Types of Central Heating Systems:
OPEN &
CLOSED
Open Central Heating System
This system have its circulating water pressure at the highest point is near atmospheric pressure because feed and expansion tank open to atmosphere. An open central heating system must have a small water tank called feed and expansion tank at the highest point in the house. Usually, the F&E tank located in the loft or roof space by the side of or above large cold water storage tank. The Expansion vessel may or may not be directly connected to a water supply. It should be about 1/3 full so that it can accommodate the expanded water. There is always air dissolved in the water without it the fish can not survive! When the water is heated in the boiler the dissolved air will separate and try to escape. This air will find its ways out through the F&E tank as it is open to the atmosphere. As air escapes water from the tank will fill that space. The water in F&E tank will be used to supply (feed) the required to fill for amount of air that escaped from the heating system. Hence there must be an arrangement to replenish the lost water. So that there will be always cold water available in the F&E tank. more
Continuous Feed Central Heating System
When the Feed & Expansion vessel is directly connected to mains cold water supply, the system will have continuous cold water supply. It is known as Continuous Feed System, meaning the cold water is always available to the heating system. Normally, the water mains supply is connected to the F&E tank via a float valve arrangement, similar to the toilet cistern. When the water level goes down the ball float will fall allowing cold water flow in and fill the tank. As water flow in, float will rise. When the pre-set level is reached the ball valve will close stopping the water supply. more
Intermittent Fill Central Heating System
If there is no water supply connection then the heating system known as Intermittent Fill Open System. As there is no automatic water supply, the heating system user or the maintenance contractor have to check the F & E tank intermittently (once or twice an year before and after winter) and top up the system. EXPANSION TANK with cold water supply BALL VALVE, EXPANSION TANK without Cold Water Supply. more
Closed Domestic Heating System
The circulating central heating water is at a pressure about 1.2 Bar, the system is closed to maintain the pressure. A closed system must have a pressurised Expansion Vessel Filling Point By Pass Valve and a Pressure Relieve Valve. more
- Filling Point: Normally, the cold water supply is taken from the house cold mains supply via a no return valve. The filling point is connected to the cold water supply by a filling loop, while filling and must be removed after filling to the required pressure. Most Combination Boiler systems are fitted as closed systems.
- By-pass Valve: When the main circuit is closed or restricted, the by pass or the bypass valve will ensure water still to circulate through the heat exchanger, preventing the boiler from over heating with water. If there is a by-pass-valve the pump's pressure will open the by-pass-valve and provide flow through the heat exchanger.
- Expansion Vessel: The vessel has a flexible neopren (synthetic rubber) diaphragm inside separating the water and Nitrogen. The nitrogen is pre charged at about 0.7 to 1 bar is on one side of the vessel. When the water in the system is heated it will expand and the diaphragm is forced out of shape into pressurized part of the vessel to accommodate the increased volume of water.
- Pressure Relive Valve: When water temperature is above 100C, it expands very rapidly and by becoming steam it can exert very high pressure. In a closed system, it can cause pipe work to burst or leak at joints. The pressure relief valve prevents damage by releasing the hot water safely. This is a SAFETY device and should be properly fitted and serviced. It is spring loaded to be normally closed and opens only when the system pressure exceeds its preset value, about 3 bar. Domestic central heating boilers
Central Heating Boilers
Gas Boilers
Solid Fuel Boilers
Oil Boilers
Open Flue Central Heating Boiler
Balanced Flue Central Heating Boiler
Fan Assisted Central Heating Boiler
Back Central Heating Boiler
Wall Mounted Boiler
Free Standing Boiler
Boiler Efficiency
SEDBUK
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Seasonal Efficiency of Domestic central heating Boilers in the UK is the average annual efficiency achieved in typical domestic conditions, making reasonable assumptions about pattern of usage, climate, control, and other factors. It is calculated from the results of standard laboratory tests together with other important factors such as boiler type, ignition arrangement, internal store size, fuel used, and knowledge of the UK climate and typical domestic usage patterns.
Gas Boilers
There are two type of gas fuel for boilers; Natural Gas or Piped Gas and Liquid Petroleum Gas (LPG).
Natural Gas Central Heating Boilers:
Given that piped natural gas is available for cooking, the natural gas boilers are the cheap boiler to install and maintain. They don't require fuel storage facilities and can be automatically controlled hence has lower running cost. more
The LPG central heating Boilers are normally adapted from the standard Natural Gas Boilers, often only require smaller main burner jets because LPG supply pressure is higher than natural piped gas. Running Cost of LPG gas boilers are similar to oil boiler. Like oil boiler the LPG gas boiler also need a storage tank and a fuel feed line from the tank to the boiler. Types of Gas Boilers Back Boiler, Free Standing Boiler,Wall Mounted Boiler, Combination Boiler, Condensing Boiler. more
List of Competent Persons who can service or repair gas central heating boilers and certify compliance to Building Regulations is maintained by CORGI for more information see http://www.trustcorgi.com
Solid Fuel Central Heating Boilers
Solid fuel boilers were the first type of domestic heating boilers used in the 50s central heating system. They were introduced by coal utilization council. However due to the need for stoking, coal lost ground to automatically controllable gas and oil. Many solid fuel boilers are now multi-fuel and can burn both wood and coal, but the heat output of the boiler depends on the type of fuel. Types of Solid Fuel Boilers, Boilers and Room Heaters, Free Standing Cookers. more
List of Competent Persons who can service or repair solid fuel boilers and certify compliance to Building Regulations is maintained by HETAS for more information see www.hetas.co.uk
The oil must be stored in an oil tank. The risk of environmental damage caused by the oil spillage from the oil tank, feeding pipe line and the boiler will need to be considered. The oil tank must be protected as much as possible from the cold weather because if the oil become very cold it becomes too thick to flow through the feeding pipe line known as waxing. Oil boiler are best in an outside boiler house ,because oil boilers make some noise and smell. An oil fired boiler can be controlled just like a gas fired boiler, all forms of automatic controls can be used. Types of Oil Boilers Free Standing Combination Boiler. more
List of Competent Persons who can service or repair oil boilers and certify compliance to Building Regulations is maintained by OFTEC for more information see www.oftec.org.uk
Central Heating Controls
Controls provide Comfort and reduce the running expenses of the central heating system. In home central heating there are three main types of controls namely Temperature, Time and Heated water Distribution.
Temperature Controls
In Home Central Heating Thermostats are used to control temperature. A Thermostat senses the change in temperature and then Open or Close electrical circuits as required, in response to the change. more
- Boiler Thermostat
The Boiler thermostat controls the temperature of the water in the Boiler. If it is set to 80 then when the water temperature reached, the thermostat will cut off power the gas valve and turn off the burners.
- Room Thermostat
The Room thermostat or Room stat is used to detect changes in the temperature of the air in the room. If the required temperature of the room stat is set to 20C then when the room's air temperature reached the set value the room stat will turn off power to the boiler and pump. This way it will maintain the comfort level and also note it stops the boiler burning gas, hence reduce the gas bill.
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Cylinder Thermostat
Cylinder thermostat or cylinder stat is fitted on to the hot water cylinder to sense the temperature of the hot water. When the set temperature is reached, depending on the system design the cylinder stat will divert the hot water from the boiler or turn off boiler and pump.
- Frost Thermostat
A Frost thermostat or Frost stat is in fact a room stat with the required temperature set at value 5 C and wired in such a way the it can over run all controls and turn on the central heating by switching on the boiler and pump even when the central heating system is switched off. Hence save the boiler and pipe work are protected from frost damage.
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Thermostatic Radiator Valves (TRVs)
A thermostatic radiator valve is fitted on a radiator in place of the hand control. It has
a temperature sensor built-in to the valve. When the room temperature reaches the set value on the valve, it mechanically closes valve.
Time Controls
The purpose of the time control is to switch ON and OFF central heating when it is required. Thus reducing the running cost of the central heating system and gas bill. Time Switches or Timers. These are simple power ON/OFF devices. They can switch the central heating ON and OFF once, twice even many times.
- Programmers
We may not want heating at the same time as the hot water. A programmer can turn on/off hot water and central heating separately.
Heated Water Distribution Controls
We require the Central Heating System to provide heating for different zones or areas (for example first floor and ground floor) at different times or at different temperatures from each other, this is accomplished by fitting distribution controls.
Zone Valve consist of a electric motorised valve and a spring. When the valve is powered the valve open and the power is off the spring closes the valve. For example we may want the bed rooms only heated an hour before we get up and then again an hour before going to bed. This can be achieved by having Zone valves on the bed rooms pipe work connected to a timer switch.
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Diverter Valve
A diverter valve can divert the heated water from the boiler into two circuits/pipe works or zones. Usually between hot water circuit and central heating circuit.