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How is my passive thermal house doing?

Rob Sigg


Joined: Feb 04, 2010
Posts: 710
Location: PA-Zone 6
So I built a brand new house that my wife and I designed, and we designed it so the main living spaces are south facing with a lot of windows and overhangs for the summer…passive thermal. There were a few things that we couldn’t do because of budget and some things that we didn’t want to do because of athestics…so….here is how my house is working.

For the most part on an average day in the winter the house temperature will stay between 68 and 72, this of course depends on how long the sun is out and air temperature which in zone 6 goes into the teens occasionally. Generally our heat doesn’t kick on for most of the day because of this since we have it set back while we are gone. Of course at night the temps drop so we keep our heat set back to about 65 and it may run a few times a night. We have a geothermal system and my basement temps seem to be consistent at 65 for the most part, sometimes even higher.

My question is, am I being unrealistic by expecting the house to be warmer more and for longer durations?  I am new to this sort of thing so I don’t know what type of results to expect. How are we doing?

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Max Kennedy


Joined: Feb 16, 2010
Posts: 461
Location: Kirkland Lake, Ontario, Canada
Without having a floor plan (how much window square footage there is vs volume of house), construction details (thermal mass characteristics, insulation characteristics etc) or the location (determines average hours of sunshine (not daylight but actual sun) and elevation) it is virtually impossible to say if your expectations are unrealistic or not.  In the words of Johnny 5, need input!


It can be done!
Rob Sigg


Joined: Feb 04, 2010
Posts: 710
Location: PA-Zone 6
OK fair enough!

The total square footage minus the garage and basement is 2600 sq ft. No windows on the east and west sides. Im not sure how to express the square footage of the windows to you, is it just width times height for each window all added up? The construction is typical for the northeast, and standard R value insulation. The seams/joints etc. have blown foam, and the rest of the house is blown cellulose, precast superior walls. 6” exterior walls. As for thermal mass, the only thing that we have is darker furniture, a darker wall, granite counter and that is about it. Our carpet and other flooring is light. Windows are a pretty standard window, it is a brand new house afterall. Our location is southeast PA, zone 6. Elevation is between 650 and 700 ft. The backside of the house which has all the main living areas is facing south and we sit just below a ridge line.

I hope this helps Johnny!
Max Kennedy


Joined: Feb 16, 2010
Posts: 461
Location: Kirkland Lake, Ontario, Canada
blitz1976 wrote:
Im not sure how to express the square footage of the windows to you, is it just width times height for each window all added up?


Yes, south facing windows only.


blitz1976 wrote:
As for thermal mass, the only thing that we have is darker furniture, a darker wall, granite counter and that is about it.


OK, in other words not much thermal mass.

blitz1976 wrote:
Windows are a pretty standard window, it is a brand new house afterall.


Double paned I would take it then without the argon gas between or special glazing for heat retention.

blitz1976 wrote:
The backside of the house which has all the main living areas is facing south and we sit just below a ridge line.


OK, does this affect the time that the sun actually starts to shine into the house?  Also, is there much roof overhang, window canopies or tree's that would interfere with the winter sun entering the house?  Also, since you seem to have had passive thermal in mind are there insulated window shutters to keep heat in at night? (see http://www.builditsolar.com/Projects/Conservation/conservation.htm about half way down the page)

Given you didn't include the thermal mass part of passive solar, a really big part for regulating night temperatures,  you don't seem to be doing too bad.  Will have to look a few things up for your area regarding winter sun hours but it seems you don't have much heating cost so it's OK.  If you want improvements look at the website above and pick your projects.  Have fun.
Rob Sigg


Joined: Feb 04, 2010
Posts: 710
Location: PA-Zone 6
OK Im going from memory on this but the windows should be at least 250 square feet, but I believe it’s a lot more since my sunroom on the back of the house gets morning and evening sun on the sides.

Windows are double paned indeed.

The ridge only affects the morning sun, we typically this time of year start getting good sun by 9am sometimes earlier. The sun goes behind some decidious trees by 4pm or so. Very little overhangs that obstruct the winter sun, but they are in place for summer sun. Only late day trees as I said above. We do pull heavy curtains back at night for the bedroom but since we are just moved in we don’t have any blinds for some of the main parts of the house, I prefer it to be open anyway…I love looking out over the valley!

Yeah I hear you about the thermal mass, a big part of it was going to be concrete floor in the sunroom but it created a few issues that we couldn’t address without a lot of headache and money. Im trying to take babysteps with my wife too, she values these sorts of things but isnt accustomed to them, and she is real picky about athestics so I have to keep the creative engineering to a minimum  wink wink Thanks for the link I will check it out.

Rob Sigg


Joined: Feb 04, 2010
Posts: 710
Location: PA-Zone 6
If this were an optimized solar situation for a passive home what would you expect my daytime temps to be and nighttime without any electric heat? I know this is probably tough to answer but surely there are people out there in much colder climates that have a passive system that have some kind of benchmark data?
gary gregory


Joined: Apr 09, 2009
Posts: 395
Location: northern california, 50 miles inland from Mendocino, zone 7
I agree that it sounds like your house is performing quite well.   

If the south facing windows are low-E, then not all the radiation is getting into the rooms that is possible.

Sounds like the house is finished, so hard to add thermal mass.   One way is to add a second layer of sheetrock.     Or dark colored decorative metal tanks filled with water.

Have you gone through a summer yet?    Does the house overheat?   That will be the signal to add more mass.   

Covering the windows at night would help but I understand about the view.     All in all It sounds like you are doing great.

If this were an optimized solar situation for a passive home what would you expect my daytime temps to be and nighttime without any electric heat? I know this is probably tough to answer but surely there are people out there in much colder climates that have a passive system that have some kind of benchmark data?


Without any thermal mass on a clear sunny day between 20 and 60 degrees, I would expect the house to come close to overheating.      [In a well insulated home]


Gary
Rob Sigg


Joined: Feb 04, 2010
Posts: 710
Location: PA-Zone 6
You bring up a good point about the low E, they aren't anything super special but they seem to block quite a bit.

I like the idea of the decorative tanks; if I can ever get my tropicals and such outside permanently I will most likely add stuff like that, right now I dont have the space.

No summer yet and I am really curious to see how it performs.

Thanks alot for the feedback, its one of those things, you take babysteps to conquering the world or saving it I should say!
 
 
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