Intelligent CH Thermostats/Radiators without Convectors

[Mary Hinge]

Looking at getting a new condensing boiler etc, already gleaned plenty of info from previous posts (thanks everyone), just a couple of questions:

1. Is there a rough way of calculating the output of older rads without convectors, although the majority are newer rads with convectors there are a few older ones without. I'm trying to get an approx value of their output but can't find any sources. For example with a double panel/no convectors can I take the average output of a double/double and divide by 1.5 or something? Not looking for exact figures, just a rough idea. I don't really want to replace them, the look in good condition and it seems silly to throw out something that is in good working order. The rads without convectors that I am looking at are:

2200x700 Double panel 750x700 Single panel 1750x500 Double panel

1. In the case of a modulating condensor, are there intelligent CH thermostats that, rather than just calling for heat or not, can say to the boiler I need x amount of heat? At present I have a CM67, is there any changes you can make to this to make it more suitable for a modulating boiler? It seems silly having a thermostat that only turns the boiler on or off, when with a more intelligent control the boiler could just modulate down to the current heat loss for the house. Maybe I am getting a bit too anal here, just interested really.

Thanks in advance.

Andy

[Andy Hall]

Very approximately, a double panel radiator has 1.7x the output of the equivalent single panel (both without fins.

If you look up the data sheet for the Myson Premier HE there is a single panel, no fin version. For sizing, simply scale the dimensions, Apply the factor above and then multiply by 0.9 because the data sheet numbers assume a higher operating temperature than is used in the UK in practice.

Left to its own devices, a modulating, condensing boiler will modulate downwards automatically as the heat requirement falls. The simple way to do this is with TRVs on all radiators except one. Then as the flow and heat load fall, the boiler will detect it and reduce power.

A CM67 can control the boiler by pulse width control - basically varying the on/off ratio for heat demand. This is effective for conventional boilers because in effect it "modulates" the temperature of water to the radiators. The objective is to prevent overshoot of room temperature. With a condensing boiler, you really don't want this action to happen to the same degree because it is not as good as letting the boiler do it. Therefore, the operating window should be set as small as possible. The situation that you want is for the rooms with TRVs to come up to temperature, and then shortly after that for the room with no TRV and the thermostat to reach its set point and for the boiler to be turned off altogether. It's not so useful to have the CM67 turning the boiler on and off in an attempt to control it, if the boiler is already modulating down on its own.

Some boilers have the ability to accept an input from a room thermostat which is able to give it a modulating control as a digital signal of the value required rather than a simple on/off.

For example, on my boiler, a MAN Micromat, you can optionally connect a Landis & Staefa QAW20 room controller.

these are intended to run with a zoned automation system in a multi-occupancy building with central boiler, but will drive this boiler quite happily. The boiler also has input for an outside temperature sensor which affects the boiler operating curve and control points. It is possible to set the relative sensitivities of the boiler to the internal temperature control input and external control input in order to optimise power level with temperatures.

.andy

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[Christian McArdle]

The main problem is that there are no standards for these, and when available, they rarely support subzoning.

The Worcester-Bosch Greenstar, for example, can have a proprietary room thermostat that sends an analogue signal to the boiler. Very nice, except that (a) it isn't programmable and (b) you can have only one zone using the system.

Christian.

[Mary Hinge]

Thanks for the answers guys.

I couldn't find a single panel, no fin version of the Myson Premier HE in the tech specs PDF on the Myson web site, don't suppose you have a link at all?

As I am probably going for a Worcester Bosch or Glow Worm I think I will stick with my treasured CM67. Are there any changes to the std CM67 config that might be worth making for a condensing boiler (my guess is no). I have always had my min burn time set to 5 mins as without that I found it had a tendency to fire the boiler for only a minute or so quite often, setting the min burn time high stopped that without any noticeable temp overshooting.

So far have contacted three "heating engineers" regarding fitting the boiler, not suprisingly they have each recommended a different boiler for exactly the same reasons! (ie the other two being "unreliable"). All three guys are pretty clued up so I guess in the end it is as much down to personal preference as anything else.

Andy

[fred]

In article , Mary Hinge writes

Here's one for Stelrad:

decode, P1 is a single panel without convector, K1 is a single panel with convector, P+ is a double panel with a convector on one panel only and K2 is a double panel with a convector on both panels.

FWIW, I prefer the look of the P+ as it is a bit slimmer than a full double convector.

have a good site that lets you see what's available and are a useful price guide even if you don't buy there.

[Andy Hall]

Send me an email and I'll reply with a PDF as an attachment.

You may need to play with the cycle times and also to reduce the size of the proportional control window.

One factor that affects it is the thermal characteristic of the house

- i.e. whether it heats rapidly with the heating starting or whether it has a larger thermal inertia.

Really, you will need to experiment a bit with the settings.

If you post some makes and models you will get some opinions on that.

.andy

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[Owain]

"Mary Hinge" wrote | So far have contacted three "heating engineers" regarding | fitting the boiler, not suprisingly they have each recommended | a different boiler for exactly the same reasons! (ie the other | two being "unreliable"). All three guys are pretty clued up | so I guess in the end it is as much down to personal | preference as anything else.

Alternatively they may be recommending whichever boiler is giving savings stamps on new monogrammed overalls or a trip to Ibiza.

Owain