Howe Dell leads the way in building an eco-school with heat pumps

In 2007, after many years of development, the new Howe Dell School building opened its doors. Built as part of a bigger development - that included housing, a community centre and other facilities.

Howe Dell was the first purpose-built eco-school and children's centre in the UK. And it included a brand new ground source heat technology - ‘inter-seasonal heat pumps'.


Howe Dell School is a 4,000 square metre building with a large playground.

The sun heats up the playground in the summer, warming water pipes in the ground. This is pumped into an ‘inter-seasonal heat store' - computer-controlled thermal banks underneath the school - where it waits until winter. In hot summers if the solar panels on the school's roof overproduce, the extra heat is also diverted to the inter-seasonal heat store.

In the winter, warm water from the heat store is pumped around the school to heat it. The system provides year-round hot water and can also capture the frost of cold winter nights, store it, and use it to keep the building cool in summer.


The inter-seasonal heat store cost £180,000.

The school cost about £11 million but the original price tag was £4.2 million. Severe delays cost a lot of money. Funding to build the new school came from:

  • the sale of the old school site - £2 million
  • the developers of a large housing estate where the school was being built - approximately £5.5 million
  • Hertfordshire County Council
  • Scottish Power - £20,000
  • the Carbon Trust as part of its mission to develop commercially viable low-carbon technologies - £244,000, part of which was earmarked for the inter-seasonal heat store and ground source heat pumps.


The school was built on a new housing estate that had pledged to be a green community. Hertfordshire County Council wanted to reflect that and build an exemplar eco-school.

Monthly stakeholder meetings were held throughout the building process. These included the head teacher, governors, planners from Welwyn and Hatfield Council and the Highways Agency.


The main challenge has been to integrate all the technologies. Since the school opened in 2007, there has not been a full year where all the technologies it uses have been working as they should.

The inter-seasonal heat transfer was not expensive and was easy to integrate into the build. But the inter-seasonal heat store leaks. Chris Dean, the school's site manager explains:

"We think the expansion and contraction of those joints in the concrete is what's causing some weeping to the system. But the unfortunate thing is when they put the headers into the concrete, they didn't make it so that you had access to the headers."

The heat from the pumps does not reach the two furthest ends of the building. So the school has had to buy some heaters.

Chris Dean says:

"If it had been zoned differently this wouldn't have been a problem. If it had been possible to shut down the heating upstairs, then it would have worked better, because the heat from the lower floor would have risen upstairs. The upper floors also get heat from the sun coming through skylights in the roof."

Key learnings

  • Insulation is key: the walls at Howe Dell are so thick that mobile phones do not work inside the building in certain places.
  • Smart metering is good value for money. For a couple of thousand pounds you can establish where the wastage is.


Head Teacher Debra Massey says:

"The main thing is that we're harvesting and it [the inter-seasonal heat transfer] doesn't just heat our building. We're onsite with a community hall which is run by Hatfield Council and we collect sunlight for them."

According to the manufacturers, inter-seasonal heat transfer saves over:

  • 50 per cent of carbon emissions compared to using a gas boiler for heating
  • 80 per cent of carbon emissions compared to using standard air conditioning and chillers for cooling
  • 100 per cent of the annual cost of running your heating system if you are entitled to claim the Renewable Heat Incentive (RHI).

There has also been an effect on the children's education. Massey explains:

"The fact that the children clearly understand that the majority of our sunlight is being collected on that playground where they play and being stored, and used at a time when we need it in the winter, is a phenomenally simple idea. Our seven-year-olds can explain to you how it works."

Local Ward Councillor Clare Berry adds:

"What I've noticed is that the children have a lot of opportunity to go and share what they've learnt through the technology in the school, in other forums. I've been at quite a few conferences where they've had children arrive to do a presentation. And it's had the advantage of making them quite confident and eloquent speakers."


Debra Massey (Head Teacher) and Chris Dean (Site Manager)
Howe Dell School
The Runway
Hatfield AL10 9AH
Telephone: 01707 263291 ext 0
Fax: 01707 258248

Visitor days at Howe Dell are held on the last Friday of every month. Contact the school if you wish to make a booking.