Rattray Head

Lighthouse Cottages, Rattray Head, Aberdeenshire.    www.rattrayhead.net

2400 litre Akvantti oval accumulator tank linked to 49kw Baxi Solo Innova log boiler.

The biomass system provides heating and hot water for a residence and hostel.

The accumulator tank stores the heat energy from the combustion of approximately 80kg of dry hardwood, which is equivalent to two firings of the log boiler.

The tank is ‘charged’ through a Laddomat 21 loading unit, which ensures a high water return temperature to the boiler and enables the tank to be filled from the top downwards with water at 78 ^oC. This results in good stratification or ‘layering’ of the water in the accumulator tank which results in readily available heat and hot water soon after lighting of the boiler.

Domestic hot water for basins, baths and showers is taken directly off the Akvaterm tank through two 70litre/min copper heat exchange coils in series. The hot water has a circulating pump and temperature is controlled by a 28mm thermostatic mixing valve.

Flow temperature in the heating circuit is controlled by a Thermomatic K constant temperature heat regulator which controls a 3 way valve. Part of the return from the heating circuit is re-circulated and mixed with the high temperature water from the top of the accumulator tank to regulate the flow temperature and to reduce the temperature of the water entering the bottom of the tank.

The log boiler is fired by the owner when a gauge at the mid point of the tank reads below 60^oC. It is possible to heat the tank fully to 85^oC after which the Baxi boiler is shut down by an internal thermostat if the combustion cycle is incomplete.  

Photographs were taken before insulation of pipework within the boiler room.