Is Eco Heating Efficient?

by Mike Hardwick
12th April 2013

Heat pump technology is an attractive proposition for those looking to lower their energy bills. The only downside seems to be that it’s powered by electricity.

Unless you have access to a reliable supply of renewable electricity, you are obliged to plug heat pumps into the mains, and mains electricity is both expensive and carbon intensive. The same goes for mechanical ventilation and heat recovery (MVHR) systems.

There are two recent events that have brought the limitations of mains eco powered appliances home to me.

The first was a client who had specified a MVHR system, but removed it after the Standard Assessment Procedure (SAP) calculations had been completed. I feared that removing a piece of eco technology would have a detrimental effect on the SAP result. However, the revised score improved by one point because of the reduction in carbon-intensive mains electricity consumption.

The second concerns an eco development in West Bowling, Bradford completed in July 2011. From what I’ve read 33 out of the 45 homes built were to Level 4 of the Code for Sustainable Homes (CSH) and each had an air source heat pump (ASHP) installed. These houses were marketed as ‘super insulated’ with the promise of lower energy bills.

In reality, average bills at the development have been around £2,000 a year (the average yearly energy bill for a UK family home is £1,261). The culprit was increased mains electricity usage from their ASHPs. Residents say they are struggling to cope because it is too expensive to live there.

Mains gas may be a fossil fuel and just as volatile in terms of prices, but it is still cheaper than mains electricity and far more efficient. A cubic metre of gas entering the pipe at one end still comes out as a cubic metre at the other end.

Electricity is barely 25% efficient after transmission losses and has a vast carbon footprint. What’s more, it still costs around three times more than gas. If shale gas fracking goes ahead, then supply is assured for decades to come.

So, if you want to go down the ASHP route then don’t let me stop you, but my advice is always to use mains gas if you have it.

2 Answers

  1. Chris says:

    Interesting points, Mike, and it’s very true that powering an eco heat source with what’s considered relatively ‘dirty’ electricity can harm a SAP assessment.

    But there are various ways to minimise this – you’ve pointed out one option, in the form of using renewable electricity. This is becoming a far more affordable option thanks to the advent of the Feed-In Tariff, and solar electric panels are probably the most cost-effective route for doing this (despite the recent tariff reductions). The other way, of course, is to use an energy supplier that produces green electricity in the first place.

    Another consideration has to be the quality of specification and installation at a given development. Was this up to scratch in the cases cited above? Or perhaps the houses as-built don’t offer the insulation performance they were originally designed to achieve?

    As you know we’ve featured plenty of readers in the pages of Build It magazine who are very happy with their heat pump / mvhr systems. So clearly they can and do work for many self builders and renovators – but only where they’re specified and installed correctly. You could say the same of any heating system, of course…

    Chris Bates, Deputy Editor, Build It magazine

  2. Julian Owen says:

    As an architect advising self builders, I would only recommend heat pumps if the following conditions apply:
    1. Underfloor heating is being fitted.
    2. Mains gas is not readily available.

    As I understand it, heat pumps get more inefficient the bigger the gap between the input temperature (from the ground or air) and the output temperature. Underfloor heating works at lower temperature than conventional radiators so the gap is less. The biggest inefficiency is when lots of hot water for washing etc. is needed, because the heat pump often needs extra energy from the main electricity supply to make up the gap.

    My intuition is that the efficiency levels claimed by suppliers of heat pumps are very optimistic. Also I have been told by some heating specialists that the ‘pay back’ (i.e. the time it takes for energy savings to cover the cost of installation) for a ground source heat pump can be longer than the likely life of the equipment.

    Perhaps if a heat pump supplier reads this, they can comment.

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