Ground water’s contribution to Low Carbon Design and reduction in CO2 emissions
In order to improve upon current best practice, particularly in relation to the Low Carbon Design Initiative, the client and the CPD design team are currently assessing the suitability of using ground water abstraction to meet cooling requirements for a new development in Omagh. The design team includes architects, M&E engineers, civil engineers, an external consultant hydrogeologist and CPD's drilling team.
Preliminary investigations indicated that the estimated cooling demand of 200-300kW would require groundwater abstraction of 10-15l/s, provided a temperature differential of 5oC could be maintained. Since a yield in excess of 10l/s was feasible based on other boreholes in the bedrock aquifer, the project progressed to the exploration stage. A 120m deep pilot borehole was drilled by CPD’s drilling team and a borehole pump was installed, so that the hydrogeologist could test the actual aquifer yield and the chemical properties of the groundwater. The pilot borehole and associated tests determined that a yield of 4l/s and a temperature difference of 6oC could attend from the pilot borehole. Hence it was highly likely that a groundwater abstraction system would be capable of meeting the cooling needs of the development on a sustainable long-term basis, providing 3No abstraction and 2No injection boreholes were used. The client then approved the drilling of remaining abstraction / injection boreholes. So far 4 of the 5 boreholes have been drilled and yields of between 2-10l/s have been attained.
The proposed building’s CO2 emissions will be lower than traditional developments, as the attention has been paid to the following parts of the design:
- U-Values for walls, floors and roofs shall be in the region of 0.1, which is a substantial improvement on Northern Ireland’s current and proposed building regulations. This reduces the CO2 emissions associated with the building fabric losses.
- Infiltration values will be reduced and the building will be pressure tested, to at least the English building regulations (which do not currently apply to Northern Ireland). This reduces the CO2 emissions associated with the infiltration losses.
- Central chiller plant will not be required as the ground water abstraction installation will provide all the chilled water required for the air handling units, fan coils and cooling coils. This substantially reduces the CO2 emissions associated with chilled water installation, as borehole pumps will consume considerably less power than electrical chillers.
- The air handling units will be supplied with preheat coils, which will be supplied with chilled water from the ground water abstraction installation. During cold periods, when the external air is colder than the ‘chilled’ water, these preheat coils will temper the fresh air, again reducing the CO2 emissions.
As the project develops updates will be added to the web site.