An Innovative Device for the Hot Water Circuit in Hospitals to Save Energy Without Compromising the Safety and Quality of Water: Preliminary Results

Abstract

Legionella colonization of water systems represents a potential hazard for humans within healthcare facilities. It is possible to contain its spread through continuous disinfection systems and the correct management and maintenance of the systems. The hygienic and sanitary quality of the water cannot be ignored in an evaluation of the management and energy costs. The Fondazione Policlinico Universitario A. Gemelli IRCCS in Rome has installed the “ME.SI. MR ACS” (MEthod of SavIngs Maximum eneRgy for hot water) device, which allows the system to activate, when necessary, avoiding continuous water recirculation. The objectives of this study are to evaluate the health and hygiene quality of the hospital water network and to evaluate the thermal and electrical energy savings and chlorine dioxide consumption, with and without this device in operation. This study involved three phases of microbiological sampling in the facility under study: ME.SI. MR ACS device installed but not running, with the boilers’ setpoint temperature at 60 °C; device running with the boilers’ setpoint temperature at 60 °C; and device in operation with the boilers’ setpoint temperature at 45 °C. The microbiological analyses were carried out in accordance with the ISO standard. The data show a constant absence of Legionella spp. in all samples. The application of ME.SI. MR ACS on the hot water recirculation circuit leads to a reduction in the daily consumption of electrical and thermal energy of 68.6% and 48.6%, respectively, for a savings of approximately EUR 23,000/year per circuit. Furthermore, with the device in operation, there is a 50% reduction in the chlorine dioxide consumption with a savings of EUR 11,500/year. ME.SI. MR ACS guarantees thermal and electrical energy savings associated with a reduction in chlorine dioxide consumption, maintaining the hygienic and sanitary quality of the water network.

1. Introduction

The quality of water distributed within healthcare facilities is a primary determinant of the safety of patients, operators, and other users hosted in these structures. Furthermore, water provided in healthcare facilities for drinking, hygiene, and for other medical assistance usage can represent a hazard [1,2,3,4]. The quality of water is conditioned by the complexity of the hydraulic systems, obsolescence of pipelines, and their proper maintenance and management that characterize large buildings. Some ubiquitously distributed microorganisms in the environment can colonize water networks, becoming potential pathogens, especially in wards that host immunocompromised patients. In this scenario, bacteria belonging to the Legionella genus are particularly relevant.

Legionella bacteria occur naturally in aquatic environments, such as rivers, lakes, and wetlands, and readily colonize artificial water systems, including city pipelines and building plumbing (reservoirs, pipes, fountains, and pools). These artificial systems can amplify and spread the bacteria, posing a health risk to humans [2,3,4,5,6,7]. The risk of Legionella infection depends on environmental, bacterial, and host-related factors [8,9]. Key environmental factors promoting Legionella growth include stagnant or slow-flowing water; the presence of protozoa (e.g., amoebae), which can harbor and support bacterial replication; biodegradable substances that contribute to biofilm formation; the presence of metallic elements (iron, copper, zinc); scale and mineral deposits; disinfectant resistance; and water temperatures between 20° and 50 °C [10,11,12,13,14]. Although currently, it is not possible to eradicate Legionella spp. from water systems, the solutions currently in progress for containing its spread are accurate management and maintenance systems of water networks, combined with continuous disinfection systems [15,16,17,18,19].

In addition to the periodic maintenance of water systems, the Fondazione Policlinico Universitario A. Gemelli IRCCS (FPG) in Rome has installed a continuous disinfection system that employs chlorine dioxide. The effectiveness of maintenance systems and continuous disinfection can be evaluated through microbiological monitoring. However, the hygienic-sanitary quality of the water supplied to the hospital, in order to comply with patient safety indicators, cannot be exempt from an assessment of the management and energy costs related to water systems. In this regard, the company ERIS SRL collaborated on the installation of one of the hot water recirculation systems (WRSs), the “ME.SI. MR ACS” (Italian acronym for “MEthod of SavIngs Maximum eneRgy for hot water”, where ACS is the Italian acronym for Sanitary Hot Water, Acqua Calda Sanitaria, in Italian) device, patented by ERIS SRL itself. This device, if installed on the hot water recirculation system, allows the latter to activate only when necessary, avoiding unnecessary activity and maintaining the performance of the system.

The main objective of this study is to evaluate the microbiological quality of the hospital water network in which the ME.SI. MR ACS has been installed, through the detection of Legionella spp. At the same time, the other relevant objectives are to assess the thermal and electrical energy savings and consequently the economic advantage generated by the installation of the ME.SI. MR ACS device on the hot water production and distribution system, as well as the action of the chlorine dioxide injection system with and without the device running.

2. Materials and Methods

2.1. The Hot Water System and the ME.SI. MR ACS Device

The hot water system available for the FPG facility under study is supplied by two hot water tanks, each with a capacity of approximately 1000 L, which are always running. The water from these tanks is distributed to the building’s utilities via two circulation pumps that remain active 24/7. The water is replenished with drinking water at room temperature on the return circuit input to the two boilers. The ME.SI. MR ACS device installed on this water recirculation system exploits the thermophysical properties of fluids, according to which a fluid changes its temperature and pressure more quickly or slowly depending on whether it is in a dynamic or static state, for the purpose of evaluating the possibility of increasing the energy efficiency of the thermal systems. By detecting the water temperature on the recirculation circuit via software, the ME.SI. MR ACS device can activate or deactivate the circulation system, ensuring that the water temperature is maintained at a comfortable level for all the utilities supplied. The circulation system is deactivated for a few minutes when the set temperature is reached (in this study, it was set at 45 °C) in the recirculation network. Below 45 °C, the recirculation pumps are reactivated to reach the set temperature.

The installation of the device is straightforward and did not necessitate any alterations to the hydraulic piping system. For installation, the device necessitates the following:

• Continuous monitoring of the temperature of the circulating hot water by connecting to the hydraulic circuit with a thermocouple.
• Connection between the device and the relay responsible for activating the circulation pumps for hot water.

Moreover, the installation does not result in the forfeiture of the compliance certificate for the existing electrical system.

Figure 1a illustrates the hot water system without the ME.SI. MR ACS device, while Figure 1b shows the hot water system with the ME.SI. MR ACS device installed. Prior to being distributed to the building’s utilities, the hot water network is treated using a continuous disinfection system with chlorine dioxide (ClO₂), a gas produced on-site by mixing precursors, such as sodium chlorite, and a strong acid, or by electrolytic generation [1,20]. Specifically, the system uses two chemical substances at the right concentration, diluted hydrochloric acid and a sodium chlorite solution, also appropriately diluted. The solution produced by combining the two substances is stored in a tank and then added to the water flow based on demand, using a dosing pump. The dosage is proportional to the volumetric flow rate, in order to maintain a constant desired chlorine dioxide concentration in the drinking water (approximately 0.2 mg/L).

2.2. Microbiological Sampling

This study involved three phases of microbiological sampling in the facility under study:

Phase T0: ME.SI. MR ACS device installed (mid-December) but not running until 21 January, with the boilers’ setpoint temperature at 60 °C.

Phase T1: ME.SI. MR ACS device running (from 22 January to 3 March 2022) with the boilers’ setpoint temperature at 60 °C.

Phase T2: ME.SI. MR ACS device in operation for six and a half months, with the boilers’ setpoint temperature at 45 °C from 4 March to 4 August.

For each sampling phase (i.e., T0, T1, and T2), the sample size was calculated using the methodology proposed by Cochran et al. [21].

The samples were collected from the outlet of the two tanks named boiler 27 and boiler 28 (mixed water and from the recirculation loop). For all three phases (T0, T1, and T2), the samples were collected on two different days (eight samples collected from the recirculation loop and eight samples collected from the outlet), with a one-week interval. The samples were labeled with progressive numbers.

Each sample was collected after 1 min of flushing and 1 min of disinfection with 70% ethanol, followed by 1 more minute of flushing, in accordance with the Italian national guidelines [15]. One liter of sample water was collected in sterile bottles with the addition of 0.01% sodium thiosulphate in order to neutralize any residual chlorine [15].

For each water sample collected, the temperature was recorded at the time of sampling.

Water samples were transported in a cool box, protected from direct light, and processed within 2 h from collection.

2.3. Microbiological Analysis

The microbiological analyses were carried out in accordance with the ISO 11731:2017 standard [22], using the membrane filtration concentration method with direct membrane placement on the culture medium. In brief, 1000 milliliters (mL) of each water sample was divided into two 500 mL aliquots and filtered through 0.2 μm (µm) filters. One aliquot was treated with 30 ± 5 mL of acid solution (acid buffer Biotec srl. Grosseto, Italy) for 5 min, while the other aliquot was left untreated. Both aliquots were then treated with 20 ± 5 mL of saline solution (PAGE’s saline Biotec srl, Grosseto, Italy). The filters were removed and placed directly on BCYE or GVPC culture media. The samples were incubated at 36 ± 2 °C under aerobic conditions in a humid environment with 2.5% CO₂ for 11 days and checked daily.

2.4. Statistical Analysis

In order to compare the mean temperature of the recirculating water before and after the installation of the ME.SI. MR ACS device, both parametric (paired t-test) and non-parametric tests (Wilcoxon signed-rank test) were performed according to the distribution of the variables; the distribution was investigated using the methodology suggested by Shapiro et al. [23].

All analyses were performed using a significance level of p < 0.05 and conducted using STATA 17 (StataCorp LP, College Station, TX, USA). To determine the number of samples to be collected for each phase to achieve statistical significance, the following formula [24] was applied:

Sample size

$$n_0={\displaystyle \frac{Z^2\times PQ}{e^2}}$$

where z² (-) is the abscissa of the normal curve that cuts off an area α at the tails; P (-) is the estimated proportion of an attribute that is present in the population; Q (-) is 1 − P; and e² (-) is the allowable error.

$$n={\displaystyle \frac{n_0}{1+\left(\frac{n_0-1}{N}\right)}}$$

Considering a value of 1.96 for Z, 0.03 for the proportion of population, and 5% as the allowable error, then the sample size is as follows:

$$n_0={\displaystyle \frac{{\left(1.96\right)}^2\times 0.03(1-0.03)}{{\left(0.05\right)}^2}}$$

Adjusting the sample size value for a small population (i.e., 100), the required sample size is the following:

$$n={\displaystyle \frac{45}{1+\left(\frac{45-1}{100}\right)}}= ~31$$

According to this formula, it was calculated that 31 samples are needed for each phase (T0, T1, and T2) of this study, for a total of 93 samples.

2.5. Energy Consumption Analysis

The determination of thermal and electrical energy savings was carried out by comparing the daily consumption of the heating system both with the device turned off and running, under the following operating conditions:

• Temperature of the hot water sent to the users;
• Measurement of thermal and electrical energy consumption during equal periods of time;
• Amount of water consumed by the users.

To measure the temperatures of the hot water delivered to the users, the PT100 probes of the existing Sauter Visual Center monitoring system and the probes of the ME.SI. MR ACS were firstly calibrated and compared with the temperature probes of the PT9T9-SYS PT900 instrument (Baker Hughes, Houston, TX, USA) (an ultrasonic flow meter for liquids), provided by the Fondazione Policlinico A. Gemelli IRCCS and thereafter employed to perform the measurements of thermal energy consumption. As far as electrical energy is concerned, its measurements were carried out using the following calculation [25]:

ELECTRICAL ENERGY (Kilowatt hours − kWh) = POWER (watts) × TIME (hours)

With the ME.SI. MR ACS device running, the actual operating hours of the circulation pump were recorded daily. In order to compare the data on electrical and thermal energy consumption with and without the ME.SI. MR ACS device running, data regarding volumes of daily consumption of cold replenishment water were similar in the two situations, amounting to roughly 1700 m³. For data comparison, in addition to the criterion of a similar volume of cold replenishment water used, the temperature of the replenishment water was used: the higher the temperature, the lower is the energy consumption. In this case, the lowest replenishment water temperature was detected for the consumption with the device on, with a slightly higher water temperature when the device was off.

2.6. Set-Up of Chlorine Dioxide Pulses and Consumption Analysis

The hot water network under study is treated through a continuous automated disinfection system with ClO₂. The ClO₂ system, managed by TECHNODAL SRL, allows for the remote control of the water temperature, of the amount of ClO₂ injected into the circulation system with the ME.SI. MR ACS device on and off, and ensures that the ClO₂ value detected at the “return loop” point of the system falls within the expected range values (0.15–0.25 mg/L) through a programmed number of pulses per minute. For optimal ClO₂ dosing, the automated system was set as follows: 10 pulses/min, with 0.30 mg/L ClO₂ injected per pulse. In the presence of the ME.SI. MR ACS device running, the ClO₂ automatic system was set as follows: 4 pulses/min, with 0.30 mg/L ClO₂ injected per pulse. The real-time data reading of ClO₂ consumption was conducted remotely using the BG08 STEIEL RW14 software 2023 version.

3. Results

Water sampling for the detection of Legionella spp. was carried out firstly with the ME.SI. MR ACS device installed but turned off (T0 phase) and then with the device running (T1 and T2 phases). During the T0 and T1 phases, the boiler temperature was maintained at 60 °C, which is the optimal value to avoid Legionella spp. growth, whereas in the T2 phase, six months after the activation of the device, it was lowered to 45 °C, a temperature considered at risk for the proliferation of the bacteria. For each phase, 32 samples were collected. In total, six samplings were conducted, with 16 samples collected from the hot water tank outlet and 16 samples collected from the return loop, for a total of 96 samples.

Table 1. Microbiological results for Legionella spp. at phase T0 (device off), T1, and T2 (device on).

Phase	Sample ID	Sampling Site	Legionella CFU/L
T0	1–8	hot water tanks	0
T0	9–16	Return loop	0
T0	17–24	hot water tanks	0
T0	25–32	Return loop	0
T1	33–40	hot water tanks	0
T1	41–48	Return loop	0
T1	49–56	hot water tanks	0
T1	57–64	Return loop	0
T2	65–72	hot water tanks	0
T2	73–80	Return loop	0
T2	81–88	hot water tanks	0
T2	89–96	Return loop	0

shows the phase (T0, T1, and T2), the sampling point in the water circuit (outlet and recirculation loop), and the corresponding identification number of the samples. The data from the microbiological tests consistently showed the absence of Legionella spp. in all monitored samples and in each phase as reported in Table 1.

The data concerning the temperatures (Figure 2) detected in the water samples show that the water leaving boilers N° 27 and 28 remains nearly constant both with the ME.SI. MR ACS device off (T0 phase, samples 1–8; 17–24) and running (T1 phase, samples 33–40; 49–56), with an average value of 58.08 °C for the T0 phase and 61.2 °C for the T1 phase. The T2 phase outlet samples, coded with numbers 65–72 and 81–88, show an average temperature of 46.58 °C, in line with the set values. During the T0 phase (device off), the recirculation temperature shows constant values (samples 9–16; 25–32), while the recirculation samples of the T1 phase (samples 9–16 and 25–32) with the device running allowed for discriminating when the recirculation pump is off (samples 44–48) compared to when it is on (samples 41–43, 57–60). Specifically, water samples 44–48 were collected when the recirculation pump was off, and the lower temperatures are therefore related to the replenishment water. In this way, it was feasible not only to evaluate the microbiological quality of the recirculation water but also to intercept and evaluate the quality of the water that feeds the boilers following the replenishment of incoming water. The recirculation samples of the T2 phase (73–80 and 89–96), taken with the recirculation pump on, show constant but lower temperatures (mean temperature 44.08 °C) compared to those recorded in the T0 phase (mean temperature 56.58 °C) and T1 phase (samples 41–43 and 57–60) taken with the pump on, with a mean temperature of 55.62 °C. Analyzing the data regarding the recirculation temperature, there is also a statistically significant difference between the average water temperatures between the T0 phase and the T1 phase (p < 0.002) and T2 phase (p < 0.001). In the recirculation phase, a decrease in temperature was observed in both the T1 and T2 phases compared to the T0 phase when the device was off.

The extracted data regarding the daily consumption of electrical and thermal energy are reported in

Table 2. Extracted data consumption of thermal and electrical energy with the ME.SI. MR ACS off and on.

Sample Collection Date	Device Status ME.SI. MR ACS	Recirculation Cold Water (m3) Daily Consumption	Cold Make-Up Water Temperature (°C)	Hot Water Delivery Temperature (°C)	Electrical Energy (kWh) Daily Consumption 24 h	Thermal Energy (kWh) Daily Consumption 24 h
21 January 2022 8:00 a.m.	off	1692	16	62.1	4.75	629.78
22 January 2022 8:00 a.m.	off		19.4	60.9
26 January 2022 8:00 a.m.	on	1711	13.2	59.3	1.45	344.66
27 January 2022 8:00 a.m.	on		12.4	62.2

. These data show that, for a daily hot water consumption of nearly 1700 m³, the application of the ME.SI. MR ACS device on the hot WRS results in a daily energy savings of approximately 68.6% (1.49 kWh compared to 4.75 kWh) and a thermal energy savings of approximately 48.6% (322.55 kWh vs. 640.68 kWh).

Considering the cost of electrical energy, the installation of the ME.SI. MR ACS device in the hot water recirculation system results in the following approximate annual cost savings:

-

Thermal Energy = (629.78 kWh − 344.56 kWh) × 365 days × EUR 0.22/kWh = EUR 22,900 per year

-

Electrical Energy = (4.75 kWh − 1.45 kWh) × 365 days × EUR 0.21/kWh = EUR 253 per year

Overall, the application of this device to all hot water recirculation systems present in a large university hospital such as FPG IRCCS can result in an estimated savings of EUR 300,000 per year.

As shown in Figure 3, to reach the intended values of ClO₂ at the return loop and, ultimately, at the user terminals, with the ME.SI. MR ACS device off, 10 pulses/min is required, while with the device in operation, only 4 pulses/min is sufficient. Furthermore, the recorded hot water temperature values at the return loop from the remote monitoring system are also comparable. These data indicate that, by inserting the ME.SI. MR ACS device into the hot water recirculation system and reducing the pulses per minute from 10 to 4, the average monthly consumption for each operating system is 25 L of BIO GUARD 41H11 and 25 liters of BIO GUARD 41H10, for a total cost of EUR 113.00. Assuming 50% cost savings (even being conservative), the monthly cost per system is EUR 56.50. By applying the ME.SI. MR ACS device to all 17 ClO₂ generators, we can estimate a monthly savings of EUR 960.50, which corresponds to EUR 11,526.00/year.

This substantial reduction in the amount of ClO₂ is attributed to the continuous switch on–off operation of the ME.SI. MR ACS device. This system slows down the water flow rate on the return line, allowing the ClO₂ to maintain more consistent values and avoiding the phenomenon of “stripping”.

4. Discussion and Conclusions

Infections caused by inhalation of aerosols contaminated with Legionella spp. can cause severe consequences for vulnerable patients. In 2022, the Italian National Institute of Health reported 3111 cases of Legionellosis, with 3039 (97.7%) confirmed and 72 as probable, and a case fatality rate of 16.3% among those for whom the outcome of the disease was known [26]. In hospitals, water supply networks play an important role in patient safety, since water can facilitate the spread of pathogens, especially in susceptible patients. Buildings supplied with hot water recirculation networks and hot water storage tanks are susceptible to colonization by Legionella spp.; therefore, to avoid this phenomenon, temperatures must be maintained high. Hospital care practices and utilities, such as water and electricity, are responsible for a significant consumption of resources, including specialized personnel and maintenance costs associated with the provision of these services. International and national guidelines recommend maintaining hot water temperatures at a minimum of 50 °C in recirculation systems and above 60 °C in hot water storage tanks, which, combined with the proper management and maintenance of water networks, results in significant operating costs. In this study, the ME.SI. MR ACS device, patented by ERIS SRL, was applied to the hot water recirculation system of a selected facility, FPG IRCSS. This device makes use of the thermophysical properties of fluids, according to which the temperature of a fluid decreases more slowly in the static state. Therefore, when the recirculation temperature setting is reached, the device’s software detects it and shuts off the circulation system for a few minutes, maintaining the temperature of the water and resulting in a significant reduction in both electrical and thermal energy usage. The recirculation pump is reactivated if the temperature falls below the set values.

The results of this study show that with the ME.SI. MR ACS device running and with average temperatures of 61.2 °C and 55.62 °C (T1 phase) and 46.6 °C and 44 °C (T2 phase) for the hot water supply and recirculation systems, respectively, there is a 68.6% reduction in electrical energy usage and a 48.6% reduction in thermal energy usage, resulting in an annual cost savings of approximately EUR 23,000 for the facility studied. If applied to the 14 buildings of the FPG, this would result in annual cost savings of approximately EUR 300,000. These estimates are based on energy cost data for 2022, and considering the doubling of energy costs, the cost savings for 2023 would be even higher. In addition to the energy savings, despite the high temperature settings of the hot water supply and recirculation systems, the ME.SI. MR ACS device also results in a 50% reduction in ClO₂ consumption due to the continuous switch on–off operation of the recirculation pumps, leading to savings of approximately EUR 11,526 per year. This result not only represents an economic advantage but also a benefit in terms of safeguarding water networks, as ClO₂ can have a corrosive effect on hot water distribution networks over time [27,28]. Attention to the energy and management consumption of water systems must consider the hygienic-sanitary quality of the water supplied. Therefore, in this study, we collected and analyzed 96 water samples in the different experimental phases (T0, T1, and T2) to verify whether this rapid but frequent switch on–off of the recirculation pump and the rapid alternation between dynamic and static water flow phases could result in the release of Legionella spp. In fact, Legionella could be released by the detachment of biofilm, which intermittent flow can provoke [29]. The data obtained show that there are no Legionella spp. present in any of the samples taken in all three phases analyzed. Furthermore, even when setting the supply and recirculation temperatures lower than those recommended by LG 2015 and the scientific literature, the device running does not induce contamination of the water network by Legionella spp. This result is likely also due to the presence of chlorine dioxide to protect the water distribution network.

This is a preliminary, single-center study conducted at one hospital, and thus, no data concerning its application in other healthcare facilities or communities are presently available. Furthermore, it was not possible to evaluate the ME.SI. MR ACS device without the support of the ClO₂ disinfection method because, due to patient safety concerns in the wards served by the water network of this study, it is not permissible to turn off the continuous disinfection system.

These preliminary data encourage the application of such a device in all buildings that provide hot water to patients to contain energy consumption, preserve water networks, and, most importantly, continue to guarantee the hygienic-sanitary quality of the hot water supplied.