This section describes properties of different commonly found types of electric heating and how they are specified in DEAP assessments. Amongst these are storage heaters, direct electric heaters, and heaters which combine storage and direct heating.
Old storage heaters consist of a thermally massive material – such as clay bricks or ceramic blocks within the heater – which can be heated by an embedded electrical element. The principle of operation is as follows: at night electricity is passed through the element thereby heating the thermal mass. This stored heat is slowly released during the following day.
Typically, they have two controls:
If the following day is likely to be cold, then the input dial is set high so that a lot of heat is stored overnight for use the following day. If heat is required throughout the day, then the output dial is set low and the stored heat is released slowly. If heat is particularly required in the morning, then the output dial is set high and the stored heat is released quickly.
As they run on cheaper night-rate electricity, storage heaters are relatively cost-efficient to run. The main disadvantage is a lack of responsiveness. If the occupant feels cold during the day, he/she can’t immediately switch the storage heater on. It only ever gives out heat that it has stored during the previous night. As a result, in DEAP old “large volume” storage heaters such as this have poor responsiveness as seen in the table below. Also, as outlined in DEAP Appendix A, if storage heating is the main heating system, then a secondary system must be specified in DEAP.
Note that, in practice old storage heaters were usually sized to provide 90% of a dwelling’s heating requirement with direct-acting electric heaters, portable or fixed, providing additional heat when required.
There are several types of direct-acting electric heater – convector heaters, radiant heaters, panel heaters – but they all operate on the same principle: when the occupant feels cold, he/she can switch on a direct-acting electric heater and it will immediately generate heat to warm the room. They are often used as a back-up system to storage heating or may be used as the main heating system in some cases.
Modern direct-acting electric heaters may have sophisticated control systems with timers and thermostats controlling individual heaters giving excellent control and responsiveness in DEAP.
This is a storage heater (relying on stored heat generated during the previous night) and a direct-acting electric heater (which generates heat when it is switched on) contained in the same casing. The system is sized so that most of the heating load is provided by the storage heater at the cheaper night rate electricity. The system may be thermostatically controlled so that any shortfall is automatically provided by the direct-acting electric heater. Also, if the occupant feels cold, he/she can manually switch on the direct-acting electric heater to get immediate heat.
If an integrated storage/direct-acting system is the main heating system in a dwelling, then a secondary system must be specified in accordance with the guidance in Appendix A of the DEAP manual. However, these integrated storage/direct-acting electric heaters are more responsive than most other types of storage heaters and this is reflected in the DEAP responsiveness category from Table 4a. Note that a dwelling with any of the systems described above may have a poor BER because of the high primary energy conversion factor of electricity.
The following table summarises the relevant DEAP inputs for these electric heaters. All are 100% efficient, with fuel type of “electricity”. The efficiency adjustment factor in DEAP is “1”. Full detail is available in DEAP Table 4a and Table 4e. The table does not include electric boilers or underfloor electric heating.
Table 4.28 - Direct acting and storage electric heaters
| System | Control Category | Responsiveness Category | Temperature Adjustment |
|---|---|---|---|
| Storage heaters | 3 | Ranges from 5 down to 2 depending on type of storage heater as outlined in DEAP Table 4a | 0.3 or 0 depending on level of control as outlined in DEAP Table 4e, Group 4 |
| Direct-acting electric Heaters | 2 or 3 depending on level of control as outlined in DEAP Table 4e, Group 6 | 1 | 0.3 or 0 depending on level of control as outlined in DEAP Table 4e, Group 6 |
| Integrated storage/direct acting electric heaters | 3 | 2 | 0.3 or 0 depending on level of control as outlined in DEAP Table 4e, Group 4 |
DEAP Manual Section 9.3 outlines the different type of controls for electric storage heaters in DEAP assessments. There are three types of control that can be used with electric storage heaters - manual charge control, automatic charge control and CELECT-type control.
Manual: Manual controls are where the user controls the input and output of the Storage heater through the input and output dials. An input dial controls the amount of electricity flowing into the storage heater during the night, thereby determining the amount of heat stored. The user, using the output dial, sets the output from the storage heater manually, the output dial controls the rate at which heat is released.
Automatic Charge Control uses internal thermostat(s) or an external temperature sensor to control the charging of the heaters. Availability of electricity to the heaters may be controlled by the electricity supplier based on daily weather predictions. Automatic charge controls require the use of other remote thermostats throughout the dwelling or external to the dwelling to determine the charge amount.
CELECT-type control has electronic sensors throughout the dwelling linked to a central control device monitoring the individual room sensors and optimising the charging of all the storage heaters individually (and may select direct acting heaters in preference to storage heaters).
A Celect type control can control the heating times and specific zone temperatures throughout the dwelling. They require individual electronic sensors throughout the dwelling linked back to a central control device. These monitor the room temperatures and can optimise the charging of the individual storage heaters throughout the dwelling. The system can be zoned.