Earth Notes: From the Inbox (and Outbox) 2013Updated 2020-10-29 19:42 GMT.
By Damon Hart-Davis.
I receive a stready stream of emails about the site, some of which I expand into stand-alone articles (eg Going Green in Newcastle-Upon-Tyne and Solar PV in Diffuse (Cloudy) Daylight) and others of which I follow up privately. Also, I've sent unbidden an email or two to register an opinion...
Don C wrote to me 2013/03/25 to tell me about his heating-control system:
I have computerised the central heating and hot water supply in my house. This is quite a complex setup being partly radiators (Bedrooms) and partly warm water under floor downstairs, corridors and bathrooms. The system does use EXCEL but only as a means of entering settings and displaying info. The system is basically as follows.
PC Running EXCEL.
EXCEL Worksheet displays:-
- The time and temperature settings for each room or system for each day of the week. You can have as many time and temperature settings as you want but in reality I've never used more than four per day.
- The current temperature in each room and the current outside temperature.
- The setpoint for each room controller.
- The current mode of each room controller. Remote setpoint or local setpoint.
- The current status for each room controller. Heat demand On or Off.
- Various statistics such as how long the boiler has been firing during the last hour, day, week.
- Additional EXCEL Worksheets record and store data for statistical evaluation later.
- Every minute reads data from the lower control elements and saves in the various Worksheets.
- Checks if any time / temperature settings require updating in the lower control elements and updates if necessary.
- Controls communication with lower control elements via USB Interface.
USB Interface links PC to lower control elements.
Lower control elements
Interface mother board.
- Multiplexes and De-multiplexes data to / from the USB interface and communicates with the various room controller boards.
- Room controller boards and various other boards are mounted on the interface mother board.
Room controller boards.
- Reads room temperature and creates an output Heat required or not.
- Receives setpoint from PC Via upper level things or from room local display in each room.
- Communicates with room local display units.
Room local display unit.
- Indicates current room temperature.
- Indicates current room setpoint.
- Indicates if current setpoint is set by PC or set manually locally.
- Indicates if heat is required to this room or not.
- Has push buttons to increase or decrease current temperature setpoint.
- Has switch to enable or dis-able setpoint update from PC.
- Has push button to request PC to do an instant update of setpoint.
Boiler, pump and valve logic. (Located in boiler cupboard)
- Communicates with the interface mother board.
- Contains logic to determine which valves and pumps need to be activated to meet the current heating pattern.
- Contains the various relays to operate valves and pumps.
- Has On, Off or auto switching for each output device.
- Has status display for each input and output.
The Interface mother board, Room controller boards, Room local displays, temperature transmitter boards and a few others are all designed and built by myself. The chip family used is CMOS 4000. There are over 100 chips in the system which has been running for about 20 years in one form or another without any problems. I suppose that the system could be simplified somewhat but I can't be bothered to mess with something that works fine and I believe saves me about 50% on heating bills (LPG)
And in a follow-up comment:
... When I started with it I decided to follow the sort of architecture we use in the chemical industry to control dangerous chemical processes. So if for example the PC goes on tilt the controllers continue with the last setpoint until instructed to change. Another reason I decided on this setup is that the system was built over a number of years, it was convenient to have a system that could operate at a low level and be progressively finished as building progress (the house) went on. It's only in the last year that the last part of the system was commissioned. If I were to start with it now or decide to upgrade then I would look at microcontrollers and the like. ...
MHRV Actual Efficacy?
Neil W wrote to me 2013/03/21:
I read with interest your article about MHVR, particularly Vent Axia's unit.
I think I should point out that although the unit can heat incoming air, via the unit itself, up to 84% of the temperature of outgoing, that does not mean it is 84% efficient, as you article suggests.
This fan discharges twice as much air as it draws in via the unit, which means that an equivalent volume is sucked in, unheated via infiltration elsewhere. As a result, the peak efficiency of this unit is 84%/2= 42%. As this is the peak efficiency, it is safe to assume that average efficiency of heat recovery is probably about 75% of this figure or 30%.
This is very different from the kind of efficiency theoretically achievable with full scale MHVR (or MVHR), which has a much larger heat exchanger, which is not constrained by the very small dimensions of wall fitted units. Units like Vent Axia's recovery some heat, but are predominantly useful for ventilating wet areas and controlling humidity, rather than energy saving.
I responded that I might disagree with his analysis because, for example, the infiltrated air elsewhere is a good thing IMHO because the negative pressure should reduce leakage losses of warm air to outside and the MHRV has the chance to recover heat from that 'saved' air too.
I didn't say that the infiltration is a bad thing, I was just making the point that half the air coming in is replaced with outside air warmed to 84% max of outgoing, whilst the other half is replaced with cold air. I thought it was pretty clear that max efficiency is only 42%.
Out of interest I contacted Vent Axia, who confirmed my understanding.
I still feel uneasy with Neil's analysis because, for example, temperature is not a direct measure of heat content (eg dependent on volumetric ratios and even latent heat of vapourisation under some conditions, etc).
Response to Ofgem Retail Market Review Consultation
2012/10/29: in response to the RMR Consultation I have rebeliously declined to answer the full set of questions and have cut to the chase:
The sole point I wish to make in response to this consultation is for Ofgem to allow or preferably mandate a *rising* block tariff to deter especially profligate (domestic) use, with the threshold at about 500kWh/month/meter.
I have seen suggestions that a raised portion of FiT and related green levies should apply to units consumed above that threshold, and the excess free could initially be about as much as the amortised per-kWh cost of the standing charge below the threshold to avoid perverse incentives to artificially split one house over multiple meters.
Peter F wrote to me again 2012/10/04 (see previous) and said:
... During our so called summer we had the windows open so there was no point in having the fan on. I turned on the fan after the first frosty day, last week. We had the usual 2 inches of condensation at the bottom of the windows. Since turning it on we have had a few cold nights, but no condensation. Exactly what I wanted. It is pretty quiet in trickle mode, but you can still hear the sound in most places in the house. I think the fan is not properly balanced, and the sound seems to resonate, maybe because it is installed in a solid wall. Unfortunately, the same cannot be said for when it is in boost mode. It is incredibly noisy and can be heard all over the house and even outside from the front (the exhaust is on the back of the property and there is a field behind us, so nothing for the sound to bounce back from). Again, i think that it is caused by the fan being unbalanced. I'll have to see if I can remove the fan and see if anything is damaged/missing. Maybe a balancing weight has fallen off or something....
I've found that it is not quite powerful enough as a extractor when showering. The bathroom fills up with steam to such a point that it condenses and runs down the walls. I think we will still have to open the windows in the bathroom a little when showering, but thankfully they can be closed straight away after we've finished.
I did [the install] myself. It was fairly straightforward, just very very messy. I put the transformer in the loft and then ran the cable in the loft to the top of the wall. I chiselled out some of the plaster on the wall so the cable would run within it. It has produced a very neat finish which I am really happy about.
I also think that I may make a minor modification to it for spring/summer use. There is a jumper inside which will allow it to operate in either trickle/boost or off/boost. In the second state it only comes on in boost mode when the humidity reaches the normal boost trigger level. So I thought I might add a little pull cord switch in to toggle between the two modes, without having to get to the circuit board, and because they have already produce a pull cord off/on version there is already a nice slot in the housing for the pull cord to exit.
Overall, if I can sort out the noise issue, I'm fairly pleased with it. It's a shame that the boost mode is not as good as a comparable normal extractor fan, but the house does feel much fresher which was the main benefit that I wanted. So the big question, would I get another one? Well, maybe, I think I need some more time to evaluate its performance over the winter before I make my mind up.
I said that I was now definitely thinking of a second HR-25 (but not the humidistat one) for the kitchen! (My partner objects to the noise in boost mode also, and it should definitely not come on uninvited in the kitchen, eg while she's trying to talk to someone in there.)
Peter agrees that if he were to buy another he would put it in the kitchen too.
While he had me thinking on this topic again I noticed the Tempra range for which the simple pull-cord version is much cheaper, a bit more discreet, and only a tad less efficient but still good. Also it is balanced flow (though can be switched to extract only) which I think I want for any further MHRV in this house.
Ah yes, I looked at that before getting the HR25H but I wanted something flatter for the bathroom. Also I think the HR25H is slightly more efficient than that one but for the kitchen it makes a lot more sense and it only requires a 4" hole which [would] be better too.
Intraday PV Generation Data
I have not been automatically collecting anything other than daily generation data from the PV installation on my house, in part because of the increased power consumption that implied. Rather I have taken intraday data samples about once or twice per month to avoid data loss (the Sunny Beam can internally store 31 days' data.)
I haven't exposed that raw data because of strange features that I had no round tuits to correct; strange data corruption and time offsets and multiple data formats (from SMA's Windows apps and the sunnybeamtool Linux app) in particular.
2012/09/25 Rob Ferber, CEO of ElectronVault Inc, and "one of the founders of Tesla motors (the battery guy)", emailed me:
Love what you are doing and the fantastic data sets you have made available. Well done!
A question: would it be possible to get some higher frequency data (perhaps 60s or faster bins?) for a single day with some clouds and some clear? I'm trying to find some actual data like that to feed into a simulation I've built of storage smoothed systems, and while I have simulated data, nothing beats real.
Well, flattery will get you everywhere, and I gave him a bunch of my raw 10-min data (apparently intraday PV data is rare on the Web, astonishingly), and he drew me some nice graphs from it in return. Any remaining strangeness is not for want of effort on his part!
Remember that the PV system has been enlarged twice during the data set that he graphed.
Robert H wrote to me 2012/08/05 re my Register piece How I built a zero energy cost, zero carbon home server:
I enjoyed your article about the zero energy cost, zero carbon home server, of a year and a half ago. Have you looked into the new Raspberry Pi computers? $35 and (someone needs to update Wikipedia) 512 megs of memory... Two watts on a heavy load... And a fantastic community to help out, too! And you can change OS just by sticking in a new SD card and rebooting, as well...
To which I responded that I had ordered an RPi, but for a friend in the US. I wouldn't be able to use it for my main server because of the lack of a battery-backed real-time clock especially given that I serve NTP.
But I do have a CuBox sitting on my desk waiting for me to pay it some attention instead, with more memory and less power than the SheevaPlug (and more/better I/O).
Ecotricity and Mass Energy Switching
In late June (2012) Ed Davey, Secretary of State for Energy and Climate Change, challenged the TTK (Transition Town Kingston) energy group of which I'm a member to find a way to help people take advantage to their freedom to switch energy (especially electricity) suppliers to get themselves a better deal. Mr Davey had been pleased to announce in Parliament earlier in the year an average saving of £123 per household in an earlier Which? deal.
In TTK EG I think it's fair to say we'd rather energy costs went up (with protection for the fuel-poor) to focus minds on energy efficiency, so instead we were more keen on chunk of "green" along with any money savings.
To that end I sent the following to Dale Vince, CEO of Ecotricity:
As you may be aware I am a member of Transition Town Kingston's Energy Group and we have recently been made a proposal by our local MP and Secretary of State for Energy and Climate Change Ed Davey. He would like TTK to support and encourage local energy-switching and bulk energy purchase in order to alleviate fuel poverty, but, while many of us are sympathetic with this aim, we do not see it as a priority for an environmental group, unless it involves switching to green energy. But we are also aware that at the moment green energy is a bit of a luxury, something only the committed and moderately well off would buy or invest in.
Given my commitment to Ecotricity's aims [...] I have been asked to find out if there could be a good deal from Ecotricity for bulk switching, and if so, what the terms would be and whether they would make green energy a viable purchase for people suffering from fuel poverty.
Mr Vince wrote back:
We looked into the idea of mass switching when Which ran their recent big campaign. We declined to take part [as] we consider it to be unethical.
Giving better prices to new customers while making existing ones pay more is the problem, it's a bad practice that some of the industry is getting away from, consumer groups are rightly against it.
We have one price for all customers, no matter when they joined us or how they pay, and everyone's price goes up or down together. That's at the core of our ethical price policy. No lock in or exit fees being another part.
That's our basic prob with mass switching.
I'm aware politicians have latched on to it as the answer to the dysfunction in the energy market - but IMO it's an illusion, switching is not the answer, building new sources of green energy here in Britain is.
That is also the answer to the problem of energy poverty, because that problem is exacerbated by the relentless rise in global energy prices, which we depend on. Solve one and we solve (or severely reduce) the other.
I also think it's a bit odd to put the fuel poor at the forefront of green energy initiatives - there's a fundamental mis match - green energy costs more to make and the fuel poor struggle (by definition) to pay for brown energy.
So we're trying to find a slightly different tack with Ecotricity, given their principled stance on this, which I can't object to at all.
MHRV and Solar PV
Peter F wrote to me 2012/05/10 and said:
... You have inspired me to get Solar panels. Which we got installed in January using A Shade Greener and they have already generated over 1100kWh which is great.
In my quest for better efficiency for our home, I was thinking about installing a MHRV Vent-Axia HR25H in our bathroom after reading your log and also reviews on other sites. Since you had it installed for a while now I though I'd ask how it's been for the past 5 months and would you suggest getting one considering the cost? I've found it for ~ £260.
Good work on the PV!
I think that our MHRV has probably been an important factor in allowing to keep the central heating off since the end of March, ie I think it has helped the house retain heat from the day and the odd ray of sunshine without the air getting too stuffy and stale. So I would do it again, and I am considering another unit for elsewhere in the house since we need a bit more ventilation than it provides on its own.
Geraint E wrote to me 2012/04/12 and said:
I am trying to convert the numerous halogen bulbs in my kitchen to LED but am having terrible problems burning out bulbs (I've just burnt out 4 G4 LED disc bulbs which isn't so wallet friendly).
I was interested in your comment saying that for halogen bulbs, light fittings are designed to hold heat in while for LED bulbs heat needs to be dissipated. If this is the case then I can only assume that my LED bulbs are overheating and then burning out? Do you think there is any solution for this?
Also, I've only been able to find LED bulbs for sale on the internet. Do you know if they're for sale on the high street at all?
I noted that:
- The reflector LEDs that I use are all mounted in non-recessed holders, eg on bars below the ceiling, which allows them to keep cool.
- I have been buying LEDs lamps of different formats in various high-street shops including John Lewis, Maplin, and Clas Ohlson.
Geraint is going to give Maplin a whirl, having found them helpful before, and also noted that "I may need to change my transformer - I've been reading some comments on Amazon where people are saying that some transformers require a minimum power draw." I noted that a friend who was trying some of my 12V LED MR16s out had to add extra load to his existing transformers to make them work correctly for testing.
Spacetherm and Condensation
Michael K asked 2012/03/16:
How is your room doing with the Spacetherm insulation? When you said you had some condensation problems was it in this room?
Also, it sounds like when the Spacetherm is up then it would be a problem to put any shelving back up, or anything that needed to be drilled into the brickwork? This would create thermal bridging and sounds like it would be hassle with the snagging that seems to happen with drills?
I've got a sample coming to me. Not sure I will do it, but we're decorating our eldest daughter's (15) room and so need to consider options. Thinking pavadentro too. Struggling for time though to teach myself about dew points!
I said that we don't have load-bearing brickwork being timber-frame, and so I expect any new finish/board to take any load rather than fastening through it. Stainless steel screws seem to be less bad than one might imagine for thermal bridging... Fermacell-faced aerogel may be part of the solution.
As to the condensation, I said that we do have some condensation problems in general, not particularly in the aerogel rooms and certainly none on the walls that we've done that I have noticed.
I agreed that subject of dew points and interstitial condensation is a tricky one: the rule of thumb seems to be to have it most of the way out through the insulation, and with any VC inboard of that, ie so that there should never be condensation on the VCL. But I'm really no expert.
He then followed up with:
We've got a solid brick 1926 4 bed detached house. Guy who came around from Wrexham to check us out for solar thermal was cringing about insulating this place lol
The exterior is pebble-dashed (before our time) and my goal has always been to do external wall insulation with a nice render, but that ends up going in the complicated-and-expensive-so-put-it-off bin.
I'm very wary about VOCs and internal emissions in general so have stayed away from internal insulation for those reasons too. I can heartily recommend these guys for paints etc:
You don't need a gas mask when you use their gloss.
The aerogel appealed for some of those reasons: seems stable and inert....
Will let you know if I progress and share the lessons, but feel like I'm moving back to external walls....
The folks at the GreenBuildingForum.co.uk would share your inclination to EWI, because then you get the thermal mass of your bricks inside the insulation, and you can improve air- and weather- tightness of the entire structure with the new 'tea cosy'.
Maybe you don't have to do it all at once; EWI the wall(s) of the most-used room first, like I concentrated on our living room?
Biomass on the GB Grid
Danny T wrote to me 2012/03/01 with an interesting question concerning biomass-based electricity generation on the UK mainland / GB grid, with reference to the Tilbury Power Station in particular (that caught fire at the end of February):
I was wondering with Tilbury power station in Essex now having been converted to run on 100% biomass and a few 100% biomass plants under construction, is there anyway of showing this within the live grid carbon intensity page? Is it still shown under COAL or is it now under OTHER?
I can understand that with Tilbury supplying only around 1% of the UKs electricity and the embeded carbon with respect to sourcing the woodchip the overall grid intensity wouldn't be altered too significantly. But at 750MW when run at full capacity it is providing more renewable energy than hydroelectricity currently.
To which I responded:
The simple answer to your question is "I don't know", and the same will apply in a smaller way to co-firing at Drax for example.
There is no scope in the current data formats to allow that, and it will certainly add error to my results.
(OTHER is only invoked vary rarely in the data feed and is thus apparently not covering any ongoing biomass burning at present.)
Often in stats such as those from DECC, for example, solar PV is lumped in with wind as a zero-carbon fuel, and a biomass plant may actually claim to be wind in future, or a new BIOMASS column/key could be added, but I don't see any of that in the pipeline until at least the year end. You prompt me to ask Elexon though: I'll let you know if they say anything sensible.
Danny said (very thought-provokingly!):
I wasn't sure if the value of carbon intensity for coal took into account a small proportion of co-firing, though I guess this would just be likely to add more error into the calculation.
I wonder about it being under 'OTHER' as on the website for the station says that they expect it to be operational fully on biomass by the end of January 2012 and according to this graph using the NETA data 'OTHER' has been used intermittently upto the capacity of about 700MW since the end of January. Also on the graph 'other' drops suddenly from 650MW to ~150MW at a time which would coincide with the recent fire there. These could just be coincidences - it will be interesting to hear what elexon say about where it is under.
I wasn't aware that PV was lumped in under wind by DECC, but I guess whilst its peak capacity is only small it makes sense. It'd be nice for them to have a similar feature as this for UK PV, I've suggested it to the EST website but they haven't got back to me and I don't think they will.
I had in fact kinda sorta noticed that OTHER wasn't at its usual zero.
I cogitated a little more and and given RWE's ~70%-less-than-coal claim I adjusted the live intensity page to assume that OTHER is 0.3kgCO2/kWh and that it will be some sort of biomass. Probably a better approximation than 0.61 (ie like OIL) for now.
I also suggested that Danny approach SMA in the UK about doing an equivalent of its 'PV in Germany' page linked above...
70% CO2 reduction on coal given the transportation and slight reduction in efficiency really doesn't sound that bad at all. I think 0.3kg/kWh as biomass is a fair assumption to make until further information becomes available.
I've emailed SMA making a suggestion about doing a similar PV thing for the UK, surprised I didn't think to ask them first!
AlertMe and PV Microgeneration
Tania T wrote to me 2012-02-20 (edited for clarity):
Thanks for freezer comments - very interesting. I've just started using my AlertMe to monitor my Miele and I'm surprised how much it's using. Btw, did you know you can move your AlertMe so it monitors your PV? If you don't, it just includes your PV in the total electricity used - bit of a drawback.
I said that I did indeed comment on using AlertMe to monitor PV and that she is absolutely right about the problem doing so, plus the general inaccuracy anyway, in The Register, and to look at the reader comments too!
Ha! No wonder you knew what you were talking about :-) thanks for the link - that was very helpful; particularly your point about watts vs kwh/15 min. I was about to go fishing for that data.
I do really like my AlertMe, for all its foibles. It's helped clarify my thinking re how much I'm producing & how much I'm using. There are other ways of doing this, but not ones that are so neat and, especially as you don't need a subscription now, as someone said, people spend plenty more money on things that are less useful. You never hear of payback time for the latest tv/stereo/game... sorry, I'm clearly ranting to the converted here ;-)
Will be interesting tho to see how long it takes alert me to bring out a more generation friendly version...
I fear from a conversation with AlertMe that the microgen-friendly version may be some way away for rather larger reasons.
Home Energy Audit
An offer of free training to do home energy audits came up, and though I couldn't take up the training, the organiser, Kinga P, kindly provided me with a checklist that we should all consider in auditing a home's energy efficiency:
- PROPERTY DETAILS — fabric of the house, space heating, water heating & bathroom features
- Energy performance/measures — loft and wall insulation, HW tank and pipes insulation, floor insulation
- Draught proofing
- Lighting — energy efficient one?
- Appliances — age, rating
- Renewable energy systems — any installed? Could it be installed?
- Energy use and energy use awareness