Try installing a full bore maintap. That usually increase the flowrate. Cheap and simple to do. If that make not much difference in flow, then fit a cold water accumulator. A cylinder that stores cold water at main pressure. But it allows high flows. It can supply all the house - DHW and cold. Or you can have it on the DHW and maybe the cold of showers and bath, the rest direct from the mains - does a washing machine need flow? This then means a smaller cheaper unit. You will have lots of flow and pressure of 2.5 bar.
You were not proving me wrong. I know one could do it using an expensive controller, which was not integrated. I am on about off-the-shelf integrated no frills or extras boilers. The Avantaplus and the Keston are integrated. The MAN boilers are dual-temperature and a few other expensive offerings as well. I never mentioned them as they way over the top in price.
You presumably need a flow switch on the DHW feed or cold inline to the HW HE to switch its pump...
I also wonder whether that fulfils the requirement for a CH boiler interlock? Since the pumps will always be trying to bleed heat into the rads even when the house is up to temperature, leaving the boiler cycling on the cylinder stat or its internal one.
What storage capacity cylinder would you propose?
How would one adjust the house temperature throughout the day without adjusting the TRVs?
The drawing is one using a pressurised heat bank (external pressure vessel not shown), pressurised to 1 bar. Heating heat bank directly. The external vessel and the boilers vessel combine. Best make sure only the external vessel can cope.
Using a vented heat bank & system boiler: A 100kW plate heat exchanger is needed which has the flow & returns of the boiler into it. On the other side of the plate the flow and returns leave and a pump directly after the plate.
Using a vented heat bank and vented heating boiler it is the same as 1 above except an external boiler pump is needed.
Yep, and blending valve on the DHW after the plate.
The top DHW section is switched out via a cyl' stat - or two if an anti-cycle function is needed.
The bottom CH section is switched out by the modulating boiler when the weather controlled boiler setpoint is reached. If it is asking for 55C, and the whole bottom section is 55C the burner is off. The mass of water in the heat bank prevents any cycling. When a CH pump bleeds off heat and the bottom section falls below say 55C, that is when the boiler brings in the burner.
A further interlock can be done by, having a flow switch in the return pipe of the CH zones into the cylinder near the Magnaclean filter. Wire this into the not used room stat circuit. When no flow all TRVs are closed and the building is up the temp, and the boiler and boiler pump is then off 100%, But the stored water may cool off too much and the boiler's weather compensation would not be maintaining the CH section's temperature. When the TRVs open and there is flow the boiler comes in and then heats the water to the dictates of the weather compensator. The boiler may have to do some catch up.
I would not bother with the flow switch interlock and see how it goes without - the mass of water prevents any quick changing of water temp preventing boiler cycling. have full bore valve on the CH return pipe and if you want to fit a flow switch in then isolate and a quick job to fit. I would also have another vale on the other side of the Maganaclean, as it is easier to isolate and clean using full-bore valves rather than the kludgy valves they provide.
CH section: The rad capacity plus about 25%. 100 litres in the rads, the bottom section is 125 litres, going over is not a big thing. This means a full dump of heat into the rads is done on switch on in the morning. The DHW section? Depends on usage. A one bath two shower house? Around 175 litres, giving a 300 litre heat bank.
You do not adjust the TRVs, they move up and down to the room temperature. Each one adjusts itself to the room it is in.
The range:
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setups:
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Option 5, page 9. System boiler (integrated pump) This is the wiring using a 3-way valve, cyl' stat, outside sensor. Using a heat bank the
3-way valve diverts to the top or bottom sections of the heat bank, not to the cylinder and rads as in the diagram.
AVANTA 12v/18v/24v System Only Option 5, page 29. Simple weather compensated Heating with 230v room thermostat override and Priority DHW. Similar to above using a vented heating boiler which does not have an integral pump.
If going vented heat bank, then I would use the heating only boiler, the
12v/18v/24v. The bigger the boiler the quicker the reheat.
Fair enough - I had assumed it was vented with a vented primary.
Why use a 100kW HE there, when the boiler output is only a fraction of that. You can et plate HEs that will still work at a couple of degrees differential with lower power handling. They would also be significantly cheaper.
That would make for quite a cylinder in our case since I expect the primary heating circuit is about 200L (20 rads)
You miss my point... Many people don't want the house to be a constant temperature all day. For example I want different temperatures at different times of day. Say warm in the morning for getting up, cooler during the more active part of the day (at least in the sleeping zones), then warmer in the evening, and finally set back to 15 degrees or so overnight. Easy to do with a prog stat. Can't see how you would do it here. You also need to cope with women - who seem to have a habit of needing to tweak the temperature up or down on a whim.
Not just women. But I suspect it's because they have a rather better idea of whether they are at a comfortable temperature than a bit of bi-metal out in the hall.
Seriously though, adequate control of each room is not simple. TRVs are fine in principle but can't be programmed as you say, and also in most systems they are over-ridden by a wall-stat somewhere, so in effect the TRVs just become maximum temperature limiters, the room can't get any hotter than what they are set to, so it follows that if the hall stat cuts out then at least some rooms are too cool (usually the one you are in!). Then the hall stat just gets used as an on-off switch for the heating.
I think you'll need all electronic radiator control to fix this, and there are some fairly expensive wireless TRVs around now that might form the basis of this. In theory you could have a central programmer to control all the rooms individually temperature-time wise, and that could also look after turning off the pump/boiler when there is no demand. I don't think there such a system available off the shelf.
Everything sealed and unvented? Doesn't that preclude a DIY heat bank, and also prevent using a low pressure rectangular thermal store to maximise stored volume, or am I missing something?
I'm also in need of scrapping my cast iron block of a boiler and doing something a bit more techy, so swotting up on this sort of scheme too.
Indeed, and also what temperature is comfortable depends on what you are doing. Doing housework etc (DIY even!) suggests a different target temperature from sitting down watching TV.
There is always a good argument for careful system balancing. Having said that you probably want the main stat to be one of the last rooms satisfied. That comes down to balancing and also sighting of the stat.
With the heating system that came with my first house it had a fairly crude fixed rate boiler with bimetal stat and the temperature swing was noticeable - especially on windy days. Something like dribble's heat bank would have worked well there to even out the swing and make for a more comfortable equilibrium. I found however that when I replaced it with a modern modulating boiler, and a electronic prog stat, that transformed it. Even without any external temperature sensor it did a very good job of regulating the house temperature to much closer limits than before.
No, I think if you want that level of control then you would need "roll your own".
It would be quite an interesting exercise to stick a multi data capture / relay card on the end of a tiny PC and actually close all the loops in software. You could start with traditional controls and just instrument the system with sensors etc and learn how it actually performs.
I would use a heating only vented boiler (Avantaplus 18v or 24v) and a vented heat bank. From what I know, see no advantage in a sealed system boiler or a sealed rad circuit in this case.
a sealed heat bank with a Avantaplus (pump external and extra) vented boiler and a sealed system boiler. Both can be pressurised.
a vented heat bank and a vented boiler.
The bigger the plate, the more heat is transferred across the plate until saturation point. Using a 150kW DHW plate mean that a lower store temp can be achieved. Having a 80-100kW plate on a boiler means the boiler will not return back to itself water that is too hot reducing condensing efficiency.
Rads do not hold as much water as they did as they are high efficient low water content these days. I doubt more than 150 litres in the rads, probably a lot less. I managed well with a 140 litre DHW only heat bank with one bath and two showers. The boiler added to the heat in the store pumping right into the top which then was pumped into the DHW plate heat ex. The bigger the boiler the better to reduce DHW storage water content as you combine the outputs of both.
I assume you want a period of the day, when the house is unoccupied or partially unoccupied, and the temperature reduced. Easy. Have stat/programmer switching each Smart pump on each CH zone. Also have TRVs on "all" rads. Have the stat/programmer in a "representative" room in the zone. The room TRVs will be set to approx 21-22C by trial and error. Set the programmer as a "high limit" say 24-25C - the TRVs control each room and the programmer stays out. In the unoccupied time set it say to 18 or 19C, the programmer takes control. This period is not critical for exact temperature as people will not be there for long periods, or whatever.
Then a stat programmer in each CH zone and a master timer for the lot. The master timer can switch in the store to preheat the CH and switch out all CH zones.
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