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Discuss Extended S plan with 5 channels 2 pumps in the Plumbing Jobs | The Job-board area at Plumbers Forums
I had assumed, from what you said in previous posts, that the upstairs was already piped so it could be a separate zone.Yes, its that layout which has partly dictated using sub-zones. Just went back last night to see if any could be easily changed. Might be able to move the upstairs off the basic zone with some tightly fitted 22mm. Would become like your attached jpg.
I suggest starting at the beginning:
I hope you take into account the reduction in radiator output when the return temperature is reduced. A rad with a 75C flow and 55C return will produce about 80% of the quoted output. So rads have to be upsized by about 25%.You balance rads (with a condensing boiler) by setting the return to 55degC. I do it by gauging the temperature of cold side of the rad by hand. The aim to get the return to the boiler down to 55degC or so.
See CM-Zone CM Zone - Honeywell UK Heating Controlswhy not simplyfy things and use programable trvs...
what you are trying to achieve is bordering on light commercial , if you have room i would install a 54mm loop header in the boiler room with each zone branching off this controlled via individual programmable room stats and zone valves , with the header on its own programmer . this would give a constant temp and control.
I hope you take into account the reduction in radiator output when the return temperature is reduced. A rad with a 75C flow and 55C return will produce about 80% of the quoted output. So rads have to be upsized by about 25%.
Radiators only have to be upsized if their output is too low. The factor is (DTd/DTm)^1.3 where DTd= design temp diff; DTm= manufacurers temp diff which gives (45/50)^1.3= 0.87 ie at a DTd of 45degC the rads would give 13% less heat if reading values from a table based on a DTm of 50degC. This shows why it is so important to do the calcs. At least you know if the system stands a chance of performing.I hope you take into account the reduction in radiator output...
That might be true of commercial installations and large new-build housing developments where the design of the heating installation will be sub-contracted to large H&V companies. But I doubt if many self-employed plumbers or small heating companies would know where to begin.modern rad schedules take into account cooler flow and return rates so no need to do this
Agreed. But isn't that stating the obvious?Radiators only have to be upsized if their output is too low.
Presumably you are referring to the difference between mean radiator temperature and room temperature. It assumes that the actual flow and return temperatures are irrelevant, which is not correct.The factor is (DTd/DTm)^1.3 where DTd= design temp diff; DTm= manufacurers temp diff which gives (45/50)^1.3= 0.87 ie at a DTd of 45degC the rads would give 13% less heat if reading values from a table based on a DTm of 50degC.
Agreed. I didn't want to make the examples too complicated.presuming a room temp of 20 c
If all you are doing is replacing the boiler, there is no requirement to have two zones. TRVs are recommended as the system will be drained down, provided the pipework does not have to be altered.The house is just a large domestic one needing a new boiler. The plumbing has been in place about 17 years, originally with two zones DHW & CH. New building regs specify the CH has to be split into two zones. Two zones is of limited practical use so the idea of sub zones.
Opentherm should be much less expensive than the others. You will need an OT compatible boiler, but then you can use any brand of OT control.I had considered Honeywell's CM-Zone system, programmable trvs, “OpenTherm” and computer controlled lan ideas but all way too expensive.
If all you are doing is replacing the boiler, there is no requirement to have two zones.
The latest Building Regulations Part L1 specifies that in new houses with a total heated living space floor area of over 150m2 the heating circuit must be split into two, fully controlled, separate zones along with the fully controlled hot water zone.