This single-family home is located in Somió, Gijón, Asturias, Spain, and was designed by
Architect Juan Ignacio Corominas, and certified as a PHI Low Energy Building by Oliver Style
from Praxis. Patricia Borràs was the Passivhaus Designer on the project.
Casa A, Somió, Gijón: single family home certified as PHI Low Energy Building by Praxis
This single-family home is located in Somió, Gijón, Asturias, Spain, and was designed by Architect Juan Ignacio Corominas, and certified as a PHI Low Energy Building by Oliver Style from Praxis. Patricia Borràs was the Passivhaus Designer on the project. Outer walls have 12cm of external insulation fixed to 24cm honeycomb brick, U = 0.208 W/m2·K. The roof has 28cm of XPS thermal insulation, U = 0.117 W/m2·K. The walls to ground of the heated basement have 8cm of insulation, U = 0.437 W/m2·K. The suspended floor slab has 15cm of insulation, U = 0.137 W/m2·K.
Window frames are Passivhaus certified Cortizo COR-80, Uf = 0.94 W/m2·K, with low-e argon filled with triple glazing, Ug = 0.50 W/m2· K and g= 49%. Exterior roller blinds on all windows control summer solar heat gains. A 9.2 kW Baxi PBM 10 air-source heat pump provides underfloor space heating, as well as generating domestic hot water. A Passivhaus certified ventilation unit, Aldes InspirAIR Side 240, provides controlled mechanical ventilation. The Blower Door test result was N50 = 0.89 ren/h.
Lessons learned during the design and construction of Passivhaus buildings over the past 10 years in Spain, identifying the importance of the heat loss form factor, along with successes and pitfalls related to thermal insulation, windows, airtightness, ventilation and active systems.
Lessons learned during 10 years of Passivhaus projects
The Heat Loss Form Factor: Keep it boxy but beautiful!
The compacity of a building has a large influence on energy performance, measured by the form factor, which is the ratio between the thermal envelope and Treated Floor Area (Athermal envelope [m2] ÷ TFA [m2]). The greater the form factor, the greater the exposed heat loss area of the envelope per m2 of TFA, requiring higher levels of thermal protection to achieve the same level of energy efficiency. To illustrate the fact, PHPP modelling results from a range of Passivhaus Classic buildings have been analysed, for varying typologies (single-family, multi-residential, offices and nursing homes) across different Spanish climates. The Form Factor has been compared with two parameters: insulation thickness, using an equivalent thermal conductivity of 0.040 W/m·K (Figure 1) and average Uwindow thermal transmittance (Figure 2).
As expected, the results show a clear correlation: the higher the form factor, the greater the insulation thickness required, and the lower the Uwindow. The results also indicate that other factors also play a part, such as orientation, solar gain, thermal bridges and- to a lesser extent- thermal inertia.
Blower door test: the moment of truth
In timber construction, OSB boards are often used as the airtight layer and vapour retarder. Research by the Passivhaus Institut [Peper 2014] shows a wide range of air permeability between different manufacturers of OSB boards, with 22mm OSB 4 generally showing best airtightness. Table 1 shows Blower Door results in which different grades and thicknesses of OSB were used:
The sample is very small, but the results suggest that 18 mm OSB 3 is sufficient to achieve an airtightness of n50 ≤ 0.6/h, as long as all joints and connections are well sealed. Taping a plastic sheet to a 1m2 area of the OSB board (not across joints), prior to the depressurization test, can provide a simple and visual means of assessing the air permeability of an OSB board.
Airtightness in sliding windows
Sliding windows are a standard feature in Mediterranean Spanish homes, which can present challenges in terms of airtightness. Lift and slide windows can now achieve Class 4 air permeability, making them suitable for Passivhaus buildings. However, Blower Door test results with three sliding panes have shown to be problematic (Table 2), with the best results achieved at least one fixed pane. If there are several sliding panes, best results were found with the fixed pane in the centre position.
Table 2: Results of the Blower Door test of 3 buildings with sliding window frames.
Heating, cooling, and ventilation, better not together
The experience of using the ventilation system for heating and cooling, whereby a water-fed heating/cooling coil heats or cools ventilation supply air, has been shown to be problematic, above all during summer heat waves, in humid Mediterranean climates in urban settings. Conditioning outdoor air, rather than recirculating indoor air, means that the increase in heating and cooling power is far from linear as flow rates are increased. Also, flow rates are generally small, further limiting heating/cooling power. Despite thermal insulation sleeves on supply air ventilation ducts, long duct runs have been shown to incur large heat losses in heating mode, and large heat gains in cooling mode, meaning that valve supply temperatures at the end of the duct run are often much lower than those used in the calculations during the design phase.
With rising global temperatures and increasingly frequent summer heat waves, keeping cool in Passive House buildings has become a hot topic.
Keep cool and carry on: Passivhaus cooling experiences in the warm climates
With rising global temperatures and increasingly frequent summer heat waves, keeping cool in Passive House buildings has become a hot topic.
Bad jokes aside, overheating can be deadly: in France the peak mortality rate during the 2003 heat wave was higher than during the first wave of COVID in 2020, shown in Figure 1 [Parienté et al 2021].
Active cooling in all climates warmer than warm-temperate looks like it will become standard. The question is: for cool-temperature climates, is passive cooling sufficient, or is active cooling unavoidable? What are the pros and cons of the different systems? Will my client ring me up during the next heat wave and give me an ear full?
The article provides technical analysis and lessons learnt from 10 years of experience applying passive and active cooling strategies in residential Passive House buildings in Catalonia, Spain. 6 different kinds of active cooling systems that have been designed and installed in single-family Passivhaus homes are compared, assessing the simplicity or complexity of design, installation, and commissioning; upfront costs; user-friendliness, robustness, and comfort; environmental impact of refrigerants for active cooling systems; and the bottom line: measured performance and monitoring data.
Careful design, moderately sized and well shaded openings, close attention to local climate, and active users have been found to be some of the key drivers of successful passive cooling. Reduction of internal heat gains is key, with efficient appliances and compact Domestic Hot Water (DHW) systems that avoid the need for recirculation circuits. If recirculation circuits are unavoidable, they need high levels of insulation and flow rate control, with reduced DHW water supply temperatures- so long as this is compatible with Legionella prevention. Ultrafiltration and chemical shock disinfection are promising alternatives to the conventional solution of high DHW supply temperatures and thermal shock prevention.
External shading devices are essential, ideally with motorised external blinds, either user controlled or automated. Even north facing windows in Passivhaus buildings need shading: the very long time constant of Passivhaus buildings mean diffuse solar radiation can cause overheating. If only fixed shading can be used, then appropriate solutions for each orientation are key, with particular attention to east and west facing glazing, which receive more solar radiation in the summer than south-facing glazing (shown in Figure 2). Deep horizontal overhangs on southern glazing work best (or northern glazing in the southern hemisphere), with slanted vertical fins for east and west-facing glazing.
Natural night ventilation combined with thermal inertia works well when night temperatures are sufficiently low. Cool external colours, high levels of insulation on roofs, ground coupling, and ceiling fans, are also effective strategies. Figure 3 shows an example of measured data for a single-family home employing many of those strategies (but with little thermal inertia).
Passive cooling is in general simple, low-cost, easy to install, maintain and commission, and can deliver good performance. However, passive cooling strategies are highly climate dependent and rely on careful user behaviour. Where average air temperatures and levels of solar radiation are high (hot ground), minimum night temperatures do not drop below ~ 20 ºC (limited cooling power from natural night ventilation), and night sky temperatures and outdoor air humidity are high, passive cooling won’t work. In this case, active cooling is unavoidable to maintain comfort. Figure 4 and Figure 5 show an example of climate conditions in which passive cooling strategies won’t work, during the 2015 heat wave in Barcelona, Spain.
6 different cooling systems that have been designed and installed in residential Passive Houses are compared, assessing 6 criteria through a simple 1-to-5 point scoring system, shown in Table 1. Monitored data is provided for systems System 1, 2, 5 and 6.
Radiant cooling systems offer a high level of comfort and efficiency, but are more complex to design, install and commission, with higher capital cost. Humidity control and cooling power has been found to be problematic in warm and humid climates, where users go in and out of the house (garden/balcony etc.). Monitored data for an underfloor cooling system is shown in Figure 6. Figure 7 shows monitored data for a radiant ceiling system.
Low-temperature radiators (set in the floor, or wall-mounted) offer a reasonable balance between simplicity, cost, efficiency, and comfort, albeit with less cooling power than fan-coils and splits, requiring a greater number of individual units to cover the same given area than a ducted fan-coil/split system (where 1 indoor unit can cool several rooms). Figure 8 shows monitored data for this kind of system.
Supply air cooling has been found to be problematic, due to limited cooling power (a consequence of conditioning outdoor air rather than recirculating indoor air, low flow rates, and heat gain along long duct runs). Power can be increased using partial recirculation but monitored data in Figure 9 shows that temperature and relative humidity often move outside the extended comfort range. The advantages of this kind of system are simplicity and low capital cost, but the limited cooling power means passive cooling measures must be robust: once overheating has set in, the system will struggle to eliminate heat.
Conventional convective solutions through the recirculation of indoor air (i.e., ducted or wall-mounted fan-coil or split systems) have been found to be the most robust. They are generally simple to design, install and commission, have a lower capital cost than radiant systems, and power can be modulated to deal with peak loads. They are less comfortable than radiant systems. Split systems using refrigerant distribution offer greater dehumidification power (due to lower refrigerant sink temperatures than water) with a faster response than fan-coils and water distribution. However, the Glower Warming Potential (GWP) of the refrigerants and risk of leaks from on-site manipulation is an important consideration. Figure 10 shows monitored data for ducted split system. Temperatures outside the extended comfort range are during hours when the home was not occupied, and the clients report a high level of thermal comfort.
The article presents the results of a thermodynamic simulation study, comparing Wood Plastic Composite (WPC) floorboards with ceramic and stoneware floor tiles, heated with an electric underfloor heating system, for both dry and wet assemblies.
Thermodynamic analysis of an electric underfloor heating system
The article presents the results of a thermodynamic simulation study, comparing Wood Plastic Composite (WPC) floorboards with ceramic and stoneware floor tiles, heated with an electric underfloor heating system, for both dry and wet assemblies. The different floor finishes have been modelled in a multi residential building, in Madrid (Spain) climate, using the DesignBuilder-EnergyPlus simulation tool.
The objective of the study is to analyse the dynamic thermal response of each kind of floor finish, comparing heating energy consumption, peak heating power, floor surface temperature and indoor air temperature.
The Table below shows the different types of floor systems that were modelled:
The DesignBuilder tool with the EnergyPlus thermodynamic calculation engine has been used for the simulations.
A multi-residential 4 storey building has been modelled, consisting of 4 dwellings per floor, each with ~ 86 m2 of net floor area, and 342.1 m2 of total heated floor area. The second floor of the building has been modelled for the study, with the floors above and below modelled as adiabatic (they are assumed to be occupied and heated, with the same occupancy and internal heat gain conditions).
The exterior walls are cavity wall with a 14 cm perforated brick outer layer, 5 cm air-void, 6 cm of thermal insulation, and 9 cm of interior hollow brick layer, with 1cm of gypsum plaster (U = 0,39 W/m2·K). The dwellings have aluminium window frames with thermal breaks (Uf = 3,6 W/m2·K) and air-filled double glazing (Ug = 2,9 W/m2·K & g = 69%). The dwelling have mechanical ventilation with an average air change rate of 0.63 ach, with sensible heat recovery that has a efficiency rate of η = 70 %. For dwellings, air infiltration has been calculated as N50 = 5/h, converted to atmospheric pressure and applied to each zone according to its exposed area. Common areas, as the staircase, air infiltration have been modelled with 1 ach of air infiltration.
The energy consumption of all 4 homes on the second floor has been analysed, with a detailed analysis of Room 1 (oriented to the southwest).
Electric radiant floor system
An electric radiant floor system has been modelled. Heating mats with the following nominal power capacities were simulated under each type of flooring:
Wood Plastic Composite (WPC) floor (direct system): 75 W per linear metre
Wood Plastic Composite (WPC), with self-levelling mortar screed: 116 W per linear metre
Stoneware/ceramic floor, with self-levelling mortar screed & gypsum plasterboards: 116 W per linear metre
The radiant floor power for each home and for Room 1 is shown in the following table. The radiant floor has been modelled as “ZoneHVAC: Low Temperature Radiant: Electric” and inserted into DesignBuilder using an EnergyPlus script.
The heating setpoints are those indicated in Annex D “Operational conditions and usage profiles” of the Spanish Building Regulations CTE DB HE 2019:
Main setpoint: 20 ºC (07:00 – 22:59)
Secondary setpoint: 17 ºC
The 3 periods shown in the following table have been analysed:
The following parameters have been analysed:
Heating consumption [kWh]
Maximum capacity of the radiant floor heating mat [kW]
Floor temperature [ºC]
Dry installation: thermal transmittance, thermal resistance, and internal heat capacity
The Figures below show the radiant floor capacity, total thermal transmittance (according to ISO 69446), thermal resistance of the materials on top of the radiant floor heating mat, and the internal heat capacity of the materials above the radiant floor (according to ISO 13786), for each type of floor, for a dry installation.
Wet installation: thermal transmittance, thermal resistance, and internal heat capacity
The following graph and table show the radiant floor capacity, the total thermal transmittance (according to ISO 69446), the thermal resistance of the materials above the radiant floor heating mat, and the internal heat capacity of the materials above the radiant floor (according to ISO 13786), of each flooring type, for a wet installation.
Dry installation: 2nd floor, heating consumption, 1st October – 31st March
The Table and the Figure below show the results of heating energy consumption for each type of floor, for a dry installation.
The results indicate that the heating consumption of floors 2.1 Stoneware and 2.2 Ceramic with double gypsum fibreboards is 20% higher than in 1.1 WPC (direct system).
Floor consumption 3.1 Stoneware and 3.2 Ceramic with 1 dry gypsum fibreboard, is 5% and 4% higher than 1.1 WPC. These differences fall within the margin of uncertainty in the calculations (around 10%).
Wet installation: 2nd floor: heating consumption, October 1st – March 1st
The next table and graph show heating consumption results for each floor type, with wet installation.
The results indicate that heating consumption of 4.1 Stoneware and 4.2 Ceramic floors with self-levelling mortar screed, are 10% and 9% lower respectively than 1.2 WPC with self-leveling mortar screed. These differences fall within the margin of uncertainty in the calculations (around 10%).
Dry installation: Bedroom 1, floor & indoor air temperatures, radiant floor power, and solar gains, January 14th
The evolution of radiant heating mat capacity is shown in the Figures below, together with solar gains, floor surface temperature, and indoor air temperature, during the day of January 14th, for each floor type, for dry installation.
Additionally, the maximum capacity of the radiant heating mat, the time at which maximum capacity occurs, and the maximum floor surface temperature (before the effects of solar radiation) are shown.
The heating setpoint and setback temperatures (20 ºC from 7:00 – 23:00 and 17 ºC the rest of the day) determine when the radiant floor is turned on or off. Solar gains provoke sudden rises in indoor air and floor surface temperatures when the radiant floor is off.
The table and graphs above show that the delay between radiant heating mat’s maximum capacity and maximum floor temperatures, is around 4 hours for the 1.1 WPC, approximately 6 hours for stoneware floor and ceramic floor with 2 gypsum fiberboards, and approximately 5 hours with 1 gypsum fiberboard.
This is mainly because the thermal resistance and thermal capacity of the 1.1 WPC (direct system) is lower than with the stoneware and ceramic floors with gypsum fiberboards, therefore takes less time to warm up and transmit heat to the room.
Wet installation: Bedroom 1, floor & indoor air temperatures, radiant floor power, and solar gains, January 14th
The graphs below show the evolution of the radiant heating mat power capacity, solar gains, floor surface temperature, and indoor air temperature, during January 14th, for each floor type, for a wet installation.
The radiant heating mat maximum capacity, the time at which maximum capacity occurs, and the maximum floor surface temperature (before the effects of solar radiation) are shown. For the 1.2 WPC, the maximum floor temperature takes place at 12:00 due to the heat emitted by the radiant heating mat; from that time on, the increase in floor temperature is due to solar gains.
The above graphs and table indicate the time delay between the radiant floor’s maximum capacity and the floors maximum temperature, for the WPC, stoneware, and ceramic floor with self-leveling mortar screed, is around 5 hours in all three cases.
Although the heat capacity of the materials above, the radiant floor of floor types 4.1 and 4.2 is far greater than the 1.2 WPC, the thermal resistance of these materials is much lower, so the dynamic response and heating consumption is similar.
The results of the dry installations, indicate that the Wood Plastic Composite flooring has lower energy consumption (between 4% and 20%) and a slightly faster thermal response. In the case of floors with wet installation, the results indicate that the Wood Plastic Composite flooring has a slightly higher energy consumption (between 9% and 10%) and a thermal response similar to the other floor types analyzed. In both cases, given the margin of uncertainty of the calculation, the difference is minimal.
Energy consumption from DHW use is often higher than heating and cooling requirements in a residential Passivhaus. This is mainly due to the large losses inherent in storing and recirculating hot water, and because heating and cooling demands are very low.
DHW + PV: solar PV top-up for domestic hot water
Energy consumption from DHW use is often higher than heating and cooling requirements in a residential Passivhaus. This is mainly due to the large losses inherent in storing and recirculating hot water, and because heating and cooling demands are very low, thanks to an optimised fabric design that minimises thermal losses/gains. Reducing the net energy consumption of DHW in Passivhaus is therefore important.
The article presents monitored data from a solar PV installation for a single-family certified Passivhaus in Girona, Spain, designed by Tigges Architekt and Energiehaus Arquitectos, with services installed by Progetic (Figure 1 & Figure 2). The system diverts surplus PV production to an electric immersion heater in the DHW tank, where the primary generator for hot water is an air-source heat pump.
The first step is always to optimise DHW system design and reduce losses. The second step is to find simple and low-maintenance solutions for on-site renewable energy generation for DHW production. The solution implemented here is an all-electric system that reduces net hot water energy consumption, using a solar PV array to top up hot water production, with an air-source heat pump as the main hot water generator. The system avoids the maintenance problems found in solar thermal systems that are susceptible to overheating in summer months when occupants are away, where fluid dry-up in the primary circuit between panel and tank is a frequent cause of failure.
A series of calculations were done with the PHPP tool, to determine useful energy demands, final energy consumption and projected energy bills, by category. For the calculation of the energy bill, the weighted price of electricity was calculated at € 0.21 / kWh. Additionally, an analysis of DHW demand and losses by category was made. Figure 3, Figure 4, Figure 5 and Figure 6 show the results.
DHW consumption appears as the second highest energy consumer, 34% of the total. If we look at DHW demand and losses, only 33% is due to heating hot water, the remaining 67% are losses, of which 44% are due to recirculation, 18% due to individual pipes, and a 5% for storage. The total predicted final energy consumption for DHW is 1,764 kWh, an average of 147 kWh/month.
The system incorporates a PV array with 12 polycrystalline modules and a peak power of 3.18 kWp (Figure 7), and a 3 kW inverter. The main hot water generator is a 6 kW ait-to-water heat pump (wich also supplies heating and cooling, with a 500-liter DHW tank and 3-kW electrical immersion heater (Figure 8). DHW production is isntantaneous. When the sun is shining and there is more PV generation than electrical consumption in the home, a control system diverts the electrical energy from the PV panels that cannot be self-consumed into thermal energy in the DHW tank for use in the afternoon or evening (Figure 9).
This is particularly interesting in the summer in passive houses in warm climates with active cooling and only one heat pump, as it generally allows the heat pump to keep itself in cooling mode, rather than stopping, reversing and going into hot water heating mode, before reverting back to cooling (for example, when occupants return home in the afternoon and shower etc). The hysteresis in this process can mean the home is without active cooling during 2/3 hours, which can be a problem in comfort terms. The control system monitors the home’s electricity consumption and PV production, sending surplus electricity to the resistance in the DHW tank. The power of the resistance heater is modulated through a voltage regulator, due to the fact that the output power of the photovoltaic generator varies continuously according to the level of solar radiation, and that the available surplus depends on the transient electricity consumption of the house.
Monitoring data & conclusions
Monitoring data for 2018-2019 shows a total of 1211 kWh of PV production was diverted to the electrical resistance in the DHW tank, with a peak water temperature of 58 ºC. PHPP calculations projected that DHW consumption was 1764 kWh. Logically, not all of the PV energy diverted to the DHW tank is useful, as it depends on when DHW consumption takes place. Nonetheless, the system shows that solar PV top-up is effective for assisting in hot water generation, thereby reducing net energy consumption derived from hot water use, shown in (Figure 10) and (Figure 11) below.
 Feist W., Peper S., 2015, “Energy efficiency of the Passive House Standard: Expectations confirmed by measurements in practice”. Passive House Institute Dr. Wolfgang Feist, Rheinstraße 44/46, 64283 Darmstadt, Alemania.
 Grant N., Clarke A., 2010, “The importance of hot water system design in the Passivhaus”. Elemental Solutions, Withy Cottage, Little Hill, Orcop, Hereford, HR2 8SE, Reino Unido.
 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 edificiosb(refundición)”.
Given the environmental impact of the construction sector- responsible for 40% of the total primary energy consumption of the European Union- reducing both the embodied energy of materials at manufacturing stage and minimising operational energy consumption in buildings are urgent tasks.
Dynamic hygrothermal simulation and full-scale validation of a structural insulated panel made from bio-based materials.
Given the environmental impact of the construction sector- responsible for 40% of the total primary energy consumption of the European Union- reducing both the embodied energy of materials at manufacturing stage and minimising operational energy consumption in buildings are urgent tasks. Timber, agricultural residues, and bio-based materials are local renewable resources that can be transformed into buildings products and components, fomenting the creation of circular economies, and reducing the environmental impact of the sector. The objective of the European ISOBIO project, that ran from 2015 to 2019, financed under the Horizon2020 program, was to address these problems through the development of new insulating materials and renders from plant fibres, agricultural residues, and bio-based binders. The article presents the results of dynamic hygrothermal simulations and full-scale validation of a structural insulated panel made from bio-based materials, for use in the construction of nearly-zero energy buildings.
ISOBIO structural insulated panel for new buildings
The prototype panel measured 1.95m x 1.95m, with a total thickness of 33.2cm in 8 layers with 9 different materials (Figure 1). The panel was rendered external with 25mm of lime and hemp plaster, applied on a rigid 50mm hemp insulation board, mechanically fixed to a 145mm red pine timber structure, filled with hemp, cotton, and flax insulation, followed by a 12mm OSB 3 timber board. An airtight and dynamic vapour control membrane was fixed to the inner face of the OSB, followed by a 45mm service void, insulated between timber battens with hemp, cotton, and flax insulation. The battens were positioned at 90º in relation to the main structural joists to reduce the thermal bridging through the timber. The inner service void was lined with a 40mm thermo-compressed straw board, plastered on the inside with 15mm of composite clay-hemp plaster, applied in 3 layers.
Figure 3 shows the installation of the panels in the demonstrator in Wroughton, UK. A monitoring system was installed, with a meteorological station recording external climate conditions: dry air temperature, relative humidity, solar radiation, wind speed, wind direction, rainfall, and barometric pressure. A temperature probe was installed on the outside of the panel, with a heat flow and temperature probe on the inner face, for measuring thermal transmittance in accordance with ISO 9869 . In addition, temperature and relative humidity sensors were installed at 3 positions within the panel (Figure 2), to measure transient hygrothermal behaviour inside the panel and compare the results with dynamic hygrothermal simulations made with the WUFI Pro tool, following EN 15026 . WUFI Pro 1D is a tool developed by the Fraunhofer Institute in Germany for assessing the hygrothermal performance of one-dimensional building envelope cross-sections, taking into account the moisture content of the materials, their transient hygrothermal performance, capillary transport and summer condensation, with hourly outdoor climate conditions. The software version used was WUFI Pro v. 220.127.116.110
Data was measured at an interval of 5 minutes, from 24/02/2018 to 14/03/2018 in the HIVE demonstrator, UK, for a total 432 hours, or 18 days, with 5184 data points. The interior temperature was maintained at an average of 25.5 °C throughout the period, with the use of an electric convection heater.
Monitoring Results and Validation
Figure 4 shows a cross section of the modelled panel, with sensor locations. Figure 5 shows the WUFI model of the panel and corresponding sensor locations.
Figure 6 shows measured and modelled temperature and RH at position 2 (between the CAVAC rigid insulation and Biofib Trio insulation). Temperature dynamics are well reflected in the model. RH dynamics are less well reflected.
Figure 7 shows the measured and modelled temperature at position 3 (between the Biofib Trio insulation and OSB board). Temperature dynamics are well reflected in the model, with RH less so. The model nonetheless shows very close alignment with measured results.
Figure 8 shows the measured and modelled temperature and RH at position 4 (between the Intello membrane and the Biofib Trio insulation). Temperature and RH dynamics are well reflected in the model.
Figure 9 shows the measured average heat flow rate, compared with the WUFI modelled heat flow rate, showing very good agreement.
The results of the measured and modelled temperature and RH show good correlation, with dynamic temperature variations accurately reflected in the model. The short-term variations in relative humidity are not reflected with the same precision in the WUFI modelling results, possibly due to the assumption that the equilibrium water content in the materials is instantaneous, where in reality, there is hysteresis . The hourly measured and modelled thermal transmittance data show very good correlation, with a difference of only 4% over the monitoring period.
The results indicate that bio-based materials combined in a composite SIP panel of this type can offer predictable hygrothermal performance for use in nearly-zero energy buildings.
ISO 9869-1:2014 Thermal Insulation – Building elements – in-situ measurement of thermal resistance and thermal transmittance. (Aislamiento térmica – elementos constructivos – medición in-situ de la resistencia térmica y transmitancia térmica)
UNE-EN 15026:2007, Comportamiento higrotérmico de componentes de edificios y elementos constructivos. Evaluación de la transferencia de humedad mediante simulación numérica.(Ratificada por AENOR en junio de 2010.)
N. Reuge, F. Collet, S. Pretot, S. Moisette, M. Bart, O. Style, A. Shea, C. Lanos 2019, Hygrothermal transfers through a bio-based multilayered ISOBIO wall – Part I: Validation of a local kinetics model of sorption and simulations of the HIVE demonstrator. Laboratoire de Génie Civil et Génie Mécanique, Axe Ecomatériaux pour la construction, Université de Rennes, 3 rue du Clos Courtel, BP 90422, 35704 Rennes, France.
The U.S. EPA (Environmental Protection Agency) estimates that the air in our homes is 2 to 5 times more polluted than outdoor air. After spending so much time at home during successive COVID lockdowns, the importance of living in a healthy home has perhaps become clearer than ever before.
Healthy home: materials and indoor air quality
The U.S. EPA (Environmental Protection Agency) estimates that the air in our homes is 2 to 5 times more polluted than outdoor air. After spending so much time at home during successive COVID lockdowns, the importance of living in a healthy home has perhaps become clearer than ever before.
What kind of environmental conditions are we looking for in a healthy home? Operative or comfort temperatures of between 20 ºC – 25ºC, relative humidity between 40 % – 60%, and surface temperatures ≤ 3ºC of the indoor air temperature. With an indoor air temperature of 20ºC and a relative humidity of 50%, interior surfaces need to be ≥ 13ºC to prevent the risk of mould growth, and ≥ 9ºC to avoid surface condensation. Exposure to mould spores can cause health issues such as eye, skin and throat irritation, nasal stuffiness, coughing and wheezing. Alongside healthy thermal conditions, good indoor air quality is key for wellbeing, solved largely by good ventilation, but also by preventing the entrance of outdoor contaminants (such as particulate matter, radon gas etc.) and by reducing the generation of indoor contaminants due to emissions from materials, furniture, and finishes.
If continuous and controlled ventilation is key, we need to get to the root of the problem: to reduce and avoid materials that emit toxic chemicals in our home. In this article Oliver Style explains what to be on the lookout for, and presents three certification systems that are useful for choosing healthy products and materials.
What does indoor air contain?
To live in a healthy environment, we need to look at the products, materials and furniture we have in our home, since we breathe the particles they emit and we are often in direct physical contact with them.
The first step is to choose paints, varnishes, timber, ceramics, textiles, and furniture with a very low emissions of Volatile Organic Compounds (VOCs). VOCs are of both natural and artificial origin. They all share the common characteristic that they are made of carbon and other elements such as hydrogen, halogens, oxygen, or sulphur. They are present in solids or liquids and are either volatile or occur in a gaseous state at room temperature, which means they move quickly around indoor spaces. Some of them modify the chemical composition of their local environment and are harmful to our health.
Formaldehyde, a colourless, volatile, and toxic gas (classified as carcinogenic by the EU), and other VOCs, are often found in paints, paint strippers, wood preservatives, wood products, binders, glues, waxes, plastics, pesticides, aerosols, synthetic carpets, cleaning products, disinfection products and degreasers. Health effects include asthma, eye, nose and throat irritation, headaches, loss of coordination, nausea, liver, kidney and central nervous system damage. VOCs can be endocrine disruptors and cause respiratory and hormonal diseases, prolonged sleep and behavioural disorders, reproductive disorders and foetal development, cancer, and multiple chemical sensitivity (MCS).
Another harmful component to pay close attention to is particulate matter (PM)- fine particles and fibres with a diameter of 10 micrometres (PM10) or less (PM2.5 and PM 1). PM2.5 particles can reach the lungs, and PM1 can reach the bloodstream. Short and long-term exposure to these particles is associated with cardiovascular and respiratory diseases, including lung cancer. These diseases become more evident when the fibres come from highly toxic materials such as asbestos.
Which are the best materials and products to use in our home?
To avoid and minimize harmful substances inside the home, it’s best to look for products that have been modified or processed as little as possible, made with low-emission paints, varnishes, and glues, formaldehyde free, and if possible, certification for low emissions. Three such certification systems are mentioned below, which classify materials and products and quantify their harmful emissions.
Linoleum or solid wood floors are recommended because they usually contain few adhesives and generally have low emissions. Anything that has been varnished or coated in a controlled factory environment (rather than on-site) will lead to lower emissions in the home. If you use laminated timber flooring, look for one that is free of formaldehyde.
Carpets are in generally not advisable, as they end up collecting all kinds of particles, and in some cases, contain volatile coal ash or polyurethane laminates. Natural fibre carpets are recommended.
Furniture and wood composite products can be a significant source of emissions because they are often made with urea-formaldehyde adhesives. Look for solid wood or plywood furniture, free of formaldehydes.
As far as kitchen counters go, natural rock is a good option, such as quartz. Alternatively, look for Corian (a synthetic material for solid surfaces composed of acrylic resin and aluminium hydroxide).
As for thermal insulation, exposure to sprayed foam insulation containing isocyanates can cause asthma. If you use fiberglass or mineral wool insulation, make sure it’s formaldehyde free. In general, bio-based or mineral insulation are the healthiest options.
Be careful: products are sometimes sold as “ecological” due to their recycled content, but they can be harmful to your health. For example, some ceramic tiles are made with recycled glass from cathode ray tubes from old TVs, which are considered hazardous waste due to their high lead content.
Emissions & materials: certification systems
1. French certification for indoor air emissions
The label “Émissions dans l’air interieur” classifies building materials, furniture and finishing products marketed in France, being mandatory for all products sold there. The certification classifies products according to VOC emissions, from A+ to C (A+ being lowest emissions), according to the ISO 16000 standard. If a product exceeds the limits, it cannot be sold (admittedly “C” class is not very demanding…). The following emissions are evaluated:
1, 2, 4 Trimethylbenzene
1, 4 Dichlorobenzene
2. Baubiologie Rosenheim Institute certification
The IBR, Institute for Biologically Sound Construction, is a German institution that certifies healthy and environmentally sustainable consumer construction products, and includes a series of tests that measure the emissions of a product, including:
3. Eurofins Indoor Air Comfort certification
This certification systems classifies construction products into two categories: Standard level “Indoor Air Comfort – certified product”, which shows compliance with product emissions criteria established by EU authorities, and Higher level “Indoor Air Comfort GOLD – certified product”, which shows additional compliance for product emissions with the criteria set by the most relevant ecolabels and sustainable building organisations in the EU.
What you don’t measure you can’t improve
There are several testing laboratories in Spain for the measurement and certification of materials and their VOC emissions, such as Tecnalia, and SGS. What if I want to measure the indoor air quality of my home without spending a fortune? There’s affordable equipment with reasonable accuracy, such as the range of MICA sensors, manufactured by Inbiot. They measure VOC’s, formaldehydes, ozone, suspended particles, radon gas, CO2, temperature and relative humidity.
The following figure shows measured data from a MICA sensor of formaldehyde concentration in a bedroom over the course of a week.
According to the technical standard of measurement in Baubiologie SBM2015 for rest areas, values above 100 μg/m3 are already extremely significant. “The search for emission sources is a bit like looking for a needle in haystack, based on the data and measurements. But you can gradually discard sources until you find the culprit” says Maria Figols, Project Manager at InBiot.
Better living with less emissions
Creating healthy indoor environments is clearly on the agenda, with the construction sector on centre stage. Choosing the right low-emission materials will improve indoor air quality and can help reduce illness for occupants, in the short, medium, and long term. Using products with some of the certification systems shown above is a good place to start. Alongside emissions, these kind of certification systems also assess the environmental impact of a product, making sure they don’t pose a significant hazard during manufacturing, deconstruction, recycling or waste treatment phases. Reducing the source of indoor contaminants should always be the first step. The second step- and equally important- is controlled and efficient ventilation.
To Maria Figols and Xabi Alaez from InBiot for their contributions.
 Guía Edificios y Salud, Siete Llaves para un edificio saludable. García de Frutos, Daniel et al. Consejo General de la Arquitectura Técnica de España, Consejo General de Colegios de Médicos. Enero 2020.
 Monitorización de vivienda de alta eficiencia, 30 Marzo 2020. InBiot. https://wiki.inbiot.es/monitorizacion-de-vivienda-de-alta-eficiencia/
The Passivhaus standard is a voluntary energy certification standard for new and retrofitted buildings, aimed at providing maximum comfort for occupants, excellent indoor air quality and near-zero energy consumption.
Keys to the Passivhaus standard: what is it and how to achieve it?
The Passivhaus standard is a voluntary energy certification standard for new and retrofitted buildings, aimed at providing maximum comfort for occupants, excellent indoor air quality and near-zero energy consumption. It was developed in the 90’s by the Passivhaus Institute in Darmstadt Germany, and it has since been expanding across the globe. The current climate crisis is increasingly bringing the standard into the limelight due to its radical no-nonsense approach, rooted in buildings physics, a rigorous design process and an emphasis on proper site supervision and commissioning. The objective is to close the so-called “performance gap” (where buildings fail to perform as predicted), making them fit for purpose, comfortable, healthy, and resilient. A Passivhaus building typically consumes up to 90 % less energy than a conventional building.
This article, written by Oliver Style, explains some of the key aspects of the Passivhaus and what you need to do, to achieve certification.
Passivhaus: the Basic Principles
It is often said that the standard is based on the following 5 principles:
High levels of thermal insulation
High performance windows
Efficient mechanical ventilation with heat recovery
Absence of thermal bridges
Although this simplification can make it easier to understand what Passivhaus is all about, a Passivhaus building requires a holistic design process where the whole is more than the sum of the parts… and there are many parts. So, beyond the 5 basic principles, there are several other factors that are important for achieving certification and making sure a building does what it says on the tin, especially in warm climates, namely:
External shading devices to reduce solar gains and avoid summer overheating
Efficient Domestic Hot Water (DHW) systems, equipment and lighting: to reduce primary energy consumption and reduce internal heat gains in summer (helping avoid summer overheating).
Efficient heating and cooling installations
In climates with sufficiently low minimum night time temperatures: Natural night ventilation combined with thermal inertia, to remove heat from the building without relying only on active cooling.
A building designed to have very low heat losses in winter, will also keep heat out in the summer: if you fill a vacuum flask with cold water in the summer, the water will stay cool for longer than if you just left it in outside in ambient warm air. However, once the heat is inside, it will logically dissipate more slowly due to the high level of thermal protection. That is why it’s particularly important to go beyond the “5 principles” if you want to avoid overheating problems, which will increasingly become an issue as summers get warmer due to global warming (Figure 2).
PHPP: “Passive House Planning Package”
For the design of a Passivhaus building, the PHPP (“Passive House Planning Package”) tool is used, a quasi-steady-state single zone energy modelling program, based on a series of spreadsheets in Excel, that provides monthly and annual energy balances. The algorithms in the tool are based on a number of ISO standards, mainly in the monthly method of EN ISO 13790, now replaced by ISO 52016 0.
The PHPP has been calibrated with thermodynamic simulations carried on with the DYNBIL tool, developed by the Passivhaus Institute, itself calibrated by extensive validations with monitored data.
PHPP stands out for its simplicity compared to dynamic tools and can be used to model (albeit in a simplified way) a wide variety of active and passive systems, at a very affordable price. The results indicate the energy balance of the building in both summer and winter, yielding results of heating and cooling demands and total and final and primary energy consumption. Although a dynamic tool is- in principle- more accurate, the large number of parameters and input data increases the possibility of modelling errors and requires experience and time for accurate use. In energy simulation, it is sometimes better to be approximately correct than precisely wrong…
Passivhaus for new build
The Passivhaus standard for new buildings is performance based: i.e., it doesn’t limit thermal transmittance values of the different construction elements, but establishes maximum energy demands and energy consumption, calculated with the PHPP. The air infiltration level cannot exceed 0,6 air changes per hour (ACH) at a pressure difference of 50 Pascals, measured with an on-site test, known as the “Blower Door” test.
The limiting values for heating and cooling demands and total primary energy consumption, are shown in Figure 3.
There are 3 classes of certification: Classic, Plus and Premium. Classic does not have renewable energy generation. To get to Plus, you have to generate ≥ 60 kWh/m2·a of renewable energy (references to the building’s footprint)- typically at least as much as what the building consumes. To reach Premium, the building must generate ≥ 120 kWh/m2·a (or 4-5 times more than what the building consumes). This is shown in Figure 4. The advantage of this approach is that energy demands are reduced first, before considering on-site generation of renewable energy. This differs from the conventional net-zero energy approach, which inevitably favours buildings with very large roofs on which a large solar PV generator can be installed, leading to buildings with a poor form factor (the ratio of enclosed envelope area to useful floor area), higher losses and where on-site renewable energy generation is prioritised over reducing energy use.
PHI Low Energy Building
If the above requirements are not met, a building can be certified as PHI Low Energy Building, complying with less stringent requirements, shown below in Figure 5.
Passivhaus for retrofitting: EnerPHit
For the retrofitting of existing buildings, there is the EnerPHit seal, which offers two ways to achieve certification:
EnerPHit, Demand Method: performance based, with the requirements shown in Figure 6
EnerPHit, Component Method: prescriptive, with the requirements shown in Figure 7
For both methods, an air tightness test result of N50 ≤ 1.0 ach must be obtained. The Classic, Plus and Premium classes are also applicable to the EnerPHit standard.
Overheating risk in summer
For certification, overheating risk is assessed through one of the two following methods:
With active cooling: the limiting total cooling demand must be met (sensible + dehumidification), calculated with the PHPP, with mechanical systems capable of maintaining thermal comfort at all times (according to ISO 7730), with an operating temperature ≤ 25 ºC and a maximum of 10% of the hours in the year with an absolute indoor humidity ≥ 12 g/kg dry air.
With passive cooling: the maximum overheating frequency must be met, calculated with the PHPP, with a maximum of 10% of the hours in the year with an indoor operating temperature > 25 ºC.
In the case of passive cooling, it is important to stress that 10% of the hours of the year are a total of 876 hours with an indoor operative temperature above 25 °C (the whole month of August, for example). Therefore, the recommendation is not to exceed 5%, with a good design objective being 2 – 5%, shown in Figure 8.
To reduce the risk of overheating where no active cooling is available, it is important to perform stress tests of extreme climate situations with the PHPP. For this purpose, Jessica Grove-Smith of the Passivhaus Institute has developed theSummer temperature tool, which adjusts the summer temperatures in the PHPP climate file, taking into account the urban heat island effect and the increase in temperatures according to IPCC’s predictions (Figure 9). This feature will be integrated directly into PHPP version 10.
For tertiary buildings and/or buildings with areas exposed to very different indoor and outdoor conditions, it is advisable to accompany the PHPP calculation (a single zone tool) with a dynamic multi-zone calculation, to analyse specific zones that may be more susceptible to overheating (for example, the top floors in a tall building with west-facing glazing).
Additionally, if the building does not have an active cooling system, it is important to test assumptions regarding user behaviour, for example, in relation to closing blinds and opening windows at night for natural ventilation. Is it realistic to think that a person will sleep all night with the blinds open, all windows fully open, and all interior doors open? It is more likely that occupants will close the blinds before going to sleep so the sun light doesn’t wake them up in the morning. If you live in an urban area, you might want to close all windows facing the street to avoid noise. All this reduces natural night ventilation flow rates and the amount of heat that can be extracted from the building.
Although the goal is always to reduce dependence on active systems to maintain comfort, in most cases, some active cooling in summer is advisable. Fortunately, the summer is also the time when there is the most solar radiation, which means active cooling energy consumption can be directly off set with on-site renewable energy production.
Air tightness: the “Blower Door” test
Central to the Passivhaus standard is the “Blower Door” airtightness test, that measures air infiltration through a piece of equipment that pressurizes and depressurizes the building. Preliminary tests must be carried out before the interior finishes are completed (to detect and correct leaks, if found), together with a final test, according to the EN 13829 .
The “Blower Door” test is a clear indicator of build quality. What are the advantages of reducing air leaks?
Reduces energy losses and heating bills in the winter
Reduces the entrance of moisture in warm-humid climates, thereby reducing dehumidification cooling consumption and cooling energy bills
Improves comfort, eliminating air drafts
Improves people’s health by preventing the entry of radon gas, suspended particles and other pollutants from outside
An existing building will typically have an infiltration level of n50 ~10 ach. A certified Passivhaus has an n50 ≤ 0.6 ach. The Spanish CTE Building Regulations, in the 2019 update, establishes a limit for air infiltration of n50 3 ach and 6 ach according to the compacity of the building (Figure 10).
Audits and certification: quality assurance from design to completed building
The certification process and auditing begin in the design phase and conclude when on-site construction is finished. Certification can only be carried out by the Passivhaus Institute or an approved Building Certifier. As an external agent to the project, the certifier verifies that the project complies with the standard and that construction has been completed as planned, accurately reflected in a the PHPP model. The client needs to supply detailed as-built architectural and service drawings, photographic documentation showing the execution of all elements related to energy and air tightness, the final certificate of the Blower Door test, the ventilation system commissioning results, together with a letter signed by the Site Supervisor, indicating that the project has been built as designed.
Passivhaus and health
Although the standard does not specify which materials you use in a building, the PHPP manual explicitly recommends the use of low-emission materials, to reduce VOC’s (volatile organic compounds) in indoor air.
To ensure good air quality, the correct sizing of the ventilation system at design stage is checked. Once installation is completed, the commissioning of the system and the measurement and adjustment of flow rates in all supply and return valves is mandatory.
The goal is to create healthy, comfortable, efficient and resilient buildings, closing the performance gap between projected and real-life performance.
 EN ISO 13790, Energy performance of buildings – Calculation of energy use for space heating and cooling. This standard has been revised by ISO 52016-1:2017
 Criteria for the Passivhaus, EnerPHit and PHI Low Energy Building Standard, version 9f. 15.08.2016 1/30. 2016 Passive House Institute.
 Passive House Institute Summer Temperature Tool, Available at: https://passiv.de/en/05_service/02_tools/02_tools.htm
 DIN-EN 13829, Thermal performance buildings – Determination of air permeability of buildings – Fan pressurization method. (ISO 9972:1996, modified).
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