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低碳供热和制冷——动力和挑战年十月 2016

--由BSRIA可持续建筑顾问Michelle Agha-Hossein博士编写

由于降低能源成本、领先立法规定、提高绿色声誉等不同原因,客户越来越希望采用更多的可持续性建筑。此外,仅由热量排放的温室气体就能达到英国温室气体排放总量的三分之一;因此为实现碳减排目标,考虑在建筑物内使用低碳供热和制冷系统具有重要意义。热需求量取决于许多因素,如建筑物构造、运行剖面和居住者行为、以及供热系统的效率。

人们一直在通过各种政策和规划,努力改善英国建筑群内的能源使用情况。为此,受英国能源与气候变化部(DECC)的委托,BSRIAJ向其更加清楚地陈述了非居住领域“低碳”供热和制冷系统的有关当前知识和证据缺口、当前相关政策和标准的行业观点、以及有助于做出决策的建议。作为此项目的一部分,BSRIA在400名成员(设计师和施工人员)中开展了一项调查,以了解明确所使用的低碳供热和制冷技术以及使用该技术的原因。

鉴于目前人们尚未对低碳供热和制冷做出明确定义,因此出于本次研究之目的,BSRIA决定采用EPBD重铸(欧盟指令2010/31/EU)文件中确定的低碳供热和制冷技术。本研究考虑的技术包括:太阳能、生物量、热电联产(CHP)、热泵、区域集中供热和区域制冷。

虽然区域集中供热/供冷只是一种向终端用户输送热源的方法,且该方法所产生的碳的总量取决于热生成技术,但是与现场生热相比,该方法有助于节省碳资源。

据大部分调查对象说,本项目中最常用的低碳技术是热电联产(74%)和空气源热泵(67%)。太阳能是英国最成熟的可再生能源技术之一。在大型非居住建筑内安装一款精心设计的太阳能系统,能够满足每年30%-40%的热水负荷。然而,由于太阳能系统无法满足整栋建筑内的供热需求,尤其在冬天,因此需要提供备用能源技术,如燃气锅炉或热泵。

在BSRIA调查中,大约有41%的调查对象认为太阳能将是最受欢迎的低碳技术。虽然从20世纪50年代起,集中供热就已在英国兴起,但是在热需求量中仅占极小的比例(非居住建筑中的2%)。然而在本项研究中,大约30%的调查对象报告说他们的项目普遍采用了区域集中供热的方式。这一结果比我们预期的要高,但很有可能是因为这项调查中的大部分调查对象主要从事的项目位于伦敦的缘故。

虽然对于锅炉供热或热电联产而言,生物量是一种非常可靠的技术,但大约87%的调查对象说他们很少在项目中采用这种生物量,究其原因主要包括场地使用和受限空间等因素。一位调查对象指出,该技术的使用因需要实现商业办公室净能让空间 最大化而受到了限制,称:“我们的大多数项目位于伦敦,而且多为商业办事处。决定不采用这些技术的原因通常与补助金、奖励措施的实用性无关,而是因为客户希望最大限度地增加净能让空间,但这些技术将会占据太多的宝贵空间。”

除缺乏空间外,根据BSRIA调查,实施低碳供热与制冷技术的主要挑战/障碍还包括较高的建设成本、缺乏经营成本意识、缺乏对技术的了解、缺乏对技术的公众认知、当地燃料供应渠道问题、大量的维护要求以及对技术性能的评估难度。据大多数调查对象说,由于当地燃料供应不足,他们将避免在其项目中采用生物热电联产技术。正如人们预料的那样,使用低碳供热与制冷技术的主要动力是英国建筑研究院环境评估法(BREEAM)的合规性、规划审批与客户要求。

如今,使用连接到天然气管网的燃气锅炉,可满足大约81%的供热需求。燃气锅炉相当低的成本与高效益延缓了英国对再生技术的采用。在缺乏相关法规的条件下,在能够证明低碳供热和制冷技术更加经济和成熟之前,客户组织将考虑采用其他可替代方法,如改进建筑结构等,使建筑结构的风险更小且成本效益更高。

*编写该文章时,已经根据英国能源政策裁撤了能源与气候变化部,并将其合并到一个全新的部门——能源与工业战略业务部。

 

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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.