Practical implementations of step by-step-retrofit to EnerPHit standard

Author: Simon Camal, La Maison Passive

1. Towards EnerPHit as a retrofit standard for Europe
In order to meet the energy reduction targets defined by the European Union for 2020 and 2030, all new building energy retrofits throughout Europe should be strongly encouraged to reach the EnerPHit energy efficiency level. Scenarios were developed by the European project ENTRANZE, based on existing efficiency policies, expected costs and retrofit needs defined by each Member State. These scenarios show that 5% of the European building stock could be deeply renovated by 2030, bringing energy consumption down to EnerPHit/nearly Zero Energy Building levels [Entranze 2014]. To ensure that deep retrofits further proliferate, step-by-step retrofit strategies need to be developed. This will allow owners to spread the required investment over a period that is reasonable with their financing capabilities, without compromising on energy quality. The European project EuroPHit is an opportunity to implement these strategies on normal buildings facing common constraints. PHPP 9 was used with variant calculations and economic assessments to answer questions submitted by building owners and find adequate solutions for each case. A variety of buildings have been analysed: social dwellings, single family houses and non-residential buildings.

Figure 1: Heating consumption of a non-refurbished office in Rhône-Alpes, 2014 (Archipente)

2. Does PHPP work well on poor energy efficiency buildings?
The heating consumption modelled by PHPP, once updated with the actual figures of use and climate, quite accurately reflects the measured consumption of buildings refurbished to the EnerPHit standard [Keig, Heid 2014], [Bradshaw, Croxford 2013]. However, in a building which lacks insulation and/or airtightness, the indoor air temperature measured in winter can be significantly higher than the interior radiant temperatures. Calculating ventilation losses according to an average indoor operative temperature, instead of using indoor air temperature can lead to incorrect results in this context [Gasparella, Pernigotto 2012]. Is the error on the heating demand so large, that one needs to simulate the building with some dynamical software instead of the PHPP?

Considering uncertainties on the actual building components and boundary conditions, PHPP has proven to be sufficiently accurate if the existing status of the building is studied correctly. The deviation found by Sevela and Pfluger [2014], between measurement and simulation on a non-refurbished Austrian school was less than 3%. In the Rhone-Alpes office building case study for the EuroPHit project, the heating consumption (60% pellets, 40% gas) was monitored between January 2014 and June 2014. The airtightness test gave a relatively bad result with a mean n50 = 6.8 h-1 . The heating consumption derived from the updated PHPP 9 is very close to monitoring results, with monthly discrepancies of less than 10% and a deviation of less than 1% over the six month period (see Figure 1). The new “Variants” Worksheet of the PHPP 9 will serve as a powerful validated tool for anyone who wishes to set up a retrofit strategy.

3. Is it feasible to retrofit my building to the EnerPHit level?
Despite successful examples, the EnerPHit standard is still seen by many building owners as a challenge. The EuroPHit case studies aim to provide pragmatic answers, removing barriers one by one.

Figure 2: U-value of existing wall (PHPP), global cost and NPV for ETICS retrofit Envelope

3.1 Investment
The first barrier is the amount of investment required: if the owner can’t invest the total budget needed for envelope and building services, then they can invest step-by-step. In several EuroPHit case studies, the investment will be spread over two steps: energy efficiency finished before 2016, then renewable energy (solar thermal and/or photovoltaics) scheduled by 2020 or 2025. Other case studies will focus first on the thermal envelope and mechanical ventilation with heat recovery, before refurbishing hot water, heating and electricity. Costs associated with asbestos or fire protection should be treated as unavoidable costs as they have no impact on the economic efficiency of an EnerPHit rehabilitation [Ebel 2014]. They must still be carefully studied as asbestos removal for example, can cost up to €15000 per dwelling.

Investors often ask whether their partially insulated building is affected by the famous “lock-in” effect, and if EnerPHit scores better than a retrofit with minimal energy efficiency according to the national standard. The “lock-in” effect was found in the multifamily house in Courcelles. The building included 8cm of mineral wool insulation in the walls, an ETICS (External Thermal Insulation Composite System) retrofit to U=0.12W/(m².K) and q50=0.6m3 /(m².h). This showed a positive Net Present Value over 20 years (with an additional investment of €90/m²wall, to include a new render on the concrete wall, see Figure 2). This relies on the fact that this building is in Northern of France (GT=73kKh/a) and is heated by direct electric systems with an average electricity price of €0.15/kWh.

Is EnerPHit cost-effective compared to minimum efficiencies required by national standards? This topic will be closely surveyed by the EuroPHit consortium as retrofits are carried out. At the design stage on social semi-detached houses in Northern France, the additional budget needed to upgrade from the minimal energy retrofit standard (RT par éléments) to the EnerPHit standard has been estimated at €19000 per dwelling (excluding VAT). This assessment is based on real prices from French Passive House buildings. The present value of energy savings over a 20 year period are €19200 per dwelling. It is then worth investing in EnerPHit instead of the minimal energy efficiency standard, given that the investor can collect back the value of energy savings. The social housing owner rents dwellings without heating and hot water. In this case the French law doesn’t allow the owner to claim back more than 50% of the value of energy savings. The evolution of habits and laws is therefore required to give way for investments into EnerPHit projects.

3.2 Envelope
Multifamily dwellings often have to deal with balconies or external walkways, which lie outside the existing thermal envelope. In the multifamily case study in Portsmouth, as well as the student house in Paris, communal walkways will be integrated into the new thermal envelope, as advised by [Schulz 2008]. Protruding balconies of the multifamily case study in Courcelles will be kept outside the thermal envelope with mitigated structural thermal bridges.

Another common issue is the insulation level on top of the slab-on-grade foundations. High insulation layers force tenants to move out, doors must also be resized and height is lost. On semi-detached houses in Auby, France, slab-on-grade foundations in living areas are already partially insulated. The EnerPHit criterion of 25kWh/(m².a) for heating demand can still be achieved without insulating slabs in living areas; however, the insulation layer on the external wall must be extended down to the base of the foundation.

Figure 3: Left: Floor plan with simple cascade ventilation, supply (SUP) and extract (ETA) ducts. Right: Result of cascade ventilation assessment [Rojas, Pfluger 2014

3.3 Ventilation, Heating and Hot Water
Cascade ventilation is a powerful solution to reduce duct work when installing ventilation with heat recovery. The online tool presented by Rojas and Pfluger [2014] was used on the floor plan for the multifamily house in Courcelles. This apartment building consisted of social dwellings, equipped with simple centralised extract ventilation systems. Tenants did not complain about bad air quality but said that several rooms were cold and humid. Bedrooms were not directly linked to the living room, WC and bathrooms. Expanded cascade ventilation as defined by Rojas and Pfluger [2014] is not advisable here (Figure 3), but simple cascade ventilation with one supply inlet in the living room could provide very good air quality.

Another option would be to reuse the existing extract system, insert an air/water heat pump on the exhaust air to generate heating and domestic hot water. This option is less efficient than a ventilation system with an air/air heat exchanger, but it is potentially cheaper. Dynamic simulations have been conducted by Gustafsson and Dermentzis [2014] on a similar system in a single family house retrofitted to EnerPHit standard. The final energy consumption of this heat pump providing heating only, was found to be around 13kWh/(m².a) for a similar climate (London). This type of heat pump, also providing domestic hot water with a solar thermal basis could be considered in this building case study.

Figure 4: Visual summary of an EnerPHit refurbishment plan (case study Courcelles, France)

4. Management of a step-by-step retrofit
Keys for success in a step-by-step approach consist of: organising an overall refurbishment plan with the owner, defining acceptable intermediate states, and proving cost-efficiency.

4.1 Overall refurbishment plan
After an audit of the initial building status, the maintenance plan (if any) can be upgraded to an overall refurbishment plan that integrates EnerPHit quality measures when components end their service life. A visual summary of such a plan for the multifamily dwelling of Courcelles is presented in Figure 4. Infiltrations and drafts have been reported next to windows which were scheduled to be replaced in the maintenance plan for 2015. This would be a good opportunity to install passive house windows, in anticipation of the future external wall insulation. Extensive work is scheduled on the ventilation system, while replacing heaters is postponed to coincide with domestic hot water renewal in 2018.

4.2 Acceptable intermediate states.
Designers and owners are not used to retrofitting a component and anticipating the future upgrade of their neighbour. Intermediate states have to be clearly described in tender documents and clearly identified on designer sketches (Figure 5, Right).

Figure 5: Left: Global cost of EnerPHit step-by-step retrofit compared to standard efficiency maintenance (Auby, France). Right: Window installation and external insulation, showing both intermediate state and final state (Courcelles, France)

4.3 Prove cost-efficiency.
The “Comparison” Worksheet of PHPP9 helps designers in assessing the cost-efficiency of each measure. A single measure may not appear to be cost-effective when compared with the initial measure in the maintenance plan. For example: window replacement with passive house windows instead of classic PVC double-glazed windows, as passive house windows are still expensive (350-600€/m² delivered in France). However, it can be seen from the EuroPHit case studies so far, that it is still worth going for the EnerPHit efficiency standard as the annual global cost of EnerPHit is not higher than a standard maintenance with minimal efficiency (Figure 5, Left).

The EuroPHit project is co-funded by the European Commission under the grant agreement IEE/12/070/SI2.645928.

5. References

[Bradshaw, Croxford 2013]Detailing for retrofit in London; terrace houses, solid walls and internal insulation, 17th International Passive House Conference, Frankfurt, 2013
[Entranze 2014] Online Scenario Tool,, accessed 10/01/2015
[Gasparella, Pernigotto 2012] Comparison Of Quasi-Steady State And Dynamic Simulation Approaches For The Calculation Of Building Energy Needs: Thermal Losses, International High Performance Buildings Conference, Purdue University, 2012
[Gustafsson, Dermentzis 2014] Energy performance comparison of three innovative HVAC systems for renovation through dynamic simulation, Energy and Buildings 82, 2014
[Keig, Hyde 2014] Analysis of the operational energy performance of a retrofitted solid wall terraced house versus designed performance, 18th International Passive House Conference, Aachen, 2014
[Rojas, Pfluger 2014] Cascade ventilation – air exchange efficiency efficiency in living rooms without separate supply air inlets and exhaust air outlets, 18th International Passive House Conference, Aachen, 2014
[Sevela, Pfluger 2014] Energy refurbishment of heritage buildings with PHPP’s and real measurements’ feedback, 18th International Passive House Conference, Aachen, 2014
[Schulz 2008] Verglaste Balkone – eine Option für die Altbaumodernisierung?, Protokollband Nr. 37. Passivhaus Institut, Darmstadt, 2008
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