The 10-million-euro Keskuskatu District Cooling Station was taken into use by the Finnish energy company HELEN in 2018. The heat pump plant built under Helsinki’s Esplanade Park is one of very few facilities of its kind in Finland. HELEN’s heat pump facilities utilise the coolness of seawater, warmth from sewage water and heat energy produced by buildings and data centres. In addition to district cooling, the plant can also be used to feed district heating network. To verify the energy efficiency of their new installation, HELEN reached out to its partner VTT MIKES.
HELEN initially contacted VTT MIKES already in 2016, after they had selected the installation supplier. VTT MIKES was consulted already during the planning phase to ensure that proper calibrated sensors can be properly installed during construction of the heat pump installation. The actual verification measurement was performed in September 2018.
Typically, a third-party organization verifies the performance of large installations before they are handed over to the customer. Since there are few actors in the specialised field of metrology in Finland, VTT MIKES was HELEN’s natural choice for collaboration. As the National Measurement Institute of Finland, VTT MIKES has the skills and knowhow to measure accurately also electrical power, temperature and liquid flow, which were relevant for this project.
Measurement expertise put to the test
VTT MIKES and HELEN had already had small-scale collaboration in a project related to electrical energy metering, but this collaboration was of a substantially larger scope. In this case, the task was to verify the cooling power and Cooling Coefficient of Performance (COPR) specified for the installation. In order to do this, the electrical power consumed by the installation, as well as the temperatures and water flows of the heat exchangers had to be measured.
The measurements were conducted with sensors placed in several locations inside the heat pump plant. The electrical power was measured using the voltage and current transformers of the 10 kV feed for the heat pump. The transformers were calibrated on-site by VTT MIKES before their final installation in November 2017. Altogether sixteen PT100 sensors were used for accurate temperature measurements on locations prepared during the heat pump installation phase. The flow meters were ordered with custom calibration, and they installed permanently to the heat pump installation.
A temporary Ethernet network was built for the verification measurement. About 100 m of cabling was needed for controlling power, temperature and flow metering instruments. The custom measurement software prepared for this project collected readings every 1.5 seconds, providing real-time values for cooling power and Coefficient of Performance (COP) values.
A significant plus was that after starting preparations 2 years ago in the planning phase, we needed only 4 working days for the verification measurement. This time includes installation of measurement instrument, measurements and uninstallation. Thus, HELEN did not need to keep the heat pumps out of use for a long period,
project manager Jari Hällström from VTT MIKES clarifies.
The measurements conducted by VTT MIKES relied on the international AHRI standard for heat pump performance rating and behaviour measurements. VTT complemented the standard-based process with its expertise in providing measurements with an estimate of measurement uncertainty and traceability to SI system.
This was a successful project without any major issues. Large-scale problems were avoided as HELEN contacted VTT MIKES already when the planning of the installation was in early stage, and requirements for measurement sensors were discussed throughout the construction phase. For example, the voltage and current transformers were calibrated on-site in the short time between their delivery and final installation. In addition, the flow meters and inserts for the temperature sensors were installed in proper locations with unobstructed access. These requirements had to be taken into consideration when designing the layout of the plant,
project manager Veijo Noponen from HELEN concludes.
Confirmed quality through verified efficiency
After the results were analysed, VTT MIKES concluded that each heat pump delivers the guaranteed 7.5 MW cooling capacity, and the cooling coefficient is also better than promised by the manufacturer. The measurement uncertainty for both quantities was 0.5%. The uncertainty was limited by the uncertainty of the heat capacity of the water; the actual measurements of electrical power, temperature and flow were more accurate.
The positive outcome of the verification measurement was that the new heat pumps met the values guaranteed by the manufacturer. Obviously, the manufacturer was also pleased with the measurement results, as the high quality of their equipment was confirmed by an independent measurement.
After this a successful collaboration, VTT MIKES and HELEN may cross paths again in the future:
HELEN is world-renowned for its combined heat and power solutions, and the company has plans for future district heating and cooling installations. We hope that our collaboration with HELEN will continue when the company needs assistance with demanding measurements,
Jari Hällström concludes.
The experience gained on the combined measurement techniques implemented in this project can also be applied for measurement of efficiency of other large-scale installations.
