Memorandum from E W Baker
A PAPER ON THE CAUSES OF POOR HEATING STANDARDS
IN THOUSANDS OF BRITISH HOMES, RESULTING IN EXCESSIVE CO2 DISCHARGE
AND HIGH RUNNING COSTS, AND DETAILING THE MEANS OF CURING EXISTING
PROBLEMS AND PREVENTING SUCH PROBLEMS ON FUTURE INSTALLATIONS
A. History. Residential central heating,
mostly with indirect hot water supply began to make a real impact
in Britain in the early 1950s.
B. This was due, in no small measure, to
the fact that a means had been found of manufacturing small, reliable,
low-powered water circulating pumps relatively cheaply. Typical
of such pumps (and among the first) was a range of pumps bearing
the name "Thermopak", manufactured by Sigmund Pumps
Limited who later became Sigmund Pulsometer.
C. The use of such pumps conferred two advantages:
(a) Large diameter pipes (1 inch or 1.25
inch nominal bore) need no longer be used, their place being taken
by half inch or three quarter inch nominal bore pipes, the lower
cost of which frequently offset the cost of the pumps.
(b) These smaller pipes, in themselves quite
unobtrusive, could often be made even less obtrusive because the
installer, in determining their location, no longer had to concern
himself with the need to ensure gravity (thermo-syphonic) circulation.
D. It should be noted that it was the norm
for circulation between boiler and indirect cylinder to remain
thermo-syphonic, principally to ensure constant circulation between
these two irrespective of whether or not the pump was running.
Frequently, one radiator (often in the bathroom) had its pipework
tee'd into the pipework (1 inch or 1.25 inch nominal bore) between
boiler and indirect cylinder.
The reason for this was to provide a "buffer"
in the event of pump stoppage, whether due to failure, a fault
in the electrical supply, or intended stoppage, possibly caused
by clock control or room thermostat.
In such circumstances, a sudden and substantial
reduction in demand in the boiler would be expected to occur,
as a result of pumped circulation ceasing. This would result in
a rise in boiler temperatures, which would be sensed by the thermostat,
which would then shut off the air supply to the solid fuel. (The
system was designed by the BRITISH COAL UTILISATION RESEARCH ASSOCIATIONBCURA).
The cutting off of the air supply would cause the fire to subside,
but it would take a little time, so the excess heat generated
during this period of adjustment had to be absorbed in some wayhence
the gravity arrangement referred to above, and, for many years,
this arrangement was adopted for gas and oil-fired installations.
Indeed, there are those who consider such an arrangement a positive
benefit, as hot water can be obtained in the warmer weather often
in association with a hot bathroom radiator when needed, without
use of the pump or immersion heater.
E. As will be seen from the enclosed table,
there were 15 pumps in the entire Thermopak range. Also shown
is the information required to select a pump, viz:
(a) CAPACITY (Gallons per minuteGPM)
(b) RESISTANCE (FEETHEADft/hdof
(a) is the amount of water the pump
has to pass per minute and is calculated as follows:
(i) Assume a pumped heating load of
48,000 British Thermal Units per hour (Btu/hr) derived from heat
loss calculations and subsequent radiator and pipe sizing.
(ii) Assume also that at maximum flow
temperature (180°F on some appliances; 160°F
on others) the temperature of the pumped water will have dropped
by 20°F by the time it returns to the boiler. (This is
the recognised temperature drop for small bore systems; 30°F
is often used in minibore and microbore systems to keep velocity
downand hence to limit resistance in 6mm and 8mm pipework.)
(iii) From basic physics we know that
1 lb. of water, raised 1°F, requires 1 Btu (ignoring
losses by radiation etc) so it follows that, to deliver 48,000
Btu/hr, the required water poundage per hour will be (48,000 over
20) 1b/hr, because each pound of water will be dropping 20°F
(Not 1°F) in temperature. The result of the above division
is 2,400 lb/hr.
(iv) As a gallon of water weighs 10 lb,
the gallons per hour is (2,400 over 10) = 240.
(v) Dividing 240 by 60 gives us 4 gallons
per minute (GPM.)
(vi) For a 30°F temperature drop,
substitute 30 for 20 in (iii) which will give 1,600 lb/hr = 160
gallons per hour (iv) and 2.67 GPM (v).
(vii) Resistance of the pipework and fittings
is expressed as the equivalent to the pressure necessary to support
a column of water of a given height, so is expressed in feet/head
(ft/hd) of water. It has nothing to do with the height of the
installation and is purely an expression of the resistance created
to the flow of water. For 4 GPM in a small-bore system, it may
be 2.5 to 3 feet, so a CA1-A or CA1-X would be selected, using
the table. For 2.67 GPM, the resistance in minibore or microbore
pipework is likely to be much the same, owing to the lower flow
rate, and hence velocity in the pipework etc., so possibly a CR1-G
or CR1-Y would be selected.
It must be emphasised that the true resistance
can only be determined from tables.
F. All of the above is very basic and, therefore,
is known, or should be known, by any heating engineer, who should
select his pump accordingly.
G. Following the introduction of pumps such
as the Thermopak range was a pump having a far greater output
range. The reduction from maximum output to the required level
being achieved by partially closing a shutter within the pump
on the pressure (or positive) side. This resulted from turning
a knob on the outside of the pump. A spindle passed from the knob
through the pump body to support the shutter, which therefore
rotated with the knob. As time went by, the more sophisticated
method of determining the speed of rotation of the pump's impeller
H. At some stage, which may well have coincided
with the introduction of these variable output pumps, problems
of poor system performance (usually blamed on the boiler) were
I. Solid fuel appliances appear to have
suffered most, not because they are more prone to this problem,
(a) As they are, in the main, manually tended,
the symptoms are more noticeable.
(b) The excessive firing rate tends to distort
front firebars and bottom grates, also with some solid fuels,
produces clinker (the result of fused ash in high iron content
fuels) which, in turn, starves the fuel of air.
J. It has been demonstrated, literally hundreds
of times, that excessive water velocity (EWV) in the boiler causes
inhibited heat transfer from burning fuel to water (IHT) leading
to excessive fuel consumption (EFC) and, of course, excessive
flue gas discharge (EFGD), and, since CO2 and SO3 (the latter
in the case of solid fuel and oil,) are flue gas constituents,
they add, more than they should, to the "greenhouse effect"
and acid rain problem, whilst at the same time producing excessive
heating costs. The hard-earned cash of hundreds of thousandsperhaps
millionsof people is literally going up in smoke. Some
elderly pensioners have not been able to use their central heating
because it is so expensive to run.
The Cause of the problem, therefore, is EWV.
Make it compulsory for the installer to select
the correct pump and turn the selector knob to the correct setting,
following which he must balance the installation, having lit the
There is no short cut to balancing the installation.
It takes time and requires not only patience but also a sensitive
To ensure that the job is done properly he should
fill in a sheet similar to that which is attached, then hand to
the owner, a table which shows, in effect, the end result of his
NB As a point of interest, Code of Practice
requires the installer to commission the installation on completion,
without actually stipulating what the commissioning comprises.
It seems, from observations, that many installers are content
to feel each radiator in turn, thereby satisfying themselves that
circulation is occurring.
That alone is not good enough. Lack of attention
to this detail is a national scandal.
EWV can also produce reversed circulation in
the gravity pipework often necessitating the use of an immersion
heater. If EWV is the only cause of primary flow reversal (and
there are others beyond the scope of this paper) curing EWV will
also dispose of that problem.
Unless these are very carefully installed, so
that the flue gases are fully isolated from the convected warm
air, the two can mix. If the chimney is in poor condition, producing
a weak draught, flue gases can enter the room, which is clearly
a health hazard. If the chimney produces a strong draught, a high
proportion of the warmed air, if not totally isolated from the
flue gases, can be carried up the chimney and not into the room.
This brings in cold air from outside (given adequate ventilation)
which cause the appliances' thermostat to remain open, causing
vast amounts of fuel to be consumed.
Thoroughly smoketest each installation on completion.