Is the Target Flawed? (≈ 5 minute read)
As 1 of 12 benefits forming the business case for the current project I’m working on it was identified that the installation of more efficient primary plant (CHP and boilers) along with more sophisticated and energy efficient control systems, pipework insulation, wireless thermostatic radiator valves (TRV) etc. would reduce the carbon emissions of the building.
Based on the improvements mentioned above and gas and electric meter readings of the building it was estimated from the antiquated 2017 SAP carbon intensities (0.218 kgCO2/kWh for gas and 0.399 kgCO2/kWh for electricity) that a saving of 554 tonnes of carbon per annum would be achieved, this figure is enshrined in the business case and needs to be met.
Flaws…
The project identified that the building was insufficiently heated and has upgraded both the capacity of the primary plant and the pipe sizes to accomodate faster mass flow rates and therefore an adequate delivery of heat as per the only equation I remember from phase 1, Q=mdot*Cp*DeltaT… joking of course.
More heat at a better efficiency = net carbon emission increase or decrease?
The metering strategy within the building is crude with little sub-metering, coupled with the fact that the occupancy patterns and building use are highly variable increases the difficulty with assessing in any detail the realisation of the target. It was also found that the lack of insulation on the pipework was actually relied upon in some areas (Like underfloor heating) to heat the bulding fabric. Therefore by introducing pipework insulation you’re reducing the heat losses in one place (the pipe) which increases the heat demand in other places (the emitters/radiators) to compensate for the removal of the indirect heating effect. Maybe there is a net reduction in consumption from the pipework insulation, no detail exists yet.
When the target was set there was no methodology for how to track and measure its achievement, no appreciation for the diffculties involved in being able to state, with a high degree of surety, this target has been met. It is assumed that the blanket energy meter readings will be looked at when the project is finished and the hope is that they’ve reduced by 554 tonnes of carbon…
Mission creep has led to enhancements and improvements that compromise the carbon target. Design ommissions such as the removal of wireless TRVs and large scale PV arrays just increase the burden for whatever solution (Likely a closed loop heat pump) is decided upon to address the delta in the carbon target.
Was the target SMART. Specific? Yes, Measurable? Yes but with sophisticated sub-metering and an accurate baseline with extensive data to start from. Achievable? Mission creep with a lack of cohesion across the programme may have resulted in net carbon emission increase, the data isn’t there yet.
White lies? Lets say your overall carbon emissions increased from 100 tonnes to 200 tonnes, but the plant you are now using is 93% efficient whereas before it was 75%. The argument could be made that as a direct result of having higher efficiency plant, the saving you have realised over the original plant is 18 tonnes of carbon, irrespective of the net carbon emission increase. The original wording in the business case was ‘reduce emissions by 554 carbon tonnes’ not ‘achieve a net carbon emission reduction of 554 tonnes’.
Whilst I see the importance for Bottom Line up Front business cases, in this situation the lack of detail with no technical justification completely discredit the benefit and the pressing environmental need for reduced ‘NET’ carbon emissions.
Food for thought.
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Interesting post mate. My eye is drawn to the assumption that ‘the blanket energy meter readings will be looked at when the project is finished and the hope is that they’ve reduced by 554 tonnes of carbon…’
The key spanner in the works seems to be the lack of clarity of what the baseline consumption reading is and so what the comparison is against, as the saying goes, you cant improve something without first measuring it.
The UK carbon emission guidelines are a percentage reduction against 1990 levels, which I’m sure you already knew, although many local councils have now superseded these targets with far more ambitious numbers and dates. Included in the UK guidelines are building performance details and improvements that must be made. I wonder how BP is aiming to meet these overall (as I assume that the royal household has to abide by Greater London guidelines as does everybody else??) and how the heat-pump technology may fit into this plan. As opposed to (as you explain) some fairly ethereal and hand-wavy targets that were put on paper at the inception of the business case but may no longer be relevant.
The baseline was taken from a billing meter data recording website called Stark. The 2017 SAP emission factors were applied to this meterage data to estabilish the carbon emissions. The GLA now specify we should be using the latest SAP 10 emission factors for making energy centred decisions, however we need to use the 2017 rates to maintain consistency even though they aren’t an accurate reflection of the carbon footprint of energy (not ideal)
So the fact it is a Listed Building means there are exemptions in meeting Part L of the Building Regulations as per Historic England guidance: https://historicengland.org.uk/images-books/publications/energy-efficiency-historic-buildings-ptl/heag014-energy-efficiency-partll/
“The Building Regulations Approved Documents for Part L make it clear that a
reasonable compromise on the energy efficiency targets may be acceptable in
order to preserve character and appearance and to avoid technical risks. They do
this by specifically including some ‘exemptions’ and circumstances where ‘special
considerations’ apply for historic buildings and those of traditional construction.”
As we all know the correct approach is 1) Reduce demand 2) Improve energy efficiency in terms of plant, systems, distribution etc., 3) Install renewable energy production technology.
We find ourselves at the heat pump option as it is extremely difficult to make adjustments improvements to the first 2 principles of emission reduction. As a listed building any fabric improvements are met with strong resistance, and energy efficiencies such as boiler improvements have already been introduced, there is still scope to improve the control systems in the future for further reduction.
A heat pump could be installed with little resistance and achieve carbon emission reductions immediately and be quantified easily.
The foundations are being introduced for achieving points 1-3 in the form of sub-metering and a detailed BMS, however they do not have the advantage of directly achieving a tangible carbon reduction to meet the target in a short time frame such as a heat pump.
How is the carbon output measured?
What is the CHP system?
Any diagrams?
The carbon output has only been measured through the principal designer taking meter data and applying the SAP 10 2017 emission rates. That was the only carbon output measured. The new BMS system being installed will link to the new sub-metering strategy being rolled out, from that dashboards and interfaces will predict the carbon output, whilst the BMS system is being installed I’m going to take the data from whatever meters are online and do my own calculations to see what the state of the carbon output is.
Pretty sure it’s a big Rolls Royce diesel engine (300 kWe), however I will have to come back to you on that for the detail, but: In the summer it provides circa 80% of the building heating load and it regularly provides about 30% of the building electrical load with the rest being supplied by a transformer.
Diagrams are all confidential unfortunately.