Further Guidance
The primary or main heating system heats the largest proportion of the dwelling. This proportion is calculated using a count of the habitable rooms. It is not usually based on individual room heaters (although it can be), and often provides hot water as well as space heating. Main heating systems are categorised on the basis of generic types in Table 4.4 and Table 4.5. Occasionally there may be two central heating systems, for example two separate boilers used to heat different parts of the property. In this case, the calculation should be undertaken using the system that heats the largest part of the property.
In DEAP a main space heating and main water heating system (and associated fuel for each) must be specified at all times. For example, it may not be assumed that solar water heating is the main water heater in DEAP.
The secondary heating system is based upon a room heater. Secondary heating system efficiencies are taken from the HARP database, certified test data to the relevant standards or room heaters section of Table 4.4.
A secondary heating system is to be specified if:
a) the main system is not sufficient in itself to heat the dwelling to the temperatures used in DEAP or:
b) fixed secondary heaters are present (such as a gas fire, a chimney and hearth capable of supporting an open fire or a solid fuel stove, storage, or fixed direct acting electric heaters).
In case a), assume direct-acting electric heaters if no actual secondary heaters are present. A secondary system is always specified when the main system is electric storage heaters or off-peak electric underfloor heating. If none of the above conditions apply, secondary heating (or backup heating system) is not specified, in other words in the software the secondary fraction is set to zero.
Portable heaters are not counted in DEAP assessments. These are characterised as:
Fixed electric bathroom heaters are not to be counted as secondary heaters for the purposes of DEAP assessments. Also, towel rails (both electric or from a wet heating system) should be ignored for the purposes of DEAP assessments.
Occasionally, there may be a chimney present as defined here, but the open fire is not counted as a heat source in DEAP (for example, there is another secondary heat source which takes precedence). In this case the chimney must still be counted in the DEAP ventilation section.
DEAP is based on the characteristics of the dwelling and the systems installed and not on the heating practices of the occupying household. That does not preclude further estimates of energy consumption being made to take account of actual usage. Such estimates are not part of DEAP but could form the basis of advice given to the occupying household on how to make best use of the systems at their disposal.
Table 4.14 gives the fraction of the heating that is assumed to be supplied by the secondary system. The treatment of secondary systems is not affected by any control options for the secondary system.
If two systems are present and it is not clear which is the main or secondary system the system which is cheapest to use should be taken as the primary, and if there is still doubt, in other words if they are both equally cheap to use, select the system that heats the living area. The other system can still be input as a secondary system but should be entered as a room heater so that its efficiency closely reflects (but does not exceed) that of the actual system (as defined by Table 4.4) where using Table 4.4 defaults.
If two types of secondary heater are present, that which heats the greater number of rooms should be specified as the secondary system (and the other secondary heaters ignored). If that condition does not resolve the choice, the system which is the cheapest to run should be specified.
Identify the main heating system. If there is a central system that provides both space and water heating and it is capable of heating at least 30% of the dwelling, select that system as the main heating system. If there is no system that provides both space and water heating, then select the system that has the capability of heating the greatest number of habitable rooms.
Select the system that is cheapest to run if there is still doubt about the main system. This can be determined by entering each system in DEAP and multiply the resulting delivered energy by the cost per kWh for the fuel type of that heating system. The up-to-date fuel cost per kWh can be taken from the SEAI Domestic Fuel Cost Comparison available on the SEAI Website. or from fuel bills for the dwelling.
The DEAP methodology assumes that a good standard of heating will be achieved throughout the dwelling. For dwellings in which the heating system is not capable of providing the standard, it should be assumed that the additional heating is provided by electric heaters, using the fraction given in Table 4.14. For new dwellings that have no heating system specified, it should be assumed that all heat will be provided by electric heaters using electricity at the standard domestic tariff.
Some existing dwellings have heaters only in a limited number of rooms. In these cases, the usual basis of calculation, that the dwelling is fully heated, still applies. Rooms without heaters are assumed to be heated by electric room heaters. The choice between primary and secondary heating is decided as follows:
Examples. A house with six habitable rooms with one gas fire would be treated as being electrically heated with a gas secondary heater (one room out of six). If there were two gas fires (two rooms out of six), the gas fires are the primary heating and electricity the secondary. If there were four habitable rooms, and one gas fire (one out of four), the primary heating would be electric and the gas fire the secondary.
In the case of highly insulated small dwellings, item (2) in Dwellings with inadequate heating systems may not be realistic, for example a 3kW gas fire could suffice to provide most of the heating needs. Accordingly, if the design heat loss (DHL) is less than 3kW, the heating in the main room is the primary system in this case. Dwelling heat loss is defined in Estimating the required boiler size.
DEAP assumes that the installed heating systems are operational and takes no account of whether they are working or not. However, in the case where the main heating unit (such as a boiler) is missing and thus the dwelling has no installed primary heating system, the rules in Dwellings with inadequate heating systems should be followed.
The DEAP methodology assumes that the installed heating systems are properly installed and serviced. When designing and installing heating systems the following documents should be read:
Additional information for system design and installation is provided in SEAI's contractor domestic standards and specifications document and SR 54 (both aimed at retrofitting dwellings) as well as the CIBSE domestic heating design guide.
DEAP should not be used to size the heating system (this is usually up to the system designer or heating system supplier/installer). The following method can be used to estimate the required heat system power output. Note that sizing the heating system is not the responsibility of SEAI and is entirely a matter for the client or system designer.
Maximum recommended dwelling heating load: Expressed in kW. For dwelling heat load, the maximum space heat demand is calculated by multiplying the heat loss coefficient by the desired maximum temperature differential ∆T (usually -3 to 21°C). The heat loss coefficient is the heat loss in W/K of the dwelling when accounting for fabric and ventilation losses. The heat loss coefficient is called the ’Total heat loss‘ in the ‘Results’ tab, under the ‘Building’ sub-tab and includes heat lost through the dwelling fabric and ventilation heat loss.
2 to 4 kW should be added to the space heating demand for water heating depending on occupancy or floor area. The total space and water heating requirement should be multiplied by 1.1 to allow for distribution losses giving the following maximum recommended dwelling heating load:
Dwelling space and water heat requirement (W)
= dwelling space heat loss + dwelling DHW requirement
= Total heat loss*24 *1.1 + 4000*1.1
| Main heating system | Secondary system | Percentage from secondary system |
|---|---|---|
|
All
|
All secondary systems | 10% |
| Micro-cogeneration | All secondary systems | see Appendix N |
|
Electric storage heaters (not integrated)
|
All secondary systems | |
| 15% | ||
| 10% | ||
| Integrated storage/direct-acting electric systems | 10% | |
| Electric CPSU | 10% | |
| Electric room heaters | 20% | |
| Other electric systems | 10% |
Note:
Main source: SAP 2005