Part L2A 2010 – worked case study

The following example is one which BRE used at the recent Part L 2010 workshop I attended a few weeks ago. At the time I was mildly amused by the fact that they’d given us the example, but hadn’t worked out a solution themselves. Having been through umpteen iterations, I can see why.

I’m going to use this example as a way of demonstrating some key points with regards the new Part L, which I don’t think everyone in the industry has picked up yet. I am assuming of course that Part L 2010 will come in on 1 October. Perhaps no-one else shares my optimism and are ignoring the changes in the hope they’ll go away and die a slow death.

• Biomass is no longer the silver bullet it was under 2006
• EPC’s in 2010 are on a different scale to EPC’s in 2006, so cannot be compared easily (as we suspected – see the comments following this post in May)
• A building which had an EPC of 40 under Part L 2006, gaining an Excellent under BREEAM 2008, does not automatically pass Part L 2010
• a 25% improvement over 2006 does not automatically mean your building will pass under 2010 – the aggregate approach means there are no easy rules of thumb – and that table which I linked to in this post has disappeared
• An low EPC under Part L 2010 does not guarantee Part L compliance
• The efficiency of building services has by far the greatest effect on ratings

It has turned out to be a very long article so to read the whole thing, see under the fold.

It’s a one storey building, with a 2m² solar thermal array to provide a 10% renewables obligation. The original constructions and HVAC systems are described at the end of this article.

I ran the baseline case through both iSBEM 3.5 and iSBEM 4.0. I then made tweaks in both to see the effect on both compliance (BER<TER) and EPC under both 2006 and 2010. I normally wouldn’t publish this level of data for fear of it being used inaccurately, but it was rather hard to demonstrate the points I wanted to make without doing so. All the usual caveats apply – the data here is for information only, do not sue me if it turns out to be wrong or inaccurate, use your common sense and judgement, blah, blah, blah.

The biggest change to Part L has been the re-casting of the notional building. This means that instead of using a 2002 notional building and adding improvement factors, the notional building is now a 2010 notional building, which varies depending on the fuel used. It’s a subtle change, but it means that the TER changes between fuel types (see table below). The EPC is still calculated using the SER.

The slide above is taken from the IES presentation which I have linked to previously – I’ve not checked that the figures are still the same (the carbon factors have changed since this presentation, so there is a chance the SEER etc might have changed), however the principles remain the same – the TER is MUCH harder to achieve under 2010.

The 2010 results have all been modelled using iSBEM 4.0.a – the software did crash quite a few times, so I’m not convinced it’s too stable yet. There were also some inconsistencies between the EPC when calculated under Part L compliance and under asset rating which concerned me.

Note first of all the differences between the EPC’s under 2006 and 2010. They are no longer directly comparable, which to me seems illogical. I hadinitially worried that this was an error on my part, rather than intentional, so I was delighted to see David Kingstone of Buro Happold coming to the same conclusion:

“Although the definition for the Energy Performance Certificate (EPC) reference building has not changed, the way emissions are calculated for an actual building have. This will mean that the resulting EPC rating, assessed from October, will be different to that calculated now.

Consequently, this may result in a change in the EPC rating band, the number of BREEAM energy credits and even the BREEAM rating. However, only by assessing this in detail, and on a range of building types, will the result be known.

I’ve used an EPC benchmark of 40 (which is the minimum for BREEAM excellent) – to get the original building up to 40 under 2006, the only change required was changing the solar thermal to PV (an additional capital cost of ~£3k, but with the FiT, an income generator).

Note that in scenario 3, although we are not yet passing Part L 2010 compliance, the EPC is within the BREEAM requirements for Excellent under BREEAM 2008.

It is possible under scenario 5 to both gain compliance and BREEAM Excellent (assuming BREEAM remains at 40) without any renewables at all, but with some major tweaks to lighting and cooling.

If we use this exact same tweaked model, with excellent building services efficiencies, but swap the fuel to biomass, the building fails Part L compliance. THIS HAS MASSIVE IMPLICATIONS. To pass we need to add a further 20m² of PV. But look at what has happened to the EPC – we are now sitting at 25, which is the minimum standard for BREEAM Outstanding.

I wait with interest to see what happens with BREEAM and the energy credits. I have more to say with regards to Part L and PPS22, the Merton rule and renewables but that will wait for another day.

Contrary to some reports I have seen in the press, air tightness has remained at 10 m²/h/m³ at 50Pa, and has not been improved to 5 m²/h/m³ at 50Pa. I haven’t published the results I got when I changed air tightness to 5 in the table above, but for comparison, for scenario 1 when air tightness is improved from 10 to 5, the BER improves from 48.7 to 47.7 (a much lower effect than improving the lighting, at what potentially might be a much higher cost).

Baseline Constructions and HVAC systems

The initial default air permeability was 25 m³/h/m² at 50 Pa, but I’ve used 10 m³/h/m² at 50 Pa in order to meet compliance.

HVAC Systems

LTHW with floor heating serving the office area which is separately sub-metered, system is on the current ECA list, heating seasonal efficiency of 0.92

Split system with an air source heat pump, serving the workshops and laboratories. System is separately sub-metered, heating seasonal efficiency of 2.8, cooling efficiency of 2.2 and nominal efficiency of 2.75

The plant room and stores have no HVAC systems

Hot Water Systems

Local Calorifier is the same as the LTHW, storage volume of 100 litres with standard factory insulation of 80mm. This will serve the offices only.

Instantaneous hot water seasonal efficiency of 0.75 which will be serving the laboratories.

Solar Thermal

In order to meet the renewable obligation there will be a 2m² evacuated solar tube collector installed.

Lighting

T5’s in all the rooms with auto on-off occupancy sensors

Tagged as: isbem, Part L, Part L 2010