i am looking for some thoughts on how best to design and build a holiday shack on the coast about three hours south of sydney that will make the most of passive and sustainable ideas for keeping cosy/cool. I have pored through back copies of Renew, and followed threads in the forum, finding a lot of useful info, but am finding it quite hard to reconcile all the competing considerations, and integrate them into one plan.
The site is in a BAL29 bushfire zone, and my primary objectives are to maximise northern sun heating the slab during the winter, plus plenty of glass to enjoy the view of bush to the south.
I plan to have solar hws, but find the economics of solar pv hard to justify for a holiday place. maybe that will be post build add-on.
I intend to have floor to ceiling glass on the north side to maximise winter sun on the slab, plus eaves to keep the sun out during summer. For when there is a run of cloudy days in winter, should I be backing up the passive slab heating with a hydronic system, and if so, how do I heat the water for the underfloor piping. The solar hws? A wetback on the slow combustion stove? Ideally a passive system would be best, so that the room is warm from previous sunny days when we arrive on that chilly winter evening, but presumably the warmth from the sun on the slab (that heated the water in the hydronic system) would have heated it anyway. Or is the amount of heat stored by hydronic underfloor heating with water warmed via on roof solar panels over a few days significantly greater than what you can get from four or five hours of winter sun on the slab on a daily basis? If I go for hydronic back-up, it looks as though a fairly generous well insulated storage tank would be required In the interests of economy and simplicity, I am inclined to think that the passive warming of the slab, plus the ability to get the stove going to provide warmth in a relatively short period may be enough.
The south side will also be mostly glass to enjoy the view of the bush. We will have a good quality slow combustion stove, and I am inclined towards some sort of smart glass rather than double glazing ($$$$!) combined with thermally effective blinds to keep the warmth in at night.
Any thoughts or recommendations on these questions would be much appreciated?
passive solar or hydronic floor heating?
(11 posts) (6 voices)-
dixie509
MemberPosted Monday 15 Dec 2014 @ 1:20:07 am from IP # -
dlvb19
MemberAt work so will be brief:
Holiday shack - very important - you probably need to outline how many days a year you will spend there and a what time of year.
It's unlikely SHW would be economical for a house occupied only a few weeks a year. Could possibly justify a heat pump HWS - ill let somebody else do the maths.
Hydroponic heating!!! Not sure whether you mean in slab or radiators but my answer is still "lord jesus NO"! Such an expensive system for a holiday house and soooo much overkill for NSW. Get a high COP RC Air conditioner for 2.5k installed.
Also put the double glazing on the south and single glaze (with or without low-e coating) on the north.
Lots to expand on here but you really have to look at full life-cycle costs. ESPECIALLY when it's a holiday house.
Best of luck
Posted Monday 15 Dec 2014 @ 2:39:10 am from IP # -
johnmath
MemberSmart glass or low-e glass does not address thermal conduction through the windows, as opposed to thermal radiation. With large areas of glass the heat loss / gain through conduction will be significant. Curtains, which can be effective for blocking radiant heat, can actually increase thermal transfer from conduction unless they are sealed around the top and sides, by creating a "chimney" effect which draws air across the glass surface. Toss the hydroponic heating for double glazing with thermal breaks in the fames, IMHO.
Posted Monday 15 Dec 2014 @ 3:13:09 am from IP # -
dixie509
MemberI'm new to this, so please be gentle if I don't understand the etiquette properly!
dlvb19 - thanks for your thoughts. The description of it as a holiday shack is perhaps a bit misleading. wife and I are retired, and hope to spend maybe three months a year there, all seasons. We call it a shack to distinguish it from the McMansions -it will be simple and shack-like, if that makes sense!
I hate the cold, but I know that with good planning, passive sun on slab can be really effective to keep a house warm into the night on sunny winter days. I think what i am trying to work out is whether the heat imparted to the slab by passive solar alone would drain away overnight, so that each day starts from scratch, and one cloudy day means no warmth. On the other hand does an in-slab hydronic system over several sunny days load the slab up with more heat, so that it can ride out the dull days a bit better. If so, I would only contemplate it if it could be powered by solar, but my sense is that a lot of solar hot water is needed to generate the amount of hot water needed to warm up the slab.johnmath - I haven't started doing the sums yet, but I was under the impression that it is possible to combine smart glass and thermal blinds/curtains (properly sealed as you observe) to achieve similar results as double glazing, which I gather is still very expensive here
Posted Monday 15 Dec 2014 @ 6:00:49 am from IP # -
johnmath
MemberThe in-floor hydronic coils or fluid will increase the thermal mass of the floor at all, so having them will not help keep the house warm during overcast periods, unless you put heating through them, of course.
The best way of retaining the heat over several days is to not let it get out. This is achieved by super-insulating all walls, floor and ceiling, and double glazing. Think of your windows as holes in the wall - they pretty much are as far as heat loss is concerned.
Curtains are not nearly as practical as double glazing. Besides, you probably want to see the views during cold days when you still need insulated windows.
Posted Monday 15 Dec 2014 @ 9:24:27 am from IP # -
karmacoma
MemberDouble glazing isn't necessarily expensive - get a couple of quotes for Vantage frames (that's a brand name of a proprietary system of framing) - try Hanlon windows in Bomaderry - they were very competitive when I got my glazing about 4 years ago. Vantage frames are extruded aluminium - no thermal break or anything. But I can tell you that they are effective in Canberra which has severely cold nights. Perfectionists will point out that alu frames are not the best available ya-de-ya and finger-wag over the lost opportunity to spend more money on higher-spec products, but sometimes things have to be done to a price point (especially if it's not Wealth Avenue and you want to get your money back when you sell).
There is logic to the idea that hydronic heating (or 'hydroponic heating' if you intend filling the house with dope plants growing under lights) could heat the floor and the heat will remain for perhaps a few days before it fades away - so cushioning against a dull day or two. But unless you just intend to heat one zone, and a small one at that, solar heating of the hydronic water is impractical. There was a thread here in May/June about someone experimenting with a small system like that - it has merit.
On the other hand, if you do the classic things and insulate really well, limit glazing to all faces except north, and double glaze, you might find you don't need hydronic heating at all. Again, Canberra: -6oC at night etc., but this winter we never turned on the hydronic heating even once. Nor did we use any other heaters. We had to wear jumpers and woolly socks in the evenings, but it wasn't bad at all. A quantum leap better than the shocking older housing stock in Canberra where you blast the place with a huge gas wall furnace and still freeze to the bone. Basically, the house has foamboard walls, fibreglass batts inside all stud frames, and R4 in the ceiling (should be more but ah well). Minimal windows (just enough to satisfy the BCA regulations - and all double glazed) except to the north, and even then its just two double-glazed triple-light doorsets plus the north-facing bedroom window - quite conventional - not an amazing wall of glass or anything like that. The slab is insulated for the first 600mm around the edge perimeter. Canberra has a fair percentage of sunny days during winter, so that was important - we had solar heat gain almost every day, onto the slab (polished concrete, no carpets).
Once you north-orient, insulate well and do the other passive solar things, it will work -- it is actually a fairly forgiving technology. The problem is that if you are used to standard old houses, old mud-brick 'alternative' houses, or even new but cheap builder-spec houses, its hard to believe that those simple passive measures could really make such a difference. But they do.
Posted Tuesday 16 Dec 2014 @ 12:25:07 am from IP # -
dlvb19
MemberDixie,
There are threads about using solar for hydronic heating on these forums however the problem with using the sun for heating is that its often not around when you need it most. It's almost certainly not economical and if you have grid power then it would be ludicrous.
Seriously - A high efficiency RCAC and lots of insulation.
Use the WERS website when picking your windows as it resolves the U-value of the whole window - not just the glass. Get lots of quotes as prices vary wildly. Less glass is usually better but curtains and shutters will each bring up the R value by about 1.0.It seems like you really like the idea of slab heating. Don't get me wrong its very nice but it's energy hungry and very expensive to install. Maybe get some rough quotes before planning too far ahead - compare these with a fireplace + fuel and an Daikin Ururu Sarara (don't worry i don't work for them).
Also as I and others have stated before on this website - Passive SH + thermal mass is often presented as a panacea/complete heating solution. In Victoria it definitely is not. Definitely include passive solar aspects but dont get carried away with the thermal mass and plan on using another source of heat.
Posted Tuesday 16 Dec 2014 @ 5:27:42 am from IP # -
dixie509
MemberThanks again everyone who has chipped in on this.
It looks like the consensus is moving towards less focus on the slab, and more on the windows/insulation. I have tracked down a couple of earlier threads on solar heating of hydronic water, and they seem to be saying that it is uneconomic.
Unfortunately the view from our place is to the south, so we want windows on that side, as well as the northern ones for the sun to heat the slab. My parents built a place in sydney in 50's with the northern wall consisting entirely of floor to ceiling glass plus eaves for summer sun, and curtains to keep warmth in on winter nights, and it never needed any heating.
I am encouraged by the comments about the double glazing not being so expensive, and will pursue that.
Also, i am interested in the suggestions re RCAC. I have regarded the exponential growth of AC here as symptomatic of all that is wrong with design in Australia, as well as an environmental nightmare, but I guess with improvements in efficiency, and good integrated design, it has its place in some situations. I will investigate that too.Posted Tuesday 16 Dec 2014 @ 11:21:01 pm from IP # -
karmacoma
MemberRCAC is still a bit of an energy monster - not ideal - but maybe the difference now is that you can offset it with grid-connected PV panels. Especially if the house mostly keeps itself comfortable and you're just using it occasionally.
Posted Wednesday 17 Dec 2014 @ 9:12:41 am from IP # -
onrbikes
MemberI built my house n the principles you want with your holiday shack and its cost me nothing in heating or cooling. Just a but of firewood from my block.
South side of the building is usually for your sleeping areas, as they are cooler and require less light.
This link is good for a free hot water system. Check out the hand drawn ones for a plan.
https://www.google.com.au/search?q=hot+water+thermosiphon+system&biw=1294&bih=625&tbm=isch&tbo=u&source=univ&sa=X&ei=_1qRVM6hJcyB8gXdqIGoDg&ved=0CFEQsAQThermosiphoning is the term and the only rule to remember is that hot water rises. I have a solar panel, a small fireplace hooked up to a 100l copper tank, and its been bullet proof for the last 15 years
Posted Wednesday 17 Dec 2014 @ 10:35:36 am from IP #
