Poultry farmers looking to heat their sheds for young broilers face a bewildering array of choice in terms of the technology available.
Liquid petroleum gas (LPG) has been the traditional fuel of choice and has proved popular, reliable and well-regulated, according to Draper Ventilation technical manager, Julian Marris.
But renewables have grown in popularity, in part due to the attractiveness of the Renewable Heat Incentive programme.
Each type of renewable comes with its pros and cons, so producers need to weigh them up carefully at the design stage of a new project.
See also: Do woodpellets stack up?
In particular, Mr Marris identifies the following:
Pellet systems can be a good fit for poultry producers, combining efficiency with convenience, though they tend to be more expensive.
Woodpellet boilers have the simplest controls and are the closest to fossil-fuel boilers in terms of maintenance and operation.
These systems are trickier to operate, with boiler responsiveness determined partly by the fuel moisture content – the wetter the fuel, the less responsive the boiler.
It provides an opportunity to use up scrap or waste wood, which can be a viable option as fuel costs tend to be low. But this requires careful boiler and fuel feed selection.
Using poultry litter for biomass became a legal possibility when EU rules were changed in February 2014, reclassifying litter as an animal by-product, rather than a waste product.
It requires considerable capital investment, and ongoing operational and maintenance costs are high, but it has the advantage of using a low-value fuel that is available from the previous crop.
Straw can also be used in some boilers, but it is important to have DM levels at 15-18%. It also produces high levels of ash.
Renewable scheme rule changes
From 5 October 2015, fuels used in biomass boilers must meet the Department of Energy and Climate Change’s new wood-fuel sustainability criteria.
The changes affect existing and new participants under the Renewable Heat Incentive scheme, meaning producers need to comply to ensure they continue to receive payments.
Farmers need to take into account transport and storage costs of straw, which could be a major cost contribution.
Full evaluation at the design stage of both the physical and financial implications is essential.
Combined heat and power (CHP)
As the name suggests, these systems simultaneously generate electricity and heat, and can provide an excellent return on investment. CHP is also growing in popularity with the government.
The plants can be fuelled by a range of fuels, including poultry litter, woodchip, woodpellets and waste-timber products.
It is most suitable when there is year-round base load demand for heat (ideally about 8,000 hours/year), with electrical power either consumed on site or exported to the grid.
But poultry farms typically only need heat for about 5,500 hours/year, so there can be a mismatch which needs careful modelling, or additional uses for the heat to be found, in order to provide a good return on investment.
“Our experience to date suggests that small-scale CHP is difficult to implement on small poultry units, so is best suited to large, multished sites.”
Anaerobic digestion (AD)
These systems produce biogas for electricity generation, with the waste heat being used within the poultry sheds.
While the technology is now well established, AD remains expensive due, in part, to the size of the equipment. “In my view, farmers thinking of AD need to look at a joint venture to ensure the continuous, long-term operation of the plant and spread the financial risks,” says Mr Marris.
The solid residue can be used as a soil conditioner/fertiliser.
As a low carbon technology, heat pumps certainly have a place in modern poultry buildings. They operate by upgrading low grade energy from ground or water source collectors into more usable heat via the refrigeration cycle.
Maximum efficiencies are achieved at low flow temperatures (typically 32C), with a maximum flow temperature about 50C for the system to be viable.
As the efficiencies are reliant on the energy collectors, careful modelling is required to ensure there is sufficient capacity.