Controlling temperature of water in radiators.

[Anode]

Is there some setup of a wet central heating system that will let radiators be warm most of the time, and not cycling between over-hot and over-cold, as mine are now?

At present I have a 15years old gas fired non-modulating boiler with a pumped, vented, system, controlled by a wall thermostat. The controls on this system will not avoid radiators that are either on and far too hot, or off.

Thus the radiators cycle between being much hotter than is needed for just compensating for heat losses from the rooms, producing unpleasantly hot air around the radiators, and then cycling to a period of being colder than they need to be.

Is there any setup that would give me the necessary heat output but in a more balanced way, so the radiators will be on for longer but at an appropriately lower temperature, with the period in the cycle when the radiators are off being correspondingly much reduced?

As the age of the boiler is such that it could well be replaced, what kind of setup should I be considering?

Regards.

[Andy Hall]

On Mon, 3 Jul 2006 17:32:47 +0100, Anode wrote (in article ):

I have a MAN Micromat boiler. It has a number of features which achieve what you are describing:

- Burner modulates from 3-30kW

- Pump modulates continuously from 20-100% of output

- External temperature sensor is used in calculation of heat requirement.

- Detection of flow and return temperatures.

The result of this is that during the period from autumn to spring, the boiler runs almost continuously at low output with radiator flow temperatures in the region of 40-45 degrees, getting hotter only when the outside temperature falls to a point that more heat output is required.

This is a high quality German designed and manufactured product. A similar range is made by Viessmann.

Expect to pay around £1500 for such a boiler.

[Tony Bryer]

The magic word is compensator - either sensing load or weather and turning the flow temp up or down as necessary. They are available as an optional extra on a number of the better boilers.

[Anode]

Thank you for the information about the MAN Micromat, and the warning about the price.

I shall get some details.

Regards, Anode.

[Anode]

Regards. Anode.

[Andy Hall]

On Mon, 3 Jul 2006 17:59:36 +0100, Tony Bryer wrote (in article ):

True...

Not to be confused with external boiler management boxes which use an external temperature sensor. These are alleged to make some improvement in terms of energy use in that they provide the heating system with "advanced knowledge" of changes in outside temperature, but they drive the boiler on and off to do so which doesn't really address the initial requirement.

[Doctor Drivel]

Matt, what bollocks. It does address the intial requirement in that the rads are at the ideal temperature dictated by outside weather conditions. Sirry irriot. It does this by switching the burner using electronic anti-cycle control. Sirry irriot.

[Doctor Drivel]

Same boiler.

[Andy Hall]

On Mon, 3 Jul 2006 18:42:06 +0100, Doctor Drivel wrote (in article ):

No. The radiator temperatures will cycle up and down as the burner is turned on and off by the external controller.

The correct solution is to use something that is integral and analogue to the main boiler controller.

[Doctor Drivel]

Get a heat bank (thermal store). Heated by a Glow Worm condensing boiler (excellent and cheap enough. Rebadged Vaillants). The heat bank to have two cylinder stats to eliminate boiler cycling. The boiler comes in on one long efficient burn. The boiler only heats the cylidner in one continuous burn, not the rads directly.

The CH circuit taken off the store with thermo rad valves on each rad, using an auto variable speed Grundfoss Alpha pump. The CH circuit takes what heat it needs from the store, so always a continuous on-tap store of hot water with no heat fluctuations.

The heat bank heats incoming cold mains water instantly, so no need for storage tanks. In the morning the rads are instantly hot as the heat in the store of water is up to temp and pumped immediately around the rads. The thermo rad valve take care of local room temperature control.

This gives you:

1. Instant high pressure DHW at the taps and shower.
2. Temperature control at each room.
3. Boiler operating at ideal conditions with the ideal flow through the boiler.
4. Boiler lasts longer as controls do not constantly switch off and on.
5. Boiler is simpler and easy to fix when down.
6. Full electric backup of DHW "and" CH if electric immersion fitted in the Heat Bank.
7. No cold water tanks.
8. No room stat.
9. No complex expensive electronic controls.
10. Instant CH when switched on in the morning having a store of on tap hot water.
11. Local room temperature control.

[Dave Plowman (News)]

Perhaps you need to shut your windows, then, when the heating is on?

[Doctor Drivel]

Within the range dictated to by the controller.

Matt, a heat bank with a Grundfoss Alpha is the way. A continuous supply of on-tap water for the CH. If the house only needs 1.5Kw of heat, the CH circuit via the auto modulating pump, just takes the heat from the heat bank store it wants. If it needs 0.5kW for the CH it takes it and boiler cycling. No cycling or modulating of burners. Simple, easy, efficient.

[Andy Hall]

On Mon, 3 Jul 2006 19:09:24 +0100, Doctor Drivel wrote (in article ):

Which means that the boiler would need to cycle rapidly to achieve it or that there would need to be a wide range of operating temperature. The first is inefficient and the second is not what is wanted.

This is unnecessarily complicated and expensive. If the heatbank is maintained at a temperature worthwhile for HW production (80 degrees or so), the effect will still be one of hot radiators but with a large temperature differential as the TRVs operate reducing the flow.

It's far better, easier, more reliable and less expensive in terms of solution cost to use a suitable boiler suitable for the requirement in the first place.

[Aidan]

for other articles on that site by the same author. A modulating boiler would be the simplest way of achieving what you're after, given that your boiler may be due for replacement anyway.

The technology exists, but it is little used in the UK bacause our heating technicians and/or CORGI technicians are mostly clueless about it.

I have a non-condensing non-modulating boiler. This set-up lends itself to the use of a thermal store (100 or 150 litres of stored water) so that the boiler will run for some time in raising the temperature of the stored water from,say, 60 to 82 degC. If you only had the water in the system's pipes and radiators, the boiler would rapidly cycle on & off under part-load conditions , e.g., a 17 kW on/off boiler but the system only requires 2 or 3 kW of heat.

The flow to the heating system is through a 3-port mixing valve which modulates around to achieve the required flow rate. The heating (secondary) pump is downstream of the mixing valve, with a thermistor temperature sensor downstream of that.

You need to control the return temperature on a non-condensing boiler because a temperature of

[Andy Hall]

On Mon, 3 Jul 2006 19:04:06 +0100, Doctor Drivel wrote (in article ):

Unnecessarily complicated. Also requires relays to complete the control system.

This can be more effectively and efficiently achieved by running a boiler continuously at a lower temperature driving the radiators directly.

Assuming the mains cold supply is adequate

That can be achieved with TRVs anyway, regardless of the system.

No it isn't. Condensing boilers operate more efficiently at lower temperatures.

So why introduce thermostats and relays making it less reliable?

Bogus. There is very little difference between a condensing boiler with simple controls and one with an external sensor providing data for weather compensation and full modulation, unless you believe that the firmware is inherently less reliable.

Bogus. Immersion heaters are 3kW. This is not enough to provide worthwhile heating backup except under mild conditions.

No advantage

Already covered in (5)

Bogus. This can be addressed quite easily by the boiler or room stat having predictive starting

Can be achieved with any system.

>

[Aidan]

Link won't work; try this;

[Graham.]

Mmm, that thermostat is a conventional electro-mechanical affair is it?

Has it got a neutral connection to it?

No neutral equals no return for the pre-heater

Result:- thermostat still works but with excessive hysteresis.

[Doctor Drivel]

Matt, I know you are not very good at this sort of thing, but I said "Simple, easy, efficient."

There you go.

[Doctor Drivel]

Sad I know.

[Doctor Drivel]

Do you mean to the CH circuit or thermal store?

You can have them on all using a thermal store and a auto vraibel Grundfoss Alpha pump, and not room stats. I would change the system to this setup. Far better.

Do you mean the tyhermal store is bulky.

That is a problem. The heat bank/thermal store is the best way.