Q2. How many meters are used to collect data on the power consumption of the GSHPs?
Real-time power consumption data are collected every 15 minutes for the GSHPs and all circulating pumps, along with in situ borehole temperatures, flow/return temperatures, brine temperatures, building inflow/return temperatures and outside air temperature.
Q3. How many m3 /d is the production well?
The production well was fitted with a fixed-rate submersible borehole pump (Nastec 4H 06/02) that abstracts up to 35 m 3 /d (0.42 l/s).
Q4. How is the water reinjected into the aquifer?
The cooled wastewater is reinjected directly back into the aquifer via a pipe with outlet at 10m bgl, via the 18 m total deep injection well, which is also screened throughout the aquifer.
Q5. What is the effect of the abstraction well on the temperature of the water?
During abstraction a wider pulse of cold water, which developed during the previous year, is observed downstream of the current pulse developing around the injection well.
Q6. How many households would be required to meet the predicted heat demand?
Upscaling this small-scale GSHP technology solution across the 39 km 2 area of aquifer would require in the region of 40,000 systems to meet 100 % of the city’s heat demand, requiring a density of one system shared by every two households.
Q7. What is the effect of the gradient on the model outputs?
Changes in aquifer thermal conductivity showed negligible impacts on the model outputs, as heat transport within this part of the system is dominated by groundwater advection.
Q8. What is the aquifer temperature in the study area?
Monitoring data from the production well and a nearby observation borehole (CS241) suggest the gravel aquifer in the study area is also in hydraulic connectivity with Cardiff Bay / River Taff, and so this deeper cold water may partly originate from winter river water mixing.
Q9. How many GWhths of heat demand is predicted for the Cardiff city region in 2020?
The predicted annual heating demand for the Cardiff city region in 2020 is 3,213 GWhthJo urna l Pre -pro of(Cardiff Council, 2013), and a change in aquifer temperature of 2 °C represents 6-7 % of this heat demand.
Q10. What is the effect of the GSHP plant room and pipe work?
Another factor affecting efficiency is that the GSHP plant room and pipe work is located in a poorly insulated building, leading to higher heat losses.
Q11. What is the effect of the injection well on the temperature of the groundwater?
During periods of non-abstraction (and therefore no cold injection), as represented in Fig. 6b, this pulse of colder water drifts down the hydraulic gradient towards the SE, merging with the previous years’ pulse, and the aquifer source around the injection well recovers to near ambient temperatures.
Q12. What is the temperature drop at the production well?
In all cases, temperature changes at the production well resulting from changes in model parametrisation were in the order 0.4 - 0.8 °C and groundwater temperature recovered to at least 12.8 °C during the pause in GSHP operation.
Q13. What is the effect of the gradient on the flow direction of the injection well?
the groundwater gradient controlled how quickly the thermal load was transported away from the injection site, but it also influenced the width of the resulting cold plume (i.e. its spread perpendicular to the direction of groundwater flow), which increases with decreasing gradient.
Q14. What is the implication of the study?
The implication is that the groundwater gradient (and plume direction) was possibly not stable throughout the study period and the plume may have changed in size and shape in the early years of the GSHP scheme.
Q15. What is the impact of the model on the temperature of the production well?
the modelled impact on temperatures at the production well due to uncertainty in subsurface parameterisation was considerably smaller than that related to changes in well alignment relative to groundwater flow direction (advection).
Q16. What is the effect of the thermal degradation on the GSHP COP?
Under GW11/W50 operating conditions, this minor thermal degradation reduced the GSHP COP by 4 %, based on the empirically based relationship from Eq.4 in Staffell et al., 2012.
Q17. How does the vertical profile of the aquifer compare with the static logger data?
7. However, the vertical profile from February 2017 (Fig. 8) shows the aquifer temperatures decreased slightly with depth, fairly linearly, by 1.0 °C, over a distance of 7 m.
Q18. What is the effect of the variable source temperature on the whole system efficiency?
The whole-system efficiency is 450 %, which although is outstanding, was affected by the variable stability of the source temperature during the heating period, as shown in Figs. 7 and 8.