Dry
cycling
is common in boilers operating an On/Off cycle controlled by the
boiler thermostat and occurs when the central heating system is not demanding
any heat. Heated spaces
could be up to temperature or the time clock could have stopped the
circulating pump on the DHW (domestic hot water) system.
There is no useful load for the boiler to meet and in theory it
should stay shut down until the next call for heat.
In
practice however the boiler loses heat from its own outer surfaces, from
flue losses and from circulating losses and when it has cooled even
slightly the thermostat sensing boiler internal water temperature
operates to bring on the burners and raise the temperature again.
This
cycle is often repeated over and over even although there may be no true
demand and therefore no useful export of heat from the boiler.
During
dry cycling the efficiency of the boiler is zero.
Instead
of keeping the boiler permanently at the thermostat setting there is no
reason why it should not be allowed to stand idle until the next demand
for useful heat. It may
cool down significantly but the heat lost will be considerably less than
that incurred through frequent firing and cycling.
Whenever
this situation is found we recommend the M2G fuel saving
system, which has been
evaluated by the Carbon Trust and given ECA (Enhanced Capital Allowance)
approval.
These
units are much more than just simple clockwork timers that you may have
come across before to eliminate dry cycling.
The
logic behind the systems is water temperature intelligence.
A fuel saving unit is required for each boiler and strap on
sensors are attached to flow and return.
An
internal microprocessor collects water temperature values from the flow
and return every ten seconds and averages these readings out every
minute. If the boiler
thermostat or BEMS (Building Energy Management System) calls for heat the M2G will evaluate
whether or not the burner needs to fire at that precise moment.
The M2G will be able to detect the exact type of demand
based on water temperature fall versus time and will fire the burner
when its intelligence instructs it to do so.
The
software parameters for water temperature intelligence are the
result of 1700 on site tests resulting in a database of 69 million water
temperature readings.
The
software also holds in memory the flow and return temperature the last
time the boiler terminated its fire and uses this template for all
future fires combined with the temperature readings every ten seconds.
If
a zone valve opens the return temperature drops and the software will
watch this drop until eventually the boiler terminates that fire and the
M2G will hold in memory the satisfied flow and return water
temperature values as the current system condition.
The
software continually monitors and controls the system through loading
demand temperature variations.
Its
intelligence can never be more than nine seconds old and its
"decision making criteria" can never be more than one minute
old.
In
multi boiler applications installed M2G units are linked together
so that they "talk" to each other passing intelligence
information and boiler activity data from unit to unit.
One
boiler will pass information to other installed boilers relating to when
it has fired and its associated water temperatures.
The
other M2G units will be informed that a boiler has fired and the
non firing boilers through their installed M2G units will closely
monitor the water temperature rise from the burner fire.
If
the fired boiler is unable to raise the water temperature effectively
and efficiently then the next boiler will be allowed to fire to help the
load demand. This induces a
second level of both compensating and sequence control to the boilers.
In
the case of the secondary school cited above a recommendation has
been made that M2G controls should be fitted to the
three boilers. Given annual
gas costs of £27,000, even a modest 10% saving is worth £2,700 per
annum, which against investment of around £3,000 offers payback just
over 1 year.
Now - there is one other very good reason
that I like the M2G - and guys at Sabien who make it. They sell
ethically and therefore it doesn't matter whether you save £100 or
£10,000 with your M2G installation - the price of the unit control -
fully installed - is exactly the same!!!! I like that approach to
sales.
Get in touch to discuss your boiler installation