Passive Housing

A friend in the US has sent me details of passive housing, reproduced below. Comments, anyone?
Published: December 26, 2008
DARMSTADT, Germany - From the outside, there is nothing unusual about the stylish new gray and orange row houses in the Kranichstein District, with wreaths on the doors and Christmas lights twinkling through a freezing drizzle. But these houses are part of a revolution in building design: There are no drafts, no cold tile floors, no snuggling under blankets until the furnace kicks in. There is, in fact, no furnace.
The Energy Challenge
Articles in this series are examining the ways in which the world is, and is not, moving toward a more energy efficient, environmentally benign future.
In Berthold Kaufmann's home, there is, to be fair, one radiator for emergency backup in the living room - but it is not in use. Even on the coldest nights in central Germany, Mr. Kaufmann's new "passive house" and others of this design get all the heat and hot water they need from the amount of energy that would be needed to run a hair dryer.
"You don't think about temperature - the house just adjusts," said Mr. Kaufmann, watching his 2-year-old daughter, dressed in a T-shirt, tuck into her sausage in the spacious living room, whose glass doors open to a patio. His new home uses about one-twentieth the heating energy of his parents' home of roughly the same size, he said.
Architects in many countries, in attempts to meet new energy efficiency standards like the Leadership in Energy and Environmental Design standard in the United States, are designing homes with better insulation and high-efficiency appliances, as well as tapping into alternative sources of power, like solar panels and wind turbines.
The concept of the passive house, pioneered in this city of 140,000 outside Frankfurt, approaches the challenge from a different angle. Using ultrathick insulation and complex doors and windows, the architect engineers a home encased in an airtight shell, so that barely any heat escapes and barely any cold seeps in. That means a passive house can be warmed not only by the sun, but also by the heat from appliances and even from occupants' bodies.
And in Germany, passive houses cost only about 5 to 7 percent more to build than conventional houses.
Decades ago, attempts at creating sealed solar-heated homes failed, because of stagnant air and mold. But new passive houses use an ingenious central ventilation system. The warm air going out passes side by side with clean, cold air coming in, exchanging heat with 90 percent efficiency.
"The myth before was that to be warm you had to have heating. Our goal is to create a warm house without energy demand," said Wolfgang Hasper, an engineer at the Passivhaus Institut in Darmstadt. "This is not about wearing thick pullovers, turning the thermostat down and putting up with drafts. It's about being comfortable with less energy input, and we do this by recycling heating."
There are now an estimated 15,000 passive houses around the world, the vast majority built in the past few years in German-speaking countries or Scandinavia.
The first passive home was built here in 1991 by Wolfgang Feist, a local physicist, but diffusion of the idea was slowed by language. The courses and literature were mostly in German, and even now the components are mass-produced only in this part of the world.
The industry is thriving in Germany, however - for example, schools in Frankfurt are built with the technique.
Moreover, its popularity is spreading. The European Commission is promoting passive-house building, and the European Parliament has proposed that new buildings meet passive-house standards by 2011.
The United States Army, long a presence in this part of Germany, is considering passive-house barracks.
"Awareness is skyrocketing; it's hard for us to keep up with requests," Mr. Hasper said.
Nabih Tahan, a California architect who worked in Austria for 11 years, is completing one of the first passive houses in the United States for his family in Berkeley. He heads a group of 70 Bay Area architects and engineers working to encourage wider acceptance of the standards. "This is a recipe for energy that makes sense to people," Mr. Tahan said. "Why not reuse this heat you get for free?"
Ironically, however, when California inspectors were examining the Berkeley home to determine whether it met "green" building codes (it did), he could not get credit for the heat exchanger, a device that is still uncommon in the United States. "When you think about passive-house standards, you start looking at buildings in a different way," he said.
Buildings that are certified hermetically sealed may sound suffocating. (To meet the standard, a building must pass a "blow test" showing that it loses minimal air under pressure.) In fact, passive houses have plenty of windows - though far more face south than north - and all can be opened.
Inside, a passive home does have a slightly different gestalt from conventional houses, just as an electric car drives differently from its gas-using cousin. There is a kind of spaceship-like uniformity of air and temperature. The air from outside all goes through HEPA filters before entering the rooms. The cement floor of the basement isn't cold. The walls and the air are basically the same temperature.
Look closer and there are technical differences: When the windows are swung open, you see their layers of glass and gas, as well as the elaborate seals around the edges. A small, grated duct near the ceiling in the living room brings in clean air. In the basement there is no furnace, but instead what looks like a giant Styrofoam cooler, containing the heat exchanger.
Passive houses need no human tinkering, but most architects put in a switch with three settings, which can be turned down for vacations, or up to circulate air for a party (though you can also just open the windows). "We've found it's very important to people that they feel they can influence the system," Mr. Hasper said.
The houses may be too radical for those who treasure an experience like drinking hot chocolate in a cold kitchen. But not for others. "I grew up in a great old house that was always 10 degrees too cold, so I knew I wanted to make something different," said Georg W. Zielke, who built his first passive house here, for his family, in 2003 and now designs no other kinds of buildings.
In Germany the added construction costs of passive houses are modest and, because of their growing popularity and an ever larger array of attractive off-the-shelf components, are shrinking.
But the sophisticated windows and heat-exchange ventilation systems needed to make passive houses work properly are not readily available in the United States. So the construction of passive houses in the United States, at least initially, is likely to entail a higher price differential.
Moreover, the kinds of home construction popular in the United States are more difficult to adapt to the standard: residential buildings tend not to have built-in ventilation systems of any kind, and sliding windows are hard to seal.
Dr. Feist's original passive house - a boxy white building with four apartments - looks like the science project that it was intended to be. But new passive houses come in many shapes and styles. The Passivhaus Institut, which he founded a decade ago, continues to conduct research, teaches architects, and tests homes to make sure they meet standards. It now has affiliates in Britain and the United States.
Still, there are challenges to broader adoption even in Europe.
Because a successful passive house requires the interplay of the building, the sun and the climate, architects need to be careful about site selection. Passive-house heating might not work in a shady valley in Switzerland, or on an urban street with no south-facing wall. Researchers are looking into whether the concept will work in warmer climates - where a heat exchanger could be used in reverse, to keep cool air in and warm air out.
And those who want passive-house mansions may be disappointed. Compact shapes are simpler to seal, while sprawling homes are difficult to insulate and heat.
Most passive houses allow about 500 square feet per person, a comfortable though not expansive living space. Mr. Hasper said people who wanted thousands of square feet per person should look for another design.
"Anyone who feels they need that much space to live," he said, "well, that's a different discussion."
--
Graeme

Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 6 Jan 2009 06:53:11 +0000 someone who may be Graeme

PassivHaus <http://www.passivhaus.org.uk
--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
  Click to see the full signature.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks, yes, I have read the site, which is extremely interesting. I wondered whether anyone had any experience, or comments? My main concern is fresh air within the house, but I like open windows.
--
Graeme

Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If very low thermal mass, house could take ages to heat up after opening a door etc. Air locks may be required !
Lack of building space is a problem over here (planning regs etc). A super-insulated house may take up more space since the walls may be thicker. Not compatible with squeezing tiny boxes into a space. However, if I was building a new house on a good sized plot (self- build etc), I would certainly build it will very high levels of insulation. Currently still doing up my old 9" solid brick walled house. Now there's a comparison ! Simon.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If using forced air that is not a problem.

The biggest problem. You can buy a kit home from Scandinavia for £25,000 and 1/2 acre of land for £5-6,000, but they will not allow you to build it.

No thicker than the two walls we build now.

Flats are highly efficient as there is little heat loss if the outside walls are insulated.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Graeme wrote:

I think its a very intersting idea: my own calculations showed that with low occupancy rates, ad a crap location, you would need either some heating, or a massivley complex heat exchanger to get venitalion without heat loss. Because ventilation is calcualted on a per room size, not per person absis..so the regulations deny the possibility on a large room with low occupancy.
Ventilation turns out to be the key: Modern insulation regulations now have so little heat loss that the ventilation losses start to dominate.
I haven;t thought it through, but a heat exchanger/heat pump that coooled outgoing air and pumped the heat into incoming, would provide maybe a 4:1 factor on the cccupants body heat etc. So there is scope here.
An interesting puzzle for the mathematicians.
Compare the energy used by an incandescent lightbulb, with the energy loss through a window capable of providing the same input of light ;-)
Over a typical 24hour period..in midwinter..
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Tue, 06 Jan 2009 11:26:55 +0000 The Natural Philosopher wrote :

Very much so, which is why pressure testing of new dwellings was made compulsory in E&W in 2006

Been done, and in the latest version of SAP, which underpins Building Regs for new homes. What you're describing is mechanical ventilation with heat recovery (MVHR) which can recover up to 90% of the heat from air being extracted from the dwelling, this heat pre-heating cold air coming in. The system is set up to provide a controlled 0.5ach ventilation rate, air being fed into living areas and extracted from kitchens and bathrooms.
For this to work, you do need to be able to build to a much greater degree of airtightness than has been normal in the UK, otherwise you are running a fan and the air leaks out rather than being extracted via the heat exchanger.
--
Tony Bryer, 'Software to build on' from Greentram
www.superbeam.co.uk www.superbeam.com www.greentram.com
  Click to see the full signature.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You confuse ventilation losses and air leaks.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote this:-

This is not new. The house primarily needs to be "superinsulated", even the front door, and air-tight with a heat reclaim vent system. The dreaded warm air in the UK. No other country dreads them. The clever ones, like commercial systems, modulate the incoming air from minimum 10% to 100%, using re-circ air to maintain heat in the house.
But they do need heat input, but this is negligible and they try to use incidental heat from TV's, fridges, etc to maximum effect - more efficient appliances means this will get less as time goes on. Heat input can be a heater battery in the living room air supply and/or one in the hallway. Both locally controlled.
Passive oriented to the sun with correctly sized windows and shading to the angle of the sun helps a lot, the biggest contributor to heat in such a house, as does insulated shutters. Many people just forget to use the shutters at night which are also a security feature.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I've never understood this, I must admit.
If the air going out is at 20 degrees, and the air coming at 20, I can understand that we might be able to make them both 10 degrees (which I presume would be 50% efficiency) but not that we could do any better than that.
Daniele
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Jan 6, 1:13 pm, snipped-for-privacy@apple-juice.co.uk (D.M. Procida) wrote:

The air inside is at 20, but the air outside is at (eg) 0, not 20.
If you just blow a fan, the air coming in is at 0, and the air going out is at 20.
If you blow a fan through a heat exchanger, the air that eventually gets in to the house has heated up to 18, and the air that finally leaves the ventilator has cooled down to 2 (assuming 90% efficiency).
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sorry - I meant the air coming in is at 0 degrees.

OK, but I don't understand how this is possible (without the help of Maxwell's Demon).
If 1kg of hot air meets 1kg of cold air, I can't imagine a mechanism that would do better than make them both warm.
That is, I can understand how air at 20 degrees could be used to make air at 0 degrees 10 degrees warmer, but not how air at say 4 degrees could be used to make air at 16 degrees 2 degrees warmer.
How do we make the heat jump salmon-like up the gradient?
Daniele
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
D.M. Procida wrote:

cross-flow heat exchanger
NT
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@apple-juice.co.uk (D.M. Procida) wrote:

Surely there is one: a heat pump. But a mere "heat exchanger" would not do any more than you say.
I suspect something has been lost in translation.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

OK - I think I have worked out hwo it could be done.
Two rows of air represented below, the row of air coming in on top and the row of air leaving below it. The numbers represent the remperature of a block of air.
Inside it's 4 degrees outside it's 0.
In <--- 0 0 0 0 Out 4 4 4 4 --->
As the rows move past each other, heat jumps from the hot row to the cold one. As the cold row moves leftwards, it becomes progressively warmer, since more heat has jumped onto it, and the opposite is true of the hot row.
So there's always a gradient from the hot air to the colder air, and the trick is to make sure that as the cold air warms up it's brought towards air that's warmer still, and eventually we end up with a steady state like:
In <--- 3 2 1 0 Out 4 3 2 1 --->
where the air that is allowed to leave has already given up most of its heat to the fresh air coming in.
You don't need Maxwell's demon, or heat with salmon-like properties.
How cunning.
Daniele
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Jan 6, 2:35 pm, snipped-for-privacy@apple-juice.co.uk (D.M. Procida) wrote:

Congratulations! You have just invented (again) the counter current heat exchanger. http://en.wikipedia.org/wiki/Countercurrent_exchange. As you say, it's extremely cunning.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Truly ingenious. And countercurrent exchangers exist in nature too - I have one in my kidneys! How cool is that? It's never cease to be amazed at what nature manages to come up with.
Daniele
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
message wrote:

The most common is the plate heat exchanger inside combis. Plate heat exchangers on some combis are designed not to be so efficient as to drop the return water so much the boiler cannot raise the temperature on the primary flow side enough. This also may affect the delta T of the main heat exchanger and have adverse effects, such as cracking. Long thin high kW plate heat exchangers extract an amazing amount of heat from incoming water and are used on heat banks.
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
D.M. Procida wrote:

Um, yeah, that's a heat-exchanger. Pretty much any heat-exchanger (at least, I don't know why you'd want to build one any other way).
Pete
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Jan 6, 8:57 pm, Pete Verdon

I can't provide a counter example for /heat/ exchangers, but your lungs are a non-counter current gas exchanger. (Birds on the other hand use a more efficient and more complex counter current system.)
Add pictures here
βœ–
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.