Hot Water Zone Control
Unless hot water is produced instantaneously as with a combination boiler, then each dwelling with a regular boiler system must have separately controlled circuits to the radiators and hot water storage cylinder. This creates individual space heating and water heating zones.
In dwellings with total floor areas greater than 150m2 more than one hot water circuit may be provided.
Zone Control Time Control
All dwellings must have automatic time control, so the hot water and heating systems can be turned on and off at set times by the householder.
Dwellings up to 150m require separate time control for the hot water and heating. Dwellings over 150m require separate time control for heating and hot water in each zone.
This can be achieved using either a separate timer or programmer on each hot water and heating circuit, or a full programmer with separate timing to each hot water and heating circuit.
Other options include a programmable room thermostat on each timed heating circuit plus a timeswitch on the hot water circuit or a multi-channel programmer providing full control of each timed circuit from a central point.
Hot Water Temperature Control
Each dwelling should also have control of the temperature of the hot water stored in a cylinder, whenever the hot water circuit is timed to be on. (The water heating will not work if a timeswitch or programmer has already switched it off).
In fully pumped heating systems, hot water temperature control can be provided using a cylinder thermostat and motorised valves.
In a biflo system, a three-port mid-position valve after the pump will control the flow of heated water to both the hot water and heating circuits. In a twinzone system, two, two-port zone valves are used after the pump – one to control the flow of heated water to the hot water circuit and one to control the flow to the heating circuit.
A hot water cylinder thermostat then allows the householder to set a maximum temperature for the stored hot water and automatically stops it being heated by the boiler once this temperature is reached. This saves energy by preventing stored hot water being heated to excessive temperatures.
Finally, it is also important that boiler interlock is provided, so the boiler and pump switch off when there is no demand for hot water. This is achieved by the correct wiring of the cylinder thermostat, zone valves and other heating controls.
Standards
By retrofitting a cylinder thermostat alongside a programmer, room thermostat, thermostatic radiator valves and boiler interlock, installers can meet the minimum controls standard in the revised 2010 Part L and provide householders with hot water control that will deliver energy savings, cost savings and safe hot water when its required.
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