Interseasonal Store

[dhaslam]

At last starting to make some progress.

The straw arrived on Saturday.   100 bales in the car port for wrapping and the other 300 in  a covered stack.   The silage pit cover  will be used to cover the finished mound.    The solar panels are stacked up waiting for the Correx  sheets to arrive.     The 100mm sewer pipes are for the air feed to the Correx sheets and the 150mm ones to  hold the  four lengths of 22mm pipe bringing hot water back to the house, they just about fit with  two layers of pipe insulation on each.    The  heat transfer will be into  two 150 metre coils of  38mm hydrodare.   The inner one is intended for direct transfer to the  buffer tank and the outer one to preheat the  ASHP.   

Each collector will heat its own layer  with the  outer ones heating the top and bottom layers.   There will be one 60watt fan for each collector  and each one will have its own thermostat for flow temperature and  one wire  sensor for the core temperature.     The fans will probably be set  for about 10 degrees above the core temperature for it's respective layer but this may need to be adjusted.  If the temperature differential is too low the  heat gain may not  be much more than the electricity used and  if it is too high the fans may not come on very often.  There is no need to be interactive  because the temperature will change very slowly.


Should be ready to work by the end of the week. 

[desperate]

DHaslam, 

very impressive undertaking there, keep us informed of progress and eventually performance. This is the type of project I would love to be able to carry out, there is vast potential in such a system if it were to be incorporated into newbuilds in a holistic way.

My back aches just looking at that huge pile of gear you have there.

Good luck

Desperate

[billi]

... nice  and i am looking forward 

 Is the subsoil called " Blue till" as well like here in West cork ? and will you compact it ?

Pity  you are  so far away from me and my digger 

how much are straw bales  atm ?

Billi

[Fiddlers]

I'm intrigued and missed previous discussions on this one... any chance you could recap the basic design? capacity? I presume you're using water as the storage medium? looks like a great experiment!

[dhaslam]

The  ground is a bit unusual, there are successive layers of limestone   separated by heavy subsoil.      The lower layers are  harder to break up  so the test hole was  done just to see  how far the JCB could go.  It is probably  sufficient to go down three bales deep, just over a metre.   The circle is nine metres at present.   There will be six bales above ground but above ground they will be stepped gradually so the volume will be about 180  cubic metres.    This is roughly the equivalent of 45,000 litres of water.    There will be a lot of rock  which helps heat storage  capacity  and will help prevent compaction.      The greenhouse  job done earlier this year  had 2.5 metre deep  heat store  filled in by hand  and it didn't compact noticeably.       Bales are  €2 at present  plus delivery.   The bales offered for sale are loosely packed  which seems to be  OK for insulation purposes.     

The concept is probably a little different than most seasonal stores.      Hot air is used as to heat the store.  Air is more manageable than water, no problems with  freezing and boiling and quite easy to collect the heat.  But since air stores something like 3000 times less heat than water, by volume,   it is hard to transfer the heat except for very short distances.   Consequently water pipes are used to transfer the heat from the store to the house and a heat exchanger used to transfer  heat back to air to preheat the  ASHP.      It does mean a lot of pipes and plumbing fittings with effectively two systems  but the hot air collectors are very inexpensive  and seem to be more efficient than low grade  hot water collectors.   

May be able to test run a  collector in the few days.   

[dhaslam]

Finally got a  one of the collectors working.   Hans who is doing most of the work picked up flu last week, possibly from adverse working conditions in a draughty carport.     

The  panels are very heavy when everything is fitted.   and it meant using the  car trailer with the sides off to move one.   It is leaning  on a pile of sand at slightly too low angle.   After running continuously for quite a while the output temperature built up to  over 60C with input air of about  40C less.     It sound an feels like a giant hair drier.    The  face of the panel stays quite cool and all the heat is  inside the  6mm square channels.  Even with the fan off there is a strong flow  of hot air.   Assuming that the fan is putting out close to its maximum   of 280 cu metres/hour it is producing about 3kW,  in October broken sunshine.     In comparison the Navitron panels of similar area output  16 kWh for the day.    Even in  overcast conditions  with the sun just visible through the clouds the output temperature was in the high 30sC.   

It looks like the fans will have to be moved to   the input side  of the panel next summer because they probably couldn't take the full summer heat  directly  from the panel.     The thermostats will have to be moved away from the fans   to a separate position on the output side.  They should be OK for the winter but the temperature drop when running the fan is much less than expected.     

The fan is  causing the plastic cover to sag due to some small gaps between the 4" pipe  and the Corex sheets.   The next ones have three supports for the cover and also may have a bit less air leak.  The first one had one pipes cut with a jigsaw  and the second with a router, both were a bit uneven so the Corex sheets weren't a tight fit.      The next one was cut with a skilsaw and  a guide running along the side of the frame.  This made a very even cut.   
   

The store is due to be constructed tomorrow, weather is supposed to be the same as today, sunny in the morning and then showers.    I will probably set up the panels that are made  so that there is some  feedback on the temperature  rise before completing the others.   

[biff]

hi dhaslam,
        really good thread,and i am looking forward to seeing more of this solar project,
                                  biff

[dhaslam]

Some progress today but only up to ground level  so far.   One layer of pipes  installed.   It is surprising how difficult it is to handle  150 metres of 1.5" hydrodare.    It may be possible to finish the store tomorrow  but each layer of fill is taking quite a long time  and the fill needs to be on both sides of the bales to avoid pushing them out.       

[djh]

Do you have any photos showing how the bales are arranged and filled around?

[dhaslam]

Do you have any photos showing how the bales are arranged and filled around?

The bales are wrapped for the first three rows.  The two lower rows are wrapped in  heavier  plastic, the row just visible  is mostly out of the ground om one side because of the ground level being lower.    I have decided to  reduce the numbetr of rows of bales to  seven in total, one more row than is visible in this photograph and to dome the clay in the centre and the covering bales will then be  on a slight slope.   

chargingtheearth

There was a bit of constructive criticism previously,  relating to using bales underground.   The main precautions taken since then  are wrapping the bales  underground and putting in a drainage pipe all around the mound.   Inevitably there is always going to be some  constructive criticism  but the valuable benefit from  any forum is the expansion of ideas.     
The heat loss from the mound will be quite  large and that will  be known reasonably soon by plotting the daily temperatures, probably just morning and evening.I am hoping that  the large area of solar collector will make up for the heat loss but  if temperatures are not very high at will at least achieve its initial function of pre heating the ASHP as well as supply some underfloor heating. 

         

[guydewdney]

When I have seen straw bale houses done - they are very careful to close up any small gaps between bales - could you not do the same - or are you planning to fill the gaps with expandy foam or something?

[dhaslam]

Just broke up a few bales  to pack the bigger gaps.     It won't be that much of  a problem because there will be  several feet of clay outside the bales.   

[djh]

The bales are wrapped for the first three rows.  The two lower rows are wrapped in  heavier  plastic,

Thanks very much for the piccy. It looks like the bales might be wrapped individually; is that the case or is the whole wall wrapped as one?

There was a bit of constructive criticism previously,  relating to using bales underground.

That's a very generous description, thanks!

I have to say that I still think they're likely to rot, but full marks to you for actually getting out there and trying it.

I'd suggest sticking a few moisture meters in there. In the middle of the bales, towards the bottom. I suspect you can just push a rod/pipe through the bales to get them in. I think the easiest type is a block of wood a couple of inches long, with wires trapped under stainless steel screws in the wood. Then connect the other end of the wires to a regular pin-type wood moisture meter whenever you want to take a reading.

Edit: I forgot to mention that it needs to be electrically isolated from the straw. So either silicone seal over the screws or put the whole piece of wood inside a perforated box or length of tube.

[dhaslam]

The bales are individually wrapped up to ground level and the ones above ground will just have an  overall cover  over the top.     At present I am a bit more concerned about the unwrapped ones because they will absorb  trapped moisture from the clay.    I need to measure the moisture content of the  return air from the  mound and see if the humidity is  reducing.   If not I can  reduce moisture  by leaving the return pipes open to the air for a few hot days next summer.   The  input from the five  collectors may be as 25 kW on a very hot day in summer and the pipes are perforated drainage pipes.        This would also help  dry out the soil   below  ground level where the wrapped bales are.     Storage capacity would be higher  if the soil is moist  but insulation and preservation of the straw would be better  if the soil is dry.         

[dhaslam]

Finally got the  panels mounted on Thursday last and the  first panels  heating on Friday and the next two nos two and three numbered from east to west and from lowest to highest.

Oddly enough it seems to have slowed the rate  of heating instead of speeding it up.   The initial heat may be from settling of the clay.     There was very good sun on Saturday with temperatures  reaching over 70C  but the return air to the panels didn't go over 17C  so the  heat is being dissipated very quickly, probably before reaching the core where the sensors are at each level.       The  pipes  are not fully insulated before going into the mound so some heat is being lost outside the insulation layer.     Unfortunately these pipes cannot be dug out until the  clay binds on the sides, otherwise it would just move down and fill the space dug out.   It will need to be done before next summer.       

For this winter  the  system will only be used to preheat the heat pump input and this cannot be connected yet because a  drain has to be  made all around the mound to take away the rain water.      The present temperature  is probably enough to  warm the air  if it holds at this  through the winter.