28 C O N T E X T 1 4 9 : M A Y 2 0 1 7 PAUL SOUTHALL Energy efficiency for the National Trust Reviewing the energy requirements of National Trust buildings depends on understanding each building and its needs before exploring technical solutions and hiring consultants. Our first step in the process of integrating appropriate energy efficiency measures, with appropriate renewable solutions, is to understand our buildings and what conservation parameters have been set, and ask how we meet these requirements in an energy-efficient way.We previously placed huge reliance on external contractors and consultants, without understanding what we wanted, how we used buildings and what might change in the future. Unsurprisingly, we discovered that what we thought was appropriate was not always so. In our larger properties we have dynamically modelled to appraise options on a variety of possible efficiencies. To quantify the benefits, a baseline model took into consideration operation needs, occupancy, location, solar gain and staffing resources.Then we ran scenarios integrating with passive measures. Primarily this involves improving the building fabric by adding insulation and replacing glazing to improve U-values.These measures also reduce the building’s air permeability. Large roof spaces provide a good opportunity to introduce high levels of insulation.As a result of this relatively cost-effective measure we would gain a 3 per cent reduction in energy usage.This is where the difference between our large mansion properties and the smaller domestic buildings became obvious.The accepted guidance is that loft insulation will save approximately 10 per cent in energy. We found that in our larger properties most heat loss was through the many two-metre-high, single-glazed windows. Even with something as simple as loft insulation there are variables to consider: • Can we access all of the roof voids? Do we need access walkways for inspection? • Natural fibres such as wool and wood have a lower ignition point than mineral fibres. Consideration must be given to insurance implications when integrating them into large loft spaces. • How will older pipework in loft spaces react to the drop in temperatures following the insulation blocking the transfer of heat up into the loft? • Care needs to be taken not to cover electrical cables, increasing the build-up of heat. • How easy will it be to vacuum the bat poo off? The value of simply and cheaply insulating pipes and valves in large mansions or domestic homes is often overlooked. If I had a pound for every time I have been told that ‘we left the insulation off to check for leaks after we had finished’, I would be quite well off. In our haste to provide the best and most appropriate heating solution we have also been guilty of ignoring the building envelope. Surely historic windows are meant to shut properly?The refurbishment of the frames with draftproofing improves the airtightness of the windows and achieves an hourly reduction of 0.9 to 0.5 air changes. Our mansion properties have shutters.These are used to manage ultra-violet penetration and reduce damage to the contents, but they are not always closed when the building is locked up in the evenings to provide some draught exclusion and insulation.We have incorporated insulated panels to our shutters to further improve their efficiency. Similarly with curtains: do we have them? Do we close them? Are they lined to insulate more effectively? Dynamic modelling showed that if all of these measures were undertaken, we would benefit from a 13 per cent reduction in heat energy.With regard to doors: there is no point undertaking all of the other measures if the doors do not fit properly, or if they are left open. No matter what size the property is, simple, At Plas Newydd, a country house on the north bank of the Menai Strait in Anglesey, the installation of the UK’s first marine water-source heat-pump system led to an annual reduction of £40,000 in heating costs.
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