¶ Water heating controls
Table 5.1 details the “temperature factor unadjusted” and associated multiplier figures applied in DEAP based on water heating controls. Information required during site survey for selection of the factors is as follows, where a hot water cylinder is heated by a boiler or heat pump:
- Presence of a cylinder thermostat
- Separate time control of the water heating
Other factors are considered for other storage types (e.g., thermal stores, combi boilers, CPSUs) as detailed in Table 5.1. The following examples show the effect of varying time and temperature control and the effect on the temperature factor and multiplier in DEAP.
For existing dwellings, where the parameters are unknown, hot water separately timed / separate temperature control can be entered as follows:
Age bands A to I: No
Age band J onward: Yes
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Example 1: No separate time control and no temperature control
- Main space and water heating: Open fire with back boiler to radiators and cylinder
- Controls: none
- Values selected by DEAP:
- Temperature factor: 0.6 for cylinder (indirect) as per Table 5.1
- Temperature factor multiplier: 1.3 (no timer or cylinder thermostat)
Note: if an immersion is the main water heater, the multiplier is always 1 as detailed in Table 5.1 of the DEAP manual.
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Example 2: Separate time control only
- Main water and space heating: Oil boiler heating radiators and cylinder
- Controls: full programmer allowing the user to set separate times for space and for water heating. No thermostatic controls. See Here.
- Values selected by DEAP:
- Temperature factor: 0.6 for cylinder (indirect) as per Table 5.1.
- Temperature factor multiplier: As there is no cylinder thermostat, the multiplier 1.3 applies. As there is separate time control of water heating, the multiplier of 0.9 also applies. The multiplier entered in DEAP is therefore 1.3*0.9=1.17.
¶ Example 3: Temperature control only
- Main space and water heating: Gas boiler
- Controls: No time control. Has a cylinder thermostat.
- Values selected by DEAP:
¶ Example 4: Separate time and temperature control
- Main space and water heating: Oil boiler
- Controls: Programmer allowing the user to set separate times for space and for water heating. Cylinder thermostat present.
- Values selected by DEAP
- Temperature factor: 0.6 for cylinder (indirect) as per Table 5.1.
- Temperature factor multiplier: As there is a cylinder thermostat, the multiplier 1.3 does not apply. As there is separate control of water heating, the multiplier of 0.9 applies. The multiplier in DEAP is therefore 0.9.
Note: that for such systems in existing dwellings, Boiler Interlock is assumed present if there is a room thermostat and (for stored hot water systems) a cylinder thermostat. See here for further details on boiler interlock.
The following examples show systems with and without cylinder thermostats:
Example: Cylinder thermostat attached to the side of the cylinder
The cylinder thermostat is accounted for in DEAP if it provides the level of control outlined here. The following must be borne in mind:
- Does it measure the temperature of the cylinder? (YES)
- Does it switch on and off the water heating? (YES)
- Can a single target temperature be set by the user? (YES)
Example: TRV with a sensing loom attached to the side of the cylinder
This is not counted as a cylinder thermostat in DEAP:
- Does it measure the temperature of the cylinder? (YES)
- Does it switch on and off the water heating? (NO): The device is not wired back to a motorised valve, programmer, or boiler. It merely closes off the flow through the cylinder coil.
- Can a single target temperature be set by the user? (NO): The TRV doesn’t show temperatures and does not allow the user to set a temperature (e.g., 60°C).
In other instances, the water temperature of the pipework, rather than the cylinder, is being measured. Again, this does not count as a cylinder thermostat in DEAP as the cylinder temperature is not being measured.
