46 Project
If our house requires 25000kWh/pa of energy, the cost of on site renewables to generate this would be about £160k. Expensive, unrealistic, unfeasible and for a great many sites impossible. Sounds familiar?
If we build a house that only requires 5000kWh/pa, then the typical renewable cost will be in the region £32 k. Much more economic but still expensive.
However the definition is extended to provide a little leeway regarding renewable energy sources. It specifies that ‘Off-site renewable contributions can only be used where these are directly supplied to the dwellings by private wire arrangement’. So we can use off site renewables! This may help the fortunate few who can utilise a windy hilltop fairly close to their site by reducing the cost of the renewables by about 40%. Tough for the less fortunate.
[At Hockerton we have off-site renewables situated a short distance from the houses in the form of two 5kW turbines but no windy hilltop to put them on. Planning squashed that one].
Then we come across a problem.
To be a True Zero Carbon Dwelling ‘Dwellings must reach the minimum mandatory energy requirements for [CSH] level 5. This means that emissions as calculated by SAP …should be zero or better’.I have always argued that SAP calculations are fairly irrelevant to super- insulated houses, and preparing some recent calculations, found SAP predicted higher energy consumption for space and water heating than I considered was likely to be the case. I thought it would be instructive to use SAP to calculate energy use for two buildings on separate sites for which I had energy records.
The predicted energy use for hot water alone in one house was as great as the actual total house energy requirement. In another the projected space heating requirement was as great as the actual total house energy requirement.
Using SAP as a predictor for renewables to meet the zero carbon standard would have resulted in a massive overspend in each case. You can make the SAP fit the actual results by fudging here and there, altering a few figures and conjuring up the odd constant, but this begins to look like a guesstimate- not good for a rigorous assessment of building performance.
Unfortunately there is more.
‘A zero carbon home is also required to have a Heat Loss Parameter of 0.8W/m2K or less.’ The above examples and all houses at HHP have a higher HLP of 1.1W/m2k. [Excluding the sunspace areas]
This HLPis obviously not the key indicator determining overall energy performance as the houses perform considerably better than predicted. Perhaps it is just a catch all to prevent anyone avoiding stamp duty regardless of how the house performs?
And still more.
‘
..and net zero carbon dioxide emissions from use of appliances in the homes.’ and....’until SAP is updated, the appliance element of the qualification will be calculated using the formula …to approximate the average appliance energy consumption.’ More dodgy predictions?- the calculation probably qualifies for the Mark Brinkley ‘Eco bollocks of the year’ award].
And yet more.
‘This additional power must be renewable power produced either within the area of the building and its grounds, elsewhere in the development, or elsewhere as long as the developer has entered into arrangements to ensure that the renewable energy generation is additional to existing plans.’
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