Jeremy Harris Posted March 12, 2019 Share Posted March 12, 2019 33 minutes ago, Ballynoes said: I wish we had gas, but live in the country, so don't even have sewage, or decent broadband, but that's the price you pay for piece and quiet surrounded by your own fields... not complaining though. ? I still find it difficult to comprehend that you cant "feed" a hot water cylinder with two different form of heating, after all I was under the impression that you had to occasionally heat the hot water tank to a certain temperature, to make sure certain bacteria don't thrive... or is that another myth. ? To feed a hot tank from two sources is OK, but controlling them so that they can both work effectively is the challenge. For example, I installed a big thermal store initially, and pre-heated this when it was cold from the ASHP. This raised the temperature of the tank up to about 40°C, as long as it wasn't already at that high a temperature. The immersion heater, run from excess PV generation, then provided the energy needed to get the thermal store up to around 65°C. If the tank was above 40°C then the ASHP couldn't provide any useful heat to it. The need to boost the temperature of stored hot water enough to kill off legionella is probably an over-blown risk, provided that you're using mains water and a sealed UVC. Legionella cannot get into the mains water supply (the reason mains water is usually post-treated with a persistent disinfecting agent is to ensure this) so if it isn't in the supply water, and the tank is sealed, there's no way for any bacteria to multiply, as there won't be a way for them to get in in the first place. Also, legionella stop multiplying at a temperature of about 45°C, and so holding the tank at 50 to 55°C may not kill them, but will cause them to go dormant (not that they can get inside a sealed system anyway). Finally, regular hot water use will flush the contents of the tank through before any bacteria (which can't get in) have a chance to set up home. If you have a vented hot water system, then things are different, and an anti-legionella temperature cycle with an immersion heater, to heat the tank to above 60°C every week or two would be a good idea. Link to comment Share on other sites More sharing options...
Vijay Posted March 12, 2019 Share Posted March 12, 2019 I'm sure I saw some sort of heat exchanger unit, that could basically take various heat supplies and supply them to a store. For the life of me I can't find where I saw it Link to comment Share on other sites More sharing options...
Ballynoes Posted March 12, 2019 Author Share Posted March 12, 2019 (edited) This looks promising. http://www.chelmerheating.co.uk/self-build/thermal-store-and-buffer-cylinders/thermal-store-heat-bank-cylinders.html Edited March 12, 2019 by Ballynoes Link to comment Share on other sites More sharing options...
scottishjohn Posted March 12, 2019 Share Posted March 12, 2019 (edited) If you got mains elec--then why not just run ASHP for underfloor sounds like a lot of complications I have run a 2 source heat system and as has been said good control to get best from both systems is not easy when i up graded heat source to ashp from previous system --nothing was changed on the exisiting UFH just the heat source I used a mitsubishi ashp with their pre-plumbed tank+ pumps etc which does all the hot water as well simple solution the only complication Iadded was solar thermal panel ,as the tank was already plumbed for that as well 80% of hot water over the year comes from the solar thermal resulting energy savings over the lpg system+solar thermal was impressive lpg bill was £1500 --that dissappeared and my elec bil only went up by £500--so £1000 saving worh a look i feel for a simple integrated system then you get the RHI payment for next 6 years as well Edited March 12, 2019 by scottishjohn Link to comment Share on other sites More sharing options...
Vijay Posted March 12, 2019 Share Posted March 12, 2019 Out of interest, what size of hot water store should you have for a wood burner/boiler, is there a certain amount of litres per KW output? Link to comment Share on other sites More sharing options...
ProDave Posted March 12, 2019 Share Posted March 12, 2019 1 hour ago, Ballynoes said: This looks promising. http://www.chelmerheating.co.uk/self-build/thermal-store-and-buffer-cylinders/thermal-store-heat-bank-cylinders.html The trouble with a thermal store is you need to store water hotter than your required DHW temperature, otherwise it will only be able to deliver a tiny amount of water before the temperature drops. A heat pump will struggle to get a thermal store hot enough That is why an UVC is better for use with a heat pump as you heat it to the desired water temperature and it will then deliver pretty much that temperature water until it runs out. Which brings us back to the issue that is is very complicated to link a stove to an UVC. Much less so to link a stove to a thermal store. There does not seem to be an easy solution for stove and ASHP heating the same hot water system. Link to comment Share on other sites More sharing options...
Ed Davies Posted March 12, 2019 Share Posted March 12, 2019 5 hours ago, epsilonGreedy said: Relative to absolute zero (-273) your maths looks plausible but surely what is significant to ASHP is the heat capacity available down to the minimum chilling operating range of an ASHP. If an ASHP can chill to -10, then the available heat capacity at -5 is half of that available at Zero. Obviously there's a low temperature beyond which any particular refrigerant will not work but thinking about the amount of heat in the input air to a heat pump is confusing. If there's less heat in a m³ of air the cure is just to blow more air through. That'll mean a bit more electricity to drive the fan but that's all. The limitation on the CoP of a heat pump is set by the basic laws of thermodynamics. Real heat pumps will get about half this limit but do tend to scale roughly in proportion. http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatpump.html 1 Link to comment Share on other sites More sharing options...
scottishjohn Posted June 25, 2019 Share Posted June 25, 2019 (edited) plotting for this new house for various water heating systems It seems I could end up with having to remove about 40+ trees (most about 10-12" dia,some much larger and 30ft+ tall) ,to start with and possibly a lot more in due course my question to those using wood burner for water heating + large tank how long does one tree last ? Is it worth getting a wood burning unit to use them or just try to sell/get rid of them Edited June 25, 2019 by scottishjohn Link to comment Share on other sites More sharing options...
ProDave Posted June 25, 2019 Share Posted June 25, 2019 One of those trees would last me a season so that would be a lifetime supply for me. But we don't need the stove much and we don't heat hot water with it. But I would have no trouble finding people to give it too if I needed to get rid of it. Link to comment Share on other sites More sharing options...
SteamyTea Posted June 25, 2019 Share Posted June 25, 2019 17 minutes ago, scottishjohn said: how long does one tree last ? Work out the dry mass, multiple by the energy content, multiply that by the system efficiency and you have your answer. 14 minutes ago, ProDave said: One of those trees would last me a season so that would be a lifetime supply for me Takes a lifetime to grow some trees too. I wish people that burn trees would count the rings they have before they throw them on the fire. That may bring home just what an inefficient 'storage and energy' system biomass is. Link to comment Share on other sites More sharing options...
Carrerahill Posted June 25, 2019 Share Posted June 25, 2019 On 08/03/2019 at 09:28, Ballynoes said: The question is, how easy is it to connect a wood burner to a hot water storage tank, as hot water will probably be our biggest use of energy. Simple really, just match up your system components suitably. My friend has a Bosky Thermorossi which feeds two 100/120?litre water tanks for DHW and his C/H system with an injection Tee on the return - which he tuned by reducing the radiator diameter return pipe by crimping slightly which gives him the perfect balance for his needs. The tanks have there own cisterns and are vented. They thermosyphon so the pump only kicks in when demand for heating is required or the system needs to dump heat which is done with a fairly simple yet clever set of thermostats and pump controls. The underfloor heating aspect I believe always receives a trickle so that the slab temp cannot drop too low. The system is very simple, works like a dream and as he has unlimited supply of firewood it is the most economical thing in the world for him to run. In summer he can heat DHW with plate heaters in the tanks which interestingly is connected into a waste oil generator system so that is free too. His system was so successful he also designed and advised on the install of a identical system for a farmhouse where the couple were paying £1000's for gas delivery's. They now certainly buy poles (not yet logged) and prepare it themselves but I think it costs him £200 a year and the local farmer stores it for him dry and he only takes what he can split and store at any given time. Link to comment Share on other sites More sharing options...
scottishjohn Posted June 25, 2019 Share Posted June 25, 2019 17 minutes ago, ProDave said: One of those trees would last me a season so that would be a lifetime supply for me. But we don't need the stove much and we don't heat hot water with it. But I would have no trouble finding people to give it too if I needed to get rid of it. but if no other heat source --AND using that as main heat supply --how long . the thought is that in the garage?service are there will be more than enough room for multiple heat sources or changing from one to another in due course I got to cut these trees anyway as they have grown up around the house since it was last occupied in 1960,s Link to comment Share on other sites More sharing options...
bassanclan Posted June 25, 2019 Share Posted June 25, 2019 I've got a Dunsley Yorkshire wood burner with boiler, but on my next project I will definitely look at log gasification boilers as the government subsidy means they pay for themselves in 6/7 years. Worth looking into 1 Link to comment Share on other sites More sharing options...
scottishjohn Posted June 25, 2019 Share Posted June 25, 2019 2 minutes ago, Carrerahill said: DHW with plate heaters in the tanks which interestingly is connected into a waste oil generator system so that is free too. I know to use waste oil heaters in commercial application now you need a license it was favourite way to heat workshops with endless supply of used engine oil .now the cost of a clean burn approved waste oil burner etc makes it not a good choice any more in most cases Link to comment Share on other sites More sharing options...
scottishjohn Posted June 25, 2019 Share Posted June 25, 2019 1 minute ago, bassanclan said: I've got a Dunsley Yorkshire wood burner with boiler, but on my next project I will definitely look at log gasification boilers as the government subsidy means they pay for themselves in 6/7 years. Worth looking into that does not seem a good deal ,with all the effort involved in making logs to start with Link to comment Share on other sites More sharing options...
scottishjohn Posted June 25, 2019 Share Posted June 25, 2019 12 minutes ago, Carrerahill said: My friend has a Bosky Thermorossi £5k for a range -- again a life style choice not a serious economic choice -- in my mind that is Link to comment Share on other sites More sharing options...
Carrerahill Posted June 25, 2019 Share Posted June 25, 2019 57 minutes ago, scottishjohn said: £5k for a range -- again a life style choice not a serious economic choice -- in my mind that is Depends if you will see a ROI, which he has. He could have probably gone cheaper but that is his kettle and oven too. It's cost him about £100 in 12 years to run it so I would say that is very economical. As for cost of the Bosky - at today's prices: 5k / 12 / 12 £34.72 a month but he paid about £2800 at the time. So £19.44 p/m and falling with every month that passes. Link to comment Share on other sites More sharing options...
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