Energy efficiency buildings: Design looking to the past or to the future

Design looking to the past or looking to the future

Currently buildings are designed, or should be designed, in order to optimize Energy Efficiency and reach the requirement of Energy Buildings Nearly Void (NZEB).

For this, the regulations usually impose some design limitations focused on reducing demand / energy consumption. For this purpose, they often use multi-zone calculation tools in dynamic regime.

There are multiple tools for this purpose, but all of them have in common the use of a climate file with the hourly information of temperatures / radiations solar / wind / ... to be able to carry out the calculations.

The climatic files are based on obtaining historical data from weather stations close to the location where the calculation is to be carried out and then the station data is adapted meteorological conditions close to the most realistic situation of the location.

Use historical climate files to perform an energy evaluation of the building is “looking at the past”, assuming that the weather was stable would be suitable as a design basis for buildings futures.

Unfortunately it is more than proven that the world climate is changing substantially and therefore the historical data of the past are not enough
representative of the behavior of the climate in years futures.

It is necessary to have prospective climate files of the future to be able to design current buildings "looking at to the future”

Obtain prospective climate files from the future

1.-Climate files historical

Historical climate files in either EPW or in TRY2 they will be our starting point.

You can find climate files records on multiple web pages by way of example some of them are attached:

• From Energy Plus in Weather Data HERE.
• From One Building in its Climate section HERE.

2.-Scenarios prospective

The intergovernmental panel for the protection of the climate change (IPPC) has developed the scenarios that allow “predicting” the future climate based on current data. can be consulted from HERE.

3.-Obtain predictive files of the future

The University of Southampton has developed the CCWorldWeatherGen tool that allows you to transform any historical file.

The CCWorldWeatherGen tool that we can see HERE is not more than an Excel spreadsheet that feeding on the historical data in epw format and of the scenarios of forecast of the evolution of the climate elaborated by IPPC allows obtain predictive climate files for a future 2020 / 2050 / 2080.

Compare files climatic conditions

Following the procedure described above, the prepared the climatic files of a site in Barcelona for a horizon 2020/ 2050 / 2080 and will be compared with the data of the historical files commonly used by building designers.

The variables analyzed will be the air temperature, the diffuse solar radiation and solar radiation in the direction normal.

Air temperature:

There is a clear increase in temperatures both minimums as maximums or averages.

Diffuse solar radiation:

A slight decrease in solar radiation can be seen cumulative and average diffuse, while the maximum values decrease in a 2020 horizon and increase again in a horizon 2050/2080.

Solar radiation in the direction regular:

There is clearly an increase in solar radiation average and accumulated, while the maximum value presents a slight decline in 2020 to increase again in 2050 / 2080.

From the analysis of the climatic files it seems It can be inferred that there will be a slight reduction in the climatic severity in winter with increasing severity climatic conditions in summer, it also seems It can be inferred that the cold seasons will be longer longer than currently while the heating ones are they will stay pretty similar.

Remember that we also have the case study on the energy efficiency in buildings in the face of insulation... Does the calculation of the "optimal cost" is the most ambitious criterion?

Repercussion at the level of building

Once it has been verified that the weather conditions will be different in the future from those we currently consider, begs the question… how will this affect comfort for the
users?

We will consider a dwelling within a block of flats as an example and we will simulate it under the same conditions constructive and operational for different climates considered.

We will analyze the operating temperature in free float (absence of air conditioning system) throughout the year.

Displayed on the graph as temperatures free-floating operating costs tend to increase with the future evolution of climate scenarios, therefore that the risk of lack of comfort due to excessive heat becomes evident.

To obtain a unique numerical indicator, we can in each climate scenario evaluate the number of degree hours in which the building is below 20ºC (feeling cold) or the number of hours in which if it is above 26ºC (sensation of heat).

It clearly follows that periods of lack of heat comfort will become longer and more intense as that those of lack of comfort due to cold will remain quite equal with a slight tendency to reduce the intensity and duration.

CONCLUSIONS

• “Future” climate data can be obtained easily from available historical data.
• The commonly established hypotheses of consider the cooling season between June to September should be called into question, and, consequently, the hourly profiles of temperatures of setpoint, hourly profiles for activation of the sunscreens or night ventilation should adapt to the new situation so that the design of buildings is not done "looking at the past" but "looking at the future.”
• Similarly, those strategies aimed at reducing lack of comfort due to heat such as: the best air transfer management (infiltration + ventilation) or capture surfaces (size and orientation of holes) should be designed according to future needs and not based on the criteria of the past.
• We have not considered in this study the variations that will occur in the future related to habits social (greater employment, teleworking, aging of the population,...) greater presence of equipment (automation, home automation,...), reduction of internal loads contributed by equipment and lighting due to the foreseeable evolution technology (led lighting,...) or a possible evolution of occupancy levels based on the surface area of the dwellings (smaller dwellings).
• We can conclude that the studies that are carried out to assess energy efficiency, whether regulatory or energy rating are anchored in the past instead of “looking to the future”.

Don't forget to go through the article on whether a high insulation in summer for the residential sector.