The Role of Building Performance Simulation in Retrofit Optimisation

Many of the interviews included a focus on how the interviewees used BPS in the retrofitting process. Two tiers of processes were identified in relation to the targets/objectives of the building owners. For building owners with lower targets, decisions would generally be made on the recommendations of a Level 2 audit, for owners with higher aspirations a Level 3 audit and BPS would be used.

For less ambitious projects, particularly projects that did not involve major systems replacements, often BPS was reported as not being employed. Interviewees felt that consultants then used model- free analysis or relied on ‘empirical models’ consisting of previously collected benchmark data to determine indicative savings likely to accrue from particular retrofits proposed. For buildings targeting a typical level of energy efficiency improvement, Consultant C relied upon ‘hand calculations on a system-by-system basis’. These less extensive upgrades often will not economically justify the effectively fixed cost of a BPS exercise ($15 000 to $20 000, according to Consultant C). One consultant identified the initial cost of the energy audit as a common barrier to clients. Engaging a consultant to undertake both an energy audit and BPS exercise effectively doubles this cost barrier. Therefore, a prerequisite for BPS to be a part of the retrofit decision process is ‘a dead serious client who knows that they’re going to be spending a million dollars’.

There was a high level of confidence amongst the consultants interviewed that certain technologies will reliably achieve a moderate improvement in energy efficiency. For these technologies, most consultants recognised that BPS was not essential and that the energy saving opportunities can be assessed with a sufficient level of accuracy with a Level 2 energy audit. Upgrading lighting systems from T8 to T5, or to LEDs, installing Variable Speed Drives (VSDs) to fans and motors, and end- of-life chiller upgrades, to magnetic bearing chillers for example, were repeatedly identified as ‘easy wins’. This is consistent with the findings from the analysis of the Energy Saver Audits described in Section 4.2.3. For Consultant C:

First and foremost, you look at those easy wins. Can you just do a lighting upgrade, for example? Are there VSD’s on the fans that you can put in really quickly and simply? It doesn’t disrupt [the tenants] much.

Only one consultant raised non-technical retrofits, e.g. behavioural change campaigns and organisational changes. Quite possibly this is due to the business model of the companies the

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consultants worked, which were all engineering consultancies, not organisations focussed on change management. However, non-technical changes can have significant impacts for low cost. Consultant D saw organisational changes as the first to consider:

If I have an R-value for this wall, and I improve it to X, then this should have this impact. But at the same time you might think, well, if I move those persons from that side of the building to the other perimeter that will have the same impact and cost nothing.

For projects of sufficient scale to facilitate a BPS, there were several drivers for the use of simulation. These were seen to fall into three categories: compliance simulation, ‘proving-up’, and design/optimisation. Compliance incorporates BPS undertaken specifically to satisfy the requirements of a program or legislation, e.g. a NABERS Commitment Agreement, Section J Alternative Verification, or a Green Star rating. This type of simulation was mentioned by most consultants (though not generally discussed in detail). Consultants A and B, from the same company, stated that compliance was the major driver for BPS. It is likely that this is related strongly to the consultancy’s business model.

The second category of simulation was that for the purpose of ‘proving up’, where the simulation is undertaken to ‘prove’ that a particular upgrade strategy will result in a specific target being achieved. In many cases the target would have been achieving accreditation in one or more of the compliance schemes, for instance achieving a 5 Star NABERS rating. Another target of a proving- up strategy may have been sizing photovoltaic arrays to achieve net-zero energy. The crucial distinction between this type of simulation and simulation for design or optimisation is that the retrofit strategy has been decided, and BPS was used to ensure that the strategy would achieve the targets. ‘The tool validates your answer, and … proves up the strategy that you’re putting forward.’

Use of BPS as a design tool to compare different retrofit strategies was identified by several consultants, although Consultant D was the only participant for whom it was the main driver for simulation. For him ‘the main driver [for undertaking BPS] is discovering for ourselves what is the right thing to do’. This is in contrast to Consultant F, who had, ‘made most of the decisions by the time we’re doing the modelling, and the question is really, so we do all this stuff do we get to where we want to be?’ Although he saw ‘analytical enquiry rather than doing things by gut feel is becoming more prevalent.’

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Consultant F described a further category of simulation; the use of reference building models to generate approximations of energy savings for interventions in smaller scale engagements where the fee would not support a full-scale model. He explains:

The value of simulation becomes in generating rules of thumb, or indeed in testing a specific proposition in a generic model, so…OK, are we going to, you know, fiddle around with the dead-bands? What sort of saving are we going to get from that? I’ll just run it through the model. A generic modelling, not linked to that site, put it in and you go, ‘Well, in Brisbane it seems to be a two percent effect. Ok, I’ll allow for two percent in my model.’ And that’s quite cost-effective.

Representative quotes related to the roles that BPS can play in an energy efficient retrofit, identified in the current analysis are given in Table 4-2.

Table 4-2 Indicative views on the role of BPS in energy efficiency retrofitting.

Example quote

Compliance I’ve done a number of different models... covering 3 different applications

mainly, these being NABERS prediction models, JV3 alt sols for BCA compliance, and Green star modelling under the various different tools and their guidelines.

‘Proving up’ Most of the time it’s about proving up something or other. Proving up a NABERS rating, or proving up a retrofit. It’s rarely used directly as an

inquisitive model. Generally we’ve made most of the decisions by the time we’re doing the modelling, and the question is really, so we do all this stuff. Do we get to where we want to be?

Retrofit design … you might be able to submit it for Green Star, or predict a NABERS result, or

submit a Section J report. They’re sort of by-products of wanting to... model the building. … so, use it as a design tool rather than a compliance tool.

…it’s still in a way a design tool. What we’d be able to with that energy modelling is, you know, compare two different options, for example, and as a result of those comparisons be able to show the client which one of them, for the costs, is going to get them a bigger bang for buck.