c o n d e n s e r Glossary of Terms

c o n d e n s e r Glossary of Terms ARI Standard Conditions 85 F. water inlet; 95 F. water out; 105 F. condensing; 0.0005 fouling factor Flow Rate or Velocity The speed at which the condensing water travels through the water tubes. Fouling The effect of dirt and scale build up that impedes heat transfer. Heat of Compression The heat generated by the work of compressing the refrigerant gas. Initial Temperature Differential (ITD) The temperature difference between the condensing temperature of the refrigerant and the incoming water temperature. Laminar Flow Slow moving parallel layers of fluid without turbulence. Laminar flow is undesirable for heat transfer and is associated with low pressure drop. One Horsepower (hp) 15,000 Btu/hr @ ARI conditions One Ton 12,000 Btu/hr Pull Down Factor The extra energy that must be removed when a load must be initially cooled down from a warmer than normal starting point over a short period of time. Pumpdown The amount of liquid refrigerant storage capacity available in a vessel. Pressure Drop ( P) The difference in pressure between the incoming and leaving water pressure. P increases with velocity and turbulence. Specific Heat The measure of the ability of a fluid to hold and transfer heat. Total Heat of Rejection Refrigeration load plus the heat of compression. Turbulent Flow Random fluid flow pattern that increases heat transfer and pressure drop. 2

refrigeration cycle This cycle, is based on the physical principle that a liquid extracts heat from the surrounding area as it expands (boils) into a gas. Refrigerants like Ammonia, R 502, and R 22, are circulated through the system by a compressor, which increases the pressure and temperature of the vaporous refrigerant and pumps it into the condenser. In the condenser, refrigerant vapor is cooled by air or water until it condenses into a liquid. Refrigeration Cycle Refrigeration is defined as a process of removing heat from an enclosed space or material, and maintaining that space or material at a temperature lower than its surroundings. Cold and hot are relative terms that are not generally used when sizing heat transfer equipment. Objects and space being refrigerated become relatively colder and colder (or less and less hot) as heat is removed. Removal of heat lowers temperature and may be accomplished by the use of ice, snow, chilled water, or mechanical refrigeration. Mechanical refrigeration can be defined as an arrangement of components in a system for the purpose of transferring heat. Refrigerant is one of the key components that makes mechanical refrigeration work. A refrigerant is a chemical compound that is alternately compressed and condensed into a liquid, and then permitted to expand into a vapor or gas as it is pumped through the mechanical refrigeration cycle. The liquid refrigerant then flows to the flow control device, or expansion valve, where flow is metered and the pressure is reduced, resulting in a reduction in temperature. You can understand this concept if you think of carbon dioxide, as a natural refrigerant. When CO 2 is released from a high pressure fire extinguisher cylinder to atmosphere, it cools forming ice crystals, just like a like a halocarbon refrigerant, but less efficient. After the expansion valve, refrigerant flows into the lower pressure evaporator, where it boils by absorbing heat from the space being cooled, and changes into a vapor. The cycle is completed when the compressor draws the refrigerant vapor from the evaporator and, once again, compresses the gas so that the cycle can continue. The condenser is another important component in the refrigeration system. It transfers heat from a place where it is not wanted to a place where it is unobjectionable, from the refrigerant to a medium (water or air) which can absorb it and move the unwanted heat to its final point of disposal. The medium of heat transfer (usually air, water, or a combination of air and water) helps us to understand and identify the various types of condensers. Air cooled and water cooled are two types of condensers. Air is the medium of heat of exchange in air cooled condensers and water in water cooled condensers. 3

p e rf o rmance factors Coaxial are designed around a single refrigerant tube welded inside a single outer tube. The assembly is coiled to fit into tight spaces. SCH coaxial SCS coaxial SPC coaxial SCS-N coaxial marine service This booklet concentrates on water cooled condensers. There are four basic types: the thin profile tube in tube, the very versatile and powerful horizontal shell and tube, the compact and economical shell and coil, and Standard s latest advance in heat transfer technology: the plate heat exchanger. It is small in size, light weight, and designed for high efficiency and low fouling. Standard is the leading producer of all the basic types of water cooled condensers: Tube in Tube are designed around cleanable, enhanced surface copper water tubes inside a stacked series of steel or copper refrigerant tubes. The Tube in Tube narrow width design is ideal for retrofit in slender package applications. ELT steel shell, copper tube KHX steel shell, copper tube Shell and Tube are designed around a bundle of cleanable, enhanced, surface copper water tubes located inside a large steel refrigerant shell. SST Standard s best selling model HSE horizontal, super efficient HP high water pressure CA stainless steel tube MSE marine service AMC ammonia Shell and Coil are designed around an extended surface area copper coil sealed in a steel refrigerant shell. The sealed construction design provides adequate refrigerant pumpdown capacity for applications where either a compact or high pressure condenser is called for. VSE vertical, super efficient Performance Factors There are five basic factors that determine the performance of all water cooled condensers. The factors are: flow rates or velocity, pressure drop, fouling, types of fluids (refrigerants, as well as cooling fluids), and Temperature Differential or TD. Flow Rates Flow rate or velocity is the speed at which water flows through the condenser. There is an ideal rate of flow through the condenser for any fluid. Flow can be either laminar or turbulent. 4

p e rf o rmance factors; p re s s u re dro p Laminar flow is undesirable because it has a streamline pattern, with the coolant flowing in layers parallel to the wall of the heat exchange tube. The layer of fluid adjacent to the tube wall is like a very slow moving film. This layer acts as an insulator, impeding heat transfer to the layers nearest the center of the tube. Pressure Drop Pressure drop, the second factor in heat exchange performance, increases with flow or velocity due to turbulence. Pressure drop is defined as the loss of pressure due to friction. In a water cooled condenser, it is the pressure difference between the entering and leaving water sides. Pressure drop increases with flow or velocity. At excessive flow rates, the amount of pumping energy expended to overcome pressure drop will be greater than the increase in heat transfer efficiency. It is also important to remember that the maximum pressure drop and flow for any condenser application is related to the capacity of the selected water pump. Turbulent flow creates random movement and substantially increases the rate of heat transfer because it has no insulating layers. The rate of heat transfer increases with velocity up to a point. The ideal condition exists when there is sufficient velocity to obtain turbulent flow, which optimizes heat transfer. High pressure drop and excessive flow can create another problem for the water cooled condenser: impingement corrosion. Impingement corrosion, caused by high velocity and turbulence, can dramatically shorten equipment life, sometimes to a period of only months. 5

e rf o rmance factors; fouling; type of fluid; re f r i g e r a n t Type of Fluid Heat exchanger performance is also governed by a forth factor, the type of fluid in the system. The ability of a fluid to absorb heat is described by its specific heat. The specific heat of water is one. The glycols and brines used in many applications are less efficient with specific heats less than one. Fouling Fouling is another key factor governing condenser efficiency and longevity. Most water contains dissolved carbonates, silicates and dirt, that can coat the water side of the refrigerant tube surface. Refrigerant oil coats the refrigerant side of the refrigerant tube. Fouling deposits act as insulators. They inhibit heat transfer between water and refrigerant, and between refrigerant and water. There are two things that can be done to minimize the effects of fouling. First, water side fouling can be controlled with water treatment and periodic cleaning of the system. Secondly, since some degree of fouling is inevitable, reliable manufactures like Standard rate their condensers with a built in fouling factor to assure full rated capacity under normal operating conditions. Most of Standard s condensers are rated with a fouling factor of 0.0005 F 2 (hr) ( F)/Btu. It is important to remember that certain fluids and refrigerants are corrosive to copper or steel condensers. Most models are designed for use with fresh water or glycols and halocarbon refrigerants. For seawater or chlorine brines, you must specify condensers with cupronickel tubes and tubesheets. For high sulphur waters or ammonia refrigerant, carbon or stainless steel is required. Be sure to call Standard s sales department before you make a selection if you are dealing with unusual or corrosive fluids. Refrigerant The refrigerant is another fluid that must be taken into consideration. This is due to the fact that Standard s published capacity data is based on ARI standard 450 87, using R 22 at 105 F condensing temperature. Different refrigerants will yield different capacities under the same conditions. 6

t e m p e r a t u re diff e re n t i a l ; sizing a condenser high back pressure system, it s safe and convenient to size by nominal horsepower. Temperature Differential The Initial Temperature Differential, ITD, is the fifth factor that affects performance. The condensing ITD, is the difference between the incoming water temperature and the condensing temperature. The greater the ITD, the greater the rate of heat exchange that can take place in a given period of time. To understand ITD, think of two houses, each with an inside temperature of 70 F. However, one house has an outside temperature of 0 F; the other has a 35 F outside temperature. It will take much more heat to replace the heat lost through the walls when 0 F is the outside temperature. Temperature difference, or TD, can also be illustrated as the driving force that pushes heat across the heat exchange barrier. The larger the TD, the greater the force and the faster heat is exchanged. Now you are familiar with the five factors that affect heat transfer: flow rate, pressure drop, fouling, types of fluids, and temperature differential. Let s put these factors to work in learning how to select and size a condenser. Sizing a Condenser A condenser is properly sized when its capacity to transfer heat from the system is equal to the cooling load, plus the extra heat generated by the work of compressing the gas. This total is called the Total Heat of Rejection. There are some proven rules of thumb for sizing that can get you in the ball park. For air conditioning or a Sizing by Nominal hp Under General Data in our condenser catalog, you ll note that most Standard condensers are rated by nominal horsepower in a fouled condition. An SST 750A will provide 7.5 hp after being in use for some time and fouled. It will provide 12 hp when new. This means that there is additional capacity available when new. It is often possible to size a condenser by matching nominal horsepower to compressor horsepower in commercial or high temperature systems when manufacturer s information is not available. You can estimate the total heat of rejection by multiplying motor horsepower by three thousand to find the heat of compression, and then adding the load. In the following example, the nominal horsepower of the compressor will match the nominal tonnage of the air conditioning system and the Total Heat of Rejection. A 15 horsepower compressor in a 15 ton system, produces 225,000 Btu per hour total heat of rejection. That s 3,000 Btu for heat of compression, plus 12,000 Btu of load for each ton. Heat of Compression: 15 hp x 3000 Btu/hp = 45,000 Btu Evaporating Capacity: 15 ton x 12,000 Btu/hr = 180,000 Btu Estimated total heat of rejection = 225,000 Btu 7

sizing a condenser Once you have determined the total heat of rejection and the corresponding condenser capacity, you are ready to put Standard performance data to work. Looking closely at the waterflow ratings in the condenser catalog, you will note that data is provided for both tower and city. City means operating conditions where incoming municipal water is at 75 F and condensing temperature is 105 F, a 30 F ITD. requirement, and read the corresponding flows and gpm. An SST 1500A (2 pass tower) will provide the desired performance with 44 gpm and an ITD of 20 F or, 24 gpm and an ITD of 30 F. You will notice that models through an SST 4505A would also perform well. However, they will cost much more. An SST 1500A, 15 hp condenser, is the ideal choice since the Total Heat of Rejection required falls in the middle of its performance window. However, matching nominal horsepower can result in over sizing for low and very low temperature applications, and over sizing costs more. While sizing by matching nominal compressor horsepower to condenser horsepower is often accurate, the best practice is to begin by calculating the actual total heat of rejection. Tower means cooling tower supply water, which is normally at 85 F and condensing temperature is again at 105 F, a 20 F ITD. Sizing by Total Heat of Rejection To accurately find the total heat of rejection, multiply 3.4 times the motor watts at operating conditions to determine the heat of compression and add the evaporating load. Begin with the compressor manufacturer s performance data. It will tell you the power in watts and the evaporating capacity for each compressor model. In looking at the capacity data for the SST you will note that total heat of rejection, gpm, and pressure drop in psi are provided for various Initial Temperature Differentials from 15 F to 40 F. You can now look for a Total Heat of Rejection that exceeds the 225,000 Btu 8

p u m p d o w n ; p u l l d o w n For example, total heat of rejection for a system with the following performance characteristics would be calculated like this: Compressor Performance (manufactures published data) 110 F condensing temperature 10 F evaporating temperature 75 F incoming water temperature Refrigerant R 22 Evaporating Watts = 6500 Evaporating Load: 40,200 Btu watts x 3.4 = Heat of Compression Heat of Compression + Evaporating Load = Total Heat of Rejection 6500 watts x 3.4 = 22,100 Btu Heat of Compression = 22,100 Btu Evaporating Load = 40,200 Btu Total Heat of Rejection = 62,300 Btu Although the refrigerant is R 22, the condensing temperature is not the same as the ARI standard of 105 F which means that the Standard catalog can not be used to make your selection. In this case, you can call your local representative or one of Standard s sales engineers for a computer generated selection. In this case, a SST 200A (4 Pass) will perform with 7.27 gpm and a pressure drop of 1.75 psi. The 62,300 Btu load would normally require a 5 hp (SST 500A) at the usual ARI rating point of 85 F, 105 F condensing, and R 22. The SST 500A would work in this application although it is three times larger than necessary. You should always compare performance data when your application conditions vary from normal operating conditions, in order to arrive at the best match for your application. Other Considerations Remember to consider all of the factors that affect performance; not just flow rates, TD, fouling, pressure drop, and types of fluid, but also the pull down factor and pumpdown capacity. Higher loads under pull down conditions call for an additional ten percent capacity if a very short pull down time is required, or if slight increases in head pressure or water flow are unacceptable. In a 66,000 Btu system, you must add an additional 6,600 Btu for a total condenser sizing requirement of 72,600 Btu. Pumpdown requirements relate to the amount of refrigerant storage available in a condenser during operation or servicing. A pumpdown capacity of three pounds of refrigerant per ton of capacity will be sufficient for most systems. However, commercial refrigeration systems may require up to seven pounds per ton because of long refrigerant lines. Standard rates its condenser pumpdown capacities at 80% of volume. In addition to selection tables, you can also utilize Standard s computerized selection service. Just complete the information in our heat exchanger specification form and mail or fax it to our sales engineering department, or sales representative s office. Standard Refrigeration is always happy to build customized condensers if an application calls for a modified condenser with additional valves, water or refrigerant fittings, special mounting brackets, or other accessories. 9

2050 North Ruby Street Melrose Park, Illinois 60160-1133 708 345 5400 fax 345 3513 w w w. s t a n r e f. c o m Copy this page and fax it to: Standard Refrigeration Company Attn: Customer Service 708-345-3513 or via the World Wide Web www.stanref.com/cust_serv/condenser_req.html specification data Name Address Company City State Zip Phone Fax Performance inlet fluid temperature F condensing refrigerant temperature F fouling factor (.0005 ARI standard) if THR Btu/hr refrigerant pressure drop psi Fluid Circulated water % propylene glycol % sodium chloride (NaCl) % If other, specify properties at inlet temperature specific gravity thermal conductivity ethylene glycol % calcium chloride (CaCl2) % other % viscosity (centipose) specific heat Construction size: width length height materials: shell tube connections: refrigerant inlet refrigerant outlet specify ids, fpt, flange or flare Application fluid inlet fluid outlet 10

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