84 Questions
EASY What type of systems are associated with chilled water-cooling systems and hot water heating systems?
Closed loop systems
What is the purpose of a chiller in a closed loop system?
To cool the water
What type of fluids are used in closed loop systems?
Water, glycol solutions, or salt brines
Why is corrosion less likely to occur in chillers compared to boilers or condensers?
Because chillers operate at lower temperatures
What is the primary cause of corrosion in chillers?
Galvanic action
What is a characteristic of closed loop systems?
They recirculate the working fluid with minimal make-up water
What is a common issue in closed loop cooling and heating systems?
Water quality issues
What type of corrosion occurs when dissimilar metals are in physical contact with each other and exposed to a fluid?
Galvanic corrosion
Which of the following can accelerate corrosion in heat exchangers?
High fluid flow
What is the purpose of adding chemicals to the cooling system?
To eliminate corrosion
What type of corrosion occurs when one particular metal is preferentially attacked?
Selective leaching
What is the benefit of sodium nitrite in cooling systems?
It forms a protective iron oxide surface film
What is the purpose of installing heat exchangers in a specific way?
To make cleaning easier
What happens when fluid flow is too low in heat exchangers?
Deposits form
What is the purpose of periodic cleaning of heat exchangers?
To keep heat exchangers free of deposits
What type of corrosion inhibitor is molybdate?
Mixed metallurgy corrosion inhibitor
What is the estimated material cost of re-tubing a chiller?
25-30% of a new chiller
What happens when a metal gives off ions in a galvanic cell?
It wastes away and fails
What is the approximate cost to replace a chiller with a capacity of 850 tonnes?
$97 500
What is a common problem in heat exchangers, especially if there is fluid leaking into the system?
Solids fouling
What is the purpose of a bypass line with a filter in a closed cooling system?
To maintain a low level of suspended impurities
What is the maximum percentage of make-up water that should be added to a closed loop system per day?
0.1%
What is the result of water freezing in a closed cooling system?
It expands by 9%
What is the purpose of freeze stats in chillers?
To prevent freezing
What type of solution is used to prevent freeze-up in HVAC cooling coils?
Water and glycol
What is the risk in hot water closed-loop systems?
Scale formation, deposition, fouling, and corrosion
What is the risk of freezing in hot water heating systems?
In both vestibule heaters and air handling unit-heating coils
What is the purpose of using glycol and water solutions in heating systems?
To prevent freezing
MEDIUM What happens to the metal that gives off ions in a galvanic cell?
It wastes away and fails
Why is it important to keep heat exchangers free of deposits?
To reduce corrosion
What is the effect of high fluid flows in heat exchangers?
Erosion can occur at piping turns
What is the purpose of adding sodium nitrite to cooling systems?
To reduce corrosion
What type of corrosion occurs when one particular metal is preferentially attacked?
Selective leaching
What is the benefit of using molybdate corrosion inhibitors in mixed metallurgy systems?
It provides the best corrosion protection
Why is it important to install heat exchangers in a specific way?
To make cleaning easier
What happens when fluid flow is too low in heat exchangers?
Sediments can drop out and deposit on metal surfaces
What is the purpose of periodic cleaning of heat exchangers?
To reduce corrosion
What is the effect of excessively high or low fluid flows on corrosion?
It accelerates corrosion
What is the primary benefit of using a closed loop system in cooling and heating applications?
Reduce the risk of corrosion and scaling
Which of the following is NOT a common issue in closed loop cooling and heating systems?
Electrical short circuits
What is the primary cause of corrosion in chillers?
Galvanic action
What is the purpose of a pump in a closed loop chilled water system?
To circulate the chilled water through the system
What type of fluid is commonly used in closed loop heating systems?
Glycol solution
What happens to the chilled water in a closed loop system after it absorbs heat from the process fluid?
It is circulated back to the chiller to reject the heat
What is the purpose of the light blue lines in Figure 1?
To show the flow of chilled water
What is a common issue in both closed loop cooling and heating systems?
Corrosion
What is the primary method to prevent solids fouling in heat exchangers?
Using a slipstream filter
What is the approximate cost of replacing a chiller with a capacity of 1750 tonnes?
$160 000
What is the consequence of biological fouling in heat exchangers?
Decreased heat transfer efficiency and promotion of corrosion
What is the purpose of adding dispersants in cooling systems?
To keep dead biological matter in suspension
What is the risk of freezing in cooling systems that operate at higher temperatures?
High risk
What is the purpose of using glycol and water solutions in HVAC cooling coils?
To prevent freezing
What is the effect of water freezing in a closed cooling system?
It expands by about 9% and can rupture or damage pipes and equipment
What is the purpose of freeze stats in chillers?
To protect the chiller evaporator coil from freezing damage
What is the risk in hot water closed-loop systems?
Fouling and corrosion
What is the maximum percentage of make-up water that should be added to a closed loop system per day?
0.1%
HARD Why is galvanic corrosion more likely to occur in chillers?
Because chillers use dissimilar metals in contact with each other
What is the primary benefit of using a closed loop system in cooling and heating applications?
To minimize make-up water
What is the consequence of solids fouling in heat exchangers?
Reduced heat transfer efficiency
Why is corrosion less likely to occur in chillers compared to boilers or condensers?
Because chillers operate at low temperatures
What is the primary method to prevent scaling in heat exchangers?
Using a water softener
What is the primary cause of biological fouling in heat exchangers?
Microbial growth
What is the purpose of the pump in a closed loop chilled water system?
To circulate the water
What is the consequence of high fluid flows in heat exchangers?
Erosion of the heat exchanger surface
What is the primary mechanism by which sodium nitrite protects ferrous metals from corrosion?
By forming a protective iron oxide surface film
What is the primary reason why molybdate is a more effective corrosion inhibitor than sodium nitrite in mixed metallurgy systems?
Because it provides better corrosion protection for copper and copper alloys
What is the primary consequence of selective leaching in cooling systems?
Tube failure due to the preferential attack of one metal
What is the primary reason why it is important to install heat exchangers in a specific way?
To make it easier to clean the heat exchanger
What is the primary effect of high fluid flows on heat exchangers?
It strips protective chemical coatings from pipe and heat exchanger surfaces
What is the primary benefit of using a closed loop system in cooling and heating applications?
It reduces the risk of corrosion
What is the primary reason why scaling is a lesser concern in closed cooling systems compared to open cooling systems?
Because system losses and raw water make-up are minimal
What is the primary reason why it is important to periodically check and adjust nitrite concentrations?
To ensure that the nitrite concentration is within the recommended range
What is the primary consequence of biological growth within cooling systems?
It increases the formation of deposits
What is the purpose of using a brine solution of water and calcium chloride or glycol in refrigeration systems that use closed cooling loops?
To prevent freezing
What is the primary reason why molybdate is more effective at protecting brass than sodium nitrite?
Because it provides better corrosion protection for copper and copper alloys
What is the estimated cost of re-tubing a chiller with a capacity of 2650 tonnes?
$65 000
What is the primary consequence of galvanic corrosion in heat exchangers?
It leads to the failure of the heat exchanger
What is the primary method to prevent solids fouling in heat exchangers?
Using a bypass line with a filter
What is the consequence of not treating the make-up water in cooling systems that operate at higher temperatures?
Scaling
What is the primary benefit of using a closed loop system in cooling and heating applications?
To minimize system losses and raw water make-up
What is the purpose of adding biocides in cooling systems?
To remove biological fouling
What is the risk associated with hot water closed-loop systems?
Scaling
What is the purpose of using glycol and water solutions in heating systems?
To prevent freezing
What is the consequence of not using demineralized, distilled, or reverse osmosis water in cooling systems that operate at higher temperatures?
Scaling
Study Notes
Closed Loop Systems
- Closed loop systems are associated with chilled water-cooling systems, hot water heating systems, and internal combustion engine cooling systems.
- These systems recirculate the working heat transfer fluid and use minimal amounts of make-up water.
- The heat exchange fluids may be treated water, glycol solutions, or salt brines.
Chillers
- Chillers are heat exchangers that cool fluids.
- The process fluid (chilled water or brine) is continuously circulated in a closed loop.
- The chiller may use refrigerant or some other cold process fluid to chill the water.
Water Quality Issues
- Closed loop cooling and heating systems both suffer from water quality issues, including:
- Corrosion
- Solids fouling
- Scaling
- Biological fouling
Corrosion
- Corrosion can occur due to galvanic action, especially when dissimilar metals are in contact with each other and exposed to a fluid.
- Corrosion can also occur wherever deposits form, making it important to keep heat exchangers free of deposits.
- Corrosion inhibitors, such as sodium nitrite and molybdate, can be used to eliminate corrosion.
- Sodium nitrite is an anodic corrosion inhibitor that forms a protective iron oxide surface film, but it is not effective for copper or copper alloys.
- Molybdate inhibitors provide the best corrosion protection for systems of mixed metallurgy.
Fouling
- Solids fouling can occur due to fluid leaking into the system, corrosion, scaling, and biological growth.
- Strainers or filters can be used to avoid fouling, and should be cleaned or replaced about once a year.
- Bypass lines with filters can also be used to maintain a low level of suspended impurities.
Scaling
- Scaling can be an issue in closed cooling systems, especially at higher temperatures.
- Make-up water should be demineralized, distilled, or reverse osmosis to prevent scaling.
- Make-up water should never exceed 0.1% of the system capacity per day, or 2% of the system capacity per month.
Biological Fouling
- Biological fouling can occur if leaks occur, and can decrease heat transfer efficiency and promote corrosion.
- Biocides and dispersants can be used to remove biofilms and prevent biological fouling.
Freezing
- Water can freeze if the refrigerated medium is below 0°C, which can cause damage to pipes, tubes, and equipment.
- Chillers are equipped with freeze stats to prevent freezing damage.
- Glycol solutions can be used to prevent freeze-up in HVAC cooling coils and refrigeration systems.
Heating Systems
- Hot water closed-loop systems are similar to those used for chilled water, but operate at higher temperatures, which can magnify the risks of scale formation, deposition, fouling, and corrosion.
- The treatment and monitoring of these conditions is similar to those used for closed cooling systems.
- Hot water heating systems may also be susceptible to freezing, especially in vestibule heaters and air handling unit-heating coils.
Closed Loop Systems
- Closed loop systems are associated with chilled water-cooling systems, hot water heating systems, and internal combustion engine cooling systems.
- These systems recirculate the working heat transfer fluid and use minimal amounts of make-up water.
- The heat exchange fluids may be treated water, glycol solutions, or salt brines.
Chillers
- Chillers are heat exchangers that cool fluids.
- The process fluid (chilled water or brine) is continuously circulated in a closed loop.
- The chiller may use refrigerant or some other cold process fluid to chill the water.
Water Quality Issues
- Closed loop cooling and heating systems both suffer from water quality issues, including:
- Corrosion
- Solids fouling
- Scaling
- Biological fouling
Corrosion
- Corrosion can occur due to galvanic action, especially when dissimilar metals are in contact with each other and exposed to a fluid.
- Corrosion can also occur wherever deposits form, making it important to keep heat exchangers free of deposits.
- Corrosion inhibitors, such as sodium nitrite and molybdate, can be used to eliminate corrosion.
- Sodium nitrite is an anodic corrosion inhibitor that forms a protective iron oxide surface film, but it is not effective for copper or copper alloys.
- Molybdate inhibitors provide the best corrosion protection for systems of mixed metallurgy.
Fouling
- Solids fouling can occur due to fluid leaking into the system, corrosion, scaling, and biological growth.
- Strainers or filters can be used to avoid fouling, and should be cleaned or replaced about once a year.
- Bypass lines with filters can also be used to maintain a low level of suspended impurities.
Scaling
- Scaling can be an issue in closed cooling systems, especially at higher temperatures.
- Make-up water should be demineralized, distilled, or reverse osmosis to prevent scaling.
- Make-up water should never exceed 0.1% of the system capacity per day, or 2% of the system capacity per month.
Biological Fouling
- Biological fouling can occur if leaks occur, and can decrease heat transfer efficiency and promote corrosion.
- Biocides and dispersants can be used to remove biofilms and prevent biological fouling.
Freezing
- Water can freeze if the refrigerated medium is below 0°C, which can cause damage to pipes, tubes, and equipment.
- Chillers are equipped with freeze stats to prevent freezing damage.
- Glycol solutions can be used to prevent freeze-up in HVAC cooling coils and refrigeration systems.
Heating Systems
- Hot water closed-loop systems are similar to those used for chilled water, but operate at higher temperatures, which can magnify the risks of scale formation, deposition, fouling, and corrosion.
- The treatment and monitoring of these conditions is similar to those used for closed cooling systems.
- Hot water heating systems may also be susceptible to freezing, especially in vestibule heaters and air handling unit-heating coils.
Closed Loop Systems
- Closed loop systems are associated with chilled water-cooling systems, hot water heating systems, and internal combustion engine cooling systems.
- These systems recirculate the working heat transfer fluid and use minimal amounts of make-up water.
- The heat exchange fluids may be treated water, glycol solutions, or salt brines.
Chillers
- Chillers are heat exchangers that cool fluids.
- The process fluid (chilled water or brine) is continuously circulated in a closed loop.
- The chiller may use refrigerant or some other cold process fluid to chill the water.
Water Quality Issues
- Closed loop cooling and heating systems both suffer from water quality issues, including:
- Corrosion
- Solids fouling
- Scaling
- Biological fouling
Corrosion
- Corrosion can occur due to galvanic action, especially when dissimilar metals are in contact with each other and exposed to a fluid.
- Corrosion can also occur wherever deposits form, making it important to keep heat exchangers free of deposits.
- Corrosion inhibitors, such as sodium nitrite and molybdate, can be used to eliminate corrosion.
- Sodium nitrite is an anodic corrosion inhibitor that forms a protective iron oxide surface film, but it is not effective for copper or copper alloys.
- Molybdate inhibitors provide the best corrosion protection for systems of mixed metallurgy.
Fouling
- Solids fouling can occur due to fluid leaking into the system, corrosion, scaling, and biological growth.
- Strainers or filters can be used to avoid fouling, and should be cleaned or replaced about once a year.
- Bypass lines with filters can also be used to maintain a low level of suspended impurities.
Scaling
- Scaling can be an issue in closed cooling systems, especially at higher temperatures.
- Make-up water should be demineralized, distilled, or reverse osmosis to prevent scaling.
- Make-up water should never exceed 0.1% of the system capacity per day, or 2% of the system capacity per month.
Biological Fouling
- Biological fouling can occur if leaks occur, and can decrease heat transfer efficiency and promote corrosion.
- Biocides and dispersants can be used to remove biofilms and prevent biological fouling.
Freezing
- Water can freeze if the refrigerated medium is below 0°C, which can cause damage to pipes, tubes, and equipment.
- Chillers are equipped with freeze stats to prevent freezing damage.
- Glycol solutions can be used to prevent freeze-up in HVAC cooling coils and refrigeration systems.
Heating Systems
- Hot water closed-loop systems are similar to those used for chilled water, but operate at higher temperatures, which can magnify the risks of scale formation, deposition, fouling, and corrosion.
- The treatment and monitoring of these conditions is similar to those used for closed cooling systems.
- Hot water heating systems may also be susceptible to freezing, especially in vestibule heaters and air handling unit-heating coils.
Learn about closed loop systems, commonly used in cooling and heating systems, which recirculate heat transfer fluids and minimize impurities.
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