Decarbonising your home or car - which saves more?

The global carbon budget is extremely tight and we all need to do what we can, as soon as we can, to reduce the carbon emissions from our home and other life choices. I was recently asked – will I save more by replacing my gas boiler with a heat pump or replacing my car with an EV? I was surprised to find the results were fairly well balanced. Which saves most depends quite a lot on how much gas you use and how much fuel you typically use in your car. Here are some typical figures and example calculations. 

Also there is at least one other factor to consider: lock-in. If you buy a new gas boiler today you probably will not want to replace it for 15 years. On the other hand you might buy a second hand car and expect to replace it in 5 years. So the decision on a new gas boiler might have more impact over the lifetime of the boiler even if the annual carbon savings are higher for the car.

Field tests on thin insulation for internal wall insulation

There is a new report out: Measuring Energy Performance Improvements in Dwellings Using Thin Internal Wall Insulation [1]. Researchers at Leeds University performed field tests on six kinds of thin internal wall insulation: PIR, aerogel, and EPS (all laminated onto a board), cork render, latex rolls and thermo-reflective aerogel paint. They were all compared to a typical thickness of phenolic foam insulation - the conventional option. The products were installed on three different solid-wall houses (two systems tested in each). The team measured U-values (thermal conduction through the wall) directly and also the impact on air tightness. They used simulations to study the effects on damp and risk of frost damage. They recorded costs of installation, separating out the costs of materials and labour and decorative finishes. They interviewed the installers to find their opinions - you very rarely find these reported! Here I describe the main results. 

A tradeoff between cost thickness and performance.

Reduction in heat loss (percent reduction in measured U-value) obtained from Phenolic foam board and six types of thin insulation. Paint: thermo reflective aerogel paint, Latex: latex roll, Cork: cork render. The thickness is the total thickness including air gap and plaster skim, where appropriate. Data from [1]

Renewable heat installation rates

A friend asked me if I think that heat pumps are still a 'niche' technology or are becoming mainstream. She was surprised by the number of companies able to install in this area - the MCS website finds ten within 30 miles of Cambridge. So I took a look at the statistics for take up of the renewable heat incentive for heat pumps (domestic). Here is a chart showing cumulative installations.

Domestic Renewable Heat Incentive cumulative applications by month, data from [1]. The steep rise up to April 2015 includes legacy applications.

Common mistakes in energy reporting that make me groan

A conversation on Twitter recently reminded me of how often poor reporting of energy gets units mixed up - or is misleading in other ways. Here are some examples of my personal pet peeves published online : confusing power and energy, reporting power but not energy for storage, and reporting capacity but not energy for generation. I have included examples from mainstream news, trade magazines and even the IEA. If I have quoted your publication, rest assured you are not alone in making these simple, but irritating (and sometimes confusing) errors.

How have we reduced our domestic energy use?

Domestic energy bills have reduced about 20% over the last decade - in terms of energy used. We have reduced consumption in lighting, refrigeration, TV and electronics. Unfortunately, prices have risen such that the overall bill has often increased – probably that is one of the reasons why we are using less, to save money. In this post I attempt to dig deeper into the mechanisms behind these changes and see what lessons can be learnt.

Energy Ratings for heat pumps - what do they mean?

Example energy label from [1]

Do you check the energy labels when you buy appliances such as washing machines or refrigerators? I hope you do. To make comparisons easy each product has  a rating, which is generally between A and G except for some appliances it goes up to A+++. This is helpful only if you know what the best or typical rating is. In any case, the rating does not actually tell you what the efficiency is or typical energy use would be - hence my advice has always been to look for these on the energy label. I would love to be able to say the same for heat pumps but there is nothing like that on the energy label for heating appliances. The rating is the best we have to go on. Here is a picture of the design of the energy label for a heat pump with integrated hot water cylinder, so it supplies hot water for the taps as well as for the central heating system. To understand what this means I have been reading the legislation behind it [2].

Climate change stories to be cheerful about

It has been a very difficult year for several reasons. But it was not all bad. To cheer us up over the holiday, here are my favourite good news stories from 2020 - including coal consumption down, renewables up, beavers for flood management, hope for the survival of coral, help in eating more plant proteins, and changes to our travel behaviour.