Taking the heat out of the playground
Read about Howe Dell Primary School achieving 'A' rated DEC.
When Howe Dell Primary School in Hatfield relocated, a new building which incorporated the latest innovative, sustainable elements into its design was top of the agenda. The £8 million school project is the first building in the UK to utilise an underground, Interseasonal Heat store (IHT) and works in tandem with TermoDeck, Tarmac's high thermal mass and mechanical ventilation system to heat and cool the building.
Using the thermal performance of the ground to heat or cool a building is an ancient concept. However, until recently it has not been incorporated into a working solution for modern day construction. London-based Interseasonal Collection & Exchange (Icax) has developed the technology to make the concept as user-friendly as possible and Fulcrum Consulting, one of the UK's leading building services consultancies has assisted in its integration as part of Howe Dell Primary School's innovative design.
A groundbreaking system
Interseasonal heat transfer is a simple concept, yet a groundbreaking one. It works by capturing heat energy during summertime and stores the energy for use during colder winter months.
However, making this concept a reality was a challenge. Andy Ford, director of Fulcrum, Consulting explains: "The challenge for us was how to utilise the thermal performance of the ground to heat or cool a building and make it a working solution for 21st century construction. We needed to make this technology user-friendly and come up with a way that it could be installed using construction materials which are readily available."
Ford continues: "Understanding the building industry, we knew that the technology may be a good idea but it needed to be a workable solution. Importantly, it had to be affordable and not impede the construction process. Part of the process of innovating is understanding how to move a product to the market and I think by offering a package that can be installed easily, we have done that."
Heat control
The novelty with the IHT system at Howe Dell is that it is invisible and located below the school's playground.
An array of pipes has been laid just below the surface of the tarmac playground, which has high emissivity, making it perfect for transferring incoming solar radiation. During the summer, the sun warms a mixture of water and anti-freeze in the pipes, which is then transferred from 'the collector' to the computer-controlled thermal banks, which stores the energy. When heat is needed, the warm water is pumped through the pipes in the thermal bank into a heat exchanger, which circulates it directly into the underfloor heating system or pumped to an air-handling unit where it heats the passing air.
During the summer, a body of heat builds up over a period of time and then during the winter months, the heat is transferred to the buildings. It is also able to capture frost on cold nights, store it and use it to keep the building cool in the summer. On cold days, the water in the system is cooled by the frost and is stored in a separate, low temperature thermal bank. A control system then compares the difference in temperature between the thermal bank and the playground surface to determine if water should be diverted to the cold or heat store.
Experimentation brings results
Howe Dell's groundbreaking system has much to be thankful to the Elizabeth Fry Building, a TermoDeck building at the University of East Anglia which uses the thermal mass of hollowcore concrete to control internal temperatures. Built twelve years ago, the Elizabeth Fry building is still cited as one of the UK's most energy efficient buildings and importantly, provided the experimentation ground to develop IHT.
Ford explains "Working on the Elizabeth Fry building enabled me to look at where the energy used actually went. The idea behind doing this was to see if there was any way buildings could be designed that relied on underground heat sources. Gathering data in this way and from computer modelling has proved that the technology works but we needed a real-life example. Howe Dell, a school which desired the latest innovative, sustainable elements to be incorporated into its design was the ideal test-bed for the technology."
Working together at Howe Dell
One of the unique aspects of Howe Dell is that renewable energy systems like the IHT system can work in tandem with innovative technologies like TermoDeck, Tarmac's energy efficient heating, cooling and fresh air ventilation system.
The TermoDeck system actively exploits the high thermal mass of the structural, hollowcore concrete slabs integrated into the fabric of the building to control internal temperatures and distribute warmed or cooled fresh air through a building.
Geoff Russell-Smith, general manager, Tarmac TermoDeck explains how the technology works together with the IHT system: "Once the water in the pipes under the playground has been warmed during the summer, it is either circulated directly into the underfloor heating system or it is pumped into an air handling unit where it heats the passing air before being circulated through the TermoDeck system.
"The TermoDeck system works by passing the supply air through the building to maximise the passive benefits of the high thermal mass properties of concrete. The supply air passes through the holes in the hollowcore at low velocities, allowing prolonged contact between the air and the slabs. In turn, this enables a far greater area of concrete to actively behave as a heat exchange medium that releases heat to, or absorbs heat from, the air in the slabs," says Russell-Smith.
Eco design on the school curriculum
The TermoDeck system also complements the overall ethos of the school's design.
Russell-Smith concludes, "This was an exciting school project for us to be involved with and shows how flexible TermoDeck is, by working in tandem with onsite renewable technologies such as the IHT system. In addition, it not only provides significant environmental savings for the school but is also helping to deliver longterm running cost savings too. It's a real plus that the school has earned plaudits from BREEAM - the school's preliminary appraisal has shown that its innovative design achieves a level equivalent to the highest BREEAM rating, making it one of the highest achieving pilot schemes."
Read about Howe Dell Primary School achieving 'A' rated DEC.
