5 SPRING / SUMMER 19 Products that perform | Service that delivers | People that care @hamworthy @heatingatwork hamworthy-heating-ltd HamworthyHeating 4 Feature Using a low loss header or buffer vessel in a heating system ensures adequate flow, resistance and temperatures around the primary circuit. When using a vertical low loss header, the low flow velocity allows sludge to sink to the bottom which can then easily be removed from the system via a trap. They are often supplied as part of a package correctly sized and directly from a manufacturer to suit the chosen boiler’s connections. However, alteration costs on an old heating system to include a low loss header or buffer vessel can speak against this choice. Other factors could be space requirements and an insufficient number of ports (depending on how many heating circuits you want to connect to it). Plate heat exchangers Plate heat exchangers provide hydraulic separation of heating circuits and protect new boilers from dirt and debris from an existing secondary circuit, as the water does not mix. Several types of heat exchangers are available. While brazed heat exchangers can’t be taken apart, most can be cleaned. Gasketed types can be fully maintained and increased in duty (depending on the frame size) for future extension of the heating circuit. Domestic hot water plate heat exchangers are solely for the purpose of providing hot water – hence for a different temperature profile and controls. Benefits include the protection of boilers through separation and pressure protection which prolong their life. A reduced amount of water in the primary circuit means treatment becomes cheaper (less chemicals used). Downsides are space issues when both heating circuits are pressurised, and two pressurisation units needed. While it is common practice to use several boilers to prevent a single point of failure, only using one plate heat exchanger would reintroduce this risk. High micron filters to catch debris in the system and additional maintenance are also recommended. No flow boilers A no flow boiler on the primary circuit is non- dependent on the secondary circuit flow for safe operation. Instead, an internal variable speed circulation circuit ensures water movement when circuit pumps are off or set to low. Besides, differential temperature supervision controls the output power for safe operation. The high water content in a no flow boiler equals high thermal mass which allows it to fire without flow and without risk of overheating. Once the control stat stops the boiler, the thermal mass safely absorbs residual heat. These types of boilers often have dedicated return connections for low and high temperature heating circuits to ensure maximum efficiency can be obtained. The main benefit of installing a no flow boiler is that it does not require installation in a dedicated primary circuit. It also reduces the need for additional equipment such as low loss header, plate heat exchanger and pumps. No flow boilers usually have a high water capacity, enabling them to operate with wide differential temperatures. They may also incorporate high and low temperature return connections which maximise operating efficiency. What speaks against choosing a no flow boiler is the required flow isolation through non-firing boilers. This helps the system pumps to modulate which ensures flow through the firing boiler. Isolating any non-firing boiler in any system is good practice. Furthermore, the boiler should not be operating using its own thermostats or integral temperature controls but instead be integrated using a sequence controller or building management system. This improves overall boiler control for many boiler types. Space limitations (access) and weight must be taken into consideration with this option. The choice is yours Which method of hydraulic separation is preferable will be mostly determined by available plant room space, time, and budget. Depending on the choice, other considerations would be low loss header/heat exchanger sizing, type of pump(s) used and if a reverse return is required. On the one hand, hydraulic separation can be achieved by using low loss header or plate heat exchanger. This offers flexibility, as this equipment is optional. On the other hand, opting for a no flow boiler means the most integral part of the heating system determines the remaining design considerations. THE ART OF SEPARATION Energy-efficient boilers are now the industry standard. Most of those are only compatible with modern pressurised systems. In contrast to this, open vented heating systems were common back in the day and many of our customers refurbish them regularly. That’s why finding a solution to ‘bridge the gap’ between old and new is necessary. Hydraulic separation between the primary circuit (with the boiler(s)) and secondary circuit (existing old pipework) can offer a solution. In this article, we take a look at different methods to achieve this. Assessing existing primary circuit design Starting off with the examination of condition and size of current pipework, alterations for optimum performance and efficiency should be considered, such as ensuring lower return temperatures for condensing performance. When assessing water flow around the system, it’s necessary to take into account whether the boiler has an integral pump and if a primary circuit pump is required. Does the current pipework’s flow capacity match the primary/shunt pump minimum requirements? Protecting equipment Means to protect the boiler and clean the system can be the installation of 1) a dosing pot for introducing chemicals (to e.g. prevent corrosion) into the system, 2) an air and dirt separator to remove air bubbles and dirt particles from the system, and 3) strainers to catch debris. The next step is considering how to connect to the secondary circuit. Spoilt for choice There are several ways to achieve this: via low loss header or buffer vessel arrangements, plate heat exchangers or the use of a no flow boiler. Low loss headers or buffer vessels Low loss headers, also called common headers, are available as different types: horizontal, vertical and some have dual action with combined air and dirt separators. They provide a better flow between primary and secondary circuits, allowing boilers to operate at a constant flow rate while flow rates and temperatures in the secondary circuit may vary. Would you like to learn more about this or other heating and hot water related subjects? Book our free CIBSE-accredited CPD seminar New boilers and old systems - a story of separation. Find out more about this and our other CPD seminars at hamworthy-heating.com/cpd The use of a no flow boiler with twin return connections can combine low temperature (e. g. underfloor heating) and high temperature heating/hot water circuits. Possible consequences of an inadequate flow rate are not only annoying for the client but can be costly: A broken heat cell as a result of insufficient water supply costs thousands to repair, a scaled up heat exchanger causes efficiency losses and longer heat-up times as well as a shorter life expectancy. As commercial boilers are a large capital investment, it makes sense to consider what they are linked to.