Passive houses, you can heat them with a hair dryer

[jebatty]

peakbagger, I too accept the concept of the passive haus and at the same time realize that most of the media-hyped passive haus' are high end, out of financial reach of most people. But we all know it is not hard or particularly expensive to build a highly energy efficient home, even if it cannot be heated by a hair dryer. Besides, one passive haus in one location is not the same as a passive haus' in another location: local climate is important.

The extra cost to build not being worth the cost, though, is not an easy conclusion. What we have now for homes, and have had in the lifetimes of most of us, is the benefit of "cheap" energy which allows us to waste energy rather than conserve it; plus, we have advances in technology that allow in new construction approaching and and even achieving the passive haus. "Cheap" energy though has a very large cost in today's world which we are not paying; instead we are taking out a loan from nature that we will not be able to pay back. If we paid the true and real cost of energy, all of us would do much, much more to conserve energy, and then the passive haus would be within reach.

I also think we have got to let go of the concept of payback. It is artificial and meaningless in the natural world. It's only meaning is in the superstructure that humans have built on the natural world foundation of balance and sustainability to advance the human concept of profit and wealth. That foundation cannot support anything for long that does not take great care to maintain the balance and sustainability of its foundation. The facts now clearly show that the balance and sustainability of the natural world that has been around for a very, very long time is in major jeopardy.

 

[woodgeek]

I totally agree Jim. Some would point out however that the cost of energy required to make passiv haus worthwhile is significantly more than the current price of grid-tie solar w/o rebates (at least with most US lower 48 climates and solar resources). So it is always cheaper (and uses less construction materials) to just build a lossier house with a bigger PV array.

I guess, as someone who was a kid in the 70s energy crisis who gave it a lot of thought back then, I am excited that we can now build 'net zero' houses for not much more than regular code houses. And unlike the experimental houses of the 70s and 80s, they just work and are comfortable. And once a house is net zero, who cares if it meets passiv haus specs or not. IMO, the whole idea of passiv haus is becoming outdated itself, in favor of building the cheapest possible net-zero house that is both durable and uses a minimum of embodied energy.

 

[woodgeek]

Just to put in some numbers....my 2300 sq ft 1960 split level house is now patched up to the point of needing about 7500-8000 kWh of electricity for winter heat. It is coming in at around 5 BTU/sqft.hdd, which is about the level expected for current best building codes in the US.

Passive house is basically 1 BTU/sqft.hdd, about 5x better than my old house or a new code house. So, a 2300 sq ft passive house in my climate would only need 1600 kWh with a crappy ASHP; with a nice minisplit, that would only be maybe 1400 kWh for a season's heat. As you know, I could make that much solar juice with a 1 kW PV array here in PA, at a incremental cost of something like $4k. IF a structure that used twice as much as a passive haus, 2 BTU/sqft.hdd, cost $10-20k less to build (mostly by saving money on the windows), why wouldn't I go for that and just spend another $4k on the PV array?

 

[jebatty]

I think I have resolved in my head that it is a wise use of cheap energy if it is used to achieve long term, substantial conservation of future energy use, particularly if the use eliminates or greatly reduces the need for future consumption of fossil fuels. I think solar electric, made from cheap energy, fits that criteria, as well as many other energy-saving construction techniques, e.g., passive haus type construction.

Some numbers for my house. 1500 sq ft main level with full basement walkout, mostly finished into living space, 3000 sq ft total. Energy usage 2012-13: 4 cords of aspen for wood stove (primary space heating, electric backup); 6450 kwh for general service electric; 4300 kwh for electric heat to keep the walkout level livable during the winter and backup electric heat; and 1500 kwh for dhw; total 12,250 kwh. We have no air conditioning.

Converting 4 cords of aspen to btu = 2300 lbs/cord x 4 x 6050 btu/lb usable = 55,660,000. Converting kwh to btu = 12,250 x 3400 = 41,650,000. Total btu energy = 97,300,000. Hdd = 9500 (base 65). Btu/sq ft/hdd = 3.41 total energy usage.

Energy usage just for heat = 4300 x 3400 = 14,620,000 btu + 55,660,000 = 70,280,000 btu, which is 2.47 btu/sq ft/hdd.

Our house was built in 1956, we have replaced all windows and added considerable insulation. We are substantially better than the 5 btu/sq ft/hdd best building code standard. Our new 6.5 kw solar system is estimated to provide 8,580 kwh/year = 29,172,000 btu equivalent. Adjusted total energy usage as reduced by 0 carbon solar = 97,300,000 - 29,172,000 = 68,128,000 btu, which is 2.39 btu/sq ft/hdd.

I regard wood heat as 0 net carbon as well, so our estimated net carbon footprint is 68,128,000 - 55,660,000 = 12,468,000 btu = 0.44 btu/sq ft/hdd.

 

[woodgeek]

Cool. At a home heating index (HHI) of 2.47 BTU/sqft.hdd you would be closing in on net zero in a milder climate like mine (which I claimed above was doable at HHI=2).

Of course, you appear to have sized your new array to cover your plug loads and dhw. Since the electric heating load could be offset by distributing some heat from the boiler (future plan?) with another cord of wood (to ~5 total), such a route would get you to a net-zero electricity and zero-fossil carbon point. Nice.

A purely hypothetical wood free alternative based on minisplits at COP=3 (likely too optimistic in your climate) would be 70 MM BTU (heat) / 3414 (BTU/kWh) /3 = 7000 kWh (elec), which could be met easily by a 6 kW twin of your new PV array. If you didn't already have the sunk cost of the boiler and storage, it would be interesting to compare the cost of an additional array + minis, (prob with a stand alone stove to help during Alberta clippers) to a wood boiler approach.

So a hypothetical net-zeroing exercise with your nicely retrofit 1950s house using just PV is a bit of a stretch, but not totally crazy. IMO, the key enabling tech is the combination of the minisplit and grid tie PV. With a COP=3, a given collector area of solar array can deliver 15%*3 = 45% of its incident energy as space heat BTUs, which sounds lousy until you realize that you can bank summer energy in the grid for use in the winter, not possible with solar thermal.

 

[Seasoned Oak]

Well insulated home get heat from the residents as well. I know when we have a small gathering here the room temps keep going up even in winter. I purposely cool down the house a day or 2 before. And this house is POORLY insulated.

 

[jebatty]

An added plus for our house is that it faces SW, looks out over a lake, and the SW wall is mostly windows (R-8 center of glass). We get lots of passive solar heat gain in the winter with both direct sun and reflected sun off the snow cover on the lake. With 4' eaves the window are well shaded from summer sun. On sunny winter days we have little need for additional heat from the wood stove.

And you're right. Another cord of aspen would off-set our remaining carbon footprint. Ahh, the need for a simple and small wood to electric system.

 

[peakbagger]

A few comment on various posts

HVAC folks usually figure a person is roughly a 100 watt light bulb equivalent heat. Generally with gatherings, there is increased cooking and possibly refrigerator loads so there are some indirect sources.

I am not sure for humans but a piece of trivia is that a dairy cow puts out enough manure each day to generate 100 watts of power, A pig is 20 to 40 watts and a chicken is about 5.

In my opinion a major benefit to any house not just a passive house is independent inspection to make sure that the design is implemented in the field. Blower door tests are a good tool for infiltration but they do not do anything for poor or missing insulation unless foam is sprayed in which by default has better sealing. My modular house was built by a high end firm with a good reputation 20 years ago. When I opened up a wall for a retrofit I found the same quality issues as I see with standard construction, many small gaps not filled and insulation cut short and poor treatment of exterior wall outlets. If I was stick built I would guarantee before a wall was sheetrocked that gaps were filled with spray foam and insulation was done right and I don't see that happening with conventional contractors. I may not get to passive haus but I expect I would substantially improve infiltration and convective loss.

NH has a model energy code that is fairly tight that is required of all new construction unfortunately, the enforcement is left up to local building inspectors and few actually check for compliance. Rather than building one of two passive houses to inspire the locality, I would rather see the overall build quality improved.

I have a lot of passive heating aspects in my house and on a sunny day they make a difference if I am home to open and close the blinds. Unfortunately the $500 plus per window cost for automated blinds isn't a good payback. I use them when I can but I expect most of those features assume a stay at home person and few households have the luxury these days.

 

[Seasoned Oak]

A few comment on various posts
HVAC folks usually figure a person is roughly a 100 watt light bulb equivalent heat. Generally with gatherings, there is increased cooking and possibly refrigerator loads so there are some indirect sources.

I had about 8 people in my finished bsmt.(24x24) last week. Temp was going up about 1 Deg an hour. NO cooking just drinking. No other heat source. Bsmt has ZERO insulation.

 

[pdf27]

It should be remembered that 1 kWh of electricity in midsummer at midday isn't of the same value as 1 kWh of electricity at 6 pm in December - different generating plant will be used to make it, with associated different emissions. If your main local load is air conditioning, then going the Pretty Good House/large net zero PV array is optimal. If the main local electrical load is heating, you're going to need to have a much larger PV array to offset your emissions, at which point a Passivhaus approach is more suitable.

 

[woodgeek]

so you don't believe PV on a grid battery is zero emissions? Depending on the seasonal mix, couldn't it be negative carbon? Around here the nuclear fraction is higher in the winter, and lower in the summer, so summer carbon intensity is higher for conventional power.

 

[wazzu]

So just how much does one of these passive houses cost? I am guessing that for most of America it is way out of reach. Unless you can build these houses for a maximum of 200-250K it just won't work out for regular folks. The other thing is finding someone who actually knows how to build one where you live. It sure does cost a lot of money to be "green" or "sustainable".

 

[woodgeek]

There are a lot of estimates out there from $10-100/sq ft extra cost of construction. The following blog suggests that the cost of ownership is lower than a code house:

http://www.greenbuildingadvisor.com...n-misconceptions-about-passive-house-standard

IOW, if the extra cost is rolled into a mortgage, the additional mortgage payment is less than the energy savings per year.

Personally, I am skeptical of that. If a current 2500 sq ft code house (properly constructed) has a winter heating bill of $1000 on a heat pump or nat gas, than the additional cost of the passive house would need to be <$20k and the final heating bill $0 for the 'additional mortgage costs less than energy savings'.

My WAG would be a cost conscious builder of a passive house would run at least $20-30 sq ft extra, maybe an extra $40-60k on a 3 bedroom house. I think a PGH would be a significantly lower upcharge.....that is the point of the 'pretty good house' concept, minimum cost of ownership.

Of course, in a lot of the country houses are selling for north of $150/sq ft, even my estimate would only be a 15-20% upcharge.

 

[Pettrix]

There is a lot of misconceptions about Passive House designs and costs. Let me start by saying that there are one story homes that use passive solar to heat them and there are homes that are one story which are also passive house certified. Two story homes are more common because lot sizes are small in most areas and building up is feasible, while building wide is not possible.

The older designed 1970's+ era passive solar homes could "overheat" but technology and science has come a long way since the 1970's. Today, the passive house design is done using mathematical calculations, physics, algorithms, and a fairly complex equation that in the end will design a home to be very comfortable in the summer and provide passive solar heating in the winter. All without the overheating problems of the 1970's era passive solar homes.

Another misunderstanding about PH (passive house) is that they don't have proper ventilation and create a haven for germs and moisture. Nothing can be further from the truth. PH use the best air ventilation systems out there. A properly vented home is key to a PH design. The homes are built air tight and tested to achieve less than 0.60 ACH. The HRV/ERV mechanical ventilation systems are used to bring in fresh and filtered air into the home while removing stale air from the home. This creates a very healthy environment for the homes occupants and creates a very energy efficient home. More design information can be found here: http://intuswindows.com/passive-house/

We are fortunate in the USA (for now) that our utility costs are lower than other parts of the world. This will not last. As with anything, the costs of utilities continues to rise and why build an inefficient home that will remain standing for 50-100 years and be an energy hog? That's 100 years of high utility bills and wasted resources. PH is a scientific calculation and design that when utilized can create a home that is highly energy efficient, very comfortable, and has low heating bills during winter. All while utilizing the "free" heat of the winter sun.

 

[rowerwet]

my parents ranch has large glass windows facing south, on sunny days the house gets enough heat from the sun to keep the house warm. Since it was built to weather "the coming ice age" (early 80's) they have saved a ton on oil. they still switched to pellets for heat in 2009.
two story houses have the big advantage of "reusing" the heat generated during the day, as the upstairs bedrooms will be warm long after the sun has set. you don't get that with a ranch.

 

[Pettrix]

my parents ranch has large glass windows facing south, on sunny days the house gets enough heat from the sun to keep the house warm. Since it was built to weather "the coming ice age" (early 80's) they have saved a ton on oil. they still switched to pellets for heat in 2009.
two story houses have the big advantage of "reusing" the heat generated during the day, as the upstairs bedrooms will be warm long after the sun has set. you don't get that with a ranch.

The above "issue" is addressed in a Passive House by utilizing thermal mass within the home. The thermal mass will moderate the homes temperature fluctuations and it will radiate heat during the off peak hours when the sun is set. So a ranch can have the same benefits as a two-story if the ranch utilizes thermal mass within the home. Thermal mass would be an exposed concrete floor or wall. Ceramic tiles will also work but exposed concrete works best. Having the southern sun hit the exposed thermal mass works best. It will put off "free heat" at night when the sun is gone.

 

[woodgeek]

Pettrix, you seem to be conflating Passive Houses, defined as houses with heat losses and air leakage below certain thresholds (and nice HRV ventilation), with passive solar houses. Passive Houses can utilize small amounts of passive solar gain, but do not need to.

 

[byQ]

The above "issue" is addressed in a Passive House by utilizing thermal mass within the home. The thermal mass will moderate the homes temperature fluctuations and it will radiate heat during the off peak hours when the sun is set. So a ranch can have the same benefits as a two-story if the ranch utilizes thermal mass within the home. Thermal mass would be an exposed concrete floor or wall. Ceramic tiles will also work but exposed concrete works best. Having the southern sun hit the exposed thermal mass works best. It will put off "free heat" at night when the sun is gone.

I'm building a small house and I'm following this concept. It costs no more to build a house facing south than in any other direction (unless obstacles are present like trees or street orientation) so every house built should do this - for free energy at minimal cost. And radiant heat is the best kind of heat.

 

[jebatty]

It costs no more to build a house facing south than in any other direction (unless obstacles are present like trees) so every house built should do this - for free energy at minimal cost.

Could not agree more. When we bought our house in 1990 we were not aware of the passive solar potential. It took some modifications, new windows, etc. to realize the potential, and it is fabulous. Plus we have a very bright house due to natural light, also reduced need for electric lighting, and the bright winter days help to compensate for the long, dark winter evenings and nights.

 

[pdf27]

so you don't believe PV on a grid battery is zero emissions? Depending on the seasonal mix, couldn't it be negative carbon? Around here the nuclear fraction is higher in the winter, and lower in the summer, so summer carbon intensity is higher for conventional power.

I don't believe net-zero electricity consumption necessarily equates to net zero emissions - it's all going to depend on what the mix is when you're generating and when you're consuming. Where I am the winter consumption peak is much higher than the summer peak, and I'm far enough north that the PV contribution is close to zero in winter. You'd need to generate getting on for twice your consumption to break even, depending on exactly what time of day you use the power at.

http://www.gridwatch.templar.co.uk/ has got the whole UK data in 5 minute increments if you're interested...

 

[woodgeek]

we agree. I will have to look up the seasonal carbon intensity in the US, region by region, but I know the peak demand in all the US interconnects are in the summer, and they often discount power in the winter (to keep the nukes from throttling back).

My own usage follows a strong winter peak pattern (about 60% of total use Dec-Jan-Feb). I used to buy that discounted (mostly) nuke power (for $0.075/kWh) for my winter heat. When that deal went away, I switched to 100% local wind (at $0.135/kWh, currently). Of course, your comment applies just as well in principle to my case if all the wind blew in the summer, and I 'bought' my wind power in the winter.

So I looked it up: http://en.wikipedia.org/wiki/Wind_power_in_Pennsylvania Looks like a relatively constant resource, with a lull in the summer (when I use little power).

So, I don't fool myself that I am carbon neutral, but I am probably a lot lower carbon intensity than other options I have access to.

 

[Floydian]

The Passivhaus vs Pretty Good House vs Code House+Net Zero discussion is an interesting one.

Here is my take...

Passivhaus-Likely beyond a reasonable ROI for most folks but as close as one can get to a guarantee of low energy usage and the highest level of comfort. The PHPP software is probably the most advanced energy modeling tool available and if money is not an issue then going PH is great. If someone can afford this than achieving NZ would be a small additional cost.
Here is a PH that could certainly be heated by a hair dryer http://www.greenbuildingadvisor.com/blogs/dept/green-building-news/striving-passivhaus-affordability . This house comes in at 3.1kbtu/ft sq/ yr beating the PH standard of 4.75k btu/ft sq/yr by over 30%. Yet to be determined if the 1.4 KW PV system can bring the house to NZ.
Another PH with affordability in mind http://www.greenbuildingadvisor.com/homes/passivhaus-budget . This in a not so demanding climate. Probably "only" a PGH in the northeast.

Pretty Good House-IMO this is the winner. High attention to air tightness with HRV/ERV, minimal thermal bridging with high R values, triple pane windows with orientation specific glazing(high solar heat gain on south windows)+proper overhangs for summer shading and a ventilated rainscreen. Basically everything that you get with PH just dialed down a few notches on performance and cost.
The important thing for me is that a PGH should be able to achieve a high degree of comfort with simple point source heating-a mini split or two with a small wood stove. Increased durability should also be part of the PGH vs the Code House.

Code House+NZ-My biggest problem with this approach is that I feel it is skimping on the enclosure. While achieving NZ is certainly a good thing, the Code house lags behind in the comfort game, requiring more heat distribution throughout the house to achieve the same level of comfort as the PGH. IMO the additional heating system cost should go into a higher performance enclosure to take advantage of increased durability, low energy requirements for the life of the building and simple point source heating/cooling with the most efficient mini splits(+wood stove). Then add the PV to get to NZ when funds allow in the future.

Noah

 

[jebatty]

As our total energy usage/year is 97,300,000 btu, which is 28,618 kwh / 3000 sq ft = 9.5 btu/sqft/year. Just for heating (we have no a/c) is 6.9 btu/sqft/yr. Subtracting out the solar, it comes to 6.7 btu/sq/ft/yr. On a net 0 basis, if wood is subtracted out as being net 0, then our total energy usage/year is1.2 btu/sq/ft/yr of fossil fuel energy.

For a 1956 house, new windows and added insulation, on a total energy basis, I would think anything less than 10/btu/sqft/yr probably qualifies as a Pretty Good House.

 

[Floydian]

As our total energy usage/year is 97,300,000 btu, which is 28,618 kwh / 3000 sq ft = 9.5 btu/sqft/year. Just for heating (we have no a/c) is 6.9 btu/sqft/yr. Subtracting out the solar, it comes to 6.7 btu/sq/ft/yr. On a net 0 basis, if wood is subtracted out as being net 0, then our total energy usage/year is1.2 btu/sq/ft/yr of fossil fuel energy.

Jim,

It looks like you divided your KW by your square footage, so that would be 9.5kw/sqft/year. 97,300,000 btus/3000 sq ft=32.4K btu/sq ft/year. Still not a bad number for an upgraded 1956 house in your HDD area.

Passivehaus standard is 4.75K btu/sq ft/year (heating only).A 3000 sq ft PH would have a annual heat load of 14.2MM btus/year.

To me a PGH would be around 10K btu/sq ft/year. About double PH standard.

Noah

 

[jebatty]

whoops!