Is this the end of passive solar design?
I learned something about the Kingspan Lighthouse (pictured) this weekend, something that I’d completely missed when I visited it at Offsite 07 in June, where it got star billing as the first Code for Sustainable Homes Level 6 house to be completed. The Lighthouse reverses the conventional wisdom on orientation. There is only one tiny window, indicated by my arrow, facing south. The bulk of the glazing faces east, west and north. In contrast, the south face is almost covered in photovoltaics and thermal solar panels.Why? It seems the logic is thus. The space heating requirement has been all but insulated out of the house and the free heat arriving from the sunny south just isn’t needed in the winter heating season. And in the summer, south-facing glazing just leads to a mammouth overheating problem. It is, I think, the first house in the UK that identifies summer overheating as a bigger issue than winter warming.
Now whether this novel approach proves popular with the punters remains to be seen. But Potton Homes, recently taken over by Kingspan, feel very confident that the Lighthouse design approach is going to be a winner. They are busy incorporating Lighthouse into their brochure offerings and plan a launch event at the upcoming Grand Designs show, taking place at the NEC, October 5-7.
Coincidentally, this all chimes in with a talk given by Simos Yannas of the Architectural Association last week at the Nottingham Zero Carbon Symposium. Yannas has spent much of his working life studying passive solar design and admitted that he has always been attracted to the concept. Despite this, he has recently and reluctantly come to the conclusion that massive insulation trumps passive solar everytime. If you engineer the house down to Passivhaus levels of heat loss, solar gain just ends up being a problem. It’s unpredictable and uncontrollable and there are very few days in a year when actually makes a useful contribution to the heating load.
posted by Mark Brinkley @ 11:43 AM
5 Comments:
This really turns things round. Literally and figuratively. Interesting line of thought though.
Derrick
Passive solar gain and PassivHaus - the confusion around the term 'passive' rears its head again !
The term 'passive house' applied to a CONCEPT at the time of the 70's oil crisis. It tended to be used to describe homes utilising solar gain through very large south-facing windows. The issues of over-heating in summer and heat-loss through the windows in cold spells had to be addressed in various ways (shutters, thermal mass etc).
By contrast, today's 'PassivHaus' (also 'Passivhaus') is a TECHNICAL STANDARD of energy-efficiency in any building.
This system, so successful in mainland Europe these days, takes account of all aspects of energy-efficiency in the technical calculations (now referred to as the 'PHPP' software) from the beginning. It has an enviable track record of reducing energy use to the level where an 'active' central heating system is no longer needed.
Through its precise calculation tools, the PassivHaus system can establish the most cost-effective level of insulation etc needed for each particular site, orientation and style in the UK. In projects with ideal orientation to the south, or mild climates, this level is obviously different to projects where the best views are to the north, or the area is colder etc, and thicker insulation is used to compensate.
The result: buildings where substantial insulation is the first priority (just as you say it is in the view of the speaker at Nottingham); where the window area and orientation are assessed for the best possible 'passive' solar gain without over-heating or excessive heat loss; and where a host of other details (which can include thermal mass) all make a positive contribution.
In PassivHaus buildings, therefore, over-heating is NOT a problem.
The very unfortunate confusion arises because the PassivHaus (Passivhaus) STANDARD is translated by some as 'passive house' into English.
'Passive house', of course, denotes the 1970's concept, NOT the present-day technical standard!
But does anyone actually know how much energy the lighthouse uses - in reality?! When REAL data is available I would take suggestions such as the demise of passive solar more seriously.
This seems a fair description of the process described:
1. Remove 90% of a home's thermal mass by changing away from masonry and concrete (95% of new homes the other side of the English Channel are like this) to timber-frame or SIPs.
2. Discover that the house now overheats due to its lack of thermal mass (cf USA in 1970s).
3. Scratch head.
4. Decide to face the house away from the sun.
5. Electric heat (AKA use of energy-inefficient electrical appliances) now keeps the house warm, replacing the 2000-3000 kWh of free heat which in a competent house design could have come from the winter sun, since passive solar buildings with adequate thermal capacity don't overheat.
It's quite bizarre.
There's absolutely no sense in declaring one approach a "winner" to the exclusion of all others. Particularly at a time when almost all buildings in the UK are built with barely any consideration given to energy efficiency, let alone passive solar principles. The sad fact of the matter is that the "lighthouse", to judge from the image provided, would be, aesthetically, a total non-starter in the view of most homebuyers. It's hasn't "won" anything, yet.
More important is for good designers to have access to as large a toolbox as possible when it comes to low-energy design. There are no blanket solutions: the appropriate solution to a particular situation will depend on the site, the client's aesthetic and programming wishes, the current prices of various materials, the availability of labour and workschedules, and of course the abilities of the designer himself. Until all aspects of a brief have been considered, and worked out, it's simply impossible--and foolish--to say which approach will be the optimal one. Indeed, the appropriate design may incorporate elements of both. Any good designer knows not to prejudice (and compromise) the outcome by being wedded to a particular approach a priori. Perhaps this is why the building trade still needs architects, in addition to engineers.
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