37 01202 662500 | sales@hamworthy-heating.com | hamworthy-heating.com Striving for maximum efficiencies The pursuit of low ownership and operating costs from condensing boiler systems is a driver behind this. If operating temperatures are reduced or delta T widened to offer a lower return temperature, then significant efficiency gains can be made. The larger flow/return temperature differential was traditionally the reserve of large steel boilers with high water content, but no condensing capability. Now we want this capability with all the benefits associated with smaller condensing boilers - accurate load matching, high efficiencies, low NOX emissions, rapid response, and compliance. For example, with a flow temperature of 80°C and return temperature of 40°C boilers have the opportunity to condense as well as provide higher temperature water for driving a calorifier or plate heat exchanger. If using a boiler with max 20°C ∆T, the flow temperature would have to reduce to 70°C to allow for a 50°C return to enable condensing. This results in longer heat up times for hot water, or a greater heat transfer area needed to deliver the same performance. Under pressure Some modern condensing boilers can have quite significant pressure losses when operating with a narrow delta T. By using a wider delta T and thus, lower flow rate, the pressure loss can be reduced having a substantial effect on pump size. Take a modern low water content boiler with reasonably high pressure loss associated with the heat exchanger. If design differential temperature is increased from 20°C to 40°C, the flow rate through the boiler will be halved. The associated pressure loss through the boiler however is not just halved, but nearly quartered. This allows the use of smaller pumps with lower purchase cost and reduced lifetime energy consumption. The rise of the heat network More projects are now specifying dual heating sources - where condensing boilers are used to support the renewable energy source. We are increasingly seeing 30°C or 40°C differential temperature requirements in new build projects, in particular district heating networks where boilers are supporting other equipment for when the base load is exceeded. CIBSE guidance AM12 - Combined heat and power for buildings, makes specific reference to designing district heating schemes with a minimum of 30°C differential temperature. This is to keep flow rates and pipe sizes small, and maintain a low return temperature, even at low load conditions, for more efficient plant operation. Using condensing modular boilers that operate with wide design differential temperatures and high turndown ratios complements district heating system requirements. This simplifies pipe and control systems, as well as enabling rapid response to frequent and often sizeable changes in heat demand. Reducing costs Designing a system that operates with lower flow rates can provide benefits to both, the installer and owner. Lower flow rates lend themselves to smaller pipe diameters. Smaller pipes are cheaper to purchase, easier to install and waste less energy as they have lower heat emission rates due to a smaller surface area. The water content of the heating system will also be lower, having a direct saving on chemical dosing and inhibitors for water treatment. Hamworthy’s Wessex ModuMax mk3 condensing boilers and Varmax condensing boilers are both able to operate with wide temperature differentials making them ideally suited to district heating schemes. See pages 22 and 34 respectively. Changing heating system design - the increasing use of wider temperature differentials (∆T) in heat networks Traditionally, commercial heating systems have been designed at 82/71°C or 80/60°C flow and return. But, at these temperatures a condensing boiler performs only slightly better than a high efficiency non-condensing boiler. For gas boilers to condense properly, thus extracting the waste heat from flue gases, they need return temperatures below 55°C. Now designers are looking to lower return temperatures by increasing the operating temperature differential of their systems. BOILERS
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