Banking on the energy from the sun

by Edward Thompson

The sun radiates a vast surplus of heat energy down to earth each day in summer. Most of this energy escapes to the atmosphere each night. Many people talk of the impending energy crisis without realising that most of the energy that beats down from the sun each day is simply wasted. We could certainly use some of that surplus summer heat on cold winter days! What is needed is a mechanism for “banking” the surplus in summer so that we can use it in winter.

ICAX Ltd has developed a patented system called Interseasonal Heat Transfer™ which addresses this problem directly: ICAX captures surplus heat from black surfaces in summer, stores the heat in Thermal Banks™ and distributes it into buildings in winter to heat them without burning fossil fuels on site.

The first step is to capture surplus heat in the summer. Black surfaces like roads readily attract heat in the summer and can often reach temperatures of up to 60°C, even in England. Roads will continue to rise in temperature until the point when they radiate back to the atmosphere as much heat as they are receiving. You cannot walk bare foot on an asphalt surface on hot summer days without burning the soles of your feet. ICAX captures this heat by running water through a series of pipes embedded in the surface of the road. As heat is drawn off it is quickly replaced by the rays of the sun beating down, so a prolonged period of harvesting the heat is available each day.

The second step is to store the heat captured. This is done by running the hot water through a large bank of insulated ground – a Thermal Bank, usually placed beneath the foundations of a new building. It is a characteristic of the ground that heat only moves very slowly through it – at a rate of only one metre a month. Although this means that the ground does not readily accept heat, the corollary is that having done so the heat will not move very far very fast. An Interseasonal Heat Transfer system “feeds” heat into the Thermal Bank whenever the temperature in the Collector is greater than in the Thermal Bank over the spring, the summer and the autumn. This increases the temperature of the ground from its natural level of 10°C up to nearly 30°C across the large insulated Thermal Bank, before the heating season begins.

In the heating season ICAX distributes the heat collected into buildings via a heat pump, using underfloor heating.

Interseasonal Heat Transfer is a flexible technology which can be used in conjunction with other green technologies. One of these is Ground Source Heat Pumps whose performance can be transformed by employing the heat banking principles of IHT.

As a ground source heat pump extracts heat, the ground will get colder and the heat pump must work harder as the ground temperature falls. The Coefficient of Performance (“CoP”) of the pump will fall below the figure of four in the standard test assumptions, where four kilowatts of heat can be released at a cost of one kilowatt of electricity. The CoP is likely to dip down to 2.6 over the winter heating season as a whole. A heat “vacuum” or heat “overdraft” is created in the ground as the ground source heat pump draws energy from it but, given time, heat will gradually migrate back towards the overdraft to restore the balance from the surrounding ground and, ultimately, from the sun itself.

One catch is that heat only moves very slowly through the ground – as low as one metre a month. The assumption is that solar heat will eventually find its way back into the ground over the summer, before the next winter season. The amount of energy drawn from the ground therefore needs to be carefully controlled to prevent the system from slipping into permanent overdraft.

Interseasonal Heat Transfer addresses this problem by collecting surplus solar energy in the summer and transferring it to insulated Thermal Banks in the ground: this is an active process of charging the ground with heat in advance of the winter. When heat is required in winter the heat pump starts with warm water from the ICAX Thermal Bank™ instead of cold water from uninsulated ground. This greatly reduces the work required of the heat pump and increases the seasonal Coefficient of Performance of the pump from around 2.6 to around 5.4. As well as reducing the electricity needed to power the heat pump, it reduces the carbon emissions from the power station and transforms the economics of running a heat pump.

By actively assisting a natural process Interseasonal Heat Transfer (“IHT”) provides a short cut to accelerate the transfer of solar heat into the ground. It deposits it under the insulated foundations of the building. Thus by establishing a more direct – and quicker – connection, IHT transforms the performance of a heat pump, making the combination now the clear first choice for on-site renewable energy.

The principles of Interseasonal Heat Transfer were first demonstrated in a project for the Highways Agency at Toddington Service Station on the M1 where the heat collected from roads in summer was used to maintain that road free of ice in the winter.

The first building in the world to benefit from Interseasonal Heat Transfer is Howe Dell School in Hertfordshire on the old de Havilland airfield at Hatfield where the Comet, the first passenger jet aircraft, was built in 1949. Howe Dell received its first pupils when the school opened in September 2007. The Interseasonal Heat Transfer installation, designed by ICAX Ltd, was part funded by the Carbon Trust. The school was commissioned by the forward thinking Hertfordshire County Council to incorporate a number of green technologies including solar thermal water heating and photovoltaics as well as Interseasonal Heat Transfer. Debra Massey, the head teacher, is an apostle of education for sustainable development and the children are learning in a unique school which is the embodiment of it.

The school, which has been designed with a high level of heat insulation, also captures solar energy though roof top collectors to heat water for use in the school kitchens and washing facilities. Surplus heat from this source is also integrated into the Interseasonal Heat Transfer system (especially in the hot summer holidays when the school is empty) and stored for winter use.

Environmentaly friendly heating – and cooling

Interseasonal Heat Transfer provides an environmentally friendly answer for the need to provide heating to buildings. It is also well able to provide the reverse. By reversing the mechanism for heating, and using a separate Thermal Bank as a cold store to hold the temperatures collected on winter nights, IHT can also provide cooling. This may surprise some environmentalists who have come to believe that any form of building cooling is expensive and hostile to the environment. This is normally true because the standard solution is to provide air conditioning by pumping enormous amounts of electricity into chillers when a building gets too hot in summer: the problem is inherent in the mechanism because it is also hot outside when it is too hot inside and the chiller has to fight uphill to lose heat to the exterior when it is hot outside.

Natural Cooling

The more elegant solution is to exchange heat with low temperatures from the cold Thermal Bank. This solution is neater, much less expensive and in tune with the environment. It also matches the ICAX philosophy of seeking to achieve balance across the seasons instead of fighting blindly all the way to global warming.

See also: Independent report on IHT by Transport Research Laborotories