Abstract
To reach net-zero emissions by 2050, buildings in the UK need to replace natural gas boilers with heat pumps and district heating. These technologies are efficient at reduced flow/return temperatures, typically 55/25 °C, while traditional heating systems are designed for 82/71 °C, and an oversized heating system can help this temperature transition. This paper reviews how heating systems have been sized over time in the UK and the degree of oversizing in existing buildings. It also reviews if lessons from other countries can be applied to the UK’s building stock. The results show that methods to size a heating system have not changed over time, but the modern level of comfort, the retrofit history of buildings and the use of margin lead to the heating system being generally oversized. It is not possible to identify a specific trend by age, use or archetype. Buildings in Scandinavia have a nascent readiness for low-temperature heat as they can use it for most of the year without retrofit. Limitations come primarily from the faults and malfunctions of such systems. In the UK, it is estimated that 10% of domestic buildings would be ready for a supply temperature of 55 °C during extreme external conditions and more buildings at part-load operation. Lessons from Scandinavia should be considered with caution. The building stock in the UK generally underperforms compared to other EU buildings, with heating systems in the UK operating at higher temperatures and with night set-back; the importance of providing a low-return temperature does not exist in the UK despite being beneficial for condensing boiler operation. Sweden and Denmark started to develop district heating technologies with limitations to supply temperatures some 40 years ago whereas the UK is only just starting to consider similar measures in 2021. Recommendations for policy makers in this context have been drawn from this review in the conclusions.
Highlights
This section reviews the guidance provided over time by the Institute of Heating and Ventilating Engineers (IHVE), CIBSE, and other guidebooks used by the Mechanical and Electrical (M&E) service industry in the UK, where the first form of guidance to size heating systems was published as a loose-leaf volume in 1940 [12]
Back in 1955, the recommendation was to size the system for an external design temperature of −1.1 ◦ C if the heating system had a boiler with an overload capacity of
Published a consultation document where it was mentioned that “We are aware that return temperatures are often set much higher than 55 ◦ C, and many installers feel that setting temperatures too low will result in dissatisfied customers” [117]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Oversizing generates losses in efficiency, reduces equipment life span, reduces comfort for occupants, increases capital and operating costs and limits the ability to reach CO2 reduction targets. Oversizing can occur at the design stage, construction phase or due to changes in the retrofit history of the building These limitations to reach expected performances can question the ability of the construction sector to deliver net-zero buildings [9]. A review of experiences drawn from other countries, especially in Denmark and Sweden, is carried out to understand if or how lessons from abroad can be applied in the UK
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