Claire Jackson, Authorising Engineer at HC Legionella Ltd., outlines key considerations for maintaining effective hot water circulation systems in healthcare settings
We all know that hot water should leave the system at 60°C in healthcare settings. This is stated in the HSG 274 Part 2 and HTM04-01 Guidance for Healthcare. The same guidance states that the hot water at the outlet must be over 50°C in domestic systems and 55°C in healthcare. We know this, and the guidance is clear in defining our targets and expectations.
When we circulate water around a system, we have a return temperature; this is common in commercial hot water systems. Here, the expectation is outlined in the same guidance – see Table 2.1 in HSG 274 Part 2 – when returns at the point of the hot water cylinder should be above 50°C (55°C at the start of the return lines in healthcare).
Failure to achieve any of these figures is a non-conformance and increases risk. This may be caused by something as simple as a lack of insulation on our pipework, allowing for heat to be lost on the flow and/or return legs. This is easily resolved and simple to fix, and should always be the first check in poorly performing systems.
Airlocks can occur in circulating systems, where a pocket of air becomes trapped, preventing the normal circulation of water. This can present itself as a sputtering supply or, in the worst case, no supply at all. Airlocks are often a hidden challenge post remedial works.
Sometimes, the issue is much more complex and requires expert help to manage through to resolution and a better-balanced system. There may be many reasons for poor returns, but the expectation from the guidance is clear; sadly, it’s often overlooked when the flow and outlet temperatures are delivering expected results. An inadequately performing system increases risk and, therefore, exposure to risk; failure to manage and mitigate this risk exposes you to potential litigation.
Primary, secondary & tertiary loops
The primary loop in a hot water system is the main feed of the hot water system that circulates around your building; it is often in larger pipes and branches off to different areas that form the secondary loops. It is important to know the return temperatures at each loop. Some sites will all feed off the primary loop.
A secondary loop, sometimes referred to as a subordinate loop, tends to have a lower pipe bore size to aid flow and temperature retention, with the returns one size smaller again. It feeds into the primary loop and then into a smaller circuit. In large and complex systems, such as hospitals, there can be a further layer, a tertiary loop, that often feeds one or two outlets rather than a bank or broader system. Again, the bore size tends to be smaller than that of the secondary loop, and the return is one size smaller again to aid in flow and temperature retention.
When the supply takes longer than expected to reach the desired temperature, it indicates that there are issues with the system. The temperature may reach the target of 50°C or 55°C at the outlet, but it may take a full minute or longer to achieve this. While it may conform to the guidance, it’s a sign of an issue, which is why remote sensors can be helpful in certain settings.
Challenges in subordinate loops
The more complex the system, the more likely it is to encounter challenges in providing hot water to the furthest parts of the system. Think of the asset at the end of the system as the endpoint in a maze, and the hot water tries to take various pathways to reach the asset. The more complex the system, the more time-consuming and challenging the process.
The first part of any review is to check the supply. Are we providing water to the system from the heat source at 60°C? If the answer is yes, we check the return to verify the flow; are we achieving 50°C at the point of the cylinder?
The next step is to check the furthest sentinel outlets; can we achieve our target outlet temperature? How long does it take? When was the system last used? All of these questions help inform our thought process as we investigate challenges.
Solutions for circulating loops
To help move water to the furthest parts of the system, known as sentinel points, circulating pumps are often used to assist in the flow of water. Over time, these pumps can malfunction or fail, and flow rates can reduce. The supply may be effective, but if the pump fails, it may not have the necessary pressure to reach the furthest parts of the system within a reasonable timeframe.
Using the maze analogy again, dead- legs can be critical here; if a length of pipework leads to a dead-end, it impacts the temperature, provides a length of pipework to try to reach, and wastes time and energy. The more dead-legs present, the higher the stagnation and wasted energy; as with all parts of a water system, dead-legs should be removed as a priority.
Thermal balancing valves can be installed in circulating water systems. These valves dynamically adjust the water flow rate based on temperature. Once the target temperature is reached, the valves force water through to other parts of the system. This helps the furthest parts of the system achieve target temperatures if the supply is sufficient.
When these solutions are not enough, we have more comprehensive solutions, ranging from reviewing pipework sizes and optimising flow by adjusting the supply and returns in the circulating loops to enhance supply and flow.
When investigating circulating loops, HC Legionella have a tool bag of solutions to manage through to resolution. From simple servicing solutions to full re-piping of your system, our team has the knowledge, experience, and expertise to take your unique situation and work with you to improve circulation and ultimately achieve compliance. Reducing your risk; increasing your compliance. HC Legionella: your partner in water hygiene systems.
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