Energy Efficiency Standard for Social Housing: peer review

Case Study Group G

4. 1992-1998 mid floor flat, 70m ²
5. 1992-1998 mid terrace house
6. 1992-1998 semi-detached house, 74m ²

Case Study Group G: 1990 Baseline

Walls

• Compliance with the Building Standards (Scotland) Regulations 1990 required that the elemental standard U-value of exposed walls in dwellings should not exceed 0.45 W/m ².
• The RdSAP methodology v9.91 assumes a wall U-value of 0.45 W/m ².K for filled cavity walls (as built) in Scotland for age band H (v9.90 and v9.91).

Ground Floor (where applicable)

• Compliance with the Building Standards (Scotland) Regulations 1990 required the elemental U-value of floors in dwellings to not exceed 0.45 W/m ².
• Where it is not possible to determine the level of floor insulation, the RdSAP methodology assumes a solid floor with 25mm insulation for Scottish dwellings constructed between 1992 and 1998 ( RdSAP age band H).
• Based on the calculation detailed in section S5.4 of Appendix S, the U-value calculated for case study 19 is in the region of 0.39 W/m ².K which complies with the building standards in place at the time.
• The U-value calculated for case study 20 is in the region of 0.50 W/m ².K, which is in excess of the minimum building standard criteria. Specification of 50mm floor insulation, instead of 25mm as per the RdSAP default assumption (Table S11), lowers the U-value to 0.36 W/m ².K which complies with the minimum building standards.

Roof

• Table S9 in appendix S states an assumed roof U-value of 0.40 W/m ².K for a slate or tile roof featuring 100mm insulation, as specified by the 1990 baseline.
• If the loft insulation thickness is not known and table S10 from Appendix S applies, dwellings constructed in Scotland between 1992 and 1998 assume a default U-value of 0.29 W/m ².K associated with an insulation thickness of 150mm (for a pitched, slate or tile roof with insulation between joists).
• This has required further investigation to determine the validity of the baseline assumption, as discussed in Appendix E of the main report.

Glazing

• Compliance with the Building Standards (Scotland) Regulations 1990 required that the U-value associated with glazing fittings in dwellings should not exceed 3.30 W/m ².
• This corresponds to U-value detailed in table S14 of Appendix S for double glazing in Scotland installed prior to 2003.

Space and water heating

• Case study 18E specifies a factory applied foam insulation thickness of 50mm for the hot water cylinder, whereas case studies 18G and 19G specify a thickness of 38mm. These exceed the default performance assumed by RdSAP for hot water cylinders (25mm factory applied foam insulation) in Scottish dwellings constructed between 1992 and 1998.
• Case studies 19E, 20E and 20G specify factory applied foam insulation thickness of 25mm for the hot water cylinder. This corresponds with the default performance assumed by RdSAP for hot water cylinders in Scottish dwellings.

Gas heated dwellings
Space and water heating

• It is unlikely that data will be available describing the efficiency of the boiler installed in the 1990 property, therefore it will be necessary to refer to the assumptions detailed within the SAP methodology: Appendix S assumes pre 1998 gas boilers are not fan-assisted, which corresponds to an efficiency of 66% (with the exception of a regular floor mounted boiler installed pre 1979 with an assumed efficiency of 56%).
• Should any of the efficiency adjustments outlined in Table 4c of the SAP methodology be applicable, the boiler efficiency may be reduced by 5%. This means a regular, non-condensing, pre-1998 gas boiler (not fan assisted) without any thermostatic control of room temperature will be assumed to have an overall efficiency of 61%.

Recommendations:

• A floor insulation thickness of 50mm (greater than the 25mm default assumption) needs to be specified to ensure the floor U-value meets the building standards in place at the time.
• Reference should be made to Appendix E of the main report in relation to the 1990 baseline assumption for loft insulation.
• The minimum efficiency assumed for the boiler winter seasonal efficiency (applied for the space heating requirement) should be no less than 61%.

Case Study Group G: SHQS 2015

• The 1990 baseline wall and loft insulation specifications for case study group G are sufficient to meet compliance with elements 31 and 32 of Annex C.
• The case studies feature at least 25mm of factory applied foam insulation to the hot water tank. As long as the pipes are insulated, or contribute to the space heating requirement, case study group F complies with element 33 of Annex C.
• Sub-elements 34A and 34B require that the property features a full central heating system addressing all habitable rooms (excluding the kitchen and bathroom), and that it is deemed efficient. Both the storage heaters and gas boiler specified for the baseline property meet the necessary criteria
• The 1990 baseline versions of case study 18, and gas heated case studies 19G and 20G, exceed the minimum SAP rating to meet compliance with Element 35 of Annex C. No additional measures are considered for these dwellings under this stage of improvement

Electric heated dwellings
Roof

• To exceed the minimum SAP rating, in line with element 35 of Annex C, it is necessary to increase the loft insulation thickness to 250mm for case studies 19E and 20E.

Renewables: Solar PVs to 20% of roof

• Photovoltaic technology, specified for case studies 19E and 20E, will only be suitable for a limited number of properties, where they meet sufficient criteria to ensure the effective operation of the technology ( e.g. suitable orientation, sufficient space on the roof, optimal angle of roof, minimal over shading).
• Should optimal conditions associated with any of the above criteria not be met, additional costs may be incurred to try optimise operational conditions ( e.g. investment in a supporting frame to improve the tilt angle, or multiple inverters to minimise the impact of partial shading for periods of the day).

Recommendations:

• Alternative technologies should be considered to help case studies 19E and 20E achieve the minimum SAP rating for the SHQS over solar PV, where the suitability of this technology is limited in relation to a number of building specific characteristics.

Case Study Group G: Further Measures 2020

• The EESSH outlines a minimum EI rating to be achieved for electric and gas fuelled properties. These are:
  • C (70) and C (80) respectively for a mid-floor flat,
  • D (55) and C (70) respectively for a mid-terrace house, and
  • E (50) and D (65) respectively for an end-terrace/semi-detached house.
• Electric heated case studies 19E and 20E exceed the minimum EI rating, based on the measures specified for the SHQS 2015 improvement stage. Despite this, a number of additional measures are considered under the 'further measures 2020' stage.

Electric Heating
Glazing

• Post-2003 glazing is specified for all the electric heated case studies in group G.
• This is not critical to meeting the EI rating for case studies 19E and 20E, based on the previous specification of solar PV. Only case study 18E is reliant on the improved glazing to help it exceed the minimum EI rating.

Space and water heating

• The fan storage heaters, specified for all the electric heated case studies in group G, will have the same efficiency as the previous system, but will benefit from increased 'responsiveness' ^[20] and automatic controls, contributing to a reduction in the space heating requirement, and consequently an improved EI rating.
• The improvement to the hot water tank insulation, increasing the factory applied foam insulation thickness to 80mm, identifies another method by which landlords can reduce the hot water energy consumption, CO ₂ emissions and consequently EI rating.
• It is suggested that specified measures for case studies 19E and 20E be included as part of the ' SHQS 2015' stage of improvements rather than the 'Further Measures 2020'. This may help eliminate the reliance on solar PV to meet the minimum SAP rating, a technology which will not be suitable for all dwellings.

Gas heated dwellings
Roof

• Increasing the loft insulation thickness to 250mm for case studies 19G and 20G, in addition to upgrading the heating system, demonstrates a significant increase in points above the minimum EI rating.

Space and water heating

• The indicative life expectancy for a condensing boiler is in the region of 15 years ^[21] , therefore installation of a new system is appropriate for both the ' SHQS 2015' or 'Further Measures 2020' improvement stages. This also provides an opportunity to upgrade the control strategy.
• Table 4b of the SAP methodology specifies a non-condensing combi-boiler to have an efficiency of 70-74%. Any installations after 2005 will be condensing systems, thus assume an efficiency of 80-84%. The case study control specification indicates that the system does not qualify for any efficiency adjustments detailed in table 4c of the SAP methodology.
• Improved boiler efficiency will yield considerable space heating and hot water energy reductions. Standard 6.3 of the Domestic Technical Handbook specifies a minimum seasonal efficiency of 88% ( SEDBUK 2009) for gas boilers. It is proposed that this value is used to describe the efficiency for any future installations, where it represents the current minimum standards.
• A more efficient boiler will use less energy to address the load on the heating system. Any savings realised by a measure which reduces the load on the heating system will be greater under the operation of a less efficient boiler compared to a more efficient system. This is important to bear in mind when considering the cumulative effect of implementing energy efficiency measures installed over a number of stages: the benefits of individual measures cannot be added together.

Recommendations:

• The measures proposed for case studies 19E and 20E should be considered as part of the ' SHQS 2015' measures, in place of the solar PV, where a greater number of dwelling are more likely to be able to accommodate these over the renewable technology
• An assumed gas boiler efficiency of 88% is proposed in line with the minimum standards outlined by Standard 6.3 of the Domestic Technical Handbook.
• Social landlords should be reminded that the case studies demonstrate the cumulative application of efficiency measures over three stages, and the potential benefits realised by a single measure are subject to change in relation to the other measures in place.

Case Study Group G: Advanced Measures 2050

• No 'advanced measures 2050' are considered for the electric heated case studies, or gas heated case study 18G.

Gas Heating
Glazing

• Upgrading the glazing specification to post-2003 double glazing for case study allows landlords to view the potential benefits from this measure. It is suited to an 'advanced measure 2050' where it may not be necessary to replace the existing double glazing for a number of years (and prior specification has not been necessary to meet any of the efficiency target ratings).

Renewables: Solar PVs to 20% of roof

• Photovoltaic technology will only be suitable for a limited number of properties, where they meet sufficient criteria to ensure the effective operation of the technology ( e.g. suitable orientation, sufficient space on the roof, optimal angle of roof, minimal over shading).
• Should optimal conditions associated with any of the above criteria not be met, additional costs may be incurred to try optimise operational conditions ( e.g. investment in a supporting frame to improve the tilt angle, or multiple inverters to minimise the impact of partial shading for periods of the day).

Recommendations:

• There are no recommended changes to the assumptions specified for the 'Advanced Measures 2050' improvement stage, for case study 19.