Correct, but this will depend on the meter type they have.
And bearing in mind most people dont have a suitable tool for doing this how else are they going to do it?
Johnward & VicVapour
- Thread starter ecowarrior
- Start date
Correct, but this will depend on the meter type they have.
And bearing in mind most people dont have a suitable tool for doing this how else are they going to do it?
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Same principle/problem with electrics.
In no particular order ...
The original question. What the OP wants is impossible, because his question is wrong. He asks for an S plan, but wants extras - that means it's no longer an S plan by definition, since an S plan is a specific combination of motorised valves and wiring.
However, without having paid too much attention to it, I'm assuming the boiler has some terminals to which one can attach a sensor and it will vary it's output temperature. In that case, one or other of the valves has it's switch connected to trigger a relay instead of the boiler/pump. The relay has two sets of contacts - one fires the boiler/pump as would be done directly by the switch in the original S plan, the other applies a suitable resistance to change the boiler temperature.
I think someone else has also come up with the issue of interlocking the CH and DHW - otherwise you have to choose between having high CH or poor DHW reheat when both are demanded.
EDIT: that can be dealt with by judicious wiring of the controller switches and/or relay to lock out one circuit while the other is running. That then means you have to decide which has the higher priority.
As to Mysons, they used them at my last place and I pointed out that from the control POV they are horribly inefficient. Eventually when we put in some cooling, I rigged up the controls so that heating was controlled by a thermo-hydraulic valve in the supply, and the fan switched on/off with the internal pipe stat. So the heating/cooling controller would switch on the heater in the valve head, the valve would open, and the hot water would trigger the pipe stat in the Myson to turn on the fan. Once the desired temp was reached, the valve would be turned off, and when the flow stopped, the Myson would cool off and turn itself off.
But I'd answer the original question differently. I'd design a hydraulic system that wasn't fundamentally crap to start with. As has been pointed out - we seem to have a fixation with making one thing do two jobs with widely differing (and often conflicting) requirements. A prime example is the Combi Boiler which requires huge capacities for DHW, but then is grossly oversized for CH - take my flat for example, 30kW combi is **** poor at heating DHW, but is also **** poor at ranging down enough to supply CH at 2kW in the depths of winter (and a lot less in milder weather).
We also impose minimum flow rates through the boiler, when we know that we need variable (and often low) flow rates through the CH system.
Anyway, the solution I chose was to install a thermal store. Boiler is directly connected and heat the store by burning at full power and then shutting down completely in between. When the boiler gets replaced, that will also mean no pilot light.
The CH is supplied by a modulating pump and individual room temps are controlled by TRVs - there is no permanently open rad, and no bypass, so the flow rate through the CH system is what is needed as determined by the TRVs, no more and no less.
The supply to the CH pump is via a TMV which blends cool return with hot from the store to control flow temperature. Not ideal, and I do have some ideas in terms of better control with electronics.
With oversized rads, the return temp (ie what's going back in the bottom of the store) is barely above room temp.
DHW is via a heat exchanger coil that winds it's way up from the bottom of the store to the top - with the DHW gaining heat all the way. This means the cold mains will be heated by even the low grade heat in the bottom of the store (ie return from the rads). In practice, this also means the store temperature varies with position - by the time the hot water reaches the CH tap off, it's already been used for heating the DHW and is cooler than it was when it came in from the boiler.
Unfortunately, the next bit is where the boiler manufacturers are a bunch of cretins. My ideal would be to control flow rate so the boiler can heat from cold (could be 20˚ or even lower) to hot (perhaps 75˚, depends on various factors) in one pass. With the condenser handling water at (say) 20˚, it'll both condense very well, and also extract more specific heat from the exhaust. However, all the manufacturers have a maximum delta-T of 20˚ AFAICS - so that means using diverter or mixer valves to artificially increase the return temperature and reduce efficiency.
I've heard that Atmos claim their boilers can be dry-fired without damage due to a large heat exchanger and sensing directly in it - but their MIs still have this max 20˚ delta-T. When it comes to new boiler time, I'll be asking the manufacturers and see if any of them are capable of supplying usable products.
As a side effect, but one that did influence my decision, the thermal store also has an immersion heater. So not only can the DHW be supplied by electric in the event of a boiler problem, but so can the heating
Dunno if solar thermal will ever happen as it's not a good location, but if I did fit it, then with the vey low store temperatures in the bottom where the solar coil is, that should allow good performance even with low insolation levels.
The original question. What the OP wants is impossible, because his question is wrong. He asks for an S plan, but wants extras - that means it's no longer an S plan by definition, since an S plan is a specific combination of motorised valves and wiring.
However, without having paid too much attention to it, I'm assuming the boiler has some terminals to which one can attach a sensor and it will vary it's output temperature. In that case, one or other of the valves has it's switch connected to trigger a relay instead of the boiler/pump. The relay has two sets of contacts - one fires the boiler/pump as would be done directly by the switch in the original S plan, the other applies a suitable resistance to change the boiler temperature.
I think someone else has also come up with the issue of interlocking the CH and DHW - otherwise you have to choose between having high CH or poor DHW reheat when both are demanded.
EDIT: that can be dealt with by judicious wiring of the controller switches and/or relay to lock out one circuit while the other is running. That then means you have to decide which has the higher priority.
As to Mysons, they used them at my last place and I pointed out that from the control POV they are horribly inefficient. Eventually when we put in some cooling, I rigged up the controls so that heating was controlled by a thermo-hydraulic valve in the supply, and the fan switched on/off with the internal pipe stat. So the heating/cooling controller would switch on the heater in the valve head, the valve would open, and the hot water would trigger the pipe stat in the Myson to turn on the fan. Once the desired temp was reached, the valve would be turned off, and when the flow stopped, the Myson would cool off and turn itself off.
But I'd answer the original question differently. I'd design a hydraulic system that wasn't fundamentally crap to start with. As has been pointed out - we seem to have a fixation with making one thing do two jobs with widely differing (and often conflicting) requirements. A prime example is the Combi Boiler which requires huge capacities for DHW, but then is grossly oversized for CH - take my flat for example, 30kW combi is **** poor at heating DHW, but is also **** poor at ranging down enough to supply CH at 2kW in the depths of winter (and a lot less in milder weather).
We also impose minimum flow rates through the boiler, when we know that we need variable (and often low) flow rates through the CH system.
Anyway, the solution I chose was to install a thermal store. Boiler is directly connected and heat the store by burning at full power and then shutting down completely in between. When the boiler gets replaced, that will also mean no pilot light.
The CH is supplied by a modulating pump and individual room temps are controlled by TRVs - there is no permanently open rad, and no bypass, so the flow rate through the CH system is what is needed as determined by the TRVs, no more and no less.
The supply to the CH pump is via a TMV which blends cool return with hot from the store to control flow temperature. Not ideal, and I do have some ideas in terms of better control with electronics.
With oversized rads, the return temp (ie what's going back in the bottom of the store) is barely above room temp.
DHW is via a heat exchanger coil that winds it's way up from the bottom of the store to the top - with the DHW gaining heat all the way. This means the cold mains will be heated by even the low grade heat in the bottom of the store (ie return from the rads). In practice, this also means the store temperature varies with position - by the time the hot water reaches the CH tap off, it's already been used for heating the DHW and is cooler than it was when it came in from the boiler.
Unfortunately, the next bit is where the boiler manufacturers are a bunch of cretins. My ideal would be to control flow rate so the boiler can heat from cold (could be 20˚ or even lower) to hot (perhaps 75˚, depends on various factors) in one pass. With the condenser handling water at (say) 20˚, it'll both condense very well, and also extract more specific heat from the exhaust. However, all the manufacturers have a maximum delta-T of 20˚ AFAICS - so that means using diverter or mixer valves to artificially increase the return temperature and reduce efficiency.
I've heard that Atmos claim their boilers can be dry-fired without damage due to a large heat exchanger and sensing directly in it - but their MIs still have this max 20˚ delta-T. When it comes to new boiler time, I'll be asking the manufacturers and see if any of them are capable of supplying usable products.
As a side effect, but one that did influence my decision, the thermal store also has an immersion heater. So not only can the DHW be supplied by electric in the event of a boiler problem, but so can the heating
Dunno if solar thermal will ever happen as it's not a good location, but if I did fit it, then with the vey low store temperatures in the bottom where the solar coil is, that should allow good performance even with low insolation levels.
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Interesting post from some one knowledgeable. Down side to heat stores is the boiler needs to be at high flow temp so not good for condensating - plus it cycles more than neccesery by running at full power then shutting off. you perhaps haven't thought of modulating pumps rather than controlling the Delta T and the original post was regarding just replacing the old boiler for a new all singing one &( that happened to be on a proper S plan) and to get it to do the very most it could with what it had to play with. You assumptions are correct and the WC allows a fixed max flow temp under certain conditions and Yes in theory its no longer an S plan but a DHW priority using two 2 port valves. Yes Atmos & Intergas can run dry but that doesnt mean it can run stabley at any given Kw output from Zero upwards as to get a stable flame the whole burner has to be lit generating a minimum stable o/p. Reducing the fan speed will eventually make the burner lock out and really has little to do with its ability to start & run with the boiler empty of water.
Oh - and its not impossible - I do it often. You can also do it to a Y plan ( yes I know its not a Y plan if u convert it to a W plan ( join white & grey then disconnect orange) - but hey - you know what I mean)
The principal here is to 'back engineer' some old technology & do ones best to bring it up to date with minimal cost.
No chest beating here - just comments on your post. Agree with Myson Rads!
Oh - and its not impossible - I do it often. You can also do it to a Y plan ( yes I know its not a Y plan if u convert it to a W plan ( join white & grey then disconnect orange) - but hey - you know what I mean)
The principal here is to 'back engineer' some old technology & do ones best to bring it up to date with minimal cost.
No chest beating here - just comments on your post. Agree with Myson Rads!
The days of anything other than 'whats the cheapest u can do it for' went the day Northern Rock went! Yes it would be better to use a NTC on the tank yes lets change the valves & the cylinder -yes lets increase the size of the rads - but in reality 95% custards now make it cost sensitive.
Ironically the 'grant;' jobs seem to use the cheapest of everything! (and still cost the punter more than an independent would!)
Hadn't given that a lot of thought (its just a logo I use) but the party line is that they don't care what happens as long as you don'y interfere with the inside of the boiler. I suppose external controls are just that - external.Is this solution endorsed by Intergas as I’m not sure they would appreciate their logo being utilised otherwise? I suspect I already know the answer to this.
If the got upset about my little relay being in the boiler (just to keep the wiring minimal & tidy) I could put it in the wiring centre.
Well, I've done one, so I don't profess to be an expert.
I think it's the reverse. Unless you have a boiler that is a) well sized to the CH load and b) capable of a wide modulating range, then it's going to be cycling most of the time the CH is on. Since a) is often mutually exclusive with having good DHW recovery rates, then I doubt it happens much. Somewhere else there was a link posted to a report that looked into real-life performance and efficiency (as opposed to SEDBUK assumptions) and they found little correlation between property size and boiler size - suggesting that most installs were done using "favourite" boilers rather than careful sizing calcs. Of course, the requirement to maintain a minimum flow rate through the boiler often means artificially raising the return temp by means of a bypass, and that doesn't do much for condensing unless (as is the subject of this thread) you start messing around with WC and stuff.
If you look back at my post, you'll see that I address the condensing bit. If the boiler can be set up right then it will rarely (if ever) not condense - I could feed it water which is generally around 20˚.
Yes, and a lot more besides. If I could be sure the boiler would fire reliably, then I'd consider a modulating pump controlled by outlet temperature - minimum flow rate till things are lit up, then increase flow rate to maintain desired outlet temperature.
Indeed, but then in many cases I've seen, the new boiler also comes with a new DHW cylinder - I guess an awful lot of them would originally have been gravity systems and/or low performance coils.
I wasn't proposing to run at very low outputs (well not with a thermal store anyway). The boiler would generally run pretty well flat out while running, and then switch off.
But what you say does come back to the compromises of running CH and DHW off one boiler - even more so if it's a combi and hence requires a higher output. In my flat it is (still) an old Vokera, nearly 30kW and poor at making DHW (that side no longer used) - it's minimum output is 10kW, but in the depths of the cold spell 15 months ago, the heating load was just under 2kW (I measured it).
Indeed.
I'm becoming less and less convinced of that.
I think you're right - CH and DHW have different and conflicting requirements.
As Ecowarrior points out a few posts back, there's a limit to how low you can go with output ranging. If installing a boiler for CH only, then a well designed system would have a boiler sized to the thermal load. Even then, it will spend most of it's time ranged down.
However, such a well sized boiler would probably lead to dissatisfaction with DHW reheat rates - hence the tendency to install oversized boilers. Once you oversize the boiler then you exacerbate the minimum ranging problem.
Of course, the cost (not just capital, but space requirements and servicing) associated with installing two boilers would negate any savings in most situations.
Not exactly a glowing endorsement ! And the thought of having to have anything to do with BG installing it would be a deal breaker for me (even if I could afford one).
It was amusing to see one comment about being able to run his lights from it if the power went off. I believe these are, like Solar PV inverters, specifically designed to detect "island" operation and shut down. Ie, if you aren't on a live grid, they don't work. This is to avoid the safety issues (particularly risk to DNO staff) from having embedded generation trying to backfeed the grid.
I recall going to a talk about these when they were first being launched. I think it was myself that asked the speaker about this as the ability to have local generation would seem to be quite useful. The safety issues noted above were given and it was stressed that the unit really will not operate with a grid connection.
But it is. I am doing a job now.
4 heating zones - one being UFH split to a further 3, plus towel rails. All it requires is 4 extra conductors. 2 exidting for heating switching, additional 2 for hot water switching, and 2 for weather sensor.
The distance these wires take. 2 metres.
Boiler deals with the intricacies. Photo's of project so far to follow later,
Absolute POP.
hey I had forgotten about this thread
yes mate fair points but to be honest I was well done in with the drink and was trying to be neutral while stiring at the same time
I do have an affinity with the sparkies as I worked as one myself for many years
but I do have one with the heating guys too as commercial heating systems/building control/ plant more my trade now,
but you are dead right there are good and bad on both sides
Matt
yes mate fair points but to be honest I was well done in with the drink and was trying to be neutral while stiring at the same time
I do have an affinity with the sparkies as I worked as one myself for many years
but I do have one with the heating guys too as commercial heating systems/building control/ plant more my trade now,
but you are dead right there are good and bad on both sides
Matt
It's not just the complexity of the control systems - even if those presented no problems whatsoever, I question whether a single appliance to do two very different jobs - a few kW of space heating and instant delivery of hot water, where 30-odd kW doesn't go amiss, is the best approach, or if it's a compromised design and it would be better to have two appliances each designed to efficiently do just one thing.
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