The office building E-value is a calculated comparison figure showing how much purchased energy the building uses per heated net area per year, weighted with the energy form factors. The class from A to G follows directly from where that figure falls on the scale in annex 2 of Finland’s Ministry of the Environment decree 1048/2017.
What does the office building E-value actually measure?
It measures the building’s properties under standardised use, not how the building is actually used. The calculation runs in three steps: first the building’s calculated purchased energy under standardised use is determined, then consumption is weighted per energy form with the relevant factor, and finally the weighted total is set against the size of the building. The unit is kWhE/(m² year).
Ventilation outdoor air flows, room temperatures, the building’s daily and weekly hours of use, the internal heat loads and hot water consumption all enter the calculation as the starting values set per use category in decree 1010/2017 on the energy performance of new buildings (sections 10, 11 and 12), not as the property’s own readings. That is the heart of standardised use. If two otherwise identical office buildings differ only in how late the lights stay on, the calculated figure does not move.
Space and ventilation heating, domestic hot water heating, space and ventilation cooling, and the electricity demand of lighting and consumer appliances form the starting point of the calculation. From demand it proceeds through system efficiencies to purchased energy, meaning the energy that has to be bought through the meter. The certificate reports this calculated purchased energy alongside the E-value, so the client can see which parts pushed the figure up.
The building’s own properties, on the other hand, show up in the figure immediately: envelope U-values, air leakage, the annual efficiency of ventilation heat recovery, lighting power density, the efficiencies of the heating and cooling systems and the heating source are the variables the assessor genuinely moves the figure with.
Why do a kilowatt-hour of electricity and of district heat not weigh the same?
Because purchased energy is weighted per energy form: government decree 788/2017 sets the factor at 0.5 for district heating, 1.2 for electricity, 0.28 for district cooling, 1.0 for fossil fuels and 0.5 for renewable fuels used in the building.
In practice the difference is large: a hundred kilowatt-hours of purchased electricity is weighted to 120 in the E-value, while the same amount of district heat is weighted to 50. That is why the efficiency of electrically driven equipment moves the figure harder than an equivalent change in heat consumption, and why switching the heating source can change the class even when the building’s energy demand stays put. The factors are not emission factors, although they are often read as if they were.
Where do the class limits for an office building fall?
The class scales are given per building type in annex 2 of decree 1048/2017. The office building scale looks like this:
| Class | E-value, kWhE/(m² year) |
|---|---|
| A | 80 at most |
| B | between 81 and 120 |
| C | between 121 and 170 |
| D | between 171 and 200 |
| E | between 201 and 240 |
| F | between 241 and 300 |
| G | 301 or more |
The letter carries the subscript 2018 when the certificate follows the rules that entered into force on 1 January 2018. The marking matters to the client, because the energy form factors changed in the same round: with the same class limits but the new factors, a building scores on average one class better than it would have under the earlier rules. An exception is buildings that use only renewable or only fossil fuels, because the factors for those did not change. The letters on an old and a new certificate are therefore not directly comparable.
The scale is best read as distances between limits rather than as letters. Class C is 50 units wide and D only 30, so in the middle of the scale a small calculation difference shifts the letter easily, while two very different buildings can share class C. When the figure is 142, the class is C and the limit for B is 22 units away.
How does an E-value of 142 drop to class B?
The example building is a district-heated office building from 1998 with 3,420 square metres of heated net area and an E-value of 142, which is class C. The following measures and their effects are this example building’s own figures: renewing ventilation heat recovery lowers the E-value by 9 units, LED lighting with presence control by 6 units, new windows by 4 units, balancing the heating network by 3 units and correcting the ventilation time schedules by 2 units.
The calculation written out: 9 + 6 + 4 + 3 + 2 = 24 units. The starting point of 142 reduced by 24 gives 118, and since 118 falls between 81 and 120, the class is B.
Two observations. None of the measures would have been enough alone, and the class turns only once the four largest are combined: 9 + 6 + 4 + 3 = 22 units takes the figure exactly to the class limit of 120, and the fifth measure pushes it to 118. This is a package rather than one large project. And the order is not the order of the investments: balancing and time schedules are the cheapest measures on the list and together give 5 units, while the window replacement is the most expensive and gives 4.
What does not move the E-value?
The price of the electricity contract does not move it at all. Nor does the fact that users have saved energy through their own habits: the certificate also reports actual purchased energy where the data is available, but the classification rests on the calculated figure. For the same reason, the operating and maintenance recommendations in the certificate have no effect as such on the E-value or the energy class, even when they would cut the bill.
Nor does the calculation capture all of the building’s real electricity use. The use purposes of special spaces such as commercial kitchens, restaurants, canteens, cafés and laboratories are not accounted for separately; they are calculated with the starting values of the surrounding building’s use category. Technical systems not listed in decree 1010/2017 need not be included in the purchased energy calculation, for example outdoor lighting, lifts, de-icing cables and charging points for electric cars. In an office building this often explains why the property’s metered electricity consumption and the certificate’s figures do not meet.
Two different meters are easily confused here. The calculated class describes the building’s properties and is comparable with other buildings in the same use category, whereas the bottom line of the electricity bill depends on when consumption happens, on the contracts and on the demand charge, which we covered in the article on demand charge optimisation. Both are worth improving, but they are measured with different numbers. We at Iiva sell neither equipment nor electricity, so the list of measures comes out of the calculation rather than out of a product range.
Who prepares the certificate and how long is it valid?
An energy performance certificate is valid for 10 years at most, and a new or updated certificate replaces the old one. It may be prepared only by a person whose qualification has been verified and is valid and who is entered in the register of certificate preparers; the qualifications are laid down in the act on the energy certificate of a building 50/2013 and in government decree 170/2013. The register is kept by the Housing Finance and Development Centre of Finland ARA, and once the certificate is prepared in ARA’s system it has at the same time been submitted to the supervisory authority.
In an office building the qualification level has practical consequences. For a new cooled building the certificate is prepared with a dynamic calculation method, which requires the higher qualification level; an existing cooled office building may also be calculated with the decree’s alternative cooling method, and then the basic level is enough. For the client this shows in who the work can be given to and what starting data the preparer needs.
The first step is always gathering the starting data: drawings, details of ventilation and heating, and whatever consumption readings exist. From those it is quick to see which side of a class limit the building sits on and what crossing it would take.
We prepare the energy performance certificate on the basis of a site visit and tell you at the same time which measures would move the class. Order an energy performance certificate or ask for an estimate of the effect of the measures.