Monday, June 25, 2012

June 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. 

Was June horrible?: Yes! At the end of the month, the PV statistic displays what a horrible solar month June 2012 has been. You can see from this that June 2012 was worse than April and August of 2011. May was only acceptable because there was the one-week heat wave in May with 7 days of unbroken sunshine... oh how quickly we grew to take it for granted!

Heat pump Degree Day comparison
Despite the cold conditions, the GSHP consumption is not offensively high because the insulation of the house is sufficient for us to get most of the last two months without needing the heat.

24 June 2012: The bad weather continued with people in Yorkshire being flooded out (my sister in law lives in the worst hit, Hebden Bridge, although she is safe on the hillside above. England did well in Ukraine beating Sweden and Ukraine, but finally went out to Italy on penalties (after looking not good enough to beat Italy). The Dalai Lama and Aung San Suu Kyi visited England, and ASSC spoke to the UK parliament, apparently the first female foreigner to do so. She seems to be regarded as the Nelson Mandela of our decade. She is also receiving the Nobel Prize whilst in Europe. Jimmy Carr had an embarrassing time as his tax dodging was revealed by the prime minister, the PM not revealing that the source of his family wealth and that of some of his party's funders was from the same activity. In Rio, the climate summit that is meant to make the planet safe for future generations passed almost unreported - we'll find out if some decisions were made. Egypt's islamic presidential candidate won, so expect some consequences there! For the Peveril Solar house, what?

  • House annual has tipped over 5,000 kWh thanks to this lousy summer,
  • GSHP annual holding out at 2,975 kWh.
  • Solar PV looking worse at 3,148 kWh but as I only expected 2,800 when they were installed, I have to be grateful that it is above 3,000 even in this bad June.
  • Surya system is showing 2,585 kWh (and won't get back to its previous glories of nearly 3k until next April). 
  • Ground Temperature is 12.9ºC..... holding good considering the lack of sunshine.

17 June 2012: Well in other parts of the world, there are Greek elections (knife edge for destiny), Egyptian elections (another knife edge for destiny?), Football elections (who plays best wins), the slow burning farce of the US election (US billionaire offering unlimited money to buy the election for the mormon asset-stripper / failed governor). Oh, and the Queen visited Nottingham this week (with William and Kate), but somehow failed to make it to West Bridgford to check out solar panels.
  • House annual 4,995 kWh (dangerously close to 5,000 ) but biennially its 5,148 kWh/yr, so let's hope it doesn't go above that as this cold and rainy non-summer continues.
  • GSHP annual 2,972 kWh (dangerously close to 3,000 ) but biennially its 3,154 kWh/yr, so ditto about the summer.
  • PV, this is a horrible month. 3,204 kWh annual, depressingly dropped from our glorious heights of 3,450 a few months ago! We are in the 17th June now, and scored only 183 kWh in the month, and last year, we scored 317 kWh in the same time period, and 525 kWh in all of June 2011. 
  • Sunbox+Tubes annual, I won't know for a while, but as I had a new meter fitted and lost a whole month of April action, the annual amount is 2,596 kWh. Gradually this will climb, I hope, and will leap ahead next April when the missing month gets peeled off the calculation. 
  • Ground Temperature is 12.9ºC..... holding good considering the lack of sunshine.
  • The new question is to compare the performance of the Sunbox versus the Tubes. On this, Time starts on May 10th when the heat exchanger was finally in place. From 10 May to 17 June, the Tubes have captured 101 kWh and the Sunbox collected 350 kWh. I'll report on this in a separate posting. 

Wednesday, June 20, 2012

PVT as a third thermal source

20 June 2012:  [Extension] I am increasingly thinking about what to do with the south facing roof of our intended house extension. I cant let the opportunity of a south facing roof go to waste, and had initially thought of PV-Thermal as the answer. Now that the event draws near, I have been considering this in more detail, and have made contact with NewForm Energy who I met at EcoBuild 2011.
  Newform seem to be a company most in tune with what I am doing here, and have gone so far as to develop their own model of heat pump that can take solar heat directly, instead of going through the ground loop first.
     I wouldn't be able to do this with my IVT, without some modification. Actually,..... I can see how I could make an amendment to the circuit, with a controller operating a solenoid valve to make this possible - but I have to ask Ice Energy if the parameters of the heat pump can be changed to accommodate a warmer input temperature.
    Newform have several pages of case studies of solar earth charging already achieved, and which are listed in their case studies. In particular, there is one called Brambles (newbuild in Essex) and some holiday cottages in Cornwall which are using this. The most notable example for me is Walthamstow fire station with 188 sqm of PVT panels. They have also done solar-thermal-PV facade development at Warwick University.

Two PV panels would provide enough electricity to meet all the annual energy needs of all my pumps, controllers, meters, PV webrouter, and more besides - making the operation of the solar charging truly carbon zero in all senses except in the embodied energy of the copper and glass. When they are all going full blast, they use 120 watts of AC power. The additional pump, controller and meter would add a little bit more, perhaps to 180 watts total, when all systems are running.
     Two square metres of Powertherm  facing south would make an significant additional input to the thermal charging, and would be measurable. Although they are on the same loop as the Sunbox, I would put an independent energy meter on the PVT panels, and would take the reading of the existing Sunbox meter, and deduct one value from the other, so I know the individual performances.

Monday, June 18, 2012

Sunbox versus Tubes, again

17 June 2012: We've had a full five weeks of running since the heat exchanger was installed and both systems have ran satisfactorily in identical weather conditions. It's time to get back to the new big question, which is to compare the performance of the Surya sunbox versus the Kingspan Tubes.

For this discussion, Time starts on May 10th 2012 when the heat exchanger was finally in place. From 10 May to 17 June, the Tubes have captured 101 kWh and the Sunbox collected 350 kWh. The Tubes seem to react only to sunlight (to build up sufficient delta-T to start the pump) whereas the Sunbox is happy to work on overcast days, just if the air temperature in the box goes up and creates a bit of delta-T. The large mass of liquid in the sunbox means that it does run for some hours a day, and there is time for the energy to reach the borehole before it cools. (I now wish I had plumbed the original sunboxes in using 22mm pipe). Hence there is a major performance difference, a ratio of 1 to 3.5. If the tubes were on the south wall, they would fare no better (less insolation than on the roof). 

Double the quantity on a south facing roof at 37º might get closer to it, 11-12% more insolation over the whole year compared with the present position. 101 kWh times 2 times 1.12 = 226 kWh in that time period - still not enough.

On a simple linear calculation, it would seem that 3.2 times the area of the present tubes might be enough to equal the Sunbox, i.e. 6.4 sqm of tubes. But there is never a linear relationship between surface area and energy capture, because much depends on the admittance of the storage medium, rate of circulation, distance to thermal store. A water tank reaches optimum temperature, reduces its admittance as the tank temperature rises and the final result is stasis, no further admittance. A deep borehole is the best, because its volume is close to infinite in comparison to the size of the house and the solar panels. Double, treble or quadruple the panels and it could still take as much energy as we can send it. But would 6.4 metres of tubes cost a lot, plus a much larger heat exchanger? Yes they would, more than a Sunbox using solar-focus panels. The solar-focus panels are so cheap (less than £100) that one could cheerfully add another two, and make it 6 square metres, if one had enough remaining surface area.

Comparison of Sunboxes, new to old: I'm glad to see that last year (2011) in very sunny and warm conditions, the old Sunbox captured 350 kWh in the same time space of 2012 that the new one captured 356 kWh, which indicates that the new design works better, having endured 5 weeks of rain and cold with only one week of sunshine in all that time, whereas 2011 at the same time had remarkably warm and sunny conditions.

(My next big question will be to compare PVT with the two earlier installed systems.)

Sunday, June 17, 2012

Tubes solar orientation - east or south

17 June 2012: The Tubes are on the east facing roof, and there was no choice in the matter - there was a clear easy space on the main roof, and tubes on the south wall elevation would have been easy targets for the hundreds of walkers and children who pass the house along the path near that wall - through a field full of convenient stones. There would also be much longer pipe runs to get the liquid to the point where it goes down to ground. With an east azimuth you have to get used to seeing most of the action happen in the morning, with the sun going from sunrise to midday. After that, the angle is very acute or it is shade.
Left, Panels mounted on the south wall, as with the Sunbox now.
Right, panels mounted at 40degs on our east roof, as with the Kingspan Tubes now.
I did a test of the insolation on the two surfaces, and found that the east roof has some advantages. This estimation from PVGIS is mainly for PV, but the two right hand columns show the solar energy falling on each surface, per square metre. Over a year, the insolation per square meter would be 774 kWh/sqm on the vertical surface of my south wall, and it is 913 kWh/sqm on the existing east roof. The ones on the roof have a better view of the sun at midday than the wall mounted ones. 
   On this basis, I can be content with their position. 
Table of insolation on a south facing roof at 37º
(for the Nottingham Lat and Long)
showing it to be 11-12% better than the present location on the roof.
Apply the idea to a roof mounted sunbox?
Perhaps, I should also think of how one might build a roof mounted sunbox, one that can be on a roof instead of a wall, a thicker type of enclosure for solar focus swimming pool panels that could be roof mounted. It would not need back insulation, it would need a side frame, and could have a top of either ETFE or of triple skin polycarbonate. It would need to fit to standard fixing rails. This would have to be value engineered as a comparison with a bundle of tubes. 

Shader for south window and PVT

17 June 2012: [Extension] Thinking about the small south extension: we will have a large triple glazed window, the sort that lets in more heat than it lets out, computed over a year - contributes to the heating. We will also need a shader and I am experimenting with metal structures. The one in the image rotates to be virtually invisible for winter and over cast conditions.  A quick tweak of the shader angle, and it provides good shading for high summer sun.

By the way..... 
What is the purpose of the Solar PV panels?
I cannot let the opportunity for a south roof to be lost, and Im eager to try a third way of charging the earth - using PVT, PV Thermal. There's a duct in the design linking the roof of the extension to the inlet just below the existing sunbox - that can carry insulated pipes from the PV panels to the loft, and can be connected to the existing piping at that end.
   The PV would be used to charge a battery, from which we would run low wattage devices in the house - mainly the pumps in the loft, the energy meter, the printer, the broadband modem and the laptop. I have a 600watt inverter, so the total has to be below this figure. With liquid cooling, the PV capture in summer will be 15% higher than two equivalent panels would be.

Saturday, June 16, 2012

Meetings, progress

15 June 2012: I've got a bit behind with posting weekly meter reports, although the records are of course being kept. Ive been busy, but also, the weather has been lousy. Last year, replacing a cold year (2010) with a warm year (2011) there was a beneficial effect on the annual figures. Although we are now doing the reverse, replacing a warm year with a cold year, I don't expect the figures to get back to what they were in the bad old days. 3,000 and 5,000 kWh/annum for the GSHP and House seem to be the attainable targets, and I have enough readings now to take a biennium period and calculate the difference and divide by two - to get a figure closer to an annual average.

The original design. The front profile
is less bulky, and less controversial for planning
application purposes. The mirrors are optional extras.
The corner mirrors were ineffective compared to
the effort in getting them up there.
Ive had two useful meetings this week. Monday, was with Mike Siebert of EcoLogic who will help us on the construction of the extension. This is still going ahead as far as we know, and we met his ground works expert who will do our slab, with my highly insulated details. It's a combination of self-build and Mike-build, with the timber and insulation from John A Stevens of Nottingham. The superstructure will be built in hand built SIPS construction, sandwich of OSB board and PIR insulation.

Holscot, ETFE
The meeting on Thursday was with David and Leslie Joyce of Holscot who are offering me ETFE frames with which to re-front the Sunbox. They had come to view the system and more clearly understand how it worked. Although I would not normally do this till 2013, it will be possible this year because we will need some scaffolding for the extension, so might as well do the sunbox at the same time. Scaffolding will be a lot more difficult in the future once the extension is built.
   If the ETFE is an improvement, I would return to the idea of the profile being close to the wall, i.e. projecting no more than 200mm like the original sunbox. There would be the option to have a mylar covered foot mirror, like before, to bounce heat upwards. ETFE is not reflective in the way that the original optical quality polycarbonate was.

  As the ETFE is soft transparent sheet, it would not be possible to lean a ladder against it, so I shall ask them to include a centre vertical mullion (which can be stiffened by an additional angle behind). This can take the lateral force from a ladder. I shall miss the effortless ease with which one can just pop-rivet into polycarbonate sheet. A new special edge detail is required to incorporate the ETFE frame without penetrating the ETFE sheet.

Tuesday, June 12, 2012

Immersun, make use of spare power

12 June 2012: I recently became aware of this new product, Immersun, that is due to be launched during 2012 by a company based in Lincolnshire. The idea is to monitor the output of your PV installation, and when it is reaching a good peak and you are not using it for something else, to divert power to a device of your choosing - mostly likely to an immersion heater. This doesn't in any way interfere with your OfGem meter or installation because it comes after the consumer unit and is merely measuring the flow of power out to the grid.
     It is programmable, so you can decide what the power level is at the point where you slice off the surplus and feed it to devices in the building. An Immersion heater is the most suitable receiver, because it is able to manage intermittent operating. If you used it to power say a washing machine or TV, the device would keep turning off whenever a cloud crossed the sun - which would be very annoying. If the water in the tank is already fully hot, then the thermostat does not take any power and the power continues on to the grid as normal.

Comparison with Solar Thermal: I have a slight ideological objection to this, in that a solar thermal panel is highly efficient when it is working, whereas a solar PV is only converting solar energy at 10-15% efficiency. But if you have a house where you have enough PV but no further space for a solar panel, or you cannot manage the complex plumbing for a solar thermal panel, this is one interesting idea - the power source is free, from the Sun, and the wiring is simple. Normal solar thermal systems are surprisingly inefficient because they spend much of the time in Stasis. The tank gets up to temperature on sunny days, nobody is taking a shower, and the panels have nowhere else to deliver the heat. So the efficiency drops from a theoretical 90% to less than 30% or even less if the family are not using the hot water.
     A full solar thermal installation requires a lot of plumbing - a preheater tank, pump, solar controller, expansion tank and a lot of pipes and insulation, and the solar thermal panel itself - probably £2000. Some houses could not accommodate or afford this. The roof might not take a solar thermal set up because there isn't enough remaining surface area or volume in the loft. Given the current payback and tariffs, it's more effective to maximise the PV on the roof. It takes vastly less effort to divert mere electrical wires in the house compared with the high temperature insulated plumbing paraphernalia of solar thermal water heating.
      Cost wise, it makes sense. It's likely to be offered for £300, and it requires electrician installation. With a solar thermal system, each primary component costs more than that, and plumbers are more costly than electricians. If you are a low-consumption water user, then it takes a short time to pay back on £300, but several lifetimes to pay back on £3000.

Many PV-users make a lifestyle adaptation, for example, waiting for a sunny day to do the ironing, the baking, or to run the washing machine (we do this). A programmable device like Immersun enables that choice to be made automatically.
   We could not use Immersun in the Peveril Solar house because we use a Heat pump with integrated tank. I am just telling the blog-readers about it.
   I wonder if you have to modify the programme depending on the month. For example, in summer I could set it to work if PV power exceeds 3kW, but that wouldnt work in winter. We are glad to exceed 1 kW in winter months.
(PS I am not paid to post this article, I am writing my own assessment of its potential )

Horrible Spring, horrible June

11 June 2012: We have Jubilee, the Derby, the Paris Open, Euro 2012, and are looking forward to Wimbledon and the Olympics. But look at it climatically! This diagram illustrates what a horrible Spring we have had for PV and thermal capture. June is only 11 days done, more than a third of the month. If it continues this way, June would score as little as March, April or last September. Look at June 2011, in which the monthly score safely exceeded 500 kWh! This month of June 2012 looks only likely to achieve 300 kWh. More rain is forecast for the rest of this week.
    It has done a great service for gardeners in ending the drought and removing the need for regular watering!

17 June Postscript: Up to this date, June 2012 has only scored 183, and in the same time slot of 2011, the PV system scored 317 kWh. 

More about thermal storage in tall buildings

11 June 2012: In February'12, I published an outline illustration about including and distributing thermal storage in tall buildings, adapting some of the ideas in the Peveril Solar house.

Solar thermal energy collected by a large thermal array on the roof (above a roof of plant rooms and tanks and machine rooms) and delivers energy to local and intermediate stores - tanks for hot water and thermal stores for enough energy for space heating. A major store can be at roof level, and short term thermal energy stores every 15 to 30 metres vertically (4 to 8 floors).

Here is an additional image produced to help my students illustrate the concept better - it is kept very simple. It is based on their project for a three tower scheme in London.

Surplus energy is shipped from thermal stores to underground piles for inter seasonal storage, during night hours in one quick efficient night time operation using off peak power - providing a good delta-T for the next day between the collectors and the thermal stores.   It is impractical to have continuous charging of piles, the system losses of daily pumping over such a distance would be prohibitive. So it is better if pile charging is done systematically based on clock times and temperatures in the stores that you are purging.
Thermal stores are purged, but Water Tanks remain at the optimum temperature for hot water requirements.

The facade can also include solar thermal collectors, which would shorten pipe distances to the local stores - reducing cost of piping and system losses through pumping and heat loss in transmission. One of my student groups for the New York project 2 years ago had a continuous thermal store running in in compartments in a vertical duct, so that solar panels on each floor level on the south facade had only the shortest possible distance to recharge the store, and the shortest distances from the store to the apartments.

I will publish more excerpts from the drawings of the students within a short time.

Friday, June 1, 2012

Why use a Heat Exchanger?

1 June 2012: Someone from Texas replied to one of my postings about the Heat Exchanger. I thought I could summarise here why I installed one for the Evacuated Tubes. The tubes circuit was installed without one at first, but we found it to be too intermittent. It would come on, work for a minute, then go off.

There're two main reasons for using it:

• First is a time delay, allowing the block to warm up with one circuit while the other waits until it is ready to download the energy. The delay is such that when the download occurs, there's time for the warmed liquid to make it down to the borehole. Without the H/X, the Tubes are dowsed with cold liquid, reduce their temperature, and stop the pump. The liquid is only moved about 5 metres down the pipe because we have 28mm and 40mm piping to the borehole - so the direct connection has no beneficial effect on the borehole temperature. With the H/X installed, the two circuits get into a steady state, where the tubes can operate at about 21-23ºC, and the ground loop at about 12-14ºC, without stopping the pump.
• Two, It also allows the two circuits to operate at a different pressures. When the tubes are operating well, the pressure in their circuit increases and the circulating pump is more efficient.

• Sorry.... I have thought of a third! We could have had a water tank. But I don't want to bring mains pressure water up to the loft, we don't have a need for the hot water (that is below), I don't want to have to use up so much copper and a large volume of space and a heavy weight. What else? A solid block of metal cannot freeze, boil, evaporate, get algae, get legionnaires, leak or burst!

Liquid to liquid heat exchange is completely efficient in a solid block of conductive metal, if the outer case of the exchanger is well insulated - almost all the joules get across. The operating temperature is only between 20-23º and 5-6ºC, so incidental heat loss through the insulation to the air in the loft is minor risk. Inside the block is a complex set of pathways for the liquids to go past each other, ensuring good transfer without mixing. One requirement is that if one circuit is entering north and exiting south, the other has to go in the opposite direction, south to north.
  This has been a learning process - I had never seen or experienced the use of a professional heat exchanger before, although I had planned something like that, for self building - using the PCM balls back in autumn 2009. Even for this recent installation, I had planned something like a sandbox with an interweaving of copper pipes, until someone (Jason) pointed out that such things were available commercially. Turns out that our department has shelves of them, of different sizes, for different PhD experiments - and there are many in use in our labs, objects which I had not previously recognised the importance of!

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