Ratio of glazing to thermal mass?

'chelle · Mar 18, 2008 9:15 pm

I know that sounds a bit technical, but a few of you seem to be well versed in passive solar principles.

I've read elsewhere that it is important to get this ratio right and that it depends on where you live what this ratio should be. Does any one know how important this is? Will a passive solar house still "work" if this ratio is not quite right.

I keep looking at our plans and thinking...'too much glass'...'no - too much thermal mass'

We're planning to have a slow combustion heater but only want to use this as a back up and hope not to have to either heat or cool the house (yes, houses need cooling even in Tassie) for most of the year.

We're also planning to have double glazing and hope to not need curtains to keep the warmth in (privacy isn't an issue - unless the people over the valley have good binoculars). I've read a lot about double glazing in other threads but was just wondering if anyone is actually living in a house with it installed and how they find it?

thanks
'chelle

Casa2 · Mar 18, 2008 9:27 pm

If you have lots of glazing, which should be facing north, then you need to pair it up with a large amount of thermal mass. If you don't have a lot of thermal mass then in winter the house will quickly warm up, but there is nowhere to store the heat. On sunny winter days you'll end up venting the house to stop it from overheating when that heat should be stored for the evening.

So match the north facing glazing with thermal mass to absorb the heat. I'm not sure of the exact figure, but it can be worked out.

Yak_Chat · Mar 18, 2008 9:28 pm

Çhelle,
Do you know about the http://www.greenhouse.gov.au site?

Yes it is important to get the right ratios.
As your climate is relatively cool all year round, you'd need to be looking at maximum gain of heat and light into a heat bank each night, so if your designer properly understands the principles, and your climate, then trust his knowledge.

Have you seen other houses he/she has designed.

Totally with you re the no curtains. - yes it helps to keep in more heat, but I have great views and no curtains spoil it for me

So make sure your desisnger knows what you want to live like.

I don't have double glazing yet, but I'm planning on installing some this winter.

But I have lived with in the UK, and on realy cold nights it was great to leave the curtains back and enjoy the stars. Something to do with a claustrophobic feeling aussies get living in the UK :shock:

Sounds like you have a great block.
Steve

'chelle · Mar 18, 2008 9:44 pm

Thanks Steve
Yes I've been to that site. I think i've read almost every word.

I suppose the scary bit is the trust bit.
Oh and I think I'm a bit of a control freak and like to know everything about every detail of our project.
Our designer has been really good, lots of communication. We've been to a few of the houses he has designed including his own and they were all really comfortable - which is what we want.

Yeah we think the block is great. North facing, bushland, close to everything (except that big island to the north of us).

Oh and just saw your reply Casa. Thanks.

Pretty much all of our glazing is to the North, a little to the NE and NW to get the views and none to the South

. The house will be set into the back of an existing (small) sandstone quarry on the southern side and so only a small part will be above ground on the south. Is this called coupled thermal mass?
I know what you mean about not enough thermal mass as our current house which is just down the hill from where the new one will be can get too hot on a winters day, but as soon as we loose the sun all the heat goes!

Casa2 · Mar 18, 2008 10:00 pm

Earth bearmed on the south and lots of glazing to the north. You've got a great start for a thermally comfortable house.

Yak_Chat · Mar 18, 2008 10:09 pm

If his house is comfy then it all sounds good.

and the quarry will only help more with warmth and shelter from those lovely surf making winds

Steve

mek · Mar 19, 2008 11:35 am

'chelle

I know that sounds a bit technical, but a few of you seem to be well versed in passive solar principles.

I've read elsewhere that it is important to get this ratio right and that it depends on where you live what this ratio should be. Does any one know how important this is? Will a passive solar house still "work" if this ratio is not quite right.

I keep looking at our plans and thinking...'too much glass'...'no - too much thermal mass'

We're planning to have a slow combustion heater but only want to use this as a back up and hope not to have to either heat or cool the house (yes, houses need cooling even in Tassie) for most of the year.

We're also planning to have double glazing and hope to not need curtains to keep the warmth in (privacy isn't an issue - unless the people over the valley have good binoculars). I've read a lot about double glazing in other threads but was just wondering if anyone is actually living in a house with it installed and how they find it?

thanks
'chelle

Re. double glazing, we've got the whole house double glazed, and when I got home from work at 3:30 the other day when it was 39 degrees, it was nicely cool inside and I didn't need to turn aircon on.

'chelle · Mar 19, 2008 1:04 pm

Thanks mek

Did it cost a lot - the double glazing?

Our designer thinks as a very rough estimate that we've got about $100k in glazing costs, but it's something we really want. I'm hoping to try and find it a bit cheaper - well a lot cheaper if possible. I think sometimes builders and suppliers think that they can charge what they want in Tassie because we don't have as much choice as you guys on the big island.

Yak_Chat · Mar 19, 2008 11:46 pm

Holy cow $100k in glazing?

Is it crystal as well?

Seriously, what size windows are you instaling as that must be why it is so expensive.

Some dimensions for a review please.
Steve

'chelle · Mar 20, 2008 12:13 am

Hi Steve,

As I said that was the designer's very rough estimate. I don't have the exact area of the windows, I actually asked him for that the other day as I wanted to do my own sums but am yet to hear back from him. So far we have the floor plan and some renders of the exterior, they are still doing all the technical drawings and stuff.

From my rough estimate I think there could be 80m2 or more. :oops:

Looking at the floor plan there is at least 28 linear meters of floor to ceiling windows and doors. As I said, this is pretty much all north facing.

Maybe I should post my floor plans but its a PDF and I haven't quite worked out how to do that yet. I suppose I could scan it :?:

'chelle · Mar 20, 2008 10:42 am

OK here goes..

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Hope that worked.

When I said that most of the glazing faces north, maybe that should have read... most (all?) of the north is glazing. We want as much light as possible. I guess we'll be people who can't throw stones.

Yak_Chat · Mar 20, 2008 7:34 pm

Stunning

Love the design.

You're going to love this place

If not let me know when you want to sell it

So 100K for glass, well - with that much glass and floor to ceiling, yep I reckon you're going to be up there in costs.

Get some competitve quotes, just so you know it's not OTT, and from there just do it.

And enjoy the views and the warmth that you can aslo enjoy.

Steve
PS Did I say I love your design

'chelle · Mar 20, 2008 8:49 pm

Thanks Steve.

We're really happy with the design

- now we just have to get it built.

I keep telling dh that it's a lesson in patience, this whole process. What doesn't kill us will make us stronger

enigma_brennan · Mar 21, 2008 12:17 am

Quote:

I guess we'll be people who can't throw stones.

mek · Mar 24, 2008 10:22 pm

Oh wow, what a house!

I'd be double checking that 100k figure though, it seems so expensive.

3timesbuilda · Mar 25, 2008 10:38 am

I don't understand, are you having shaded deck right in front of your windows?

'chelle · Mar 25, 2008 7:43 pm

Hi 3xb

It looks like it doesn't it. Maybe I should query this with our designer.

The roof does extend out over the deck in front of some of the windows, but if you were to draw it with just the eaves, it isn't that much additional shade, is it? :?:

? You also have to take into account that the ceiling is raked and the roof will be higher out on the edge of the deck.

The designer said he has checked the sun angles, but I think I will check with him again as to when (ie which months of the year) we would expect to get sun hitting our floor. Thanks for raising that

Yak_Chat · Mar 25, 2008 8:47 pm

Chelle,

Casa posted this last year and it might be of use.

http://solardat.uoregon.edu/SunChartProgram.html

3xb - I see why you ask, (I thought the same) but with a computer generated image they have not stated a date and time, hence the shade might be required at that time of year.

The angle will let the sun in more as it traverses etc.

On another note
Has anyone actually thought what it would be like to be a architect or builder with customers always checking their capabilities every minute,?

Sure they are not always right, but with several projects under their belt, they do get to know their stuff. :wink:

Steve

'chelle · Mar 25, 2008 9:08 pm

Thanks Steve

I'll check that link out when I get some time.

I was thinking about the shading today and at this time of year we still need shade. We currently live about 100m downhill from where we are going to build and have had to have the curtains closed for the last few days to keep the house cool. The eaves aren't wide enough in this house.

Yeah, I think I need to trust his experience and not question everything...having said that I am going to speak to him about the glazing above the windows in the dining and family rooms as this is only single glazed and I think it should be double glazed.

'chelle

Casa2 · Mar 25, 2008 9:24 pm

Glazing that is high up needs to be better than glazing lower down. This is the same whether talking about a window or floors. That is, if you have high windows, make sure the topmost section is double glazed. This is where the temperature difference is the greatest (in winter) and therefore has the highest performance requirement.

Ask you're architect to give you some shading diagrams one hour apart both for mid summr and mid winter. This way you can see where the sun is at various times.

The rule of thumb is that overhangs should be 45% of the distance from the window sill to the eaves. I think this works even for Tasmania.