Does my Honeywell Modulation modulate?

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Does my Honeywell Modulation modulate?

Postby mfranken » Thu Jan 14, 2016 7:43 pm

I have a Honeywell Touch modulation (TH8210M1003) thermostat and my CV is a Nefit TopLine Aquapower HRC 45/CW6 with an EMS-OT opentherm converter for Nefit.

All running fine with Domoticz. I can override setpoint and monitor the system. What I see, but I am not an expert, is strange control of the CV. This is the log of today's Control SetPoint:

Screen Shot 2016-01-14 at 19.25.31.png
Screen Shot 2016-01-14 at 19.25.31.png (116.69 KiB) Viewed 3666 times


It seems to me that the Thermostat is not modulating or modulating very odd. Can anyone explain what is happening?
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Re: Does my Honeywell Modulation modulate?

Postby marcelr » Thu Jan 14, 2016 9:53 pm

Probably it does.

The setpoint is varying, and your boiler probably responds with a high power output and then shuts of again. Bang-bang control has no varying setpoint, so the controller tells the boiler to modulate. Whether it actually does is another matter.
What's the size of the house you are heating? You have a 45 kW boiler, which is not exactly a small one. It can modulate between 10 and 45 kW. With low heat demands, it will start to oscillate (shut down and switch on, repetitively) to lower its average output power below the 10kW. So, to be sure, if you have an OTGW, you might consider monitoring OT14 (modulation level), and check whether it changes at all.

grtz,

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Re: Does my Honeywell Modulation modulate?

Postby mfranken » Fri Jan 15, 2016 10:38 am

Hi Marcel,

Thanks for the reply, our home is 180m2, built in 1892, high ceilings, but we're not heating most of it, just kitchen and living room. The kitchen has floorheating (vloerverwarming) and is shut off at 18:00.
What's Bang-bang control?

The log for OT14 (same day as previous Control Point log):
Screen Shot 2016-01-15 at 10.26.28.png
OT14
Screen Shot 2016-01-15 at 10.26.28.png (223.51 KiB) Viewed 3595 times


The log for OT17 (same day as previous Control Point log):
Screen Shot 2016-01-15 at 10.26.01.png
OT17
Screen Shot 2016-01-15 at 10.26.01.png (219.65 KiB) Viewed 3595 times


groet,
Michael
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Re: Does my Honeywell Modulation modulate?

Postby marcelr » Sat Jan 16, 2016 1:53 pm

It's modulating allright, but also oscillating a lot. It means that currently you only need a moderate power output from your boiler (less than power at minimum modulation level).

What's Bang-bang control?


A.K.A. on-off control. You set a room temperature setpoint (which has some tolerance or dead-band set inside the controller), and the controller switches the boiler to max power when the temperature is below setpoint-tolerance, and switch it off again when the temperature is above setpoint + tolerance.
Was used in most boilers before modulating control became the standard.

grtz,

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Re: Does my Honeywell Modulation modulate?

Postby Edwin2008 » Sun Jan 17, 2016 7:12 pm

Try to turn open all radiators. That way it would pass the minimum of 10kw. If it is then regulating normally you're heating demand is lower than the min power out of heater.
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Re: Does my Honeywell Modulation modulate?

Postby mo046 » Mon Jan 18, 2016 12:41 pm

Your thermostat is requesting a desired boiler temperature and the boiler is modulating the desired power to achieve the boiler setpoint temperature. From the pictures you sent it is working good. The oscillating part between 13:00 and 15:00 h (picture in opening post) is the so-called Low Load control of the thermostat. It means that below a certain modulation level the thermostat switches from a continuous low requirement to a kind of on/off control to maintain the room setpoint. The boiler is switched on about 6 times per hour for several minutes. The boiler temperature setpoint is being set according to the calculated heat loss of the room.
Have a look at the installers manual of the thermostat. You can switch off the low load controll in the settings, and watch the effect on the control.

See also http://gathering.tweakers.net/forum/lis ... es/1619229 and http://gathering.tweakers.net/forum/lis ... es/1535288
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Re: Does my Honeywell Modulation modulate?

Postby mfranken » Wed Jan 20, 2016 9:52 pm

Thanks,

I am starting to understand my setup. I will study the stuff in more detail. Ultimate goal is to understand where I spend my money and whether I am wasting it. Right now we're burning about 25m3 gas per day.

Michael
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Re: Does my Honeywell Modulation modulate?

Postby marcelr » Wed Jan 20, 2016 10:25 pm

One m^3 of natural gas holds app. 10kWh in energy, so your boiler can burn app. 4.5 m^3 per hour, or a bit more than 100m^3 per day, at full power. You using 25m^3 per day is reflected in the percentage modulation level (which is fairly low) and the maximum modulation level graphs. Power output (so also gas consumption) is pretty much linear with modulation level.

grtz,

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