Select Committee on Environmental Audit Minutes of Evidence


Memorandum from E W Baker



  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 ASSOCIATION—BCURA). 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 way—hence 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 minute—GPM)

    (b)  RESISTANCE (FEETHEAD—ft/hd—of water)

      (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 down—and 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 was adopted.

  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 noticed.

  I.  Solid fuel appliances appear to have suffered most, not because they are more prone to this problem, but because:

    (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 thousands—perhaps millions—of 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 boiler.

  There is no short cut to balancing the installation. It takes time and requires not only patience but also a sensitive pipe thermometer.

  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 labours.

  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.

  The Solution:

  Thoroughly smoketest each installation on completion.

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Prepared 16 March 2001