Alternative source of heat brings economic benefit

Air- and ground-source heat pumps can provide a viable source of warmth for poultry sheds.

Since the introduction of the Renewable Heat Incentive (RHI) in 2011, agriculture has been quick to adopt new renewable energy technologies which offer cheaper fuel plus a secure income stream from government subsidy.

In particular, there has been a huge uptake by broiler growers of biomass boilers, fuelled mainly by wood chip or wood pellets to replace gas and oil heating systems.

But, as RHI rates for biomass boilers have been reducing, technologies such as heat pumps have become worthy of consideration, argues agricultural consultant Ray Williams.

In essence there are two technologies, both of which are powered by electricity to produce more heat than the input power. They are:

• Air source heat pumps. As the name suggests, these take heat out of the air and convert it into usable heat. The equipment is 300% to 400% efficient, which means that for every 1kW of electric you put in, you get around 3.5kW of heat out. This is called the coefficient of performance (COP).
• Ground source heat pumps. These take heat out of the ground, either by inserting pipes at a depth of about 1m, or by using a borehole. They are generally more efficient than air source heat pumps as the temperature in the ground is more stable than the temperature in the air. But the capital cost is higher as pipe work needs to be laid in the ground to collect heat and in turn heat the water in the system.

See also: Air-source heat pumps power poultry shed

“Heat pumps are a viable alternative to biomass for a number of reasons,” says Mr Williams. “Once installed, they require little management as there is no woodchip to buy and no blockages to clear.

“There is little maintenance required and efficiency will not degrade in time, unlike biomass boilers that suffer with soot build-up which adversely affects their efficiency, unless they are regularly serviced.

“During the night, heat pumps can run on off-peak electricity in order to reduce running costs,” he adds. “And they produce hot water at a temperature ideally suited to underfloor heating, but can also work with radiator based systems.”

Under floor heating has a number of advantages in that the heat is delivered to where the birds are and the flow temperature of the circulating water can be greatly reduced, using less energy to heat the water. But capital costs are higher than other systems.

Heat pump economics

The economics of heat pumps stack up primarily because the government supports this technology through RHI payments. These are index-linked and guaranteed for 20 years, based on the amount of heat used.

According to Worcester-based system provider Ecotec, a system based on using heat pumps to fuel an underfloor heating system in a broiler shed should pay for itself in less than five years.

Here’s how the numbers stack up for a ground-source heat pump on a single broiler shed:

Electricity cost 10p/kWh

Coefficient of Performance for heat pump 5:1

250,000kWh of heat from heat pump requires 50,000 kWh of electric at a cost of £5,000.

This replaces 250,000kWh of gas which, at 35p/litre, would cost £12,500

Net energy cost saved is £7,500 per year

RHI due is £17,700 per year

Total benefit is therefore £25,200/year

Payback time

Assuming the system cost is recovered in five years, this means that for the 15 years remaining of RHI payments, total revenue will amount to £378,000 per shed. With index linking, the actual benefit will be much greater.

Data compiled by Ray Williams of RW Agricultural Consultancy

Points to consider when installing alternative heating

•  Alternative heating can reduce running costs by 75%
•  Heating with hot water via an indirect system increases bird performance
•  Using indirect heating will reduce bedding costs
•  Capital costs can be relatively high
•  Many systems supported by government grants
•  Some systems may produce heat when you don’t want it
•  Some systems have a longer warm-up time than others
•  Some systems require considerable maintenance and topping up with fuel
•  Underfloor heating will be slow to respond to sudden changes in ventilation

Source: Ecotec