An Irish company has helped create a new technology system for energy efficient, heat-recovery windows for residential and commercial buildings. They prevent heat loss in winter and self-cooling in summer, writes Brian O’Brien


Author: Brian O’Brien, director and partner, Solearth Architecture Ltd, M Arch (Berkeley); B Arch Sci (TCD/DIT); Bau-biologist MRIAI

Taking problems and turning them into opportunities is what designers of all kinds live for. Two particular problems in buildings have long tantalised engineers, with transformative solutions seemingly always out of reach.

Firstly, building regulations call for large volumes of air – nowadays, this is in almost inverse proportion to how well (airtight) the building is constructed. Secondly, windows which we love for their daylight-emitting function lose significantly more heat than the walls in which they are located (by up to a factor of five). So, what if we could take the heat lost through windows and pre-heat the air coming into our building with it?

Supply air or pre-heating windows have been in sketch books for decades and over the last few years, a few have even made it onto market (some will remember Dwell Vent, a UK product that was installed reasonably successfully in a number of Irish projects some years ago). Climawin is an Irish-Danish-German product that goes much further than all of these and is Europe’s first intelligent ‘energy-plus’ window.

Not only does it gain energy by pre-warming ventilation air in temperate climates such as ours, but in warmer climates it also enhances daylighting without the heat gain that mars its enjoyment. It has been developed especially to suit the retrofit (and window replacement) market, in that its functions are self powered – reducing the trades needed to install and commission it.

Climawin is the result of a EC-funded research and development project that set out to transform an existing Danish window product into a more versatile, regulatable ventilation window suitable for all Europes climates. The EU FP7 SME project, an alliance of three SMEs and four of Europe’s top research and testing facilities, will have invested over €1.5 million in developing, proofing and certifying the new model by next year (when all tests and trials will be done).

Development progress and customer demand has has been faster than expected, meaning that the windows may be available on the market prior to the end of the EC project.

Three functions of Climawin


The Climawin system consists of a window with two integrated frames of glass, an intelligent (electronically regulated) valve, room and zone sensors, optional integrated blinds and an inbuilt photovoltaic power system. Air is drawn through the valve at the bottom of the frames through the cavity between the frames, where it is pre-warmed by heat escaping through the glass.

The air flow is modulated in response to room and outside conditions detected by sensors on the window and ceiling (signalling the windows wirelessly) and reacting to pre-set and user-specific programmes.

A reverse flow barrier that prevents condensation and a bypass that allows air in directly from outside during hot months as well as an optional cleanable air filter, completes the system for cool and temperate climates.

Climawin is a combination of a window and a fresh air ventilation system and so can be thought of as a natural heat recovery ventilation system. It works in a different way to mechanical heat recovery ventilation in that the heat recovered originates in heat being lost through conduction, not convection – ducts and fans are avoided and the air is brought in directly from outside (but pre-warmed), so is more comfortable.

Climawin relies on a constant steady air flow (the slower, the more heat is recovered) through it to both provide a building regulation mandated level of fresh air, and in turn to pre-heat that air. Some 2.5 to 4 litres per second (4 Pascals+) is achievable without diminishing the energy gains cited. Many buildings already have a constant low-level extraction system removing air from wet rooms and this can be enough to draw the air in. On buildings that do not have active ventilation of kitchen and bathrooms, a simple off-the-shelf passive stack vent extraction system may have to be fitted.

Of course, not all the windows in a building or home need to be ventilation windows, the number depends on local building regulations, use of the rooms, width and height of your windows (wider windows fit more valves) and, to some extent, wind patterns and air-tightness of the building. Climawin uses a bespoke computer tool to estimate the number of windows needed and to predict the expected energy benefits.


Climawin can be installed without rewiring, so is ideally suited to retrofit of existing buildings. The window valves and blinds are powered by solar photovoltaic cells on the frames while the zone sensors (detecting heat and CO2 in the room), which are installed on the ceiling of the room, communicate to the windows wirelessly. This means that in a project where the client only intends to replace the windows, other trades do not need to be involved and construction is far cleaner and quicker.

The system is also highly effective on new build projects and Climawin sensors and controllers are capable of integrating to more sophisticated building management systems, if required.

The system comes with both automatic and manual user control. The client’s preferences regarding desired indoor temperature and humidity are programmed into the system at installation. A small dashboard panel houses buttons that allow manual control of blind position and to shut off automation for periods when maintenance is being carried out if the user wishes to open the windows. An IT interface usable on PC or smartphone is also available.

In addition to its pre-heating function, Climawin’s warm-climate function, termed ‘self-cooling’ or ‘daylight without heat’, gives it another important dimension. Deployment of its integrated blinds allows daylight be reflected inside the building but without bringing unwanted solar gains with it. An outward-facing vent at the window head directs warm air out rather than in, so preventing the windows heating up.

Building users in warmer climates who are generally faced with the false choice of either opting for daylighting but needing electricity to remove the heat – or deploying shutters to keep light (and heat) out, but then needing electricity to light the space – will have another option with Climawin. Significant energy normally spent on artificial light in these circumstances can thus be saved.


Climawin appearance (with blinds)

The reference equated to a typical small family house in Ireland with fabric U values and performance criterion similar to 2011 building regulations (ie DEAP B2 to B3). Irish climate data (among others) was taken and assumptions that the occupants desired an internal temperature of 20 degrees Celcius were made.

The Fraunhofer and Aalborg university studies and trials showed that simply fitting Climawin to this better than average Irish house would reduce its annual energy demand by 19.9%. Other versions of the tests and models indicated it could be as much as 24%. These tests, of course, also take into account energy required to cool the buildings in warm months.

Perhaps even more importantly, from a comfort point of view, tests also showed that even on an overcast day or where walls face other than south, Climawin can recover 57% of the heat needed to make outside air comfortable (20 degrees Celcius) on its way in. This rises on a south-facing condition to meet 100% of the air heating needed and can even become a net energy gain in sunny conditions – where Climawin’s bypass and cooling functions could be utilised.

In terms of air temperature increase, on an overcast winter day, the tests showed that incoming air could be increased in temperature by 11.5 degrees Celcius and, on a sunny day (even in winter), by 20 degrees Celcius plus.

With regard to U value, the windows themselves vary from near passive standard (0.085 to 1.1 W/m2K) to – perhaps counter intuitively – a positive U value (i.e. heat gain not loss).

Climawin is a technology that can be integrated in any window section or profile. The set consist of proprietary valves, inserts, electronics and sensors that can be integrated into any window system. Licenced production partnerships with manufacturers in different regions is one route to market being considered by the developers but, in the immediate term, the product will be made in Denmark and Germany in both wood composite and aluminium.


Brian O’Brian is a partner at Solearth Ecological Architecture,  a professional architecture practice in Dublin that has specialised in sustainable and ecological design for the last 12 years and a director of Climawin Atlantic. Climawin Atlantic is the Irish partner for Climawin. He is an honours graduate of the Dublin School of Architecture and the University of California at Berkeley, where he completed a Master’s in Architecture specialising in sustainability/energy efficiency and ecological design in 1998.


O’Brien has worked with renowned pioneers in their fields Sim Van der Ryn and Pliny Fisk in the US and Edward Cullinan Architects in London. He has been the architect for award-winning green projects like the Daintree Building, the Emerald Project and the Village in Tipperary. O’Brien introduced the Living Building Challenge to Ireland in 2010 and is chair of the Living Building Institute of Ireland. O'RiordanElecclimate change,Denmark,Germany,heat
  Author: Brian O'Brien, director and partner, Solearth Architecture Ltd, M Arch (Berkeley); B Arch Sci (TCD/DIT); Bau-biologist MRIAI Taking problems and turning them into opportunities is what designers of all kinds live for. Two particular problems in buildings have long tantalised engineers, with transformative solutions seemingly always out of reach. Firstly, building...