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Archive for the ‘heat pumps’ Category

A few weeks ago, my business partner and I were walking to a meeting in Stratford when we realised we were surrounded by several heat networks (seven actually): each one standing alone, isolated from its neighbours, each dependent on its own small boilers or CHP, each its own tiny monopoly. Seven networks right next to each other, brazenly missing the opportunity to reduce cost and carbon by linking together.

Here he his, pointing them out:

 

 

The scene on that Stratford street corner highlights a failure of coordination on the part of planners and a lack of incentives to link small heat networks to each other and to larger-scale sources of low-carbon heat.

But what if we put it right? Imagine for a minute that we do stitch together groups of small networks, perhaps using the £320 BEIS funding to do it. Technically it might be straightforward, but what about commercial structure? What do you do with all those little monopolies?

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Sonderby

Heat network at Sønderby – images from linked design guide

 

When writing a recent post about the low temperature DH network at Lystrup, I contacted the author of the related technical report, Jan Thorsen. In Jan’s response he kindly included a copy of Guidelines for Low-Temperature District Heating (PDF).

This guide is essential reading for designers and operators of DH systems. It shows how DH with flow temperatures of around 55 and return temps of around 25 (also called “fourth generation” or “4GDH”) can be used to serve high efficiency homes as well as buildings on low heat density networks.

At this point you might say, hang on a minute – what are we doing considering 4GDH when we struggle to deliver decent 3rd generation (70/40) networks in the UK? And I’d say you’ve got a point. In fact, I spent a depressingly large chunk of last week trying to help salvage the efficiency of another new network that is horrendously oversized and was probably doomed to low efficiency before it even left the drawing board. So I’m sympathetic with the view that UK engineers need to get our houses in order before moving onto the cutting edge stuff.

But looking ahead to the strategies employed in more advanced, lower temperature systems helps to highlight the design principles that we should be focusing on, even on today’s projects in the UK.

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Infuriatingly, it looks like the government may mothball the Environmental Performance Standard, which would have limited emissions from new large power stations. This is despite the fact that both the Conservatives and Libdems championed the policy while in opposition.

As a result it’s likely that emissions from grid electricity will stay high for quite some time. In fact the official line is that the carbon intensity of the grid will remain roughly steady until 2015, when it will plummet towards near-zero carbon in 2040. (As an aside, is it a coincidence that the dropoff comes in 2015, given that it’s the latest possible date for the next general election?) It will be interesting to see how that drop off moves in coming years.

The announcement strongly reinforces the message from DECC that decarbonisation of heat will not be achieved through electrification. In other words, heat pumps are not the answer to decarbonising heat at the national scale.

Source is table 1 from the recently published DECC stats.

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In the UK we generate enough heat each year to meet the needs of every home in the country… and then we throw the heat away. So why should we promote the use of precious resources and expensive technologies to generate that heat a second time?

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The new SAP has a revised carbon intensity for grid electricity (set in the consultation at 0.591 kgCO2/kWh, up from 0.422). This has a big impact on the resulting carbon emissions from heat pumps, in most cases making them higher than emissions from the worst boiler you can legally install. This goes for both air source and ground source.

You can see from the graph above that at a grid carbon intensity of 0.591 even a GSHP with a COP of 4 is struggling to outperform an 86% efficient gas boiler. The real world COPs seen at Barratt’s Chorley scheme (2.6 for GSHP) and recent field trials by Mitsubishi  (3.0 – 3.4 for ASHP according to a letter from Mitsubishi in the latest CIBSE mag) mean that heat pumps would emit significantly more carbon than the boiler.

And yet in the low carbon transition strategy, DECC state that heat pumps will be eligible for the Renewable Heat Incentive (pdf – see para 1.22), rewarding them for being a renewable energy source! What the hell are they thinking?

Here’s how I did the numbers:

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Last night, Lord Hunt came back with his amendments to the Energy Bill and, as promised, here’s an update. For electricity feed in tariff, he’s proposed:

  • Feed in tariff for renewable generation up to a maximum of 3MW (excellent).
  • Qualifying technology: biomass, biofuels (oh dear), fuel cells, photovoltaics, water (including waves and tides), wind, solar power, geothermal sources, combined heat and power systems with an electrical capacity of 50 kilowatts or less.
  • No timetable for implementation (as far as I could see – is it buried in there somewhere? What will the Baroness say?)

On a heat incentive:

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At first glance, the green credentials of ground source heat pumps (GSHPs) look unquestionable: because you’re harvesting free heat from the ground, you can get up to four times more energy out of the system than you put into it. Sure, it runs on electricity, which is more carbon intensive than gas, but because of this favourable ratio of output-to-input (called the COP for coefficient of performance) the system should still emit less carbon than a gas boiler – in theory.

But the claimed benefits are reliant on incorrect assumptions. A new house will emit about the same carbon using a ground source heat pump as with a new gas boiler. Here’s why:

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