Low carbon heating and cooling - drivers and challenges
Written by Dr Michelle Agha-Hossein, BSRIA Sustainable Building Consultant
Clients increasingly expect more sustainable buildings, for different reasons such as a desire for low energy costs, staying ahead of legislation, and enhancing a green reputation. In addition to this, heat alone generates about one-third of the UK’s total greenhouse gas emissions; hence in order to meet the carbon reduction targets, it is important to consider implementing low carbon heating and cooling systems into buildings. Heat demands are dictated by various factors such as buildings’ fabric, operational profile and occupant behaviour as well as the efficiency of the heating systems.
Efforts have been underway to improve the energy use of the UK’s building stock through different policies and schemes. In line with this, BSRIA was commissioned by the Department of Energy & Climate Change (DECC)* to provide them with better understanding of the current knowledge and evidence gaps in relation to “low carbon” heating and cooling systems in the non-domestic sector, industry view on current relevant policies and standards, and recommendations to help the policy making process. As part of this project, BSRIA conducted a survey aimed at 400 of its members (designers and constructors) to find out what low carbon heating and cooling technologies are currently being used and why.
As there is no clear definition for low carbon heating and cooling at the present, for the purpose of this study, BSRIA decided to adopt the low carbon heating and cooling technologies identified in the EPBD Recast (Directive 2010/31/EU) document. Technologies considered in this study include: solar thermal, biomass, combined heat and power (CHP), heat pumps, district heating and district cooling.
Although district heating/cooling is only a method for delivering heat to the end users and that the amount of carbon it generates is dictated by the heat generating technology, it can facilitate carbon savings compared to onsite heat generation.
The majority of the respondents reported that CHP (74 per cent) and air source heat pumps (67 per cent) were the most commonly used low carbon technologies in their projects. Solar thermal is one of the most mature renewable technologies in the UK. In a large non-domestic building, a well-designed solar system can meet 30-40 per cent of the annual hot water load. However, as solar thermal systems, especially in winter time, cannot supply the full heating demand in a building, there needs to be back-up technology, e.g. a gas boiler or heat pump.
About 41 per cent of the respondents to the BSRIA survey selected solar thermal as popular low carbon technologies. In terms of district heating, while the system has been used in the UK since the 1950s, it still only supplies a very small proportion of the heat demand (2 per cent in non-domestic buildings). In this study, however, about 30 per cent of the respondents reported that district heating is commonly used in their projects. This result is higher than we expected but most likely linked to the fact most of the respondents to the survey have mainly been working on London-based projects.
Although biomass can be used as a reliable technology, both as heat only boilers or as CHP, about 87 per cent of the respondents said they rarely use biomass in their projects. Factors such as site access and limited space were reported to be the main issues. One respondent drew attention to the constraints due to the need to maximise net let-able space in commercial offices stating that “Most of our projects are London based and are commercial offices. The decision to not specify these technologies is not usually based on availability of grants, incentives, etc. They are not adopted because they take up too much valuable space within the building that the client wishes to maximise as net let-able space”.
In addition to lack of space, the main challenges/barriers for the implementation of low carbon heating and cooling technologies found through the BSRIA survey include high capital cost, lack of awareness of operational costs, poor understanding of technologies, poor public perception of technologies, sourcing local fuel supplies, significant maintenance requirement and difficulty evaluating the performance of the technology. Most of the respondents said they would avoid adopting bio-CHP in their projects mainly due to the insufficient local fuel supplies. As expected, the main drivers for low carbon heating and cooling technologies were found to be compliance, planning approval and client requirements through BREEAM.
About 81 per cent of the heating demand is met today using gas-fired boilers connected to the natural gas network. The comparatively low initial costs and high efficiency of gas boilers have slowed down the adoption of renewable technologies in the UK. In the absence of regulations, until low carbon heating and cooling technologies are shown to be more cost effective and proven, client organisations will consider alternative approaches such as building fabric improvements, which are less risky and more cost effective to implement.
*Since this article has been written, DECC has been abolished with UK energy policy set to be merged into a new ministry called the Department of Business, Energy and Industrial Strategy.