Terrassa Haus: Passivhaus Living in the heart of Catalonia

In the bustling city of Terrassa, Catalonia, Spain, an innovative residential development is redefining sustainable living. Terrassa Haus is the first multi-residential building in the city to achieve Passivhaus certification, setting a new standard for energy efficiency and environmental consciousness in the region. Developed by Cambolico and designed by architects Antoni Espona & Xavier Torcal, with Passivhaus consultancy, HVAC design, and Blower Door testing conducted by Oliver Style and Bega Clavero from Praxis Resilient Buildings, the project represents a bold step towards a greener future.

Commitment to energy efficiency and sustainability

At first glance, Terrassa Haus blends modern design with eco-friendly features. The building comprises four floors, including ground-level commercial spaces and three floors of thoughtfully designed apartments ranging from 76 m2 to 154 m2. With a total floor area of 1142m2, the development offers residents a range of amenities, including a communal co-working space, bike room, gym, and a communal pool.

What truly sets Terrassa Haus apart, however, is its commitment to energy efficiency and sustainability. Built upon an existing concrete structure abandoned during the economic crisis of 2007, the building underwent a comprehensive retrofitting process to achieve Passivhaus certification. An external thermal insulation system with EPS insulation was meticulously applied over ceramic brick, supplemented by an additional layer of Knauf Insulation mineral wool in the service void, chosen specifically because it incorporates a bio-based E-Technology binder, free from added phenols and formaldehydes, protecting both the workers on site and future occupants from harmful emissions.. The roof is insulated with XPS insulation, ensuring maximum thermal performance throughout the building envelope. With an impressive n50 value of 0.6 air changes per hour, Terrassa Haus passed the Blower Door airtightness test with flying colours, reaffirming its status as a beacon of environmental responsibility and cutting-edge construction practices.

The attention to detail extends to the windows, heating, cooling, and hot water provision

The attention to detail extends to the windows, where Rehau PVC frames with argon-filled low-emissivity glazing were installed. Swisspacer insulated glazing spacers further enhance the windows’ energy efficiency, minimizing heat loss and maximizing natural light penetration.

For heating, cooling, and hot water provision, Terrassa Haus relies on individual Hitachi all-in-one heat pumps installed in each apartment. These state-of-the-art systems offer residents personalized climate control while minimizing energy consumption. Mechanical ventilation with heat recovery is achieved through individual Soler & Palau Passivhaus certified ventilation units, strategically positioned to draw in fresh air from the façade walls and extract stale air to the roof via shared ducts.

Terrassa Haus serves as an inspiring example of what can be achieved through innovation and collaboration

Terrassa Haus not only showcases the feasibility of Passivhaus principles in multi-residential developments but also demonstrates the economic viability of sustainable building practices. By prioritizing energy efficiency and environmental sustainability, Terrassa Haus offers residents a comfortable, healthy living environment while significantly reducing their carbon footprint.

As cities worldwide strive to combat climate change and promote sustainable development, projects like Terrassa Haus serve as inspiring examples of what can be achieved through innovation and collaboration. By embracing Passivhaus standards, developers, architects, and building professionals can pave the way towards a greener, more sustainable future for generations to come. Terrassa Haus stands as a testament to the power of visionary thinking and a beacon of hope for sustainable urban living.

Photos: terrassahaus.com

Passive House Database iPHa

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!

The academic year kicks off in Praxis! We interviewed two of our students to find out how they got along.

The academic year has also started in Praxis. For this autumn we’ve prepared two Passivhaus courses that we’re very excited about. On October 24^th, we start our Construction Verifier course, and on November 7^th we’ll begin our Site Supervisor course. Both courses (currently in Spanish only, but soon available in English!) will help you gain advanced skills to successfully meet the on-site challenges of large-scale Passivhaus builds.

We want to share with you the experiences of two of our students, who are successfully skilling-up in Passivhaus construction. We’re really happy to see how more and more professionals are working towards creating sustainable and energy efficient architecture. We spoke with Toni Picó, CEO of Growing Buildings and Passivhaus Tradesperson, and Álvaro Martínez, CEO of Martinez Gil, technical architect and Passivhaus Designer.

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Check out our next courses (currently in Spanish only, but soon available in English!)

Learnlife’s Eco Hub wins the Low-Tech Prize in the prestigious Green Solutions Awards 2022-2023

Learnlife’s Eco Hub, the Passivhaus Classic certified pop-up learning space located in Castelldefels, Spain, has won the Low-Tech Prize in the Green Solutions Awards 2022-2023!

6 experts from the sector analysed the submissions and praised the Eco Hub for the social aspect of its spaces, as well as the non-permanent structure, which blends in with nature and reduces the environmental impact of the building.

Designed by Sol Espoille, with Ramiro Chiaradia as collaborating architect, and Praxis Resilient Buildings delivering Passivhaus Consultancy and Blower Door testing, the Eco Hub is a pioneering learning space, sustainability, and innovation centre, built on the sea front in Castelldefels, near the city of Barcelona. The project provides a scalable, modular, prefabricated construction system for the rapid assembly of healthy learning spaces with good air quality and thermal comfort, fit for warm climates.

Learnlife is an organisation based in Barcelona whose goal is to build an open ecosystem for a new lifelong learning paradigm alongside existing education systems. Christopher Pommerening, Learnlife Founder, said: “We’re honoured to receive this prestigious award. The Eco Hub was designed to provide a learning environment that enables children to flourish, connects with nature and has a positive environmental impact.

“The award recognises this and highlights the possibilities for change in developing purpose-inspired learning spaces that have wellbeing and the environment as pillars of their design.” 

The Eco Hub is built from a series of prefabricated lightweight timber modules, built off-site, and assembled in-situ, installed on screw pile foundations, meaning it can be disassembled in the future, moved, and re-assembled elsewhere. The design team prioritised the use of healthy, low emission materials, with low embodied energy, including internal finishes with low-emission paints on fibreboard made from recycled gypsum and cellulose fibres from post-consumer waste. The module is equipped with a Passivhaus certified Zehnder mechanical ventilation system with heat recovery, and a 2.73 kWp solar PV array that generates around 90% of the building’s energy consumption.

Do you want to build or retrofit a nearly-zero energy learning space with excellent air quality, great comfort, and absurdly low energy bills?

Contact us here and let’s talk through your project.

Photos: Jordi Vila Marta – Argotphoto

Links:

• International Passivhaus Projects database
• Spanish Passivhaus Platform (PEP) project database
• Construction 21 Spain project database
• Learnlife website

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. 

Passivhaus in the Mediterranean? Strategies for keeping cool in a Passivhaus on the beach

According to the climate modelling presented in the study “Study on Climate Change and Energy in the Mediterranean” carried out by the European Investment Bank, countries in the Mediterranean basin will experience an increase of between 3ºC – 6ºC in average temperatures between the period 2070-2099, based on the 1961-1990 period.

The need to tackle overheating is addressed directly in the European Directive 2010/31/EU for nearly zero energy buildings (nZEB), which states the following: “Priority should be given to strategies that improve the thermal performance of buildings in the summer. To this end, measures should be promoted to prevent overheating, such as shading and sufficient thermal inertia in the construction of buildings, as well as to improve and apply passive cooling techniques (…)” [2]. This article presents the strategies used to improve the thermal performance in summer of a passive house in a Mediterranean climate. 

Caste study: “Esencia Mediterránea”…passive house on the beach 

The home, “Esencia Mediterránea,” has a useful area of 173m2, over two floors, located about 50 meters from the beach, 3 m above sea level (Figure 2, Figure 3, Figure 4) It has an architectural design very much in line with the Mediterranean vernacular tradition, was designed by Guillermo and Iciar Sen, built by House Habitat, and is Passivhaus certified. 

The project team:  

• Architects: Guillermo Sen, Iciar Sen 
• Technical Architect: Javier García Garrido – Garcia & Sala Arquitectes  
• Builder: Pere Linares – House Habitat  
• PHPP & building physics: Oliver Style, Bega Clavero  
• HVAC design: Vicenç Fulcarà – Progetic 
• Passivhaus and Blower Door Certification: Micheel Wassouf, Martín Amado – Energiehaus 

Passive cooling strategies 

Many of the strategies used to improve the summer performance of the home are rooted in traditional Mediterranean vernacular architecture and combined with modern solutions. For the thermal analysis presented here, a PHPP model of the house was prepared to meet the minimum requirements of the Spanish Building Code (CTE). Subsequently, the impact of each strategy on cooling demand is presented, until the limiting cooling demand value required by the Passivhaus standard is achieved. 

Shading analysis 

In order to be able to more accurately check the impact of design strategies for the summer, a shadow study was carried out with the DesignBuilder – EnergyPlus thermo-dynamic tool(Figure 7, Figure 8, Figure 9). The results were used to calculated shading reduction factors for each window, that were later introduced in the PHPP shading tab. 

Thermal inertia and natural night ventilation 

Combining thermal mass with natural cross ventilation is a key Mediterranean passive cooling strategy. Cooling power is logically limited when minimum night-time temperatures are not sufficiently low (< 18 ºC), so the strategy tends to work best in climates that are inland and at a higher altitude than coastal areas. While lightweight Passive Houses in warm climates have shown good summer performance [3, 4], some thermal inertia, in combination with night ventilation, clearly helps to modulate indoor temperatures and dissipate heat, improving comfort conditions and reducing cooling energy consumption. The house in question was built with a lightweight timber system – inherently low inertia. To incorporate some mass and enhance the effect of natural night ventilation, a 5 cm of mortar layer with ceramic floor tiles were installed on the floors of both floors, providing a specific capacity of 85 Wh/K·m² inertia (compared to a very light building of 60 Wh/K·m²). With tilt-and-turn windows partially opened at night, a minimum night ventilation air change rate of 0,8/h was calculated with the PHPP tool, provided by simple, cross and stack effect ventilation. 

Reflective surfaces: walls and roofs 

White painted walls and roofs are another feature of traditional Mediterranean architecture. The house has a white silicate mortar render, with a white roof, both with a solar absorption factor of α = 40 % (black α = 95 %). This helps to reflect more solar radiation and reduces transmission heat gains to the interior of the house. 

Shading devices and solar control 

Solar gains are reduced with balconies set back from the façade, exterior shading devices, and solar control glazing with a solar factor of 36%.

Thermal insulation 

Thermal insulation reduces transmission heat gains, especially through roofs. It is important to find a balance between the insulation thicknesses needed for winter and summer, since an excessive thickness of insulation can in some cases prevent heat dissipation at night in the summer. On the ground floor, 15 cm of wood fibre insulation was used, U = 0.264 W/m²·K. On external walls, 20 cm of wood fibre insulation was installed between the timber structure with 6 cm of external high-density wood fibre insulation, U = 0,158 W/m²·K. The roof has 26 cm of wood fibre insulation, for a U = 0,152 W/m2·K 

Air infiltration 

Reducing air ex/infiltration is a strategy that comes from cold and temperate climates, where the priority is to reduce winter heat losses, when there can often be an indoor-outdoor ΔT of 30 ºC. Outdoor air temperatures would have to be 55 ºC to have the same ΔT in summer. However, reducing air infiltrations in coastal Mediterranean climates with high humidity can help reduce latent cooling loads when active cooling is on and windows are shut. In the case study home presented here, reducing air infiltration from n50 = 5 ach (a typical value for newly built homes) to n50 = 0.4 ach, the latent cooling load is reduced by 39% and the latent cooling demand by 7%. 

Mechanical ventilation with heat and moisture recovery (enthalpy) + automatic bypass in summer 

Mechanical ventilation with heat recovery (MVHR) is another solution that originated in central and northern Europe. Does it work in a Mediterranean summer? When outdoor temperatures rise above the indoor comfort temperature (> 25 ºC), users in air-conditioned Mediterranean homes typically close windows and turn on the cooling system, with negative consequences for indoor air quality. A mechanical ventilation system with heat recovery and automatic summer bypass, ensures constant air change and high air quality. When T_out > T_int the heat recovery unit reduces the temperature of the inlet air, shown in Figure 10, where heat recovery reduces the temperature of incoming air from 35.5 ºC to 29.5 ºC:

When T_out < T_int the automatic bypass opens, providing free cooling and bypassing heat recovery. Additionally, an enthalpy unit reduces the amount of water vapor that enters the house in summer when the absolute humidity of the outdoor air is greater than the extract air (which is often the case in warm humid climates in homes with air conditioning / dehumidification). When the air conditioning is off, users can of course open windows at any point.  

Discussion and conclusions 

Figure 11 shows the PHPP simulation results for each of the strategies described above. The reduction in cooling demands from insulation on the roof is less than on the walls – a result that seems surprising. This is due to shading from the tree canopy, which means the reduction is less than in the walls. The results show that the combination of all strategies is greater than the sum of individual strategies. Cooling demand is reduced from 33 kWh/m2·a with the CTE code-compliant building, to 18 kWh/m2·a, meeting the requirements for the Passivhaus certification in a Barcelona climate.  

Combining traditional Mediterranean passive cooling strategies with solutions included in the Passivhaus standard, the summer performance of buildings can be improved with a reduced need for air conditioning.  “Stress testing” your design with a tool such as PHPP in the early stages of the project is essential, and post-construction monitoring and evaluation is highly recommended to learn from mistakes and improve.

References 

[1] Somot, S. (2005), “Modélisation climatique du bassin Méditerranéen: Variabilité et scénarios de changement climatique.” Thése de Doctorat, Université Toulouse III-Paul Sabatier. UFR Sciences de la Vie et de la Terre. pp 347. Toulouse, Francia, 2005. 

[2] Parlamento Europeo (2010), “Directiva 2010/31/UE del Parlamento Europeo y del Consejo, de 19 de mayo de 2010, relativa a la eficiencia energética de los edificios (refundición)”. Parlamento y Consejo Europeo, Bruselas, 2010. 

[3] Wassouf, M. (2015), “Comfort and Passive House in the Mediterranean summer – monitorization of 2 detached homes in Spain Barcelona”, 19th IPHC, Leipizig, Alemania.  

[4] Oliver Style (2016), “Measured performance of a lightweight straw bale passive house in a Mediterranean heat wave”. 20^th International Passivhaus Conference, Darmstadt, Alemania.