Anode wrote:
Is there some setup of a wet central heating system that will let radiators
be warm most of the time, and not cycling between over-hot and over-cold, as
mine are now?
At present I have a 15years old gas fired non-modulating boiler with a
pumped, vented, system, controlled by a wall thermostat. The controls on
this system will not avoid radiators that are either on and far too hot, or
off.
Thus the radiators cycle between being much hotter than is needed for just
compensating for heat losses from the rooms, producing unpleasantly hot air
around the radiators, and then cycling to a period of being colder than they
need to be.
Is there any setup that would give me the necessary heat output but in a
more balanced way, so the radiators will be on for longer but at an
appropriately lower temperature, with the period in the cycle when the
radiators are off being correspondingly much reduced?
As the age of the boiler is such that it could well be replaced, what kind
of setup should I be considering?
http://www.pmengineer.com/CDA/Archiv...0000f932a8c0__
Search for other articles on that site by the same author. A modulating
boiler would be the simplest way of achieving what you're after, given
that your boiler may be due for replacement anyway.
The technology exists, but it is little used in the UK bacause our
heating technicians and/or CORGI technicians are mostly clueless about
it.
I have a non-condensing non-modulating boiler. This set-up lends itself
to the use of a thermal store (100 or 150 litres of stored water) so
that the boiler will run for some time in raising the temperature of
the stored water from,say, 60 to 82 degC. If you only had the water in
the system's pipes and radiators, the boiler would rapidly cycle on &
off under part-load conditions , e.g., a 17 kW on/off boiler but the
system only requires 2 or 3 kW of heat.
The flow to the heating system is through a 3-port mixing valve which
modulates around to achieve the required flow rate. The heating
(secondary) pump is downstream of the mixing valve, with a thermistor
temperature sensor downstream of that.
You need to control the return temperature on a non-condensing boiler
because a temperature of 60 degC would corrode the boiler. My set-up
limits the opening of the valve whilst Tr 60 degC, but this only
happens during warm-up from cold.
I got this system working mid-way through 2004/05 winter. Well worth
it. The heating is on all the time. The radiators are usually warm to
hot; you can usually keep your hand on them without needing hospital
treatment. However it can, and does, wind up to the 82 degC full Monty
during cold weather or during warm-up from cold. Heat up is spread over
about 10 minutes and you don't get the usual clicking & tapping of pipe
expansion when the timer or thermostat starts the heating.
Room temperatures are (and this is the important bit) right; not too
cold and never too hot. TRVs on all, but one, radiator. No problems
with TRV whistling noises, because of the modulating flow temperature.
I'd thought I may need a variable speed pump if this was a problem, but
I needn't bother. Disadvantages, it takes up a lot of space relative to
a wall-hung boiler, so not practical if space is tight. Mixing valves &
controllers are expensive.
There was a significant drop in gas consumption, but other energy
conservation work was also going on, so I can't estimate how much was
due to the heating amendments alone
I recently made enquiries about prices for a modulating condensing
Vaillant boiler for someone else. This boiler had an optional extra
electronic gadget & outdoor sensor to malke it a weather compensated
system. When I asked about the price of that gizmo, the man commented
that he'd never sold one before. I was also told by Vaillant that the
flow temperature is set by the outdoor temperature and it doesn't have
the facility to boost this temperature to warm-up from cold. this can
be a problem with basic systems (which is why I asked) .
..