Business Green reported an interchange last week between the Mayor and Green Assembly Member Darren Johnson in response to his question about the Mayors position on Zero Carbon homes. Boris’s reported response was
“What we are looking at is making sure that we can continue, through the London Plan, to ensure that Zero Carbon Homes are delivered in London and we will be issuing further guidance in due course to provide industry with the certainty it needs about how to do that.”
Boris reported that London aims to achieve a 60% reduction in CO2 by 2025 and has achieved 14% to date. This represents a per capita reduction of 20% as London’s population has grown by 600k during the reporting period.
It is heartening to hear these words from the Mayor, and I hope that the candidates for the Mayoralty are listening. If devolution is to mean anything it should promote the ability of cities in the UK to sidestep the damaging and short-sighted environmental policies of central government.
Having recently completed a large zero carbon scheme at Hanham Hall with low-rise construction and learned what it means for most of the UK’s housing development, I thought that it would be useful to share below some analysis that we have done to assess how tall buildings can achieve the zero carbon standard. Given that many of the buildings that are proposed for the capital in future are going to be tall it is interesting to assess how the regulations might affect those building types.
The analysis has been done for a twenty five and a forty storey tower with six units per floor to demonstrate how different systems meet the targets. We tested gas boilers, CHP with gas backup, all-electric heating and hot water and finally Air Source Heat Pumps. Three of the four rely on a communal hot water distribution system, the all electric system being the exception.
What the research shows is that for taller towers there is no difficulty in meeting the current definition of zero carbon. In fact it shows that achieving it is technically easier than achieving the London Plan, as the London Plan has a lower emissions target than the Zero Carbon definition. This is assuming that there is no special treatment for electric heating or hot water, unlike the current version of SAP which is based on comparative performance rather than on a definite figure as set out in the Zero Carbon Hub’s definition.
Based on these figures I would say that towers should be forced to meet the lower emissions target of 10kg/CO2/sqm since in both gas-based options this target can be met. Perhaps an all-electric version could be left as it is at the higher 14kg/CO2/sqm.
It also shows that a very efficient 25-storey building can meet the targets irrespective of the energy system used, the top graphs shows that it can achieve the target in all four options, even an all-electric option. The 40-storey is not so easy. My assumption is that only the roof can be used to house renewable energy, but for the 40-storey version it would be necessary in the electric options to put some pv panels on the facade to reach the target.
But of course the technical success is not the full picture. In addition to the Fabric Energy Efficiency target of 39kwh/sqm/yr that apartments have to hit, and towers have no difficulty doing so, there is the Carbon Compliance which is shown in the graphs above, and again there doesn’t appear to be much of a problem for towers, but finally there is the Allowable Solutions element which says that whatever CO2 emissions remain must be offset. This offset is achieved by multiplying the tonnes of CO2 emitted, by the figure of 30 years, and by an agreed sum for each tonne. Currently the GLA uses £60/tonne. This produces a figure of approximately £1,000 per apartment to offset the emissions elsewhere.
Sadly the all electric system is unwelcome in London as it it not seen as ‘futureproof’ according to the gas-led ideology preferred by the GLA. This is understandable as an all-electric system does not emit the lowest CO2 emissions possible, at current levels of grid CO2 intensity. What will be interesting to see is how long before the grid CO2 intensity drops to a low enough level to change that thinking. The Committee for Climate Change has suggested that we need to stop burning gas by 2035 to meet our carbon budgets. What is the point in investing in gas burning equipment and networks now if they have to be decommissioned in less than twenty years time?
Certainly an all-electric system is the cheapest to install, avoiding the central distribution system, and it could be argued that an all electric system is just as futureproof as a hot water led system as the Grid is inherently flexible. Interestingly our research also suggests that in the majority of cases an all-electric system is cheaper than a communal system for residents as the standing charges are lower, even if the energy bills are higher than gas. The standing charge is used to create a sinking fund to replace the communal system. If there is no communal system the sinking fund is either not needed or is much smaller, thus lowering residents total bill. The cheapest system of all to run is an individual gas boiler, but no-one would consider installing that into a tower, and it has a higher maintenance and replacement cost than an all-electric system.
A major hole in this analysis is that it is carried out using SAP, which is pretty poor at dealing with apartment buildings. The energy for pumping heat around the building is ignored, as is the energy for ventilating corridors, pumping hot water, lifts, communal lighting etc, etc. Since the communal spaces in these buildings are not heated, SBEM isn’t particularly useful either. As buildings get taller these additional energy uses and losses will become more a more significant part of their energy use, we need better tools to assess them, and more regulations to deal with their particular demands.