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start [2019/02/06 13:38] 79.246.102.94 [Introduction to WikiSIS] |
start [2019/02/07 10:17] (current) superman [==== Chemical Water Treatment and Water Conditioning ====] |
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| Many heating and cooling systems suffer from chronic problems.No matter whether they are small domestic systems or large commercial systems in hospitals or airports. | Many heating and cooling systems suffer from chronic problems.No matter whether they are small domestic systems or large commercial systems in hospitals or airports. | ||
| - | The most common problems are known to all installers and maintenance companies, like sticking thermostatic radiator valves, frequent pump failures, blocked valves, noisy boilers, leaks, increasing energy consumption, system pressure dropping and requiring frequent top-ups, black sludge and reddish-brown water. | + | Many of the symptoms are known to all installers and maintenance companies, like sticking thermostatic radiator valves, frequent pump failures, blocked valves, noisy boilers, leaks, increasing energy consumption, dropping system pressure and requiring frequent top-ups, black sludge and reddish-brown water. |
| Often these problems are seen as normal and unavoidable. Left untreated they will inevitably lead to component and in the end even complete system failure. Power flushing and chemical treatment often fail to cure the problem | Often these problems are seen as normal and unavoidable. Left untreated they will inevitably lead to component and in the end even complete system failure. Power flushing and chemical treatment often fail to cure the problem | ||
| - | and can even make the problem worse. | + | and frequently make the problem worse. |
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| - | Sick Installation Syndrome is a collective term given to water related problems in heating and cooling systems. The common symptoms of SIS are well known such as reddish, brown or black water,seized pumps, noisy or failed boilers, leaks, stuck valves, cold radiators,gurgling noises and clogged pipes. Systems showing these symptoms suffer premature component failures, higher maintenance costs and greatly reduced efficiency. | + | Sick Installation Syndrome is a collective term given to water-related problems in heating and cooling systems. The common symptoms of SIS are well known such as reddish, brown or black water, seized pumps, noisy or failed boilers, leaks, stuck valves, cold radiators, gurgling noises and clogged pipes. Systems showing these symptoms suffer premature component failures, higher maintenance costs and greatly reduced efficiency. |
| The aim of this WikiSIS is to explain why systems suffer from SIS and how the root causes can be identified and rectified. | The aim of this WikiSIS is to explain why systems suffer from SIS and how the root causes can be identified and rectified. | ||
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| - | All the symptoms described above can be linked to one thing: They are caused by corrosion and its associated effects.Corrosion comes in many forms and can be a very complex subject.In heating and cooling systems the most common form by far is [[wiki:dokuwiki|Uniform Corrosion]] | + | All the symptoms described above can be linked to one thing: They are caused by corrosion and its associated effects. Corrosion comes in many forms and can be a very complex subject. In heating and cooling systems, the most common form by far is [[wiki:dokuwiki|Uniform Corrosion]] |
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| - | The function of pressurisation is to maintain the pressure in the system between pre-determined limits.Traditionally an open header tank above the system was used to take up expanded water volume and maintain pressure.In modern systems this task is performed by a sealed expansion vessel using a bladder or membrane. A gas cushion in the vessel maintains the pressure. In larger commercial systems sometimes a compressor or pump are used to regulate the system pressure. | + | The function of pressurisation is to maintain the pressure in the system between pre-determined limits. Traditionally an open header tank above the system was used to take up expanded water volume and maintain pressure. In modern systems, this task is performed by a sealed expansion vessel using a bladder or membrane. A gas cushion in the vessel maintains the pressure. In larger commercial systems sometimes a compressor or pump are used to regulate the system pressure. |
| ==== Expansion ==== | ==== Expansion ==== | ||
| - | When water changes its temperature its volume will change.Water is not compressible and therefore in a closed heating system this expanded volume needs to be accomodated to ensure the system does not burst. In most modern heating installations this function is performed by the expansion vessel. | + | When water changes its temperature its volume will change. Water is not compressible and therefore in a closed heating system, this expanded volume needs to be accommodated to ensure the system does not burst. In most modern heating installations this function is performed by the expansion vessel. |
| The volume of expansion in a system can be calculated: | The volume of expansion in a system can be calculated: | ||
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| ==== Membrane Expansion Vessel ==== | ==== Membrane Expansion Vessel ==== | ||
| - | Membrane expansion vessels are the most commonly used especially in domestic heating installations.Typically a vessel consits of two dished ends which are connected by a rolled circumfrential seam. The membrane is clamped by this rolled connection which acts like a seal. The mebranes are usually made from an elastic rubber such as EPDM as it needs to stretch to take up expanded water from the system.The membrane divides the vessel into two chambers. One side is filled or pressurised with a gas ( Pre-charge pressure) while the other side contains the system water. As the membrane is flexible the pressure from the gas side is transferred to the water side as soon as the water enters the vessel. EPDM membranes are not gas tight and over time gas will diffuse through the membrane into the water. To ensure that this effect does not contribute directly to corrosion vessels are sometimes charged with nitrogen instead of air. However pressure loss will still occur and regular re-charging is required. | + | Membrane expansion vessels are the most commonly used especially in domestic heating installations. Typically a vessel consists of two dished ends which are connected by a rolled circumferential seam. The membrane is clamped by this rolled connection which acts as a seal. The membranes are usually made from an elastic rubber such as EPDM as it needs to stretch to take up expanded water from the system. The membrane divides the vessel into two chambers. One side is filled or pressurised with a gas ( Pre-charge pressure) while the other side contains the system water. As the membrane is flexible the pressure from the gas side is transferred to the waterside as soon as the water enters the vessel. EPDM membranes are not gas tight and over time gas will diffuse through the membrane into the water. To ensure that this effect does not contribute directly to corrosion vessels are sometimes charged with nitrogen instead of air. However, pressure loss will still occur and regular re-charging is required. |
| {{:expansion_tank.jpg?100|}}{{:cutaway_membrane_vessel.jpg?100|}} | {{:expansion_tank.jpg?100|}}{{:cutaway_membrane_vessel.jpg?100|}} | ||
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| ==== Bladder Expansion Vessel ==== | ==== Bladder Expansion Vessel ==== | ||
| Some higher quality vessels make use of a bladder instead of a membrane. The design of the bladder means that rubber does not have to stretch and therefore a more diffusion tight butyl rubber can be used. | Some higher quality vessels make use of a bladder instead of a membrane. The design of the bladder means that rubber does not have to stretch and therefore a more diffusion tight butyl rubber can be used. | ||
| - | In this case the gas pocket is between the vessel and the bladder whereas the water is inside the bladder.Due to the fact that butyl is more diffusion tight they can be charged with normal air. The construction of these vessels is often discuss shaped and the two halves are welded not crimped. The combined effect of a welded construction and the Butyl bladder is that they maintain their gas charge much longer than other vessels. | + | In this case, the gas pocket is between the vessel and the bladder whereas the water is inside the bladder. Due to the fact that butyl is more diffusion tight, they can be charged with normal air. The construction of these vessels is often discuss shaped and the two halves are welded not crimped. The combined effect of a welded construction and the Butyl bladder is that they maintain their gas charge much longer than other vessels. |
| {{:wiki:statico_sd.jpg?100|}} | {{:wiki:statico_sd.jpg?100|}} | ||
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| ==== Bag Expansion Vessel ==== | ==== Bag Expansion Vessel ==== | ||
| These are similar in construction to the bladder but for larger vessels from 140l to 5000l. | These are similar in construction to the bladder but for larger vessels from 140l to 5000l. | ||
| - | Larger vessels are usually cylindrical and stand upright. The rubber bag is suspended from the top of the vessel. The gas charge is on the outside of the bag while the water is on th inside. | + | Larger vessels are usually cylindrical and stand upright. The rubber bag is suspended from the top of the vessel. The gas charge is on the outside of the bag while the water is on the inside. |
| {{:wiki:statico_sg.jpg?100|}} | {{:wiki:statico_sg.jpg?100|}} | ||
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| ==== Expansion Vessels (Constant Pressure)==== | ==== Expansion Vessels (Constant Pressure)==== | ||
| - | There are some systems which are able to regulate the gas charge in order to keep the pressure constant no matter how much water they have taken up. In construction they are similar to a bag vessels but when the system water expands and water is forced into the vessel a relief valve will spill air out of the vessel to maintain a constant pressure. When the system cools and spills back into the system a compressor maintains the gas pressure. | + | There are some systems which are able to regulate the gas charge in order to keep the pressure constant no matter how much water they have taken up. In construction, they are similar to a bag vessel but when the system water expands and water is forced into the vessel a relief valve will spill air out of the vessel to maintain a constant pressure. When the system cools and spills back into the system a compressor maintains the gas pressure. |
| - | Mainly used for large systems it is important that they have a diffsuion tight membrane as the compressor works with air and not nitrogen. | + | Mainly used for large systems it is important that they have a diffusion tight membrane as the compressor works with air and not nitrogen. |
| {{:compresso_c10_f_connect.jpg?100|}} | {{:compresso_c10_f_connect.jpg?100|}} | ||
| - | Another type is the spill and fill system. | + | Another type is the spill and fill system. |
| These systems do not use a gas charge at all but maintain a constant system pressure by spilling the water through a solenoid actuated valve and filling it back into the system with a pump. The whole process is regulated by a pressure sensor which activates either the spill valve or the fill pump. | These systems do not use a gas charge at all but maintain a constant system pressure by spilling the water through a solenoid actuated valve and filling it back into the system with a pump. The whole process is regulated by a pressure sensor which activates either the spill valve or the fill pump. | ||
| - | The big adantage of spill and fill systems is the nearly 100% vessel acceptance which makes them best suited to compensating for very large expansion volumes.Diffusion of oxygen into the system water is still a problem with these systems as the air side of the vessel is open to atmosphere. This problem is aggravated when the vessel is also used as a degassing system. Water is constantly flushed through the vessel increasing the chance that oxygen will diffuse and enter the system. | + | The big advantage of spill and fill systems is the nearly 100% vessel acceptance which makes them best suited to compensating for very large expansion volumes. Diffusion of oxygen into the system water is still a problem with these systems as the air side of the vessel is open to atmosphere. This problem is aggravated when the vessel is also used as a degassing system. Water is constantly flushed through the vessel increasing the chance that oxygen will diffuse and enter the system. |
| {{:transfero_tv_connect_front.jpg?100|}} | {{:transfero_tv_connect_front.jpg?100|}} | ||
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| There are also tables available that help to estimate the system volume based on the duty of the boiler or chiller. But care needs to be taken if systems have unusually long pipe runs or have additional buffer tanks. These need to be added separately. | There are also tables available that help to estimate the system volume based on the duty of the boiler or chiller. But care needs to be taken if systems have unusually long pipe runs or have additional buffer tanks. These need to be added separately. | ||
| - | If the volume is estimated it is recommended to err on the high side. This may mean that the expansion vessel is larger than required but this doesn’t matter. In fact the additional capacity can be utilised to increase the water reserve Vwr. | + | If the volume is estimated it is recommended to err on the high side. This may mean that the expansion vessel is larger than required but this doesn’t matter. In fact, the additional capacity can be utilised to increase the water reserve Vwr. |
| ==== Expansion Volume ==== | ==== Expansion Volume ==== | ||
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| ==== Water Reserve ==== | ==== Water Reserve ==== | ||
| - | In addition to the expanded water the vessel also has to accomadate a reserve. The reserve ensures that when small amounts of water are lost from the system then Expansion vessel can still transfer its pressure from the gas cushion to the water side. An empty vessel cannot maintain system pressure. | + | In addition to the expanded water, the vessel also has to accommodate a reserve. The reserve ensures that when small amounts of water are lost from the system then Expansion vessel can still transfer its pressure from the gas cushion to the water side. An empty vessel cannot maintain system pressure. |
| The reserve Vwr=0.005.Vs (min. 3l or more) In accordance with EN12828 | The reserve Vwr=0.005.Vs (min. 3l or more) In accordance with EN12828 | ||
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| ==== Vessel Acceptance or Pressure Factor ==== | ==== Vessel Acceptance or Pressure Factor ==== | ||
| - | Every fixed gas charge vessel has an acceptance. The acceptance is the amount of water relative to the total vessel size it can absorb without exceeding a maximum pressure. In other words the vessel must leave room for the gas side. The more the fixed gas filling is compressed the higher the pressure in the vessel and thus the system. | + | Every fixed gas charge vessel has an acceptance. The acceptance is the amount of water relative to the total vessel size it can absorb without exceeding a maximum pressure. In other words, the vessel must leave room for the gas side. The more the fixed gas filling is compressed the higher the pressure in the vessel and thus the system. |
| - | The acceptance of a vessel is dependant on the working pressure range of the system. That is why the acceptance is determined by the pressure factor Pf.To calculate the pressure factor it is first necessary to determine the gas fill pressure P0 and the maximum or end pressure Pe. | + | The acceptance of a vessel is dependant on the working pressure range of the system. That is why the acceptance is determined by the pressure factor Pf. To calculate the pressure factor it is first necessary to determine the gas fill pressure P0 and the maximum or end pressure Pe. |
| **Pf=(pe+1)/(pe-p0)** | **Pf=(pe+1)/(pe-p0)** | ||
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| ==== Gas Fill Pressure ==== | ==== Gas Fill Pressure ==== | ||
| - | The gas fill pressure is the pressure of the gas pocket inside the expansion vessel. It is very important that this is set correctly. Most expansion vessels are supplied pre-charged to a `standard´pressure usually 1 or 1.5barg. However this pressure must always be checked before installation and adjusted to suit the specific system it is installed in. The position of the expansion vessel in the system also needs to be taken into account. | + | The gas fill pressure is the pressure of the gas pocket inside the expansion vessel. It is very important that this is set correctly. Most expansion vessels are supplied pre-charged to a `standard´pressure usually 1 or 1.5barg. However, this pressure must always be checked before installation and adjusted to suit the specific system it is installed in. The position of the expansion vessel in the system also needs to be taken into account. |
| **P0=Hst+0.3 barg** | **P0=Hst+0.3 barg** | ||
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| - | If the next biggest vessel size is selected it is possible to use the extra capacity as additional water reserve. | + | If the next biggest vessel size is selected it is possible to use the extra capacity as an additional water reserve. |
| The new water reserve can be calculated | The new water reserve can be calculated | ||
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| * Incorrect pump position | * Incorrect pump position | ||
| - | ===== Types of corrosin Monitors ===== | + | ===== Types of corrosion Monitors ===== |
| There are a number of ways that corrosion can be monitored either directly or indirectly. | There are a number of ways that corrosion can be monitored either directly or indirectly. | ||
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| Devices such as micro-bubble separators, pressure step degassers, automatic air vents etc. cannot prevent corrosion. The oxygen in the air bubbles reacts very quickly with the steel it comes into contact with.This happens faster than the separators can expell the air. If the expelled ´air´is analysed it is found to be mainly consisting of nitrogen. | Devices such as micro-bubble separators, pressure step degassers, automatic air vents etc. cannot prevent corrosion. The oxygen in the air bubbles reacts very quickly with the steel it comes into contact with.This happens faster than the separators can expell the air. If the expelled ´air´is analysed it is found to be mainly consisting of nitrogen. | ||
| - | ==== Chemical Water Treatment and Water Conditioning ==== | + | ==== Chemical Water Treatment and Water Conditioning==== |
| The condition of the fill and system water can have a marked effect on the corrosion potential. Water is a cheap and plentiful medium and is, therefore, the preferred liquid. Water isn't just water and water chemistry is very complex. It can be highly corrosive to steel and other metals if certain values such as pH and conductivity are unfavourable. | The condition of the fill and system water can have a marked effect on the corrosion potential. Water is a cheap and plentiful medium and is, therefore, the preferred liquid. Water isn't just water and water chemistry is very complex. It can be highly corrosive to steel and other metals if certain values such as pH and conductivity are unfavourable. | ||
| There are different methods of achieving the right water chemistry. The water can be either conditioned or chemically treated or both. | There are different methods of achieving the right water chemistry. The water can be either conditioned or chemically treated or both. | ||
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