Appendix: Heater Rating Model Instructions
Introduction
The Excel heater rating model is designed to be operated by a user familiar with Excel, although the operation of the model has been kept simple. The output of the model will also be much better understood by someone familiar with the dimensions on which home heating options can vary, such as thermal efficiency, operating costs, particulate emissions, etc. The model has not been designed for use by the public but as a means of assisting Ministry for the Environment staff to develop information and provide advice to the public.
The model works by determining the heating requirements to heat a specified type of house, calculating the expected performance of a range of heating options to meet those heating requirements, and then rating from 1 to 5 different aspect of the heaters' performance. A higher rating indicates the heater has performed better than a low rating. The rating results and information on the performance of all the heaters modelled are then displayed for the user.
Before using the model
The performance of heating options for a dwelling will depend on the characteristics of the dwelling, the usage of heating by the occupants and the location of the dwelling. In the model these variables are described as the heating scenario.
The first task the user of the model needs to undertake is to decide what heating scenario they are interested in obtaining information about. For example, is it for a large, well-insulated house in Auckland, or a small, poorly insulated house in the South Island? The second task is to decide on their heater weightings; that is, what is important to them in selecting a heater. For example, are they most concerned about the operating costs, the capital costs or the environmental impacts? Or are they concerned about a combination of the costs and the convenience? The criteria the user decides to use in selecting a heater are called their heater 'weightings', because this determines the importance or weight that is given to different aspects of all the heaters' performances when developing an overall rating for the heating options.
Once the user has decided on the heating scenario and their heater weightings, they can input this into the model and the model will produce information on the performance of a range of heating options. It will also rate the effectiveness of the heating options on a number of dimensions and give an overall rating of the heaters that reflects the user's ideas of what is important in a heater.
Operating the model
The user will need to follow a number of steps.
- Start model: open the heater rating spreadsheet and move to the Scenario worksheet.
- Select heating scenario: in the Heating Scenario table at the top of the sheet the user must select options to develop their heating scenario. This is done by clicking on the yellow highlighted cells under the column headings and by selecting an option from the pull-down menus. The column headings indicate the various dimensions of the heating scenario, including:
- geographic area (where the dwelling is located)
- city versus regional/rural (again the location of the dwelling)
- availability of natural gas
- type of house (single-storeyed, two-storeyed, flat/apartment)
- insulation (from no insulation through to the best possible)
- heating behaviour (the times of the day the house needs to be heated)
- size of house (small through to large)
- whole house versus main living area (whether a single room or the whole house needs to be heated)
- Choose weightings: the user has a choice regarding the weightings they use to select an appropriate heater for them. The user can use the default weightings contained in the model, or they can select their own weightings. These two options involve the following.
- The default option means the user only has to click on the 'Default Ratings Display' macro button at the bottom of the Scenario worksheet and the model will automatically operate and develop the ratings and predictions of the performance for the heating options.
- If the user wishes to select their own weightings, then they must move to the Weighting worksheet. A Weightings Ratings Table will be displayed which has the weighting criteria in the left column and user-assigned weightings in the right column, highlighted in yellow. The user needs to alter the assigned weightings by typing in a percentage weighting to the criteria they wish to favour when selecting a heating option. The percentage weighting can vary from 0% to 100% for any criterion, but the sum of the percentage weighting across the criteria must equal 100%. Once the user has selected their weightings they click the 'Weighted Ratings Display' macro button at the bottom of the Weighting worksheet.
- Display ratings results: once either of the macro buttons is clicked, the results of the ratings analysis will be displayed to the user by the model. The Ratings Results worksheet displays the ratings for the heater options across nine attributes. The heaters are listed by their overall heating ratings, with those with the highest overall ratings at the top of the list. In all heating scenarios, some heating options will be regarded by the model as not suitable, so they will be assigned a zero overall rating and listed at the bottom of the Ratings Results table.
- Heater performance information: more detailed information on the performance of all the heaters can be seen by the user if they move to the Heater Information worksheet.
If the user wishes to explore a different heating scenario they must return to the Scenario worksheet and repeat the five steps described above.
