Wednesday, June 30, 2010

Payback for Sunboxes?

Is there a Payback aspect to Sunbox augmentation of a ground source heatpump? 
   I have been thinking more about Payback, in respect of Photovoltaic. But does that apply to Sunboxes? 
   Only a couple of winter's testing will prove that conclusively, in terms of reduced electricity consumption. More significantly, in our article for Shanghai, Blaise and I have pointed out that if the sunboxes are effective and permanent installations, then the size of the ground loop can be reduced - perhaps saving the entire cost of the sunboxes. 
   Our ground loop is presently calculated to get 9,800 kWh from the ground annually. If we put 2,500-3,000 kWh of solar heat down in the same time and recover most of it, then the ground loop or borehole depth can be recalculated for only 7,000 kWh. The original boreholes were 48m deep and cost £4,500. Could we have reduced this by £1,000?
  However..... I would say No..... the deeper the ground loop, the more effectively you can bury the heat from the sunboxes - well away from the seasonally changing upper surface. So if you can afford it, have the full depth borehole or horizontal ground loop, and just enjoy the reduced electricity bills and faster heating cycle by the GSHP. The full size ground loop is a precaution against a future occupier misusing the sunboxes or not repairing a failed thermostat or solenoid valve.

  Could we improve the performance of the Sunbox system by doubling the number? We presently have 4 sqm of black panel. I don't reckon we could. Heat is transferred by 'delta-T' that is the transfer of heat by temperature difference. So just doubling the area would not make the liquid hotter, just more of it. 
   One idea could be to use a professional quality solar thermal panel, delivering temperatures of up to 40-60ºC which could be better for Summer charging. I am against that on technical and cost grounds, but mostly because the performance in Winter would be very poor compared with the solarium style panels that can tolerate freezing. The pipe diameter in a solar thermal panel is small, so the GSHP would not like the pressure drop, and you would need an intermediate hot water storage tank with a larger diameter coil going through it - costly! My sunboxes were performing well in the cold spells of March - and I look forward to the coming winter to prove that they will work well all through the cold season.

Monday, June 28, 2010

Page all about Photovoltaic

28 June: On the Rushcliffe Solar Website, I published a page with Frequently Asked Questions about Photovoltaic installations. There is also one on the Financial aspects. There are many such pages on the web, and most of them agree, especially since a few months have gone by since April 2010 and pages have had time to update. But I get asked these questions all the time at meetings with people, so I thought that it was time to answer many of these, succinctly.
   One thing I have been getting my head round is Payback on PV installations. Instead of the Simple calculation (divide cost by income) you can do a Compound calculation, assuming that energy prices will increase over the years, and that the Feed in tariff will be index linked. In that case, it shortens the payback period by 10% or more. £1000 a year income over 25 yrs sounds like £25k, but if energy prices grow by 3% annually, that is £36.5k.

   Sorry that I have been a bit quiet on these pages about Charging the Earth, but it's a long summer with not much heating to do, and lots of solar heat being buried into the boreholes. The GSHP is performing well, using 39 kWh less in June than it should have done by normal expectations.
   I do have projects in mind, particularly, the addition of the Savita panel to the south wall, activating the spare PV panel, and some Heat Recovery ventilation. And Rushcliffe Solar has now taken off, taking much of my time for the summer.
  I have a holiday coming up, ten days in France. I will probably turn the sunboxes off, to reduce the pumping energy consumption (because I believe that the most efficient use of these is when the GSHP is regularly pulling the heat out in the same day). In summer, pump could be 0.8 kWh per day, and although this is mostly powered by the roof, the system continues to run until 10pm or 11pm. Alternatively, I can push the activation temperature from 20 to 30ºC ensuring it runs only when the sun shines.
    Interseasonal charging to make the GSHP more efficient in Nov/Dec will not really be affected by whether they will be on or off for ten days in July)

Good Energy supporting the little generators

28 June: This a non-commercial plug here, because of course, everybody makes their own choice of whom to supply electricity - based on price usually, but the change can also be made on ethical grounds. We made the choice 4 years ago to change to Good Energy as they are the only UK electricity supplier who are 100% renewable based energy - under their charter they can only deliver electricity in quantities that they can procure as completely renewable.
   They do have a wind-farm of their own at Delabole, but they need more power suppliers if they want to take on more customers. Therefore they are extremely eager to sign up Home Generators and give them plenty of support. Before the Feed-in Tariff began in April 2010, they were paying us a sort of early feed in tariff of 15p per unit (instead of the normal selling price of 5p per unit) from 1st October 2009 to 1st April 2010. So even if the FiT had never happened, they would still have provided income for some payback.
   If you do not have your own generating capacity, you pay a bit more than the cheapest, but what you pay is furthering investment in wind-farms and home generation.

Tuesday, June 22, 2010

Celebrating the Solstice

21 June: It was nice that the last two solstices, Dec 21 and June 21 were both sunny days, so one could compare. In this diagram, the two Poisson curves are at the same time and power scale, and show the difference, impressively comparing the day length and the solar intensity. Other people might go and watch the Sun rising over Stonehenge or Glastonbury Tor.... me? I check the PV meter and the SMA website, measure the time of the sunrise over Sharp Hill etc.... How sad is that! .... :)
   Because we have the high Sharp hill to the south, the winter sunrise is an hour later than on level ground, and the sunset an hour earlier. So in the morning, there is daylight, but not sunlight, hence the tail in and sudden steep rise just after 0930 at the start of the December solstice. By March equinox, the hill has less effect. At this time of year in June, the roof is consistently outperforming all the predictions, and with the sun rising and setting in the north quadrants, the hill has no impact on the performance, because the Sun is rising and setting to the north. We should have up to 2,250 kWh harvested by the end of June (at the present average), and then we have three summer months of July, August and September to bring us to our PV anniversary of October 1.
   We have had no payment from the Feed in Tariff yet, the first one can't be expected until October. I need to chase Good Energy for payment up till the April 1 date, as they are promised to pay some sort of tariff prior to starting the main FiT.

Thursday, June 17, 2010

Weather Comment and Form filling

17 June : Weather: A good time for PV!
April had about 40% more sunshine than we might have expected from the computer prediction, and
May had about 25% more - if the real output of my Photovoltaic roof is anything to judge by.
June started badly with some days that reminded me of February, but has now caught up nicely with a sequence of sunny days, and the colder air temperatures giving us good solar capture. We have had a couple of 'Best of the Year' days where combinations of good sun and north wind (cold air) have produced over 25 kWhrs in a single day - on the 4th and 16th June. I don't expect more than this for the remainder of the year.

Form Filling
If anybody reading this now has solar PV panels installed, don't forget to register as a Microgenerator. There are forms to fill out and send off, but don't be put off by this - you are, after all, signing up to receive quite a substantial amount of money from the electric utilities for the next 25 yrs, equivalent to more than twice your total installation cost... so a little bit of checking is required. You are likely to have to ring up your electric utility to get some of the details finalised (eg your 'generating station number' and ROC ID).  For form filling you also want to have meter reading handy, especially at the key moments of April 1 and October 1.

Read the meter regularly:   It is also worth recording your meter readings, either daily or weekly, so you can compare your actual installation with what is theoretically possible according to the computer model. There is no tuning you can do, other than checking for bird shit on the panels... well rotating the house to face south better would do better, but that's slightly more difficult.
  If you have a handheld meter, the numbers will roll off when they are 30 days old, but you can download them with a USB cable to your PC/Mac, and of course you can read daily totals off your LCD display on the inverter. If you are really information minded, your inverter may be able to take a Web router, that sends data to the SMA website in Germany and stores/displays your data for ever - every day for the last or the next ten years!.
  My meter readings are a bit manic, as you can see from http://tinyurl.com/peverilmetering but you don't have to be quite this obsessive! If you do want to be this obsessive, then do not be afraid to ask for copies of the spreadsheet formulae, so that you can use dates and times to computer daily generation and consumption.

Wednesday, June 16, 2010

Summer! - 17p Resistor tunes GSHP efficiency!

June 16 2010: I have been too busy to do anything on the earth charging project in the last week due to the end of term shenanigans at the university, a non stop round of marking, re-marking, filling in feedback and spreadsheets, attending examiners meetings etc.


But, hey! it's summer, and the system is working well, energy is being captured by the roof, energy is being pumped deep into the earth, and the whole process is being metered, all along awhile.
   The datalogger is still working fine, but there's not a lot to report. The GSHP remains in sleep for such long periods. So we may unplug it (label the cables for reconnection next autumn) and put the datalogger on other projects at the Uni. So there's not a lot to say right now.

   One small thing remains - the external air temperature is a primary way to control the actions of the GSHP and the Underfloor heating system. The external air temp GT2 drops below 15º in the night time so the Underfloor heating pump wants to run all night, checking the temperature. But as it always gets a 'warm' response, the GSHP does not do any heating. ergo, 2-3 kWhr is wasted everynight with pumping around the floor for no result. (We wouldn't want the heating on at night even in winter).
   In a cold house this would be necessary. In a very well insulated house, this is unnecessary, even in the depths of winter - the temperature holds good most of the night, losing one degree at most even with a bedroom window open.
  Now I have followed David Atkins' advice and rigged up 17 pence worth of resistor, all 4.7 kilOhm of it, inside a domestic 2-way light switch. When this is switched to the external thermistor, GT2 displays the correct temperature. When switched the other way, the GT2 temperature climbs to 25.0 ºC, and then sits there - tricking the GSHP into thinking it's summer - all night long! We can now leave the GSHP on 24 hours to avoid HW pasteurisation, but have no heating required until late September perhaps. Having underfloor circulating pump turned off, and using the GSHP's own timeclock to prevent water or heating during the night,  we hope to use even less electricity in the 24 hour cycle.

July Postscript: This Resistor has improved efficiency, along with my mastering the inner timeclock of the GSHP, and the warming effect of the sunboxes. During June, the GSHP should have used 110 kWh in the month for water heating. The actual consumption was 71 kWh, nearly 40 kWh less than expected.

Tuesday, June 8, 2010

Timeclocking and Switching the Heatpump

8 June 2010: After a discussion with David of Ice Energy, I managed to work out how to use some timeclock functions within the GSHP's controller that allow us to have On-Off-times that will turn the Hot Water and the Heating OFF overnight, but not affect the calculation of the Pasteurisation time.
    Also, we wish to turn off the heating circuit off while the GSHP is in sleep without having to turn it off altogether - so that the time-counting for the pasteurisation cycles isn't affected. So by attaching a relay wire from an internal connector to an external switch, we can force the compressor off. I discovered that this does NOT actually turn off the auxiliary pump that sends liquid around the underfloor system (checking the temperatures) - the sleeping GSHP still sends power to the pump. In such a well insulated house, we just don't want it wasting 125W pounding water round and round all night, audibly, just to check the floor temperature while the GSHP slumbers.
   So in this case, David advises that a 4.7 kilohm resistor can be switchable on and off on the bellwire that comes to-from the external air temperature sensor on the north wall. This will trick the GSHP into thinking that it is a hot summer's day, and will force the underfloor heating system to sleep.

Monday, June 7, 2010

Pasteurisation in mornings

7 June 2010 : Since I wrote wrote on the 14 April that the GSHP seems to think it's a 'kettle', I have now got used to the overheating of the water in the mornings. 
   The GSHP is designed to be left on all the time, 24/7, and the time for 'Pasteurisation' can be set to a time difference, such as every 2 weeks, or every three weeks. So left to itself, the DHW will remain at or near the target, and perform economically with small heating cycles, and only have one bigger heat up every 2 weeks or so. Pasteurisation means boosting the water to 61º or 62º C. This is a safety precaution, in case Legionnaires bacteria have had time to grow in the tank. 

What seems clear, now that we are well into the summer, is that the GSHP checks its internal clock at start up. There must be a measured time of 'Off' after which it will embark on a full Pasteurisation cycle. We don't know if it is 8 hours, 12 hours or what. It is somewhere between. If it's off for 3-4 hours it does not do this, but in the mornings after a night of Off (e.g. 10 to 12 hours), it does do this.
   We have got used to it now, it does turn off correctly after reaching 62ºC, a full 11 degs C greater than the target temperature of 51ºC.  The earth is so warm after a night's recovering and distributing the heat that was put down the previous day that the morning warmup cycle is acceptably quick. I would willingly leave it on all night, if it wasn't for the fact that it circulates water round the underfloor heating circuit at night, using pump power of 125W and making a small amount of noise. We don't want to be hot at night.

Small tuning changes to the system....

7 June : Two small changes recently:-  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. This only happens when the air temperature in the sunboxes is less than 20ºC. This often happens on cold cloudy days or in the early evening.
    To make the Delta-T less of a hindrance, I reduced it to 4 degsC, instead of the 5 degs that I have used since March.
    The algorithm in the heat pump's controller likes to calculate the outgoing glycol to construct a difference of about 3.6 degC between the input and output temperatures. This makes me think that while I can reduce the delta-T to 4.0, I should not be tempted to reduce it to anything less than 3.6 degsC. There has to be enough delta-T to push energy from the air temp into the moving liquid in the panels, through a wall of polypropylene.

Paper for Shanghai August '10

7 June: Blaise has been working on an 8 page conference paper describing recent monitoring of the Sunbox system. This is for the SET conference in Shanghai, August 2010.
  As this only describes the 6 days of monitoring back in May, at a time when the weather was very benign, it is difficult to draw decisive conclusions from the monitoring. We conclude by saying that another paper will be presented in a year's time, describing the monitoring of winter time performance, over 2010-2011. It is quite rare for people to look forward to winter, but in my case.... I am looking forward to seeing how the system will work compared with winter 2009-2010. It's unusual to wish for the winter to come more quickly...

Quoting from my conclusion:
"The manufacturer’s estimate is that annual heating demand is 14,600 kWh of which 9,800 kWh must be drawn from the ground. The most that the 4 sqm of sunbox can put down is 3,000 kWh, less than one third. Therefore, there can be no intention to raise the temperature of the soil – prevention of long term cooling is the primary hope. The research team will continue to monitor performance of the GSHP and Sunboxes into the Winter 2010 and Spring 2011, and this will be the subject of later articles on inter-seasonal performance."

Sunday, June 6, 2010

Good Sunny days in June

6 June : Soon we will be at the Solstice and I will have to accept sometime that weekly statistics will get worse as the equinox approaches. In the last three days, we have had something like 20.5, 24.9, 20.5 kWhr. You can see that the days either side of the 4th June had slightly higher peaks, but the best days are when we get consistent sunshine, but low temperature (red line indicates temperature). I guess that 24.9 or 25.0 is the best we can expect all year, as June, July and August will have hotter air temperatures.

Tuesday, June 1, 2010

Removing a redundant valve

31 May : Just a small plumbing change. I have done less on the blog and the project recently as I have student essays and work to mark. But I made a quick change to the plumbing in the loft. The original Danfoss 2-port solenoid valve is now redundant, as the 3-port one just above the heat pump is now the primary valve.
   Now, when the thermostat says Yes!, the 3-port valve down below gets the command, opens, then relays power up to the pump to operate.
   I am sure I shall find a use for the 2-port in a future project, and perhaps the actuator can be modified to be used as a servo motor to open and shut louvres electrically.

[October '10 Post script: This plumbing arrangement is what I call 'Trickle and Whoosh' - on the system in East Leake, I shall use 'Trickle while we Work' which is necessitated by the narrower diameter pipework, but might be more efficient. If this turns out to be the case, I might even cut my losses and revert this system to the Trickle while we Work. See Glossary.]

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