My Viessman boiler journey

[marshian]

26 minutes ago, John Carroll said:

Wonder was it cycling due to the minimum boiler output being more than the rad demand or due to a roomstat switching it off when room temperature reached its SP.

Former yes - Latter no

 

TRV don’t intervene on majority of rooms - WC flow temp and elevated room targets that cannot be hit with WC flow temp and heat loss of the rooms. So cycling was down to the house/rads not getting rid of the energy in the circuit.

 

was first warm night 8.5 deg C so boiler flow temp would have been 26-27 deg C max and heat loss of the house maybe around 1.6 kWh (so on that basis I’d expect the boiler to fire for 15mins in the hour

 

minus temps over night and it’s firing 45 mins in the hour

 

the 9 cycles might be a one off or I may need to tweak the curve a bit more to align (lower) the flow temps at higher OAT 

[John Carroll]

1 hour ago, marshian said:

Former yes - Latter no

 

TRV don’t intervene on majority of rooms - WC flow temp and elevated room targets that cannot be hit with WC flow temp and heat loss of the rooms. So cycling was down to the house/rads not getting rid of the energy in the circuit.

 

was first warm night 8.5 deg C so boiler flow temp would have been 26-27 deg C max and heat loss of the house maybe around 1.6 kWh (so on that basis I’d expect the boiler to fire for 15mins in the hour

 

minus temps over night and it’s firing 45 mins in the hour

 

the 9 cycles might be a one off or I may need to tweak the curve a bit more to align (lower) the flow temps at higher OAT 

Do you know the total T50 rated output of those 9 rads and what room/house temp you are aiming for.

[marshian]

26 minutes ago, John Carroll said:

Do you know the total T50 rated output of those 9 rads and what room/house temp you are aiming for.

 

Yes I do - actually every damn rad dimensions and T50 output is in a spreadsheet

 

I used it when I was working with the heat loss v rad output at various flow temps to work out where I needed to target the flow temp for the weather compensation at -2.4 Deg OAT

 

Some of the individual rads I've tweaked the flow rates from where it was but overall system balance has remained the same.

 

Front Hall, Toilet, Utility and Study remain on scheduled heating (heat loos of those rooms is a lot more because 3 external walls all on north facing side of the house

 

All other rooms 24/7

 

Heat loss is overstated due to the software wanting higher ACH than I was comfortable with.....

 

I also utterly badgered the dining room calc gave it a vaulted ceiling with no heated room above - Ooops

 

True heat loss is absolute max 4.0kWh at -2.4 Deg C OAT (probably 3.6 kWh based on actual energy used if my monitoring is more accurate)

 

Rooms & Rads.xlsx

 

Edited Friday at 17:00 by marshian
Forgot target room temps

[John Carroll]

I just used 12 rads output (ignored the ones in yellow) and calculated for a 9 rad output, I reckon that the 12 rads have a total T50 rating of ~ 17.6kW so 9 rads = 13.21kW (T50), the required max output seems to be ~ 4.77kW for those 12 rads = ~ 3.58kW for 9 rads.

 

The required flowrate (for 9 rads) is ~ 0.475m3/hr, this then results in

flowtemp/returntemp/dT/rads output. 41.55C/35.1C/6.48C/3.58kW

At a (your) flowrate of 0.4m3/hr and flowtemp of 28.9C gives (my calcs)

flowtemp/returntemp/dT/rads output. 28.9C/26.42C/2.48C/1.15kW

Your data gave a calculated flowrate of only 0.06m3/hr (15% of 0.4m3/hr)

flowtemp/returntemp/dT/rads output. 28.9C/20.4C/8.5C/0.6kW

clearly something amiss somewhere?

 

 

 

 

WC Rooms & Rads Mars Rev1.xlsx