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General: passive annual heat storage by john hait

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    • CommentAuthorhowdytom
    • CommentTimeNov 29th 2007 edited
     
    After reading his book, I started thinking how i could use his ideas on a "normal build" house in the UK.
    I would like to ask this forum for your comments, practicality's, costs, effectiveness of this... If we build ducts, say 1.5m deep under the base slab up the north wall and into the loft space. In summer we could have a small PV cell powering a fan so when the sun shines it pumps the warm air in the loft space down through the base slab. Obviously it would require some form of back draught control, umbrella ground insulation etc. Could anyone calculate the cost/payback viability ?
    • CommentAuthortony
    • CommentTimeNov 29th 2007 edited
     
    Keep reading the book! The duct would need to be deeper down, maybe 6m, or the heat will come back up while it is still summer!

    It is viable now so long as there is no ground water. Indeed ground water could be the big drawback to this here in England.

    Visions of the ground steaming! Clay drying out and shrinking causing subsidence.

    I am thinking of building an inter-seasonal thermal store -- huge tank full of water and solar heat it.

    I am sure that your system would work under my present house.
    • CommentAuthordickster
    • CommentTimeNov 29th 2007
     
    Hello Tony,

    It took me a while to realise that a super insulated (think vaccuum flask) tank (think swimming pool) of solar summer heated water could act as an energy store for the winter.

    If you look at old CAT photographs, I believe they had a go at it in the 70s ? Couldn't find any more about it.

    With a bit more thinking, I realised that food is the same thing, hay for animals used for meat, veg stored for winter use.
    • CommentAuthorNiggle
    • CommentTimeNov 29th 2007
     
    If water store is created from rainwater, primarily intended for domestic use, does anyone know if the mechanics, or is it the physical laws and practicalities would allow use of the water, assuming natural irregular replenishment, solar heating this essentially underhouse tank and drawing off heat during wintertime, when most replenishment (cool) rain will arrive.
    Apologies for confusing summary but my point is While Theory seems perfect, don't the many pracical difficulties vitiate the otherwise grand idea?
    • CommentAuthortony
    • CommentTimeNov 29th 2007
     
    You would not draw off any water but heat exchange the heat out of it to use, retaining the same volume of water in the thermal pond.

    Rainwater recycling is something slightly different.
  6.  
    I am a great fan of John Hait's book 'Passive annual heat storage' and would like to see more variations along the theme. Your average house sits on the ground so why not use it? why bother with massive tanks of water?

    Surely the key is do the minimum for maximum return! work out the energy load of the house and the generating capacity of your heating (air solar, earth tubes etc) and balance the two! More insulation or more generation! there is normally a short full so size the storage (umbrella size) appropriately.

    I believe the key is each project needs a dynamic computer model to establish the maximum return for minimum invested!
    • CommentAuthorjon
    • CommentTimeNov 30th 2007
     
    Hi Jeff

    Yes, balancing loads is the way to go

    I ran through a few early tests on this using a very simplified model but could not get worthwhile results out of ground storage because of dissipation. Using an insulated tank does seem to get more worthwhile results. however, trying to annualise the heat storage doesn't work well because of the losses.

    I think you're right: A dynamic time based model perhaps that can import 3-D models from CAD would be the only way to do this properly: Does anyone know of such a system?
    • CommentAuthorjon
    • CommentTimeNov 30th 2007
     
    By the way:

    If you're using either a liquid or a material with a high relative conductivity as the storage medium, you can accurately approximate losses over time by using time as the finite element: Means that the basic setup of the model can be a steady state.
    • CommentAuthorjon
    • CommentTimeNov 30th 2007
     
    Is this the book:?

    Passive annual heat storage: Improving the design of earth shelters, or, How to store summer's sunshine to keep your wigwam warm all winter (Paperback)
    by John N Hait (Author)
  10.  
    Hi jon,

    Yes that is the book, a good read, it keeps things simple the way I like it.

    The book called the ground a semi-conductor and some of people that have the dynamic software explain it is straight forward to simulate but none have had the time to invest.
    • CommentAuthorhowdytom
    • CommentTimeNov 30th 2007
     
    http://www.enertia.com/Science/HowItWorks/tabid/68/Default.aspx
    got this link from jeff on a different tread looks very intersting

    dickster, the system at CAT got ripped out years ago, not sure why, could be that it was in open ground rather than under a house, I will try and find out.
    tom
    •  
      CommentAuthorfostertom
    • CommentTimeNov 30th 2007 edited
     
    John Hait's PAHS has been further developed, made more versatile, cheaper and more controllable, by Don Stephens' AGS. Here's the key links:

    http://www.primedesign.us/self_heating_houses/pahs_article_1.html - all you need to know, really, about John Hait's PAHS, the purist no-machinery concept
    http://www.primedesign.us/self_heating_houses/self_heating_houses_files/frame.htm esp frame 18 of this Powerpoint by Engineer Joe Anderson
    http://www.EinsteinCode.info to buy the ebook

    http://www.greenershelter.org/index.php?pg=3 - all you need to know about Don Stephens' AGS, which judiciously uses machinery to make it work better, in more situations
    http://www.greenershelter.org/TokyoPaper.pdf - ditto
    http://www.greenershelter.org/index.php?pg=2 - comparison between PAHS and AGS

    The penultimate one is the best intro – gives the key features reqd, used in many different mixes/combinations.
    • CommentAuthordickster
    • CommentTimeNov 30th 2007
     
    Howdytom

    Thanks for that, I got all excited when I saw CAt photos, but I guess they did the work and found out that it didn't... saved me the bother!
    • CommentAuthortony
    • CommentTimeNov 30th 2007
     
    It is working on a commercial scale for a district heating scheme in norther Europe that collects solar energy -- we have talked about it on here.
    • CommentAuthorhowdytom
    • CommentTimeDec 3rd 2007
     
    Help !!!
    I've read the books, followed the links, seen the comments, umbrella insulation is the way forward if you have the space, 20foot (6meters) The problem for me is this.... the barn is on sloping ground (10' at a guess), the north side is a concrete yard (shared access) I've got 20 foot west to the wall, 35 foot south an 20 foot east. unfortunately the south slopes uphill. the question is would an umbrella work sloping away from the building ?, maybe add a vertical drop near the wall ? the heat transfer, if I read correct, is conductive only so uphill should still work !.
    There's not many level sites with a clear 20 foot all around them so we need solutions and how do you get around the odd tree, I would hate to cut them all down, could you carefully remove the top soil around them place some form of insulant, then cover it with the soil or would that spoil the whole thing.
    tom
    • CommentAuthorjon
    • CommentTimeDec 3rd 2007 edited
     
    Wow!

    That's exactly the same solution I came up with for a similar project. However, I also concluded that it was relatively cost-ineffective. Anyone made it work cost effectively?
    •  
      CommentAuthorfostertom
    • CommentTimeDec 3rd 2007
     
    The 20ft/6m is a rule-of-thumb that comes from the estimate that a temperature wave will propagate through subsoil at 1m per month, so if storing 6 months summer heat, that's how far it will travel before the heat flow reverses. No need to cover the ground beyond the point where the heat reaches to. That's an over-simplification and could be greatly improved upon by proper thermal simulation. You can say that 20ft/6m is something like right; but the more the better; however the optimum, however you define that, might be quite a bit different.
    Don't despair - it's 20ft/6m outward from where you put the heat into the ground. So if your floorplan is wide/long enough, and you're putting your heat into the ground under the centre of the building, then the floor slab covers much of that 20ft/6m 'radius' and the outdoor remainder can be less than 20ft/6m. In fact what you can do is insulate well under the centre of the slab, so subsoil stored heat doesn't escape upward through the central part of the slab, but only comes up around the perimeter, where the window/wall heat loss is.
    Uphill/downhill slope of the insulation doesn't matter - as you say it's all conductive so 'heat rises' (convection) doesn't apply. However, the cape is a waterproof as well as a heatproof thing, i.e. rainfall collects on top of it (the idea is to keep the subsoil beneath dry) so you have to carefully drain water away from its lower edge, if it slopes toward the house. Let the odd tree poke up through - it's not that critical. Same with shrubs - just cut the cape around it, maybe let it rise close to the surface to clear over the roots.
    • CommentAuthorzenbiscuit
    • CommentTimeJan 14th 2008
     
    I started a discussion on this last February. Got good advice, especially from the links mentioned here by fostertom, and constructed a 3m deep (by 3m x 2m) pit under my extension. Placed 9cm of polystyrene around the outside edges of the pit. Put 100m UFH pipe around the bottom of it. 15cm sand over that, then placed a network of soil pipe on top of that. Drilled some holes in them and passed the 3 pipes up into my roof space. Also ran an unconnected outlet pipe (armoured cable pipe) so that air pressure doesn't build up. Then filled pit with hardcore, loads of hardcore. UFH pipe will be connected to 2 arrays of solar thermal panels +- 8m2. Air pipes are run to a point just below roof tiles and will suck hot air into the pit from 30m2 of tile. I've double battened the roof to get better air flow and placed a foil barrier below the felt to reflect heat back into the air space instead of transferring it into the extension during Summer.

    Also, dug another pit just outside of the extension at 2m. Placed an earth pipe array in this and run 100m of MDPE around the pit for heating. MDPE will be attached to smaller solar arrays stood in the garden. Pit has been well insulated and water proofed. Water proofing runs up to house walls. Earth pipe runs at an angle from 20m away into the ground and down into the pit. The earth pipe enters the building through the floor in the extension and should provide pre-heated air in Winter.

    Solar panels will be self-built from scrap double glazing I've got lying around and some materials that I bought e.g. microbore copper tubing.

    Cost (excluding solar panels) is about £4000, panels will add perhaps £500 for 12m2.

    Have taken photos of the stages and will do a detailed write up on my website when I get the time, probably in a month or so.
  19.  
    Excellent Zen, I will keep checking on your progress:bigsmile:

    What is your web site address?
    • CommentAuthorStuartB
    • CommentTimeJan 15th 2008
     
    zenbiscuit - What is MDPE? - not on list of abbreviations.
    • CommentAuthorzenbiscuit
    • CommentTimeJan 15th 2008
     
    Thanks Jeff some of what I did was also influenced by the floorstore link that you posted. I think that if I did this again I'd save money and follow the floorstore model placing the Summer heating piping below the hardcore and slab and not dig so deep.

    I've placed some piping into the heat pit which extends upwards to floor level that'll allow me to measure the temperature so I'll be posting the changes on my site over a 3 year period to see if it works for me.

    I haven't got anything on the web yet, I'm working two jobs to pay for things as well as doing some of the building work myself. I've just thought that I'll address the page http://dev-software.co.uk/ass/ ;-) so I'll re-post the link when I finally get something up.

    StuartB - MDPE = Medium density polyethylene, basically modern water pipe, type MDPE into http://www.wikipedia.com/. Not great on thermal conductivity but I've hopefully got enough buried in the garden pit for it to release it into the soil before it returns to the solar panel. I've got a temperature pipe for a probe here as well. Anyway, if it isn't dumping the thermal load I'll put a zone valve on it so that I can direct it into the bermer beds against the extension wall and use some old radiators to dump into this soil.
    • CommentAuthorfastfilly
    • CommentTimeJul 20th 2008
     
    hello Jeff from NZ We are building an earth house using the PAHS system. is there any one in NZ that has done one? Would love to chat with you about solar, and other topics. where abouts in nz are you? We are in north otago
    •  
      CommentAuthorfostertom
    • CommentTimeJul 21st 2008
     
    Have you seen this? http://www.greenershelter.org/index.php?pg=2

    PAHS results in rather large interior temp swings - 17oc in winter to 24oC in summer - it's inevitable when relying on purist passive means to transfer heat from the interior into the heat store in summer, and to retrieve heat from the heat store into the interior in winter. Heat doesn't flow unless there's a decent temp differential.

    That's part of why Don Stevens evolved PAHS into his AGS method: http://www.greenershelter.org/TokyoPaper.pdf

    Very good luck!
  24.  
    Posted By: fastfillyhello Jeff from NZ We are building an earth house using the PAHS system. is there any one in NZ that has done one? Would love to chat with you about solar, and other topics. where abouts in nz are you? We are in north otago


    Great to hear fastfilly, I am now in Christchurch not to far away!
    I would be interested in your progress, I can be contacted through my web site www.greentech.co.nz
    Jeff
    • CommentAuthorraw1943
    • CommentTimeJul 28th 2008
     
    "PAHS results in rather large interior temp swings"

    This is a misleading and incorrect statement. The temperature swings will be much smaller if a buildings has a sufficient amount of thermal mass and winter solar heat gain, such as in an uninsulated subterranean structure composed of reinforced concrete. Stephens is referring to the problems encountered when using unforced air movement in buildings that contain smaller amounts of thermal mass, such as when assembled from straw bales or rice hulls. Hait's PAHS design will transfer a large amount of heat directly to/from the surrounding insulated and dry soil by conduction, twenty-four hours a day, every day of the year, independent of convection, and it will transfer a large amount of additional heat by convection/conduction through a set of earth tubes in response to changing temperature differentials. A well designed PAHS uninsulated subterranean home constructed of reinforced concrete and with 1-2 m of earth overhead and protected by a waterproof insulated umbrella may experience an annual temperature fluctuation of no more than 3-5°C.

    I am in the process of designing a PAHS house based on Hait's book and concepts. I plan to have it built by Davis Caves, which has some experience building PAHS structures. http://www.daviscaves.com/index.shtml I would be happy to discuss design, analysis, and construction details with anyone who is designing, building, or has already built and is lining in such a structure. Unfortunately there isn't much information available on PAHS performance in various climates around the world.
    • CommentAuthorjon
    • CommentTimeJul 28th 2008
     
    "Unfortunately there isn't much information available on PAHS performance in various climates around the world."

    Depends what you are planning to build: For some types (particularly buried or semi-buried), there are large amounts of information: What are you planning to build Roger?
    • CommentAuthorraw1943
    • CommentTimeJul 28th 2008
     
    First, I'm planning to build in central Illinois, USA. The region has an average annual temperature in the middle 50° F (9° C) range. Temps rarely exceed 90° F (32° C) or fall below 0° F (-18° C). Humidity can be uncomfortable about half of July and August. http://www.city-data.com/city/Peoria-Illinois.html

    I'm planning to build a rectangular 34 x 75 foot (10.4 x 22.9 m) subterranean house into a southeast facing hill with roughly a 20% slope. The south-facing side of the house will be 15° east of south, so its long side will be about 30° off the hill's contour lines. Thus the northwest corner will protrude farther into the hillside than the northeast corner. The south and east walls will be exposed. The south-facing wall will be 11 feet (3.4 m) high and the north facing wall 8 feet (2.4 m) high. South and east windows will equal about 20% of floor space. This would be too much solar gain without the massive amount of 1.0 foot (0.3 m) thick reinforced concrete roof, and north and west walls, along with a tiled reinforced concrete floor. And the large amount of dry soil directly adjacent to the roof, walls, and floor will also help moderate temperature swings, along with the earth tubes. Sunshine is a little below national average but it isn't too bad.

    My biggest issue right now is the best way to arrange the eight 4-inch (10 cm) diameter earth tubes to get the best heat transfer to/from the house and surrounding insulated earth. Space is not an issue. The soil is clay and the walls will be backfilled with gravel. The footings will be well drained. Controlling subsoil moisture should not be an issue if the umbrella is carefully constructed following Hait's instructions. Comments from folks with experience installing earth tubes and constructing Hait's insulating umbrella would be helpful.
    • CommentAuthorjon
    • CommentTimeJul 28th 2008
     
    Sounds like a fairly standard semi-subterranean house. As you've noted, drainage could well cause a problem (of the Mohr slip type) if not performed adequately. I'm not sure that I would rely on a book to evaluate this unless you are completely sure of the soil characteristics.

    Good luck with it and let us know how you get on. If you have similar constructions in Illinois, might be worth a visit to get an idea of real living conditions.
    • CommentAuthormike7
    • CommentTimeJul 29th 2008
     
    If it's any help this source http://www.sbc.nrcan.gc.ca/software_and_tools/gs2000_e.asp (thanks to Paul in Montreal) gives useful information on diffusivity etc for different soil types and dampness. (It may well be a lot easier these days, but when I was looking at this sort of issue n years ago, data on soil properties was hard to find.)
    • CommentAuthorwelshboy
    • CommentTimeJul 29th 2008
     
    Hi raw1943,
    I don't know if this helps but the principle seems similiar to what you are going to do.
    http://www.ces.purdue.edu/extmedia/AE/AE-99.html Figure 9 about halfway through shows a diagram together with a description of transferring heat to a storage area using drainage tubes and getting it out again using drainage tubes

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