THE DISPLAY® METHODOLOGY

From Display Documentation in English

Latest revision as of 14:27, 21 October 2010

The poster generation tool uses a calculation instrument to calculate the information shown on the Display® poster. In the following, a detailed description is given on how this calculation instrument determines the characteristic values and how the classification of the building is made. An extensive list of all used conversion factors is presented in the appendix.

Structure of the calculation tool

Conversion of Final Energy into Primary Energy and calculation of CO2 Emissions

The General Approach

Starting from the final energy consumption data the Display® calculation instrument uses conversion factors to calculate the equivalent primary energy consumption. For this conversion it applies the cumulative energy use factors. These factors describe the overall primary energy consumption which is linked with the creation or use of a product or a service, including all preproduction chains (extraction + transport + transformation) but without primary energy that is used as materials such as wood for the construction of a building or petrol for synthetic material. Furthermore, the energy utilised for the disposal (i.e. passive energy contained in the materials) is not taken into account. Since there is not a widely used abbreviation in for this factor in English so far we use the German abbreviation KEV in this users’ guide. Contrary to the cumulative energy use factors the cumulative energy demand (CED) factors that are defined in the German guideline VDI 4600 include the amount of primary energy that is used as materials and that is reflected in the lower heating value of the product. They also take into account the energy input for the disposal.

The German Institute for Applied Ecology (Öko-Institut) has developed the life-cycle analysis program and database GEMIS. This program is capable of calculating the cumulative energy (KEV) use factors for a variety of different energy sources and processes. On the basis of the processes linked to a service or a product the program also generates the greenhouse gas emissions related to the production or consumption of a product, given in kg of CO2 equivalents per kWh of energy. Since the respective conversion factor takes into account the sum of all greenhouse gas emissions on the chain of energy transformation it is cumulative, too. As already mentioned in chapter 2 the term CO2 emissions is used for means of simplification to express these greenhouse gas emissions.

The Display® calculation instrument uses conversion factors based on the GEMIS program, but produced by different sources:
The conversion factors for the energy sources gas, fuel, and coal result from a GEMIS version 4., calculations made by the Institute for Housing and Environment (IWU) Darmstadt, Germany. They are also used for the certificate of residential buildings developed by the German Energy Agency (dena). The factors for wood, the production of hot water by a solar thermal collector, and for the production of photovoltaic electricity in the building are taken from the ProBas database which is run by the Umweltbundesamt. This data source is also used to provide most of the factors for the national electricity mixes. The conversion factors that are used for district heat by default are also taken from a GEMIS version 4.14 calculation made by the IWU.

Currently, the calculation instrument distinguishes only between one value for district heating networks with and one without cogeneration plants. It is intended to provide more precise conversion factors for the specified type of plant in the future. However, it is already possible to enter individual factors which are more adapted to the local situation by specifying the distribution of the energy sources consumed in the different heating production plants. This distribution is necessary in order to calculate the correct distribution of the different energy sources (Fossil, Nuclear, and Renewable).

There are different system boundaries for conversion factors that are used. For gas, fuel oil, and coal the system boundary is the transfer point of the building, including the heat generator. The conversion factors for wood do not include transport and the heat generator. Concerning all different utilisations of electricity, the conversion factors only include the generation of electricity. They do not take into account the transport of electricity or transformation processes in the building of the consumer. For the use of a solar thermal collector, the conversion factor takes into account the energy input up to the transfer point of heat at the outlet of the device. Further devices that are necessary to run the heating system are not included. The system boundaries are valid for energy conversion factors as well as for the C02 Emission factors. In order to calculate the contribution of different energy sources (Fossil, Nuclear, Renewable) to the overall energy mix used in the building it is necessary to know the composition of the national energy mix for the production of electricity. For this purpose the Monthly Electricity Survey in its version from October 2005 that is published by the International Energy Agency (IEA) is used.

Local weather correction

As the energy consumption of a building depends on the climate conditions and since these climate conditions vary for one certain geographic region over the years, the consumption data have to be corrected for the local climate. Otherwise, it would not be possible to compare the results of the calculation instrument for one building in the different reference years.

In order to include a weather correction factor the final energy that is used for space heating is multiplied by the weather correction factor. After this step, the total climate corrected final energy consumption of the corresponding energy source is multiplied with the specific CED or KEV factor. The result is the associated primary energy consumption.

Thus, a weather correction factor larger than one that represents a relatively mild winter simulates an increase in the amount of energy consumption of the building. This is necessary as the building would have consumed more energy under average climate circumstances. As a result, the different energy consumption ratios are comparable over the years.

The local climate correction factor comes from the comparison between the average of the winter temperature for the reference year and the average for the winter period over a long period fixed by the country (for example 30 years in France, 20 years in Germany). It is also possible to calculate this factor from the degree days (DD): average DD (+- 20 years) / reference year DD.

Two assumptions are made in case you have not entered the exact contribution of one energy source to space or heating purposes which means that data has been entered only in the total field:

• In case there are entries in the total field for electricity and at the same time for other energies or energy sources (gas, fuel oil, coal, district heating, wood) the whole amount of electricity is assumed to be used for other purposes other than space heating whereas the other energies or energy sources are assumed to be solely for space heating purposes.
  

• If there is no entry other than electricity, a percentage of 70% is assumed to be used for space heating. The rest is assumed to be used for all other purposes and this energy consumption is not taken into account for the weather correction.
  

However, to make buildings situated in different climatic zones comparable, it is necessary to apply a specific classification scheme to each corresponding climatic zone. In order to keep the classification scheme concise and not too complicated the Display® calculation instrument uses an identical classification scheme for all participating cities. By applying such a uniform classification scheme, the results show in which buildings huge improvements can still be made. It is known that, if national classification schemes were used, buildings that were formerly well-classified could be graded harsher than with this uniform classification scheme. Therefore, the Display® classification scheme is a scheme where good ratings are rather hard to obtain. Please note that thermal solar energy is always linked with water heating.

Which data are used to calculate the regional weather correction factor?

With the goal of harmonising the Display software and increasing the accuracy of your calculations, the weather correction factor is calculated using normalised European statistical data at a regional level from the European statistical institute: Eurostat.

Are those data less precise than the ones obtained from your local meteorological station?

Yes and no. As the new factors are calculated at a regional scale we are aware that some cities may have entered data that are more precise.
Therefore, if you have the capacity to calculate your own local weather correction factor you will be able to replace the default regional factor with this figure. This solution has been preferred because of its European and normalised dimension.
If you do not have more precise data, the regional weather correction factor will be automatically taken into consideration.
If you want to obtain your local weather correction factor, ask your energy service provider or a meteorological office.
The local climate correction factor comes from the comparison between the average degree heating days (DD) and the reference year i.e. : average DD for your city / reference year DD.
NB. This calculation is for your local area. Do not compare the degree days for your reference year with the average for your country or another region. It must be compared with the average for your city. The correction factor normally lies between 0.85 and 1.15. A figure of 0.85 signifying a particularly cold year and a figure of 1.15 a warm year.

Is it important to have a correlation between the period that you enter your consumption data and the weather correction factor?

Yes. As the European data are collected from the 1st of January to the 31st of December each year, to create your poster for 2010 you will be required to wait until January 2011 and are also required to enter your consumption data using the same time period i.e. 1st of January to the 31st of December of each year. If you use your own local weather correction factor please make sure that the time period that you collect your consumption data correlates with the time period for your heating degree days.

Why is it important to use a weather correction factor?

Temperature-corrected energy consumption data are useful as they allow the correct interpretation of energy consumption trends and provide an accurate basis for the development of an energy policy. It avoids a potential “false” decrease of energy consumption which might come from hot weather instead of real technical or behavioural improvements.

Which data and assumptions are required to calculate the regional weather correction factor?

In order to implement a weather correction factor for final energy consumption, the following elements must be known:

• Actual final energy consumption (available from your bill or your energy meter)
  
• The share of energy used for space heating
  
• The number of heating degree-days (severity of the cold in a specific time period, taking into account the outdoor temperature and the room temperature) (calculated by Display from the Eurostat data).
  
  

How is the regional weather correction factor calculated?

To ensure a common and comparable basis, the following method is used to calculate heating degree-days:

• (18°C - Tm) x d if Tm is lower or equal to 15°C
• zero if Tm is greater than 15°C

where 15°C is the heating threshold and Tm is the mean (Tmin + Tmax / 2) outdoor temperature over a period of d days.

The weather correction factor (relative heating degree-days for eurostat) is in turn defined as the ratio of long-term average degree days (30 years) to actual degree-days (be careful, it is the opposite for Eurostat). A relatively long base period is desirable to balance out the influence of short-term changes in mean temperatures. Furthermore, the degree-days and climate correction factor have to be calculated at regional level (temperature data sets from a large number of individual weather stations). Finally, the relative degree-days are weighted by population. A case study (United Kingdom) allowed us to measure the precision of two different regional levels. Although the differences observed were not significant, the more detailed regional level was finally chosen, as many public, private and academic users expressed their interest in obtaining such figures.

Please note that the weather correction that is applied in the Display® calculation intrument does not take into account climatic differences between two geographical zones.

What is the source of the data and how have regions been defined?

The raw temperature data from 1500 weather stations are collected and processed by the Joint Research Centre (JRC) - IPSC / Agrifish Unit / MARS-STAT Action. Using a fine grid (50 km x 50 km), the JRC applies a meteorological model (during the whole year and not just the heating period (October to May)) to establish the best set of weather stations for the interpolation of temperature data at regional level (according to NUTS - Nomenclature of Territorial Units for Statistics). Once this selection has been made, the actual interpolation consists of a simple average, corrected for altitude difference. After the calculation of representative daily temperature data (maximum, minimum and mean temperature) for each grid cell, daily temperature sets are compiled for all the relevant administrative regions (régions in France, Länder in Germany, cantons in Switzerland…) to produce area-weighted averages. A further refinement through weighting by population is then made using the average annual regional population data available from Eurostat. The result is the calculation of the monthly and annual actual degree-days for the country aggregate on the basis of administrative regions weighted by population, used by Display®, taking as a reference period the years 1980 to 2009.

From Eurostat Statistical Book: Panorama of Energy, Energy statistics to support EU policies and solutions (2007)[[1]] Chapter 3 - Recent development on Energy Statistics in the EU

Print screen of the roots of Eurostat data base

Non-Electrical Energy Consumption

The calculation instrument automatically takes the CED and KEV factors for the energy sources gas, fuel, coal and wood.

If the building disposes of a solar thermal collector, its production of hot water will be converted into primary energy. In order to ensure the simplicity of the calculation instrument it is assumed that a flat-plate collector is used.
If there is a cogeneration unit in the building the calculation instrument assumes that either natural gas, fuel oil (diesel) or biogass is used.

Furthermore, having subtracted the amount of gas that the cogeneration unit consumed for producing electricity, the remaining amount of gas is taken into account for weather correction although it still includes a certain amount of gas that is used for providing hot water. If the gas used for the supply with hot water does not make up a substantial part of the overall gas consumption the variations can be neglected. However, in case of a significant demand for hot water, e.g. in school buildings containing a swimming pool or a gymnasium, this procedure is not appropriate and falsifies the classification of the building. This deficiency will be removed in the future.
Concerning district heating, the calculation instrument uses standard factors which are appropriate to the district heating network that you have specified the distribution of the energy sources. If you have entered individual factors the Display® team will check if these factors meet the requirements.

Electricity Consumption

Since there are a lot of suppliers offering electricity that is produced using very different energy sources the calculation instrument cannot take into account every possibility. It implements four possibilities:

• The first possibility is to purchase conventional electricity. Hereby conventional electricity signifies that it is purchased with supply contracts that do not contain an agreement about the contribution of specific primary energy sources to the overall energy mix. Therefore, it can be assumed that this electricity is composed similarly to the national electricity production. For this purpose the data were obtained from the results of the GEMIS version 4.5 calculation published by the Öko-Institut.
  

The possibility to specify the global mix of the electricity production is used for the distribution of the energy sources (Fossil, Nuclear, and Renewable).

The purchase of “green” electricity means that it is provided by using supply contracts that define a certified “green” energy mix. The calculation instrument assumes that wind power and hydro energy each contribute 50 % to the overall energy mix since both are the most frequently used renewable energy sources for the production of electricity. The specific factors are sourced from GEMIS version 4.13 calculation made by the IWU.

If the building is equipped with photovoltaic panels for which a production of a certain amount of electricity has been declared the calculation instruments assumes that the system consists of polycrystalline silicon. As this is by far the most widely used technique, this simplification will normally not result in a false calculation. The conversion factors were obtained from the ProBas database.

In case of a cogeneration unit in the building the calculation instruments takes into account the possibility of supplementary electricity fed into the grid. However, there are no further credits given for this extra electricity. The justification for this proceeding is that the corresponding amount of electricity should normally already be rated at the point where it is finally consumed. The following example gives a detailed description of the calculation process for a cogeneration unit in the building.

CO2 Emissions

Compared to the calculation of primary energy consumption the C02 emissions are treated in a similar way. For each energy source they are calculated on the basis of the climate corrected final energy consumption. The conversion factors depend on the energy sources and in case of electricity additionally on the country.

Calculation of the Ratios and Applying the Classification Scheme

The primary energy ratio is calculated by dividing the overall primary energy consumption per year by the gross internal floor area. The CO2 ratio and the water ratio are determined in an analogous way, whereas in the case of water the unit is converted from m3 to l. . An exception is made for swimming pools, where the water ratio is expressed in l/users. Afterwards, the building is placed in the classification scheme, depending on the calculated ratios and the declared type of the building. Detailed information on the classification scheme is given in appendix 1.

Specification of the Contribution of Different Energy Sources

The calculation instrument divides the energy sources into the three categories fossil, nuclear, and renewable. Hereby, the following assignments are used:

• Fossil:
  
  • gas, fuel oil, coal,
    
  • district heating (fossil fuels incl. waste incineration),
    
  • electricity (conventional: fossil fuels)
    
• Nuclear:
  
  • electricity (conventional: nuclear power)
    
• Renewable:
  
  • wood, solar (thermal),
    
  • district heating (biomass, solar [thermal]),
    
  • electricity (conventional: renewable sources), electricity (PV)
    

For the school building of example C almost all of these values are already available, except for the contribution of different primary energy sources to the overall energy mix used for the production of conventional electricity. The calculation instrument takes the data published in the Monthly Electricity Survey in October 2005 by the IEA which shows the contribution of primary energy sources in the three categories for a certain country. The further proceedures are described in example C.