If it makes any difference, some of the specs from the boiler manual are:
Max heat o/p Qmax(80=B0/60=B0C) =3D 28KW Min heat o/p Qmax(80=B0/60=B0C) =3D 5.6KW Max heat o/p (50=B0/30=B0C) =3D 29.7KW Min heat o/p (50=B0/30=B0C) =3D6.1KW Working efficiency at max o/p (80=B0/60=B0C) =3D 97.6% Working efficiency at max o/p (50=B0/30=B0C) =3D 103.5% Working efficiency at 30% max o/p (Average T=3D50=B0C) =3D 107% Working efficiency at min o/p (80=B0/60=B0C) =3D 98.2% Working efficiency at min o/p (50=B0/30=B0C) =3D 107% Max heating temp =3D 90=B0C Min heating temp =3D 20=B0C
If analogue control means it has a manual control knob to adjust heat o/p then it has one for heating and one for DHW. It also came with an outside probe (which I'm assuming is the mentioned weather compensator). It says this must be fitted for maximun efficiency.
Yes, I did mean that the most efficient method to heat store was direct first, then PHE and lastly coil. I see that you believe that using a PHE uses about 95% of boiler's output. If it is assumed that directly heating store uses 100%, looks like there is not much in it from that point of view. DPS were quoting me =A375 inc VAT for PHE. Then pump on top.
You can't? New to me. The heat load for the boiler is very predictable indeed and the boiler runs in an ideal hydraulic environment.
Which means it is very suitable for a heat bank indeed and will promote condensing.
..and well suited for modern condensing boilers too operating at lower temperatures and wider delta Ts.
We do? Prey tell....
It is...let us hear...
7 kW is 25,000 btu/hr which is afair amount of heat injected into a heating system that may only require 0.5kW (1,500 BTU/hr). This will result in boiler cycling. And as most boioer only go to around 10 kW minimum the problems is well...a big problem.
..good observation.
..that mean a lower store setpoint and lower boiler return temperatures, improving efficiency.
..yes...and...
You can do this with the store, have the DHW section at a higher temperature than the CH section which can be controlled via an outside weather compensator.
Taking the rads off the boiler direct with TVRs all around is a poor substitute with great setbacks. As one rad needs to be controlled by a wall stat and the auto by-pass will lower efficiency greatly by short circuiting the boiler. The boiler needs to be complex and may have a short life because of low flows through the heat exchanger (in a poor hydraulic environment) and constant off switching when on part load (boiler cycling).
That is a nice wide modulation range, which is good. When you subtract the heat loss of the house from the lower figure it probably means that the boiler can run the rads from almost no nett input which is ideal.
That will probably just be the flow temperature cut off stat....
I was thinking more along the lines of the type that can signal the actual temperature to the boiler, rather than just a call for heat.
Ah, now that probably does present you with a control that will allow you to something useful, i.e. arranging a higher flow temperature when replenishing the store, and usually lower for the rads.
The efficiency loss with the PHE is only only one of recovery time since the boiler can modulate...
Blending valve added as it was suggested on the original thread that the temperature difference between the boiler flow and return should be around the 20 deg mark to allow optimum condensing. To be fair, when I asked DPS for a quote, they included a blending valve too on their spec. In fact they said it should be a 28mm version for boilers of >20KW as the internal parts on a 22mm were too small.
According to their spec, Reliance Water Controls (RWC) Heatguard see
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you load the Panex tool and go to the Designer then click on the green help bar to the right of the "No GX Primary" option, it brings up about the GX circuit. Last paragraph says about the mixers and if you click on "valve Sizing", gives you a graph.In fact if you click on any of the green bars and then click on the Next and Prev buttons at the top left corner, it gives a good explaination of the Pandora and GX systems.
Thinking about the whole argument of the rads off or not off the store, I guess new condensing boilers are designed largely to run rads direct from boiler so it wouldn't be wrong and should be efficient enough. However, the it is possible that more efficiency may or may not be obtained feeding from the store. I guess neither is wrong and looking at the big picture, there probably isn't much difference in efficiency.
Thanks I had not looked into their latest additions.
New boilers are primarily designed for the replacement market and to mate up with a system designed for 80 flow 70 return, temperature difference. More heat can be delivered with a higher flow/return temp' difference. So a condensing boiler may just do it at lower temperatures. The idea of burner modulation (more complexity) is also to get the best efficiency out of the system. Keston condensing boilers, up to about 5 years ago, were the most simple boilers on the market - of any type. No pcb, no modulation, Super simple and reliable. When these when connected to thermal stores/heat banks they were the ultimate.
One is better than the other and that is CH from the store, especially when zoning. There is no central wall room stat to screw up the heat distribution to the rooms, and heat can be injected to the rads from 0kW to the max they can take.
The problem when using TRVs all around is the auto by-pass, these really drop the efficiency when the house reaches temperature. ....and that is when they are set properly, which 90% plus are not. Also, they are responsible for many heat exchangers burning out as when not set properly or when they run out of setting with wear, as they may restrict flow through the heat exchanger. Best avoid that situation entirely if you can .....and you can!!!!!!
Having the boiler operate at the optimum efficiency when re-heating the store, you should really aim for too. And having the boiler only heat the store this can be achieved.
As you are implementing a heat bank it is best take the two CH zones off the store, and get the best system available. The cost is minimal for little outlay.
Therein is the rub. Will that small difference pay for the extra hardware required, and extra installation time taken to include the rads fed from the store (assuming the difference is even working in your favour)?
You also need to think about how you will include a boiler interlock (a building regs requirement) that stops the boiler firing once the house is to temperature. Monitoring the store temperature alone is unlikely to do this well enough.
Oh my God. The ramblings of an amateur. The difference is large. A modern low capacity water content boiler connected to a TRV rad system is a compromise. And it has serious setbacks too. Read what I write..it is much easier that way.
He has TRVs all around. They close down when the house is up to temperature. Then when the heat store is up to temp it switches out the boiler. The boier is not firing when the hosue is up top temp. Got it? I doubt it.
Would you care to define "large"? Given that we are talking about a boiler with a SEDBUK rating in excess of 90% here - a rating that is based on a model that includes seasonal adjustment, typical control and usage patterns in a domestic environment, and many other "real world" factors. The scope for "large" would seem to be only for very small values of "large"
(remember that that 100%+ efficiency values you think you can get do not actually happen with the physics we use in this world).
What, being used in the way it was designed to be operated?
Hmmm....
Actually reading what you write is never easy. You border on functional illiteracy much of the time, and much of the rest is parrot like repetition of other cruft.
Even with the large phase lag you introduced with the store huh?
A non TMV equipped rad and a programmable thermostat (per zone) will do a better job and make for more practical comfort.
Chav, they happen in the heating world. From Mikrofill:
"This ETHOS; is a high efficiency, condensing, combination Boiler. Flues are cooled below condensation point by a Spiranox heat exchanger made of stainless steel. This produces an additional heat which will contribute to the boiler efficiency, which is in excess of 107%. The European calculation method assumes 100% efficiency for appliances which do not condense and efficiencies higher than 100% for condensing appliances. "
Did you notice the "The European calculation method assumes 100% efficiency for appliances which do not condense and efficiencies higher than 100% for condensing appliances."?
This tells you that the method of calculation is flawed, and it will yield a nonsensical answer. If you deliberately under specify the energy content of the fuel when performing the calculation, but accurately measure the heat output, you may well get a calculated efficiency of over 100%. This does not mean that actual efficiency is over 100%, just you have demonstrated GIGO yet again.
Let me make this quite clear for you. No combi boiler, condensing or otherwise is going to violate the laws of conservation of energy.
I've not posted here before but have been following the discussion and would like some advice.
A comment by Dr Drivel in the summer got me thinking:
'This is where a thermal store comes in. Take all the zones from the water store and the boiler only heats the store with one long efficient burn.'
I'm renewing the boiler and propose to use a combi as a replacement. For HW I'm happy with the flow rate this will give. We use modest amounts of hot water don't need a big store in reserve.
The CH is another matter - it is where way most of the energy goes. I want to zone each room because of the number we don't use all the time and the variable use throughout the day: Guest rooms, second bathrooms, daytime office, first floor lounge only used in the evening and so on. Our use is pretty predictable so thermostat timers in the rooms and valves on a central flow and return tree going up the middle of the house will work fine I think
Now that could, of course, all be wired into the boiler as it is modulating and has an adjustable bypass valve. But I wondered if it might be better to have the boiler heating up a cylinder which could be placed in a cupboard in the heart of the house (It's a three storey terrace) where no boiler could ever go. Then use the cylinder as a heat store to feed the central heating.
Separpate pump required of course but I'm attracted by:
Boiler has a very simple job to do and can be carefully controlled. Nice clean water with no radiator bits going through the heat exchanger Pair of thermostats and a latching relay on they cylinder to widen the on/off temperature to stop the boiler topping up the store too quickly when the load is small Possibility to time the heating of the store in, say, the morning before a demand for DHW so that the CH continues to function when bath/ shower running. Possibility of electric immersion back-up for limited CH if boiler breaks down
Downsides (and this is where I hope folks will help me the most):
Might be needlessly complicated More expensive Maybe unfeasable or inefficient for reasons I haven't anticipated. For instance I imagine using a conventional rapid recovery copper cylinder of a suitable size with indirect connection to the boiler and the CH flowing through the (vented) cylinder. But I've a feeling that might be a little inefficient though necessary to get enough flow to the radiators. Or am I straying badly off piste here? I haven't complicated things further by considering the use of heat exchangers as yet but would welcome suggestions.
I look forward to hearing folks views. I want to get this right and good information is hard to find so please help as much as you can.
A snippet. Yes, a CH buffer is the best way. For each room have a Wilo Smart pump at £44 from Screwfix instead of zone valves. Simpler, more reliable and better flow. A whole bank of them neatly on the wall. Have a header off the cylinder of 28mm pipe and take all the pumps off this. Or if possible two headers, upstairs and downstairs.
A boiler can go inside the house not on an outside wall. Look at the Keston which can have 60 foot of cheap plastic waste pipe for the flue.
Frank, a bit late so I will get back to you tomorrow. You appear a bright man.
I want to end up with a system that is as low on wasted energy as is compatible with a high level of convenience and flexibility. (So no surprise there then.) Of course this has to be balanced by an increase capital outlay and time (my time so 'free' ha ha) for installing. I can swallow a bit of a capital hit as the present set up seems designed for maximum inefficiency. I hope to make good savings.
I'll try to describe what I plan as fully as possible to help you make further suggestions.
The house is a stone terraced mid Victorian thing on three floors in Edinburgh. There is a central stairwell going the full height in the middle. The foot-print isn't huge but I reckon ten zones: G/F
1) Stairwell - full height so thermostat placement will be in interesting one.
2) My office (I work from home),
3) Kitchen & main living area inc. D/S loo and utility room (I thought of putting the utility on a trv as it will need to be on all the time that Zone 3 is but not as warm).
8) Guest Room
9) Bathroom plus small second guest room on TRV
10) Wife's study
Every one of the is Zones is justified by need according to the criteria of 1) need to be on at different and nearly always predicable times during the day/week and/or 2) benefit form individual temperature control.
Of course all this assumes that he doors are kept closed and the inter- room insulation is reasonable. This is the case I think except possibly for Junior's bedroom door... (Nurse! the electrodes please.)
I plan to put the boiler on the second floor (in a cupboard off the small guest room/store) where it is well placed for flue exit and access. This location is directly above the first floor bathroom and almost adjacent to the second floor bathroom so good for HW delivery. The run from the boiler to the CH cylinder would also be fine from here with plenty of space for good insulation of the flow and return. the compact nature of the dwelling means that no zone is very far from the central nest of control valves or pumps as you suggest.
Okay a few specifics.
I'm thinking in favour of the Vaillant 937 boiler. As I'm sure you know this had the 15l heatstore in it and blends the outflow to produce rapid HW in at high pressure in good quanities. We don't use much HW so what we do use must be instant and plentiful. The extra cost of the heatstore thing in the Vaillant can be reduced by having smallish timed windows when it is got up to and kept at running temperatuire by the boiler. It is well insulated and blends even when it has cooled down a bit so if it is poised and ready to go twice a day for about an hour to coincide with morning ablutions and long-hot- soaks I think we should be fine. Experience will tell if this has to be altered much when we have guests. It's a 28kw boiler I think so not over large but quite big enough to run the CH via a heat store. My expectation is that the extra cost of keeping the heatstore hot will be almost irrelevant due to the low amount of HW used and the far greater expense of the CH. The 937 is about 1K trade so is not cheap for a modest sized combi. I think the benefits are worth the outlay. Once again other folks experience here would be appreciated.
The roof is well insulated with Tri-Iso and I intend having a generous CW storage tank. Whilst the CW to the shower mixer will have to be from the mains the CW to the baths, basins and loos can be from the tank. As I see it the advantages are: Warmer cold water so bigger bath for your money; more comfortable when washing hands etc; loo cystern won't drip condensate. Added to this if the tank is a reasonable size then it ca be set to refill quite slowly and thus reduce thepressure drop of incoming mains at a time when that might be most needed. If the tank refills slowly there should be no chance of a tedious whistling of the pipes.
I wonder in no particular order:
1) What type and size of cylinder I should use for the CH heat store and exactly how it should be configured. I'm not sure putting the return in at the base is best as quiet warm water would hit cold water and so total mixing rather that stratifying w
2) Whether to use the wilo smart pumps or valves for the zoning. Pump noise would drive me bonkers. Obviously if I use the valves there will be at least one pump. Certainly the valves are likely to break down and need replacing earlier but they are a bit cheaper. Wilos are supposed to be very quiet though... I'll probably need to try one and see. They could be carefully mounted and vibration insulated. Some of the zones are only be one radiator and mostly microbore. Whooshing we don't need. Will the lowest speed be low enough? The pumps will have valves either side for servicing so the flow cold be restricted but then that puts the pump under more strain. I'd be interested to know what people think about this.
Finally - For now - thre is an anomaly in the system. The Kitchen is about as far as it can get from the boiler. The Vaillant boasts about
15l per min flow. in 15mm pipe allowing a but for resistance I reckon on better than a meter per second. It's 18m to the kitchen. Do I want to wait 15-18s for HW? I think I might put a small Santon 10l mains pressure electric aquaflow under the sink. Bigger outlay but could be on a timer to warm once or twice a day and mains pressure HW would be there instantly in the small quantities needed without waking the boiler up. Amazing how much less HW we use at the sink once a dishwasher is dong it's thing. As an aside I tend to plumb DW and washing machine in with just a cold supply. The under sink Santon could easily be retrofitted if HW from the boiler was found to be unsatisfactory.
Okay. Thanks for reading. I look forward to Dr Drivel and other folk's comments and suggestions.
The first approach I would look at is a heat bank/thermal store heated by a Glow Worm HXi vented "heating" boiler, not a combi.
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24 kW version is £638.03 Including VAT at 17.5% Made by Vaillant. It is small in size. A set speed pump is needed to heat the heat bank cylinder.
This give a CH buffer and instant mains presure DHW. Look at:
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200 litre model.
As the cylidner is central in the house with rads above it, an F&E tank must go inthe loft.
Your zones.
You can have simple cheap timeclocks in bank in a central location, saving on clock/stats, so all the rooms can be set and switched on or off without running around the house. And have one master time clock to switch all of the system off, so the 10 timeclocks are slaves. to the master clock. Have TRVs on each rad then. No wall stats needed. The Wilo Smart pump will automatically run up and down speed depending on pressure. If all TRVs on one zone are closed, or near closed, it runs down. Most of the time the pump is at reduced speed saving power and reduced noise. If all are fully off the pump is off, well runs very slowly. They are quiet. They have three settings, probably setting 1 is fine for all but one zone. If one rom only need 0.25 kW of heat the Smart pump just gently injects it into the rad(s). Get good quality full bore rad valves, then no restriction.
Cost per zone using a Smart pump, TRV and simple time clock is about the same as a clock/stat and 2-port zone valve (only use "good" quality zone valves and they are not cheap).
Pump/zone headers:
Off the heat bank cylinder have a 28mm header pipe out of the flow tapping and tee off all zone pumps from this. A check valve after each pump. The same for the return, a 28mm return header with all return pipes teed into this. I would put a full bore 12/4 turn isolating valve here so the whole zone can be isolated and drained to avoid a full drain down.
Have a Magnaclean filter on the return to thye cylinder. Make sure enough inhibitor is in the system.
So you have:
- one heat bank cylinder giving DHW and CH buffer.
- one simple vented boiler
- centralised time control (you can have the odd one local in a room if neede be).
- No by-pass needed.
- small boiler. The 937 is the size of a washing machine.
- more reliable temperature control
- more reliable zoning using a pump.
- more reliable simple boiler.
- buffering of CH.
- no Boiler cycling.
- reduced size boiler as a thermal storage system only needs the boiler to be sized for avearge use, not peak use.
In the morning when CH come in, not all zones at the same time it appears, the rads are heated instantly as the water is dumped into the rads from the cylinder. The boiler comes in re-heats at full belt. The rads then do not require full heat from the cylinder and DHW can be served quite easily.
What sort of equipment do you have in here, other than you?
I would question whether you will ever reap any return on the cost and complexity of system required to support this number of zones. Remember that individual temperature control in a room can be achieved via its TRV.
Before going much further in this you need to do some detailed heat loss calculations for the building. Once these are done you can factor in the effect of leaving particular rooms unheated, and see how that changes the overall heat loss picture (and hence running costs).
I expect you will find that the difference between 10 zones and say three (e.g. "all day" spaces, evening spaces, sleeping spaces), will be negligible in terms of difference in running costs and day to day comfort.
Have you thought about what your hot water requirements are? i.e. showers, baths, one or two at a time?
Have you established if your mains supply is capable of meeting your hot water requirements on demand without any storage facility?
"Don't user much", and must be "plentiful" sound like contradictory requirements. Could you clarify?
That's the multi foil stuff?
Why mains to the shower mixer if you are planning to run gravity hot?
Not really... where does the heat come from that warms the cold water? You pay for it all in the end.
You need to do the heatloss calcs first to have any idea.
If you are going for HW from a thermal store then it would be simple to implement a secondary circulation loop for the sink. That would ensure instant hot water there.
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