This news article was originally written in Spanish. It has been automatically translated for your convenience. Reasonable efforts have been made to provide an accurate translation, however, no automated translation is perfect nor is it intended to replace a human translator. The original article in Spanish can be viewed at La ventilación de confort como sistema de ahorro energético

Rehabilitation to turn a House into passive (project efficient house Mz)

Comfort as a system of energy-saving ventilation

José Ramón Ferrer and Josep Castellà. Zehnder Group IC Ibérica, S.A.

16/07/2013

The challenge was to intervene, in only 120 days, a house built in 1918 while retaining original volumetry and facade, becoming passive to improve performance of thermal and acoustic comfort. Construction systems and materials used for rehabilitation allowed the goal, at the same time reducing energy demand. Housing reduces the energy demand of 171 17 kWh/m²year, using very high efficiency of Zehnderheat recovery ventilation system Comfosystems.

This project has been the challenge of rehabilitating a housing built in 1918 while retaining the volume and original façade to the street but improving performance of thermal and acoustic comfort. Construction systems and materials used in rehabilitation have allowed the goal, reducing at the same time the energy demand of 171 17 kWh/m²year (energy rehabilitation of factor 10), transforming a traditional building in a passive house in just 120 days. Bad orientation and little volumetric freedom, the maximum execution time very limited and a very limited budget, have been very important factors for the development of the work.

One of the key factors to make a passive house is to incorporate a ventilation system with very efficient heat recovery.

The obligation to make a passive house is logical. We are talking about a construction that seeks to reduce energy consumption, with some demanding insulation and a leak so high that hardly allows any natural air infiltration 10 times. It is at this moment when we must ensure through a mechanical system the internal ventilation. If we speak of a passive house this ventilation must be done through a system of heat recovery that allows air by reducing the energy cost to almost zero. If heat recovery is not very high efficiency, minimizing the heat load of ventilation, this same burden implies a consumption of heating that would make impossible to reach the minimum energy that requires a passive house.

1 Ventilation system used

In the project 'The House efficiently Mz', installed a complete set of ventilation with heat recovery Zehnder Comfosystems.

Full ventilation system includes all the 'ComfoFresh' air distribution system, from the external socket until the mouths & interior design grates. Also includes systems 'ComfoWell' air silencers, and all through the heat recovery unit model ComfoAir 200, certified by the PassivHaus Institute and with 94% efficiency. The system allows to ensure both strict balance of flows and outflows in each individual mouth.

It's a complete system that all references and accessories are standards and standardized for Zehnder, so that all the elements of the system are compatible among them, ensuring a tightness and efficiency of the system hard conseguible with panel or sheet metal duct systems. This system also makes it possible that entire ventilation installation can be carried out in 2 or 3 days, something very important precisely in this project due to the short lead time.

Figure 1. Distribution scheme in Star of ventilation in the two floors of rehabilitated housing and location of heat recovery.

Below you can see several photographs taken during the installation phase of the ventilation along with some pictures of the after housing.

Figure 2. Reproduction of heat recovery Zehnder CA200 specific for installation in false ceiling, used in the efficient house Mz.

Figure 3. Photograph of heat recovery Zehnder CA200 installed on the ceiling of the interior of the House.

Figure 4. Photograph taken during the installation of the distribution system of ventilation, in which tubes are passed before closing the walls through which passed the entire installation. It is observed as the tube reaches the terminal (discharge side) element that is enclosed with a white plastic lid during installation.

Figure 5. Photograph of the interior of the House once where only a grid of white air drive can be seen in the upper right of the image.

Figure 6. Photograph of the interior of the House facade. It is a ventilated wooden facade, behind which external drive and removing the system of ventilation outlets are located.

2. Principle of ventilation system

Fan unit contains within it a heat exchanger where the exchange between indoor air filled with energy that we extract housing extraction mouths located in humid areas (mainly kitchens and bathrooms) and the fresh outside air to be introduced into the housing through the ducts of drive which comprises the air up to the mouths of drive in dry areas occurs (salon(, bedrooms...).

Figure 7. The upper images show a high efficiency heat recovery, with the flow counter-current inside heat exchanger.

There are plenty of ventilation heat recovery, but housing the most used are the cross flow (of relative efficiency) and flow (high efficiency) countercurrent.

2.1. The air cross flow heat exchanger

Flow crossed, because of the geometry of the heat exchanger, heat recovery get efficiencies that rarely exceed 55-60%.

Figure 8. Example of operation of an air cross flow heat recovery. Note that without energy consumption it pushes air to the interior of the House at 13 ° C, recovering 58% of sensible heat.

2.2 Air countercurrent flow heat exchanger

Heat recovery of flow upstream, thanks to the path of the air flow and to the design of the blades and their micro-channels, get efficiencies can exceed 90-95%.

Figure 9. Example of performance of a heat for air counter-current flow recovery. Note that without energy consumption it pushes air to the interior of the House at 20 ° C, recovering 94% of sensible heat.

It is important to note the difference of efficiencies in both cases. Cross flow heat recovery sends air to the interior of the House at 13 ° C. Countercurrent flow heat recovery sends air to the interior of the House at 20 ° C without extra energy consumption:

Figure 10. Comparative table of operating temperature of a system of comfort ventilation with heat recovery efficiency of 94% compared to a heat recovery efficiency of 58%.

Despite the apparent low difference of efficiency between 58% and 94%, the reality is that air that drives high efficiency (94%) at 20 ° C single recovery must be elevated temperature in 1 K. The air of efficiency 58% recovery must raise its temperature in 8 K. I.e., the counter-current flow recuperator is 8 times more efficient than the cross-flow. In this way we can define relative Factor of energy efficiency as the ratio of the thermal breaks to lift in the fresh air:

Obviously this efficiency Factor grows asymptotically as the efficiency of the recuperator is approaching 100%, and this growth is responsible for major differences of real efficiency that offer different types of recuperators. If we take as a reference a standard efficiency 55% recovery and compare different recovery we will obtain the following graph:

Figure 11. Graph Factor (f) energy efficiency of different recovery efficiencies between 40% and 98% compared to a standard recovery efficiency 55% (f = 1).

3 Benefits in terms of energy saving

As we mentioned previously, in an insulated and airtight House such as a passive house, it is imperative to ensure a constant ventilation. On the contrary, to reach energy demands as small as it requires a passive house, is can not assume energy loss involved in having to heat the air of renewal.

Ventilation heat loss, is the heat loss more important that nowadays has a standard dwelling built according to the demands of the current CTE, since this requires important and continuously ventilate homes, assuming a very important thermal load. Efficient in-house Mz, thanks to this kind of high-efficiency ventilation, only 36% of the demand for heating is due to ventilation needs.

In the case of this particular project, the total heat load of dwelling reduced 2.131 to 1.332 w, 38%, with 94% heat recovery system, thus managed to reduce the demand for heating of 27 w/m² to 17 w/m².

Figure 12. This chart compares the thermal demand of 'Efficient house Mz' heating, using the system of heat recovery from 94% efficiency, with a system of ventilation without heat recovery.

In short, the important insulation you need a passive house necessary double flow ventilation. This concept of tight and efficient housing is which requires to use a very high efficiency recovery to get these almost null consumption Without very high efficiency heat recovery passive housing is impossible.