Energy efficient houses

stephendv · October 2009

...started this thread from this one: http://forum.solar-electric.com/showthread.php?p=41708#post41708

Regarding the R values for a planned Passivhaus in Northern Spain:

- Exterior walls: 7.94
- Roof: 7.52
- Triple glazed windows: 1.43
- Double glazed south facing windows: 1.0 with a g-factor of 62% (in our climate more solar transmission with worse R value is better than less transmission with higher R value).
- Basement walls: 5.68

icarus · October 2009

Re: Energy efficient houses

Thanks Stephen,

Just as a casual observation, it sounds like your R-values are pretty low by modern standards. Most north American codes are in the neighbourhood of R-40 in ceilings, R-20 in walls, R-20 in floors.

It as always been my contention that it is way cheaper to add more insulation, (particularly in the ceilings, for a much bigger gain, than it is to add fancy triple glazings in most climates.

BB. · October 2009

Re: Energy efficient houses

Hmmm--something does not make sense... I wonder if there is some difference between US and Spanish "R" Values.

A standard "2x4" wall with standard fiberglass bats is around R11 or so... The current Energy Star Government recommendations are:

[FONT=Fixedsys]
Zone   Add Insulation to Attic      Floor
   Uninsulated Attic   Existing 3-4 Inches of Insulation
(zone)   (attic)        (wall)         (floor)
1        R30 to R49     R25 to R30     R13
2        R30 to R60     R25 to R38     R13 to R19
3        R30 to R60     R25 to R38     R19 to R25
4        R38 to R60     R38            R25 to R30
5 to 8   R49 to R60     R38 to R49     R25 to R30[/FONT]

Note: Zone 1-2 Florida and south Texas; Zone 3 southern US; Zone 7 far north/Alaska.

R25 would probably be hard to do with standard 2"x4" stud wall construction... They are recommending (if siding is removed for other reasons) to install R5-6 insulation sheathing under the weather sheathing.

I will second that adding Double Pane Windows makes a huge improvement over old/leaky single pane wood/aluminum windows (late 1930's construction with zero insulation). Adding ceiling and wall insulation made a nice improvement. I added under floor insulation--but I am not sure how much it helped (however, I would do it again).

Home, in (90-100+F) hot weather, always was equal to or hotter than outside weather (in summer). Now, home lags outside summer temperatures by 10-20 degrees (typically around 15 degrees) with no A/C use.

Now home is kind of a bit cold during our mild summers without using heat (around 65-75F--especially downstairs)

-Bill

stephendv · October 2009

Re: Energy efficient houses

Ah, I must have botched the conversion. I'm working with U-values and did a R=1/U to get to R values, but it seems this converts to the SI units of the R value, but the commonly used form in the US is the imperial....(you really should have kicked those out along with the brits

)

so need to multiply all those values by 5.678263 to get to US R values

(Hope I got it right: http://en.wikipedia.org/wiki/R-value_%28insulation%29)

- Exterior walls: 45.01
- Roof: 42.63
- Triple glazed windows: 8.11
- Double glazed south facing windows: 5.67
- Basement walls: 32.25

I guess a similar sort of climate as zone 4 in the US. Interesting to compare these numbers with the energy star recommendations. My roof is quite average in comparison, but exterior walls (and I guess basement walls too) are spectacular.

I'm using a spreadsheet issued by the passivhaus institute to calculate the effect of various changes to the design. There are quite a few aspects which influence the overall efficiency and it's nice to be able to toy with the variables and see how it affects the final heat demand.

For example, the current levels of insulation in the roof and walls are at a point of diminishing returns - I'd have to add a lot more to them to have a significant impact. But insulating only slightly underneath the foundations would have a bigger impact for less insulation material.

stephendv · October 2009

Re: Energy efficient houses

Regarding the triple glazing, I wasn't really that keen on it, but when I went to price up the windows the triple was only very slightly more expensive, but with quite a difference in R value.

icarus · October 2009

Re: Energy efficient houses

It is interesting to me that the prescribed R-value for the roof is essentially the same as that for the side walls. I can't remember my formulae, but I know it is intuitive that the roof structure will loose more heat on a sq ft basis than a similar area of wall structure, hence the design suggestion to have more in the roof. Our old rule of thumb was double the amount that is in the walls and the floors for the ceiling as a minimum.

My little house I chinced out, since it is so small and so easy to heat. We are R-13 hi-density batts in the wall, R-21 in the ceiling and R 20 in the floor. (Keeping the floor warm is a priorty). As it is, at -30 we seldom use the window quilts, and many evenings we have the windows in the doors open a crack.

Tony

niel · October 2009

Re: Energy efficient houses

stephendv,
although the rest seems fine, i too am confused by the roof being less than the walls as the roof will gain or lose heat more than the walls will. i don't know what type of insulation you have up there or if you'd have room for more, but i'm inclined to say add some more in the roof even though i'm sure you will be comfortable as it is. i also question some of the r factor claims for multipane windows, but triple is good in basic insulating even without inflated claims and it will deaden sound better too. did you do anything special for entrance doors?

icarus · October 2009

Re: Energy efficient houses

I've never seen a triple glazed window get much over R-3.5, even exotic gasses etc.

Tony

westbranch · October 2009

Re: Energy efficient houses

a little reading on 'lites' aka window panes

note the reference to STC well into the page...

http://ths.gardenweb.com/forums/load/windows/msg0711460219892.html

Eric

stephendv · October 2009

Re: Energy efficient houses

Ok, I've played around with the modelling software to see what the effects of adding or removing insulation from the walls and roof would be like. With the R - values above, the heating energy consumption would be 15.3 kWh/m2/year.

If I took half the insulation out of the walls, and put it into the roof, it would be:
R-value roof: 59.14
R-value walls: 25.8
The then heating load would be: 19kWh/m2/year

Trying a smaller tweak, like taking 20% out of the walls and adding it to the roof:
R-roof: 50
R-walls: 36
Heating load: 16kWh/m2/year

and 10% more in the roof than in the walls:
R-roof: 45
R-walls: 42
Heating load: 15.4 kWh/m2/year Which is interesting, because this means I'd use less insulation material in total and get a similar overall result! Thanks guys

Using these last values, the software predicts the following heat losses for each of the structural elements. The rightmost column is heat loss in kWh/year.
The windows are responsible for the greatest heat loss, but the south facing windows are also responsible for the biggest heat gains (which isn't shown in that page).

stephendv · October 2009

Re: Energy efficient houses

...and here's a graph which shows the overall picture. Heat losses, solar (and internal) heat gains and the heating demand which I'd have to provide through central heating or whatnot. The Y-axis is in kWh/m2

icarus · October 2009

Re: Energy efficient houses

Interesting numbers!

What I a not sure of, is how you can reduce the amount of insulation in certain assemblies. Clearly in the ceiling, adjusting the amount of blow in cellulose is pretty easy. Adjusting the R-value in the walls or floors (fibre-glass batts/rigid foam or spray foam or blow in) might be pretty hard. For example, a 2X6 wall, you can put in a R-11 batt, (why would you!) or you can put in a R-19 batt. With little variance I don't know how you could put a R-15 batt in the same wall.

Tony

stephendv · October 2009

Re: Energy efficient houses

In Spain it's fairly easy because we're using masonry contruction for the walls, so the cavity can be whatever we want it to be.
The wall assembly would be (inside to outside):
Plaster -> Ceramic brick (14cm) -> blown cellulose (28cm) -> facing brick (8cm) -> Exterior plaster.

icarus · October 2009

Re: Energy efficient houses

Stephen,

My point however, is that in a 28cm wall cavity, I don't know of a way to fill it with say 14cm very easily.

Tony

stephendv · October 2009

Re: Energy efficient houses

Ah yes, need to get it right from the start!

westbranch · October 2009

Re: Energy efficient houses

Stephen, in your design modeling can you include the gains/ savings from a solar water heater or pre heater? My thought is that a large heat sink in the foundation could hold X BTUs of summer heat for use in the early winter months reducing the energy demand... ?? and as you live in sunny Spain, there should be some decent solar gains in the winter. Here is a interesting article on winter gains ... note the outside temps...http://www.wsetech.com/Solar%20Water%20Heating%20Webinar.pdf

As I see it at this point, the model does not really allow for non conventional energy sources, ( I may have glossed over it) it is designed to minimize the amount of 'conventional energy' consumption, ie electricity. I guess what I am getting at is to use 'natural' heat siphoning to vent excess heat in the summer, by opening a couple of windows, top and bottom, rather than having to use electricity to run a circulating fan.. We were in Cuba a few years ago and visited a hospital, wife is a Nursing Instructor, and the entire building was elevated 3 feet or more above ground for natural heat siphoning, and the interior was quite cool even to a northern dweller...

Where I am having trouble is with the 'modern sealed structure ' concept when off grid it can require excessive amounts of PV and other energy forms to be 'livable'.. and I think there are viable alternatives to be found that eliminate those 'manufactured' energy needs ...

Does this building have a basement?

Open for a good discussion on this one .

cheers,
Eric

stephendv · October 2009

Re: Energy efficient houses

Hi Eric, unfortunately this software doesn't allow modelling heat storage in thermal stores - it's certainly a good idea, but it could also require substantial engineering to get right, like putting down vertical insulation below the foundations and making sure that the soil that is heated is kept dry to reduce heat loss. Something like this: http://www.earthshelters.com/Ch_1.html

The passivhaus concept is all about reducing total energy demand for both heating and cooling, no matter what form that energy is delivered as. The only "free" energy that isn't taken into account in the calculations is passive solar gains. All other energy that's used to heat or cool is counted towards the 15kWh/m2 quota. This includes PV, Wind, wood burning, gas, etc. So even if the house was completely self sufficient for all it's heating through wind and PV for example - it might still not qualify as a passivhaus if it exceeded the 15kWh/m2 demand. These Germans take the "passive" part very literally.

I'm quite in favour of the sealed structure approach firstly because it gives me some choice. If it's cold out and I want to keep as much warmth in as possible, then I can turn on the MVHR and close all the windows and doors. But if it's a nice day, I can always open the windows and let the outside air in.
If the house was never built to a high degree of airtightness, then I wouldn't have these options. It would be draughty summer and winter. With an airtight house, I can effectively turn the leaks on and off

The other big reason is energy efficiency in winter. Once you get down to high levels of insulation, heat loss through ventilation plays a bigger part, so you need some way of reducing this. HRV with heat recovery fit this gap.
But the comment about sucking valuable power from an off-grid installation is a concern and I'll have to add a few extra panels to accomodate this. What hurts most is that the ventilation will be more active in winter, precisely when the PVs aren't producing that much. Still, overall I think the energy saved in heating is worth it (will have to see if this is the case in practice).

We're taking a few approaches to reduce the need for cooling (and hopefully we won't need an AC at all):
- Using cellulose as insulation which has both a high R value and can retain the heat in it's structure, so it can add to the thermal mass of the house
- Using thermally massive material, a local ceramic brick called "termoarcilla" which also insulates and retains heat. The main structure and floors will be from poured concrete also adding to the thermal mass.
- The intake to the HRV will be through 50m of thin walled plastic tubing buried 1m below the soil. This should temper the incoming air in summer - and also heat cold winter air before it arrives at the HRV.
- We're in wine country so will be using vines and trellisis to provide shade around the house during summer. There are no eastern or western windows either.

Yep, the house will have a heated basement, i.e. it will be inside the thermal envelope but we probably won't actively heat it.

The Passivhaus is quite a few years old now and they've had time to refine their modelling software and verify it with real homes (currently 15 000 have been built). but is only now being actively promoted outside Germany. There are proposals for it to become a European wide standard by 2012. It's certainly not perfect, but I think the principals are sound - and it will be interesting to see how the design behaves in a Mediterranean climate.

peterako · October 2009

Re: Energy efficient houses

High Stephendv, i build a similar house in Greece.

It works great i have a few problems in the summer i use shades to control temp.
The window frames are not wind tight as i like even using three rubber seals. and in the winter there are more dark rain days so i still needed to heat a little. but i 80 % of my winter days around 30 degree Celsius no external heating.

p.s. i am using a floating floor plus under floor heating/ cooling as heat storage.

Greetings from Greece

Dave Angelini · October 2009

Re: Energy efficient houses

Western exposure windows can be dealt with or avoided. It is Northwest windows that are really tuff because the sun angle will not support overhangs and a full shade of the window must be used. The angles are critical!

Keep in mind that a small mini-split AC unit such as the Fugitsu or Sanyo can be used in a low speed mode (about 350 watts) all day long during hot spells. It gets ahead of the heat gain of the structure, is pretty cheap for what you get, is a perfect load for solar offgrid once you batteries are charged, and with a tracked array can be run until 7 or 8 pm when you need it the most.

At some point you have to balance the cost of designing and building an exceptional passive home against getting it done in a reasonable time!
I think the method above probably is more "earth friendly" easier to accomplish, and far less expensive in many locations that get above 95F.

I do like your Frexinet........

stephendv · November 2009

Re: Energy efficient houses

Peretako, I know about underfloor heating, but underfloor cooling? Was this an off the shelf system that can do cooling too, or did you design it yourself?

Dave, the cost issue is something I'm keenly aware of but I haven't done any detailed sums to work out at when a passive approach will pay for itself compared to more active heating and cooling. I like to think of this as a very long term investment, 100+ years and I hope that a passive approach should payoff sooner than that

Thanks for the pointer about the AC, seems like a useful size for a well insulated home.

(Have to agree on the Freixenet, it makes the best party drink, especially if you have a tub of it

)

russ · November 2009

Re: Energy efficient houses

With the 'underfloor' cooling you have to stay above the dew point or there is a big problem coming.

A contractor tried to sell me a GSHP including 'natural cooling' - meaning not operating the compressor but only the pumps - but with our 16 deg C ground water temp plus the above mentioned problem I declined.

peterako · November 2009

Re: Energy efficient houses

Sorry for the delay ( i wash in other threads working and forgot this one

)

The cooling is a simple setup.
At ground floor i have 30 seq. M floor exposed to the sun for heating in the winter. Above there is a glass roof and the south wall are based on sliding double glassed doors.
In the summer i am closing a shade above the roof Automatically by temp.
The inner building is based to work as thermal storage. and using a passive roof ventilation to remove heat. if temperature from the floor is above 30 degree Celsius.The underfloor heating pumps start running and as well in the basement there the floor is colder so it takes the heat to the basement and comes cooler back.:D

In the evening /night i keep the sliding doors a little open and the cool air comes in and the warm is raising out using the roof vent. This looks like a second chimney from outside the inner dimensions are 0.7 by 0.7 M.

I am living in Greece and in general the summers are dry so condensing is not a issue.
Heating is by fire place using a special build in heat collector build in Italy.
http://www.jolly-mec.it/index.php/english/Foghet-system/Foghet-Diritto-Acqua.html?phpMyAdmin=5f8677cfd58d71c585b3fadb5eefd3ce

Or by LP gas using a normal heater. all this connected to the underfloor heating.

A yes i designed the setup after studying and reading a lot on internet and talking to the architect specialized in ecological house design incl passive house.

But having a family with three young children and my wife ventilates the house using Greek a system :grr. ( you open windows and forget

)
So passive house will not work for me.

Greetings from Greece

p.s. on this moment early morning outside temp. 11 C inside 25.5 C and i am not heating.:D

Mangas · November 2009

Re: Energy efficient houses

We used Rastra block filled with rebar and grouted along with triple pane windows. A little more money upfront but when you amortize the difference over 30 years it doesn't matter.

Don't know if you have that product where you're located but insulated block sure made a difference for us. House is quiet too when mother nature gets frisky.

Also, we had installed aluminum retractable/adjustable shutters which help conservation not to mention security.

peterako · November 2009

Re: Energy efficient houses

I forgot to inform about my wall type.
It is using from inside to outside, hollow brick wall 30 CM , 8 CM Insulation based on sea weed and wood cuttings pressed in sheets using portland cement, and then a 40 CM stone Wall. the floor beams and columns structure is based on high pressure concrete. (I am in a earthquake zone)

I am not a where what the insulation level is but it is good for me. and looks very good.

Greetings from Greece

Energy efficient houses

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