How Not To Confuse Efficiency With Efficacy

The constant cry for efficiency often seems to mean reduction.  It’s a valuable aim when it comes to energy or work. Why would we waste resource where it isn’t required?

FActory occupants and processesBut, it’s only efficient if it does a job. Any expenditure of energy is wasteful if there is no useful outcome, and it’s this part of energy efficiency that isn’t often considered in our New Zealand building design and operation processes. For example, air conditioning a building with no occupants, materials or processes that need a fixed environment is wasteful; anyone can see that. But what are we doing about reducing waste when we really do need a good outcome? There is only one way to answer that and it is with another set of questions:

• What do you need for your occupants or process?
• What can your building achieve before supplementary systems are employed?
• Which issues, if remedied, would improve that situation?
• What size do mechanical or electrical systems need to be to meet any gap?

Knowing what we need is the vital first step. Very often at InsideOut we see specifications that ask for ‘high’ thermal comfort and ‘low’ energy. It’s fine in the first paragraph of the spec but more concerning when a detailed read does not reveal any form of measurement for these ‘high’ and ‘low’ requirements.

Reaching for Comfort

If we look at thermal comfort, although the concepts are similar in the fields of visual comfort, acoustics and indoor air quality, we find that there are a variety of measures each useful in specific situations. The stumbling block to providing a suitable measure in the specification must be which to use and why, and where to set the benchmark. We can’t be intending to simply leave it to chance.

Adaptive Thermal ComfortThere is often an assumption that thermal comfort can be predicted by air temperature alone. Whilst this might be the case where the radiant thermal environment is largely the same as the air temperature, it often isn’t. There are uneven room surface temperatures, thermal mass, thermal bridges, and the radiant exchange through glazing to take into account. And that is before the variation from daily and annual cycles, occupancy patterns and the impact of air flows play their part. More complex measures are suitable where spaces are air conditioned and constantly occupied; and different ones again for naturally ventilated, hybrid and transient spaces.

Without setting the required levels for thermal comfort suitable to each space and its usage, servicing type and geographical location it is almost impossible to say whether the systems used to provide thermal comfort are energy efficient or not.

Specifying Efficiency

Eraldo Banovac reminds us that “Good managers don’t set a goal to increase efficiency, but rather an implementation of business process improvements that result in higher efficiency as well.” and so it is the case in building design and operation. Once we’ve described the levels of comfort we want to achieve, which means understanding why we need them, it is a much simpler matter to identify the energy efficiencies that can result.

So if we make our primary driver a building which meets the needs of its occupants and their activity we can start to address whether that can effectively be done with better energy efficiency. Again, finding a measure for energy consumption will be a part of the value set for the overall design.

Here in New Zealand we are familiar with the requirements of NZBC H1 which has a number of ways of indicating some level of energy efficiency. In our experience, the usage of energy can be very different between buildings even when they are designed to simply meet code. This can be further stretched by variable use of good passive design and low energy technologies. At InsideOut we often use a comparator between buildings of the annual energy expenditure for heating and cooling per square metre of floor area.

Performance and promisesSometimes it is not the milestone of a particular kWh/m²/annum that is important. It is simply that there is an affordable energy saving measure which can be applied on the project whilst maintaining or improving the occupant experience. That is the process put simply. Often it is a combination of designs by various specialists which when put together result in a ‘high’ comfort, ‘low’ energy building and one which will work with the budget.

Finding expertise in setting your ‘highs’ and ‘lows’ and evidencing and engineering aspects of the design to reach efficiency with efficacy is what your building performance engineer is there for.

Author: Ruth Williams – Principal, Buildings That Work InsideOut Ltd

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