Self builders are the leaders of the ‘green’ building phenomenon - specifying and installing an increasingly diverse range of energy efficient and environmentally friendly products into their properties.
One of the areas with the greatest potential - both for manufacturers and for self builders is ground source energy; essentially using the constant warmth which is in the ground as a heat source.
Proven Track Record
Companies like REHAU which have been supplying renewable energy products across Europe for many years are now bringing their technologies into the UK and introducing products which have the key advantage that they have already been proven in use. Real rather than predicted performance figures can be quoted, as well as paybacks based on hundreds or even thousands rather than tens of successful installations.
This is of course reassuring to pioneers in the self-build sector who are benefiting from huge amounts of product development and application expertise gained from mainland Europe.
Ground to Air Heat Exchange & Ground Source Heat Probes
Two main product ranges on offer - ground to air heat exchangers and ground source probe/collector systems. Both are ideally installed during a new build development, but can be retrofitted if required. They can make a significant impact in reducing a home’s carbon footprint as well as being a cost effective way to meet the thermal efficiency requirements of Part L of the Building Regulations.
The AWADUKT Thermo ground air heat exchanger is a controlled ventilation system which uses polypropylene pipework treated with an antimicrobial layer to deliver pre-warmed air to houses in winter and cooled air in summer. As well as eliminating the need for air conditioning in some circumstances, it also reduces noise and draughts from open windows and can be fitted with an F7 pollen filter to reduce exposure for allergy sufferers.
The concept of AWADUKT Thermo relies on the fact that at depths of 1.5 to 2m below the surface the earth’s temperature is a constant 8-12ºC throughout the year. This constant temperature can be used to provide a heating source in the winter and a cooling source in the summer by using a fan to pass ventilated air through a network of specially designed polypropylene pipes. These are laid approximately 2m below ground around a property and fed by an air inlet column.
Using the correct sizing of pipe work and controlling the airflow, energy is recovered from or disposed to the earth via a ground-air heat exchanger. The system works in a variety of different soils although the soil conditions and the amount of local moisture will affect the outputs.
Case Study
At a recent installation in the home of a leading London architect, two 59m runs of 250mm pipe were laid in parallel 1m apart around the perimeter of the property. The pipes feed into a courtyard atrium and their outlet is being used to ventilate the house. The system provides a maximum inlet air temperature to the house of around 20º (with an external temperature of 30ºC) and a minimum inlet air temperature of around 3ºC (with a -3ºC external temperature). This equates to net cooling of 1,600 kWh/a in summer and net heating of 2,839 kWh/a in winter.
A condensation collection shaft is required or the system can be set up to drain off through a building’s own drainage system.
A Coefficient Of Performance (COP) of around 50 can be achieved using AWADUKT Thermo compared with a COP of between three and four for a conventional heat pump which makes it a very efficient option. It has already attracted interest from both Germany’s Passive House Institute and the UK’s Carbon Trust.
Complementing AWADUKT Thermo and based around the same basic concept, REHAU’s RAUGEO ground source probe/collector systems rely on harvesting ground heat via a system of probes or collectors and heat pumps. Probes are manufactured using cross-linked polyethylene and sunk at depths of up to 100m to harvest ground energy which is then extracted via a heat pump usually to an underfloor heating or cooling system. Obviously, the pipework used needs to be very durable and resistant to pressure and damage but there are a growing number of specialist contractors carrying out this work using the PE-Xa pipework.
Typically, heat exchangers can collect between 30 and 80 watts of energy per metre of pipe installed to create 6.6 - 8kW of heat - sufficient to meet the requirements of an average family home of 120-160m².
Further details of renewable energy products, including ground source heat exchange and ground source heat pumps visit www.burdensenvironmental.com or Tel: 0845 600 5505.
