Category Archives: passive house

Some day houses for sale will have MPG stickers on them

There is sorta such a thing today.  It’s called HERS.  100 is a “normal” house.  0 is a “net zero energy” house.  And negative means you have even more PVs than you need.  Nice.  Someday websites like realtor.com, redfin.com, etc. will let you search on such things.

The best house I’ve seen is this -33 HERS of Carolyn and Kyle Cave in Hadley, MA.   It’s also nice to know what a house is pre-PV to get an idea of how efficient the house and it’s occupants are.  Oh, and a house in Maynard MA is -8 HERS.

Anyway, good work Caves!  Your house follows the important rule of thumb I now encourage people to use — Build (or pick)  your house with a lot of good roof space for PVs.  Small footprint houses like ours are a little more efficient, but we don’t have nearly as much room for PVs.  Dumb.

(Oh, and our house is nearly 0 HERS.  I am not exactly sure what — I forgot to ask for the pre-PV score and if I recall correctly the PV offset used the wrong KW total.)

(Oh, and read about the limitations of HERS at the link at top…)

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If you are pondering indoor air-quality…

If you are pondering indoor air-quality in your home… I urge you to look into the issue of flame-retardants in furniture — specifically in the foam used in mattresses and couches.

Here is an upsetting recent article on the topic PBDEs and chlorinated Tris (I knew about PBDEs, but hadn’t considered that (DUH!) the replacement would probably be just as bad or worse. And that they don’t even work!)

Some good practical advice here (if you are a millionaire)

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Filed under corporations, erik-green, green, health, HVAC, IAQ -- indoor air quality, passive house, science, superinsulation

New house? Changing exterior door knobs? — use levers

Are you building a new house or fixing one up — passivhaus, zero energy, or otherwise energy efficient to some degree? Some simple advice: Use levers not knobs. At least for the exterior doors since those are the ones that are going to be sealed up tight with gaskets and such. And also since your house might be quite tight, especially in the winter when all the windows are closed… you are pushing/pulling against this “vaccuum”. So no draft, but the door is also a little harder to open and close.

Maybe not noticable for an abled adult, but it is noticable if you have little kids. Yes, you say, but turning the knob/lever is different than pushing/pulling the door open and I am only changing the opener not the gaskets. But I am telling you. FROM EXPERIENCE… they are related!!! My 4 year old cannot easily twist the knob and simultaneously push/pull our exterior doors open. I think if they were levers (like a storm door we have)… it would be much easier.

To me this is both a safety issue and a respect for children issue. And you’ll be happy too (and guests) if you are maybe older or injured and are having trouble with the knobs. General “accessibility” I guess the word is.

I’ve heard levers are better. It’s now obvious to me that this is quite correct and important and not to be ignored. Do it!

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Filed under green, kids -- freedom and responsibility, passive house, superinsulation, zero energy home

Our PECs: site vs source (primary) energy

Another good way to weigh one’s home energy usage is per person. (not arbitrary per sqft or per HDD, etc.). PEC=Primary Energy Consumption. Makes sense if we are trying to be “green”.

That’s what Marc Rosenbaum is proposing here.

If I am understanding the gist of what he is saying it is as follows as applies to us:

1. Here in MA/New England, power plants are about 33% efficient. They waste 2/3 of the energy (mostly fossil fuels) in making a unit of electricity. The exact number Marc uses is 1/2.7, not 1/3. (37% efficient source to site.) So… since we have used approximately 11000KWh/year, that is 29700 KWh/year in source energy that we REALLY used.

(Worry about PVs later… in step 3.)

2. We are 4 people, so look up our “fair share” according to his “people = bedrooms+1″ equation and we should be trying to meet 13,600 KWh/year in source energy. For everything… heating, cooling, hot water, appliances, cooking, lighting.

3. One should be able to offset some percentage of hot water and electricity usage from onsite generation. Marc explains (I believe) that the Passivhaus PHPP allows up to 20% offset for a traditional solar hot water system, so in his mind, why not allow up to 20% of electricity use as well. And indeed… we heat our hot water with an air-source heat pump too, so I am lumping it all together. And actually, since I am dealing with real data, not estimates, I see from my record keeping that in the last year we have exported 5600 KWh to the grid. So that is the equivalent of 2.7 that much in “source energy” that we have offset = 15,120 KWh

So if we reduce our 29,700 by 15,120 => 14,580 KWh/year

4. 14,580 > 13,600 KWh (Marc’s limit for 4 people)

So we didn’t meet Marc’s proposed criteria for PEC for a Passivhaus in New England, even assuming my generous PV offset based on our grid export numbers.

Pretty close though. Why didn’t we meet it? I assume:
- Our house is too big (1741 TFA via PHPP)
- 2 of us work at home and waste energy
- Windows and HRV not efficient enough
- We should use more solar thermal heating (I have plans on this front)

‎”Your house is a leaky bucket and the sun is a hose. To raise the water level, you need fewer leaks or a bigger hose.” — Nick Pine in a discussion of his “box on the lawn” solar collector design in http://tech.groups.yahoo.com/group/SolarHeat/

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Our house vs passivhaus / passive house

BTW, as a followup to my last post. Our house misses the passivhaus PHPP standard for Specific Space Heat Demand.

= 4.75*1000*1741/(3412) = 2423 KWh used per year is what the PH Certificate requires as a max for “Specific Space Heat Demand” (for our 1741/sqft TFA)

Give that we *used* an estimated 2300 KWh (2338) for heating, and given we can estimate our (non hyperheat/h2i) heat pumps at 2.25 COP overall (as a 15% adjustment from the “North Carolina” temp zone rating–I think I looked up once for our unit’s seasonal HSPF… 15% adjustment: as they seem to do in Canada since the COP is temp dependent.)

That would be:

5260 KWh of actual heat *delivered* from the 2338 KWh our minisplits *used*.

So we are 1/2 or 1/3 as good as a passive house I guess. Probably 1/3 since it was a mild winter.

So you can see why people think passivhaus might be extreme. We are talking about $350 (our house) vs $120 (a similar-sized passivhaus) in heating given $0.15/KWh electricity. I still think it makes sense, especially since people are getting practiced at doing it panelized/modular. (See Green Mountain Habitat for Humanity in VT for example.)

COMMENTS:
- roughly 68F max in winter, roughly 78F max in summer
- I should do a per HDD calc

FUDGE FACTORS (+ or -) in my “1/2 or 1/3 as good as a Passivhaus” calc:
- Weather/climate in PHPP is a 30-year avg. This 2011/2012 winter was mild.
- COP of our heat pump is a guess (maybe I guessed way too low?)
- Previously mentioned guess for % (10%) of heat used for hot water heating
- Some inaccuracy of the emonitor device (vs direct submetering)
- Any errors made in the PHPP (our house used a number of non-certified products… windows, HRV so guesses had to be made)
- Related to above… our windows and HRV are also not as efficient as those typically used in a passivhaus.

That said, obviously there are some houses that don’t use Passivhaus” equipment — like this one — that do MUCH better than the PH standard. Occupant behavior matters a lot.

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2011/12: The year in heating

We have an emonitor gizmo that tracks our home energy use by circuit. One circuit is the air-source minisplit heat pump (the heat and cool in the house).

For the YEAR ending April 2012, the heatpump circuit shows:

3,009 KWh (total for year, heating and cooling and some hot water)
2,598 KWh (Oct-Apr — 7 mostly heating months)

Remember that we also heat our water with an air-to-water heat pump in the conditioned basement, so during the heating months, it is stealing heat from the house. So the 2598 includes some of that. Let’s pretend it is 10% of our total load (no idea) so that would be

2338 KWh (Oct-Apr — mostly heating months. HOME HEATING ONLY)

If we pretend the price we pay for electricity is $0.15/KWh (it’s more complicated than just a simple number like that with this and that charges) but close… then that is:

$350.70 (our estimated heating bill for winter 2011/2012)

Nice.

(Well, and actually… minus some significant fraction of that which is covered by our PVs (electric solar panels). We don’t have net metering, so our electric bill is rarely $0 even in the summer. I just don’t unclude the PVs cause I generally think of them as an offset. Not an important part of the house.)

SMALL IMPROVEMENTS “FOR SOMEDAY”:
- The silly 20KWh/month our minisplit uses whether it is on or not. Nothing to do about that at least in the winter. But I could flip the dip-switch for 5 months of the year.
- Someday I will add a submeter for the minisplits since the emonitor is probably 10% off in some direction. (I believe that’s the spec I’ve seen.)
- More PVs, perhaps this string with a central inverter and small battery for:     – night-time (since no net metering) and
    – power outages (we have a well so it would at LEAST be nice to have running water when the power goes out.)

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Filed under energy, energy-efficiency, erik-green, HVAC, passive house, superinsulation, zero energy home

We’d be net zero but…

Our house would be net zero source energy but…

- well filters: we avg 54 KWh / month
- well pump: 10 Kwh / month
- radon fan: 40 KWh / month
- 2 home offices: 60 KWh / month
- Mitsubishi minisplit: 20 Kwh / month (EVEN WHEN OFF DUE TO A COIL HEATER THINGY!)
- electric lawn mower: (not much, but just sayin’)

What else did I forget?

TOTAL:
So that’s 54+10+40+60+20 = 184 KWh / month
= 2208 / KWh per year

… that we can’t help that some other net-zero types of house don’t have since our house has a well and 2 home offices and a mitsubishi mr slim air-source heat pump with what I would consider a design flaw!

We use approximately 10,000 KWh per year for everything (heat, hot water, lighting, cooking, etc.) And our 6.9 KW PV panels make about 8,400 KWh so if we didn’t have the extra 2200 KWh, we’d be easily net zero.

BUT… then there is driving. Someone who lives in a city in and walks everywhere is blowing us away. We drive maybe 15000 miles per year at 20 MPG (minivan). There goes net-zero.

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Filed under contrarian, energy-efficiency, erik-green, HVAC, passive house, superinsulation, thinking, zero energy home

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)

OVERHEATING RISK

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.)

Advantages:
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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Filed under contrarian, erik-green, passive house, simple, solar, superinsulation, zero energy home

Hot water heaters in New England

Crazy but true… we heated our hot water this month for only ~$8 according to the eMonitor.

EDIT: What do I mean “only”?
Only in that… solar hot water heating systems are $8000 or so it seems. So if we spend $150 on hot water heating per year (lets say), and let’s say we offset this fossil fuel usage with a generous donation of $150 to the New England Wind Fund, then that’s $300 a year for hot water. Assuming a solar hot water system only is 50% solar fraction, then we are saying that we are saving only $150 per year. So the break-even vs another sustainable method of hot-water heating is 53 years. And that assumes it is working in 53 years?

And… the hot-water heat pump cooled and dehumidifed the basement a bit for free. And the washing machine is on the same circuit too! So add that in as well I guess — free laundry. (We hang dry our clothes on racks… but they are almost dry when they come out of the front-loader spin.)

Two explanations for this low usage:
1) the hot water heat pump works (it’s a little loud and I have it on a timer to run only at certain times. made possible by a 105 gallon marathon tank used for storage) We have a Nyle Geyser.

2) we don’t use a lot of hot water (even with 4 adults and 4 kids in the house). We do about a load of dishwasher a day but don’t go too crazy on showers and tubs for kids. And the showers have 0.6GPM showerheads. According to the water meter I use ~3gallons pretty consistently per shower.

I think I commented once that we seem to average 52 gallons a day with 8 people and we were at around 26 gallons with 4 people. I should do some calculations to see if this jives with the $8/month number (assuming $0.15/KWh at Hudson Light and Power here in MA)

So would I buy a Nyle Geyser again? I guess so. The noise used to bug me but the timer system (a 15amp 120v cheapo timer) we’ve got now seems to work fine. And I wonder about the sense of heating more in the winter (which is what ends up happening a bit to make up for the cooling when the Geyser sucks some heat out of the basement air to put it into the water). But I bet if I mustered the brains to do the calculations it wouldn’t seem too bad. Especially when it’s running when it’s not TOO cold outside and our air-source-heat pumps (our house heat) are operating relatively efficiently.

A hot water heat pump seems to be a no-brainer in climates where it is at least warm most of the time. And if you have a place where the noise won’t bug you (maybe other brands aren’t quite as loud?) I will measure the actual dBAs sometime with my radioshack meter to give you an idea.

RETROSPECT:
I’m glad we didn’t install a traditional solar-DHW (domestic hot water) system. I think it was money better spent on the HW heat pump and more PVs. From the studies I’ve seen… traditionally-sized solar hot water systems in New England average only around 50% solar fraction in a year, so what would have been the other 50%? A hot-water heat pump probably!?!

FUTURE IMPROVEMENTS:
Perhaps try home heating with wood. Or with solar thermal (still pondering the best low cost approach for this…) Our heating bill is probably in the ballpark of $500 a year. And offset to basically $0 with the PV (solar electric) panels — we are nearly net-zero even with 8 in the house. But still, that’s $500 in fossil fuels as far as I am concerned. I don’t count the PVs. So that’s $500 which would be better spent heating with wood or the sun. And this would in turn mean the hot water in the house will be indirectly heated with wood or solar.

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Filed under erik-green, passive house, solar, zero energy home

Hazy Hot and Humid

HHH today. 88F and humid and it’s only 11:30am. One funny thing about this house is that the basement is currently the DRYEST part of the house. (The temp/humidity sensors I have scattered about are telling me.) This despite also being where we often hang clothes to dry. (We don’t have/need a clothes dryer.) The basement is dry because of a few reasons I assume: 1) basement is very well sealed and insulated, just like the rest of the house. 2) more people upstairs… breathing, taking showers, cooking mac and cheese, etc. 3) we heat our hot water with a heat pump that sucks humidity out of the air (there is a condensate drain) and that’s in the basement.

Anyway, point is… it’s nice not having a dedicated dehumidifier running 24/7 in the basement.

Another interesting piece of info from the temperature sensors is that the HRV is bringing in that fresh 86F air and turning it into 78F air before it sends it out to the house. So we are getting fresh air even in the summer when the house is closed up for AC on HHH days. But that also means that the AC needs to run a tad more with the HRV running. Not that we used much. It’s projected we will use $8 in AC this July. We used $3 last month. And this is with 8 people living in this small house. So not bad.

I think people in more typical houses could achieve nearly the same thing in their basement if they insulate and seal their basements so that they are part of the “inside part” of their house. The walls and the rim joists are easy enough. One problem is the slab and whether there is insulation or poly underneath it keeping moisture out since that seems to be a tricky problem. I think the idea there is to insulate it and have a drainage mat that leads to an interior perimeter drain. Ask someone more clueful than me!

See also:
- Marc’s basement retrofit (in 2 parts)
- A good overview of these issues is Deep Energy Retrofit Workshop
Foundation Insulation Retrofits – BuldingScience.com

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