Minibems biomass heat network control delivers outstanding operational efficiency

Fenton Farm Cottages, Haverfordwest, Pembrokeshire

Fenton farm is located within the Pembrokeshire Coast National Park and provides self-catering holiday cottages to the public.

The site consists of a main farmhouse with ten self-contained cottages, which was previously provided heating and hot water from an inefficient oil boiler. In 2015 the existing plant was replaced with a 320kW biomass boiler and a Minibems network control and monitoring solution was implemented.

The Minibems biomass heat network installed in October 2015 was to achieve the following operating objectives:

1. Control and reduce flow temperatures using weather compensation and smart heat requests

2. Control and reduce return temperatures and thus increase temperature difference

These objectives were achieved and resulted in increasing the temperature difference from the industry standard of under 10°C to 31°C on the buffer tank and boiler thus reducing boiler cycling, fuel usage, equipment maintenance and prolonged boiler life.

The plant room of Fenton Farm consists of the following three software modules; Turbomat 320 Boiler, buffer tank and an export circuit. The export circuit supplies district heat to the farmhouse and ten cottages which each have a Minibems heat interface unit (HIU) installed.

 

Minibems performance

Control and reduce return temperatures & thus increase temperature difference

The excellent temperature difference observed in the plant room is due to Minibems controlled heat interface units (HIU’s), this control ensures a low return temperature, hence a high temperature difference. The below graph demonstrates Fenton Farm’s biomass boiler performance over a period of two days.

The green line in the graph (‘segment 1’) is the temperature of the top of the buffer. When the blue line (‘Want Heat’) is 1, the buffer has got too cold and the Minibems software is telling the boiler to charge the buffer. The Minibems software runs the boiler until the entire buffer is charged; thus at the end of charging the boiler return temperature is high. When the buffer is charged, the blue line (‘Want Heat’) is set to 0 and the boiler turns off.

 

Control and reduce return temperatures & thus increase temperature difference

The below table summarises the key information from the graph:

 

Control and reduce flow temperatures using weather compensation and smart heat requests

The below graph of the export network at Fenton Farm, illustrates Minibems variable flow temperature control in action:

Minibems varies the ‘export flow temp’ from the plant room based on weather compensation and what downstream equipment is currently running. The close correlation between the ‘requested flow temp’ and the ‘export flow temp’ indicates that set points are well met. The difference between the ‘buffer temp’ and the ‘export flow temp’ illustrates the efficiency savings Minibems provides; on average flow temp is reduced by 14°C, increasing the time until the boiler is turned on.

The site is performing very efficiently with good temperature difference values, low boiler return temperatures, long boiler burn time and a small number of daily boiler cycles. The result of this will be to greatly prolong boiler life, reduce fuel consumption and reduce equipment wear and running costs.

In summary it is estimated that the use of flow and temperature control with weather compensation is providing fuel savings of 30% to 50% in comparison to a typical constant flow and temperature heat network.

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