Header image

EMBODIED ENERGY | HEATING SYSTEMS that the larger ASHPs have a lower kgCO2e/ kW than smaller-capacity ASHPs. System-level calculations were carried out by multiplying the product-level embodied carbon results by the quantities for each residential typology. Individual and communal heating strategies were explored across the four residential typologies. The individual systems included a gas boiler baseline, heat pumps, VRF, direct electric, and exhaust air heat pump; the communal systems included an active ambient loop, passive ground loop, and connection to a district heating scheme. See Figure 3 for the embodied carbon emissions for a range of systems in a 100-unit residential development. The range of embodied carbon impact in kgCO2e/m2 is large in the scenarios explored in this study. In a multi-residential development, the strategy with the lowest embodied carbon, excluding refrigerant leakage, is direct electric, with 36kgCO2e/m2, and the highest is an active ambient loop in a 15-unit scheme, at 201kgCO2e/m2. For upfront embodied carbon (A1-A5), heating and hot-water systems could represent between 1% and 9%.1 For total embodied carbon (A, B, C) over 60 years, they could represent between 3% and 25% (excluding refrigerant leakage). In the case of a VRF system with R134a, the embodied carbon impact of the heating and hot-water system is above the current best-practice whole-building target when refrigerant leakage is included (832kgCO2e/m2). When excluding refrigerant leakage, an active ambient loop has the highest embodied carbon impact. As residential schemes get larger, the uplift compared with other systems is reduced. It is important to note that active ambient loops can have very low operational carbon emissions. Refrigerant leakage can be significant. This is especially true for VRF systems where the evaporator and condenser are split, with refrigerant piped through the building. Factory-sealed heat pumps should be prioritised, and low global warming potential refrigerants used.2 Refrigerant choice can increase the embodied carbon impact of a VRF system by a factor of nine and of a heat pump system by 30%. The study also explored the impact of a business-as-usual (BAU) fabric (based on a space heating peak load of 30W/m2) on the embodied carbon impact of two heating strategies: a gas boiler and an ASHP for a terraced house. For the ASHP scenario, the upfront embodied carbon increases by 75% when the terraced house has a BAU fabric compared with an ultra-low energy fabric. The dotted line indicates the average generic embodied carbon value Figure 2: Embodied carbon emissions for different sizes of ASHPs References: HVAC study for office refurbishments 1 This assumes the embodied carbon impact of a new home is 800kgCO2e/m2 based on a LETI C rating (LETI, 2021). This was chosen because it represents current best practice for buildings being designed today. 2 Refrigerants and environmental impacts: A best practice guide, Hamot et al, 2020, bit.ly/CJNov21ref Over the next six months, CIBSE and Elementa will concentrate on heating, ventilation, and cooling systems in commercial schemes, to develop TM65.2 . As part of this study, information on the material breakdown of various HVAC products is needed from manufacturers. Those that provide information will be acknowledged in TM65.2 (see panel, Embodied carbon webinar for manufacturers). CJ Many thanks to the following manufacturers that contributed information to the TM65.1 study: Vaillant, Lochinvar, Ideal, Hamworthy, Upton, Stratton, Aldrich, Fulton, Glen Dimplex, Mitsubishi, Daikin, Rhoss, Kensa, Nilan, Merriott, Stelrad, Cetetherm, Rhico, ACV, Flamco, Swegon, Danfoss, Recoup, Kingspan and Uponor. YARA MACHNOUK is a graduate environmental designer and was a runner-up in last months CIBSE ASHRAE Graduate of the Year award EMBODIED CARBON WEBINAR FOR MANUFACTURERS bit.ly/CJNov21TM65 embodiedcarbon@cibse.org DEFINITION OF EMBODIED CARBON Product stage: Construction process stage: Use stage: End-of-life stage: 30 November 2021 www.cibsejournal.com CIBSE Nov21 pp28-30 TM65.indd 30 22/10/2021 15:28