4 Further Development of Heater Rating Model and Recommendations
This project has demonstrated that a programme can be developed which will provide objective advice concerning the suitability of heating options in a variety of situations. A reasonably large number of factors concerning the heating situation of the householder can be modelled and considered in providing this advice. There are two main ways in which the model could be further developed: testing it against real housing stock requirements, and adapting it to be used by the general public.
The model relies on the information from Designing Comfortable Homes, prepared by the Energy Efficiency and Conservation Authority (EECA) for its underlying estimations of the heat energy requirements and peak output requirements for the different heating scenarios. These estimates were limited by the fact that they were prepared for new homes with Code-compliant insulation or better, and the estimates have had to be adapted for the heater rating model to suit the wide range of potential heating scenarios that might occur in New Zealand.
The adaptation of the EECA estimates was done to be as accurate as possible given the information currently available from a variety of sources about how the different heating scenarios would influence the EECA estimates. However, it was not possible within the scope of the project to test whether the results are consistent with the requirements of actual housing in the current New Zealand housing stock. So, for example, the model has not been tested to determine if its ratings and outputs regarding heating energy and peak output needs are accurate for housing with no or little insulation.
If the accuracy of the model's results across all heating scenarios is critical, then it is recommended that the model's outputs be compared against the predictions of a housing energy model, such as the Building Research Association of New Zealand's Annual Loss Factor (ALF), based on examples of representative housing. This will involve first determining the characteristics of representative small, medium and large houses in the different climate regions, which is not a trivial task given the wide range of possible combinations of factors that are present in New Zealand housing stock. For instance, houses can have a wide variety of construction methods, insulation levels, orientation to the sun, design layout, etc., and choosing a house to model that is representative of all these variations can be difficult. Assuming representative houses can be chosen, then the housing energy model could be used to determine the heat energy and peak heat requirements of these representative homes. The results of the housing energy model could then be compared to the outputs of the heater rating model, and the heater rating model could be modified if necessary.
It should be noted, though, that the purpose of the heater rating model is to provide a comparative analysis of a range of heating options under a specific scenario, and one of the main outputs of the model is an ordering of heating options from most suitable to unsuitable for each scenario modelled. This means that even if the heater rating model is not always highly accurate in predicting heat energy and peak heater output requirements, the model will generally still provide useful results in terms of suggesting which heating options may be the most suitable for a given heating scenario.
The second area in which the model could be developed is to make it more 'user friendly' and suitable for use by the public. At the moment the model is designed to be used by someone familiar with Excel, and who will use the model often enough to become familiar with its method of operating. A version of the model aimed at the public would need more instructions about how to operate it, and would progressively lead the user through the steps to input their heating scenario. The outputs would also have more extensive explanations and might be presented differently. Help functions would need to be added, and possibly additional questions might need to be addressed. For example, the whole perception of the security of supply of electricity might need some discussion.
Finally, if the heater rating model is to be used to provide advice to the public regarding their heating requirements, then it is important that the limitations of the model be pointed out to the public by those offering the advice. The model can not take into account all the potential variations in the characteristics of houses that may affect their heating requirements. It does not consider the orientation of the house, the extent of glazing (and if there is double glazing), the construction materials of the house, shading of the house, exposure to winds, rising damp and other dampness issues, whether there is access to the above-ceiling or underfloor spaces to allow the installation of ducting, whether the house would need re-wiring to support electric heating, what heating the house currently has and the condition of that heating, etc. All of these issues could affect what is the most practical and desirable heating option for the house concerned and can not be considered in a heating rating model. Consequently it is recommended the householder seek specific advice for their dwelling from a range of heating experts.
