Surrounded By Zulus – Member

My dissertation was on the thermal performance characteristics of solar collecting water heaters. Looks like a decent system for the moeny you’ve paid.
*falls over*

Does it actually work then, I mean, I can’t see the amount of sun we get in this country being sufficient to heat an entire house just from heating some pipes.

And there’d be even less in winter, when you’d need the heat. So you’ve got to then burn fuel?

I’m assuming it’s more efficient than a ‘normal’ system, but I am ignorant of such new fangledness, and curious as to how it works and it’s benefits. Does it really save a significant amount of energy and money over a conventional system? Plus, it seems to take up quite a bit of space, and require quite a lot of materials and equipment.

It works pretty well. Energy from sunlight equates to 1kw/m^2 even in winter.

Good for water heating for 2/3 of the year. Less useful for space heating.

It works pretty well. Energy from sunlight equates to 1kw/m^2 even in winter.

So about a tenner then?

Aye, around a tenner. Then around £20, then around £50, then this time next year Rodney we’ll be millionaires.

😆
1Kwh/m2 ain’t much sweetpea, or you could educate me.

Just stumbled across this thread and I’m mighty impressed; that’s a hell of a big collector you’ve got there. I wouldn’t worry about thermal losses, you’ve got excellent insulation and any thermal loss will be a tiny proportion of what you’re collecting.

Latest on my own system is that I’ve fixed up a “dump” circuit to the main house cylinder downstairs with a neat little 12v diverter valve supplied by Peter at Solarproject. Just before this, in late April in really sunny weather we had our first boil, we got home from a day out and found the panel temp up to 108c, the pump had shut down and the cylinder top was at about 66c. It was completely un-dramatic, nothing happened and when the sun went down it all cooled down and went back to normal operation. Anyway now I’ve got the diverter set up we can send excess heat down and dump it into the main house cylinder if the attic cylinder is up to temperature. We have re-timed the boiler to come on at 7pm in order not to waste any of the excess energy.

1Kwh/m2 ain’t much sweetpea, or you could educate me.

It isn’t a Kwh. When the sun is at 90 degrees to the surface of the earth and it is a clear day, the energy that strikes the surface of the earth is about 1000w per square metre. Using something like a solar thermal panel you can capture that free energy and use it to heat the water in your home. They are usually installed alongside another heat source as solar is ‘as well as’ and not ‘instead of’ in most places. Even in winter you can usually raise the water temperature a few degrees, so your other heat source doesn’t have to raise the temperature as far to get it to a useful temperature, thus saving energy and therefore your cost.
So – once the panel is installed and working and other than maintenance, you have free energy.

looks good stoner, i live in worcs, would like to have a look at your system sometime ? thks

Archie – youd be welcome to. email in profile.
Im between malvern and upton.

global – because I have the suppression system in the boiler (linked to the store) I decided not to bother with a dump. For suppression a temperature sensor (95deg) opens a valve on a mains supply through an indirect coil. When it opens cold mains water runs though the coil extracting energy and runs out into a pan.

If I did need a dump, Ive got a spare control cable running from the boiler room to the UFH manifold & pump. On overheat I could just get the UFH pump to run and draw energy into the floor slab (1,500 sq ft of screed and limestone should take a fair bit! 😉 )

Interesting the differential of 108deg to 66deg in your tank on overheat. Is your pump running fast enough do you think?

Ive got to pop out and buy another length of 22mm. Then its on with some more spunky soldering.

aprooval here. nice work.

<pedant>Free other than the cost of the pump / controller / valve electricity.</pedant>

I’m tempted by this – roof of the garage looks like a good location for the panels, back of the garage for heat store. It’d be good to get it working as a thermo-syphon to the main hot water cylinder – just wondering what size pipes I’d have to run? 3/4 inch seemed to be the size when I ripped out a back boiler 25 years ago.

Murray – the bit I wasnt able to do on my own when specifying was work out what size pipe to use.

For a single panel with not too long runs Peter sells a 12mm silicon hose.

He and others suggested I use 15mm given my runs. I decided to go all the way to 20mm (DN20) steel hose so that if I ever wanted to add another 40 tubes to mine (making 100 in total) Id have the flow rate. The copper work is all in 22mm (except for the header feeds) as the coil is 22mm and it makes sense to maintain the same bore throughout.

BTW, re “free”, it’s a very good point. Its also why I dont favour heat source pumps as you are still pegged to electricity prices, although at a factor of between 2 and 3 to 1.

In this case, the pump will be run at position 1 which draws 35W.

coincidentally, a tube on average over the year yields about 35W.

So one tube per year replaces the energy that the electrical pump is consuming. The other 59 tubes are all mine 😉

very slow business this soldering lark.

Not going to win any beauty pageants but Im getting better at it and they’re water tight too.

Tails from where the DN20 hose comes into the boiler room. Bleeder’s on top.

Elfinsafety – Member
Does it actually work then, I mean, I can’t see the amount of sun we get in this country being sufficient to heat an entire house just from heating some pipes.

It’s not really to heat the house its primary use is to heat the water.

It’s not really* to heat the house its primary use is to heat the water.

* although a substantially sized collector and large enough thermal store can have a measurable impact on the amount of fuel you need in winter. But as brick says, primary use is DHW.

Its not air temperature that youre using remember, but insolation.

Direct and diffuse insolation over the year. (@Dublin)

Link: http://www.solarbook.co.uk/solar-insolation.html

If it’s not for heating the house what heating do you have and are you going to install under floor heating as that runs off hot water ?? I’m all for what you are doing as I think it’s great, it’s lucky ghat you know you can stay in the one house for such a long time.

It is for heating the house to some extent as above.
The house has UFH throughout downstairs – water drawn from the middle of the thermal store (40-60degs) and mixed with return water to get to 40deg. With additional space heating from a log burner. Upstairs are low vol al radiators controlled by a separate controller and pump from the boiler tank and served at boiler temp (65-85deg) and individual thermostatic valves control room temps.

Do you need such a high boiler temperature, Stoner? Before I replaced it with a wood burner I experimented with different combi-boiler temperatures. With the thermostat clicking on at 33° the radiators were plenty hot enough to reach 18° + with negative temperatures outside. The lower the temperature the more efficient the boiler and the lower the losses. The lower temperature also meant that the temperature in the house was more stable as the thermostat had time to react and no longer allowed an overshoot.

My friend that uses underfloor heating fed by a heat pump uses 25°C water.

Don Simon – I dont get your comment. What are you trying to say?

edukator – the difference in our approaches is the use of the thermal store and biomass. The boiler raises the store top temp to 85deg from 65deg (switch on) to maximise efficiency of generation (biomass cycling is inefficient, combis are efficient when cycling). The store is substantially insulated to minimise high temp losses.

And just realised there’s a thermo mixer on the boiler that mixes flow and return to rads to bring temp down from system temp. Prob closer to 50-60deg.

I reckon 25deg water in UFH is too low in mid winter. Mine’s set for 35-40deg but the room thermo is set at 17.5-18.5deg

EDIT: also 25deg might be all he can get from the heat pump anyway and so uses that temp by default.

Also I dont see the point of running a pump continuously (c100W on pos 3) for UFH.

PLEASE use the thicker pipe insulation you should make sure the corners are covered 100% and that auto vent is toooo exposed

Explanation understood.

The temperature needed depends on how well the house is insulated, in his case 25°C water is fine. The whole heat pump assembly is inside the house so energy used by pumps isn’t lost. It’s an impressive system that takes heat from the ground (about 10°C in winter) and is about 450% efficient. Expensive though, over 15 000e several years back.

ts – that thinner insulation is on the cold side.

exposed vent is something I do need to look at though def.

450% efficient.

really? Ive not heard of GSHP getting better than a COP of 3.

Our barn is v well insulated (pleasure of converting an old building under modern regs). The 40deg is needed because it’s feeding 6 zones, 1,500 sq ft or about 500 metres of UFH pipe. Much less than that and it wouldnt deliver enough energy into the floor slab I reckon.

Yup really. It’s what he claimed and having quickly checked a few sites it’s an entirely plausible figure for an efficient heat pump that only needs to raise the temperature of the water from 10° to 25°. Do a bit of Goggling and you’ll find COPs of up to 4.5 are often quoted.

I had a quote done for a 12 000e system that claimed 4 if I wanted 35°C water and drilled vertically to find ground temperatures of around 12°C. the idea at the time was a straight replacement for the central heating boiler but in the end I opted for the wood burner.

pump & heat transfer tech must have come on a bit since I was looking at them then.

Since GSH can only ever augment an alternative energy source do you think COP of 4.5 all year is high enough when you can get much higher COP equivalent with solar thermal in summer and just higher during spring/autumn?

This site is interesting because it make the point that there’s no point having a system with a COP of less than 3.3 as you’d be less efficient using electricity generated with fossil fuels to power your heat pump than burning the fossil fuel yourself at home.

Ed can you translate this for me please?

ou d’un forage sur nappe phréatique)

That site doesnt actually say why 3.3 is the minimum…does it?

In order for that figure to be right, doesnt it mean that distribution losses and generation inefficiency of carbon elec gen would have to be 1-(1/3.3)?

…and…anyway, Im talking fincancial efficiency, not bunnyhugging!
😉

No need to wink, I agree entirely. Everything I’ve done so far will pay for itself within 12 years. Some of the initial insulating paid for itself in four or five years though the stuff I’m doing now will only save me sweat chopping wood. The wood burner will pay for itself in six years (including the cost of a chainsaw and other tools) though it would have been nearer 15 years if I bought chopped wood. The PV is on target for 6.5 years and the solar thermal will be 11 or 12 years. Even a more efficient oven will pay for itself in about 10 years.

Edit and the translation: “drilling into ground water (the aquifer)”. Quite easy where I live, the neighbour has a well with water at 3m.

nicely planned out.

Its hard sometimes to justify incremental capital cost.

For example my Biomass boiler is £10k compared to say, £3k for an oil set up.
Solar thermal is £2k
Log burner for £1.6k (including new flue)

So £10.6k incremental capital cost to try and recover in savings…

From my SAP DER
My DHW requirement is c. 6,000 kWh
Heating of 18,800 kWh

the TER is 7,500 kWh and 23,000 kWh respectively so my insulation already makes an impact

Ive still got to knock out c.25,000 kWh a year for this house but even at oil price of 5p/kWh that’s only £1,250. Hard to make much savings from that to pay back £10k+ unless oil inflation really gets going.

PV will be my next experiment. Need to have a good look at FIT vs capex.

This house is much smaller, the ground floor is only 68m2 and there’s no need to heat the loft. The previous owner (two people) was getting through 2000kWh of electricity and over 1000m3 of gas (about 1300e worth at current prices). We got down to 2200kWh of elec and 230m3 of gas before fitting the wood burner. We now use 2200kWh of elec and 5000kWh of wood (a lot more than we were using in gas). :-/ Something to do with three of us and especially madame taking delight in throwing on logs and feeling no guilty conscience.

Edit: The PV produces 3300kWh a year so we have a net production of 1100kWh.

I think we’re closer to 3,000 kWh of elec a year based on last 3m readings, but then we work from home.

How do you calculate your wood kWh?

Three and a bit “steres” of poor quality wood is about 5000kWh

Interesting measurement:

Un stère correspond à un m3 d’encombrement, soit à un cube d’un mètre de coté (bois + air). Mais en matière de pouvoir calorifique, un stère de bois frais de bouleau n’a rien à voir avec un stère de charme sec.

check this out too:
http://www.cosi.co.uk/Logs%20for%20sale.htm