There are many advantages to living and working in the open countryside; however it does bring some challenges too. When we first opened our holiday cottages in 2001 being “off grid” meant that we had no access to mains gas and instead were restricted to bottled gas, electricity or oil for heating and hot water. Our decision to use oil fired central heating in the holiday cottages provided guests with reliable instant heat but over the years has led to increasing frustrations due to reliability and running costs, so we decided that it was time we sought out a new solution.
We first discovered the Renewable Heat Incentive (RHI) shortly after we installed solar panels on some of the farm buildings; it’s a Government backed scheme to encourage the uptake of renewable heating technologies and therefore reduce reliance upon fossil fuels amongst homes and businesses across the UK. The scheme offers financial incentives for the installation of these technologies with the aim of encouraging uptake and innovation, leading to lower installation costs for others in the future.
We considered several approaches for heating the holiday cottages, then realised that it made sense to expand our scheme to heat the farmhouse and a nearby property too. We looked at technologies such as burning biomass grown on the farm (straw from the arable crops) and using solar collectors but after extensive research chose to install a large Ground Source Heat Pump (GSHP) and district heating system.
How does it work?
Ground Source Heat Pumps are a relatively new technology in the UK but have been used extensively within many parts of Europe for several decades, often heating very large housing and office complexes as well as providing hot water too.
The video below (from the BBC One Show) gives an excellent explanation of how GSHP's work, we don't have a large underground mine here though so imagine that bit is our bore holes instead!
The picture below shows the drilling rig drilling the first of 11 bore holes, each 150m (500ft) deep which are used to collect heat from the ground just as heat is collected from the water in the video above.
Each bore hole is connected back to the plant room, this picture shows the flow (un-insulated) and return (insulated) pipes for some of them which then connect in to much larger pipes to run to the plant room.
Within the plant room we have two heat exchangers, each capable of operating independently or together depending upon heat requirements and offering a failsafe if we have any technical problems. The pumps take a glycol mix returning from the boreholes at around 12C and concentrate the heat into 4000 litres of water held in insulated storage tanks. The heat in these tanks is maintained at around 50 – 60C ready for distribution to the holiday cottages and houses.
Another set of pumps constantly circulate this hot water through the district heating system. This comprises of a pair of buried, highly insulated pipes (a flow and return) serving each cottage, ensuring that hot water is always available when needed. Each cottage has had the old boiler removed and instead we’ve installed a heat exchanger; this removes heat from the circulating hot water in the district heating system and transfers it in to the central heating system or hot water supply as required, before returning the cooler water back to the heat pumps in the plant room.
Will I be warm enough?!
It is a common misconception that GSHP’s can’t produce hot water for a bath and that they only heat houses at a low temperature through under floor heating. In reality our pumps are capable of producing hot water too hot to wash with and heating which could be unpleasantly warm; it’s just that the efficiency drops off in order to achieve this. The maximum efficiency from the system is achieved by running the heating at a slightly lower temperature for longer periods of time and so you’ll find that the heating is on for longer than it often is with traditional fossil fuelled heating systems. This means you don’t get the cold house feel when you arrive home early followed by the rapid warming of the property, instead we aim to keep the holiday cottages and houses warm all of the time. The hot water is supplied at the maximum permitted temperature for rental properties and most people will still want to add cold water to a bath before they get in it.
How efficient is the system?
It’s too early to judge the exact efficiency of the system at the moment but we are expecting to achieve a minimum useable heat output of 3.5kw of heat for every 1kw of electricity put in to the system. We also intend to draw a lot of this power from our existing solar panels, hopefully enabling us to reduce the amount of electricity drawn from the National Grid still further. Considerable time and investment has gone in to this project but we hope you can see that it will benefit our guests, the environment and our family for years to come.