Ping Andy Hall re flowswitches

[IMM]

It is a major issue, that is why quick recovery cylinders can be downsized.

You size the cylinder to suit with a boiler prioritised to send all its output to the cylinder. You have quick reacting cyl stats. You could have a flow switch so that the boiler always comes on immediately water is drawn off. Simple and easy to do.

You put a restrictor on the hot bath tap. A bath fill of 5 minutes is very acceptable to 99% of people. remember the point is using a small cylinder to save space, so the system has to be balanced to suit.

The 30kW boiler will give about 12-13 litre/min in draw-off flow. Have a blending valve on the coil to allow only 82C water to enter the coil will give better results. It will dump 82C heat at the top of the cylinder and far batter stratification will occur. So if a shower is drawing 8 litre.min the boiler will heat the cylinder faster than what is being drawn off. Draw-off 16 litres/min into a bath of hot only, BS recommendations, and added cold a full bath of over 100 litres will be filled in about 5 mins. Easy.

< Snip stuff from person no experience in the field of such things >

[Andy Hall]

Well.... it's like this.

If you put a liquid in a rectangular shaped receptacle, you can determine the depth by dividing the area of teh footprint into the volume of the liquid.

I was able to do this from aged 8 or 9.

.andy

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[Andy Hall]

I know I did.

I took that into account in the U value of the plasterboard. The insulation of the rest of the house and the gas consumption to heat it has absolutely nothing to do with this.

If you draw off a bath, even a pee-widdly 100 litre one like you are suggesting, the water temperature in a 115 litre tank will be pretty much at mains cold water temperature.

There will be some mixing, but we have already demonstrated that unless the water in the tank remains unused for several days it won't have gained significant temperature anyway.

Also, as the tank water becomes warmer, it will not gain heat so quickly anyway. I didn't allow for that in the calculations - it actually makes the situation worse - neither did I allow for heat loss through the insulation surrounding the tank.

It's worse because more cold water from the main is filling the tank.

It makes a small diffference. the calculations clearly show that it is not significant.

It's negligible

.andy

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[Andy Hall]

Within reason on larger sizes, yes.

On such a small size, the stored water runs out very quickly, and the system becomes equivalent to a rather poor combi.

The amount of energy stored is proportional to the volume, and this is just too small to make a significant difference.

I assumed all of that by saying that the stored content of the cylinder is drawn off in two minutes and using the example of a 30kW boiler with 100% efficient heat transfer run for a two minute period. Implicit in that was that the boiler starts and is up to full output the moment the tap is turned on. In reality, the situation is much worse as even with all of the detection, it would probably take the boiler at least 30-60 seconds to be delivering full output after the tap goes on.

The simple and easy thing is to do the job properly and install an adequately sized cylinder in the first place rather than throwing all sorts of complexity at an untenable situation.

This is a joke, You can't supply statistics for that.

The space saved between a 45 and a 100 litre cylinder is pretty small.

If you are going to go down this line, you will have compromised the system so much that you might as well put in a cheap combi nd gain even more space.

Based on what? That is a completely meaningless statement without giving a temperature rise. For 12 l/min, 30kW gives a dT of 35 degrees

More complexity. The boiler water should be at 82 degrees anyway, so what is the blending valve going to achieve?

We're not talking about showers and 8 l/min for one is pathetic.

Pathetic and inadequate on both counts.

.andy

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[IMM]

Equiv to a rather good combi. It will fill a bath very quickly, and re-heat the cylidner ina few minutes.

You need to look at this in more detail. Oh don't bother, no don't bother..

You balance the system to suit. Asll systems should be.

Say there was no balancing and the cylinder was exhausted in 3 minutes or so. The boiler would then act an infinitely continuous combi and deliver hot water at a lower flowrate. You would never run out of hot water. You would have a speed hot water supply. So the overall bath fill up would still be around 5 mins, which is totally acceptable to 99% of people.

An quick recovery cylinder can be sized to suit. A 45 litre will deliver one bath with DHW priority and an insertion cyl stat. Something you can't understand.

5 minutes in unacceptabel as a bath fillup time? Please.

It isn't. And in small British homes it can make a lot of difference.

Compromised? Please. A high output combi is a real alternative. The Alpha CB50 stored water model is good and a two speed flowrate too.

Have a look a combi specs. that will give ypou a good idea.

As I said "to allow only 82C water to enter the coil". When the cylinder is cold 82C may not be coming from the flow , no matter if the stat is set to that.

8 l/min is not pathetic at all.

A 5 min bath fillup is totally acceptable to 99% of people. Most probably would be faster.

[IMM]

You never.

It will not.

Do them again at 25C

Not so.

[IMM]

Stop reading schule books.

[Andy Hall]

It would be better if you said that in English.

Yes it will because unless the water has been in there for several days the temperature wouldn't have risen. Therefore, dumping in 100 litres of water at 5 degrees is going to result in a tankful at very close to 5 degrees.

If the water in the tank had remained at 5 degrees, the heat transfer would increase to 20/13 the value as at 18 degrees.

The result would be to warm the water in the tank in 5 days rather than 8.

I hope that most people bathe more frequently than that.

The influence is therefore not significant.

I can't help it if you are unable to understand the simple physics of heat transfer.

.andy

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[Andy Hall]

5 minutes is not very quickly.

I already did. There is no point is looking at a more rigorous model of this because you are unable to grasp even the simple principle of linear heat transfer.

You can't balance your way out of something that fundamentally is inadequate for the job.

It would be 2 minutes at a typical flow rate of 20 l/min

???

You have no stats to justify that remark.

I can understand that it won't unless you set the requirement spec. to a very poor level.

That's a joke, especially if "full" means 100 litres of tepid water.

It's no good if it doesn't do the job, and this is definitely a poor compromise.

The discussion was not about combis.

I know that the standard for a combi is the flow rate achieved at dT=35 degrees. This is not rocket science.

This is waffle.

It's almost at electric shower level. Pathetic.

Unless you can find some heat from somewhere, sorry but no. There is little point in saying that 99% of people will accept a 5 minute bath filling time because you have no data to back it up.

You are simply attempting to move the goal posts to justify an untenable position. This is your normal MO, of course, but it doesn't really fool anyone. I am surprised if you think that it might.

.andy

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[IMM]

It would help if you had some experience of these in the field.

[IMM]

It is.

flawed.

You lack understanding.

Not so.

I have a lifetime of knowing.

You have no experience of such matters.

It does the job.

You brought the combi in, not me.

Then there you go.

Very clear. How long have you been hard of thinking?

It is not.

< snip drivel >

[Andy Hall]

You can flannel as much as you like, but I'm afraid things in the field as much as anywhere else follow the laws of thermodynamics.

.andy

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[Andy Hall]

It's behind you.

Nope.

Not really. You are trying out your normal smokescreen tactic which fools nobody.

Sure it would. I showed the calculation.

Being known, you mean.

Sure I do. It's common sense and a matter of simple arithmetic.

Do the sums.

It does a job, as long as one is satisfied with a small amount of water run slowly into the bath.

You're starting with the premise that a 45 litre cylinder will provide for the requirements of a house. Then you seek to adjust the expectations of the user to meet that premise come hell or low water. Convoluted logic to put it mildly.

I never have.

The only way to achieve what you are suggesting is to effectively circulate the primary water back to the boiler for a short while to allow the temperature to build up rather than directing through the thermal load of the cylinder. This does not achieve a great deal. There is no point in doing anything other than directing the whole flow from the boiler through the coil. The so-called stratification that you are talking about is irrelevant because the cold water is going through the cylinder at a rate of half a cylinder-ful per minute. There won't be any time for stratification.

It's behind you.

.andy

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[IMM]

As you understand them, yes..

[Andy Hall]

I do, so that's one of us at least....

.andy

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[IMM]

You lack understanding.

You lack understanding.

Being known to know.

You lack understanding.

One bath.

People like you always say that.

It does. See the Danfoss site.

It is clear you lack understanding.

It will not. It will be balanced, as all systems should be.

There will.

[IMM]

Bath or a shower.

It will. Read the albion web site on superduty. One thing a cylidner makers does not do is undersize. If anything they oversize.

"Ultra fast recovery of hot water allows for a reduction in cylinder size." "A practical example is to compare the hot water available from a CF45 against that from a standard indirect 900 x 450mm cylinder. Using a 15Kw boiler the standard cylinder will deliver approximately 175 litres of hot water per hour (based on 40minutes recovery). The Superduty CF45 will produce approximately 340 litres in these circumstances (8 minutes recovery)."

There are lots of Eno people around like you.

You are right. You would not understand anyhow.

Not undersized.

What has thermodynamic have to do with this? is engineering.

A 45 litre is adequately sized.

You lack understanding.

You lack understanding.

[IMM]

Yes, as you view them.

[Andy Hall]

There's nothing to be viewed.

This is first form physics. Did you never do the various experiments with a calorimeter?

I thought not.

.andy

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[IMM]

Because you view them strangely.