Passive House Design

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daylen
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Passive House Design

Post by daylen » Mon Apr 10, 2017 1:34 pm

It has come to my attention that passive homes are rarely talked about around here, so I though I would provide a general introduction to spark discussion.

A passive home is a just what it sounds like. There clearly exist a dimension of passivity that every home can be projected into. At one end, there are the traditional style homes that require lighting, plumbing, active temperature control, active humidity control, and active air ventilation. At the other end, there are homes that do not require any of these active systems and nearly no maintenance (aside for a change of filter every now and then).

I would like to extend the idea of a passive home even further, into the realm of sustainability. A sustainable home makes use of the resources in its immediate environment (photons, rain, geothermal) and minimizes waste. Ideally the sustainable home would be completely decoupled from societies infrastructure. Sustainable houses are naturally passive since passive systems are more sustainable.

So how can you create a sustainable home?
  • Water catchment: store rain fall from roof in large containers for later use. In many parts of the world this can provide you with all your water needs. If the containers are stored high enough, you can use gravity to assist in transporting the water to the location of use. If you want to filter for drinking then gravity will not be enough though. For hot water heating you can create a thin chamber with a glass wall to be heating by the sun, then use gravity to feed directly from the tank for on demand hot water during the day. Otherwise an electrically powered solar hot water heater can be used.
  • Passive solar: capture the suns energy in a large thermal mass with high conductivity (concrete, rock, water, soil). The basic idea is to have windows on the sun facing side of the house, with high thermal mass walls surrounded by an insulated envelope. If done right, this system evens out temperature extremes by absorbing and releasing heat to the surrounding air to reach thermodynamic equilibrium. This works excellent at night when the temperature drops. During the winter the sun is at a lower angle than in the summer, hence you can create an window overhang to keep out the sun in the summer when you don't need it. The parameters of this system (window area to house area ratio, amount of thermal mass, amount of external insulation) all depend on your climate. One idea for increasing thermal mass in an already built traditional home is to put large black barrels full of water near the windows. A word of warning: you want to avoid insulated on the inside of the thermal mass, this disrupts heat exchange. So minimize carpet area and drywall. Also make sure you insulate the thermal mass from the ground below, otherwise the earth acts as one massive heat sink!
  • Solar power: solar panels for all the energy you ever need. Use a battery bank if you need to even out the extremes.
  • Materials: wood, rock, concrete, soil, straw, clay, sand, used tires, cob, cordwood, earth bag, cans, used plastic or glass bottles, garbage (get creative). The idea is to use locally available resources, whatever is available! Tires can be used for structural support; just fill with soil, rock or any other material with high thermal mass. Tires can also be used for roofing, and there is probably somewhere nearby that is begging people to take them for free! Otherwise they have to transport them to a dump half way around the world. Cob is just water, clay, sand, and straw. Cob is very versatile for non-structural needs. I have seen a house that used cob and plastic bottles to make a sealed wall that let light through (free alternative to windows). Straw can be obtained for cheap or even free and makes a great insulator if kept dry.
  • Passive air circulation: use natural flow of air to ventilate. There are several designs for how to do this, but the basic idea is to use air-to-air ventilation by burring several long pipes inclining up to the house. The system uses the constant temperature of the ground to moderate the temperature of incoming air. You can build a pit near the bottom outside the house to capture a cold pocket that condensates before entering the house. A filter can be placed on the house side to be easily exchanged. In general, with a sustainable house design air can be circulated more aggressive since the heat is stored in the walls and floor (thermal mass) instead of the air (like a tradition home). This is great for your health and also for decreasing stagnate, humid air. At this point I should also mention that there is not really a good way to create a passive dehumidifier that I am aware of, but this shouldn't be a problem unless you are in a tropical area.
  • Geothermal: this is not about geothermal energy (though definitely make use of this if available!), but about using the ground temperature. About three feet below the earth the ground a constant 45-55 (7-13 C) degrees all year around. During extremes, this area can be utilized to moderate the temperature. This resource can be used in many ways. For instance, say you live in an area with a high variation in temperature year around and you want to build a storage shed. You could just build a hole in the ground (hobbit style) and the surrounding earth would keep the temperature steady and cool (ideal for storage purposes). The only problem with this is drainage, but if you include a drainage system then problem solved. As mentioned in the "Passive air circulation" section you can also use the ground to moderate the temperature of incoming air. Another application is to use a geothermal heat pump to help control temperatures inside the house. These systems require electricity though and add complexity to the design.
  • Lighting: by limiting the length of the house in the north-south dimension you can negate the need for lighting systems. With passive solar, the sun facing side will allow natural lighting. During the night you are asleep anyway, and this system just helps to reinforce a consistent sleeping pattern. minimize internal walls and locate less used areas towards the non-sun facing side of the house
  • Plumbing: separate grey and black water systems to be used in productive ways. Grey water (shower, sink), can be reused for watering your garden or for a toilet (if you do not want to use a composting toilet). Black water can be drained into a long underground pipe that can diffuse into the surrounding soils, increasing their fertility. The black water system can be completely avoided by using composting toilets. All you need is a bucket, some saw dust (or other dry, organic, absorbent material), and some green organic matter high in nitrogen. Just do your business, cover it with saw dust and the green material. If you are a guy, you can just urinate outside somewhere so that the bucket doesn't become overwhelmingly wet (this triggers the composting process and creates smell). If you do urinate in the bucket just make sure you use enough saw dust to absorb it. You can use biodegradable toilet paper if you want. No, it does not stink, trust me, I have used one. When the bucket is full just throw it into a compost pile and wait a while until you use it as soil. This is completely safe to do; as long as you are not dumping your manure directly on the actual plants that you want to eat.

The biggest downside to passive homes is public acceptance. These designs are unlikely to meet codes and regulations in many areas. This would normally be a problem for finding someone to build the house for you, but since these homes are so simple, the skill level is low enough that you and your friends could do it. Getting someone to build a house is two-thirds of the total cost on average!

So there is a brief primer to the topic. Resources are readily available by searching for key terms. Here is a list: earthship, passive home, passive solar, passive ventilation, thermal mass, straw bale construction, cob, passivhaus

George the original one
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Re: Passive House Design

Post by George the original one » Mon Apr 10, 2017 3:22 pm

daylen wrote:
Mon Apr 10, 2017 1:34 pm
Solar power: solar panels for all the energy you ever need. Use a battery bank if you need to even out the extremes.
Sorry, but solar panels just do not carry you through the winter in a sustainable fashion. There's a 3x-6x difference between summer power production and winter power production, so if you size the system to meet your needs for winter production (the time when you most need the power because the daylight lasts only 7-8 hrs above the 45th parallel), you'll have a massive surplus in the summer (when daylight lasts ~15-16 hrs). See the performance statistics at http://www.arttec.net/SolarPower/9_Stats/index.htm for an example.

Yes, it's possible to sell the summer surplus if you're hooked to the grid. However, the best payoff for electric generation is to offset your needs rather than generate a surplus that is sold off at lower rates. If you're off-grid, then the excess power is wasted.

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daylen
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Re: Passive House Design

Post by daylen » Mon Apr 10, 2017 4:39 pm

@george That doesn't mean that it can't be the only power you need. I didn't say that there wouldn't be waste.

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BRUTE
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Re: Passive House Design

Post by BRUTE » Mon Apr 10, 2017 6:13 pm

a house with low heating needs and LED lights wouldn't use much energy anyway, so buying a bit from the grid wouldn't be too bad. depending on region, alternatives like wind or water could make sense.

passive housing obviously works best in temperate or mediterranean climates, not in extremely cold or hot ones.

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jennypenny
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Re: Passive House Design

Post by jennypenny » Mon Apr 10, 2017 6:29 pm

Selling off the excess from solar isn't always an option. I live in a coal state so it's not promoted and sometimes not available. If I get solar I might try to figure out how to share the excess with neighbors in the summer. I have a good friend next door who faces the wrong way for a good solar set up.

Some towns have laws against water catchment systems and reusing grey water. I have the perfect layout for using the grey water from our laundry in the garden so I'm going to push the township on that one.

I'm not arguing with you daylen, only sharing what's hard to do in my area. OTOH, some of it is easy to do. I have solar lanterns I use at night indoors. I also try not to need heating and cooling. Part of our house has a glass roof which allows for indoor gardening and solar heating in the winter. We move our furniture around to match the seasons (i.e. dining table near the fireplace in the winter and in the sunroom the rest of the year.

I also agree with passive living ... sleep when it's dark, cook/bake on the coldest days to heat the house, hang laundry to dry inside when you need extra humidity, eat mostly raw foods in the summer, etc. 'Don't swim against the tide' so to speak.

ThisDinosaur
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Re: Passive House Design

Post by ThisDinosaur » Mon Apr 10, 2017 7:10 pm

PV panels are usually set a few inches above the roof, not flush with it. Does this shading effect help reduce HVAC use at all in hot climates?

How practical is a green roof made of food crops? How does it complicate things if you also have PV panels up there?

I've considered using either south-wall trellises or a climbing vine to block solar radiation. I'd only do this if it was an edible crop (maybe winged beans or passion fruit?) Any thoughts on how effective this is, or which vines to use? (Prefer high yield crops that form thick enough foliage to block most light.)

Alternatively, you could let the wall heat up in the day and use the stored heat at night to warm plants that are frost-sensitive.

Are there any movements/businesses/resources devoted to doing ordinance-friendly 'passive house' upgrades to existing houses?

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daylen
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Re: Passive House Design

Post by daylen » Mon Apr 10, 2017 8:35 pm

PV panel shading well not make much of a difference since the roof should be highly insulated anyway (this is where there is the greatest potential for heat loss).

I wouldn't use a green roof unless you are really tight on land space. A green roof would require more structural support and it would be a hassle to access unless the house is earth rammed on a side. In general, it is easier to build wide than tall if you have the space.

Not sure on this one, but there are many ways to block light. There are shade tarps that will block a certain percentage of light (these can easily be taken down for seasonal purposes). You could use ground solar panels as well. If you are just worried about heating up the house, external insulation would make this concern largely irrelevant. For glass sections of the south facing wall, an overhang designed to reflect the summer sun (when it is highest) will work.

This technique is used all the time. You don't even need an entire wall, large, half buried rocks work as well.

I would look for a local resources targeted at your particular location. There are many things you can do to an existing traditional home to improve efficiency (such as the water barrels I mentioned in the original post).

ThisDinosaur
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Re: Passive House Design

Post by ThisDinosaur » Tue Apr 11, 2017 6:40 am

Thanks for starting this topic daylen.

Ozzie Zehner, author of Green Illusions, argues that trees shading a roof are better than PV panels connected to an HVAC for temperature control. Since HVAC is the largest part of most household energy budgets, its a major point. That's why I asked about PV panels shading the roof, and vertical gardening on the southern wall. I figure, you might as well do something useful with all that sunlight rather than just block it from your house. I've also seen window overhangs made of PV panels. Web of Goals n' such.

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BRUTE
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Re: Passive House Design

Post by BRUTE » Tue Apr 11, 2017 7:26 am

the trees likely work better because there's airflow between the leaves and the roof of the house. the 2 inches below the hot PV panel might not create enough of a buffer, and there might not be enough airflow, to stop heat from entering the house. brute's seen "double tarp" setups, where another tarp was erected over the one humans sat in, with lots of air in between for the heat to get carried away.

ThisDinosaur
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Re: Passive House Design

Post by ThisDinosaur » Tue Apr 11, 2017 7:32 am

I think its usually more than that, but i dont have numbers handy. How much distance would be needed to get enough airflow? How far separated is a double tarp?

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jennypenny
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Re: Passive House Design

Post by jennypenny » Tue Apr 11, 2017 7:55 am

The tree would have to be far enough away from the house that the growing roots didn't affect the foundation, so there would be plenty of air flow.

ThisDinosaur
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Re: Passive House Design

Post by ThisDinosaur » Tue Apr 11, 2017 8:09 am

I meant, how much distance between PV panel and roof to get significant airflow. I want to have my cake and eat it, too. Passive climate control, passive food production, and enough kWhs to power my pc and appliances.

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jennypenny
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Re: Passive House Design

Post by jennypenny » Tue Apr 11, 2017 8:18 am

Ha, sorry.

I'm looking at the estimate we got for solar and it doesn't say specifically how far they mount the panels from the roof. I'll add it to my list of questions for the guy.

McTrex
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Re: Passive House Design

Post by McTrex » Tue Apr 11, 2017 8:26 am

It's about 7 centimeters for our installation. I was also hoping for a cooler roof because of the shading, but the panels get bloody hot on a sunny summer day, so my guess is, the roof might be even hotter than without panels. Haven't measured this, though.

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Riggerjack
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Re: Passive House Design

Post by Riggerjack » Tue Apr 11, 2017 9:09 am

First, if you are interested in this, go to greenbuilding.com and building science.com

Building science will get you a good idea of the functional issues we discovered when we started sealing houses for more energy efficiency in the 70-90's.

Greenbuilding is greenbuilding pros meet enthusiasts. So, a certain amount of shooting down stupid and or impractical ideas, but plenty of encouragement. Read everything twice.

When you get into greenmods, please understand that climates vary, and what works in California, often doesn't in Maine and Georgia.

In the above examples, a few notes. 2 inches of clearance between a roof and PV panels would be fine for a sloped roof. Convection will move air. PV will cool the roof, but the attic should be insulated, regardless. Please note, there should always be airflow on the dry side of a roof. If you insulate in rafter spaces, leave that gap.

A Green roof is awesome. Do not convert to a green roof. They are heavy, with their own drainage issues. If you experience an earthquake, all that weight as leveraged as possible will maximize damage if you haven't built in appropriate shear strength in your walls.

When people grow plants against houses, they often find expensive repairs in their future. This is probably less of a problem in drier areas. But plants cut airflow, and increase humidity. Perfect for composting your siding. This is less of an issue with stone and brick siding, but check your weepholes.

Most of daylen's post is optimized for so Cal. I don't know if he is from there, but most green Building concepts start there, and most don't translate well.

My house has double framed, 14" thick, R-50 walls, a GSHP I installed myself, and LED lights. I'm not against new, better ideas. But most green Building ideas are long on unintended consequences and short on practical application. Do your research before you go too far with this.

ThisDinosaur
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Re: Passive House Design

Post by ThisDinosaur » Tue Apr 11, 2017 10:06 am

Riggerjack wrote:When people grow plants against houses, they often find expensive repairs in their future.
I've read this before about climbing vines. That's why I consider tall trellises or espalier trees instead, which would also expand the options of what crops to use. Are you aware of any practical way to do what I'm describing? (Specifically, making every conceivable surface of a house multi functional.)

Thank you for dropping all this knowledge. I'll be pestering you for more specifics as I go through those links.
jennypenny wrote:I'll add it to my list of questions for the guy.
Sweet. I don't remember if you've posted anywhere, jp, your installation costs, and how much power you generate?
daylen wrote:If you are just worried about heating up the house, external insulation would make this concern largely irrelevant.
Where I live, I'm more concerned about cooling than heating. Its much easier to keep individuals warm indoors, than keeping them cool indoors.

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daylen
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Re: Passive House Design

Post by daylen » Tue Apr 11, 2017 11:02 am

@riggerjack I live in kansas. There is a group that builds earthships around here without HVAC. I tried to make this post general enough to be useful in most climates. This post is really just meant to expose the readers to possibilities for more sustainable housing. There is no reason why you cannot just use some of the ideas. If nothing else, thermal mass is an underused technique.

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Re: Passive House Design

Post by 7Wannabe5 » Tue Apr 11, 2017 2:10 pm

Interesting topic. On related note, I just finished reading "The Year-Round Solar Greenhouse" by Schiller and Plinke, and highly recommend. Based on this book, which touches on many of the same passive systems you listed, it seems like about the best I could do sensibly is passively take my moderately sunny, cold temperate climate to something approximating a somewhat more humid 3 season Mediterranean climate. The main takeaway from this book is that you have to intelligently fit the design of your greenhouse (or house) to your site and micro-climate. For instance, a cold, very sunny location like Colorado would demand the reverse ratio of glazing to insulated wall as a cool, cloudy site like much of the Pacific North-West with cold, moderately sunny Midwest site like mine falling somewhere in the middle.

The book also offers very sensible, easily understandable pros and cons, likely problems and alternate solutions, for a wide-range of alternatives from underground construction to incorporating aquaculture. For instance, as much as I would love to raise some yellow perch in a tank also serving the function of thermal mass on the northern wall of my greenhouse, this would require a level of precise automation or constant maintenance that doesn't fit well with my personality or building budget, so I crossed it off my plan for the near future.

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BRUTE
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Re: Passive House Design

Post by BRUTE » Tue Apr 11, 2017 6:04 pm

The Year Round Passive Greenhouse For All Humans
Step 1: Humans move to San Diego

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Re: Passive House Design

Post by 7Wannabe5 » Tue Apr 11, 2017 6:17 pm


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jennypenny
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Re: Passive House Design

Post by jennypenny » Tue Apr 11, 2017 7:08 pm

You could always enclose your house in a greenhouse instead of retrofitting all the different systems.

George the original one
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Re: Passive House Design

Post by George the original one » Tue Apr 11, 2017 9:02 pm

Who washes the windows and how often do they get washed? Doesn't the winter wind blow branches down and break windows?

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Ego
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Re: Passive House Design

Post by Ego » Tue Apr 11, 2017 9:39 pm

George the original one wrote:
Tue Apr 11, 2017 9:02 pm
Who washes the windows and how often do they get washed?
At the Y we have two pools. For no good reason, one is housed in a glass enclosure similar to that one. A few weeks ago I ran into the window washer at 6am. He was finishing the last few interior windows with this cool telescoping power widow washing rig. Of course, I asked him about it and then offhandedly asked him when he had started. 4pm the day before. Yikes!

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BRUTE
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Re: Passive House Design

Post by BRUTE » Tue Apr 11, 2017 10:35 pm

Ego wrote:
Tue Apr 11, 2017 9:39 pm
telescoping power widow washing rig
intriguing

Campitor
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Re: Passive House Design

Post by Campitor » Tue Apr 11, 2017 11:08 pm

This guy has a nice off-grid house: Norcal veteran coder customizes off-grid home with sensors.

I think a passive home is completely doable in northern climates if you maximize all inputs, i.e., insulation, heat sinks, solar, thermal, wind, battery, etc. Even if you not completely off-grid, your consumption would be so low that you would be paying very little to the utility companies. Water I think would be the biggest problem depending on your locale.

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