Friday, May 28, 2010

Cold days boost the power! Less from the Grid....

28 May 2010: The changing weather that has given us a couple of cold days, with some sunshine, which proves my earlier point about PV operating worse when it is hot. 27 May, I kept my pullover on all day, and never felt too hot, but I got home and was astonished to see a score of over 23 kWh for the day on the PV. Today is also cool with sunshine and we seemed set for another high score - nearly 25 kWh!
    This morning, we had the Heat pump (heating and hot water), Washing machine and Dishwasher all running at the same time, and the entire load was still more than met by the more than 3 kW that the roof was providing - no power imported from the Grid. We have adapted lifestyle to run more things in daytime, especially on sunny days.
   It is ironic that we both have shares in the National Grid, and as there is a share issue, we actually bought more shares yesterday (posted the forms today) and yet, I am trying every way possible to reduce the import from the Grid. But if there was no Grid, I would have nowhere to post all our surplus electrical power back to!
   We also have shares in Good Energy, which is another reason why we are committed to staying with them, no matter how many telesales callers and bargain deals websites offer us deals to switch.

Wednesday, May 26, 2010

Could Augmentation of GSHP be incentivised?

26 May : Feed in Tariffs apply, or will apply to Sustainable Energy Technologies, not only for microgeneration.  GSHPs are included in the tariff but it is not clear how payments are assessed - based on a notional assessment of the house size, insulation, heating load, heat source etc.  I presume that only accredited contractors can assess this. This may be one reason why I was told yesterday that the new Govt will tighten up the rules about who can be accredited, which will be bad news for small installers and startup companies. So much for the 'Small Business' sector!

With the feed in tariff applying to so many categories, there is now the question of the best value for money of public funds - GSHPs are all very well, but they should they also be eligible for an augmented tariff if they are augmented in their performance - in the way that the congestion charge in London does not apply to electric, hybrid or LPG cars, it is a way of using tax rules to become an incentive. Perhaps the tariff should not available to GSHPs unless they are augmented! 
     There are similar rules that used to apply to the Low Carbon Grants, the house had to be already insulated etc. Although this was based on self certification, and nobody checked.
     Of course, someone might just take the augmentation subsidy and leave the panels turned off (although why turn off something that saves you money?) They could do the same, by having a heatpump in the house, turned off, and heat the house with patio heaters... are there such people? I guess not. If you have spent what a heatpump costs, you do not want to leave it idle.

For Sunboxes to be accredited for F.i.T. they would have to be made by a sizeable company, and sold through the accredited network, eg by outfits like EvoEnergy and Ice Energy. Their standard of performance would have to be proven, and it is a pity that it takes a winter or two winters to fully prove them. I want to get these onto buildings by 2016!

The only way to calculated the F.i.T. seems to be some sort of algorithm based on the theoretical capacity of the ground, the operating specification of the pump, the heating load of the house, based on size, age, occupancy, etc. (This is how the GSHP F.I.T will be calculated anyway.) The smaller the consumption in meter readings, the more the reward! perhaps .... someone could work that out. For me, and for many others who like to see mechanisms finely tuned, I would not need the incentive of an F.i.T. on the GSHP, and not on the Sunboxes. Although I would be happy to see reduced bills, I am not doing it just to scrape a few pence off (the payback is too long for that), but to see the system operating efficiently, with less energy consumption.

Tuesday, May 25, 2010

Larger Sunbox for MVHR

25 May : Having thought about this more, I could build the Heat Reclaim unit (MVHR) in the loft first with the air intake in the centre position between the present sunboxes, just below the glycol pipes.

This would be the right position for a later project to develop a tall centre sunbox with a ground level air intake, to use the 'stack effect' to help drive warm air to the intake. Taking this idea even further, the air intake could be moved to below ground, drawing air from pipes underground, for winter. The polycarbonate here could be double or triple skinned, to gain but not lose heat as it rises... or perhaps remain clear, because the rate of flow is too fast for significant heatloss.

The earlier idea, of a 1.3m wide sunbox, would need to evacuate this box twice a minute to maintain 0.6 ac inside the house. One that is 2.4 wide, covering the two small windows, would only require one evacuation per minute. During summer the polycarbonate in these can either be lifted off, or slid back.... Hmmm... I prefer to keep it to the smaller size.

This all takes time to think out and is a more radical intervention on the house, so needs to be done gradually. First an MVHR with intake on the south side....

This is becoming a bit like the Solarventi that my friend Karina has, although this is on a larger scale!
If the Solarventi can push through a good volume of air with such small boxes, perhaps the 1.3 m wide one would be enough. The Solarventi SV30 claims a throughput of 120m3 per hour, just right for the number of airchanges we need.
Hmmm..... something to think about.

25 May PS: Had a chat with my professor and he is strongly against MVHR, mainly because very few houses in the UK are airtight enough for it to really count.  If it is left on all year (it may need to be because the law requires that extract required for toilets) then it is quite an overhead if you haven't got PV to pay for the electricity. In our house, we would have it off from April to October, and just use the existing extractor fan. But it's an expensive bit of kit to use only from October to April. errr... however... our house is recently built, and a lot more airtight than most British houses. We could have an air leakage test done on it. The point about it being parasitic on the power supply for 6 months of the year is also worth considering.
   I also had a phone call with SolarVenti. I am interested that their units are only 100mm deep, but the 3m x 1m unit (SV30) can still channel up to 120 cu.m/hr into the house - so perhaps my proposed 5m high x 1.3m wide unit isn't so weird if I do it at all.
  Had a chat on the phone with David Atkins, and discussed the idea (above) added to which could be the idea of charging the ground under the air pipes, using the Sunbox mark 2.

Temperature reducing the PV harvest: proof

24 May: EvoEnergy rang me today because some of their customers are confused by seeing their PV harvest not being as good as expected in this hot spell. They are grateful that they can direct customers to look at my Sunny Web box output, and see how temperature affects PV.
In this chart (from Sunny Portal) you can see 3 days of generation, plus the last month of generation, set against the red line for max daily Module temperature, that is, the surface of the panels.
   The best ever day was May 11th, but you can see that the temperature was particularly low, compared with the 2 weeks after that date - when it has been a lot sunnier, but also much hotter on the surface and in the air. The red line dips at the end, because I screen-captured it at 1 in the morning, so it is suddenly dipped.) In recent days of high sunshine, we have had surface temperatures touching 50ºC, on the East roof!
   I am not expecting it to get more than 24 kWh in a single day in June unless we get another strong north wind combined with clear skies. But if there are lots of 20-22 kWh days, I will be happy!

Monday, May 24, 2010

Hot days, Pyranometer and Joel

23 May : It really feels like summer now. Our Sunboxes recorded the highest ever delivery today of over 20 kWh, and the PV was over that amount. Blaise called in the evening, downloading the datalogger readings, and bringing the Pyranometer again for me to fix up in daylight.

I will get up there in a ladder, the first time I have had to do this. I have to find a way to bring the datalogging wire into the house... :( Its probably easiest to push a drawstring through the electrics pipe and pull the cable through than to push from outside, even on a ladder.

My dissertation student, Joel, is handing in tomorrow. He seems to have grasped enough of the subject to do a reasonable write up in such a short time. Let's hope so.

24 May: Postscript : the Pyranometer is up, and as it's a temporary installation, it is simply led through an ajar window, and down to the datalogger. It was easy to climb a ladder and tie it with rope to the sunbox gutter pipe.
    Normally, a pyranometer would be level, measuring the dome of the sky, but here it is hung vertically, measuring the curvature of the sun's progress through the sky, facing due south.

Sunday, May 23, 2010

MVHR on the horizon, and under the ground?

23 May: I am now seriously researching and considering design ideas for an Mechanically Ventilated Heat Recovery (MVHR) system, perhaps using future Sunboxes as a inlet route, and perhaps combined with Ground-Air exchange. The ground pipes for the air inlet could be done along the gravel path to the south of the house. Easy to dig and lay pipes in.  The reason for this is that in a very well insulated house, the heat loss through ventilation can be double that lost through the fabric, as in the Peveril Solar house.

I don't think a 200mm deep Sunbox on its own could provide enough if you are trying to get 0.6 ac/hour into a 285 cu.m house. There is sunshine in the winter months, and a vertical sunbox picks up a surprising amount - well, I was surprised how well mine did during March. But a 200mm deep sunbox, 1.25m x 5m high would have a volume of only 1.25 cu.m, which means that to provide 0.6 ac/hr to the house, it has to be exhausted of air more than twice a minute (136 times per hour). During the Winter, it could hardly contribute much, although during the Summer, a louvre could be opened for it to give all its heat to the Ground loop sunboxes. (All these louvres could be operated from the bedroom windows.) Any microclimate creator is worth having, but is it worth the cost of the scaffolding, polycarbonate and aluminium?
     I would be prepared to try it as a research project - one of my great interests already is the 'Double Skin Facade' and a long time ago, I had thoughts of converting this south facade to glass.

The Savita Sunbox could be redeployed to pump liquid heat into the zone around a Ground-Air exchange pipe, with circulating pipes buried below the large diameter pipes - instead of being added to the GSHP ground loop. Even at only 1.5m depth, there is considerable temperature stability - and on the South side of the house, it is getting free underground heat from the field behind. And the heat coming up from the ground could pass through a Sunbox on its way up to the duct into the house.
   I must check out the ReHau site as that may be a source of info. I went to a Rehau lecture a while back, and they seem to be the experts on Ground-Air exchange. Their site mentions the AWADUKT system, although most of it could be done with conventional drainpipes.
   Now I know a lot more than I did a year ago about valves and relays, and programmable thermostats, and 'difficult' plumbing, so many more things become thinkable... and then perhaps possible.
    The pipes would all have to run upwards in an external duct, as I don't want to drill much more in our house interior.

Should I tell Mrs NC about these ideas yet? (the cost is met from my 'Aunt' research fund, but the noise of me drilling, sawing and swearing has to be suffered by her.)

Heat restrains PV harvest

23 May : The photovoltaic harvest is very good at the moment, we are ahead of the expectation calculated by the JRC PVGIS site. I notice that although the sun is getting higher in the sky and showing for longer periods, our best score is still no more than about 22-23 kWh per day.
    The common view is that PV performance declines if the panel surface gets hot - this seems to be true! Today for example, our mini weather station which records surface temperatures has gone right off the scale - way above 40º, with air temps touching 30º in mid afternoon! For the first time.

I am guessing that the PVGIS might have a compensation factor for just this, as it shows June's harvest prediction to be poorer than May or July. How can that be?

Our best ever day was May 11 with over 24 kWh, but that day was notable for having cold temperatures (North Wind). I am not complaining, as it is only the 23rd May and we have already reached the PVGIS expectation for May. But the 'competitive' in me would still like to do better in June and July.
    Meanwhile today, we have burst through the 1600 kWh barrier at a gallop (this is for 'annual PV generation') That puts us well more than half way to our target of 2800, and with the rest of May, June, July, August and September (to meet our PV-Anniversary of October 1, we look easily positioned to get past 3000.

When the long months of winter come, and I have the depressing sight of the PV getting worse again day by day, I shall be compensated by the interest provided for me in the experiment to charge the ground below with hundreds of summer time kilowatt hours of solar heat, to see how the heatpump fares with next winter's heating loads.

Saturday, May 22, 2010

Short term Cooling balanced by Short term Warming

22 May : Watching it today, I realised that there is nothing much to worry about here. The 6 deg and 21º regime is working fine. And I see that the short term cooling is balanced out by short term warming.
      I watched it today and in steady state, it was circulating at 30 watts (6 L/min), lazily trickling heat down at about 20ºC when sunboxes were about 40º-42º. When the heatpump came on for a heating cycle (to do hotwater) there are suddenly 2 pumps working, and 230 watts of power flush all that warm glycol down to the earth before the cold comes through. So the earth below gets this sudden rush of 20º glycol at about 18 litres/min, giving it a quick surge of warmth just as it is required to return this warmth back up to the GSHP. So no time for the warmth to escape to the clay, it comes back up and helps the GSHP.

The number of litres in this 2 minute short term heating gain is equal to the litres in the post-heating 10 min period. As the heat gain near enough balances the heat loss, I shall no longer worry about this short cooling period, and I did record an example of figures either side, which I will post later in the form of a Table.

Postscript: Blaise emailed me in reply to this, and agreed that the datalogger shows that for a short while there is a beneficial 'blip' whereby the COP briefly appears to rise to 6 or 7, when the warm glycol in the Sunboxes suddenly rushes through the GSHP at 18 lit/minute.

Friday, May 21, 2010

Short term Cooling effect from Sunbox

21 May : Since the diverter valve was fitted, I noticed that there is sometimes a short term cooling effect, only after a GSHP heating cycle. Blaise has noticed this in the datalogging record. I have noticed it at exactly the times he sees it on the datalogger – after the morning warm up of hot water 9-11 and in the evening when a bit of heating or hot water is needed again. He suggests raising the Delta-T or the operating temperature that triggers the thermostat.
    When the GSHP ceases a heating cycle, there is a short time (about 10 mins) when the loft pump has to flush the cold glycol that was still in the pipes through the panels. The slow pump is working at about 360 litres per hour, so as the panels and pipes are equiv to about 60 litres, that takes 10 mins or so. In the meanwhile, it is using warmer glycol that was coming up from the ground to push the glycol through. If there is enough delta-T it continues to pull slightly warmer glycol up from the ground loop until the temperatures balance out. If after ten mins, the warmer glycol reduces the delta-T, the loft pump goes to sleep. If there is a valid Delta-T, the glycol going round is still being warmed so this short 10 min flush-out it is not really cooling the ground. 
   This process doesn’t take longer than 10 mins, I let it happen – as it balances out fully later in the day when more real heat is put down. Overall, it is not a loss.I really do trust the thermostat, it has shown itself to be pretty reliable in the two months since mid March.
   I can avoid this by having a higher delta-T than five degs, or by having a higher SB temperature (more than 20ºC). I think in winter this cooling is an overhead that is not too serious because I haven't seen it happen until the weather got warmer – it seems more of a summer problem. Or perhaps, more likely, it is after I put in the diverter valve that moves All the glycol through the boxes when the Thermostat says Yes.

During the summer, I might stop Night time circulation (by raising both those numbers as per Blaise's Suggestion) to reduce pump consumption when sun is not shining and no PV power for the pump. I no longer want the pump to run through the night based on ambient night time warm air, as the 30W pump energy consumption would eliminate the benefit of the energy gained. During the sunny time this morning, the Sunboxes were at air temp of 40 degrees, even with cooling glycol running through them, this is good heat!
So for tomorow, I will try a delta-T of 6 and a Sunbox T of 21.... and do some weekend 'watching', to see how it goes.

Charging up a Finite Mass in a closed box

21 May: At the moment, we heat the house from, and solar charge to an infinite mass, although the volume we are influencing and influenced by is about the 3,600 cubic metres, as previously stated.
   If you put all the earth into a completely insulated box, there is no chance to recharge it randomly from the surrounding earth as we now enjoy - you would have to have a mathematically perfect balance, year after year.
  The solar charging pond at Beaufort has an uninsulated bottom precisely so that excess heat or excess chill can be balanced out with the surrounding earth. If it reaches either extreme, the delta-T is such that the earth around will rush in to balance things out.
  If you have a closed container, the temperature must not raise higher than the heat source. i.e. if we had a volume of earth equivalent to say, our garage, and that had to rise to 150 degrees C to have enough capacity to heat the house all year, that is not practical, we cannot heat higher than about 40-50 with high performance solar panels.
  The way the house works is continuous trickle of heat in and out, but with more taken out in winter, and more put in in during summer. Over the year this must balance. The proportion of heat that the GSHP must find 9800 kWh from the earth annually to meet our requirements (see earlier article) averages at 27 kWh per day, with a peak during January of 55 kWh per day.
   We have yet to know what the Sunboxes will put down at their peak, in July, but during May we are getting double figures nearly every day. If the average is 9 kWh per day (3300 kWh per annum) that means we put down 3300 and get up 9800 kWh - the earth has to provide the balance.
  This suggests that simply having 3 times the area of Sunbox would make a perfect balance. But it's not only quantity that counts, it is delta-T that also counts. If the Sunboxes only send a max of 17-18 deg C down below, that would be the warmest it would get - it would reach stasis. 18 would not be enough to get through the winter, from a Closed heat source.

If you want a closed box to work all year, you could put glycol down from a pro-quality flat plate panel that gets to higher temperatures (for fewer hours per year). I estimated that if 37degs would be an ideal maximum temperature (same as Blood temperature) and you heated the house all year from that, and permitted it to drop to zero, the volume of clay would be about the same as the house interior - 260 cu.m. The reality is that we are trickle charging, so we never need to rise to 37 or to drop to 0.
    Panels accumulating the equivalent of 27 kWh/day would exactly meet the heating demand of the house. But for this to work they would need to have a high peak in July, perhaps double the average, same as the 55 kWh/day that the GSHP must draw in January. How could one put up panels or sunboxes able to absorb and bury 55 kWhr per day when the ones I have now average at 10 ? Five times the area is not possible, there is not enough wall.

So, I am suggesting:
  • One could have a caisson type foundation under the footprint of the house, with polystyrene-concrete (Becoform-type polystyrene concrete formwork, such as we have in some of the Uni of Nottingham Ecohouses) as a basement wall, 
  • The depth could go down 3-4 m, and be backfilled, have a suspended concrete floor above this (to avoid settlement), 
  • Have an earth bottom (to allow natural earth heat to balance out excess), and 
  • Add to the backfill a 3D grid of Pipemesh for the solar and GSHP ground loop.
  • Have insulation over the earth store so that the house doesnt feel uncomfortably hot when the store builds up.
  • Have high performance solar panels injecting heat (not sunboxes)
  • Use sunboxes on spare remaining facade, for winter MVHR with their function changed to augmenting the solar charging during the summer months.
This is expensive compared with a borehole, and if you are going to the cost of making a sort of basement, it would be nicer to have one that could contain tanks and storage. Building a vast water tank under the house (much better heat distribution) is expensive as it would have to be filled and watertight. And one has the extra cost or making much of the facade and roof into solar panels.
 Therefore our present arrangement of deep boreholes and sunbox augmentation seems pretty good as a working compromise..... :)

Rethinking the theoretical borehole

21 May : I have recalculated the volume and mass of the borehole, to make more sense. 

The distance that heat travels depends on the delta T. We now know that we can't raise the temperature massively, we are there to reduce chilling. Therefore the delta T between our pipes and the broad earth mass around will be smaller. I have reconfigured the theoretical radius of the boreholes from 5 metres to 3.6. It might be less than that, even. 
   Both David Atkins agrees that the amount of soil that we are affecting is a lot smaller, diurnally, perhaps only a metre around the pipes (before it smooths out), but the Annual thermal store for the GSHP serving the entire house (in the absense of sunboxes) is likely to be more like 3.6 around. This accords with the figures I derived from reverse engineering the borehole calculation give in the VPW2100 website.
   It is all theoretical, but makes more sense. I am debating myself whether to go back and alter figures in the blog, or just make new entries, leaving the previous ones unchanged. handed in yet? I think I will change the Introduction and permanent documents, and leave the blog entries as they were. 

Changing the RANGE of the borehole bottleshape from 5 to 3.6 metre makes a change in the other numbers, it makes the volume to a rather neat 3,600 cubic metres (the numerical coincidence is just that!), and that makes the tonnage to 8000 metric tons. Thats a lot easier for thermal calcs, and a lot less discouraging.

On this basis, the thermal capacity of that mass is:
Q (heat required in kJ) = 0.92 x 8,000 x 1000 x 1 kJ for one degree
Q=7,352,000 kJ/K, which is equivalent of 2,042 kWh per degree change. 
That is a lot more realistic. Only 200 days of continuous Sunbox pumping (without pulling heat out) to raise it by one degree.

Thursday, May 20, 2010

More thoughts on Borehole or thermal store

20 May : Earlier, I wrote: "In the work by companies like ICAX, they use an entire large playground or carpark for heat collecting, but we are using a humble 1.1 cu m of Sunbox, and 4.2 sq m of black collector, so can only expect 2kW at best."

So if one built a full 'double skin facade' on the south wall, filled with black thermal collectors, how much more could one use this to heat the house? Judging by the earlier calculation, would it be any better than just 4 sqm? The existing boxes are doing a grand job of contributing to realtime/diurnial heating and at reasonable pump and material cost compared with the GSHP itself. Could 12 sqm do a better job? Could one also harness some MVHR to bring some of the heat in directly as warm air?

My feeling about this is that in its present form, the cost would outweigh the advantage because polycarbonate, metal and the plumbing costs rise, and the huge volume of uncontained deep soil remains unknown and would still dissipate the heat more than we could use. The glycol going through the panels would reach its optimum temperature earlier, and just go through the remaining panels without picking up any more heat - because it's the Delta-T that decides how much it will pick up.
    It now seems clearer that if one can work out a finite capacity for a fully insulated container that can be permitted to get hotter, there is a good possibility of relating heating demand to thermal store capacity. It has to be big enough to ride the highs and lows, just like water reservoirs have to be balanced with predicted rainfall. So such a store doesn't have to be big enough to store the entire annual heating demand exclusively -  perhaps only 6 or 3 or 1 month's worth, because it is being trickle charged every day. And one can tolerate a body of clay getting high the Summer and descending to single figures in the winter.
   I am quite excited at the possibility of calculating this, based on what I have learnt recently. Could it be cheaper than drilling deep boreholes. Could it just be in the foundation under the house? Does it have to be under the garden (would not need concrete if a box is formed in close fitting polystyrene). This comes full circle to my original conversation with Mike Siebert.
Let's look at this later on.

Earning overtakes Spending

19 May: On the Peveril Metering spreadsheet, I keep a track of the electricity cost and PV generating income since First of January 2010. The Feed in Tariff didn't come in till April 1st, but once it did the growth rate changed and the two columns were transformed. At £ 435 pounds, on May 19th, the Earning column overtook the Spending, galloping past it, with the summer to come, so consumption reducing and power generation increasing. There will be a closing up again as winter sets in, but no catching up!
  In 2011, the two horses will start more equally, with the Feed in tariff in place and the Sunboxes making their contribution to reduce the consumption.

Heatloss estimation and approx COP

19 May: I did a bit more calculation, to find out what is required to heat this house.
    This isn't as detailed as a SAP (Standard Assessment Procedure), but SAP is difficult to use when the scenario is made complex with a heatpump and underfloor heating, integrated water tank and sunboxes.
    This is using more old fashioned methods of just adding everything up, and multiplying out! - ignoring, of course, the PV roof and the effect of Sunboxes.... treating the house as just a house, not a weird research rig full of pipes and sensors!

Having worked out the heatloss, I then compared it with the electrical consumption for the previous 2 years, and came up with a very approximate COP over 2 full years from Aug 07 to Aug 09 = simply a ratio of the heat it is required to produce, compared with the electricity it actually consumed while doing it.
    This algorithm is now added to the Peveril Metering spreadsheet in case I want to elaborate it.

Future electricity calculations will be more complex, as the daily meter readings since Sept 2009 will be muddied by the fact that power is generated from the roof in daytime, and for certain periods in daytime, the meter stands still, even when appliance and the heatpump are on. We will have to apply the Feed in Tariff rule of approximately 50-50 ratio of power used in house and power sold to Grid.

Once you have insulated a house well, I now see how strong is the argument for MVHR (Heat Reclaim unit) to recycle the air. In this calculation, 4295 is through fabric losses, and 7345 through air replacement. I wish we had installed this during construction, as it so much more difficult to do later.

Wednesday, May 19, 2010

House-Heatpump Electricity Table

19 May : More about the long call with David Atkins. Over the coming year, with good records being maintained, we will have to chance to see actual electricity consumption compared with theoretical. The figures we have already are very encouraging.
Let's look at the house and heatpump more closely.

Last night, I came up with a figure of approx 14,500 kWh for the year for our house, based on some very rule of thumb calcs for UValues and Airchanges, floor space, volume and average fenestration.
    He ran the details of our house through the estimating web page provided by IVT (VPW2100) and I hope in future that I can have an access ID to use the same. I have found similar sites with 'VPW2100', eg the Bosch site, but it is entirely in Danish and much of it in Flash, so google can only translate the first page.
   For our house size and occupancy and location, David's software came up with an annual heating demand of 14,590 kWh. I am quite pleased at how close that is to my first estimate.
   14,590 kWh can be approximately divided into 11,600 kWh for space heating and 2990 kWh for domestic hot water (based on a predicted percentage split). That is still a long way lower than the average British gas heated medium size house of about 25,000 kWh.
  Of this 14,590 kWh, the predicted heatpump overhead is likely to be 4,800 kWh for pumping, compressor etc, and the expended heat goes into the house. Therefore, the amount extracted from the ground is expected to be 9790 kWh. The VPW page prints out a Histogram with monthly estimates. The table below starts in September 2009 when I put a meter onto the GSHP, and compares the predicted workload and performance for the GSHP compared with the actual. If these figures are to be believed, it seems that a very pessimistic expectation is made for the COP. We also have an extra overhead that during the winter, the underfloor heating system pump burns 125W all the time, also working through the GSHP's meter. This pump adds 60 kWh per month to the monthly figures, which makes our March and April figures look even better, as the theoretical figures predict the GSHP performance without the auxiliary pump.
We shall see after a year how all this pans out. Here's the table.

Monthly 'Expected' GSHP and PV Roof performance, against 'Actual',
balanced by contribution from Sunboxes. PV harvest indicates 'sunniness'.
Month  GSHP expect 
consume kWh
kWh expect
from Ground 
w/o aux
PV Roof PV
 Oct 09 259 530 221 190 170.6 166
 Nov 09 580 1284 405 345
109.3 81
 Dec 09 721 1548 681 621
64.4 49
 Jan 10 820 1730 797 737
57.3 70 Snow
 Feb 10 742 1558 750 690
122 Cold
 Mar 10 652 1423 513 453 227 281.3 217 SB start 7 Mar
 Apr 10 424 910 213 193 321 428.7  323 Sunny
 May 10 156 254 155 135 280 491.0 421 cold-sun-cold
 Jun 10 110 139 71 71 375 513.0 407 HW only
 Jul 10 110 139 45 45 315 432.6 427 HW only
 Aug 10 110 139 66 66 302 382.8 362 HW only
 Sept 10 110 139 100 90 280 278 263 HW + Heat
Our heatpump workload is generally lower than expected because we turn it off overnight, due to the good insulation of the house, and the wish to reduce floor circulating noise. The figure was higher in Feb due to the colder winter, and the GSHP sensors misbehaving and over using additional heat for some days. That has been fixed.

It is too early to be sure until more months elapse, but at first glance, the reduction in workload for the GSHP in April is quite stunning, it is less than half the expected amount. April was a sunny month. Then the first 2 weeks of May were surprisingly wintry, and the May GSHP consumption finished up as 155 kWh, about the same as the VPW prediction, because of the very cold start (and end) to the month.
I shall return to this article later when the monthly figures roll in.

Can we be sure of the Boreholes?

19 May : I am enjoying this deeper investigation into numbers, and wish I had done it before. I am particularly prone to work on the basis of enthusiasm and hope, and it can be healthy to do some numerical checks. Now that I have dissertation students working on it, we need more calculated numbers.

Had a long telephone call with David Atkins of Ice Energy, checking my sums for the borehole and for the house heat loss. It seems that the borehole estimate was about right - i.e. we should not expect the earth down there to rise noticeably in temperature, as a whole. We could not be sure if it had, unless we had some very accurate measuring equipment down there. There is a thermocouple down there, but I forget now how deep it is, and how well taped it was to the black borehole pipe.
    Any attempt to measure this (e.g. to find out if it takes 200 days to charge it up 1 degree) is complexified immediately by some significant variables:
• we are putting energy down there, daily, at amounts determined by the weather.
• we are getting getting energy back up, every day, dependent on the season and heating demand.
• the putting and getting of energy causes 'thermal rings' around the pipes and with two pipes, we have overlapping rings.
• we do not really know how large the 'effective radius' is - we estimate the 5 metres, but the immediately effective radius may only be 1.
• the 'bottles' are not contained in an insulated jacket - they are infinite.
• the soil below may be stratified - if there were some air pockets, or gravel layers, the calculation would change.

Diurnally, we observe that we are getting good performance from the immediate clay around the plastic pipes. Perhaps we should no longer measure the ground temperature in the evenings because it is too 'ringed' with cold and warm rings as a result of daytime charging and evening heating. We should do a Morning Ground test after it has spent a night resting, and not expect it to rise dramatically. Or, we could measure the ground at midnight, about 2 hrs after it is turned off for the night.
    It is written that the COP of the heatpump is estimated to rise 3% with every additional degree C in the warming medium - so if our heating and cooling is working to a more limited radius, eg one metre around the pipes, we are seeing that at least 5 degrees warmer than in March just before the sunboxes started work.

Joules, Watts, Kelvin, degree days and all

19 May : I have been trying to get to grips with some basic physics, to back up my ideas about Solar Geocharging.

The problem is that I haven't done it for a long time, and if you make one mistake (at one point you ask if something is watts, at another it is kW, or it is Seconds or Hours or Days we are talking about? Do we multiply or divide by 3600 or 24... ? and so on...)
I ought to get a fresh heatloss calculation done on the house to be sure of emissions, consumption etc. Let's start with the Borehole.

 As I see it, from my 3D model, there are 9700 cubic metres of Marl that our pipes can interact with. At density of 2200 kg / m3 that should be 20,000 metric tons (assuming that it is contained and not leaking.)
 If the thermal capacity of dense clay is 0.92 kJ/kg K then for ONE degree raise that should be:
Q (heat required in KJ) = 0.92 x 20,000 x 1000 x 1.... that would require 18,400,000 kJ

As Watts are Joules per second, we convert to hours by dividing by 3600, giving us 5,111 kWhrs !!
If our Sunboxes are putting down an average of 10-11 kWhr per day, that makes me think it would take 500 days to raise it by one degree, assuming no outward loss and no heat being pulled up? Seems like near infinity.... :(
If this is the case, then there is little hope of significant interseasonal storage from my humble little 4 sqm of sunbox, although it is already evident from what I observe that the heatpump is benefitting from Realtime and Diurnial warmth stored below in the clay immediately around the pipes. Can any of my readers help me here?

Like a Plugged in Laptop
It seems my earlier 'laptop' analogy fits here. You can run the laptop for a few hours, then you have to recharge. Like a laptop working with only its battery, the house draws energy from the ground all winter, and during the summer months, the ground is recharged by heat returning from the surrounding solar warmed earth.
But if you can work with your laptop plugged into the mains all the time on trickle, it will never overcharge the battery, but it will not run down either. Higher demand (e.g. in 3D rendering) drains the battery a bit, but continuous trickle charging brings it back up again.

Therefore it is becoming clearer:-
•••• Our ground is not likely to chill, but it will not get noticeably hotter. ••••
In the work by companies like ICAX, they use an entire playground or carpark for heat collecting, but we are using a humble 1.1 cu m of Sunbox, and 4.2 sq m of black collector, so can only expect 2kW at best.

Next task will be to do a heatloss calculation on the house...

PS Note that on 21 May, I have recalculated the 'Active Mass' of boreholes to have a radius of 3.6 metres, which gives a volume of 3,600 cu.m, a mass of 8,000 metric tons, and a Thermal capacity of 2,042 kWh/degree C, which would be a theoretical 200 days of charging to raise one degree.

Monday, May 17, 2010

Savita Panel unfurled

17 May : During the open day, I showed the visitors the Sunbox mark 2, otherwise called Savita panel. It is presently mounted on the Garage wall, just for display. There are interchangeable fronts, one is PV panel, the other is a millimetrically identical aluminium frame with clear 6mm polycarbonate at the front.
  I have now purchased many of the plumbing parts required to go ahead with this, ordered another Danfoss 3port valve today, and have other pipes and joints, ready to instal.

18 May : As time goes on, I think that I really want to compare the Savita and the Surya with the same operating conditions, i.e. both having a clear frontage. This would compare the performance of the metal and plastic collectors inside the volume. If this is to be a marketable product one day, the thermal performance is the prime question to answer. I can mount the PV panel separately to use it to power the pump

Thermostat + electric improvement

16 May : When David Atkins and Chris Wood visited on 5 May, there was a discussion about the thermostatic trigger for the sunbox pump - it has been using a delta-T of 5 degs C since soon after I worked out how to program the thermostat. So, for all this time the thermostat has turned on the solenoid valve, which has activated the pump in the loft.

We have one problem with that 'differential' setting. The sunboxes do not turn themselves on in the morning unless it gets really hot, early on, or unless we manually turn on the GSHP. If we left the GSHP on 24 hrs, this would not be a problem, but we are not willing to do this. Overnight, the Cold Pipe sensor rises to room temperature,  21ºC or 22ºC. So the Sunbox air sensor would have to rise to 26º or 27º to get started, but at 0900 or 0930 at any time before June, it is still something like 19º or 21º, so the sunbox system will not self start. The moment we turn on the GSHP in the morning, cold glycol flows down the pipe, and the sunboxes come on without hesitation. But we have lost an hour of possible morning charging by this time.

I woke up Sunday morning thinking about the Open Day, but also thinking about this problem. I know that the thermostat has TWO channels, i.e. can perform different actions based on data from the same two sensors. Currently one channel powers the pump, and the other channels set the neon lights and the relay. So I moved all those wires all to one channel, then programmed the spare channel to work on a single trigger Temperature, pure and simple. Then wired both channels to the pump so that either can set it running.

    From now on, if the Sunboxes get to 20º (regardless of what the cold pipe says) they will come on. Over time, I have discovered that the ground temperature never rises much, and certainly not past 15º, so it seems that 20º trigger temperature is a fair guess. In the evening I watched this working, and it is good. If there is the usual 5 degs difference it comes on, and when the temp rises above 20, it comes on...  it is Either-Or.
     An Amber light comes on to indicate 'Cold working' i.e. it is operating below 20º, driven only by temp difference. If both channels are OK, Amber goes off, and a single Green light shows. There is a Red light to show that the ground loop is being pumped, and I plan to add another Red neon to indicate that the underfloor heating circuit is running.

17 May : I swapped the purpose of the Amber light, so that when the sunboxes are working with a cold temperature (based solely on delta-T) only the Green light shows On, and Amber remains Off. When the sunboxes are working with an air temperature higher than 20ºC, the Amber light comes on to symbolize sunshine. Secondly, I have taken a wire from the underfloor heating pump to an additional red neon indicator, so we can see if that loop is circulating.
   I also installed a 2-way switch so that later, I shall be able to swap between the Surya and Savita with a simple touch of a switch.
  A tiny disadvantage of adding in the extra trigger (>20ºC) is that in summer, it will now start up before we even get up in the morning, so I may have some days of not knowing the time of start up on the Hour meter. For the same reason, the only time I can safely do a deep ground temperature measurement is about midnight, not in the morning when it may have had an hour of warming before I get up.

7 June : Two small changes recently (see later in the blog), I added a pushbutton switch that allows me to force the system on even when the thermostat says No! this allows me to read the digital clock. But also, it enables me to kickstart the system when there is warm glycol in the panels, but everytime warmed glycol rushes down from the sunboxes, it changes the delta-T and turns the sunboxes off again. To make the Delta-T less of a hindrance, I reduced it to 4 degsC.

Sunday, May 16, 2010

Open Day 16th May

16 May: For our part in the West Bridgford Transition/ Greening campaign Ecohouses Open day, (after Saturday's Summer Gathering), we had 13-14 visitors on Sunday, all seemed interested in the design ideas in the house, particularly how we enjoyed the PV roof (which all could use), and how we justified it economically.

   The ground source heatpump was of more academic interest because it's so difficult for most people to fit unless they are building new. Quite a few of the visitors were eco-renovating their houses in some way, one of whom seems definitely interested in a GSHP, and perhaps if I my experiment this coming summer and winter prove it will make it more efficient, a Sunbox addition. Actually, for a larger house, or a Victorian house with more heatloss, I feel that it is more strongly justified, providing you can find somewhere to put it, as the heatpump on its own is going to have a tough workload.

  I made a Powerpoint before the visitors arrived, and although this only got one showing, it is useful to have one now for future lectures on the topic of the GSHP and Sunboxes. I will try to make it available to readers here as a PDF on line.
  Tina Holt and Tim Saunders. joint organisers of the event joined the visitors. Let's hope the whole Transition adventure continues.

Datalogging proves it! and Summer Gathering

15 May: Blaise came and downloaded the last week's of data, with the sunboxes on for 3 days and off for three days. The results are very good - he seems now pretty well convinced about them.
(left, is our assistant datalogger).

Also, we had the Summer Gathering of West Bridgford - unfortunately I didnt get a photo. This was like a fair, in the West Bridgford Park, with stalls from all things like reflexology, to bric a brac stalls, but plenty of firms present showing sustainable technologies, including Evo Energy.  A few people signed up to come to the Peveril Solar house for the Open Day of 16th.

Friday, May 14, 2010

Open Day 16th May - visit the house!

14 May :  There is an Open Day in 16th May for ecohouses and other households using sustainable ideas in the district of West Bridgford, Nottingham. Ours is on the list to be open, although people have to book to visit the day before, at the Green Streets 'Summer Gathering 2010' festival in West Bridgford Park 15th May. Or they can book here and be put on the list.

I shall also have the Sunbox Mark 2 on display - if not on the wall, then it will be set up in the garden for discussion purposes. Lets hope it's a nice day, so that the Surya Sunboxes are performing to their best!

See the special West Bridgford Ecohouses website about the open day.
See also the article about the other WB ecohouses.

PS, as this date is now past, you can still visit the house, please email me directly for a suitable time. Evenings are OK.

Pyranometer for datalogging Sunboxes

14 May : Blaise has offered to install additional Datalogger instruments and channels. It's very important to have a comparison of the Sunboxes' energy output and the daily solar radiation, therefore he is planning to bring a Pyranometer on Saturday, so we could also record solar radiation. This will also help to compare results when the sunboxes are on and off for the same conditions (solar radiations and ambient air temperature). The sunboxes do not only work on direct sun light, they work in cloudy bright sky conditions. The air temperature in the sunboxes is influenced by the solar radiations.
Later, after sunset, the air in the sunboxes has residual heat released by the brick wall, solar heat that was absorbed earlier in the day - assisted by the absence of wind chill.

We already have a pyranometer on the roof, next to the PV panels, but their reading of air temperature is influenced by being attached to roof tiles (which stay hot after sunset for a while). The readings are broadcast live to the internet, via the SMA website. We now need on on the South wall.
The pyranometer was bought with part of his PhD fund for his experiments on Solar collectors. He will need it for his next experiment, which may be due in the next two or three weeks. So I better not drill permanent holes in the wall for this unless the holes can be re-used later.

20 May : PS We decided not to fit the Pyranometer because the one we have on the east roof is good enough for recording weather data. It is very expensive and could only be out for a short while and would require another hole in the wall.

More about sunspace - air flushing

14 May : Thinking more about the Sunbox versus bare Panel argument (12 May), I am thinking of yet another Plumbing Adventure..... (David Atkins is keen to see how the panels would work on their own.)
    It would be possible to reorganise pipes and valves so that when diverted, the GSHP ground loop can go ONLY to the sunboxes, and not use the ground at all - a simple short circuit from the sunbox return pipe directly to the ground loop inlet of the GSHP, using a diverter valve.

   I know from observation that when the sun shines, the temp in the sun boxes goes up to nearly 20º or past 20º quite easily - sometimes up to 40º - so keeping them Tightly Shut is the best strategy most of the day time.
   If one pulled heat out of the black panels solely, without using the ground loop, there is a danger that the air in the Sunboxes wrapped round the black panels could become a 'Pool of Cool', becoming colder than the ambient air, especially at night and cold cloudy time.
   If the GSHP is busy-busy-busy, and using only the black panels, it could pull the air temp to below 12º even on a nice sunny day.
    The thermostat we have has a second channel, and if we had motorised hinges on the sunbox ventilation louvre, then the thermostat's second channel could send an 'Open the Vent louvre' command when the temperature is below 12ºC - enabling fresh air to be brought in if the sunbox internal temp got cooler than ambient temperature at night or cloudy-time. I have servo motors already, because that is what the solenoid valves are - 230v activated servos that open 90 degrees of angle - instead of turning a valve, they can turn a louvre.
    I would be prepared to risk testing this method for a few days (monitoring the condensation risk all the time). However, the 3 dimensional difficulty of plumbing in such a bypass in such a tight space might be impossible! And if I am going to make mechanisms to rotate the louvres automatically, I might need to get a welding kit!

Wednesday, May 12, 2010

Why have Sunboxes?

12 May 2010: I was asked by David Atkins of Ice Energy, and by a student today, why have Sunboxes? (getting heat from the microclimate in the sunbox), when we could simply hang black panels out on the wall, simpler and cheaper (getting heat directly from the air).
    If we had bare black panels externally they would have to be encrusted with Ice to work effectively in Winter (using latent heat of freezing), and would not be possible to control thermostatically - they could work all day and night, and use a lot more loft-pump energy (longer hours and a more powerful wattage of pump), and the thermostatic control would be by the GSHP - and to me they would negate the point of using Ground Source because the GSHP would be working long hours putting glycol out at below freezing - and perhaps we would need 8 panels not 4 - this hasn't been tested (need another house and a lot more plumbing!). (A small advantage is that they could be on the roof, not wall)
   We have no wish for below-freezing pipes to run around the loft, dripping bucketloads of condensation in the house and risking us dry rot - and causing a higher workload for the GSHP than it already has because temperatures would have to be seriously low.

    The Sunboxes work by exploiting the principle of the 'Sunspace' (solarium)....  contain very warmed up air that works all year round (even in winter on bright days with cold exterior temperatures), and the thermal sensor can hang in the airspace just above the black collector to monitor the performance and know when the thermostat should trigger the pump - consequently the pipes are never below freezing, and the pump is never working when there is no heat worth downloading. The thermistor has a bonnet of reflective foil to make sure it responds to air temperature not merely to direct sunshine.

  Millions of Solar Cookers work on the same principle in India, and I must post more information about those.

   The ground remains our prior source, but for the small amount of time that the sun shines in Dec / Jan / Feb, there is still going to be restoration of the heat into long term storage, thus avoiding chilling. Actually, being vertical on the wall, we have found during March that the Sunboxes were still quite effective at lower sun angles.

Prodigal Student appears, and 3 drawings

11 May : I mentioned on 2 December another of the dissertation students, Joel Carter who formalised with me the idea of forming the polycarbonate enclosures. But I never saw him again after that meeting! It was so long that I would no longer recognise him if passing in the coffee bar.
  Suddenly he appeared again today, anxious to get on and complete the dissertation. It is obvious from the conversation that he has been reading this blog quite thoroughly, so I was willing to discuss it further and with some urgency. Let's hope it's a good one - the hand in is near the end of May.
   The earlier dissertation, by Robert the B.A student, has already been printed and handed in, so I look forward to seeing a copy of that.

The PhD student, Blaise sent me three revised drawings of the circuit (in different operating modes) that he intends to use in our co-authored write up on the project.  I made some small corrections and returned them for his approval. They show:
  1. the heatpump working without the sunboxes, 
  2. the heatpump working as a hybrid system with both ground and sunboxes, and 
  3. the sunboxes working when the heatpump is 'sleeping'.
The Illustration on the right is of option 2.

    Monday, May 10, 2010

    Press Drill fixed and some light shopping...

    10 May : The press drill I borrowed back in December had a faulty chuck so all the recent metal drilling has been done with the hand drill. After a long hunt for a replacement chuck (which also included intense difficulty in getting the old one off), I managed to get a replacement from Cromwell Tools in Beeston.
        This was also a good day for small shopping, so I bought some pipe and lever ball valves to kick off the piping for the Sunbox mark 2. (and last Saturday, bought a 600W inverter for use with the PV panel).
    So tiny bits of progress being made....

    3 days on, 3 days off, for testing

    9 May : As soon as the 3-port Danfoss solenoid valve was installed, and the system restarted Sunday morning, it seemed as if the Sun came out to welcome the new installation, the first sun we had seen for a week. With the system off, the temperature in the Sunboxes had climbed to over 40º, and when I turned it all back on, there was an immediate improvement. The flowrate to the sunboxes is now driven by the water pump in the GSHP assisted by the one in the loft, and so delivery of heat from up there is much more rapid. It's amazing to see liquid returning from on high with a temperature in the low twenties, or high teens. Is this what it will be like in high summer?

    When the GSHP has completed a heating cycle, it goes back to sleep (quickly now) and leaves the slow low-power pump in the loft to quietly continue circulating heat, always charging. If the GSHP has just been heating, then it has temporarily chilled the pipe of the ground loop, so the liquid from the Sunboxes is preventing any chilling effect - it is restoring stability very quickly.

    Blaise came round in the evening to check the datalogger, and as the change of the Danfoss is a major change in performance, we decided to download what we have already, clear the datalogger memory and make a fresh start.
       As he wants some clean comparable figures, we agreed that I run the house with the Sunbox system ON for three days, Mon, Tue and Weds, and then run the house with the system turned OFF for Thur, Fri and Sat. The datalogger can record the performance. We have to hope that the weather will be roughly equivalent for the week.
      Everything has to be ON again for Sunday 16th May which is when we have the Open Day. Meanwhile, I am working on the ArchiCAD drawing to update the circuit diagram to show this new valve.

    Complicated Plumbing/Electrical alteration

    9 May : With a very long hard slog of plumbing work, I got the 3-port Danfoss installed above the heatpump. I was still working on it in the early hours of the morning, about 3am. That included refilling glycol into the system with a small jug.

    It took so long for two reasons.
    1. The incredibly tiny and tight three dimensional space I was working in made it very difficult to reach or work (plus all the dangling datalogger wires hanging everywhere.... made it difficult to have a flame from a blowlamp). The order had to be perfect because it was nigh impossible to pull such large diameter pipes apart to push into joints (and the pipe cutter could not work in such a space, so cutting had to be done with a bare hacksaw blade.
    .... and 2. because I was doing it on a Saturday night, and I only had exactly the parts that were needed. If I was short of a part, or damaged an olive or ran out of gas, I could be in big trouble as the only place open on Sundays is B&Q and they don't normally do 28mm fittings. So I had to be very very painstaking and patient. (Should have bought one more of everything on Saturday morning).

    Sometime after the system was working in mid-March, I assumed (or hoped) that I would never do anything with 28mm again, and took all my 28mm copper stuff to the plumbers merchant and gave it all to a random lucky customer who was there to shop. Later, I have found what an advantage it was to work with such large size, as I can now modify it the way I have done, with ALL glycol going through the Sunboxes when the thermostat says Yes!  So I had to go and buy some more 28mm stuff on Saturday morning. Doh!
          Sunday morning, I rejigged the electrics, so that there is a Red Neon light in the loft and by the GSHP to indicate when it is in a heating cycle, and also so that the new 3-port Danfoss internal relay now switches on the 2-port Danfoss and Wilo pump up in the loft.

    Thursday, May 6, 2010

    West Bridgford Ecohouses

    5 May : My eco-friend Karina Wells has created a blog site dedicated to writing up houses in the West Bridgford area that have eco-friendly features. .
       This is connected to the West Bridgford Transition Nottingham project, and was started because of the Open Day being held on May 16th.
       There will be a Summer Gathering in West Bridgford the day before, and people can view posters of the houses, and sign up to take part in a tour of the house.

    The site will remain open after May, and I hope that it could be built up wth new material as more eco-renovations occur, and used year after year. It can build up a growing list of case study houses.
       The Peveril Solar house has quite a detailed write up.

    Expanding the Datalogging

    5 May : In the evening, Blaise came round, and downloaded the information collected so far. We found that the datalogger's memory was full, and stopped recording about a week ago.
       So now, it is re-programmed to record every 15 mins instead of 5 mins.
      We added two more channels, the Air temperatures in the Sunboxes and externally on the north wall.
      We also wanted to record other things too. With a bit of inspired guesswork and a phone call to Chris Wood, we managed to attach three digital data channels :- a counter from the Supercal energy flowmeter, and a On/Off state from the Sunboxes and from the GSHP. We still have two counters and two digital channels left for us to think of things to connect to.

    PS we later found that the Datalogger has a built in battery that keeps it going even if the power is turned off, so being turned off for short periods during maintenance is not a problem - it just keeps recording!

    Wednesday, May 5, 2010

    Visit of David Atkins, Darius, and Chris Wood

    5 May :  This was quite a 'key day' for the project, having David Atkins and Darius (Ice Energy), and Chris Wood (Uni of Nottm) visit the house and discuss the system at length. We also discussed how further to take it, and how to monitor the performance, and how the Sunbox 2 would work, if we decide to use it.

    The team had a thorough look at every aspect of the project, and were far too absorbed in the technical discussion even to think about tea and coffee (which I had to force on them eventually! :-)
       At various times during the sunny morning, the heat pump and the sunboxes performed perfectly, coming on and off correctly. We discussed how best to fit the 3 port diverter valve above the GSHP. This is now a vital next step to making it more effective.

    We also discussed the application of the Sunbox mark 2 (Savita). Although this is an interesting evolution from the first version, it would be better installed on another house (for comparison purposes) or even at the University, running as a lab project. If it is to run on the Peveril Solar house, it cannot run simulaneously with the Mark 1s (Surya). Of course, for heating purposes it could - but for data monitoring, it would completely confuse the data collection. What we can do is to install Sunbox 2, but have a diverter valve so that only one or the other can run, but never both.  David delivered a box of goodies - an energy flowmeter, another AKO thermostat and another water pump. If we decide to make the Sunboxes 'Either-Or' with a diverter valve, then we will not any of these, as the existing controls and pump will be able to activate either of the sunboxes.
      Darius (from Poland) is a specialist in thermal modelling with computer, and said that this project gave him many ideas for modelling projects.
      Chris and David have worked together before on research projects, so the discussion was very interesting, highly technical, and sometimes beyond me - but I feel that the project has great momentum now, and we had a discussion on how one might make low cost mass production sunboxes, should there ever be a demand. The whole idea of there being an obligation to augment ground source heat pumps would have a great impact, but at the moment, nobody knows how to do this except the team and readers of this blog!

    Monday, May 3, 2010

    Sunbox mark 2 first view

    May 3 : Here are the first photos of the assembled Sunbox Mark 2 (Savita). These are a compact version of the ones already built, but these are prefabricated at speed, and are plug-in. Four anchor bolt holes, and one hole for electrics and both pipes to pass through. This model should need a half day mini scaffold tower hire to get it up - unlike the first one where the scaffolding was up for over 3 months! After that it is only interior plumbing and electrics to do, and the design for those is well refined now.
      The plastic sheeting is still applied, to protect the polycarbonate during construction.

    I had a deadline to meet, which is the visit of David Atkins in 2 days time. I can't do any more on it now, as it's bank holiday and I can't get copper pipes to complete the plumbing.
    The plastic and aluminium is less than 100pounds worth, and the thermal collector is an off the shelf radiator. So its inexpensive!

    PS. during the Bank Holiday weekend, I have done some wiring in the loft, leading cables to the future location of the pump and thermostat for the Sunbox 2.

    4 May : Just in case the PV panel for the Sunbox 2 does not work, or blocks too much solar heat from the black thermal collector, I have built an identical panel (same aluminium section, and identical frame size) that can have clear polycarbonate, and can be dropped into position into the same grooves. I will run the panel with both types, each for a few weeks.  I was aiming to get the sunbox built and the panel made in time for the visit of David from Ice Energy.

    Scaffolding: There is the problem about how to change the panel without incurring high scaffolding charge. I must decide either to hire in a mini tower and erect it myself, or to make a demountable frame of steel or aluminium that can be stored behind the garage, or even buy some scaffolding, and store it safely when not in use.

    Sunday, May 2, 2010

    May day readings - example of charging

    Sample readings during May 1 - heat is going down, and staying down, judging by the return temperatures. This was an afternoon with air temps from 11-15 during the day, and the GSHP mostly pretty dormant. I see this every day now, so won't bore you with more than 4 typical samples. Later, the datalogger readings will make it easier to understand as it will provide figures that can be converted to graphs.

    Time 1400 1430 1500 1700
    SunBox Temp 26.5 29.8 31.2 23.7
    Temp going down 16.1 16.8 16.4 14.8
    Temp coming up 14.0 13.9 13.9 12.9

    Progress on the Sunbox Mark 2

    1 May : Made it! Part of my 'value engineering' approach for the Sunbox Mark 2 was that it should be quick and easy to make, and designed to be replicatable for others to build from drawings - and having been made, to be virtually 'Plug in' so that a one day mobile scaffold or cherry picker is enough. 

       So, although a bit of painting and drilling was done in the days earlier, the essential construction was all done in one afternoon. It was quick, even though that included quite a bit of downtime, either to do a bit of hoeing in the garden, tea, or just rethinking something, trying to ensure decisions were final, redoing things that didn't quite fit, or trying different screws. Really, all that remains is the Plumbing element. It helped that it had been so thoroughly designed beforehand, so that all the aluminium cutting was done in advance. I had to cut some polycarbonate with circular saw and jigsaw, and for production, these would be lasercut and delivered ready to use.
      Again, a virtual hug for the delightful Mr Makita who designed my all purpose drill.

    Thoughts about Pitch Angle
     My new Sunbox mark 2 is PVT and is sloping at 70º, facing south, but this is a function of it being wall mounted and not wanting it to project too much - there needs to be enough for the airspace behind, and enough to accommodate the thermal collector behind. For electrical harvesting, it would be best at 36º.
       I have considered it at 60º as a compromise, but the projection from the wall is just too much. The Sunbox 2 is built now, I have cut aluminium and polycarbonate for the prototype so must live with it now and monitor the performance, thermally and electrically. I would have to order a whole lot more polycarbonate, causing more delay.

    PV generation for March and April 2010

    1 May : The last two months of Photovoltaic generation have been very good, both months exceeding the JRC expected amount by about 40%.

    • March should have been 207 kWh but was 281. 
    • April should have been 306 kWh but turned in a score of 429.

    The amount by which these exceeded expectation were more than the entire months of Jan and Feb combined, which rather makes me think that you should not worry if sun angles or long shadows in the months of Dec and Jan are not going to be favourable. It seems better to optimise for the spring to autumn months.
    Looking at the charts here, the final weeks of April were astonishing, we had a run of nine days in a row, all touching or above 20 kWh, apart from one freakishly cold dark day on 15 April. The lower illustration is a typical run of days, from April 15 to 21. Even though our roof faces east, the early morning sun gives us good performance. I notice a pattern whereby days often end with cloudier afternoons after a good start - enough to put me off recommending a west roof where an east one is available.

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