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Plouasne
Lets see what my peers think of this, you will have to open the links (marked "Produit") to see what I am on about, never mind the French, pictures speak louder than words
Solid Fuel Boilers, and the differences between, Open vented central heating systems, and Closed or Pressurised central heating systems
There are two different types of installation of solid fuel central heating boilers, The Open Vented System commonly to be found in the UK, and the Closed System common on the continent
The open vented system relies on an expansion tank in the roof space, to keep the heating system topped up with water, and provide an expansion space for the water, when its heated
The closed system is filled with water, in the first instance with water directly from the mains, to between 1 and 11/2 bar pressure, the expansion of the water is taken up by an expansion vessel (a steel container, with a rubber "bladder", inside the vessel, pre-charged with Nitrogen gas) when the water in the system is heated, the expansion of the water is taken up in the expansion vessel, by the water compressing the nitrogen gas on the other side of the "bladder"
Both systems have good and bad points, but on the whole it is my opinion that the open system has more bad points then the closed system
The Open System
The good point of an open system, is that being open to the atmosphere the water will boil at 100°c and not above, nor will it pressurise the system to above atmospheric pressure
The bad points are, the position of the circulating pump is critical to avoid "pump over", "air entrapment", extra pipe work, a tank in the roof space, the expansion / vent pipe extending above the tank (150 mm plus an extra 50 mm, for every metre between the bottom of the boiler and the water level in the expansion tank), the risk of frost freezeing the water in the expansion tank, metal expansion tanks can be found in the suppliers in France, but they are not common and not the same as the UK type, these are manually filled, and are not supplied with a ball valve to feed top up water to the tank like in the UK to replace any water lost due to evaporation etc
An open system should be fitted with a safety valve to allow for boiling water to be discharged safely to the open atmosphere safely without causing any risk, by using a product like this
[DLMURL="http://www.thermador.fr/www/product.asp?objectid=26748&objectkind=5"]produit[/DLMURL]
The Closed System
The good points of a closed system is no extra pipe work, no tank in the roof space, which means that just about all the roof space can be used for accommodation, little risk of freezing
The bad point of a closed system, is that the expansion vessel can loose the pre-charged pressure (re-pressurise it with air from a car tyre pump) or the "bladder" can split which means a replacement expansion vessel
A closed system should be fitted with a safety valve to allow boiling water to be discharged safely to the open atmosphere safely without causing any risk, and at the same time allowing mains cold water to replace the lost boiling water, with a product like this
[DLMURL="http://www.thermador.fr/www/product.asp?objectid=26704&objectkind=5"]produit[/DLMURL]
Both systems should also have a "heat dump" (an un-valved radiator fitted to a gravity or semi gravity circulation part of the system) to allow surplus heat to escape in case of pump failure / power cut, when the boiler is on full load
Solid Fuel Boilers, and the differences between, Open vented central heating systems, and Closed or Pressurised central heating systems
There are two different types of installation of solid fuel central heating boilers, The Open Vented System commonly to be found in the UK, and the Closed System common on the continent
The open vented system relies on an expansion tank in the roof space, to keep the heating system topped up with water, and provide an expansion space for the water, when its heated
The closed system is filled with water, in the first instance with water directly from the mains, to between 1 and 11/2 bar pressure, the expansion of the water is taken up by an expansion vessel (a steel container, with a rubber "bladder", inside the vessel, pre-charged with Nitrogen gas) when the water in the system is heated, the expansion of the water is taken up in the expansion vessel, by the water compressing the nitrogen gas on the other side of the "bladder"
Both systems have good and bad points, but on the whole it is my opinion that the open system has more bad points then the closed system
The Open System
The good point of an open system, is that being open to the atmosphere the water will boil at 100°c and not above, nor will it pressurise the system to above atmospheric pressure
The bad points are, the position of the circulating pump is critical to avoid "pump over", "air entrapment", extra pipe work, a tank in the roof space, the expansion / vent pipe extending above the tank (150 mm plus an extra 50 mm, for every metre between the bottom of the boiler and the water level in the expansion tank), the risk of frost freezeing the water in the expansion tank, metal expansion tanks can be found in the suppliers in France, but they are not common and not the same as the UK type, these are manually filled, and are not supplied with a ball valve to feed top up water to the tank like in the UK to replace any water lost due to evaporation etc
An open system should be fitted with a safety valve to allow for boiling water to be discharged safely to the open atmosphere safely without causing any risk, by using a product like this
[DLMURL="http://www.thermador.fr/www/product.asp?objectid=26748&objectkind=5"]produit[/DLMURL]
The Closed System
The good points of a closed system is no extra pipe work, no tank in the roof space, which means that just about all the roof space can be used for accommodation, little risk of freezing
The bad point of a closed system, is that the expansion vessel can loose the pre-charged pressure (re-pressurise it with air from a car tyre pump) or the "bladder" can split which means a replacement expansion vessel
A closed system should be fitted with a safety valve to allow boiling water to be discharged safely to the open atmosphere safely without causing any risk, and at the same time allowing mains cold water to replace the lost boiling water, with a product like this
[DLMURL="http://www.thermador.fr/www/product.asp?objectid=26704&objectkind=5"]produit[/DLMURL]
Both systems should also have a "heat dump" (an un-valved radiator fitted to a gravity or semi gravity circulation part of the system) to allow surplus heat to escape in case of pump failure / power cut, when the boiler is on full load
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