The HC Legionella team specialises in legionella control and water hygiene for the healthcare, industrial, and commercial sectors. They share an example of their work here
HC Legionella Ltd was asked to attend a healthcare site that had recently installed a new return line to an uncirculated area of the existing water system due to the unacceptable time it took to deliver hot water, but was struggling to get the circulation to work. Our client had requested that we attend to investigate the fault and provide advice on rectification.
Upon attendance, it was noted that there was a hot water cylinder within the building that supplies four departments (A, B, C, and D for the purposes of this study). Three of these (A, B, and C) had already been on a circulating hot water system, while the fourth department (dept D) had only recently had a return line fitted.
There were three separate return lines in the plant room, all with individual hot water circulation pumps and all coming to a single confluence point. The additional return line had been connected into one of these lines, with thermal balancing valves in place on the new line only.
Bacterial counts were present
Discussions with the client identified that bacterial counts were present within one of the departments (department B) fed from this system. Upon further investigation, it was found that the circulation within that department was also not correctly operating and was back-feeding through the return line when the outlets were operated.
No balancing valves were installed on any of the existing return lines, and although the common return to the cylinder was found to be operating within the temperature profiles identified in the client water safety plan, the individual lines were not.
Circulation pumps replaced with balancing valves
It was recommended to the client that the circulation pumps be removed and replaced with balancing valves, that the three-way confluence point be re-engineered to allow a more fluid balance, and that a single return pump be installed on the common line.
The client authorised the work, and it was undertaken.
Hot water was present in all departments, and the back-feeding return line identified in Department B was no longer running backwards. Bacterial results were noted to decrease within the space of four to six weeks.
Water pressure
However, a small issue with inconsistent pressure and temperature delivery within the new line in department D remained, so further investigation was continued.
In this area, the hot water circulates around the outer walls of the building, travelling up one side of the corridor and back down the other. A connection was identified that travels upstairs to the staff areas on the first floor. When tracing this line fully, it was found that it then travels back downstairs and rejoins the hot water flow towards the end of the run.
An inconsistency was found in that on some visits, the ground floor was operating within the water safety plan temperatures and with good pressure; on other visits, this was not the case. A pattern was identified that the lack of pressure and temperature only occurred when the outlets upstairs were being operated.
The first-floor outlets were reconfigured, and the returning connection to the ground floor at the end of the run was removed, implementing a new, balanced return line for this subordinate loop.
Continued bacterial monitoring
Works were completed, and the balance was returned to the system. All hot water flow and return lines within the system delivered temperatures that were in line with the client’s water safety plan and balanced around all departments.
Continued bacterial monitoring has shown a further improvement in the bacterial counts, with no detected legionella results delivered post-flush around all departments.
This work is licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International.
![Figure 1. Systemic immune responses elicited by oral dmLT-saponin combinations compared to injected vaccines (A) Cryo-electron microscopy (cryo-EM) image of the dmLT and saponin formulation demonstrating the formation of acid-stable micelle particles upon the addition of saponin to dmLT. (B) Preclinical evaluation of systemic serum IgG and IgA antibody responses following prime/boost vaccination. Antibody levels against the microbial protein antigen included in the vaccination were assessed two weeks post-final vaccination in immunized mice. Groups were stratified by vaccination route (intramuscular [IM] or sublingual [SL]) and adjuvant formulation (dmLT [D] and/or saponin [S]). Comparisons with unvaccinated controls (white bars) are shown. Statistical significance between groups is indicated (*P < 0.05), with the SL D+S group achieving the best IgG and IgA responses to vaccine antigen.](https://www.openaccessgovernment.org/wp-content/uploads/2025/01/Figure-01-100x70.jpg "New strategies for an old problem – Oral vaccines research")
