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Climate data in Archicad 17
Whether you are designing new constructions or deep energy retrofits, the basis for an energy efficient design is an understanding of the climate that you are working in. Local climate has has always been one of the main factors shaping vernacular architectural design throughout the world, and, ultimately, the goal of any building is to protect the occupant from external climate factors. Therefore, an effective thermal envelope of a building should bridge the gap between the desired health and comfort conditions for the occupants and external weather conditions.
When it comes to energy modeling or computer simulations of highly efficient buildings, such as those that are designed to the Passive House standard, sourcing relevant, reliable, complete and accurate climate data is a necessary step in the early design process. However, obtaining a complete and pertinent set of climate data that fits your design needs can be more complex than it may seem.
First of all, what is climate data?
Climate data is the statistical record of weather events that occur in one specific location – the weather station – over a specific period of time.
This data usually includes monthly mean values of air temperature, relative humidity, sun radiation, wind direction and speed, pressure, and rain data. It is important to understand that the weather stations where this data is collected are usually located at local airports, where weather conditions need to be constantly under control. Other weather stations can often be found in places dedicated to scientific research and/or weather forecasting.
GETTING STARTED: Questions to Ask Yourself
To get started on an energy evaluation of your building, these are the first few questions you should ask yourself regarding your climate data:
1. What kind of simulation are you doing? The extent of detail in your planned simulation can help you decide how accurate or what kind of specific climate data you need to find in order to get accurate results. When isolating climate statistics, continue to think about the specific simulation you will be running. Are you investigating the yearly energy consumption? Do you need to estimate the heating/cooling load for your thermal envelope (for an HVAC design, for example)? Are you about to run a hygro-thermal analysis? Do you need to make a finite element calculation to assess mold and condensation problems?
2. Where is my building located? You should have the address, the geographic site coordinates (making sure you know the reference system they refer to), and the altitude from the sea level.
3. What is around my building? Is it in a city, or in the countryside? Are there trees/buildings blocking sunlight and/or wind?
4. What weather stations are located near my site? Is there one, or more than one? Do I have access to that data? Is that data complete? Is that data reliable? This part may actually take quite a while.
5. What kind of building are you designing? What is the relationship between the climate data and your thermal envelope? Different efficiency levels of the thermal envelope of your building require adjustments in the way the data is handled.
KINDS OF CLIMATE DATA: Good, Better, and Best
The most basic set of climate data set should include
- monthly mean values of temperature,
- relative humidity of outside air, and
- solar radiation (direct, diffused, and divided by orientation).
Additional basic climate data could include monthly values of wind speed and direction.
More detailed data include values such as ground temperature (usually at two different depths), as well as sky temperature.
Advanced climate data sets provide rain data, which would be necessary for a complete hygrothermal simulation.
Besides the data kind (temperature, humidity etc.), data interval is very important too. Depending on the set, values may be expressed as monthly, weekly, daily or hourly mean values. Some dynamic simulation softwares require the data to be expressed by 15 minutes steps. If you want to know what kind of climate data you need, you need to look into what kind of simulation you are going to use the data for.
SOURCES OF DATA: Location, Location, Location.
Climate data is collected in weather stations that are very rarely located on your project site. For the data to be statistically valid, values need to be collected for several years in a row, so installing a weather station on your project site may be of very little help too, unless you are willing to wait.
You should also consider the fact that a weather station, even if located near your site, may not be representative of micro climate conditions of your specific site.
For example: weather stations that are located at airports may not have much in common with your specific site. An airport is a large, open site, usually located outside city limits. The average temperatures recorded at an airport are usually lower than the ones in the center of the city because of heat island effect. Furthermore, the wind speed is usually higher. Local speed and direction of the wind at your project site is usually influenced by specific obstacles, such as trees and buildings, that may block it or create localized tunnel effects. Sun radiation is also subject to the boundary conditions of each project: surrounding objects cast shadows onto your building, decreasing the values of solar radiation in some cases.
Depending on the kind of simulation you are running, these site-specific factors should be taken into consideration.
FUTURE ACCURACY: The Effects of Climate Change
That’s right: the polar bear on the ice sheet. World climate is changing. If you don’t believe that, please feel free to use any kind of climate data you want.
IPCC climate data (cilck image for source)
If you do understand that the world climate is actually changing, then you realize that your climate data needs to be up to date. Depending on the country where your project is located, finding up-to-date climate data sets can be tricky sometimes.
In Italy, for example, the official climate data set (UNI 10349) is based on the 1961-1990 period. Obviously, due to climate change, current temperatures are commonly higher than the recorded ones from over 20 years ago. More recent climate data is available and allowed for energy simulations. However the majority of professionals unfortunately base their calculations on outdated data simply because it is what is readily available, and it is listed as “official”.
When adjusting climate data to more accurately reflect current and future scenarios, the 2007 and 2012 IPCC reports can be very helpful (a subject which we will be addressing in a separate article).
One thing is clear: designing comfortable and energy efficient buildings is going to be a learning process for architects of the 21st Century.
BUILDING ENVELOPE and CLIMATE DATA: a Two-Way Relationship
It is true that all buildings are affected by the climate they are built in. However, some building are affected more than others.
A high quality thermal envelope can go through waves of heat and frost almost untouched, while a lower quality one will suffer and the occupants will need to consume energy to remain comfortable. The combination of internal thermal capacity and transmittance of the envelope structures build up the time constant of the thermal envelope: for continued use buildings (such as residential), the longer time constant, the better. This is one of the many reasons that we are supporters of third party standards like Passive House, which prescribe high quality thermal envelope design.
When it comes to climate data for your energy simulation, you need to know what kind of envelope you want to simulate, to be able to adapt the data to the design time constant.
Conclusions
In order to achieve a comfortable internal environment for your building occupants without the need for excessive consumption of energy, it is essential that you have a solid understanding of the main impacts on the thermal envelope of your design. Climate data and the specific site conditions that may affect your climate data are a fundamental part of this.
Since climate is one of the most important factors in the energy balance of a building, finding accurate and pertinent climate data is one of the most important of the energy design process.
“If you can not measure it, you can not improve it.” – Lord Kelvin
No one ever said that designing for the 21st Century was going to be easy.
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