How much does our heat pump cost to run?

An eminently sensible and simple question… …that is surprisingly complicated to answer. Hang on, here goes. The heat pump keeps track of the electricity it consumes – that’s a good start. Here are the numbers for December. So in December the heat pump used 692 kWh of electricity. There’s two problems – firstly there’s no way of knowing how accurate these numbers are – they are certainly inaccurate when the heat pump spends a lot of time in standby – Mitsubishi admitted there was a bug. In December the heat pump spends most of its time heating so, fingers crossed, … Continue reading How much does our heat pump cost to run?

Heat pumps in cold weather

It’s usually the first question that is asked “Does your heat pump keep the house warm in cold weather?” Yes it does. Shortest post ever… …but maybe a bit more detail would be helpful. In cold weather the house loses more heat energy. For a back of the envelope calculation the heat energy lost is proportional to the difference between the inside and outside temperatures. We typically heat our main room to 20C in the evening, at 0C outside the house will lose twice as much heat energy as at 10C, at -5C it’s two and a half times more … Continue reading Heat pumps in cold weather

Sticky post

Heat pump must knows

Considering replacing an oil or gas boiler with a heat pump? Good idea but there are a few things you really should know in advance to ensure a successful changeover. Discuss with companies interested in your business – see how they respond. 1. You are almost certainly going to need bigger radiators. It’s not companies quoting for unnecessary work. Heat pumps work best when the radiators can heat the house using water at 30 – 40C. Your boiler probably supplies water at 60C plus. A bigger surface area is needed to transfer the energy at lower water temperatures – so … Continue reading Heat pump must knows

12 months of heat pumping

Our heat pump is now one year old and we have a complete year of data to report/study/ignore/geek out over. See for yourself. The graphs are from the MELCloud app – our system only has the standard metering provided with the heat pump – Mitsubishi call this ‘indicative data only’. For all but 4 days at the start of Dec 21 the heating has been running in room control mode with ‘auto adaptation’ turned on. There’s a couple of things to note in the graphs. In May and June last year we were using the immersion heater powered from solar … Continue reading 12 months of heat pumping

Powerwall predicts the future!

Take a look at our Powerwall charge level over the last couple of days. In winter our Powerwall is set in ‘Time-based control’ mode so it charges up overnight on cheap electricity that we then use during the day – saving us money. We reserve 20% of the useable battery capacity for use during grid outages so if the battery charges fully overnight that’s 80% * 13.5 kWh of energy from the battery which is 10.8 kWh. On our current Octopus Go tariff that saves us 10.8 x (30.78p day – 8.25p night) – a potential £2.43 a day – … Continue reading Powerwall predicts the future!

Keeping warm with a heat pump

The first question we are asked about our heat pump is always ‘Does it keep your house warm enough?’ The answer is yes – let’s take a look at the details. The red line in the graph above is the target temperature we have set for our main room. The heat pump control system tries to maintain that temperature 24 hours a day – that doesn’t mean the heat pump is working 24 hours a day as we will see in a moment. We set an overnight temp of 17C, at 6am the target temp is 18C which is fine … Continue reading Keeping warm with a heat pump

Always on – cost vs convenience

More and more devices in our home are designed to be ‘always on’ making them ever so convenient to use with no waiting. Over the last few years ‘always on’ has become part of our lives with voice assistants, wireless speakers and other smart home devices ready to leap into instant action. However ‘always on’ comes at a cost to your energy bill and to CO2 emissions. In Ourhomeelectric we’ve started to think more about what devices are always on and if the convenience really outweighs the costs – to us and to the planet. Some things need to be … Continue reading Always on – cost vs convenience

Vampire microwave!

Vampire devices have become a bit of a thing recently with the increasing cost of electricity. We’ve been a bit sceptical – often seems to be used as a distraction by energy companies to shift focus away from their rocketing prices. However thought we’d take a look at our microwave – it sits there in the kitchen permanently plugged in displaying a clock (when we can be bothered to set it). There is no benefit to having it always on – you can turn it on and start cooking pretty much instantly anyway. So what are the numbers? The microwave … Continue reading Vampire microwave!

Do heat pumps really save CO2?

If by ‘save’ we mean cause less C02 emissions than an oil or gas boiler to generate the same amount of heat then the answer is an absolute yes. Let’s look at the numbers – source is carbonindependent.org – other sources are available with slightly different figures – choose your favourite – it won’t change the answer by much! In our case we moved from heating oil which emits 2.96 kg of CO2 per litre burnt and we used around 1600 litres of oil per year in our old boiler. That’s a total of 4.7 tonnes of CO2 per year. … Continue reading Do heat pumps really save CO2?

Heat pumps and hot water

Heat pumps not only have to heat your home they also have to provide hot water which presents several new challenges. Traditional oil and gas boilers work at high flow temperatures, usually greater than 60C, which are perfect for heating hot water to a sensible temperature for household use. Well designed systems can heat water and house radiators at the same time. There’s sufficient power available that many households have ‘combi’ boilers that heat water as required, doing away with the need for a hot water cylinder. Heat pumps can’t work this way. The flow temperatures used for heating are … Continue reading Heat pumps and hot water