Introduction to biomass boilers system design and integration

Biomass system design is relatively simple with a large number of systems operating both in the UK and more widely in the European market. Most of the larger system designs will incorporate a thermal store due to the slower reactive nature of biomass boilers compared with oil or gas, and the way in which they are sized in order to best accommodate the load of the buildings peak / base demand. Other such feature are common to biomass boilers like “backend protection valve with pump” to prevent corrosion within the boiler, and various safety devices preventing the fuel from burning back to the source. It is also very important to look at the way in which your fuel will be delivered as this will affect the cost of wood chip / pellet per ton supplied.



System integration

The only way to fully understand how to integrate a biomass system is to understand what you are trying to achieve by connecting it, and what equipment you are trying to replace. Although this seems to be stating the obvious in reality it can be quite complicated. Firstly you should determine if the system you have is a “wet system” and if the equipment is “directly heated” or “indirectly heated” this will then give you an idea of how many pieces of equipment you need to replace (Energy wise, as the vast majority of boilers can remain in place, giving you 100% redundancy), Also check whether they are all in one plant room location or multiple location. If you can determine that there is only one point of connection then it should be a relatively simple process to connect your biomass boiler system directly into your existing system, although careful consideration needs to be taken regarding the existing system water quality and the size of the expansion vessel if the system is sealed.

If there are multiple direct fired units, or there are multiple plant rooms, then it is best to deliver the heat via heat exchangers / emitters, this way you can control the delivery of heat to specific areas regardless of the type of system that is currently installed (sealed or open vented).



Control strategy

If your property has a building management system, it would be wise to control your new heat exchangers / emitters from this point, as it will normally be more energy efficient. This can be done in a similar manner to the way your current fossil fuel heating works, but it would be wise to look at the specific heat demand of any given building to ascertain if a thermal store would be needed. (Example, If the heating controls were set to come on 3 times a day for 2 hours with a 2 hour interval in between, then this would create a large demand every time it came on, and it would therefore be wise to look at a thermal store in the area of delivery to your system, If your heating comes on once a day for a long period of time this could be controlled via timer delays)



District heating and control

If you will need to install a district heating network in order to provide heat to multiple buildings then there are several important factors to consider. The first is to check the manufacturer’s literature regarding heat losses on the pipe used, as this can vary considerably. The second is to check the life span of the pipe at the temperature and duration you wish to deliver the heat at. The third is to look into the thermal properties of the pipe over time as the insulation will degrade and the losses incurred in year one will not be the same as year 10. The fourth (and in my opinion most important) is the way in which the heat is distributed to the buildings, only using the heat when required will minimise your losses and extend the life span of the pipe. (Example, Let’s assume we are to connect two buildings, one a swimming pool and the other a library, and both have equal district heating runs of 100m. The heating demand to the swimming pool will mean that the use of heat / hot water will require a relatively constant demand even in the height of summer and therefore a constant temperature circuit could be used or 3 port valve to the heat exchanger. The library however will have a large demand in the winter but during the summer this will be minimal, and may only require the heating of hot water for 2 hours per day, under this scenario it would be wise to use a variable temperature circuit or 2 port valve as there is no point constantly circulating water when there is only a demand for 2 hours per day)