Reheat delivers significant efficiencies for the National Trust's biomass and district heating system at historical site, Lyme Park

• 87% distribution efficiency achieved, reducing distribution losses from 54% to 13%
• 85% reduction in electrical consumption as a result of Variable Speed Drives solution
• 20% increase in biomass boiler efficiency, whilst reducing fuel consumption by 40%

Located in the Peak District, Lyme is a 1,400-acre estate owned by the National Trust with a grand historic house, a building dating back 600 years which contains a collection made up from thousands of precious artefacts. Like many heritage sites, Lyme was heated using oil, but undertook a 550kW biomass installation in 2013 designed to provide conservation and comfort heating.

However, the system suffered from significant efficiency losses, and as a result of an investigation by Reheat, it was assessed that it was oversized relative to the areas to which it was providing heat, and could be optimised to deliver far better performance. There was also a lack of control over the heat flow rate across the district heating scheme, leading to high heat losses.

The effective operation of the biomass heating system was critical to the conservation of the historical building, as well as its contents and resident for heating – it also plays a key role in the National Trust’s decarbonisation strategy. As a result of Reheat’s assessment, The National Trust was presented with several issues and risks:

• Having two oil fired boilers on site at the time of the project, a fossil fuel the National Trust’s strategy is proactively reducing its reliance on
• The oversize of the existing biomass boiler meaning the running performance was not being maximised, increasing the maintenance and fuel usage of the system
• The storage of heating oil at any given time within such a sensitive site made the consequences of any leakage very severe
• Unpredictable budget implications on heat oil costs

Reheat designed and undertook a substantial scope of work to overcome Lyme’s district heating issues and optimise its biomass system performance, using sophisticated alterations and additions to achieve far greater efficiencies.

This included converting the existing biomass and district heating system from constant flow to a variable flow system, meaning only the volume of heating water required to satisfy the heat load is used. Dynamic distribution pumps were also installed, replacing a fixed speed pump, varying the speed of the pumps inorder to lower overall heat and electricity consumption.

Reheat also put in place a new control system to actively regulate both biomass boilers, allowing them to operate only when required, one at a time, and rotating them to allow for even run times. This overcame the major issue of the biomass boilers not being controlled effectively, which was leading to short cycling and causing substantial operational issues and low efficiency.

With effective controls now in place, the biomass boilers efficiencies have seen improvements of 20%. The new controls allow the National Trust to view on a web browser for local staff to easily change operating times or temperatures. A remote data monitoring system has been used for the optimisation and fine tuning of the control system, and to confirm the required controls operation. 

In addition, electrical consumption on the system, from the biomass boilers and distribution pumps, has now been reduced by 85%. The variable flow rate solution has also led to a reduction in distribution losses from 54% of heat produced in the biomass plantroom to 13%, giving an overall distribution efficiency of 87%.

Overall, the system supports the National Trust in its efforts to decarbonise a large site of historical importance. The ability to heat its main house and buildings nearby is critical to maintaining the integrity of historical artefacts, as well as maintain comfortable levels of heating for the thousands of tourists visiting Lyme annually.