05 Jan 2018

Comfort comes first

Comfort is fundamental to the purpose of a building. So why do we find it so hard to ensure our buildings are actually comfortable? Why does our ‘world-class’ architecture still fail to provide comfortable buildings to live, work, learn and play in? Here, Architect and Passivhaus Designer, Elrond Burrell, explores the level of comfort a Passivhaus can offer.

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The Passivhaus standard is known as the world’s foremost building energy-efficiency standard. And it is that, but it is also a comfort standard. The Passivhaus standard delivers radically energy-efficient buildings with excellent occupant comfort.

“After all, what is the point of a building being energy-efficient (or low carbon for that matter) if it compromises the functionality and comfort of the people who use the building?”. By definition, “a Passivhaus is a building, for which thermal comfort can be achieved solely by post-heating or post-cooling of the fresh air mass, which is required to achieve sufficient indoor air quality conditions – without the need for additional recirculation of air”.

The internal temperature and the constant supply of fresh air is provided by ventilation, so the air in a Passivhaus is unlikely to get stale meaning there is no real need to open windows. Bad smells and unwanted moisture will also be extracted.

“They provide exemplary comfort for the occupants by maintaining a healthy, comfortable temperature, by being quiet, by having fresh air and by being draught-free.

“Architects and designers rarely give much attention to specifically eliminating draughts and as a result most buildings are not draught-free. And it only takes a tiny hole, gap or crack to allow a cold draught to whistle through into a building and cause discomfort. People rarely think about how much discomfort even a small draught can cause since we’re all pretty used to the odd cold draught here and there. The reality is though, to be comfortable when we feel a cold draught, we need the room to be a few degrees warmer to counter the discomfort the draught causes. This is another example of designing or constructing a building that doesn’t perform as it should, and then consuming more energy in an attempt to remedy the situation.”

The insulation in a Passivhaus doesn’t just keep the property warm in winter, but it also it keeps the heat out in summer meaning with the use of ventilation, both temperature and humidity can be effectively controlled.

“The Passivhaus standard is a ‘fabric-first’ standard, which means that the building must be insulated to an optimum level for the climate it is located in. Contrary to what is sometimes thought, Passivhaus doesn’t require a set U-value (or R-value) for walls, floors and roofs. The U-value is dependent on what climate the building is in, more insulation is required in extreme climates and less insulation in milder climates.

“Having an optimum level of insulation ensures that the inside spaces stay warm in cool seasons and cool in warm seasons. Importantly, it also means that the inside surfaces of the building fabric (the walls, for example) maintain a comfortable temperature and never feel like cold radiators!

“Being a fabric-first standard means Passivhaus also requires higher performance windows and doors than is typical in most locations. This means that in the UK, for example, triple-glazed windows are required. However, in milder parts of New Zealand, for example, it is possible that high-performance double-glazing is suitable. The result is the same for insulation – comfortable inside temperatures and comfortable surfaces on the inside of the glazing. Many of you will no doubt be familiar with the cold radiant effect of a typical window in winter if you live in a cool climate like I do in the UK – you don’t stay near it for long!

“Keeping the temperature so stable inside does mean the sun needs accounting for; external shading will often be required. Overheating is a risk that mustn’t be forgotten, even in relatively cool climates like the UK. Good Passivhaus design and modelling will ensure the right shading is included to prevent excessive solar gain in summer.

“The Passivhaus standard requires that the building fabric is airtight. This ensures that the heat inside the building doesn’t unintentionally escape out through small gaps and cracks in the construction. Even a tiny gap can compromise the insulation performance, never mind the moisture risks it introduces.

“In most climates, the Passivhaus standard requires mechanical ventilation with heat recovery. This ensures that the warmth inside the building isn’t thrown out the window when fresh air is needed. The ventilation system recovers the heat from stale outgoing air. This heat is used to warm up the fresh air being brought into the building. This way fresh incoming air arrives at 16°C or more, certainly not at the freezing outdoor winter temperatures!

“All this adds up to excellent indoor temperatures that are more easily controlled by the people. Did you ever notice that with ‘natural ventilation’ you have no choice when it comes to comfort? (Except in perfect climates!). If you want fresh air in winter, you get cold when you open the window. And, in summer when you want fresh air, you get hot!

“There are also fewer fluctuations in temperature to contend with. Of course it gets warmer and cooler depending on the sunshine, the heating system and people’s activities. But the fluctuation is comfortably low.

“Similarly there is very low stratification of internal temperatures. This might seem like a minor detail, however, having cold feet (for example, with an unheated concrete or tile floor) and a warm head can be very uncomfortable!

“With Passivhaus, being a comfortable temperature is more than just the number on the thermostat!”.

Passivhaus is a tried and tested approach to designing and constructing low-energy buildings, with a number of examples built over the last 20 years all over the world. In adopting Passivhaus, the sector can be confident in providing buildings that really deliver the cost-effective, long-term energy performance targets clients are asking for.

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