Biomass case study

Case Study

Biomass Boiler Installation at Lochaber Leisure Centre, Fort William

IntroductionLochaber Leisure Centre, in Fort William, is one of the largest leisure facilities in the Highlands; it is owned and operated by Highland Council. The Centre has a 25m swimming pool, a hydrotherapy pool, a sauna and a steam room on the wet side, and a fitness room, exercise studio and squash courts on the dry side. A major refurbishment of the leisure centre commenced in 2010, and the opportunity was taken to introduce a biomass boiler to heat the Centre. The Campbell Palmer Partnership Ltd (CPp) was engaged by the Carbon Trust’s Biomass Heat Accelerator (BHA) to undertake a biomass feasibility study.

Project HighlightsA 400kW wood pellet biomass boiler and 9,000 litre thermal store installed at Lochaber Leisure Centre, Fort William has resulted in an annual cost saving of £95,000 while providing over 97% of the annual heat energy demand from biomass at a seasonal efficiency of at least 89%. Careful design and control integration ensured that the thermal store meets demand peaks with the oil boiler firing only when absolutely necessary, and then for the shortest possible time.

One design team was appointed to redesign the building services including a major re-build of the plantroom. Subsequently the Carbon Trust & Highland Council contracted CPp to design a biomass system and oversee its hydraulic and controls integration with a new oil fired system in the plantroom while working in collaboration with the other design team. The objectives of the biomass element of the project were to reduce CO2 emissions in support of the Council’s renewable energy policy, and to reduce operating costs.

The feasibility study identified two possible solutions. One would require the construction of a new external boilerhouse and fuel store, while the other could be installed within the existing plantroom. The internal solution was chosen because it was substantially less expensive than the other option, and was made possible by the Council’s shift to use wood pellets as the biomass fuel, Construction commenced in November 2010, with commissioning and handover of the plant in March 2011.

Oil & Biomass Flues

periods storing excess heat when the heat demand is less than the boiler’s peak output as illustrated in the load profile graph.

In the first 10 months of system operation the energy produced by the biomass system was very close to that predicted by the Tool with a net seasonal efficiency for the biomass system of just over 89%.

A detailed heat loss model of the Centre was created to produce a heat load profile for the design winter day, and this was used as an input to the Tool to size the biomass system. While the peak load was calculated as 730kW, the Tool indicated that a biomass boiler rated at 400kW in combination with a 9,000 litre thermal store would be able to supply up to 99% of the annual energy required based on a design external temperature of -2ºC. A large thermal store allows the biomass boiler to fire for long

Biomass Boiler Decision Support ToolThe BHA had engaged CPp and the Energy Systems Research Unit at the University of Strathclyde to develop a software design aid to help designers optimise the sizing of biomass boiler systems. The Biomass Boiler Decision Support Tool1 was used to size the biomass boiler and thermal store to achieve the maximum possible annual energy output from the biomass system based on equipment which it was physically possible to install within the existing plantroom.

1 The Tool and a manual for its use can be downloaded from the Carbon Trust’s website at: www.carbontrust.co.uk/biomass-support

9,000 Litre Thermal Store

Lochaber Leisure Centre Load Profile for a typical January day average outside air temperature 5ºC

Biomass case study

Thermal Store Charging

Thermal Store Charging

• Followingahighloadperiodwhichhasdepleted the thermal store, the oil boiler is allowed to operate until the thermal store has partially re-charged and the temperature as measured at sensor T1 has reached 88ºC.

• Aplateheatexchangerisusedtoseparatethebiomass system from the oil boiler and the rest of the plantroom. In the event of a biomass system failure the building management system enables the oil boiler to maintain uninterrupted service to the Centre while simultaneously permitting maintenance work to be carried out on the biomass system.

Design Principles & System OperationThe very high system efficiency (>89%) and the very high percentage of annual energy from biomass (>97%) are achieved by operating the boiler into a large thermal store. The boiler, in combination with the thermal store, meets the peak loads for most of the year, and also allows loads less than the boiler’s minimum output to be met from the thermal store without the need for the boiler to fire. All this is achieved with a boiler rated at 55% of the Centre’s peak load which has the advantage that, even in summer, the majority of the 24 hour load period is within the boiler’s turn-down ratio. Referring to the schematic diagram below, the key operating features of the system are:

• Thebiomassboilerhasbeensizedtofirecontinuously charging the thermal store 24 hours a day operating at its maximum flow temperature of 90ºC.

• ForaslongasthetemperaturemeasuredatT1 (near the top of the thermal store) is greater than 75ºC the oil boiler is disabled.

• MotorisedvalveMV2mixesreturnwaterwith water from the thermal store to maintain a temperature of 82ºC as measured at temperature sensor T2 on the secondary side of the plate heat exchanger (PHE).

• Wheneverthetotalsystemload,asmeasured by the sum of heat meters 2, 3, 4 & 5, is greater than 400kW the PHE secondary pump operates at a speed able to deliver the peak load. When the total load is 400kW or less this pump operates at a lower speed limiting the power delivered to the PHE to a maximum of 400kW.

• Theoilboilerisfittedwithamodulatingburner and, when the system load is greater than 400kW, its output is governed by the difference between the total load (measured by heat meters 2, 3, 4 & 5) and the output of the biomass system (measured by the heat meter HM1).

Biomass case study

BoilerBackendValve

MV1

9,000 LitreThermal Store

MV2

Thermal StoreMixing Valve

T1

PHE Primary Pump(Variable Speed)

750kW Plate Heat Exchanger(PHE)

PHESecondary Pump

440kW Oil Burner

Oil BurnerPump

CentreHeating

SwimmingPool

HydrotherapyPool

DomesticHot Water

Catfire 400kW Biomass Boiler

Boiler Pump

Outline schematic of biomass boiler system and its integration with the oil boiler and load circuits

The Biomass Installation A Catfire 400kW automatic ignition biomass boiler was installed because it had one of the smallest footprints possible for a boiler of this size enabling it to fit into the existing plantroom while maintaining acceptable safety clearances between it and other items of plant. The boiler has vertical fire tubes with an automatic cleaning mechanism, and no manual fire tube cleaning is required outside of annual maintenance periods. While the boiler can accept either wood pellets or woodchips up to 35% moisture content, the fuel drying zone is contained within a cylinder of refractory material making the boiler up to 2 tonnes lighter than other 400kW boilers. The small quantity of refractory lining also results in a thermally responsive boiler with a turndown ratio of 3.6:1.

The biomass boiler has full MODBUS connectivity enabling a comprehensive read out of boiler functions and parameters for display on the Centre’s building management system.

An internal installation was possible because the existing plantroom had a ceiling height of 6.5m which allowed many items of equipment, including pumps, the plate heat exchanger, pressurisation and expansion equipment to be installed on elevated steel platforms above the biomass and oil boilers. A prefabricated steel wood pellet tank able to accept 16 tonnes of pellets was suspended from supporting steelwork above the swimming pool filters.

Biomass case study

400kW Catfire Biomass Boiler

750kW Plate Heat Exchanger

Project Costs & SavingsThe capital costs for the biomass element of the project, which was financed wholly by Highland Council, are detailed in the table on the next page.

The calculated annual heat energy demand of the Centre is 1.19GWh, with the biomass plant generating at least 97% of this or 1.15GWh. Prior to the refurbishment, the Centre consumed £99,860 of fuel oil (at current prices November 2011) whereas the calculated annual fuel cost from wood pellets and oil in the first year is £43,070 giving an annual saving of £56,790. The biomass boiler operates at a minimum net seasonal efficiency of 89% making the cost of heat from the boiler 3.86 pence per kWh.

The installation will attract inflation linked Renewable Heat Incentive payments as detailed in the table on the next page.

The effective total annual energy cost saving from installing biomass is calculated to be more than £95,000 giving a simple payback of a little over 2 years.

Biomass case study CTS384

Project Cost for 400kW Biomass Boiler System Cost £’s

400kW wood pellet boiler £82,395

Wood pellet storage tank & fuel transport auger £19,571

Cyclone grit arrestor £1,453

9,000 litre thermal store £11,496

Flue system £19,340

750kW plate heat exchanger £6,930

Pressurisation & expansion system £6,147

Steelwork & elevated platforms £3,399

Mechanical & electrical installations £27,825

BMS biomass outstation £10,425

Transportation & delivery £5,336

Testing & commissioning £8,318

Documentation £2,916

Total Project Cost £205,550

2 The Tier 1 tariff as at November 2011 is 4.9p/kWh and will be inflation linked for 20 years3 The Tier 2 tariff as at November 2011 is 2.0p/kWh and will be inflation linked for 20 years

Biomass Installation Capital Cost Breakdown

Tariff Name Heat Generated per Tariff (kWh) Tariff (p/kWh)

RHI Value per year

Medium biomass Tier 1 heat generation = 1,314 hours x boiler rating (400 kW) = 525,600 kWh

4.9 2 £25,755

Medium biomass Tier 2 = 97% of annual heat demand less Tier 1 = 1,188,000 kWh – 525,600 kWh = 626,760 kWh

2.0 3 £12,535

£38,290

The biomass installation at Lochaber Leisure Centre has been innovative, it offers us an effective solution to enabling significant carbon reduction and energy saving at the site. The Council are pleased to have gained benefit from the Biomass Heat Accelerator, it has raised our understanding and knowledge of the operation of the systems and I would note this as a good example of what can be achieved

Eddie Boyd Principal Engineer at Highland Council

Projected income from the Renewable Heat Incentive

January 2012