Posted By: billtbut this isn't a passivhaus by any stretch.

That may be the key to it, as well as the UFH adding a bit, the extractor fan is drawing in warmer air from the rest of the building.
It should be easy to test though. Turn the heating off in there, close the door, leave to stand for a while on a cold day, measure the temperature, then turn the fan on and see what happens.

ST - you're a clever bloke, please just go away and have a think about this for yourself, as it's really not rocket science.

It also doesn't need figures or evidence to point out that you've got the complete wrong and of the stick, and can't get your head around the fact that this is all about reducing heat loss to the point where the body can comfortably maintain it's own temperature and not about actually warming the body up.

Think about someone camping under canvas in a sleeping bag in the middle of winter. Neither the walls of the tent, or the sleeping bag thamselves are actually transmitting heat to the person, they're just slowing down the emission of heat from the person to the outside air to the point where the body can comfortably maintain it's heat at the required temperature. As I said earlier, we're not reptiles, we're warm blooded creatures who create our own body heat.

As for - 'if this was such a good idea they'd have been doing it for centuries.... don't be daft, the idea relies entirely on the external face of the wall being heavily insulated, with a network of pipes between the insulation and the wall to transmit the heat into the wall, plus a solar collector to gather the heat in the first place. Without either of these factors the system wouldn't work, and they've only become available in the last few years.

The other point being that in these rooms you're not just reducing the heat escaping via the walls, which in many rooms is the greatest route for heat to escape outside of air changes. You're actually changing that wall from a source of heat loss into a source of heat gain, meaning that the actual heat requirements for that room are significantly reduced vs any other heating medium that would still be needing to meet the heat loss through the wall on top of the other heat loss routes.

Posted By: billt
I'm struggling to see how these schemes will work in the UK climate with long periods of cloudy weather. Lots of cloud = no useable energy however low the collector temperature. Last week we had 4 cloudy days. I have 20 sq.m. of evacuated tube collector. On the first day the collector temperature got up to 19C, second day to 32C briefly and harvested .26kWh of heat! Third day collector got to 25 and on the 4th day got to 34 but no heat was collected as the boiler had been lit and the stored water was too hot to let the pump operate. Of course those temperatures are with the system stagnated, which means they are unrealistically high and don't imply that there is any energy to be had. And those are autumn days with a reasonable day length. In the winter with about 4 usable hours and the likelihood of a fortnight of dull days it seems incredibly unlikely that you can heat a building satisfactorily only using solar heat. The other issue is that these schemes are going to be expensive. Covering walls with UFH pipe is going to be costly in terms of installers time, if not material costs.

I too would be sceptical that 100% of heating requirements could be covered this way, but would think that somewhere in the region of 95-99% of the original heating requirements of the building could be covered in this way once you factor in both the solar heating, and the reduced heating demand stemming from the external wall insulation on a solid walled house.

I'm assuming that the house already had 300mm+ lift insulation and double glazing here btw.

This then leaves the option of either a small heat pump to feed the wall heating in the absence of solar input, or a wood burning stove, or even just small resistive electric heaters if the heating requirements really are only going to be about 1-5% of what they previously were. Which I think is what Viking House was suggesting.

Costs - I'd think the main cost is the external wall insulation, and the main market for this would be as an additional extra for those already considering external wall insulation. Once you're going down that line, if you were considering UFH anyway, then I'd expect the costs would be lower or the same for using the UFH pipe on the wall vs the floor, as you'd need to insulate the floor and probably screed it. The other advantage obviously being that you don't need to clear the house to do it, the work can be done almost entirely externally. The only additional costs then being the solar panels, which really aren't that expensive if you're buying in these sorts of bulk quantities.

I don't see this as a one size fits all solution, but it's certainly one with a lot of potential for houses that are currently seen as being hard to treat, and will actually turn the solid walls into an asset instead of a liability in energy terms.

Hi ST, My TV room has 2 Radiant Walls (see the pic), they will be connected to my 20-30m2 Solar array when I have it installed, but for now they're connected to my Gas boiler. I often watch TV with the IR thermostat close by, the 2 Radiant Walls are usually 22°C, the external wall is usually 16°C and the neighbouring wall is usually 19 °C. The TV room is usually 19°C degrees and very snug.

I have to applaud any attempt to use solar energy, no matter how it turns out. So bravo Tom and Co for
A Thinking it up in the first place - and B. Being convinced enough yourself to convince the client to have a go. Been there, and not an easy task, unless the client is very forward-thinking themselves.

If all objections must first be overcome, nothing, as the man said, will ever be attempted. Ask Edison. And if it does prove successful, then the theoretical physics which prove it can't be done mean nothing. As science finds to its cost regularly. Without experimentation and pushing the envelope, our espousal of the advancement of science - our knowledge base in fact - means little.

My own concern with this, as one committed to using solar thermal for space heating (putting Steamy's and Gavin's arguments and counter-arguments to one side for the moment), even if it does prove successful, is the controllabilty of the collected energy. Am I right, Tom, in thinking that at times there will be surplus energy which 'has' to be emitted? Because if so I would be concerned that the comfort level of 'x' (X being those times when solar irradiation is aplenty) is high. But those times of year are the warmer times anyway. What happens when low solar incidence and cooler temperatures combine? As they do. When the homeowner is used to those warm summers with extra-warm radiation? Or am I barking? Now there's an open-ended question inviting certain parties to respond...

VH: Is that MLC pipe you are using?

Gavin: That's a bit sexist - aren't nut-less people also allowed this experiment?

The Drain-Back Solar Roof system we use has the following benefits;
No overheating issues.
No freezing issues.
No heat exchangers that reduce efficiency.
No glycol that needs replacing every 5 years.
No Compex controls.

... basic question: Is there a standard height off the floor being used when describing room temperatures?
Only ask because we're currently comfortable without heating, but the air temperature at table top height reads as 17 degrees as opposed to 19 degrees at head height .........

Yes we need to make the collectors much cheaper, also optimised for ultra-lo-temp collection. Not sure that standard avail ST panels wd do it, without add-on cost/modification.

Looking at built-in-situ collectors, much like UFH is, which wd serve as roof covering for entire, shaped slopes, edge to edge top to bottom, forming eaves, verges etc. Thus offsetting their cost against not only omitted roof tiling or whatever, but also omitted edge-joints to tiling that normal 'inset' panels still incur. Could even serve as roof structure too! i.e in lieu of raftering for a complete slope.

That cost saving by offsetting is in addition to omitting costs of multiple durable 'picture-frame' casings and plumbing connectors/manifolds that factory-made modules imply.

I like the rest of what you say but I'm a bit cautious about this bit:

Posted By: fostertomCould even serve as roof structure too! i.e in lieu of raftering for a complete slope.

Generally speaking you want to keep the thermal mass of a solar collector as low as possible which counts against the bulkier bits of the structure being too tightly integrated.

Posted By: fostertomOr are you talking about 5yrs direct experience with completed systems of this type? Well, that's a bit chicken and egg!

It is indeed very much chicken and egg and that is why I would like to see some research data from as broad a range of sources as possible.

Just looking at one of the examples which Viking House posted "Kilcloon Passive House" the PHPP calculation for it was 12W/m2/a and it has a solar slab capable of storing 750kWhr of heat energy.

Whilst in my own case I'm at around 22W/m2/a and have a 135m2 passive spec insulated slab of 100mm of concrete. My latitude is also 2 degrees further North.

If I'd looked at the possibility earlier I could probably have upgraded to include a larger solar heat dump in my slab without huge extra cost but it's too late for me now on that score.

It's only with hard data that you can really identify what parameters are critical to the success of winter solar heating. Some of the questions I have are: Is a solar slab or other solar heated thermal mass critical? Or can running 25 degree water in a 100mm concrete slab suffice? During dull spells do you have to run warm water from another source (direct electric probably) through the slab or can the indoor temperature be maintained by an Air to Air heat pump which should be cheaper to run?

In my own case I still haven't ordered any heat source for the house, so my options are still open. Within budget I could install an air to water heat pump or about 40m2 of solar thermal or about 30m2 of solar thermal plus an air to air heat pump to maintain the indoor temp during dull spells.

If anyone can give any guidance I'd be delighted to hear it

I went back to visit this (below) Solar enhanced Passive House yesterday, we built it earlier this year, its working well so far but we haven't had much cold weather yet. It has a larger 40m2 Solar Array than the Kilcloon Solar Enhanced Passive House and a smaller 36m3 store.

My brothers Passive House http://www.viking-house.co.uk/1st-irish-factory-built-certified-passive-house.html hasn't had the heating on yet either, I stayed there last night.

Hi Tom,
We've been making them up on site with over 2 years now, we cut the fins to the size of the roof and build the solar panel from ridge to gutter on site, but its hard to keep an eye on the quality, so we're now working on a cost effective factory produced adjustable solar roof, clear black with no lines.
You can see some scuff marks on the panels in this picture and the effect of soldering them on site where the manifold meets the fins, we later spray painted these areas with black paint, but in order for it to look well all the time it needs to be done in a factory I feel.

Thanks Seamus, I made a quick comparison of my data compared to the Kilcloon passive house last night.
My total annual irradiation is about 10% higher than Kilcloon but in the critical winter months it's about 35-40% lower. Given that my heat demand is almost twice that of Kilcloon 22kWhr/a vs. 12kWhr/a and I have no solar slab I think I would be really up against it going for solar heating in the winter months.

There is a 45% grant available here for PV so self installing 5kWp will end up costing me about £4,000 and should reduce my electricity costs by about £350-£400 a year so going with an ASHP and PV looks like the way to go for me.

The Build-It-Solar blog is a good source for ideas of this sort. E.g., most recently a big solar collector on a green roof:

http://www.builditsolarblog.com/2012/10/large-diy-solar-space-and-water-heating.html

(I think you'd have to be very careful using long horizontal pipes in a drain-back system, though.)

well. After many hours trying to make the wood stoveboiler / thermal store / solar / gas combination work for our quote on the building I mentioned up thread, I've ended up coming back to what Viking house was saying and deciding to simplify everything and spend the saved budget on extra solar panels.

so my preferred option is now 15m2 of solar thermal feeding a 300l dual coil cylinder, then the UFH system via a heat exchanger (I think), then an 8kW high efficiency / low emissions wood stove for the main room for direct space heating only (one of the navitron ones that look very good for efficiency, heat ouput and emissions), all backed up by an 18kW condensing gas boiler.

I worked out that I think the shading shouldn't be too much of a factor until mid november, so the solar should aid with space heating until then on top of the water heating, and I'll target this at the low UFH systems where the rooms will hardly get any solar gain, vs the rooms with skylights.

I'll be relying on the thermal mass of the UFH screed to soak up and store the solar heat from the afternoon to slow release it through the evening, and they'll probably then need to use the gas to boost it in the morning.

Fingers crossed I'll be able to have a system installed in the not too distant future to be able to test and monitor the ideas discussed on this an previous threads.

Thanks to Viking House for the input up thread, as well as his case studies, which partly gave me the confidence to recommend this option.