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Author Topic: Change from gravity to pumped?  (Read 662 times)
Jr. Member
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« on: July 08, 2018, 11:24:47 AM »


I've been thinking about this for a while now and I can't decide if having a pumped system would be better or not.

Currently I have a hunter herald 80b on a 28mm gravity circuit feeding / heating a 475ltr store. Once the store hits 67c the central heating kicks in and continues to pump until the water in the store hits 55c.  This is working well for us and heats 280m quite nicely. Depending on the starting tank temp the initial CH firing takes the longest to achieve with each subsequent firing becomes quicker ( assuming I keep the fire loaded up) as the trvs shut down the radiators and the heat requirement becomes less.

The stove sits in a room that is 10m *6m and has a minimum height of 3.5m and a Max of 6m, so it needs all of its theoretical 9kw to the room output. This coupled with the fact that the theoretical total radiator output is greater than the 12kw output of the water side means that the fire is rarely just ticking over.

Whilst our winters are slightly milder than in the UK the house sits pretty much at around 18/19c. Chilly for some I know but perfect for us.

Taking all that into account, it takes about an hour to an hour and a halve from firing up the stove to be able to say, "ah yes, that's better the heating is on " and start feeling the place warm up.

Whilst not impossible, I could break into the CH circuit and pump directly, which would decrease the amount of water being heated. This would very much cause consternation within the household as all the decorating is now complete. So it would need to be a spectacular result in reducing heat up times for this to be a solution!

Would fitting a laddomatt or something similar significantly decrease that initial warm up time?



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« Reply #1 on: July 08, 2018, 03:12:06 PM »

Not an answer to your question, but in case of interest:

We have cast-iron skirting radiators, nothing zoned at all.  Its possible to turn individual ones off, but that's about it.

We have a 5000L accumulator, and a log batch-burn boiler.  The boiler is sized sized bang-on for us, which turns out to be handy ...

In the early days I did all sorts of stuff with temperature sensors, and we had a go with a thermostat in the hall ...

... now we know that if we do a "burn" it will take around X-hours and heat the tanks from 45C (lower is useless for our Rads) to 90C (the point at which boiler damps down automatically, and then in effect smoulders-the-wood.) The boiler will achieve this with the radiators' pump on too.

Our building is relatively well insulated and has good thermal mass / density.

So now we don't bother with any thermostat / sensors etc. we just light the boiler and put radiators' pump on.  After X-hours the boiler burn finishes, the radiator pump timer goes off and the accumulator is at 90C

Accumulator at 90C is what we need to have enough heat, tomorrow morning, to heat the house until we light the boiler again, on an averagely cold winter day (on a once-a-decade very-cold Winters day we will light the boiler twice a day).

We played around with 50% fill the boiler, in the Autumn and Spring, but there is some "overhead" to "doing a burn", so instead we found it worked better to start the Autumn with two-burns-a-week, and then move up to every other day. The net effect is that we overheat the house on those days, during a full burn, but that basically just heats the fabric of the building more, and means that we need no heat the following morning, use up the accumulator during the evening of Day Two and light it again on Day Three. If Day Two is a bit colder, say Water is down to 60-65C, then we might do a 50% burn.  That gets us between the early season twice-a-week and the late Autumn every-other-day.

So basically its burn, store and adjust by using the timed length of pump run, rather than any sort of temperature control per se. I have a lag, from lighting boiler, of a good couple of hours, but provided the accumulator is over 40C then it provides "low grade heat" (at a time when room temperature is falling, but not already cold), and by the time, later in the evening, when the heat loss is exceeding the low-grade heat input the boiler has got hot and taken over the load, so the rads temperature is 60C+ and later into the evening water to the rads is 80C+.

Not sure a Google Nest Thermostat has that ability though Smiley
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