Gas & Oil Fired Central Heating

This page is all about boiler fuel saving technology.

Novitherm radiator panels for all wet central systems with radiators are on a separate page - click anywhere here

Lets take a typical example of something we came across very recently (March 2003!).

Three boilers were surveyed as part of an audit of a major secondary school for one of the Scottish Councils.

The boilers were observed to fire up when Return flow reached 165^oF or 74^oC, which represented a very small drop from the output temperature of 170^oF and is indicative of a phenomenon known as ‘dry cycling’.

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 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 Multi-Save 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 call for heat the Multi-Save unit will evaluate whether or not the burner needs to fire at that precise moment.  The Multi-Save 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 Multi-Save 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 Multi-Save 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 Multi-Save units will be informed that a boiler has fired and the non firing boilers through their installed Multi-Save 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 Multi-Save 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.

A fully automatic, self-adjusting, maintenance free, electronic central heating management system designed for both domestic and commercial properties with conventional boiler plant.

It can cut fuel consumption by up to 50% on any system controlled by conventional timer, room and boiler thermostats and radiator valves.  BoilerSaver will operate on any fuel system (gas, oil or lpg) and will work with combi boilers. 

BoilerSaver incorporates a microprocessor that receives information from remote sensors to constantly monitor the temperature inside and outside the building and also the temperature of the hot water on both flow and return. 

The optimising and compensating circuits within BoilerSaver enables the “U-value” of the building to be calculated and this is incorporated into the intelligent control of the boiler to maintain even room temperatures and ensure that hot water is always available.

Basically BoilerSaver ensures that the burners are only activated when strictly necessary reducing fuel consumption whilst maintaining heating services.  The unit can be isolated by one push of a bypass facility button for maintenance purposes.  

Although we can’t prove it we sincerely believe that fitment of BoilerSaver will extend the life of the boiler and pump by reducing unnecessary firing.  There is also a built in pump operation (20 minutes in every 24 hours) for those days when no heating services are required to clear the system of sediment, scale and rust.

The Concept  

Conventional central heating systems are controlled by a combination of boiler thermostat, hot water cylinder stat., room thermostats and TRV’s (radiator valves).

In order to maintain the temperature of hot water in the boiler within the limits of the internal boiler stat the burners keep firing on and off – even when there is no demand on the system – this is called DRY CYCLING.

When the room stat calls for heat residual water in the boiler is circulated to the radiators.  As the water returning to the boiler is now cooler than the boiler stat lower limit the burners are fired up to heat the circulating water.   When the room stat is satisfied the pump switches off and the water stops circulating.

 The boiler continues to fire and water which is no longer being circulated goes on heating until the boiler stat upper limit is reached – a process called burn-on.  This period is often elongated by closed loops round the pump circuit.

Traditionally the timer control is set to bring on heating to warm the property in readiness for occupants rising from bed of arriving in to work, usually at least an hour prior to first occupancy.  Up until now only very sophisticated and of course expensive control systems have incorporated weather-compensating technology to automatically change the operating patterns in response to changing climate.

The following are examples of where conventional control can prove wasteful and where BoilerSaver can eliminate the losses:

Burn-On  -  each time the room thermostat of a central heating system which is not fully pumped stops calling for heat the boiler keeps firing until its own internal high limit stat is satisfied – 2-5% saving