The passive adaptivity index graph in ECOTECT allows you to evaluate the passive performance of a building. This thermal calculation plots temperature of the selected zone against the prevailing outside temperature for the selected priod, and then draws a 'line of best fit'. This gives an index value between 0.0 and 1.0, where a lower index value indicates better passive performance.

This article looks at how you can use this index to evaluate and improve the passive performance of a zone within an ECOTECT model. This article uses the SimpleThermalModel.eco found in the ECOTECT Examples folder (with the Perth weather data file), so you may want to experiment for yourself as you read along.

The following passive adaptivity index graph shows Zone 1 in the example file over the course of an entire year :

Passive adaptivity index for Zone 1 in its default state, with an index of 0.86

Note the colours used to plot the relationship between zone and outside temperature - green represents times when both the zone/outside temperature fall within the defined thermal comfort band. Blue represents times when the temperatures are above the thermal comfort band (indicating a cooling load is required), while red representes times when the temperatures are below the thermal comfort band (indicating a heating load is required). With an index value of 0.90, this suggests that this zone does not perform particularly well from a passive perspective; note also that the distribution of blue plotted points indicates that a significant cooling load is required in this zone.

If we change this zone to be fully air-conditioned and then re-calculate the index, note how all points are now coloured green, and the measured index value is 0.50. While this suggests ideal comfort conditions all year round, this is only due to the use of air-conditioning, which requires significant amounts of energy to operate. Note also the temperature plots terminate sharply at the lower and upper limits of the thermal comfort band - this is where air-conditioning is required to maintain thermal comfort. Thus, the goal is to reduce the measured index value as much as possible before turning to energy-consuming heating and cooling systems.

Passive adaptivity index of 0.50 for a fully air-conditioned zone. However, this would require a lot of energy to achieve.

Let's start by using materials with better insulation properties. Set the HVAC Active System for the Zone 1 back to Natural Ventilation, and then change the wall material to ReverseBrickVeneerR_20 and the roof material to MetalDeck_Insulated. Recalculate the index - the index has now been reduced to 0.61, a significant improvement.

Using materials with better insulation properties improves the index from 0.90 to 0.61.

Next, try changing the material used in the windows to high-performance glazing, such as DoubleGlazed_LowE_TimberFrame. When you recalculate the index, it reduces again slightly, to 0.59

Using high performance glazing reduces the index a little bit more.

Looking at the temperature plots on the current passive adaptivity index, the requirement for heating has significantly reduced with the changes we have made to the model. Let's now look at the cooling loads.

Try opening up the building to cross ventilation by increasing the infiltration rate for Zone 1 to 50ach. When we re-calculate the index, this has made the passive performance of the building worse, because we haven't specified when the building is to be cross-ventilated.

Increasing the infiltration rate across the entire year actually makes the passive adaptivity index worse.

However, if we are more specific about when the building is to be cross ventilated, the results are very different. Create an operational schedule for the infiltration rate that only opens up the building during the night in summer. When you re-calculate the index, it has now reduced again, in this case down to 0.49.

Limiting the cross ventilation to only summer nights reduces the index significantly.

Now that we have significantly improved the passive performance of the building, re-activate full air-conditioning for the zone. Note how the index is now lower than previously calculated index for full-airconditioning. This indicates that this zone will not require as much energy to maintain thermal comfort, as its improved passive performance reduces the need for air-conditioning.

The index with air-conditioning is now only 0.37 - a significant improvement.

Summary

As can be seen, the passive adaptivity index in ECOTECT is an easy to use analysis tool for assessing the passive performance of a building. By making progressive alterations to the model, the index can be used to conveniently assess the effectiveness of each change, without the need to analyse more detailed calculation data. This is particularly useful in the early stages of the design process. The colour-coded temperature plots also make it simple to visually interpret the results - the more green dots the better!