1. Understand the Site Heat Profiles
Unlike conventional fossil fuel boilers, a biomass boiler cannot be sized by simply applying a factor to the peak heat load of the site. Instead, the size of a biomass heating system should be based on the diurnal and annual heat load profile of the site and the type of heating circuits that will be supplied by the boiler. It is important that these heat demand profiles are accurately modelled at the start of the feasibility process – quick assumptions made early on can easily lead to incorrectly sized biomass heating systems further down the line, therefore it is important to quantify the heat demands accurately from the beginning.
2. Consider Options for Thermal Storage
Once the site heat load profiles have been modelled, an evaluation can be made of whether the load profile will benefit from thermal storage. For sites with variable heat loads, thermal storage will offer the opportunity to reduce the size of biomass boiler relative to peak loads, allow the boiler to operate more continuously, reduce boiler cycling and increase seasonal efficiency.
3. Correctly Size the Boiler and Thermal Storage
It is vital that both the biomass boiler and thermal store are correctly sized, as capital cost, seasonal efficiency and maintenance levels are all directly influenced by system size and therefore overall project viability is particularly sensitive to correct sizing.
4. Fuel Selection and Storage Design
There is more to fuel selection than just considering the cost and density of the different wood chip and pellet options. Effective systems are designed and installed with particular attention to fuel delivery logistics and frequencies, design of delivery systems, cost evaluations based on energy densities and other factors that may affect delivered fuel cost over the project lifetime. A biomass heating system needs to deliver returns over a 20+ year life time and so capital cost savings on fuel storage at the start of the project may increase operating costs in the long run; for example, a smaller fuel store may be cheaper to construct but will require smaller, more frequent wood fuel loads to be delivered – this may cause the delivered price of the fuel to raise and cost substantially more over the project lifetime than building a larger fuel store. If applying for government incentives like the RHI or RO, it is important that the fuel selected meets all required sustainability criteria.
5. Equipment Specification
There are many biomass boiler technology options now available. Before approaching suppliers, it is important to specify the system requirements clearly in terms of the grate type, heat exchanger and equipment design that best meets the specific site requirements, so that different supplier offerings can be assessed on a like for like basis.
There are different ways to procure a biomass installation; either as a single turnkey contract or multiple contracts. There are obvious cost advantages to multiple contracts as competitive tendering can be undertaken for each element, however, there are times when a single contract is more appropriate. Whatever the contract method, a clear scope of work and project specification will allow more accurate tender response costing and comparative scoring of tender returns.
7. Value Engineering
Following tendering, Value Engineering should be undertaken to ensure best solution and best cost for the completed installation.
The conformance to design should be checked regularly throughout construction phase, rather than waiting until completion. Even experienced installers regularly use subcontractors who may not have the experience to fully implement the brief as required. One of the key roles of the ‘Client’s Engineer’ is to accept and sign off key work packages and advise on the release of staged payments.
8. Commissioning and Acceptance Testing
Once construction is complete, a schedule of system commissioning should be witnessed by a qualified independent party. If commissioning control strategies and combustion parameters are not addressed following installation, this can lead to poor performance and even premature failure of the biomass boiler. Acceptance testing verifies that all safety interlocks are functional as well as measuring combustion and seasonal efficiency.