The RELaTED project partners Metro Therm and DTI presented a novel microbooster heat pump at the 4th International Conference on Smart Energy Systems and 4th Generarion District Heating, that took place in Aalborg (Denmark). Read the following article to learn more about this study.
AUTHORS: Matteo Caramaschi, R&D Engineer at Metro Therm A/S, Kasper Korsholm Østergaard, PhD, R&D Manager at METRO THERM A/S, and Christian Holm Christiansen, Senior Specialist at the Danish Technological Institute.
Ultra-low temperature district heating aims to improve overall networks efficiency and operational costs by reducing supply temperatures below 50 °C. Lower supply temperatures allow for: transmission and distribution heat losses minimization; performance improvement potential of heat generation plants; integration of low temperature heat sources with low marginal costs as solar, geothermal, excess heat from cooling processes, industrial waste heat, etc.
District heating supply temperatures of 35-45 °C can optimally fulfil requirements of new buildings with low temperature heating systems. However, these temperatures are not sufficient for domestic hot water preparation due to risk of Legionella growth and comfort requirements.
This study introduces a novel domestic hot water booster heat pump with built-in water storage tank located on the secondary side, connected in parallel to a floor heating system. The unit exploits district heating supply at 35-45 °C to directly pre-heat domestic water stored in a tank via a coil. Domestic hot water temperature is further lifted by the heat pump operation, which simultaneously cools the heat source to the desired return temperature.
This study introduces a novel domestic hot water booster heat pump with built-in water storage tank located on the secondary side, connected in parallel to a floor heating system.
Energy performance of the booster heat pump was measured on a working prototype and on field test units according to tapping profiles and methodologies of standard EN16147. Domestic hot water coefficients of performance of 4.8 and 8.0 were measured for heat source supply temperatures respectively of 25 and 40 °C and return temperatures of 22 and 30 °C.
Moreover, a system analysis of a building equipped with an ultra-low temperature district heating substation was carried out. Floor heating is supplied through direct heat exchange and domestic hot water through the micro booster solution. The overall primary energy consumption of the building, calculated with the Be18 software, resulted in 32.1 kWh/m2, which fulfils the requirements of the Danish Building Regulation 2018. The proposed system was compared to a solution based on conventional district heating supply temperatures. In the specific case, when the benefits of heat losses reduction in the transmission line are included in the overall analysis, the novel solution resulted to be a possible competitive alternative from a primary energy consumption perspective.
The novel solution resulted to be a possible competitive alternative from a primary energy consumption perspective.
From an economic point of view, it was found that the most sensitive factor is the price of heat. If reducing the supply temperatures from 70-80 °C to 35-45 °C is not followed by a heat price reduction, for the final user, it is more convenient to have installed a district heating system with conventional temperatures of supply. The future trends of primary energy factors and energy prices may play an important role in the economic feasibility and the market development of this technology.
The study did not analyse the possibility to flexibly operate the booster heat pump only in periods of low electricity prices. An additional possibility to be investigated is to operate the heat pump booster to produce hot water and to simultaneously produce floor cooling during summer periods. In non-heating periods, using the building and the floor systems as free source of heat for the heat pump may allow for the reduction of yearly operational costs.