how much heating oil does the boiler use?
The need was to meter the use of oil for billing purposes. I solved it easily and inexpensively. This was before the days of home automation – but it nevertheless meets a need inexpensively. (A smart oil use meter is an idea for another day.)
Central heating boilers burn heating oil – it’s done when there’s no access to the gas that’s piped around the UK. (Oil is a 25% more expensive than gas). My need was to meter how much oil is used by a boiler. The obvious solution was a diesel oil flow meter that would operate at 3 litres an hour – but the oil flow meters I found were more suitable for 100 litres a minute, not 10 litres a day. The mini-flow meter at Rapid (below) was for measuring slow oil consumption. Another, from Ada fruit seemed ideal – though its data sheet said its accuracy was 10%. The deal breaker was that the devices needed reliable plumbing – so I changed tack …
My chosen solution was a 240v hour meter. It’s the part you’d find on a machine where it would count the time until a service was required. A key requirement was a timer that wouldn’t reset if ever the power failed. The boiler man wired the meter in parallel with the heating circuit – so that the meter would only count when the boiler was burning oil. The meter would not count when the boiler was simply ‘on’. He succeeded by trial and error. The meter cost £5. (The oil flow meters i found cost up to £150).
How is the meter calibrated?
The meter measures burning hours, and if we know the oil nozzle flow rate, we can turn that into litres. A test of oil use over several days confirmed that 3.7l oil is burnt in an hour and that we now have a way to meter oil use.
You’d might be sceptical that this solution was accurate so I ought share my full picture: I need to compare the oil use of two identical boilers which draw on the same oil tank. I’m using the ratio of working hours towards dividing up the cost of the last tankful of oil.