MUSE – Monitoring Closed-loop systems and Open-loop systems

David Boon (BGS) and Ignasi Herms (ICGC), 11 December 2020

Monitoring heat pump performance

The complete instrumentation and long-term performance measurement of ground source heating and cooling systems is key for evaluating their real-world energy performance, running costs and CO2 emissions. The method for evaluation of instantaneous performance of the heat pump (Coefficient of performance or COP), is described in EN‑145111i. The performance criteria developed by the SEPEMO projectii provides common metrics to assess the Seasonal Performance Factor (SPF), defined as the ratio between annual total system electrical power input and annual total heat output. In contrast with the European norm EN-14825iii, the SEPEMO methodology can be applied to existing installations under operation, offering a wider range of meaningful indicators. These indicators are being updated by the IEA HPT Annex 52 projectIV. Performance monitoring may be required to prove systems meet key performance targets, such as SPF’s and CoP’s required to receive government subsidies. Environmental monitoring, such as groundwater abstraction volumes and allowable/tolerable temperature change (ΔT) may be a condition of an abstraction licence or discharge consent set by the environmental regulator. Continuous monitoring benefits the building owner and helps tracking the long-term health and running cost of their system enabling planning of maintenance.

Monitoring parameters

Figure 1 depicts the types and locations of sensors for monitoring ground source heat pump (GSHP) systems based on experiences shared within the MUSE project consortium. The principal parameters in the plant room production side are: 1) all the electrical consumptions, 2) heat generated, 3) the heat exchanged from the ground / aquifer by accurate measuring of the flow rate and temperatures of the circulating fluid using sensors to enable calculation of ΔT.

Figure 1. Essential set of sensors allowing effective monitoring of performance and environemtnal impact of a Ground Source Heat Pump system in an urban environment. Outlet brine temperature is TBrineout in Figure 2.

Close-Loop Systems (CLS): Besides in CLS, the key parameters to assess the performance of borehole heat exchangers are: (1) the inlet and outlet temperatures of the brine that circulates through the buried probes (example data in Figure 2), and (2) the ground temperature. Depending on the location and number of sensors, these parameters will allow the operator to evaluate the effects of unbalanced heating and cooling loads and the GSHP efficiency evolution. The groundwater level should also be measured in unconfined and perched aquifers as large seasonal variations in soil and rock saturation can massively affect the ground thermal and physical properties and performance and coupling of the BHE.

Open-Loop Systems (OLS): OLS differ from CLS in that they have a variable-speed submersible borehole pump and use groundwater as a heat source. Therefore, for whole system SPF calculation the key metering parameters are: (1) Electricity consumptions of the submersible pump(s); (2) production and injection water flow rate (in-line) and temperature (e.g. +/-0.1°C accuracy PT100); (3) In-well aquifer temperature, level, salinity and turbidity in the production and injection wells, and surrounding monitoring wells; (4) water chemistry and pH (e.g. annually). Other ‘good practice’ monitoring activities include occasional water well inspections using CCTV, and review of injection pressure and water level data to identify potential clogging of the well screen and reduced injection capacity. Servicing and maintenance records should be kept and backed-up to evaluate lifetime performance and running costs against original designs. The CIBSE Code Of Practice 3 (2019)V describes minimum and best practice requirements for monitoring from a UK perspective.

Figure 2. Weekly-averaged values of Tbrineout over a continuous 4 year period for a closed loop GSHP system in a Mediterranean climate (Tremp, Catalonia) (left). The ground source temperature decreases by 10°C during the winter heating season and increases in summer cooling season maintaining an annual average of approximately 15°C.  Minute-resolved readout of Tbrineout and Tbrinein during a typical day in summertime (right) in cooling mode. Rise of Tbrinein (red line) corresponds to the time when the compressors in the GSHP are active and transferring heat to the ground whilst simultaneously cooling the building.  


iEN 14511, 2008. Air conditioners, liquid chilling packages and heat pumps with electrically driven compressors for space heating and cooling.

iiR. Nordman, O. Kleefkens, P. Riviere, T. Nowak, A. Zottl, C. Arzano-Daurelle, A. Lehmann, O. Polyzou, K. Karytsas, P. Riederer, M. Miara, M. Lindahl, K. Andersson, M. Olsson, R. Nordman, SEasonal PErformance factor and MOnitoring for heat pump systems in the building sector SEPEMO-Build: FINAL REPORT, 2012.

iiiEN 14825, 2010. Air Conditioners, Liquid Chilling Packages and Heat Pumps, with Electrically Driven Compressors, for Space Heating and Cooling d Testing and Rating at Part Load Conditions and Calculation of Seasonal Performance.

iVIEA HPT Annex 52. Long term performance measurement of GSHP Systems serving commercial, institutional and multi-family buildings.

vCIBSE, 2019. CP3: Open-loop groundwater source heat pumps: Code of Practice for the UK (2019)

Other MUSE Posts: