Dry-lining versus a hemp and lime insulating render - University of ...

Figure 9: The error bars represent the 5% range reported for the heat flux sensors and all dry conductivitymeasurements. Qw = Winter Heat Flux total, DL = Dry Lining, SS = Qw-Value calculated from SteadyState U-value where Q = - (U-value x (Tout-Tins)), Meas = Measured in-situ value.The DL wall clearly outperforming the Hemp wall (figures 8&9). The Hemp wall isperforming with a U-value effectively 42% worse than predicted. The most likelyreason for this is that the Hemp wall is still drying. This is conclusion is collaborated bythe hemp wall‘s in-situ falling overtime (Figure 10) as compared to the DL which isreasonably static suggesting the hemp wall is still drying.Figure 10: Change in calculated 14 day U-value overtime. This figure shows the change in average U-value for the Hemp and DL walls. The grey shadows are the 95% CI. It can be seen that whereas the DLU-value is relatively static the Hemp U-value slowly declines throughout the winter. The shaded areashows a period after none occupancy when internal RH rose as temperature fell.These results have implications for evaluating the carbon budgets for both wall types, asthe DL is more energy efficient than thought highlighting how using steady state U-value models to estimate thermal performance could lead to significant errors whenassessing actual thermal performance. Clearly at present the high RH behind the DLdoesn‘t appear to be causing any deterioration in thermal performance although thismay change over time if moisture accumulates as the WUFI model suggests. Cottage 2will be continued to be monitored to see how these 2 alternative renovation techniquescontinue to perform and to hopefully establish an effective U-value for the Hemp wallonce it is fully dry.4.3 WUFI modelThe simulations that matched the first 10 months of real recorded data from the cottageconfirm that the model gives a reasonable representation of reality (figure 2). The11