Dr Sarah Price

This study investigates the hygrothermal impact of various internal wall insulation (IWI) systems on embedded intermediate floor joist ends by utilizing, with a novel approach, transient hygrothermal modelling (BS EN 15026) with the WUFI® Pro software and three-dimensional steady-state thermal modelling with TRISCO3D. The research evaluates the effects of thermal bridging on heat flow and assesses hygrothermal performance across four UK climate zones, two orientations, and multiple IWI retrofit methods. Five IWI strategies were examined: no insulation in the floor void, 95mm glass mineral wool with variable or standard vapour resistance membranes, 60mm phenolic foam with plasterboard, and multifoil insulation. Additionally, three brick types and two stone types with varying absorptivity were considered. The findings indicate that the 95mm glass mineral wool with a variable vapour resistance membrane performed best, showing no to moderate risk in 19 of 50 modelling cases. Regarding specifically the risk of rot at the embedded timber joist ends, avoiding the installation of IWI between the floor joists (whilst maintaining the airtightness of junction) presented the lowest risk with 28 in a total of 50 modelling cases showing no risk to moderate risk. However, as this option is associated with unintended consequences such as excessive heat loss due to thermal bridging and risk of mould growth and surface condensation due to low surface temperatures within the floor void, further investigations took place to identify the optimum IWI strategy in the intermediate floor void. Further analysis identified an optimal strategy using vapour-open, hygroscopic woodfibre insulation in the floor void, tailored to climate, orientation, and wall type, to minimize rot risk, heat loss, and condensation. This approach ensures balanced hygrothermal performance while mitigating unintended consequences.

The fragmentation behaviour of protonated O,O-dimethyl ethylphosphonate and its isotopomers deuterated in the α- and β-positions of the ethyl group and their fragment ions, particulary EtP(O)OMe+(IV), have been investigated both experimentally in an ion trap mass spectrometer and theoretically by electronic structure calculations at the B3LYP level. Of particular interest is the finding that the phosphonium ion IV eliminates ethene with hydrogen/deuterium loss from both the α-and β-positions. The initial step for both routes involves ethyl migration from P to O to form the ion MeOP+OEt which then loses ethene by two mechanisms, both of which lead to the same products. That a unitary branching ratio for α- and β-elimination is not observed indicates that although the final step of dissociation into product ion and ethene is energetically the most demanding, it is not rate limiting and the large entropy change associated with the dissociation allows earlier processes to determine the branching ratio. This demonstrates once again that free energy, not enthalpy (or energy), determines the course of gas phase ion processes.

Whole house heat loss or heat transfer coefficient (HTC) measurements are rarely undertaken to validate the performance of retrofits installed in homes. This means policy, certification and householders must rely on predictions made by energy models. Multiple domestic energy models exist, with varying underlying rules and input requirements. This means predictions made by different models may not always agree. However, few studies have compared the predictions from these models with each other, and with measured whole house heat losses for a home before and after a retrofit. This paper compares the HTC of a three bed, semi-detached, solid-walled home measured via the coheating test, with the HTCs predicted by the Reduced Data Standard Assessment Procedure (RdSAP), Building Research Establishment Domestic Energy Model (BREDEM), Dynamic Simulation Modelling (DSM) and the Passive House Planning Package (PHPP). The results show that most predicted HTCs from the models are not similar to the measured HTC, and there is a large variation between the different modelled HTCs. The paper explores why these differences occur and reflects on how to improve the accuracy and consistency of domestic energy models.