best room thermostat

[gasafengineer]

Typical of the arrogance on this forum, never heard so much BS & he's supposedly a heating engineer? , D-hailsham has explained it to you in black & white , what don't you understand?

Instead of googling for info take head of what Iannian is telling you.

 

[D_Hailsham]

I've obviously started a heated debate here.

No, you didn't start it.

am I correct that a Honeywell digital is probably the best to get ?

Yes.

 

[D_Hailsham]

The "TPI" controllers referred to are compatible with the WB Ri boiler range, but they do not modulate the flow temperature. They actually switch the boiler on and off quite frequently even when the room temperature is below the desired temperature, in an attempt to reduce the flow temperature. This results in the boiler firing at full power for short periods as it tries to do the exact opposite, which is maintain the full flow temperature.

I have also been concerned about this for exactly the same reasons. On a non-modulating boiler the effect of firing the boiler for a reducing proportion of a fixed time period, e.g from running full out to running 1 minute in 10, is to reduce the flow temperature as the proportion gets smaller.

Boilers need controls which will modulate the output according to external requirements. A modulating boiler with an on-off stat, even a TPI type, is effectively nothing more than a boiler with automatic range rating.

 

[mysteryman]

The best control is weather compensation - it keeps the boiler condensing by modulating the flow temperature.

 

[D_Hailsham]

The best control is weather compensation - it keeps the boiler condensing by modulating the flow temperature.

Are you trying to start another argument/discussion?

 

[mysteryman]

There is no argument!

 

[D_Hailsham]

 

[gasafengineer]

I have also been concerned about this for exactly the same reasons. On a non-modulating boiler the effect of firing the boiler for a reducing proportion of a fixed time period, e.g from running full out to running 1 minute in 10, is to reduce the flow temperature as the proportion gets smaller.

Problem with this approach is back end corrosion , simply shutting boiler down before return temp has reached critical set point (55k) will lead to condensation issue within flue/heat exchanger. , unavoidable @ initial start up but detrimental for prolonged periods.

 

[DP]

You will not get the room temperature rising above the required setting with these temperatures as they take into account the fact that the rads continue to give of heat. It's called TPI control

Interesting reading indeed. Initial demand leads to boiler staying on. As target temperature nears, thermostat starts 'pulse width modulation' (term that sits best in my mind)

DH, a room thermostat controls a motorised valve. Are you suggesting TPI control will open/ close a motorised valve to maintain control?

My oven has pulse width modulation for precise temperature control so my ginger biscuits come out perfect every time. Heating systems do not need to be + or - 0.1 degree C. In fact 1 degree Centigrate over or under will not even be noticed by the occupants in a house unless the woman in the house is going through a change of life (in which case she will put an axe through the roomstat regardless of it being digital, mechanical or steam driven even). The swing gets big if mechanical roomstats are wires incorrectly (rest assured plenty are).

When I moved to my current house, about five and a half years ago it had the traditional electro-mechanical stat with anticipator. The first years gas consumptions was about 30,000kWh. I then installed a Honeywell CM67 followed by a CM927. The consumption has gone down to about 24,000kWh; a reduction of 20%.

I would be inclined to believe there is a reduction in fuel useage but comparison is likely to be flawed. DH, are you running the CM927 in the manner that a programmer plus old clockwork stat functioned i.e. timer switches on and stat then waits till desired ambient temperature achieved instead of six changes of temperature to suit lifestyle. I am not splitting hair, just questioning the figures. If it is any consolation, I have two progstats to control 2 heating zones giving six variable temperatures in each zone...

 

[gasafengineer]

unless the woman in the house is going through a change of life (in which case she will put an axe through the roomstat regardless of it being digital, mechanical or steam driven even)

, why do think i reverted back to a cheap £12 stat.

 

[D_Hailsham]

Interesting reading indeed. Initial demand leads to boiler staying on. As target temperature nears, thermostat starts 'pulse width modulation' (term that sits best in my mind)

PWM describes it exactly

DH, a room thermostat controls a motorised valve. Are you suggesting TPI control will open/ close a motorised valve to maintain control?

That's what happens. Danfoss recommend turning TPI off if you have motorized valves indirectly controlling the boiler as he delay in opening and closing the valve could mean that the actual firing time is shorter than that requested by the TPI controller. Honeywell don't have anything to say about this.

I would be inclined to believe there is a reduction in fuel usage but comparison is likely to be flawed. DH, are you running the CM927 in the manner that a programmer plus old clockwork stat functioned i.e. timer switches on and stat then waits till desired ambient temperature achieved instead of six changes of temperature to suit lifestyle.

Our lifestyle, since moving into the house, is that of a retired couple, i.e. home all day.
The first and last times are set for initial wake up (0630, 20C) and bed time (2300, 5C)
The four middle settings are all set to 21C, starting at 8am, at evenly spaced times throughout the day. This means that if someone feels a bit cold and turns the stat up a degree or so, it will automatically revert to the standard 21C a few hours later.

 

[D_Hailsham]

Problem with this approach is back end corrosion , simply shutting boiler down before return temp has reached critical set point (55k) will lead to condensation issue within flue/heat exchanger. , unavoidable @ initial start up but detrimental for prolonged periods.

Isn't this more of a problem for boilers with cast iron heat exchangers?

I was concerned about this for my Apollo Fanfare until I learned that the heat exchanger is made of copper specially coated to prevent corrosion.

 

[gasafengineer]

Problem with this approach is back end corrosion , simply shutting boiler down before return temp has reached critical set point (55k) will lead to condensation issue within flue/heat exchanger. , unavoidable @ initial start up but detrimental for prolonged periods.

Isn't this more of a problem for boilers with cast iron heat exchangers?

I was concerned about this for my Apollo Fanfare until I learned that the heat exchanger is made of copper specially coated to prevent corrosion.

Ever seen the first potterton suprima HE boiler , absolute disaster , wasn't so much the cast iron heat exchanger but the combustion chamber would rot , burners would rust along with pin holes through the combustion chamber floor , don't forget these boilers were designed for condensing , the apollo fanfare wouldn't 'fare' to well either when operated @ part load. , not forgetting the acidity of condensate eating through copper Hex.

 

[mysteryman]

PWM or rapid on-off control is OK for electric heating, but it is not a good way to control a gas burner. Gas burners should run in long carefully regulated burns. Boilers now have modulating control, and premix burners typically give their best thermal efficiency at about 30% of full output. It is simple enough with modern electronics to vary the set flow temperature continuously to meet varying demands. Heat demand varies inversely with outside temperature - heat loss is more in colder weather. This simple and effective form of control has the additional benefit of making the boiler condense for as much of the time as possible. This uses minimum gas whilst maintaining comfort. The method has been the norm on the Continent for several decades now. It is called weather compensation.

 

[D_Hailsham]

the apollo fanfare wouldn't 'fare' to well either when operated @ part load. , not forgetting the acidity of condensate eating through copper Hex.

I will be finding out fairly soon what the effect has been on the hex as the boiler is being swapped out for a shiny new one.

If TPI causes so many problems to boilers, why are all the digital stats made by Honeywell equipped with TPI? The only stat they make which does not have TPI is the T6360. Presumably the "problems" are more theoretical than real.