July 2010
In this report we present our findings and recommendations for the development of the carbon
compliance tool. This follows six months of effort by anexpert task group drawn from the wide range of industrysectors engaged with house building, including developers, designers, product manufacturers, consultants, professional bodies and academics.Carbon compliance is not the most approachable of subjects, but it is a key element in any strategy to deliverzero carbon homes. The compliance tool is the means by which we measure the carbon performance of new homes. Without an effective tool, we simply cannot tell whether a new home has been built in line with the zero
carbon standard.
The aim of the expert group was to identify the most appropriate compliance tool, standard assumptions and related regulations (collectively referred to as the carbon
compliance regime in this report) for the effective and efficient delivery of low energy/zero carbon new homes from 2016. The group acknowledged that the current compliance tool (SAP) is also used for other purposes, such as to produce EPCs for existing homes, and that other compliance tools (such as SBEM) are used for non- domestic buildings However , the group’s focus was on the most appropriate tool to guide effective decision making for the construction of new zero carbon homes.
Overheating - the need to effectively model overheating was highlighed as a key concern for future compliance.
"Overheating risk is a significant concern, with implications
for carbon emissions, health and consumer choice.
There is some anxiety that homes we are building today
may be at risk of overheating even in the current climate.
Given the prospect of significant warming, well within the
expected lifetime of homes, this risk will increase with
potentially serious consequences.
The assessment of overheating by SAP and other modelling
tools, including dynamic models which simulate change
during the day, shows little consistency. Further work is
urgently needed to understand and model overheating
effects, including how design features may help to mitigate
the risks. It is also necessary to confirm whether dynamic
modelling does indeed provide a more robust reflection of
reality, not just more comprehensive results.
The output from this work should be used to develop an
improved simplified overheating test. The test will
inevitably be used as a design tool (because compliance
defines the market) and it must therefore adequately reflect
the effects of both passive and active design features.
If an improved simplified test can be developed, SAP
should be retained as the carbon compliance tool. If
however an adequate simplified test cannot be found, a
dynamic modelling (or similar) approach will be required
to model overheating. This will beg the question
whether then other aspects, such as space heating
demand, should also be modelled in this way.
This work and subsequent decision is both urgent and
important. Whichever model is ultimately used, it should
be based on the projected future climate at a sub-
regional level including urban heat island effects.
Current regulations do not explicitly prevent homes
being built which are at risk of overheating. This needs
to change. Alternatively, regulations might simply assume
that active cooling is present and include the associated
carbon emissions within the compliance calculations if an
overheating risk is identified."
"SAP’s use of monthly averages fails to reflect the impact of
overheating. Extremes of temperature are important both for the
health and comfort of the occupants and for how they may adapt their
behaviour . An average temperature of 26° may not sound so bad, but
if it comprises 20 days at 21° and ten days at 36°, people’s health and
behaviour will certainly be affected, especially if the ten days fall
consecutively. In order to reflect this, a model is needed which maps
the impact of temperature peaks and does not rely on averages"
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