All posts by Helen Rook

Heat pump or Gas boiler?

What are the decision factors for heating and hot water systems for large buildings?

For many years natural gas boilers have been the option of choice for providing heat in buildings of all types. They are cheap, reliable, easy to maintain and economical to run. However even with the widespread use that we see today they are often installed on poorly designed systems that do not enable the boiler to achieve its efficiency potential. Additionally, as the electricity grid de-carbonises, gas boilers are now a higher carbon heat source when compared to other technologies.

Combined heat and power generation units, generally reciprocating engines at the relevant scale, have been the low carbon choice over the last 10 years or so for larger buildings. However, even these are becoming unsustainable in terms of electricity carbon intensity when compared to a heat pump supplied with low carbon electricity.

The reality is that the grid is de-carbonising (for example, through increasing wind/solar farms and decreasing electricity usage) faster than is reflected in the calculations used by regulating bodies. Therefore the actual real world carbon performance of technologies is not reflected in decisions made using standard regulatory calculations. This means that when choices of technology (i.e. heat pump or boiler) are made, the actual carbon performance in real world conditions is not considered.

It can be seen on the graph below that around this year it is expected that a cross over point is reached and that even a modestly well performing heat pump will out perform a boiler in carbon emissions.

As global temperatures rise and we experience greater numbers of days at extremes, the requirement for cooling will also increase. A well designed heat pump system can also provide cooling. Combined with thermal storage, it becomes a highly efficient system both for primary energy cost and carbon emissions. This type of system is prevalent in Europe, with many being installed successfully.

Installing a heat pump? There are generally three challenges;

1. Space – heat pumps and associated equipment are generally larger, especially ground collectors and thermal storage. However ground collectors can be situated under fields if boreholes are used. Thermal stores can be weather proofed and sited outside.

2. Capital cost – The purchase and installation costs are significantly higher than gas boilers. The general solution to this is to arrange a finance package based on repayments that do not exceed expected Opex (e.g. green deal) and many companies offer this. Buildings such as hospitals, schools, libraries etc. have the advantage that they are not going to change use or ownership and will use consistent amounts of energy and so should be able to attract favourable terms. Alternatively a community energy scheme could be considered.

3. Expertise – Heat pumps are new to most M&E companies; who do not have the expertise to correctly design the system. It is vital that the system (central heating and hot water generation) are designed to support the efficient operation of the heat pump. Expertise is available from specialist companies who should be given the authority to dictate design decisions.

The ideal situation is for the implementation of a heat pump to be considered at the very start of a project, as once past the procurement of the main contractor, incorporating at this stage can be very challenging and costly. 

Installing a gas boiler?  Why not commit to a 100% green gas tariff? This would make the heat and hot water very low carbon.  Additionally, why not consider designing the system in a low temperature format? This means that in the future there is the possibility to change to a heat pump should this become an option.

Green gas originates from bio-digestors and in the future is likely to be supported by hydrogen from renewable electricity plants (for example, excess wind power is converted to hydrogen at source and injected in to the gas grid). However there are some ethical concerns regarding the source of the bio-digester feedstock; where it is grown specifically for gas production and in competition with food. Bio-gas is sold using a market of certification of inputs and outputs, the supply is limited and price likely to rise given the expected increase in demand. Whilst green gas presents an easier choice now it may be open to challenge and increased costs in the future. 

(Tim Rook, previously Tech Director, Woodpecker Biomass Boilers, Director, EcoFirst Renewbles,  Head of design E.ON) 

Wilding Wivey

Written by Geoff Johnson

We can create amazing wild habitats right here, in and around Wiveliscombe, in which nature can thrive.

Our natural world is in crisis.  We are living in a time of mass extinction, the last being 66 million years ago when an asteroid ended the dinosaurs. This is a terrible tragedy in itself, and extremely dangerous for humankind; we depend on a healthy ecosystem.  We’re not finished yet, but a mammoth effort is required. 

Here are some simple things we can do in our gardens:

  1. Create a pond.  Even a mini pond using a washing up bowl or old bath can be  valuable.  Put a plank or rocks in so that creatures can climb out.
  2. Stop using bonfires or sending green waste to the council. Mulch lawn clippings. Establish ‘beetle piles’ by putting cut garden waste, twigs and branches into a chicken-wired contained area, or just a pile.
  3. Create insect and small mammal ‘hotels’ – hollow stalks in bundles, logs with drilled holes or old air bricks.
  4. Establish permanent ground covering plant ‘corridors’ throughout your garden to enable animals to move around. Create holes in your fences and walls so small animals aren’t trapped and can move to different environments as needed.
  5. Turn off exterior lighting as this badly affects moths and other insects.
  6. Put bells on your cats, and keep them in at night. 55 million birds are killed in the UK annually by cats. 
  7. Encourage areas of lawns to be wildlife gardens, or simply not cut until autumn. This can be just a strip in a small garden.
  8. Establish a wildflower garden rather than a lawn. 
  9. Put up bird boxes. Make your own from cheap off-cuts.
  10. Leave untouched logs piles for hedgehogs and reptiles. …and fungi.
  11. Don’t cut down your ivy. Contrary to belief, it does not strangle trees! The nectar, pollen and berries are essential for insects and birds during autumn and winter when food is scarce. It also provides shelter for insects, birds, bats and other small mammals. The high fat content of the berries is a nutritious food resource for birds and they are eaten by a range of species including thrushes, blackcaps, wood pigeons and blackbirds.
  12. Put up bird feeders – for seeds and nuts.
  13. Cover your walls and fences with climbing plants including ivy.
  14. Host a ‘Wilding Rave’ where party goers create a wild habitat.
  15. Choose plants that provide food and nectar for as many months of the year as possible. Choose ‘pollinator’ plants as named on the package. Choose British native plants such as lungwort, purple toad flax, cow parsley, cow slips and lavender – the bees love it!
  16. Plant hedges to replace or be next to fences. The variety of plant species in the hedges should be chosen to benefit wildlife; native plants with fruit, berries and nuts. Why not make your whole hedge edible!
  17. Don’t cut your verges until mid-September, and then sweep up and compost the clippings.
  18. Don’t use peat – it is a carbon store. (Check the label of any compost to see that it doesn’t include peat.)
  19. Harvest all apples, store those not being eaten, and put piles of them on your lawn every fortnight throughout winter for blackbirds and other wildlife.
  20. Have an untidy garden.
  21. Plant trees that flower and provide food e.g . cherries or plums.
  22. Provide drinking water with lots of bowls and buckets with rocks in them – some sunk to ground level.

I’d love to hear your ideas. Perhaps you have questions or are willing to help others. Contact me on

See resources and references with further information

Image at top shows a small wildlife pond created in a Wiveliscombe garden 4 months ago: already 4 frogs!