Re: relay logic for 2-pump wet central heating system
- From: Ed Sirett <ed@xxxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 05 Sep 2006 18:16:21 +0100
On Mon, 04 Sep 2006 16:28:05 +0000, John Stumbles wrote:
[I tried this query on the uk.d-i-y newsgroup without getting a solution.
I'm x-posting it there for info to that group as I hope it may be useful
to others, with followups to s.e.d]
I need to fix up proper controls on a wet (what I think leftpondians call
'hydronic') Central Heating system that has separate pumps driving the
space heating (CH) and water heating (DHW) systems. Each part of the
system has a time switch and thermostat determining when the pump for that
system's hydronic circuit needs to be driven. When the CH or (Boolean-OR)
DHW systems are running the boiler must also run. The boiler has a
'Switched Live' terminal which, when energised, causes it to run.
I know I can do it with 2 relays with their contacts wire-ORed to drive
the boiler Switched-Live:
<pre><tt>
L -----------+--------------------------+-------------+--------------+
| | | |
o | o | o | o |
| CH - programmer - HW | | A | B
o | o | o | o |
| | | |
| | | |
| | +-----------+--+
o | Room o | HW |
| thermo | cylinder |
o | -stat o | 'stat |
| | ----------
| | | SL |
+----+----+ +----+----+ | |
| | | | | boiler |
| ----- | ----- | |
pump (>) | RLA | pump (>) | RLB | | N |
| ----- | ----- ----------
| | | | |
N ------+---------+----------------+---------+---------------------+
However I think I've seen somewhere a single relay solution (but can't
remember where!). The only way I can think of doing it would be to wire
the relay coil between the live terminals of the two pumps which I suppose
would work but seems inelegant.
240V~
L -----------+--------------------------+-----------------------+
| | |
o | o | o |
| CH - programmer - HW | | A
o | o | o |
| | |
| | |
| | |
o | Room o | HW |
| thermo | cylinder |
o | -stat o | 'stat |
| | ----------
| ----- | | SL |
+---------| RLA |----------+ | |
| ----- | | boiler |
| | | |
(>) pump pump (>) | N |
| | ----------
| | |
N -----------+--------------------------+-----------------------+
My MIL's house (built 1982) has a two pump system but the controls are in
'10'/Gravity mode. So the boiler and HW pump is fired from the HW timer
and the CH pump is fired from the timer + wall stat.
When the system packs up (boiler is a Netaheat so it may go for years)
then I'll sort the whole lot out to a modern standard.
I wonder if there is a relay with two coils either of which will
close the contacts?
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html
Gas Fitting Standards Docs here: http://www.makewrite.demon.co.uk/GasFittingStandards
.
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