4.3.2. Environmental Savings

Comparative LCA results of heat pumps and gas boilers are calculated for the UK in a previous study [44]. In this study, Orkney results show that there is a significant reduction in most categories when it is compared with the results for the UK (Figure 10). The main reason for that is the change in the use phase. In UK results, the use phase was dominating the remaining categories. However, the amount of electricity used for the heat pump throughout the lifetime (20 years) is reduced because of higher efficiencies (2.8 SPF used for the UK study and the average optimized SPF modelled for archetypes in Orkney is 4.5). Moreover, electricity is produced mainly from wind energy. Therefore, the negative consequences are decreased.

The highest reduction occurs in the Ionising Radiation (IR) category with a nearly 99% decrease. The main contributor to this category is electricity from nuclear. Therefore, renewable electricity helps to reduce this impact. Other high reductions occur in agricultural land occupation (ALO), terrestrial ecotoxicity (TE) and national land transformation (NLT) categories, with 98%, 98%, and 96%, respectively. The reduction in ALO and TE categories is relevant to electricity produced from biomass which exists in the UK electricity mix but not in Orkney. NLT category is relevant to the fossil fuels that exist in the UK electricity mix.


**Figure 10.** Lifecycle environmental impacts of heat pump uptake scenarios by house archetypes.

The lowest changes occur in freshwater ecotoxicity (FE) and marine ecotoxicity (ME) categories with a 9% and 14% reduction. The main processes that contribute to these categories are the manufacturing and disposal of scrap metals so as there are no changes in these phases the results remain similar and only the use phase creates these differences. urban land occupation (ULO) and metal depletion (MD) categories also have 19% and 34% lower results mainly because of the differences in the electricity mix.

The climate change (CC) category results decreased from 44,320 kgCO2e to 5621 kgCO2e on average. Even though the average value is very low when compared with the UK figure, results vary based on the archetype and building specification. It can reach 6284 kgCO2e if the building is an unrefurbished detached house or decrease to 5295 kgCO2e if it is a new semi-detached house. The new buildings category shows 14%, 5%, 7%, and 9% lower results for detached, semi-detached, end-terraced, and mid-terraced archetypes, respectively.

The highest changes in one impact category exist in FE, ME, and ULO categories. The differences between an unrefurbished detached house and a new building end-terrace house could be as high as 78% in FE, 73% in ME, and 49% in ULO category. These results emphasize that not only the environmental impacts of different space heating technologies are important, but also the house archetypes and specifications. A refurbished house and a new building category have 5% and 10% lower results than an unrefurbished one in the CC category. The highest change occurs in the FE category with a 16% and 30% reduction in refurbished and new building categories. ME category shows similar reductions with 15% and 29% for the same building specifications. ULO category also shows reductions of around 11% and 22% with EEI.

Figure 11 illustrates the breakdown of GHG emissions for the baseline scenario and total emissions for future scenarios. Oil is responsible for 77% of total emissions (20,552 tCO2e), followed by coal with 16% (4248 tCO2e) and electricity with 6% (1612 tCO2e) in the baseline scenario. Wood and LPG account for only 1% (269 tCO2e) of total emissions. RE and CE scenarios reduce total emissions by 79% and 98% respectively. RE scenario expects an 81% reduction in fossil fuel emissions and a 44% reduction in electricity emissions. CE scenario replaces all heating technologies with heat pumps, so the emissions are 659 tCO2e coming from electricity, which is very low when compared with the RE scenario. Even though the demand is higher in the future with around 2000 more new dwellings, ambitious EEI targets also help to reduce both demand and emissions. The UK's net zero target is an ambitious target and requires ambitious steps, including not only a shift in the heating system, but also a shift in EEI.

**Figure 11.** Comparison of current and heat pump uptake scenario GHG for house archetypes contributed by fuel type.
