On Sun, 19 Sep 2004 10:38:33 +0100, "Tom"
wrote:


"Andy Hall" wrote in message
.. .
On Sun, 19 Sep 2004 08:32:57 +0100, "Tom"
wrote:
snipped


The flow switch idea does have its uses in that it could be used to
shut down the boiler and pump when the flow reduces. However, the
inexpensive ones with a magnet and reed switch are not very accurate.
You can adjust their effect a bit by putting a bypass around the
valve, but really they are intended for sensing little flow or no
flow. For example I have one for my secondary heating circuit for
the workshop. The pump and controls are in the workshop and I
didn't want any electrical signalling connections to the house. The
workshop circuit is heated via a heat exchanger from the main system
and has a zone valve to allow water from the main system to the
primary side of the exchanger. There is a flow switch in the
secondary side in the house which detects when the pump is running (at
all) and opens the valve. I'm not trying to sense low flow with it.

Much obliged for your detailed reply,

I've been mulling over this flow switch idea and had mused on using it to
shut down the boiler and not the Alpha in the hope that when a TRV next
opened, the Alpha would increase it's flow against the reduced resistance,
the flow switch consequently switching the boiler back on. I assume the
Alpha uses little power when throttled down so to speak.
I realise that this would require careful balancing of the system
perhaps incorporating a permanently connected pressure gauge on the pump
outlet and manual throttling valve(s) to facilitate balancing.
What do you think?

I doubt if you need to make it that complicated. As long as the
boiler output is not hugely larger than the house requirement, simply
using a room thermostat, TRVs and an Alpha should give a good result.

If you get the radiator without the TRV adjusted to the correct
operating point such that the TRVs are not completely closing as the
room thermostat operates, you will get the desired effect.

Another approach would be to get one of the optimising room
thermostats which controls the boiler and prevents temperature
overshoot - e.g. CM67 or TP75. This will give a more controlled
result than a simple thermostat.


..andy

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