Monday, July 30, 2012

Energy requirement for French Properties

29 July 2012: Just back from Limoges, France. This photograph is of an estate agent (realtor)'s front window. We saw windows like these in all the towns and cities we visited in the region.
 I noticed that all properties for sale have an EPC (Energy performance certificate) displayed, and the only ones that do not have to are the ruins being offered for renovation, or purely summer homes (rien de chauffage). 
   There's no critical link between price and EPC, but one can't help feeling that the constant presentation of the EPC begins to make people think more about energy efficiency, and will affect the price - take on an inefficient house, and you know you face large bills in the winter, or some costs for insulation and boiler replacement.
  I didn't meet anyone with 'the knowledge', so wasn't able to ask techie questions about subsidies for wind farms, feed-in tariffs etc.

Sunday, July 29, 2012

July 2012 Reports

For those recently arrived, I do a meter reading every night, but summarise the annual figures every Sunday. As we seem to get oscillating years (2010 cold, 2011 v warm, 2012 v rainy) I am also compiling an average over 2 years to smooth out these bumps.

PV Solar: May 2012 was saved by a 7-day heat wave, but June and July 2012
were uniformly grey and rainy, well down on 2011 figures.
Summarising July 2012: Another bad month weather wise with the PV 100 kWh down on the previous year, (June was worse, 150 kWh less than in 2011) so all my figures look unhappy. Correspondingly, Sunbox capture is also down on 2011's figures. However. It has not been cold enough to require Heating, so for June and July, the GSHP is only concerned with Hot water, and those figures are holding level.

29 July 2012: There is a gap because Ive been on holiday and not able to collect data. During the week, the GSHP was turned off, and it was a sunny week, so a decent amount of heat was buried, although the Tubes failed to work.... they overheated and got an airlock, it seems. The problem was on the ground loop side, not the tube-side. In other parts of the world, it was the week of the Olympics build up, culminating in the excellent opening ceremony, choreographed by Danny Boyle, with this cauldron sculpture by Thomas Heatherwick.
For the Peveril solar house, annual figures in kWh/yr:

  • The House meter is still hovering just over 5,000 and the GSHP just below 3,000, and a few days on holiday makes little difference (as we tend to leave the fridge and some lights on, and one year ago, it was so hot that little power was being used). 
  • PV is slowly improving at 3,095, and the buried solar heat is 2,566. For those recently arrived, you may have noticed that I regularly mention 3,000 as the figure for buried energy. We had a two month period this spring of the system not working, plus months of rain+cloud, so the figure is crawling slowly upwards from a low of 2,500 kWh.
  • Ground temperature is well above 13º, being 13.6º on Saturday and 13.8º on Sunday evening.

15 July 2012: Another rainy week, with more predicted for the coming week. Annual figures are level, as we continue to wait for some sunshine. Never mind, it's better than living in Kansas - the drought in the US is worse than it was in the dustbowl depression of the 30s.
  • House 5,007 kWh (improving), GSHP 2,983 kWh (level), PV 3,033 kWh (worrying), Sunbox, 2,529 kWh (lower), all annual . The House meter used to keep pace (always 2,000 more than the GSHP), but it is running away a bit because the PV has performed so poorly in the weeks of rainy weather. The GSHP meter is holding level because there is still a reasonable amount of recharging taking place.
  • Until the weather improves, it won't get better. 2011 was such a fantastically mild year, it's impossible to beat!
  • Ground Temp 13.1ºC... quite good considering the gloomy weather.
With this dull weather, the Sunbox has not been so productive either. From 23 April to 15 July it produced 686 kWh, and in the same period last year 886 kWh and 883 kWh the year before. However.... based on my thermal modelling, the energy level below ground is at least up to what it would be after an entire summer of natural recharging - so any more that goes down in August is a bonus.

8 July 2012: July continues as wet as June, so far with more floods in the UK. I would hate to be an Olympic organiser now, it must be very worrying for the outdoor events. Here's an interesting page on the BBC website by David Shukman explaining how the static Jetstream position is bringing us this bad weather. This is what it must be like in the Orkneys all the time, except that it gets even colder and windier up there. Despite the bad weather, the Peveril Solar house is performing reasonably well.
  • House 5,021 kWh, GSHP 2,983 kWh, PV 3,076 kWh, Sunbox, 2,558 kWh, all annual 
  • Until the weather improves, it won't get better. My sister in law's house flooded yesterday, so other people have far more troubles to worry about, compared with my meters.
  • Ground Temp 13.2º, because the heat pump has little work to do, and there is still warmth in the air, despite the quantity of rain. I am very content for it to be above 13.0º !
What else happened in the world? Well Tom Cruise and Katy Homes broke up, the rich banker Bob Diamond decided to resign after his bank's wrong-doing, pocketing 2 millions pounds as a pay off from the bank. Wouldn't it be great if all crooks and swindlers could get payoffs just before they go to jail. Biggest news for world science is that the Higgs Boson was announced on Monday, as something very very small and heavy that had been discovered (having been predicted 40 years ago. The British TV comedian Eric Sykes died at 89 and the US Oceanic Survey declared that after years of compiling records and reports, they could declare that there are no such things as Mermaids. The Wimbledon finals completed, with Serena Williams winning the women's. Roger Federer beat Andy Murray after a very good (rain interrupted) final, and Murray had done brilliantly to beat Ferrer and Tsonga in previous rounds. Wimbledon becomes a sort of addiction, I am sure that some British wish it could go on for ever like the Archers. Finally for this week, we saw the London Bridge Shard tower completed and opened - the highest skyscraper in Europe until the Moscow tower is completed. I am hoping to get a private viewing of the interior in September, watch this space!

1 July 2012: Good riddance to June, but July doesn't look likely to be any better. A week ago, the Daily Express claimed that we have a sizzling summer of sunshine ahead of us, but the agency they use just provides filling for the front page when others are reporting real news, and are always wrong. The reality is that we've had another week of rain and grey and have one coming up in the next forecast. This was front page on a day when all the other papers reported on Cameron's proposed attacks on the young, cutting housing and other benefits even more for the under-25s. Don't vote for the millionaire Etonian next time, folks! A week later, the same newspaper predicts more months of rain.
  The biggest news of the week in the UK has been the collapse of the RBS computer system at the same time that Barclays admitted and were fined for serious corruption in tinkering with the LIBOR rate. Only 2 years ago, RBS laid off 3,000 IT staff in the UK, and employed a few hundred offshore, even though they had been saved by the British taxpayer - is it any wonder that when there are major computer glitches, they haven't got the staff to sort it out? So far, Tory govt seems to resist calls for an enquiry or prosecutions, despite the eagerness to put teenagers into prison a year ago for nicking trainers or bottles of water during the riots.
  At Wimbledon, Nadal was knocked out early, and Murray has survived to the second week. The tennis has only been possible thanks to the covered centre court, and the programme going on to 11pm! In the Ukraine, Spain won the final of the Euro football with a cracking 4-0 victory over Italy! England had serious floods in many places in the first part of the week, while in the US, they have had yet more unprecedented levels of heat wave (and the fires that result), followed by major snap thunderstorms and wind speeds on the east coast, coming out from the interior. Pity that the majority of them believe that it's God doing it to them, not putting the blame on decades of carbon build up in the atmosphere, made worse by the heat wave air-conditioning and forest fires. The Olympic flame passed through Nottingham and West Bridgford, and I went into town to see Torvill and Dean in the last stage of the day.
   For Peveril, the annual figures are just about holding position at the moment, not improving. June this year has had less solar radiation than April or August of 2011. 
  • House 5,006 kWh annual, 5,152 kWh biennial
  • GSHP 2,980 kWh annual, 3,153 kWh biennial
  • PV 3,130 kWh annual, 3,206 kWh biennial
  • Sunbox, 2,580 kWh annual (with the omission of most of April 2012). Until the weather continues, it won't get better. It is almost cold enough in July to need some heating in the evenings!
  • Ground Temp 13.4º, a good figure considering the sunless weather for the recent month. That means it is at optimal temperature already for the summer, with months of warm weather yet to come. Further deposition of energy usually widens the energy bulb rather than making the borehole warmer.

Solar performance during the week

29 July 2012: Its been a mixed week. The weather has been very good, and I have come back to find a good score on the PV and on the Sunbox, averaging a combined score of 30 kWh/day.
   However, the Tubes only did as well in the week as one typically good day, and appear to have reached high temperatures but not circulated much. Both the tubes and the heat exchanger got up to 100ºC, revealing that the heat was not being taken away to the ground. Normally these temperatures are never higher than 24º.
   The solar controller was displaying a distress message. There must have been a small leak as one of the drip trays was full of coolant, and the overall liquid level has reduced, and an airlock must have got into the system. I just pray that the main circulation to the Sunbox has not leaked (difficult to tell) because it could need scaffolding again.
  Before I departed, all systems worked reliably day after day, but since May, we did not have a single sequence of hot days for me to see how it performed. I have to check out the leak, purge airlocks, top up the system and observe frequently.

Week in Limoges

19-28 July 2012: We took a holiday in France for a week, in the old city of Limoges - capital of the Limousin region. Its about 3 hours ride on the TGV south of Paris. There is an airport and Ryan Air at Limoges, but somehow, travelling by rail is so much less stressful. The station staff are helpful, and you can carry as much with you as you like.
It's good to see the vast number of land-based wind-farms during the ride, especially on the flat-land regions south of Paris. Gracefully turning in the breeze, but almost invisible due to being so white and slender. (couldn't photograph as they are almost invisible, and the train is moving at TGV-speed).

Urban form of Limoges - from Order to Chaos
The municipal museum of Limoges had a series of models showing the city over the centuries. We were staying in an apartment building next to the roman bridge that was the start of the original settlement. These two photos are at the same angle and scale, looking from the west. The city was larger in Roman times than in later times, until the industrial revolution brought the railways, and porcelain making transformed the economy.
   The grid plan suggests that in more stable times when military security provided safety, the city form expanded in a permeable grid based on the trading potential of the river, with the longitudinal streets (cardus) taking the easy slope down to the river and the crossways (decumanus) staying on the contour.

 In the chaos of the middle ages, with Papal wars, the Hundred Years War and other such events, the entire city resolved into two distinctive hill town settlements, surrounded by ramparts, moat and walls, with tall buildings along narrow streets. With such urgency to build defensive outer walls, the old roman town just became a quarry for stone, until it disappeared under grassland. A few streets (including the one our apartment was on) retain the old roman line. The buildings tended to be one storey of stone, and four storeys above of timber frame. Many of these still exist, although a fire in the 1860s removed many of them.
   There was a magnificent amphitheatre just west of the town, which was quarried year after year, and which still existed in the 16th century, in ruins. As the town expanded since 17th C, all trace of it disappeared, apart from a triangular park, and some street names to commemorate it.
The modern Limoges, from the same angle on Earth Google, shows how the amphitheatre is still revealed as a park, and the modern outer town area has found it useful to follow parts of the Roman plan.   What a pity that the Roman street plan could not have been retained. There are cities in northern Italy which can still identify the original cardus and decumanus. the roman city resembles the modern US city in some ways, with a permeable grid.
Dense 5 storey medieval structures. There was a fire in about 1862, but many of these survived.

 The French are more open to interesting architecture and architectural juxtapositions than the Brits. The main railway station is a magnificent piece of inter-war Arts Nouveau, with a high clock tower to commemorate rail travel, and a recent sky-bridging structure over the nearby car park is as high tech as any modern architect could wish for.

The station frontage as in this very wide angle multi-photograph is quite magnificent, and faces towards the city like a giant jaw, with a here dome above. Touchingly, like english victorian infants schools and their terracotta titles over the doors, the entrances either side of the arches are titled Arrivals and Departures, a remnant from the slower days of rail transport. Even in 1860, the railways had arrived here, as a deep underground tunnel that came from the south and ran below and between the hill towns, emerging on the north side. I wish I had photographed all of the scale models of the city's development.

Thursday, July 26, 2012

Interseasonal heat storage in Suffolk

26 July 2012: I see from the Architect's Journal that planning permission has been given for a house in Suffolk that will use solar power for its electrical and heating needs. It will use interseasonal heat storage. The architect is Jerry Tate who is one of my students from the 1990s and to whom I once sold a Mac computer!
The client for this is a scientist and has developed his own design of solar panel (that will be solar thermal), that will be grid connected, but will store electricity also, in batteries, and will dump heat to the ground for recovery by a GSHP.
I will write more about this when I get back, meanwhile, I only have limited access to the web.
Jerry used to work for Grimshaws, the architects of the Eden Centre, and he is an expert on Gridshells, so the house is a gridshell, not an ordinary looking house like mine!

Thursday, July 12, 2012

Degree Days providing warmth

11 July 2012: I was talking again to Professor Hasan from Finland, and discussing simulation again. My recent model was based on data obtained from my meters, but what about working up a model based on generic climate data of this region? We have FLUENT in the department, but it's used only by PhD students, or Masters specialising in that topic. For the time being, I am happy to write my own software using the GDL language. I will ask about using FLUENT some time during the vacation. There is also the question of finding reasonable weather data.

Degree Days
There is a marvellous website, that seems to provide access to weather data all over the world, and offers it free for the last three years. It is possible for commercial outfits to pay a bit and have data going back further. It can be used to derive data for heating and for cooling. I recently used it for some weather data in Singapore, where cooling is the only consideration. Degree Days are based on air temperature, so a bit of sunshine is a bonus! I am grateful to the site operator who, a while back, upgraded my access level for a week to enable me to download data for the last Ten years, and I was able to check out climate records for New York, Nottingham, Abu Dhabi and Singapore, where my students are designing.
Natural heating and cooling Base 12ºC, Nottingham region
Natural recharging by solar and air temperature
I suggest that the natural rate of discharge and recharge of the ground is partially influenced by air temperature, and not solely by solar capture. Many areas of ground (e.g. woodland or urban areas) manage to recharge even if the ground does not have direct sunlight, although it's still a slight wonder to me how this happens. One has to think not in years, but in decades, of the slow transfer of heat downwards. The heat coming up from the magma is very very small, but it must have a small stabilising effect deep down. Undergrowth and vegetation are thin in winter and provide less insulation, but perhaps allow winter sunlight to have a beneficial effect when it happens.
     Measuring air temperatures at the moment, they are consistently 15º or 16º at about 11pm, even though we have been having such a rainy few months - the air temperatures have been good even if the general outlook is damp and miserable. The graph above demonstrates the Degree Days Below and Above 12ºC, which indicates how many months or days in which the air temperature is able to help raise or lower the ground temperature. in Nottingham over the last three years, the DDs when colder than 12º are twice those when warmer. Where the graphs overlap you have diurnal conditions, where there are warm days and cold nights.
  I know that in Scandinavia with colder winter air temperature there are more ground source heat pumps than in the UK, but with their steeper sun angles (but longer days) in Summer, it's still a wonder how enough heat gets down for the GSHPs to bring back up (unless you charge it actively with solar heat).

Cooling Degree Days, base Zero, June 2009-June 2012
Top: Monthly intervals, Bottom: Weekly intervals.
Three year temperature curve resembles model
This diagram is of Degree Days (cooling) in Nottingham with a Base of Zero, for the last three years. 'Cooling' means that it shows when there is greater warmth in the atmosphere than Zero. The curve look remarkably similar to my recharging graphs in the model - a steep fall-off in winter, followed by a longer, climb-out in spring and summer. The various ups and downs in the model help me to remember past weather events, such as the 2 winters of 2010, the mildness of 2011, the mini winter in Feb 2012, and the two one-week-summers of Mar and May 2012. The final spike in 2012 indicates that air temperatures are at least warm, even if conditions are miserably rainy.

Wednesday, July 11, 2012

Accelerative effect of Solar Earth Charging

10 July 2012: Having worked on the thermal simulation for the interaction of GSHP and borehole, I still have a question. The solar augmentation undoubtedly lifts the energy levels above the line representing the best summer peak, but we are getting a greater than expected advantage from it - which is why I use the word 'accelerative'.

Metered figures compared
The Sunbox puts down approx 3,000 kWh, but the house needs about 9,000-10,000 kWh annually, there is still the majority, perhaps 6-7,000 kWh to come from natural recharging. These figures, and the orange line in the diagram below suggest that the improvement is welcome, but not much more than 15%-20%. The true results, as recorded by meter, is that the annual electrical consumption was cut by about 40%, from more than 5,000 kWh to less than 3,000 kWh. These figures vary slightly with seasons, but they represent the typical figure achieved. Why is the effect of solar augmentation accelerative?

I have explained this some months ago in a posting, but I want to explain it again in the light of the recent thermal modelling efforts.

Local zone of warmth or coolth
Looking at the plan of the boreholes, it's clear that the zone immediately around the borehole pipes is the most active zone. We have a global annual radius of about 3.6 metres which is the distance that energy is likely to move in an out from, seasonally, but on a daily basis, it is probably less than a meter. It cools most quickly when the GSHP is working, but it is also replenished most quickly by the Sunbox.
   Also, with twin boreholes, we have a beneficial warm zone between the boreholes that nurses the solar heat put down by the Sunbox. If there was no Sunbox, this zone would be malicious, as it would nurse 'coolth' and make natural recharging more difficult.

Seasonal behaviour
There are more concepts to consider besides COP (coefficient of performance), and one of these is the SPF (seasonal performance factor). COP can be measured at any single moment, and varies according to conditions. When a heat pump starts work in the autumn, it's finding plenty of source energy and had a good COP, and in January after the heat source is exhausted, the COP is very bad. SPF shows how the GSHP has performed over the seasons. If the COP is frequently improved by solar energy, then over the length of a year, the SPF will be improved.
• During the Summer, the added solar heat energy must move outwards and fill the larger space (until it meets the energy being pulled in by natural recharging) and after that equilibrium, whatever else we can add is a bonus. If we add too much, there would be leakage.
• In the Equinox periods, the zone is more active because you have mild and sunny days, but still you have cold evenings. Therefore, daytime solar energy is put down, and raises the energy level of earth immediately around the pipes, and the heat pump gets this back 3-6 hours later, having had no time to escape, even a metre from the pipe.
• During the Winter, we are reliant on long term stored energy, but it is surprising how many bright clear but cold days there are, when the GSHP is busy working, but the Sun is shining onto the panels and giving a temporary boost to the zone around the pipe.

If during Equinox, the energy levels lead the HP to perform as if it is Summer, and if during Winter, the HP performs as if it is Equinox, then that will show up at the end of the year as a very good SPF.

Volumetric difference between model and reality
My thermal model treats the energy bulb as one large cylindrical mass, and assumes uniform conductivity. Because conductivity is slower in the real world, the warmth put down stays near the pipe for longer, and returns more willingly. Also, the real world model has the benefit of the 'nursed zone' between the boreholes. Hence, the improvement seems greater than one would expect from the annual figures - hence, accelerative.

Another accelerative effect: restoration
Time plays another important role: another clear example of accelerative effect is the restoration of energy level immediately after the GSHP completes a heating cycle. The ground has briefly been cooled, there is a good delta-T, and for a period of time, perhaps 20-30mins, the Surya system is pumping warmer liquid down, to restore the energy level. I can see this happening after each heating cycle, the little green light glimmering as warmer glycol is buried. Since the sensors were re-arranged, this has worked better. The upper one is attached to the surface of the black collector, and the lower one is attached to the up-coming liquid.

Horizontal systems are possible
This accelerative effect means that one can apply solar charging to horizontal systems. The short term return would work just as well, and in winter, it would reduce the risk of freezing the ground - defrosting it after each heating cycle if there is a glimmer of a bright sky. In summer, the interseasonal charging would not work well because it could overheat the upper layer of soil and dry out the grass.  If an insulation layer is buried in the ground above the slinkies, there could be an element of solar charging inter seasonally, and this would lessen the risk of drying out the grass. David Maritan (in Pavia Italy) has done this successfully with the 'Compact Collector', a vertical grid of pipes.

More thought on Nicads

11 July 2012: Ive been talking to SAFT , Britain's leading supplier of industrial/solar NiCads, and I think they are linked to AlCad, as the call came as a result of an email and voicemail I sent to AlCad. It seems that the idea of a large NiCad battery will be too expensive for my off-grid system, as applied to a very small house. As a rule of thumb, they are about ten times the cost of the equivalent Lead-Acid.
   If this house was truly and entirely off-grid, the NiCad would be practical as the cost of about £1000 is in line with other costs in a new-build process, but for retrofit, it is too much, compared with about £100 for a deep charge Lead-Acid battery.
   As my system is one that I hope people will learn from and copy, it goes against logic to get something so expensive. It is justifiable to spend serious money on energy meters or data loggers, these are written off as a 'research overhead'. The operating components of a system must be cost effective if they are to be emulated.  The house is already Net-Zero, so any additions to it are useful research tools, but are not essential to meet the target of Net-Zero.
   The only chance of getting a NiCad is to ask for one that is end-of-life as far as its first purpose is intended, e.g. emergency lighting in a large building, but having enough residual life for a small non-essential system like mine. I will ask some local businesses. My contact in Saft (who very kindly rang me to discuss the idea) will put my enquiry to possible sources of batteries for recycling.

Net Zero Energy Building

10 July 2012: The professor who visited my house last week was Prof Ala Hasan of the Aalto University in Finland, and he is the President of the IBPSA-Nordic, (The Nordic Affiliate of the International Building Performance Simulation Association I emailed him with news of my efforts with the GDL thermal modelling simulation was delighted to get an email from him this week:
   Dear David, This is interesting!Your house is fulfilling the definition of Net-Zero-Energy Building (related to the electric loads for heating) according to the definitions we have in IEA SHC Task 40: Towards Net zero Energy Solar Buildings

This is similar to the Active House concept to which I am 100% subscribed. Far more interesting than Passivhaus!
.... and there is a link to the EnOB website, which has a world map of the Energy Optimized Buildings on their database. 

I shall have to see if these worthy organisations can add the house to their list of Net zero buildings. I have plans to take it further, with the addition of further PV panels and further solar thermal panels on the new extension.

Tuesday, July 10, 2012

Assumptions about natural charging

The real boreole is a twin-set
but for simulation, I have started
with a single cylinder
9 July 2012: Part of the thermal model, the most important and unknown part, is to make an assumption about how the borehole recharges itself naturally. The compilation of meter readings is comparatively easy. As the winter progresses, the bulb of energy shrinks, but the delta-T is stronger, and so it works harder to pull energy in from the surroundings, even from a distance. In summer, the bulb could grow so large that some energy will be lost as the delta-T allows energy to escape far enough to stay out.
  The job is made easier by thinking of the borehole as a vertical cylinder - which it is! This can't expand upwards or downwards. The aspect ratio of height to width is similar to a high rise building, in which the facade is doing most of the work - the roof and footprint are minor surface areas by comparison. If you apply the idea of Thermal Capacity to the volume, it holds several thousand kilowatt hours worth of energy, and this quantity is shrinking or growing, depending on the time of year.
   The notional idea of the energy bulb volume growing and shrinking is therefore related to the increasing and shrinking radius of the theoretical cylinder - not growing cubically in all directions, but like a fattening cylinder around an axis, absorbing replacement heat only through the 'facade' of the cylinder. The solar heat that is in the earth that feeds the borehole comes from above and around the borehole, and not below.
the contours of temperature may
fluctuate during the day but the
natural energy is coming from the
side, not from deep below

   In the case of the Peveril Solar house, it is actually two cylinders, but I had to start somewhere, with one cylinder. I can consider the Perimeter which is 2*PI*R but that is irrational as the perimeter shrinks in winter just as the delta-T is stronger. The volume of the cylinder is a function of its cross sectional area, and that is based on the Square of the Radius - PI*R^2.
   I think of the pull of energy as being like something elastic. If you have a very strong spring, bungee or catapult or bowstring that is stretched, and you can assume that if it doesn't break, the pull back to the centre grows stronger as a proportion of the Square of the distance, not the Linear distance. Doubling the distance will quadruple the force. The Potential Energy in a spring is 1/2 * k * x^2 . Hooke's Law.....

Some of the parameters in the GDL simulation model
Also, in Newton's Law of Gravity, the force attracting masses is inversely proportional to the distance between them. Hooke and Newton were contemporaries (and rivals), but the concept of the inverse square seemed to to be agreed by them.

Practically, what does this mean? when the bulb of energy has nearly reached its summer maximum, the rate of natural charge slows to almost nothing (due to the inverse square law), but the Sunbox input might be pushing it beyond that during a hot summer. When the energy bulb is shrunken in winter, its desire to spring back is strongest. Imagine a cylinder of flexible foam rubber, with a steel rod down the axis to prevent linear extension. As this was more deeply compressed (e.g. underwater), its resistance (desire to spring back) would become strongest when it is approaching its smallest radius.
  How does one equate volume here if the temperature is changing? Well imagine that we use thermal capacity equations (Energy=Thermal Capacity * delta-T) to assume that the temperature stayed always at the mean temperature of 12.8º, but the volume that would be at that temperature would increase. So in winter, when the temperature is 5º, the real world volume is the same, but we could calculate how small the energy volume would be if it was still at 12.8º. When the summer temperature is 13.5º the real world volume is the same but, we can recalculate what the energy volume would be if the temperature was only 12.8º.
   By the way, it helps to assume a uniform material. Thermal capacity is Mass • Thermal capacity coefficient, so I have to assume the Clay-Marl that we have down there.
   I have found that with natural recharging only, the ground in late summer seems to return to 12.8º. I have also observed that when solar charging is applied, the ground seems to maximise at just under 14º, after which one can only assume that the energy bulb is moving outwards. During the day, the ground is frequently at 14.5º or 16º or even 20º temporarily around the pipe. I always leave the measurement until midnight after a sunny day, to allow the energy bulb to mellow out for several hours after sunset.

Applying the idea
I experimented with this concept of the inverse square, and found that the result made sense. The curve looked credible. Because I am dealing with thousands of kilowatt hours, the Constant needed to be about a millionth. The user of the model needs to be able to apply a tiny amount of adjustment to this, depending on some other factors in the model, so it might be 0.00000013, so the user enters a figure of 13 and the formula applies the millionth. A small error of judgement about this variation and the borehole can shrink to nothing (because the heat pump draws more than the Sunbox puts down), and then it would be trying to find the square root of a negative number. In the other direction, it can balloon out too far, which would be obviously wrong. With some practice, one can get it nicely tuned.
   The other consideration is to nominate the Pivot Energy point - the energy level that is the maximum likely in Summer. It is like a football that is at rest, at its natural size. If the bulb grows beyond this, more energy input will cause a loss. During the winter-time, this is the normal size of the energy bulb that the shrunken energy bulb wants to return to - it defines the distance that the 'spring' is pulling that radius back to summer levels.
  I also have to nominate a Starting Energy level. If the model started in Winter, or if it starts in March or October, I have to make an assumption about the size of the energy bulb based on where it starts from. The dynamic simulation then continues on from that point.
  More about this later. Please comment if you can shed more light on this.

Sunday, July 8, 2012

More about electrical storage - NiCads!

Map from Googlemaps
8 July 2012: Last weekend, I had the pleasure of talking to my wife's first cousin's husband. we were at a family re-union of about ninety people!
   He's called Simon, and he lives on a remote island in the Orkneys, completely off-grid. He owns the island and a herd of special sheep, cultured to eat seaweed. When the tide goes out the island is nearly doubled in size, and over time the sheep have become used to the briny diet. They graze on the foreshore during low tide.

He brings in gas bottles for cooking, and has a back up diesel generator, but prefers to get his power from a number of small wind turbines, chargin batteries. There is one thing his island has, all the time, day and night, and that is wind!

There is a lighthouse at the southern tip of the same island, and that is nearly self supporting too, with back up of diesel, of course. Their batteries are large industrial NiCads, of the sort that commercial buildings use as backup systems for emergency lighting an power. NiCads of this sort can survive going completely flat, they can survive thousands of recharge cycles, survive freezing or sweltering temperatures, and cope with the sort of intermittency that you get with wind or solar. Even a cloud going across the sun would cause intermittency, and they can cope with that easily. They are far more expensive than a lead-acid battery, but have far longer life.
Deep charge Caravan/Marine battery
   Large property owners such as supermarkets, hospitals and universities have to replace their NiCads at intervals, for maintenance reasons, and a second hand one is perfectly good enough for the demands of a domestic property. Simon manages very well with second hand NiCads from the lighthouse.

Looking again at Lead Acid, one has to get a deep charge battery of the sort used on Caravans or Boats - which are good for general power needs and not needing the explosive power of a car battery that has to operate a starter motor. Even the best of these have a limited lifetime of the number of cycles. I shall probably end up getting one of these, as they are much cheaper than NiCad. But I shall make an effort to get a second hand NiCad.
NiCads for industrial use some in all sizes.
I am investigating!

There are many suppliers of deep charge lead acid such as Advanced Battery Supplies.

For the industrial NiCads, there are fewer options. However, I was recommended to try ALCAD, who include NiCads suited for solar applications. Ive requested a quote, but am still waiting for a reply.

I have a feeling that they are MUCH more expensive than Lead Acid, so I hope I can ask for a reconditioned or second hand one. I might even consider going to ASDA or Marks and Spencer and ask if their batteries are due for replacement.
Teresa, Simon and Hamish carrying cured fleeces to be taken to Kirkwall on the MV Enbarr. Simon stayed behind alone on Auskerry. The rest of the family will return in the summer. The lighthouse is visible at the south end.

© Copyright Ian Balcombe and licensed for reuse under this Creative Commons Licence

Thoughts on Electrical storage

Deep charge Caravan/Marine battery
8 July 2012: The idea of using PV-Thermal on the extension lead to thinking about ways of storing the energy.
  • The thermal portion will be added to my existing Surya plumbing circuit. That's been explained in an earlier posting on this website.
  • The PV production cannot be added to the Grid, as we have reached our 4 kW limit, and must not risk changing the Feed-in-Tariff. It must be stored in a battery, and then used through an invertor.
If I have two 155W panels on a sloping pitch facing south, I can expect up to 310 Watts on sunny days, and quite a decent amount at other parts of the season. That is about 2000 kWh of solar energy per annum, converting to about 250 kWh of electrical energy. It could possibly be more, as that calculation assumed 10% loss due to temperature, which will not happen with PV-Thermal.

PVGIS estimation of 300W
at 15ºpitch, facing nearly south.
   Not all this energy can be stored. Once a battery is filled, it does not accept more change, so further electrical capture is wasted.
   At time of highest 'capture', there will also be 'demand', as the liquid pumps in the house will be working flat out, but these are low energy demand pumps. I shall also put additional demand onto the battery, such as the laptop, printer, broadband modem, hard disk, cordless phone. All useful in case of a power cut in the grid.
    You have to get the balance right. If demand exceeds supply, then systems do not work, but worse than that, a fully flat lead-acid battery is difficult to restart.

More on Thermal Modelling

7 July 2012: While Serena Williams has won her fifth Wimbledon, and the unseeded Jonathan Marray becomes the first Brit to win a Wimbledon Final for 76 years (upstaging Andy Murray's noble efforts by one day), I've had a share of my attention on continuing to improve this thermal modelling project using GDL. It has gone really well, and I can now keep the model and graph going, in parallel with my meter readings during the year - it will grow, day by day. Also, this is undoubtedly the stuff for my next WSSET and CIBSE paper, there's been a tremendous amount of thought put into it, and I am glad of the opportunity to explain it all.

Screen capture of some of the working windows

The Algorithm
The dynamic simulation takes every single daily meter reading from September 2009 to now, and calculates the thermal energy extracted from the earth by the GSHP, the solar energy injected into it by the Sunbox and Tubes, and the heat brought in from the infinite surrounding earth. From this, it calculates the theoretical volume of the thermal energy bulb.
   The earth energy extracted from the borehole is done by considering the electric power consumption, making an assumption about the COP (coefficient of performance), and thus deriving the amount of energy drawn from the borehole. If the COP is 3, it should draw 2 kWh for every 1 kWh it uses. (Correct me if I am wrong, please.)
   The Sunbox energy put down is read from the meter, but in reality there must be some system losses (e.g. heat from pipes, heat lost going through water in the manifold). But this is fuzzy assumption, about as fuzzy as a guess of the COP, so I can let the user enter a parameter for system loss, and see what that does to the curve.
   In Winter, as the energy level in the earth reduces, it creates a delta-T between itself and the infinite surroundings and pulls thermal energy from around proportional to a fraction of the square of the distance. In Summer, if the solar panels put down too much energy in the summer, some of this will migrate outwards and be lost. The algorithm takes care of both of these cases.

Could this be done with a spreadsheet?
Now that I have solved it in GDL, it is tempting to go back to Googledocs and develop a spreadsheet version of it using the same algorithm. The use of parameters is perfectly possible in a spreadsheet. I have reached the limit of what Googledocs can manage, and I have had to cut my spreadsheet down and move it to a new document. There is a theoretical maximum number of formula based calculations it can do, and I have passed that point.

Chart showing thermal model WITH SUNBOX above, and WITHOUT Sunbox below

Explaining the graph
This graph very accurately represents the weather patterns we have had during the last three years. Data from meters is recorded at daily intervals, apart from the odd holiday or weekend away - so it is following the meter readings with over 300 points per annum. If you enlarge the diagram, the dates are printed at fortnightly intervals, and the year points are marked by vertical lines. The top diagram is the actual pattern based on real data over three years. The lower diagram is the same pattern, with the Sunboxes recording zero.

Here are some weather notes, explaining the curve shape.
  1. The light vertical line in 2010 is the date of installation of the Sunbox, and the twin vertical lines in 2012 are the month in which I had no Sunbox and no Tubes. Once they were installed in early May 2012, the line grows upwards, satisfactorily. Despite the rainy weather, the heat pump has not been overworked. Solar energy put down is reduced, but so is the energy withdrawn.
  2. The winter of 2009 shows a steep dive because the heat pump was quite overworked, with severe winter conditions in Spring 2010, a regular resort to 'additional heat', and slightly less insulation and air tightness than we had later. 
  3. 2010 also had a short summer and a dive into a very cold winter, so the energy level fell, but not as much as it would have done without the first Sunbox. 
  4. 2011 was a year with no winter at either end, so we achieved record high figures for PV and Sunbox solar capture, for reduced GSHP and house consumption.
  5. There was almost no winter from 2011 into 2012, but suddenly in February 2012, we had a period of snow and cold, followed by nearly 6 months of unseasonal low temperatures and the highest rainfall statistics in weather history. The two short one-week heatwaves of March and can be seen as blips in the curve. 
Note, that the curve does not represent actual energy levels, precisely. There are too many unknowns. However, it represents the Pattern. The shape of the graph is the same even with a few parameter changes - the shape is based on the data, and this is influenced most strongly by the weather patterns.
  What does the Horizontal line represent? it is user definable, for example, in this one, it is at the line of the lowest energy level, at the start of March 2010 after a prolonged very cold spell and no Sunbox. It can be moved to any height, and the polygon is re-formed for fit it.

Does this prove anything?
Well, it demonstrates the general hypothesis with which I set out to do this project, proving that there is truth in it. Now it is a theory!
   After first installation, the GSHP appears to do quite well, initially. After the first Winter, it seems to perform less well and uses more electricity, is on for longer hours. But after a while, it rapidly settles the same pattern of curve, but at a lower energy level - how far precisely is dependent on the size of the house, the depth of the borehole, the variations of the summer or winter, but following much the same shape - steep winter fall-off, long slow climb out in summer.
   With solar augmentation, the borehole is refreshed every summer, and seems to settle into the same curvy pattern, but at a higher energy level - this means that the COP of the GHSP will be improved because the COP improves if its energy source is warmer.
The proof of the pudding has been in the eating, whereby the ground temperatures reflect this curve. However, they level out at just below 14ºC because after that the energy bulb is widening, not getting warmer. This diagram finally demonstrates what is really happening.

The three year charging cycles overlaid onto a single diagram.

Simulating COP changes  
The lower graph (Sunbox off) is still influenced by the Sunbox even if it is turned off because the consumption of the GSHP is reduced by the SB and I can't change the readings, but perhaps I can tweak the COP factor. The GSHP uses vastly less power as a result of its improved COP. Maybe I should alter the model to make the GSHP use more electricity and draw less from the ground if the Sunbox is turned off. So in later versions, I can introduce a worsened COP - ironically, I found that this draws less heat from the ground because the GSHP burns more power electrically. 

Additional Heat effect
Another thing I cannot compensate for is that in the early days, until March 2010, the GSHP used to resort to using 'additional heat' (AH) if it couldn't get enough heat from the ground. This explains why the curve in the winter of 2009 descends so deeply. This AH was done for pasteurisation, but it would do it frequently whenever it wasn't getting energy from the earth quickly enough - an average of 220 hours per annum in its first two years. This increases the consumption by 4 kW immediately, and is equivalent to adding 8-900 kWhs per annum to the total consumption. I am not sure whether to tinker with the model and introduce a modifier for the readings from Oct 2009 to March 2010, but have decided to leave it as it is, and explain it here.

Complications of the 2012 additions to system
I thought you might ask this question! I bought a new meter for the Sunbox, and moved the old energy meter to the heat exchanger for the tubes. So I compile the data in a spreadsheet first and copy and paste it to the data file for the model. the spreadsheet can bring in the meter readings, and apply the correct additions and subtractions, based on the reading taken just before the meters were swapped. If you look at my Peveril-Metering spreadsheet, you can see the page on which the data is prepared before being read by the GDL model.

Any comments, please leave below!

Friday, July 6, 2012

Thermal Modelling ideas

6 July 2012: Well while Federer and Djokovic slug it out at Wimbledon's semi-final on the small screen in the corner of my monitor, I've been doing the same with my metering data. (Roger won, by the way)...

Visiting Professor suggested this
On 5th July, I had a visit by Blaise and a professor from a university in Finland, who has been visiting the school for a few days. This house was part of his visit. He said that he would not have gone this far without first dynamic thermal modelling. I replied that there are no yardsticks to work with, or comparable examples of such unknown quantities that could be trusted. By going ahead and doing it full size, and collecting real world data, I am in a better position to feed data to the model. I benefit from the reduced bills, and have fun doing it.
Screen capture of part of the script window, note that I started this in April 2011,
and got discouraged by the difficulty and abandoned it, until starting again in July 2012
There are so many variables that any sort of modelling using existing software with existing parameter types is inaccurate to the point of being useless. What commercial software has swimming pool panels or polycarbonate boxes to use as parameter types? Which one has a GSHP driving cold glycol through a Sunbox in the autumn and winter, enabling it to retrieve energy even when the Sun does not shine? How many GSHPs have an array of evacuated tubes feeding them with solar energy through a heat exchanger?
    Also... I am 64, and cannot wait several years before starting. I want to get on with it, and benefit from the cost savings from reducing the energy consumption of the house.

Second attempt at simulation
I first attempted some dynamic simulation in April 2011, following a chat with some of our PhD student. However, I made the mistake of going directly for a 3D solution, representing an actual full scale borehole in 3D, changing in size to represent the energy bulb, and changing colour too, and displaying the resulting temperature. This was far too difficult. So in July 2012, I started out seeking only to make a 2D graph, similar to my graph of ground temperatures.
The curve shape is established through ground temperatures.
Fast fall off in autumn to winter, slow climb-out in spring and summer.

2D curve for a single year
This is my own dynamic simulation, using REAL metering data collected during the year of 2011, and written using GDL, the software that is a programming language that I have taught and written about.
Top: GSHP working without benefit of Sunbox, from 1 Jan-31 Dec 2011.
Bottom: Borehole energy level refreshed by Sunbox in the same 2011.
This graph is for the year of 2011 from new year to end of year because it is the only clear year without any significant system changes. The problem though is that 2011 has been the warmest year on record with no winter periods, no snow, hardly any rain.

Energy Level is different from Temperature
The graph is not showing the ground temperature but the energy level in the ground. The only real feedback I have from the borehole is the weekly ground temperature level, because the real energy level is invisible. Energy level should be thought of as a bulb of soil that has achieved a certain temperature - that has a theoretical thermal mass of several thousand kilowatt hours. As more energy is poured in or drawn out, the temperature does not change drastically, but the bulb of soil at that temperature changes size.
    The ground temperature has a characteristic curve shape that one can see emerging from this energy level simulation - a steep fall off in the months of winter, and a long slow climb out during spring and summer.
   The only way I can simulate this is to quantify the energy taken out and the energy put in, and then apply a Delta-T assumption for the heat being received from the infinite surroundings. Assuming a COP of 3 for the GSHP, I have assumed that the amount taken out of the ground is twice the number of kilowatt hours of electricity burnt by the GSHP.
   Variables unknown are many, the precise volume of the borehole, how much of the heat energy from the house is drawn from it, and how much the sun box puts down, how quickly the energy level in the borehole is restored from its infinite surrounding. The borehole is not an insulated store. The solar panels have never been calibrated (or yardsticked) in any table of data from CIBSE or similar.
    What I have assumed for the delta-T suction of energy from the infinite surroundings is that the colder the borehole (in the winter), the faster it will draw heat from outside. Conversely, I have had to assume that if the energy level rises too far, some of that energy will be moved out of reach, or lost due to system losses.  The rate at which it does this is proportional to the square of the volume of the bulb (because the area of the circular cross-section is PI*Rad^2). 
   Getting the balance right requires the application of a variable. Because we are talking of squaring thousands of cubic metres of borehole, we are having to divide by millionths. With some practice, the familiar shapes above appear. 

  •  In the top diagram, with the Sunbox disregarded, the energy level is restored over a long summer, but not quite to its level of the year before. The shape of the curve seems very close to the temperature readings. There is a steep drop until the middle of March - the end of the long winter when there has been heating but also there has been little sun. As March turns, the heating load of the house reduces and the solar radiation increases (either through the sunbox or the natural ground) and there is a long slow climb-out until the end of September when the heating goes on again. (2011 was exceptional, in that Spring came early, and the Summer lasted well into October.)
  • In the lower diagram, with Sunbox refreshing the borehole, the lowest energy level is reached earlier in March, and does not reach such a low energy level, as the diurnal solar capture is restoring the energy level before the bottom is reached. There is the same long climb out during the summer, but a higher peak is reached. When the heating starts in October, there is the same rapid descent, but at the end of the year, the energy level is higher. 
The data used here is the list of actual meter readings for the GSHP and the Sunbox.
Next task is to widen it to include 2010 and the first half of 2012. 

Wednesday, July 4, 2012

Circuit diagram with PVT

4 July 2012: Here is a modified circuit diagram for the addition of PVT panels on the south wall. The PVT will be on the south wall of the house.
    It will need more than the usual care with metering because the PVT energy will go though the same energy meter as the current Sunbox. I will have to read all three meters and then deduct the energy readings to calculate the Sunbox energy and volume flow.
    In terms of connection, it is relatively simple, as I can Tee into the existing pipes at the north end. These pipes will go through the wall into a vertical duct that can be seen in the rendering of the house extension.
     If I can I will do it with 15mm piping so that the liquid spends the least time possible in the duct. I have learnt from my earlier work that fat piping had some advantages (less flow resistance), but has disadvantages too apart from cost and bulk - mainly that too much of the liquid has to move before it gets to where it needs to go - to the borehole. If warm liquid sits in the pipe when the pump stops, all that useful thermal energy sits in the pipe and never got to the borehole. Each unit has its own pump, and has check-valves to prevent them interfering with each other.

Higgs Boson found?

Photo of the Hadron collider
4 July 2012: As i am writing this, I am watching the live broadcast from CERN of the Higgs Boson discovery....  Is it just a blip in millions of pieces of data, or is it a brief flash of a pixel on a screen? It's still a bit of a mystery as to how they know they have found it, but hopefully the Guardian or another publication will finally explain it! If this 'god-particle' finally proves that god doesn't exist, that will be interesting! (Google for 'Cern webcast' to find the page). At this time, we just have to 'believe' them.

It's quite interesting that they credited world wide grid computing for providing the power to find it. And they have analysed 500 trillion particle collisions.... (just trying to imagine it... thats the number of fine sand particles to fill an Olympic swimming pool, I hear)
  Here's a video of CERN's Joe Incandela trying to explain it:

Monday, July 2, 2012

Ground Temperature good

1 July 2012: Despite the weather having been so dire, we have managed to push decent amounts of energy down below, about as many or more than in the same time period last year. The ground temperature was tested and is 13.4ºC, about as hot as it gets in any normal summer.
   Hopefully this is because of:
1. the more efficient Sunbox design and the addition of Tubes, and
2. partially that it was cold enough to keep the GSHP heating for longer, which always helps to draw more energy from the Sunbox.
3. I haven't lifted the manhole cover to the manifold for a while, but the good temperature also hints that more energy may be going down if the manifold stays dry.

From 10 May to 1 July 2010601 kWh (SB). [PV 891 kWh], Must have been a good summer!
From 10 May to 1 July 2011: 508 kWh (SB). [PV 863 kWh]
From 10 May to 1 July 2012: 488 kWh (SB) and 145 kWh (Tubes) = 633 kWh.  [PV 733 kWh]

The graph above shows how strange the spring temperatures have been.

ETFE in 2013 perhaps

1 July 2012: I have written to Holscot asking them to delay supplying the ETFE front panel until spring 2013. I am convinced that ETFE would reward us with more solar capture on the Sunbox, and am curious to get it up there so I can measure it.
   The priority this year is the house extension, and that means the PVT becoming the next system for solar capture using my Surya method. I can't manage both of these at the same time, as the University term will be rocketing towards me, timewise, with the autumn term starting end of September. If it goes up, the PVT will be measured against the existing Sunbox for this coming year, and then I can consider the ETFE in 2013.
   Any new system that I proposed for another house would undoubtedly use ETFE if possible. The circumstances of my system at Peveril Solar house is that it is a prototype, and needs to be accessible for frequent maintenance or modification. The ETFE is quite a hazard if I am using a ladder, it could not take the weight of ladder legs leaning on it.

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