Category Archives: simple

Overheating, Passivhaus Style

One limitation of the PHPP modelling used in the Passivhaus / Passive House certification process is that the only kind of solar thermal heating which is modeled is windows (passive solar… BTW, not to be confused with “passive house”… 2 different things!) and not fancier (active solar) stuff with anything movable insulation and/or small fans and/or externally located solar-air-heaters like:

1 – commercially available solar air-heater SolarSheat or Sunmate (great example here)
2 – low-mass thermally isolated sunspace ala Nick Pine / Norman Saunders / William Shurcliff
3 – “solar siding” ala Nick Pine (essentially a very large solar-air heater, kinda like SolarWall or solar tempering)
4 – DIY downspot heaters ala Scott Davis
5 – a solar “yard furnace” ala Nick Pine (see messages in the SolarHeat yahoo group — always free membership required).
6 – Commercial or DIY solar water heating used for heating (via radiant floor heating or an water-to-air heat exchanger)


So the only thing you can do in PHPP is (in New England) optimize the windows for high SHGC (for the winter-time gains needed, winter being the main energy hog here in 2011) and add overhangs (ideally movable, like a trellis of greenery) or exterior shades (like they used in switzerland and france) to deal with the summer risk of overheating (since it still gets hot and sunny here). Also problematic for overheating are periods of the fall and spring when the sun is still low and leaves are not on the trees but it’s warm outside. Yes, you can open the windows. That will help a bit. Yes, you can install a concrete floor. That will help a bit to even out the swings, though it’s slow to react. But this is what Nick Pine and others like to call “living inside the heat battery”. Temps swing around a lot and you have little control over it besides turning on the heat or AC or moving shutters and insulating shades and such around manually. If you have the time.

A better way is keeping the solar collection on the outside of the thermal envelope of the house and optionally automatically store some for later in a huge highly insulated water tank in the basement (though that gets more complicated and/or expensive) (Getting close to 100% solar heating means being able to get thru quite a few days of no sun, so do your BTU/KWh heat load and storage capacity calculations over at the SolarHeat yahoo group.)

1. You can have pinpoint control over how much of that solar heat you let into your home!
2. Not blinded by all the light pouring thru lots of windows
3. Not as limited in architecture. Want bedrooms to the south but not wanting light blocking shades, etc, etc. Bad view on the South? Just add a huge air collector… no windows needed!
4. Easier to add solar heating existing homes/retrofit

So back to the overheating. To summarize the reasons to think carefully about cooling/preventing overheating in a passivhouse or otherwise superinsulated home:

1. too much passive solar. Big windows on S with high SHGC and no overhangs? Look out!

2. point source cooling on first floor (A BE2012 presentation about the VT Passivhaus by Habitat for Humanity detailed the warm 2nd floor)

3. warm bedrooms in summer. (related to point 2). bedrooms are often on second floor. If you are using air-source mini-split heat pumps to heat/cool your house and there is not an inside head in a bedroom, then guess what… on those summer nights when it doesn’t cool down outside and you need to keep the windows closed, it’s going to get warm in the bedroom… you’ve got 300Watts per person and warmish air coming in thru the fresh-air ventilation system (HRV or ERV) and how is it going to cool off? That’s right… it’s not. People should worry A LOT about this. Winter time is no problem with point source heating downstairs (or down the hall in our case). It’s a tad cooler in the bedroom, but the body heat — 300W per person — helps mitigate. Plus most people like it a “little” cooler for sleeping.

4. Global Warming. Not to get too pessimistic, but some scientific predictions are than NH weather will be like NC in 30 years. LINK. And Southern VT is already like PA in the 1960s. Yikes. It’s worth considering!

That said, the basic idea of worrying more about the heating load than the cooling load in New England and the midwest is a valid one. There are many many more HDD (heating degree days) than CDD (cooling degree days). So optimize for heating first. But have a cooling plan too! It still gets very HOT AND HUMID in Massachusetts and Minnesota!

Also not allowed in PHPP is counting PVs as a solar hot water heater. Instead of buying an expensive and complicated traditional solar hot water heating system that still might only provide a 60-70% overall solar fraction for the year, I explored building one myself for $1k and ultimately decided to just increase the KW of our PV (solar-electric) array to meet the hot water demand (I calculated) a full 100% (net for the year). Marc took the same route described here.

I am of course very open to correction on my assessment of the current state of the PHPP (circa 2010-12) with regard to solar.

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Small houses for families or multiple families WITH KIDS

Get real people.

1. It’s a mess out there. I believe I read recently that there has been a substantial percentage increase in the number of families doubling up — Kids (and families) moving in with parents or grandparents. Duh!

2. All the small home books show houses typically designed for a couple. Or maybe one neatnik toddler. And that’s it? The (sole?) exception being Little House on a Small Planet, 2nd: Simple Homes, Cozy Retreats, and Energy Efficient Possibilities
I liked that book.

OK, so what makes a small house design workable when there are 8+ people (especially with kids) living under that one roof? This post will collect my ongoing thoughts on the topic.

Topics to be expanded upon someday, perhaps. Biased toward northern homes:
- design patterns. loops are important with kids. this is counter the idea of getting rid of wasted hallways spaces but I have thoughts on that. (Namely, do it anyway, a little)
- winter months are brutal indoor times
- huge mudrooms. kitchen and bathroom right off main entrance and key.
- laundry area with ample drying space. as in basement. (upstairs closets are no good unless you have giant bedroom spaces wasting away)
- more small rooms is better than 1 bigger room, I think
- noise between bedrooms. cellulose in the walls? separate bedrooms by bathroom?
- get real. There is probably a TV and laptops, game machines, tablets, etc. in your future. Where will it/they go? I am not personally a fan of having this stuff in bedrooms away from action. So where does the action go?
- basically the issue is balancing public and private space. And open space vs some small rooms.

Gotta run. Watch this space.

See also:
Here are endless articles on the “move in with parents” theme from recent months/years from the NYTimes

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Techno Life Skills

- Power Tools for kids

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Experimenting and sharing the results

“I built a [solar thermal heating] system that I subsequently figured out didn’t make the most sense – why can’t others discuss the shortcomings of their experiments? People must like story-telling more than science.”
– Mark Sevier, PE (our “neighbor”)

From article:
Using Sand to Store Solar Energy
Assessing the controversial claim that solar thermal heat gathered in summer can be stored in sand for winter use

Go Mark! I think also, people are busy, and so after they have built a house, and perhaps it doesn’t work as well as hoped for — in terms of being 100% solar, or zero-energy, or meeting the passivhaus standard (or pick your criteria) — then people are loath to brag/blog about that. But I think it’s certainly useful and will help others learn from our experiments and/or mistakes.

Our house is *pretty much* working as expected I think, but I don’t think quite as well as the PHPP perhaps estimates, and certainly there are lots of things I would advise people to do differently, but that’s ok! (*”Pretty much” as in… our heating bills are VERY VERY low — like maybe 1/5th or a 1/10th of typical house of this size?) We are on target to use approximately 10,000Kwh total for all purposes for the year (june2010 thru may2011) I think. That’s heating, hot water, electricity, lawn mowing, etc). But that’s minus car use, buying stuff, food, etc. We could be living much greener! We’re working on it!

See also:
- Mark’s House — a 14 HERS house in Sudbury, MA
- Other comments from Mark at GBA
- — favorite Solar Homes section
- Solar heated buildings of North America: 120 outstanding examples by William A. Shurcliff
- Edision: The experimenter’s journal

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Monitoring your house (or solar heating system) temps

What fun is having a superinsulated, almost passivhaus, almost(?) net-zero energy house without monitoring temperatures and relative humidity I say! So here is a summary of what I’ve figured out on that topic here in 2011:

I have no doubt that the accuracy and the resolution of the Onset HOBO units are far better, but here is a price comparison between a home-monitoring solution using the “weatherdirect” LaCrosse TX-60U-IT vs Onset HOBO U12 data loggers vs the even more expensive wireless Onset solution of ZW Series “Wireless Data Nodes”. The latter is what I would want (if I went with Hobos) because I am not satisfied with stringing wires all over the house and I don’t just want to “log” temps, I also want to be able to monitor/view them in at least somewhat real-time fashion. So one either needs a way to string wires outside windows and up the side of the house, or run the sensors thru cat-5 wire (telephone/ethernet lines already in the house) or… something.

OK, so here is the rundown:

Both offer:
- some substantial data storage on device if wireless connection (router to device) or internet connection (router to internet) go down
- no computer needs to be on (BUT… hobo needs to be connected somewhat I think since the ZW-RCVR connects via USB to a computer instead of via ethernet direct to a router.)
- no ongoing subscriptions needed for monitoring of temps/RH

Lacrosse Advantage:
- low price
- wireless sensors
- automatic FTP storage of data
- uses normal AAA batteries
- total no-brainer. no software install. No computer needed.
- each sensor has internal temp and rh sensors plus a external connection (and 6 foot waterproof wire and sensor) for measuring another temp
TOTAL PRICE FOR MONITORING 3 indoor locations, 1 outdoor: Approximately $120 total (1 router, 3 sensors) all available from Amazon website


Hobo wireless advantage:
- resolution
- accuracy
- looks like you might get nice graphs with the “HOBOware Pro/HOBOnode Manager” software . though using the FTP option with lacrosse one could pull that off easily enough I think.

TOTAL PRICE FOR MONITORING 3 indoor locations, 1 outdoor:
$200 receiver — HOBO Data Receiver – ZW-RCVR
$239 x 4 — HOBO ZW-003 Temperature/Relative Humidity (RH) Data Node
(or maybe there is a way to do 3 but use one model that has plugs for external sensors and buy 2 $35 6 foot temp sensors. That might bring the total price down slightly??? Call Onset to get the exact number of course.)
~$1156 plus shipping


Summary: I went for the Lacrosse solution since it is ~10x cheaper and so far so good. It might be interesting to compare temp readings between a Lacrosse and Onset unit. I’d love to do a review of the Onset stuff but can’t afford it.

Contact me if you have a better idea! I’d love to hear it! “One-wire” sounded intriguing, but I need plug and play and most look like kits.

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Things I would do differently…

Not to be a downer, as the house is really AMAZING, appears to be performing right in line with estimates we made for heat load and UA and the more detailed PHPP workup. But I can’t help it, there are definitely things I would do a little differently if I were to build a house again.

  1. Our property has a 2-bedroom deed restriction, which we knew going in, and it’s totally fine, but if I were to do it again, I would have been in communication with the town’s building inspector (who is also the zoning enforcement person) early on in deciding — show him our rough plans, what we were going to build — instead of waiting until submitting formal plans. Novice mistake. Luckily things turned out fine.
  2. Don’t be afraid of stock plans. I don’t think one necessarily needs custom home plans to build a superinsulated house. Certainly if you are trying to do passivhaus then you probably do since it will mean really messing with window sizes and placement, but otherwise, I would advise that, if you already have a plan that you really like, just go with it, and ask your builder to build 12″ or so double walls, rather than the 2×6 walls shown in the plans. Spend that money you save on something else!
  3. If I were to do it again, I might not be quite so enamored of strict strategies for reaching/approaching passivhaus in New England. A passivhaus would use 2.5x less energy than our house, approximately (assuming the same TFA) but we’re talking maybe $200 in heating PER YEAR vs $600 PER YEAR. I am not at the moment convinced it is worth the substantial extra effort/expense due to slightly unusual methods needed and products. It’s still tricky to do this stuff and so it means having a team — a builder and architect — who are obsessed I would say. Correct me if I’m wrong! So, do all of the items on the passivhaus checklist that are low-hanging fruit, but pass on items that are stretches. Might as well do 6″ of foam under the slab and edge, for instance. But have nice views on the North, East or West of your house? I would say not to feel bad about putting in nice windows there! That’s me. (I would aim for R40 walls including basement, R80 roof, R5 windows, R20 slab)
  4. On the other hand, I would also ENCOURAGE everyone to VERY EARLY in the project to seek out a Certified Passivhaus Consultant (such as ours in the Boston, Massachusetts area: DEAP GROUP) and have them model your house plans in PHPP. Even if you don’t follow all the Passive House advice, you will be very well informed!
  5. On Solar PV panels: I really like the Enphase microinverter approach we took, but I can’t help but think that the grass-is-greener — IOW, a central inverter. I like that a central inverter approach would have 1) been a little cheaper, and 2) allowed for a “hybrid” grid-tie AND small battery approach, and 3) w/ battery, allowed for some degree of “off-grid” use in case the grid goes down during storms and such. Ah well, I probably would be wishing we had microinverters had we gone with a central inverter approach! I am remembering that I think part of my decision for microinverters had to do with worrying about shade. I should have trusted the solar survey more! We are pretty much totally shade free except at the beginning and end of the day. Which microinverters don’t help much with I don’t believe.
  6. I would probably try to use as little foam as possible. Cellulose all the way! And generally, vapor-open envelope assemblies seem like a Good Idea. I now like this thinking better than the Lstiburek “perfect wall” approach which is closer to what we have. Ah well, grass is greener…
  7. I would use bigger windows in some spots and remove them in others. I guess trying to be a bit more site-aware. Where are neighboring houses… where are views, etc. We did this to some extent, but there are a few misses where I wish there was a double bank of windows. That sort of thing.
  8. I would have looked into unusual choices IN PERSON a bit more. I think it would have helped, for instance, to visit a house with had the Thermotech windows we were considered upgrading too. We were feeling stuck on using double hung (which we love) vs casement (which we do not). But maybe we would have been swayed seeing them in person?
  9. Sorta related to that… I would have in some cases gone with the experience of the subcontractors (on paint brand choice) but in other cases, considered using a different contractor who had specific experience using an uncommon but greener product (OSMO Poly-X floor finish). So there are 2 alternate sides to the same issue of trying too hard to use a product that is maybe greener, but if it also gets installed wrong might mean expensive undoing or redoing. And “wasting” green ($) is not green! :-)
  10. I said not to worry about custom house plans, but on the other hand, I will admit that it is a Very Good Idea to have it worked out ahead of time exactly where the HVAC ductwork will go. I think it is wrong to leave it to the contractors. Better to have it worked out ahead of time.
  11. I might have considered more seriously a “backwards saltbox” approach (we face south, so the long roof would be in front) since it would give more room for panels.
  12. I think everyone who builds a house feels this way, but there are definitely a few spots where I wish a light-switch or outlet was in a different spot. Our electrician did a great job helping us with this, but maybe there is a way to get this even MORE right. Not sure how without living in it first.
  13. OK, that’s a pretty short list actually. More as I think of it…

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VS: home heating — heat pumps vs wood (or solar)

There are many in green circles — superinsulated/zero energy home/passivhaus circles — who think that heating with electricity (ideally with an air-source heat pump) is the ideal way to heat a house with solar electric (PV) panels on the roof (well, or yard). Example link

As someone with a house that is exactly that, let me chime in.

Heat pumps: PROS
1. No hole needed in house for exhaust or air intake
2. No air-quality or safety concerns since no burning of wood or fossil fuels in the house
3. Math is easy if you are trying to be net-zero. If everything is electricity, then there is no complicated math to do converting gallons of propane or cords of wood burned into KWh. (not much of a reason)
4. Now you have AC too. OK, so you saved a few bucks. Window ACs are only $80 though. And you house probably doesn’t need much more than one of those. Really.
5. No baseboards taking up space. But there are other approaches (forced hot air and such) to deal with that.
6. Quiet inside. Wow, very very very quiet. No furnace, furnace fan, or boiler making a racket. (Aside: And no humidifiers in winter… thanks to the tight superinsulated house part…)
7. Electricity tends to be price-stable vs the price of propane and heating oil which seems to whip-around a lot.
8. Usually a bit cheaper to install vs a “central” system esp in a very small house. But add in the price of the HRV or ERV stuff if you have that too.
9. Point source: I list “point source” below as a con too. Some like point source heat since it allows zoning, getting cozy by the “fire” and such. Flip side to everything.
10. Future safe. Electricity can come from many primary sources.

Heat pumps: CONS:
1. Can be a bit loud outside (well not LOUD, but there is a fan running, like for central air-conditioning, all winter) So if you are noise sensitive maybe there is a quieter heating approach? Not sure what qualifies as the quietest. Radiant floor heat?
2. PVs should not be thought of as anything more than an offset in my opinion. Don’t think of that electricity your panels made as yours. Who cares WHO uses it. The point is to reduce CO2/greenhouse gases overall. In other words, if you make electricity, dump it into the grid for your neighbor to use, and burn some wood to keep warm instead, then you are ahead (in my eyes) of someone using that electricity directly to heat their house with a heat pump.
3. In very cold areas, you will need either a HYPERHEAT model that keeps up with sub-0F temps, or some back up (maybe electric space heaters). Most other air-source heat pumps drop their output by a lot when it is VERY cold.
4. Power outages. You will have no heat. Now, that might not matter as much, because your superinsulated house has a certain amount of “passive survivability” built into it with all that insulation, but if we are talking comfort here, then grab a wood stove or a propane heater needing no electricity to run. There are a few!
5. “Non-traditional” Looks: Some might think they are ugly. I don’t mind them. Just different. And controls. Our Mr Slim one has a “remote” vs a traditional thermostat. And the model we got doesn’t control all 4 internal heads. So like a house with zoning, you have to walk around and set each individually.
6. Point source: We have 4 of these inside “heads”. One on a wall on each floor (basement, 1st, 2nd, 3rd (attic)) But there is not heat/coolth pumping into every last room. Doesn’t matter much, but bedrooms are a little cooler — 5F? Coldham/Rocky Hill study seems to say. Ask google.

Wood: PROS
1. Local
2. Carbon neutral
3. Ambience
4. Simple technology (especially if not pellets and not catalytic)
5. No electricity needed (heat when power outages)

Wood Stoves: CONS
1. Lugging stuff
2. Might be difficult to vent properly in a very tight house. Indoor Air Quality risk. Especially with a pellet stove which loses electricity.
3. Even the smallest pellet stoves will overheat some houses that are superinsulated. But big whoop. Run it on thermostat-mode. And open the window if you must!
4. Particulate pollution. You might live pretty near other people or in a town or city that prohibits wood burning.
5. Related… Gotta know what you are doing. (slow-burning, smoldering wood stove fires pollute like crazy and smell up the neighborhood.)

Solar Thermal Heating: MIGHT BEAT WOOD IF…
1. You have sun
2. You have a spot to put the solar thermal panels and a HUGE 1000 gallon tank in your basement
3. You have already done energy efficiency fixes — insulation, CFLs, etc. (see
4. CON: Up front cost is going to be higher than the wood (at least a pellet stove vented out the side of a house) unless you are a DIY person (see

Prius: PROS (W/holistically speaking, maybe this is a better place to start…)
1. Do the calculations in KWh. If you cut the number of gallons of gas you use in half by driving a hybrid or electric car, how much is that in KWh?
2. Energy Independence: coal and nukes (for making electricity) are “local” to the US, vs gasoline comes mostly from other countries. Propane is 90% from US. Natural Gas is ???
3. Use as a backup generator for house

So what would I do?
Well right now we use an air-source heat pump to heat our almost passivhaus ZEH. But I hope to do more solar-thermal heating in the future. 5 days of storage would get you to 97% solar “if cloudy days are like coin flips”. And the no-electricity propane heater is intriguing, especially for a little backup. Check back in a year!

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VS: electricity vs propane — New England style

1 gallon of propane is $2.80 right now on avg in the US says the web.

If you assume 90% efficient boiler or furnace, that is how many KWh of heat delivered to the house?

1 gallon of propane has ~91500 BTU = 26.82 KWh * 90% efficient = 24.13 KWh delivered for $2.80


So how much does that amount of heat cost with an air-source heat pump if you pay $0.15/KWh and assume a COP of 2? (being very conservative… our seasonal avg COP is supposedly 2.7 I think I estimated once using Canadian (cold) figures from service manuals)

24.13 KWh / 2 COP = 12.065 KWh * $0.15/KWh = $1.81

Even if you are heating with straight resistance electricity (no heat pump trickery), the cost is only $3.62 (vs $2.80 for propane). Not bad, $-wise.

1. The propane would be much greener since electricity from power plants is very dirty in the northeast. IOW, the carbon/KWh heat delivered is 3 times higher due to inefficient power plants using fossil fuels. Better to use the fossil fuel directly.
2. If you are in a warmer climate, the math for the heat pump is even better, since you COP will be 3+.
3. If you can use zoning (heating one room) with an electric heater, you will probably be ahead (in both $ and green) vs central-heat using propane.
4. Wood heat or solar beat everything.

Next week: electricity vs heating oil

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Picasa Users — use tags and only tags!

I know the people/faces feature in Picasa is seductive, but JUST SAY NO! The data is stored in a specialized Picasa database on your hard drive which doesn’t work perfectly in my experience. (Whereas “tags” are stored *in the images themselves* in a standardized way — IPTC — and cannot be lost/mangled!)

It has been my experience (as well as many others — ask Google) that this Picasa-only method (for labelling faces) is flawed in the following ways:

1. Using one shared photo collection amongst many home computers (say on a NAS) is difficult if you rely on special features of Picasa (or iPhoto I assume). Not impossible, but only for extreme power-users. If you ignore most of the fancy features of Picasa and stick with tags, you should be ok.

2. Many people have experienced problems with picasa losing track of their database (and hence all of their face data). I believe there might be ways to “get it back” — again, ask Google — but you really don’t want to go thru this nightmare!

So.. just stick with hitting “Ctrl-T” and adding tags for the people or other labels you’d like to add. Captions are safe too. Those are stored in the image file too! Or if tags scare you too, add the data to the file name!

Yes, I know you will lose the cool feature where you outline the face allowing you to visually see 100s of your kid’s face in a collage, etc. But I bet you will be able to add that back in in some future year pretty easily — the faces tool in Picasa and other photo apps will only get better and better. And you’ll have already tagged many of your photos so you’ll be half way there.

Wanna test it? Add some tags to a photo, then go look at the image file in Windows Explorer or Mac Finder and view properties. Your tags (and/or caption) will be there! Search works great in Windows too (as well as Picasa). Just click “search file contents” and your tagged images come right up! You can even make the tags visible in the results. It’s an optional column in Windows. And you can of course add tags right in Windows. Picasa just makes it easier.

Cool! Simple! And future safe!

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