The building energy consumption represents about 40% of total energy consumption across Europe, this is fundamental to proceed with a massive renovation of the existing housing stock and the new homes must consume the lower possible amount of energy.
Different labels and standards for energy renovation have been developed during the las decades and often both users and investors have some confusion about the real energy level achieved following the different standards and about the real cost to reach them.
To clarify the situation some lectures have been given. During the meeting in Treviso in 2019 two important labels have been faced: the Passivehouse standard and the NZEB. During the meeting in Epinal in 2020 two different NZEB case study were presented: one in Italy and the other in UK.
Passive House costs by Stefan Reuther, PlanungsgruppeDrei
It’s important to specify that it’s very complicated to speak about of money for architect. It must be considered what kind of cost are we talking about? Construction costs, building services costs (technical staff), special costs (foundation), planning costs are all part of the total expense. Architects are focused on construction costs, not about life house costs.
On the other hand there is the value, that is different from the cost. In the value we have the energy saving, the sustainability, the comfort, the architectural quality, etc.
To discuss about the costs two case studies are presented.
The Buildtog in Darmstadt is a 3495 m2 a passivhouse. To reach the standard it was necessary to use very good windows, well designed insulation, ventilation with heat recovery, detailing thermal bridges. To make a comparison to identify the extra costs for the passive house a comparison with a “standard building” (simulated) was done.
Costs differences are connected with heating demand.The cost difference is about 470’900€ (less insulation, less performing windows, standard ventilation). The building construction is cheaper, including the planning costs and the extra costs. On the other hand the heating system is more expensive.
The second case study was Bremen passivhouse. It has 1475 m2 heated floor area. The standard building simulated has an increase of heating requirement of about 369%. In this building the cost difference is about 191’600€ due less insulation, less performing windows, standard systems etc.
Talking about rental costs: in Bremen they charge 6,50€ for a standard building and 10€ for apassivhouse. It must be considered that Bremen is not considered an easy place to build apassivehousesince the climate is cold and there is not much local know how so usually the cost is higher when you are the first in the market.
What is an NZEB and how much does it cost for new and refurbished buildings - case studies by Isaac Scaramella, greenLab
The concept of “NZEB” (Nearly Zero Energy Building”) was first defined in 2010 thanks to the European Directive 2010/31/EU. The EU definition says: nearly zero-energy building means a building that has a very high energy performance, as determined in accordance with Annex I.The nearly zero or very low amount of energy required should be covered to a very significant extent by energy from renewable sources, including energy from renewable sources produced on-site or nearby.”
Each member state must write a specific definition of NZEB including numerical indicators on primary energy use expressed in kWh/m2 per year.
At the moment it seems that local definitions are still lacking in many member states. Italy gave its definition in 2013 and the Regione Lombardia decided that from 1st January 2016 all new buildings in Lombardy have to be NZEB. Unfortunately even though this obligation the controls are not very strict so the obligation is not fully complied.
Basically a NZEB according to Italian definition is a building with very low energy consumption that uses renewable energy sources and produce renewable energy in place.
To be a NZEB you have to respect some parameters that take into account both winter energy saving and summer behavior. Among the different parameters some are more centered on the envelope while other on the system efficiency and energy production.
One parameter, called H’T, is the average global heat transfer coefficient for transmission per unit of dispersing surface. In its formula is clear that you can reach this parameter with low U value, but also thermal bridges are very significant, so you need to pay attention in details.
Asol,est/Asup, utile is the solar area per useful surface area, this parameter take into account the summer overheating, a real problem in Italy.
Energy performance (EP) for heating and also for cooling have different limits, so it’s difficult to reach both parameters and this parameter doesn’t take into account the real inertia of the building.
EPglobal considers all the factors and compared the designed building with a reference building with same parameters (place, area…). It’s very difficult to satisfay this parameter, because if you change something in the design it changes also in the reference building.
Talking about renewable energy an NZEB building must cover at least 50% of energy consumption with renewable energy and at least 50% of hot water must be produced with renewable energy. It’s possible to reach the first request with little consumption and a heat pump, but for the second one solar panels must be added.
According to this definition every building can be a Nzeb so both new buildings or existing building renovated.
Two case studied are presented: one about newbuild and the other about renovation. Both of them have similar characteristics in terms of system, insulation, renewable energy production.
The renovation has been a deep renovation with total internal demolition which lead to a total cost of 1331€/m2 (excluding design and VAT).
The new building is an home (not social housing building) easy to ménage, connected with the surrounding nature. The cost for a new NZEB is about 1704€/m2 (surface considered is the total net area, excluding design, VAT, ground). After one year monitoring is possible to see that pick of consumption is during winter time. The biggest amount of renewable energy production is in summer period, when the production is higher than the consumption. During winter solar panels are not enough. In 2019 energy production was 92% of energy consumption, considering heating, cooling, ventilation, hot water, lightning and electric equipment. Considering only heating, cooling, ventilation and hot water, as the NZEB definition do, the total coverage is about 160%. The monitoring shows another interesting thing: during the owners holiday, in winter, the building had an high consumption compared with other periods. The problem is that in this period there weren’t solar gains, because solar shadings were totally closed. This underline the importance of user behavior.
UK progress toward Nearly Zero Energy / Carbon Home by Gordon Watts, SYHA
After Brexit UK is going on its own way, different from EU; at the moment there is a strong commitment to decarbonisation. Housing sector produce around 20% of UK emissions and the biggest issue is existing homes.
Sustainable Energy Association is studying houses decarbonisation for 2050 under 5 different scenario, but Further Ambition Scenario is the only one to reach the NZEB target. For social housing sector they have a specific scenario until 2050 and new buildings have different standards than existing buildings. The future home standards for new buildings introduce an interim uplift in energy efficiency standards. Standards are very high and there is a much greater focus on testing end evidence.
At the moment there aren’t minimum standards for retrofit project in social housing sector.