1. Institute of Energy and Sustainable Development Monitoring of a Large Scale Ground Source Heat Pump System - S.Naicker, Dr. Simon Rees IESD, De Montfort University PhD Conference, May 21 st 2010 Hugh Aston Building Ground Source Heat Pump (GSHP) System Heating/ cooling Heat extraction / Heat injection Borehole Heat Exchanger(BHE) Heat Pumps work

2. Institute of Energy and Sustainable Development Contents 1. Introduction 2.GSHP system design and experimental validation 4. Instrumentation & Monitoring System 4.1Data acquisition and logging 4.2Temperature measurement 4.3Flow measurement 4.4Temperature calibration 3. Details about Hugh Aston Building and GSHP system 3.1 Hugh Aston Building 3.2 GSHP system at Hugh Aston building 3.3 Heat Pumps & Borehole Heat Exchanger 5. Details of preliminary data collection 6. Estimation of thermal conductivity of the ground 7. Conclusion& Recommendation

3. Institute of Energy and Sustainable Development 1. Introduction Ground Source Heat Pump (GSHP) Systems are considered as a viable and effective way of reducing carbon emissions for heating and cooling applications in the Non-domestic buildings. The application of GSHP systems can be improved through better design and simulation models. To assess the validity of design models, availability of high quality field data is critical The Validation field Data already exist for domestic scale GSHP installations. This project monitors a GSHP system in a large educational building at De Montfort University.

4. Institute of Energy and Sustainable Development 1. Introduction The monitoring data can be used for –Borehole Heat Exchanger (BHE) model validation; –Heat Pump model validation; –Large scale system performance evaluation; –Study of system operation and control strategies. This paper describes overview of the GSHP system, monitoring system, preliminary analysis of the monitoring data and ground thermal conductivity estimation.

5. Institute of Energy and Sustainable Development 2. GSHP system Design and experimental validation Long term transient performance of ground and system components significantly affects the performance of the GSHP system. So, the multiyear simulation becomes important tool for designing GSHP systems. The proper design of GSHP systems require the application of heat pump and borehole heat exchanger simulation models. A number of BHE and Heat Pump models exist but validation efforts have been limited. This project would provide required data set. The literature review revealed the need for continuity in experimental data, carefully calibrated data collection systems and monitoring from beginning of the building operation.

6. Institute of Energy and Sustainable Development 3.1 The Hugh Aston Building Opened in spring 2010 and is the home of the DMU Faculty of Business and Law. The Floor area - 15,607m 2 Accommodation includes classrooms, offices, library, retail outlets and large lecture halls The building has been awarded BREEAM rating of excellent at design stage. Other sustainable design features includes grey water recycling & solar hot water generation

7. Institute of Energy and Sustainable Development 3.2 GSHP System at Hugh Aston Building Four reversible heat pumps that supply all of the cooling needs and a portion of the buildings heating demand. The ‘source-side’ of the system consists of the BHE arrays to which the heat pumps inject or extract heat. The ‘load side’ of the system has warm and chilled water headers. Each heat pump can switch between these headers. The headers are connected to the building’s heating and chilled water distribution systems.

8. Institute of Energy and Sustainable Development 3.3 Heat Pumps & Borehole Heat Exchanger Heat Pump: The System has four Water Furnace EKW130 heat pumps that are two stage reversible devices with two scroll compressors and plate heat exchangers. Borehole Heat Exchanger: Includes 56 boreholes, each with a diameter of 125 mm and depth of 100 meters. Each borehole has a U-tube inserted that consists of SDR11 pipe with outer diameter of 32 mm. The borehole is partly backfilled and grouted near the top. Grout thermal conductivity has been specified to be 2.0 Wm -1 K -1. The borehole heat exchanger is served by a variable speed circulation pump with flow rate capacity of 30 l/s.

9. Institute of Energy and Sustainable Development 4. Instrumentation & Monitoring System The overall efficiency of the GSHP system can be determined by comparing the heat exchanged with the ground with that delivered to the building The main measurements are the heat transfer rates in the ground loop and header systems. These are determined by primary measurements of fluid flow and return temperatures and flow rate. Measuring this data at relatively high frequency would provide the characteristics of the heat pumps and the control system operation.

10. Institute of Energy and Sustainable Development 4.1 Data Acquisition and Logging The Data Acquisition Units Fluke 2640 NetDAQ Networked unit and Fluke 2635 Data Bucket. Each data logger provides 20 channels for measurement. The manufacturer’s software packages are used to configure the instrument and acquire data. The data logger stores the measured value for every scan in its internal memory and these values are retrieved by a host computer.

11. Institute of Energy and Sustainable Development 4.2 Temperature Measurement The temperature measurements are required at inlet and outlet of the borehole field, chilled water header, and warm water header Resistance Temperature Detector (RTD) sensors are chosen as they have high accuracy and repeatability. Industrial type probes - Omega Pt100 DIN B head type,160mm & 250mm length and 6mm diameter are used as they are robust and suited for plant room installation. A four wire system is used for sensor connection throughout the installation as they provide high accuracy The borehole temperatures are measured through consultant installed pre-calibrated 3 k Ohms thermistors

12. Institute of Energy and Sustainable Development 4.3 Flow measurement Three ultrasonic flow meters are used non invasive clamp-on type, also provides high accuracy. Each flow meter is configured for the appropriate pipe thickness, pipe material, and fluid properties. The sensors are positioned on carefully chosen positions of Ground, Cooling and Heating Loops in accordance with the manufacturer’s guidelines. The measurements are logged into internal memory of the meter and this is periodically downloaded.As the dynamic nature of the GSHP operation is of interest flow measurement data is currently logged every minute.

13. Institute of Energy and Sustainable Development 4.4 Temperature Calibration Apparatus includes Highly insulated container, Reference digital thermometer and readouts In order to minimise the instability and gradient in the temperature, the positioning and immersion of each sensors in the bath was carefully controlled Fisher Scientific traceable digital thermometer with accuracy ±0.05 C and resolution 0.001C used as a reference thermometer. Sensor readings were recorded using Fluke 2640 NetDAQ data logger The temperature of the bath was varied in a number of stages between near freezing and approximately 65 o C The sensor and reference thermometer values have been correlated and a linear correction defined for each sensor.

14. Institute of Energy and Sustainable Development 5. Details of Preliminary Data Collection

15. Institute of Energy and Sustainable Development 6. Details of Preliminary Data Collection

16. Institute of Energy and Sustainable Development 7. Estimation of thermal conductivity of the Ground Accurate Estimation of ground thermal properties is critical for proper design of the Borehole Heat Exchangers The ground properties like thermal conductivity and specific heat capacity of the whole borehole are not directly measurable. These properties have to be derived from secondary measurement like heat transfer rate and temperature.

17. Institute of Energy and Sustainable Development 7. Estimation of thermal conductivity of the Ground K- Thermal conductivity; Q- heat injected ; H-depth of Borehole; m-slope of Fluid average temperature curve over natural time log From line source model,

18. Institute of Energy and Sustainable Development 7. Estimation of thermal conductivity of the Ground

19. Institute of Energy and Sustainable Development 8. Conclusions and Recommendations The performance of GSHP systems and the operational and first cost can be improved using accurate models in the design process. This paper has explored the necessity of high quality monitoring data and its importance for validation of BHE, heat pump models and System simulations. The GSHP system at the Hugh Aston Building, De Montfort University is being monitored to derive dataset that can be used for model development and validation as well as analysis of the GSHP performance. Details of the monitoring and instrumentation systems have been discussed and some preliminary data presented. The thermal conductivity estimation has used simple line-source model and more rigorous parameter estimation approach is suggested for further investigation.