“If we are to hit our national carbon reduction target of 80% by 2050, almost every building in the country will need a low energy makeover. That means we have to improve nearly one building every minute, and we have to get the interventions right, first time. That is a challenge.” – The Retrofit Challenge: Delivering Low Carbon Buildings. The Centre for Low Carbon Futures
A majority of 2050’s building stock has already been built according to a United Nations Environment Programme estimate. From a Lifecycle Approach, 80% of greenhouse gas emissions occur during the period of building use. In order to significantly lower carbon emissions, it is clear that retrofits will have to play a crucial role.
Considering the long lifespan of buildings, it is important for designers to bear 2050 targets in mind already, so that investments and upgrades made now remain beneficial and relevant in the long run. The 2014 UK Part L regulations require a 9% reduction in CO2 emissions from new build projects. If this is expected within 4 years for new builds, we can assume that within the next 10 years, retrofits would realistically have to achieve around 20% reductions, and above.
So let’s look at an example of a potential retrofit project to be carried out in 2014. Our goal is to ensure our retrofit strategies remain relevant to any potential future carbon targets within the next 10 years.
Our example building is an existing retail space and residential project in Leyton, East London. The table below shows a baseline concept that meets 2010 Part L regulations.
Initial analysis tell us that our building is heating dominated.
Looking in more detail at the chart in Fig 3 above, we see that heat is lost mainly through conduction and infiltration. Our retrofit could therefore focus on improving our building fabric and air tightness in order to reduce our heating load.
The pie chart (Fig. 4) shows that most of our fabric conduction loss in descending order is through the roof, the glazing and finally the walls – these are the elements in our building that need our attention.
We could also adjust our HVAC system where possible to improve our heating efficiency.
In addition, the heat gain chart in Fig. 5 tells us most gains come from the sun suggesting we could introduce shading where possible in order to reduce our cooling load. However, we will need to size our shading devices properly to make sure that we don’t block out beneficial heat gain in the winter.
One strategy for improving the building’s fabric would be to increase the U-Values for the roof and walls. Insulation could be applied to the facade of the building to maintain the existing building floor area.
Another strategy would be to switch from a light to a medium core structure with the aim of increasing the building’s thermal mass. Exposing thermal mass through the floors can be done by taking away carpets and replacing it with a polished concrete finish.
Reducing the building leakage levels give a considerable 12% reduction in CO2 production.
In combination, this strategy offers a 19% reduction in CO2 levels, a 35% reduction in Energy Consumption as well as a 61% drop in Annual Space Heating. Cooling has increased by 2% considering the building is now much warmer overall.
Shading & Glazing
Upgrading the facade glazing in addition to horizontal shading contributes 3% to our CO2 reduction but also reduces Annual Space Heating by 11%.
By changing the Heating Efficiency of our boiler from 0.7 to 0.9, we gain a CO2 reduction of 7%, Energy Consumption drops by 13% whilst Annual Space Heating reduces by 22%.
A Bundle of All Three Strategies
By combining all three strategies, our design benefits from a 23% saving in CO2 production and a 43% reduction in Annual Energy Consumption. The 4% increase in Annual Space Cooling can be attributed to the tighter envelope and as a result, a warmer interior. A staggering 77% saving in Annual Space Heating makes this combination worth investigating further.
Some useful typical values for specifying building efficiency