DIY Heatbank - fine tuning of system (incl CH)

"basic" in the context of a modern boiler is a bit of a oxymoron. None are exactly simple, and even the simplest will have extensive electronics controlling its operation.

No, not at all. Why would you want the HW supplied any other way?

If have a vented primary circuit then you could heat it directly or indirectly. Personally I favour a sealed primary, and hence would opt for indirect heating of the store.

Or cut the complexity, go for a boiler with a decent modulation range, and let the boiler drive the rads directly.

(dribble prefers his one size fits all solution using the store for everything, as you can probably judge from the previous messages)

I think when you do the heatloss calcs your will find there is little to be gained by going beyond a handful of zones. If you leave a room unheated then you just increase losses from the rooms that surround it, and it ends up being heated indirectly anyway. You also would need to work out how to plumb it. With lots of zones controlled from a central location you are going to have masses of pipework, which aside from being expensive to purchase, will require lots of install time and lots of hacking about of the house.

If you really want lots of zones you may be better with a pair of largish primary "backbone" pipes providing flow and return points for each floor, and then teeing off them for the individual rooms / zones. The zones could be enabled by valves (or pumps if you prefer) locally - even if you take the control back to a central location.

If the store is well insulated it will make little difference. In the winter any heat it looses will pass beneficially into the house anyway.

OK, not huge then. I tend to find that a couple of PCs running 24/7 is usually enough extra heat to require very little input from the heating.

So is 20 lpm the best flow rate you can get?

If so this negates some of the advantages of having a thermal store arrangement for HW production since the supply would not be able to keep up with multiple simultaneous users of the water even if the store could.

You may find a combi with its HW output feeding the shower, and a fast recovery indirect cylinder on a zone on the heating side of the boiler would meet that requirement better. Fast flow rate for the bath from the cylinder, and high pressure for the shower from the mains, but without over stretching the mains supply. (you could throttle the cold tank replenishment rate if you have a largish tank)

If you can predict likely times for use, having a timer control on the loop ought to achieve that. (you just need to accept that you will need to run off some cold water and wait a bit should you use the tap at other times). Failing that, if you do use a combi, then perhaps it can supply the kitchen tap if not too far away.

Just take care not to insulate under them - you need a little heat loss to stop them freezing.

All the difference to what?

Can be done - there is another thread running in the group on that at the moment. It has also been discussed before.

Just got round to measuring flow rate and opening all cold taps at once and measuring total quantity of water in 1 minute, it looks like I have a flow rate of about 37L/min. Hopefully, that is pretty good. As to pressure, don't have a guage for this but believe it to be very strong. can't hold thumb over tap without water still spurting out quite forcefully. (Very scientific I know but seem to remember someone suggesting that once!)

Also checked existing pipework and as I currently have a combi, pipework to bath is in 15mm. Is it necessary to upgrade it 22mm? Would be bit of a pain if need to as bathroom all tiled etc. Would mean a long route of going downstairs then back up again.

The HXIs are simple enough and well made.

It is outside, but follow the thread and you can make one yourself . I gave instructions on how to do it. I will try to dig them out.

You can do. What is wrong with putting the whole DHW on the plate heat X?

About £70 from DPS I hear. Gledhill will supply them as standard replacement parts too, for around £80

No. If you have a house that needs 24 to 27 kW for CH a 200 litre cylinder will do CH and DHW. Find out the Kw requirements of the house (heat loss)

No, directly

Yep.

Install spreader pipes.

Keep the cylinder direct it is more efficient.

The two could be heated directly by the one boiler. Two pumps or one pumps and a 3-way "diverter valve. DHW has priority. When DHW calls its cylinder gets all the boilers heat. Then it drop back to heating the CH cylinder.

The more zones the more money - simple.

You could get a combi to match your DHW needs and then have a CH buffer heated by the boiler using a fast recovery coil.

Not startling at all.

You might want to consider an accumulator tank and a combi. The accumulator is simple to fit - a tee into the mains pipe, anywhere on the cold water mains. . Then high pressure and adequate flow and stored water backup if water is off from street.

A time clock and a pipe stat.

Just have an adequate combi or heat bank.

Gfx a thread is already on this:

Try just having a cylinder as a CH buffer heated by a combi via a fast recovery coil, or a plate heat exchanger and pump. The plate & pump and direct cylinder may work out cheaper than a fast recovery coil, and it operates far better too.

Have a combi suited to your DHW needs and fit an accumulator tank. Then no open tanks in the loft, except one F&E tank supplying the CH buffer cylinder. Look at: Replaceable Membrane Potable at:

If you need 100 litres of cold water storage, then get a 200 litres model. The membranes are replaceable. Pump up with car pump.

Please stop guessing. Best have direct all the way and elimate heat exchangers and improve efficiency.

Which is an expensive more complex boiler and non modulate down low enough and an auto by-pas has to be used reducing efficiency on part load. You need to understand buffering. Big in Germany. Fitting one combi does not make you a heating engineer.

....an amateur heating man speaks

Pumps under the floors? Shishhhhh. Best have all controls in one place. This pipe will just return back to the boiler raising the return temp lowering efficiency.

Er no..... Best have a cold water accumuator.

Yup, that is very good.

It does not take much static pressure to defeat the thumb over the end gambit ;-) 1.5 bar would do it.

At mains pressure that will probably be fine.

Until another taps is turned on.

As you have said yourself on many occasions, the efficiency of a plate heat exchange is very good. Sealed systems are generally preferable when they can be used.

More hand waving dribble? How much more complex?

Answer - very little difference. Different gas valve perhaps, but these rarely fail anyway. Still has much the same burner layout, electronic controls, ignition, forced induction, condensate collection and disposal etc. Price difference? hundred perhaps. Hardly figures in the grand scheme of things does it?

Posting ill thought through "solutions" on usenet does not make you one either. Neither does you inability to maintain any grip on capital cost of your projects.

Who suggested under the floor? You it seems. You are right though, daft idea.

With a boatload of pipe running to and from each zone...

Which pipe?

I think you will find flow and return pipes with rads strung across them is pretty much how most heating systems work (if you ignore old single pipe systems). Perhaps you should read up on the background a little.

Ah right, and how much does that cost?

Note also if you go back to the OPs requirements: "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."

Its funny how you flipflop between "a combi is ideal because there is no room for tanks in small British houses", to "Oh just slap in a 300L accumulator alongside the heatbank" depending on which way it suits your argument.

(not suggesting an accumulator is a bad idea in general - it has a place in some installations. Just entertained how your solutions run on and on sucking in ever more hardware to get yourself out of corners you have designed yourself into, with no concept of capital cost)

But not better than direct which eliminated them completely.

Are they? New on me. Since when?

A lot. Look at a Glow Worm HXi inside. Not much there at all.

Says the amateur.

A top quality boiler that modulates low, none go low enough, with decent control is north of £1K more like £1.5k

I am one. That is obvious as you learnt a lot from me :-)

How many projects have you undertaken? Mmmm...none!! Apart form fitting your own combi.

Local control from loop pipe means local equipment in odd places, usually under the floor.

....and ease of fitting, maintenace and setting up. The pipe to rads can be microbore. The heat bank/buffer is in a central location. The OP stated that.

This loop you are on about. What other pipe were you on about?

You were advocating a loop, which is a glorified header around the house giving off heat where not needed.

His house is big. He explained that. The accumulator can go in a garage, loft, garage loft (where I have put them) or just about anywhere. He has the choice of open cold tanks or an accumulator which will give superb mains cold water flow and pressure, eliminating pumps

If he had no space then a high flow combi and a new mains pipe to the street is the way.

They change to what the OP responds as he releases more info. I can't mind read. If I was him I would make up a DHW/CH buffer heat bank and fit an accumulator. First I would see what the cost and difficulties are to get the mains pipe upgraded. Even if it costs £500 then I would have a new mains pipe and drop the accumulator. The accumulator is a get out of jail solution to poor mains pressure problems, although a brilliant one. It stores cold water, gives it at high flow and pressure eliminating pumps, enables the use of mixer taps all around with aerated heads to use less water, no pump noise, electricity used, etc.

Hi Folks Frank here again.

Just to say thanks again for all the input.

I have been through the whole thread now and found DD's description of how to convert a cylinder from August 2007.

Also a couple of useful schematics.

Just getting my head round the responses overnight and today.

I'll try to come back with some thought out final system options that suit my pocket/ability/temperament and some sensible points for clarification later on.

I think this house is pretty leaky/poor u values. there is more to do in the draught exclusion dept. The IDHEE calculator said I needed a

Is there a good heat loss calculator for rooms I could use? It has been mentioned several times. How should I apply the info?

More later.

Thanks again.

Frank Front

A bit more...

If 25lpm @ 2.0bar 25lpm @ 1.5bar might be a problem as you seem to suggest (measured at top of house) would it help to replace the 15mm from the stop c*ck at ground level with 22mm pipe? I think the lead inside diameter is more than 15mm but less than

(Doing my best to give you all the relevant info without writing a book.)

Frank

That was the point I was making to dribble about modulating boilers. The fact that the boiler can't modulate from 0kW to full output is generally neither here nor there since the house will still have some heat losses. Even a reasonably well insulated place is going to leak a few kW - so a boiler that modulated from say 6kW will be able to run giving a nett contribution of only a couple of kW upwards. This will allow efficient running with relatively little cycling even without the thermal store.

One thing a store does very well, is allow very high flow rates of hot water at mains pressure - but this is something you have said you are not that fussed about. They were also very good in the days when boilers only ran at high fixed outputs - acting as a buffer allowing the boiler to do longish burns heating the store, while in turn it fed heat to the house at a slower rate. While this is still the case, a modulating boiler can make a pretty good stab at doing this all by itself these days. So, IMO, the advantages are far less significant. The 90%+ SEDBUK ratings on modern boilers assume typical setups and controls, so even if you can improve on the efficiency and squeeze few % more out of the system, you need to assess if the extra hardware and install costs of the store are going to give worthwhile returns. There is a fair chance that in financial terms alone they never will unless you have huge gas bills. So will you get improvements in comfort or functionality to make the cost worthwhile?

If you genuinely are leaking 20+ kW then you need to spend money on insulation and draft proofing as a matter of urgency! Having said that many of these heat loss calculators tend to overestimate. You can probably get a much better feel for the actual numbers if you just do it with a spreadsheet.

(I have an example sheet if you want a copy - but see the end of this email for a worked example).

I found on my place (5 bed semi, three storey, 9" solid wall + render, dg all round, and top storey insulated to modern standards) that worst cases losses (i.e. -3 degrees C outside) were about 8.6kW. With the outside temp at a more typical 10 degrees, that falls to 3.5kW.

There is a Myson one that is not bad - used to be available on their web site but IIRC is not currently. Andy Hall may be able to lob you a copy if you email him. Failing that, a spreadsheet, some u-values, surface areas, and air change estimates will mean you can DIY.

Heat loss for a room:

you need to compute the area (in m^2) of each of the main surfaces. You need to know the target temperature for your rooms, make a gustimate at the likely air changes per hour, and know something of the construction of the walls etc.

Typical room parameters

Room type Room temp Air Changes Lounge 21 1 Dining Room 21 2 Bedroom 18 0.5 Hall and Landing16 1.5 Bathroom 22 2 Kitchen 18 2

Material parameters:

Materials u-Value Wall - outer 9" solid brick 2.2 Wall - internal plaster over 4" block 1.2 Wall - internal PB over stud 1.8 Floor (ground) - solid concrete 0.8 Floor - PB + joist + FB flow up 1.9 Floor - PB + joist + FB flow down 1.5 Roof pitched with felt + 100* insulation 0.3 Window - wood DG 2.9 Window - wood - low E 1.7 Door single glaze 3 Wall Insulated 0.6

• insulation assumed to be high performance foiled PIR foam

Example room:

Room Surface Area Tdelta u-value Loss AirC Vol

Lounge Front Wall 4.40 24 2.2 232 1.00 31 Window 4.80 24 2.9 334 Party Wall 8.40 0 2.2 0 Hall Wall 8.40 5 1.2 50 Rear Wall 6.90 0 1.2 0 Floor 13.45 24 1.9 613 Ceiling 13.45 3 1.9 77 Total 1307 267 1574

So in this example you can see there is 4.4m^2 of outside wall (and

You compute room volume (31m^3 in this case, the floor area x the room height). That is 0.36 x TDelta x Num air changes per hour x volume. (the

Add the two together and you get a total for this room of a tad under

Thank you very much for that John.

I think losses can't be as bad as the calculation I gave you and I've a feeling that included hot water needs. If that makes a difference.

The radiators in the rooms aren't huge and they do okay without the existing very ancient Potterton kingfisher ll being cranked up to more than just over half on the temperature knob. It seems to be about

In the rooms where the chimney losses are controlled and the shutters get closed things are fine. However when the rads go off on a particularly cold evening it becomes apparent pretty quickly.

On a slightly different tack I would be very interested in what the inefficiencies/short-comings you and DD reckon would result from the following (as it would help me to compare better with the outcome of the heat bank method).

So considering CH only now:

Using a boiler for the CH complete the usual frills - weather sensor, modulation, user adjustable bypass valve. What exactly are the efficiency short-comings going to be if I zone that output (I've manged to crunch down from ten zones to seven) using simple room stats linked to centrally placed timers and conveniently located valves?

It would be very easy in my set up to pop a simple thermostat into every zone with out any making good necessary.

In the bumf for most boilers it seems to assume one is going to just fit TRV's to all the radiators and have a thermostat in the kitchen by way of interlock block. This would be wasteful and inconvenient for the way we use our house. (Though I do take your point about a cool room sinking heat from a warm one.)

With the set-up I've outlined above I am not sure how to create the interlock block. A 'master' stat might spoil it for some other part of the house if it switches off. I imagine a secondary circuit linking all the room stats in parallel would be needed so that when none of them are calling for water the boiler stops. Is that right?

Incidentally taking our lounge for an example the floor area is about

Thanks again to you and DD for your time and insights. I look forward to your responses to the above.

Frank.

They probably do... whether you need to depends on the type of water system you have and your usage:

Traditionally they would add on say 5kW for HW and assume use of a mid position valve that would allow the HW to be heated at the same time as the rads. The cylinder coil would have been limited to approx 5kW transfer anyway (which would give slow recovery times), so it made sense to add the HW load to the heating one and run them together.

With a storage system that has fast recovery, it may well be able to take all (or a sizeable part) of the boilers output, hence the configuration that assigns priority to the water heating. Get the HW reheated quick and then switch back to the CH after.

With a combi, then you can ignore the CH side altogether in most cases and just size it for the HW requirements. Again it assigns priority to the HW in that it can only heat one at a time.

If you have any marginally sized rads, then now would be a good time to change them. Allowing for use of lower flow temps is also a good idea. In many cases swapping single panel to double or ones without fins to finned ones can let you do this with relatively little upheaval.

Which sounds like you have quite high rates of air change in these rooms. Sometimes just fixing drafts from windows etc can make a difference even if you leave a chimney open since it prevents a through draft.

I would be surprised if you could not loose a few more zones by lumping together some rooms that have roughly similar usage even if not identical.

You may want to consider using a prog stat in place of a conventional one and timer. Not only do they tend to be more accurate stats than the bog standard mechanical ones, they allow much better control of temperature to suit your usage.

Yup, if you choose the room in the zone to be the one that is hardest to heat, and stick TMVs on the other rads in the zone.

Well you can do similar - but with a stat per zone etc.

If you have a stat for every zone then that achieves the goal. Once the house is to temperature, there will be no call for heat from any of the stats.

They can in effect be wired in parallel to generate a call for heat. When they are all satisfied there will be no call. (you may choose to implement this using the switches on the zone valves rather than the signal directly from the stat. A neon can also then wired up for each valve to give you a handy "valve failed" indication by lighting up when volts are applied to one side of its switch from the stat, but the switch remains open)

Efficiency shortgains are that by-pass opens on part load to create a direct shortcut to the boiler raising the return temp far too high. That is if it is set properly, which most are not, and even then they can run out of setting in time. They can also restrict flow through the boiler too, causing heat exchanger damage. When heating a thermal store cylinder directly there is always full flow through the boiler. The boiler is operating in an ideal hydraulic environment, which means it will last longer and be more efficient.

But no central control.

Best have TRVs all around and no stat to cut out when some rooms require heat.

Oh my God, Chav, you really haven't a clue. Most boiler don't go below 8Kw when up to temp the house will be calling for less than 8kW and then inefficient boiler cycling occurs with the by-pass valve opening and then efficiency drops like a stone.

A heat bank/thermals store can trickle kWs into a heating system and no impair boiler performance, efficiency and longevity either.

Cha, you are getting it.

They are still very, very good, nothing has changed.

A poor stab at it I'm afraid. Modern boilers are designed for the replacement boioer market, where rads were designed to run at 82C, hence modulation which is not that effective a sthe boiler makers tells us. Then TRVs on all rads makes matters worse for the boioetr. When having TRVs all around best have them fed froma buffer cylinder (thermal store)

A boiler can be running at over 100% if set up properly heating a store.

Chav, you just made that up.

Most certainly!

Heat Loss:

If a boiler is correctly sized for the heat loss at say -3C outside, when -3 it should run flat out continuously. Few do as most are oversized, then boiler cycling occurs.

A great thing about a thermal store is that doesn't care how large the boiler is, as long as the flow and return pipes are sized correctly. If a house requires say 15kW and a 30kW boiler is coupled to the store cylinder, it will just heat up faster and still no cycling. A boiler twice the size of CH requirements directly heating rads will cycle like hell.

Also having the CH and DHW off a thermal store 100% electric backup is available to CH & DHW, and also a second cheap backup boiler can be coupled directly to the store too. So, a cheapie B&Q job boiler can act as a backup. It will last as it will only be used once in a blue moon - so full cheap to run on gas, 100% backup. Or have both boilers on and zippo re-heat. Great when there is multiple showers and baths going on.

John thanks for that. All grist to the mill. I'm hoping we'll hear some more from Dr Drivel soon. In the mean time I take your point about prog stats however my thinking was to keep the cost of zoning down by using basic analogue stats which are cheap and have bimetallic strips so (I imagine) have a wider hysteresis that digital so would reduce activity at the valves. If I used centrally placed timers for the zones - as DD pointed out less running around - they could be basic two channel timers normally used for CH and HW but on this occasion two zones. The CH channel will likely have a 'boost' facility which could be given to the most deserving of the two zones controlled. This is the cheapest way of zoning I could think of.

As you say TRVs on the secondary radiators on any given zone.

I like the idea of the neons for the valves. Nothing like a steady red light for comfort.

Hope to hear more from Dr Drivel soon as you both seen to have different and very informative views on the same things.

More thought required by me on the best overall approach and specifically which way to jump on the HW provision - combi or HB...

Regards,

Frank.

Not often you read that in this group ;-)

Horstman prog stats are only about £24 in screwfix.

at the expense of bigger swings in temperature - the prog ones do make a noticeable difference to comfort.

It looses the ability to have the temperature of the zone vary over the day though - this is one of the big wins with a prog stat. In a bedroom for example to have it warmer as you wake and go to bed, but then setback overnight and during the day etc.

Would be easiest to wire so that they only come on when a valve has a demand, that has not been satisfied... but yes in general a cheap LED or neon can make a massive difference to the ability to diagnose problems quickly.

Dribble seems to make it a matter of principle to adopt a contrary view on everything. ;-)

The choice is yours... ;-)

You tend to get this:

You absolute God. The Coral Si is perfect, though they may even be able to do better, because for a small cost. used for CH and HW but on this occasion two zones. The CH channel

He could just have the timer switch on the bedrooms evening and morning. Simple.

Chav, I am a pro not an amateur. I look at thing logically, not what I have fitted in my own house - which in your case is one combi.