System layout
I have followed these threads with great interest - and some confusion. I would be interested to hear other users' observations on the following:
I have a 1963-built 3-bed bungalow which I have refurbished/extended to create a partially open-plan ground floor layout with one bedroom and study plus a small en-suite bedroom on the first floor (the loft). The total floor area is 170 m2 and work was completed in 2011.
The heating is based on the pre-existing (pre-2008) Worcester Bosch Junior 14i combi used as a system boiler supplying three zones of heating and 210 litre HW storage.
The heating is zoned with Tado wired stats in the open plan SITTING ROOM (includes the dining area, kitchen and utility), STUDY (including garden room), and main BEDROOM (plus first-floor bedroom). The DHW is controlled separately and runs for an hour at night and an hour during the day. Each zone has one radiator without a TRV, but some dumb TRVs were installed for limiting purposes (although careful radiator sizing and balancing seem to do the job). TRVs on the first floor are set to a minimum and never fully open.
Today it's zero degrees outside and all heating zones are calling - rising in 0.5 deg increments through the day from 20 deg at 7:00 am to a max of 22 deg (SITTING ROOM). The setback temperature (10:00 pm to 7:00 am) is 17.5 deg. The boiler temperature is set to 3.5 on the dial, marked from frost (0) to max (7). The boiler hums along quietly (nearly silent some of the time) almost constantly with a dT of 12 deg (58-46).
One of my concerns is that the most distant radiator has a flow temperature up to 10 degrees below boiler temp.
Comments
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A temperature drop of 10°C in the flow pipe suggests the water is flowing very slowly in that section of pipe. This could be due to an obstruction in the pipe, but it's most likely due to too much water flowing through the other radiators on the circuit.
You can rule out a blockage by completely closing the TRVs on one or two radiators. This should encourage flow through the last radiator.
If the cause is lack of flow to the radiator then you should close the lock shields slightly on the other radiators. Less water will flow through those radiators allowing more to flow through the index radiator. Ultimately you may need to increase the pump speed to increase the overall flow through the circuit, but I'd try to avoid this. Increasing the pump speed may decrease your dT and generate more noise in the radiators.
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Thank you for your comments.
My most distant radiator is one of just four on the most distant circuit. The other three are already slightly throttled as part of the balancing, causing a higher dT on those rads. My concern is that the whole group have relatively low flow temperatures due to their distance from the boiler at the opposite end of the house. I believe a lack of insulation is a significant factor. I intend to investigate.
Correct me if I am wrong, but it seems to me that, for a given circuit, if the dT of the rads is (say) equal to the dT of the supplying pipework, then half of the energy flowing in that circuit has been lost via the pipework. That is a serious matter!
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Do you know the pipe diameters for the pipework supplying the 4 radiators? And the combined heat output for all four radiators. In theory 15mm copper can deliver over 12KW of heat, but in practice it's best to plan for a maximum of 6KW for 15mm pipe. The actual value depends on the dT and the flow rate.
Also, you need to balance each heating circuit as well as the individual radiators. With multiple TRVs and zones opening and closing it helps to use a proportional speed pump, rather than a fixed speed pump. With fixed speed you may not have enough flow when too many valves are open, but noisy radiators when many valves are closed.
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@GrilledCheese2 Thanks again for your comments. You were spot on regarding balancing the zones. I gave some attention to that and now have all zones with a similar boiler to rad dT of about 4 or 5 deg. Given that the dTs across the rads are not much larger, I still worry that the pipework is dumping quite a bit of heat. The pipes are mostly plastic, btw.
It was minus 5 this morning so with boiler output at 60 deg the system was struggling but as the morning wears on we have massive solar gains on the main living areas so measurement/control is a nightmare. In the circumstances, the Tado wired stats do pretty well.
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