tube design has one tube inside another and the tubes are coiled into a “donutform to attenuate area necessities. The heat transfer from the refrigerant to the water takes place when the refrigerant flows through one tube whereas water flows in the opposite direction by means of the other tube. This counter stream enhances the transfer of heat.
The shell in tube design is very comparable besides that there’s a bundle of tubes contained in a shell. The refrigerant in the shell is around the water flowing via the tubes. This association allows the tubes to be cleaned out in case of fouling.
The brazed plate design is a extremely environment friendly and compact design. This heat exchanger has stainless steel plates which are embossed with small channels to offer a number of contact factors and elevated fluid turbulence thus providing excellent heat transfer whereas lowering the potential for fouling. The plates are stacked and brazed collectively to form two unbiased circuits operating in alternate layers.
Since one of these unit is constructed with stainless steel plates and copper alloy brazing, it gives a excellent corrosion free surroundings. Not solely does the brazed plate know-how considerably scale back floor house requirements over typical shell-and-tube or tube-in-tube evaporators, brazed plates are additionally way more efficient. As with the shell and tube design, the refrigerant and water have counter move to additional enhance the transfer of heat.
As talked about, water condensed units are more efficient than air condensed, often working in the range of 15 EER or higher (EER: vitality effectivity ratio or BTU per hour per Watt vitality consumption). Water cooled chillers require a supply of cooling water, similar to cooling tower water, to extract heat from the refrigerant at the condenser and reject it to the ambient atmosphere. The everyday condensing temperature in a water-condensed chiller is 105°F.
One other various to the air or water-cooled condensers described above is the evaporative condenser. Evaporative condensers are like cooling towers with inbuilt heat exchangers. Refrigerant passes via a copper tube bundle within the evaporative cell. Water cascades over its outer surface and airflow counter to the flow of water causes a few of the water to evaporate. This outcomes in the environment friendly cooling of the refrigerant.
Varieties of Compressors
At the guts of any chiller is the compressor. Because the identify suggests, compressors are used to increase the stress of the refrigerant. There are quite a lot of compressors out there in the marketplace, the commonest are the reciprocating, scroll and screw compressors.
Reciprocating compressors are pushed by a motor and use pistons, cylinders and valves to compress the refrigerant. These compressors are available in airtight, semi-airtight or externally pushed versions.
In a airtight unit, the motor and compressor are enclosed in a typical housing, which is sealed. Because the components will not be accessible for repair, the entire compressor unit must be replaced if it fails.
Within the semi-airtight unit the motor can be part of the unit, however it isn’t sealed so it is serviceable.
In a direct drive unit the motor and compressor are separated by a flexible coupling. A lot of these models make the most of older technology and are usually not generally used as we speak.
Scroll compressors perform at greater efficiency levels than reciprocating compressors. The compressors operate with out cylinders, pistons or valves so it offers:
Contained in the scroll compressor, two spiral-shaped members fit collectively forming crescent shaped gas pockets. One member stays stationary whereas the opposite orbits relative to first. This movement draws gasoline into the outer pocket and seals off an open passage. Because the spiral motion continues, gasoline is compelled toward the middle of the scroll design, creating more and more larger gasoline pressures.
With a number of pockets of fuel concurrently compressing, you obtain a nearly steady compression cycle. Fuel discharges from a port at the middle of the fastened scroll member. With both radial and axial compliance, the scroll members put on in slightly than wear out.
A screw compressor’s moving elements include a major and secondary rotor. It additionally has vital advantages:
The screw compressor’s suction, compression and discharge all occur in one route. Suction fuel is pressed into one grooved rotor by the second comparable rotor. The screw-like rotor motion continues towards the top of the compressor’s working house. In this way, refrigerant quantity steadily reduces or compresses until it reaches the stationary finish of the compressor. It’s right here that the vapor discharges to the condenser.
As a consequence of this design, the necessity for compressor elements is low. Due to this fact, familiar components, reminiscent of oil, assume new roles. As a substitute of lubrication, oil now performs as a dynamic sealer. By design, motor cooling occurs with refrigerant gasoline or vapor passing via holes in the rotor which also capabilities as a “built-inliquid separator. The scroll design also allows greater evaporating temperatures, useful to all functions excluding these with low temperature circumstances. The screw compressor is also extra forgiving to liquid slugging.High
Capability Management and Heat Stability
Essentially the most elementary principle in course of cooling is heat balance. This means that the amount of heat generated by the method is to be removed by the chiller: no extra, no much less. Regularly applied strategies for capability management and heat stability are:
Compressor cycling is one technique to regulate the extent of cooling in a chiller. It includes using a thermostat and a predetermined refrigeration temperature referred to as the “set point When cooling reaches the set point, the thermostat stops the compressor from circulating refrigerant through the system. Since the coolant circulation pump continues to function, the process gradually raises the temperature of the process water. The thermostat detects this rise and turns the compressor back on.
The drawback of compressor cycling is the additional wear positioned on the compressor motor windings when the compressor is started. With the current spiking up to 600% of its normal operating level, compressor cycling over an prolonged period could trigger premature failure.
Sizzling Fuel Bypass
Scorching gasoline bypass is used to supply the compressor with a steady full load whereas the chiller is catering to partial load circumstances. Normally, the compressor provides vitality to the refrigerant by increasing its stress and temperature. The ensuing scorching fuel goes to the condenser. The condenser removes heat from the gasoline and permits it to go to the thermal enlargement valve (TXV) as a liquid. This flow path adjustments with a scorching fuel bypass. Because the compressor satisfies the method load, water begins to over-cool. A thermostat senses this drop in temperature. At a preset temperature situation, the thermostat opens an electric solenoid sizzling fuel bypass valve-allowing refrigerant to take the trail of “least resistance./p>
A portion of the refrigerant bypasses the condenser and the TXV valve. The un-condensed fuel mixes with the refrigerant that has passed by way of the TXV. Since the mixture of liquid and gaseous refrigerant loses some capability to remove heat, a “free wheelinghappens: With out heat elimination from the refrigerant, the water in the chiller begins to rise in temperature. Again, at a pre-established temperature, the thermostat detects the temperature rise in the chiller and closes the bypass valve when water reaches the set temperature. In this manner, the hot gas bypass prevents the compressor from short cycling when the chiller operates underneath partial load conditions. This valve is especially essential when working a semi-hermetic compressor for the reason that compressor must obtain a full quantity of refrigerant for motor winding cooling.
Capability control additionally happens by way of compressor cylinder unloading. A thermostat energizes a solenoid (or solenoids if there are multiple cylinders in the compressor) that forces the discharge valve to stay open. Since the cylinder chamber is open to the discharge manifold, no refrigerant fuel compression can happen. The result’s a drop in refrigeration capacity that’s in direct proportion to the variety of cylinders being “unloaded.The torque on the electric motor reduces and ends in lower power consumption. Cylinder unloading is most fascinating as a method of capacity management since it balances a chiller’s capability to the process load and saves power consumption.
There are some functions where failure of refrigeration tools might end in critical monetary loss beyond the tools repair expense. In such instances, it is advisable to think about a a number of compressor chiller system.
Under partial load circumstances, the compressors could also be cycled in and out of service as required in addition to providing a stage of redundancy within the event one of many compressors ought to fail. Although the system will function at a lower capacity if a compressor fails, it should not be allowed to run on this condition for lengthy durations of time to stop potential harm to the other compressors in the chiller.Top
Water Regulation and Fan Cycling
Condenser water regulation for water- cooled chillers, or condenser fan cycling for air-cooled chillers, are other strategies of capacity control. Either methodology has limitations in its capability to scale back a chiller’s capacity.
If the incoming water (or air) temperature drops due to seasonal adjustments, the colder water (or air) will enhance a chiller’s capability. If the method load remains fixed throughout this variation, throttling the condenser movement (or cycling the condenser fan) solely reduces the chiller’s capacity within a limited range. As such, neither technique is truly successful as a means of capacity control.Prime
Non- Corrosive Elements and Safeties
Another consideration in choosing a chiller is its building. A noncorrosive component that prevents water corrosion in process gear is crucial for lengthy and upkeep free life of not simply the chiller, however the tools it’s servicing.
For CTI products, all chiller circulating pumps, evaporators and reservoirs are constructed with stainless steel and pipes are made with copper. All CTI chillers are fitted with a Ystrainer on the water inlet to stop any particles from clogging up the evaporators. As could also be surmised, CTI’s selection of components supplies efficient operation and reduces gear maintenance.
There are different types of refrigerants generally obtainable out there. Since the passing of the Montreal Protocol, many refrigerants of the HFC, or Hydro Fluoro Carbon, family have been phased out. CTI uses HCFC-22 (Hydro Chloro Fluoro Carbon) refrigerant in its complete product line. HCFC-22 is an permitted refrigerant till the year 2020 for CTI’s class of equipment.Top
A tower provides an economical strategy to cool giant quantities of water with minimal energy requirements. A tower system is normally used to cool heat hundreds with 85°F water. This is the optimum working temperature for hydraulic oil, chiller condensers (to cool refrigerants), and auxiliaries resembling mold temperature controllers or air compressors. Nevertheless the advantages and limitations of cooling towers must be understood before the equipment is selected for or applied to process cooling.Top
Cooling Tower Theory
The controlling precept of a tower system is water’s inherent nature to lower its own temperature as it evaporates. By evaporating a small a part of the process water, the temperature of all process water is lowered.
Tower cells accomplish this by spraying fine water droplets in a contained environment. The droplets fall through a stream of upwardly moving air. The more contact time of the air and water, the greater the quantity of evaporative and heat transfer. To significantly improve the quantity of contact time, cells embrace “fillmaterials to cut back the free falling of water and enlarge the floor area of water to air. The result’s greater exposure of water to air. With an increase in exposure, there is a corresponding increase in cooling capability.
Air must absorb water for evaporation to occur. The upper the extent of humidity, the less air is ready to absorb water and, because of this, the much less efficient the tower system in cooling. Sometimes, cooling tower systems capacity are rated to lower 95°F water to 85°F at 78°F wet bulb. Wet-bulb temperature of the air is the lowest temperature doable for evaporation resulting from ambient or surrounding environment so the temperature of the water can’t drop under the prevailing wet bulb temperature of the air.
Each tower system must be specifically sized for every geographic area’s prevailing summer season wet bulb temperature. While some geographic areas could experience cold climates, a tower’s cooling capability is normally set at no colder than 70°F during winter months. Excessive effectivity mechanical draft towers cool the water to inside 5 or 6°F of the wet-bulb temperature, while natural draft towers cool within 10 to 12°F.High
Varieties of Cooling Towers
There are three primary kinds of towers. The primary, a forced draft tower, has a sensor to thermostatically management the cooling tower fan. The sensor monitors the process water temperature after it exits from the tower. The fan engages or disengages when the method water temperature rises both above or below the specified set point.
A second type of tower, induced draft, has a fan in the wet air stream to attract air by means of the fill. Cooling Expertise usually recommends the sort of tower cell for industrial processes.
A third type, ejector pure draft tower, has no mechanical means to create airflow. In this case, water pumps to the tower, enters a manifold with nozzles, and ejects beneath excessive strain that induces a draft of air. The finely sprayed water contacts freeflowing air to perform the evaporation process.
In all kinds, towers use the power of gravity to drain water into an indoor pump and tank station. The pump delivers the water to process by way of piping where it picks up heat. The now-warmed water continues to flow back to the outside tower by means of return strains. The cycle repeatedly repeats.
Cooling Tower Systems
There are two primary varieties of evaporative cooling tower systems designed by CTI:
A traditional open cooling tower system has an outdoor tower cell. As water cascades through the cell, it cools itself via evaporation and the cool water flows right into a tank. The tank is usually indoors to avoid hazard of freezing. To enhance temperature stability, the installation of a dedicated pump for tower water recirculation and a baffle within the tower water reservoir is really helpful together with a course of water pump, the cooling tower system becomes a two-pump system.
With a two-pump system, warm process return water is remoted to 1 aspect of the baffled tank. The circulation pump circulates this warm water by the tower where it cools. The tower cascades water to a second, coldwater sump. It is from the chilly sump that the method pump circulates water again to the method.
The standard system is the simplest and least expensive, nevertheless, a significant drawback of a tower system comes from water’s inherent affinity to seize mud and air borne contaminants at the open tower. If left unchecked, the contaminants foul down stream tools causing poor heat transfer at the method and process equipment breakdown.
Whereas filtering tower system water can take away dust and dirt particles, minerals remain. With the addition of water treatment chemicals, many (not all) minerals precipitate out of the answer. Thereafter, removal can occur by way of mechanical filtration equivalent to a sand and gravel filter system.
Closed-Loop Cooling Tower Systems
This system combines the economies of an open cooling tower with the heat switch effectivity of a refrigeration system. Water-associated problems frequent with open cooling towers are eliminated with the closed-circuit system because as soon as the water is filtered and chemically handled, it stays pure so long as there isn’t a leakage to replace.
A closed-circuit system is just like a conventional cooling tower besides that a heat-exchanger is used to isolate the method water from tower water and enables the transfer of heat from one to the other without process water contamination. One other design characteristic distinction entails the reservoir. In a closed loop system, the tower reservoir is built both with two completely separate compartments or two separate tanks. One compartment or tank holds course of water that’s piped to the process and back to its separate compartment or tank with out coming in touch with the tower water. The second tower water compartment or tank holds the tower water. In a completely separate loop, the tower water circulates to the tower cell and back to the reservoir compartment or tank.High
Tower effectivity can also be dependent upon the bodily placement and orientation of cooling tower cells at the power. If the tools is next to a wall, precipitation from the tower can cause building wall paint to peel, gutters to rust, or icicles to kind. Recirculation of the wet air discharge, from the tower alongside a wall and again to the gear, will lead to raising the getting into wet-bulb temperature and dramatically decreasing system efficiency. In an analogous situation, if the tower discharge enters a second tower cell that additionally has its intake dealing with the wall, airflow experiences restriction and poor efficiency follows.Prime
The pipeline transporting tower or chilled water to a process needs to be sized so it doesn’t compromise the available pump stress. This line ought to also be sized to beat pressure drops resulting from friction losses within the pipes and fittings.
Pipe pressure drop is a perform of fluid viscosity and water move velocity. When a line is undersized, the fluid strikes through the pipes at a high velocity, which creates noise and hastens the corrosive process. An even bigger pump, which requires more energy, is required to overcome the stream resistance of an undersized pipe.
Tower Capacity Control
Three strategies can be found for controlling the capacity of a cooling tower: ·
For any tower system, tower water losses happen from three major areas:
For Extra Info
Now that you’ve got a primary understanding of course of cooling and the various tools involved, please check with our more detailed product and service information. Ought to you may have any questions or need for additional info, please do not hesitate tocontact us.
Request for Citation
Cooling Expertise, Inc. | 1800 Orr Industrial Ct. | Charlotte, NC 28213 | Cellphone: 704.596.4109 | Fax: 704.597.8697Contact Cooling Expertise|Site Map| Privacy Coverage |© 2015Cooling Know-how, Inc.