Is it true what they say, that passive houses use very little energy and are super comfortable? This article presents monitored data from a Passivhaus-certified home, located in the town of Collsuspina, province of Barcelona, at 888 meters above sea level. The results show a heating bill of 50€ per year, a high level of comfort in both winter and summer, and a good indoor air quality.

Table 1 shows the characteristics of the thermal envelope, heating, hot water and ventilation systems.

Ground floor slab	U = 0,164 W/m2·K
External walls	U = 0,146 W/m2·K
Roof	U = 0,147 W/m2·K
Windows	Uw instal·lada = 1,09 W/m2·K
Frames	Uf = 1,22 W/m2·K
Glazing	Ug = 0,60 W/m2·K ; g = 47 %
Shading devices	External venetian blinds & retractable awnings
Airtightness	N50 = 0,31/h
Mechanical ventilation	Zehnder ComfoAir 350
Heating	Electric radiators
DHW	Airsource heat pump Aerotermo 300 Plus

The house was built with a lightweight prefabricated timber system filled with straw insulation. On-site construction took 5 months. The home was monitored between 2015 and 2016, measuring outdoor temperature and humidity, and indoor temperature, humidity and concentration of CO2, on the ground floor main bedroom, and 1st floor sitting room (open plan, shared with dining room and kitchen). Electricity meters were also installed to measure the electrical consumption for heating (electric radiators), DHW (air source heat pump), mechanical ventilation and general electrical consumption (household appliances & lighting). Monitoring was self-financed between the following companies: Progetic, Farhaus, Zehnder Ibérica, with a contribution from the city council of Collsuspina. The house is occupied by 2 adults and 2 young girls.

Winter comfort

Figure 12 shows the indoor temperatures on the ground floor and first floor, and the outside temperature, during the winter of 2015/2016. It can be seen that temperatures remain between 20 °C and 25 °C, except when the house is unoccupied. The average temperature on the ground floor in that period was 21.2 ºC, and 21.3 ºC on the first floor. The total heating consumption (electric radiators) in this period was 251 kWh, or 52€, calculated with a price of electric energy of € 0.21/kWh, according to actual bills. (The consumption results can be seen in Figure 16 and Figure 17).

Summer comfort

Figure 13 shows the outdoor temperature and indoor air temperature on the First Floor (being the most susceptible to overheating), during the heatwave of July 2015. It can be seen that temperatures remain below 26 °C, except when the house is empty.

Figure 14 shows the temperature and relative humidity on the first floor, between June and October 2015, separated between hours with and without occupation. It can be seen that, during busy hours, the temperature and relative humidity are generally maintained within the optimum comfort range (22 ºC to 25 ºC at a relative humidity of between 30% and 70%, according to the comfort model of Dr. Schnieders, based on ISO 7730).

Indoor air quality

Regarding indoor air quality, measured through the concentration of CO2, Figure 15 shows the level of CO2 in the bedroom and in the living room, for a week in November 2015 (where no windows were opened for ventilate). It can be seen that the CO2 level exceeds 1,000 PPM at specific times, with an average of 722 PPM in the bedroom and 706 PPM in the living room. The results indicate a high quality of indoor air in winter.

Consumption & energy bill

Figure 16 and Table 3 show the energy consumption by category, between October 2015 and October 2016. Heating consumption was 251 kWh (52€/year), 970 kWh for Domestic Hot Water (200€/year), 264 kWh for mechanical ventilation (54€/year), and 1,681 kWh for appliances and lighting (346€/year), with a total consumption of 3,165 kWh/year, or 652€/year.

Conclusions

The results indicate that the house has an almost zero energy consumption, a high level of comfort and a good indoor air quality. A larger study of Passivhaus buildings in Spanish climates is required to be able to further analyze the actual behavior. However, the results of this particular house are very positive.

It should be noted that, in the last instance, the energy consumption in a home depends on the performance of the users. In this case, users are very active, taking care of energy consumption, and lowering blinds in summer to avoid overheating. Another point to highlight is the openings surface: project reasonable openings and avoid large window areas, it is key to reduce overheating in summer, without active cooling. Finally, it is important to take into account that, for this climate is possible to maintain thermal comfort in summer without refrigeration, because temperatures tend to fall below 20 ° C at night, making heat evacuation effective by natural night ventilation. In climates where night temperatures remain above 22 °C with higher relative humidity (coast areas, for example), it is very difficult to maintain comfort during summer without active cooling and dehumidification.

Acknowledgments

Albert Fargas – Farhaus; Jordi Vinadé & Itziar Pagés; Ajuntament de Collsuspina; Zehnder Ibérica;

An Energy Audit is a tool that allows companies to substantially improve the energy efficiency of their facilities.

The building energy efficiency regulations RD 56/2016 require large companies (250 people or a turnover bigger than 50 million euros) to carry out an energy audit every 4 years. It transposes the European regulation 2012/27/EU and aims to unify the criteria of energy efficiency for the entire European community.

In order to carry out the audits correctly, UNE-EN 16247 must be complied with, in buildings, processes and fleets of vehicles.

For companies with facilities within the country, it is important to determine that each audit must comprise 85% of the total final energy consumption of all the facilities, not just the headquarters. In each audit, an extensive study of the building is carried out, studying the operation of the facilities and analysing energy consumption, based on energy bills and the data obtained from energy meters.

When the consumption information is compiled and analysed, a series of proposals are made, to reduce energy consumption, CO2 emissions and improve the energy efficiency of the building and/or activity, without affecting performance or indoor comfort. The implementation of monitoring equipment in the facilities is essential, to be able to know and understand where energy is being used and to propose improvements.

In each audit, we specify the cost of the proposals as well as the payback time, always considering the life cycle of the equipment to be replaced. However, the implementation of good habits and responsible use are also important, together with measures such as the reduction of contracted power, being zero-cost improvements that can save substantial amounts of energy and money.

We tailor each audit to the needs of the company, and recommend that the proposed measures are implemented, even if the regulations don’t make it obligatory. Otherwise, an audit will be done every four years without actually improving anything. Energy audits are the first step available to companies to begin reducing their carbon footprint and reduce their environmental impact.

Heat pumps are increasingly used for heating, cooling and domestic hot water production (DHW) in buildings. Their high efficiency and the fact that they are powered by electricity make them ideal for use in residential buildings, especially in low-energy homes.

A heat pump operates by extracting heat from one source and moving it another. During the winter, heat is extracted from outside air or from the ground, and transferred indoors. In the summer, the cycle is reversed. In the case of air-source heat pumps, a refrigerant gas is used for heat transfer, due to the fact that it has a low boiling point, and- under varying pressure conditions- absorbs large amounts of heat with it evaporates, and vice versa when it condenses.

Previously, heat pumps had on-off operation, so they would only work at nominal power when they were on. Thanks to compressors with variable frequency drives, heat pumps can now modulate power according to demand. There are a few important design aspects to bear in mind:

• Despite a variable frequency drive, the thermodynamic cycle of the refrigerant requires a minimum operating time, which requires hysteresis in the operation of the thermostat, with a minimum of 30 minutes. 
• For low volume systems, a thermal inertia tank is needed, to allow for the hysteresis described above.
• Power can usually be modulated to a minimum of 30% of nominal power. This is important when dimensioning the inertia tank and the components that deliver thermal energy.
• As mentioned before, it is important to match the nominal power of the heat pump to the thermal load of the house. If the heat pump is oversized, demand will often be below 30% of nominal power, resulting in a high number of starts and stops for the compressor, reducing its useful life and increasing energy consumption unnecessarily.
• The thermal power and coefficient of performance (COP) of a heat pump depends on two temperatures: outdoor air temperature (in the case of air-source heat pumps), and the heating/cooling water temperature. It is important to ascertain that the heat pump power will be capable of supplying the thermal load of the house under extreme temperature conditions, both in winter and summer.

Against the environmental impact of the construction sector – responsible for 40% of the total primary energy consumption of the European Union – reduce both the energy embedded in the materials in the manufacturing phase, as well as the energy consumption of the buildings in their phase of use are urgent tasks. Wood, agricultural waste, and materials of biological origin are local renewable resources that can be used to promote the circular economy and reduce the environmental impact of the construction sector. This article shows an example of a prefabricated structural insulating panel, made with materials of biological origin, for new buildings of almost zero consumption.

ISOBIO New Build Panel

The prototype of the panel that was monitored measures 1.95m x 1.95m, with a total thickness of 33.2cm in 8 layers with 9 different materials (Figure 1). It is composed by an exterior plaster of 25mm thick lime and hemp, applied on a rigid 50mm hemp thermal insulation, mechanically fixed to the 145mm thick red pine wood structure. Among the timber structure there is hemp, cotton, and linen insulation, followed by a 12 mm OSB 3 board. On the OSB an airtight and dynamic vapor control membrane has been fixed, followed by a 45mm thick service void filled with thermal insulation of hemp, cotton, and linen, between wooden battens, rotated 90º from the timber structure to mitigate the thermal bridge through the wooden elements. The void is closed with a thermo-compressed straw board 40mm thick, revoked inside with a clay and hemp compound, applied in 3 layers, 15mm thick.

Installation and monitoring of demonstrators

Figure 3 and Figure 4 show the installation of the panels in the demonstrators in Wroughton and Seville. A monitoring system was installed with a weather station recording the external conditions, a temperature probe on the outer face of the panel, a heat flow sensor and a temperature probe on the inner face, in accordance with ISO 9869 [1]. Additionally, temperature and relative humidity probes were installed in 3 interstitial points (Figure 2), to measure the dynamic hygrothermal behavior inside the panel and compare the results with the WUFI model, according to EN 15026 [2]. Data were measured at an interval of 5 minutes. The indoor temperature was maintained at an average temperature of 25.5 ° C throughout the period, with an electric air heater.

Results of monitoring and validation of calculation models

Table 1 shows the calculation results of the U of the ISOBIO panel according to ISO 6946 [3] in steady state. For the thermal conductivities of the materials, the values measured in the laboratory were taken (for the dry material at 10 ° C, with a water content w = 0), and were recalculated with a model developed by the University of Rennes 1, for the material at a relative humidity of 50%, being a more realistic water content. For the comparison with the experimental data, the thermal effect of the structural elements of wood was neglected, since their incidence in the measurements of heat flux, temperature and relative humidity were considered negligible.

The results of the period 02/24/2018 to 03/14/2018 are presented in the HIVE demonstrator, United Kingdom, for a total of 432 hours, or 18 days, with 5,184 data points. Table 2 and Figure 5 show the results of the thermal transmittance measured in situ according to ISO 9869, and its comparison with the value calculated in steady state, according to ISO 6946. Figure 6 shows the thermal transmittance measured in situ, compared to the dynamic value calculated with the WUFI tool. Figure 7, Figure 8 and Figure 9 show the temperature and relative humidity measured and calculated with WUFI, inside the panel, in the 3 positions indicated in Figure 2.

Conclusions

The result of the average thermal transmittance measured in situ (Figure 5), is 7% higher than the value calculated in steady state, being a minimum difference, within the range of uncertainty of the measurement. The results indicate reliable behavior and a close correlation between the calculated and measured. It highlights the importance of taking into account a realistic moisture content in the materials, when making a simplified calculation of thermal transmittance, where the only parameter is thermal conductivity.

The hourly thermal transmittance measured in situ and the dynamically calculated values with the WUFI tool (Figure 6), show an even better correlation, with a difference of 4% between the average of the U measured in situ and the U calculated with WUFI . It indicates that the coupled calculation of heat and humidity transfer of the WUFI tool accurately reflects the dynamic thermal transmittance for such a building element, with materials of biological origin.

Finally, the results of the temperature and HR measured and modeled with WUFI in positions 2, 3 and 4 (Figure 7, Figure 8 and Figure 9), show that dynamic temperature variations are very well reflected in the model. Short-term variations in relative humidity are not reflected with the same precision in the model, possibly because of the assumption that the content of water in equilibrium in the materials is instant, when in reality, there is a hysteresis [4]. However, the results show a very good correlation between the measured and the calculated, demonstrating that the materials of biological origin in such a composite panel can contribute to the reduction of the energy consumption of a building in its operation phase, with a minimum amount of energy embedded in the materials in the manufacturing phase.

Acknowledgments

The ISOBIO project was carried out thanks to grant No. 636835 granted by the European Union. http://isobioproject.com

Based on the article de 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.