Reducing the Cost of Solar Thermal: Integrating a Novel Freeze Tolerance Approach with Flat Plate Solar Thermal Panels

在英国和欧洲大部分地区，用于家庭热水应用的太阳能热系统需要包括防冻策略。这是必要的，因为在这些条件下，太阳能收集器内包含的任何流体都可能膨胀并使流体通道破裂，从而永久损坏收集器。目前采用了几种策略来防止这种情况发生，最常见的方法是在集热器加热回路中使用乙二醇防冻液来间接加热家庭使用的饮用水。添加二醇试剂可显著降低冰点温度，从而降低霜冻损害发生的风险。然而，这种方法的缺点是由于所需热交换器的材料购买和制造而增加了系统的成本和复杂性。对于大多数客户来说，这意味着他们现有的热水箱需要更换。另外的缺点包括储存罐内的热交换器的额外重量，这增加了运输和安装工作量，以及在热交换器材料失效的情况下饮用水可能被乙二醇污染。Soltropy公司已经开发并申请了一种保护太阳能集热器免受冻结的替代方法，该方法不需要单独的乙二醇加热回路和热交换器。该方法涉及在太阳能收集器的铜歧管内插入可压缩的硅胶管。在霜冻事件期间，由于相变引起的任何流体膨胀被管吸收，从而防止可能潜在地破坏收集器的压力的积累。这种方法比乙二醇加热回路替代方案便宜得多，而且还具有额外的优点，即它允许使用不具有内部热交换器的标准热水箱与太阳能集热器阵列耦合。此外，通过从间接系统切换到直接系统，有可能改善系统的热性能。然而，目前这种解决方案仅用真空管太阳能收集器类型进行了测试和评估，该真空管太阳能收集器类型在其流体通道设计方面与平板收集器明显不同。平板集热器约占欧洲集热器市场的75%，因此将防霜技术与平板集热器相结合的工作具有巨大的潜力。该项目旨在与英国集热器制造商AES Solar合作，为平板集热器开发低成本防霜策略。Soltropy有限公司专利硅胶管集成到平板集热器中用于防霜，将涉及设计和开发一种新的平板集热器设计，该设计将在英国制造。这将包括一些研发活动，包括：数字建模，原型制造，实验室和户外测试，以及营销/知识产权相关行动。这种防霜策略的成功实施将导致系统成本的降低，并有可能提高系统的性能。

Solar thermal systems used for domestic hot water applications in the United Kingdom and much of Europe require the inclusion of a frost protection strategy. This is necessary as under these conditions any fluid contained within the solar collector may expand and rupture the fluid channels, permanently damaging the collector. Several strategies are currently employed to prevent this from occurring, with the most common approach to use a glycol anti-freeze fluid within the collector heating loop to indirectly heat the potable water used by the household. The addition of a glycol agent substantially reduces the freezing point temperature and consequently the risk of frost damage from occurring. However, the penalty with this approach is the cost and complexity added to the system due to the material purchase and manufacture of the required heat exchanger. For most customers this means that their existing hot water tank needs to be replaced. Further drawbacks include the additional weight of the heat exchanger within the storage tank which increases both transportation and installation effort, and the possible contamination of the potable water with glycol in the event of heat exchanger material failure. Soltropy Ltd have developed and patented an alternative method of protecting solar thermal collectors from freezing which does not need a separate glycol heating loop and heat exchanger. The method involves the insertion of a compressible silicone tube within the copper manifold of the solar collector. During a frost event, any fluid expansion due to phase change is absorbed by the tube preventing the buildup of pressure which may potentially destroy the collector. This method is significantly cheaper than the glycol heating loop alternative and furthermore has the added advantage that it allows the use of a standard hot water tank, which does not have an internal heat exchanger, to be coupled with a solar thermal collector array. Additionally, by switching from an indirect system to a direct one, there is potential to improve the thermal performance of the system. Presently this solution has, however, only been tested and evaluated with the evacuated tube solar collector type which with respect to its fluid passage design is significantly different to the flat plate collector. As the flat plate collector type makes up approximately 75% of the collector market in Europe, work to integrate this frost protection technology with this collector type has tremendous potential.This project aims to develop a low cost frost protection strategy for flat plate collectors in collaboration with the UK based collector manufacturer, AES Solar. The integration of the Soltropy Ltd patented silicone tube into a flat plate collector for frost protection will involve the design and development of a new flat plate collector design which will be manufactured in the UK. This will include a number of R&D activities including; numerical modelling, prototype fabrication, laboratory and outdoor testing, and marketing/intellectual property related actions. Successful implementation of this frost protection strategy will result in reduced system cost with potential to improve the performance of the system.