El Niu: Andorra’s Pioneering Passivhaus Plus Certified Building

In the heart of Andorra, Europe’s 6th smallest state, a groundbreaking architectural marvel named “El Niu” is redefining sustainable living. Meaning “The Nest” in Catalan, El Niu is a testament to innovative design, energy efficiency, and environmental consciousness.

Passivhaus Plus Certification

El Niu proudly stands as Andorra’s first multi-residential building to achieve the prestigious Passivhaus Plus certification. This accolade, awarded by Passivhaus Certifier Oliver Style of Praxis Resilient Buildings, is a testament to the collaborative efforts of the development team, including Lluis Lopez Castro of Propietats y Gestió and architect Antoni Martí.

Bernabé Rodríguez’s expertise in mechanical and electrical services engineering, coupled with Pere Marcé Coma’s airtightness Blower Door tests, played important roles in attaining this esteemed certification. Months of dedication and meticulous attention to detail, together with countless rolls of airtight tape, have marked a transformative milestone for Andorra’s architectural landscape.

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In conclusion, El Niu represents a paradigm shift in Andorran residential construction, blending architectural innovation with environmental responsibility. As a Passivhaus Plus certified building, it not only provides a haven for its occupants but also sets a precedent for sustainable living in Andorra and beyond. El Niu is more than a nest: it’s a beacon of hope for a greener, more energy-efficient future.

For more technical information, check out our project data sheet here and in the International Passivhaus Database

Prefabricated passive houses, a cornerstone of Construction 4.0

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Is it possible to build a prefabricated Passivhaus building? Of course it is! Below you can find some examples

LILU´s House: bio-based Passivhaus Plus

Passivhaus design and consultancy, for this single-family house in Abrera, Barcelona, designed by architecture firm OMB Arquitectura and built by House Habitat.

Single-family home in Sitges

Single-family home in Sitges Passivhaus design & consultancy, Blower Door Tests, M & E design, Site supervision Description Passivhaus design and consultancy, M & E engineering, and…

Learnlife Eco Hub: Passivhaus learning space

Passivhaus design & consultancy for a pop-up learning hub in Castelldefels, Barcelona, designed by the Learnlife team.

Original article written by Oliver Style and posted at caloryfrio.com

Praxis is delivering three presentations at the Spanish Passivhaus Conference in Valencia

From November 29th to December 1st, the fifteenth Passivhaus Conference will take place at the Valencia Conference Center. Organized by the Spanish Passivhaus Building Platform (PEP), this event has become a reference meeting point in the sector and one of the main forums for innovation in Passivhaus on the Iberian peninsula.

At Praxis we are very happy to be able to participate as speakers in three presentations. Oliver Style and Bega Clavero will make their interventions on November 29th and 30th. We’d love to see you in Valencia!

LILU’s House: the exception that should be the norm 

Two stories 

First story: a client calls me, the self-builder of a home with Passivhaus Plus certification and tells me: “Outside it’s – 4 ºC and inside we’re at 19.6 ºC, with no heating on.”  

Second story: a family calls me, recently installed in their newly built home, and tells me: “We’re at our wits end… we’ve turned up the temperature of the underfloor heating to 51 ºC and we’re still cold! We have really high energy bills and we’re just not comfortable. Can you help us?” 

Both homes have an energy performance certificate with an “A” rating. Why, in 2023, is the second story still happening? Why, after having made the biggest investment of their lives, with the expectation of living in a comfortable house with low energy bills, are there families going through what this family is experiencing? The second story is all too common. The first story is an exception, that should really be the norm. 

LILU’s House: bioPassivhaus Plus  

LILU’s House is the home referred to in the first story above, and it really works. It brings together, under one roof, an office, a home, and a research unit on timber construction. Developed by Pere Linares and Montserrat Lucas, the house has a treated floor area of 142 m2 distributed over two floors. Architect Oriol Martínez has created a modern and compact design with carefully designed and protected openings to maximize solar gain in winter and prevent overheating in summer. 

The house has a mixed structure of light weight timber and CLT (cross laminated timber), where healthy materials with a low environmental impact have been prioritized. With a fully industrialized construction system that was prefabricated off-site, quality and precision have improved dramatically, with reduced on-site assembly times, less waste, less dust, less noise, and a lower carbon footprint. 

LILU’s House aims to be a laboratory for the dissemination of knowledge about timber construction with biobased materials, certified to the Passivhaus standard.  

The home is being monitored to evaluate it’s real-life performance, where data is being recorded on indoor CO2 concentration, air temperature, relative humidity, VOCs, energy consumption, and solar PV production. The house has a roof-integrated solar photovoltaic array with 126 photovoltaic tiles and a nominal power of 6 kWp. Each year, the building will produce, on average, 42% more energy than it consumes. 

This is LILU’s House: an exception, which should really be the norm. 

Radon gas: invisible and lethal. What is it and how to prevent it?

Radon gas is a naturally occurring radioactive gas that can enter buildings. It is currently the second most predominant cause of lung cancer after tobacco. It’s colorless, tasteless and has no smell, and is produced from the natural radioactive decay of uranium, present in many types of soils and rocks.

How is radon gas measured in a building?

Becquerels (Bq) is the measurement of radioactivity. A becquerel corresponds to the transformation or decay of 1 atomic nucleus per second. In the air, radon concentration is measured by the number of transformations per second in one cubic meter of air (Bq/m3).

The national annual average reference level, set out by WHO in its “WHO Handbook on Indoor Radon: A Public Health Perspective”, is 100 Bq/m3. If this level cannot be reached due to country-specific conditions, the level should not exceed 300 Bq/m3.

Radon measuring devices are divided between passive and active detectors, with an uncertainty range of between 8% and 25%, depending on the type of device. The most common devices are usually passive, logically cheaper than active ones, and incorporate trace sensors for alpha particles, or ion electret chambers, to measure radon concentration.

As the concentration of the gas in indoor air can increase significantly in the short term (hours), is recommended to take long-term measurements (for example, 3 months). If the building has a ventilation or HVAC system, it is convenient to take measurements with the system on and off, in both cases for a long period time.

There are low-cost types of equipment such as the RadonEye RD200, or Airthings Wave, shown in Figure 2 and Figure 3.

Radon gas and the Spanish building regulations

In 2019, and for the first time, Spanish building regulations established the scope and requirement of radon gas with a reference level for the average annual radon concentration inside habitable premises of 300 Bq/m3 (triple of what is recommended by the WHO).

Applicable to all new buildings, extensions, changes of use, or refurbishment of existing buildings, the regulations require the following measures, according to the risk area:

Level 1:

• Radon barrier between living spaces and the ground
• Ventilated air gap between the living spaces and the ground

Level 2:

• Radon barrier between living spaces and the ground
• Additional protection system:
  • Ventilated air gap between the living spaces and the ground
  • Ground depressurization system that allows the gas to dissipate from the ground.

The radon gas map of Spain according to the HS6 level 1 and 2 classification is shown in Figure 4.

How does radon gas enter a building and how to avoid it?

Radon enters a building through the fissures and openings in the envelope, especially in parts of the building in contact with the ground (slabs, basement walls, etc.), where the concentration of the gas is generally higher on the floors above (ground and first floor, etc). This is accentuated in the building during the heating period, where warm air rises, and the stack effect creates air infiltration of air on the lower floors (and exfiltration on the upper floors).

Radon gas entry is reduced and/or eliminated by a gas-resistant membranes, with a diffusion coefficient against radon less than 10-11 m2/s. An example is shown in Figure 5. The barrier must be continuous, taped and sealed at all joints and service penetrations. It is advisable to conduct a Blower Door test during the construction phase to detect leaks and repair them.

In Level 1 areas, as an alternative, it is possible to build a ventilated crawl space between the living areas and the ground, although it is a less safe solution than a radon barrier.

In Level 2 areas, the radon barrier is essential, along with a ventilated crawl space or a ground depressurization system.

The ground depressurization system consists of installing a network of perforated intake ducts, with mechanical extractors that conduct the air to the outside, above the building. This system has the same drawbacks as the ventilated crawl space and depends on a mechanical system.

Although few epidemiological studies have been conducted on the possible link between radon gas in drinking water and the incidence of stomach cancer, a study by Kyle P Messier and Marc L Serre of the University of North Carolina, USA indicates that increases the risk of stomach cancer. Therefore, water becomes a double entry route, by ingestion of contaminated water or by breathing radon gas evaporated from drinking water. Under normal circumstances, the amount of radon inhaled when breathing is greater than that ingested when drinking.

Radon in drinking water can be reduced and/or eliminated by employing granular activated carbon filters, but the filter itself can accumulate radioactivity and should be located outside the thermal envelope (in a garage, for example), taking care of its treatment as toxic waste at the end of its useful life.

Study of the incidence of radon gas in 122 homes in Ireland

Barry Mc Carron, Xianhai Meng, and Shane Colclough conducted a radon gas measurement study on 122 homes in Ireland, 97 Passivhaus-certified homes, and 25 conventional homes (reference). The results can be seen in Figure 6. The average level of radon gas inside the Passivhaus dwellings was below 40 Bq/m3, both on the ground and first floors. However, in conventional homes, the average level was 104 Bq/m3 on the lower floor, and 69 Bq/m3 on the first floor.

The differences clearly show the effectiveness of airtight construction to prevent the entry of radon gas: one of the requirements of the Passivhaus certification is to have a level of air infiltrations n50 ≤ 0.60, verified by an air-tightness test.

But not only this, Passivhaus homes have a mechanical ventilation system with heat recovery, which constantly renews the air, eliminating stale and polluted air, and introducing fresh and filtered air. This can be seen in the graph in Figure 7, where Professor Walter Reinhold Uhlig of the HTW University of Dresden, measured radon gas in a Passivhaus dwelling with a mechanical ventilation system on and off. With the ventilation turned off, in certain rooms the radon level increased to 350 Bq/m3, having remained below 100 Bq/n3 with the ventilation working.

Considering how lethal it is, radon gas has- surprisingly- gone unnoticed among many professionals in the sector, public administrations, and health professionals. Thanks to increased awareness and the update of the Spanish building regulations, it’s an issue we clearly can’t ignore: we need to prevent radon from entering our buildings, and ensure correct ventilation! The empirical results shown above indicate that an air or radon gas barrier, together with a mechanical ventilation system, is a highly effective combination to reduce the entry of radon gas into a building and thus protect the health of users.

Freshen up: active cooling with radiant ceilings in a Passivhaus retrofit

The article presents an active cooling system using the supply air of the ventilation system with radiant ceiling panels, installed in a multi-residential building in the historic center of Girona, certified Passivhaus EnerPHit – Demand method. For each apartment, the system consists of an air-source heat pump, a mechanical ventilation unit with heat and moisture recovery (MVHR), a coiling coil on the supply air stream, and radiant ceiling panels. Control is carried out with a home automation system, with temperature and humidity sensors in each room. The solution offers both heating and cooling, working quietly and at low temperature, providing high thermal comfort and efficient performance when used with a heat pump. Reliable performance depends on correct system sizing, proper commissioning of the control system and of ventilation flow rates, and user maintenance and replacement of filters in the MVHR units. Systems such as this are not a good solution in homes where windows are open a lot on the summer and are better suited to warm and dry climates with lower levels of humidity. 

The building is a multi-residential 6-storey building in the historic center of Girona, certified by Passivhaus EnerPHit – Demand method [Figure 1].  This private initiative – which was the first of its kind in Catalonia – put 4 new apartments of 129 m2 and a duplex of 162 m2 on the market.  

Due to local heritage building regulations, insulation had to be installed inside, with some loss of thermal inertia. Active cooling using a cooling coil on the the ventilation supply air is a relatively simple concept which can be cost effective to install. However, thermal power can be limited when temperatures peak. The system presented here combines supply air cooling with radiant ceiling panels, to provide sufficient power to cover peak cooling loads.  

The project data and team are shown below: 

• Certification class: Passivhaus-EnerPHit – Demand Method 
• Useful / gross floor area: 678 m2 / 1.038 m2 
• Developer: MBD Real Estate Group  
• Builder: Busquets Sitja  
• Architects: López-Pedrero-Roda Architects  
• M & E Engineering: PGI Engineering 
• Control/home automation: Progetic 
• PHPP, Passivhaus design: Oliver Style, Bega Clavero 
• Passivhaus Certification: Energiehaus Arquitectos  

Description and operation of the system 

Given space and floor-to-ceiling height limitations, 2 cooling systems were initially considered: 

1. Ventilation supply air cooling only 

2. Ventilation supply air cooling + radiant ceiling panels 

The second option was chosen, given that operative temperatures in the summer could not be maintained at ≤ 25ºC using ventilation supply air cooling only. With 19 m2 of radiant ceiling panels (covering around 15% of the ceiling surface area), peak cooling loads could be met, calculated for an outdoor air temperature of 34.1 ºC, with an absolute humidity = 10,5 g/kg [1].  

For each apartment, the system included the following equipment: 

• Heat pump: Daikin EWYQ005ADVP air-water monobloc heat pump (5.20 kW cooling / 5.65 kW heating) [Figure 2] 
• Heat & moisture recovery ventilation unit: Zehnder ComfoAir550 enthalpic [Figure 3] 
• Cooling coil: Zehnder ComfoPost CW10 [Figure 4] 
• Radiant ceiling panels: Zehnder NIC 150 & NIC 300 [Figure 5] 
• Control system: 

• 1 temperature & humidity sensor per room 
• 1 Loxone mini server [Figure 7] 
• Various elements providing on/off control of the heat pump, 3-stepped control of the ventilation flow rate, and on/off control of each radiant ceiling circuit and control of water supply temperature to the radiant ceiling panels with a 3-way valve

In heating mode, the heat pump generates hot water, circulating it through the radiant ceiling panels at a supply/return temperature of 45 ºC / 40 ºC. At the same time, the coil on the ventilation supply air stream heats the air to around 40ºC. The fan speed is controlled to avoid excessively high flow rates, and which can lead to low relative humidity of indoor air. 

In cooling mode, the heat pump generates cold water, circulating it through the radiant ceiling panels at a supply/return temperature of 7 ºC / 12 ºC. At the same time, the coil on the ventilation supply air stream cools air to around 15 ºC. The coil also provides some dehumidification of the supply air, lowering the ambient indoor air dew point temperature and preventing condensation on the ceiling panels. In cooling mode, controlling the temperature of rooms individually is not possible given that the cooling coil only works for the entire apartment. 

The heat and moisture recovery ventilation unit also helps to increase the relative humidity of the indoor air in winter and decrease it in summer, improving thermal comfort and reducing the dehumidification load that the cooling coil needs to overcome. 

With the ventilation flow rate of 0.4 ach (135 m3/h), radiant ceiling panels typically cover – for both heating and cooling – approximately 65% of thermal loads. The ventilation system with the heating/cooling coil covers the remaining 35%. 

Radiant cooling systems must have a robust control system, to avoid problems of surface condensation. Temperature and humidity sensors were therefore installed in each of the 5 rooms where the radiant panels were located (dining room, kitchen and 3 bedrooms). The water temperature of the panels is adjusted with a 3-way mixing valve, based on the temperature and humidity data from the sensors in each room, ensuring the panel surface temperature remains above the dewpoint, avoiding condensation.  

The control system also modulates the ventilation unit’s fan power, lowering or raising the flow rate depending on the temperature setpoint and dehumidification needs. A schedule prevents the fan from operating as full flow at night, to avoid noise problems. If maximum power is required at night this can be a problem. The control allows you to set different setpoint temperatures according to specific schedules or occupancy rates, for each day of the week. 

In its default setting, the ventilation system works automatically with pre-established schedules (with the possibility of manual adjustment by occupants). Figure 8 summarizes its operation: 

Conclusions 

Cooling with radiant ceilings can offer an efficient solution that adds power to ventilation supply air cooling systems in Passive Houses in the summer. As the system is predominantly radiant and running at low temperature, it provides good comfort and can be more efficient than convective systems. Ceiling panels can be sized to meet heating and cooling loads, which in residential buildings retrofitted to Passivhaus standard means a coverage of between 15% to 30% of the ceiling surface area. This replaces ducted fan-coil or split systems, which take up more space in suspended ceilings, often a limitation in retrofit.  

The control system presented here offers a flexible solution at a reasonable cost, with a relatively user-friendly interface. The possibility of visualizing and monitoring data remotely and in real time, facilitates the optimization of the system and helps in terms of preventive maintenance. 

Systems such as this are not a good solution in homes where windows are open a lot on the summer and are more suitable for use in hot dry areas, since, in areas of high humidity, the power of the system will be limited depending on the humidity level of the indoor air and the proximity to the dew point. Robust operation depends correct system sizing, proper commissioning of the control system and of ventilation flow rates, and user maintenance and replacement of filters in the MVHR units.