CHAPTER THREE: ASSUMPTIONS AND LIMITATIONS
3.1 Due to the limited monitoring information available, it was not possible to determine the impact and effectiveness of the different sustainability features for every development. As outlined in Section 2, the Sustainable Energy Appraisal was carried out for 3 developments. The assumptions and limitations of the appraisal are outlined in this section.
Assumptions
3.2 The accuracy and value of the Sustainable Energy Appraisal relied upon the following information:
- information on the case studies and the sustainability features;
- data for SAP assessment and drawings from architects; and
- energy consumption statistics, patterns of use and cost information.
3.3 Due to the limited information available on the case studies, thermal bridging values have been assumed at a 'y' value of 0.08 (highlighted in the Annex one result tables). For each development, the percentage of low energy lighting was estimated from previous housing association projects. For the Dalfaber development, Aviemore, which is off the gas grid, it was assumed that the site has a gas connection option.
3.4 There were limitations using Plan Assessor Version 3.1 SAP software, which meant that it was not possible to accurately input the Glenalmond Street heating system. SAP does not distinguish between types of collector and, following discussions with NHER Technical support, the 'Heat Pump - Wet System' option was used for both West Windygoul, Tranent and Glenalmond Street.
3.5 SAP includes a series of standard assumptions, including the following:
- temperature setting of 21 oC;
- 100% of Zone 2 (rooms other than lounge) is heated;
- 2 heating times (weekdays - 3hrs/morning, 7hrs/evening and weekends - 16 hrs/day); and
- average cooker, electricity and hot water use.
3.6 Other assumptions that were made include:
- boiler efficiency 78%;
- air permeability rating ( APR) of 15m 3/h.m 2 ; and
- thermal bridging 0.08.
3.7 The economic information presented in the results is only indicative and is based on the generic assumptions within the SAP software used. No billed information was available at the time of the research study. The SAP economic data is based on Plan Assessor Version 3.1 assumptions which incorporate current energy price information.
3.8 The cost performance information presented for the Glenalmond Street, Dalfaber and West Windygoul case studies in the Economic and Environmental Performance section is related to the space heating, hot water and lighting within the homes. Using the NHERSAP Plan Assessor Version 3.1 software has allowed additional cost information, relating to the use of appliances and cooking, to be included in the assessment. This information has been sourced as part of the National Home Energy Rating ( NHER) scheme.
3.9 The environmental performance information (in terms of CO 2 emissions) presented for the Glenalmond Street, Dalfaber and West Windygoul case studies in the Economic and Environmental Performance section is also related to the space heating, hot water and lighting within the homes, however it does not include CO 2 emissions relating to the use of appliances and cooking. The NHERSAP Plan Assessor Version 3.1 software does not allow for additional information to be included in the assessment in this regard.
Limitations of results
3.10 The results of the Sustainable Energy Appraisal, and conclusions drawn in
Sections 5 and 6 of this report, should be viewed in the light of the assumptions listed above.
3.11 It was not possible to give an accurate account of economic and environmental performance due to the lack of available quantitative monitoring information ( e.g. from data loggers and energy bills) available during the research study. However, we consider that the standard information and assumptions used for the specific dwelling types provides sufficient worthwhile information to inform decisions on future sustainable social housing projects.