designing a central heating and hotwater system

hi,

Any recommendations for sources of information on designing a central heating/hotwater system for please.

have found sites that provide info on rating the boiler/rads but nothing on the actual design. type of heat storage etc.

duncan

Reply to
duncan
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cheers Andy

i'll go have a look at that one.

I'm more than happy with the installation side soldering etc. just need the detail to get things right with for upto date specs etc.

duncan

Reply to
duncan

What do you intend to do? As you are a DIYer go the combi route. Buy a high flowrate combi. Not all combi's give a trickle for hot water. They are easy to install with minium design in CH pipework and rad sizing. You connect up 5 pipes, run a power supply and a wire for a thermostat or thermostat/clock from the combi. Superb for high pressure showers. A doddle.

Don't go for complicated cylinders, tanks, motorised valves, control systems, etc when there is no need to. The rad sizing can be done by using one of the many on-line rad calulators. No need to size a combi boiler as it will do 80-90% of most UK homes the CH output is so high. Any further points ask me.

Reply to
IMM

How is recommending the best rote for a DIYer a put down. This is uk.d-i-y.

A one box solution that professional experts have incorporated all the design and components is by far the best option.

That's why I said get back to me.

They give a good ballpark figure.

Reply to
IMM

I would disagree about the "ball park figure" being adequate to start with, the odds are you will end up with a boiler and radiators which are too small. Bigger IMO works best for heating systems, this applies to boiler and radiators. Of more importance, where are the 10 year maintenance and running costs factored in on a combi system without soft water. How do these costs compare with a traditional conventional vented boiler, even allowing for a tank replacement every 10 years? Thinking about it, are there any boilers of any type with a 10 year warranty even with soft water? In the past, my boiler life achievements were in excess of 20 years, have these days gone forever?

Regards Capitol

snip

Reply to
Capitol

Ballpark is fine. There are a few on-line calculators. It is best to use a few. Ad 5 to 10 % extra if you like.

The smallest of comi's will do the CH on a "very" large house. The boiler sizing is not a problem if it is not a big house.

Always have a de-scaler on a combi, or on "any" system in hard water.

Firstly, a combi is a system boiler with a water section. Many share the same components. Secondly, a combi has most of the "system" in one box. Only the rads and a wall stat are ouside the box. So when you start comparing breakdowns and longevity compare like with like. On a cylinder/tank set up include any problems with the F&E tank, the cold water storage tanks, the cylinder, the 3-way zone valve, the cylinder stat, the programmer, all the associated pipework, etc. Then you will find that a combi is no less reliable, and get a good make of combi, probably far more reliable overall.

Got it? :)

I had a Potterton Neatheat for over 20 years. The boiler was very reliable in itself because there was not much in it. In that time I went through 3 pumps, a zone valve, a zone valve motor, a cylinder, cylinder stat, room stat and a programmer. On the boiler a relay, flue fan and a pressure differential switch. Overall the "system" was not that reliable. I am certain a good Vaillant would have given far less trouble over 20 years.

Reply to
IMM

"IMM" wrote | > >Don't go for complicated cylinders, tanks, motorised valves, | > >control systems, etc when there is no need to. | > Come on. It's not that difficult. | A one box solution that professional experts have incorporated | all the design and components is by far the best option.

Microsoft

Owain

Reply to
Owain

Because you are suggesting that a single box combi solution is the most appropriate for a DIYer on the basis that it is apparently simple.

The reality, of course is that there are a whole load of issues such as incoming water mains pressure and flow, appropriate sizing of pipework, flow restrictors and a whole raft of other issues to deal with to make it work properly.

You don't know what the usage requirements are so how can you be so sure that this is the right solution. Why not a thermal store, or have you gone off those this week?

You know full well that there is more to it than that.

I have seen U values in at least one that are out by a factor of 3:1 on a material that mattered. This led to a 2:1 discrepancy with calculating by hand using the Building Regs numbers. The latter was correct.

That is not to say that the programs arenot useful, but just using them blindly without understanding the maths that they are doing is a recipe for problems.

On an investment of this size in money and time, it makes more sense to sit down for a couple of hours with a piece of paper and a calculator and to check properly.

.andy

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Reply to
Andy Hall

You are getting there. It is simple. And..will most likely fit the bill.

That is why I said get back to me.

That is why I said get back to me.

Not much more. So no need to complicate matters and best buy the ideal, simple, one-box, off-the-shelf solution. Clever people these boiler engineers.

Reply to
IMM

But doesn't answer the question which was asked, which was how to go about designing the complete system.

That certainly is not a case of trotting along to B&Q, buying a combi boiler, a few radiators and plumbing bits and sticking it all together and hoping.

Radiator and pipework sizing need to be done properly whichever solution is chosen.

For a combi boiler of sensible capacity to be useful, it is often necessary to upgrade the gas supply from the meter - this may be non trivial. The water main may need to be upgraded, also non-trivial. If there is existing internal pipework for hot and cold water, it is likely to need modification and re-routing in order for the relative flows to work reasonably well. Flow restrictors may need to be fitted, etc. etc.

A conventional boiler and system may be more suitable since it is likely that none of the above issues will need to be addressed. If somebody is capable of working out radiator, boiler and pipe sizing correctly and of doing the required plumbing work properly (which would need to be done whatever the system) then fitting of a pump, motorised valves and cylinder and tank are not a stretch of ability or intellect. It is also a more scalable solution in terms of meeting a range of requirements.

Clever enough not to assume that one size and one technology fits all.

.andy

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Reply to
Andy Hall

It does answer the Q. Most of the design is inside the box, done by experts. The only design is the rad sizing and the pipe run. Not difficult.

Not hoping. It is not far off what you say. Just a combi with the correct flowrate and size the rads and buy them.

That is why I said get back to me.

One pipe run is trivial, when looking at the whole system.

It may not need an upgrade.

It may only require a small modification. Flow restrictors on all taps are easy and cheap to fit.

Maybe, but unlikely.

Reply to
IMM

Hey guys

What a response.

Its funny that not matter how you pose a question on here about heating/hotwater it always ends with combis in the red corner and conventional systems in the green corner, fighting it out. LOL

I feel that I'm a well confident DIYer having now nearly completed the whole house extension myself. Wouldn't choose a combi for its convenience unless it fits the bill.

Andy - I've sent away for that book so will take a few evenings reading that.

With combis its even more important to get the piping sizes correct and design right to prevent hot water not feeding enough sources (kitchen, shower etc.)

It is still bothering me that having two showers in use in the morning is still gonna be a problem with a combi. Plus the missus likes a bath and not sure that she has the patients to wait for it.

Thermal stores - any suggestions on them please.

What sort of cylinder should I go for if i go down the convential route?

duncan well at least i'll have all weekend to read the response lol

Reply to
duncan

Sorry I don't buy that. From the high level functional point of view, the combi is simply bringing into the box the pump and an alternative means of providing the hot water. Granted, it does reduce the component count vs. a cylinder system.

However, from a *design* perspective, there is little or nothing involved in provisioning a vented cylinder, motorised valve(s) and pump. One is going to choose a suitably sized cylinder for the application, hopefully of a fast recovery type. The only design decision there is to try to make sure that the boiler is adequately sized to provide enough heat to recover the cylinder in a sensible time. This will imply a certain flow rate and pipe size for the primary connections to the cylinder - normally 22mm.

Motorised valves are completely standard, so no design decision there.

If the boiler is not a system one and does not have an internal pump then in a proper design, one would normally work out the required flow and head in order to select the right pump type and setting. However, with electronically controlled pumps such as the Grundfos Alpha this is largely taken care of anyway.

No it isn't, but that is where most of the *design* work is - not in the boiler.

... and checking the provisioning of services, adequacy of plumbing and so on.

That depends on where it has to run

Agreed. I am simply pointing out that it may do and that can be difficult and expensive, which in turn may be a decision factor in what to do. It is better to point this out up front so that it can be checked, rather than glossing over and potentially having a nasty surprise.

Fine, but it should all be taken into account.

We have no data to say one way or the other.

.andy

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Reply to
Andy Hall

After I had hopes for you too, and you say that.

You are getting there. Or are you? It vastly reduces the design aspect too.

There is, especially for a novice.

It is easy enough, and about the only complex part in fitting a combi.

It is not a Middle East oil pipeline.

Reply to
IMM

More old wives tales! Some combis have pre-hearted heat exchangers and some with small pre-heated hot water vessels to give pronto hot water at taps.

Are you on about cylinders?

Reply to
IMM

A waist of time for a DIYer doing a one-off.

The hot and cold water pipes must be sized right, but that is ballpark

More old wives tales again. There are high flow combi's around that will do two showers and fill a bath pronto.

Go Heat bank not a thermal store. There is a difference

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"Integrated" heat banks are available that are pretty idiot proof. They come complete with all controls, pumps, etc. You mount your boiler, connect up the boiler flow and return pipes to the heat bank, connect up the flow and return of the rad circuit from the heat bank, supply power to the heat bank control box, run a wire to the room stat, run a wire to the boiler and connect up the cold mains and hot water draw-off pipes. Simple, and a state of the art solution.

More expensive, but as you are doing it yourself a hell of a lot cheaper than getting a professional in.

Reply to
IMM

It will give you a good appreciation of the steps in radiator and pipe sizing, radiator derating and so on plus the issues with pump selection and setting, organisation of pipes to avoid pumping over problems etc.

You can then get a lot of information from manufacturer's web sites.

It does mean that care needs to go into the sizing and branching off of pipes so that there is reasonably good balance of flow naturally. Then there are techniques with flow restrictors, blending valves etc. if you need to go further.

This is the big advantage of a cylinder. You can make it adequately sized to be sure that you will always have a plentiful supply, regardless of the draw rate.

For example, I have a cylinder with multiple tappings on the top which will take 22mm pipework. It is fed from the roof tank in 28mm pipe. The effect is that I can run two baths at full tilt or a bath and a shower or two showers at 25 litres/minute each.

You can go for very large combi boilers and get a flow rate of up to about 20 litres per minute with a 35 degree temperature rise. For a lot of the year when the mains water is warmish - say 15 degrees and above, you will be able to mix the heated water with quite a lot of cold - e.g. in a shower mixer.

However, if you are concerned about the worst case, that would be in the winter when the water supply can be well below 10. If you consider that the user temperature in a shower is around 40 degrees, you can see that almost all of the boiler hot water will be needed and little opportunity to add cold. Therefore you end up with 20 litres per minute between two showers - i.e. 10 each. Then it becomes a matter of opinion as to what you find acceptable. Personally I feel that 15 litres/min in a power shower with adjustment between hard jets and drench mode is about the minimum - others say less or more. If you already have a shower in place, try measuring the flow rate with a bucket and stop watch to get a feel of what you are getting.

The well known site on these is DPS.

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although the cylinder manufacturers are making them as well.

The main advantages that you can get out of one of these are that

- the primary circuit can remain vented so that the bulk water in the cylinder is not pressurised. Sealed cylinder pressurised systems require a BBA or IoP approved installer to fit them

- The cylinder can store water at higher temperatures than if it is used for hot water. It can be at 80 degrees rather than 60, so a third more energy is stored in the same space. The mains cold water is fed through a plate heat exchanger external to the unit and then the primary water from the tank is pumped through the exchanger when there is demand to heat the water. This type of exchanger is highly effective on heat transfer and so if the water supply is up to it, much greater flow rates than with a combi can be achieved.

As the store is being used, the boiler will be adding heat back in, although typically at a lower rate than you are using it. To give a simple example, you might be drawing hot water at a rate such that 60kW is required to heat it to the extent required. If the boiler is able to deliver 30kW into the cylinder, then the net rate of use is 30kW. Therefore the amount of hot water that you can get at the 60kW rate is twice as much if the boiler is adding heat in, using this example. Once the stored energy runs out, the flow rate would have to be halved to maintain the same temperature rise. Make sense?

The same additive effect occurs in a conventional cylinder of course - the difference being that the amount of energy stored is 25% less.

If you are going the condensing boiler route, it won't be as efficient with a thermal store as it can be with a conventional cylinder because the operating temperature is higher. It's also better to run the radiators separately from the primary circuit than from the store.

A fast recovery type. Vendors of these include Albion and Telford among others. These have various arrangements to increase the surface area of the coil - e.g. more turns, multiple pipes, etc. The point is to increase the transfer rate of heat so that the water is heated more rapidly, and if you have hot water priority arrangement that the boiler is not taken from heating the house for too long.

There should be plenty of those. Thrills and spills for all the family :-)

.andy

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Reply to
Andy Hall

Please explain precisely how it reduces the *design* NOT the implementation aspects.

This is a put down.

Please explain what is difficult about these aspects.

Do you have some exact design rules? Please quote an example and give the basis of calculation such that it can be adapted to different situations.

It might as well be if it involves ripping out the floor or wrecking the decorations of a kitchen.

.andy

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Reply to
Andy Hall

Need to size with a combi as it never runs out of hot water.

Most store water at 75C these days.

You know little of HVAC.

If the rads are run for the store backup electricity can be incorporated. High wattage immersion cols are available.

The system should a DHW priority system when using these.

No need to go tank/cylinder as a combi or heat bank will be far better all around.

Reply to
IMM

I am not sure where waists come into this. A number of contributors to this NG have bought this and found it useful, even if it has been for a one off installation. So far, you appear to be the only dissenting voice, but why would I find that surprising?

Spending £20 in the context of a cost of materials of typically between £1000 and £2000 is nothing and the information is from the recognised industry association, derived from the relevant official and informed sources.

That's a matter of opinion and expectation of performance.

.andy

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Reply to
Andy Hall

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