A Chara, - I welcome your coverage of the Dolmen Eco-Tourism Centre at Portnoo in north-west Donegal (The Irish Times, June 30th), but I would like to clarify a couple of aspects. All space heating in the centre is effected by renewable energy. The mainstay is a heat-pump system - a geothermal solar system, which utilises the solar energy banked in the earth. One metre down, the earth temperature is always 7 to 8 degrees Celsius, a storage of the sun's continuous radiation of heat upon our planet.
This bank of solar energy is harvested by means of a chilled fluid loop (a collector) which is buried outside the building in an area of approximately 700 metres squared. The collector system consists of an array of 12 circuits 150 metres in length, each buried to a depth of 1 metre and brought back from the underfield to a manifold chamber near the building. These loops feed into a single major flow (and return) throughput into the plant room. Here three heat-pumps, or heat-exchangers, deliver a nominal 15 kwh of heat each to the building when called upon. This heat is brought into the building in increments of 3 to 4 degrees Celsius. It is transferred from the collector loop which uses a glycol-based refrigerant liquid, by means of the heat-exchangers (each of three evaporator plates served by 5 hp compressors to condenser plates), and thence delivered to a water matrix which is laid underfloor throughout the entire building in polypropylene piping. The fluid in the interior matrix is water-based and is controlled by sensors and activators. The building is zoned into five different areas, thermostatically controlled in the rooms and time-controlled in the plant room. The water in the underfloor slab is always below 50s0] Celsius, generally in the low- to mid-40s. This heats the entire floor slab to the required level. The heat-pump system is time-controlled so that the maximum amount of useful heat is harvested at off-peak rate. It is also programmed to background boost the 1200-litre hot water system should the other renewable energy installations - the solar panels on the roof or the turbine generator on site - not furnish heat above 40 degrees Celsius during the rest of the day (because of weather conditions). All three renewable energy systems are inter-linked and complement each other.
ERDA is the designer of the overall integration of the energy systems in the complex. I congratulate The Irish Times for giving of space in its columns to projects such as the Dolmen Centre. This is practical, working green productivity in action. - Is mise,
Barney Walsh, Partner, ERDA, (Environmental Research and Design Associates), Gleneely, Carndonagh, Co Donegal.