Grand Designs innovative ground source heating

[Kes]

I'm fairly familiar with the principle of ground source heating but not too much of the detail. On last night's Grand Designs the building sat on 46 10-metre deep concrete piles, and wired to the reinforcing cage were loops of the heat pump pipework. (See http://www.channel4.com/4homes/ontv/grand-designs/houses/M/maidstone-bungalow-gallery_image3.html and http://www.channel4.com/4homes/ontv/grand-designs/houses/M/maidstone-bungalow-gallery_image4.html) This adds up to just about 1 km of pipework, not in one giant loop but attached via manifolds.

As the pipes are embedded well into the concrete, will they pick up enough heat from the ground? And at 1 km, won't this need some hefty pump to circulate the fluid around the pipes, and thus negate some of the energy gain?

There was also a ground air heating system, where a large dia pipe was set 1.5 mtr underground and air pumped through it, but I can't find any details of that.

I'm not criticising the program (although most of the grand designs I end up hating), I'm just curious about the techniques. the house isn't finished so there's no final test wether it works or not.

 

[Agile]

This kind of thing would largely depend on the thermal mass of the ground to provide enough heat for long enough.

The problem is that for a few days it might be adequate but with a prolonged cold snap it might just end up freezing the ground to a 10 m depth.

Tony

 

[PlanetThanet]

Hi

I was a bit curious as to how effective it would be as well.
I wondered how well the 'solar' roof will work being buried in concrete, as was the UFH. It's normally screed isn't it.
Not sure I would be happy living under 50 tonnes? of roof They manage to use GSHP in Canada...lots of prolonged cold spells! Info on technology in UK here... http://www.energysavingtrust.org.uk.../CE82 - Domestic Ground Source Heat Pumps.pdf


Thanet.

 

[Kes]

In a (prototype!) system which is integral with the foundations there's no possibility of tweaking if it doesn't work too well. It's do or die.

There seems to be two unknowns - apart from the inordinate length of the pipes - one being that there would be no sun playing on the ground from where the heat is extracted, to 'recharge' the heat source, and the other being that the house sits directly on an area of ground which is being cooled, like trying to heat a house sitting on an iceberg.

 

[JohnD]

I don't know but:

large cold stores have to have heating pipes under them (and round the outside of the walls if underground) to prevent them creating a bulb of frozen ground (permafrost) since the refrigeration draws heat out of the ground, and there is nothing adding more heat to warm it up, so the frozen area just gets bigger and deeper and bigger and deeper

 

[Kes]

More here - http://www.roger-bullivant.co.uk/news/12/chathams-grand-design.html

It's warm air that's being pumped through the pipework (I guess it starts out as cold air).

Skanska seem to do this sort of thing in a big way, so I guess there's some previous, as they say.

 

[elliottt]

Bore holes usually work because they are taking the heat from the Earth rather than the heat from the Sun, geothermal. If you're using trenches IE 1m to 3m deep this is more heat from the Sun.

Agile quotes rubbish, a cold snap will never freeze 10m down!!! Get real! Cold mains water pipes to your house are down 750mm to 1350mm and they don't freeze.

Heat pumps work really well although I wouldn't like to have a prototype system such as loops of pipework in the piles. I'd like tried and tested boreholes or trenches for my house! The grand designs system should work though, if he's thought about it well enough. He seemed quite confident.

You won't freeze the ground under the house the heat from the Earth's core will warm it up. If the loops were in a shallow pond the pond would freeze around the loops.

 

[oilman]

Agile quotes rubbish, a cold snap will never freeze 10m down!!! Get real! Cold mains water pipes to your house are down 750mm to 1350mm and they don't freeze.

It's not the cold snap reezing the ground, it's the heat pump extracting the heat doing the freezing.

If the earth is being re-heated by the earths core, how is it that a building on the radio astronomy site to the west of Cambridge is built with a 1m thick covering of soil, and it's temperature hasn't changed by more than around a degree in years? There is no cooling in the building.

 

[Agile]

It's not the cold snap reezing the ground, it's the heat pump extracting the heat doing the freezing.

Thank you for stating the obvious for Mr Eliott's benefit ! Problem is that whilst its obvious to us professionals its not to DIYers who read this. They dont know the difference between the professionals and Mr Elliot, a heating layman.

Well said Doctor D. Some sense at last!

Mr Elliot even thinks that "Dr Drivel" talks sense! He has probably not noticed that Dr D has been banned from this site because he was repeating total nonsence on some topics.

Tony Glazier

 

[Kes]

The grand designs system should work though, if he's thought about it well enough. He seemed quite confident.

Confident? He was spending the in-laws' money on his pet theories, it seemed to me. I thought the programme was quite sad, the elderly couple hardly consulted and ending up with a building the majority of which I thought they didn't really want. I would have thought that they wanted a low maintenance house, suitable for wheelchair use, with some assisted door and window opening mechanism, with a reliable heating system. I bet there'll be maintenance men in there fettling the system for years.

 

[doitall]

A lot of the usual rubbish posted again.

10m bore holes stand a very good chance of freezing not only the ground but compromising the integrity of the foundations, ok we don't know how many bore holes has been installed, or what they are taking out, Boreholes are normally 100m average and there would be 2 maybe 3, depending on the terrain and heating load.

If Skanska had anything to do with it, nothing would surprise me, The Bath Spa project was one of their babies, nearly £60 million over budget.

And how long is galvanised footing going to last

 

[Kes]

Skanska didn't do this install, but they show this type of install on their website.

' Groundworks began last July with the creation of 46 piles to a depth of 10m. Sections of augered flight measuring 1.5m long and 300mm in diameter were installed using a 12t piling rig and connected to one another. Removal of the augured flights brought material to the surface. The presence of heavy clay in the soil allowed the 300mm diameter voids in the ground to remain open long enough for reinforcing cages to be inserted.
Harnessing the warmth of the ground to heat the property involved use of heat transfer tubes, which were secured to each reinforcing cage and inserted to full pile depth. Warm air is drawn through the pipes to serve a reversible heating and cooling system, installed by the clients beneath the floor.
Self builder Paul Tarling said: “There is enough stable temperature at a depth of 10m to provide sufficient warmth for a building of this size. I would hope that this development proves to be carbon neutral. It made good sense for us to attach the heat transfer tubes to the pile reinforcing cages, which were being installed in any case to provide a durable foundation.”
Each pile was later filled with ready mixed concrete and completed with a 760mm diameter circular pile cap.
Delivery to site of over 50 lightweight galvanised steel foundation beams followed, and a pair of operatives placed 20 different lengths of the ‘SystemFirst Homes’ foundation by hand. Each beam spans between a pair of pile caps and is shot fired to each cap to provide a secure connection. The longest span was 3.3m and the shortest was 0.9m.
Clear labelling on each beam avoided the potential for confusion over which section belonged where. “This is one of the first projects on which we have installed the galvanised steel version of the SystemFirst Homes foundation,” says RBL’s Paul Emblin. “It is cheaper to manufacture and proved to be lighter and quicker to install than a previous version of the foundation made from stainless steel.”
Additional steel cross members – known as ‘ladder racks’ – were installed between the main foundation beams to provide added support, before square panels of polystyrene were dropped into place to offer insulation. The bungalow’s floor was completed with the installation of underfloor heating and a 100mm thick concrete screed.
Each main beam features a pair of troughs to receive a pour of concrete and the completed foundations support a single course of 365mm thick ‘Ziegel’ blocks, which form the perimeter and internal walls of the bungalow.'

I'm surprised by the comment that air will be used instead of fluid in the pipes. What's the take on that, D?

As for galv footings, there seems to be almost unprotected polystyrene on the underside. How long will that last?

 

[doitall]

I assume the technology would be similar or the same as an air source heat pump, at that depth I would imagine you could get a temperature around the 12-15c mark (guess) before anyone asks.

The interesting question I would like to know is how they harvest it through collectors, what the design temperature is, and how they maintain it.

An heat pump works fine down to 0c then the COP drops off rapidly, and after the initial start-up I cannot see how they can harvest the heat quick with air to make it viable.

As for the galvanized bit and the insulation there has to be something under the insulation, doesn't there all sounds a bit like the prefabs they chucked up during the war.

 

[r.bartlett]

I assume the technology would be similar or the same as an air source heat pump, at that depth I would imagine you could get a temperature around the 12-15c mark (guess) before anyone asks.

The interesting question I would like to know is how they harvest it through collectors, what the design temperature is, and how they maintain it.

An heat pump works fine down to 0c then the COP drops off rapidly, and after the initial start-up I cannot see how they can harvest the heat quick with air to make it viable.

As for the galvanized bit and the insulation there has to be something under the insulation, doesn't there all sounds a bit like the prefabs they chucked up during the war.

Not too sure what you mean by 'harvest'?


I visited the Misubishi air con HQ in Hatfiled last year where their building (or part of it) is maintained by a GSHP. Seems they are very pleased with the results.

http://www.mitsubishi-aircon.co.uk/...ircon.co.uk/mitsubishi_electric.asp?id=154355

I was also slightly involved in the first commercial install of Mitsi in the UK at Soho sq London (about 5 years ago now) with several of these units feeding off boreholes -again no real hang ups.

The major players are moving into this area in a BIG way as it's -as they say- big in Japan. The next phase is the swap from HFC's to CO2

http://www.sanyoaircon.com/products/hydronic-products/co2-waterheaters.aspx

It appears to be the 'future' and energy savings seem good -but just wait for the repair costs!!

Cheers

Richard

 

[JohnD]

I wonder what the return on capital will be.