Is this unique to Alpha?

[Harry Bloomfield]

Your system sounds good, but I'm not quite with you there Harry. I wasn't thinking of controlling room temperature by the boiler control-stat, just reducing the flow temperature to increase condensation. But still hot enough to warm the house until the roomstat is satisfied (as currently).

And that was what I was discussing, and explaining that I attempted to set up something quite similar.

I went on to explain that in my experiment, it failed, but I went onto a much more capable design of system.

BTW my control-stat is a filled system (I think is the term for it) not bimetallic. Don't know if it's any better for hysteresis though.

The simple way to find out, it to clamp it on a hot pipe, and test it by turning the dial - see how far you need to turn it, between it clicking on, and clicking off a few times.

 

[fixitflav]

I went on to explain that in my experiment, it failed, but I went onto a much more capable design of system.

OK, I thought you meant you only cured it with a new boiler.

The simple way to find out, it to clamp it on a hot pipe, and test it by turning the dial - see how far you need to turn it, between it clicking on, and clicking off a few times.

I could if it were a problem, but it isn't, it works fine, the boiler only fires on/off via the control-stat in HW (only) mode, never in CH. And I haven't got a bimetallic stat to compare it with!

 

[fixitflav]

It reads maybe a little out of date,

Not only that, some of it is nonsense! It says
"S&Y plan systems are a longstanding barrier to condensing boilers actually condensing"

Condensation can happen if there is adequate rad area relative to boiler output, if there isn’t it can’t be blamed on the S&Y plan. No doubt condensation can be enhanced by weather comp, but that can be fitted (or retrofitted) to S&Y plan.

S &Y plans were introduced in the 1970s or 80s presumably as with W-plan simultaneous CH and HW isn’t possible. I never found that to be a problem, but it’s interesting that I’ve not seen any suggestion, on this forum or elsewhere, to avoid weather comp due to it incorporating PDHW.

 

[Mister Banks]

Not only that, some of it is nonsense! It says
"S&Y plan systems are a longstanding barrier to condensing boilers actually condensing"

Condensation can happen if there is adequate rad area relative to boiler output, if there isn’t it can’t be blamed on the S&Y plan. No doubt condensation can be enhanced by weather comp, but that can be fitted (or retrofitted) to S&Y plan.

S &Y plans were introduced in the 1970s or 80s presumably as with W-plan simultaneous CH and HW isn’t possible. I never found that to be a problem, but it’s interesting that I’ve not seen any suggestion, on this forum or elsewhere, to avoid weather comp due to it incorporating PDHW.

Assuming the boiler temp is set at 65c then when heating the hot water cylinder the return temp will be around 60c so the boiler will not be condensing until the hot water cylinder reaches temp. Thats a barrier to condensing boilers condensing.

At the moment my system is setup to heat HW and CH at the same time which results in the boiler not condensing until HW is satisfied (thats about 1.5hrs). I'm going to experiment having the HW come on outside of heating hours and see if that effects heat up time and gas consumption.

 

[fixitflav]

Assuming the boiler temp is set at 65c then when heating the hot water cylinder the return temp will be around 60c so the boiler will not be condensing until the hot water cylinder reaches temp. Thats a barrier to condensing boilers condensing.

IMO that's normal. Even with weather comp, in HW mode the flow temperature must be set high enough to do the job, so condensation unlikely.

At the moment my system is setup to heat HW and CH at the same time which results in the boiler not condensing until HW is satisfied (thats about 1.5hrs).

Depending on your boiler output and rad area, I expect in HW + CH mode the flow temperature does not reach the control-stat setting, and if it's much lower it's not surprising it takes a long time to heat the cylinder. But at least there might be some condensation!

I'm going to experiment having the HW come on outside of heating hours and see if that effects heat up time and gas consumption.

Worth a try. It should heat up the cylinder much quicker. You could also raise the control-stat setting. That will speed it up, and I doubt it will affect condensation in CH mode as if it's like mine it doesn't get there anyway. Though that might be worth checking, my control-stat is at about 70°C.

 

[Harry Bloomfield]

Condensation can happen if there is adequate rad area relative to boiler output, if there isn’t it can’t be blamed on the S&Y plan. No doubt condensation can be enhanced by weather comp, but that can be fitted (or retrofitted) to S&Y plan.

Well, I would suggest the main issue, is a single boiler output temperature. It has to be hotter than the 60C cylinder stat, and will usually be the default temperature for CH.

A better scheme, is where there are two boiler flow temperatures, CH and HW, but not available with a standard, original Y-plan. Only once the ebus type schemes came along, was the boiler aware of what it was producing it's heat to serve, was it able to use two separate flow temperatures. The icing on the cake, for efficiency, is where the boiler is controlled and modulated, knowing not only that there is a demand, but how large a demand for heat is needed. Basically knowing the present actual temperature, knowing the desired, and having an idea of likely heat loss, by knowing the outside temperature.

 

[fixitflav]

Well, I would suggest the main issue, is a single boiler output temperature. It has to be hotter than the 60C cylinder stat, and will usually be the default temperature for CH.

A better scheme, is where there are two boiler flow temperatures, CH and HW, but not available with a standard, original Y-plan. Only once the ebus type schemes came along, was the boiler aware of what it was producing it's heat to serve, was it able to use two separate flow temperatures. The icing on the cake, for efficiency, is where the boiler is controlled and modulated, knowing not only that there is a demand, but how large a demand for heat is needed. Basically knowing the present actual temperature, knowing the desired, and having an idea of likely heat loss, by knowing the outside temperature.

That's right, preset temperatures for HW and CH mode better than nothing, better still in theory is weather comp, giving variable CH temperature. If it's clever enough to compare actual room temperature with setpoint, and modulate accordingly, a bonus.
Weather comp can be retrofitted to S or Y, but wired for PDHW, so mid-position not used (Y-plan) and both valves don't open at same time (S-plan)

 

[Mister Banks]

Well, I would suggest the main issue, is a single boiler output temperature. It has to be hotter than the 60C cylinder stat, and will usually be the default temperature for CH.

A better scheme, is where there are two boiler flow temperatures, CH and HW, but not available with a standard, original Y-plan. Only once the ebus type schemes came along, was the boiler aware of what it was producing it's heat to serve, was it able to use two separate flow temperatures. The icing on the cake, for efficiency, is where the boiler is controlled and modulated, knowing not only that there is a demand, but how large a demand for heat is needed. Basically knowing the present actual temperature, knowing the desired, and having an idea of likely heat loss, by knowing the outside temperature.

On my S plan system with condensing system boiler I have the boiler temp set at 65c and the HW cylinder at 55c. When calling for heat (CH) I get return temps of 45-50c but when CH is off and the HW calls for heat I get a return temp of about 60c.

 

[Harry Bloomfield]

On my S plan system with condensing system boiler I have the boiler temp set at 65c and the HW cylinder at 55c. When calling for heat (CH) I get return temps of 45-50c but when CH is off and the HW calls for heat I get a return temp of about 60c.

I think the return at 60C, when servicing the HW, is unavoidable, my own return is similar, though for HW my boiler flow is set higher, as is the cylinder temperature.