Imagine a perfectly insulated house, as if it was covered with a protective layer that keeps the cold out during the winter and the heat out during the summer. A place where only minimal heating is required, but remains cool on those hot summer nights. This is known as a passive house or Passivhaus – as per the Passivhaus Institute in Germany where the principles were developed.
1) Why “passive“
The concept of the passivhaus is that the heat from the inside of the house (being alive, electric) and the one created outside (sunshine) is sufficient to heat a home. An occupied building that does not lose internal heat does not need heating to stay pleasant to live. The heating only serves to compensate for the minimal heat loss.
2) What is there a problem with heating?
The main issue is the resources used and the pollution caused through burning of fossil fuels. The use of energy required to heat a home releases carbon dioxide and other chemical compounds in to the atmosphere. Some energy sources are renewable and better for the environment, but their use is still minimal and the only way to reduce pollution is to reduce the amount of energy required to heat a home. Pollution of the atmosphere by various releases (coal, oil, gas) is the most important, but is not the only cause: audio, visual and olfactory pollution accompany all traditional heating systems.
Radiators are one of the most widely used pieces of heating equipment, but they are often not to everyone’s tastes. They can be noisy, produce a smell from burning dust and of course take up a large area of the wall and be unsightly. Fortunately there are heating systems which can be integrated into the structure of a building (walls, skirting, underfloor), but they can create other problems associated with development and maintenance which can be costly.
Hot and cold zones within your home are also an issue. If your heating is focused in certain areas you create hot spots, and so logically, cold areas too. The more you heat, the more difference between the hot and cold zones can become.
Finally, the cost which is necessary to pay for heating is inevitably going to increase. A central heating system, also represents a significant investment and general maintenance.
3) How to keep the heat?
Insulation is one of the most important and readily available ways of retaining heat within your home. It is quite clear that to keep the heat in a house (or leave it outside when it’s hot), walls must be insulated. Because the major losses occur during the passage of heat through these walls: firstly the roof (warm air rises), and then the walls and the floor. Doors and windows are considered to be the weakest points in the walls.
In addition to efficient insulation of the walls, special attention must be paid to the removal of the passage of heat by specific points of the structure, referred to as “thermal bridges” because they are passages (bridges) that promote heat loss. In practice, the insulation from the outside should be preferred, because it removes those crossing points.
Doors and windows are less insulated and form areas of greater heat loss, it can be difficult to increase insulation here. The use of quality triple glazing is advisable, even necessary to achieve adequate performance of insulation in a passivhaus.
Ventilation and sealing to avoid thermal losses, a passivhaus must avoid any passage of air. Cold drafts can become very unpleasant and require increased heating costs to alleviate. Before the existence of the controlled ventilation, these passages allowed the renewal of air, essential to the well-being of the inhabitants. They are now eradicated because they endanger the thermal performance necessary for a passivhaus. Just like insulation, tightness of fittings is therefore an essential criteria in a passivhaus.
A passivhaus recovers the outgoing heat, as any modern and comfortable house which is well ventilated. But as the ventilation draws cold air in through the warmth of your home and then our again it is important to quickly heat any incoming air. When insulation is satisfactory, ventilation becomes an important channel of heat loss. So, the idea is simple: to recover heat from the warm air exiting the house to warm the new cooler air coming in. This is known as a ‘counter-current exchange’ system and is used in nature by many animals, where warm blood flowing away to the extremities (limbs) is used to warm the cooler blood flowing back to the body. This allows them to survive in extremely cold conditions. This can be used as a very efficient way of retaining heat within your home without the use of large volumes of energy.
To create this system the passivhaus is most often equipped by a so-called “dual stream” ventilation (inflow and outflow through the ventilation system) with heat exchanger. To have its place in a passivhaus this system must be able to retrieve more than 75% of the heat from the outgoing air to communicate it to the air entering.
It is now possible to make even more savings, to recover the heat of ‘ greywater ‘ (dishwasher, washing machine, shower, wash basins) outbound to preheat the incoming water coming from the network (or air).
4) Are all passivhaus’ weird looking?
No, a passivhaus is not necessarily weird looking. From classic to the more eccentric, architects can design passivhaus just like a traditional one.
Climate and regional habits remain the major influences on the architecture of a passivhaus. However, they have often thick walls, to provide a large area of insulation. You will also often see large windows facing south to take advantage of solar gain and little windows north to avoid losses.
Similarly, it is advisable to design compact houses to reduce the surface of the area to insulate. There again, the climate and economic constraints influence the architecture.
There is often confusion with bioclimatic architecture. A bioclimatic design is neither necessary nor sufficient to build a passivhaus. It is not necessary, because we can build a passivhaus even if the orientation is imposed. The urban environment is incompatible with the bioclimatic design, while it lends itself to liability. It is not sufficient, because a bioclimatic designed house will not necessarily meet the criteria of a passivhaus. In fact, the connection is tenuous: a bioclimatic design can often reduce the cost of construction of a passivhaus. Take advantage of free solar energy and protect themselves from the cold winds to decrease investment in insulation.
5) Is a passivhaus ecological?
Yes, because compared to a house thermal current standards, passivhaus saves a lot of energy. The energy consumption for heating must be four times less than that of a house according to heat codes from 2005 (and ten times less than a building pre-dating this). As we have seen above, this energy saving greatly reduces the impact of housing on the environment.
However, it may not be considered ecological unless the house is built entirely from natural or recycled materials. A passivhaus can be built with many materials, from the more artificial to the more natural.
Studies are formal: the biggest impact of a dwelling is not during its construction, but its energy consumption during its years of occupation.
That said, it is entirely possible to have both: ecological design and construction and performance of a passivhaus. Almost all of the current homes have none of the two qualifications listed above. But if the choice (for reasons of cost or architectural), it’s greener to build a passivhaus in polluting materials.
6) Is a passivhaus expensive?
Yes, if we take into account only the initial investment. The thermal study, the quantity and the quality of insulation and other materials, the use of specific joinery significantly increase the cost of construction of a passivhaus. It is estimated at 15-25% for an individual house, 5-10% in multi-family housing and a little less for offices.
No, if we take into account the cost of operations. Thanks to energy savings that allow the passive construction, the cost of operating a passivhaus will be less than that of a “regulatory” building for decades. The value of the construction will increase well before the end of the occupation of the property. Is this not the characteristic of a good investment?
The compromise between initial investment and economy of operation should always be considered before you embark on such a house. The criteria encrypted to design a passivhaus are from an economic calculation that optimizes investment and not an estimate. If you are interested in passivhaus it’s probably that your horizon is not limited to next year… One of the advantages of a passivhaus is to be ahead of the current thermal regulations. In building (or renewing) according to the criteria of the passive habitat, you know that the resale of your property will be much easier than that of the vast majority of the housing stock. The heritage value of a passivhaus is certainly higher than that of an equivalent regulatory home, it’s value can only increase parallel to the increase in the cost of energy.
7) Is the technique of construction imposed?
No. The technique of construction of a passivhaus is free: from steel construction with straw to the more standard use of concrete and wood. There is no specific recommendation on the construction technique that should be used. There are common features in all passivhaus’: very reinforced insulation, double flow mechanical ventilation , and optionally, in warm regions a Canadian well (also called Provençal well). Furthermore, new thermal stresses are the support of innovations in the building. The use of insulation vacuum, special glasses, new heat recovery devices, phase-change materials and new prefabrication techniques emerge to meet the new needs expressed by the construction of passivhaus’.
A number of UK organisations have been approved to assess and issue the Quality Assured Passivhaus Certificate, and the EnerPHit certificate (for retrofit projects).
• The need for heating must be less than 15 kWh/m²/year. It is the result of economic optimization (no independent heating system). For a house of 100 sqm, this represents therefore a maximum of 1,500 kWh a year.
• The air tightness is difficult for a non-professianal to understand, just know that this air tightness is tested using the ‘Blower Door Test” and it means the absence of leaks and air passages.
• Consumption of primary energy less than 120 kWh/m²/year. Energy saving is sought, it is not reasonable to waste in devices other than heating (air and water), lighting, electrical appliances and any other consumption. According to the source of energy used, the conversion of primary energy in final energy is harmful or not. In all electric, this gives 44 kWh/m²/year at the meter, which is low. Renewable energies are more favoured by this conversion.
Certification through the validation of the design and calculation of consumption, then by (“Blower Door Test”) airtightness testing and monitoring of consumption is required to class a house a ‘passive’.
8) Is ‘positive’ better than ‘passive’??
A positive home is often seen as a panacea ‘sustainable’ habitat, because it produces more energy than it consumes. The concern is that it often produces when it is unnecessary and consumes as much as others when it does not produce. The final gain is not obvious, all for very important investments in equipment and an impact on the environment which is not necessarily positive. Generating energy at full price should not be a substitute for a significant decrease in consumption. A passivhaus, due to its low energy consumption, is the right basis for a positive energy house. It is much easier and cheaper to compensate the low energy consumed by a passivhaus than that consumed by a standard accommodation.