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Heating Controls

 Heating Controls Questions Answers: 

Space-Heating Zones

 

Water-Heating Zones

Water Temperature Control

Timeswitch/Programmer

Room thermostat/Programmable

       

Cylinder thermostat                                                                                    

Motorised valves

Thermostatic radiator valves 

Frost protection

 

Weather compensator

Delayed Start

Pipe Thermostats

Radio controls


 

 

Boiler Interlock






 
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zoned-central-heating-system



Space-Heating Zones

Dwellings with a total usable floor area up to 150m2 require at least two space-heating zones with independent temperature control, one assigned to the living area.Dwellings with a total usable floor area greater than 150m2 require at least two space-heating zones, each having separate timing and temperature control.Single-storey open-plan dwellings with a living area greater than 70% of the total floor area do not require zoning.Replacement systems should be dealt with as for new-build except where the boiler only is replaced; then reasonable provision would be to control as one zone. 

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Water-Heating Zones
All dwellings require separate hot water service zones in addition to space-heating zones. Separate hot water zones are not required if hot water is produced instantaneously, as with combination boilers.
Time control of space and water heating requires:
        • A full programmer with separate timing to each circuit
         
 Two or more separate timers providing control to each circuit; or
• Programmable room thermostat(s) to the heating circuit(s), with separate timing of hot water

For Dwellings with total usable floor areas greater than 150m2, timing of the separate space-heating zones can be achieved by any of the following:
 
• Multiple heating zone programmers
• A single multi-channel programmer
• Programmable room thermostats
• Separate timers to each circuit
 A combination of programmable room thermostats and separae timers to each circuit Where hot water is produced instantaneously, time control is only required for space-heating zones.Temperature control of space heating - separate temperature control of zones should be provided using any of the following:
• Room or programmable room thermostats in all zones
• Room thermostat or programmable room thermostat in the main zone and individual radiator controls on all radiators in other zones
• A mixture of the above   

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Temperature Control of Hot Water Service System
Domestic hot water systems should have a cylinder thermostat and a zone valve, or a three-port valve to control the temperature of stored hot water.
In dwellings with total floor areas greater than 150m2, it could be reasonable to provide more than one hot water circuit, each with separate timing and temperature controls by means of any of the following:
          • Multiple heating zone programmers
          • A single multi-channel programmer
        • Separate timers to each circuit

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Timeswitch/Programmer
Ensure that the intended model is suitable - timeswitches can only switch one circuit, e.g. heating for combination boilers whilst programmers can switch two circuits, e.g. heating and hot water. Multi-channel programmers may be able to switch three circuits or more and are normally used where a house is divided into several heating zones.
All the timer and programmer types are available either in daily (1 day), weekday/weekend (5day/2day) or weekly (7day) cycle format.

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Room Thermostat/Programmable Thermostat
A temperature sensing device used to maintain the air temperature within a room to a set level whenever the heating circuit is timed to be on.The best location is in a room which is always heated and is the slowest to heat up, lounge or master bedroom when the heating is split into two zones. It should be set to the desired temperature for that room and TRVs in any other rooms should be set to prevent local overheating. Room thermostats should not be fitted in rooms with secondary forms of heating, such as open fire or stove.
Since room thermostats operate by sensing the air temperature, it is important that they are in a clear flow of air that is representative of the room temperature. Do not locate in areas such as corners, behind furniture units or curtains and in areas where the air-flow will pick up extraneous heat such as close to TVs, computers, wall lights and other heat generating devices, or direct sunlight. Also avoid any cooling position such as outside walls and ensure that no draughts are directed on to or into the thermostat from any direction.Room thermostats should be fitted in an area where they can easily be read and adjusted. Thermostatic Radiator Valves (TRVs) should not be installed in the same room as the room thermostat.
Programmable Room Thermostats operate in the same manner as room thermostats and the same positioning rules etc. apply. They have the additional feature of being able to provide different temperatures at different times of the day or night.Some models have a remote temperature sensing availability to overcome any conflict between the ideal temperature sensing and accessibility locations.

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Cylinder Thermostat
A temperature sensing device used to control the temperature of the stored hot water within the cylinder whenever the hot water circuit is timed to be on.They should be fitted between a quarter and a third of the way up the cylinder unless otherwise directed by the manufacturer. It is important to have a good, clean contact with the metal cylinder wall when fitting a strap-on thermostat.The recommended temperature for storage of domestic hot water is between 60oC and 65oC, being high enough to kill off the harmful bacteria in the water, yet low enough to deter the production of scale.Since storage cylinders are quite likely to be located within a hotpress, it is important to make the Cylinder Thermostat as accessible as possible. 

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Motorised Valves
Electrically operated valves to permit, prevent or direct the water flow within a system.Both 2 and 3 port valves are commonly used and the choice depends on the application, pipework layout and preference.3 port valves are suitable for providing separate heating and hot water circuits. There are two types of 3 port valves, one type only diverts the full flow of water whilst the other provides a mid position so that shared flow to both hot water and heating is possible. For more than one heating zone, in addition to a hot water zone, use a separate 2 port valve for each additional zone. Auxiliary switches on valves are wired to switch the boiler/pump off when there is no demand for heat or hot water.
Thermostatic Radiator Valves (TRVs)
Thermostatic valves to control the flow of water through individual radiators.They should be installed together with a room thermostat to provide boiler interlock.

Frost Protection (Air and Pipe Thermostats)
A pipe thermostat is a device set to detect low air temperature and switch on protection to avoid frost damage. It is usually arranged to over-ride all other controls.Where both air and pipe thermostats are used, the electrical contacts should be wired in series from a permanent live supply that is not switched by timeswitch/programmer or thermostats. i.e. protection needs to be available 24 hours a day. Note that all new outside boilers should include their own frost protection.

Weather Compensator or Other Units with External Sensors
Where a unit includes an external sensor it is important to position the sensor on a north facing wall, out of direct sunlight and away from other heat sources to avoid complaints of under heating.

Delayed Start/Optimum Start
Delayed start feature will only reduce heat-up times during mild weather to avoid heating the dwelling too early and so save energy. Optimum start feature may reduce or increase the heat-up times dependant on the weather in order to ensure the dwelling reaches its desired temperature at the required time.

Pipe Thermostats
A sensor measuring the temperature of water flowing through a pipe. Normally used in conjunction with other controls such as a frost thermostat or boiler management control sets or for solid fuel systems.

Radio Frequency Controls (RF)
These controls are battery operated controls designed to transmit and receive signals from (room thermostat) to switch the boiler and pump by radio signals through the air to avoid the need for normal costly electrical wiring.
Boiler Interlock
For both new-build and replacement systems, boiler-based systems require boiler control interlock arrangements that ensure the boilers and pumps are switched off when there is no demand for either heating or hot water. Thermostatic Radiator Valves alone do not provide interlock.

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