Miek Posted June 16, 2019 Share Posted June 16, 2019 1 hour ago, scottishjohn said: An even more simple over heat protect would be heat dump linked by a mechanical themostat that diverts when temp gets too hot - Not fail safe in the event of a powercut though. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 16, 2019 Share Posted June 16, 2019 Just now, Miek said: Not fail safe in the event of a powercut though. That's my primary concern, too. I believe that our neighbours problems may well stem from one or more of the relatively frequent power cuts we get around here, as the system relies on being powered up in order for the boiling prevention controls to work. I don't like the idea of this at all, and would want a system that's fail safe when the power goes off and the sun is shining. Link to comment Share on other sites More sharing options...
SteamyTea Posted June 16, 2019 Share Posted June 16, 2019 (edited) If using ET on a drainback system, is there not a problem with the longevity of the ETs. The only Drainback system I have seen up close is the one that had an acrylic cover (it was formed into 3 large 'bubbles'). I think the company that made them went bankrupt a few years back (about the time FiTs started). Edited June 16, 2019 by SteamyTea Link to comment Share on other sites More sharing options...
Miek Posted June 16, 2019 Share Posted June 16, 2019 2 minutes ago, SteamyTea said: If using ET on a drainback system, is there not a problem with the longevity of the ETs. The only Drainback system I have seen up close is the one that had an acrylic cover (it was formed into 3 large 'bubbles'). I think the company that made them went bankrupt a few years back (about the time FiTs started). Filsol I believe you are referring to. You can still get their drain back tank direct from the manufacturer. Ive never fitted a drain back ET system, but if sized correctly there shouldn't be a great deal of 'off time' though I can see what you mean about potential overheating. Personally I'm not a fan of the budget ET panels (navitron, Chinese clones etc) and the good ones like the original thermomax are far too expensive. Link to comment Share on other sites More sharing options...
SteamyTea Posted June 16, 2019 Share Posted June 16, 2019 5 minutes ago, Miek said: Filsol That name rings a bell. They had one at the university I taught at.. It was meant to be for testing and training. Just after they got it, the company went pop, so no idea if it is still about. I liked the simplicity of the system as it was basically a panel and a pump, differential temperature controller and a pressure relieve valve. Link to comment Share on other sites More sharing options...
dnb Posted June 16, 2019 Author Share Posted June 16, 2019 3 hours ago, scottishjohn said: none of these technologies have to be roof mounted if that is the reason for not having balanced mix . size of tank and where you put the solar heat in and where ufh coils are will make a tremendous difference as to how much of the year they can contribute. Don't forget that my conclusions are specific to my new house design. I made no assumptions on requiring roof mounting. All I assumed was that there would be a fixed area of collector and it would be filled with the most efficient distribution of PV and ETs for DHW (I am planning no wet UFH - it is a complication that the house does not seem to need if the AC system works like the predictions say). In practice, the roof is the only sane place to put solar equipment so that it is not shaded by the nearby trees. I assumed a 500 litre tank. It doesn't have much bearing on the situation because both the PV and ETs will be feeding it, and sooner or later it will be filled. I had a cunning plan for dealing with thermal over supply so this on its own does not deter me. But the bottom line of payback time for the cost of installation unfortunately does have to be a significant factor in system design. So unless I can find another few percent of efficiency from the ETs (modelling might be pessimistic?) the ET "business case" for want of better words doesn't appear to work for me purely on investment terms. Granted, it's really close. If I have over-estimated ET costs by 20% then they win hands down. Similarly, if I have underestimated the cost of PV panels by 20% then ETs win. Similarly, if I have underestimated my demands of DHW by a significant margin then ETs win. Why does it have to be a photo finish? I wanted a clear winner!! Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 16, 2019 Share Posted June 16, 2019 1 minute ago, dnb said: Why does it have to be a photo finish? I wanted a clear winner!! One thing that might make a difference is your choice of hot water storage device. We have a Sunamp that is electrically heated, takes up a fraction of the space that a hot water cylinder or thermal store would and has much lower losses. After a bit of a glitch, when Sunamp radically changed the heating and control system when they redesigned their units, Sunamp seem to have now resolved the control problems with the electrically heated UniQ range and we're finding that it works very well. Link to comment Share on other sites More sharing options...
jack Posted June 16, 2019 Share Posted June 16, 2019 5 hours ago, scottishjohn said: Istill believe a mix of both with,suitable tank size and DESIGN and control will be good economical system But if you do both, you're paying for two complete sets of infrastructure, with increased complexity of control systems, increased maintenance costs, and increased risk of something going wrong. I think you're better just sticking to one technology. 1 Link to comment Share on other sites More sharing options...
scottishjohn Posted June 16, 2019 Share Posted June 16, 2019 (edited) 3 hours ago, JSHarris said: One thing that might make a difference is your choice of hot water storage device. We have a Sunamp that is electrically heated, takes up a fraction of the space that a hot water cylinder or thermal store would and has much lower losses. After a bit of a glitch, when Sunamp radically changed the heating and control system when they redesigned their units, Sunamp seem to have now resolved the control problems with the electrically heated UniQ range and we're finding that it works very well. you can heat sunamp with solar thermal --does not have to be PV just a heat source- just lower pump speed on cooler days so you get high water temp but lower volume -so you only have water over your 56 c going to it It was orginally designed to be a user of waste heat from production processes. the argument of complicated systems is not that good ----solar thermal is very simple --panels +pump +sensors --thats it I never had a problem with power cuts causing problems in summer with a pressure accumulator in circuit the panels can stagnate at 140c, providing pressure in system is enough -no problem ,but again if running both and a wee battery back up --to run controller/pump on 12v --that is another belt and braces now if the accumulator was not big enough on some systems then pressure could rise so high it could blow water out of system --again specing the thing right- I was supplied with too small an accum in first instance--I fitted another 27litre accum along with the 18litre supplied and pumped them up to 3 bar charged system to 3 bar It could mean a manual pump up of system where your mains water pressure is below 4 bar -panels I had was fit for 10 bar --and had a pressure relief valve at 5 bar you can run on lower pressures if you wish and if you do make sure you have tank big enough that it cannot get to close boiling in one day .my thermal cut off was set at 92c-set lower if you like all the possible problems you state revolve around the accepted fact of how good it is at heating water !!! Edited June 16, 2019 by scottishjohn Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 16, 2019 Share Posted June 16, 2019 1 minute ago, scottishjohn said: you can heat sunamp with solar thermal --does not have to be PV just a heat source- just lower pump speed on cooler days so you get high water temp but lower volume -so you only have water over your 56 c going to it It was orginally designed to be a user of waste heat from production processes. Sadly that option isn't at all easy to do. It could be done with some careful controls to ensure that the charging hot water circuit is always over 58°C and below boiling point, but it would need something like the control system that was used in the old Sunamp PV, with a flow sensor, temperature sensors and a variable speed pump. I've looked at doing it (during the long debate about Sunamp charging methods) but it's not exactly easy to do. Link to comment Share on other sites More sharing options...
SteamyTea Posted June 16, 2019 Share Posted June 16, 2019 7 minutes ago, scottishjohn said: he argument of complicated systems is not that good ----solar thermal is very simple --panels +pump +sensors --thats it followed by 10 lines of text about how complicated it is. It is not just control systems, there are accumulators, pressure valves, safety cutouts, replacing fluids. When a car boils over, you can just fill it with some water, but you really need to fill it with anti-freeze as well, and find out why it has overheated, which could be, in no particular order: broken hose faulty waterpump faulty thermostat internally blocked radiator externally blocked radiator failed head gasket broken fan broken fan motor broken fan belt and a few more things. The above are some of the reasons I think PV is a lot simpler and reliable. 1 Link to comment Share on other sites More sharing options...
scottishjohn Posted June 16, 2019 Share Posted June 16, 2019 2 hours ago, SteamyTea said: followed by 10 lines of text about how complicated it is. It is not just control systems, there are accumulators, pressure valves, safety cutouts, replacing fluids. When a car boils over, you can just fill it with some water, but you really need to fill it with anti-freeze as well, and find out why it has overheated, which could be, in no particular order: broken hose faulty waterpump faulty thermostat internally blocked radiator externally blocked radiator failed head gasket broken fan broken fan motor broken fan belt and a few more things. The above are some of the reasons I think PV is a lot simpler and reliable. how can you list car problems when talking about solar thermal of that list only 2 things could be even considered as similar to a car I know that's what i have been doing for last 40 years anyway just state you don,t like solar thermal and leave it at that please don,t invent things that have no bearing on the subject ,its just scaremongering to people who do not know about these things,same as talking about electronics to those who are not conversant with them as for antifreeze --yes. I used car antifreeze in my system ,the red -sealed for life type -very economical and no need for changing ever and also a very good corrosion inhibitor Link to comment Share on other sites More sharing options...
scottishjohn Posted June 16, 2019 Share Posted June 16, 2019 (edited) 2 hours ago, JSHarris said: Sadly that option isn't at all easy to do. It could be done with some careful controls to ensure that the charging hot water circuit is always over 58°C and below boiling point, but it would need something like the control system that was used in the old Sunamp PV, with a flow sensor, temperature sensors and a variable speed pump. I've looked at doing it (during the long debate about Sunamp charging methods) but it's not exactly easy to do. a std commercial process controller would do that and all your pv and heating system at same time ,all programmed with a lap top would have thought it would be right up your street @JSHarris as for temp control you could use a simple analog blender vlave same as you would use to set dhw temp,if you want to keep away from 21st century control systems --.its not rocket science ,just different than PV you could even use both pv +solar to obtain correct min temp ,but keeping as much pv energy as possible for other things Edited June 16, 2019 by scottishjohn Link to comment Share on other sites More sharing options...
SteamyTea Posted June 16, 2019 Share Posted June 16, 2019 29 minutes ago, scottishjohn said: just state you don,t like solar thermal and leave it at that please Quite the opposite, I did my BSc final year project in solar thermal. Since then, the world has moved on and in my opinion, PV is the way forward for domestic use. 2 Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 16, 2019 Share Posted June 16, 2019 31 minutes ago, scottishjohn said: a std commercial process controller would do that and all your pv and heating system at same time ,all programmed with a lap top would have thought it would be right up your street @JSHarris as for temp control you could use a simple analog blender vlave same as you would use to set dhw temp,if you want to keep away from 21st century control systems --.its not rocket science ,just different than PV you could even use both pv +solar to obtain correct min temp ,but keeping as much pv energy as possible for other things No it won't, as the problem is not one of the controls, but of getting the physical system to respond within the defined limits. Variable speed pumps have a non-linear relationship between speed, flow rate and head, hence the need for the flow sensor, and the flow sensor is adversely affected by things like dissolved gas content (this caused problems with the Sunamp PV). Add in the wide range of heat output from the ST system and the things gets to be more trouble than its worth for a domestic system. It's a heck of a lot easier to just use PV, as electricity is a lot simpler to control. It really comes down to simplicity being a very significant advantage for any domestic system that has to operate, with a minimal degree of servicing, for a couple of decades. Link to comment Share on other sites More sharing options...
PeterW Posted June 16, 2019 Share Posted June 16, 2019 48 minutes ago, scottishjohn said: as for antifreeze --yes. I used car antifreeze in my system ,the red -sealed for life type -very economical and no need for changing ever and also a very good corrosion inhibitor Do you know how poisonous Ethylene Glycol is ..????!!! There are some very very good reasons why you don’t use car antifreeze in solar systems - the big one being that if it leaks in the tank (which is entirely possible) then you contaminate the whole of the water system with something that can put you in hospital. It’s dangerous ok ..?? As in the next person who owns your system could end up in hospital because you saved £50 on antifreeze...!! Solar rated glycol may be expensive but it’s because it’s Propylene Glycol based. It’s not poisonous. It’s doing what it’s designed to do - not some half arsed replacement that’s cheap but has great big poison warnings on it ..!!! 1 Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 16, 2019 Share Posted June 16, 2019 By the same token, the antifreeze used in any heat pump installation also has to be the more expensive stuff. The consequences of the risk of contamination from using something like car antifreeze doesn't bear thinking about, and it would be foolhardy in the extreme to use it in a domestic water heating system. Link to comment Share on other sites More sharing options...
Onoff Posted June 16, 2019 Share Posted June 16, 2019 1 hour ago, scottishjohn said: I used car antifreeze in my system I won't be doing that. One of the coils in the cylinder splits and you could be cleaning your teeth with the stuff! Link to comment Share on other sites More sharing options...
jack Posted June 16, 2019 Share Posted June 16, 2019 1 hour ago, scottishjohn said: just state you don,t like solar thermal and leave it at that please Just state that you're one-track minded about solar thermal and leave it at that please. Link to comment Share on other sites More sharing options...
SteamyTea Posted June 16, 2019 Share Posted June 16, 2019 28 minutes ago, Onoff said: One of the coils in the cylinder splits and you could be cleaning your teeth with the stuff Judging by your picture, it looked like you bathed in it. Are you auditioning for a part in Chernobyl. Link to comment Share on other sites More sharing options...
dnb Posted June 16, 2019 Author Share Posted June 16, 2019 2 minutes ago, JSHarris said: It really comes down to simplicity being a very significant advantage for any domestic system I think you can drop the "domestic" from that statement. Simplicity usually wins. If a system looks complicated then chances are you haven't finished designing it yet! The choice of storage vessel for DHW heat is of little importance to the payback time of the choice of thermal or PV as long as it is large enough. My maths assumes it is something that accepts heat and gives it up with a nominal daily loss. I might win a bit of the loss back with some systems, but this is not the question that I am trying to answer at the moment. I really wanted solar thermal to work out. It is simple - the fewest steps to collect the energy - but the "business case" (how I hate those words!) just does not add up for my situation, even assuming zero servicing. Each ET "bank" removes apprx 900Wp of PV from the system (keeping the collector area constant) and costs more than 3 PV panels in parts alone. It might function better, but unless it can offset the cost disadvantage a simple single technology wins. About the only thing now that will tip the balance is if 3 phase electricity is required for the all PV system but not for any of the alternatives with thermal. (3 phase would be useful in the garage of course. Everyone needs a good machine shop for their own personal use!) Link to comment Share on other sites More sharing options...
scottishjohn Posted June 17, 2019 Share Posted June 17, 2019 17 hours ago, PeterW said: Do you know how poisonous Ethylene Glycol is ..????!!! There are some very very good reasons why you don’t use car antifreeze in solar systems - the big one being that if it leaks in the tank (which is entirely possible) then you contaminate the whole of the water system with something that can put you in hospital. It’s dangerous ok ..?? As in the next person who owns your system could end up in hospital because you saved £50 on antifreeze...!! Solar rated glycol may be expensive but it’s because it’s Propylene Glycol based. It’s not poisonous. It’s doing what it’s designed to do - not some half arsed replacement that’s cheap but has great big poison warnings on it ..!!! yes i do know what it is made from but again it is scaremongering for it to get where it can touch dhw it would need to perforate a single piece s/s coil in the tank and then perforate the s/s coil that is used to heat the dhw from the thermal store that is never going to happen 2 x one piece s/s coils to have holes at same time !!!! Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 17, 2019 Share Posted June 17, 2019 4 minutes ago, scottishjohn said: yes i do know what it is made from but again it is scaremongering for it to get where it can touch dhw it would need to perforate a single piece s/s coil in the tank and then perforate the s/s coil that is used to heat the dhw from the thermal store that is never going to happen 2 x one piece s/s coils to have holes at same time !!!! In your case, maybe, but not for most systems, where there will just be a single thickness of pipe, most probably copper, between the toxic antifreeze and the hot water storage. Link to comment Share on other sites More sharing options...
PeterW Posted June 17, 2019 Share Posted June 17, 2019 4 minutes ago, scottishjohn said: but again it is scaremongering It’s not. It breaches water regulations. It is poisonous. End of. Please stop spouting rubbish that could potentially cause harm to someone. 1 Link to comment Share on other sites More sharing options...
Ed Davies Posted June 17, 2019 Share Posted June 17, 2019 40 minutes ago, scottishjohn said: 2 x one piece s/s coils to have holes at same time !!!! How would perforation of either of those coils become apparent? Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now