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Car Forum / Land Rover Cars / February 2008More Generating 240 volt AC
As the last thread seemed to meander off, I thought I would start afresh. As mentioned earlier in that thread, it is very common to hang an additional 240 volt alternator onto marine engines. They are fitted and driven the same as the charging alternator. Companies Like Sterling Power should able to help. Sorry no contact details. > As the last thread seemed to meander off, I thought I would start afresh. > As mentioned earlier in that thread, it is very common to hang an > additional 240 volt alternator onto marine engines. They are fitted and > driven the same as the charging alternator. If it's not some sort of constant velocity engine how on earth do they get it to generate 50Hz. The obvious answer is that it's a 12 or 24 volt alternator that is connected to some sort of regenerator which is buried somewhere within the guts of the thing. Generating AC power at a constant frequency by mechanical means in not a trivial matter, even for generating companies.  SignatureWilliam Black I've seen things you people wouldn't believe. Barbeques on fire by the chalets past the castle headland I watched the gift shops glitter in the darkness off the Newborough gate All these moments will be lost in time, like icecream on the beach Time for tea. >> As the last thread seemed to meander off, I thought I would start afresh. >> As mentioned earlier in that thread, it is very common to hang an [quoted text clipped - 5 lines] > >The obvious answer is that it's a 12 or 24 volt alternator Dynamo, shirley? Then a DC to AC converter, so that you can control the frequency/voltage? Regards, Simonm. Signaturesimonm|at|muircom|dot|demon|.|c|oh|dot|u|kay SIMON MUIR, BRISTOL UK EUROPEANS AGAINST THE EU http://www.eurofaq.freeuk.com/ GT250A'76 R80/RT'86 110CSW TDi'88 www.kc3ltd.co.uk/profile/eurofollie/ >>> As the last thread seemed to meander off, I thought I would start >>> afresh. [quoted text clipped - 9 lines] > Dynamo, shirley? Then a DC to AC converter, so that you can control the > frequency/voltage? As a general rule an alternator produces a form of AC, albeit usually of a rather distorted nature. This is then passed through a 'diode bridge' to produce DC. AC can then be generated by an AC inverter. It's a hell of a lot more rugged than a DC dynamo because the DC dynamo uses a comutator, and comutators fall to bits with depressing regularity. SignatureWilliam Black I've seen things you people wouldn't believe. Barbeques on fire by the chalets past the castle headland I watched the gift shops glitter in the darkness off the Newborough gate All these moments will be lost in time, like icecream on the beach Time for tea. >As a general rule an alternator produces a form of AC, albeit usually >of a rather distorted nature. This is then passed through a 'diode [quoted text clipped - 5 lines] >uses a comutator, and comutators fall to bits with depressing >regularity. Yes, point taken. The essence is that you need to invert from DC at the end though, otherwise you can't control voltage and frequency independently of the power source. Regards, Simonm. Signaturesimonm|at|muircom|dot|demon|.|c|oh|dot|u|kay SIMON MUIR, BRISTOL UK EUROPEANS AGAINST THE EU http://www.eurofaq.freeuk.com/ GT250A'76 R80/RT'86 110CSW TDi'88 www.kc3ltd.co.uk/profile/eurofollie/ > If it's not some sort of constant velocity engine how on earth do they get it to generate 50Hz. I think that was my mistake. It isn't constant frequency but it is a controlled voltage. nigelH >> If it's not some sort of constant velocity engine how on earth do they >> get it to generate 50Hz. > > I think that was my mistake. It isn't constant frequency > but it is a controlled voltage. That's not hard to do. What's really really hard is keeping the phase and frequency constant and managing the 'power factor' in such a way that it doesn't all run a touch hotter than the design temperature. "When I we'r an apprentice" I was taught at Hull Tech by an old guy who remembered balancing power stations coming on-line with two phase meters and a clutch lever... SignatureWilliam Black I've seen things you people wouldn't believe. Barbeques on fire by the chalets past the castle headland I watched the gift shops glitter in the darkness off the Newborough gate All these moments will be lost in time, like icecream on the beach Time for tea. > "When I we'r an apprentice" I was taught at Hull Tech by an old guy who > remembered balancing power stations coming on-line with two phase meters and > a clutch lever... The trick I saw was three light bulbs across the switches. As you came to speed they flicker more and more slowly and finally as they creep through the 'out' part of the cycle and you drop it onto the grid and it is locked synchronous. Then you can wind up the power and the speed doesn't change, you just watch the power meters start to run up until it's 'about right' and then you can come off the grid. I think it was a similar trick to come back on. <sigh> This was in the days when UPS meant a big set of Napier Deltics ready to roll and I was a raw, new graduate who thought he knew about transmitters because he understood big transistors. ho hum... nigelH SignaturePosted via a free Usenet account from http://www.teranews.com > <sigh> This was in the days when UPS meant a big set > of Napier Deltics ready to roll and I was a raw, new > graduate who thought he knew about transmitters because > he understood big transistors. If you're playing with the big boys it still does, it's just that you have a huge capacitive inverter and some seriously clever switch gear between the generator, the grid and the site... SignatureWilliam Black I've seen things you people wouldn't believe. Barbeques on fire by the chalets past the castle headland I watched the gift shops glitter in the darkness off the Newborough gate All these moments will be lost in time, like icecream on the beach Time for tea. > "When I we'r an apprentice" I was taught at Hull Tech by an old guy who > remembered balancing power stations coming on-line with two phase meters > and a clutch lever... When I we'r an EE student, we had a motor/alternator set that we ran into the grid, synced up etc, then drove harder and harder until we broke sync - then the motor starts to accelerate out of control.... Bloody machines lab is all computer trickery now - not proper engineering at all. Steve > As the last thread seemed to meander off, I thought I would start afresh. > As mentioned earlier in that thread, it is very common to hang an > additional 240 volt alternator onto marine engines. They are fitted and > driven the same as the charging alternator. This is certainly not common - I've never heard of it being done at all. Many yachts fit additional 12v alternators and use fancy charge control devices but the idea of 240v on a yacht at sea is a bit scary in my opinion. Quite a few plug into 240v shore power and do indeed have a 240v circuit but unless you are talking ships rather than boats it's new to me. TonyB > As the last thread seemed to meander off, I thought I would start afresh. > As mentioned earlier in that thread, it is very common to hang an > additional 240 volt alternator onto marine engines. They are fitted and > driven the same as the charging alternator. > Companies Like Sterling Power should able to help. Sorry no contact > details. I have a circuit diagram (well more of a "which wire to swap") to convert a normal 12/24V Alternator into a 240V genny - just depends on engine speed as to what Volts you get. Big problem is that you also get the rated amps of the alternator, if any part of the circuit fails you get an onsite cremation!! I'll not contradict any of the experts here, I'm only stating the fact that they are readily available and commonly used on yachts (not ships). Quote from Living On Board:- http://www.livingonboats.co.uk/27/mains-electricity-onboard-boats/ 240 volt AC Alternator These devices attach to the boats main engine. They are similar to a car alternator except they produce 240 volts AC current instead of 12 volt DC current as a car does. Again, these come in different outputs to suit your needs but remember power is only generated when the boats main engine is running. If your mooring dries out at low tide this could be a problem. I've since found that the engine must be set to run at a certain revs to give 50Hz. If the alternator needs 3000rpm then a smaller pulley on the engine end will mean the engine only has to run at low speed to provide the correct Hz. (Still can't find who sells them though). Apparently there was a US version that controlled itself at any speed, but it wasn't reliable! But after all this it seems that this may not be ideal for water wheel design after all! Cheers, Peter PLEASE CONFIRM RECEIPT TO AVOID DUPLICATE MAILINGS > I'll not contradict any of the experts here, I'm only stating the fact > that [quoted text clipped - 19 lines] > But after all this it seems that this may not be ideal for water wheel > design after all! Actually it may be. Water wheels are reasonably constant in speed because the mill pond will have a weir with a 'gate' that allows the level to be regulated, and you're going to need some sort of gear box or heavy duty clutch between the generator and the wheel or any problems will tend to do some serious mechanical damage. SignatureWilliam Black I've seen things you people wouldn't believe. Barbeques on fire by the chalets past the castle headland I watched the gift shops glitter in the darkness off the Newborough gate All these moments will be lost in time, like icecream on the beach Time for tea. >> I'll not contradict any of the experts here, I'm only stating the >>fact that [quoted text clipped - 27 lines] >between the generator and the wheel or any problems will tend to do >some serious mechanical damage. And reasonable constant is all the OP needs. He isn't trying to sync to the mains. He simply wants to run a small pump and a relatively low powered immersion heater, neither of which are over sensitive to frequency. Signaturehugh Reply to address is valid at the time of posting > I'll not contradict any of the experts here, I'm only stating the fact that > they are readily available and commonly used on yachts (not ships). [quoted text clipped - 14 lines] > engine end will mean the engine only has to run at low speed to provide the > correct Hz. I'm sure you meant a BIGGER pulley on the engine end! Most marine engines aren't even run at 3000rpm. Martin (Still can't find who sells them though). Apparently there was a > US version that controlled itself at any speed, but it wasn't reliable! > But after all this it seems that this may not be ideal for water wheel > design after all! > Cheers, > Peter Oily, you're right, I meant a smaller pulley on the alternator end, or as you say a bigger pulley on the engine end. Although your comment on marine engine revs, doesn't apply anymore to the modern high revving Volvo's etc. Cheers, Peter PLEASE CONFIRM RECEIPT TO AVOID DUPLICATE MAILINGS > Oily, you're right, I meant a smaller pulley on the alternator end, or as > you say a bigger pulley on the engine end. > Although your comment on marine engine revs, doesn't apply anymore to the > modern high revving Volvo's etc. Volvo hand grenades with a lifespan measured in the hundreds of minutes running time. >> Oily, you're right, I meant a smaller pulley on the alternator end, or as >> you say a bigger pulley on the engine end. [quoted text clipped - 3 lines] > Volvo hand grenades with a lifespan measured in the hundreds of minutes > running time. I dont know if any of your saw the programmes "Its not easy being green" on BBC a year or so ago - With Dick Smallbridge. He looked into all this, and sourced a fancy alternator/dynamo/power source which he connected to a water wheel. He accepted that the power went into 12/24v batteries and then was inverted to basically light the house. He also had a wind turbine which via a battery powered a water pump to fill the cold water tank. I am no engineer, but I suspect that the OP should give up on the idea of heating water with this power, and just set up a thermostat to control a switch to power a 12V pump for the swimming pool water. Giles >I am no engineer, but I suspect that the OP should give up on the idea of >heating water with this power, and just set up a thermostat to control a >switch to power a 12V pump for the swimming pool water. Just as an aside, today was the first sunny morning (here) for a while, and our solar water heating kicked in at around 0930. Currently (midday) the panel temp is around 46C and the tank coil exit temp (roughly equals tank temp) is 40C. We've got about 8sqm of panels on the roof, but at this time of year there are long shadows across it cast by the chimney stack, so probably only about 4-6sqm actually productive for most of the morning. I don't know how much energy the pump has used - I ought to measure it really (see another thread, etc.). That's about 30 gallons worth, not counting the upper part of the tank which _may_ also have been solar heated to a similar temp (depends exactly when the rest of the family showered this morning!). It's not 'free' energy, of course, but IMHO it's paying back the investment nicely. Regards, Simonm. Signaturesimonm|at|muircom|dot|demon|.|c|oh|dot|u|kay SIMON MUIR, BRISTOL UK www.ukip.org EUROPEANS AGAINST THE EU www.members.aol.com/eurofaq GT250A'76 R80/RT'86 110CSW TD'88 www.kc3ltd.co.uk/profile/eurofollie/ >> I am no engineer, but I suspect that the OP should give up on the idea of >> heating water with this power, and just set up a thermostat to control a [quoted text clipped - 8 lines] > morning. I don't know how much energy the pump has used - I ought to > measure it really (see another thread, etc.). Run the pump off a solar cell - no sun, no pump. More sun - hotter panel - pump faster. Steve >>> I am no engineer, but I suspect that the OP should give up on the idea of >>> heating water with this power, and just set up a thermostat to control a [quoted text clipped - 13 lines] > >Steve Could do, but the present one is a standard central heating pump - simple, cheap and relatively reliable. Sorting out a 12v (or whatever) equivalent plus the panels etc. strays away from the 'simple-is-elegant' approach. I might look at it in the summer... Regards, Simonm. Signaturesimonm|at|muircom|dot|demon|.|c|oh|dot|u|kay SIMON MUIR, BRISTOL UK EUROPEANS AGAINST THE EU http://www.eurofaq.freeuk.com/ GT250A'76 R80/RT'86 110CSW TDi'88 www.kc3ltd.co.uk/profile/eurofollie/ > Could do, but the present one is a standard central heating pump - > simple, cheap and relatively reliable. Sorting out a 12v (or whatever) > equivalent plus the panels etc. strays away from the 'simple-is-elegant' > approach. I wonder what flowrate you actually need to move the heat available ? I bet its not as much as a CH pump can deliver is it ? I certainly wouldn't dream of inverting a 12V panel to drive a CH pump - like you said "Keep it simple" Steve >> Could do, but the present one is a standard central heating pump - >>simple, cheap and relatively reliable. Sorting out a 12v (or whatever) [quoted text clipped - 5 lines] >wouldn't dream of inverting a 12V panel to drive a CH pump - like you >said "Keep it simple" I wasn't thinking of a 240V inverter, as much as the problem of finding and maintaining a lower voltage pump (and potentially altering the control system). The big advantage of the present system is that the components are standard, and it has a single moving part (no valves etc. required). It's not a circulating application either - it's a lift pump, and it's not quite as simple as "when there's sun, pump", as there needs to be an over-temp cut-out (it's a drainback system, for efficiency and safety). Mine currently cuts out at about 102C, and it's very necessary in summer. I've recorded temperatures as high as 107C at the panels (that's the roof's outlet manifold, not the actual panel(!) and I don't know the accuracy of the thermometer at that extreme). If steam were ever produced in quantity the system would be thoroughly dangerous (yes it's got a safety valve, but even so...). So on balance, although it probably could be done by solar generation, it's probably best left as it is. I suppose I ought to be able to work out how hard the pump is working, as there are flow meters and I know the head it has to produce (about 15-18 ft). It's quite a lift really. Worth pondering though - I'll give it some thought whilst huddled round the candles later this w/e :^) Regards, Simonm. Signaturesimonm|at|muircom|dot|demon|.|c|oh|dot|u|kay SIMON MUIR, BRISTOL UK www.ukip.org EUROPEANS AGAINST THE EU www.members.aol.com/eurofaq GT250A'76 R80/RT'86 110CSW TD'88 www.kc3ltd.co.uk/profile/eurofollie/ >> Could do, but the present one is a standard central heating pump - >> simple, cheap and relatively reliable. Sorting out a 12v (or whatever) [quoted text clipped - 5 lines] >wouldn't dream of inverting a 12V panel to drive a CH pump - like you >said "Keep it simple" ours runs a small CH pump at minimum speed. Probably takes about 100W, but it only runs when there's a temperature difference of (IIRC) 5 degrees between the tank and the collector, and if it drops to 3 degrees it cuts out again. Those levels are customisable, if you can be bothered. In summer, the water mostly gets heated by the sun. In winter, it'll get the water to about 40 on a really good day, or about 20-odd on a crap day, which is still above the normal CW temp of about 10 degrees or less. I think the record was to have the whole tank at about 85C, in the summer. Of course, you have to be careful of the hot water then, especially if you have young children. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! You might need to install an automixer to maintain a safe water temperature. Common on boats where the water is heated via a calorifier from the engine water to 85C+. Cleghorn Waring do them. > You might need to install an automixer to maintain a safe water temperature. Plenty of options here http://www.rwc.co.uk/product.aspx?page=CAT1 >>> Could do, but the present one is a standard central heating pump - >>> simple, cheap and relatively reliable. Sorting out a 12v (or whatever) [quoted text clipped - 10 lines] >between the tank and the collector, and if it drops to 3 degrees it cuts out >again. Those levels are customisable, if you can be bothered. Sounds like the same controller as ours. I've got mine set to +6 on +2 off, which is probably too optimistic at the off- end. >In summer, the water mostly gets heated by the sun. In winter, it'll get >the water to about 40 on a really good day, or about 20-odd on a crap day, [quoted text clipped - 3 lines] >Of course, you have to be careful of the hot water then, especially if you >have young children. Ours gets to that too, but I'm thinking of dropping the over-temp cutout down a bit, for the same reason. It's rather hot if you aren't expecting it, and the thick insulation on the pipes only adds to the element of surprise :-( Regards, Simonm. Signaturesimonm|at|muircom|dot|demon|.|c|oh|dot|u|kay SIMON MUIR, BRISTOL UK www.ukip.org EUROPEANS AGAINST THE EU www.members.aol.com/eurofaq GT250A'76 R80/RT'86 110CSW TD'88 www.kc3ltd.co.uk/profile/eurofollie/ >Sounds like the same controller as ours. I've got the panels and pump but the controller looked a bit expensive, where's yours from? I'm actually in no great rush to fit anything because the cost of the plumbing looks a bit high as I'd need to fit a second dhw tank downstairs because of space limitations. On the too hot water issue: how about looking at a thermal store with plate heat exchanger rather than mixer taps? It gives the ability to store more heat. AJH >>Sounds like the same controller as ours. > >I've got the panels and pump but the controller looked a bit >expensive, where's yours from? Resol, "Deltasol B." It's obsolete now, but the manual is here: <http://www.resol.de/PDF/DeltaSol_B.mon.en.pdf> They do a range of controllers, the closest current one probably being the Deltasol BS. It was part of the package, so I don't know what it costs separately, but there's practically nothing to it (three thermocouple inputs and one 240V switched output), so it shouldn't be pricey. >I'm actually in no great rush to fit anything because the cost of the >plumbing looks a bit high as I'd need to fit a second dhw tank [quoted text clipped - 3 lines] >plate heat exchanger rather than mixer taps? It gives the ability to >store more heat. It's all in and functioning now - 2-coiled 75 gallon pressurised tank (Telford Tempest). I wanted a thermal store but was talked out of it because of the difficulty of plumbing it in (condensing gas boiler to consider too). Broadly speaking, if the primary loop doesn't have sufficient delta (7C from memory), the boiler can't operate in condensing mode and is therefore inefficient. The hotter you get the tank the harder it is to achieve the necessary delta. Solar complicates matters with a thermal store too, because it has to couple to the primary circuit somehow. With a 2-coil 'conventional' system there's no complex interaction between the two (or three) different heat sources. Solar takes 1st priority heating the water. If it gets it hot enough without help the boiler (or immersion heater) never fires up, otherwise they provide topping-up heating as required. The only drawback is that when there's little solar energy available (like now), the effective tank capacity is greatly reduced. I am looking at adding a second "pre-heat" tank (say 30-40 gallons), so as to make better use of the solar energy when it is available. On balance I'm very pleased with the setup, as it certainly works very well on sunny days, and it's not complex and near-zero maintenance. If you're interested it was done by Southern Solar, and I'd recommend them for tidiness and efficiency (can't compare prices easily so I don't know, but they weren't extortionate by any means). HTH. Regards, Simonm. Signaturesimonm|at|muircom|dot|demon|.|c|oh|dot|u|kay SIMON MUIR, BRISTOL UK EUROPEANS AGAINST THE EU http://www.eurofaq.freeuk.com/ GT250A'76 R80/RT'86 110CSW TDi'88 www.kc3ltd.co.uk/profile/eurofollie/ >>On the too hot water issue: how about looking at a thermal store with >>plate heat exchanger rather than mixer taps? It gives the ability to [quoted text clipped - 7 lines] >condensing mode and is therefore inefficient. The hotter you get the >tank the harder it is to achieve the necessary delta. Yes but the reason you have the 75 gallons is to store solar heat for a few days not the heat from the gas boiler. So the idea is that the gas boiler thermostats are set to only warm the top of the tank, sufficient only for any requirements that the gas cannot keep up with. It's better to store the energy outside of this as chemical energy in the gas. Thus if the thermal store is capable of 90C (and I service a solar system with one than can store 3000 litres at 90C) and there is a call for gas heating for dhw at 50C then there will always be a return temperature of <50C thus ensuring condensing mode. >Solar complicates matters with a thermal store too, Don't get me started ;-). I snagged the system in a block of flats that red ken opened and they still don't believe me when I tell them what's wrong with the design! >On balance I'm very pleased with the setup, That's good then, I've just been involved on a thread in uk-diy about how my father was sold a set up which wasn't installed or run properly. The general consensus there is that commercial installations aren't likley to be a good return on investment, at current fuel prices, in UK but it's difficult to quantify satisfaction. AJH >Yes but the reason you have the 75 gallons is to store solar heat for >a few days not the heat from the gas boiler. So the idea is that the [quoted text clipped - 5 lines] >a call for gas heating for dhw at 50C then there will always be a >return temperature of <50C thus ensuring condensing mode. [timidly] Ah, but isn't that a circulating DHW system. Ours couldn't be (easily) plumbed that way. I take your point about gas top-up generally. In summer the boiler goes for days/weeks without firing at all. In winter, 35 gallons at 70C isn't enough to cover a day's worth of demand, and the tank/pipework lagging isn't good enough to store hotter water efficiently (I'm working on that). >>Solar complicates matters with a thermal store too, > [quoted text clipped - 9 lines] >aren't likley to be a good return on investment, at current fuel >prices, in UK but it's difficult to quantify satisfaction. The existing arrangement is elegantly simple. In particular I like the way the solar system doesn't need to alter or interact with the conventional gas system and its controls. I'm contemplating a variation (with an additional tank) because we have excess collecting capacity on the roof for most of the year, and I want to take better advantage of it, but I've no firm plans just yet. Regarding payback period, I think it depends on how you consider ROI. If you take the 'blunt instrument' approach that fuel savings are directly balanced against capital cost, then payback is probably more than a decade (not good). That however assumes no residual value for the system, which is unrealistic. The system we have is virtually maintenance free, with a design life in excess of 20 years (external corrosion is likely to be the biggest factor). Thus a certain capital value will inevitably be factored into the price of the property should we sell it meanwhile. The exact value one couldn't say at this stage, but it's not a poor capital investment in that sense. And there's a nice feeling about running a hot bath of entirely solar-heated water in the summer! Regards, Simonm. Signaturesimonm|at|muircom|dot|demon|.|c|oh|dot|u|kay SIMON MUIR, BRISTOL UK EUROPEANS AGAINST THE EU http://www.eurofaq.freeuk.com/ GT250A'76 R80/RT'86 110CSW TDi'88 www.kc3ltd.co.uk/profile/eurofollie/ >[timidly] Ah, but isn't that a circulating DHW system. Yes but the thermal store has its own pump, the hot water is at mains pressure. Like you I haven't done it because my current gas central heating has life in it and in my case my dhw demand is low. I use a couple of wood burners for space heating (but the gas fires up radiators in the kitchen and living room for first thing. AJH What IS the way to use solar and a combi-boiler ? Any pointers ? Steve >What IS the way to use solar and a combi-boiler ? Any pointers ? UK diy is a good place to ask for general plumbing advice, there is a faq on central heating and boilers. As to the specific question the easiest way is to heat a tank with the solar and then take the output from that to the combi, via a heat exchanger, except many combis do not like a hot feed, this way the combi tops up the water from the solar tank. You'll need a plate heat exchanger to manage the power transfer. AJH > You'll need a plate heat > exchanger to manage the power transfer. For a low flow rate like a combi ? Steve >> You'll need a plate heat >> exchanger to manage the power transfer. > >For a low flow rate like a combi ? Really, don't go there :( Regards, Simonm. Signaturesimonm|at|muircom|dot|demon|.|c|oh|dot|u|kay SIMON MUIR, BRISTOL UK EUROPEANS AGAINST THE EU http://www.eurofaq.freeuk.com/ GT250A'76 R80/RT'86 110CSW TDi'88 www.kc3ltd.co.uk/profile/eurofollie/ >> You'll need a plate heat >> exchanger to manage the power transfer. > >For a low flow rate like a combi ? > >Steve It's the heat transfer from the thermal store to the mains pressure water that counts, the combi is just topping this up if necessary, when the solar heated store is cold it simply makes no difference from a normal combi installation. It can get more complicated as I said because many combis don't like a hot inlet, so the solar tank heats the mains cold inlet which is blended in parallel by the combi to the desired temperature (about 50C). I'm not very au fait with the wet side. AJH >>What IS the way to use solar and a combi-boiler ? Any pointers ? > [quoted text clipped - 8 lines] > >AJH I defer to m'learned colleague, however in a typical domestic installation the Irish answer applies - don't start from there! We have a condensing system boiler (heats a tank of HW), not a combi. The tank is tall+thin and has two heating coils. The lower coil is heated by the solar array, and the higher coil by the gas boiler. If the solar array produces enough heat, there is no need for the gas boiler to fire up, and it doesn't. There is no connection between the two control systems, as it's not necessary. The boiler is timed to switch off in time for the tank to empty of hot water at the end of the morning rush, so that the solar starts the day with a full tank of cold water to heat. This optimizes the thermal transfer, especially at this time of year when you can't collect as much energy. The boiler kicks back in late afternoon/early evening, and tops up the temp. as needed. Works for us... Regards, Simonm. Signaturesimonm|at|muircom|dot|demon|.|c|oh|dot|u|kay SIMON MUIR, BRISTOL UK EUROPEANS AGAINST THE EU http://www.eurofaq.freeuk.com/ GT250A'76 R80/RT'86 110CSW TDi'88 www.kc3ltd.co.uk/profile/eurofollie/ >I defer to m'learned colleague, Don't get me wrong I'm no expert but I've been dumped in the deep end because one of our pellet boilers backs up a big solar system, in fact it doesn't even keep it afloat if the temperature sits in the single digits for a few cloudy days, one thing about solar enthusiasts is their optimism! >however in a typical domestic >installation the Irish answer applies - don't start from there! We have [quoted text clipped - 3 lines] >produces enough heat, there is no need for the gas boiler to fire up, >and it doesn't. This is how my father's was set, trouble was the gas coil was only just above the solar when it would have been better nearer the top. >There is no connection between the two control systems, In fact there is, the temperature gradient in the tank, this is sufficient feedback path for the rest to work with no electrical connections. > as it's not >necessary. The boiler is timed to switch off in time for the tank to [quoted text clipped - 5 lines] > >Works for us... Yes that's how it should be but there is a case for changing the way the solar contribution is made between winter and summer. Now that delta T problem, preventing condensing mode, you earlier referred to would be solved by better heat transfer in gas coil, which is limited because it is a coil. AJH >This is how my father's was set, trouble was the gas coil was only >just above the solar when it would have been better nearer the top. I agree. 50:50 seems to work for us, except in the winter (see previous post etc.) >>There is no connection between the two control systems, > >In fact there is, the temperature gradient in the tank, this is >sufficient feedback path for the rest to work with no electrical >connections. Quite understood. It's this elegant solution that I like. >Yes that's how it should be but there is a case for changing the way >the solar contribution is made between winter and summer. Indeed. Ideally, if I get the extra tank it will be the heat exchanger for the solar system. I'll move the gas to the lower coil on the main tank and either ignore the higher one or fit a valve to give the choice of either. There are unused spigots for a circulating DHW system I can use to connect in, such that it should convect nicely if the tanks are in reasonable proximity. >Now that delta T problem, preventing condensing mode, you earlier >referred to would be solved by better heat transfer in gas coil, which >is limited because it is a coil. Indeed. I wanted a thermal store for that reason (and the ability to cope with peak demand better than a tank), but nobody locally was up for it. On balance it hasn't worked out too bad, and we do notice the reduced energy use from the solar 'boost'. Yes, our bills have risen, but probably not nearly as badly as they might have done. Regards, Simonm. Signaturesimonm|at|muircom|dot|demon|.|c|oh|dot|u|kay SIMON MUIR, BRISTOL UK EUROPEANS AGAINST THE EU http://www.eurofaq.freeuk.com/ GT250A'76 R80/RT'86 110CSW TDi'88 www.kc3ltd.co.uk/profile/eurofollie/ >>Sounds like the same controller as ours. > [quoted text clipped - 8 lines] >plate heat exchanger rather than mixer taps? It gives the ability to >store more heat. that's a thought. trouble is, in summer you don't need heat. Now, if you could save it in a bottle for winter... BMW's new hydrogen car stores its fuel at -250-odd degrees C, and they reckon the tanks would, if used for this, keep yer coffee hot for 6 months. So it is possible to achieve that sort of insulation. Ideally, I guess, you'd have a really big HW storage tank, super-insulated, and a system that took water at over (say) 60 degrees and took it off into said tank, whenever it was available. SignatureAustin Shackles. www.ddol-las.net my opinions are just that Travel The Galaxy! Meet Fascinating Life Forms... ------------------------------------------------\ >> http://www.schlockmercenary.com/ << \ ...and Kill them. a webcartoon by Howard Tayler; I like it, maybe you will too! > BMW's new hydrogen car stores its fuel at -250-odd degrees C, eh? That I really don't believe. It might store liquid Hydrogen but it will be at normal temperature but a rather high pressure. I suspect some semi educated mejia graduate journo has just looked up the temperature that hydrogen liquifies at under normal atmospheric pressure... SignatureCheers Dave. >> BMW's new hydrogen car stores its fuel at -250-odd degrees C, > > eh? That I really don't believe. It might store liquid Hydrogen but it > will be at normal temperature but a rather high pressure. I suspect some > semi educated mejia graduate journo has just looked up the temperature > that hydrogen liquifies at under normal atmospheric pressure... Or even the correct figures, which show that the maximum available boiling point for liquid hydrogen is -240 C at 13 bar. At atmospheric pressure, it's -253 C. Liquifying Hydrogen at normal ambient temperatures involves pressures "off the scale" according to NASA's handy webpage on the subject. :-) The -250 C figure is straight off the BMW website, by the way. ;-) SignatureTciao for Now! John. > Or even the correct figures, which show that the maximum available > boiling point for liquid hydrogen is -240 C at 13 bar. At atmospheric > pressure, it's -253 C. Liquifying Hydrogen at normal ambient > temperatures involves pressures "off the scale" according to NASA's > handy webpage on the subject. :-) That off the scale pressure doesn't surpise me. I still doubt that the stuff is being stored at -250 ish deg C though. See Mr Taylor's comment about a metal hydride system. > The -250 C figure is straight off the BMW website, by the way. ;-) OK so s/semi educated mejia graduate journo/semi educated marketing droid/ SignatureCheers Dave. >> Or even the correct figures, which show that the maximum available >> boiling point for liquid hydrogen is -240 C at 13 bar. At atmospheric [quoted text clipped - 5 lines] > stuff is being stored at -250 ish deg C though. See Mr Taylor's comment > about a metal hydride system. I did, & I checked. Current state of the art seems to be that MH storage is too low in hydrogen storage density, & too complex to run to put into a series production vehicle. The tank BMW quote is about 55Kg total weight to hold 8Kg of gas, (About 15% of the storage weight is fuel) MH storage density is currently peaking at about 10% of the metal hydride weight, then you have the parasitic weight of the heat exchangers, pressure vessel & general plumbing complications to recover the gas from the hydride. Cryogenic liquid storage at reasonably low pressure seems to be the most efficient storage method at the moment. Lets face it, if it could be done with less weight for the same fuel flow rate as cryogenic tanks, NASA would be using it instead of liquid hydrogen for rocket fuel. :-) >> The -250 C figure is straight off the BMW website, by the way. ;-) > > OK so s/semi educated mejia graduate journo/semi educated marketing droid/ <Shrug> The figures quoted support other reading I've done over the last year or two in general science magazines here & in France. SignatureTciao for Now! John. >> BMW's new hydrogen car stores its fuel at -250-odd degrees C, > > eh? That I really don't believe. It might store liquid Hydrogen but it > will be at normal temperature but a rather high pressure. I suspect some > semi educated mejia graduate journo has just looked up the temperature > that hydrogen liquifies at under normal atmospheric pressure... I thought there was supposed to be a metal hydride tank system which avoided the need for high pressure storage ? Steve |
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