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Invention increases boiler efficiency

Posted: 06/03/2008

An innovative add on designed to make condensing boilers even more efficient has been launched by UK boiler manufacturer, Ravenheat. Named Energycatcher, the invention recycles the heat in a domestic gas boiler’s exhaust fumes and uses it to preheat and store hot water for use in the home.

The specially designed heat exchanger reduces the temperature of a modern condensing (Band A) boiler’s outlet flue gases, normally about 60°C, down to lower than 20°C. The manufacturer claims that virtually all the heat is recovered and recycled into the home's hot water system. The device can be retrofitted to most existing boilers (subject to manufacturer’s approval).

The heat exchanger technology is said to make energy savings of up to 90 per cent possible on domestic hot water during winter months and cut overall carbon emissions by 7.5%. The device is also compatible with most solar systems and enhances their effectiveness.

According to the company's managing director, Louis Pickersgill, “The heat exchanger cuts heating bills, carbon dioxide and other noxious gas emissions. It also reduces the amount of mains water used and associated environmental impact and carbon saving from the supply. The water heated moves by convection so no additional power is needed".

The principle of preheating water is as old as leaving a kettle on a warm open stove before boiling it. Modern condensing boilers work well to deliver hot water and central heating to the home, but the outlet exhaust fumes are still hot enough for it to cause water vapour (mistaken by many as smoke) a sure sign of wasted heat.

Now, instead of being wasted into the open air, the heat from boiler’s exhaust gas, at a temperature of about 60°C, can flow over the heat exchanger and be transferred to the incoming cold water. The now warmer water moves under convection into a storage tank.

The exhaust gases, considerably cooler, then vent to the atmosphere. When the boiler receives a demand for hot water, it draws water from the storage tank and at the same time preheats cold mains inlet water via the exhaust fumes. If the water is hot enough the boiler need not fire or can operate at reduced power. In other scenarios, in which it needs to fire, the increase in temperature required is greatly reduced compared to unadapted systems

Carbon dioxide emissions are reduced as are other gases, such as Nox. The temperature of the flue gas is too low to sustain the water vapour produced as a by-product during boiler combustion. The water vapour therefore condenses and is discharged in its liquid form, retaining further gases.

Ravenheat has carried out extensive field trials of the Energycatcher system in the UK and elsewhere in Europe. These include housing associations in the UK and the Ballymun Regeneration project in Dublin. All of the tests have shown significant savings on gas bills and reduction in carbon emissions - case studies are available on request from www.energycatcher.co.uk.

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