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New research from Germany shows that most heat pumps installed in existing multi-family buildings may have to operate close to their water temperature operating limit (WTOL), making them unable to to provide elevated temperatures above 60 ºC. The researchers cautioned, however, that proper installation procedures and new types of heat pumps can help solve this problem.
Researchers at Germanys Fraunhofer Institute for Solar Energy Systems ISE have investigated how existing multi-family dwellings (MFH) using radiator heating systems can be retrofitted with heat pumps (HP) in an effort to accelerate their adoption on a mass scale.
However, they warn that a number of challenges associated with high temperature requirements may represent a considerable barrier to their deployment.
“Renovating existing buildings with heat pumps is challenging, as the temperature requirements for heating and domestic water heating are much higher than in new buildings,” Manuel Lämmle, lead author of the research, explained to pv magazine . . “In addition, the ideal is to reuse the existing heat transfer and distribution system. Sometimes these systems have to be adapted to make them suitable for heat pumps.”
The scientists explained that the novelty of their work consists of a systematic analysis of the relationship between operating temperatures and HP performance based on data from field measurements. “The overall objective is to quantitatively evaluate the influence of heat source temperatures, maximum HP supply temperatures, and heat sink temperatures using statistical methods,” they explained.
The group stressed that currently HPs are not particularly well-suited to reliably supply heat at elevated temperatures above 60ºC. However, in MFHs, the required temperatures are often between 60ºC and 70ºC, which means that the HPs have to work close to their operating water temperature limit (WTOL).
The academics highlighted that there are several HPs, such as various brine/water or water/water models, that can reach a WTOL of 65°C, as well as several outdoor air HPs that also reach a WTOL of more than 70°C.
“This leads to the conclusion that, while 80% of the HP on the market are limited to temperatures below 60ºC, there are 135 models available that reach temperatures of 70ºC or higher”, they stressed. "Given recent market trends toward R290 systems, this distribution is likely to see a significant shift toward higher WOTLs in the coming years."
The group analyzed the performance of 58 HP systems installed in existing buildings taking into account HP type, specific heating demand, building type, year of construction and heat transfer system. The group concluded that high-pressure systems can be successfully integrated into existing buildings, provided that careful planning is carried out on a case-by-case basis.
“Although existing buildings – especially when the existing radiator system is reused – require higher supply temperatures, the ambient temperature is not affected in appropriately sized systems,” explained Lämmle. “Heat pumps are capable of supplying the necessary supply temperatures, although with lower efficiency than with underfloor heating systems.”
According to the research team, there are several factors that need to be taken into account to further reduce PH implantation. These are: economies of scale; standardization of heat pumps and systems; more experience in the design, optimization and operation of the most complex and sensitive systems; and new technologies such as propane heat pumps and PVT collectors.
The academics described the model in the paper “ Heat Pump Systems in Existing Multifamily Buildings: A Meta-Analysis of Field Measurement Data Focusing on the Relationship of Temperature and Performance of Heat Pump Systems ” meta-analysis of field measurement data focusing on the relationship between temperature and performance of heat pump systems), published in Energy Technology . |
