Hot water system

[Christian McArdle]

No.

The boiler is a Worcester-Bosch Greenstar HE System. Does this have the ability to have call for heat signals at different nominal flow temperatures?

The system will be a Honeywell 'S' plan. Initially, it will have 3 zones, upstairs, downstairs and water heating. This will ultimately be expanded to

5 zones, for the loft conversion and conservatory. As planned, there is no hot water priority. Although I could possibly contrive such a system, it might require relays or similar to disable the heating circuits when the water valve is open. I'd prefer to avoid this, unless it will significantly improve performance.

Probably. I can turn the blending valve up in cold weather. If I install a blending valve, do I need an additional pump on the heating circuits?

Christian.

[Christian McArdle]

I suppose I could implement priority simply using a 3 way diverter valve and then subdividing the heating port later on. I don't know if Honeywell have a letter for this type of system. Although I've already got the three 2 port valves, I'll have needed a couple more later on anyway, so the one freed up won't be wasted.

Christian.

[IMM]

temperature,

Christian.

This is a DHW only heat bank. So you will be having a diverter valve for either CH & DHW, with the CH running directly from the condensing boiler. A condensing boiler with load compensation control will reduce the rad temps for the vast majority of operation, except on warm up in winter which will be rather high. You can have a high temp limit on some boilers, so no over hot rad temps.

A blending valve can reduce max rad temps, but there is other ways of doing it. What you want is the boiler at full temp when DHW is being called and then a lower temp for the CH mode. In a simple boiler this is achieved by having the boiler stat on full, and a pipe thermostat on the boiler flow. When calling for DHW the pipe stat is switched out, when CH is called it is switched in. Very simple, and very effective.

To keep the return temps cool you could have:

1. Oversized rads
2. Install a plate heat exchangers on the return to the boiler with the cold water mains entering this first. It will act a pre-warmer when the boiler is operational either for DHW or CH and hot water is being drawn off. It will also reduce the return temp into the boiler. It will also impove the flow rate when the boiler is operational. You could have the control system so that the boioer always fires on DHW when water is drawn-off, as a combi does. Plate heat exchangers are not that expensive.

What make & model of cylinder thermostat is DPS using on the Pandora heat bank? What kW rating is the coil?

[IMM]

Drayton do a 3-port diverter valve with an end switch using the normal syncron motor. Most do not have the end switch. Also the mid-position Honeywell can have a 2-port actuator fitted to convert it to a diverter. May be a little too expensive for you to buy two valves, but easy enough to convert a system from mid-position to priority diverter. But it may have been better for you to buy the Y plan and convert.

[Andy Hall]

OK.

I am not sure about this boiler - it was not one that I looked at when I was searching.

I wonder whether otherwise you could alter the behaviour of the boiler by arranging a zone valve and bypass in effect across the flow and return of the CH circuits - i.e. to open when any of the CH zone valves open.

.andy

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[Christian McArdle]

My original intention was to use no diverter valve, just 2 ports on every circuit. Now, I'm not so sure. I may install a diverter valve for the hot water and use 2 port valves for the heating sub circuits.

I don't know. However, the cylinder appears to be made by Telford, so I might have a look to see what their standard coils are rated at. I suspect it will be less than the boiler's maximum output, hence why I wasn't too concerned about priority operation.

Christian.

[Christian McArdle]

Not quite sure I get you. Do you mean mix some flow water into the return so fooling the boiler to modulate down?

To be honest, I'm surprised boiler manufacturers don't have facilities to control the flow temperature programmatically. It seems a common requirement, particularly for underfloor heating and now that condensing technology promotes lower radiator temperatures (but still requires nice hot water in the cylinder).

Christian.

[IMM]

Coil areas:

80 litre Telford Typhoon cylinder has: 1.2 squ metres coil surface area. 120 litre Telford Typhoon cylinder has: 1.55 squ metres coil surface area. Calculated to give 12-16 minutes recovery time.

125 litre Tornado unvented cylinder has: 0.704 squ. metres coil surface area.

[Christian McArdle]

It is a 180L, so it couldn't be a Typhoon. I'll need to examine further to see what it might be. It could just be a standard indirect cylinder, or a special order item for them.

Christian.

[IMM]

It probably uses standard coil sizes, so the next one up from the 120 it may be. I can't see DPS using a Part L coil.

[Christian McArdle]

They say they use coils in excess of that required by the British Standard, which is pretty meaningless really. TBH, I don't really care. I'm sure it should be well overspecced for my storage needs. I'm pretty close to running two baths simultaneously with a 180L with no regeneration at all. I'm going to be running the hot water circuit 24/7. I've never run out of hot water with a 120L gravity indirect cylinder, so I'm not planning to start now.

Christian.

[Andy Hall]

Exactly. If you think about it in terms of an electrical circuit, it becomes clear.

I know. It would make sense, wouldn't it.

At this point, heat banks are not that common, but the idea of being able to transfer maximum energy into even a conventional cylinder via coil so that the boiler is off line with respect to the CH for the minimum time is pretty obvious and a common scenario.

The CH might have a max allowed temp. of 82 degrees if you are replacing an old boiler and not the radiators - it will still modulate down when the weather is warm enough not to need full output (and this is virtually all the time); 70 degrees if you increased radiator capacity so that there is enough heat output even when it's very cold and as you say UFH with max temperature of 50 degrees. Since there are cases where at least two of these might be in use plus DHW, controllers should really be more flexible. After all, with a decent controller, essentially firmware based, there is zero incremental cost to do this.

I suspect that the reason it isn't widely done is because the average installer is conservative anyway and often does not make three digits regarding IQ.

.andy

To email, substitute .nospam with .gl

[IMM]

Christian,

Who sized your 180 litre heat bank?

[IMM]

Christian,

You should be able to see the coil inside the cylinder through the immersion, or other, tappings. The quick recovery coil has about 4 soft copper coils.

[Christian McArdle]

Me, supported by the simple table on their website and a quick chat with their sales director. It is based on having a bath and a shower simultaneously.

Christian.

[IMM]

Christian,

A 140-150 will do a bath. Arrange the system so that the boilers output is combined with the heat banks and a greater flowrate with a smaller cylinder and then the cylinder is exhausted it will revert to the boilers output, which in your case will give around 10 litres/min.

[Christian McArdle]

It is an indirect coil, so it won't have this ability. It needed to be indirect, because I needed a pressurised sealed CH circuit, which obviously isn't possible with a direct cylinder with atmospheric pressure water.

It is sized so I don't need to rely on recovery for it to work. The sizes only affect the height of the cylinder, so there is no space implication in going for a 180L instead of a 150L or a 120L. It's going in the loft.

Christian.

[Peter Smithson]

You take your personal hygene seriously! :-)

[IMM]

That doesn't make any difference. Put a 3-way diverter valve on the flow from the boiler to the coil of the cylinder, and take a pipe from one port to another plate heat exchanger. Have the cold water coming into the boilers plate and then out into the heat banks plate.

The outputs are combined. The heat bank assists the boilers output, which will be at full belt. This way the stored water is kept long. When the heat bank runs out of hot water an electronic quick acting pipe stat with an insert pocket will cut out the heat banks plate heat exchanger pump preventing the cool heat bank water cooling the boiler heated water, then only the boiler will provide DHW, meaning you can never run out of DHW whatsoever. When there is no flow the boiler immediately starts to re-heat the heat bank. The boiler should be full on and the heat bank will top up the shortfall. This way you will get around an extra 10-11 litres per minute of flowrate, never run out of hot water and a smaller cylinder can be used.

There is also backup in case the heat banks DHW pump fails. All for the cost of a plate heat exchanger, pipe stat and a 3-way valve. You have to arrange the control system of course.

BTW, did DPS leave the CH tappings on the heat bank?

[Christian McArdle]

Oh yes. It's a great way of washing your hair. ;-)

Christian.