GROUND-AIR HEAT EXCHANGER SYSTEM FOR CONTROLLED VENTILATION
Ever improving insulation and air tight construction of buildings means that controlled ventilation is becoming ever more important. The ground-air heat exchanger makes a considerable contribution to this, especially when used in conjunction with a heat recovery unit.
As well as increasing the quality of life within the building, this also provides significant energy savings by using the embodied ground energy to pre-condition the incoming ventilation air.
The ground-air heat exchanger takes advantage of the fact that the temperature of the ground, 1.5 to 2m deep, remains a relative constant temperature between 7°C -12°C throughout the year.
The incoming air passes through an undergound pipe system to pre-heat it in winter and to pre-cool in summer. Experience shows that a ground-air heat exchnager makes it possible tor aise the temperature of air taken in by up to 9°K in winter, and to reduce it by up to 14°K.
AWADUKT Thermo Features and Benefits:
– Antimicrobial inner layer
AWADUKT Thermo pipes feature an inner layer unique amongst ground-sir heat exchanger pipes. This is achieved by a specialist process that incorporates silver particles into the inner layer of the base polymer. The result is that the fresh air inside the system is hygienic, containing virtually no germs.
– Solid Wall Polypropylene (PP) pipe
The optimised PP pipe with enhanced conductivity provides excellent heat transfer between the ground and the air, thereby ensuring a high degree of thermal efficiency.
Radon is a natural, colourless, odourless radioactive inert gas encountered in rocks and in the ground. Radon diffueses through the ground, dissolves in water and escapes to the atmosphere at the ground surface.
– High longitudinal rigidity
The high longitudinal rigidity of AWADUKT Thermo pipes prevents sagging, so that condensation is safely discharged instead of forming puddles at the lowest points. Pipes with inadequate longitudinal rigidity are not to be recommended for ground-air heat exchangers.
– Inlet Units
Inlet units are also availaeble, the air is passed into the ground-air heat exchanger through an air inlet tower. The air is filtered bu either a course of fine filter to BS EN 779, eliminating dust and pollen.
1) Air Inlet Tower
With a range of filters (G4 or F6) for hygienic, dust and pollen free air supply.
2) AWADUKT Thermo Pipe System
– Solid walled PP pipe for optimised heat conductivity
– Antimicrobial inner layer to prevent microbial growth
– High longitudinal rigidity for reliable condensation discharge
– Radon-proof by virtue of special sealing system
– Wide range of fittings
3) Condensation discharge
This is installed towards the end of the system to remove any condensation formed during the heat transfer
4) Heat recovery unit
5) Distribution of fresh filtered air
6) Extraction of warm, stale air
7) Ring Seal
For a typical domestic application, a minimum of 40m of pipework is required. This is either with a loop around the building or by a meander pattern. The optimum pipe diameter for air flow rates of up to 300m3/h is 200mm. For air flow rates up to 450m3/h, DN250 pipe is used.
AWADUKT Thermo is also well suited to commercial applications, in particular in the health and education sectors. These buildings require a constant source of fresh, filtered air due to the high occupancy levels. Otherwise carbon dioxide build up can be a problem.
The cooling effects of the ground-air heat exchangers are of particular benefit to large buildings in summer. It is possible to achieve significant air conditioning energy savings and, in some cases, even remove the need for air-conditioning completely. A ground-air heat exchanger can in some cases supply 10% of a commercials building’s energy demand from on-site renewable sources. Pre-heating the ventilation air also provides significant cost savings on the heat recovery unit.
A large open area is normally required for commercial applications (e.g. a sports pitch is ideal). However, sometimes it may be beneficial to put the pipes under the foundations. It must be noted that this method does not allow for solar gain, which favourably increases the temperature of the ground, but still provides an effective solution and saves costs.
On commercial applications, it is usual to use a Tichelmann layout. This is a self-balancing system: whichever path the air flows, it travels the same distance, reducing the pressure losses.
Usually DN200-250 pipe is used for the heat transfer and DN 500, 800, 1000 or 1200 is used for the ditribution pipe. The required air flow dictates the optimum pipe diameters.