Hi all,
Stumbled over this site whilst looking for something to do with stacking firewood and spent several hours reading threads ... as you do
. Before joining some discussions I thought it might be helpful to describe where I'm at.
In January 2009 I installed:
60kW HDG Turbotec batch (log, gasifying) boiler
2,500L Primary Thermal Store from Akvaterm with 2 x DHW coils, 2 x Solar coils, 2 x 9kW immersions.
2,500L "Unsophisticated" Secondary Thermal Store from HDG
(2,500 Litres = 660 USA Gallons)
(2 x Thermal Stores because we did not have enough ceiling-clearance for the tipping-angle of a single 5,000L tank but, actually with benefit of hindsight!, 2x tanks is better for us as in Summer we disconnect the Secondary and use just the Primary as heat-dump for Thermal Solar thus getting 2,500L up to "hot" water, rather than having 5,000L of "tepid" water).
Original central heating system was oil boiler & radiators, open-vented. New boiler / thermal store / accumulator is pressurised, so due to worry about whether existing radiators would cope with being pressurised we left the central heating circuit open-vented and put a heat exchanger where the old boiler had been - thus we have two (Wilo low-energy) pumps, first from Thermal Store to Heat Exchanger, second from Heat Exchanger around the radiator circuit.
We also have a pool, and added a second heat exchanger in place of where the pool (oil) boiler used to be. The first Wilo pump is used to get hot water to the pool heat exchanger, and the pool's filter pump gets the pool water to the heat exchanger. (Actually we have since moved the Boiler and Thermal Stores from the garage, which adjoined the house, into the main part of the house and both heat exchanger are now in the new boiler room, rather than the pool room as previously, so that we bring the "cool" pool water to the heat exchanger, rather than the "hot" thermal store water to the heat exchanger, as the heat losses in transmission are less. (In Winter I don't care, it's all within the envelop of the building, so heat losses become space-heating). Moving the boiler / thermal stored INTO the house has resulted in a significant reduction of fuel, so "subjectively speaking", as no two winters are identical
, the heat loss from having the boiler / thermal stores in an "outhouse" was significant. This is, of course, obvious but over here in UK I see lots of installs being recommended in "outbuildings", as not many houses have space for all this lot within the envelope of the house, and my Number One Top Tip would be to ensure that the boiler / store is INSIDE the house envelope.
Originally we had 2 x coils in the thermal store for DHW (Domestic Hot Water). The first low in the tank as a "pre heat", the second at the top for a final heat. There is then a mixer valve (joined to the cold feed) that regulates the output hot water (to 65C / 150F I think). The thinking was that if the tank was hot, top-to-bottom, the output from the bottom coil would be close-to 65C, and thus there would be no/little additional heating at the top coil, and thus no/little impact on stratification. If the tank wasn't so hot then I'd have to live with stratification in order to be sure to get DHW. Top part of the primary tank is "reserved" for DHW - i.e. the feed/flow to central heating Radiators is lower in the tank.
There are then 2x Solar coils (also in the Primary thermal store). If the top half (of the primary) thermal store is below 60C / 140F then solar heating only goes to top coil (and solar panels have to get hot enough so that their dT is 10C-or-so higher). Once the top half reaches 60C then solar heating switches to bottom half (at which point the dT is more easily achieved as it only has to be 10C higher than the (cooler) bottom of the tank)
The electric immersion heaters are an emergency fall back in case the boiler breaks. Previously our oil tank was inside the house (no longer permitted in UK, or at least not with the old-style tank we had) so to continue to use oil we would have had to have a new tank, out in the garden somewhere, and pipe that across the drive to the house. Big job, lots of collateral damage to make good, and our primary objective was to be more Eco Green ... so Oil was out ...
In Summer it was quite difficult to get top half of 2,500L tank to be consistently above 60C to provide DHW at 60-65C. So we added a separate DHW tank, which has Solar Coil (top-to-bottom), Boiler Coil (top half only) and two immersions - boost at the top, and another at the bottom for "full tank" mode. In principle we want to leave some "cold" water at the bottom of the tank so that the Solar has something to heat.
We use the original 2x Coils in the Thermal Store, previously used to provide DHW, to pre-heat the water going into the hot water tank (so, in principle, the hot water tank should be refilled with water at 60C in Winter, maybe as low as 40C in Summer during any not-very-sunny periods)
Once Solar has heated the DHW tank it switches to dumping heat into Thermal Store. If there is enough of that then it is available to a) pre heat water for the hot water tank or b) to dump into the pool.
We thought long-and-hard about stratification of the thermal store, and considered buying a fancy tank with all sorts of baffles and devices to mitigate the problem. In the end we went for "simple" instead and that saved me a lot of money; Looking back: I'm happy with the decision.
Since then we have added an extension to the house, and that has under floor heating (lower temperature). The extension is built to Passive House standards, so needs very little heat (although we have chosen to keep it warmer than we used to have the main house so it is very cosy, and reduced the temperature of the main house, so the Passive House extension does use some heat).
We have also added more thermal solar panels dedicated to heating the swimming pool. The swimming pool filtration circuit can now pass the water through a) the dedicated solar panels then optionally b) through the Thermal Store heat exchanger (either taking heat from the thermal store, if there is some spare, or I light the boiler at the same time). In practice the Solar Panels are sufficient except for the very start / end of the swimming season (for us that is late March to early November - which is probably 4 - 6 weeks longer than would be normal for a pool in this area without serious commitment )
For Winter Heating we evolved a method that suits us over the first couple of years. We found that lighting the boiler in early afternoon, which then ran for about 6 - 7 hours on a "batch", heated the house nicely in the evening. The boiler stopped at about the time we went to bed, which seemed ideal. There would then be enough heat in the thermal store for the morning heating run (before we get up), and any "boost" in the morning if it was cold (I work from home). In the afternoon we would load the boiler between half-and-fully-full depending on how low the store temperature had fallen. Below 40C / 105F it then has no "guts" for heating the house via radiators; in practice in the UK the day temperature in Winter is 5C and night temperature 0C, so with a reasonably sunny day there isn't a need for much top-up heat until afternoon / early evening. Of course we also get Arctic conditions at times (we get -10C to -15C for perhaps a week's duration about once a decade) and on those occasions we light the boiler in the morning, and top-up the "burn" during the afternoon, but it is rare to need to do that - mild winters not at all, average winters maybe 5 days of the year, cold winters maybe 10 days. In mild winters we get away with a full-load every-other-day, as we do in Autumn / Spring (maybe only having a burn 1-in-3 days in early Autumn / late Spring).
We found control using convention thermostats wasn't getting us what we wanted. Thermostats wanted to heat the house when the temperature fell below X-degrees, but that might compromise the Thermal Store if its temperature was getting low. OTOH if we put too much wood in the boiler the house would heat up in the evening, the thermostat would cut off, the thermal store would heat up and, at around 85-90C / 185-195F the boiler would damp-down, and we'd just smoulder the remainder of the fuel "wasting it".
So we changed the controls so that we now have a "forced central heating on" timer. If the Thermal Store is down to 40C we load the boiler full, and force the central heating on for 6 hours. That will heat the house well, in 6 hours, and leave the thermal store at Max just as the fire goes out - if we judge it right! (if not I can just put the central heating on for another hour to lower the Thermal Store temperature and then the boiler fan will resume). If the Thermal Store is nearer to 60C then we half-load the boiler and set the force central heating timer to 4 hours.
If, by this means, we heat the house hotter, in an evening, than the old thermostat setting would have allowed, then we go to bed one or two degrees warmer, and wake up with less heating required in the morning (house has very little air leakage [about 2-3 ACH @ 50 pascals, or whatever the test is!] and reasonable insulation + double glazing). The house has concrete 1st floor and flat roof, since augmented by pitched roof and lots of "loft insulation". In the Passive House Extension all the internal walls are dense blocks, so the thermal-mass of the building is very high indeed, and thus over-heating the house is "slow" and stored well by the building's fabric. I guess this approach won't work for everyone
The Solar Thermal for the Pool doesn't need to heat the pool in winter (and I regard it as a waste running the filtration pump just to dump solar heat), so we have a bare pipe around the Conservatory as a heat dump. It gives off very little heat in Winter (but it is not good for the Solar Panels to overheat), and we just switch the plumbing over to heating the conservatory in winter, and turn the Pool Pump "solar switch" off. I have some plants in the Conservatory and they are happy with any boost heat they get.
In case of interest the full installation details are on a UK Forum:
http://www.navitron.org.uk/forum/index.php/topic,5875.0.html
Stumbled over this site whilst looking for something to do with stacking firewood and spent several hours reading threads ... as you do
. Before joining some discussions I thought it might be helpful to describe where I'm at.In January 2009 I installed:
60kW HDG Turbotec batch (log, gasifying) boiler
2,500L Primary Thermal Store from Akvaterm with 2 x DHW coils, 2 x Solar coils, 2 x 9kW immersions.
2,500L "Unsophisticated" Secondary Thermal Store from HDG
(2,500 Litres = 660 USA Gallons)
(2 x Thermal Stores because we did not have enough ceiling-clearance for the tipping-angle of a single 5,000L tank but, actually with benefit of hindsight!, 2x tanks is better for us as in Summer we disconnect the Secondary and use just the Primary as heat-dump for Thermal Solar thus getting 2,500L up to "hot" water, rather than having 5,000L of "tepid" water).
Original central heating system was oil boiler & radiators, open-vented. New boiler / thermal store / accumulator is pressurised, so due to worry about whether existing radiators would cope with being pressurised we left the central heating circuit open-vented and put a heat exchanger where the old boiler had been - thus we have two (Wilo low-energy) pumps, first from Thermal Store to Heat Exchanger, second from Heat Exchanger around the radiator circuit.
We also have a pool, and added a second heat exchanger in place of where the pool (oil) boiler used to be. The first Wilo pump is used to get hot water to the pool heat exchanger, and the pool's filter pump gets the pool water to the heat exchanger. (Actually we have since moved the Boiler and Thermal Stores from the garage, which adjoined the house, into the main part of the house and both heat exchanger are now in the new boiler room, rather than the pool room as previously, so that we bring the "cool" pool water to the heat exchanger, rather than the "hot" thermal store water to the heat exchanger, as the heat losses in transmission are less. (In Winter I don't care, it's all within the envelop of the building, so heat losses become space-heating). Moving the boiler / thermal stored INTO the house has resulted in a significant reduction of fuel, so "subjectively speaking", as no two winters are identical
, the heat loss from having the boiler / thermal stores in an "outhouse" was significant. This is, of course, obvious but over here in UK I see lots of installs being recommended in "outbuildings", as not many houses have space for all this lot within the envelope of the house, and my Number One Top Tip would be to ensure that the boiler / store is INSIDE the house envelope.Originally we had 2 x coils in the thermal store for DHW (Domestic Hot Water). The first low in the tank as a "pre heat", the second at the top for a final heat. There is then a mixer valve (joined to the cold feed) that regulates the output hot water (to 65C / 150F I think). The thinking was that if the tank was hot, top-to-bottom, the output from the bottom coil would be close-to 65C, and thus there would be no/little additional heating at the top coil, and thus no/little impact on stratification. If the tank wasn't so hot then I'd have to live with stratification in order to be sure to get DHW. Top part of the primary tank is "reserved" for DHW - i.e. the feed/flow to central heating Radiators is lower in the tank.
There are then 2x Solar coils (also in the Primary thermal store). If the top half (of the primary) thermal store is below 60C / 140F then solar heating only goes to top coil (and solar panels have to get hot enough so that their dT is 10C-or-so higher). Once the top half reaches 60C then solar heating switches to bottom half (at which point the dT is more easily achieved as it only has to be 10C higher than the (cooler) bottom of the tank)
The electric immersion heaters are an emergency fall back in case the boiler breaks. Previously our oil tank was inside the house (no longer permitted in UK, or at least not with the old-style tank we had) so to continue to use oil we would have had to have a new tank, out in the garden somewhere, and pipe that across the drive to the house. Big job, lots of collateral damage to make good, and our primary objective was to be more Eco Green ... so Oil was out ...
In Summer it was quite difficult to get top half of 2,500L tank to be consistently above 60C to provide DHW at 60-65C. So we added a separate DHW tank, which has Solar Coil (top-to-bottom), Boiler Coil (top half only) and two immersions - boost at the top, and another at the bottom for "full tank" mode. In principle we want to leave some "cold" water at the bottom of the tank so that the Solar has something to heat.
We use the original 2x Coils in the Thermal Store, previously used to provide DHW, to pre-heat the water going into the hot water tank (so, in principle, the hot water tank should be refilled with water at 60C in Winter, maybe as low as 40C in Summer during any not-very-sunny periods)
Once Solar has heated the DHW tank it switches to dumping heat into Thermal Store. If there is enough of that then it is available to a) pre heat water for the hot water tank or b) to dump into the pool.
We thought long-and-hard about stratification of the thermal store, and considered buying a fancy tank with all sorts of baffles and devices to mitigate the problem. In the end we went for "simple" instead and that saved me a lot of money; Looking back: I'm happy with the decision.
Since then we have added an extension to the house, and that has under floor heating (lower temperature). The extension is built to Passive House standards, so needs very little heat (although we have chosen to keep it warmer than we used to have the main house so it is very cosy, and reduced the temperature of the main house, so the Passive House extension does use some heat).
We have also added more thermal solar panels dedicated to heating the swimming pool. The swimming pool filtration circuit can now pass the water through a) the dedicated solar panels then optionally b) through the Thermal Store heat exchanger (either taking heat from the thermal store, if there is some spare, or I light the boiler at the same time). In practice the Solar Panels are sufficient except for the very start / end of the swimming season (for us that is late March to early November - which is probably 4 - 6 weeks longer than would be normal for a pool in this area without serious commitment
)For Winter Heating we evolved a method that suits us over the first couple of years. We found that lighting the boiler in early afternoon, which then ran for about 6 - 7 hours on a "batch", heated the house nicely in the evening. The boiler stopped at about the time we went to bed, which seemed ideal. There would then be enough heat in the thermal store for the morning heating run (before we get up), and any "boost" in the morning if it was cold (I work from home). In the afternoon we would load the boiler between half-and-fully-full depending on how low the store temperature had fallen. Below 40C / 105F it then has no "guts" for heating the house via radiators; in practice in the UK the day temperature in Winter is 5C and night temperature 0C, so with a reasonably sunny day there isn't a need for much top-up heat until afternoon / early evening. Of course we also get Arctic conditions at times (we get -10C to -15C for perhaps a week's duration about once a decade) and on those occasions we light the boiler in the morning, and top-up the "burn" during the afternoon, but it is rare to need to do that - mild winters not at all, average winters maybe 5 days of the year, cold winters maybe 10 days. In mild winters we get away with a full-load every-other-day, as we do in Autumn / Spring (maybe only having a burn 1-in-3 days in early Autumn / late Spring).
We found control using convention thermostats wasn't getting us what we wanted. Thermostats wanted to heat the house when the temperature fell below X-degrees, but that might compromise the Thermal Store if its temperature was getting low. OTOH if we put too much wood in the boiler the house would heat up in the evening, the thermostat would cut off, the thermal store would heat up and, at around 85-90C / 185-195F the boiler would damp-down, and we'd just smoulder the remainder of the fuel "wasting it".
So we changed the controls so that we now have a "forced central heating on" timer. If the Thermal Store is down to 40C we load the boiler full, and force the central heating on for 6 hours. That will heat the house well, in 6 hours, and leave the thermal store at Max just as the fire goes out - if we judge it right! (if not I can just put the central heating on for another hour to lower the Thermal Store temperature and then the boiler fan will resume). If the Thermal Store is nearer to 60C then we half-load the boiler and set the force central heating timer to 4 hours.
If, by this means, we heat the house hotter, in an evening, than the old thermostat setting would have allowed, then we go to bed one or two degrees warmer, and wake up with less heating required in the morning (house has very little air leakage [about 2-3 ACH @ 50 pascals, or whatever the test is!] and reasonable insulation + double glazing). The house has concrete 1st floor and flat roof, since augmented by pitched roof and lots of "loft insulation". In the Passive House Extension all the internal walls are dense blocks, so the thermal-mass of the building is very high indeed, and thus over-heating the house is "slow" and stored well by the building's fabric. I guess this approach won't work for everyone
The Solar Thermal for the Pool doesn't need to heat the pool in winter (and I regard it as a waste running the filtration pump just to dump solar heat), so we have a bare pipe around the Conservatory as a heat dump. It gives off very little heat in Winter (but it is not good for the Solar Panels to overheat), and we just switch the plumbing over to heating the conservatory in winter, and turn the Pool Pump "solar switch" off. I have some plants in the Conservatory and they are happy with any boost heat they get.
In case of interest the full installation details are on a UK Forum:
http://www.navitron.org.uk/forum/index.php/topic,5875.0.html
Last edited:
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