Mixing header and pumps

[IMM]

< snip tripe >

[Andy Hall]

The commercial environment is totally different to the domestic one in terms of products and how they are used anyway.

I am sure that they staff and train to cover the majority of cases. You can't really complain if most of the department can't cover a one in a thousand corner case as long as there is at least somebody to which a question can be escalated.

It is the point. It isn't economic to train up a support department on every possible corner case in the hope that it might come up sometime in 2006.

Why? If the output is less or equal to the requirement of the load, why would the burner shut down?

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Why? What is the mechanism and reason?

How and why?

Which ones?

What is your definition of a "simple boiler"? The one implied by DPS's blurb is an on/off non-modulating type. I accept that that will obviously cycle if the output exceeds the load requirement.

If you are talking about a modulating boiler, using any form of detection for modulation, please explain the mechanism and reason by which it will cycle if modulated down to a level equal or less than the load.

You are not comparing apples with apples and are also introducing other applications.

A buffer store is only interesting for non modulating boilers and for mixing heat sources, likewise a neutral point and boiler anti cycle.

Hot water is a separate issue.

There isn't a contest. There are applications where a heatbank is useful, but this is not one of them.

[IMM]

Go to a company that supplies and installs and they strongly recommend a thermal store.

A low lost, or any other type of header is only of benefit when the boiler is on an outside weather compensator. Either built-in, which then modulates the burner down, or externally, and switches the boiler to main the flow temp (with anti-cycle control in the compensator). The problem is then supplying 3 systems: low temp UFH, rads and DHW, all at different temps. The header has to be at the highest temp for the rads. The system can be a priority system favouring DHW and switching to max temp when DHW calls. The problem is then the two temps of the two different heating systems.

UFH primary loops with condensing boilers are only any good on weather compensators. AS boiler may have a 25C flow return temp differential (delta T), yet most of the time this may be only a few degrees because hot water is sent straight back to the boiler. It is running at a low efficient temp, but could be lower on the return side maximising efficiency.

A sectionalised thermal store gives you this. A weather compensator can maintain the lower section of a thermal store. No hot water is sent right back to the boilers return to keep the return temp up. Boiler cycling is then vastly reduced/eliminated. Then there is the neutral point the store naturally gives you.

NB: Boiler manufacturers want a minimum flow rate through the boiler and the delta T not exceeded. That is all. I know most commercial design companies ignore everything else the makers say, as their knowledge of complete systems with all the various sub elements is minimum. The designers only want the flow and delta T and any control requirements for frost protection, anti-freeze, fluing, inhibitor, etc. They really don't want or need their advise on systems. They only make the heat source.

[IMM]

The point is product knowledge.

Don't you believe it. Most of the time kid answers. I rang Ravenheat and young girl answered obviously talking from a crib sheet.

Their advise on systems is not wanted as they are out of their depth.

Not the point, they are supposed to know their product and systems in general, they do not.

Stats

When demand is lower than boiler output.

The Greenstar heating boilers are simple. No pumps, load compensation, weather compensation, etc. Just an externally switched gas valve. It does modulate to flow setpoint, which is the only complication. Other boilers are similar.

It will not when on a heat bank with appropriate stats.

It can modulate when demand is less than the lowest boiler output.

You are confused. BTW, I like your boiler.

This application is three: DHW, UFH and rads.

Get real.

I hope you are happy with your purchase. You don't even know about networks never mind HVAC. Sad but true.

[Andy Hall]

I had never viewed them as a serious manufacturer.

OK, so if that happens then the answer is to shop elsewhere.

Come on - you'll have to do better than that.

Obviously. I was specifically referring to the case where demand is equal to or greater than output.

That does not appear to be the definition used by DPS. They are talking about the case without electronics. Modulating boilers, however the modulation is done are going to use electronics.

Obviously, but this was not the discussion point.

I think you meant cycle and that is obvious. However, DPS is not using that argument.

I am clear and to the point.

Yes, but the DPS application note was based around UFH.

I am being real. Once again you are trying to obfuscate the issue.

>

[IMM]

You mean their boilers are not boilers? They are now a big player.

No. Designers go for varioousl boioer out of spec and price. They don't need the makers advise, just their spesc on what the boiler needs and advise on fluing, if needed.

OK nuclear controllers. That better?

Read it again.

The point was a system to have DHW, UFH and rads run to max efficiency and comfort conditions. The UFH and rads are staged. Primary point was the use of a header in a doemestic situation.

No you are not. You have an obsession with justifying your purchase.

That piece was explaining UFH. Look elsewhere on the webs site and they show DHW, UFH and rads all integrated.

You are an obfuscation.

[Andy Hall]

OK, not one from whom I would entertain buying anything.

For domestic applications??

Don't be silly. Were you saying that a modulating boiler uses a thermostat to control the modulation?

I have and that is the implication.

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With a modulating and condensing boiler........

What on earth are you talking about? I haven't referred to what I have in this part of the tread at all and it isn't relevant anyway.

If I were to do that, you wouldn't even notice.

[IMM]

My God! Because he doesn't like them they don't matter or exist.

Any? I have met makers reps on site regarding boiler problems are we have wiped the floor with them their knowledge was so poor. So much so we told them not send their people any more as our time was being wasted.

And how a superior setup using a simple cheaper boiler and a neutral point for all cicuits can be obtained.

You always home into, and carp on about one point, of how a modulating boiler solves all, which it does not. A boiler is only one aspect of a system.

Mr Aston would be better off with a dedicated boiler on an outside weather compensator to ensure low temp, high efficiency operating temperatures, serving the UFH. Better a combi version as they are about the same price as system boioers. No valves headers etc.

Another boiler, preferably a combi version, as they are about the same price as system boilers, to supply the rads. This may also have a separate outside weather compensator to give a slope for its circuit. One two stage controller to bring in the two boilers to accuratly give room temps. Then spread the DHW combi loads around the house: split the showers, etc. and combine the two for the bath. Very cheap, very effective, power showers and no DHW water storage, or tanks.

If stored water is desired for DHW, then the rad boiler may be on a diverter valve and supply DHW. The rads will only be for boost so this boiler will be for DHW for most of the time.

Using one boiler will mean adding a heat bank, or headers & pump etc, and the price will rise accordingly. Headers, etc are a compromise to make a system work off one boiler. Boilers are cheap now and well worth using multiple boilers for dedicated applications.

- two condensing combi boilers: approx £1200-1300

- two compensators: £320.

- one two stage controller inc room temp sensor: £130

- one time clock: £25-40

Total: £1800 maximum. £1640 if only one compensator used. Piping on top. That is for instant DHW and power showers and seamless accurate control of UFH/rads. and limited redundancy.

[Andy Hall]

It's simply an illustration of poor service so shop elsewhere. What's so difficult about that?

Coming from you, that is rich as well as untrue.

Obviously.

I wondered when we'd get back to the two-combi solution.

What about the small matter of the water supply? They are all crap according to you.

[IMM]

That is not the point. The point is that boiler manufactures advise is not set in tablets of stone. In fact quite the reverse when system design is concerned.

Missed the point again.

Read what you write. You can't stick to the point(s) in question.

Since when have you thought like that?

It is cheap and effective, and in this case the obvious solution as dedicated boilers simply matters.

All? Most are, some are more acceptable. It is worth re-newing the water main back to the street...in any type of house.

[John Aston]

I've had a look at the

website. My main cold water supply is borderline flow rate for an unvented system. I was thinking about using a Dualstream accumulator/cylinder to maintain flow rates so I'll have to think carefully before using a thermal store instead.

Leaving aside the cost of each system, is your argument that (A) a thermal store with zones for underfloor heating and hot water, is more energy efficient than (B) a weather-compensated modulating boiler running DHW (as priority) + two different heating systems?

On the Heatweb website it says that, to get maximum efficiency from a condensing boiler, their heat bank will hold the return to the boiler at a pre-set temperature, typically 53°C, until the entire store has been heated to this temperature. I thought that (B) controlled the return water temperature too! Clearly, after much discussion, I'm still failing to understand this basic point.

OK. I just used them as another source of information to throw into the discussion knowing that they had considerably more experience than me.

[Andy Hall]

It's completely the point. If a manufacturer doesn't provide you with the product and service that you want, buy from another one. What is so difficult about that concept.

Always.

Ah, so a different situation to your other post.

[IMM]

A thermal store can be used with a DuralStream accumulator.

Yes. And much simpler. With (B) keeping the two heating circuits at differnmt temops is a problem, altjough ECo-Hometec do a duel temp boiler (a con really as it is one boiler with two boiler stats.

Correct.

At (B), it depends on the boiler. Some modulate the flow down which in turn modulates the return down too. But the problem is having a high temp for the rads. So, when you have UFH and rads the system is to the high temp, then the UFH has to blend down to its lower temp.

A heat bank can have a dedicated low temp section at the bottom of the store. Look at the heat bank with the injection pump for UFH on the heat web web site. Instead of the injection pump and return pipe from the bottom section to the top section, have another pair of flow and return pipe in the bottom section back to the boiler (the makers will do this). Both top and bottom sections may have a pump each on the flow with a non-return valve. The UFH bottom section has an outside weather compensator with a sensor on the return pipe. The top section for rads and DHW. A weather compensator maintains the large bottom water section to a low temperature for UFH (the UFH is taken off theis section). This eliminates boiler cycling. The large mass of water cools and heats much slower than water in a header or a pipe. A nice buffer. This bottom UFH section would be at a very low temp promoting high efficiencies and as UFH will be the main source of heating high efficienies for most of the time.

The system would have to be a priority system, in that when the top section called for heat the top pump would be on and bottom pump off, with the boiler running up to full temp, or near it (the weather compensator is disengaged by a relay), for a fast recovery for rads and DHW. When satisfied it reverts to the low temp. When heating the top or bottom section will there be no boiler cycling. Wheh heating the top section the return tenp can be held to ariound 50-53C until near heated. It heats top down with no mixing and the water is heated through the boiler in only one pass.

Of course get info from all angles.

Having a poor water mains may mean a Dualstream, which can be used with a thermal store. The sell an Ariston unvented cylinder, not cheaply either, and mate it onto their accumulator.

A thermal store is best because of your duel heating zones of very different temperatures. It is a great buffer and neutral point, and means you don't require a very expensive boiler and boiler cycling is eliminated.

Even if you stay with a large tank in the loft, a heat bank.thermals store can be used by having a booster pump on the system.

[John Aston]

You've may have seen a preliminary design that I've posted earlier based on a weather-compensated boiler. (Message news:4198dbf7$0$102$ [e-mail]...) I'll ask Heatweb if they can quote me for an alternative heat bank system.

Unfortunately, GAH won't sell their Dualstream accumulator without the Ariston cylinder. :(

[John Aston]

Does that mean that the water for the rads, the UFH and the baths/showers are ALL heated by the heat store? I can't see a "three zone" store on

[Andy Hall]

Read the claims on the Heatweb site very carefully, John.

Not all are concurrently possible.

e.g. heat store with 75 degrees at the top, 25 degrees at the bottom, a boiler with 25 degree temperature rise and the water being heated in one pass do not fit together.

There are curate's eggs here. These are good in part and are useful for achieving certain things, but not all are possible at the same time. To be fair, the applications are mainly separately described, but be careful not to assume that all claimed benefits will happen if the heat store is doing all of the things.

The story about reducing boiler cycling can only happen in cases where the minimum heat output of the boiler exceeds the load. Since you are considering boilers which will modulate down to 3-4kW and are connected to a large heat load, this is not going to happen a lot anyway.

In my set up with the MAN Micromat, the hot water is handled by closing off the CH and opening the DHW coil flow - the boiler controls the valves. It is a 210litre cylinder and is initially given a full power from the boiler. As the DHW temperature approaches set point, the boiler modulates down a little and the temperature gently rises to set point for the last degree or so. There is no cycling.

When driving the radiator central heating, if the combination of room and ouside temperature is high enough, the boiler doesn't come on. At cold temperatures, the boiler will be modulating between its minimum and some proportion of its maximum output according to the conditions. As long as the heat load exceeds the boiler minimum, the boiler runs continuously at the required level. When the weather is cool enough that house heating is needed but at low level, the boiler will come on with a flow temperature of around

40 degrees.

The only case where cycling occurs is when a little heat is required but the amount is less than the boiler minimum. However, there are several points.

- A fairly large store of water in the radiators is in play anyway - more than 100 litres in a large system.

- When the heat output of the radiators is low as in this case, the water temperature in them is low. Thus, the rate of heat transfer is much less than when the radiators are at say 70 degrees. Remember the mean water to air temperature corrections for radiators?

These points mean that the rate at which the boiler cycles on and off is very long compared with what a non modulating boiler would do operating above the load level. The boiler electronics also introduce some hysteresis to allow the water to cool before reigniting the burner. When that does happen, it is doing so between off and a few kW, not full output.

For UFH, there will be a similar effect because of the thermal mass of the floor.

Therefore for modulating boilers of the ilk you are considering, I don't believe that the so-called buffering effect of the thermal store will have any value.

There could be a value for you in using a heatbank for the DHW.

A pressurised cylinder will give you a flow rate of whatever the mains will deliver until it runs out. BTW, in terms of hot water stored, I think you would be OK with the amount (I have 210 litres with 4 people and showers/baths run concurrently or in rapid succession. My concern would be the ability of the mains to deliver the volume required, although I notice you added an accumulator.

With a heatbank you could store the water at 80 degrees and heat the DHW via a plate heat exchanger. This would give you an equivalent of

330 litres of 60 degree water. Plate heat exchangers do transfer heat very effectively for their size, and you could reduce the size of the cylinder if you wanted and have the same equivalent capacity. The other advantage is that you can DIY this, but can't a pressurised cylinder.

[IMM]

No, you missed the point.

That is sad.

You are very confused. How is Little Middle England today?

[IMM]

The last time I contacted them they would. You can use the accumulator with a combi too. You can still use a cold water tank with a booster pump.

[IMM]

Yep. All of it. The boiler only heats the store. A separation of functions.

I can't see a "three zone" store on

deliver. Three zones in a store is not common, but two is, so they go for two. Have a look at some of the customers specifications they have delivered.

[Andy Hall]

Other than expecting the manufacturer to give you what you want, there isn't really a point. You seem to want them to respond with full technical backup to corner case schemes that you devise. Why would they want to do that?

If you think that your ideas are so good, why don't you start a company and sell solutions based on them?

I wouldn't know. I'm not in England today, Little Middle or any other variety.